Class. BooL 537^ 3g CoiJyriglit]^°_ OKRIGHT DEPOSm MANUAL OF Plant Diseases BY PROF. DR. PAUL SORAUER Third Edition — Prof. Dr. Sorauer In Collaboration with Prof. Dr. G. Lindau And Dr. L. Reh Private Docent at the University Assistant in the Museum of Natural of Berlin History in Hamburg TRANSLATED BY FRANCES DORRANCE MANUAL OF Plant Diseases BY PROF. DR. PAUL SORAUER Third Edition— Prof . Dr. Sorauer In Collaboration with Prof. Dr. G. Lindau And Dr. L. Reh Private Decent at the University Assistant in the Museum of Natural of Berlin - History in Hamburg TRANSLATED BY FRANCES DORRANCE Volume I NON-PARASITIC DISEASES BY PROF. DR. PAUL SORAUER BERLIN WITH 208 ILLUSTRATIONS IN THE TEXT ^v n'?>^ Copyrighted, 1922 By FRANCES DORRANCE . g)S!.A6o9795 S)^ ERRATA. Contents, page X, line 2t,, for Leguminaceae, read Leguniinosae. Page 8, line 23, for stems, read shoots. 23, " 16, " preventive, read preventative. 53, " 5, " Prunualus, read Prunulus. 93, Fig. 4, caption, for Schomiinzach, read Schonmiinzach. 99, line 34, for Mvcor spinosa, read Mucor spinosus. 167, " 22, " Arahanose, read Arabinose. 204, " 37, " Fusiarium, read Fusarium. 232, " 5, " Leguminoseae, read Leguniinosae. " 21, " Dioscora, read Dioscorea. 265, " 19, " Zolites, read Zeolites. ^73' " 6, *' B. suhstilis, read B. sttbtilis. " 7-8, " Clostridium gelatinosa, read Clostrid'mm gelatinosum. " 18, after Mold fungi, insert (Mucor stolonifcra and Asper- gillis niger). 293, " 20, for homogany, read homogamy. 338, " 30, " fruit spears, read fruit spurs. 339, " II, " Fruchtuchen, read Fruchtkuchen. 420-22 " Leguminaceae, read Leguniinosae. 430, line II, after inner growth, insert (internal intumescences). 442, Fig. 80, caption, for Acacia pendulata, read Acacia pendida. 461, line 24, after rough places, insert (scurvy spots). 498, " I, for Chapter XL, read Chapter XL 548, " 24, " psycho-clinic, read psychroTclinic. 696, " 22, " Bacillus pseudarabinus, read Bact. pseudarahinum. 723, " 38, " Grapholithia, read Grapholitha. 765, " 36, " Boulle celeste, read Bouillie celeste. 802, Fig. 186, caption, for forniaton, read formation. 855, line II, for Trula, read Torula. " II, " vernatis, read vernalis. Vll TABLE OF CONTENTS. Page PREFACE to the German edition 3 IXTRODUCTIOX. Section I. THE NATURE OF DISEASE. 1. Limitation of the conception of disease 5 2. Production of the disease 8 3. Relation of the plant to its environment ro 4. Parasitic diseases ^3 5. Epidemics ^9 6. Artificial immunization and internal therapy 23 7. Predisposition ^5 8. Predisposition and immunity 27 g. Inheritance of disease and of predisposition 3i 10. Degeneration 34 Section 2. HISTORICAL SURVEY. Historical Survey 4i^"70 APPENDIX 70 DETAILED EXPOSITION. Section I. DISEASES DUE TO UNFAVORABLE SOIL CONDITIONS. Chapter I. The location of the soil 72 1. Elevation ahove sea level T^ a. General changes in habitat. In relation to herbaceous plants 1^ Development of the aerial axis of woody plants 76 Adjustment of the root body of woody plants 78 b. Special cases of disease 81 Retrogression in the cultivation of the larch 81 Lack of success with tropical plantations 84 2. Slope of the surface of the soil 86 a. Too steep slopes 89 b. Growth of stilts, elevation of the roots of trees 92 c. Too deep planting 9° Too deep planting of trees 98 Too deep sowing of seed ^^ Roots from the tips of grain seeds Ho 3. Greater horizontal differences ^-O Glassy grain kernels ^^9 4. Continental and marine climates ^31 5. Influence of forests ^34 Chapter II. Unfavorable physical constitution of the soil T38 1. Limited soil mass ^38 Root curvature ^^ Dwarf growth ( Nanism ) ^■^- Too thick seeding ^47 2. Unsuitable soil structure ^4o a. Light soils ^4« Disadvantage of sandy soils ^4o Lowering of the ground water level '50 The dying of alders ^^3 Street planting ^53 Effect of drought on field products ^55 Effect of drought on germination ^57 Treatment of tree seeds ^5° Blasting in grains and legumes i"" Vlll Page Thread formation in the potato (Filositas) i6i Diaphysis (Growing out) of the potato 163 Formation of tubers without foliage 164 Aerial potato tubers 165 Premature ripening of fruits 165 Rusty plums . ._ 166 Further phenomena of premature ripening 166 Mealiness of fruit 166 Bitter pit in the apple 168 Stoniness of pears and lithiasis 170 Varieties of fruit suitable for dry soils 174 Stunting of plants 175 Pilosis 177 Lignification of roots 179 Ball dryness of the Ericaceae 181 Means of overcoming lack of moisture in the soil 182 Irrigation 182 Cultivation of the soil 183 Mulching of the soil 184 Soils with a plant cover 185 Forest litter 186 Forests 187 Fallow land 188 b. Loamy soils 189 General characteristics 189 Covering of the soil with silt 191 Improvement of soils which are becoming compact 194 Inundations 195 Conversion of lands into swamps 196 Burning of plants in moist soils 199 Delayed seeding 200 Souring of seed 201 Souring of potted plants 203 Injudicious watering 206 ' Use of saucers under pots 208 Running out of potatoes 208 Sensitiveness of the sweet cherry 209 Tan disease 209 Girdling of the red beech 219 Root disease of the true chestnut (Mai nero) 219 Rootblight of sugar and fodder beets 220 Tropical plants 227 ■ Root-rot of sugar cane 227 i ■ Diseases of cotton 228 Castor bean cultures 229 Tobacco 229 Cofifee 230 Cocoa and tea 231 Other tropical plants 231 Means for overcoming the disadvantages of heavy soils 232 Harrowing 236 Use of lime, marl, and plaster 237 3. Disadvantages of moor soil 240 Acids in the soil 240 Raw humus 241 Meadow ore 243 Poisoning of the soil by metallic sulfur 250 Susceptibility to frost of moor vegetation 251 The usefulness of the spruce 253 Changes in moor soil through cultivation 256 Rotten bark 258 Horticultural moor plants 260 Specking of orchids 261 Chapter III. Unfavorable chemical soil constitution 264 r. Relation of the food stufifs to the soil structure 264 A. Soil absorption resulting from chemico-physical processes 264 B. Work of the soil organisms 268 IX Page 2. Relation of the nutritive substances to tlie plants 274 A. Lack of moisture and nutritive substances 27s a. Lack of moisture i 275 Influence of the various plant coverings 275 Wilting 276 Change in production due to lack of moisture 278 Discoloration of woody plants 279 Red coloration in grain 281 "Reds" of hops 282 "Leaf scorch" of grapes, "Parching" of vines, "Red scorch" 283 Yellowing due to the grafting stock 284 Premature drying of the foliage 284 Burning out of grass 285 Silver leaf 285 Water core of apples -. 286 b. Changes in production due to a lack of nitrogen 287 Starvation conditions in Cryptogams 287 Production of sterile blossoms ( Sterility ) 289 Seedless fruits 292 Behavior of weak seeds 295 Dropping of the fruit 296 Drying of the inflorescences on decorative plants 296 Formation of thorns 297 c. Changes in production due to a lack of potassium 298 d. Changes in production due to a lack of calcium 301 e. Changes due to a lack of magnesium 305 f. Changes due to a lack of chlorin 306 g. Lack of iron and "jaundice" (Icterus ) 307 h. Changes due to a lack of phosphorus and sulphur 312 i. Changes due to a lack of oxygen 313 General phenomena 313 Brusone disease of rice 31S Diseases of gladioli 316 k. Changes due to a lack of carbon-dioxid 316 B. Excess of water and nutritive substances 319 a. Excess of water 319 Moisture 319 Clogging of drain tiles 319 Sprouted grain 320 Rupturing of fleshy parts of plants 321 Woolly streaks in apple cores 324 Ring disease of hyacinth bulbs 326 Springing of the bark Z^~ Shedding of the bark 328 Water sprouts 331 Union of parts Z2>Z Compulsory twisting (Spiralismus Mor.) 334 Dropsy ( Oedema ) 335 a. In small fruits 335 b. In stone fruits 338 Swellings on the St. John's Bread tree 339 Retrogressive metamorphosis (Phyllody) 340 Barrenness of the hop 342 Forked growth of grape vines 34S Falling of the leaves 346 Leaf casting diseases 349 Leaf-fall in house plants 352 Dropping of the flowering organs 353 Shelling of the grape blossom 354 Shedding of the young flower clusters of hyacintlis 356 Twig abscission 357 b. Increase of food concentration 360 Changes in meadows 362 Sewage disposal fields 364 Scurvy disease 367 Progressive metamorphosis 372 Pressure of the buds (Blastomania A. Br.) 378 X Page Goitre gnarl of trees 378 c. Effect of an excess of nitrogen 387 Over-fertilized seed 387 Over-fertilized beets 389 Over-fertilized potatoes 390 Chile saltpetre with woody plants 391 Over-fertilization of vegetables and other field crops 392 Excessive nitrogen fertilization for decorative plants 393 Leaf curl of the potato 395 d. Excess of calcium and magnesium 399 Excess of calcium with grapes 402 e. Excess of potassium 403 f. Excess of phosphoric acid 405 g. Excess of carbon-dioxid 406 Section 2. INJURIOUS ATMOSPHERIC INFLUENCES. Chapter IV. Too dry air 408 Injury to buds 408 Defoliation due to heat 411 Honey dew 412 Heart rot and dry rot of fodder and sugar beets 415 Fault}' development of the blossoms 416 House plants 419 Hard seeds in the Leguminaceae 420 Chapter V. Excessive humidity , 423 Mode of growth with continued atmospheric humidity 423 Influence of moist air on plants injured by drought 425 Cork outgrowths 426 Cork disease of the cacti 428 Bitten or perforated leaves 430 Formation of cork on fruits 432 Yellow spots (Aurigo) 434 Intumescences 435 Tubercle disease of the rubber plant 449 Skin diseases of hyacinths 451 Glassy condition of cacti 453 Chapter VI. Fog 458 Chapter VII. Rainstorms 461 Chapter VIII. Hail 463 Chapter IX. Wind 471 Chapter X. Electrical discharges 480 Flashes of lightning 480 Blight of conifer tops 487 Differences between lightning and frost wounds in conifers 489 Injuries to trees in cities and towns 493 Effect of spray lightning on grapevines 493 Spray lightning on fields and meadows 495 Disadvantages in electro-culture 496 Chapter XI. Lack of heat 498 A. General survey 498 Life phenomena at low temperatures 498 Autumn coloration 500 Frosting and freezing to death 504 Theories as to the nature of frost action 507 Disturbances due to chilling S13 B. Special instances of frost action 514 Turning sweet of potatoes 514 Running to seed of beets 516 Frosty taste in grapes 518 Changes in the blossom organs 5^8 Rust rings in fruits 523 XI Page Behavior of older foliage with acute frost action 524 Deficient greening of younger leaves [ ]] [526 Defoliation due to frost 527 Behavior of beet and cabbage plants in frost !!.'!! 531 Frost blisters 53-? Comb-like splitting of the leaves [.[ , 53" Heaving of seeds 536 Internal injuries in young grain "507 Internal injuries in the grain stalk g^g Lodging of the stalk 542 Condition of sterile heads ] [ '542 Phenomena of movement due to frost 547 Freezing back of older branch tips ]] .553 Dying of the cherry trees along the Rhine 555 Branch blight in forest trees " I558 Freezing of the spring growth \ '55P Freezing of roots '^62 Frost clefts ' | "^55 Frost blisters \ 'egg Frost wrinkles c-i Bark tatters and cork holes 575 Phenomena of discoloration in trunks and branches 576 Frost line ^jg Internal splitting of the trunk and branches 581 Open frost tears ' ' ^g^ Canker ( Carcinoma) 585 a. Canker of the apple tree 586 b. Crotch canker in fruit and forest trees 593 c. Canker on cherry trees ^g^ d. Canker (Scab) of the grapevine 596 e. Canker on Spiraea 598 f . Canker of the rose 602 g. Canker of the blackberry 606 Corresponding features in canker swellings 607 Blight (Sphacelus) 608 Aggregations of parenchyma wood 613 False annual rings, double rings, etc 615 Experimental production of parenchyma wood by frost action .".617 Theory of the mechanical action of frost 620 Rupture of the cuticle 623 Protective measures against frost • 624 a. Snow covering 624 b. Use of water 626 c. Effect of wind 627 d. Smudge 628 Frost prediction 630 Hardy fruit varieties 631 Snow pressure, ice coating and icicles 634 Chapter XII. Excess of heat 638 Death from heat 638 Poor development of our vegetables in the tropics 639 Postponement of the usual seed time in our latitudes 639 Sunburn of leaves in nature 641 Sunburn spots in conservatories 643 Defoliation 6^ Sunburn in blossoms and fruits 645 Injury to grapes from sunburn 646 Sun cracks 647 Influence of too great soil heat 648 Failure of the pineapple 650 Classiness of orchids 651 Failure in forcing blossom bulbs 651 Seed which has suffered from self-heating 652 Chapter XIII. Lack of light 654 Etiolation 654 Shading .657 Xll Page Lodging of grain 662 Lack of light as predisposition to disease 666 Chapter XIV. Excess of light 671 Section 3. ENZYMATIC DISEASES. Chapter XV. Displacement of enzymatic functions 675 General discussion 675 Albinism (Variegation) 677 Mosaic disease of tobacco 684 Pox of tobacco 689 White rust of tobacco 690 Disease of the peanut in German East Africa 690 Shrivelling disease of the mulberry 690 Sereh disease of the sugar cane 692 Cobb's disease of the sugar cane ^96 Peach yellows 697 Gummosis of the cherry 699 Exudation of gum in other plants 707 Exudation of gum in the Acacia 707 Gummy exudation of the bitter orange 708 Black-leg of the edible chestnut 709 Gummosis of the 'fig tree 710 Exudation of manna 711 Resinosis 7 r i Formation of resin in dicotyledonous plants 716 Section 4. EFFECT OF INJURIOUS GASES AND LIQUIDS. Chapter XVI. Gases in smoke 71S Sulphurous acids 718 Hydrochloric acid and chlorin 724 Hydrofluoric acid 729 Nitric acid 730 Ammonia 730 Tar and asphalt fumes 732 Bromine 735 Chapter XVII. Solid substances given off by chimneys and the distillates they contain "jT)"/ Hydrogen sulfid 742 Soda dust 743 Control plants 744 Illuminating gas and acetylene 744 Chapter XVIII. Waste water 748 Waste water containing sodium chlorid 748 Waste water containing calcium chlorid and magnesium chlorid 751 Waste water containing barium chlorid 752 Waste water containing zinc sulfate 752 Waste water containing iron sulfate 753 Waste water containing copper sulfate and copper nitrate 754 Chapter XIX. Injurious effects of cultural methods 756 Coating substances 756 Anaesthetica 765 Injuries due to fertilizers 767 Section 5. WOUNDS. Chapter XX. Wounds to the axial organs T/2 General discussion 772 Scarification wounds 776 Inscriptions 781 Injury due to wild animals 781 Overgrowth of cross wounds in many-year-old trees 783 Overgrowth processes in year-old branches 785 Girdling callus 787 Xlll Page Injuries to the bark 797 Historical survey 797 Personal observations 805 Bending of the branches 810 Twisting of the branches 815 Effect of constricting the axis 817 Branch cuttings 821 Utilization of various axial organs for cuttings 825 Grafting 829 Oculation, or budding 833 Copulation and grafting 838 Longevity of grafted or budded individuals 839 Mutual influence of scion and stock 841 Natural processes of coalescence 847 Wound protection 850 Wound gum 851 Slimy exudation of trees 854 Root injuries 856 Gnarly overgrowth edges 859 Bark tubers .861 Leaf injuries 871 Leaf cuttings 873 Injury to the foliage 879 Supplement 881 XIV LIST OF ILLUSTRATIONS. Fig. Page I, 2. Roots of Quercus Pedunculata grown between rocks 79 3. Spruce root with fleshy compensatory root 81 4. Stihed spruce near Schonmunzach 93 5, 6- Stilted pine from Grunewald 95 ", 8. Resin galls on stilt-like roots of the pine 96 9. Rye seedling with too deep sowing 112 ■ 10. Cross section through the lowest node of young rye plant 1 14 II. Wheat -grains with roots from testa at tip of seed grain 116 12, 13, 14. Microscopical enlargements of Fig. 11 117, 119 15. Dwarf specimen of Thuja obhisa ^ 1-^3 16. Cutting from potato tuber with the filament disease 162 ■ 17. Proliticated potato 163 - 18. Parenchyma cell from ripe apple after treatment with undiluted glycerin 169 ■ 19. * Pear diseased with Lithiasis .171 " 20. Cross-section of stone cell from pear snown in Fig. 19 173 f.2ij 22. Corr-esponding sections through a cultivated and a wild carrot 181 ■ 23. Apple root with ruptured tan spots 210 ' 24. Cross-section through a tan spot in an apple root - 211 25. Bark of apple tree trunk with tan spots 212 26. Cross-section through tan spot on trunk of apple tree 213 27. Cherry branch with tan cushions 214 28. New wood on a bark wound of a cherry trunk 216 29 A "meadow ore pine" 246 30. Roots of an oak in meadow ore 247 31. Moor pine with flatly extended roots 248 ^ 32. Canker-like, wounded place on the moor pine 249 33. Spruce family produced by natural layering 254 34. Oak with a formation of sinkers 255 35. Mouldy bark scale of a moor pine 259 36. Seedless pear 294 \37- Cross-section through branch of Rhamnus cathartica 298 ^ 38. Cross-section through thorn of Rhamnus cathartica 299 39. Leaf injuries from a lack of potassium 302 40. Buckwheat plant grown in a normal nutrient solution 307 41. Buckwheat plant grown in a solution free from chlorin 308 42. Bean plant split as the result of excess of water 322 43. Apple core with woolly streaks 324 44. Rupture of carpel of apple due to a woolly streak 325 45. Elm bark with protruding tissue islands 328 46. Elm bark with bark excrescence (cross-section) 329 47, 48. Fasciated branch of Picea excelsa 332 49. Fasciation of Alnus glutinosa 333 50. Dropsy in Ribes aiireuin 33^ 51. Transitional stages between normal and leafy hop catkins 343 52. Carrot diseased with deep scurvy 3^7 53. Lentical formation on the potato skin 369 54. Cone disease in the Scotch pine 373 55. Sprouting pears 374 56. Larch cone with growth of the axis continued 375 57. Rosette shoot of a Scotch pine 377 58. Peeled, gnarled growth of the maple 379 59. Gnarl formation on branches of Mains sinensis 380 60. Cross-section through a gnarl cushion 380 61. Longitudinal section through the spikes of a gnarl 381 62. Gnarl formation in the black currant 382 63. Cross-section through twig covered with gnarls 383 64. Cross-section through bark of the black currant 383 65. Medullary ray in the first stages of gnarl formation . . • • ■ 384 66. Diagrammatic representation of mutual relations of fertilizers 400 •67, 68. Cross-sections through the bud coverings of Quercus and of Pinus 409 XV Fig. Page 69. Cross-section through the apical region of a closed blossom of Hippeastntiii robustutn 418 70, 71. Cork excrescences in Phyllocactus 428, 429 ^2. Perforated potato leaf, due to cork formation 431 y2- Grapes with cork warts on fruit stems 432 74. Cross-section through the warty fruit stem of a grape 433 75. Leaf intumescences in Cassia tomeiitosa 436 76. Intumescence in Myrniecodia echinata 437 //. Intumescence on the stem of a grape 439 78. Intumescence on the lower node of an oat plant 441 79. Intumescence on stem of Lavetera triincstris 442 So, 81. Intumescence on branch of Acacia pciuiiila . .442 82. Cross-section through intumescence of Acacia pendiila 443 83. Intumescence on blossom of Cymbidimn Lozvi 444 84. Cross-section through intumescence on perianth of Cymbidntm Lozvi 445 85, 86. Intumescence on pea-pods 446, 447 87. Cross-section through leaf tubercle of the rubber tree 450 88, 89. Hyacinth bulb with pustules of the skin disease 451, 452 90. Glassy place in Cereus nycticalus 456 91. Effect of hail on a blade of rye 464 92, 93. Head of wheat broken by hail 465, 466 94. Cross-section through tomato wall, injured by hail 467 95. Wind bent and broken spruces 473 96. Craspedodromous and Camptodromous venation 478 97. Oak, struck by lightning 482 98. Cross-section through spruce with overgrown lightning wounds 484 99. Cross-section through annual ring of a spruce, in year it was struck by lightning 485 roo. Cross-section through a blighted spruce tip 487 loi. Pine, artificially frosted 490 102. Spruce, showing traces of artificial lightning 492 103. Cross-section through petal of apple, injured by artificial frost 520 104. Cross-section through young receptacle of apple injured by frost 521 105. Primordia of apple flower bud, injured by frost 522 106. Autumnal abscission layer of a horse chestnut leaf 528 J07. Cross-section through a frost boil in an apple leaf 533 108. Horse chestnut leaf, injured by frost and torn during unfolding 535 log. Young rye leaf, injured by frost 538 no. Natural cavities in the rye leaf 539 III. Leaf node from a rye plant, injured by frost 540 T12, 113. Membrane swellings on leaf sheaths of a rye blade, injured by frost 540 114. Different forms of sterility 543 115. Cross-section through internode of a sterile rye blade 544 116. Cross-section through the node of the sterile stalk 545 117. Cross-section through a spruce branch, showing red wood formation 551 118. 119. Red wood and strain wood in the spruce 552 120. Cherry sapling infected with J'alsa leucostoiiia 557 121. Buds of the cherry, injured by artificial frost 560 122. Frost ridge on the trunk of Acer caiiipesfre 567 T23. Oak stem, cleft by Polyponis sulfureus 569 124. Starch structures formed in the willow branch by chloriodid of zinc treatment 572 125, 126. Frost boil on a sweet cherry branch 573, 574 127. Torn cork lamellae on branch injured by frost 576 128. Splitting of a pear branch by artificial frost 578 129. Swelling of eel! walls after artificial frost 580 T30. Interna] splitting of cherry branch from artificial frost 582 13T. Bud cushion of a larch branch, injured by artificial frost 584 T32. Overgrowing frost split in apple branch, produced by artificial frost 586 '^32,^ 134, 135. Apple canker '. 587, 588 136. Juvenile condition of apple canker 590 137. Injury to base of branch by frost .S9i T38. Crotch canker 593 T3Q. Cherry canker 595 140. Canker excrescences in the grapevine 596 141. Canker on Spiraea 599 142. 143. Rose canker 602, 604 XVI Fig. Page 144. Canker of the wild blackberry 606 145. Frost spots on pear bark 608 146. 147. Blight spots on pear trunk 610, 611 148', 149. Internal frost wounds on an oak branch 618, 621 T50.' Curve for finding night frosts 631 151. Cross-section through sunburn spot in leaf of Clivia nobilis 643 152, 153, 154- Light and shade leaves of the beech 660 155.' Twig of cherry with gum cavity 701 156. Nuclei of gum-forming tissue 704 157. Tracheidal parenchyma of Pinus Strobus with resiniferous layer 713 158. 159, 160, 161. Resin centers in amber 714-716 162. Oat leaf killed by chlorin fumes 726 163. Beech leaf affected by sulf urous acid 727 164. Birch leaves injured by sulf urous acid 728 165. Rose leaf inj ured by chlorin fumes 728 166. Beech leaves injured by chlorin fumes 728 167. Birch leaves injured by chlorin fumes 729 168. Virginia creeper, strawberry and rose leaves injured by tar fumes 733 169. 170, 171. Apples injured by spraying with Bordeaux mixture 763, 764 172. Apple leaf with dead spots and holes after spraying with Bordeaux mixture.. 765 173, 174, 175. Scarification wounds 777, 778 176. Hollow pine trunk 779 177. Section of trunk of Picea vulgaris with overgrowth of the resin channels. .. .780 178. Overgrowth of the cut surface of a branch 783 179. t8o, 181. Cross-section of a year-old cherry branch 786 182, 183, 184, 185. Ringing wound on a grapevine 789-795 186. Callus formation from young bark cells in a barked trunk 802 187, 188, 189. New tissue formation on a barked cherry trunk 805-808 190, 191, 192, 193, 194. New tissue formation at bend in an apple twig 811-813 195. Injury to a branch due to twisting 815 196. Constriction in branch due to a wire ring 819 197. Fuchsia cutting 822 198. Rose cutting 823 199. Budded rose 832 200. Bark graft of Aesculus, with adventitious buds 837 201. Pine with natural in-arching of a second trunk 848 202. Stoppage of ducts in a grapevine, due to wound decay 853 203. Alder root, barked by the tread of feet 856 204. Gnarlly overgrowth cap of the stump of an oak branch 860 205. Bark tubers from an apple trunk 866 206. Isolated wood centers in the bark of a year-old pear branch 869 207. Callus formation in a leaf of Leucojnm vernum 872 208. Leaf cutting of a begonia 875 MANUAL -f^„ OF Plant Diseases BY PROF. DR. PAUL SORAUER II Third Edition—Prof. Dr. Sorauer In Collaboration with Prof. Dr. G. Lindau And Dr. L. Reh Private Docent at the University Assistant in the Museum of Natural History of Berlin in Hamburg TRANSLATED BY FRANCES DORRANGE Volume I NON-PARASITIC DISEASES BY PROF. DR. PAUL SORAUER BERLIN WITH 208 ILLUSTRATIONS IN THE TEXT SIS 7-3 Copyrighted, 1914 By FRANCES DORRANCE GEP 29 1914 ©CI.A380596 THE RECORD PRESS Wilkes-Barre, Pa. PREFACE TO THE GERMAN EDITION. For the third edition of my manual I have requested the assistance of Professor Dr. Lindau and Dr. Reh. In the second volume of the work, the former has treated of vegetable parasites and in the third volume the latter, the animal enemies of plants. Such help seemed necessary because, since the appearance of the second edition, the published results of investigations have been so numerous that too long a time would have been required for mastering the material. Other- wise when the last sheets appeared the first would have become obsolete. Even with this division of the work, this unfortunate condition has not been entirely overcome and an attempt has been made to obviate the difficulty by listing some of the more important recent material in a supplementary biblio- graphy. If the absence of some works, especially of the earlier literature, is noted the explanation lies in the fact that we have emphasized especially those studies necessary for the support of our presentation of the subject. A more detailed bibliography would be possible only if the individual diseases were treated in monographs. I kept for my own work the revision of the first volume, comprising the non-parasitic diseases. The fact that this volume is the most extensive is ex- plained by my standpoint, already sufficiently characterized in the preface to the second edition, — because I lay the chief weight on a knowledge of the diseases produced by atmospheric, soil and cultural conditions. The distur- bances caused by these factors are not only the most abundant and perma- nent but also often form the starting point for parasitic diseases. On this account, supported by my own studies and the observations of other investigators, I was especially anxious to show how the same plant species could be changed structurally and in habits of groAvth according to position and the constitution of the soil. Individuals are sometimes more disposed to a definite form of disease or are more resistant to it, according to the difiference in their constitutions. This holds good also for their behavior towards parasitic organisms. It is thus evident that not only must the latter be combatted by directly destruc- tive methods but also the chief emphasis should be laid on the possible con- stitutional change of the host plant. Therefore, we will find the most essen- tial task to be the breeding of resistant varieties. At the time the first edition of this work was published, the undersigned stood alone as represen- tative of this theory of predisposition to parasitic attack, but now many of the most prominent investigators are counted among its supporters. And thus I hope that the idea for which I have fought since the be- ginning of my scientific activity, that is, the formation of a rational plant hygiene, will finally come to full recognition. Primarily, we must learn to protect the organism from disease, and then, through force of necessity, may take steps to heal an organism which is already diseased. In the first volume, the first section of the introduction treats of the na- ture of disease, while the second takes up the history of its investigation. It should be understood by the term "historical" that I did not wish to write a history of phytopathology, which would have taken much more thorough pre- liminary study, but did consider it desirable to attempt to sketch the process of the development of this branch of knowledge, in order to show how the present point of view had developed in the course of time. In looking through the specialized part, the reader may also find that even in the present edition conclusions once based on a considerable number of my own investigations have been abandoned. The aid of illustrations, so absolutely necessary in phytopathology, has been made use of to an appreci- ably larger extent in describing diseases. In accordance with the character of the book, new anatomical drawings especially have been added. In the vol- ume on parasitic diseases many tables have been gathered together for the sake of comparison, in order to make clear to the reader the different genera of one family in their distinctive characteristics. The new drawings were made by Fraulein H. Detmann and Fraulein E. Liitke, whom I thank very much for their work. Most of all, however, I wish to thank my collaborators. With me, they had to solve the difficult problem of presenting the material in a space deter- mined by contract before the revision. During the revision, we found our- selves confronted by the cjuestion either of giving to the whole subject a briefer form than was originally intended, or of working up some chapters in detail while summarizing others. We chose the latter course and treated the seemingly most important sections thoroughly and the groups, which had been sufficiently worked over in other books, in a correspondingly limited way. Schoneberg, October, 1908. PAUL SORAUER. INTRODUCTION. Section I. THE NATURE OF DISEASE. I. Limitation of the Conception of Disease. Our first task is evidently the necessity for defining the province of which we will treat and for expounding what we understand by the term "Disease." If we call "sick" only those cases in which the organism undergoes such a disturbance in its functions that its existence seems threatened, we will be in a dilemma when we consider the changing developmental forms of our cultivated plants, for we will then discover that the above explanation is in- sufficient. We know, for example, that our species of cabbage, kohlrabi and cauliflower are descended from a plant similar to bank-cress which, in its natural development as a wild plant, shows no tendency toward the forma- tion of large leaf -buds such as cabbage heads, nor of root-like sw^ellings of the stem, as kohlrabi. These vegetables have been produced by selection and cultivation and are characterized by a condition which we term parenchy- matosis, because the woody elements have been replaced by a tender parenchyma, due to the high degree of nitrogen continuously supplied from generation to generation. In dry, hot summers young plants grown on soils poor in food materials begin to show a marked ripening and, in connection with this, a reddish blue tone in their leaves. In case kohlrabi, under such con- ditions, makes any development worth mentioning, it becomes "stringy," that is, its flesh is traversed by tough, hard fibres, making it "woody." Investi- gation shows that the kohlrabi plant by the curtailment of the supply of water and food materials is well on the way toward again developing a wood-ring with prosenchymatic elements, as found constantly in the wild plant. Very similar conditions are found in carrots in which our normal uncultivated plant possesses a solid woody root, rich in starch. Our cultivated varieties, on the contrary, have become thick, fleshy structures ; the best containing no starch at all but the greatest possible amount of sugar. Only in the so-called fodder varieties, as, for example, the white giant carrot, is still shown an abundance of starch. Hofi'mann-Giessen has experimentally developed our cultivated carrot back to the wild form. Now, is the cultivated form a diseased condition since it actually suc- cumbs more easily to certain disturbing influences, or is the reversion of the cultivated plant to the normal wild one to be considered a disease ? In any case this reversion is a condition which must be combatted as it is evidently unfitted for our cultural efforts. In considering such examples we see that, in treating questions of dis- ease, we shall have to follow two lines of work. We must naturally first keep the organism's aim in sight. And this aim, which the organism derives from its very origin, is to live, and in fact to live as long as possible. Every- thing which has once been originated ])ersists as the effect of the causes leading to its production, until a stronger factor arises which disturbs the fixed order and brings about other groupings of material, form and function (an inseparable trinity). But, up to the time of interference of such a factor, the developed individual, with the sum total of the forces inherent in its substance, maintains its then existing order, that is, its individuality, to which a generally definable age limit is set. This necessary mechanical defense of its individuality against the constant attacks of exiernal factors may be termed the "force of self-preservation." In following the second line, the aim of cultivation, developed from the relation of the plants to human needs, is an added important factor. These conditions of the vegetable organism opposing our cultural endeavors will be combatted as inexpedient. But such conditions need in no way threaten the existence of the individual and there- fore, according to the above explanation, are not diseases. Yet they belong to the province of the pathologist as disturbances which must be considered and overcome. In limiting the conception of disease, we meet with similar difficulties in double blossoms, in as much as this doubleness is due to the fact that the stamens have been changed into petals and in doing this have deformed the pistil. This leads to sterility. The length of life of the individual plant is not injured in any way by this sterility, but, on the contrary, is actually length- ened as, for example, in double petunias. But the aim of the species is affected since such double blossoms are no longer able lo^ produce seeds. If this kind of doubling becomes general, such species unist die out in case all vegetative reproductive organs are missing. This variation in structural development, threatening the existence of the species, however, is directly sought for in cultivation and any reversion to the normal, seedbear- ing form is selected out. Here indeed the aim of cultivation contradicts the natural aim and pathology tries hard to overcome the natural trend opposed to the momentary direction of the cultivation, although in doing this, it di- rectly threatens the existence of the species. Such antagonisms are very numerous. In the list of cases in which only individual organs become diseased, one such local disturbance can in- fluence injuriously the organism as a whole, but can yet be useful to the mdividual. We would call attention here to the dropping of young fruit due to drought. The cultural aim is naturally interfered with but the economy of the tree reaps the benefit in as much as it saves the reserve materials, which would have been used in maturing the fruit. As a result of this, the tree is not only in a position to develop the next set of leaves, but also to set numerous fruit buds, which would have remained suppressed had a full crop exhausted the store. When late frosts injure the blossoms and young fruit, the individual organs are certainly severely sickened and fall off later ; but the tree itself has the advantage of saving a quantity of food material. As often happens, the cultural purpose can also profit in this case, because the blossoms developing after the action of the frost yield more perfect fruit and thus an increased revenue. This defines clearly the difference between pure and applied science. Pure science studies the process of disease in itself and can be only cellular pathology, while applied science takes into consideration the effect on the diseased individual and its agricultural significance. We must unite both forms of science since we take the purely scientific studies as the basis of our consideration and explanation of the economic effects of the attack of sickness. The consideration of the cultural needs forces us to the following division of our subject; first of all, we will have to consider all cases which threaten the individual aim of the organism, i. e. its longest possible life;— these are absolute diseases. Then we must discuss the disturbances which the momentary cultural aim experiences and which we term relative diseases. I'hese relative diseases may vary since what cultivation considers worth striv- ing for to-day may be neglected to-morrow. For example, with savoy, every reversion of the plant to Brussels sprouts is a disturbance of the cultural aim to be avoided by changing the seed. If we intend growing Brussels sprouts, however, each variation of these plants toward the savoy form is a deterioration, undesirable in cultivation. Finally, malformations are usually unimportant agriculturally but must be considered. Such malformations may be a maturing of organs in a manner differing from the usual process of development. These natural occurrences, which, we believe, may often be traced back to changes in pressure conditions and other mechanical in- fluences due to the formation of the organs, constitute a special branch of knowledge, — Teratology. This is, however, to be considered as one branch of pathology and we will have to draw into our discussion these phenomena so far as their causes are known or may be surmised with some certainty. The method of treating the material which falls under the province of the study of plant diseases or Phytopathology, will have to be according to the following scheme : — ■ I. Paihography or symptomatics, i. e., the description of the disease according to its individual signs or symptoms. II. Pathogeny or etiology, namely, investigation as to the cause of the disease. Only after the causes are known is it possible to bring into use III. Therapy or the study of healing methods and to draw into the discussion IV. Prophyla.vis or some method of prevortion. 2. The Production of the Disease. If we have said that we must begin with the individual cells when judg- ing a disease, we must know first of all how complicated an organism the cell is and how its structure and function depend on the constitution, position and action of the micellae composing it. Let us, for example, examine some efifects of "swelling." The cell wall at a given time is saturated to a definite degree with water of imbibition, that is, the cellulose micellae held together by cohesion are provided with a water sheath with a certain amount of distention. The micellae will be separated further from one another or will approach one another more closely as the water supply varies; that is, the walls will sometimes become more dense, sometimes more flaccid. Such fluctuations are brought about in the protoplasm of the cell by the action of substances which withdraw water osmotically. Similar processes are observed in chloroplastids, for example, in grain leaves if acted upon by weak chlorin fumes or by sulfuretted hydrogen. The chlo- roplasts are seen to shrivel with the use of chlorine while the chlorophyll grains become pale green, doughy, almost gelatinous bodies with sulfuretted hydrogen. In the cell wall, marked phenomena of flaccidity may often be restricted to single spots. The so-called "bead-cells" in winter grain may be taken as examples of this. Individual cell groups near the larger vascular bundles show bead-like convex centres of flaccidity on the inner side of their walls, which later lose their cellulose character. If young, vigorously growing potato stems are exposed to frost, different groups of leaf parenchyma cells will be found later whose walls seem swollen in lines to four times their normal thickness. In this may be observed the browning and decay of the more dense wall lamellae into stripes which lie imbedded in a homogeneous, lighter parenchyma. In the case of very flaccid membranes, however, molecules will be able to penetrate the greatly enlarged micellar interstices, v/hich cannot force an entrance through the smaller ones, because of their size. If changes in the constitution of the protoplasm have been caused by frost, we find substances passing in and out which could not have been transferred before by the plasma body. The red coloring matter and the sugar in frosted red sugar beets (Beta) pass easily from the parenchyma of the beet into the surround- ing water. This would be impossible in the cut beet, if it had not been frosted previously. The loosening of the structure of the organic substance is a very normal process the intensity of which depends on the action of ex- ternal factors, such as water supply, light, warmth, etc. If these normal processes exceed a certain limit, they lead to disturbances which so alter the structure and function of the cells that they become unable to maintain life. Every other process of cell life may be similarly afi^ected. Under the influ- ence of different factors of growth, the process may be hastened or retarded. We know that each fife function oscillates between wide limits, according to the action of each individual vegetative factor. We call these limits the minimum and maximum and the degree of functioning at which a life pro- cess most favors the development of the organism the optimum. The field of oscillation of the functions about the optimum, ivithin the limits promoting development may be called the "latitude of health." This should not be confused with "tlie latitude of life," for the organism can still live outside the latitude of health, but its functions are so weakened that its development undergoes arrest or retrogression and this condition is disease. If this cessation of the function is temporary, the condition falls under the conception of "check" and we speak of check from cold or from darkness, etc. But we must guard against the belief that the appearance of sickness or a condition of check or of death in any species is connected with any pre- cise numerical values for the separate factors of growth. If, for example, we take two cuttings from the same plant and cultivate them for some time in sand sterilized by heat with the same quantity of food materials but keep one cutting in a hot house and the other out of doors, in the end the tv/o will show a very different susceptibility to frost and other atmospheric factors. The specimen grown in the hot house freezes more easily ; that is, its mini- mum for the maintaining of life is raised. Temperatures, at which the speci- men grown in the open air remains within the latitude of health, arrest the life processes of the hot house specimen. Experiments to determine the maximum and minimum of other factors of growth show .very similar variations so that we may arrive at the conclusion that for each habitat each plant has its own scale of needs, its oiun optimum, maximum and minimum and therefore possesses its ozvn specific latitude of health. Further, the circumstance that the dift"erent functions are lost at differ- ent times should be considered. If, for example, potato tubers are left for some time at a temperature of about — i°C., it will be found that respiration ceases sooner than the conversion of starch into sugar. This results in an accumulation of sugar in the tuber which is called "turning sweet of the potato." If the temperature is raised more slowly to possibly -\-io°C. the stored sugar disappears through the increased activity of Ihe protoplasm and respiration. If cucumbers, tobacco and other heat loving plants have to withstand a temperature of +5° to 8°C. for some time, they show a yellow- leaf condition, which disappears with continued increase of heat. The plants do not die, but assimilation and growth are so suppressed that proces- ses, such as the formation of gums, may be introduced, leading to the prema- ture death of the individual. As in the preceding case of deficient heat, deficiency in food materials or light, — in short, every decrease of any vege- tative function, — so retards the normal direction of the functions that the in- teraction of these for the purpose of a beneficial metabolism is misdirected. Other combinations and functional directions (for. example, fermentations) are now produced, which initiate the ending of life prematurely. The same effect will necessarily appear every time the maximum of any vegetative factor is exceeded, or even approximated. lO In very many cases a sickness which has already set in is indicated by chlorosis, beginning inconspicuously and progressing slowly. Even if it is possible to observe the very beginning of chlorosis, the beginnirig of the sick- ness itself has in no way been discovered since the first molecular changes, which have led to the yellowing of the chloroplast, still remain unknown to us. The boundary line where any single factor of growth ceases to be bene- ficial and becomes a retarding factor may indeed be determined experiment- ally but in this we see only the final result and not the course of development ; i. e., the processes initiating this final result. vSo far as our powers of obser- vation are able to discover, hcalih and disease represent conditions icliich imperceptibly pass over into one another. 3. The Relation of the Plant to its Environment. In the attempt, undertaken in the previous section, to demonstrate how health and disease present interdependent conditions like the links of a chain, we kept in view first of all the so-called constitutional diseases. By this are understood the disturbances in nutrition which influence the whole organism sympathetically and are the results of deficiency or excess of one of the necessary vegetative factors. Local diseases due to accidental interference must be opposed to these general diseases. In them the organism as a whole in its full reactionary capacity is exposed primarily to a disturbance affect- ing only one individual organ. While the action of the necessary inorganic factors of growth come under consideration in constitutional diseases, in local diseases the important influences are those mutually exerted on one another by the organisms. There are insects which seek out the plants in order to satisfy their needs for nutrition or for habitation, or the plants themselves mutually in- fluence one another. We find as the most pertinent example the influence of street trees on the plants growing on the other side of the hedge row. We notice especially in times of drought that the grain and potato plants found within reach of the tree's shadow are not only weaker in development but wilt sooner and to a greater degree than the other plants in the same field. This disadvantage is due chiefly to the tree which keeps off the rain and its roots which withdraw the soil water. In the field itself we frequently find different places in which the seed has grown very poorly because the wind grass has choked the grain. The seed was not sown too thin but the germi- nation and first development were choked by cold and deficiency in oxygen because of impervious spots in the field. In spring the soil does not dry so quickly in these places and the moisture is retained longer; the soil conse- quently warms up less easily and suffers for need of oxygen. The wind grass (Apera spica venti) which occurs everywhere in grain fields is less sensitive and under such conditions develops more quickly than grain. Because of its greater size, it chokes out the seedling grain. Similar con- ditions arise in connection with other weeds, which, developing more rapidly, not only take food materials out of the soil and away from the cultivated II plants, but also injure them b}^ shading. Actually, howcA'cr, this struggle for room is the factor first manifested in each plant community and makes itself felt in all field and forest plantations. In the grain field and in every forest tract, the individual first grooving most strongly chokes out its weaker neigh- bors. It is the universal question of the strong driving back the weak which must find expression in all community life. The kind of community life just described in its relation to spacial sep- aration can be termed neighborhood in distinction from the mutual influenc- ing of organisms when united in space. A relationship of this latter kind (symbiosis) must be the more intimate since one organism lives with the other. De Bary (1866) distinguished a miitualisiic symbiosis from an antagonistic, according to whether the influence is mutually beneficial or detrimental. The terms chosen by A^uillemin (1889) for this relationship "symbiosis" and "antibiosis' seem less fortunate to us. We find examples of a mutualistic community also termed commensalism by van Beneden in 1878, as companionship at table, in the little bunches of roots of the sago palm (Cycadeae) which occur on the surface of the soil, rigidly branching like witches' broom^s and which harbor numerous chains of Nostoc in the large holes in their bark. The genus Gunnera shows similar conditions. Further, the case is often mentioned in literature, in which a water plant, Azolla caroliniana, resembling our Salvinia nutans, in the axillary hollows of the leaves, gives shelter to another Nostoc with longish members (Ana- baena). The most accessible example of mutualism is offered by the struc- ture of the lichen body, in which fungus and alga remain connected per- manently, to their mutual benefit, — Lichenism. In the same way may be explained the s}mbiosis of certain mycelia and the roots of Fagus, Corylus, Castanea and some conifers, the so-called root fungus or mycorrhiza which is usually considered a necessary and universal arrangement. In connection with the mycorrhiza should be mentioned the protective device called Bacteriorhiza by Hiltner^ and Stormer (in Beta and Pisum). Bacteria penetrate from the soil into the outer cell layers of the roots, actually causing a browning of these layers, but otherwise not especially disturbing the health of the plant. According to Hiltner, however, these bacteria prevent the penetration of other injurious organisms (Phoma, etc.). Finally we will consider the arrangement of root tubercles, which may be found in different forms and grouping on the roots of the Lcguminoseae and form those well-known grape-like bodies in alders, which not infre- quently may be observed as spherical nests of short branched roots as large as one's fist. The organisms in the tubercles making the nitrogen of the air available for the plant and described by the students of legumes as Rliiz- obium Lcguminosarum Frank, or Bacillus radicicola Beijerinck, are bacteria 1 Hiltner and Peters, Untersuchungen iiber die Keimling-skrankheiten der Zucker- und Runkelriiben. Arbeiten d. Biolog-. Abt. am Kais. Gesundheitsamte. Vol. IV. Part 3. 1904. 12 just as the producers of the silver white tubercles in Isopyruin hitcrnatum which, according to MacDougal^ develop extensively in soils free from nitrates. On the other hand, the recent investigations of Bjorkenheim- seem to prove that a fungus is concerned in alders. In antagonistic symbiosis, de Bary has used the expression saprophytism and Johow in 1889 defined the idea more closely by distinguishing holo- saprophytes (those lacking chlorophyll) from Iicniisaprophytes (those con- taining chlorophyll). Bischoff has contrasted with this the conception of parasitism. Ac- cording to Sarauw^ the expression "parasite" was brought into use in 1729 by Micheli f6r the Balanophoreae*. In agreement with the classification of the saprophytes, Sarauw has distinguished holo parasites (those without chlorophyll) from hemiparasifes (those provided with chlorophyll). Saprophytism is the ability of an organism to take its nourishment from decomposing organic substances, while the parasite drav/s nourishment from the living organism. If we test this classification, based on the forms of nutrition, we find that here, as in all branches of science, a sharp systematic subdivision is assumed only by representatives of a young school, while those of the older and more experienced school are convinced that transition forms exist between the dift'erent groups. If relative adjacency be compared with nutrient association (symbiosis) each forest and each grain field shows how constantly one organism influences the other, according to whether the one leaves any food materials, water and light, for the other. Just as spacial separation sets no fixed limitation to the form of nutrition, the sub-division of the organisms into those with purely mineral nutrition and those dependent on organic substances should be abolished. Although plants suited for independent self -nourishment can draw their nutrient material from purely mineral substrata, yet the process actually present consists in their taking humus substances which furnish the food materials in an easily absorbable form because of the activity of a rich bac- terial flora in the soil. The advantages of supplying our fields with animal manures should be thought of in this connection. Modern views have strongly modified this distinction between sapro- phytism and parasitism, since they have brought forward numerous exam- ples showing that the organisms called obligate parasites may become de- pendent on saprophytic nutrition in definite developmental phases and con- versely that saprophytes in many instances can assume the parasitic mode of feeding. Miyoshi's^ investigations give us a clear insight into the way 1 Minnesota Botanical Studies 1894. * 2 Bjorkenheim, Beltrage zur Kenntnis des Pilzes in den Wurzelanschwellungen von AInus incana. Zeitschr. f. Pflkr. 1904. p. 129. ■'• Sarauw, G. F. L., Rodsymbiose og Mykorrlizer saerlig hos Skovtraerne. Botan- isk Tidsskrift 1893. Parts 3 and 4. ■i But Tournefort in Mem. Ac. Paris 1705, p. 332, speaks of plants which grow on other plants. 5 Miyoshi, Manaba, Ueber Chemotropismus der Pilze. Bot. Zeit. LII, 1894, pp. 1-27. 13 m which such a change takes place in nutrition. The experiments under- taken at Pfeffer's Institute in Leipsic show that fungus hyphae are irritable chemically and that the direction of their growth may be influenced either towards the stimulating substance, (positive chemotropism) or away from it (negative chemotropism). Indeed their mode of growth also can be changed since, for example, a tendency towards sprout formation sets in with a higher concentration of the solution. The commonest mold species, which occasionally become parasitic (Mucor, Penicillium, Aspergillus) show an irri- tability with substances which almost always can be presupposed to be char- acteristic of phanerogamic plants. Besides dextrin and the neutral phosphoric acid salts, sugar especially attracts fungi, in case the concentration is not too high. Thus, for example, grape sugar in a 50 per cent, solution acts repel- Icntly for Mucor stolonifer, the active agent of decay of fruits. A.cids, on the contrary, and alkalis from the beginning act repellingly. The germination tubes of the summer spores of Urcdo linearis, a grain rust, are attracted by a decoction of plum and wheat leaves. Especially interesting are the cultural results with Penicillium glaucum, whose hyphae bore through the cell walls of a leaf impregnated witJi a 2 per cent, cane sugar solution. In the same way they penetrated artificial cellulose membranes and the epidermis of bulb scales which lay on a nutrient gelatine. These are especially important clues capable of explaining the numerous case of sickness from Penicillium. It is well known that this mold, the most abundant agent of decay in stone fruits, first begins to spread when the ripening process has converted the starch into sugar. In connection with the penetration of Penicillium into the scales of bulbs, we find abundant examples in the cases of decay in the tulip, hyacinth and lily bulbs which occasionally lead to lawsuits. This decay occurs especially extensively when wet years prevent the maturing of the bulbs or if the bulbs are stored when containing an unusual amount of sugar and then used pre- maturely for forcing. Thus we see hozv the cell contents and the cell ziolls of the host plant can determine the penetration of hyphae and the transition of the saprophyte into a parasite. 4. Parasitic Diseases. Supported by various carefully studied cases of parasitism, many ob- servers so generalized the conception of parasitic diseases that they assumed them to be present wherever organisms are found gathered together. In many cases this is supported by experiijients in which the parasitically living organisms were injected into the host and were able to produce a local dis- ease in the tissue. With this method the apparent proofs of parasitic disease were accumu- lated in such a way that one was forced to the assumption that there could be scarcely any disease which was not caused parasitically. Infection ex- 14 periments in the laboratory led gradually to the knowledge that in many cases of 'disease no specific parasites were present but universally distributed fungous and bacterial forms. The further the studies advanced, the more cases were listed in which inoculation with spores of the most common molds, as Botrytis, Penicillium, Cladosporium etc., also the most widely dis- tributed soil bacteria. Bacillus subtilis and B. vidgatus, develop disease in healthy tissue. And finally was recognized the importance of the question how organisms universally present could at times be parasitic in their mode of life and, at other times, saprophytic. Corollary to this question is one which was deduced from rapidly increasing discoveries in many experiments with the same methods of infection; certain varieties or even individuals were resistant while others succumbed easily to the parasitic attack. What is the cause of such dififerences? Some of the investigators brought forward the theory of virulence as an explanation of such cases. It was emphasized that in each separate case parasitism as a struggle between two organisms had depended necessarily upon which was the stronger. If the weapon of attack of tjie parasite, for instance, be an enzyme, able to dissolve the cell walls of the host, then it would be explicable that this process would take place more quickly in pro- portion to the increase of solver.t ferment formed in any given unit of time. Since it was now possible to prove experimentally that the strength of the attack varied in cultures of different nutritive substances, it could be said that, where it became the active agent of disease and its production of enzy- mes especially abundant, it must have been especially virulent. Bacterial cultures furnished the greatest number of examples of change in virulence. Yet such cases were also determined with fungi. De Bary's statement con- cerning the frequently encountered mold, Balryiis cinerca, is well-known. He states that the mycelium must develop by the customary saprophytic form of nutrition up to a certain strength before it becomes parasitic and successfully attacks the living parts of the plants. I succeeded in getting like results with the conidia of this fungus. Masses of spores were strewn on delicate Begonia leaves and kept very damp. After several days it was possible to observe that, where these spores had lain in thick masses, the leaf had become diseased, showing a browning of the tissue. Where the spores had lain isolated, however, no attack could be discerned. The action of the quantity of ferment excreted by the individual spores therefore proved in- sufficient, while the excretion from a mass of spores brought about infection. It can thus easily be understood that parasites, like every other organism, de- velop most strongly when the nutritive conditions are most favorable and that the stronger and the more abundant the formation of their vegetative organs, the greater the excretion of the enzyme and accordingly the increase in strength of their attack. Therefore their virulence is raised. But these processes are not sufficient to explain the fact that in one field when a number of varieties are grown in a single plantation, certa'n ones may be completely destroyed while others standing next are but little injured. 15 or perhaps absolutely iinattacked. Since in such cases the parasite is quickly and extensively distributed on one variety and not on the other, although the atmospheric conditions and other factors of vegetation are equally favorable, the specific constitution of the host plant in these two cases must have deter- mined whether it would become diseased. Thus vve arrive at the conclusion that for the production of a parasitic disease the presence of the parasite alone is not determinative but the constitution of the host organism is also a determining factor. The many infection experiments have led to a classification of the living creatures infesting other organisms and capable of attacking the tissue, in which one group is described as obligate parasites when able tc attack the host plant in all stages of its normal development. Of this group there have been separated as zvound parasites all such organisms as cannot attack the organism possessing normal protective devices but need the changes in tissue offered by the surface of a wound. In a great many in?tances, however, we have recognized the fact that the parasite only finds the environment re- quired for its development when the host has been affected and its functions weakened. Such conditions will appear here as were also decisive in the experiments carried on by Miyo.shi (see preceding section). This group bears the name "parasites of weakness." To this last group especially belong the numerous species which during many generations live on dead organic substances. They therefore must be spoken of as saprophytes which occasionally become parasitic, — facultative parasites. Therefore the boundary between parasitism and saprophytism is lost here and even in those species which are always parasites (obligates), such as the varieties of smut, we find developmental phases with a sapro- phytic mode of nutrition. If we now, however, study more closely the families of our closest para- sites among the fungi, namely, the smuts and rusts, we will find one fact brought into prominence by the most recent investigations and repeatedly substantiated; namely, that the energy of grozvth of the parasite depends on the host plant. We have examples proving that the same fungus occurs in different species of the same host genus in the same habitat, sometimes grow- ing luxuriantly in many large centres, sometimes sparsely in small forms, according to whether the one species has fleshy leaves and the other thin ones. Indeed, the rusts are so dependent upon their host plants that biologic races are formed which, agreeing formally, nevertheless show differences in adjusting themselves to definite host plants and either cannot develop at all, even when carefully injected upon a related host plant, or develop only slightly. Thus we have a special form of the common black rust of grains on rye, another on wheat, another on oats etc. Mycologists cherish the con- viction that this development into individual races through the accommoda- tion to a special host plant is a widespread phenomenon constantly increas- ing. What else can such a race formation indicate than that parasites in their demands have been and still will be most closely connected with the i6 constitution of their suhstraiiimf If, however, as previously shown, the closest parasite is thus very dependent upon its host plant, it only goes to show how completely it agrees with non-parasitic plants in its demands for very definite nutritive conditions, and that with a change in these the para- site changes its character and either adjusts itself or disappears. Stahl's observations^ on myxom.ycete plasmodia show that we must take these phenomena of adjustment into consideration. If the water in the cul- ture glass was replaced by a ^2 per cent, grape sugar solution, the plasmodia either died from this sudden change or shunned the sugar solution. Grad- ually, however, they accepted it, having accustomed themselves to a more concentrated solution (perhaps by a certain loss in v/ater) and indeed in such a way, that, replaced in pure water, they showed considerable injury. In regard to the formation of races, Pfeffer- expresses himself thus ; "Present discoveries . . . make it clear that the tropistic reaction of the same species of bacteria, flagellates etc. gradually changes in accord with the existing cultural conditions. Thus it should be understood that in the same species in nature and in artificial cultures there is found at times a very appreciable ability to respond to reactions and changes, varying to a disappearing point, according to a definite stimulus. Indeed after wide ex- perience it seems possible to breed races in which a definite reaction to tropism has been partially or entirely lost." Parasitism is nothing extraordinary. Possibly it is not a factor which has newly appeared since plant cultivation was begun. It should be con- sidered as a nutritive form which arose gradually with the developrhent of organic life and a necessary one, to be looked upon as the last link in the chain formed by the mutual interaction of organisms. This last link begins with those organisms which have the ability of forming organic substances from inorganic material through the action of light. Joined to these are the plants with the lesser need of light, such as are found among the bacteria living in humus where an addition of quickly decomposible organic sub- stances presents essential aid to the nutritive process. As the struggle for light gains in importance with an increasing number of organisms, the more pertinent becomes the development of groups of organisms requiring but little light and an ever greater need of a method of nutrition by which the raw material is offered in the form of organic, easily re-worked substances. Such conditions are found at present in saprophytism. With the struggle for light in the case of a constantly increasing num- ber of individuals comes also the struggle for space. In the course of time the lack of space will lead finally to those forms of adjustment in the plant world which require soil for their habitat only in the beginning, if at all, and have chosen some other organism as a centre of colonization. The mutual interrelations forming under such conditions are partly friendly, partly hos- tile, just as they occur in mutualistic and in antagonistic symbiosis. 1 Stahl in Bot. Z. 1884, pp. 163-66. 2 Pfeffer, Pflanzenphysiologie, 2 Edition. Vol. II, p. 763. Leipzig 1904. 17 Among the species of plants using some other organism as a habitat, we find the formation of very different devices for the means of nutrition. Be- ginning with lichens, the assistance given by thalH acquires greater and greater significance, up to the formation of a myceHum. The myceHum is satisfied with dead bark, or rather that attacked when dying, or with the leaf substance of its host, or it can only eke out its existence when, with the help of the enzyme which it excretes, it attacks the living organic substance and then calls parasitism into existence. But in all these relations the one fundamental law becomes evident that each organism is associated with the definite constitution of its substratum. This substratum must have the exact requirements for satisfying all the de- mands of the organism, otherwise it cannot thrive. Therefore all the organ- isms which we call parasites make very definite demands on some host. How narrowly limited these demands may often be is shown di recti}' by the bac- teria, for which at times slight fluctuations in the amount of heat, the acidity of the nutritive mixture etc., lead to the replacing of certain species by others better adjusted. In order to cite only a few new examples we will mention the investiga- tions of Thomas Milburn^ who cultivated fungi as well as bacteria. Of the former he found in the case of Hypocrca rnfa that an increase of osmotic pressure first suppresses the formation of pigment in the conidia and finally inhibits the formation of conidia. In this fungus the color of the conidia changes with the reaction of the medium. If the reaction is acid, green spores are formed; if alkaline, yellow spores. A well nourished mycelium forms no fruit in the dark but does develop conidia when poorly nourished. The yellow color of the mycelium of Aspergillus niger is very sensitive to light and when exposed to it turns black within a few hours. The Bacillus ruber balticus found on potatoes, the so-called "Kieler bacillus"^ which, according to Laurent, forms acids on certain nutritive soils and al- kalis on others, is so influenced in its production of coloring matter by the nutritive substratum that it develops a violet color on an acid substratum and orange red on an alkaline substratum. Lepeschkin'* observed that the strictly aerobic bacteria from the sputum in pneumonia. Bacillus Berestnewi, can develop a branching growth on strongly alkaline and on strongly acid substrata, but gradually acidifies the alkaline substratum. In the presence of sugar (dextrose) a pinkish color appears together with the disintegration of the little rods into oidia. In the presence of larger amounts of nitrogen compounds (aspargin, lecithin, peptone) the whole mass of bacteria turns yellow. The optimum for growth bes probably at 25°C. Even at 35°C. the bacterium grows very slowly and at 38°C. is no longer able to grow. It is killed at 55°C. 1 Thomas Milburn, Ueber Aenderungen der Farben bei Pilzen und Bakterien. Centralbl. f .Bakteriologie usw. II. Division 1904. Vol. XIII. Nos. 9-11. 2 See Breunig, Unter.suchungen des Trinkwassers der Stadt Kiel, 1888. 3 Lepeschkin. Zur Kenntnis der Erblichkeit bei den einzelnen Organismen usw. Centrabl. f. Bakteriologie usw. II. Division. 1904, Vol. XII. Nos. 22-24. i8 // dependence on 'the constitution of the nutritive substrata may he proved for parasites, naturally the strongest agent in combalting them is the removal of the favorable nutritive substratum and its alteration into one un- favorable for the special parasite. Since cultivated plants, by the fact of their division into susceptible and resistent varieties, demonstrate that there is a possibility of altering the nutri- tive substratum produced by living plants, the production of such resist oil individuals through cultivation is the first aim of our work, in regard to overcoming parasitic diseases. It is more effective than the present method of fighting parasites locally or preventing their attacks, a method which was deduced from a narrow point of view. At most this may be carried through effectively for small centres of disease but for mechanical reasons is im- practicable for general use. From this point of view parasitism is not such a great menace as it has been represented to be. If parasitism is a definite nutritive form of certain groups of organisms which has become necessary in the natural development of the living being, it must have its stage of equilibrium in the sphere of nature. Arrangements must exist which counterbalance parasitism. It must be possible to hinder its effectiveness by factors simultaneously effective, for otherwise the nutri- tive organisms could no longer exist. This counterbalance is found in the very definite, often narrowly restricted environment which determines the existence of the parasite. That condition of a living creature which we are accustomed to term "healthy," without being able as yet to define it, is one such restricting limit which the parasite under normal conditions is not able to overcome. For, since the defenders of the extreme theory have represented such parasitic micro-organisms as dangerous which are con- stantly present everywhere saprophytically and as yet have not killed the host plants as a whole, these plants must thus possess some protective devices in their normal development, which are repeated in the same sense from gene- ration to generation. We constantly find occurring as such, unbroken de- posits of wax and cork, definite acidity of the cell content etc. That we now find more and more adherents to our theory is proved by the statements of one of our most important students of parasitism, Met- schnikoff^ of the Pasteur Institute. After giving a number of examples to show that the production of the parasitic disease is conditioned by tzuo causes, first, the parasite and secondly, susceptibility of the organisms, he says, (page 7) "if these internal conditions are powerless to arrest the development of the excitor of a disease, the disease is produced. If, how- ever, the organism firmly resists the development of the bacteria, it is pro- tected and thus proves itself immune." (Page 6) "One can no longer be of the opinion that, every time an excitor of disease penetrates a susceptible organism, the presence of the same inevitably calls forth this specific dis- eased condition. Loffler's discovery of the diphtheria Bacillus in the pharynx 1 Immunitat bei Infektionskrankheiten by Elias Metschnikoff, Professor of the Pasteur Institute in Paris. Authorized Translation bv Dr. .Julius Meyer. Jena, Gustav Fischer, 1902. 19 of healthy children has been repeatedly substantiated since that time and yet it is impossible to doubt the etiological significance of this bacillus for diph- theria. On the other hand it has been proved that Koch's Vibrio, although the real inciter of Asiatic cholera, nevertheless, occurs in the digestive system of healthy people." The healthy organism thus possesses a natural immunity and any distur- bance of this aids the possible parasitic attack. 5. Epidemics. If we can define endemics as a local malady, whose production is con- nected with definite conditions, narrowly limited locally, then epidemic may be called a community malady. The expression "malady" indicates the mul- tiplicity of the diseased individuals in contrast to isolated cases of disease. Epidemic thus describes that condition in which numerous individuals suc- cumb to a given form of disease, developing over large territories. If an epidemic breaks out, conditions must be present which disturb the functions of the organism in numerous individuals so strongly that their lives are either threatened with a premature end or are finally brought to this end. This disturbance arises from external causes. If these causes are parasitic organisms, their existence, as was shown in the preceding chapter, is dependent on the factors of growth favorable to their extensive increase. Among these factors belongs the breaking down of the immunity of the nutritive organism. Even with the assumption that a parasite not indigenous to the countries which suffer from the disease might have caused the epidemic by its incur- sion, this circumstance in no way changes the fact that the factors of grozvth already existing are determinative for the production of the epidemic. For. whatever may wander into the country, be it animal, fungus or bacterium, this incursion would not produce an epidemic, if the newcomer found no opportunity for great increase and wide distribution. For example, who does not remember very efifective representations of the importation of the Colorado beetle as the destroyer of our potato crop, or the extensive intro- duction of the wSan Jose scale as the destroyer of our fruit trees? Initiated persons know how often embargo regulations and compulsory disinfection have advanced protection against the importation of parasitic fungi ("White Rot of the Grape" etc.) and they have partially succeeded in getting it. Experience has taught that no theoretically imagined but practically im- possible complete destruction or quarantine of such parasites has possibly protected us from epidemics but the circumstance that they did not find the necessary climate and soil for their increase. Conveisely, the Phylloxera plague should be remembered wdiich, despite all human endeavor and the spending of many millions, became more and more widespread. The Phylloxera finds, even in Europe, sufficiently favorable conditions for exis- tence and on this account defies such means for fighting it as embargo, dis- infection, processes of extermination etc. Upon consideration, it becomes 20 gradually clearer that small living creatures, in fact, the smallest which are introduced by means of articles of commerce or can be easily distributed by dust and wind, may be kept out of small enclosed places but not away from extensive open localities, and that one proceeds better by presupposing the possibilities of a widespread distribution of such organisms although real danger is to be recognized only if an easy capacity for its increase has been proved. If now in all parasitic incursions, not the presence of the parasite but the conditions favoring its spread are proved decisive for the production of the epidemic, then a change in these conditions is the best means for com- batting them. In regard to measures for its suppression and prevention, however, the epidemic furnishes special pointers in that, when it occurs over extensive areas, it excludes as causes all the factors which vary from one another in the dififerent diseased districts. For, since the malady attacks large plan- tations despite the variations in such factors as, for instance, situation, com- position of the soil, agricultural methods etc., these factors cannot be the cause. Rather the cause should be sought in those influences which are the same throughout the whole country. Actually, this can only be the climate. On the other hand, in endemic diseases, conditions of the soil usually act de- cisively. They are to be considered either direct causes of disease since, through unfavorable chemical or physical pculiarities they permanently dis- turb the functions of the plants, or they act indirectly, favoring the increase of the parasites and the strength of their attacks. In this, as a rule, they suppress at the same time the growth energy of the host plant. Soil damp- ness is the condition most favoring this. When the capacity of thick, heavy soils for retaining water is very great on the level or in hollows, an accumu- lation usually occurs which finds no outlet and produces a deficiency of oxy- gen, with an excess of carbon dioxid. The plants indicate this functional disturbance by a change in the chlorophyll apparatus. The leaves, gradually turning yellow, form a suitable growing medium for certain groups of fungi. In all endemics and epidemics a simultaneous sickening of a great num- ber of individuals indicates a considerable period of preparation leading up to the actual outbreak of the malady. For, according to our conception of all the phenomena of life as dynamic processes, each case of disease may be characterized as the immediate or in- direct result of mechanical disturbances exercised by the separate factors of growth on the composition and function of the substance. The life of a cell is a constant struggle between the oscillatory forms momentarily present in the unstable organic compounds and the disturbances constantly exercised upon them by the factors of growth. A change in the substance and with it one in its function appear at once if the disturbance in one factor of growth is so strong that it is able to change the form of oscillation existing up to that time. So long as the dis- turbances as a whole have the effect of contributing to the development of the organism as a whole, that is, the vegetable individual, the plant remains 21 within the latitude of health. Disease follows if the cell or the cell complex is so changed that ultimately the whole structure suffers. Now, however, the fact, always confirmable by examples, that certain cultivated varieties show a tendency to disease not shown by others under similar conditions of growtli, furnishes us proof that in the different individ- uals the organic substance may oppose a differing amount of resistance to the same attacks. This would mean that more attacks are necessary for one individual than for another in order to carry it out of the latitude of health. If, in an epidemic, only large numbers of individuals always suddenly become sick, besides the especially susceptible ones there must also be others among them for which a greater number of attacks and therefore a longer period of action is necessary, in order that they may become sick. Therefore a longer period of the influences producing the disease must have led up to the outbreak of the epidemic and these influences are to be seen in the atmos- pheric factors. Therefore, according to our theor}', each epidemic is, so to speak, the explosion of a charge which had been slowly accumulating for some time. Its cause therefore is not to be sought, at least exclusively, in the existing factors of growth present at the moment but in the accumulation of attacks which for some time previously have been effective in the same way. In parasitic epidemics the extensive occurrence of the micro-organism in no way represents the first stage of the phenomenon but is a final effect of long preparation. This preparation consists on the one hand in .the gradual pro- duction of life conditions favorable for the enormous increase of the micro- organisms, on the other hand, in the gradual weakening of some functions of the host which we believe are always connected with tliis and a correlative increase of other functions. If, for example, we study the best known fungous epidemic, potato blight, observation shows that a period of warm, dull, sultry days usually precedes the outbreak. The fungus Phytophthora infestans is always present. Its astonishingly rapid increase, however, takes place out of doors only if abundant atmospheric precipitation and a warm motionless air con- tinuously favor the production and the scattering of the swarm spores. Dur- ing weather of this kind the potato plant develops a greater amount of sugar, a more rapid stem growth and a great number of young leaves ; that is, it produces an especially susceptible environment for the development of the fungus which scorns organs that have become old. In this way we find that whole fields may become diseased in a few days. On the other hand we do not find the Pytophthora epidemic if the same amount of precipitation occurs in the same space of time but in cold weather. The epidemic cannot develop if, with increased warmth and a clouded sky, persistent strong winds keep blowing. A similar relation is shown in rust epidemics of grains. Like the majority of fungi the grain rusts loye con- tinuous moisture. Yet by no means do we always have rust epidemics in wet years, although there might be scarcely one grain field in which the rusts 22 would not be present every year. The epidemic develops at the time when the leaves are young and only during periods of warm days with frequent even if almost unappreciable showers which make possible a longer retention of moisture among the plants. Cold, wet summers generally prevent the development of rust epidemics. Similar conditions may be observed in bacterial epidemics. Therefore, epidemics are forms of disease which mature only because of far reaching factors. Only certain weather combinations of longer duration may be considered as the initial cause. Naturally the intensity of the epi- demic will vary locally because local factors will produce special favorable conditions. In this way is explained the occurrence of centres in which the malady appears first and disappears last, in case not all the individuals are killed in a short time. In this way is explained further the retrogression of epidemics into endemics ; that is, into narrowly confined centres of disease. Among the epidemics produced by animal parasites, those caused by grain flies are the most abundant with us. They usually take place during periods of continued warm, dry weather after the winter conditions have been favor- able for the individual grain flies which in some regions are always present. So far as statistics now go, preferred centres and points of departure may often be determined for this plague-like distribution. Thus, for example, the province Posen is proved to be especially favorable soil for grain flies. From Posen as a centre an epidemic usually radiates towards Brandenburg, Pomerania and- West Prussia. The whole Eastern part of Germany suffers more from injuries due to flies than does the Western part. North Western Europe is usually visited more frequently and intensely than South Western and South Eastern Europe. According to the point of view here developed any treatment of the epidemics by fighting the symptoms as they appear must ofifer the least pros- pect of success, because these are only the result of initial stages which existed long before. If the parasites arc present in enormous quantities the desire to kill the micro-organisms is seen to be a vain one since no insecticide or fungicide can even approximately reach the main mass and still less cause its death. Thus as the pestilences are induced by general factors acting uni- versally, they must be combatted by broad means which undo the life con- ditions of the parasite and change the constitution of the host, that is, the functional direction. If, for example, long wet periods permit the bacterial rot of potato, which we call "zvet rot," to appear in epidemic proportions, any other means than increased ventilation of the soil can scarcely be used successfully. So far as specific anaerobic bacteria are concerned, the factor favorable to growth (lack of oxygen with excess of carbon dioxid) is re- moved by an increase of oxygen and also by the decrease for them, as well as for other bacteria, of the condition fundamental to their abundant in- crease, an abundance of water. Nature generally works in this way. If, after the rainy periods, dry, windy weather continues for some time so that the soil dries and the air circulates freely, the progress of the disease comes naturally to a standstill. The recommendation of every regulation for the prevention of infection by the removal of infected potatoes from the field, or by deep subsoil cultivation, or the burning of diseased straw in grain epi- demics, we consider to be a work with insignificant results as contrasted with the effect of changed life conditions for the parasite. The amount of in- fected material in extensive districts does not come under consideration at all. At times in the case of damp rot, soil bacteria co-operate and form a dense condition of the soil. If atmospheric influences make themselves so felt in certain soils that certain bacterial groups are able to attack potatoes or other fruits of the field, the number of the causative agents of the disease originally present is almost of no significance. The last named examples of parasitic epidemics due to such micro- organisms as may be assumed to be constantly present in the soil or the air, make clear to us, however, how little prospect of success is ofl^ered for com- batting an epidemic once it has broken out. A greater protection for our cultivated plants lies in preventive methods. Such a preventive process in epidemics, aside from the formation of an universal plant hygiene, can, how- ever, be induced by the drawing up of a chart of pestilences; that is, a sum- mary of plague centres for each individual epidemic. In the correspondence of certain characteristics for a number of plague centres, single factors are especially distinguished as fundamental for the production of an epidemic ; for example, dryness in light soils is shown to be favorable for fly epi- demics of grain or for the heart-rot of sugar beets etc. Having thus deter- mined weather and soil combinations dangerous for each individual epidemic one can make one's attack prophylactically by means of cultural regulations as soon as the threatening combination of conditions continues for some time. Direct means which kill the parasites, such as sprinkling with copper sulfate or dusting with sulfur, will then act only as hinderances to the epidemics if used preventively. 6. Artificial Immuniz,ation and Internal Therapy. It is quite natural that in phytopathology the same course of ideas has developed as in animal patholog}^ and accordingly it is not strange that there has gradually become evident a theory of immunizing plants artificially ; i. e., of so changing their bodily composition that the parasites will no longer find the nutritive soil necessary for colonization, for their wider distribution. There already exist several works along this line in which, following in part serum therapy, use is made of immunifying substances obtained from the parasite itself, and again v/here mineral salts are used. Along the former line belong Beauverie's^ investigations with Botrytis cinerea and those of Ray- with very different kinds of parasites. The latter obtained 1 Beauverie, J., Essai d'immunisation des vegetaux contre les maladies crypto- g-amiques. Compt. rend. Paris 1901. 11, p. 107. - Ray, J., Cultures et formes attenuees des maladies cryptogamiques. Compt. rend. Paris 1901. II, p. 307. 24 the result that parasitic organisms may be influenced in artificial cultures by the nutritive medium used. In this their virulence is proved always to be less than it is under natural conditions. By leeching the cultures, fluids may be obtained which may be used for the immunization of the host plants against the organism concerned. The author concludes further that the in- fected plants are actually cultures of the parasites concerned. In this maceration and extraction of the diseased plant parts must furnish fluids which would exercise an efli^ect similar to that of the parasite itself. When modified by increased temperature, these fluids can be used for immunization. E. MarchaF should be especially mentioned as a representative of the other line of immunization experiments. He worked with mineral substances, some of which were nutritive, while others should be considered poisonous. He sowed lettuce in Sachs' nutrient solution with the addition of substances which kill fungi. The young seedlings, after the development of the first two or three leaves, were infected with the zoo-conidia of Bremia Lactucac and then kept in a moist atmosphere. The plants, not rendered immune by the substances in the nutrient solution which would kill fungi, were at once attacked. Of the salts used, the addition of from three to four ten-thousandths copper sulfate to the nutrient solution was clearly proved to increase the resistance. The addition of i-ioooo copper sulfate no longer showed any immunizing effect whatever. Manganese sulfate acted less com- pletely; ferrous sulfate had no effect at all. Calcium salts also (up to 2-100) could increase the resistance while nitrates and also, curiously enough, phos- phates lessened it. The idea of increasing each individual's susceptibility to vegetable para- sites by changing the cell sap through the addition of foreign substances was also taken up by zoologists who preceded in accordance with the discovery that parasitic animals, for instance, scale, seek out weakened plants especially. Now, however, was associated with this the thought, that universal con- ditions of weakness in cases of constitutional disease as well as conditions of susceptibility to parasitic attack could be healed by supplying salts of some definite kind to the plant body extra-radically. This taking up of substances otherwise than through the roots was called "Internal Therapy'' and was developed methodically. In 1894, I. Schewyrjov- published an article on "the impregna- tion of the wood in living trees with solutions of coloring matter" (Ueber die Durchtrankung des Holzes lebender Baume mit Farbstofflosungen"). In it he describes the apparatus which he constructed for this purpose which we will call nutrition tube and nutrition basin. The tube is of steel, pointed at one end, which is driven into the bark, while the other end is closed by a cork, through which passes a gimlet. The tube is filled with the experimental liquid, through special openings, by means of a rubber tube. Then the gimlet 1 Marchal, E. De rimmunisation de la laitue contre le meunier. Compt. rend. 1902. CXXXV, p. 1067. s Schewyrjov Iwan, Berichtigung usw. Zeitschrift flir Pflanzenkrankheiten. 1904. p. 70. 25 is bored slowly down into the wood to the desired depth so that the liquid but no air can penetrate into the canal thus formed by the gimlet. The author who had constructed other apparatus also mentioned Hartig's ex- periments which had the disadvantage of letting air penetrate into the wound. He then began experiments on the healing of chlorosis which were carried out in 1895-6 and in 1901, by garden owners in the Crimea. Later Mokrzecki^ published a number of successful experiments on the healing of chlorosis in fruit trees carried out according to the above method, in which he also pointed out that the scale had disappeared from the healed branches. He, as well as Schewyrjov, built great hope on this pro-> cess, not only for the prevention of constitutional disturbances in nutrition but also especially for the expulsion of parasitic organisms. My personal attitude toward this question is much cooler and I think that the effectiveness of the methods will be very limited. According to my experiments on the introduction of poisonous solutions into the trunk, the effect usually remains local but in the most successful cases radiates grad- ually from the_ point of introduction to a number of branches and to a con- siderable distance into the trunk. The constitution of the plant, conditioned by root nutrition, was not changed by this. I found in my experiments with oxalic acid that gum was produced on a number of cherry tree branches which later partially died. However, the production of gum did not progress further the following year and the trees, moreover, made a healthy growth. Like this poisonous solution, each nutritive mixture or healing serum remains limited within narrow boundaries and, as in the most favorable case, only temporarily exercises any beneficial influence. The physiological direction of the work of the whole plant will not be changed permanently. 7. Predisposition. We term "predispositivon" that condition of certain individuals which renders them more easily and quickly susceptible to any cause of disease than are other individuals of the same kind. That such cases exist is proved by daily discoveries as to the quantitative growth of cultivated plants. These discoveries have already found expression in the common use of the terms tender and hardy varieties and individuals which have been made less resistant. Observations show that not only diifer- ent cultural varieties of the same species but even single individuals of the same variety possess a varying power of resistance to weather extremes, as, for example, cold and heat, or to parasitic attack. Li the latter connection, it suffices to mention that practical workers as well as scientific investigators have now set themselves the task of breeding more resistant varieties. At present we are only in a position to indicate the direction in which a greater individual inclination to succumb to any parasitic attack may be pro- 1 Mokrzecki, S. A. Ueber die innere Therapie der Pflanzen. Zeitschr. f. Pflan- zenkrankheiten. 1903. p. 257. 26 duced. In the previous divisions we have considered investigations showing that different groups of substances produced in the plant cells, as, for in- stance, sugar, act attractively for certain fungi in definite concentrations and repellantly in others. The number of these groups of substances is deter- mined by very different factors, as will be shown more thoroughly in the next chapter. This metabolism will be found favorable for the nutrition of the parasite or unsuitable for it, according to the quantity produced. In order to cite at least one example in this connection, we will refer to the investigation of Viala and Pacott^ on the black rot of the grape. The cultures, undertaken wij:h the fungus Guignardia Bidzvellii which pro- duces the disease, determined that the development of the fungus is depen- dent primarily on the sugar content of the nutrient substratum and its organic salts. Only young leaves were affected. They contained 1.75 per cent, tar- taric acid and 4.3 per cent, glucose, while the old leaves showed only traces of these substances. The berries were susceptible from the time they began to swell and this susceptibility continued up to the beginning of the ripening stage. During this time they contained 32 to 24 per cent, of acid and 11 to 56 per cent, of sugar. During ripening the acid content falls from 9 to 2 per cent., but the sugar content increases so greatly that the fungus can no longer attack the berries. The conditions for the white rot fungus, however, are exactly reversed. By this relation is explained the strikingly different resis- tant capacity of different kinds of grapes. In the same way is explained the circumstance that black rot epidemics generally occur in summer after periods of cold weather with subsequent light rainfall. At this time the acid content is especially large and the formation of sugar scanty. Similar fluct- uations in the concentration of the cell sap combined with the phenomena of perforation of the membrane, the varying processes of tension in rhe tissues and other mechanical changes also in the plants cause a state of greater sus- ceptibility to weather extremes. The more recent investigation is endeavor- ing to find more macroscopic and microscopic characteristics also demarking the stages of susceptibility to injurious parasitic attacks. The conditions pictured in the preceding example of the increased tend- ency of the grape to become susceptible to the black rot fungi are entirely normal developmental phases which are influenced by the weather. On this account we may speak of such states as normal predisposition. In contrast with these we should distinguish as abnormal predisposition the case in which the plant or one of its organs has fallen into a condition of weakness or of disease from other influences and in this conception of one cause of disease is first given the desired point of attack. As an example, we will call attention to the infection of leaves affected with honey dew by the black fungi, to the attacks of the so-called parasites of weakness and the migration of wood- destroying fungi from wounded surfaces. 1 Viala, p., et Pacottet, Sur la culture du black rot. Compt. rend. Paris 1904. Vol. CXXXVIII, p. 306. 27 8. Predisposition and Immunity. In an earlier part we have pointed out that our theory as to the produc- tion of parasitic diseases has obtained support from the most renowned in- vestigators. Metschnikoff\ who, as professor in the Pasteur Institute for infectious diseases, may be incontestibly considered as an exact con- noisseur of pathogenic micro-organisms, expresses himself as follows, "Exact bacterialogical mvestigations have led to the knowledge that, in the abundant bacterial flora harbored by the healthy human body, representa- tives of pathogenic bacterial species may also be found. Aside from the Bacillus of diphtheria and the Vibrio of cholera which so often have been proved to be fully virulent in perfectly healthy human luMngs, it has been shown that certain pathogenic micro-organisms, the Pneumococci, the Sta- phylococci, Streptococci and Colibacilli, are present regularly or almost con- stantly in the microbe flora of healthy persons. This discovery has of necessity led to the conclusion that besides the excitor of the disease, still a second cause of infectious diseases must exist, namely, a predisposition or a lack of immunity. An individual which harbors one of the species of pathogenic bacteria above-named would be resistant either permanently or for the time being. But as soon as this immunity dis- appears, the excitor of the disease becomes uppermost and produces the specific disease." In regard to the immunity of plants, Metschnikofif calls attention to the investigations of de Bary- on Botrytis, which we have already men- tioned. The mycelium of this fungus penetrates the cell walls by giving off a fluid "which contains a digestive ferment and the oxalic acid necessary for this ferment. De Bary could prove the presence of this kind of toxin by the maceration of the mycelium of Sclerotinia .... If the resulting fluid is heated to 52°C. it can no longer digest the cellulose membrane but is still able to cause plasmolysis .... The results of de Bary's investigations have been confirmed and in part completed by Laurent.'"^ We have repeated Metschnikoff's words in order to characterize his way of considering the matter. The chief factor under consideration here, viz., the efifectiveness of the ferment on young membranes and its ineft'ective- ness on older ones, gives the author reason for comparing the Botrytis dis- eases with the infantile diseases in human beings (measles, scarlet fever). In other cases the different processes of cork production, or suberization, found, for example, in wounds, act in a way similar to the membrane changes in the ageing of the cells. In regard to these, Metschnikoff, supported by the investigations of Massart^ points out that the organs respond difl:"er- ently to the traumatic stimulus according to their age. Young leaves of Clivia, for example, re-act by forming callus, older ones simply close the 1 Metschnikoff, Immunitat bei Infectionskrankheiten. Jena, 1902, p. 6. 2 De Bary Bot. Zeit. 1866. 3 Laurent, Annal. de I'lnstitut Pasteur. Vol. XIII, p. 44. 4 Massart, La Cicatrisation ciiez les plantes. Brlissel 1897. 28 wound by means of a deposition of cork. Further protective means are oils, resin, balsams, milky juices and gums exuding from injuries. Metschnikoff thoroughly treats of Laurent's^ studies which are mentioned in connection with other bacteria in the second volume of this, work. At this point, however, we will emphasize especially the immunity precautions against bacterial attacks. The species of the Colibacillus, with which Laurent worked, secretes a ferment dissolving the cellulose of the potato tuber and produces also sap with alkaline reaction, the presence of which is necessary for the process of assimilation on the part of the bacteria. Now, to be sure, Bacillus Coli communis is naturally not a plant parasite but it can be changed into one. This happens when it is first cultivated on po- tatoes whose resistance has been weakened by having been dipped into alka- hne solutions As a result of such cultivation the bacillus can act as a plant parasite when carried over to the same species of potato. The struggle be- tween the Colibacillus and the potato depends therefore really on the chemi- cal action of the alkaline secretion of the bacillus on the acid cell sap of the potato. After fertilization with potassium salts and phosphates, carrots and potatoes resist the bacillus. On the other hand, a phosphate fertilization showed in (Topinambur) that this plant then became more susceptible to the Botrytis form of Sclerotinia Libertinia. Just as clearly by strong nitrogen fertilization potatoes are made less re- sistant to wet rot. According to our observations abundant fertilizing with nitrates, ammonia salts or stable manure, causes even the most resistant species to succumb to the potato rot. Laurent explains the difference in the action of parasites under the same method of fertilizing by the fact that with bacteria the secreted ferment can attack the cell membrane only in alkaline juices or weakly acid ones. An increased acidity of the cell sap, incited by the formation of acid salts resulting from phosphate fertilization, renders the plants immune to this fission fungus. I obtained the same results for phosphoric acid by fertilization experiments on sugar beets, in which the Bacillus betae was widely disseminated and had produced the bacterial for- mation of gum or tail rot. The rapid increase of bacteriosis with the abun- dant use of fertilizers which contain nitrogen might be explained in this way: — that the acid of the cell sap is thereby decreased. According to de Bary, the conditions for Sclerotinia are exactly reversed. Their ferment dissolves the cell wall only in an acid fluid. Most mycelial fungi act similarly. If, by a change of constitution of the cell sap, sometimes a factor of im- munity presents itself and, at other times, a condition predisposing to para- sitic disease, we are referred by Metschnikoff (1. c. p. 39) to a further pro- cess. He cites the investigations of van Rysselberghe- who found, especially in the epidermal cells of Tradescantia that if these cells were 1 Laurent, Recherches experimentales sur les maladies des plantes. Annal. de rinst. Pasteur. Cit. Zeitscher. f. Pflanzenkr. 1900, p. 29. 2 Osmotische Reaktion der I'flanzenzellen. Memoires couronnes de I'Academie r. d. Belgique. Briissel 1899. 29 brought into a more concentrated solution than was normal to them, they showed an increase of intra-cellular pressure. iT the experiment was re- versed, the pressure decreased. These changes in osmotic pressure are caused by the difference in concentration of the cell sap which may again be considered as a result of chemical changes. If the cell comes in contact with a solution too highly concentrated, it forms oxalic acid which acts strongly osmotically. With Tradescantia, van Rysselberghe proved the presence of malic acid in the normal sap and only in rare cases any traces of oxalic acid. After the plant had been kept some days in strongly concentrated cane sugar solution, oxalic acid was found in clearly appreciable amounts. The plant gradually adjusts itself to the higher concentration of this medium, produc- ing oxalic acid in order to increase the pressure of the cell sap. The acid is supposed to be formed at the expense of grape sugar. The increased acid content will act as a protective means against bacterial attacks. It is also suggested by some investigators as a protective weapon against the attacks of snails and leaf lice. Experiments with Tradescantia made in the opposite direction seem to me to be very significant. If tissues from this plant were taken from the highly concentrated solution and put into some strongly diluted solution, precipitates of calcium oxid crystals were observed in the cell sap, thereby initiating a decrease of osmotic pressure. When the plant was put back into a stronger solution the oxalic crystals were seen to re-dissolve and result in a new formation of acid. I found that part of the calcium oxalate crystals disappeared during the sprouting of potato tubers which also may well be ascribed to the increased formation of acid. Pfeffer^ also takes up this automatic regulation of the acid con- tent since he calls attention to the frequent production of turgidity through the organic acids combined with bases. Since this remains constant during and after growth, the formation of acid must be hastened quantitatively in correspondence with the volume increase of the cell and the dilution of the cell sap thereby produced. Each unusual increase of turgor, as, for example in the effort to overcome an opposing higher concentration, will be connected with a corresponding increase in the acid production. Conversely, for exam- ple in the Crassulaceae, the decrease of the acid content has been proved with an increase in temperature and by illumination. In this same sense the experiments made by Charabot and Hebert- have succeeded. In the shade, the quantity of combined organic acid increases very considerably. The free volatile acids also increase. These are found in greater amounts in etiolated plants than in others. The suppression of the inflorescences in- creases in the leaves at the expense of the other organs. In considering predisposition and immunity, we have brought forward the sugar content in addition to the examples of acid content. To what 1 Pflanzenphysiologie, II Edition, Vol. I, p. 487. - Charabot, Eug-., et Hebert, Recherches sur 1' acidite veg-etale. Conipt. rend, hebd. 1904. CXXXVIII, 1714. 30 fluctuation this is exposed by changes in temperature is best seen in Fischer's^ investigations cited by Pfeffer-. In the so-called starch trees, like the linden and birch, it is found that starch is formed in the bark within a few hours after the branches have been brought into a warm room from a winter temperature. In the cold, sugar is again produced from this starch. This conversion may be repeatedly produced and this kind of sugar forma- tion seems to appear in many plants with a lowering of the temper- ature. If now-, for any reason w^hatever, the sugar formed from the starch is conducted away from the organ the whole tissue may be im- poverished. Pfeffer furnishes proof of this by the experiments carried out in his institution by Hansteen^ and Puriewitsch*. By a con- tinued removal of the sugar by diosmosis, it was possible to cause an ejection of starch from the isolated endosperm of grasses as well as the cotyledons of Phaseolus which had been cut ofY from the plant and a giving off of the glucose from the separate scales of the bulbs of Alliiim Ccpa. If only a little water was present into which the sugar could pass from the organs the ejection came to a standstill because a two to three per cent, sugar solution inhibits the conversion of the starch. Therefore, either a good deal of w^ater must be present or some other means for the removal of the starch if the ejection should be completed. Con^ersely, a refilling of the organs with starch could be determined if a still more concentrated solution were used. These examples may suffice to show how in the plant body all the me- tabolic processes and all the resulting constructive processes succumb under constant quantitative changes which radiate in all directions from the first form of attack of the factor causing the change. Each change occurring locally is a disturbance in the condition of equilibrium existing up to that time in the molecular organization. If the disturbance is completed in one cell it must, so far as diffusible substances are concerned, be continued in the neighboring ones as are all dynamic processes. Each place in which a new structure is formed becomes a centre of consumption. The supply of food to this new structure leads to a reduction in other parts. Each local increase in photosynthesis exerts its influence on the immediate surroundings not concerned in this process. The different factors of growth now act uninterruptedly on the plant body and disturb the momentary equilibrium, first in this direction, then in that. We have there- fore a continued fluctuation in all life processes which is increased still more by the capacity for reaction peculiar to the individual, for we dare not forget that in restoring the disturbed equilibrium the organism must endeavor to increase its production of different substances. If, for example, there sets in an increase of the basic compounds conditioned by nutrition, an increased acid content will have to be brought about and conversely. And within the constant fluctuations which are a necessarv result lies the condition which 1 Fischer, A., Jahrb. f. wiss. Bot. 1891. Vol. 22. 2 Physiology I, p. 514. 3 Hansteen, Flora, 1894. Supplement. 4 Puriewitsch, Ber. d. Deutsch. bot. Ges. 1896. p. 207. 31 we term normal predisposition. Thus the same condition which represents a state of predisposition toward a definite cause of disease can act as a state of immunity to some other cause of disease. Proofs of this are offered by the examples above cited of the hyperacidity of the cell sap which has been shown to give immunity to certain bacterial attacks and predisposition to those of fungi. In the increased sugar content, which is connected with the influence of the acid in increasing the turgidity, we recognize a condition predisposing to injuries arising from frost and, on the other hand, a pre- cautionary means against the disturbing action of drought. In the very natural development of the organism, therefore, we con- stantly face conditions of predisposition and immunity. These are present in varying degrees in each indi\'idual since each organism has special nutritive relations and utilizes differently the same factors of growth. This explains the phenomenon that different individuals in the midst of a community of the same species become sick or conversely, in the midst of a centre of disease, remain healthy^. 9. Inheritance of Diseases and of Predisposition. In the last four decades further experiments have been made by many important investigators to explain theoretically the nature of heredity. In this, special consideration was given to the most juvenile condition — the embryonic plasma — as a transmitter of the capacity for inheritance and the substance which might be indicated as the chief transmitter of inheritance was sought in part in the cell nucleus. The above-mentioned hypotheses of biologists were drawn up to explain especially the repetition of the formative processes in the successive genera- tions of the organism. We will call attention only to Darwin's "gemmules," Haeckel's "plastidules," Weismann's "germ plasm" as an "heredity plasm," Nageli's "idio-plasm," de Vries' "pangene," etc. 1 The parasitic theory as generally accepted at present either still needs an explanation of these facts or is restricted to the theory of resistance. The different capacity for resistance to atmospheric extremes and other non-parasitic influences has remained unconsidered. Thus Alfred Fischer* observes "Individual variations indeed occur often enough even in man; a personal immunity of an inexplicable kind seems to exist which in part falls under the conception of predis- position. Even with ag-e natural immunity varies as shown by infantile diseases. The question may be left undiscussed as to whether even these may not be con- sidered as immunizing: diseases which are said to prepare tlie youthful mortal for an existence surrounded by bacteria and to fortify him.'' On the other hand, Alfred Wolff** explains "In all essentials the natural power of resistance to toxins advances in proportion to the organ's capacity to hold the molecules of the poison and to prevent their action on the brain. Thus only quali- tative and no quantitative differences exist between apparently so diametrically opposed phenomena of an innate non-susceptibility and a high grade of susceptibil- ity in individual animal bodies. These differences lie only in the different capacity of the organs in different animal species for the formation of toxin and an eventual neutralization." ♦Fischer, A., Vorlesungen uber Bakterien. 2. Ed. p. 347, Jena, Gustav Fischer, 1903. **Alfred Wolff, Ueber Grundgesetze der Immunitat, Centralbl. f. Bakteriologie, Parasitenkunde usw. Sec. I. Original. Vol. XXXVII. Part 3, p. 701, 1904. 2>2 According to our theory there is needed for the explanation of the pro- cesses of inheritance, neither any special locality such as the embryonic cells, nor any special cell or plasm germ or inheritance mass or any ancestral plasm, for inheritance is a "mechanical must" a necessary universally present me- chanical result of the structure of the organic substance. As soon as the organic substance, like the inorganic, is considered as an atomic union which retains its character and therefore its specific peculiarities, since the atoms in the molecules exist in definite arrangements and fluctuation, then this sub- stance presents the stage of equilibrium of definite forms of motion. If one cannot define the countless combinations of molecular fluctuations and can- not construct the distention and other mechanical results arising from the dififerent arrangement, one may yet characterize each organic structure as the result of a sum of very definite coml)inations of molecular motions which are conditioned by each other. Accordingly the cytoplasm of the pear is a plasma whose different micellae show in general the molecular fluctuation forms of the plasmatic substances but still possess specific relations of fluct- uation and arrangement which distinguish them from similarly located micellae of the apple cytoplasm. Therefore, in each smallest particle in each biogen of any organic indiz'idtial ivhatever, an individual character may be found which must remain constant as an expression of the sum of definite forms of motion resulting from the law of inertia. This constancy is a mechanical necessity ; — for every motion continues in its existing form as long as it is not m.odified by another demonstration of force and each substance which is the expression and bearer of the motion retains this form and character until other reactions cause molecular changes^ If, for example, we speak of protoplasm, we must be conscious that we do not designate thereby a homogeneous substance with a fixed chemical nature, but a large group of substances containing many forms. The same is true for cellulose, sugar, tannic acid etc. The assumption of the existence of as many variations of substances as there are individuals loses its strangeness as soon as we remember that we see about us daily an equal number of variations of figures, — for, as a fact, no one individual resembles another absolutely. If, however, each biogen is a specific unit, it retains its character with the provision that no substance coming from without may change its molecular grouping, no matter where it is located in the plant body, nor whether it occurs in the form of cellulose or as somatic or embryonic tissue. For all these substances are indeed only groupings proceeding from one another. The biogens which are utilized in the formation of the embryo, that is, at the beginning of the new generation, find an expression in the new individual as in the old for the form of fluctu- ation which they represent. This retention of the molecular form of motion 1 This view of the specificity of each biogen in every organism has already been expressed by Noll, since he states that the egg cell of a linden in its totality is already a linden and cannot be anything else nor become anything else. Noll, Beobachtungen und Betrachtungen uber embryonale Substanz. Sond. "Biolog. Centralblatt." Vol. XXIII, Leipzig 1003, p. 325. 33 in the new generation is hercdiiy. We are not in the least astonished to find carrot substance reproduced from carrot seed. We are also not astonished to find a table carrot produced from a carrot which is rich in sugar and not a cattle carrot rich in starch. Thus the same combinations of substances are transmitted which represent the characteristic peculiarities of our cultural varieties. If in practical agriculture we should plant side by side both of the above-named varieties of carrots we would have opportunity to observe that with the appearance of a certain degree of frost, the table carrots would freeze while the cattle carrots would remain uninjured. The susceptibility to cold of the substance of different varieties of the same species is the most easily observed example of the inheritance of such peculiarities as represent predisposition to disease. Each fruit grower can name varieties of fruit which are injured by frost in his orchards while other varieties standing nearby are not affected or injured. The same rela- tions are found among flowers and with grain it is a universal experience that, among the different varieties of wheat, for example, the square-heads winter-kill most easily. Tlie same variation in the resistance of differ- ent cultural varieties is found also in relation to other causes of disease, as, for example, overheating and drought, excess of water etc. A great deal remains to be learned of the cultural varieties and their study deserves greater attention than has been given to it up to the present. Thus cultivation has furnished us with an ornamental plant, coxcomi) (Cclosia cristato), which has a stem with a broad, much curled vegetative tip. This broad, band-like transformation of the original cylindrical stem (fasciafion) has become constant in the seed. Double blossoms are retained from one generation to another. Weak or one-sided formation of the sex- ual organs can become an hereditary peculiarity, as, for example, in the black currant or in the strawberry culture in /\lten Lande near Hamburg, c From such examples one sees v.diat far reaching differences from the usual mode of development are transmissible through the seed. Each vari- ation indicates a direct thrust against a previously existing peculiarity which is so strong that it is al)le to shatter this peculiarity permanently. The peculiarities of the organism possess a varying degree of stability, i. e. the form of motion which they represent is often disturbed by a weak thrust, while in other cases it can not be changed by the strongest attacks of the surrounding factors of growth. Among the least fixed peculiarities belong the colors of the blossoms, the water and sugar content and the size pro- portions of the organs which can vary even in the natural habitat. Hardest to alter or cause to vary are the relative positions of the organs and the com- position of the biogens, viz., the type of substance forming cabbage head or of a pear tree as such, and distinguishable from that of other plants. No peculiarity of an organism may be considered as indestructible but a num- ber of peculiarities will be retained from generation to generation in their present form because no thrust has existed up to that time of sufficient strength to shake them. These peculiarities, however, which are ac- 34 cessible for factors existing at the time may succumb to the thrust according to the strength of the attack and thus be changed. These changes, because indicative of molecular transpositions, are constant as forms of fluctuation, due to the law of inertia until new thrusts give a new direction to the motion. They are retained also in the organs which we call seeds and must accord- ingly be continued in the new individual and therefore must be hereditary. At times also, conditions contrary to the purpose of the individual, and which therefore initiate the shortening of the life period of the individual, such as a lesser firmness of the substance, will be hereditary. In this sense we will have to reckon with an inheritance of diseases and of conditions which make them especially inclined to predisposition to a disease. Besides the transference of such physiological peculiarities which pro- mote disease in the host organism from one generation to the other, the pos- sibility of an inheritance of parasites through the seeds of the host plant has recently been disputed. Erikfeson^, one of the most prominent investigators of rust diseases, describes a number of instances in rust of grain leaves which have led him to believe that with rust fungi embryonic developmental stages exist in which the fungi as naked plasma, Mycoplasm, appear united with the plasma of the host cell. Such s3mibiotic conditions can be present during the maturing of the seed and can exist as a dormant germ of the rust disease in the succeeding generation. With weather con- ditions favoring fungous development, the rust disease becomes apparent by the mycoplasmated spots transmitted by inheritance in the form then known. The extraordinary difficulty of the question as to the existence of parasites in a mycoplasmatic stage has precluded as yet any fixed decision concern- ing Eriksson's point of view. If the possibility of mycoplasmatic conditions must be admitted, we still think, however, that Eriksson's assuredly correct observations may have this significance since the forms described have as yet been found only near mature spore centres. 10. Degeneration. Erom time to time, especially in practical work, it is asserted generally that our cultivated plants tend to degenerate, i. e. the quantity and quality of their crops diminish, and that certain varieties run out. The degeneration of such favorite cultivated forms, said to take place simultaneously in differ- erent localities, is often traced to senility since it is asserted that even those groups of forms, which we are accustomed to call sorts or varieties, like in- dividuals, are not able to live beyond a definite age. This point of view is supported especially by observations on our fruit trees, the varieties of which are known to be constantly propagated asexually by grafting or budding. Such varieties as a rule originate from one individual plant grown 1 See Literature in "Zeitschr. f. Pflanzenkrankh." Annual numbers for 1903 and 1904. 35 in a definite region, the branches of which are at once distributed as scions. It is now thought that all individuals produced by asexual propagation act- ually represent only the continuation of the tree first developed from the seed. Now, since each individual has its own life period, this many-headed individual which we call a "variety" must fall victim to death after a definite length of time. In this way is explained the universally simultaneous sick- ening and dying out of many a variety. As examples of this kind are given Golden Pippin and Borsdorfer, two varieties of apple, on the degeneration of which there developed an extensive literature in the seventies of the last century^. Other old fruit varieties (especially apple) are said to sufifer simultane- ously from sterility wherever grown, become cankered and die. Potato var- ieties, formerly widely acknowledged to be excellent, are no longer true to type and disappear from the market. The orange trees found formerly in European gardens as most vigorous old specimens become diseased every- where in spite of the greatest care. The celebrated orangeries at Sanssouci, Dresden, Cassel, Versailles etc. have vanished or are represented only by a few often sickly trees. Indeed, even in Italy, large plantations of lemon and orange trees have been attacked by diseases at present apparently incurable. The cause is said to be a weakness of growth which makes itself gradually increasingly felt, together with a diseased condition of the root. The same may be affirmed of grape vines and of olive trees, pomegranates, the Ericas (heathers) of Cape Colony, the Australian Papilionaceae and Myrtaceae, ■which formerly, as "Javanese" plants in special conservatories, formed the decoration and pride of gardeners. Even in our species of grains, we have noticed the disappearance of the good old varieties. This is the opinion of the representatives of the theory of degeneration. The theory of the continuity of an individual through all the scions, for which the stock, or the parent plant rather, serves only as nurse, is based on the presupposition that this individual retains all its characteristics un- changed during its whole existence as a variety wherever grown and on the different stocks. For, at the moment when it must be granted that the habi- tat or stock may change any peculiarities, a variation in the length of life due to different nutrition must also be considered a possibility. For this reason those who defend the theory of degeneration and a fixed life period of varieties (especially Jensen among botanists) insist upon the fixity of characters and support their theory by the fact that the varietal character always remains constant in seeds and in cuttings as well as in grafts. Defi- nite shoot variations produced on any one specimen (variegated leaves, split leaves, forms with weeping branches, fasciations etc.) which can always be transmitted by grafting on new stock are proofs most often stated. 1 "Wearing out of varieties," Gardeners Chronicle 1875. "Do the varie- ties wear out?" ibid. "Degeneration from senility" in the Fruit Manual 1875. "Golden Pippin degenerated" in Gardeners' Chronicle 1875. Compare "Bericht iiber die Verhandl. d. Sektion fiir Weinbau in Trier," 1875, etc., etc. 36 Such statements are refuted by the increasing resuUs of grafting which show the mutual influence and change in individuals, incited by grafting. It IS known that a form of albinoism, i. e. the condition of having white leaves, which we can perhaps call "marbled," is transmissible from scion to stock. Differences in the development of a scion dependant upon its being grafted on dwarf species or wild stock are known. Just as abundant are the examples of changes in size, structure, coloration and taste of the fruit ac- cording to the habitat and climate. Finally it should not be forgotten, that, in extensive cultivation of varieties, we always find some which "do not hold," that is, which from the time of germination show so weak a growth that they soon disappear. This indicates a dying out of very young varieties. In this instance the theory of senility does not hold. In connection with the statement that varieties of fruit formerly highly prized no longer thrive and simultaneously run out wherever grown, it is interesting to compare some reports dating from the time when the question of degeneration became one of paramount importance, which concern directly some of the varieties of fruit said to be running out. Hogg stated in 1875. in "the Fruit Manual," that Knight had complained of the "English Golden Pippin" as a variety at that time degenerating because of senility. He says that Mortimer, almost a hundred years before Knight, had spoken similarly cf the "Kentish Pippin." Healthy specimens of both varieties, however, are still found in England. The length of life and strength of cultivated varie- ties (says Hogg) may be proved by the "Winter-Pearmain," which may be taken as the oldest English, variety of apple, since it was mentioned in manu- scripts as early as about t2oo. The Borsdorfer apple and the well-known plum "Reine Claude," are very old. According to Bolle\ the "Reine Claude" must have originated in the 15th Century since it was named in honor of Claude, the consort of Louis the XII (T490). These few examples show that the theory of degeneration due to sen- ility of individual cultivated Aarieties or due to other causes has been formu- lated because a persistent retrogression has been observed in production and healthfulness from time to time iti many localities, from which observations general conclusions have been drawn. The fact that in many regions culti- vated, well-preserved forms no longer show a thrifty growth and may be replaced by others, is undeniable. But this fact only proves that, since each culti\ated form makes definite demands in soil and climate, these demands can not be satisfied further in many places. Degeneration may be spoken of when a cultivated variety runs out universally, even in places where suitable conditions have been retained. However, proof of this is lacking. The breaking down of the varieties after long cultivation may be due to twofold causes, either the cultural conditions have been changed or the character of the variety has become different. In the first place, the fact that cultural conditions in any one locality are different every year is one to 1 Quoted in Oberdieck, Pomolog. Monatshefte 1875, p. 240, Bouche and Bolle, Monatsschrift d. Ver. z. Beford d. Gartenb. 1875, p. 484. 37 which we usually pay too little attention. Aside from the fact that the weather of one year always varies from that of the preceding year, the soil too is always different ; indeed partly because the time and method of working as well as the fertilization and previous cropping in themselves ahvays eft'ect changes, and partly because this changed arable land is also subjected to changed weather conditions, so that it differs every year physi- cally and chemically for the same variety. In the main portion of the book a sufficient number of examples of the influence of planting, previous cropping, mechanical soil constitution and such factors will be cited and it will be shown how these can influence the character and power of resistance ; as, for example, to frost. In the second place wq think that the running out of a cultivated variety can also arise because the variety itself changes its character. According to our hypothesis, there is, in all organisms, no stability ; there is no strict ma- terial or formal repetition of any process, because the organism changes in the smallest unit of time, at each moment confronts the same factors of growth as a different organism and strides forward to adjustment. Thus each variety, like every term of relationship or of classification, is only a frame work made up of common characteristics in which individuals con- stantly fluctuate because of lesser variations. An excess of nitrogen develops a plant substance different from that produced by moderate nitrogen nutrition, a deficiency of potassium makes an organ different from that grown with an abundance of potassium. Abun- dance of light and deficiency of light develop the cell wall in dift'erent ways, great warmth produces more sugar than scanty amounts of heat, etc. Exact examples are given in the chapters on the action of individual factors of growth. Therefore the organism is like wax which, because of the thrusts of the individual z'rgetatiz'e factors, is constantly pressed into other material forms. The material constitution of the plant body, however, is changed by the \ariations of the molecular arrangement which we call chemical changes, as well as by the mechanical ones in which the chemical composition remains constant. The mechanical disposition of water in the tissues, the substances carried in in the water, the tension conditions in the cell wall and the cell contents, are all factors which change constantly and as constantly influence each other differently. The slightest increase in the supply of light is a thrust which not only influences the assimi'atory process, but must also in- directly exercise an effect on all other functions. This does not depend at all upon wdiether we can define these effects ; — the proof that they must take place is enough. Let us now consider how the thrusts of individual factors of growth act normally on the plant body. Here we notice a peculiar alternation. xAt day- break the action of light begins ; — assimilation, evaporation, thickening of the cell wall etc. are increased, the whole structure reflects all the phenomena of the light reactions. At nisfhtfall. when the after effects of the lieht have 38 ceased, processes of oxidation come to the front, phenomena of increased turgidity, conversion of starch and the like. The same changes may be ob- served in the media surrounding the plant, in the air and soil. A decrease of warmth and increase of water content must act powerfully on the plant body. With the change between day and night is associated the influence of the seasons, which forces upon the plants a period of rest after a time of production. Therefore we find in nature a "corrective periodicity." Amid these regularly alternating fluctuations of the vegetative factors, the plant balances its growth and completes its normal course of development. Since the duration and action of these periods in each year differ, the production of each plant differs also and the individual years are thus char- acterized. We speak of dry and wet years and know from experience that in the former, the yield of grain is noticeably large, while the straw yield is less on account of the shortness of the stalks. In wet years this is reversed. And although the farmer then complains that the baking quality of the flour has suffered, yet he emphasizes the fact that he finds compensation in the greater straw harvest. This example, taken from general practice, shows how great single vari- ations in the average periodicity at once becomes noticeable since the prefer- ence is shown for different peculiarities of the plant body. As long as this kind of one-sideness in development does not threaten the existence of the individual plant we may leave the results out of consideration and seek to equalize possible cultural variations (as, for example, by the crossing of grains possessing poorer baking qualities with those rich in gluten which come from dry, warm regions). However, the single prevalence of a definite atmospheric factor can also lead to direct disease since the effects are cimiulativc. Such an accumulation of effects may be compared to the increase in celerity in falling bodies where the distance of the fall equals the square of the time. If, instead of gravity, we assume another factor, such as v/et, cloudy weather, it will in one day in- crease the water content of the tissue while the wall thickening remains be- low normal. On the second day, the first day's action is doubled and the already porous tissue becomes still more porous. The thrust against the plant body, which in itself would not produce disease, is cumulative to an extent ultimately threatening the plant's existence. Practically v/e find this even within one vegetative period, as, for example, lodging of the grain in rainy seasons. The moisture has lengthened considerably the cells at the base of the stalk while the deficiency of light has essentially arrested the thickening of their walls. The result is that the weakened base is not able to sufficiently resist the strain of the wind and gives way. The development of the grain is weakened or inhibited, according to the extent of this lodging and the phenomena resulting from it, so that the stalk iself is also brought to a premature death. Corresponding to the above mechanical changes in the wall, the cell contents are subjected to changes leading to a diseased condition in the case 39 of other influences on the part of the vegetative factor which accumulate along one line. We find in heavily fertilized nurseries, whole plots of lux- uuriantly growing sweet cherries with open or hidden gum spots and in forests whole tracts and healthy looking beds of conifers which show in their wood-tissue the beginnings of a resinous condition. In garden cultures especially, which on an average are worked with the largest quantities of nitrogen, whole plantations suddenly become diseased and are abandoned because the "plants will not grow." Enough cases of this kind have reached me, in which individual breeders have announced that Begonias, Primula sinensis fl. pi., carnations, lilies-of-the valley, cyclamen and others which at other times under the same cultural methods had always been produced in the greatest perfection, retrogress from year to year and "degenerate." Sim- ilar conditions may be observed in field cultures. Entire fields of potato varieties which formerly gave faultless crops now easily become black specked. Sugar beets grown in the soil best suited to them tend to root rot. It has been observed in the root rot of beets that plants grown from trans- plants became diseased especially easily, while seedlings from the best and heaviest sugar beets showed almost no root rot. Cucumbers forced under glass, and those grown in fields in wet, cold years are spoiled by gummosis, and the like. My experience in remedying such occurrences leads to the conclusion that an increase of one definite line of development is concerned in these cases which is usually called forth by excess of nitrogen and water. Our constantly increasing intensive cultivation not infrec[uently leads to a showy luxuriance of the plants and then to a sudden collapse, if the equaliz- ing factor is not able to act in a corresponding amount. Accordingly in cases of a shown great nitrogen supply, I found the use of calcium phosphate to be very advantageous. Such one-sided lines of development will also appear necessarily in the development of the seed. If it is cultivated from generation to generation under the same nutritive conditions, as when first produced, definite peculiari- ties of its place of growth must become hereditary through habit. Accord- ing to our theory that all peculiarities of an organism represent dynamic conditions and molecular vibration-groupings, the habit would necessarily be explained as inerfia. The law of inertia of all matter requires that it re- mains exactly in the same course and at the same rate of motion. Thus the organism keeps on vibrating as it has once been impelled, until some factor of vegetation changes the rate of its growth or the direction. Practice utilizes this circumstance in the "change of seed," that is, in the use of seed from other places which have developed a definite desirable peculiarity. Thus the use of Swedjsh grain by Middle-European agricul- turalists has become more extensive because it is desirable to take advantage of the shorter vegetative period of the northern varieties. While an especially developed mealy condition is typical of English wheat, regions with opposite climate conditions produce chiefly hard wheat etc. 40 Just as useful types of grain arise as the products of atmospheric and soil conditions, weakened conditions of the cultivated plants may also be produced locally and transmitted through seeds. If these weakened con- ditions are repeated from generation to generation by the persistence of causes and accumulate, they may lead in the end to a complete decline and to premature death. Yet this is, however, no degeneration of the species or variety, for all these characteristics may l^e reproduced under other cultural conditions. We perceive this from the fact that the useful special characteristics introduced by a change of seed, are retained only a few years. Then the imported culti- Aated forms become changed and assume characteristics such as are due to the climatic and soil conditions in the place where they are cultivated. Such is also the experience in practice work which constantly attempts in some way to accustom (acclimate) highly productive species of a different climate, to some one cultural region. If it seems desirable to apply the term "degeneration" to the above cases of the accumulation of peculiarities leading to a weakening of production and to premature death, it is possible at most only to speak of local transi- tory degeneration of a number of individuals. It is, however, really only a depression of the direction of development, which can be raised again by external factors, such as cultural methods. A persistent depression in growth as a result of the senility of an originally long-lived variety, is not to be assumed within any definite epoch. The disappearance of cultural varie- ties is explained by a decreased profitableness resulting from a deficient power of adjustment to our agricultural methods, which are constantly be- coming more intensive. SECTION 2. HISTORICAL SURVEY. In any branch of knowledge so young as phytopathology, any history of the science can scarcely be presupposed. And in fact the date after which the teaching of plant disease was set up as a special branch is so recent that we are still able to survey completely the course of its development. If, however, the form of investigation is still new, the material, viz., leports on plant diseases, is very old, extending far back in history. We can not go astray in assuming that there have been diseases since the existence of the plants began and that observations on these began with their cultivation. For we constantly see what heavy injuries are produced by atmospheric ex- tremes, and indeed not only ])y those flisturbances which instantly kill the plant, but rather by such as weaken the individual in structure and form, and slowly lead it toward a premature death, — i. e. make it sick. The action of injurious atmospheric conditions must have existed always and have made themselves evident in different forms. One of the oldest names which we find for certain forms of sickness, is "blight." On this account we will attempt to trace the growth of our branch of knowledge by following the observ.ations of the diseases which this name connates. As the later reports show, at first all those phenomena were character- ized as "blight," which appeared to the eye to have the color of burned or charred matter, that is, black. Accordingly "blight" comprised on the one hand the groups of tree diseases, in which the dead bark assumed a black- ened appearance, on the other hand also the injuries to grain, the causes of which we trace back to smut and rust fungi. If we look first in the Bible for mention of diseases and especially of "blight," we find, for example, the following: — ^"If there be in the land famine; if there be pestilence, blasting, mildezv, locust, or if there be caterpillar ; if their enemy besiege them in the land . . . ." Again : — '-"The Lord shall smite thee with consumption and with a fever, and 1 First Book of Kings, Chapter VIII, 37. Second Bool\ of Chronicles, Chapter VI, 28. 2 Deuteronomy, Chapter XXVIII, 22 42 with an inflammation, and with an extreme burning, and with the sword and with blasting and with mildezv; and they shall pursue thee until thou perish." From these verses Eriksson^ concludes that these statements, which are more than two thousand years old, refer to smut and rust in grain. He cites the word Schiddafon (heat) for mildew or blight and Jerakon (yellowness) for rust. The following sentences already quoted by Pammel" point to mildew in grain : — "I have smitten you with blasting and mildew : when your garden and your vineyards and your fig trees and your olive trees increased, the palmer-worm devoured them "^ Descriptive of the extent of the failure in the harvest is the verse in Haggai* : "Since these days were when one came to an heap of twenty measures, there were but ten : — when one came to the pressf at for to draw out fifty vessels out of the press, there were but twenty, I smote you with blasting and with mildew and with hail in all the labors of your hands . . . ." Among the Greeks, Aristotle (384-322 B. C.) mentions the years of rust and Theophrastus of Eresus (371-286 B. C.) recognized the varying susceptibility of the different varieties of grain to rust'\ He reports also a second kind of phenomena termed blight, i. e. the bark blight of trees, since he says (Book 14, Chapter 14) that the cultivated tree? are subject to several diseases. Among these, some are common to all trees while others attack only certain tree species. One universal disease is the attack by worms or by blight. Theophrastus, whose statements, according to Kirchner*', are certainly based on his own observations, speaks especially of the blight and canker of fig trees and mentions in this connection that diseases of trees (as of animals) seem to be determined by climate, since in some regions these same trees are healthy. The fig tree, he says further, is attacked mostly by blight and canker. Blight (Sphakelismos), however, is spoken of when the roots become black, canker (Krados) when the branches become so. Tlic zvild fig tree, on the contrary, has neither canker nor blight. The statement, that some fatalities are due to the influence of atmos- phere and habitat, indicates to us the cause of the disease. Such phenomena can not really be termed disease, as, for example, freezing and what some call blight. In some places certain winds also kill and burn the plants, as at Chalcis in Euboea, where the northwest wind is cold, if it blows shortly be- fore the solstice. It blasts the trees and dries them, almost more than the sun. 1 Eriksson, Die Getreideroste. Stockholm 1894, p. 8. (Here detailed historical reports on rust). 2 Pammel, L. H., Weems, J. B. and Lamson-Scribner, The Grasses of Iowa. Des Moines, Iowa, 1901. 3 Amos, Chapter IV, 9. 4 Haggai, Chapter II, 16-17. 5 Naturgeschichte der Gewachse. Translated and explained by Sprengel. Al- tona 1822. I. 6 Kirchner, Die botanischen Schriften des Theophrast von Eresos. Sond. Jahrb. f. klassische Philologie. Leipzig, 1874. 43 It is doubtful whether the disease mentioned here as canker bears any resemblance to the outgrowths at present called canker. It is certain, how- ever, that woody excrescences were also observed. If actual canker swell- ings are not concerned here, yet the phenomena may well have been meant, which we would now call knarls. Theophrastus found this kind of swellings in olive trees and called them nails or scurf (loxaslopas) because they represent bowl-shaped nails on the trees. Sprengel says of these nails, that they have occurred recently very abundantly on the olive trees in Italy. They appear as round, warty outgrowths of the bark, depressed in the centre like a bowl. Among them may also be found similar swellings of the wood body. It is scarcely credible that the points of view expressed by closely ob- servant scholars of Aristotle, concerning the phenomena of disease here men- tioned, changed essentially in the course of the following centuries, for other- wise the celebrated encyclopaedist Plinius Secundus', who lived from 23 to 79 A. D. and who possessed a wide knowledge of literary sources, would have brought forward further material at the time he recorded scien- tifically the statements of Cato (de re rustica) and others as to the influence of the stars and the death of trees resulting from cold, heat, unfavorable position, soil, fertilization, incorrect pruning and the like. The discoveries set down in his "Natural History" contain much worthy of notice regarding the influence of atmospheric factors, cultural mistakes, circumstances pre- disposing to disease etc. In the edition of the "Romischen Prosaiker" by Osiander and Schwab, the translator of Pliny (Kiilb) has given a summary of Pliny's sources and special remarks on the authors instanced in his "Natural History." There is rich material here for a complete history of phytopathology. We must content ourselves with a reference to these carefully collected Greek and Roman sources and perhaps show by only a fev; more quotations what exten- sive discoveries had been made at the beginning of our era. According to this, there may be found in the seventeenth book of Pliny's "Natural History," Part XXXVII., his statement of the action of frost. He says, "Not the weak- est trees are endangered by frost, but the largest ones, and, therefore, when they do suffer, the highest tips become blasted, because the sap arrested by the cold can not reach that point." We find the following note about the phenomena, which we would now call "frost blight," — "The evil influence of the stars depends entirely on the Heavens; on this account there must also be included among these effects, hail as well as blight and the injury caused by white frost. The blight especially attacks tender plants if, enticed by the warmth of spring, they venture to break through the ground and it singes the juicy buds of germinating plants. In blossoms this is called blasting." In regard to carefully cultivated grape vines, one reads — "Another bad influence of the stars (atmospheric factors) is the covering with dew 1 Plinii Secundi naturalis Historiae libri XXXVII edit. Janus. Book 17, Chap. 37. 44 (roration, the falling on them of cold dew. Kiilb) while they are in bloom, or when the berries become hard grains and spoil before they mature. They also become diseased, if they freeze and the blight injures the buds after pruning. Untimely heat has the same results, for everything has its definite measure and goal." At present we summarize the experiences more exactly in our teaching of an optimum and of minimum and maximum limits for the factors of growth. In reference to defective cultural methods it is stated that diseases arise when the vine-dresser ties the vines too tightly or injures the roots when digging around them and ])arks or bruises the trunk. Under all these con- ditions they (the vines) endure wet and cold much less easily because each injury penetrates into the wound from without. Scarifying is recommended as a remedy because the thickening bark fastens the stems together and plugs them. As a protection against the frosts of winter, is mentioned the method by which water-ditches are dug about the grape vines in winter, when the ground is covered with snow, so that the cold can not blight them. The most abundant information as to cultural methods and the evils attendant on them may be found in the collection of excerpts from old agri- cultural authors, which was made in the tenth century, the "Geoponika." We base our discoveries here on the books of the four well-known Roman Geoponicists, Marcus Cato, Terentius Varro, Palladius and Junius Modera- tus Columella, in which special attention is paid to the practice of fertilization and grafting. A compilation of the books on agriculture by the authors here named appeared in Cologne in I530\ From this work I will choose those places which show that the term "rust" as a cause of disease is of very early origin. Thus Varro mentions in the first chapter, among the gods, "qui maxime agricolarum duces sunt" . . . . "Quarto Robigum, et Floram, quibus propitiis, neque rubigo fru- menta, atque arbores, corrumpit, neque non tempestive florent. Itaque publicae Robigo feriae, robigalia. Florae ludi. floralia instituti." The ex- pression "rust" was used probably for all rust colored, diseased discolor- ations in plants, for we find the word Robigo used by Columella to designate a disease of grapes which can be avoided, when frost threatens, by smudging the vineyards. In his book, "de arboribus," Chapter XIII treats of: Ne rubigo vineam vexet. It is recommended "Palearum aceruos inter ordines uerno tempore positos habeto in uinea : cum f rigus contra temporis con- .'^uetudinem ne intellexeris, omneis aceruos incendito, ita fumus nebulam et rubiginem remouebit." The following place is found in the "Enarratio priscarum vocum" in regard to the interchangeable usage of "Robigo" and "Rubigo" ; "Robigo, deus, quem putabant rubiginem auertere, est aute Rubigo morbus segetum"-. 1 De re rustica M. Catonis liber I., M. Terentii Varronis lib. III., Palladii lib. XIV. et I. M. Columellae lib. XIII. Pri-scarum vocum in libris de re rustica enar- rationes, per Georgium Alexandrinum. Coloniae, Joannes Gymnicus. Anno MDXXXVI. - Here, as in the following' citations, we will follow our sources exactly. 45 The next fifteen hundred years accepted the observations and theories of the Romans, which may be found collected in Pliny. For E. Meyer^ leports from Petrus de Crescentiis who wrote his great work in 1305, the first eight books of which treat of agriculture, that since Palladius no one had' written anything in Latin on agriculture. Only fragments of the Greek collection of the Geoponika were to l)e found. The older works of Varro and Columella we';e no longer suited to existing conditions, so that there was need of an up-to-date book on agriculture. Yet the book by Petrus de Crescentiis actually contained less than the books of the older authors, al- though he strived for a sciei:tific foundation for agriculture and gave num- erous directions for grafting various kinds of trees, in accordance with the favorite pursuits of antiquity and of th.e middle ages. In the same way in 1600 Colerus" also only repeated the earlier statements regarding the cutpushings of the bark, — "Inflammation of trees" ("Schwulst der Bewne") under which there develops a putrid Ii([uid. In this book the iniluence of the stars was believed in, with unshaken firmness. For example, in his "Horti- cultura" published in 1631, the renov/ned Professor Peter Lauremberg'' of Rostock relates that certain stars like Orion, the Pleiades and others exert an especially injurious infiuence and that, as a result of injurious atmos- pheric influences, the so-called "secret evils" arise, among whicli belong rust, carbuncle and mildew. We can naturally expect to find progress in the recognition of the sig- nificance of disease among practical workers, whose cultural efiforts are most sensitively disturbed by injuries making themselves felt in their work. The book of the "Electoral Superintendent of Gardens," — Heinrich Flesze^, — which was famous in its time, is interesting in this connection. He speaks of the blasting of the branches which he calls "blight and cold," "otherwise there are three chief causes for the blighting of trees. First, superfluous moisture which, with inflammation of the sap, is collected be- tween wood and bark, distending the latter and blighting and blasting it. The second is this, — that of times, thoughtlessly and v/ith a lack of judgment, the tree is set in a postion dift"erent from the one in which it stood before. This is very injurious, since the bark where it is brownish and has been exposed to the east or south, is therefore much harder than on the sides toward the north or west. These are generally green, tender and immature. Therefore, some injury must inevitably arise from this, since the north side is not at all accustomed to the southern sun and is not only blasted by the great heat but in the spring is injured by the hard frosts ; the bark is raised, then later in the day dried up and scorched by the sun. From this the blight at once arises, since it is commonly noticed on th.e southern side." Flere we have posi- tive personal observations. The author relates further that he has never- 1 Geschichte der Botanik. Vol. IV, p. 148. - M. Joannis Coleri, Oeoonomia und Haussbuch etc. Ander Theil. Wittenberg 1600. Book V. Chapter 12. 3 Petri Lauremberg-ii, Rostochiensis Horticultura. Francofurti 1631. Cap. XXXV. 4 Heinrich Heszens, Neue Gartenlust etc., enlarged and provided with three useful indices by Theodorum Phytologum. 1690. Chapter VIII. 46 theless preserved trees thus reversed in position by placing a covering of cow manure, oat chaff, glue and ashes on the side of the tree unwisely turned toward the south. "The third case, however, arises when a bread knife is used in grafting etc." Perhaps Hesze has in mind here some parasitic in- fection and attempts to explain it. Hesze (p. 312) writes "that canker ("Krebs") really orginates from the grafting of a tree at the time when the moon lies in the sign of the crab or scorpion . . . ." "This disease may be recognized by the fact that here and there the bark throws up little hummocks under which the tissue is dead and black. This spreads further and further, ultimately infecting the whole trunk. Many scattered causes of canker have been brought forward, but the one given above is the most probable of all." The Editor makes the following addition to this statement, — "So far as canker is concerned, no one can deny that it often arises high up on the trees, and, in fact, in the accumu- lations of dirt which collect between the trunk and the branches at their crotches. On this account, it is most necessary that the crotches always be kept clean and freed from all dirt. Thus the canker often arises from the same rising sap which produces blight and the two diseases often have but cne cause." The author clearly describes the phenomenon which we now term limb canker and, instead of "ascending sap," we insert, injuries due to frost with a subsequent infection by Nectria ditissima; his presentation corresponds with our present conception of blight and canker. About this time in France, de la Quintinye wrote "Le parfait jardinier"^ which is still much sought after. In this we find canker briefly mentioned as a kind of gall (signifie une maniere de galle ou de pourriture seiche), formed in the bark and the wood and often found on pears (Poire de Robine, Petit Muscat, Bergamotte), on trunks as well as branches. The conception of the swellings of the wood indicated by the term "canker" Is found further in the writings of later horticultural authors, as, for example, in Fischer-. The boastful Agricola^ (born 1672) stands independent, that is, on his personal, repeated and practical experience. His actual service is found in his numerous experiments, carried out from 1712-1715, on the vege- tative reproduction of plants (especially by roots). He devotes the fifth chapter to "occurrences and diseases" and expresses himself, for example, as follows : — "Mildew, Rubigo, however, prevails at times, as a pestilence among trees. In spring, when the earth opens and the enclosed vapors be- 1 Le parfait jardinier etc. Par feu Mr. de la Quintinye. Paris 1695. Vol. I., p. 31. 2 R. P. Christophori Fischeri soc. j, Fleissiges Herrenauge etc. Niirnberg 1719. 5 Section I., p. 168. 3 Georg- Andrea Agricola, Philosophiae et Medicinae Doctoris und Physici Ordinarii in Regensburg, Versuch einer allgemeinen Verhmehrung aller Baume, Stauden and Blumengewachse anjetzo auf ein neues iibersehen usw. von C. G. Brausern. Regensburg 1772. The original title read, — "A new and unheard of ex- periment, well founded in nature and in reason, for the universal increase of all trees, bushes and flowering plants," 1716. 47 gin to rise, it injures most of them and is nothing else than a very sharp and biting dew, originating in the earthy vapors and conducted from them .... In the third place a disease occurs among trees, which is called sunblight, or blight, livedo, which, however,_may be of two kinds. First, when a fine rain or dew falls or settles on the leaves while the sun shines, the ducts or tubes, becoming flabby and distended, are contracted at once by the heat of the sun. Thus the leaves are scorched, begin to turn brown and black and fall. In the second case, the urcdo or blight is found in the inner parts of the trees, in the pith .... The true cause, however, for the blighted pith, when the tree is transplanted, may well be, that the common gardeners have the habit, in transplanting, of pruning all the roots and do not understand how much they are injuring the tree. For the smallest roots draw the most sap from the earth, and these are the ones they cut ofi .... Now because the root, together with the pith, is open and exposed, moisture can penetrate and injure the pith . . . ." In regard to canker, we find the ''ascending sap" emphasized as its cause in the horticultural lexicon by Riedel published in 1751'. "Can- ker, tree-cancer, canker, devourer," thus is listed the injurious attack on the trees which appears in the bark, — since it forms hummocks here and there and springs up. — And therefore, if the devouring evil is not overcome in time, one branch after another, and eventually the whole tree, is ruined . The real cause, however, of this injurious attack on the trees is cither the evil peculiarity of the earth and the evil juices produced or arising from it which become so inflamed within the bark that this looks black when removed, or the ascending superfluous rank juice, which, finding no escape, must clog and spoil, thus becoming the cause of the out-pushing and bursting of the bark." Instead of the ascending sap, the expression — "congestion of the sap," is used at present. As a remedy for canker, this author recommends cutting out the dis- eased places and coating with grafting wax. If the cause lies in the soil, this should be removed up to the roots and replaced by new soil. When the sap is excessive, the base of the tree trunk should be bored in February, and the hole wedged open for i to 2 days Math a firm wooden peg or a strong root should be split, " since the superfluous sap will then be drawn downward." Philipp Miller- traces phenomena of disease directly back to frost, and calls them "bUght." Miller's decisions are essentially a repetition of Hale's theories that by blight (blast) not only frost but also sun scorch etc. are understood. Hale's^ statements are important because he men- tions the transmissability of canker in budding and of its occasional heal- ing by being cut out. The observation of this English experimentor on the 1 Riedel, Kurz abgefafstes Gartenlexicon usw. Nordhausen 1751. p. 420. 2 The English Garden Book or Philipp Miller's "Gardener's Lexicon" etc. From the Fifth Edition translated into the German by Huth. Nlirnberg 1750, p. 136. 3 Statical Essays containing Vegetable Statics etc. by Steph. Hales. 2nd edition. London 1731. I. 35ff., 147, 369; II, 265. 48 influence of the dry spring winds, which scorch the foHage is worth noting: — "The considerable quantity of moisture which is given off from the branches of trees during the cold winter season, plainly shows the reason, why, in a long series of cold, northeasterly winds, the blossoms and tender young set fruit and leaves are so frequently blasted in the early spring, viz. by having the moisture exhaled faster than it can be supplied from the trees." DuhameP pays great attention to injuries from frost and states that trees are often attacked by swellings which may be more easily healed in } ounger than in older trees. At some place on the trunk, the bark is loosened from the wood and a devouring pus occurs between the two. Devouring ab- scesses of this kind are called "canker" which is counted among the diseases produced by a superfluity of sap. Das Niedersachsische Gartenbuch- finds the cause from blight and canker in too thick standing of the trees, in un- favorable soil etc. While in ancient times and in the middle ages observations on plant dis- eases were usually limited to a perception of the mature phenomena visible to the naked ^ye and the solution of the questions of plant life were sought almost entirely among experiments of budding, we find that the experiment itself attained its own importance with Hales and Duhamel. Simultaneously with experimental physiology came the wider classifi- cation of plant diseases. We follow here Seetzen's'' treatment of the subject and its history. Seetzen states that Tournefort had a finished system*. His first class mcludes the diseases due to internal causes, as opposed to the sec- ond class, the diseases produced by external causes. To the first class he as- cribes : — I -La trop grande abondance du sue nourricier; 2-le defaut ou manque de ce sue; 3-quelques mauvaises qualites qu'il pent accjuerir; 4-la distribution inegale dans les differentes parties des plantes. In the second class belong: — i-La grele ; 2-la gelee ; 3-la moisissure : 4-les plantes, qui naissent sur d'autres plantes : 5-la piqueure des insectes ; 6-differentes tallies ou incisions, que Ton fait aux plantes. We find Tournefort's point of view in our modern systems. We group the diseases caused by excess or deficiency of water and food, with injuries produced by weather extremes (frost, hail) etc. In the same way, we treat wounds as a separate division. The parasitic diseases appear for the first time as such in Tournefort's book. Less fortunate is Zwinger's"^^ system which appeared shortly after Tournefort's and which also is formed of two main groups, — (r) General 1 La physique des arbres par Duhamel du Monceau. Paris 1758. p. 339. - Caspar Bechstedt, Vollstandiges niedersachsiches Land- und Gartenbuch. Flensburg- und Leipzig- 1772. I, p. 151. a Systematum generaliorum de morbis plantarum brevis diiudicatio. Publico examini submittit Ulricus .Jasper Seetzen. Gottingae MDCCLXXXIX. 4 Observations sur les maladies des plantes par M. Tournefort. Mem. de I'Ac. Roy. des Sciences a Paris 1705, p. 332. 5 Jo. Jac. Zwingeri, Diss. med. inauguralis de valetudine plantarum fecunda et adversa. Basileae 1708. 49 and (2) Specific diseases. The first includes : — La gangrene — le desseche- ment — la surabondance de sue — le branchage excessif — une espece de galle, qui manche I'ecorce. In the second main group we find : — Le dessechement des racines — la separation de leur ecorce — la grosseur excessive des racines, qui retienent tout le sue de la plante — les excroissances — les coups et les biessures. It is evident from this division of closely related phenomena that the author had not fully mastered his material. Eysfarth's^ system gives a classification which the layman easily grasps. It uses as its basis the difl'erent periods of the plant's life. In the first class are the diseases of the period of germination ; in the second, those of the actual vegetative period and in the third class, the disturbances of the sexual period. LTnder each class are discussed the influences of weather extremes, injuries due to animals and other wounds. In this book there is also a chapter "a rubigine aut pruina." The thoroughness of the classification shows that the author had well worked out his material. Adanson^ returns to Tourne fort's division since he sets up as his first main group the "maladies dues a des causes externes," and as the second, the "maladies dues a des causes internes." Even the introduction shows the advance in microscopic investigation and the increased attention paid to parasitic fungi ; under the first main group, the difl^erent chapters take up, for example, Le givre ou Jivre (Erysiphe Fabricii) — la rouille efiu^tifyj Theophr. (Rubigo) — le charbon (Ustilago) — la pourriture (Caries Fabr.) etc. Adanson often uses the terminology of Fabricius who probably had published his studies in separate treatises before his classification had ap- peared as a whole, for his complete classification did not appear until 1774^. Fabricius certainly based his views on his own observations. This is less noticeable in the formation of the main groups than in the sub-divisions of the difl^erent chapters, in which a classification of the cases according to their different causes has been stated, even when the external appear- ance was similar. Thus, for example, we find in the first main group : — "Vfrugtbargiorende Sygdomme," i. e. the disturbances leading to sterility ; a section "Dovhed" which may be translated by etiolation or the yellows. This is divided into D. af Regn, af Kulde, af Rog etc. His observation that, besides rain, cold and other factors, "yellows" may be produced by smoke is also worth notice. In the second main group, "Udtaerende Sygd," i.e. the at- rophias, there is found under the section "Quaelelse," etiolation from "stedets Indslutning" (too close planting), from "paa Lys" (lack of Hght) and from clinging plants and insect injuries. Another group is separated from these phenomena, — -""Taering" (Tabes, Jaunisse in Adanson) where the yellowing is due to insufiicient nutritive substances, unsuitable soil conditions, ex- 1 Christ. Sigismund Eysfarth, Diss, piiys. de morbis plantarum. Lipsiae 1723. 4°. - Adanson, Sur les maladies des plantes; in "Families des Plantes." Vol. I, p. 42. 1763. 8°. 3 Fors6g- til en Af handling om Planternes Sygdomme ved Joh. Christ. Fabricius; ind der kongelige Norske Videnskabers Selskab skrifter femte Deel. Kjobenh. 1774. Sid. 431-492. 50 cessive evaporation after transplanting etc. The third main group is taken up with "Flydende Sygdomme," that is, sap-currents, under which is included honey-dew. In the fourth group are found the "Raadnende Sygdomme" which, according to our point of view, might be termed soft rot, putrefying bacteriosis or scrofula. Among the causes figure also the "Snylte-Planterne," i. e. parasitic plants. In the fifth and sixth groups, wounds, frost splits, galls and monstrosities are treated. In 1779 appeared the German translation of the Zallinger^ classi- fication with the evident endeavor to utilize the terminology of animal path- ology in plant pathology. Zallinger makes five classes: — (i) Phlegmasiae or inflammatory diseases; (2) Paralyses seu debilitates, laming gouts or de- bility; (3) discharges and draining; (4) Cachexiae, bad constitution of the body; (5) chief defect of the dififerent parts. In order to characterize his theory, let us look for the disease which, with blight, forms the main example in our entire presentation, — viz. canker. Zallinger puts this in the class of the Cachexiae, in the subdivision of the ulcers, under which he includes rachi- tis or abortive growth, leontiasis or rough warts on the skin and others. He mentions blight, Gangraeno s. Sphacelus as an abnormal Cachexia, together with Phthiriasis or lousy disease and Vermiculatio, the production of worms. From this classification it may be concluded that the author has let himself be guided by the frequently similar appearance of the phenomena, for the dead places in the bark offer a favorable centre of attack by insects. What we now term grain smut is found as Ustilago, or deformity of the seed, under the class of draining. Fabricius had placed "Kraebs," Cancer, in the class of diseases of decomposition. Batsch-, in his introduction to the knowledge of plants, also pub- lished a survey of the diseases which he divided into those based on the ''de- composition of the firm and fluid parts," i. e. on the constitution of the plant, and into those caused by "animals and plants." Any one, however, looking for our cr3^ptogamic parasites in the latter section would be deceived. These are rather to be found in the first class, in agreement with the conviction already advanced by Zallinger fs. Ustilago), that the parasitic organisms are not independent plants but only develop- mental forms of the higher plants. Thus Batsch under constitutional dis- eases has one group "Brandige Veranderung des Wesens," change of char- acter due to blight, the first family of which includes the phenomenon, where a decomposition of the tissue into powder "smut, Ustilago" takes place. The second family contains the transformation of the tissues into "a spongy mass (Ergot, Clavus)." These views remained in force for some time, as will be seen from the following section. 1 Abhandlung- iiber die Krankheiten der Pflanzen, ihrer Kenntnis und Heilung-; translated from the Latin by Job. Count v. Aauersperg-. Augsburg 1779. 8°. 2 A. J. G. C. Batsch, Versuch einer Anleitung zur Kenntnis and Geschichte der Pflanzen etc. I. Theil. Halle 1787. p. 284. 51 By means of the works of the authors mentioned and the discoveries of practical horticuUure, as well as the great sensation called forth by the tree wax for injured trees which was discovered by William Forsyth in 1791 and universally overestimated, the conviction of the agricultural significance of plant diseases was extended over so wide a circle that special books could now be published for this branch of knowledge. The year 1795 makes us acquainted with three such works. The first one written by Plenk^ treats of the diseases of all cultivated plants of importance at that time and is based on thorough observations. He de- scribes thus :— "a spongy large outgrowth at some place on the trunk from which exudes, even in the most scorching weather, a caustic moisture which corrodes the whole extent of the swelling." Thus Pyrus Cydonia, standing near a swamp, was attacked by tree canker while other quince trees planted in a higher place were healthy. The sap, it seems, becomes so caustic from the acidity of the standing water that it eats up the ducts. There are two kinds of tree canker determined by the difiference in the location of the dis- ease; first, open tree canker, when the canker knots appear on the external surface of the bark ; second, hidden canker, when a sharp cancerous pus collects between the bark and the wood but does not escape from the bark in any place. In both cases the tree becomes incurably wasted, when the parts attacked by canker are not cut out at once and covered with wound wax. In this blight Plenk distinguished between a dry and a moist blight. By the first he means "a black and dry wilting of the leaves or of some other part of the plant" and by "moist blight" he designates the "moist and soft degeneration of the plants into a putrid pus." We find almost the same terminology in the explanation of canker in Schreger's- book which otherwise gives many of his personal obser- vations. In regard to the phenomena of blight in which the bark or other parts of the tree appear black and soft and are consumed, he says, "Such black spots of the bark grow further and further round about themselves even attacking the wood so that the bark itself at last splits ofif, as if dead, and the wood appears dry and black, as if burned." This explanation cor- responds exactly with the phenomena which we perceive when frost causes considerable injuries to the bark. In fact this observer arrives at the same conclusion as we do in regard to the cause. "Bruises from hailstones give rise to its production and also cold frosts. This frost is more injurious in low and moist regions than in high dry ones. For this reason there is less injury from frost on windy nights than on clear, cold ones. If the trees freeze in winter and die, the cause of their death is usually a blight induced by this freezing. This happens sometimes when the severe cold comes too early in the autumn while the sap is still flowing actively ; sometimes in the spring when the sap, so to speak, has begun to run. The latter case is the 1 Plenk, Physiologie und Pathologie der Pflanzen. Wien 1795. 2 Erfahrung-smassig-e Anweisung zur richtigen Kenntnis der Krankheiten der Wald- und Gartenaume. Leipzig 1795. 52 most dangerous of all. Even in midwinter with very great cold they rarely freeze ; it might be when it has rained the day before." On pages 420 and 500, he says of apple and pear trees that "an excess of fatty, oily fertilizers easily develops blight and canker," i. e. creates a predisposition'. The third one of the books published in 1795, the one by Ritt^r v. Ehren- fels^ is even more specialized, for he treats only of fruit trees. He declares that all kinds of trees would be subject to blight and that "this decay which appears first in the bark and then in the wood" is the most common disease of trees and in some books is termed canker. The description which he gives is so clear that it can be identified as the phenomenon now known as Nectria-canker. He says, "the indication of this evil attack is first of all a black or blackish bark which, six or eight days after its appearance, is often pushed out, forms little splits and gradually loses its connection with the trunk of the tree so that it clings only loosely to the shaft. After some time the loose bark is entirely separated from the trunk and exposes the wood. In this new stage the vitality of the sick plant does its very best to help itself and unceasingly throws oft' the unfavorable or sick parts, but this vitality finally becomes weakened and the tree dies. The tree attempts to form a new bark which grows in folds more or less overlapping and tries to cover the exposed places" .... He ascribed the cause to injuries as. for example, from injudicious pruning, injuries due to insects and the like, "even at times the tendency to blight lies in the disposition of the tree itself, — a disposition which the trees obtain from the soil in which they grow, from their descent and from an unwise cultivation." In the pomological glossary published at the beginning of the last cen- tury, Christ" added to the above by the further statement, that the blight "often is due to freezing in winter." Burdach^ also bases his statements on his own observations and says of blight, "this disease is an indirect result of weakness and commonly arises in those trees whose growth has been hastened by strong forcing and fertilizing or which have been transplanted to a poor garden soil where only the upper part of the ground has been improved. In cherry trees, still an- other evil effect arises from the same cause, viz. the exudation of resin or gum." The theory of the influence of the soil and fertilization, as among the most important causes of plant diseases, is now laid aside for some time and attention is given to the manifold and extensive investigation of the province of fungus life. Although antiquity had already recognized a number of edible and poisonous fungi, yet their attentive observation and systematic study began 1 Ritter v. Ehrenfels, Ueber die Krankheiten und Verletzungen der Frucht- und Gartenbaume. Bresslau, Hirshberg- und Lissa 1795. - Pomologisches theoretisch-praktisches Handworterbuch. Leipzig 1802. 3 Systematisches Handbuch der Obstbaumkrankheiten. Berlin 1818. 53 first in the Middle Ages with the foundation of classification of the vegetable kingdom. According to the statements of Corda^, Andreas Caesalpinus (1583) was the first to gather together the fungi in his celebrated book "De plantis." He describes sixteen genera, Tuber, Peziza, Fungus, Boletus, Suil- lus,Prunualus, Prateolus, Familiola, Scoroglia., Fungus marinus, Gallimaceus, fungus panis similis: Lingua, Digitellus, Igniarius and Agaricum. As it seems, even marine animals have been included here. After almost one hun- dred years appeared Joannis Raji's "Methodus plantarum" Londini 1682. In 1710 Boerhave followed with his "Index plantarum horti Lugdano-Batavi" and in 1719 Tournefort appeared with his "Institutiones Rei herbariae." The chief work to which modern mycology must refer appeared in 1729 in Micheli's "Nova plantarum genera" in which the fungi are most carefully described and illustrated in more than 100 pages and with 12 plates. Micheli studied their life phenomena more closely and was the first to observe the attachment and dissemination of spores. Among the genera there described are found those which are considered in plant diseases, Aspergillis, Botrytis, Puccinia (now Gymnosporangium), Mucor and Lycogala. There now follow in cjuick succession "Methodus fungorum" by Gled- itsch (1753) and the "P^ungorum agri ariminensis historia"by Battara (1755), in which a special chapter treats of the usefulness and injuriousness of fungi. The close systematic description of the different genera and species begins with Linnaeus' "Systenia Naturae" (1735), the "Methodus sexualis," the "Genera plantarum," the "Corollarium generum" and the "Philosophia botanica." The third edition of this book, published in 1790 by Willdenow, contains an exact list of all botanists up to 1788. The work also mentions a number of diseases (Fames, Polysarchia, Cancer, etc.). On page 245 of the present edition by Willdenow, are found the following remarks on parasitic diseases : — "Erysiphe Th. est Mucor alhus, capitulis, fuscis ses- silibus, quo folia asperguntur, f requens in Humulo, Lamio. Acere" etc. . . . "Rubigo est pulvis ferrugineus, foliis subtus adspersus, frequens in Alche- milla, Rubo saxatili . . . ." "Ustilago, cum fructus loco seminum fari- nam nigram proferunt. Ustilago Hordei C. B., Ustilago Avenae C. B." . . . Then follow notes on Ergot, galls and other malformations, changes in color etc. It is of importance to pathology that this exact systematist can not sup- press the fact that really no two individuals resemble one another and that climate as well as soil constantly act in a modifying way on the organism. It is stated in fact in the Philosophia botanica, "Varietates tot sunt quot differ- entes plantae ex ejusdem speciei semina sunt productae. Varietas est planta mutata a causa accidentali : climate, solo, calore, ventis etc. ; reducitur itaque in solo mutata." .... Scopoli's book "Dissertationes ad scientam naturalem pertinentes" (1772) treats especially of subterranean plants. In 1780 the publication of BuUiard's "Herbier de la France" was begun in Paris, in which the different genera are illustrated on 6(?o colored plates, (among others Mucor, Trichia,Spliaerocarpus,Nidularia. Hypoxylon). After 1 Anleitung zum Studium der Mykolog-ie. 54 Batch's "Elenchus fungorum" had appeared in 1783 in Jena and, between 1788 to 1791, Bolton's "Historia fungorum, circa HaUfax sponte nascentium," in which only Linnean genera are described, there was published in 1790 in Ltineburg Tode's valuable work which abounds in personal observations, "Fungi mecklenburgenses selecti." The extremely careful illustrations include among others, the genera Acrospermum, Stilbum, Ascophora, Tubercularia, Helotium, Volutella^ Hysterium, Vermicularia, Pilobolus which we now find among the excitors of disease. A. v. Humboldt, in his "Florae fiibergensis specimen" (1793) has also described a considerable number of genera. But all these works, nevertheless, are to be considered only "contribu- tions." A comprehensive methodical classification was first given by Per- soon's "Synopsis methodica" (Gottigen 1801), for long a standard. There appeared in England, from 1797 to 1809, a work by James Sowerby con- taining 439 plates of valuable illustrations with the title "Colored Figures of English Fungi or Mushrooms." Mycologists now tended more and more toward the study of the mi- croscopic fungous forms even if the optical instruments of the time did not make possible more exact observations. This applies first of all to Linck's "Observationes in Ordines plantarum naturales" published in the "Schriften naturforschender Freunde zu Berlin" (3. Jahregang 1809-1810) and the illustrated work by Nees v. Esenbeck, abounding in copies from earlier books, "System der Pilze und Schwamme," Wiirzburg 1817, which contains a sum- mary "of the theories of the lower vegetation stages in hi.storical fragments." Here also are the statements of investigators believing in spontaneous gene- tation. The author himself, if we understand correctly his grandiloquent natural philosophical presentation, considers the parasitic fungi in the lowest possible groups as structures produced from the mother plant itself. Thus he says, for example, of the Entophytes, "Their most peculiar characteristic is that they belong to the overloaded or exhausted life and generally, if not always, develop first under the common covering without any mixture ex- tending over the whole, and originally only in isolated places, formed in- dividually from the life of the whole. The dependence of the mfusorial cell on the higher organisms is always shown by its superior position, due to its more or less lengthened stem. The cell grows before it has become free and its elongation on this foundation is the expression of the condition of polar- ity which has been brought about, not suddenly but organically, and which passes over into the cell from the main plant." Under the genus Cyathus (one of the puff balls) (p. 141) it is said "the whole trunk species which we have described is only a thread of dust originating from the earth itself. The dust of the puff balls begets itself . . . ." At this time Elias Fries' classic work was published including all the known varieties of the fungus kingdom with clear diagnoses of genera and species. 1 Systema mycologicum T. I to III. I.undae 1821, Gryphiswaldiae 1829 to 1832- Elenchus Fungorum. Gryph. 1828. 55 The literature now begins to be increased by single works, scientific as well as practical manuals and writings on both agriculture and horticulture which treat of diseases (Tessier, Jager, Hopkirk, the text books of Willde- now, Nees, de Candolle, Wenderoth, Reichenbach, Re and Kieser) to such an extent that we can now emphasize only those publications which deal most fully with the history of pathology. Among these belong primarily F. Unger's^ "Exantheme der Pflanzen" published in 1833 and giving the results of the most industrious and conscientious studies. This physician, living in a small isolated Alpine valley, supplements his observations by many very careful original drawings, true to nature, on which he constructs his theory of disease. "Most plant diseases are located in the juices .... The faulty formation and the numerous abnormalities in the chemical process of the nutritive juice as well as similar faults in the more highly active life-sap, are the causes of innumer- able diseases which become evident in a scanty formation of the plant sub- stance, the accumulation of excretory substances, the breaking up of the parenchyma, the changed constitution of the secretions etc., or by conditions of an opposite character. In every case, most of the quantitatively and quali- tatively changed processes of the vegetative "chylopoese" might be taken as the source of diseases which may be recognized from the change in sub- stance rather than from that of form. The position into which a large number of the plants are transplanted often acts so detrimentally upon them that at least the greater part deserve to be called diseased." Although, according to this presentation, we must suppose on the whole that Unger would consider diseases as functional and formal variations in the life-history of the organism, he, nevertheless, arrives at the conclusion that disease is something foreign. "For just as the cosmic and elementary is related to the organic, child-like, antitypical, as something parental or typical, in the same way the organism is related to the disease zvhich is nothing else than a second lozuer organism whose elements already lie hidden in some other higher one." In this theory lies the continuation of the thought ex- pressed by Batsch on the nature of the parasitic organisms. Unger states that "among the plant diseases least betraying any depen- dence upon the organism attacked and which in their root formations are still so intimately interwoven with this organism, there belong indisputably those forms which we designate by etiolation, dropsy (anasarca), jaundice (icterus), tympanitis, tabescence(tabes), failure of crops, proflu via and others. These form in fact by far the majority. Greater independence is shown by the vast army of malformations, at the basis of which always lie deiicicncies in the amount of sap and therefore a retardation in lower developmental stages. Honey-dew (Sac char ogensis diabetica) is more important than these. Its pathological course was first recognized by L. Treviranus and its more universal significance by Dr. H. Schmidt. Mildew is indisputably related to 1 Die Exantheme der Pflanzen und einige mit diesen verwandte Krankheiten der Gewachse. Wein 1833. 56 this disease : the straining toward a more complex organization of the exuded juices is made evident here by organic formations wliich are missing in honey-dew. These organic formations are still more independent in rust dew (Fuligo vagans). Finally the disease organism appears in the excre- tions and the forms nearly related to them as a peculiar, complete entity. Parasites belong here— the highest among them, such as some kinds of Lor- anthus, seeming to have separated themselves entirely from the mother body." Unger's views are also shared by Nees v. Esenbeck and A. Henry^ who state in regard to puff balls that "the fungi clearly stand here at the lowest level . . . ." "They are correctly considered as the ma- terial of disease, as secretions of the higher plants." "The leaf fungus is formed in general by a coagulation of the juices discharged into the inter- cellular passages." Theodor Hartig also wrote his work on the red and white rots of the pine under the influence of this theory. In this he confirmed first of all the co-operation of fungi (Nyctomyces)'. He traced the production of these fungi to a decomposition of the cell walls. Of the works which take up general constitutional diseases and scarcely touch upon the fungi, we will name those by Geiger^ and Lindley* which in all essentials are based upon practical experience. On the ether hand, however, Wiegmann's^ statements are evidently based on microscopic studies and the bearings of chemistry, for example, he states that the pus of the blight, as well as that of canker, contains putric and huniic acids, but that that of the blight contains more putric acid. To him both diseases appear non-parasitic in nature and he thinks canker (Caries, Necrosis) always arises from "a stoppage and deterioration of the juices, even if these were never present in excess." Among the causes mentioned are injuries to the roots, or injuries from frost and unfavorable soil conditions, as, for example, "If the subsoil is moist, sour, stony or other- wise unfertile, or contains swamp ore." Meanwhile, after Corda's*^ great work on fungi had begun to ap- pear, Meyen's" "Pflanzenpathologie" was published as a standard, which even now warrants consultation. He divides his material into "External Diseases" and "Internal Diseases." Among the former, besides the injuries due to man and to animals, the formation of gnarls and galls, he includes also phanerogamic and cryptogamic parasites, of which the Ustilagineae and the Uredineae as well as other fungi are treated in detail, according to 1 Das System der Pilze, Section I. Bonn 1837. 2 Abhandlung- liber die Verwandlung- der polycotylen Pflanzenzelle in Pilz und Schwammgebilde und die daraus hervorgehende sogenannte Faulniss des Holzes. Berlin 1833. 3 Die Krankheiten und Feinde der Obstbaume. Miinchen 1825. 4 The Theory of Horticulture. London 1840. 5 The Krankheiten und krankhaften Mifsbildungen der Gewachse von Dr. A. F. Wiegmann sen. Braunschweig 1839. 6 Icones Fungorum hucusque cognitorum. Prague 1837 to 1854. '^ Pflanzenpathologie. Lehre von dem kranl^en Leben und Bilden der Pflanzen. Published after the death of the author by Dr. Gottfr. Nees v. Esenbeck, Berlin 1841. 57 the standpoint of the time. Meyen no longer shares Unger's view that the parasites as excrement-organisms are the product of a formative development latent in each plant, the disease occurring in a more or less developed form and state of independence according to the constitution and strength of the host-organism. On the contrary, his Plant-Pathology, in the discussion of smut fungi, emphasizes especially that "observations on the production of the smut show most clearly that we have to do here with true entophytes : we will find that some smut species are shown as particular parasitic growths in the interior of the cells of the plants attacked by them and that the smut mass is not to be compared with animal pus." The whole title of Meyen's "Plant Pathology" really reads : — "Hand- buch der Pflanzenpathologie und Pflanzenteratologie" edited by Dr. Chr. Gottfr. Nees v. Esenbeck. Vol. I, "Plant Pathology." According to this, a second part, Teratology, was to be expected. Meyen himself intended to work up such a volume, but, according to the Editor, left no material for it. Just as Nees v. Esenbeck was about to undertake this himself, there appeared tlie "Elements de Teratologic vegetale, au Histoire abregee des anomalies de I'organisation dans les vegetaux ; par A. Moquin Tandon, Doct. scienc. et med. etc., director du jardin des plantes de Toulouse. Paris 1841." C. F. Jaeger "Ueber die Missbildungen der Gewachse" (1S14) and Thomas Hop- kirk. "Flora Anomala" (1817) should be mentioned as forerunners of this work. We learn from the German translation of Moquin Tandon's^ book, that the translator, C. Schauer, was able, as specialist, to call attention to many misunderstandings and errors made by the author, especially in the German citations and to make additions from his own observations. Moquin Tandon says, "By the expression 'malformations', 'monstrosities' (monstra) is generally understood innate, more or less important and complicated vari- ations from the type of a species, which are disfigurations and oppose the regular course of a functioning by hindering or arresting it." We are better satisfied by de Candolle's definition (Theor. element. I. ed. p. 406), by which monstrosity is any disturbance in the economy of a plant, which is followed by a change in organic form and arises from an internal disposition, almost never from a visible cause. Moquin Tandon's book is still indispensible to every specialist because of its admirable bibliographical references. About this time, the science of infectious diseases received a new im- petus because of the rapid spread of the potato disease which is still worthy of especial attention. It is one of the most dreaded enemies of agriculture, and is described in the text books as potato Phytophthora rot. We owe one of the first publications on this subject to Martins- and from that 1 Pflanzenteratologie. Lehre von dem regelwidrigen Wachsen und Bilden der Pflanzen. By A. Moquin Tandon. Translated and supplemented by Dr. J. C. Schauer. Berlin 1842. 2 Die Kartoffelepidemie der letzten Jahre. Miinchen 1842. 58 time on a flood of publications, proportionate to the very severe injury to national property from these diseases. We will emphasize among these pub- lications only those of Focke\, Payen-, Schacht", Speerschneider^, v. Holle\ Kuhn" and de Bary^ (Further bibligraphical references may be found in the detailed discussions of the different diseases). It was natural that a phenomenon, such as the potato epidemic, would necessarily bring fungous diseases into prominence and increase the whole study of mycology. At the same time the economic importance of smut fungi also began to receive greater and greater consideration. Tillet^ Tes- sier^, and Prevost^", had early studied the smut of grains and at present we have accjuired a considerably extended insight into the nature of those dis- eases and also into the means of combatting them from de Bary's^^ investi- gations and Bref eld's studies, extending over many years. The prevalence of smut diseases has led to the development of the sterilization of seed. In the second volume of this work, which treats of parasitic diseases, the overpowering number of mycological works will be mentioned, — we will here mention only some of the most important ones, treating of fungus families as a whole. Elias Fries' great work completed in 1832, has already been considered. In 1831 the first part of Wallroths "Kryptogamenflora"^^ appeared and in 1833 the second part. In this book the cryptogams were worked up by Math. Joe. Blufif and Carl Ant. Fingerhuth. In 1842 Rabenhorst's "Kryptogamenflora"^^ began and in 1851 Bonorden's "Hand- buch der Mykologie"^*, which has proved to be very useful because of its cuts of microscopic fungus forms, although these had been sufificiently considered in the illustrations of Schaffer, Persoon, Greville, Sowerby, Sturm, Krombholz and Nees sen. To be sure Corda's "Icones fungorum" had already been published and his "Anleitung zum Studium der Mykologie"^^ which is provided with very small drawings; leaving the peculiarity of his classification out of the question, however, Corda limit- ed himself to the easily visible developmental stages, while Bonorden sought to determine the tissue structure. This author, in opposition to Unger, em- phasized the fact that parasitic fungi are unquestionably independent organ- 1 Die Krankheit der Kartoffeln im Jahre 1845. Bremen 1846. 2 Les maladies des pommes de terre, des betteraves, des bles et des vig-nes. Paris 1853. sSchacht, Bericht iiber die Kartofflepflanze und deren Krankheiten. Berlin 1854. 4 Das Faulen der Kartoffelknollen. Flora 1857. Bot. Z. 1857. 5 Ueber den Kartoffelpilz. Bot. Zeit. 1858. 6 Die Krankheiten der Kulturgewachse, ihre Ursachen und Verhutung. Berlin 1858. T Die Kartoffelkrankheit. Leipzig 1861. 8 Dissert, sur la cause qui corrompt les graines de ble, 1755. 9 Traite des maladies des graines, 1783. 10 Memoire sur la cause de la carie des bles, 1807. 11 Untersuchungen liber die Brandpilze. Berlin 1853. 12 Flora cryptogamica Germaniae auctore Ferd. Guil. Wallrothio, Med. et Chir. Doctore etc. Norimbergae 1831-33. 13 Kryptogamenflora von Deutschland, Vol. I., Leipzig 1844. 2nd Edition. I-VII. 1884-1903. 14 Handbuch der Allgemeinen Mykologie etc. with 12 plates. Stuttgart 1851. If* Anleitung zum Studium der Mykologie nebst kritischer Beschreibung aller bekannten Gattungen. Prag 1842. 59 isms, but maintained that "it is the stomata which take up the spores and bring them to development in the air cavities connected with them." He said that algae, hchens and mosses which have no stomata and, for the same rea- son, young branches and twigs are free from parasites. He expresses his point of view in regard to the action of parasites, as follows : — "That they 6rst cause an hypertrophy and degeneration of the parts heavily infested with them but when isolated they do not disturb the growth of the leaves." Ac- cording to him, dry weather is essentially propitious for the spread of the parasites, "because it favors the scattering of the spores. On this ac- count Caeoma and Phragmidium are never found more abvuidant than in dry summers, as also the Caeoma ccrcalium, the yellow corn smut so in- jurious to seeds, which caused such great damage in 1846." Kiihn in his "Krankheiten der Kulturgewachse" (Berlin 1858) attained, in the happiest manner, the end for which Meyen strove, viz. of uniting scientific studies with practical experience in the treatment of plant diseases. However necessary and important purely scientific investigations may always be in phytopathology, yet they achieve their full significance only by being tested in practical agriculture. Only by practical work can it be decided vvhether the conditions of nature and of the laboratory favor the develop- ment of the same parasites or other excitors of disease. So it is necessary to build phytopathology upon a practical knowledge of agriculture and horti- culture. The dififerences which have developed in medicine between the scientific investigator and the practicing physician must also necessarily arise in the science of plant diseases. We term this practical side, — the pro- fession of "Plant Protection.'" Mycological studies are a part of the indispensible fundamentals of plant protection and for this reason, we have given them the greatest possible at- tention in the history of phytopathology. Continuing with this in view we will name first of all the masterly plates in the book by the brothers Tulasne "Selecta fungorum carpologia," Paris. The English work by Berkeley "Outlines of British Fungology," London i860, is most welcome as a col- lective work although it is mostly provided with very rough illustrations. De Bary's works continue to be of especial value. His results in this con- nection may be found summarized in the "Morphologic und Physiologic der Pilze, Flechten und Alyxomyceten," Leipzig 1866. We owe further important investigations to O. Brefeld, in his "Unter- suchungen iiber die Schimmelpilze," Leipzig 1871, 1872 and following, and Cohn for his "Biologische Mitteilungen iiber Bakterien," Schlesische Ges. f. \aterl. Kultur, 1873, as well as for his "Untersuchungen iiber Bakterien" 1875 and for other studies contained in his "Beitrage zur Biologic der Pflan- zen." In these Cohn has successfully advanced the history of the develop- ment of Bacteria. His pupil, Zopf, essentially extended these studies in the work "Die Spaltpilze," Breslau (3rd Ed. 1885). Among the summaries of this time mention should be made of Eidam "Der gegenwartige Standpunkt der Mykologie mit Riicksicht auf die Lehre von den Lifektionskrankheiten," 6o Berlin (2nd Ed. 1872) and further Winter, "Die Pilze Deutschlands, Oester- reichs und der Schweiz," Leipzig 1884. Rabenhorst's "Kryptogamenflora" brings the subject to completion. The most comprehensive systematic summary of all the fungi is con- tained in P. A. Saccardo's "Sylloge Fungorum." The eleventh volume with a "Supplementum universale" was published in Pavia in 1895. Sydow's "In- dex universalis et locupletissimus nominum plantarum hospitium speciarum- que omnium fungorum," Berolini, Fratres Borntraeger 1898, carries the work further. This book contains all the fungi known up to 1897. Further sup- plemental volumes (XIV-XVI) were published in 1899-1902 and others arc to follow. Saccardo supplemented this great work on fungi with 1500 illus- trations which were published from 1877-1886 under the title "Fungi italici autographice delineati," Patavii. In place of the sketchy drawings of this work, A. N. Berlese began to publish a series of most careful, colored illustrations under the title, "Icone^ fungorum ad usum Sylloges Saccardianae adcommodatae," Abellini. The Sphaeriaceae Hyalo phragmiae were furnished in parts IV-Y, which appeared in 1894. To our knowledge, the author had not finished the work at the time of his untimely death. In the same way, we find colored illustrations in Cooke's "Mycographia seu Icones fungorum," London : — the first part ap- peared in 1879 with cuts of the discomycetes. The publications on fungi and bacteria now become so numerous that they are no longer to be mastered and make any further citations impossible. This compels us to refer to the "Botanischer Jahreshericht" which has been appearing since 1873. It is natural that Teratology has also developed further since Moquin I'andon. Among the works treating of the material as a whole, emphasis should be laid on M. Master's "Vegetable Teratology," London 1869 and O. Penzig, "Pflanzenteratologie," systematisch geordnet, Genua 1890-94, which may be designated as the most complete book of reference on this subject. Because of limited space we must forego all further citations of my- cological literature. The reader will find the desired supplementary infor- mation in the second volume of this work. However, a brief reference to the numerous publications descriptive of fresh and herbarium material must be made in a presentation of the history of the development of this science. Among the herbaria which pay especial attention to plant diseases, there should be mentioned here, F. v. Thiimen, "Herbarium mycologicum oeco- nomicum," Teplitz, 1873-79, Rabenhorst, "Fungi europaei exsiccati" con- tinued by Winter and Patzschke; L. Fuckel, "Fungi rhenani exsiccati," 2nd Edition 1874; Jak. Eriksson, "Fungi parasitici scandinavici," Stockholm 1882-1895 ; G. Briosi et F. Cavara, "J funghi parassiti delle piante coltivate ed utili essicati, delineati e dcscritti," Pavia, fasc. I-XII (1897) ; W. Krieger, "Schadliche Pilze unserer Kulturgewachse," fasc. I. 1896; A. B. Seymour and F. S. Earle, "Economic Fungi, Cambridge. Following in close connec- tion with Rehm's ascomycete collection, published many years ago, are many 6i Herbaria representing the general fungus flora of different countries, as, for example, those by Saccardo, Sydovv, Vestergren, J. B. Ellis, Jaap, Bubak and Kabat, Posch etc. Although the science o"f plant diseases would refer to teratological phe- nomena only when it can prove, or at least suppose as a cause of the indi- ^ idual phenomena, some definite disturbance of nutritive or structural con- ditions, it has been forced to take the animal world more and more thor- oughly into consideration. The following publications summarize the entire material or the larger part of it, are comprehensive and should be used for further study : — Ratzeburg, "Die Forstinsekten," Berlin 1839-1844 and "Die Waldverderbnis," Berlin 1866-1868; A Gerstacker, "Handbuch der Zoolo- gie," Vol. II., Arthropoden, Leipzig 1863 ; E. L. Taschenberg, "Entomo- gie fiir Gartner und Gartenfreunde," Leipzig 1871, and "Die der Landwirt- schaft schadlichen Insekten und Wiirmer," Leipzig 1865. Further Nordlinger, "Die kleinen Feinde der Landwirtschaft," Stuttgart 1869. Kaltenbach. "Die Pflanzenfeinde aus der Klasse der Insekten," Stuttgart 1874, and Ritzema Bos, "Tierische Schadlinge und Niitzlinge," Berlin 1891. The "Handbook of the Destructive Insects," by C. French, published in Melbourne in 1891 by order of the Department of Agriculture of Victoria, is less rich in material but better adapted to the practical needs of the layman, because of its colored plates. In the same year H. R. v. Schlechtendal published a smaller special work on gall formations, — "Die Gallbildungen (Zoocecidien) der deutschen Gefasspflanzen," Zwickau 1891. Ten years later G. Darboux and C. Houard jjublished a comprehensive systematic work, — "Catalogue systematique des Zoocecidies de I'Europe et du Bassin mediterraneen," Paris 1901. The "Forstliche Zoologie" by K. Echstein, Berlin 1897, may be especially recommended because of many careful original drawings. The popular writings of H v. Schilling are especially useful for horticulture ; we recommend "Die Schadlinge des Obst-und Weinbaues," "Die Schadlinge des Gemiisebaues," Frankfort a. O. 1898 and the "Practischer Ungezieferk- alender," Frankfurt a. O. 1902. The "Schutz der Obstbaume gegen feind- liche Tiere" by E. L. Taschenberg (3rd Edition by O. Taschenberg), Stutt- gart 1901, is also well adapted for practical needs. As the science of plant protection develops there is a corresponding at- tempt to produce reference books treating some of the most important culti- vated plants, such as Eisbein "Die kleinen Feinde des Rlibenbaues, 1882, with carefully prepared colored plates and Emile Lucet "Les insectes nuisibles aux Rosiers sauvages et cultives en France," Paris 1898, with numerous plates in black and white. Most complete is the work being done in the United States in protecting plants from these animal enemies. The Zoolo- gists in the several State Experiment Stations and the "Bureau of Entomol- ogy" of the Federal Department of Agriculture in Washington, are advanc- ing rapidly the study of the enemies of cultivated plants, by new investiga- tions and by the distribution of popular treatises. More detailed references to zoological literature are to be found in the third volume of this manual. The number of text-books and manuals of phytopathology has grad- ually been increased since the publication of Kiihn's "Krankheiten der Kul- turgewachse," as the understanding of the national economic significance of phytopathology has increased. First of all comes Orstedt's "Om Sygdomme hos Planterne, som foraarsages af Snylteswampe, navnlig om Rust og Brand," Kjobenhavn 1863. This work was followed in 1865 by later reports on the alternation of hosts by rust fungi (Gymno sporangium Sabinae). About this time Hallier's^ book appeared which must be given more especial attention in a history of plant diseases because of the author's stand- point. Hallier's views leading to sharp literary disagreements, especially with de Bary, may be found in extenso in his later writings-. In his "Festkrankheiten der Kulturgewachse," he gives a list of investigations on the Peronosporeae and believes he has permanently established by these the correctness of his "Plastiden Theory." At the time of the "Cholera meeting" in Weimar (1868), Hallier first made the assertion that the forms, summarized as Fission fungi (Schizomycetes) by Nageli were not indepen- dent organisms, but represent the products of the plasma of diiTerent groups of filament fungi. Hence Nageli's family of the Fission fungi should be stricken out of the classification and infectious diseases as a whole be traced back to the action of such plasma-products ("Plastiden"). "In order there- fore to discover the origin of infectious diseases, it is necessary in every case to ascertain by investigation which definite fungus produces the cells of con- tagion from its plasma (bacteria, micrococcus etc.) and in what way this takes place." In regard to the potato disease produced by Phytophthora, he does not question whether this fungus is the cause of the disease, but only whether it may cause it less directly than would bacteria. "I have proved first and foremost that the bacteria which are the absolute cause of the pota- to pest, are produced by the "Plastiden" of the Phytophthora and that these, when once formed, are absolutely equal to the production of the plague; that there is no further need of the mycelium and buds of the Phytophthora." His numerous experiments ultimately led him to the view that, in all in- fectious diseases, human, animal and vegetable, three main points undoubted- ly come under consideration: (i) The absolute cause; (2) External or general furtherance (chance causes or predisposition) ; (3) Personal fur- therance (susceptibility of the diseased individual). Sorauer in the first edition of his "Manual of Plant Diseases," Berlin, Paul Parey, 1874, first introduced into plant pathology the view, that in all diseases not only the direct cause but also the earlier preparatory stages and, in parasitic attacks, the accessory conditions favoring the development of the parasites, including the disposition of the host organism, should be taken 1 Phytopathologie. Die Krankheiten der Kulturgewachse. Leipzig 1868. 2 Die Plastiden der niederen Pflanzen. Leipzig 1895. — Die Pestkrankheiten (Infektionskrankheiten) der Kulturgewachse. Stuttgart 1895. 63 into consideration. This statement was definitely established in the second edition (1886) and in an abstract written especially for the practical agri- culturalist, "Die Schiiden der einheimischen Kulturpflanzen," 1888. The delayed acceptance of these ideas is shown by the text-books which im- mediately followed. Of these the one especially valuable because of its num- erous personal investigations is "Lehrbuch der Baumkrankheiten" by Robert Hartig, Berlin 1882 (2nd Ed. 1889). The third edition, in which the author rather unreservedly acknowledges a predisposition and differentiates local, temporal, individual, acquired and morbid predisposition, appeared in 1900 with the title "Lehrbuch der Pfllanzenkrankeiten" — Berlin, Julius Springer. A study of the phenomena of the decomposition of wood, with the title "Wichtige Krankheiten der W^aldbaume," Berlin 1874, is an intro- ductory work for this textbook. Sorauer's Manual was followed first by Frank's detailed elaboration, "Die Krankheiten der Pflanzen," Breslau 1880 (2nd Ed. 1895). The "Lehrbuch des Forstschutzes" by H. Nordlinger, Berlin 1884, is devoted especially to cultivated forest plants. Solla's book, "Note di Fitopathologia," Firenze 1888, is more comprehensive and contains an atlas. This was pre- ceded in Norway in 1887 by Brunchorst's "De vigtigste Plantesydomme." To this decennium belongs also a number of noteworthy articles by Jensen, among which (according to Rostrup) is: "Kartofifelsygen kan overvindes ved en let udforlig Dyrkningsmaade," Kjobenhavn 1882. While up to this time scientists had classified diseases according to their proved or assumed causes, Kirchner in 1890 published "Die Krankheiten und Beschadigungen unserer landwirtschaftlichen Kulturpflanzen," Stuttgart, arranged especially for practical use. The diseases are listed here ac- cording to the different cultivated host plants and described according to their visible habit of growtli. Systematic scientific supplements are collected at the end of the book. In accordance with the line of investigation of this author there appeared in 1895 a richly illustrated book treating of parasitic diseases only, — "Pflanzenkrankheiten, durch kryptogame Parasiten verur- sacht," by Karl, Freiherr v. Tubeuf, Berlin, Julius Springer. Parastism was here developed as a form of sym.biosis and thereby referred to an "internal and an external" predisposition for becoming diseased. The internal predispo- sition depends on "the energetic condition of the living protoplasm of the host cell," while the external one "is determined especially by anatomical condi- tions." In the same year Prillieux published a two volume work abounding in personal investigations, "Maladies des plantes agricoles et des arbres fruitiers ct forestiers," Paris. This, the most comprehensive work in French on the subject, describes only parasitic diseases. They are treated scientifically and yet the practical side receives attention in so far as means for combatting disease are considered. An unlooked-for advance in the studies on bacteria resulting from their many-sided economic significance, made a revision and enlargement of de Bary's "Vorlesungen iiber Bakterien," necessary. In 1900, in Leipsic, Mig- 64 ula, enabled by his own work, produced a new edition to wliich he added exact bibligraphical citations. Meanwhile, as the necessity of familiarizing practical circles with the nature of plant diseases became increasingly more evident, it led the large German Agricultural Society to undertake the issuing of suitable publica- tions. In 1892 appeared the first edition of Sorauer's "Pflanzenschutz," and in 1896 its second edition, revised by A. B. Frank and P. Sorauer. The authors strived for the briefest presentation possible, classified the diseases according to the host plants and treated each disease under three headings : — Recognition, Production and Control. The text was supplemented by num- erous illustrations on colored plates. In the same way, Frank published a more detailed work with the title : — "Kampfbuch gegen die Schiidlinge un- serer Feldfriichte," Berlin 1897 and Sorauer one, entitled, "Schutz der Obst- baume gegen Krankheiten," Stuttgart 1900, provided with numerous figures in the text. Of books in foreign languages, there appeared about this time, W. Kriiger's treatise on the diseases of sugar cane in the "Bericht der Versuchs- station fiir Zuckerrohr in West-Java, Kagok-Tegal," published in 1896. This treatise took up thoroughly the Sereh disease with a conscientious use of the pertinent literature. Subsequent to it appeared in Leyden in 1898, H. Wak- ker and G. Went's "De ziekten vom het suikerriet op Ja\a," which should be recommended because of its many plates. Delacroix treats the diseases of coffee especially in his book, "Les mala- dies et les ennemis des Cafeiers," Paris (2nd Ed. 1900). Two years later D. McAlpine, in Melbourne, published "Fungus diseases of stone-fruit trees in Australia." The last named publication considered cultivated plants only. The need of a comprehensive treatment of the whole field of diseases was shown and after a long interval, a response, the manual, "Plantepatologi" Haandbog i Laeren om plantesygdomrae af E. Rostrup, was published at Kjobenhavn in 1902. This book, elegantly gotten up and attractive because of its many careful original drawings, lays emphasis on fungous diseases, the known number of which the author by his many personal observations, published after 1871, had increased. To facilitate the consultation and discovery of the dififerent diseases, a list was placed at the end of the book, arranged accord- ing to the host plants. In 1903 the Japanese published a book which should be considered as a significant cultural advance. We have a German translation of this entitled "Lehrbuch der Pflanzenkrankheiten in Japan," Ein Handbuch fiir Land- und Forstwirte, Gartner und Botaniker. Von Arata Ideta (3rd Ed.) Tokio 1903). This work is provided with a glossary of technical terms in German, English and Japanese and contains 13 plates and 144 text figures carried out in fine line-drawings (mostly after German authors). In a science like phytopathology, in which the results of all investiga- tions are intended for use in practical industry, the need is at once felt of 65 making the forms and causes of disease more easily comprehended by the layman, by means of colored illustrations. On this account, without regard to special works on fungi, we often find the text supplemented by colored pictures of the habit of growth. An attempt to present the most important diseases in the form of a portfolio with short descriptions of the figures on the plates could be undertaken only after a more widely extended under- standing of the importance of this branch of knowledge had insured a suf- ficient number of purchasers. Accordingly, since 1886, Paul Parey of Berlin has issued Sorauer's "xMlas der Pflanzenkrankheiten," of which six folio numbers have already been published. The especial care used here, in hav- ing the difi'erent colors true to nature, made the price such that the publica- tion had a smaller circulation among practical workers than in scientific in- stitutes, and accordingly a need was gradually shown for the publication of a less expensive work. This appeared under the title, "Atlas der Krankhei- ten und Beschadigungen unserer landwirtschaftlichen Kulturpflanzen." edited by O. Kirchner and H. Boltshauser and published by Ulmer, Stutt- gart. This is now completed in six numbers. INIeanwhile the Deutsche Landwirtschafts-Gesellschaft discovered, by its publication of "Pflanzen- schultz," that at present the time is ripe for the extension of the knowledge of diseases among practical agriculturalists, and that it can be carried through most successfully by such brief guides. The society published the third edition in 1904, revised by Sorauer and Rorig, with seven carefully pre- pared plates. The "Atlas des Conferences de Pathologic vegetale" by Georges Delacroix, Paris 1901, should be mentioned as of special service to the systematic study of diseases. This gives the most important diseases of cultivated plants in 56 plates in black and white. In 1902 Delacroix pub- lished by order of the French Agricultural Department a small work, "Mala- dies des plantes cultivees," Paris, which was written chiefly for general use and is supplemental to the above. The most significant scientific advance is the publication of monographs covering the separate fields of disease. This method has also appealed especially to recent workers in plant pathology. In accordance with the im- portance of the disease, thorough study has been devoted to the rust fungi, especially of grain. In 1894-95 the German edition of a 463-page work by Jakob Eriksson and Ernst Henning was published.— "Die Getreideroste, ihre Geschichte und Natur, sowie Mafsregeln gegen dieselben," Stockholm. This work, which attracted much attention, appeared as a volume of the "Meddelanden fran Kongl. Landtbruks-Akademiens Experimentalfalt," and its 13 colored plates show clearly the diseases due to grain rusts. It proves the specialization of parasitism in the fungi of grain rusts. Besides this, the Avork takes up the discussion of the determinative factors and tests the posi- tion, the physical and chemical constitution of the soil, the previous cropping, time of seeding etc. In 1904, H. Klebahn published an equally careful work with a larger field and based on his personal studies, entitled :— "Die wirtswechselnden 66 Rostpilze," Versuch einer Gesamtdarstellung ihrer biologischen A/'erhaltnisse. Berlin 1904. Gebr. Borntrager. A chronological table gives a list of the heteroecious rust fungi discovered since de Bary's first investigations made in 1864 with Puccinia graminis. The text treats in the greatest detail and with pertinent bibliographical references, gradation of dififerences, limi- tation of species, specialization and theory of descent, susceptibility and transmission of rust diseases in seed. With this is also discussed thoroughly the mycoplasm theory brought forward about 1897 by Eriksson. This point has already been discussed (see p. 34). Eriksson's latest studies appeared in 1904 in the publications of the Schwed. Akad. d. Wissensch. under the title : "Das Vegetative Leben der Getreiderostpilze." A further important advance in the creation of scientific foundations is shown in the "Pathologische Pflanzenanatomie" by Ernst Kiister, Jena 1903, published by Gustav Fischer. Guided by the discovery that a distinct sepa- ration of the natural forms into normal or abnormal can not be carried out, Kiister tests the phenomena from the physiological point of view, i. e. as to the functional efficiency of the tissues. "The tissues are prevented from de- veloping into functionally efficient, i. e. normal tissues, by influences of some kind or functionally efficient tissues undergo subsequent changes in which they forfeit entirely or partially their functional ability, or new tissues are produced in the plant body of such a nature that its diseased and deformed organs either accomplish nothing for the organism as a whole, or less than those which we designate as normal." We find in this work a successful attempt at presenting the developmental mechanics of the vegetable organism. A periodical literature developed along with the attempts to organize the protection of plants. The guiding principle was the practical question, how the spread of disease and the enemies of cultivated plants may best be prevented and how their direct control can be most advantageously accom- fjlished. This question was considered more closely first in the United States of North America, since in 1887 stations were formed by the Department of Agriculture for the study of phytopathology and of insects. These most active institutes and experiment stations first of all issued annual reports and then later special publications of scientific investigations. The report of 1889^ gives a closer insight into the organization of the service. We learn from it that the Phytopathological Division published its investigations in a definite periodical "The Journal of Mycology" and also distributed pop- ular bulletins of some of the most important diseases. Correspondence con- sisting of replies to queries consumes much of the activity of these stations. For example, in 1889 the questions sent by practical agriculturalists de- manded 2500 replies. These scientists desire chiefly to test results of lab- 1 Report of the chief of the Division of Vegetable Pathology for the year IS Published by the authority of the Secretary of Agriculture, Washington 1890. 67 oratory studies by field experiments. With the intention of carrying out such practical agricultural experiments, the pathological division has installed cer- tain supervising agents. When the results of such experiments, conducted in the open in different regions, corresponded sufficiently well, general conclus- ions were drawn and the results published as speedily as possible. In Germany the first attempt toward organization was shown at the Agricultural Congress in Vienna in 1890, where Eriksson and Sorauer brought forward a proposition .recommending to the government regulations similar to those already carried out in America. With the intention of work- ing out a special plan and the development of effective activity, an "Inter- nationale phytopathologische Kommission" was formed by representatives of all European agricultural countries and Sorauer, as secretary, was com- missioned to bring out suitable publications. This furnished an incentive for the foundation of the "Zeitschrift fi'ir Pflanacnkrankheiten" the first annual series of which appeared in 1891. In the same way the interest in establishing experiment stations and similar institutions for the special culti- vation and the protection of plants in dififerent countries, was stimulated and successful. In iSSo^ Korn-Breslau published in Prussia a very thorough report, "Ueber die Begrundung einer wissenschaftlichen Centralstelle behufs Beobachtung und Tilgung der Feinde der Landwirtschaft aus dem Reiche der Pilze und Insekten." The Imperial Government should have re- sponded to such stimuli through the German Agricultural Council. In June, 1889, Julius Kiihn. through whose endeavors the experimental station under IloUrung was established in Halle a. S.. brought this same subject before the German Agricultural Society and in 1890 the Society established a "special committee for the protection of plants" whose Board of Directors was form- ed by JuHus Kiihn, A. B. Frank and P. Sorauer. This special committee estab- lished a net-work of information bureaux for practical agriculturalists which covered the whole German Empire, and published successive "Annual Re- ports from the special conimittee for the protection of plants,"- after Sorauer had begun in 1891 a statistical revision of the rusts of grains. In 1890 the Phytopathological Laboratory at Paris was opened under Prillieux and Delacroix and in Amsterdam on the nth of April, 1891, the Netherland section of the International Phytopathological Commission was estabhshed. This commission called Ritzema Bos to Amsterdam in 1895 as director of the "Phytopathologisches Laboratorium Willie Commelin Scholten." In this year, at the instigation of the Holland Phytopathological Association and of the Phytopathological Division of the Botanical Society Dodonaea, the "Tijdschrift over plantenziekten," edited by J. Ritzema Bos and G. Staes was published. Meanwhile, an experimental station was found- ed at the Pasteur Institute for the purpose of combatting injurious animals by means of contagious diseases. In 1894 this was placed under the direction of Metschnikoff. As director of the "Experimentalfaltet" at Albano, near Stockholm, Eriksson was untiringly active. In 1895 he published test ex- 1 Archiv des Deutschen Landwirtschaftsrates, Part 8, p. 307. 2 Jahresberichte des Sonderausschusses fiir Pflanzenschutz. 68 amples for the special forms of grain rusts after which, in February 1901, the State granted him a fund of io,ocxd Kronen because of these studies. The question of rust which is also of the highest significance in Australia led in 1888 to the annual meeting of a Congress of Members of the Austra- lian Colonies which, for a considerable number of years, published an official report, "Rust in wheat Conference." In Germany, Sorauer's "Zeitschrift fiir Pflanzenkrankheiten" was fol- lowed in 1892 by C. v. Tubeuf's Forstlich-natiirwissenschaftliche Zeit- schrift" which devoted especial attention to plant diseases. In 1898 the"Kgl. bayrische Station fur Pflanzenschutz" was founded with von Tubeuf as di- rector. Besides this, reports in the collective work, "Just's botanischer Jah- resbericht," published since 1873, became much more abundant, since a greater number of periodicals now included the subject of plant diseases in their programs. Among these belongs first of all the "Centrolblatt fiir Bak- tcriologic, Parasitcnkwidc und Infektionskrankhciten" issued by Uhlworm and Hansen, as also "Hedwigia," edited by Hieronymous and P. Hennings, the "Botanische Centralhlatt," elaborated by Lotsy, also Biedermann's "Centralblatt fiir Agricvdturchemie," edited by Kellner, the "Naturwissen- schaftliche Zeitschift fiir Land-und F orstwirtschaft" by von Tubeuf and L. Hiltner and the "Practische Bliitter fiir Pflanzenhau und Pflanzenschutz" by L. Hiltner. We find thorough reports, especially on tropical cultivated plants, in "Tropenpflanzer" Zeitschrift f. tropische Landwirtschaft, by O. Warburg and F. Wohltmann as well as in its "Beiheften" (supplements) which form the organ of the "Kolonialwirtschaftliches Komitee zu Berlin." In the German East- African colonies, Zimmermann is especially active in pathological fields as is shown by his "Mitteilungen aus dem biologisch-land- wirtschaftlichen Institute Amani" In Austria the "Zeitschrift fiir das Land- wirtschaftliche Versiichszvesen in Oesterreich" was founded in 1898. In the following year P. Nypels began a series of publications under the title "Mal- adies des plantes cultivees" Bruxelles. In 1900, v. Istvanfii published the first volume of the "Annales de ITnstitute Central ampelologique Royal Hongrois" as the report of the Central Vineyard Institute which had been placed under his direction. Here also especial attention was paid to diseases. The same is true also of the "Jahresberichte der Kgl. Lehranstalt fiir Obst-,Wein-und Gartenbau" published by Gothe and later by Wortmann in Geisenheim a. Rh. and the annual reports of the "Ueutsch-schweizerische Versuchsstation fiir Obst-Wein-und Gartenbau zu Wadensweil," Ziirich, revised by Miiller- Thurgau. This list of periodicals which in part review German and foreign litera- ture and in part publish original articles, gives an insight into the unusually rapid growth of material which necessarily demands a unified summary in some collective work. Hollrung devoted himself to the working out of such a summary and since 1899 has been publishing a "Jahresbericht iiber die Neuerungen und Leistungen auf dem Gebiete der Pflanzenkrankheiten," Berlin, publishing house of Paul Parey. 69 Thus the new science of phytopathology has taken to itself the same literary methods which the older branches of knowledge use and which are undisputably necessary for scientific progress. But the practical side of phytopathology, viz., the protection of plants, has also found a desired de- velopment. The idea of establishing special institutions, suggested in 1880 by Korn, actively advocated in 1889 by Kiihn and further developed by Sorauer at the International Agricultural Congresses and in the "Zeitschrift fiir l^flanzenkrankheiten" was brought in 1891 to general attention in the Pruss- ian Abgeordnetenhause (Chamber of Deputies) by Schultz-Lupitz in the form of a motion. On the 27th day of April of the same year the "Reich- sanzeiger" gave out that the motion of Schultz-Lupitz had been referred to the Royal State Administration for discussion and at once the Department of Agriculture attempted to^ test the question in how far the production of plants could be advanced by the enlargement of the scientific institutions sub- ordinate to that purpose. As the question received a more thorough- con- sideration, it became evident that the best interests of the protection of plants could only be had from an Imperial Institution. Such was now formed in connection with the Imperial Board of Health as a "T^iologische Abteilung fiir Land-und Forstwirtschaf t" and since 1905 this has been an independent institution of the Empire. The department, at present under Aderhold's di- rection, possesses in Dahlem, besides the proper laboratories, a very expensive experimental field and has published its results at indefinite intervals since 1900. Besides these scientific works the "Biological Division" also pubhshes popular bulletins and colored posters and in this way promotes the knowledge of the most abundant animal and vegetable agencies injurious to plants. In- formation as to their control is also distributed gratis, directly to these workers. Besides the above mentioned imperial institution which now bears the title, "Kais. Biologische Anstalt fiir Land-und Fortszvirtschaft," we find in the different German States many organizations for the furtherance of plant protection, which in part are associated with the already existing high schools and experiment stations and in part are independent establish- ments. Among these, besides the institutions already mentioned at Halle and Geisenheim, there should be named also the Anstalt fur Pflansenschuts in Hohenheim, founded in 1902 and now under the direction of Kirchner. We also find in the other European countries an active development of the study of plant diseases, proved by the publications of many institutions. Among these belong the "Bulletin de la Station Agronomique de I'Etat a Gembloux," Bruxelles (Em. Marchal), and "Travaux de la Station de path- ologic vegetale," by Delacroix, Paris, the "Tijdschrift over Plantenziehten" (Ritzema Bos) already mentioned and the "Landbouwkundig Tijdschrift," the "Oversigt over Landbrugsplanternes Sygdomme" Kjobenhavn, in the "Tijdsskrift for Landbrugets Planteavl," Kjobenhavn (Rostrup), the "Upp- satser i praktisk Entomologi," Stockholm (Lampa). "Beretning om Skadein- sekter og Plantesygdomme," Kristiania (Schoyen). "Berattelse ofver skad- 70 einsekters upptradande i Finland" (E. Retiter), in the "Landbruksstyrelsens meddelanden," Helsingfors, the "Annual report of the consulting botanist" (Carruthers) in the "Journ. Royal Agric. Soc," London. It is a matter of fact that countries outside of Europe have not been backward in the endeavor to increase plant protection. This branch of knowledge has been most advanced in North America where the Department of Agriculture at Washington has devoted special attention as well to animal enemies. Besides establishing the "Division of Entomology" which, by its valuable investigations, contributes essentially to the knowledge of animal injuries, the organization of meetings of agricultural zoologists is especially noteworthy. In these meetings questions of general significance are dis- cussed. Besides this, many investigators in the Universities and Experiment Stations are working along these lines with gratifying results. Of the latter, we will mention the Agricultural Experiment Station of the State of New York at Ithaca and the New Jersey Agricultural College Experiment Station. Further statements are made in our detailed exposition in which the different bulletins of the institutions for the advance of plant protection are mentioned. Besides the numerous publications of the United States of North Ameri- ca, the magazines of other countries also furnish noteworthy contributions to the knowledge of the diseases of cultivated tropical plants. Among them belong the "Mededeelingen van het Proefstation voor Suikerriet in West Java," the reports of the "Proefstation voor Cacao to Salatiga," Malang, the "Boletim da Agricultura," S. Paulo, "Boletim del Instituto Fisico-Geograph- ico de Costa Rica," "Queensland Agricultural Journal," "Australian fungi" (McAlpine), in the "Proceed. Linnean Society of New South Wales," "Ad- ministration Reports, Royal Botanical Gardens," Ceylon, "Report of the De- partment of Land Records and Agriculture," Madras, and "The Journal of the College of Science, Imperial University of Tokio," Japan. We must refer to the "Botaniker-Adressbuch" by J. Dorfler, Vienna, 1902, for the numerous other institutions and individaul investigators. APPENDIX. In the above statements we have mentioned not only the literature on the subject but also given expression to the leading ideas of the different periods in order to show how the science has gradually developed to its present standpoint. To be sure, changes in the points of view on the nature and role of parasitic organisms are not without interest, but no less interest- ing are the references of the various authors to the influence of the stars, i. e. the atmospheric factors, which may be traced as a red line through all the reports. On this account we have often restated at length the earlier points of view and find a striking agreement with the oldest periods since emphasis is always laid on the dependence upon climatic and soil conditions and in part 71 also upon cultural habits of those phenomena, which we have learned to recognize as parasitic. This idea, which is also the guiding principle in the present book, has led the author to undertake the first experiments for collecting the Statistics of Plant Diseases. These experiments which, as already mentioned, were begun with the help of the German Agricultural Society and continued by its "Special Commission for Plant Protection," have now found recognition, for the "Kais. Biologische Anstalt fiir Land- und Fortswirtschaft" beginning with 1905 has assumed the collection of statistics of plant diseases. Doubt is often expressed as to the importance of such statistics for our subject and reference made to the fact that our most dangerous diseases are constantly present and the statements of the statisticians concerning the intensity of the attack and the amount of agricultural loss appear to be influenced so individually that all certain positive figures can never be attained. In opposition, it should be emphasized that I did not undertake the collection of statistics in order to obtain precise figures as to the dis- tribution and agricultural effect of the diflferent diseases. (Besides, in this connection, the making of reports will gradually, with the increased educa- tion of the body of observers, become as exact as it is in all provinces of organic life). The chief undertaking in the collection of statistics lies in the proof of the relations which the different diseases bear to climatic and soil conditions felt locally or universally, as well as to cultural factors. The study of the extreme forms of disease, easily verified, and the determination as to which factors have produced these extreme forms makes up the productive field of the statistics. In these studies lies the future of patholog}^ However valuable in themselves the observations as to the formal po- sition and the life requirements of the parasitic micro-organisms may be, nevertheless, they form only one link in the chain of investigations and be- come important only in the determination of their relation in nature and in the usual practice of agriculture. And this we can recognize by means of a carefully arranged statistical office showing the conditions governing the in- crease or decrease of diseases. This knowledge leads to the prevention of diseases by means of an ever- developing plant hygiene and plant pathology must develop further in this direction in the future. DETAILED EXPOSITION. SECTION I. DISEASES DUE TO UNFAVORABLE SOIL CONDITIONS. CHAPTER I. THE LOCATION OF THE SOIL. Even if the diseases which are due to an unfavorable location of culti- vated land are better understood by means of the different factors because of which this position becomes injurious to plant growth, we have still con- sidered it necessary to describe in the following section the general conditions due to different locations. We have done so because it is of special impor- tance to the guiding principle of this manual and to any reference to a pre- disposition to certain diseases which is developed from this location of the soil that it be shown how the material and formal structure of any plant species changes with the condtions of the habitat, how thereby separate func- tions may sometimes be suppressed, sometimes advanced, and -how accord- ingly the different localities impress their definite characteristics on the plants which, on this account, must behave very differently in relation to the differ- ent injurious causes. I. ELEVATION ABOVE SEA LEVEL. a. General Changes in Habitat in Relation to Herbaceous Plants. There is no need of discussing further the fact that the temperature al- ways falls with an increase in elevation of any cultivated surface above sea level and that this fall in temperature is a determining factor for limiting vegetation, on which account the time of harvest in mountains must always be later than on lower levels. It is an universally recognized fact that this later harvest brings with it great difficulties in curing the grain and not in- frequently makes necessary special precautions in high m.ountains, and that despite these precautions there often takes place a blackening of the grain as a result of the beginning of fungous growth. An example with exact figures 73 is given by Angot\ according to whose observations the harvest of winter rye in France is delayed on an average about four days, as the elevation increases about lOO meters. Attention should be called, however, to the circumstance that, with increasing height, the air being thinner is less warm so that there- fore it must have an appreciable effect on the development of vegetation. With this should be reckoned conditions of moisture which, aside from the phvsical constitution of the soil, are different for plants of Alpine regions in lower latitudes than for those from plains in the Arctic zone. Within the same degree of latitude mountains, as colder bodies, will condense more water vapor and thereby bring about more abundant precipitation than takes place on plains. On this account more snow will fall and the warmth needed to melt this greater mass of snow is withdrawn from vegetation. Even after the snow has melted in spring, the plants in the mountains will ne\ ertheless at first be less able to benefit from the sun's warmth than those on the plains since the inequalities of the upper surface of the soil become eft'ective. A square meter of very broken ground surface has a much greater upper sur- face, divided into many slanting levels, over which the same amount of warmth must be distributed, than has perfectly level land, the different par- ticles of which are raised to a higher temperature. This is the case in moun- tain chains in contrast to level plains. It is evident from these statements that with increased elevation above the sea these processes of weathering and decomposition must be retarded since they are essentially favored by warmth. It is also evident that such peculiar combinations of vegetative factors will produce characteristic forms, of which the best known feature is short, repressed growtli. Such forms of growth are kept constant, first of all, in the seeds. Climatic forms which have become hereditary in this way have been termed "Oecolocjical variations"'-. If it was said at first that the temperature of the air at higher levels is lower, it must also be emphasized, on the other hand, that at higher levels the intensity of the illumination increases and produces accordingly greater soil zvarmth. On this account climate of the lower and middle latitudes, on ac- count of the greater intensity of light and greater warmth of the soil, would differ favorably from that of those plains in a Polar zone where the tem- perature of the air is the same. The lesser atmospheric pressure in moun- tains must result in an increase of transpiration as stated by FriedaP and the increased supply of light in an increase of the assimilatory activity of the leaf. Consequently the typical mountain plant works more energetically and in this way is explained its shortened vegetative period. According to the observations of Bonnier-*, who made experimental gardens on Mt. Blanc and in the Pyrenees, in Alpine climates with a 1 Der Naturforscher, 1883, No. 24. -' Lebensgeschichte der Bltitenptlanzen Mitteleuropas. Von Kirchner, Loew und C. Schroter. Stuttgart, Ulmer 1904. p. 116. 3 Friedal, Action de la pression totale sur I'assimilation chlorophyllienne. C. rend. 1901. Cit. Bot. Jahrcsb. 1901. Section II, p. 221. i Bonnier, Etude experimentale de I'influence du climat ali)in sur la veg-etation etc. Bull. Soc. Bot. France. Vol. XXXV. 35. 1888. 74 greater number of herbaceous plants, the shoots became shorter, leading to nanism. In specimens from high mountains, the palisade parenchyma is more strongly developed and contains more chlorophyll. Accordingly, the assimilatory work has been increased. If the leaves of the same species from specimens grown on plains and in mountain gardens, are cut off at the same time and tested, the leaves from the high mountains showed a stronger de- velopment of oxygen in an equal length of time for equally large surfaces. It is said that such Alpine characteristics can be artificially bred in plants by packing them in ice at night while leaving them during the day under normal growing conditions^ In a later report, Bonnier- calls special attention to the increase in temperature and assimilation which, taking place in Alpine regions, may easily account for the fact that plants from the plains, brought into an Alpine climate, develop relatively greater amounts of sugar, starch, volatile oils, coloring matter, alkaloids and other products of chorophyll activity. How greatly this specific climatic character immediately influences the mode of development of any plant species is shown by the well-known ex- periments on structure carried on from 1875 to 1880 by Kerner v. Marilaun-^ with seeds taken from the same parent plant which had been grown with precaution against cross-fertilization. Part of the seeds were sown in an Alpine experimental garden on the top of Mt. Blaser in the Tyrol (2195 m. elevation), others in the botanical garden in Vienna. The germination of the seed on top of Mt. Blaser took place soon after the melting of the snow which had been 1.5 m. deep, between the loth and 25th of June. The germination and growth of the seedlings therefore took place when the sun was highest and the days longest. The seedlings were exposed at once to a temperature which was just as high or perhaps somewhat higher than that furnished the experimental plants in the botanical garden at Vienna, when the March day was twelve hours long. At the end of August and the be- ginning of September blossoms were observed on the plants which had not been killed by the several frosts in June, July and even in August, for ex- ample, on Satureja hortensis, Lepidium sativum, Agrostemma Githago, Cen- faurea Cyanus, Turgenia latifolia etc. The plants grown in the Alpine experimental gardens differed from those in the botanical gardens at Vienna in that they were strikingly shorter and their stems developed a greater number of parts. It was found further that in the Alpine specimens, for instance, Viola arvensis, blossoms developed even from the axis of the third and fourth leaves while at Vienna they came only between the seventh and eighth leaves. The number of blossoms was fewer and the petals, like the leaves, were smaller, as a rule. A part of the 1 Palladin, Onfluence des changements des temperatures sur la respiration des plantes. Revue gen. de Botanique, 1899, p. 242. 2 Bonnier, Gaston, Influence des hautes altitudes sur les fonctions des vegetaux. Compt. rend, de I'Acad. scienc. Paris. Vol. CXI. 1890. Cit. Bot. Centralbl, 1891. No. 12. 3 Pflanzenleben. Vol. II, pp. 453 ff. Wein. 1898. 75 annual species from the plains which had had sufficient time and warmth to develop seeds were longer lived on the top of Mt. Blaser since in the follow- ing year, new sprouts were developed from the lower part of the stems. An earlier blossoming could also be observed. Corresponding to the fact that the intensity of the sunlight increases with increased elevation, the color of the blossom, depending upon the antho- cyanin, also became more intense. Blossoms, which were white on the plains, had in the Alps petals which were violet underneath. The glumes of grasses, green on the plains, or only pale violet, became dark brownish violet in Al- pine regions because of a more abundant formation of anthocyanin\ The leaves of Sedum acre, S. album and S. hexangulare became purplish red. On the other hand, leaves of Orohtts vermis, Valeriana PIiu and Viola cnciil- lata turned yellow from the excess of light in the Alpine experimental gar- dens while in the valley in shaded places their foliage remains green. The mountainous region affects not only temperatures in the annual seasonal average but especially the moisture content of the atmosphere. Warmth and humidity in their total amount and in their distribution during the seasons together vvith the supply of light are determinants of growth. As already mentioned, atmospheric moisture influences the amount of light available for the plant, for a humid atmosphere absorbs about five times as many light rays as does a dry atmosphere. Since the absolute content of the air in water vapor decreases with the elevation, less light will be absorbed in the mountains, especially since the rays of light have a shorter distance to traverse in order to reach the earth as compared with regions at sea level. The fact that the absolute vapor con- tent of the air decreases with the elevation is a matter of course for, since the temperature becomes lower and lower, the air must condense its water vapor and give it off in a liquid form. But the relative moisture increases in the mountains which explains why we call a mountain climate damp and rainy. Cloudiness is also relative to the moisture of the air. This increase of the relative moisture and the decrease of temperature form the reasons for the rapid ending of our cultural eft'orts so far as these concern the obtaining of seeds in mountain regions. We know that the for- mation of blossoms and seed requires an increase of warmth proportionate to the length of the growth period. For this reason we find, as mentioned at the beginning, that grain often does not ripen in the mountains and that therefore clover and other legumes furnish an insufficient amount of seed. Yet another condition must be added to those already mentioned, to which Pax has called attention-, viz., that the insects are onlv half as num- 1 The theory that anthocyanin is developed for the protection of the plant against too strong sunlight is held by many investigators. Kerner (1. c. Vol. I, p. 508) assumes that, in the reddening of blossoms which appears with a lack of heat, the loss to the blossoms of the directly conducted heat is compensated "by the heat obtained from the rays of light by means of the anthocyanin." We believe we have observed that the red coloring matter indeed does develop abundantly with a lack of heat, but can also set in with an abundance of heat if, in proportion to the heat, an excess of light makes itself felt in the tissues which contain sugar. 2 Das Leben der Alpentlanzen. Zeitschr. d. d.-ostr. Alpenvereins 1898, p. 61. 76 erous at an elevation of 2300 m. as on the plains. On this account labiate plants play a considerable role on high mountains. Also the increased diffi- culty of insect fertilization is partly equalized by the fact that an asexual reproduction also takes place (Polygonum viviparum, Foa alpina, Saxifraga ccrnua) ; further, ten-elevenths of all kinds of small bushes and even Viola tricolor, an annual with us, become perennial in the Alps. Besides this, reference should be made to the fact that, with unlimited cultural experiments at high elevations, short-lived mountain varieties are form.ed which, to be sure, furnish seed in smaller amounts but more satis- factory in quality. This offers greater possibilities of yielding a good har- A'est in the mountains and (according to Schiebler)^ has the advantage of retaining at lower levels its shortened period of growth and there- fore can be used advantageously in Northern climates. Development of the Aerial Axis of Woody Plants. In contradiction to a widespread opinion, it should be mentioned, that divarf grozvth in high mountains is not to be ascribed to the pressure of the snow since we have tree-like forms in those regions where the most snow falls. It is known that the snow covering does not become thicker, the great- er the elevation of the mountain, but with us increases up to perhaps an elevation of 2500 m., that is, only to the upper boundary of the dwarf coni- fers, dwarf alders and the Alpine rose. Higher up the amount of precipi- tation decreases. Spruces, larches and the cembra-pine suffer less from snow pressure when they stand alone or scattered because their elastic, slop- ing older branches let the accumulated snow slip off" more easily when the wind blows. Other trees, like Salix serpyllifolia and Rhamnus pumila, fre- quently escape excessive snow pressure by their growth on steep rocky cliffs from which the snow slides rapidly. However, trees exposed to the full pressure of the snow can scarcely be made to grow closer to the earth be- cause of the burden of the snow or of windy weather. Rather, we may as- sume with Kerner that it is the soil warmth which, in the immediate prox- imity of the earth, affords them the best conditions for existence. In the higher Alpine regions the soil is much warmer than the air which absorbs less sunlight on account of its increasing thinness and its rapidly decreasing water content. The above quoted author cites that, for example, on the top of Mt. Blanc (4810 m.) the intensity of the sunlight is 26 per cent, greater than at the level of Paris. On the Pic du Midi (2877 m.) a temperature of 33.8°C. was observed in the soil on which the sun shone while the air showed a temperature of only io.i°C. This warmth of the soil together with the intensity of the light explains the speedier development and blooming of Alpine plants. Vochting-, in opposition to Kerner, thinks, on the ground of his observations with Mimulus Tilingii, the young branches of which at a defi- 1 Schiebler, Die Pflanzenwelt Norwegens. Allg. Teil. Christiania 1873. - Vochting, H., Ueber den Einflufs niedriger Temperatur auf die Sprofsrichtung. Ber. Deutsch. Bot. Ges. XVI. ]SP8, p. 37. 77 nite age incline downward in spring when the temperature is lower and straighten up later with increased warmth, that the creeping habit of growth of Alpine plants may be ascribed in part or entirely to the influence of the low temperature. We can not agree with this theory. Rosenthal' made investigations concerning the mode of growth of trees in Alpine regions. He found that in all the species of wood studied the annual ring is narrower in high countains than in the lowlands. The ec- centricity of the branches is usually very great but the direction of the great- est increase of growth varies. The vascular system, on account of the in- creased evaporation, is more extensively developed. In dicotyledons, a higher percentage of the vascular tissue is obtained by a narrower annual ring; in conifers there is a considerable decrease of the late wood ring. The landslides which continually take place in inountains because of storm conditions displace the trees and thereby change their woody develop- ment. Hartig- pointed out the formation of broad annual rings and so-called "red wood" (wood with short tracheids and strong lignification) on the underside of the trunks and branches of the spruce as soon as they bend toward the horizontal, while slender annual rings and "strain wood" (long tracheids with weak lignification) are formed on the upper side. Ac- cording to Giovanozzi'' this difference in the formation of the wood ring of conifers is made use of in hygrometric measurements by the inhabi- tants of the Piedmontese Alps since the small celled, thin-walled red wood possesses hygroscopic characteristics very different from those of the strain wood. The red wood side of a peeled branch becomes concave in dry air, convex in moist air. According to the investigations of Cieslar^ the lignin content of spruce wood seems to be less near the upper boundaries of the tree zone than in lower positions. It will be concluded from Cieslar's' observations, that the suppressed growth in Alpine forms is hereditary for the immediately following generation, according to which spruces from seeds of trees grown in moun- tainous regions grow more slowly when cultivated on the plains than do plants raised from seeds of trees from the plains similarly grown. Engler has made the same observation in seeding experiments at the forestry experimen- tal station in Ziirich. From germination experiments with the seeds of spruce, pine and other forest trees, M. ICienitz" concludes that the minimum, optimum and maximum germinating temperatures of spruce seed indigenous to lower regions are higher than for seeds grown in higher positions. 1 Rosenthal, M. Ueber die Ausbildung der Jahresringe an der Grenze dea Baum- wuchses in den Alpen. Dissect. Berlin, cit. Hot. Centralbl. 1904. No. 43. - Hartig, R., Holzuntersuchungen. Berlin. Springer 1901. 3 Giovanozzi, Sul movimento igroscopico del rami delle Conifere. Malpighia XV, cit. Bot. Jahresb. 1901. Sec. II, p. 191. •I Cieslar, A., Ueber den Ligningehalt einiger Nadelholzer. Mitt. a. d. Forstl. Versuchswesen C)esterreichs 1897. Part XXIII. 5 Centralbl. f. d. g-esamte Forstwesen, 1894. Vol. 20, p. 145. 6 Kienitz, Vergleichende Keimversuche mit Waldbaumsamen aus klimatisch verschieden gelegenen Orten Mitteleuropas, Ref. Bot. Zeit. 1879. p. 597. 78 In plantations in high altitudes, however, it must further be taken into consideration that the elevation acts differently according as it presents iso- lated peaks or high plateaux. Since the earth's illumination and radiation have considerable influence on the temperature of the layers of air covering it, vegetation at equal heights is exposed to very diverse temperature fluctu- ations. On the high plateau the decrease of warmth with elevation is less, when the sun shines, than on the mountain peak which stands alone. If, however, the sun disappears and radiation becomes determinative, then the lower air layers above the high plateau also cool off more. Thus the daily fluctuations in temperature are nivicli greater here and the seasonal ones as well. On high plateaux the temperature can fall, even to frost, while the isolated peaks remain protected. The same relation is shown between valley and heights ; we have recently observed a number of examples from Italy. Passerini makes ^ the following observations from the neighborhood of Flor- ence and cites, as an especially good instance, the night of April 19-20, 1903, when the temperature, which on the 15th still showed -j-i8.3°C. sank to — i.i"C. and rose again, nine hours later, to -|-I2.2°C. While the vegetables and grains were not injured, the leaves and blossoms were seriously frozen. Only 50 m. higher the injuries were no longer noticeable. In mountainous regions clouds and mist act as a protection from frosts. Thomas^ observed in Thiiringen that the young beech foliage did not suffer from frost at heights covered by mists while in the valleys and gorges the leaves were injured. The artificial prevention of frost by the production of smoke has been founded on the peculiarity of mists which prevents the sharp fall in temperature. Adjustment of tpie Root Body of Woody Plants. In mountains the adaptation of the wood body to the rocky soil and the compensatory structures which appear on this account are especially interest- ing. In the following figure i, we see the root of an oak which has made its way through a fissure in a rock and by its continued growth in thickness within the split has developed into a flattened, board-like form. After leav- ing the rock, the root resumed its cylindrical form. This example shows first that, despite the pressure which the strong root had withstood for so many years, the ability to conduct water and plastic material has not been interrupted in the board-like part. In the second place, we notice above the board-like flattening the appearance of adventitious roots. Both processes correspond to the phenomena caused by artificial constriction. So far as we have been able to investigate roots which had been flatten- ed in, the clefts of rocks, we could observe that the board-like flat places in the root body were produced because the wood rings formed every year were very strongly developed on the sides where they could develop freely. 1 Passerini, Sui danni prcdotti alle piante del ghiacciato etc. Bull. Soc. Bot. ital. 1903. p. 308. 2 Thomas, Fr., Scharfe Horizontalgrenze der Frostwirkung an Buchen. Thiir. Monatsblatter. April 1904. 79 therefore, in the direction of the split surface, but, on the other hand, they were reduced to a minimum on the side where the roots were pressed against the rock and were finally irrecognizable. On the free side of the wood the vascular bundles developed very abundantly, in some annual rings, in fact, the wood was very broad and provided with a thick bark ; on the side of the root pressed against the rock, the wood lacked all vascular formation, was short-celled and formed from wood fibres inclined diagonally instead of Fig-. 1. Roots of Quercus Pedunculata grown between rocks. Fig-. 2. (After Dobner-Nobbe.) running vertically. Finally, dififerentiation into annual rings could not be observed and only a very slender cork layer is seen lying on the occasionally formed short-celled parenchyma, without any recognizable differentiation into medullary rays. Nevertheless, the cambial activity was not lost in the board-like part of the root as was evident when the pressure ceased, for the flattened part grew normally in its cylindrical form. Anatomical changes in the roots pressed between the rocks approximate so strikingly the results obtained by artificial 8o constriction of the aerial axis, that we can refer in this connection to our subsequent studies in the chapter on "Wounds." Figure 2 shows a different root, also from Quercus pedunculata, which probably has only been pressed between stones. In meeting with this ob- struction to its growth in length it was bent and. when growing further, be- came flattened. With increasing age the pressed root surface again reached the open and with the removal of the pressure came an increased formation of the wood ring in great luxuriance like callus rolls. The squeezing which the roots had undergone, might have acted like girdling and have produced in this a kind of girdling roll above the place of pressure. (See Girdling in the chapter on "Wounds"). We can get an idea as to the anatomical conditions in the first stages of such flattening of the root from the investigations of Lopriore\ He observed adventitious roots in the germinating plants of Vicia Faba which were forced to grow under the lateral pressure of cotyledons which had not separated from each other. Within the sphere of pressure these tender roots appeared flattened like ril)bons but after leaving the region of pressure, they again became normally cylindrical just as was noticd in the oak roots. In the very young roots of the horse bean (Vicia Faba) Lopriore found that the epidermal cells on the sides not pressed upon by the cotyledons had developed into root hairs. On the compressd sides, however, not only the epidermal cells were tangentially flattened but also the two or four outer layers of the bark were considerably pressed so that they formed a kind of peripheral girdle around the root on these sides, whereby the radial walls of these com- pressed cells seem folded zigzag as in a bellows. The cells subjected to the pressure of the cotyledons were also proved changed materially since their membranes either developed into cork or "together with their lumina were impregnated with a kind of protective gum." We have already called attention to the fact that in figure i several adventitious roots had been formed above the board-like flattening. As may be seen, th^ root had made a curve here before entering into the split in the rock and under the influence of this twisting, a new formation of adventitious roots had been started on the free convex side. We perceive in this a result of the stimulus of twisting which Noll- has discussed in detail in his work. It is easy to observe that roots which have become twisted because of a pressure, hindering their growth in length, develop new side roots on the convex side at the point of twisting. In water cultures in glass vessels this phenomenon may l)e observed when strong roots reach the bottom of the vessel and grow against it. In mountains emergency precautions are met widi in the flatly growing, younger tree roots if the tip of a rootlet has been lost through injury or from 1 Lopriore, G., Verbanderuns; infolge ^nunzach in Stiibewasen. (After L. Klein.) A case, due probably to the same conditions, which cause the stilt-like growth of spruces, was shown as recently as the 8o's of the last century in Kohlhasenbruck near Neubabelsberg (District of Potsdam). The stump of an old oak, about 75 cm. high on the village street, had formed a broad hollow cylinder by the rotting of all of the heart wood. This was half filled with rotten wood and earth and a healthy oak, possibly thirty years old, stood in this as in a sheath. In spruce plantations one finds at times the so-called "Harp-trees" m which a number of side branches have becomp elevated at right angles to the 94 main trunk which the wind has blown down, part of whose roots, however, still remain in the soil, and therefore are still living. Adventitious roots serve the needs of these growths for nutrition. The spruce is certainly the one of all the conifers which can most easily overcome all injuries by develop- ing adventitious organs. It also withstands pruning very well and can therefore be used ad- vantageously for hedges, only the hedges must be thinned constantly, or they become bare underneath. The ability to form new tips when the old ones have been removed, a characteristic of spruce and Araucaria, is taken advantage of in horticulture, in propagating by cuttings. On the other hand, the regeneration phenomena of tlie older pine are most stable and fixed. The second type of stilt-growth occurs especially with this tree, if, in a hilly place, the porous sandy soil slides downwards from the effects of grading. In the struggle for existence, however, the pine when grown from seed can withstand much better exposure of its roots than spruces and firs ; this is because the roots habitually grow perpendicu- larly into the ground. In the two illustrations which reproduce two examples of Pinus silvestris from the Grunewald (back of Paulsborn) near Berlin, this perpendicular downward growth is shown especially well in the side roots. Figure 5 shows two pines standing back of one another with the bases of their trunks about i meter above the ground. The strong main roots send their side branches (arising directly on the underside) into the ground in parallel and perpendicular directions, indicating that the pine roots deeply. The front tree is possibly 60 years old ; the specimen behind it is younger. Figure 6 is taken from another side and shows the side roots starting at right angles from the main branches which spread horizontally from the root crowns. However, in the middle of the stilt appearance, may be dis- tinctly recognized the original main root which as a prop has grown directly into the earth and which endures the chief strain of anchoring the tree in the sandy soil. The tree is still well covered with needles. One more important phenomenon must be mentioned in connection with this form of stilt-growth, viz., many woody tubers with a dense covering of bark grow in rows on the upper sides of the strong roots. These in figure 7, reproduced natural size, form hemispherical, wart-like prominences up to 1.5 cm. high, with a crater-like depressed centre. They correspond with the rest of the root in color and bark. It is supposed that this arises from an adventitious sprout formation in which the young shoots have died immediately and a heavy scar has been formed. The fact that these growths come only on the upper side lends strength to this supposition. It is well known that when there is this ten- dency toward adventitious growths in trees, the formation of such buds of all sizes occurs most strongly on the side toward the light (Tiha, Acer). This supposition has not been generally confirmed, as the cross-section (Fig. 8) shows. This illustrates a seven years' overgrowth of a centre of disease formed by a homogeneous mas^ of resin. This resin gall, produced by resin- 95 Fig-. 5. Stilted piue from Grunewald near Berlin. (Uriy.) Fig. 6. Stilted pine from Grunewald near Berlin. (Orig-) 96 osis of the wood, ruptured on the outside and was overgrown in the follow ing years. The edges of the over- growth, still connected in the first few years, have grown back farther and farther; — in this way, a crater-like opening was produced at the top of the woody tuber. The new annual rings turn to resin every year and always in the first spring wood, which consists in part of parenchymatically formed cells. The resin holes (H) are pro- duced by the drying up of the resini- fied tissues, in part also by exudation of the resin. The edges of the over- growth are further apart each time so that the last ones (U) are widely sep- arated. In this, they show a most ir- regular construction often changing between every two medullary rays in the same annual ring. In the drawing G is the normal wood in cross-sec- tion and M the regular course of the tracheids in longitudinal section. These are in the same annual ring just as in true gnarls. Fig. 7. Resin galls with gnarl growth on the upper side of the stilt- like root of the pine (natural size). (Orig.) F'or this reason these structures must be classed with the resin galls. So far as their production is concerned, it must be assumed that the exposed root shows small centres of injury from extremes of weather on its upper side, i. e. the one most exposed to such extremes. These centres of injury have caused a resinosis of the tissues, or rather, a com- plete resinous liquefaction. Wq may assume that frost has caused the injuries, and especially late frosts, since these appearances are al- ways found in the first formed spring wood. The production of these resin Fig. 8. Cross-section through a resin gall on the ,i i ^^ . ,^ i. stilt-like root of the pine. (Orig.) galls shows that the roots 97 exposed in the stilt-like growth are very sensitive. Tt this is true, less extreme cases will have to be taken into consideration and a further w^arning be given ; when possible the root body must be guarded from complete exposure. When roots are partially exposed their bark is Hable to be broken on the upper side by pedestrians, with the result that much stronger annual rings develop on the under side which is protected from such injuries by the earth. The cultivation of seedlings of the different species of our common coni- fers under the same conditions gives the best demonstration of these root systems. Nobbe^ carried his experiments out with the following re- sults: — Six months after sowing, the pines had 3135 root fibres with a total length of 12 meters, the spruces 253 fibres, all together 2 meters in length and the fir, 134 fibres with a total length of i meter. In one year, in fertiUzed sandy soil, the tap-roots of the pine seedling penetrated almost one meter deep, while the spruce and fir, under absolutely the same experimental con- ditions, went down only one third as far. At the same time the young pine developed five series of roots, the spruce four and the fir three. In decid- uous trees, oaks and beeches, Tharandt's experiments showed that in the same way they form even in the first year a widely branched root system with tap roots nearly a meter long. Spruce and fir with their weaker root apparattis, v/hich almost im- mediately spreads out flat, need a moist soil, while the pine can do without moisture, in fact, easily suffers from it. In seedling plantations, where fir and spruce thrive, the pine ver}^ often shows pathological resin ducts in the wood of its young trunk. The deep growth of the pine also explains its so- called "contentment" and its heahhy growth in almost sterile sand. Like the lupin it understands how to meet its need for water and food from the deep layers of the soil but it demands good drainage. This natural advantage of a tap root penetrating at once to great depths is made use of only where seeds are planted in forests without necessity for transplantation. In the controversy in forestry circles as to the best methods of planting, in considering the pine, we would always place ourselves on the side of those favoring sowing in the permanent place. For the spruce and fir, we consider transplanting from the seed bed to be more advantageous. In any event the method of seeding is not the only factor in a healthy devel- opment, but soil and position are often decisive. We can not consider ad- visable the present endeavor to plant pines everywhere, because they give the quickest and therefore the best return from the soil. In our own forests comparisons of the trees in deep lying or marshy places with those on free, dry regions show that in the marshy localities there is an impoverished growth and often a premature dropping of the needles, and that in hilly sandy soil, with deep lying ground water, the trees develop to their full strength, even f;eing well-preserved when their roots are exposed on stihs. Rechinger- 1 Dobner's Botanik fiir Forstmanner. IV Edition, revised by Fr. Nobbe, Berlin. Paul Parey. 1882, p. 130. 2 Rechinger, Bot. Beobacht. in Schur. cit. Bot. Jahresber. 1902, I, p. 337- mentions the occurrence of stilt-roots in marshy forests, in which Alnus glutinosa predominates while isolated Quercus pfiuncidaia, Rhamnus Frangula and Sali.v cinerea occur. A third cause of the stilt-like growth still remains to be mentioned which is different in that the trees are positively elevated, while, in the cases already mentioned, the base of the trunk remains at the place where the seed was sown. White^ describes occurrences of this kind. He thinks that on rocky soil, where the roots must grow flat, the trees are gradually forced out of the ground by periods of frost and draught to which they are peculiarly susceptible. c. Too Deep Planting. Too Deep Planting of Trees. Almost all our trees, in their later life, stand in a position different from that of the seed beds in which they develop. For fruit trees must have a sec- ond transplanting when young in order to obtain an abundant ramification of the root body. Since these trees must be so transplanted great care should be taken that they are not planted deeper than they originally stood. Exper- ience teaches that trees can indeed be destroyed through a disregard of this warning. In fact many practical workers recommend that each tree in its new position be oriented exactly as before in regard to the points of the compass, since they think that many kinds of bark injuries from heat and frost can thus be avoided. Otto- has attempted to decide the question whether the branches of apple, pear and cherry trees develop differently in the several points of the compass. By chemical analysis, he found essential differences in the com- position of the differently oriented one year old branches. The water and nitrogen content is the smallest on the east side, while the content in dry sub- stances is the greatest there ; but the water and nitrogen content is greatest on the north side. This would indicate that the branches v/ere not so fully ma- tured here as on the other side of the tree. ' Kovessi^ considers the cause of a decreased formation of blos- soms to be the greater amount of water and the lesser ripening of the wood of the branches. The number of blossoms and fruit was certainly proved to be dependent on the water supply of the previous year. The tree bears better, if the water supply is scant. Anatomically, the differences in the maturity of the branches, according to the points of the compass, can scarce- ly be determined since the structure of the same annual ring fluctuates too greatly within the different internodes of a branch*. 1 WTiite, Theodore, Mechanical elevation of the roots of trees. The Asa Gray Bull. Cit Bot. Jahre.sb. 1897, I, p. 85. - Otto, Arbeiten der Chemischen Versuchsstation zu Proskau. Cit. Bot. Cen- tralblatt 1900, Vol. 82, Nos. 10-11. 3 Kovessi, F., LTeber die Beziehuna;- des Wassers zur Reife der Holzpflanzen. Biedermann's Centralbl. 1902, p. 161. ■* Sorauer, Beitrag- zur Kenntnis der Zvveige unserer Obstbalinrie. Forsch. a. d. Gebiete d. Agrikulturphysik, Vol. Ill, Part 2. 99 Also, we know nothing definite, at least nothing which holds good in general, of the anatomical changes taking place when trees are planted too deep. In some cases it has been observed that the ducts are filled with brown, gum-like stifle masses, in others they are filled with tyloses accom- panied by a brown discoloration of the walls. Gummy swellings of the mem- branes are not infrecjuent. But these are all only occasional observations and experimental study of the question is still needed. We will limit ourselves on this account to the enumeration of the dis- coveries already made as to the influence of the two factors occurring most generally when trees have been planted too deeply — the lack of oxygen and the excess of carbon dioxid. We know that plants without a supply of oxy- gen gradually die. If the living cell can take up no oxygen, it changes the direction of its life-functions. Later it passes over into a state of rigidity, since the phenomena of movement cease in the cytoplasm., the sensitiveness to stimuli is lost and growth becomes inhibited. The plant, however, does not die immediately. It continues to give off carbon dioxid for some time and, with a renewal of the oxygen supply, it can even re-assume its usual functions after a rather long apparent deatli. In this continuation of life without oxygen (anaerobic) the oxygen necessary for the life pro- cesses must be furnished from the substance of the plant itself and has been called intra-moleciilar respiration. Lechartier and Bellamy^ in a series of experiments, have proved that alcohol is formed in the parenchyma cells growing without a supply of oxygen, not only in our pitted and other fruits, but also in the roots and leaves. Stocklasa has also proved most recently tiiat there is a forma- tion of lactic acid. Even in fungi (Agaricus campestris) , Muntz- found alcohol and hydrogen in considerable quantities if the fungi were kept for some time in air free from oxygen. The material for this alcohol can have been furnished by the kind of sugar alone present here, named man- nose, while in other fungi, producing only alcohol, (without hydrogen) in an atmosphere of carbon dioxid, the trehalose must have l.een fermented. If the lungus is not kept too long in the oxygen- free air, it can take up again its normal life-functions, as has recently been proved by Krasnosselsky'' for Miicor spinosa and Aspergillus niger. Adolf Mayer* had earlier expressed his opinion that fermentation produced by yeast, is a re- sult of respiration in the absence of oxygen. Pasteur'' and Bohm" had really proved already that all more highly organized land and water plants behave in a very similar way. since, in media free from oxygen, they 1 De la fermentation des pommes et des poires. Compt rend. t. LXXIX, p. 949. — De la fermentation des fruits ib. p. 1006. 2 Comptes rend. I.XXX I, p. 178. s Krasnosselskv, Atmung und Garung der Schimmelpilze etc. Central))!, f. Bakteriologie etc., 1904, Vol. XIII. Nos. 22-23. 4 Mayer, A., Untersuchungen uber die alkoholische Garung. Landwirtsch. Ver- suchsstationen, 1871. •"' Paits nouveaux pour servir ^ -la connaissance de la theorie des fermentations proprement dites. Compt. rend. 1872, p. 784. 6 Bohm, Ueber die Respiration von Landpflanzcn. Sitzungsber. d- k. Akad. d. Wissensch. 67. Section I. lOO reduce a part of their substance by fermentation to carbon dioxid and alco- hol, as do the yeasts in self-fermentation. The green parts of plants at any rate, with sufficiently intensive illumination, can establish an atmosphere suited to their normal respiration by decomposing the carbon dioxid which had been given off immediately before. Aerobic and anaerobic respiration are interdependent and anaerobic is able to withstand total destruction for some time, even if growth is impossible This retardation becomes greater as the temperature is lower. Thus, for example, Pfeffer^ cites the observations of Chudiakow, that the failure of the carbon dioxid production, i. e. the pos- pibility of living, begins after twelve hours in seedlings of maize at a temper- ature of 40°C., after 24 hours at i8°C. and only after some days at a lower temperature. If an organism or one of its members always has a lower vitality, it also will keep alive longer in a place free from oxygen. Thus, under such conditions, apples and pears at a moderate temperature have been kept growing and ripening for months while rapidly growing moulds and aerobic bacteria went to pieces quickly. In seedlings of phanerogamic plants (Vicia Faha. Ricinus etc.) there is an increase in the intra-molecular exchange. Stich's^ experiments show that single plants at times, or parts of plants, at first exert no influence on the oxygen content in the air by their respiration since, in a hydrogen atmosphere, they form exactly as much car- bon dioxid as in air. With 8 per cent, of oxygen in the air, the respiratory cjuotient was still normal, — with a lesser content (2 to 4 per cent.) it was changed in favor of carbon dioxid because an intra-molecular respiration took place. When the plants were kept for a longer time in an atmosphere poor in oxygen, the normal respiratory quotient was gradually produced to- gether with a decrease of the absolute amount of oxygen and carbon dioxid. In a gradual withdrawal of the oxygen, the intra-molecular respiration is first stimulated by a considerably lower percentage of oxygen than when the oxygen diminution is sudden. Brefeld's^ experiments lead to the conclusion that alcoholic fer- mentation in all plants, from the lowest to the highest, takes place as soon as the oxygen supply ceases. A very essential difference is shown, however, in the different organisms which produce alcohol. While generally in yeast (Saccharomycetes) the phenomenon of fermentation is to be considered the climax of the normal activity of the organisms (which actually grow during the process of sugar decomposition)^ it appears in the cells of phanerogams as an abnormal process ending prematurely in the death of the cell. This differs essentially from the pure fermentation of yeast producing only alcohol and carbon dioxid, by the appearance of further products of decomposition among which fusel oil and acids are especially noticeable. There is a great 1 Pfeffer, Pflanzenphysiologie, 1897. Vol. I, p. 544. 2 Stich, C, Die Atmunj? der Pflanzen bei verminderter Sauerstoffspannung und bei Verletzungen. Flora 1891, p. 1. 3 lUeber Garung III, Vorkommen und Verbreitung- der Alkoholgarung im Pflan- zenreiche. Bot. Zeit. 1876, p. 381. 101 difference in the ability of fungi to endure alcohol, as is shown among those which still introduce an actual alcohol fermentation. For Saccharomycetes, 12 per cent, of the weight is the limit of growth ; 14 per cent, the limit of fermen- tation. In Mucor racemosus, which lives on sugar without free oxygen, the limit of growth and of fermentation lies between 4^4 and 5^ per cent, alco- hol ; Mucor stolonifer, on the other hand, no longer grows and can not be- gin fermentation with 1.5 per cent, alcohol. It should be concluded from these results that imder the same external conditions even phanerogams succeed in forming alcohol of very different percentages and endure it in different amounts. Later Muntz^ speaks very generally of alcohol as one of the decomposi- tion products of organic substances formed on the surface of the earth as well as in the soil and in the depths of the ocean and distributed in the at- mosphere according to the laws of the tension of gases. It can not be surprising that organic acids, among others acetic acid, occur in the fermentation of alcohol. It is very probable that the accumu- lation of such acids must ultimately act as a poison upon the organisms and that in roots, which are entirely or almost entirely cut off from atmospheric oxygen, there will begin a gradual dying back. When trees have been planted too deep and the roots need an abundance of air, perhaps more than the top part of the plant, the lack of oxygen will be felt more quickly the greater the power of the soil to hold water and the more the parts are cut off by water-. Water near the living roots becomes more and more a source of danger for the larger, healthy roots and for the sunken bases of the trees, since the water becomes more and more charged with carbon dioxid. If healthy plants are set in water containing much carbon dioxid they begin to wilt and the leaves begin to die back'\ Kosaroff's^ studies on the absorption of water in insufficiently drained soils, i. e. those poor in oxygen a..d rich in .^arbon dioxid, are especial- ly interesting. The water absorption and tianspiration were proved to be repressed by the carbon dioxid. Plants whose roots remained in an at- mosphere rich in carbon dioxid lost their turgidity immediately and be- came limp ; when kept there longer they disintegrated. In experiments in an hydrogen atmosphere where, therefore, only the lack of oxygen becomes de- pressing, it was shown that this circumstance does not act in any way as in- juriously as an excess of carbon dioxid. Therefore, in the roots of trees lying too deep, death by poison begins by attacking first the tender organs, later the older ramifications of the roots. At the same time the putrid products of decomposition make the whole soil unfit for the growth of plants. Bohm-^' cites an example in the dying 1 From Compt. rend. Vol. I.XXXXII, p. 499. cit. in Biedermann's Centralbl. 1881, p. 709. - Mayer, Agrikulturchemie, 5th Edition, 1901, Vol. I, p. 116. 3 "Wolf. W., Tageblatt der Naturforscher-Versammlung- zu Leipzig, 1872, p. 209. ■i Kosaroff, Einfluss verscliiedener ausserer Faktoren auf die Wasseraufnahn\e der Pfltinzen. Dissert. Leipzig, 1897, cit. Naturw. Rundschau, 1897, No. 47. 5 Bohm, J., Ueber die Ursache des Absterbens der Gotterbaume und uber die Methode der Neubepllanzung der Ringstrasse in Wein. Faesy & Frick. 102 Ailanthus trees of the Ringstrasse in Vienna which had been planted too deep. These trees years before had fallen off in growth, for in the first year after they were planted, their annual rings were more than 3 cm. broad, in the last year the growth was 0.5 cm. At the time of death the earth about the roots was found to be so injurious that seeds of different plants sown in the soil in the open and under bell jars began to decompose at once. Seeds developed luxuriantly, however, after this soil, rei^eatedly washed with water, had been exposed in thin layers to the atmosphere for eight warm days in July. Similar experiments were undertaken by Mangin^ who, before this time, had ascribed the diseased appearance of tlie street trees in Paris to the bad composition of the soil. Seeds and tubers sown in soil re- moved from around diseased roots showed an interrupted development. The air tests made near the diseased roots of Ailanthus showed a de- ficiency of oxygen and a preponderance of carbon dioxid and Mangin- suspects that the lack of oxygen may be traced back to a reduction by sulfids. Certainly numerous micro-organisms co-operate in the decom- posing process of the roots. However, such an attack by the suitable bacteria would not have taken place if the oxygen in the soil had not begun to be deficient. When trees with spongy bark have been planted too deep, as in the above mentioned Ailanthus trees in Vienna, the bark under the soil is found entirely rotted away. According to the age and the liark structure of the tree, as well as the physical constitution of the soil, a disturbance of the ab- solutely necessary circulation of the air will appear sooner or later in the buried base of the trunk. This disturbance will be felt also in both the ven- tilatory systems of the trunk, viz., in the vascular system of the wood body and the bark system communicating with it by means of small hollow spaces. The green bark parenchyma protected by the more or less strongly developed cork is bathed by the atmospheric air; it penetrates through the lenticels into the intercellular spaces where it circulates. The air penetrates the ducts of the wood, partly through the water from the roots, but largely by diffu- sion from the sides and is also in circulation, as mentioned above. In fact, as may be assumed from the investigations, of O. Hohnel", a daily periodicity probably takes place in this circulation. The ducts originally filled with water are partly or entirely emptied in the course of the day, since the superior and surrounding tissues draw away the water. The trans- piring leaf body of the tree needs a very large amount of water and draws it from the wood tissues of the branches which make good their losses from the trunk, in which therefore a suction wave advances down toward the base and thence out into the roots. 1 Mangin, L., Sur la vegetation dans une Atmosph&re viciee par la respiration. C. rend. 1896, p. 747. - Mangin, L., Sur I'aeration du sol dans les promenades et plantations de Paris, C. rend. 1895, II, p. 1065. 3 V. Holinel, i?eitrage zur Luft- und Saftlievvegung in der Pflanze. Pringsh. Jahrb. f. wissensch. Bot. Vol. XII, Part I, p. 120. 103 Since more water is drawn away from the ducts than can be replaced instantly, a space partially filled with air appears in these ducts causing a negative pressure (suction) which is so much the greater the less the amount of air present at the beginning or slowly diffused through the membranes, for so much the more must the originally small volume of air be distended to fill out the hollow space which is always becoming greater. In the night, when the evaporation is arrested or very much repressed, the ducts of the trunk again suck up great amounts of water, in fact, this suction is often increased by the pressure proceeding from the roots which can press so much water into the ducts that a great part passes through the membranes into the surround- ing cells and intra-cellular spaces. If this liquid drawn up from the root body or pressed up by it is liealthy, a considerable infiltration into the intercellular spaces will take place without disadvantage to the body, as has been shown by MolP. If, however, the water mass is already laden with the products of fermentation from the putrefying root tips, we see that these poisonous substances get into the especially sensitive sapwood and bark and thus the dying back easily spreads. Trees planted too deep, however, usually die only in heavy soil per- manently loaded with water. In light soils they suffer but do not die. If the heavy soil with its water burden surrounds the base of the trunlc and pre- sents intercellular ventilation by means of the lenticels, alcoholic fermenta- tion and the formation of acetic acid must naturally appear in the bark cells and lead to a dying back which is continued radially to the cambial zone and the young sapw^ood which is especially active in conducting water. Thus there remains from year to year a cylinder of heartwood in the middle of the trunk which is always becoming smaller and smaller and which usually has to meet the water need of the aerial part. The heartwood which is poor in water, however, is less suited for conducting it and the dead tis- sues of the wood, which at any rate can still conduct water mechanically, will not be able with their help to meet the need of w^ater in the crown. Con- sequently, the tree ultimately wilts or fails to put out buds in spring. The fact that the non-parasitic processes of decomposition in the buried end of the trunk cease near the upper surface of the soil leads to the theory that processes of decomposition are not able to attack healthy plant cells but only those weakened and functionally abnormal. Such weakening is actually present. It was mentioned at the beginning that cells full of life and rich in content, when shut away from the oxygen of the air, begin at once to de- velop alcohol through the activity of fermentation (alcoholases) which was not present previously and which disappears again if the plant regains its atmospheric air. It has been proved further that the plant, in the absence of oxygen, continues for some time to eliminate carbon dioxid in considerable quantities (respires intra-molecularly) but that these amounts of carbon 1 Untersuchungen iiber Tropfenausscheidung und Infektion, 18S0, p. 78. Sep. aus Verslag en Mededeeling d. Koninkligke Akad. Amsterdama, cit. in Pfeffer, Pflanzenphysiologie, 1881, I, p. 159. 104 dioxid are still smaller when the experiments are continued longer than those of plants respiring in air which contains oxygen\ Since the carbohydrates (starch, sugar) furnish the material for respiration, it should be assumed from the above facts that these material contents of the cell are made use of abnormally in the absence of oxygen. With Pfeffer- respiration can be conceived of as a process set up .by two dove- tailing processes. The first is the intra-molecular respiration ascertained in the phenomena of fermentation which Borodin^ named internal oxidation. The second process, possible only with a supply of oxygen from with- out, is the immediate further oxidation of the products of fermentation in the moment of their production. Jf this last act, absolutely necessary for the life of the cell, is suppressed, not only the zone of the trunk of the tree, planted too deep and lacking oxygen, loses its respiratory material, that is, always becomes poorer in reserve substance, but it also forms those products which lead to decomposition and the death of the cell. Insufficient respir- ation therefore is a necessary preliminary condition for the dying back and, to the degree in which the buried part approaches the surface of the soil, gradually getting more and more oxygen, the ferm^entation will become weaker and weaker and pass over into the normal process of oxidation so that decomposition gradually reaches its limit. It is thus Only a question whether the tree has the possibility of forming new roots in the soil above these limits in order to meet the loss of water produced by the transpiration of the foliage. The stunted production frec[uently observable in early years disappears as the more plastic material can pass downward and be used for the new structures in the wood ring of the trunk and the roots. The more rapid the growth, the greater the energy of respiration (as shown by Saus- sure) and the more the flat new root body is reached by Hght, so much the more will the production of carbo-hydrates and its absorption of oxygen and production of carbon dioxid increase*. The behavior of the trees planted too deep or only partially buried de- pends naturally upon their specific character. In willows and poplars, for example, the part 'sunk in the earth may indeed be found to be dead, but near the top of the soil, the decomposition appears to have been stopped. Numerous adventitious roots have been formed from the trunk v«hich, some time after the tree has been buried, starts a healthy development of the crown. The tree is therefore saved if it is able to produce new roots quickly near 1 Wortmann (Ueber die Beziehungen der intramolekularen zur normalen At- mung der Pflanzen. Inauguraldissertation. Wiirzburg- 1S79) states, to be sure, that the amounts of carbon dioxid are equally large in intra-molecular and normal respiration; it seems to me, however, that the short duration of his experiments also caused the observation of the after effects of a previous normal functioning. He, himself, admits (p. 31) that in a longer period with no addition of oxygen a smaller amount of carbon dioxid was produced by the plants under experimentation than had been the case in the constant presence of oxygen. 2 Pfeffer, Ueber das Wesen und die Bedeutung der Atmung. Landwirtsch. Jahrb. 1878. 3 Borodin, Sur la respiration des plantes pendant leur germination. * Borodin, MSmoires de I'Aead. imperiale des sciences de St- Petersbourg. VII s6rie. 1881. 105 the earth's surface. It is well-known that Ericaceae and Epacrideae are especially sensitive to too deep planting. In these species the base of the trunk dies even when the root has not suffered very much. When the sap- ling shows moss and lichen growths at the base, there is every reason for being careful. In nurseries no one general rule holds good in regard to the depth of planting. Aside from the important physical composition of the soil much depends in grafted trees upon the stock. Fruit varieties grafted on wild stock should be so planted that the root neck remains in the plane of the surface of the soil or even projects a' little above it. In fact in marshy soil, with a great deal of moisture, planting is made in hills. Pears grafted on dwarf stock (on quinces) and apples (on Doucin and Paradise apples), on the other hand, must be planted at least so deep in the soi! that the place of grafting is found at the surface level of the soil; i. e., the whole stock under the soil. From this a considerable number of adventitious roots develop which are especially useful for nutrition. Bouche^ has given a splendid summary of practical experiments. He refers first of all to the fact that in old healthy trees the strong roots are seen to appear above the soil and that this appearance of the root neck is normal. Many trees can survive deep planting when young, since they put out new roots from the base of the trunk just below the surface (elms and lindens) ; others, on the contrary, are very sensitive, as, for ex- ample, pears, maples, oaks, most of the Rosaceae, plane-trees, walnuts, red and white beeches. Also most conifers require care in planting, as, for ex- ample, the genera Pinus, Picea and Abies and at times also Thuja, especially Thuja (Biota) orientalis and related species, while deep planting has been proved to have been endured by Thuja occid entails, T. IVarreana, T. plicata. Bouche found trunks 5 to 8 cm. thick putting out a number of new roots from their buried bases whereby they were very much strengthened. Juniperus communis must be planted shallowly but J . Sahina and related species sur- vive deep planting with advantage. It has already been stated of poplars and willows that deep planting is counterbalanced at once by the formation of new roots on the surface of the soil. In weak trunks it is often found that the roots formed just below the surface get the upper hand over the older, deeper ones. It is actually even more advantageous to plant many bushes deeper than they stood before because they strengthen themselves by numerous new roots from the buried base of the stems. This is noticeable for example in Calycanthus, Cornus alba and C. sibirica, Ribes, many kinds of Spiraea, Viburnum Opulus, Aesculus macrostachya, Symphoria, Ligus- trum, Rosa gallica etc. On the other hand Caragana, Berberis, Colutea, Cornus mascula and C. sanguinea, Corylus, Cytisus, Rhamnus, Sambucus, should be planted at the old level. 1 Bouche, C, Ueber das Tiefplianzen '"on Baumen etc. Monatsschr. d. Ver. z. Ford. d. Gartenb., v. Wittmack, 1880, p. 212 and Wredow I.e. p. 75. io6 In planting streets, besides the embankment which sometimes becomes necessary, Ihe asphalting and cementing of the street causeways is also very injurious to the roots of the trees. The injury is due not only to the shutting off of the atmospheric air but also the loss of precipitation from the air, upon which trees in large cities become so much more dependent, as the level of the ground water has fallen because of canalization and the workings of the subsoil in building. Young trees which are planted after the falling of the level of the ground water strive to reach this despite the increased depth of the springs. Consequently in order to facilitate this, the holes for planting the trees must be made considerably deeper in such localities. According to Bouche, this increased depth amounts to 60 cm. in Berlin so that now the holes for planting trees must be dug i. 5 cm. deep. Too Deep Sowing of the Seed. The discovery has also often been made that from a plentiful sowing of good fresh seed a comparatively small number of plants is produced. As is generally believed, the cause lies more frequently in sowing the seeds too deep. When harrowed in or hoed under in places, as is customary with barley^, some seed grains necessarily come to lie too deep, others too superficially. Uniformity can be obtained only by planting with a drill. But even the gardener, who can cover his seeds very uniformly in seed pans, not infrequently obtains only a low percentage of plants in sowing very fine seeds even if the seed was good and of high germinating quality. The processes causing the loss, however, are not always the same, and do not always take place under the same conditions ; on this account it is impossible to generalize. In order to protect oneself from injury in this connection, there is nothing to be done except to understand clearly the in- fluence of the different factors to be observed in sowing seed and to see' which combinations exist in every individual case. There are three phases in germination. Each can be disturbed and cause failure. The first stage consists of the swelling of the seed and is a mechanical process, in which (probably by water condensation) an increase in temperature has been observed. This introduces the second stage, the mobilisation of the reserve substances, a chain of chemical phenomena, and these accompany the third act, that of the formal development. Disturbances in the stage of swelling have often been obser\'ed. Nobbe and Haenlein- found especially in Papilionaceae and Caesalpiniacea, that the seed shell at times is so hard that water can not enter, that the seeds retained the embryo for years without development, but always in a healthy condition. The seed did not germinate because it did not swell. In clover seed, the superficial shell or hard layer containing the coloring matter, is 1 Eggers-Gorow, Versuche iiber den Nutzen oder Nachteil einer flachen oder tiefen Bestellung der Gerstenkorner. Mecklenta, landw, Ann, 1874, No. 23. - Nobbe und Haenlein, Ueber die Resistenz von Samen gegen die aufseren Faktoren der Keimung. Versuchsstationen 1877, p. 71. 107 shown to be so impermeable for zvater that clover seeds can He from one to two weeks m Enghsh sulfuric acid, and for years in water, without losing the coloring matter which in itself would be soluble in water. In such cases only mechanical treatment is of any use. Gaiter and Klose^ mixed the seeds of lucerne (alfalfa) and varieties of clover with fine sand and trod for ten minutes on the bag containing the mixture. After this treatment, 13.4 per cent, of the seeds of the lucerne were found to be more capable of swelling, 10.2 per cent, of the white clover and 37.8 per cent, of those of the bird's-foot, without showing any especial injury. Nobbe cites examples"-' of an unexpectedly long retention of the germinating power. 32 per cent, of seeds of Piniis silvestris, gathered in 1869, after ha^'ing been kept 5 years in closed glasses in an occupied room, still germinated, and after 7 }ears 12 per cent. With red clover seeds (Trifolium pratense), preserved in the same way, 10.5 per cent, germinated after 12 years, peas (Pisum sati- vum) 4y.y per cent, after 10 years, Spergula arvensis 20 per cent, after 12 years, flax (Linum iisitarissimum) 49 per cent, after 6 years and 3 per cent, after 11 years. Out of 400 seeds of the locust (Rohinia Pseud-Acacia) after ten days, longer than which the tim.e for practical purpose does not last, 71 grains germinated ; at the end of the year, 55 grains ; in the next year 18 ; m the following year 7 and, after 7 years, one seed; all were kept contin- uously in distilled water which was renewed periodically. From these ob- servations it seems credible to us that many buried seeds, unimpaired in life- power, survive for very long periods. Even in the locust seeds mentioned above, the remainder, left ungerminated after seven years, was still perfectly healthy. A slight injury to the seed shell resulted after a few hours in a swelling up and also, as a rule, in rapid germination. Disturbances of the second phase of the process of germination, the stage of chemical action converting the solid reserve substances into the easily transpired constructi^'e matter, are observed very frequently. The fact that many hard seeds such as Crataegus, Rosa, Juglans, Prunus, lie un- harmed for a year in the soil, is not to be confused with real disturbances. The difficulty of swelling may partly be to blame here; — during the dry time in summer the seeds again become dormant. On the other hand water may have permeated them already and have given rise to the formation of ferments, which lead to the mobihzation of the reserve substances. But this action of the ferment is in itself too slow, up to the beginning of the dry summer period, to sufficiently nourish the embryo. In different individuals and varieties of all species which germinate with difficulty, germination and development is found the spring following autumn planting. This takes place especially if the seeds are sown soon after harvest ing and when possi- ble with the entire fruit. "Stratification" has been pro^'ed still m.ore effec- tive, i. e. the placing of the seed in layers in vessels filled with sand for the 1 Gaiter und Klose, Quellungsunfahigkeit von Kleesamen. "Wiener landw. Zeitschr. 1877, No. 17, cit. Jahresb. f. Agrikulturchemie, XX. Year, 1877, p. 181. - Dobner's Botanik fur Forstmanner, 4th Edition, revised by Nobbe, 1882. p. 382. io8 winter. The actual disturbances are found to be the lack of external con- ditions necessary for germination. Besides moisture and warmth there be- long here the unimpeded supply of oxygen and the observance of the time when the seed is capable of re-acting. The time within which the seed responds to the action of the external conditions necessary for germination by a normal transmutation of the re- serve substances and the development of the embryo varies greatly, for the different families and species, even for individuals of the same variety. It is well-known that seeds of willows, poplars and elms must be sown im- mediately after harvesting, since they lose their power of germination after a few days or weeks, while cucumbers and melons often give stronger, more fertile plants, if the seeds have been kept for a year. To be sure, the seeds of many of our fruit and forest trees usually germinate after one or more years, but the number of the slozv grozving, weakened specimens increases with the age of the seed. Oxygen should be considered the most important factor next to water, necessary for swelling. For germination the seeds never need as much water as their substance can take up; the vegetative activity of the seedling begins before this time\ If in the beginning there is a scarcity of water which can be taken up endosmotically, the seed also takes water up hydro- scopically from the atmosphere". Water vapor also condenses on the outer surface; in fact, after the manner of all porous bodies, it condenses also hydrogen, nitrogen oxygen and other gases. Deherain and Landrin^ found that the swollen seeds take up comparatively more oxygen than nitrogen from the atmosphere so that more nitrogen remains in the en- closed space. After three days the seed begins to give off carbon dioxid and this increases so fast that soon more carbon dioxid is present than the oxygen enclosed in the volume of the air would warrant, the oxygen has gradually disappeared. The excessive production of carbon dioxid is therefore to be considered as a product of the processes of oxidation of the inner burning, beginning in the seeds. These authors pictured to themselves the beginning of the chemical actions in the seed in such a way that the rapid condensation of the gas de- termined at first for the various seeds will necessarily free the latent warmth of the gas and this warmth sufficiently increases the temperature of the en- closed oxygen so that oxidation can begin. With this is given the impetus for the normal solution of the reserve substance of the seed ; the heat, freed by oxidation, favors these processes more and more and they become evident externally by the production of carbon dioxid. 1 Jahresb. f. Agrikulturchemie, 1880, p. 213. 2 Hoffmann, R., in the Jahresbericht der agrikulturcheniischen Untersuchung- station in Bohmen, 1864, p. 6. and Haberlandt, F., in Zeitschrift fiir deutsche Land- wirte, 1863, p. 355. Both worlds may be found in abstract in the Jahresb. f. Agrikul- turchemie, Jahrg. VII. 1864, pp. 108 and 111. 3 Compt. rend. 1874, Vol. LXXVIII, p. 1488, cit. in Biedermann's Centralbl. f. Agrikulturchemie, 1874, II, p. 185. I09 The preparation for the germination of the dormant seed, according to this theory, is the loosening" undergone by the shell of the seed, as the result of its swelling with water. The broken cell layers which have become per- meable for gases now permit their rapid penetration and their condensation therefore gives the first impetus for the process of oxidation which causes the transformation of the reserve substances into diffusible forms. Since it can be observed with the seed albumen of plants that the breaking down of the starch in the seedling begins in the cotyledons in monocotyledons, it can be assumed that the part richest in nitrogen, i. e. the embryonic tissue, under the influence of oxygen will begin the metabolic reactions and by the develop- ment of abundant enzymes act upon its surroundings. The disturbance in the second phase of germination can result only from a lack of oxygen or also from an excess of carbon dioxid. The state- ments of Th. de Saussure confirmed by Deherain and Landrin show that no gas is so detrimental to germination as carbon dioxid. Seeds which are kept in a mixture of oxygen and hydrogen germinate just as in atmospheric air; yet an addition of a few hundredths of carbon dioxid to an atmosphere of oxygen is enough to absolutely inhibit germination, when only the little roots have appeared. If the amount of carbon dioxid is very considerable seeds will not germinate. Carbon dioxid in excess is very injurious to other dormant parts of the plant. Van Tieghem and Bonnier^ found in bulbs and tubers (Tuli- pa, Oxalis c'renata) which respired further in air containing a great deal of oxygen, and therefore^ produced carbon dioxid, that they formed alcohol in an atmosphere of pure carbon dioxid. Tulip bulbs which had been kept for a month in air free from oxygen were suffocated and remained without fur- ther development. When seed has been sown too deep there is also an excess of carbon dioxid and a lack of oxygen. The thick soil covering brings about injuries and hinders the germination of the seed but can not, hov/ever, be expressed in definite figures. Aside from the different requirements of the different species, the optimum thickness of the covering differs for the same species according to the com[)osition of the soil, the amount and distribution of pre- cipitation etc. On this account the results of the experiments often under- taken to ascertain the best depth for sowing differ from one another as soon as a definite statement of figures is undertaken. They all agree, however, that in doubtful cases it is better to sow with too shallow a covering than too deep. The purpose of the covering is to hold the young seed firm and to retain a sufficient degree of moisture. The shutting out of light comes less under consideration. The retention of sufficient moisture for germination must be primarily considered. If enough is present, the roots themselves will pene- trate at once into the soil even when the seed lies superficially. On this ac- 1 Bulletin de la societe botanique de France, Vol. XXVII, 1880, p. 83, cit. in "Wollny's Forschungen auf dem Gebiete der Agrikulturphysik. I 10 count a perfectly superficial sowing of the seed would be advisable if periods did not occur in spring which dry up the surface of the soil to such an ex- tent that a temporary or even a permanent inhibition of tlie life activity takes place in the seedling. The more porous the soil, the greater is the danger of drying out and therefore the greater the depth at which the seed must lie. In regions where the spring is dry a heavy soil will give a more uniform germination even if the sowing is shallow. The same soil and the same depth of sowing become dangerous when strong rainfall and great heat alternate rapidly and form crusts on the upper surface of the soil cutting off nearly all access of air to the seeds then in a most active stage of metabolism. The air enclosed in the seeds does not last long. Ventilation of the plant body is, however, absolute- ly necessary, even the germinating seed suffers extremely if the air contained in it be removed. The formation of heavy crusts on the soil can make the depth of sowing of the seed become the cause of considerably injury, which in itself would not be injurious. How much the lack of air influences the germination capacity of seeds is evident from de Vries^ citations. In this connection Haberlandt injected curly beet seeds with water under an air pump and observed that the seeds took up 71.13 per cent. ; of these seeds thus partially deprived of air only 30 per cent, germinated as against 90 per cent, of the normal seeds kept as a control. In a second experiment all the air was replaced by water forced in by the air pump and only 8 per cent, germinated as against 72 per cent, in the control. Also the time required for germination was shorter in the normal seeds. It may well be assumed that the removal especially of oxygen from the seed and the hindered diffusion of this gas in new quantities into the intercellular spaces is the cause of the loss in germinating power. Dutrochet- found even in mature plants that death often occurs if water is injected. In the rapid thawing of frozen fleshy parts of plants which, as a result of an infiltration of the intercellular spaces with water, have a glassy, translucent appearance, the exclusion of the air from the cells by water may contribute essentially to their death. From the many experiments carried out practically in order to obtain j)recise numerical values for the best depth for solving seeds, those of Roes- tell, Tietschert, Ekkert and W'ollny are the most thorough. Roestell" gives 2 to 4.5 cm. as the most favorable depth for porous, strong, field soil. Tietschert* experiments endeavor to determine the maximum boun- daries of the most favorable seeding depths in soils differently con- structed physically; — 10 cm. was seen to be the rational maximum depth for 1 De Vries, Keimungssreschichte dor Zuckeirube, Landwirtsch, .Tahrb. v. Thiel 1879, p. 20. 2 Dutrochet, Memorires etc. edition Bruxelles p. 211, cit. by de Vries 1. c. 3 Annalen der Landwirtschaft, Vol. 51, p. 1. ^ Tietschert, Keimungrsver.suche mit Roggen and Raps. Halle. 1871. Ill sandy soil, 8 cm. for humus soil and 5 cm. for clay and loamy soil containing lime. The last two kinds of soil suffer from dry weather so that shallow seed- ing gives poor results. The experiments repeated later in the year (August to September) gave for all kinds of soil a depth of 2.5 cm. as very unfavor- able because of drought ; in this case clay soil was proved most favorable in seeding at a depth of 10 cm. It is evident from this that dehnite figures must be accepted with great reserve. Ekkert' experimented with rye, oats and barley, in loam, in pond slime (silt), in sandy soil and garden earth. In seeding rye in separate wooden boxes no difference in the growth of the plants was shown between 2 to 8 cm. of covering (as a result of uni- form ventilation from all sides). In experiments in the open ground stem formation seemed more favored by a lesser depth of the seed, yet this refers more to the time of the appearance of the sprout than to its cjuality. Oats and barley survive a deeper sowing than does rye. In smnmer a deeper sow- ing of the seed is better than in winter. The minim.um covering for grain m.ay be 1.5 to 2 cm. ; the maximum favorable for results is 6 cm. Later experiments of the same author- bring another important factor into consideration which for the same soil acts as a modifier of the favorable depth for sowing. The qualiiy of the seed is at times decisive. The quality of wheat seed, however, with which the first experiments were made did not seem to have any influence on the capacity for germination but the development of the young plant with equal depth of sowing was better, the better the quality of the seed. With a medium 5 cm. depth of sowing (experiments with sandy soil) all qualities gave the longest straw and the longest heads. The relation of the weight of the grain yield to that of the straw is lower, as the seed is poorer and the sowing deeper. Experiments with barley confirmed the results obtained with wheat ; the less the depth of sowing and the better the quality used for the same depth the earlier the seed sprouted. The sum of the sprouted plants was no less with inferior seed but the influence of the depth of sowing was so felt in this quality that a shallow sowing gave a much longer straw. In general it must be said that Ihe depth of sowing, conditions otherwise being thought equal, will influence first of all those developmental stages which are connected with the early stage. How^ever, the quality of the grain depends upon the early develop- ment in the number of sprouts and the length of the heads as well as the for- mation of the young heads and is therefore infiuenced by the depth of the sowing. On the other hand the quality of the harvested grain depends upon the nutritive and weather conditions of the current year, and will therefore be scarcely more influenced by the first development or inherited peculiarity of the grain. 1 Ekkert, Ueber Keimung', Bestockirig- unci Bewuizelung- der Getreidearten etc. Inauguraldissertation. Leipzig 1874. - Ekkert, Kulturversuch mit Weizen und Gerste verschirdener Qualitat etc. Fiihling's Landw. Zeit., 1875, Part 1; 1876, Parts 1 and 2. 112 Soaking of the seed, which has often been recommended for Ught soils when the time for seeding has been continuously dry, should be used with due care. If the weather becomes dry and the water which has been taken up in swelling is not enough to make the primary rootlets grow into the soil, then there is an unavoidable interruption in growth. This is the explanation of WoUny's discovery^ that soaking produces plants maturing later. Wollny's- studies on the suitable depth of sowing are most thorough ; he determined for grain that sowing 2 to 3 cm. deep furnishes the Fi£ Rye seedling- with too deep sowing- of the seed grain. Elevation of the node of the sprout near the surface of the soil. (Orig.) best results in yield. Over and above this a noticeable retrogression is found already especially emphasized by Jorgensen^. The last named author also found rye to be the most sensitive and wheat the least sensitive. For most of the Leguminoseae the depth of the sowing is less important. In con- trast to this, varieties of clover and rape have been proved very dependent 1 Bot. Centralbl., Vol. XXX, No. 15. 1S87, p. 48. ~ Wollny, Saat und Pflege der landwirtschaftl. Culturpflanzen. Berlin, 1885. 3 Jorgensen, S., Versuche titaer das Unterbringen der Saat etc. Annalen d. Landw. in d. Kgl. Preuss. Staaten. Wochenblatt 1873. No. 11. II' upon the depth to which the seeds are covered. It seems desirable to have this still less than for grain (0.5 to 2.6 cm.). Wollny's experiments showed that in dry years a deeper earth covering was more advantageous, in wet years, a lighter one. Corresponding to wet and dry weather the time of har- \ est was retarded with an increasing depth of sowing, the number of plants, which germinated at all and still more, the number which came to harvest, was decreased. But it must be emphasized again and again that precise figures for the most favorable sowing in the different localities can be collected only directly by the local agriculturahst since not only the composition of the soil and the weather but also the character of the variety must be con- sidered in the matter, as has been shown by Stossner\ This same holds good for tubers, bulbs and pieces of roots which are used for seeds. In these the soil conditions have an especial weight because these fleshy organs which are rich in water are essentially and quickly in- fluenced by the soil supply of oxygen . For potatoes, experiments by Nobbe- and Kiihn^ have shown that in questionable cases the more shallow sowing will be the most advantageous one. In the forcing of bloom- ing bulbs excessive losses arise at times from the fact that the bulbs (hya- cinths) have been planted too deep in the pot, or when in the pots are cover- ed too deep with earth after the rooting has been sufficient. Especially if the soil covering is heavy and damp and the bulbs have not matured sufficiently the year before on account of wet weather, the "Rotz" (see this in Vol. II.) usually appears very easily. The oiitomatic regulation of the depth of sowing on the part of dift'erent plant races is interesting. In grasses, and in fact, best seen in our grain species, the first internode is the part which is destined, when the seed grain has been sown too deep, to push the second node which hides the stem eye and the side buds, i. e. the node which forms the stem, into the porous, well ventilated upper layer of soil. In the adjoining figure 9 we perceive the seed grain which is already almost empty and its weakly retained (primary) roots which had been formed in the grain. From the seed grain the first (over-elongated) internode has pushed the second node nearly up to the upper surface of the soil. In this favorable position the secondary roots, which exist during the whole life of the plant, have been developed, the eyes of the side shoots have attained a further maturity. In shallow sowing both nodes lie close to one another and give in cross-section such a picture as is shown in figure 10. The nodal tissue seems divided radially by browned vascu- lar strands. The vascular-bundle cylinders are those of the primary roots and become diseased during or soon after the formation of the secondary roots. The ground tissue of the node shows the first circle of vascular bundles (g) of the young blade close to the pith shield (m) with its few cells. Branches of these bundles, recognizable from their wide ducts (g'), may be seen fur- 1 Stossner, Unter.suchung-en liber den Einfluss verschiedener Aussaattiefen etc. Landwirtsch. Jahrbiicher 1S87. 2 Nobbe, Handbuch der Samenkunde, 1S76, p. 184. 3 Kiihn, Berichte aus dem physiolog-. Laborat. Halle, Part I., p. 43. ."4 ther out in the axis. 'Phis yoiinij; Made jiosscsscs on the side marked f uniformly eonnecti'd l)ark tissue'; on the o])i)()sile side /\ iiowever, the first sheath- formed leaf (sell) vvhii-h remains eolorless, and the hud ol the next hij^hcr leaf, the lirst j;reen one (hi), which is comi)letely developed later, have been differentiated from the bark tissue. In the axis of this first leaf may be seen the meristematie position of the fu'st lateral bud /" A';; jwhieh ])ushes out the i^reen leaf hint; in front of it with its already clearly de\eloped e[)i- Fig. 10. Cross-section lhroui;li tlie lowest node of a youny rye plant. lOxpla nation ol" lettering in text, (t)rig.) dermis (c ) ; e is the epidermis of the sheath leaf which is already being differentiated from the axis. If the (dotted) tissue of the bud of the first green leaf (hi) be traced backward in this cross-section toward the side marked [' it is seen that this passes over into a colorless tissue ring char- acterized, however, by its comparatively large intercellular spaces contain- ing air (i) ; the bark tissue of the young blade. It is seen from this that each grain leaf is a direct continuation of the bark of the blade. This bark ring PART II. MANUAL OF Plant Diseases BY PROF. DR. PAUL SORAUER Third Edition—Prof. Dr. Sorauer In Collaboration with Prof. Dr. G. Lindau And Dr. L. Reh Private Docent at the University Assistant in the Museum of Natural History of Berlin in Hamburg TRANSLATED BY FRANCES DORRANCE Volume I NON-PARASITIC DISEASES BY PROF. DR. PAUL SORAUER BERLIN WITH 208 ILLUSTRATIONS IN THE TEXT ^^^ Copyrighted, 1915 By FRANCES DORRANCE L^ ©CI,A401186 THE RECORD PRESS Wilkes-Barre, Pa. MAY 29 1915 115 is connected on the side V with the tissue of the sheath leaf and it is worth noting that this sheath, even in so young a stage of blade differentiation, must have finished its work since the tissue is entirely impoverished and begins to be full of holes (I). While therefore in the Gramineae the accessory apparatus, which with too deep sowing brings the vegetative tip into the abundantly aerated par- ticles of soil, consists in the elongation (observed up to 9 cm.) of the lowest internode and, in case of necessity, also of the one above it, we find in the Leguminoseae and other dicotyledons a different arrangement. In beans, for example, we notice first of all an increased elongation of the hypocotyle corresponding to the need, so that finally, with very different depths of sow- ing, the growing tip of the stem in all plants is found at approximately the same height. Naturally the strength of the plant from the same kind of seed is decreased as the depth of sowing is greater. The more the hypocotyle must be lengthened, in order that its upper part, comparable to the curved back of the burden-carrier, can break through the load of the soil and bring the cotyledons to the light, the more reserve substances will be used up. It is therefore very evident that plants coming from greater depths are weaker even if they have not lost reserve substances in the seed through strong intra-molecular respiration. Such will be the case, however, if continued wet weather sets in after too deep sowing so that a shortage of oxygen results. The experiments by Godlewski. and Polzeniusz^ show what amounts of reserve substances can be lost through intra-molecular respiration and the formation of alcohol. Sterilized peas, in evacuated air, produced in the first period almost as much carbon dioxid as in normal respiration in the air. The whole amount exceeded 20 per cent, of the original dry substance of the seed. The amount of alcohol formed corresponds to that of the carbon dioxid. Only during the sixth week did the production of carbon dioxid cease in the peas which lay in sterilized water and up to that time possibly 40 per cent, of the dry substances present had been broken down to alcohol and carbon dioxid. This is also the case in grains. In grains the action of the secondary roots on the nodes of the stem counteracts this weakening. In legumes a similar process of self assistance can now take place, since, as Wollny proved, adventitious roots are formed from the over-elongated hypocotyle member. He observed this on the parts of the stem which had been covered with soil, not only in field beans, but also in peas, sweet peas, lentils, lupines and plants of other families, — rape and sunflowers. But the legumes often are not capable of using such an accessory apparatus since, with normal depth of sowing and capacity for germination, they easily suc- cumb to other dangers which will be described in the section on "condition of hard shells." 1 Godlewski und Polzeniusz, Ueber Alkoholbildung: bei der intramplekularen Atmung- hoherer Pflanzen. Anzeig. Akad. d. Wiss. Krakau, cit. Bot. Jahresb. 1897, p. 142. ii6 Roots From the Tip of Grain Seeds. It seems best to add here an account of a case which, because of its pecuHarity and rareness, deserves a permanent place in science. The agricultural teacher, Wolfes in Dargun (Mecklenburg-Schwerin), sent me in 1876, fourteen wheat grains in which, through hypertrophy, the embryo did not lie to one side of the endosperm, but occupied a middle position. The grains were sown in the fall and in the spring they had partly rooted but without developing plumules. They were either slender, pear- shaped or even cylindrical at the one end, tapering rapidly at the other like the neck of a violin. In many grains (Fig. 11-12) tlie elongation of the slender end opposite the embryo was so marked that a neck was formed, possibly 2 to 3.5 mm. long, and twisted toward the upper end. In twelve grains the length of which varied from }i to ij4 cm. the neck bore a large number of very thin, thread-like roots i to 2 cm. long, closely arranged like a brush. These were pubescent almost their entire length. Upon attempting carefully with a needle to raise the wrinkled and oc- casionally ruptured testa of the grain it was found to be closely attached to Fig. 11. Wheat grains with roots not originating- from the embryo but springing from the hypertrophied testa at the tip of the seed grain. the grain in different places and, when broken off, was usually of a darker color. On the other hand its upper part was firmly connected with the beak- like growth along almost its whole length and could be raised from the grain proper like a straw cap (Fig. 12). The neck therefore at the time of the investigation was not connected with the actual grain except by the testa from the substance of which it also seemed to be formed. In the fresh con- dition of the grain this had been firmly set on the seed since various concave places on the inner wall of the cap, perceptible through the microscope, fitted on to the small convex elevations visible on the seed grains. There was another equally noteworthy phenomenon, namely, that the fissure, normally present, was lacking in these wheat grains. The grain, which had been dug up, also failed to show the seedling which lies at the base of the normal grain and is easily recognizable through the seed coat; it was not noticeable in the seeds observed. The endosperm itself, when cut apart, finally showed only a small degree of the white color of the healthy grain. There were long, glassy, translucent and yellowish streaks extending from the edge, inward. It had a rancid odor. The blue iodin reaction for starch was strong only in those particles of the grain which, on the freshly cut 117 Fig. 12. Wheat grain with hypertrophied testa and root formation at its tip. Embryo central instead of lateral. Explanation of letters in the text. (Orig.) ii8 surface, were found to be white and mealy, while on the glassy places there was only a slight reaction. The glutinous layer in the Mecklenburg grain was not developed at all, the thin seed shell only incompletely. In place of this glutinous layer (Fig. 12 k) a plate-like parenchyma was found, the content of which did not differ essentially from that of the underlying tissue. The most striking thing connected with this abnormal wheat grain was, however, the position of the embryo on the opposite end from that which bore the roots (Fig. 12 iv) and exactly in the middle of the grain (as in Typhaceae) equally surrounded on all sides by the tissue of the starch- containing endosperm. While in the normally constructed wheat grain the seedling lies without, at the base of the grain, and is connected with the endosperm by a special organ, the scutellum (the cotyledon), the seedling lies here (Fig. 12 e) without cotyledons in a central cavity (Fig. 12 h) of the grain. This cavity in some of the grains is elliptical, in others triangular. In some it extends possibly to the middle of the grain, in others, becoming narrower and narrower toward the top, it reaches to the tip, even penetrating into the tissue of the cap. On the inner side it is lined with a layer formed of two plate-like rows of cells of a glutinous content (Fig. 12 a) which clearly resembles the glutinous layer deposited in healthy grains outside the endosperm. The young leaves of the seedling, folded over one anotlier, show no essential variation. On the contrary, the number of secondary roots formed in whorls at almost equal distances (Fig. 12 r) steadily increases up to 6 to 8 and these roots appear to be covered by a parenchymatous layer arranged in the manner of cork cells, 6 to 8 cells thick and free from starch. On this tissue lies the combined and modified seed coat (Fig. 12 sf) which in dry grain becomes thicker walled with more abundant cells toward the tip and develops imperceptibly into the cap which the root bears at its tip (Fig. 12 w). The vascular bundle is continued into the cap from the roots. Here are often found several bundles united at the tip of the cap into a ring-like, thicker network of ducts running horizontally and resembling a node of the stalk. Still further back from the tip these vascular bundles (Fig. 12 g), iso- lated near the outer edge of the inside of the cap, are seen to run backward (Fig. 12 gg). The endosperm normally has no fully developed vascular bundles and the cotyledons only embryonic ones. Here, however, the vas- cular bundles take an often irregular course through the endosperm and, in the individual grains, surround the seedling in a semi-circle and have not developed even though the grains lay in the soil over winter. By cutting cross-sections from the diseased grains and submitting them to microscopic investigation, the probable cause of this striking mal- 119 ffiTn formation was seen at once. The inability of the seed covering to free itself entirely from the grain was due to a connected firm, homogeneous, some- what dark mass (Fig. 13) ; the presence of thick, much ramified mycelial threads, often provided with short skein-like groups of branches, could be proved. The threads of the colorless, strongly refrac- tive mycelium grew trans- versely through the very thick walls (Fig. 13 m) of the fruit cells and seed coat which had been merged into one another. The mycelial threads grew more thickly when the cells were richer in content and thinner wall- ed, entirely filling some cells of the endosperm (Fig. 13 mm). Near such places the starch had been dissolved and the cytoplasm had be- come solid as if it had been dried. In other cells a firm network of protoplasmic material scarcely distinguishable from starch could be seen. These were almost imperceptible in the starch grain but yet were there. This substance was apparently deposited about the starch grains but upon examination there were no grains present, only the corresponding cavities. In some such way originated the yellow- ish, translucent places between which lay groups of cells especially rich in mixed regions gave the reaction under a weak starch. These proper iodine magnification. The variation in the structure of the diseased grain is best shown by compar- ing figures 13 and 14. The latter repre- sents a section from a corresponding part of a healthy gain. The seed coat (Fig. 13-14 fs) in the diseased grain is more than three times as thick as in the healthy grain. In the abnormally developed seed coat there is a com- pletely developed vascular bundle with a clearly recognizable sheath (gs). In the diseased grain the growing fruit membrane passes directly over into Fig-. 13. Hypertrophied testa traversed by mycelia. Fig-. 14. Normal fruit and seed membrane together with the gluti- nous layer. the endosperm (e), and in the heakhy one the gluten layer (Fig. 14 ^)lies between the two tissues. Investigations of such grains in the "imported" seed show a similar condition. The seeds seem malformed and the fact that the malforma- tion manifests itself in the position of the embryo as well as in the develop- ment of the endosperm and especially in the thickened growth of the seed coat proves that this malformation must have been completed when the grain was forming in the head. Fertilization has nevertheless taken place normally since the embryo displays leaves and growing point as well as roots (the latter in increased numbers). But some local stimulus must at once have incited a cell increase in the fruit tissue and thereby displaced the em- bryo from the side towards the middle of the endosperm. This stimulus was active during the whole development of the seed and increased the vege- tative activity so that the character of the endosperm underwent a change, for the vascular bundles are those of a vegetative axis. We observe a most important numerical increase of the cells in the tips of the seed, assuming the character of a vegetative axis and, by means of the entangled vascular bundles, resembling a stalk node. Abundant roots develop at these stalk nodes 'and it is not improbable that leaf buds might have begun had there been a greater aeration of the soil layers. We would then have had a case similar to that in dicotyledonous plants when, as has often been observed, vegetative axes develop from their fruit nodes. .For such processes, however, the seed lay too deep. There was no ac- cessory apparatus for raising the seed to the upper surface of the soil, such as the elongation of the first internode in the seedling. As a result bacterial decomposition followed, due to the lack of oxygen, as was shown by the rancid smell of butyric acid. This is the reason for mentioning the -present case here. Had it been possible to determine exactly the causative fungus the case w^ould have be- longed under parasitic diseases. As it was impossible to make the my- celium fruit, the case becomes hypothetical as to the nature of the parasite. Only one thing is certain^viz., that the stimulating mycelium did not belong to the black fungi (Cladosporium, etc.). According to Brefeld's latest in- vestigations on the penetration of the smut into the blossoms, it is highly probable that the smut spores, which have entered the blossom, germinate soon after the fertilization of the grain, and by the slow advance of their mycelia have exerted the stimulus on the seed coat. 3. Greater Horizontal Deeeerences. The individual development within the same plant species is influenced by horizontal changes in the place of cultivation from north to south, or east to west, as well as by the vertical elevation of the habitat. De Candolle^ laid 1 Sur la methode de sommes de temperature appliquee aux phenomenes de vegetation. Separatabzug der Biblioth^que universelle de Geneve 1875. 121 down the principle that with approximately equal latitude and elevation, the temperatures above 0° in shade are higher for the same developmental phase (time of blossoming, defoliation, etc.) in the western parts of Europe than in the eastern ones. Observations show that in Europe the length of the growth period decreases toward the northeast and increases towards the southwest. Because of the many mountain chains and plateau-like inter- ruptions the phenomenon is less clearly evident in western Europe than on the great level plains of Russia. Kowalewski's^ very remarkable work re- ports on this phase. This is based on the statements of 2200 agriculturalists scattered throughout all parts of European Russia, who had reported the time of sowing and harvesting of the grain. Since cultivation must be adapted to climatic conditions, the usual times for sowing and harvesting show the existing vegetative conditions. The sowing of winter rye takes place in the southern part of the Gov- ernment of Kherson on the 15th of September-, at Archangel, on the first of August. The localities of simultaneous plantings of winter rye do not run parallel to the degrees of latitude, but are inclined from N. W. to S. E. ; therefore, they run almost in the same direction as do the isocheims. The difference in the time of harvesting winter rye in the far north (Archangel) and in the south (Kherson) extends, like the time of sowing, over a month and a half. The seeding period for summer grain in the far north is one- third to one-fourth as long as at the southern limit. At the western it is two to two and a half times longer than at the eastern. The time of harvesting in the north is likewise one-third as long as in the south ; in the west once and a half to twice as long as in the east. The localities of simultaneous ripen- ing of summer grain run from S. W. to N. E., corresponding therefore in their direction with the isotheres. The growth period in southern and southwestern Russia is only 85 to no days for rye, buckwheat, flax and barley,- — but no to 125 days for sum- mer wheat, millet, oats and peas. Sugar beets, maize and potatoes have the longest growth period, — 150 to 165 days. Thus, in the south, the longest growth period is almost twice as long as is- the shortest. On the other hand, in the north, the periods concerned are not only shorter everywhere but are also more simultaneous. In the far north and northeast the difference be- tween the longest and the shortest growth periods does not exceed 10 to 20 days. For the same cultivated plant, in European Russia, the rate of develop- ment increases on the average with the latitude. Thus, for example, oats in the Government of Kherson (south) have a growth period of 123 days, wheat and barley one of no days. In the north, however, (Archangel) the growth period of oats decreases to 98 days, that of wheat to 88 days, of bar- 1 Kowalewski, W., Ueber die Dauer der Veg-etationsperiode der Kulturpflanzen in ilirer Abhangigkeit von der geographischen Breite und Lange. Arb. d. St. Peters- burger Naturforscherges., XV, 1884 (russisch), cit. Bot. Centralbl., 1884, No. -^1, p. 367. - All dates are given old style as still used in Russia. 12.2 ley to 98 days. In the same geographical latitude, a longer vegetation period is found in the west than in the east. The causes of the shortening of the growth periods, therefore, cannot lie in the warmth which the plants receive at a corresponding degree of lati- tude, for otherwise the plants in the south would have passed through their development considerably more quickly than in the north, also since the southern black soil is raised to a higher temperature than the heavier, often clayey and damp soil of the north. Besides this, the lack of moisture in the south hastens maturity very greatly. Some other factor must therefore be determinative. Kowalewski states this to be the length of the insolation. He now assumes May 5th to be the mean time for sowing oats and August 20th as the mean time for harvesting them, finding thereby an insolation period of 2000 hours for the 98 days of vegetation in Archangel. If the period of bright nights be added to this, there is an increase amounting to 2240 hours. Kherson oats are sown on March 20, harvested on July 20th. In this 123 days of vegetation, however, only 1850 insolation hours obtain. Further, as Kowalewski says, it must be noted that the cultivated species of the north are adapted to a lesser degree of warmth. Therefore, when brought to the south, they ripen comparatively earlier. This result agrees with the one found by Schiibeler^ which will be mentioned later. Similar observations are said to have been made in Canada also. In further explanation of the change in the length of vegetation, Kowa- lewski brings forward the greater intensity of illumination, the small cloud masses and the greater humidity of the atmosphere and, supported by Fa- mintzin's investigatjons, he believes, for example, that the hght optimum for assimilation is exceeded in the south and therefore has a retarding in- fluence. This would correspond to the yellowing of the shade-loving plants, when grown in high mountains. It is not necessary to fall back upon the theory of the retarding action of the southern excess of light, if Wiesner's theory be accepted. In explaining the utilization of light on the part of plants in the far north, Wiesner- emphasizes, according to his investigations, the fact that in regions of the far north (Tromso), with an equal elevation of the sun and an equal clouding of the sky, the chemical intensity of the daylight has been shown to be greater than in Vienna and Cairo, but less than in Buitenzorg in Java. The light factor of the far northern regions is dis- tinguished in its illuminating quality by a relatively marked equability which obtains in no other locality where plants flourish. The plants of the arctic vegetative zone receive the greatest amount of light as a whole. Here, in the low growing plants there is no self-shading due to their own foliage, and even woody plants in adjacent southern regions show only a minimum amount of shade-producing branches. 1 Schiibeler. Die Pflanzenwelt Norwegens. 2 Wiesner, J., Beitrage zur Kenntnis des photo-chemischen Klimas im arktis- chen Gebiete. Sitz. Akad. d. Wiss. Wien CVII, cit. Bot. Jahresb. 1898, I, p. 586. 123 Wittmack has reviewed earlier cultural experiments as to the behavior of plants indigenous to any given locality when artifically introduced to a region farther south^. His conclusions follow; — plants from the north de- velop somewhat more slowly in middle Europe, catch up later with the in- digenous ones, however, or even exceed them. It is evident, therefore, that the short growth period, which has become habitual in the north, is often still more shortened by the increased warmth of the southern habitat, pro- vided also that the climate be dry. The damp climate of England with its low maximum temperatures retards ripening. The humidity of the air is a factor of great power and can delay ripening; just as, conversely, regions with great periods of drought, the climate of the steppes and similar con- ditions, not dependent on tbe degree of latitude, form limited centres where plants ripen prematurely. Too great drought certainly retards development, as has been determined experimentally. Stahl-Schoder's experiments, cited in the chapter on "Excess of Water," treat of soil dryness. The period of the in- fluence of heat is very important and is indeed expHcable. Heat in July and August is more advantageous than in May and June but the reverse is true for rain. Wittmack's summary in general shows the significance of the physical structure of the soil in relation to the early ripening; — that the vegetative time in eastern regions is shorter for the same varieties of grain than in western ones. Based on the observation that the varieties cultivated in northern climates retain their shorter growth period in the immediately following developmental periods, an active trade in northern seed has been developed. Meanwhile the quantity of the harvest should not be lost sight of. Abundant supply of nutrition being uniformly assumed, the quantity depends always on the length of the vegetative period, — i. e., the time of the formation of shoots. The longer time the grain has for the formation of vegetative organs (as in damp, cool seasons) the more abundant is the growth of shoots and with it the formation of a greater number of ears from the in- dividual seeds. H we should carry into the east varieties produced in the west, which are long-lived and characterized by great productivity, we would run the risk of frosts. This is most strikingly true in the English varieties of wheat, from the squarehead group, which toward the east come less and less true to seed, because they winter kill. Experience shows in regard to frost-resis- tance, that seeds from northern regions give plants in southern latitudes M-hich at times not only ripen earlier, in spite of an initial retardation, but also better withstand frost. From the result of Schiibeler's^ observations, it should be emphasized, that the quick growth, which has become habitual in northern or Alpine 1 Ueber vergleichende Kulturen mit nordischem Getreide, Von Dreisch, Kor- nicke, Kraus, Vilmorin and others, referred to by Wittmack. Landwirthsch. Jahrb. 1875, p. 479, and 1876, pp. 613 ff. 2 Schiibeler, Die Pflanzenwelt Norwegens, 1873, pp. 77 ff. 124 climates because of a short vegetative period, is lost after four or five years of cultivation in lower latitudes. Conversely, long-lived varieties accustom themselves in a few years to a short vegetative period. Yellow chicken maize from Hohenheim, for example, which ripened in 1852 at Christiana in 120 days after repeated sowings, shortened its growth period to the extent of 30 days in 1857. In Christiana the developmental period of barley is 90 days, but seed brought from Alten (the 70th parallel) needed only 55 days (see Kowalewski). Of the chemical properties developed in a northern habitat, which in great measure correspond to the changes in plants in high elevations, the fact that the sugar content of the fruits decreases toward the north while the aroma increases is of especial importance. Bonnier and Flahault main- tain also that not only the size of the leaves increases in the darkness of the north but also their green color^ Schiibeler's experiments in summary- give the following special examples : — In wheat brought from Ohio and Bessarabia, the grain became darker in color each year until it was as yellow brown as the native Norwegian winter wheat. Similar results were obtained with maize, beans, peas, celery, etc. Celery taken from a region extending from the Caucasus to Hindustan, grows in Africa (Egypt, Abyssinia and Algeria) and may be found in Europe from the Mediterranean to the Baltic ; it now extends even into Finland up to the 69th parallel. There, however, the root stalks are poorly developed; — the aroma, nevertheless, becoming more pungent^. The greater intensity of color in the blossoms, as already men- tioned, a peculiarity shown to correspond with an increasing elevation above sea-level, also appears in most garden flowers as cultivation advances to- wards the north. In regard to the formation of aromatic substances, be- sides celery, juniper may also be cited as an example. In Norway it is much richer in oil than in Central Europe. Onions also and garlic are uncom- monly pungent in Norway. Strawberries are sour but aromatic, while, according to Gotze, they are exceedingly sweet in Coimora, but almost with- out any aroma. Plums often remain so sour that, compared with fruit brought from more southerly regions, they still seem immature. A similar condition exists with grapes as shown by comparing the sweet Portugese grape with the less sweet but aromatic Rhenish grape. In considering the horizontal differences, expressed in the decrease of rainfall and increase of clearness of the air, from the west towards the east, in the conditions of light between southern and northern regions etc., we should not forget one circumstance, to which de Candolle* has already called attention. This, to be sure, has not been sufficiently verified experi- 1 Bonnier et Flahault, Observations sur les modifications des vegetaux suivant les conditions physiques du milieu. Annal. d. sc. nat. Botanique, t. VII, Paris 1S79, p. 93. 2 The effects of Uninterrupted Sunlight on Plants. Gard. Chron. 1880, I. p. 272. 3 Hansen, C, Der Sellerie. Gartenflora, 1902, p. 18. 4 de Candolle, A., Sur la methode des sommes de temperature appliquee aux phenomgnes de la vegetation. Archiv. des sc. physiques, etc. Nouv. ser. LIU. LIV. Genf 1875, cit. Bot. Jahresber. 1875, p. 585. 125 mentally, but finds repeated substantiation in practical experience. It is namely the greater, more complete dormant period of plants. According to Thne^, trees which thrive normally in Central Europe and in Coimbra put out their leaves possibly a month earlier in Coimbra and their autumnal change of color occurs about a week and a half later than with us. Thus their dormant period is about six weeks shorter there. The length and com- pleteness of this dormant period, however, must influence greatly the rate of subsequent development. It may indeed be assumed that, with the con- tinuation of a temperature which does not stop the functions entirely, a number of vegetative processes continue with a slow but steady consumption of materials (process of oxidation) and without any compensation to the plant through newly assimilated substances. Besides this, it seems that many enzymes, which affect the energy of metabolism, either succeed in de- veloping to the necessary amount only during a complete dormant period, or are made ready for it. If no complete rest takes place it may be observed especially in the two or three year old bushes and in the buds on branches of woody plants. These are forced earlier and produce w^eaker organs (smaller leaves, a greater number of sterile blossoms). The increased weight of the seeds in northern latitudes has already been considered. There are, however, some experiments by Petermann- which prove a higher germinating pozver of Swedish seeds of clover varie- ties, timothy (Phleum pratense L.J, and of spruces and pines as compared with German, French and Belgian seeds. The Swedish seeds, which actually, on an average, possess a greater weight, show greater power of germination, not only in the number of fertile seeds which can germinate, but also in the energy with which germination takes place. These results may be explained very well by a greater developmental energy in the plants, due to a more complete winter rest. These observations have a very noteworthy practical bearing in so far as they affect the culture of seeds obtained in exchange. It is not enough merely to introduce seed from other regions, but it will seem necessary lo ask above all, what characteristics it is desired to improve in the cultivated plant and in what climates these characteristics attain a higher development. Taken from such localities the seed will then give the desired results. The cultural results, obtained by using plants of other climates, hold good as a rule, however, only for a very few growth periods. Often the in- fluence of the present habitat is felt in the second generation when the plants of foreign importation have assumed the habits of the native varieties. Fruit trees taken from Angers grew and bloomed on Malorka even at the end of February, while the native ones did not blossom until a month later^. A shipment made two years later from Angers showed the same phenom- 1 Ihne, Phanolog-ische Mitteilungen. Cit. Bot. Jahresb. 1898, II, p. 409. 2 Petermann, Recherches sur les graines originaires des hautes latitudes. Extrait du t. XXVIII. des Memoires couronnes et autres Memoires publies par I'Acad. Royale de Belgique, Bruxelles, 1877. 3 Gartenzeitung von Wittmack, 1882, p. 374. 126 enon. The fruit trees of the first shipment were now, however, blossoming later, i. e., simultaneously with the native ones. The transition from the hereditary form of growth to the new one determined by the climatic con- ditions is rarely effected as rapidly as it is lost when returned to its former habitat. Yet, in our vegetables, we have examples of a rapid change in pecularities. In a tropical climate these keep approximately their own char- acter only in the first year. Already in the second year the seeds of these imported plants produce elongated, lignified specimens\ These are our cul- tivated forms which are beginning to vary from the normal. No rapid changes are noticeable in species growing wild, as has been shown by Hoff- mann's experiments with parallel seeding of certain forms of Phaseolus and Triticum in Giessen, Genoa, Montpelier, Portici and Palermo-. On the other hand, Hoffmann mentions slow changes, first taking place in the course of many generations. Thus Ricinns communis becomes tree-like and perennial in the tropics, in the same way Reseda odorata becomes more or less persistent in New Zealand and, conversely, Bellis perennis becomes an annual in St. Petersburg. Among the changes in mode of growth, which are only slowly com- pleted, belongs the formation of the annual rings in our trees. At any rate the distribution of vascular spring wood and the slightly vascular summer wood within the same degree of latitude fluctuates in each year according to the amount and distribution of precipitation. But in the changes of the average weather, due to changes in latitude, the same dif- ferences become constant and form thereby ecological varieties. Bonnier^ treats thoroughly such anatomical differences in the development of the same species in northern and southern positions. He compares examples of the linden, red beech, acacia and others from the region of Toulon (with its 260 days of active growth) with those at Fontainebleau (growth period 178 days) and found that the spring wood develops better in the south, having more abundant, often wider ducts. In this the abundance of precipi- tation in the spring in the Mediterranean district surely has a definite bear- ing. The summer wood of the south, however, is richer in libriform fibres and often consists only of these, while at Fontainebleau numerous ducts are formed, even in summer. The leaves of the Toulon plants were shown to be one-third to one-half thicker and provided with more layers of palisade parenchyma in comparison with the plants grown in the north. The stomata are more numerous, the sclerenchyma is greater and the cuticle strength- ened. The Toulon plants exhibit the character of Mediterranean flora in general. The greater intensity of the color of the blossoms, as the plants advance from the plains to the mountains and from lower latitudes to northern 1 Deutsche Gartnerzeitung, 1883, No. 17. 2 Hoffman, H., Ruckblick auf meine Variationsversuche von 1855 bis 1880. Bot. Z., 1881, p. 430. 3 Bonnier, Cultures experimentales dans la region mediterraneenne, etc. Cit. Bot. Jahresb. 1902, II, p. 299. 127 regions, has already been considered. Recently attention has also been di- rected to the increased change of color in foliage leaves and its peculiar significance as a protective adaptation has been suggested. MacMillan^ treats of these conditions very fully. He speaks of "luarming-up colors" meaning especially the red coloring substances which are more abundantly represented in colder regions. Alpine and arctic plants are more often found with blue or violet blossoms than with yellow ; the ends of the twigs are often reddened. The temperature is somewhat raised by the red coloring matter and the influence of cold somewhat weakened. If one thermometer be covered with a green leaf and another with a purple one, while both are exposed to the sun, in a short time the thermometer protected by the purple leaf shows a rise of 6° to io° of temperature. In the same way he found that a thermometer, stuck in a bunch of violets, shows a higher temperature than one in a bunch of cowslips, after an equal exposure to the sun. The autumnal coloring may be conceived as a definite reaction of the plant to the lowered temperature. The plant provides warmth for itself in its red coloring matter. On this account so many spring flowers are red and violet and autumn flowers blue or red. In warm climates plants often assume peculiarities directly opposite to those of arctic or alpine plants. In tropical plants the storage cells are less strongly developed than in related species from colder regions. The buds are less protected, pubescent coverings more rare on leaves and twigs (with the exception of desert plants). Many winter habits disappear. There are fewer biennials. The warming-up colors recede m.ore and more, while white, yellow and spotted blossoms (Orchids) predominate. Nature would develop red coloring matter to prevent loss of the super- fluous light and to transform it into warmth and to use it as a stimulus to growth. We cannot support this theory of the premeditated. utility of the red coloring matter as an apparatus, producing warmth and weakening the light, even if we had such an inclination. If the red coloring matter has once been produced, it will be effective in the way given. The idea that the plant can produce it as a protection against cold, when the temperature be- comes lower, is not plausible, because in the hottest summer temperature leaves can be reddened. In the Rosaceae which are rich in tannin (Crataegus, for example), I have been able to produce the red autumnal coloring after a few weeks in the middle of summer by girdling the twigs. The fact that in summer the underside of many leaves, when reversed, becomes red within a few days is universally known. Parasites furnish further instances. On the same cherry tree, for example, the leaves of branches attacked by Exoacus Cerasi turn glowing red, while the healthy ones remain green. In many spot diseases the circular fungus centre appears surrounded by red. Amaryllidaceae, whose leaves die down in summer (Hippeastrum etc.). develop carmine spots and stripes. 1 MacMillan, Conway, Minnesota Plant Life Saint Paul, Minnesota, 1899, p. 417. 128 Thus we believe that the red coloring matter may be looked upon as a necessary reaction of the cell to the influence of different factors connected with a relatively over-abundant supply of light. One of these factors may be the lowering of the temperature due to a change in the latitude or longi- tude of the place of growth. If we look back to the many changes undergone by the plants in their morphological and chemical structure because of any change in latitude of the place of growth, we cannot shut our eyes to the conviction, that not in- frequently in these changes of place may he sought the reason for a predis- position toward disease or, on the other hand, toward greater immunity. We have mentioned that the western squarehead wheat grown in eastern regions has greater susceptibility to frost and now remind the reader that parasitic diseases may also be dependent on the dift'erent mode of development of the host plant inherited in the seed. One should con- sider, for example, the fact that many parasitic fungi appear or are especial- ly abundant at definite periods. In case such fungi only attack young leaves, the presence of young leaves when the spores are ripening will determine an epidemic. The rapidity with which a plant passes through its develop- mental cycle in any given climate is a determining factor in this question. If it develops slowly, its leaves are young and remain susceptible for a longer time, giving a greater danger of fungus infection. If a variety matures quickly (for example, one introduced from more northern or eastern regions) then the leaf may be fully matured at the time of the actual distri- bution of the spores and therefore be resistent to many parasites. Such circumstances deserve greater consideration than has been given them as yet. They will also be a factor in the discussion of the "biological races" of individual parasites, for it is most probable that often infections of the most closely related host species fail because the host plant at the time of infection is already in an advanced developmental stage, in which the leaf is more mature, i. e., has thicker walls and less cell-content. The fact that the fungus infection is connected with a definite developmental stage of the host plant is shown, for example, in the rust fungi of grains. Eriksson^ states that the rust occurs earlier in the varieties ripening early and recent observations show that the different forms of Puccinia have defi- nite periods for attacking grain. Thus it was shown in 1904- that Puccinia glumarum appeared first and foremost in wheat, then followed P. dispersa which, however, attacked only those organs and varieties which were still immature. Later, slowly ripening varieties of wheat were found badly at- tacked by P. dispera and slightly by P. glumarum, while the converse is true for varieties maturing early. P. graminis was found in stored grain. 1 Eriksson, J., Sur I'origine et la propagation de la rouille des cereales par la semence. Ann. scienc. nat. Bot. VIII. ser, Vols. XIV. and XV. Paris 1902. - Jahresb. d. Sonderausschusses f. Pflanzenschutz. Deutsche Landw. Ges. 1905 Getroiderost. 129 Glassy Graix Kernels. These must also be considered, as the result of climate influences. Grains are called glassy when their endosperm is hard, almost trans- lucent and grey or reddish in cross-section, while in the normal mealy kernel the endosperm appears soft, white, porose and easily friable. . This glassiness of the kernels occurs usually more abundantly in the north and east of Europe than in the west, which fact points to the influence of atmospheric dryness with a higher light intensity. Tn damper, western regions the vegetative organs obtain a greater ascendancy. Thus Lieben- berg^ states, for example, that the otherwise excellent northern barley has two disadvantages ; — viz., too large a percentage of glassy grains and too dark a color which is caused by rain falling on the grain when ready for harvesting. These gusts of rain at harvest time naturally play no part in the development of grains which mature during the dry season. With the lengthened light action, varieties of rye also become intensively colored. The same author reports that at the grain exhibition in Sv.eden, the oat samples, on an average, possessed only 22.66 to 32.04 per cent, of chaff by weight, while in the Austrian and French varieties it fluctuated between 25.23 and 38.37 per cent. In general there is truth in Haberlandt's- state- ment, that a continental climate produces glassy grains, but that, on the other hand, cool, wet summers or an artificial abundance of nutritive sub- stances and water produce mealy, specifically lighter grain kernels, poorer in nitrogen. The glassy condition of the grain, according to Gronlund's"' investiga- tions on mealy and glassy barley, exists in the fact that the cells of the albu- men in the mealy grain which contain the starch show that the spaces between the starch cells are filled with cell-sap, while in the glassy grains these spaces are filled with protoplasm. Johannsen's'* work assumes a greater air content not only between the walls of the mealy grains, but in their whole mass. In germination, the glassy grains become mealy. Ac- cording to Gronlund, who, moreover, acknowledges no relation between weather and the production of the glassy conditions, glassy kernels germi- nate more easily and better and give stronger plants. Although he assumes as mcontestible that glassy kernels may be produced from soil containing much nitrogen, yet he believes that poorer, sandier soil, poorly cultivated, pro- duces this peculiar formation much more certainly. He found that mealy grain was produced by pure potassium fertiliaafion. Moreover, both forms occur at times in different stages in the same head. I would like to assume for the production of glassy kernels that the process of starch formation is 1 V. Liebenberg-, Bericht iiber die allgemeine nordische Samenausstellung etc., 1882, cit. Bot. CentralbL. 1882. No. 43. p. 115. - Habeiiandt, Die Abhangigkeit der Ernten von der Grofse und Verteilung- der Niedei'schlage. Oesterr. landw. WocbenbL, 1875, p. 352. 3 Nach einer Preisscheift des Verf. cit. im Jahresbericht f. Agriculturchemie XXIII (1880), p. 214. 4 Allg-. Brauer- und Hopfenzeitung, 1884, Nos. 78 and 79. 130 shortened in sandy soil, which dries quickly, and, since potassium makes the corn mealy, I would much sooner believe that the action of the potassium is stopped too soon and indeed because other processes, viz., those of ripening, take place too early and too intensively. This will happen much more quickly with strong action of light and warmth and when the water con- tent is less. Sanio's^ statement that in East Prussia the glassiness of wheat is due to its becoming overripe on the stalk supports the theory of the predominance of the ripening process at a time when starch formation should be taking place. This opinion is analytically supported by R. Pott's investigations- who found on an average a higher percentage of ash in glassy varieties of wheat than in mealy kernels. The kernels, in the too rapid ripening, had not completely consumed the mineral substances in forming organic substances. Compare here the high percentage of nitrogen in the grains of oats plants, which suffered from a scarcity of water or from its excess (see chapter, "Excess of Water"). Petri and Johannsen'' have made investigations which throw much hght on the nature of glassy kernels. The former, as early as 1870, stated that glassy kernels, when softened by water, become mealy and the latter substantiated this observation. Two hundred kilos of barley were moistened with half that amount of water, until they had taken up 15 per cent. They were then dried immediately, spread and turned until the original weight was again obtained. The percentage of mealy kernels now" was 50 per cent., while in the original material it amounted to only 19 per cent. In cultural experiments it was found that, in early seeding, a mealier barley, poorer in nitrogen, had been formed, while in later sowing the harvested product was richer in nitrogen. This discovery indicates that in this glassiness of the kernels there is only a mechanical difference, which develops if ripening is very much hastened by a scarcity of water with an excess of light and \varmth. A gradual ripening process gives a longer time for developing an increased starch content with the retention of a larger water content in the substance which is later partially replaced by air. This refers especially to the protoplasm in the endosperm cells. The starch grains lie embedded in this. With quick ripening, the cytoplasm sticks close to the starch grains, making the kernels appear glassy. With slower ripening and greater water content the cell is more loosely constructed, while between the starch grains more cell sap and later more air are present, and then, because of the larger intercellular air spaces, the grain is opaque and mealy. As the protoplasm predominates, the tendency is toward glassiness, and on this account, even normally, the outer layers of the seed, as, for example, in maize, are glassy, the inner ones mealy. These conditions explain Schindler's observations* that, in wheat grains, mealy and glassy portions can alternate. 1 Botanisches Centralbl., 18S0, p. 310. 2 Jahresbericht f. Agriculturchemie 1870-72, II, p. 5. 3 Johannsen, Bemerkungen liber mehlige und glasige Gerste (Ugeskrift for Landsmaend), 1887, cit. Biederm, Centralbl., 1888, p. 551. 4 Schindler, Lehre vom Pflanzenbau auf physiologischer. Grundlage. Wien 1896. 131 The above explanation of the production of glassiness is substantiated by the experimental results, which have been obtained by the Deutsche Landwirtschafts-Gesellschaft^ The report states: — The glassiness of the kernels depends more on the conditions of growth than on the variety. Varieties with a shorter vegetative period are glassier — such as Lupitzer, Strube's bearded and Cialician club wheat in comparison to Schlanstedter and Noe wheat. The productive power of the varieties in general stands in inverse relaton to the glassiness of the grains. 4. Continental and Marine Climates. The characteristic distinction of regions influenced by the ocean con- sists in the lesser fluctuation between summer and winter temperatures, — since the summers are longer and cooler, the winters warmer. We find that, under the influence of the Atlantic Ocean, spring comes earlier, while au- tumn is delayed longer than in regions with a continental climate. Yet the effect on vegetation is not the one expected, in spite of the earlier spring, for the blossoming time of wooded plants is at most only a few weeks earlier, because of a cooler spring temperature and the ripening of the fruit is scarcely earlier, indeed, it is often delayed and occasionally does not take place at all. Consider, for example, grapes which do not ripen out of doors in England. Throughout the year, the air is more moist and in the change of season extensive heavy mists often prevail. Haberlandt's opinion has already been mentioned, according to which early maturity of plants may appear with the same ease in northern latitudes as in southern ones, and thus lead to the production of con-esponding varie- ties. Conditions of humidity also act determinatively in this and all become evident in the great fluctuations in a continental climate in contrast to an uniformly damp coast climate. Haberlandt's culture experiments- gave results as follows. Seed brought from damp climates gives proportionately more straw, but less grain, — the grain is also more easily subject to lodging. On the other hand, in seed from dry regions, with a short spring and hot, dry summer, there is a production of less straw and greater grain crops, and plants from such seed better withstand drought. When exchanging seed it is more advantageous to take it from countries with a continental climate. The hard winters influence the grain product in such a way that the plants produced are less apt to winter kill than those which have been transplanted to the East from the moister west with its milder climate. The continental climate produces smaller but specifically heavier grain, while a cool and damp summer or an artificial abundant supply of water and food substances increases the size of the grain, to be sure, but at the same time causes more porous contents, since, instead of the glassy con- 1 Mitteilungen der Saatzuchtstelle iiber wichtige Sortenversuche. Saatliste vom 6. Dez, 1914. Deutsche Landwirtseh.-Ges. - Haberlandt, Fr., Ueber die Akklimatisation und den Samenwechsel. Oesterr. landw. Wochenbl., 1875. No. 1. 132 dition, a mealy one appears, together with a decreasing specific weight and decreasing nitrogen content. Finally an important observation bearing on the exchange of seed is the fact that winter grain coming from regions above the 45th parallel of latitude and cultivated by us in the spring, does not produce shoots, while on the other hand, that taken from lower latitudes behaved with us like summer grain. Because of the great interest on all sides in the colonies, it is necessary to take tropical conditions into consideration. Here the differences of tem- perature on the land and between land and sea attain a greater significance. Thus, for example, Fesca^ reports, in regard to the great warming of the land in direct sunlight as compared with that of the sea, that the tempera- ture of the tropical ocean rarely exceeds 30°C. while the rock is heated up to 60° to 70°C. Pechuel-Loesche observed a soil temperature above 75°C. on the west coast of Africa in the 5th parallel of south latitude, not less than 36 times between January ist and March 4th. In contrast to this, however, stands the nightly cooling down to I5°C. and less. Daily fluctua- tions of the soil temperature from 30° to 40°C. are very frequent in the tropics while, on the other hand, the daily fluctuations of the sea might at most reach i°C. As a result of the dift'erences in the morning quality of land and sea, a low barometric pressure must be produced on land in the day with the in- tensive sunlight, so that the air from the sea streams in that direction and, conversely at night. These sea and land breezes are considerably more in- tensive in the tropics and sub-tropics w-ith the stronger contrasts in warm- ing land and water and form a factor to be reckoned with. According to Saito" the air above the sea is almost free from mould fungi, bacteria and yeast germs, while the air above the land (street and garden air in Tokyo was investigated) w^as especially rich in germs in wet and warm periods. Thus the sea breezes act as purifiers of the air. The sea breezes decrease towards the poles, since the sea gradually assumes a higher mean heat than the land and also because the daily fluctuations of the soil are less. For the same reason the changing annual winds, the monsoons, corres- pond to the periodic daily winds in the strong warming of the great conti- nents to which vegetation must adapt itself. The amount of precipitation occurring as rain depends also on the re- lation to the sea and the temperature and, accordingly, it is most abundam in a w^arm sea climate, scantiest in a continental one. An annual mean of 9°C. approximately holds for all the German North Sea coasts. With an 80 per cent, saturation, the air would contain 7.26 g. water vapor in a cubic meter. If the air cools down to 4°C. it can hold only 6.9 g. water vapor per cubic meter and the difference must therefore be eliminated as precipitation. 1 Pflanzenbau in den Tropen und Subtropen, p. 23. - Saito, Untersuchunsen iiber die Atmospharischen Pilzkeime. Journ. College of Science, Tokyo. Vol. XVIII. 133 If tropic air reaches 25°C. with the same saturation (80 per cent.) it con- tains 18.48 g. water vapor and ehminates 1.18 g. water per cubic meter when cooled down to 5°C. This amount of precipitation therefore is more than three times that of air at 9°C. when influenced by the same decrease in tem- perature on the North Sea coasts. Thus are explained the heavy tropic rains and especially the heavy fall of deiv which, in places, must suffice for a certain period in hot climates as the only source of water. Just as in cultivation experiments, soil analyses and mean temperature offer no sufficient insight into a possible utilization of food substances on the part of cultivated plants, just so little can the annual rain fall indicate the moisture conditions of a region. For it depends essentially upon the soil conditions and the distribution of the precipitation in the different months. Over a greater part of the desert of Sahara (see Fesca) the same or a greater cmount of rain falls than that sufficient for Germany's agriculture (60 cm.) without its having there any essential effect. For, on a highly heated soil, moisture exaporates immediately. The most desirable distribution of rain in the tropics is not the one extending uniformly throughout the whole year, but, viz., at the beginning of the vegetative period an abundant precipitation and then a time of dryness. The abundant clouds in the rainy season con- tribute essentially to the production of a cooler temperature which is es- pecially favorable for the development of the vegetative organs. Along the coast the climate is cloudier than it is inland. In regions of great atmospheric dryness, as in the Mediterranean basin, often there is only 20 per cent, cloudiness as an annual average : in the dryest months often only 10 per cent., — in the moist tropics not infrequently more than 80 per cent. Since, however; the cloudiness decreases the taking up and giving off of heat, the temperature of the lower latitudes is less and that of the higher, greater. Many cultivated plants require these lower temperatures and cloudiness. We believe, with Zimmerman^ that many diseases in coffee plan- tations, especially the excessive production of fruit, may be due to insuf- ficient shading. In the same way it may be that the great susceptibility to fungous diseases which has appeared in the last 15 years^ since tea has been cultivated in the Caucasus, has been due in part to the difference of the Caucasian climate from that of the regions from which tea was introduced. The development of the plant body is of course adaptable to the climatic conditions and factors of growth. The m.ore recent biolog}^ takes these cir- cumstances into consideration as is shown by the work of Hansgirg^. He speaks of stenophyllus wind leaves (as in the willow type) ; of leather (coriaceous) and wind leaves (palm type) ; of xerophyllus leather leaves (Myrtus, Laurus), of dew leaf types (Bromeliaceae, Pandaneae) ; thick 1 Zimmermann, Sonderberichte uber Land- und Forstwirtschaft in Deutsch- Ostafrika. Vol. I, Part 5, 1903. 2 Speschnew, Travaux du jardin bot. de Tiflis VII, 1 Verhandl. d. Internat. landwirtsch. Congresses in Rom 1903. 3 Hansgirg-, A., Phyllobiologie nebst Uebersicht der biologischen Blatttypen etc. Leipzig, Borntrager, 1903. 134 leaves (Crassula and mesembryanthemum types) etc. The most conspic- uous example is the vegetation of the sea shore with its halophytic character. Brick^ explains the fleshy and glassy constitution of the vegetative organs as due to the abundance of sodium salts, which makes the parenchyma ex- tremely turgid. The greater the number of examples showing the adaptation of the plant to climatic conditions, the more marked will be the untenability of the theory, that the climatic relations formed in each place of cultivation can be changed at will without causing injury. If the whole sum of the climatic factors should correspond in two widely separated localities this would be no guarantee that the given plant would thrive as well in the new home as in the old, since the distribution of light, heat and moisture can be proved to be very different in the different periods of growth. The diseases of the New Holland and Cape plants which, adapted to a dry climate, must pass their lives in our sunless, damp conservatories, give the most abundant proof. Decay of stem and root, dying of the twigs caused by Botrytis etc., constantly cause injuries to the successful cultivation of these plants. The so-called damping off of the shoots of Pimelea, Chorizema, Pulteneae, Cor- rea, Boronia, Agathosma, and Borosma, of Helichrysum, Humea etc., is a result of the great humidity in our conservatories which can not be over- come. 5. Influence of Forests. The forestration of a locality modifies the influences of the position and soil constitution and to this point patholog)^ must pay especial attention. The influence of forests is like that of surfaces of water, for, since organic substances possess a higher specific warmth than do mineral substances, the overgrown soil will be cooler, with an equal exposure to the sun, than the naked rock or sand. The summer heat is also moderated by forests. With the abundant evaporation of the foliage, the air becomes more moist, the thicker the growth and the less motion in the air. Corresponding to the greater evaporation, there is a more abundant cloud formation over forests which is not so easily dispersed. Since the relative humidity of the air is greater in and above the forest, much more dew is formed. The force of the rain gusts is decreased. Since torrential rains, especially on slopes, cannot be taken up as quickly, the mass of water runs off from the naked earth and at the same time carries away the fine humus from the higher fields to the lowlands. The annual repetition of this process so changes the conditions of the fields that the higher places become impoverished and retain only a slightly fertile soil skeleton, while on the low lands the humus layers keep on growing. The power of the soil to retain water decreases with the loss of humus and injuries due to a scarcity of water show themselves. In heavy soils the steady beating of the rain drops in severe storms tends to form a crust. 1 Brick, Beitrage zur Biologie und vergleichenden Anatomie der baltischen Strandpflanzen. Cit. Bot. Jahresb. 1888, I, p. 765. 135 All these unfavorable conditions are overcome by the forest, the tops of the trees catching the rain and partially retaining it. Nevertheless the water, which passes through and runs down along the trunks, is retained by the moss and the dry leaves in deciduous forests, forming the upper surface of the soil or the humus, thus becoming of benefit to the vegetation. Furst's'^ "Illustriertes Forst- und Jagdlexikon" gives some positive figures on these theoretical discussions. Based on the observations of the forest meteorologi- cal stations, it is stated that the temperature of the air in the annual average is possibly o.8°C. lower under the close roof of tree crowns of the forests, than in the open. The difference is greatest in summer (up to 3°C.) while it approximates the annual average in spring and autumn and almost dis- appears in winter. "The fluctuations in temperature are less under the shelter of the tree crowns than in the open." The temperature of the forest soil is from i to 3°C. lower at all seasons of the year than that of open land. The absolute moisture does not differ in the forest and in the open; but, on account of the lower temperature, the relative moisture in the forest during the winter, spring and autumn is from 4 to 8 per cent, higher than in the open, and in summer from I2 to 20 per cent. The evaporation from a free surface of water in the forest is from 50 to 60 per cent, less than in the open; "the evaporation of the water from the soil is reduced from 80 to 90 per cent." Of the precipitated moisture, 10 to 50 per cent, will be retained by the crowns of the trees, according to the species, the age and dimensions of the forests as well as the amount of precipitation, and in light rains it often amounts to 100 per cent. In general 60 to 80 per cent, reaches the soil in the forest. "In Central Europe the annual and the summer temperature will be lowered 1° and 2° to 3°C. by the dimensions of the forest and the relative moisture raised ca. 5 per cent, and 15 per cent." Since the amount of the distant action from extended forestration has not yet been determined, the question as to the influence of the forest on climate must remain open. But one effect of the foTest on the immediate vicinity cannot be denied and this phytopathologists must consider. Differences in insolation are felt slightly in the forest, but very quickly and strongly in the open field. The soil is warmer; the layers of the air lying above it must necessarily produce an equalizing air current which is most significant in spring when vegetation awakens. Hesselmann's- investigations give an insight into forest vegetation. He observed the regular dying of the twigs which takes place within the crowns of the trees and found that in birch and mountain ash the leaves were still strongly active in assimilation ; but in the hazle-nut markedly less so. If well-lighted branches die, phenomena of correlation are at fault. Trees which can live in shade develop distinct sun and shade leaves ; trees 1 Illustriertes Forst-und Jagdlexikon, 2nd. Ed., revised by Dr. Hermann Fiirst, Berlin 1904, Paul Parey, p. 384. '^ Hesselmann Hendrik, Xur Kenntnis des Pflanzenlebens schwedischer Laub- wiesen. Jena, Fischer, 1904. 'Cit. Bot. Centralbl. v. Lotsy, 1904. No. 49. 136 which require Hght do not show this difference. The assimilation activity of the flora of the forest floor is ver}^ rapid in spring when the trees and trunks are still bare and decreases with the foliation more slowly in shade trees, because of their structure, until it finally ceases entirely. The respira- tory intensity decreases with the decreased "food consumption." Detached shade leaves of Convallaria majalis etc., form more starch in the sun as well as in the shade than do sun leaves treated in exactly the same way and they also fix carbon dioxid more rapidly in the same amount of light than do these. Moreover in Convallaria the storage of starch was found to be less, the drier the soil. Equally large leaf surfaces containing palisade cells tran- spire much more strongly than do those leaves having the structure of shade leaves. It is evident from these statements that changes of great importance must take place in the economy of trees accustomed to shade, when suddenly exposed to light, viz., w'hen left standing by removing parts of forests. In parks too strong and sudden an exposure to light by the removal of num- erous trees not infrequently results in the partial or total death of the crowns of the specimens left standing. We must turn our attention to still another point. If plantations of fruit trees along streets on level land, especially cherries, be examined, many cases will be found wih trunks split open on the south or southwest side, with the bark torn into tatters and often showing lumps of gum on the wounded surfaces. These injuries are very evidently due to frost. The ex- planation lies in the fact that the level, cleared lands are exposed in spring to extreme temperatures. The February and March sun shining intensely on the trunks, and strengthened in its action by the reflection from the soil, starts the reserve plant food prematurely and the tissues, being richer in water and sugar, at once succumb to the action of the frost. A moister atmosphere in the neighborhood of water or wooded areas equalizes the temperature and serves as a protection from frost. Naturally in regions with greater soil elevations and more noticeable differences between valleys and mountains these factors co-operate determi- natively and often decisively, but on the plains the forestration is a very considerable factor. Cutting considerable forest tracts on wide plains often is a source of injury avenged not only on the owner but on the whole neigh- borhood, since it increases the chance for damage from late frosts. In this connection many small forest tracts, scattered over a large plain, would be of use since no considerable distant action from one single large forest may be reckoned upon. There is a further advantage to be derived from forests, — that of protection against the zvind (windbreak) when there are no mountains. Just as every bright side has its shadow, forests can exert an injurious influence on the adjacent fields. The forest properly located can withhold the summer rains, usually coming from the west, from a given field so that there will be dry, windless streaks across the fields in its immediate prox- 137 imity, — or, on the other hand, the forest may make streaks across the field accessible to rains and prevent the rapid drying off of the seeds. In the first case, the forest may become a harboring place for injurious insects. It has often been observed in the case of dwarf cicades that they begin their de- vastation of the fields from the dry edges of the forest. The more severe attacks of Puccinia, Ophiobolus and Leptosphaeria herpotriahoides serve as examples of the influence of moisture, near the border of the forest, upon fungous diseases. Goethe's discoveries^ as to the influence of the place of growth upon the canker of fruit trees, caused by Nectria ditissima, must be considered. The tendency to disease from canker is favored by an in- creased humidity as ofi:ered by higher regions or also by cold valley soils. "The trees show in such places a meagre growth and are covered with mosses and lichens. Similar conditions are observed also near extensive forests, out of which cold, damp air streams even in the summer." 1 Goethe, Rudolph, Ueber den Krebs der Obstbaume. Berlin 1904. Paul Parey. CHAPTER II. UNFAVORABLE PHYSICAL CONSTITUTION OF THE SOIL. I. LIMITED SOIL MASS. Root Curvature. For practical agricultural and forestry purposes, the question as to the limitation of space in the soil plays a subordinate role when there is no scarcity of food stuffs, since disturbances in nutrition, arising from the overgrowth and rubbing of roots pressed tightly against one another, or by their growth in crevices of rocks, have no agricultural significance. The matter is quite dift'erent, however, in gardening and the cultivation of house- plants by the plant lover. In these circles, however, opinions as to the influence of too small soil space on the spreading of the roots are divided. Predominant and also clearly expressed on the part of many agricultural chemists is the opinion that the mechancial eft'ect on roots, closely pressed on one another and tangled by repeated curvature, has no influence on the thriving of the plants. They think that in limited soil space only a scarcity of food may ever be involved which would make itself felt very quickly and could be corrected advantageously by fertilizing. The best proof should lie in the cultivation of the so-called "market varieties" by commercial growers in large cities, who, conforming to public taste, grow very vigorous specimens of all blos- soming plants (Fuchsias, Pelargoniums, Begonias, etc.) in relatively very small pots. The fact is correct, the explanation, however, inconclusive. The restriction of a large root mass in a small space results first in the increased production of lateral roots. This may be observed easily in water cultures. If one of the large roots reaches the bottom of the glass container and its tip is forced to bend around, new lateral roots are produced im- mediately. NolF has given special study to this. He found that on the bent portions of the main root, the lateral roots were formed only on the con- 1 Noll, F., Ueber den bestimmenden Einfluss der Wurzelkriimmungen auf Enststehung und Anordnung- der Seitenwurzeln. Landwirtsch, Jahrbucher XXIX (1900). p. 361. 139 vex surface, the concave surface remained free. This is true of both main and lateral roots and not only under mechanical influences, but also as a result of geotropic and hydrotropic stimuli. Pollock^ has pointed out, in this connection, that twisted roots contain more water in the cells of the convex side than in those of the concave side. Noll ascribes this growth of nev/ lateral roots at the point of curvature to a perceptive power of the plant to the formal relations of its own body ( M or phaesthesia) . This expression may be accepted if by it is understood a mechanical transfer of material resulting from the stimulus of curvature on the afifected tissues. The process is similar to the one occurring after direct injury when the cytoplasm has accumulated in the cells adjacent to the wounded surface. Of course laterals are found also on concave parts of twisted roots, but, in such cases, the buds of the laterals were present before the twisting of the mother root had taken place. In trees grown in the open the development of lateral roots on the convex side can be of practical advantage, since the plant is thus more firmly anchored and extends over a greater area of soil containing food stuffs, where otherwise the root branches might not have penetrated. But where the whole root ball has only a definitely limited soil space at its disposal, as in potted plants, disadvantages arise which must find expression in the pro- duction of organic substances. We can perceive these disadvantages at once, if we observe more closely a pot said to be "root bound." The greatest number of young roots have grown out towards the periphery and been so pressed against the porous sides of the flower pot, that many fibres are broken oft" when the pot is removed. Part of the root fibres have stuck fast like bands or membranes and have died. The latter circumstance is especially apparent in palms and Dracaenae, in which the dead roots consist only of the stele and the outer bark, which has shivelled up like a papery covering. The straining of the roots toward the side of the pot may be attributed to the need of oxygen. Naturally this demand is less easily satisfied as the network of roots fills the ball of earth more closely. To this must be added the secretions of the root Itself. Czapek" determined that these secretions may be ascertained in moist air as well as in water cultures. In air saturated with vapor they are frequently observed as drops on the root hairs, the re- sult of a strong internal pressure in the cells. Minimum amounts of potassium, calcium, magnesia, sulfuric, hydro- chloric and phosphoric acids are eliminated. Potassium phosphate, causing the well-known reddening of litmus paper, is somewhat more abundant. In regard to acids, Czapek found that the presence of lactic and acetic acids could not be proved, but that,on the contrary, formic acid is found not in- frequently in its potassium salt as a diffusion product of the living, youngest 1 Pollock, James, The mechanism of root curvature. Botan. Gaz. Chicago, XXIX, 1900. pp. 1 ff. - Czapek, Fr. Zur l^ehre von den Wurzelausscheidungen. Jahrb. fiir Vi^iss. Bot. 1896. Vol. 29. Part III. 140 parts of the roots. Potassium oxalate was eliminated by hyacinth roots. Carbon dioxid, however, must be considered primarily and causes the rock etchings, as it occurs dissolved either in the water of the root-hair cells or of the soil interstices. Monopotassium phosphate and carbon dioxid among the root secretions must be especially considered. In pot cultures the latter is of especial importance. It is retained in the root balls in great quantities, the more thickly matted they are and the wetter they are kept by the grower. The production of carbon dioxid is greatly increased by the respiration of the soil micro-organisms which in their metabolism decompose the carbo- hydrates and other organic substances. For instance Stocklasa^ found alcohol, acetic acid and formic acid in forest soil and finally carbon dioxid and hydrogen. The hydrogen often unites with oxygen to form water. Lack of oxygen and the excess of carbon dioxid kill part of the roots and the process is gradually evidenced when plants are grown in small pots, even if over-abundant foodstuffs be given them by fertilizing. However, if fertile earth alone is used, without subsequent additions of fertilizers, the roots, becoming thickly matted on the walls of the pot, do not touch the ball of earth actually as they develop on top of older roots. In such cases, they cannot further draw from the soil the food materials needed in growth. Early investigations by Hellriegel" prove that excessively limited soil space in itself limits production. To perform these experiments many annual and perennial agricultural plants (barley, peas, buckwheat, clover, etc.) were sown in glass containers of different heights in as uniform gar- den soil as possible and were grown with an observance of all the precautions used in sand and water cultures. In order to prevent any question as to the exactness of the results obtained due to a different amount of soluble nutri- tive elements control experiments w^ere made with an abundant addition of fertilizers, under otherwise similar conditions. The result was, that no difference in production whatever was shown in favor of the fertilized plants, that those not fertilized must thus have found in the unfertilized garden soil all the nutritive substances that they needed for their production. An indirect proof lay also in the results of the experiments given by the unfertilized plants when compared with one another. The yield showed in fact, that clover in the first year had produced about as much dry material as the other varieties of plants. This did not prevent the clover, however, from producing in the second year on the same soil a second crop and in fact a crop two or three times as great, and even in the third year it produced as much as in the first year. From this it is evident that the amount of nutritive substances could not play a role in any of the experimental pots, since they were everywhere present in excess. If now, however, the amount of dry substance increased with the size of the container, this result could be ascribed only to the influence of the 1 Stocklasa and Ernest, Ueber den Ursprung, die Menge und die Bedeutung des Kohlendioxyds im Boden. Centralbl. f. Bakteriologie etc. Section II, Vol. XIV. 1905, p. 723. 2 Hellriegel, Beitrage zu den naturwissenschaftlichen Grundlagen des Acker- baues. Braunschweig. Vieweg, 1883. pp. 184-224. 141 volume of the soil. The plants under experiment stood in glass cylinders of the dimensions and contents given below, received steadily from 30 to 60 per cent, of the water required by saturation of the soil and resulted with clover, as follows : Height of the Cylinder. Diameter in the Clear. I. 96 to 99 cm. 14 cm. II. 65 to 67 cm. 14 cm. III. 34 to 35 cm. 14 cm. IV. 18.0 cm. 14 cm. Earth content. Harvested dry substances, Air dry. Absolutely dry. in the years 1872, 1873, 1874. 19^500 g. 18,600 g. 417-2 g- with 6.92 per cent, pure ash 13,000 g. 12,400 g. 254.6 g. " 6.97 " " 6,500 g. 6,200 g. I73-0 g. " 8.08 " " " " 3,250 g. 3,100 g. 76.8 g. " 8.45 " " " " Since, in the containers with a very large soil volume, too great a con- solidation, therefore somewhat abnormal conditions for some plants, has appeared, because of the sudden addition at first of great amounts of water saturating the soil to 60 per cent, of its water capacity, Hellriegel, in his harvest tables, explained especially the results for the sizes HI and IV. From this it appeared that, with peas, an amount of soil of 3,100 g. gave on the average, 29.97 in dry substances. 6,200 g. " " " " 47-94 " " For peas, therefore, the proportion of the soil was i :2. " " harvest was 1:1.6. For beans, therefore, the proportion of the soil was 1.2. " " harvest was 1:1.8. In 1872, exactly the same proportions in harvest results were found for barley as for beans. We omit here the repetition of the figures, since those cited show clearly enough that, in two equally wide, but unequally tall ves- sels, both containing nutritive substances in excess, and steadily receiving the favorable amount of water, the harvest came out as i :i.6 up to 1.8, if the amounts of soil bore the proportions of i :2. Thus a strikingly evident influence of the soil volume may be confirmed and the question now is, how this influence may be explained. Hellriegel found that the height of the yield stood in inverse ratio to the amount of the mechanical resistance, which opposes the development of the root-network of the plants under experiment. If commercial growers get apparently opposite results and find that the growth in small pots is great and quick, the explanation lies in the fact that they use a very rich earth and highly concentrated solutions are present in the soil. Comparative measurements showed, however, that the root development in rich nutrient solutions is essentially shorter than in weakly concentrated ones. Hence the demand of the root fibre is actually smaller. 142 However, in the same length of time, the root makes a stronger growth when kept under glass, or in hot beds, than where the plants are in the open ; — for these glass cases all have bottom heat. Finally, the aerial axis finds itself under conditions making possible an especially rapid and abundant develop- ment. The atmosphere rich in water vapor and carbon dioxid develops the largest individual cells possible with comparatively little transpiration, hence, the turgid and significant large size of the foliage. Therefore, in garden cultures in small pots, the root is better and earlier formed and utilized, so that the injuries due to root curvature and bruising make them- selves first felt at a time when the aerial axis has already made a consider- able growth. That growers, however, clearly recognize the disadvantage of small pots and, when possible, do without them is evident from the so-called "feeding cultures" (forcing). In this the specimens are shifted into larger pots as the root branches penetrate to the sides of the pot. Dwarf-growth (Nanism). The dwarf conifers found in trade under the name "Japanese or Chinese Trees of Life" show an interesting effect of the influence of a limited soil space. The figure on the next page illustrates a living specimen which has been classified by the well-known firm J. C. Schmidt (Berlin) as Thuja ohtusa and kindly placed at our disposal. The tree, with the pot, is 86 cm. high in all, — and 60 cm. high above the soil. At its greatest width the crown is 80 cm. across. The base of the trunk, divided into several pro- truding ridges, has a diameter of 19 cm., the trunk at the height of the crown, where the branches appear, one of 12 cm. This healthy specimen, with a dense crown, whose age is estimated to be 100 years, cost $87.50. In literature, notes may often be found referring to the skill of the Japanese and Chinese in growing dwarf specimens of trees, hundreds of years old for table-decoration^. Our examination of the trunk from a dead tree destroys the halo of the miraculous, with which these productions of Japanese and Chinese hor- ticulture have been surrounded. A section 8 cm. long and 6 cm. at its widest diameter showed most excentric annual rings. The distance of the pith from the bark amounted to 1.5 cm. at one side of the trunk and to 6.5 cm. at the other. Counting with a magnifying glass showed 30 annual rings on the wider, but only 15 on the narrower side. On the side favored in growth, a great variation in the breadth of the annual rings was noticeable. Four 1 In an article on "dwarf growth in the veg'etable kingdom,"* Grube quotes a report by Sir Geo. Staunton, from "des Grafen McCartney Gesandtschaftsreise nach China," Berlin 1798. Staunton snw in Ting-hai, spruces, oaks and orange trees none of which were more than 2 feet high and on which fruit had set abundantly. At the base of the trunk the soil was covered with layers of stones weathered and covered with moss giving the pots the appearance of great age. "Throughout China, there is a great liking for these artificial plant dwarfs for we found them, as a rule, in every house of any pretention whatever." It is there further related that the "liliputian" trees were propagated by binding loam or garden soil around different branches. This was kept moist until the branches developed new roots in the earth ball; they were then cut off. We still use this process in the layering of branches or top shoots and the covering of the cut places with moss. This plan 143 zones could be distinguished. Each of these ended with very slender rings, the tracheids of which had especially narrow lumina and had become browned through resinosis. Otherwise the w^ood was healthy. In its dimen- sions the bark corresponds to the section,- — i. e., on the side of the narrower rings, it w^as 1.5 mm. thick, on the other side 4 mm. On the narrower side, a depression w^as found, in w^hich a scantier development of the wood had been equalized by a thicker formation of bark,- — up to 5 mm. There was shown here a tendency to loosen the individual bark scales between the flat cork layers resembling full cork. Fig. 15. Dwarf specimen of Thuja obtusa, 60 cm. high and 80 cm. wide. (Orig.) At the base of the trunli may be seen the division of the aerial axis into a number of root branches projecting above the pot. Thus the statements as to the great age of the trees are seen to be erroneous. These cannot be more than some thirty years old and their dwarf growth, in our opinion, can be obtained by keeping the plants in the very was followed in China, because it had been observed that an artificially produced dwarf character is hereditary. When the tendency has become hereditary it is strengthened in the new individual by turning down the end bud of the main shoot and bending it with wire in another direction. "If it is desired to give the dwarf tree the appearance of an old, already half dead tree, the trunk is often covered with syrup to attract ants and these, after they have eaten the sweet, immediately injure the bark, giving it thereby a brownish, half-weathered appearance." Rein** describes the Japanese process which is somewhat different. They call the dwarfing or "Nanisation" "Tsukurimono." This expression is not used in the new book by Ideta***. According to Rein, the dwarf growth is secured by choosing 144 smallest pots until they are root-bound ; then transplanting into a large pot, in which the root crown is raised up above the pot in order that the root ball may have full benefit from the soil. After the year of transplantation, wide annual rings are produced at first, which become narrower as the plant be- comes root-bound until the growth has become very slight and the last annual ring formed is made up of a few, browned autumn-wood tracheids. In this way the stilt-like trunk bases, borne on the freely exposed root branches, are produced. The crown is probably kept thick by a light cutting back of the tips of the branches, obtaining thereby a greater ramification. In the same way the root balls might have been pruned at each transplanting. We conclude from the porous places filled with full-cork, which occur scattered in the bark, that the trees have been kept wet. At any rate we would have no difficulty in growing trees in such decorative dwarf forms from the genera Thuja, Thujopsis. Biota, Cupressus and similar ones by limiting the soil content. A corresponding treatment is recommended here and there for de- ciduous trees and plants. In forcing woody blossoming plants it is desirable to have for sale small specimens as full of bloom as possible. To attain this end, the bushes are planted in small pots, cut back and kept until spring, as long as possible, in cool dark cellars in order to retard the growth beyond the natural time of awakening. Ice cellars serve best in this connection. When vegetation has advanced considerably out of doors the plants are brought out. They now find a very dififerent combination of vegetative factors for the maturing of their growth. Instead of moist spring air, a comparatively slight warmth of the sun and long, cool nights, the plant finds dry, bright, long days with little precipitation. As a result the branches re- main short and the eyes easily develop blossom buds. It will not be out of place to call attention to the fact, that in keeping the bushes in warm cellars, an opposite result is obtained, — namely, abso- lute unfitness for forcing. The warm, dark place where they are kept pro- duces deformed, very premature shoots, which, when brought at last into the open air, either dry up or gradually and slowly lengthen to whip-like, blossomless wands. The stored-up material has been wasted in the cellar in forming the deformed shoots. especially small seeds from under- developed plants. These little trees are prun^ed and transplanted frequently into as small pots as possible. The cross-section described above in the text shows this. Further, the trunk and branches are twisted and bent toward the horizontal. It is said that the root ball is cooled. Among- varieties of plants used especially in .Tapan for the growth of dwarfs are mentioned the tov varieties of Acer p^lmatum, which are budded, "greffe par aporoache." Further Pinus massoniana and P. densiflora, Podocarpus Nageia, Sciadopytis verticillata. Among fruit trees the Kaki plum. Diospyros Kaki, is suitable for this, the Mume-plum. Prunus Mume and Sakura, Prunus Pseudocerasus, as well as Amygdalus Persica. Among decorative plants are mentioned Evonymous Japonica and the bamboo. * "Zwergbildung- im Pflanzenreich" Gartenwelt, 1904, No. 49. ** Rein, J. J., Japan nach Reisen und Studien. Leipzig-, Engelmann. Vol. II., p. 315. *** Ideta Arata, Lehrbuch der Pfianzenkrankheiten in Japan. 3rd Ed. Tokio, Shokwa.bo, 1903. 145 The most frequent occurrence is dzvarfing due to scarcity of zvater. Like every other organism, the plant has the abihty of adjusting itself with- in wide limits to dififerent conditions. An individual, accustomed from its youth up, to a very scanty amount of water, can pull through with half the amount of water used by a plant of the same species and variety, which had developed with excessive water. Naturally the structure of the whole in- dividual is adapted to these conditions. More thorough investigations have been made with barley^, which was cultivated with a varied water content in the soil (lo, 40, and 60 per cent, of the soil's capacity for absorbing water). The most favorable water content for growth might be found possibly be- tween 50 and 60 per cent, of saturation. In the experiment it was shown that the plant even with only 10 per cent, of water had regulated its organization. Little leaf and root substance had absolutely been formed, but the proportion between grain and straw was normal ; therefore about as much dry substance in the form of grain as in the form of straw. With the same amount of food in the soil, the dry substance increased as the roots obtained additional water. With too much water, i. e., more than 60 per cent, saturation, very little dry substance was produced absolutely and this small amount was worthless since the pro- portion between straw and grain was changed, — to the detriment of the latter. Measurement of the leaves showed that the grains grew longer and wider, when water was supplied regularly and more abundantly. These larger leaves, found with a greater water supply, are due partly to the in- creased number of cells, partly to their greater distention. If the individual cells of the upper epidermis are larger, it may be assumed from the very beginning, that the respiratory apparatus (the stomatal cells) will share in the greater stretching of the upper epidermal cells and will also appear to be the more widely separated thereby. Direct measurement confirmed this assumption, so that therefore for each square centimetre of a leaf grown with abundant water, fewer but larger stomata will be found, than when plants are grown with a scarcity of soil water. H. Moller has determined by experiments- that plants dwarfed by lack of water (Nanism) are structurally different from plants whose dwarfishness is due to a scarcity of mineral substances in too weak solutions. In the latter the narrower leaves are probably not due to narrower cells, resulting from water scarcity, but to a smaller number of cells, since measurements show the same cell breadth and the same size of the stomata in plants from a satisfactory nutri- ent solution and from an insufficiently concentrated one. These differences are easily explained. When the mineral substances are insufficient the cell increase will suffer only from water scarcity. The cells are less distended. As shown by some of Moller's experiments with Bronius mollis, this nanism is not hereditary, since specimens of huge size can be grown from the seed 1 Sorauer, Einfluss der Was.serzufuhr auf die Ausbildung- der Gerstenpflanze. Bot. Zeitung- 1873, p. 145. - H. Moller, Beitrage zur Kenntnis der Verzwergung (Nanismus), Landwirt- schaftliche Jahrbiicher von ThieL 1883, p. 167. 146 of dwarf plants. Yet, with equal vegetative conditions, seed from normal plants produces more vigorous specimens than that from dwarfed plants. The case of nanism due to scarcity of nutritive substances, which Moller studied, is not rare in sandy soils. The lack of nitrogen plays the chief part here. This nanism is usually characterized by the fact that, be- sides the general reduction, the relations of the separately produced organs have been changed. In proportion to the whole growth, the root undergoes a greater distention ; but the sex organs sufifer a greater retrogression. The number of blossom eyes is very small. Instead of a cluster or a head, there is often only a single blossom. Where a greater number of blossoms are formed single seeds develop which can germinate. It is easy to understand that the leaf-forms are simplified. In discussing dwarf growth, the phenomena of bud var'mtion must be considered. These have no connection with soil conditions or other external vegetative factors. The form of growth up to this time is so changed by some impulse or stimulus, acting temporarily or persistently, that the organic substance is used up in the form of more numerous, shorter, usually thicker, short-leaved branches instead of fewer slender, large-leaved ones, in this way producing witches-brooms. In many cases the incitement to such a changed direction of growth may be found in parasitic attacks. The fungus genus Taphrina (Exoascus) especially irritates the branches of various deciduous trees resulting in the formation of witches-brooms (see Volume II, page 179). In other cases we find rust fungi or mites of the genus Phytoptus. Besides these forms due to parasites, however, some surely exist in which other organisms are not active. We find especially in her- baceous, quickly growing plants (Campanula, Pelargonium) the occurrence of a bud disease (Polycladia) as a correlation-phenomenon. In sickness or loss of blossoming branches, small fleshy bunches are formed, at times, at the base of the stem, made up of closely set bud-eyes, some of which grow out into sickly branches. In diseased thickets growth is often exhausted by a continued new formation of short branches, because the blossoming axes no longer lengthen, but stop growing and turn yellow. In Callima vulgaris, instead of long blossoming branches, we find blossomless bunches of twigs, pyramidal in form, which might also be called witches- brooms. In other cases polycladia and bushy forms are produced by the develop- ment of normally formed but still dormant lateral eyes, when the buds of the tips have been injured. This takes place when wild growths choke out cultivated ones. In conifers, the heart buds grow out and form bushy crowns, which are called "rosette-grozvths." The so-called "cozv-bushes" — due to injury to beeches, alders, etc., from the grazing of cattle, are similarly explained. Pure bud variations are numerous. In them the growth in length of the individual branches is restricted without any recognizable cause, result- ing in a greater and more rapid development of lateral branches. Among 147 the actual forms of witches-broom, the tendency at present is to place under this head of bud variation the numerous spherical bushes of the spruce witches-broom\ The greatest number of examples is furnished by the many cultivated plants of our gardens in the so-called globe forms of coni- fers and in the dwarf forms of blossoming bushes. In the short-lived sum- mer plants (Ageratum, Zinnia, Tagetes, etc.) we find that the dwarf growth can become an hereditary peculiarity, persistent in the seed. Too Thick Seeding. A limitation of the soil space and a struggle for water and nutritive substances is always produced by too thick seeding. The struggle of the plants with one another for their food appears earliest and sharpest in sandy soils. Besides the dwarfing of individual specimens, the weakening of repro- duction deserves especial consideration. This becomes evident not only in the decrease of the blossoms, but also in the change in their character and becomes especially perceptible in horticulture, because staminate blossoms are produced predominantly. The unavoidable scarcity of nitrogen is also a factor. The greater the amount of nitrogen supplied, the more abundant the meristem, rich in cytoplasm. Hofifmann- gives the results of many cultural experiments in pots and open ground, to determine the influence of too thick seeding for dififerent plants. In this, for every lOO pistillate blossoms there developed the follow- ing number of staminate ones : — With a more seat- In With Too Thick Seeding, tered position of the plants. Lychnis diiirna 233 125 " 200 77 " vespertina 150 73 M ercurialis annua lOO 90 Rumex Acetosella 152 81 Spinacia oleracea (average of several sowings) 283 76 In Cannabis his results were contradictory, which may be explained by a consideration of Fisch's statement^ that the proportion of the sexes in hemp is already determined in the seed, — that, therefore, external in- fluences can bring about no further changes. Belhomme maintains that the form of the hemp seeds admits of conclusions as to the sex of the future plant, since the longer or the more spherical form, as in bird's eggs, indicates a staminate or a pistillate individual. Since the phenomena appearing with too thick seeding may be traced essentially to scarcity of food substances, further examples will be cited when the scarcity of nitrogen is discussed. 1 Tubeuf and Schroter, Naturwissensch. Zeitschr. f. Land- u Forstwirtschaft. 1905, p. 254. 2 Hoffmann, H., Ueber Sexualitiit. Bot. Zeituns". 1885, No. 16. 3 Fisch, Ber. der Deutsch. Bot. Gesellsch. 1887. Vol. 5. Part 3. 148 2. UNSUITABLE SOIL STRUCTURE. a. Light Soils. Disadvantages of Sandy Soils. The way in which the individual soil particles are related to one another, is termed the structural condition. If the constituents of the soil are simply laid one above the other in separate grains we speak of a separate granular structure. In soils under cultivation, however, the individual soil particles are found united into different kinds of aggregates, called a friable structure. While, in the first case, each soil grain has a homogenous constitution, the soil grains in the second case are porous and not homogenous, therefore can be more easily transformed. The content in soluble salts, the activity of the animal world in the soil and the action of plant roots and their se- cretions, as well as the physical processes of working the soil, determine the formation of a friable structure. The amount of space between the indi- vidual grains will vary according to their size and arrangement. Ramann calculates the porosity volume of equally large soil particles, according to whether the particles are arranged regularly in rows on top of one another or between one another, as fluctuating between 47.64 per cent, (greatest porosity) and 25.95 P^^ cent, of the whole volume (closest stratification)^. While in the friable structure, because of the different individual par- ticles, a continuous change in size and arrangement takes place, due to me- chanical and chemical influences, in the separate granules, most distinct in stony and gravelly soils, the physical relation is more regular and therefore more significant. We have already spoken of the influence of actual sandy soils and the changes which roots can experience when growing in cracks in rocks. The injuries to vegetation, which are caused by too loose a structure of stony soil at the disposal of the root, seem lessened when the blocks of stone are weathered to rubble. Fine, earthy particles are produced, especially when the stones are easily decomposed (many granites, Gneiss, Syenite, etc.) af- fording the roots more abundant food and firmer support. Next to the great possibility of being rapidly heated through, the factor acting most injuriously is great dryness, which prevents a decomposition of organic substances lead- ing to the formation of humus ; this, under certain circumstances, forms moors. Forestry in mountains must take such conditions into account. Sandy soils come under consideration for field cultures on the level. As soon as these possess greater admixtures of clayey substances (loamy sand) or of humus, they form most productive soils and therefore find in this discussion no further consideration. Sandy soil is unfavorable for cultivation only when the sand is truly quartz sand and is either pure or is present in a very high per cent. (70 to 90 per cent.) 1 Ramann, Bodenkunde, 2nd. Ed., p. 222. Berlin, J. Springer, 1905. H9 In such cases, the slight absorptive capacity should be mentioned first of all as a hinderance to cultivation. The diseases caused by scarcity of water and food substances are pre-eminently peculiar to sandy soil. The more clayey and humus admixtures present, the more the danger disappears, in so far as it is not brought about again in another way by the washing away of considerable amounts of easily soluble mineral substances. Such an erosion takes place much the more quickly when the decom- position of organic substances, which occurs easily under the influence of warming and aeration, is increased by other conditions. On this account one must be especially careful in removing forests and litter. In deep, sandy soils, the removal of the litter holding its moisture is disadvantageous since the organic substances present are but very little decomposed by atmospheric influences and bacteria, and accumulate as raw-humus, which can finally give rise to the formation of meadow ore. According to Ramann, in lower positions the deposition of raw-humus gradually leads to complete marshi- ness, as in the large moors of North Germany, which almost without excep- tion have originated from land which at one time was covered by forests. The humus is beneficial only when mixed with sand, since the friability of the soil and its water content is increased and its capacity for heating re- duced. This capacity for heating and giving off heat of sandy soils is an essentially harmful quality. Pure sand possesses the greatest capacity for giving ofif heat and consequently the greatest capacity for becoming wet with dew. The process of taking up and giving off heat decreases as the sand is finer grained and whiter. Sand of the latter kind, for example, is that rich in calcium, while, of colored sands, the ones rich in iron hydroxid are very warm and cool ofl: slowly, behaving therefore like sand mixed with some clay. Associated with the great fluctuations in temperature peculiar to sand is the poor capacity for conducting warmth. As a result of difficult equali- zation its subsoil has a more even temperature, since it is warmer in winter and cooler in summer than under more binding soil coverings. The danger from frost is increasedly greater and more injurious. The rapid warming in spring days forces vegetation prematurely and the great drop in tem- perature at night is injurious, while the plant would be uninjured if it started later in a soil containing water and rich in clay. The sandy soils of fine constitution and slight coherence present the greatest possibilities for injury to crops. The injurious effects of drifting sand are shown in the sand dunes. Even if the dunes reduce the severity of the sharp sea winds for plants near the coasts, they are nevertheless injurious since they advance further and further inland, covering all plants. The inability of the land breeze to blow back during the night the sand which the sea breeze has swept over the land by day is due to the fact that the land breeze is heavily laden with dew and tends to compact the sand again. If the danger of being covered with sand threatens and artificial protection is 150 too expensive, one must try to bind the movable sand hills by some natural method. Sand grasses are here most valuable, since, by the rapid root de- velopment of the nodes of the buried stolens, they constantly advance over the upper surface and bind it together. Arundo arenaria, L. and Elynius arenarius L. are most frequently used. Besides these, Arundo baltica Schrad, and Carex arenaria L. should be recommended, and, with sufficient moisture, even our quack grasses as well. Among the dicotyledons, Hip- pophae rhamnoides, L. is \try good. Depending upon the admixtures in sandy soil, experiments may be attempted \vith Salix arenaria L., Lyciuni bar- harum, L., Ulex europaeus L. and the lime-loving Genista species. No matter whether we are concerned with sandy soil in the interior, as in the Mark Brandenburg, Oldenburg and Hanover, or with the sand of dunes, the first planting must always take place with the idea of binding the sand with low, rapid growing vegetation. Where nature, in the course of years, has spread out a' thin vegetative covering, this should be protected by every possible means, since, in it, we have a basis which cannot be valued highly enough for the ultimate aim of all cultural endeavors, viz., to obtain a protective forest. Even if the vegetation is ever so thin, it still restrains the sand and makes the planting with young conifers possible. With their deeply growing roots they are better satisfied with poor nutritive conditions. In the beginning attention should be paid to the production of a bushy growth and only later extended inland to the cultivation of tree forms. At the sea shore, on all woody plants, a great many branches will always be found which have been killed back by the action of the wind. The most important cultural method is to leave these dead branches on the plants. They break the force of the sea wind and form a natural protection, keeping the foliage alive. Lowering of the Ground Water Level. The building of canals and the regulation of rivers tend to lower the water level in sandy soils and act most disasterously on plant growth. In contrast to the "soil moisture" of the upper masses, the ground water trickles down in the depths, collecting on the impenaous soil layers and forming the reserve supply for roots in times of continued drought. In regions like the Alpine provinces and the Bavarian plateau, which have a high absolute amount of precipitation and smaller evaporation, the fluctuations of the ground water level controlled by the annual precipitation are of scant significance for vegetation. In regions, however, with scanty absolute amounts of precipitation, and great evaporation, where the annual fluctuations of the ground water level depend on the amount of evaporation, as, for example, on the flat lands of Northern Germany, and where the reg- ular slope of the ground water curve indicates a gradual flowing away through springs and rivers (see Ramann loc. cit. 275) a lowering of the water level by canals and rivers will have the most serious influence. The soil dries out very greatly towards the autumn and vegetation becomes de- 151 pendent on the water of capillarity. This becomes scantier and scantier, the sandier and coarser grained the soil. AA'ithout the supplemental gromid water tree growth cannot persist. If, in the course of years, the level of the ground water fluctuates a half metre in average height the plant growth will adjust itself to the change when an equilibrium has been reached. Both the water content and the water requirement of plants are correlated with the soil moisture, as Hedg- cock's^ comparative cultures in quartz sand, loam, salt soil, humus, etc., show. Root activity depends also on the water content of soil and plant and this activity is by no means passive but, as Sachs- and more especially Mohsch^ have shown, is essentially active because the secretions of the roots decompose the inorganic and organic substances in the soil. The last named investigator calls attention, in this connection, to the circumstance that un- injured roots, in contact with a dilute solution of potassium permanganate, become covered with a precipitate of brown stone, removing the oxygen from the solution. The experiment is unsuccessful with stems and leaves. With easily oxidizable bodies, as, for instance, guaiacum, pyrogallic acid and humus, the root secretion acts as an oxidizer. A guaiac emulsion is turned blue by it. Molisch considered the root secretion to be a self-oxidizer by passive molecular oxygen, thereby making the oxygen active and bringing about the oxidation of substances which are readily oxidized. In the presence of tannic substances (pyrogalHc acid, gallic acid, tannin,) which are more easily oxidized than the guaiacum, the blue color does not appear. In the same way it is absent in the presence of rapidly oxidized humus sub- stances. When absolutely uninjured roots were dipped into dilute cane sugar solutions, a reducing sugar became evident after some hours — probably this transversion is caused by a root-ferment. Starch paste, put on the growing roots of seedlings, did not give the starch reaction after a few hours, but w^as turned a reddish violet by iodine. The starch on touching the roots had been changed to erythro-dextrin and was soluble, passing over into the reducing sugar. The root secretions, perceptible on the tips of the root hairs, not only impregnate the membranes of the cells but can pass in the form of drops into the deeper tissue of the roots when much water is suppUed and trans- piration reduced. They can erode minerals with their acids (they turn blue litmus red) and decompose organic substances. This action of the roots becomes less with increasing dryness. Roots, accustomed to a wet place, when brought into a dr}^ one, do not absorb as energetically even after water has been supplied, if the plant has been wilted, as if it had not been wilted. Hedgocock thinks that the root hairs actually die. 1 Hedgcock, G. G., The relation of the Water Content of the Soil to certain Plants, etc. Botanical Survey of Nebraska. VI. Studies in the Vegetation of the State. 1902. 2 Experimentalphysiologie p. 189. Bot. Zeit. 1860, p. 188. 3" Molisch, H., Ueber Wurzelausscheidungen und deren Einwirkungen auf organische Substanzen. Sitzb. Kais. Akad. d. Wiss., Wien, Section I, October, 1887. 152 The production of carbon dioxid forms a measure of the energy pro- duced by a root in raising water, boring into the soil and other life-functions. Kossowitsch has furnished quantitative determinations on this points He found that mustard plants in water cultures assimilated about three times as much carbon for the life processes of their roots, as was necessary for the formation of the roots themselves. The strength of the root activity, especially in lifting water, might de- pend also on the differences in temperature between the atmosphere and the soil. The greater this difference, the more energetic the work done. MacDougal's- experiments in the New York Botanical Gardens prove how great such differences may be. He found in June, that the soil temperature at a depth of 30 cm. was at times 20°C. lower than that of the air. Naturally the water content of the soil here becomes a decisive factor and the differ- ences decrease as the soil becomes drier and more accessible to the air. The moisture holding capacity and, in sandy soils, the amount of production will depend, in the same soil, on its granular structure and will be the greater as the sand is finer grained. Livingston and Jensen^ experimented on this subject. They cultivated different plant species under similar conditions, in soils which contained admixtures of different sized quartz grains in the different experimental series. It was shown that the best growth always occurred where the quartz sand was very fine. By means of the above observations we get an insight into the distur- bances which must take place, in the activity of the roots, if the water supply of a region is less, because the ground water level has been lowered. An old tract of trees survives, because part of the deep growing roots reach the ground water level and are able to compensate the loss by evaporation of the tree crowns, when the soil water is reduced to a minimum during periods of extended dryness. The roots lying in the earth, permeated by the ground water, are adapted to these conditions. When these roots are per- manently exposed to drought they are destroyed or function feebly. Not only the economy of the tree suffers from the insufficient water and food supply, but even the soil itself, since, entirely aside from the paralysis of bacterial activity, the secreting ability of root hairs and tips affecting the decomposition of the soil also ceases. The soil becomes "lean" and the trees begin to show dead branches in the periphery of their crowns. Since parasites settle on dying parts completing the destruction of the tissues, this blight of the tree tops is explained in the majority of cases as a purely parasitic disease and treated as such. 1 Kossowitsch, P., Die quantitative Bestimmung der Kohlensaure, die von Pflanzenwurzeln v^^ahrend ihrer Entwicklung ausgeschieden wird. (Russ. Journal f. experim. Landwirtschaft, 1904, Vol. V, cit. Centralbl. f. Agrilculturcliemie, 1905, Part 6, p. 367). 2 MacDougal, D., Soil Temperatures and Vegetation. Repr. Monthly Weather Review for August 1903, cit. Just, Bot. Jahresb 1903, II, p. 557. 3 Livingston, B., and Jensen, G., An Experiment on the Relation of Soil Physics to Plant Growth. Bot. Gaz. Vol. XXXVIII, cit. Bot. Centralbl. 1904, No. 50, p. 617. 153 The Dying of Alders. Alders are most sensitive to a lowering of the ground water level and it is easy to find diseased tracts of alders near newly cut canals or regulated river beds. In the works of the Royal Biological Institution for Agriculture and Forestry at Dahlem, near Berlin (1905), AppeP has published a study of the death of alders well worth consideration. He found on the dying branches a species of the genus Valsa known to attack diseased or dead branches, — namely, J^alsa oxystoma — and stated that the fungus is parasitic only when the alders become susceptible, owing to abnormal circumstances. Drought is the chief determinative factor. Other disturbances in nutrition (injury to the roots, girdling, etc.) can also create a predisposition to fungus attacks but, if the alders are enabled to make a healthy growth, the disease disappears. When alders are found dying on apparently moist, imperme- able, ferruginous soils, drought may be considered to be the cause. On such soils, the alder spreads it roots only very superficially and in continued dry weather there is a very marked scarcity of water in the upper soil layers, which at once makes the alder foliage wither and drv^ The beautiful tracts of trees in the Tiergarten in Berlin, especially the oaks, unfortunately show similar results from surface drought, and to an ever increasing degree. Naturally canal and river bed regulations do not always necessarily cause the lowering of the ground water level. In the old Botanical Garden in Berlin, for example, the building of the subway dried up the water in the ponds and as a further result the tree crowns rapidly became blighted. In other instances we found that the spread of brick-paving and clay- diggings near forest tracts accelerated the death of the alders because the deep clay pits had withdrawn water from the forests. The dangerous effects of lowering the ground water level often fail to impress us sufficiently, since, in some tracts of woodland, the same tree species (suffering from blight of the crowns in soils from which the water has been removed) thrive in very dry places. Under such circumstances the fact that the lack of water in itself does not cause the death of the trees, but the abrupt transition from a previously well-watered condition to great drought in the deeper layers of soil is overlooked. We may plant all our trees in very dry soils and the individuals will adapt themselves to the existing vegetative factors and the leaves will become small and coarse, the internodes short. But a sudden great change in this condition will have most serious results. If, however, such changes are unavoidable, our theory gives only one line of action to preserve the plantation, — namely, to plant young trees between the old ones. These will adapt themselves to the changed vegetative conditions. Street Planting. The preservation of trees along the streets and small parks is of the greatest importance for the hygiene of cities. The greatest injury results 1 Vorlauflg'e Mitteilung in d. Naturwiss. Zeitschr. f. Land- u. Forstwirtschaft. 2 Jahrg. 1904. 154 from the present methods of street paving which fill the spaces between the stones with a binding material, and even at times the asphalt covers the soil entirely. The injury to the trees is two- fold; on the one hand, the air is cut off, on the other hand watering is insufficient. This affects the older trees principally. For young trees, the circle of sod around the tree is sufficient, especially if an iron grating laid over it prevents passers-by from tramping the soil. We find that old trees die much more quickly when a regulation of sidewalks and a lowering of the ground water level is com- bined with street paving. In large cities another factor must be added, i. e., laying pipes for gas, electricity and sewers. In all this work, the chopping off of the larger root branches is unavoidable. Therefore, the root space is not only limited by the pipes, and the soil dried, but also the trees' organs for the absorption of water are decreased. To this cause may be ascribed the gradual break up of old trees as shown by the dying branch tips. Different varieties of trees suffer in varying degrees and the linden, a favorite and most frequently planted species, is among the most sensitive of varieties. In it the dryness of the soil, with which is associated also dryness of the air, is expressed by a premature defoliation. The large leaved linden suffers more quickly than does the smaller leaved variety, and it is a well known phenomenon, that, in the summer months, when the in- habitants of the city want shade most, the linden and chestnuts often for some time have leaves only on the outermost tips of the branches. The older leaves, covered with red spider, have dried up and fallen. The city adminstration endeavors to overcome this condition by abundantly watering the ground about the tree thereby favoring a second leafing out in the late summer, which is produced even without artificial watering when the trees have lost their leaves prematurely. In this buds are forced to unfold which should develop in the following year ; under such conditions a second time of blossoming is also often produced (Aesculus, Robinia). Many of the shoots artificially produced by this watering do not mature sufficiently and are injured by frost. Thus in different years, in the middle of the favorable early summer, the twigs die off accompanied by fungous infection. The winter, therefore, did not kill these less mature twigs, but made them susceptible to fungous attack, thus giving the primary cause for later death. This theory also explains the death of the cherry trees along the Rhine, which has occupied the attention of investigators during the last few years^ A Valsa (J'\ leucostoma) plays a part here as in the case of the alders. We will return to this case in the chapter on injuries due to frost. Such bad conditions in street planting may be avoided by a choice of less sensitive varieties. First of all, the elm should be recommended as such ; this has the added advantage of being very resistent to the acid gases of smoke. Also oaks and plane trees are used with advantage according to the kind of soil present. In broad, airy streets Acer platanoides also 1 Cf. Deutsche Landwirtschaftl. Presse 1899, Nos. 83, 86, and 1900, No. 18. 155 thrives well, but suffers often from honey dew. The Robinise, especially the so-called ball acacia, retain their foliage well even in great drought, but offer only a little shade and put out their leaves late, usually losing them early in autumn. Therefore, when Robinia is planted, arrangements for watering should be made, in which drain pipes perhaps Yi metre below the pavement are put at the distance from the trunk where the newer roots lie. These pipes can be .filled Mdien necessary from hydrants. However, atten- tion should be called to the fact that watering through drain pipes can be used only in the hot summer months, because otherwise there would be an excess of water in the soil with much more disasterous results than those due to a scarcity of water. Finally, we think that a sprinkling of the tree crown at night should be recommended especially where watering may be carried out only through the ground about the tree. We must emphatically state that watering by means of water drains can be recommended only for light soils with a permeable subsoil. By constantly watering heavy soils with a large water content, the soil will be- come baked and compacted, resulting in a scarcity of oxygen and an excess of carbon dioxid as elsewhere described, which combination will bring about the decomposition of the roots. Mangin's^ studies will be cited here as a single warning example. He worked especially on the meagre growth of trees in city plantingf and found the soils choked to such an extent that the carbon dioxid content of the soil air increased from i to 5 and 8 per cent, and even to 24 per cent., while the oxygen content fell to 15, 10, 6 and even o per cent. As a matter of course all the trees with such an environment will die. (Compare "Too deep planting of trees," p. 98.) Effect of Drought on Field Products. The results of continued scarcity of water, felt most cjuickly in sandy soils during great heat, are determined naturally by the time the dry period begins. If it sets in in May, as in 1904, i. e., when growth is most rapid and the activity which should furnish the material for maturing of fruit is re- duced, the effect is most serious. In grain, sowing of summer seed suffers most under our cultural con- ditions, when planted at the usual time. This is easily understood when we consider that winter seeds sown in the autumn can, during the whole autumn and the early spring, fully develop their roots and obtain a sufficient formation of shoots. They thus utilize the undisturbed activity of their lower leaves. In this way the winter seed meets the dry period in a strong and well-prepared condition, while summer seed, even where it sprouts normally, enters upon the hot, dry period at a much younger developmental stage. Accordingly the leaves ripen prematurely, their period of work is therefore more limited and even if the plants develop blossoms and the ovaries, comparatively little organic matter is present for filling out the 1 Mangin, L.., Veg-etation und Durchliiftung des Bodens. Annal scienc. agro- nom. 2 set-. 1896; cit. Centralbl. f. Agrikulturchemie, 1898, p. 638. 156 grain. The endosperm is only scantily filled with starch ; the grains slender and light. A second injurious effect is the shortness of the straw. This appears especially in summer oats, which on light soils have red stalks and grow scarcely a foot high, maturing only a few small heads instead of the full ones. Barley shows less injury, wheat comes next and finally rye, the most resistent. If the dry period makes itself felt as early -as seeding time, the plants come up late and unequally. This leads to a double growth, i. e., to a very irregular maturing of the grain. At the time of harvest many green blades are found among the ripened ones. The former come from the seeds which were left on top at the time of sowing, and which at first did not start, while those more deeply placed fotmd moisture enough for a speedy germi- nation. In this, limited local conditions often become effective. Thus, for ex- ample, one early crop may have drawn more water from the soil than an- other, or a potassium fertiliser is irregularly distributed and keeps the soil more moist in the spots where it has accumulated. The whole development of the plant is also changed by this. I found under otherwise equal conditions that the root shortened when the concentration of the nutrient solution in- creased and the plant's need for water became less. This is of great signifi- cance in soils imperilled by drought. In the cultivation of sugar beets and all vegetables, grown as seedlings in small spaces and then planted out in the field, the dryness of the soil makes itself felt most of all by preventing the growth of the seedlings since no new roots can be formed in dry soil. Next under consideration is the drying of the foliage, which stops the development of the beets. Experience teaches^ that, as with grain, zvell fertilised fields survive drought better. Varieties also show differences in this regard. It has been observed that varieties of sugar beets with outspread leaves wilt more easily than do those with erect petioles. The influence of long continued drought on potatoes shows more in its effect on the maturing of the tubers than upon their setting. The tubers remain small and ripen prematurely. As a rule, this premature ripening of early potatoes is of less consequence economically because they are adapted by nature to a shorter vegetative period and because, in the second place, they are rapidly consumed. Only the premature ripening of the later varieties is disasterous, because the tuber has a small content of starch and its keeping quality is much impaired. Leguminoseae suffer greatly from continued drought when they are grown for fodder. Clover and alfalfa burn out in spots or the second crop fails. The most frequent results with fruit trees are the premature ripening and poor keeping quality of the fruit and premature defoliation. 1 Jahresberichte d. Sonderausschusses ftir Pflanzenschutz. Deutsche Landw. Ges. 1904. 157 Among the special forms of injury which can set in during long con- tinued, intensive drought, especially in light soils, one especially deserving more thorough discussion is The Effect of Drought Upon Germination. When the water scarcity occurs after the seed has passed the first stages of germination, the results are less serious, if dry seed has been sown on open ground than if seed previously soaked has been used. These dis- advantages affect the development of the young individual in varying de- grees dependent upon the kind of seed and the age of the seedlings when the drought takes place. According to Will's repeated experiments^ with seeds of monocotyledons and dicotyledons, the seeds of the former seem in general to be somewhat more resistent. The cereals without glumes (wheat and rye) are very little sensitive to a period of drought, if it occurs during germination. Barley and oats, however, are injured more easily, and the horse-tooth maize has very little power of resistance. Saussure- found that maize, beans, poppies and garden campion are very susceptible to drought during germination. Nowoczek'' in his experiments repeatedly in- terrupted the supply of water, until the power of germination of the seeds was quite lost, and found that the seeds of grains resist the changing con- ditions of moisture and drought better than rape, flax, clover and peas, which lose their germinating power earlier, but even after a period of drought these seeds can be revived. Experiments on the Gramineae showed that after each drought period the fibrous roots, already formed, died, and the outermost leaves dried up, but that, when water was again supplied, new adventitious roots were formed from the first node (see Vol. I, p. 102) and the last leaves developed further. This statement applies especially to oats and to a greater or less extent to barley, wheat and maize. It should be considered as universally well-established that soaked and then carefully dried seeds, when put again into water take it up more quickly than do air dry, non-soaked seeds of the same size. Such seeds in fact germinate a few days earlier. Tautphous* and Ehrhardt^ made experiments giving results which were expected at the start,- — viz., that plants suffer so much the more, the further germination has advanced; i.e., the more developed the plumule is when the drought begins, the greater the damage. Will found the seed of peas in part especially sensitive to dr3dng out. The testa was broken by many small cracks in most cases reaching into the inner layers. With re- peated soaking, the palisade layer was broken into unequal pieces, the 1 Will, Ueber den Einfluss des Einquellens und Wiederaustrocknens auf die Entwicklungsfahigkeit der Samen. sowie iiber den Gebrauchswert "ausgewach- sener" Samen als Saatgut. Landwirtsch. A^ersuchsstationen XXVIII, Parts I and 2 (1882). 2 Annales des sciences nat. Bot. 1S27. Janv. 3 Ueber die Widerstandsfahigkeit junger Keimlinge. Wissensch. prakt. Unter- suchungen etc. von P. Haberlandt, Vol. I, p. 122; cit. Biedermann's Centralbl. I, p. 344. 1876. 4 Freiherr von Tautphous. Die Keimung der Samen bei verschiedener Be- schafCenheit derselben. Miinchen 1876; cit. Bot. .Jahresber. 1S76, p. 882. 5 Deutsche landw. Presse, .Tahrg. VIII, No. 76; cit. von Will, 158 testa became slimy and shortly decomposition set in, affecting the cotyle- dons, which hindered the development of the seedlings. The production of these cracks is due to the increase in volume of the seeds, when soaked, to more than lOO per cent.^ This produces a pressure on the testa and dis- tends it, making it porous. This porosity can lead with dr}-ing even to' rupturing. Through these cracks in the testa, the embryo, when moistened a second time, gets much more oxygen for the food-reserve already be-, ginning to decompose, and also large Cjuantities of water are more c}uickly absorbed. Further, the dissolved organic materials are transferred more easily osmotically. These may act unfavorably on further development. A testa slowly and equally distended, remaining uninjured, will there- fore probably more completely utilize the reserve substances of the cotyle- dons and perhaps indeed force the fluids into the tissue of the cotyledons and the dissolved reserves into the embryo by the turgidity produced by soak- ing. We cannot enter here more closely into the enzymes occurring in ger- mination and their action, but refer in this connection to the works of Newcombe- and Griiss^. From these experimental results it can be safely asserted that the use of seeds, which have been soaked until germination has started and then dried off, should be avoided. I am also of the opinion that soaked seed is to be used sparingly every time especially in dry regions. In the first place, in dry regions, the conditions already brought about artificially by drying soaked seeds can be repeated most easily in nature by continued heat and drought and act much more injuriously than if the seed, in such a condition, lay ungerminated in the soil. In the second place the plants become ac- customed from the beginning to an excessive water supply. The tissue be- comes more porous, richer in water and, requiring more moisture, dries up much earlier with the occurrence of great periods of drought than if the plants had developed with a scanty supply of water. The evaporation in the former condition is greater than in the latter. On this account, growers often follow the rule that for vegetable plants developing rapidly (cucum- bers, beans and cabbages) watering must not be discontinued, if the plants have had abundant water when young. I have often found that plants from soaked seeds are less thrifty than plants grown from the same seed which had not been soaked, but which depended upon the natural moisture of the soil. Treatment of Tree Seeds. If the germination of tree seeds is interrupted by drought, the results are very disasterous. This is felt most in planting trees whose seeds retain their germinative power only a short time. Nobbe* found that the seeds of 1 Nolibe, Handbuch, p. 122 - Newcombe, F. C, Cellulose-Enzymes. Annals of Botany 1899, No. 49; cit. Bot. Jahresb. 1899, II, p. 179. 3 Griiss, J., Beitrage zur Enzymologie. Berlin 1899. Festschr. f. Schwendener, Ueber Zucker- und Stiirkebildung: in Gerste und Malz, III u. IV. Wochenschr. f. Brauerei 1897, 1898. 4 Dobner-Nobbe, Botanik f. Forstmanner. 4tli. Ed., 1882, p. 382. 159 willows lose their power of germination in 5 to 6 days after they have been blown from the parent tree. The seeds of poplars and elms are also proved to be very short lived. Acorns and beech nuts, as a rule, are capable of germination only until the following spring. On an average, ash, maple and fir come under the same head. On the other hand, a large percentage of spruce and pine seeds germinate after 3 to 5 years ; however, the seedlings are apt to be less vigorous. The maturing of the seed and the care of it after it has been gathered are important factors. For example, Nobbe found that seeds of Pinus silvestris, which had stood in closed glasses in a living room, germinated after 5 years to about 30 per cent, and after 7 years, to 12 per cent. In fact, even after 10 to 11 years, individual seeds were still found capable of germinating. Under the same conditions, seed of Trifolhim pratense, after 12 years, germinated to 10 per cent., Pisum sati- vum, 47 per cent, after 10 years and in one experiment, Spergula arvensis 25 per cent., another year 67 per cent. It is stated that cedars and Italian pines (Pifion) have germinated after 30 years\ It is advisable to sow fine seeded conifers soon after ripening. The time of planting, whether summer, autumn or spring, is a question of practical importance. The summer is the most difficult season because the moisture fluctuates to a great extent in the soil ; therefore, with trees whose seed must be sowed immediately, as willows and poplars, propagation by cuttings will obviate this difficulty. Autumn sowing is much better and necessary with oaks, chestnuts, hazel nuts, etc. It is recommended for very hard shelled seeds like those of Crataegus, Prunus, Ilex, Sorbus, Rosa, Cornus, Berberis, Ribes, Carpinus, Staphylea, Clematis, etc. The last named kinds often do not germinate for 2 to 3 years, especially in sandy soils. Spring sowing is best because the danger of winter and all injuries due to animals are eliminated. In order not to lose the time between the autumn and spring, the seeds are placed in layers between sand, which is kept damp. This process is called stratification. The importation of seeds of prized decorative trees from their native countries has become a large business. It is important to know the loss of germinating power during transportation. Count von Schwerin- in the German Dendrological Society has called attention to the fact that maple varieties cannot withstand any long transportation, so that, for years, not one of the maple seeds brought from the Himalayas had germinated. Also, the seed bed should not be broken up too soon, since many seeds retain their vitality for a long time in the soil. Thus, for example, Chamaecyparis Laic- soniana often lies 4 years in the soil, especially in dr)^ years. For years, in the trade in Magnolia hypoleuca from Japan, either no seeds germinated or so few that the costs of transportation were not paid. The seeds dried during the journey. Y^ry encouraging results have been obtained recently by leav- ing these seeds in their fruit and packing them in powdered charcoal. 1 and - Ueber das Keimen von Geholzsamen. Der Handelsg-artner 1905, No. 14. i6o To the statement made heretofore that the seed of Acer retains its germinating power until the following spring, the qualifying statement must be added, that maple seeds of the Campestre group (Acer obtusatum, A. Italum, etc.), as a rule, germinate only in the second year. Only occasional seedlings may be found after the first year. In many botanical gardens, how- ever, trees of the Campestre series are said to furnish seeds usually germinat- ing early. The explanation of this is that in seeding in such places, the first seedlings are used for propagation. From this it may be concluded that the peculiarity of producing seeds, which germinate promptly, may be made constant by selection. This point of growing the earliest germinated seed- lings separately as seed bearers, when making large seedlings, might be recommended for the consideration of plant breeders. Blasting in Grains and Legumes. Under these circumstances the seeds do not mature since the plants do not have enough water. Such a condition of great drought is most often found on soils of a verv^ porous structure where evaporation is very great and the capillary movement of water from the subsoil is slight. Yet great scarcity of water will not always produce a blasting of the blossoms. This depends essentially, as Hellriegel's experiments with grains show, on the development of the plant when the water scarcity makes itself felt. If, following the experiments^, a grain plant has had only a scanty amount of water at its disposal, beginning at the time of its germination, it reaches maturity in a period of the same length, or perhaps somewhat longer, yet the whole growth is weak. The proportion of the harvested grains to the dry substance, however, is always normal ; i.e., approximately half of the dry substance is harvested in the form of grain. As in all vegetative conditions, there is here also a minimum ; if the water supply is kept below this, no product worth naming takes place. If great scarcity of water occurs immediately after germination begins, the grains remain alive for a long time (in the experiment up to six weeks) and later develop vigorously, when the water is supplied in abundance. A period of drought appears to be still less injurious if the grains are still in the milk stage, i. e., have reached their normal size, but have not finished their inner development and become hard. The work of the plant, which now forms no new dry substance, consists in transposing the sub- stances produced in the leaves to the storage organs, the seeds. In all periods of growth between sowing and ripening, a longer scarcity of water acts more injuriously the younger the plant is at the beginning of the drought. When the long drought sets in while the seeds are sprouting vigorously, the setback resulting therefrom cannot be overcome. The results of continued drought are the more severe, the more water the plant has had in its youth. If a plant has grown luxuriantly with abundant soil, up to the 1 Hellriegel, Beitriige zu den naturwissenschaftl. Grundlagen des Ackerbaues. Braunschweig. Vieweg 1883, pp. 589 to 620. i6i setting of the bloom, and then receives a check from a long drought, the grain is not set ; a greater or less extensive failure of the harvest takes place, which we may call the blasting of the grain. Ritzema Bos'^ experiments with "Maartegerst," or winter barley sown in March, are very interesting. A sowing was made on a field where autumn sown winter barley was frozen out. Only a few of the autumn sown plants came through the winter and produced stalks during the summer so that the same field produced autumn and March sown barley. The plants from the March seeding suffered dur- ing the hot summer from blasting, while the plants of the autumn sowing, scattered among them, bore a full harvest of grain. With us, besides grain, peas suffer most. Naturally in other plants as well, a failure of the seed harvest can take place, due to the blasting of the blossoming parts. Thread Formation in the Potato (Filositas). In this disease ("mules" — of the French) the eyes are deformed; from them grow slender, thread-like stems as thick as medium sized yarn. Not infrequently the eyes of tubers comparatively rich in starch did not sprout at all, or if they did, the sprouts were weak ; they are unable to break through even a shallow soil covering. The tubers decay usually with the appearance of dry rot, yet the disease has occurred extensively only where the soils, being easily heated, have to withstand long droughts. Fig. i6 shows the basal part of a cutting grown in a water culture from a potato affected by Filositas ; the proportions of the stem, leaves and tuber correspond to the natural size and it is seen that the stems actually are only as thick as a strong thread of yarn. The stolons {st.) are also more delicate and have formed tubercles {k) , some of which have lengthen- ed at the tip and grown out to green sprouts (h) or developed scale-like green leaflets {d). The cutting here reproduced came from an experimental culture, the results of which are given in precise figures in the second edition of this manual and lead to the conclusion that in the thread disease of the potato we have before us conditions of premature ripeninq zvhlch had become hereditary. Reports from the localities where the disease has occurred, especially from the March f eld near Vienna", of the cultural methods fol- lowed there, substantiate this theory. The potatoes, which were of the earliest varieties, were forced artificially and planted as soon after as possi- ble. Sandy soils on the March f eld near Vienna, lime soil near Poitiers", had a small water capacity and heated rapidly, consequently with the in- creasing summer temperature and the superficial position in the upper soil layers the growth of the aerial axes stopped at once. Tubers are formed about this time, but they do not mature, they are filled with starch so that they can be marketed ver}^ earl)' and command high prices. 1 Zeitschr. f. Pflanzenkrankh, 1894. p. 94. - Altvatter, Das Marchfeld und seine Bewiisserung\ Oesterr. laiidw. Wochenbl. 1875. No. 51. 3 Journal d' Agriculture pratique; cit. Biedermann's Centralbl. f. Agrikultur- chemie, 1873, No. 10 und Annalen d. Landwirtsch., 1873, Wochenbl., No. 16. 1 62 When young tubers are checked, ripen prematurely and are harvested, the eyes have not developed normally. Shoots developing from these eyes must naturally be weak. If such tubers are used the following year as seed Fig. 16. The basal portion of a cutting grown in water from a potato tuber with the filament disease (natural size). (Orig.) for similar cultivation, these phenomena of weakness must gradually m- crease and result finally in the growth of thread-like stems only. According- ly the disease is the result of a continued unwise cultural method ; viz., an i63 admissible shortening of the vegetative period of growth. To overcome this difficulty the seed must be changed since the method of cultivation will not permit the return to normal seeding. DiAPHYsis (Growing Out) of the Potato. In summers with little rainfall, as, for example, in 1904, one of the most frequent complaints was that the potatoes remained small or when ap- proximately normal size, showed an uncommonly large formation of sec- ondary tubers (" Kindelhildung" ) . In Fig. 17 is illustrated one of the most bizarre forms, which shows two kinds of diaphysis (growing out), viz., the actual "formation of secondary tubers" and "water ends." The stem end of the tuber (at the left side in the drawing) shows two daughter tubers '^k ' ■ W V ^ Fig. 17. Proliflcated potato; at the left the beg'inning- of complete lateral tubers; at the right, subsequent elongation of the tip end (water ends). (Orig.) growing on either side at about the same relative position like the arms of an armchair. Toward the tip we find the daughter tubers becoming smaller and smaller, until near the conical end of the tuber (right side of the picture) they are recognizable only as small hemispherical processes. This malformation is caused by Prolepsis, i. e., a premature or hurried development of the eyes. The explanation of this phenomenon is easily found. After prolonged foliage development the imderground eyes of the potato plant develop tubers which store the already manufactured starch. The drier the summer, the more quickly the tuber ripens, since, with the regular enlargement and increase of its cells, the starch grains enlarge and the cell walls thicken. The cells (except the youngest about the eyes) grad- ually lose the ability to increase in size to any extent. If now, after prolonged drought and advanced ripening, a considerable amount of water is forced up into the tuber, this abundant absorption of 164 water increases the cell pressure, especially in the young eye cells with their still elastic walls, so that the eye begins to grow. Young shoots sprout from these eyes ultimately reaching the upper surface of the soil. This more un- usual condition occurs only after continued wet weather. As a rule, only passing periods of rain force the water into the tubers, an efifect lasting but a short time ; then the sprout remains short and thickens to the secondary tuber (Kindel). The cork layer (the skin, smooth in young tubers) shows very clearly how the cells of the ripening tubers lose their elasticity. When the tubers are very ripe the skin becomes rough in most varieties of potato, especially red ones. At first the cells of the cork layer are closely connected with one another but, with the increasing pressure of the swelling parenchyma, the cells are forced apart, tearing the skin. Under these tears new cork cells are formed. This splitting of the skin is greater or less with different varieties. The more split a tuber of an otherwise smooth-skinned variety is, the riper it is and the richer in starch. Diaphysis of the tubers in many cases has a bad influence in that the quantity of starch which may be regarded as influenced by the soil, is de- posited in a less available form than in normal development. Together with the large tubers a great many small ones are formed, which are less mature and therefore poorer in starch. According to the investigations of Kiihn^ and Weidner-, the tubers already present do not become poorer in starch when the secondary tubers are formed. The starch of the secondary tubers does not come from the original tuber, but directly from the leaves. Only in plants, whose foliage is dead, does a suddenly renewed supply of water pro- duce secondary tubers at the expense of the starch content of the older ones. Both old and young tubers have only the starch content of the healthy tuber, which has not grown out. So-called "water ends" are nothing but the result of a renewed growth of the apical parts of the tuber excited by a subsequent supply of water. These are thereby lengthened into a conical form and are filled with new starch (see the right side of Fig. 17). The starch filling is just as scanty as in the real secondarj^ tuber, "Kindel." Formation of Tubers A^'ithout Foliage. If tubers, at the time they would sprout naturally, are not put in the earth, but are kept in a dry, poorly lighted room until the next period of harvesting, a number of small tubers will sometimes begin growth. These stand either close against the mother tuber or hang from short stolons, which have developed from the eyes. While, with a timely supply of water and light, these eyes would have grown into leaved, green sprouts, in the dry, dark store-room, the sprouting eye has developed into a thread-like runner (stolon) beset with scales instead of leaves, the tip of which has thickened into a tuber. 1 Zeitschr. d. landw. Centralver. der Prov. Sachsen 1868, p. 322. 2 Annalen des Mecklenb. patriot. Ver. 1868, No. 39. i65 Aerial Potato Tubers. When tubers are not planted deeply, nor hilled up, the plant remains green, while the root is liable to be greatly injured by drought or animals. If subsequent rains cause the weakened roots to function sufficiently to keep the aerial axes alive, small, colored tubers are developed on them from the lateral eyes. This process is possible also under different conditions, yet the root must be diseased and able to convey only very small amounts of water from the soil to the leafy stems. If cuttings are taken from the older parts of the stem, they can be forced to form tubers in the leaf axils. Premature Ripening of Fruits. In years of continued drought, as, for example, 1904, complaints be- come most numerous that fruit does not keep. Summer fruit indeed ripens more quickly and can be brought to market one to two weeks earlier, but the flavor leaves much to be desired. Winter fruit remains smaller, as a rule, is less juicy and well-flavored and decays more quickly, or it needs a much longer time in storage in order to become fit to sell. The former may be observed with light soils, the latter has often been found^ when, with heavy soil, rains occur after a period of drought, causing a further growth of the fruit which, until then, had been retarded by a scarcity of water. The condition here pictured is explained in the discussion of the fact that the quality and keeping qualities of the fruit depend upon two factors. First of all, each fruit must have sufficient time for the penetration of the water and food substances necessary for its maturity; this takes place at the time of swelling. Then the oxidation processes of ripening set in grad- ually, in which the reserve material, stored in the form of starch, is used up in respiration. The longer time the fruit has to store up the material sup- plied by the leaves, the better provided it is for the process of ripening and the better are the keeping qualities. If this process is interrupted ahead of time by drought, the processes of ripening, the conversion of starch into sugar, find comparatively little material present. In normal summer weather, i. e., alternate sunshine and rain, the fruit during the process of ripening also takes up mineral elements besides water, as Pfeiffer and I have proved. An absolute increase in mineral substances takes place shortly before complete ripening. This naturally appears relatively small in com- parison v/ith the greater increase in organic substances. With a continued scarcity of water this increase does not take place and the fruits quickly use up the scanty materials. The acid store is scanty, the formation of sugar still less, which accounts for the insipid taste and the poor keeping qualities. In winter fruit, processes of ripening are completed only in storage. But in all other respects the same point of view holds good. If the weather during the summer is favorable for the absorbing of large amounts of re- 1 Monatsschrift fiir Pomologie unci praktischen Obstbau von Oberdieck und Lukas, 1863, p. 272. i66 Serve substances, the fruit is well prepared for storage and keeps sound a long time. If the reserve substances are scanty, the fruit rapidly spoils. In seasons after a long period of drought, which has practically stopped the development of the fruit, if a time of continued cool, dry weather comes, the fruit may start its growth again and renew its life processes. If the fruit must be harvested in the autumn, it is put into storage in a compara- tively immature condition and thus needs more time to become ripe. These are the cases (on the whole less frequent) in which the fruit must lie dis- proportionately long in storage and does not become mellow, but remains tough. Rusty Plums. Fox red discoloration of plums setting in some weeks before the normal time of ripening is a phenomenon of premature ripening. The fruit is still absolutel}^ hard and, on an average, about half as large as that normally ripened. As a rule, the rusty plums fall prematurely. The phenomenon occurs only in continued hot, dry periods and is found especially on sandy soils. This discoloration occurs at different times for dift"erent varie- ties and is similar to the premature coloration, which takes place in wormy or otherwise injured fruit. It should be emphasized that the dry locality it- self is not the cause of the rustiness of the fruit, but it is due to a scarcity of soil water succeeding a period of normal precipitation. Trees whose water supply is scant, adjust themselves to conditions by dropping the fruit, which they cannot develop, shortly after blossoming. The disease only ap- pears on those trees which have held their fruit until summer under normal moisture conditions, which are then followed by a long, dry period. An abundant supply of water must be provided to overcome this, and should not be too long delayed, else not only the rusty fruit but often all the fruit, will fall. Further Phenomena of Premature Ripening. As a matter of course, the results of continued soil dryness after a nor- mal spring moisture are observable in all kinds of fruit. The dropping of leaves and fruit is of frequent occurrence. The scanty maturing of the organs remaining on the plant is a less common phenomenon. This produces also poor keeping qualities in stored fruits and potatoes and small grains in the cereals. We will return later to the discussion of other cases, when we consider the results of unusual dryness of air. Mealiness of Fruit. Especially in hot summers on sandy soils it has been observed that fruit, especially early varieties, does not become juicy and crisp, but is tought, poor in sap, insipid rather than aromatic in taste, and when put under pressure, makes a mealy paste. In cooler years and in other localities even the same varieties do not become mealy, but change at once a firm con- dition to a liquid, winey, doughy or a decomposed condition. 167 I know of no special investigations of the case at hand. On this account it can be stated only hypothetically that the mealiness of the fruit depends upon a definite act in the ripening process, which has been directed into other chan- nels because of the scarcity of water. This change in direction might not be as- sociated with the connection of the fruit and the tree, but may set in late in the development of the fruit, about at the time when the intercellular sub- stances generally dissolve. In normal ripening of fruit, after passing the stage of great sweetness, in which the fruit is already "mellowing," i. e., the cells of its flesh are easily separated from one another, there occur at the expense of the sugar first an alcohohc and finally an acetic acid fermen- tation. The fruit becomes winey and doughy with a constantly advancing oxidation or browning. According to PYemy^, a part of the alcohol thus formed is combined with the fruit acids to form the ethers, which condition the flavor of the fruit. A cool temperature prevents the rapid oxidation of the sugar. The supply of water from the branch to the fruit, becoming less with ripening, explains the fact that, in great summer heat, the fruit develops with extraordinary rapidity and in this gives oft' carbon dioxid and water abundantly. In fruit, however, the flesh is poorer in water and is very easily warmed through; the reduction of the intercellular substances, which we reckon among the pectines, cannot take place in the usual way. A. Mayer- considers the pectines as condensation-products of Galactose and the pentoses, Arahanose, and calls attention to the peculiar fact that they are jelly-like because of a special enzyme and are hydrolized by another to the pentoses. It may indeed be assumed that these processes are changed quantitatively and qualitatively when the fruit becomes mealy. This is indi- cated by the circumstance that in mealy fruit a firm connection always exists between the outer skin and the flesh of the fruit, while in the normal winey- doughy condition the outer skin can be raised easily from the flesh, i. e., the intercellular substance is dissolved. The insipid taste of mealy fruit is ex- plained by the scanty content of acid and the quick destruction of the sugar. When establishing the theory that an excess of warmth can cause a relative lack of organic acids in fruit, attention must be called again to the fact that the acids formed in the leaves during the night are in great part used up again during the following day. This process of oxidation will also take place in green fruit and it is indeed conceivable that in the long, hot summer days, this is so intensive that a large part of the acids already pro- duced disappears. Under such circumstances no vinous fermentation takes place. The fact that I was able artificially to produce the mealy process in apples favors the theory that the mealiness of fruit appears with the scarcity of water in the cells and a pasty decomposition of the cellular substance, if the conditions necessary for a vinous fermentation are not present. Fruit of various sorts was packed in layers in dry sand after ripening normally 1 Compt. rend. LVIII, p. 656. 2 Agrikulturchemie, 5th. Ed. Vol. I, p. 141. Heidelberg- 1901. i6g on the trees and was kept from autumn until the next summer in a cool, light cellar^ in order to let the fruit mature as slowly as possible. In this it was proved that some fruit with an absolute uninjured wax coating was still sound in August, but absolutely insipid in taste and of a mealy consistency ^ Bitter Pit. In the flesh of fruit, especially of apples, brown, tough, scattered spots are produced, which sometimes taste bitter. If these are found just beneath the skin they become noticeable as somewhat depressed tough places, which, at first paler in color, finally become brown. The phenomenon is most fre- quent with porous soil in dry years, such as 1904. The firm fleshed varieties suffer less. Although a fungus Spilocaea pomi Fr. is given by some in- vestigators as the cause, I still would like to consider the phenomenon as the result of a too rapid maturing in individual cell groups in the flesh. In each fruit the tissue of the flesh seems unequally filled with reserve substances. If premature dryness of the soil prevents the accumulation of the proper amount of organic material for the complete maturity of the fruit, different tissues will remain especially poor in contents and actually complete their life 1 In mealy fruits, as well as in those normally juicy, the state of ripeness is characterized by the appearance of peculiar substance groups becoming visible immediately after the sections have been put in undiluted g-lycerin. The adjacent figure shows a cell from an apple (Gloria mundi) when the section had been placed immediately in g-lycerin. The delicate plasmatic primordial utricle which had been contracted into folds is partially omitted in the drawing-. The content is pushed together more or less. Also the very large vacuole at once notice- able in most cells, usually lying in one corner (which I would like to call an acid vacuole), is omitted in the illustration so that the substances appearing with the glycerin reaction may be more clearly apparent. Emphasis should be laid upon the fact that all cells do not show this response. The outer flesh of ripe apples, pears and peaches reacts especially well. The investigations indicate that a substance closely related to sugar is present in the cells in various transitional forms. This substance is found between isolated larger vacuoles or the numerous very small ones; it might be imbedded in the cytoplasm or be free in the cell sap, either as separate cloudy drops or in rectilinear masses which, from their appear- ance, may be dough-like in consistency. Often they are found in more strongly refractive and solid forms as tuberous, warty, irreg-ular growths. This most solid state appears also in the form of very small, sandy grains imbedded in the cell wall, attention to which is first called when they swell up to drops or (by forming vacuoles) to small bubbles in the g-lycerin. All three forms have a capacity for swelling in glycerin. When observed under water, the drops become indistinct and disappear, but in extracted apple juice they remain visible and may be distinguished from the different vacuoles. The radiating middle structure of the figure shows the most marked results of the swelling-, while the doughy condition of the substance is indicated by the shaded surface with curved outlines lying below this. The sur- roundings represent the part of the cytoplasmic sack, which lies in the same plane and which encloses the grains of coloring- matter and two vacuoles. The process of swelling- is the same in the three masses described above, but occurs in different intensities. It appears most rapidly and furthest developed in the drop form and decreases the firmer the substance becomes. With the addition of water the drops disappear first, in their place there remains at times a finely ground residue at the edge of the cytoplasm; somewhat later the doughy masses become invisible and the dividing line formed through the cytoplasm becomes circular. The polyp forms become slowly transparent; the warty masses gray grained and cloudy without dissolving entirely in one day. If, at the beginning of the entrance of water, cloudy balls, generally lying along the walls imbedded between the vacuoles, are observed, there is frequently noticed a swelling of different groups of cell contents beginning at the inside, which increases up to the formation of vac- uoles. A similar phenomenon is found with glycerin where the process sets in more slowly and the changed conditions are retained longer. By this process of swelling of the substances imbedded in the cloudy drops, the inner part of these appears at times filled by one or more vacuoles in such a way that an actual cloudy mass occurs only as a slender ring enclosing the vacuoles. This becomes more and more 169 cycle so much the more quickly. The beginnings of the disease must be sought in a rather early stage of the fruit's development. I often found in diseased cell groups, recognizable by browned and corked membranes, many grains deposited on the cell wall. These slowly colored blue with iodine and therefore must be spoken of as starch. Some of them showed a warped seam which remained whitish. Further, a splitting of the browned tissue is observed often in the tough fleshed early apple, varieties which are most inclined to become specked. These splits are explained by the fact that when transparent in water until it can no longer be recognized. No actual dissolving- of the substance has been observed. If fresh sections are laid first in water, cloudy drops do not appear, from which it may be concluded that the substance is taken up by the water. Indeed, in several cases, it was observed (in Reinettes) that if the drops had disappeared after a rapid temporary action of the water there was left a fine grained residue. With the addition of glycerin the solid grains either form drops or separate filament-like pouches. Per- haps it is only these grains which, imbedded in the drops and the remaining, above-mentioned forms claimed to be different aggregate conditions of some ground substance, swell up to polyp-like radiations. It is seen especially in the drops which are enlarged to a thick-walled vesicle by a vacuole that only some places may be elongated like pouches or chains of beads which in individual cases can reach the wall layer and thus transverse the cell as knotted bands. With the continued slow swelling in glycerin the figures change constantly whereby the substance, which becomes more and more doughy, more weakly refractive and stringy, shows an attempt to return to the drop form. Either some of the chief arms of the above represented polyp-figure take up more and more substance and become broad bands which finally draw together into spherical drops, or separate beads of the chain show a stronger growth with a constant increase in size and decrease in refractive power, whereby the smaller spherical links of the chain and the thread-Ike substance possibly connecting them becomes more slender, finally tearing apart and be- coming drawn into the larger drops. In most pro- nounced cases these drops were recognizable after 96 hours, but later could no longer be found nor pro- duced again by reagents. The reason that I place the substance mentioned in the list of sugars, or between sugars and ferments, is their occurrence in the same cells, which contain large, strongly refractive drops capable of being drawn together by glycerin, or separated by alcohol and showing a copper reaction into which it seems to me pass over the small, above-mentioned drop forms. The large syrup drops which may be drawn together in certain parts of the cytoplasmic sac by glycerin and which gradually disappear again, may be partially fixed by the use of the potassium bichromat since a persistent brown -grained precipitate is formed. In pears I found this phenomenon after the action of dilute sulfuric acid on the glycerin preparation in which the walls of the stone cells became the color of wine. Ferric chlorid gives no special color reaction. If a piece of caustic potash is put in the glycerin prepar- ation the syrup balls color an intense yellow and the remaining cell content a lighter yellow. Chemically pure grape sugar behaves similarly but, dissolved in pure water, it gives only a weakly yellow liquid. The addition of calcium chlorid or calcium nitrate will hold the drops in form somewhat longer. They then retain their strong refractive power from 2 to 4 days. With the use of silver nitrate a brown grained precipitate is produced in many syrup balls, which consists either of many very small grain bodies or less numerous larger tuber-like ones. A part of the drops disappear without giving any precipitate. It seems to me that we are concerned here with an extremely easily changed substance, easily soluble in water and alcohol, but less soluble in glycerin, which occurs in the same cell in different transitional stages, thus howing different re- actions Even exposure to the air brings about a change, since an apple, which shows a quantity of drops on its freshly cut surface, does not show any drops on this same cut surface after a few hours when acted upon by glycerin, and these may only be found again deeper in the tissue. Fig. 18. Parenchyma cell from the flesh of a ripe apple after treatment with undiluted glycerin. (Orig.) 170 the fruit was attacked by the disease, while the cork layers were swelling, the specked tissue had already lost its elasticity. The dying of single tissue groups of this kind as the result of an in- sufficient storage of reserve substances will take place so much the more easily as the deposition of starch is made more difficult by the one-sided in- creased nitrogen fertilization. In fact, practical fruit growers have also observed that this specking is especially abundant, if the trees have been excessively fertilized with sprouted m.alt, hornshavings, etc. Wortmann^ substantiates our theory in regard to the non-parasitic character of the specks and of their occurrence with a scarcity of water. He ascribes the appearance of the dead cork cell groups to an excess of acid which is brought about by the concentration of the cell sap of the fruit as a result of unreplaced water loss. The absolute acid content decreases with the ripening of the fruit, but the relative acid content becomes increased with scarcity of water in the cells. Wortmann concludes from his investi- -gations of the epidermis that the larger fruits evaporate more than the smaller ones and the specked varieties (reddish Reinette, Goldgunderling, King of Pippins, Landsberger, green Stettiner, Danziger) evaporate more than do the varieties not inclined to specks. He found a greater thickening of the outer walls of the epidermis in the non-specked varieties, the peeled specimens of which evaporated more than did peeled specked apples, li the fruit of non-specked varieties was pricked with a needle and laid in acid or alkaline solutions (potassium, tartarate, limewater) specks were pro- duced which could not be distinguished from natural ones. The phenomenon of the so-called "fly specks" should not be confused with this. Very fine little black points united into groups are found on the apple peel, which appear to the naked eye like a cloudy bloom and under the microscope look like accumulations of fly specks. Fungi, especially Leptothyrium pomi Mntg. and Fr. and Phyllachora Pomigena (Schw.) Sacc. are given as the causes. Often actual insect secretions are found in which fungi grow. Since the skin under the "fly-specks" does not seem to have been injured in any way, rubbing with a damp cloth is enough to make the fruit again fit for sale. Another phenomenon, often called specking, is the "rusting of the peel." This term comes from the change in color oi the outer skin. During the process of sivelling, the skin gets stellate or den- tritically-branched tears, which are closed by the formation of cork. Stoniness of Pears and Lithiasis. When pears are grown on poor soils, in dry years the flesh is solid, but grates between the teeth when eaten, in wet years the flesh is tender and does not grate between the teeth. This grating is due to the extraordinarily large amount of stone granules formed in the years of drought. Practical workers often maintain the theory that the formation of stone cells in pears is the direct result of great drought. 1 Wortmann, Jul., Ueber die sog. Stippen der Aepfel. Landwirtsch. Jahrbiicher 1892, Parts 3 and 4. in Investigations of young fruit show, however, that in each variety of pear in normal development aggregations of coarse-walled schlerenchymatous cells are always present unequally distributed. These stone cells are in fact an anatomical characteristic dififerentiating pears and apples\ Therefore, it is not the occurrence of the stone cells but only the greater thickness of the walls already formed which is the result of the drought. In many varieties they remain relatively thin-walled. To this should be added that their con- nection witji the surrounding tissue is tougher and closer in dry years. In the so-called stoniness of pears, only the increased wall-thickening- of the normally deposited schlerenchy- ma cell centres is concerned and there- fore no increase of the elements, while we find in Lithiasis an accumulation of stone cell elements produced subse- quently by cell increase. These finally may also extend over the surface of the fruit and then form light brown circular specks, either equally distrib- uted or clustered on the sunny side or even map-like etchings due to the run- ning together of the specks (Fig. 19), the upper surface of which shows a crumbly construction. Not infrequently the same varieties of pear suffer also from Fusicladium (see Vol. II). Nevertheless, the Lithiasis specks may be easily distinguished from the smooth, usually blackened, fungous specks, be- cause of their crumbly constitution and the raised edges of the wound. So far as observations have shown as yet, only certain varieties suffer from Lithiasis. Many, in fact, form predominantly roundish specks, while in others usually zigzag gapping cracks are produced. Stone masses are not always depressed, often they occur on the upper surface as pale cork-colored cushions. An entirely normal construction may be found in the healthy parts of the pear attacked by the stone disease ; i. e., underneath the small celled, not Fig-. 19. Pear diseased with Lithiasis. (Orig.) 1 Turpin, Memoire sur la difference qu'offrent les tissus cellulaires de la pomme et de la poire etc. Paris. Compt. rend. 1838, T, pp. 711 ff. ~ The substance, of which the stratified thickened walls of the stone cells con- sist, has received the name of glycodrupose from Erdmann*. He used this name because he thought that the chemical composition of these cells is the same as that of the tissue of stones of plums and cherries (Drupaceae). The substance, decom- posed by moderately concentrated hydrochloric acid, gives half its weight in grape sugar in solution. The half remaining undissolved is called drupose; when boiled 1^2 very thick-walled, colorless epidermis (Fig. 20 e) lie three or four layers of usually tangential ly elongated or cubical parenchyma cells (/>) which are richer in cytoplasm than the deeper lying tissues and contain chlorophyll, but no starch. The starch is found to appear gradually first in the inner flesh and its grains usually increase in size toward the core. Underneath the outer cell layers, rich in chlorophyll, the deposition of the stone cell centres begins {st). These form groups of a few cells in the normal flesh; in the coarse fleshed fruit they are separated only by small intermediary areas of delicate parenchyma (-/'). From the periphery toward the in- terior of the fruit, the stone cell groups become more scarce and the sur- rounding parenchyma assumes a stellate arrangement. In the first stages of the disease, we find in fruit, which is always green and hard, that, underneath the uninjured and colorless epidermis, individual cells contain no chloroplasts, but have a brown, strongly refractive cell con- tent, which is massed together in lumps. The number of these browned cells gradually increases and ruptures the outer skin. Beneath the ruptured place which, by the drying and crumbling decomposition of the tissues forms a depression {gr), a brown- walled dying tissue {hr) is found in the midst of the flesh, which later may rupture and form cracks. Often in these cracks, and always in the open peripheral pits {gr), may be found a colorless slender mycelium which is a subsequent infection and may hasten the decomposition of the tissues. A most striking phenomenon is the fact that when the pit has been formed the flesh tissues no longer die and closed masses of newly formed schlerenchymatic tissue begin to push out like cushions with a radial struc- ture (/). These cushions of stone cells force the dead bark {t) tissue out and off. In cross-section the individual elements of the stone cell cushions are square or rhomboid, and lie almost unbrokenly upon one another. Even in with nitric acid and washed with water, ammonia and alcohol this leaves behind a yellowish white celk^lose. Erdmann concludes from his investigations that the substance of the stone cells may be produced from a carbohydrate by the loss of water and nitrogen from starch or gum, while in the normal process of ripening, water must be taken up for the formation of the sugar. The theory that the formation of sugar and of cellulose are most closely connected is given expression by DeVries**. He says that usually an accumulation of grape sugar is found in those young cells which later strongly thicken their walls. For example, the bast fibres of clover as well as fibres of the inner fibrous sheath of the vascular bundles, which appear to be very thick walled in a mature condition, are rich in grape sugar in their younger, still thin walled stage, while the surrounding tissue is poor in sugar or lacks it entirely. DeVries found the same conditions in the young bast fibres of potato and maize. Even in the hairs, which are thick- walled later, an accumulation of sugar takes place before the thickening of the walls, thus, for example, in the hairs of young clover leaves, in whose parenchyma, however, no sugar could be proved. In the same way, according to DeVries, sugar can not i)e found in the root parenchyma of this same plant, while in the young root hairs it occurs abundantly. The possible transversion of cellulose to dextrin and sugar by the action of dilute sulfuric acid after heating is well-known. With this the recent investigations on the Hemicelluloses; mannen, galactan and araban, should be compared. * Liebig's Annalen, Vol. 138, p. 101; cit. im Jahresbericht f. Agrikulturchemie 1866, p. 99. ** Wachstumsgeschichte der Zuckerriibe, in den Landw. Jahrb. 1879, p. 438. 173 early stages they color a bright yellow with Anilin sulph. and when oldest will dissolve easily in sulfuric acid without any observable precipitation of gypsum crystals. While the normal stone cells usually remain yellow Cross-section of a stone cell cushion from a pear diseased with Lithiasis. (Orig-.) Explanation in text. 174 from the effect of sine iodid of chlorid, the elements of the schlerenchyma cushions, which were formed later, turn blue after some time, either throughout or in the innermost lamellae of the walls. The growth of these schlerenchyma cushions takes place in a meriste- matic layer (w) formed underneath the dead bark and appears at first as if it would develop into a flat cork layer, cutting off the centre of the diseased tissue, as may be observed in the Fusicladium cushions. This, however, is not the case. The meristematic layer is active as long as the fruit is green and growing. Toward the periphery it forms new thin-w^alled bark cells (usually in small numbers) which again are gradually attacked by bacteria and fungi, while on its inner side, toward the (usually seedless) core, the thick-walled elements of the stone cell cushions are increased. The radial arrangement of the cell rows in these is explained by the tension of the tissues which the swelling of the unripe fruit causes. If, in this, the new formation of stone cells is greater than the distension of the parenchymatous tissue of the fruit flesh, the stone cells are pushed out like cushions. As a rule, however, both processes keep step and finally, by the death of the pathogenic meristem itself and the breaking of the connection between the outermost stone cells, is produced the crumbly constitution of the stone spots. It is a matter of course that fruit attacked by Lithiasis is unfit for consumption. Since this phenomenon is not found in all varieties, and not ever}^ year even in the same varieties, but is a destructive factor only on dry soil in dry years, the supposition, that the stock used in grafting influences the problem, seems probable. Weakly growing stock which cannot take up sufficient amounts of water from a dry' soil for a rapidly growing top, because of its small root area, will favor this stony condition. If, on this account, the dis- ease should occur repeatedly in the case of dwarf trees on light ground, an attempt should be made to graft pears on the most rapidly growing varieties of quince. When standard trees are in question, an attempt to overcome the difficulty should be made by renewing the soil, fertilizing the sub-soil and watering abundantly ; in obstinate cases, by means of renewal of the top by pruning after fertilization. Some method of forcing the fruit to swell as rapidly as possible might best protect it from an excessive formation of stone cells. Varieties of Fruit Suitable for Dry Soils. The guiding idea of our manual is that many diseases of cultivated plants may be prevented by a more careful consideration of the relation between the character and habits of the plant and its environment. In accordance with this plan in treating diseases favored by drought, we men- tion a number of well-known varieties suitable for dry soils^. 1 Oberdieck, Deutschlands beste Obstsorten, Leipzig, Voigt. 1881. L. indicates that the variety i.s recommended to the agriculturist. Str. suitable for planting along streets. The name of the month after that of the variety indicates the time of complete ripening. 175 Apples: Summer Rose, End of July. L. Str., Scarlet Pearmain, Au- tumn. L. Str., Landsberg, Autumn. L. Str., Dantziger, Autumn. L., King of Pippins, Winter. L. Str., Orleans, Winter. Str. (For the agriculturalist where the soil is better). Yellow Bell flower. Winter. L. Str., Alant, L., Deutscher Gold Pepping*, Winter. L. (must be left on the tree until the middle or end of October), Kassler, keeps from winter until summer. L. Str., Purpurroter Cousinet*, winter till summer. Pears for dry soils: Hannoversche Jakobsbirne*, end of July. L. Str., Clapp Favorite. August. L., Archduke, August. L., Yat, beginning of Sep- tember. L. Str., Kuhfuss*, beginning of September. L. Str., Treyve, Sep- tember. Autumn Melting (Downing), end of September. L. Str., Bosc, end of October. L., Marie Louise, beginning of November. L. Str., Mecheln, December. Madam Korte*, January. Kemper, cooking pear for the whole winter. L. Str. Cherris, as is well-known, prefer a well drained, dry soil; on the other hand, plums, on the average, flourish best in a moist, heavy soil and also they bear sweeter fruit. It is desirable to know a number of varieties re- quiring less water. Biondeck, beginning of August ; early Apricot, middle of August; Lawson, end of August; Bunter Perdrigon, end of August; Berlepsch, beginning of September; Altham, beginning of September; Jerus- alem, beginning of Septembr; Anna Spath, middle of September; German prune, end of September. As a street tree, the plum is not very desirable because of its habit of growth. As varieties which grow well on dry, light soils in the climate along the coast, should be mentioned^ : i. Apples: Landsberg, Purpurroter Cousi- net*, Oldenburg. Geflammter Kardinal*, Bauman ; the Prinz (Downing) is especially suitable for the provinces along the Baltic and the North Sea. 2. Pears: Yat Bosc, Red Bergamot, Summer Doyenne. 3. Plums: House Plum. 4. Cherries: The common sour cherry. Stunting. Since almost everywhere in nature similar effects are obtained by different means, a limited soil space may be only one cause of dwarf growth ; another is the lack of available nutriment due to either a scanty supplying of raw soil solution to the roots or to the decrease of organic reserve nutriment. This latter case we will have to consider again later in the "PIncement Grin," I. e., in the pruning of leaves to prevent the sprouting of the buds found in their axils and in the production of dwarf seedlings by cutting off the cotyledons which are rich in nutrition. In nanism, however, caused by soil physically unfit because of too great porosity, water scarcity alone must be considered. Given a soil rich in mineral or organic food substances, the size of the plant depends upon the distension * Name of variety given in the German original, not reported in the United States of America. 1 From a written communication of Mr. Klitzing- (owner of a nursery) in Ludwigslust. 176 of the individual cells, due to the turgor produced by the water from the roots, and the conclusion is at once reached, that a scanty supply of water during the time of growth must produce small dwarf specimens. Each excursion through sandy regions, in which a damp subsoil is either lacking or lies very deep, furnishes examples enough for this fact. I have published detailed measurements concerning the shortening of cells due to a scarcity of water\ MoUer- furnished experimental proof of dwarfing due to scar- city of other food substances with an excess of water and also confirms the principle that in slightly concentrated nutrient solutions the root increases relatively in size. Mobius^ has arrived at the same result in his comparative cultures with Xanthium in sand and loamy soil. He found the roots and stalks of plants grown in sand branched more than those of plants grown in loamy soil, while the leaves were more slender and the glandular hairs fewer in number. On the other hand, in plants grown on loam the content of calcium oxalate crystals seemed smaller. The thorns were smaller on sandy soil, but the walls of the lignified cells seemed considerably thicker. Comparative studies of the influence of dry or wet localities were made by Duval-Jouve"*. These proved that in dry. hot places, a formation of the hard, bast bundles is especially favored, but is retarded in shady, wet posi- tions. Volken's observations"' on Polygonum amphibiunt in the forms grown in sand, heath and water, are very thorough. In the sand form the circum- ference of the stem is smaller, at the expense of the central air canal ; the bark cells are more heavily thickened, while between the bark and the phloem, a rather broad ring of uncommonly thick mechanical cells is en- closed. A closed wood cylinder is formed, the vascular system in which is almost 2 to 3 times as strongly developed as in the water-grown stem ; in the latter, the absence of thick-walled elements and the occurrence of large air holes facilitate floating. The petioles of the water form, which have no mechanical reinforcement, may become six times as long as in the land form, the midribs of which are strengthened by strong collenchyma cords. The palisade cells are more strongly developed in the water plants, but these lack, on the other hand, the strongly developed bristles on the upper sur- face and here also the somewhat larger epidermal cells which in the land form contain a slimy content, explained by Volkens as a water reservoir in times of great drought. In the well-known Rose of Jericho (Anastatica hierochuntica), that plant of the desert which closes together like a head when dry, the inclination of the branches toward each other arises from the fact that the wood cells on the different sides of each branch possess a different capacity for swelling longitudinally, which goes hand in hand with an unecjual lignification. 1 Sorauer, Bot; Zeit. 1873. 2 Moller, Beitrag-e zur Kenntnis d. Verzwerg-ung. Landw. Jahrb. 1893, p. 167. 3 Mobius, M., Ueber den Einfluss des Bodens auf die Struktur von Xanthium spinosum usw. Ber. d. Deutsch. Bot. Ges. 190.'j, Vol. XXII, Part 10. 4 Duval-Jouve, Anordnung der Gewebe im Blatte der Graser. Bot. Jahresb. v. Just 1875, p. 432. 5 Volkens, Beziehungen zwischen Standort und anatomischem Bau der Vegeta- tionsorgane. Jahrb. d. Kgl. Bot. Gartens zu Berlin. Vol. Ill, 1884, p. 46; cit. Bot. Centralbl. 1884, No. 46. i;7 From the beginning one must note that every Hmited supply of nutri- ment which leads to nanism must express itself mostly in the amount of additional growth, i. e., in the formation of the secondary tissues. An ana- tomical proof of this has been furnished by Gauchery®, who cites cases when the cambium has formed anew only a few rows of cells. Often he could no longer determine any meristematic zone whatever between phloem and xylem; therefore, the original cambium must have passed over at once into permanent tissue as the result of deficient nutrition. In the plants which are forced to grow in sandy or stony soil, often with a lack of water, a form of hyperplasia^ (arrested developments) appears. It is not so much the number of the cell elements which seems to be decreased, as their size. Thus specimens are formed which we would like to call "stunted plants." By this is understood woody plants, the growth of which is not retarded to dwarfing but which, by the striking shortening of their axial organs, show a repressed, knarly habit of growth. In this habit of growth the very evident, increased spiral twisting of the woody elements of the trunk counts as a typical characteristic. The finest examples are seen in Syringa and Crataegus. We can explain the production of the increased spiral twisting if we think of the direction of the woody cells as the diagonal of the parallelogram of two forces. At the apex of each elongating axis there is, on the one hand, an efifec- tive striving toward growth in length in which the elongation of the pith body becomes a decisive factor of swelling; on the other hand, the general enlargement of the young cells acts also as the cause of the radial enlarge- ment of the trunk. In considering a very young wood cell in the cambial layer, stretching longitudinally, we see that, as the growth in length predomi- nates over the growth in thickness, it is relatively difficult to divert the cell from its longitudinal growth. However, as the abundantly formed young wood cells, during elongation, are pressed outward by the growth in thick- ness of the medullary cylinder in the direction of the radius of the trunk, proportionately just so much the sharper will be their spiral twisting. On this account we find long slender shoots with a slight spiral twisting in plants on moist nutrient soil, and on sandy soils poor in water, or with other checks to growth in length, plants having short axes with strong twistings. Confirmation of the hypothesis is found in the "enforced twisting" to be mentioned later. The more the stems are distended like barrels, the sharper is the spiral twisting of the cords of the leaf spur. We mention this point because the occurrence of such strongly twisted stunted plants is valuable as a symptom in judging the soil conditions. Pilosis. Plants grown on dry soil soon have a hairy appearance, even if no more hairs are formed than on specimens of the same variety growing in damp 6 Gaucherv, Recherches sur le nanisme vegetal. Ann. sc. nat. Bot. 1899. VIII. ser., t. IX. 1 Kiister, E., Patholog-ische Pflanzenanatomie, Jena 1903, p. 21. Here abundant bibliographical citations. 1/8 places. If a definite number of hairs are formed on a leaf, these are closer together in a given small area, because the epidermal cells separating them are shorter. This partially explains why alpine plants appear to be less pubescent when grown on plains. These plants grow more luxuriantly, the dimensions of their organs become larger and the hairs are separated further from one another. But, in fact, even in dry locaUties, an increased hair for- mation takes place. Thus Moquin-Tandon^ cites observations by Lianeus, that the Lady's Thumb (Polygonum Fersicaria L.j seems very smooth at the edge of bodies of water, but beset with hairs in dry places. Our field thyme (Thymus Serpyllum L.) loses its glaucous surface at the sea shore and acquires a short, hairy covering. Our Turk's cap lily (Lilhim Maria- gon L.) when cultivated for some time in gardens is glaucous, but becomes pubescent again, like the wild plant, when grown on poorer soil, etc. Such phenomena may be observed also in garden plants which, self-sown, grow on sandy places in the fields. An unusual hair growth takes place, further, in many parts of plants when they no longer develop normally. According to Moquin-Tandon, the stamens of the triandrous bindweed are covered with thick wooly hairs. The stamens of several kinds of Mullen (Verbascum) behave similarly if the anthers become deformed. The peduncles of the smoke tree (Rhus Cotinus) are almost without hairs before blossoming and if they bear seed. If, on the other hand, the fruit does not mature, the stems of the sterile blossoms grow longer and numerous, long, violet colored hairs appear on them. The last-mentioned formation of hair does not belong among the phenomena connected with drought, but should be considered as a process of correlation. The water and nutritive substances, which should be utilized in the maturing of the anthers or seeds, are used in a greater measure for the benefit of other parts of organs, when the sexual organs are destroyed. Possibly the phenomena recently observed in parthenogenesis belong in part here, where the micropyle is stopped up as the result of the hair-like elon- gated cells of the style tissue or of the integuments-. Also, we find in the root system that pubescence varies according to the place where the root is kept. In the same varieties, the whole system can develop into the form of long, slender, whip-like, scantily branched, bare, or almost bare roots, if the root axis dips into water or into porous sand saturated with water. The root branches become shorter, more knarled, branched and pubescent, the drier the soil is in general ; — the more, therefore, that the root is obliged to depend only on the moist air of the soil interstices. In air which is absolutely dry, the roots (according to Per- secke^), do not develop any more hairs. If the roots are exposed to moist air, the young tips, just behind the growing apex, become very hairy, be- cause almost every epidermal cell has pushed out into a hair. 1 Pflanzen-Teratologie, translated by Schauer, 1842, p. 61. 2 "Winkler, H., Ueber Parthenog-enesis bei Wikstroemia. Ber. d, D. Bot. Ges., Jahrg-. 1904, Vol. XXII, p. 573. 3 Persecke, Ueber die Formveranderung- der Wurzel in Erde und Wasser. Inauguraldissertation, Leipzig- 1877. 1/9 In the aerial parts of plants, which are accustomed to dry air, the de- gree of humidity must be strikingly low if the formation of hair is to be greatly stimulated as C. Kraus^ states when writing of potato sprouts. In very moist air potato sprouts from the same variety are hairless, or have only a few shortish hairs. Therefore, in aerial organs, it is the influence of moist air in contrast to dry air which prevents pubescence. In roots, de- pending mostly on water, the same effect is obtained by a continued supply of water just as the influence of moist air favors pubescence. An extreme formation of hair on aerial and subterranean axes is there- fore the result of causes acting in the same way ; the usual necessary amount of water is withheld from the plants at the stage in which they are develop- ing. In explaining the fact that greater dryness of the environment favors the formation of hairs, Kraus and Mer- have cited the phenomenon that the organ's growth in length is modified or arrested with the formation of hairs. Both investigators are of the opinion that the material saved by the arrested elongation of the cells of the axis, is utilized for the formation of hairs. Besides the examples of Rhus, etc., cited above, Heckel's" observa- tions support the theory that a scanty formation of other organs goes hand in hand with a very abundant development of hairs. Meckel found speci- mens of Lilium Martagon L. and Genista aspalatholdes Lam. with an un- usual hair covering together with a reduction of the blossoming parts. Kraus emphasizes the fact that, with the decrease of growth in length, an increase in turgor takes place transversely in the whole organ (as we have assumed in the development of the pith of stunted plants) which extends to the epidermal cells and excites these to the pushing out of hairs. Vesque'', like Mer and Kraus, states that increased transpiration favors hair for- mation. Attacks of parasitic animals often excite the epidermal cells to an enormous, fine growth of hair, for example, such as mites which injure the young leaves with their mandibles and thus produce the so-called felty dis- ease. These hair formations are described under galls. In the older my- cology, such hair felts, produced by the sucking stimulus of mites, are de- scribed as fungi (Erineum Pers. Taphrina Fr., Phyllerium Fr.). LiGNIFICATION OF RoOTS. The lignification of tuberous roots is due to the return to the original prosenchymatous woody condition of cells in the vascular bundles which, under cultivation, have become parenchymatous. The carrot, for example, which serves us as food, descends from a plant whose root consists of a 1 Kraus, Beobachtungen liber Haarbildungcn, zuniirhst an Kai-toffelkeimen. Flora 1876, p. 153. 2 Mer, Recherches experimentales sur les conditions de developpement des polls radicaux. Compt. rend. LXXXVIII (1879), p. 665. " Hecliel, Du pilosisme deformant dans quelques vegetaux. Compt. rend. t. XCI, 1880, p. 348. ■t Sur les causes et sur les limites des variations de structure des vegetaux. Cit. Bot. Centralbl. 1884. No. 22, p. 259. i8o strong, hard, wood body with a thui, tender bark. The cells of the wood tissue, like all the other wood cells, are thick-walled, spindle-shaped and wedged between one another. In the cultivated root, instead of these wood cells, thin-walled, short cells are present, ending almost bluntly against one another and even the ducts which lie in scattered groups between the par- enchymatous cells are but little lignified. The latex tubes already formed in the bark, when spiral porous ducts are produced in the wood body, have broadened like all the cells of the bark. Instead of the starch which, in the wild carrot, fills out the whole bark tissue, occurring here and there in the wood body also and increasing to 70 per cent, of the dry weight, sugar has been formed usually in good table carrots so that only traces of starch may be found. The better the variety, the less the starch content as in the Dutch pale yellow and the Duwicker carrot. Gradual transitions are found back toward the wild plant in other cultural varieties used as fodder, such as the Altringham carrot and the white horse carrot. Specimens of all varieties found on poor soil go to seed as a rule in the autumn and are dis- tinguished by a thin, often divided, root which, because of its lignification, recalls clearly the ancestral wild carrot. The same behavior is character- istic of the turnip-rooted cabbage, Swedish turnip, radishes. Kohlrabi, etc. These differences are best made clear by comparing the anatomical structures. In Fig. 21 is shown a longitudinal section through a two-year old wild carrot. In this figure a is the vertically elongated parenchyma of the pith-like central part with scattered spiral, porous ducts ; b the xylem, made up of spindle-like wood cells together with ducts and the part of the medul- lary ray which extends toward the secondary^ cortex ; c the cambium which has become an elongated, thin-walled parenchyma ; d the secondary cortex with its resorption spots which follow the course of the latex ducts ; e the primary cortex ; / cork. Fig. 22 is a corresponding section from a two-year old cultivated carrot. The letters in both figures indicate the same parts and a comparison of the similarly designated tissues makes very clear the change in the wood tissue and the increase in the dimensions of the secondary cortex in the cultivated carrot. In all tuberous vegetables lignification also occurs normally when they grow too old and then this process, as in individuals lignifying prematurely, is accompanied by a partial disappearance of the sugar. It is well-known, from experience, that many of our vegetable plants lignify in hot climates. Precautions against this latter condition will be hard to find since the tropical warmth and excess of light favor rapid lignification. In cultivation in temperate climates, lignification can certainly be avoided by abundant watering and fertilizing; — only care should be taken in this that the land is deep and the seed good. Special attention should be given to the choice of seed, because seeds from dr}^ localities carry with them a great- er tendency to lignification and to a repeated division of the root. iSi Ball Dryness of the Ericaceae. The peculiar sensitiveness of the roots to drought must be taken into consideration when growing the numerous species and varieties of the Ericaceae as Erica, Azalea, Rhododendron, etc. These plants cannot endure 2. ^ a complete drying out of the roots. While other plants can survive lack of moisture, even repeated wilting, without showing any noticeable injury, and even continue growth after being again supplied with water, the fine root branches of the Ericaceae do not seem able to resume their functioning when once entirely diy. In one case I investigated the roots of an Erica l82 gracUis which, after they had dried out, had been subsequently soaked 24 hours in water, and found that the fine root ends were still shrivelled despite the soaking. The character of most Ericaceae, as moor and heath plants, is shown by the fact that (with the exception of a few varieties) they thrive best in a freely watered, easily drained, aerated soil. In growing plants in small pots the need of roots for air must be given the greatest possible consideration. The Ericas soon become root bound. The plants easily become sour in large pots. The Erica and Azalea drop their leaves when dried out. It is wrong, however, to try to repair the previous mis- take by setting the pot in water and, after soaking up the earth, to place the plants in closed cases in order to reduce evaporation as far as possible and to cause turgidity. The plants should be left, on the contrary, in their customary place, but strongly shaded during the middle of tlie day. Means of Overcoming Lack of Moisture in the Soil. If a lack of soil moisture is manifested by the failure of vegetation or by its degeneration, as usually occurs more frequently in sandy soils, one naturally seeks relief in irrigation when possible. This artificial supply of water not only refreshes the tissues, but also, by dissolving the nutritive substances in the soil, it is possible for the plant to utilize and distribute these. Irrigation. With the frequent lowering of the ground water level, irrigation be- comes a vital question and an acquaintance with the results of Konig's^ investigations on the effects of irrigation water is interesting. One learns accordingly that when a meadow is being irrigated the water loses much of its nutritive material and appreciably more during the warmer seasons, than in the colder ones. This loss, however, is not true of all nutritive substances. If the carbon dioxid content of the irrigation water .rises, the calcium and magnesium nearly always increase instead of decreasing. As in the case of carbon dioxid, this quantity seems to rise and to fall with the intensity of the oxidation in the soil. In contrast to the above-named nutritive sub- stances, potassium appears to be absorbed at any time by the soil since, with irrigation, even in the winter, a slight reduction of this important mineral can be proved in the water. Sodium, or rather sodium chlorid, just like nitric and sulfuric acids almost always showed a slight increase during winter irrigation, while during the growing season they decrease, i. e., they are taken up directly by the plants. Konig concludes that the oxygen of the water acts as a purifier of the soil by oxidizing the organic soil contents. This oxygen content varies according to the kind of water used in irrigation and the season. Konig found it greatest -in spring, smallest in summer, increasing again in the autumn. Spring water is much richer in oxygen than river water which has passed through inhabited places. The opposite is true of the suspended 1 Journal fiir Landwirtschaft. Jahrg-. 1880. Vol. 28. Part 2. i83 organic substances which are taken up from the soil by impoverished spring water, which has a small oxygen content, but are deposited, on the other hand, by the richly saturated river water. At a depth of 40 cm. during the colder seasons temperature observations show that irrigated land is warmer by varying amounts, even up to 2.8°C. To this increase in temperature may be ascribed the fact tliat in irrigated meadows, growth begins earlier in the spring and continues later in the autumn. Konig showed by an experiment in which he artificially mixed sewage with the irrigation water, how quickly the subsoil shows its absorption qualities, if the soil is not saturated and the irrigation water is heavily charged with fertilizing matter. After the water had been used once, it could be proved that the soil had taken up 84.5 per cent, of the organic substances; 74.2 per cent, of the ammonia; 81.6 per cent, of the potassium and 86.8 per cent, of the phosphoric acid. After the same water had been used twice again the presence of these substances in it could not be proved at all. Of course these figures hold good only for this experiment and vary according to the saturation of the soil and water; they have therefore, for example, no value in irrigation with liquid manure, in which the soils must become surcharged with nutritive substances in a comparatively short time. Nevertheless, experiments show what varied advantages can be obtained with the right use of irrigation. The importance of watering the soil arti- ficially is becoming more and more acknowledged. The best proof is found in the transactions of the land cultivation division of the German Agricul- tural Society^ in which questions referring to the direct supplying of water, raising of the ground water level, have already been brought up. The sys- tems known at present have been partially explained by means of illustra- tions. The transactions have led to a direct commission from the Directors of the society, "that they should take up the question of the watering of land with the greatest possible energy." Cultivation of the Soil. At present, in large plots of land, it is possible only in the rarest cases to provide for irrigation without considerable expense and therefore cheaper, if less effective, means are more often utilized. Such resources are found in working the soil. The breaking up of the soil is most advisable. Some practical workers maintain that cultivating the field soil cannot possibly aid in the retention of soil moisture, but that this manipulation must rather be considered as the quicket way to remove more water from the soil. This point of view is erroneous, as is shown by many experiments. The most thorough are Wollny's", who has worked with control experiments and has found that if the uppermost layers of the soil are broken up, they dry more 1 Die Moglichkeit der Ackerbewasserung- in Deutschland. Arbeiten d. Deutsch. Landwirtsch.-Ges., Part 97, 1904, p. 75. 2 Wollny, Einfluss der Bearbeitung- und Diingung- auf die Wasserverdunstung- aus dem Boden. Oesterr. landw. Wochenbl. 1880, p. 151. I §4 quickly, to be sure, but, by this means, save to a greater extent the water supply in the lower layers of the soil. The warming of field soil by insolation, its aeration when winds blow over its surface and all such influences, remove the water from the upper layers of the soil to a greater extent than can be restored by capillary at- traction for water from the lower layers. If now, by breaking up the sur- face, the interstices between its particles become considerably enlarged, the capillarity is decreased and the water no longer rises into the larger in- terstices of the now crumbly soil. The more quickly the soil is broken into coarsely friable pieces by chopping, hoeing and removing the turf, the more the drying out of the lower layers, where the roots are found, is delayed. The opposite result is obtained by rolling the field land. In this case^ most of the spaces, where capillarity did not act, are rolled close together. Capillarity at once becomes active and the upper surface remains moist for a longer time. Under certain circumstances, however, rolling may also be recommended as a means of retaining moisture in the soil. This will be expressly suitable for all very porous soils with a scanty water capacity and an abundant subsoil moisture, since, by hardening the surface, its evaporation is reduced, while the conducting of water from below is increased. In heavy soils, with a high saturation capacity, rolling would naturally be di- rectly injurious. Mulching of the Soil. Instead of breaking up the soil, its surface may be covered with a more porous material. In this connection advantageous results can be obtained even by covering the surface with sand. This changes favorably the con- ditions of moisture and of warmth at the same time, for, according to WoUny's investigations', the temperature of the soil is considerably re- duced by breaking it up, since the conducting of heat in the friable layer is decreased by the considerable amounts of enclosed air. In the same way soil provided with a sandy covering is colder in the warm seasons than un- covered soil, because the light colbr of the surface decreases the absorption of the heat rays, and the considerable amount of water held back under the sand is warmed with greater difficulty. If the upper surface of the soil itself dries up, its temperature must increase because the evaporation which uses up heat is at once prevented. Breaking up the soil and covering it, therefore, modify the extremes of temperature, but are also valuable in still another way. According to WoUny (loc. cit. p. 337), it is shown that during the warm seasons con- siderably more water from the same amount of precipitation can filter through the soil when covered with sand than through uncovered soil. This takes place because the soil covered with a layer of sand (even if only one 1 Wollny in Oesterr. landw. Wochenbl. 1880. p. 214.- Nessler, Bad. Landw. Corres- pondenzblatt 1860, p. 230.- Wagner, P., Vei'suche uber das Austrocknen des Bodens bei verschiedenen Dichtigkeitsverhaltnissen der Ackerkrume. Bericht der Ver- suchsstation Darmstadt 1874, pp. 87 ff.- v. Klenze, Landw. Jabrb. 1877. 2 Einfluss der Abtrocknung- des Bodens auf dessen Temperatur-und Feuch- tigkeitsverhaltnisse. Forschungen a. d. Geb. d. Agrikulturphysik, 1880, p. 343. centimetre thick) remains richer in water, i. e. becomes saturated more quickly and therefore lets more water flow into the deeper layers of the sub- soil. The same result is shown by covering with ochre, such materials as stable manure, straw, tan bark, and even with stones. Soil covered with growing plants is even less pervious than the naked earth. Some practical workers recommend the use of peaty earth on sandv soils. . Thus Walz^ made use of the upper layers of a peaty deposit which were 6 to 8 cm. deep and useless for fuel, in order to cover a field of poor sandy soil 2 cm. deep, in Februar}^ Later this surface which had been covered with peat and one adjoining it, but not so covered, were richly fertilized with stable manure. In the heat and drought of summer, maize planted on the field mulched with peat showed a better growth and furnished a higher percentage of yield. In the same way, later crops were found to be more luxuriant on the plat of ground mulched with peat. The value of the peat, which Nerlinger- has demonstrated in exact har- vest results, arises from its ability to soak up and retain the fertilizing substances which otherwise, in sandy soil, would be washed away. I have determined experimentally^ that fertilizing makes it possible for the plants to give a better yield with less water, which explains the more favorable be- havior in time of drought. Soils With a Plant Cover. It has already been said that soils with a cover of living plants allow the least water to drain through. This is explained by the fact that plant roots absorb the water. Comparative experiments* prove that the water in the soil is more quickly exhausted with a thick stand of plants, even if this exhaustion does not increase proportionately to the density of the plant growth. From these results, the difference between a bare, broken soil and one covered with a dense turf during hot, continued dry weather, can be ascer- tained. Therefore, in nurseries on porous soil, it is by no means a matter of indifference whether it is often hoed or whether turf and weeds are al- lowed to form a dense covering. It is not a theoretical conclusion but an often demonstrated fact that occasionally premature ripening and sterility are produced in fruit trees, because the weeds and turf have taken up the scanty supply of water. In forestry and trees in beds, if the seedlings do not make a dense growth, their development is threatened. Gravelly soils without sufficient humus content are also a menace for older plants from 10 to 15 years of age, especially if protection is not given on any side by larger plantations. 1 Zeitschrift d. Landw. Ver. in Bavern 1882; cit. in Biedermann's CentralbL 1883, p. 136. 2 Fiihling-'s landw. Zeit. 1878, Part 8. 3 Sorauer, Nachtrag zu den Studien iiber Verdunstung-. Forsch. auf d. Geb. d. Agrikulturphysik, VoL VI, Parts 1 and 2. 4 Wollny, Der Einfluss der Pflanzendecke und Beschattung- auf die physikalis- chen Eigenschaften und die Fruchtbarkeit des Bodens. Berlin, Parey, 1877, p. 128. i86 The forester considers turfed land as a favoring factor, since it retains the water of precipitation and by the quick evaporation withdraws the water of the subsoil. Places almost circular are sometimes found in forests about the base of the trunks where no second growth lives. This circumstance is ascribed to the reflection of the sun's rays from the smooth barked, branch- less trunks (beeches, birches, firs). The sun rays flashed from the mirror- like bark dry the soil to a great extent. This condition can be overcome by various means, among which growing plants by natural seeding is recom- mended, since the plants so produced will adapt themselves to the locality. In places, which must be planted, material should be used which has been transplanted once in the nursery and, after the plants are set out, the soil should be shaded most carefully. Besides this, all conditions should be con- sidered which in general may be recommended for overcoming the lack of moisture, such as the protection of seed beds by walls, fences, rows of trees, or by closely set brush, hilling and especially breaking up the soil, or even fertilizing, since this means a saving of water. Sprinkling with water is advisable only in the most extreme cases of necessity. In brushing the edges of the beds the use of conifers, especially the Weymouth Pine, is most to be recommended, for spruce brush sheds its needles too quickly and makes a warmer cover. Fir may easily be set too densely and the leaves on branches of deciduous trees wilt too quickly, hence they do not afford shade to the soil which dries out too rapidly. Wollny has shown by experiments that seed and turf burn out if sown too thick, while vegetation on the same plot of land remains uninjured if the growth is more broken. He found that when the seed had been sown with a drill the soil be- tween the rows lost less water than that in the rows themselves and the further the plants stood from one another, the more water was retained in the rows as well as between them. Therefore, the proper adjustment of the quantity of seed to be sown on soils poor in water, will also assist in correct- ing injury due to drought\ Only in very definite cases can an overplanted soil be proved more ad- vantageous than bare soil. By an open growth of short-lived plants as a cover crop, water can be retained on sandy soils for later seeds. If seeding of the quick growing plants takes place in the autumn or early spring, the time these plants most need water will come during the autumnal or spring wet season, so that when the dry season comes, they are ready to set fruit and require relatively little w^ater; — rather, by shading the soil and by the forming of dew, they retain for the more superficial layers a pretty even moisture in which seeds sown later, and also delicate seedlings, can be developed which otherwise would have dried up on bare soil. Forest Litter. It should not be forgotten that any covering of the soil retards the aeration of the land and therefore, for the maintenance of fertility, the 1 Oesterr. landw. Wochenblatt. 1880, p. 233. i87 supply of carbon dioxid in the soil must be depended upon to disintegrate and dissolve the fragments of rock ; hence great care must be used in the choice of the soil covering. How much the mulching disturbs the circu- lation of the air is shown by Ammon's experiments\ With 40 mm. of water pressure in an hour there passed through a layer of earth 19.6 sc]. cm. in cross-section and 0.5 m. deep, the following amounts of air: — \\'ith a Grass Covering. Straw Covering. Uncovered. 1.60 1. 6.30 1. 7.32 1. In better aerated soils more carbon dioxid will also be produced and this, in spite of its increased elimination into the air, will make itself felt iii an increased amount in the soil. The result of letting the soil lie fallow con- sists directly in the greater production of carbon dioxid due to the action of micro-organisms and to the greater decomposition of the rock debris. Another disadvantage of mulching is the lessened availabiUty of the precipitation for such covered soil. The amount of this disadvantage will vary according to the kind of covering. It will increase with the increased sponge-like substance of the covering. Riegler's- statement may serve as an example of this diversity. He tested various forest litter and peat moss (Sphagnum) as to permeability. Of the 500 g. of water, sprinkled daily in a fine stream on the air-dry litter, the following amounts were absorbed or ran throught : — - Beech Litter Hemlock Litter Sphagnum Turf Ran through-absorbed. Ran through-absorbed. Ran through-absorbed. 1st day.. .400.3 99.7 441-3 5^-7 216.0 284.0 g. 8th day.. .487.6 12.4 499.6 0.4 493.5 6.5 g. This sprinkling corresponded to 10 mm. of rain and accordingly possi- bly 20 per cent, of the falling water was retained by beech litter, 12 per cent, by fir and 57 per cent, by moss. The mulch was 8 cm. deep all over. From Riegler's other tables it is found that, in the next 3 or 4 days, still greater amounts were absorbed daily, gradually up to the 9th day the litter became so saturated with moisture that almost all the water which fell upon it ran ofif. Ten mm. of rain setting in after hot, continued dry weather, w^et the earth under the beech mulch only to a depth of 8 mm. ; under the fir mulch, 8.8 mm. ; and under the moss, 4.3 mm. Besides this, the conditions vary according to the strength with which the water falls on the mulch. If the water, finely distributed, was sprayed on the moss cushion, 70 per cent, of the given moisture was soaked up, while of the same amount of water, supplied in the form of a fine running stream, only 14 per cent, was retained. Forests. The proximity of larger tracts of trees, viz., forests, must be considered as a means of saving the moisture in the soil of cultivated land. According 1 Biedermann's Centralbl. 1880. p. 405. 2 Forsch. auf. d. Geb. d. Agrikulturphysik, 1880, pp. SO-96. to Matthieu's^ observations, extending over ii years, the air in forests, 1.5 m. above the soil, is on an average colder than above bare ground, the difference being the greatest in summer. The forests exert the same de- pressing influence on the mean air temperature as they do on the temperature extremes, which are less in forests. When the temperature differences amount perhaps to only o.5°C., they are perceptible when a rain cloud passes over the region. Air will become saturated above the forest sooner than above uncovered land. Thereby the rain will begin sooner and be more abundant than on the land which is not forested. In fact measurements of Matthieu and Fautrat- prove greater amounts of rain above forests. Hygro- metric determinations have shown that the weight of water vapor in one cubic meter of air above a spruce forest amounted, on an average, to 8.66 g., while above forests of deciduous trees it amounted to 8.46 g. ; above un- covered soil at the same height (104 to 122 m. high), at a horizontal distance of 100 m. from the conifer forest, to 7.39 g. ; at the same horizontal distance from the deciduous trees, to 8.04 g. Thus the proximity of the forest in- fluences the moisture vertically and may also exert the same influence horizontally. Fallow Land. "Fallow Land" has less effect on the retention or increase of the water supply in the soil than on the accumulation of nutritive substances. Accord- ing to Wollny's" statements, the peculiarities of fallow land may be sum- marized as follows : — Soil lying fallow is warmer in summer and colder in winter. Fluctuations of temperature are greater ever}'where in fallow land than in soil overgrown with plants. During the time of growth the soil covered by plants has always a lesser water content than when lying fallow. This greater moisture content is retained in bare soil even when worked more frequently. Bare soil also gains more from atmospheric precipitation since, during the time of growth, considerably larger amounts of water per- colate through soil lying fallow, than in fields provided with a growing plant covering. From the standpoint of nutrition the carbon dioxid con- tent of fallow land is most noteworthy. WoUny's researches show that the air in fallow soil contains approximately 4 times as much carbon dioxid as in grass land. Therefore, the means for the solution of mineral elements in the soil are present much more abundantly; which explains in part the greater accumulation of nutritive substances in fallow land. This greater enrich- ment also depends partially on the quicker decomposition of the organic substances because of the greater temperature fluctuations, the increased moisture and the more vigorous activity of the micro-organisms. It should, however, be pointed out finally that soils with less power for holding water and in greater depths (sandy soils) with their greater permeability lose 1 Matthieu, Meteorologie comparee agricole et forestiere. Paris 1878; cit. in Forschungen auf d. Geb. d. Agrikulturphysik 1879, pp. 422-429. 2 Fautrat. Ueber den Binfluss der Walder, den sie beriihrenden Regenfall und die Anziehung der Wasserdampfe durch die Fichten. Aus Compt. rend. 1879, Vol. 89, No. 24; cit. Biedermann's Centralbl. f. Agrikulturcliemie. 1880, p. 241. 3 Wollny, Die Wirkung der Braclie. Allgem. Hopfenzeitung 1879, Nos. 55, 56. 1 89 considerable part of the plant nutritive substances which are washed away into the subsoil. Such soils therefore, conversely, must be kept under a covering of plants. Local conditions must show which one of these means can best be used to prevent a lack of moisture. In any case it is evident that we do not stand powerless in the face of drought. b. Loamy Soils. General Characteristics. In considering physical influences injurious to vegetation, we need not distinguish between loam and clay soils. We are concerned always with mixtures of clay and sand and only the proportions of these two elements differ. The sand content decreases more and more from sandy or "mild" loam to strictly loo my soil and to clay soils, which are plastic in a damp con- dition ; in them predominate the fine particles so easily washed away. In our agricultural land, mixtures of lime and humus will also be of importance as modifiers. Lime will make heavy soils more open by increasing their friobility. Fertility is directly dependent upon friability, hence plastic clays are sterile. Non-friable clay soils are impervious to water, and, in level places, easily give rise to the formation of swamps. The smaller the size of the soil particles, the greater will be their water absorptive power so that very significant changes in volume occur with extensive, rapidly successive differ- ences in the supply of water. LTpon this depends the characteristic cracking of clayey soils when drying out. Soluble salts can be washed out of clay soils only with difficulty. This drying out is much more dangerous as the soil approaches pure clay. When once dr}% clay takes water up again very slowly since it can penetrate only with difficulty between the closely packed soil particles. These peculiarities decrease proportionately as the admixture of sand in- creases. Drying out in summer becomes at times more dangerous in heavy soils than in sandy, especially if a vigorous grow^th of trees has developed in regions which at best are poor in precipitation. The summer rains do not then suffice to make good the loss of water. These soils are dependent on the winter moisture. Hence the plant growth suffers here much more in dry springs, in years when the winter moisture has been less and the snow covering has failed, than on sand. This explains the fact that, after hot, dry summers and winters, poor in precipitation, a blighting of the tops of old trees (i. e., a drying of the branches) sets in because of the lack of moisture, even if the spring has abundant rain. Sandy soils with moderate spring rains are saturated more quickly and the water is at the disposal of the roots. Heavy soils remain "cold." This is explained by their high water con- tent which increases with the fine granular structure. In many regions im- ported conifers (Abies Pinsapo, Biota orientalis aurea, Taxus hibernica, 190 Picea orientaUs) die quickly. This is ascribed to winter frost but upon closer observation it is discovered that low temperatures become harmful only when the soil is very wet^. A deficiency of soil aeration is the most harmful factor since upon the aeration depend the phenomena of decay in the decomposition of organic masses. Thus in judging loamy soils as to their fertility not only the de- gree of friability, but also the depth to which this extends, becomes decisive. Since the firm loam layers of the subsoil are aerated only with difficulty, the spreading out of the root system takes place only in the friable layers. Therefore a special value should be laid on the maintenance of this friabil- ity. This must be taken especially into consideration in forests, where the litter IS constantly raked away. Ramann's investigations- show that, in re- moving litter, the soil becomes densely packed and works harm to the forest tract. The packing of soil and the necessity for loosening it should especially be considered in growing all tropical plants, as Vosseler" has proved. He describes the soils characterized by Koerts as "older red loam," and especially the primeval forest soil of East Usambara thus; — "The red soil consists mainly of fine loam and clay which is pervious but too finely porous to take up small humus particles ; besides, chemical action takes place possibly in the upper surfaces alone and thus prevents their penetration into the lower soil. Since the soil itself is the final pro- duct of decomposition, it lacks the advantage of i)rocesses of loosening up which possibly take place during such action." Here also, therefore, the loosening of the soil is given as the first requirement for successful culti- vation. The more clayey the soil is, the more slowly the vegetable refuse will be decomposed because of the lower temperature. While in sufficiently friable soils, a normal decomposition takes place, masses of raw humus collect on thick clay soils, i. e., particles of plants, which are only slightly decomposable, remain deposited on the soil because the conditions are un- favorable for decomposition. If very fine grained soils with a greater moisture holding capacity, i. e., ability to retain large amounts of water w ithout giving it ofl^ in the form of drops, acquire so much water that it overcomes the continuity of the substance particles by penetrating between them, thus forcing them apart, the soil becomes softer. This condition is especially peculiar to strong clay and red soil ; such a disintegration occurs less frecjuently in loamy soil. Such reduction of the soil is doubly dangerous, if it takes place in the autumn or spring. On the one hand, the soil washes away at once and the seeds are soon exposed to drying or to freezing as the case may be. On the 1 Cordes, W., Fieitrag- zum V'erhalten der Coniferen gegen Witteriingseinflusse. Hamburg- 1S97. 2 Ramann, E., Untersuchung streuberechter Bdden. Sond. Z. f. Forst- u. Jagd- wesen, XXX .Jahrg; cit. Bot. Jahresb. 1900, II, p. 415. ^ Vosseler, Ueber . einige Eigentiimlichkeiten der Urwaldboden Ostusambaras. Mitteil. a. d. Biol. Landwirtsch. Institut Amani, 1904. No. 33. 191 other hand, this condition also retards working the soil and planting the fields, thus becoming a cause of poor harvests. Especial consideration should be given to the fact that, for all our cultivated plants, the usual planting time has been determined by observing the behavior of the plants in our climate. It can be shown at any time that variation in the periods of cultivation pro- duces changes in the character of the plants (the change from winter to summer grain). Such a delay of the seeding time often acts injuriously, as, for example, in peas. The same seed that furnishes a fine crop of healthy plants, when sown early in spring, very often produces low plants with small pods, greatly injured by mildew, if sown in summer. Kohlrabi, planted too late in spring, easily become woody, etc. Similar phenomena may be observed in fine sandy heath soils (loose loam). Grabner^ characterizes this form of soil as consisting of sand grains almost as fine as flour with only small clay admixtures. The whole mass when wet looks like loam. In a dry condition, however, it may be dis- tinguished from loam proper by its porosity. Thus, as a result of its very fine granular structure, it can become as hard as stone. In places which are cultivated constantly and kept loose by means of animal manure, such soil is often valuable but in forestry it is not, for, after the usual single loosening, the fine sand is at once packed together by rain and too little oxygen from the air can get to the roots of the trees. The Covering of Soil with Silt. In heavy rain storms and floods soils with a large content of very finely broken particles are washed together and, after the evaporation of the water, are left in the form of a thick, close crust. The moisture holding capacity of a soil increases with the fineness of its pulverization, as has been men- tioned above. Increased pulverization of the particles deepens the upper surface and the power for retaining water depends on surface attraction. By pulverizing a soil mass, consisting of coarse pieces of quartz from i to 27 mm. in size, which had an absolute saturation capacity of 7 per cent., the capillary absorptive power was so increased that a fine sand produced from the quartz, the size of its grains being 0.3 mm., held back more than 6 times as much water. One sees that under certain circumstances the kind of mineral may be unimportant and only the mechanical constitution of value ; that, therefore, even quartz dust can assume the role of clay. Naturally this dustlike sand has no coherance whatever, and can therefore never in itself take over the role of a binding substance such as clay. Principally, however, it is clay soils which suffer from erosion in the form of silt and, by making air tight layers, cause the decay of seeds and plant roots. At times the roots form accessory organs in order to find the necessary air in marshy soils. In this connection, attention should be called to the knee-like outgrowths of roots which struggle to the upper surface of the soil, as those 1 Grabner, Handbuch der Heidekultur, 1904, p. 200. 192 of Taxodium distichum and of Piniis serotina which are not formed on dry soils, and are described by Wilson' as aerating organs. An example of the injury to vegetation, due to a direct deposition of silt, is furnished by Robinet- of Toulouse, where the nurseries had stood for only two days under water. At the base of some plants very little mud was deposited. These remained healthy. But when the mud covered the base of their trunks, possibly 10 to 12 cm. deep, the damage was great. Almond, acacia, cherry (even the mahaleb cherry) mountain ash, Ligustrum, Ma- honia, Evonymous and most conifers were killed. Individual specimens of Crataegus, Pirus Communis (of which those grafted on the quince suffer less) Pirus Malus, Castanea, Mespilus, Catalpa, etc., which had stood 8 to 10 days under water, blackened at the base and died when the silt was not removed. Platanus. Alnus, Ulmus did not suffer, and Populus, as well as Salix (weeping willow), developed many roots from the base of the trunk out into the silt. All the specimens of Sophora, Fraxinus, Carpinus, Fagus, Betula and Robinia did not die ; the leaves of the survivors, however, turned yellozv. The linden and chestnut lost all their leaves. Evergreen plants, and even a part of the conifers, lost their leaves when they had been covered by water. Of double importance is this change in the physical constitution of the soil in regions exposed to frequent inundations and, among them, the soils suffer most which are flooded by sea water. Aside from the injury to vege- tation from the large salt content of the- soil, there is found, according to A. Mayer^, as a resulting phenomenon of a dense covering, noticeable at times only in the second year, a formation of a black layer, strongly im- pregnated with iron sulfate, which may further injure vegetation. Von Gohren* also emphasizes the formation of such kinds of ferrugi- nous layers called "Knick" in West Friesland in very humus, loamy and clayey mud deposits of sea and river m.arshes and explains their production by the fact that the ferric oxid in the loam is reduced to ferrous oxid by the organic substances in the absence of air. This ferrous oxid combines with the crenate acid to form crenic ferrous oxid. Crenic ferrous oxid, distributed in every direction, is gradually oxidized again, cements together all parts of the soil as ferric hydroxid and co-operates in the formation of meadow ore of such ill-repute. We will finish considering the formation of meadow ore when discussing the peculiarities of swamp soil and now turn first to the phenomena of silt covering under the influence of salt solutions found in the use of fertilizing salts. Mayer's experiments show that particles of clay suspended in water are precipitated differently when they are in suspension in pure water or in water containing sodium chlorid and other admixtures. In pure water 1 Wilson, W. p. The production of aerating organs on the roots of swamp and other plants; cit. Bot. Jahresber. 1889, I, p. 682. - Revue horticole; cit. Wiener Obst- u. Gartenzeitung 1876, p. 37. 3 Mayer, A., Ueber die Einwirkung von Salzlosungen auf die Absetzungsver- haltnisse toniger Erden. (Forsch. auf dem Gebiete d. Agrik.- Physik. 1879, p. 251.) 4 von Gohren; Boden und Atmosphare. Leipzig 1877, p. 56. 193 the particles are deposited according to size (more exactly, according to the proportion of their surface to their mass). The finest particles remain un- commonly long in suspension since they are held by the attractive power of the water, which is almost comparable to a chemical solution. The at- traction of gravity for these particles is powerless in opposition to this attraction. After the clay, which has been dissolved in a glass cylinder for the experiment, precipitates from a salt solution, it is noticeable that a layer consisting of close, fine clay particles has formed with a comparatively very clear fluid above it. Because of the presence of sodium chlorid, all fine clay particles are precipitated more as a whole (coagulated, according to Schlosing). "Flocculency" is thus produced. The fall of the somewhat coarser particles among these appears to have been held ba^k, while that of finer ones has been somewhat hastened. It has been assumed that probably the presence of the salt has decreased the attraction between clay and water, since the w-ater then lets the clay fall more completely. On the other hand the attraction of clay to clay must have been increased, and it is therefore more compact. Durham- explains the process by the fact that every bit of the attraction of the water otherwise required entirely for the suspension of the clay is satisfied by the salt of the solution. According to him, sulfuric acid acts like the solution of sodium chlorid, and, according to Mayer, all mineral acids behave in the same way. The same is true of mineral salts even in an excess of fixed alkali or ammonia. According to the theories now prevailing, electrolytes act flocculently. i. e. all bodies which in an aqueous solution are partially split up into "Ions." Non-electrolytes have no action. At any rate, an electric current precipi- tates the flakes. It should therefore be assumed that the particles distributed in the water are charged with electricity and the cause of the oscillation may be sought in this electric charge^. The chief point, worth considering for all cultivated clay soils, lies in the fact that the nitrates, so far as deposition of the clay is concerned, ap- proximate the chlorates and, on account of the ease with which they are washed away, rapidly cause the packing of the soil. By this is explained the mechanical destruction of soils rich in clay, when repeatedly fertilized ex- clusively zvith nitrates. At first fine crops are obtained but later retrogres- sion takes place. Sodium chloride fertilising used for certain plants has naturally the same destructive effect. Behrens* calls attention to the real disadvantage of an excessive use of fertilizing salts. Their osmotic action comes especially under consideration. Because of this osmotic action of the soluble salts in the soil, it is more difficult to supply the water needed by the plant and the plant responds by a suitable modification of its organs. In correspondence with the physiolog- ical lack of moisture, the plant reduces its evaporation by forming fleshier 1 Biedermann's Centralbl. 1883, Nov., p. 786. 2 Chem. News; cit. "Naturforscher" 1878. p. 112. " Ramann, E., Bodenkunde, 2nd. Ed.. Berlin. .J. Sprinfrer, 1905. p. 225. ■i Behrens, J., Ueber Diangungsversuche. Jahresb. d. Vertreter d. angewandten Botanik, II Jahrg. Berlin, Gebr. Borntrager, 1905, p. 28, 194 leaves with smaller intercellular spaces ; this may be found in plants near salt springs and on the sea shore. Among our cultivated plants, tobacco suffers most; it reacts exactly as in hot, dry summers and forms fleshier leaves with a reduced burning quality. Hunger^ confers these observations, made in Europe, and says of the cultivation of the Dehli-tobacco on Sumatra, that the leaf most valued, most grown and most carefully selected, is large, thin, poor in oils, and develops only in the presence of abundant water as in continued rainy weather, while in dry weather small, thick, less valuable leaves, covered with many glandular hairs, are formed. The Improvement of Soils Which Are Becoming Compact. The improvement of the easily packed clay soils will have to lie in the increase of their ability to be worked. Heavy soils are unyielding, i. e.. they offer great difficulty by sticking to the farm implements, when damp, and by hardness, when dry. Great clods are produced which generally do not fall apart easily if the clay or red clay soil is poor in humus. It is well-known that the best plan for working soil for spring planting is to break it up in the fall and let it lie in rough furrows. The freezing of the water in the interstices during the winter months reduces the tough clods to a mellow crumbling mass. These advantages are available only for spring planting and disappear after the heavy rain storms of the summer. Therefore care must be taken to prevent caking by supplying humus or marshy earth ; fertilizing with long strawy manure is very greatly used. However, Umintj and marling the soil have given very effective results. Practical experience has shown that the addition of calcium, which is in solution in the soil as the bi-carbonate, will hinder its caking. A definite amount of all salts, even of the most effective, calcium and magnesium, must be kept in solution in excess of the amount necessary to start action if any deposition of the clay particles is to take place. Even in rivers the flocculent action of dissolved salts makes itself felt since, for example, the sediment in rivers flowing from lime regions is more quickly deposited than in those from regions poor in lime-. For agriculture, fria- bility becomes directly important since upon this depends the proper state of tillage. The small bits of the soil behave similarly to the clay flakes. Hil- gard proved the action of lime by tempering solid clay soils with i per cent, quicklime. While the original clay soil became as hard as stone after drying, that mixed with lime was found to be crumbly and mellow. Since, besides a continuous mechanical working of the soil, the salts also condition its looseness, this must be the case, to an equal extent, in forest soil also. If the soluble salts, determining the friable structure, are decreased, as by excessive use of litter, covering with raw humus, the leaching of the upper layers, etc., a packing of the soil must take place. 1 Hung-er, F. W. T., Untersuchungen und Betrachtungen liber die Mosaikkrank- heit der Tabakpflanze. Zeitschr. f. Pflanzenkrankh, 1905, Part V. - Ramann loc. cit. p. 226. 195 A top dressing of waste lime from sugar factories is often made use of in the cultivation of beets. The mechanical efifect makes itself felt not in- frequently by the fact that, as a result of increased capacity for being heated and the scanty supply of water, these soils later cause heart rot and dry rot. Hilgard's statements^ on the "alkali soils" of California are of great interest. The alkali places often found between excellent cultural lands con- tain so much salt that they become noticeable by efiflorescence on the surface. Those which contain alkaline carbonates (and partially also borates) are dis- tinguished by the difficulty or almost impossibility of producing a really friable soil. After each rain, a coffee brown, clay water, colored by dis- solved humus, stands at times for weeks on those places, recognizable be- cause of their lower position. The same working of the soil which gives good soil the consistency of loose ashes makes the alkaline land a mass of rounded clods varying in size from a pea to that of a billard ball. After evaporation, heating and saturation with carbon dioxid, the blackish brown solution, leached from alkaline soil, gives 0.251 per cent, in- combustible residue. Of this 0.158 per cent, was redissolved in water and this soluble part consisted of 52.74 per cent, sodium carbonate, 33.08 per cent, sodium chlorid, 13.26 per cent, sodium sulfate, 1.83 per cent, sodium triphosphate. The 0.093 PC cent, insoluble residue from the heated water extract con- tained 14.02 per cent, calcium carbonate, 5.37 per cent, calcium triphosphate, 5.77 per cent, magnesium triphosphate, 24.37 P^^ cent, silica soluble in NaoCo.,, 50.47 per cent, of ferric oxid, aluminium oxid and some clay. In this case, as well as in many other alkaline soils in California, the ad- dition of a sufificient amount of gypsum (land plaster) produces a striking effect. The caustic action of the alkaline carbonates on seeds and plants stopped at once so that where previously only "alkali grass" (Brizopyrum) and Chenopodiaceae grew, maize and wheat were produced without difficult}'. The gypsum naturally requires a longer time for the mechanical change of the soil surface and its greater loosening. Inundations. In opposition to the frequently widespread anxiety when volumes of water break over cultivated land, it might be emphasized that, naturally, aside from the washing away of nutritive substances and the mechanical injury due to the pressure of the waves, vegetation is not extremely sensi- tive to a water cover over the soil for some time. A\^oody plants especially, as floods show, possess a great power of resistance, which continues as long as the water keeps moving. Stagnant water, remaining for a long time on the surface of the soil, works the greater harm ; for a shorter time, inundations in the form of 1 Hilg-ard, Ueber die Flockung- kleiner Teilchen und die physikalischen und technischen Bezichunsen dieser Erscheinung. American Journal of Sciences and Arts. XVII, March 1879. For.sch, auf d. Gebiete d. Agrikulturphysik, 1879, p. 441. 196 dammed up water may come under the head of useful factors of cultivation. At any rate inundation will always' be more dangerous than those methods of irrigation where the soil always remains accessible to the air. The oxygen content of irrigation water increases oxidation in the meadow soils since water filtering ofif through the soil shows a lesser amount of oxygen and, at the same time, an increased amount of carbon dioxid and sulfuric acid in comparison with water in use for irrigation^. So long as sufficient oxygen is present the slow phenomena of oxidation of organic substances into carbon dioxid, ammonia and nitric acid, which we term decomposition, are accomplished chiefly by the action of micro-organisms. If a scarcity of oxygen occurs, however, due to continued retention of the water, that process of decomposition begins, partly of a purely chemical nature, partly with the co-operation of bacteria, which we call decay, whose final products are compounds which may still be oxidized. If the water accumulates in places where impervious layers of soil entirely prevent any vertical flowing away and all horizontal flowing away is also made difficult, the land becomes marshy. With the excessive wetting of the soil, the symptoms are again seen, which usually appear gradually with root decay. In deciduous trees, especially fruit trees, and with grapes a premature yellow leaf (chlorotic) condition becomes noticeable, which advances from below upward. This advancing death and falling of the leaves from the base of the branch to- ward its tip bear witness to the fact that the growing branches strip ofif their older leaves in order to mature their younger ones, which happens also in a gradual drying up. By this means, yellow leaves ma)^ be distinguished from the pale leaves resulting from the action of frost, in which the young leaf apparatus is disturbed and its normal chlorophyll action retarded. Conversion of Land Into Swamts. R. Hartig's- observations show that stagnant water is most injurious in forest plantations since the sensitiveness of the trees to frost is increased and freezing and heaving occur in the seed beds. Hartig'' observed decay of the roots to a devastating extent in the tracts of the young pines in Northern Germany. It begins between the 20th and 30th years when, after a short period of weak growth, the trees, still covered with perfectly green needles, topple over as soon as a weight of snow touches them or a high wind acts on them. It is found that the tap root (see Growth of Stilts, p. 92) is wet and rotted up to the base of the trunk while most of the lateral roots appear to be healthy. Such a decay of the roots may indeed be found in spruce plantations, but it is less noticeable because the superficially extended 1 "Wollny, E., Die Zersetzung der organischen Stoffe und die Humusbildung'en. Heidelberg 1897, Carl Winter, p. 351. - Hartig, R., Lehrbuch der Pflanzenkrankheiten, 3rd. Ed. Berlin, Springer 1900, p. 263. 3 Die "Wurzelfaule, Zersetzungserscbeinungen des Holzes, Berlin, Jul, Springer, J878, p, 75. 197 root system makes the tree less dependent on the few roots growing down deep into the soil. It may be observed, especially in the province of Brandenburg, that the healthy condition of pines ceases if the sand flats most suitable for this growth have depressions in the ground where the accumulated water forms marshy pools. Up to the edge of these marshy places the trees stand erect and are comparatively long needled. At the point where the black moor begins, the growth becomes weakened, the needles shorter and the tree shows very small annual rings which not infrequently cease entirely. In the increased planting of the very profitable pine trees, carrying them even on to damp soils, it is not surprising that root decay is found there to a very marked extent. It is advisable to limit the culture of pines to sandy, open positions and to choose for heavy, wet soils, such species of trees as are found by experience to best endure moisture. In places where no definite agricultural system regulates the tracts, the suitable kinds of trees make a natural appearance in the course of years, because of their greater power of resistance in the struggle for existence. It is approximately the same as the gfadual control of the position in frost holes by the kinds of trees which resist frost (hornbean, birch, aspen). The red alder can best endure the strain of stagnant water. Besides this, black and silver poplars, as well as most willows and the sweet birch, thrive on moist soils. The ash is often found also, but under these conditions the trunks are entirely covered with moss and canker-like swollen spots. In order to overcome the injury due to turning land into swamps, its cause must be determined exactly. At times the condition is due only to a lack of air circulation, and here the partial clearing of the land of its tree vegetation by the removal of the undergrowth and the lower branches of the trees, together with proper thinning, would be beneficial. Even when the land only becomes slightly swampy, especially in mountains, it may be re- stored by planting with conifers (Spruces). This holds good for the cases when increased evaporation of the upper surface is sufficient to overcome the accumulations of water in the soil. As the trees grow, and because of their close proximity, their evaporating surface not only increases but also less and less water can fall to the soil, because of the thick shelter of leaves. The very radical means of removing the water by drainage or ditches should be used in forest tracts only after careful consideration of all local conditions since this method is often attended by greater disadvantages than advantages. This is especially true in mountain forests where the lowering of the water level of one district may easily have wide spread effects on the surrounding region. In some cases, areas, especially slopes, with a strong tree growth, where there is no excess of water, become drier. Trees accus- tomed to the former amount of moisture deteriorate and may partially die. On plains such sharp changes due to drainage are less to be feared. It would not be necessary to further discuss the formation of marshes if, aside from the exhalation of gases, injuries to cultivated land did not I. 11-75 COo 2.48 CH, 2. 12.62 5.68 '' 3- 34-99 29.03 " 4- 55-81 42.54 " 5- 56.00 42.70 " 6. 45-9 54-1 " 7- 43-3 56.6 " 198 follow attempts to drain the marshes and boggy places. The injury to meadows should be considered especially in this connection on account of the frequent use of injurious marsh and boggy water for irrigation. The conversion of irrigated meadows into marshes by overfilling the soil with sewage may be considered only in passing. The statements of Bischof and Popoff^ should be cited in connection with the exhalation of gases. The gases produced are often rich in hydro- carbons, especially methane or marsh gas (CH^). Popofif investigated the gas developed in a cylinder which contained a slimey mass consisting of kitchen refuse and substances of similar character. This slime was kept 33^ weeks in the cylinder, at first at 17° C, later at 7 to io°C., and gave gas mixtures of the following percentages of composition in the successive investigations which took place usually at intervals of 2 to 4 days : — - 4.71 O. 81.06 N. 81.70 0.0 O. 35-98 N. 0.0 " 1.65 " 0.0 " 1.30 " 0.0 " 0.0 " 0.0 " 0.1 " These figures show that at the beginning of the experiment part of the air found in the cylinder was driven out, and part used up, while the oxy- gen oxidized the organic fragments in the slime. So long as free oxygen was present, the formation of carbon dioxid exceeded that of marsh gas,- — ■ on the other hand, this proportion was reversed as Soon as the oxygen was exhausted. Proceeding with the hypothesis that it is the cellulose in the slime which is decomposed, assisted by the action of the lower organisms, Popoff put clean filter paper with a small quantity of slime into a flask. On investi- gating the gas formed after some little time, he found its composition to be 34.07 per cent, carbon dioxid, 37.12 per cent, marsh gas, 1.06 per cent, hy- drogen and 27.75 per cent, nitrogen. Near marshes, however, we also frequently detect the odor of hydrogen sulfid. This comes partly from the decay of protein bodies which form leucin, tyrosin and other substances by their decomposition and finally car- bon dioxid, marsh gas, ammonia, etc. Erismann's- observations, cited by Detmer, make possible the determination of the quantitative composition of the gas given off in 24 hours from 18 cubic m. of excrement placed in a poorly ventilated cess pool. The whole mass gave 11. 144 kg. carbon dioxid, 2.040 kg. ammonia, 0.033 ^S- hydrogen sulfid and 7.464 kg. marsh gas. In this decomposition oxygen and nitrogen were also set free. 13.85 kg. of oxygen are said to have been taken up by the 18 cubic m. in 24 hours. 1 Bischof's Lehrbuch der chemischen und physikulischen Geolcgie, 2nd. Ed. Popoff in Pfliiger's Archiv f. Physiologic, Vol. X., p. 113. 2 Zeitschr. f. Biologie, Vol. XI, pp. 233 ff. 199 Thus a comparatively very slight development of HoS is found and it must be assumed therefore that, if large amounts of HoS are formed in marshes and other places, they must owe their origin to a reduction of sul- fates in the soil, conditioned by the organic substances present. PageP and Oswald summarized the results of their investigations on such reduction processes in the substances of marshes and found that, in the absence of air, sulfur metals occur, as well as hydrogen sulfid, and that, together with this reduction of the sulfates, ammonia is set free from the marsh substances containing nitrogen. The authors do not state defi- nitely whether these substances are produced only in the absence of air, but in their production may lie the harmful quality of stagnant water. The Burning of Plants in Moist Soil. In summers, remarkable because of great temperature extremes, it has been observed that on hot, clear windy days, plants of rapidly growing, large leaved crops, such as hops, wilt greatly, particularly when grown in damp places. The lower and middle leaves of plants growing in damp hollows are sometimes seen to turn yellow and brown at the edges and partially to dry up so that they can be rubbed to a powder in the hand. These specimens have been partly burned by the sun. The noticeable feature is that the burning takes place directly on those places in the field, in which, through- out the whole year, sufficient moisture is present, while in higher, drier portions, still more exposed to the wind, the plants usually suflier less. My comparative experiments- throw sufficient light on such cases. They prove that plants, which from the beginning produce their roots in a soil contain- ing much water or even in water cultures, evaporate much more water per square centimetre than do plants of the same strain grown under conditions exactlv similar except with a lesser water supply. It is an interesting but not very well-known phenomenon that many of our cultivated plants from very different families grown under optimum conditions, in producing one gram of mature, dry substances, evaporate approximately equal quantities of water,, — indeed the transpired water varies from 300 to 400 g. in amount. If the plants grow in localities which, like soils with an impervious subsoil, constantly have a great deal of water at their disposal, a constant nutrient solution will be present in the interstices of the soil, more or less highly con- centrated according to the soluble materials present. If the concentration exceeds the amount favorable for the plant species, the plant grows less vigorously, remains short-limbed, small-leaved, but usually dark green. If the concentration is exactly right, the growth is very rich and luxuriant and the absolute water requirement is very great, but is small if reckoned per gram of dry material produced. Under such conditions the plant finds the soil water of great value. In excessively damp places, however, it often happens that the soil solution is poor in different nutritive substances. 1 Landwirtsch. Jahrb., Vol. VI, Supplement, p. 351. 2 Sorauer, Studien iiber Verdunstung. Forsehung-en auf dem Gebiete dei" Agrikulturphy.sik, Vol. Ill, Parts 4 and 5, pp. 43 ff. :2o6 The weather requirement is greatest under such conditions just as if the plant made the greatest struggle to produce as much as possible from the very scarce nutrient substances present. The leaves, then formed, are very large and well spread, but are very little resistent to cold as well as to heat. They react unfavorably to influences which pass over other plants without leaving any ill effect. Such disturbances occur earlier in plants in moist localities. On hot and especially windy days, evaporation is enormously increased, the amount of water transpired is then considerably greater than that supplied by the axial organs. Consecjuently the leaves on many plants wilt. The smaller the normal transpiration per square centimeter surface, the longer the amount of water brought by the stem, even on extremely hot days, will compensate for the loss of transpiration. The plants of damp localities which, as ex- perimentally determined, evaporate much more water in the same unit of time than do plants from dry places, have thereby first of all reached the limit when lack of moisture in the cell acts injuriously. In these plants the leaves dry up first and not the very youngest nor the very oldest but, as a rule, those working most actively and in part still elongating.. Proper drainage to remove the water from those particular tracts of ground is the surest method of overcoming the trouble. Delayed Seeding. As a result of damp soil the time for planting is frequently delayed. The following are the results of experiments by Fr. Haberlandt^ and H. ThieP. The most detailed experiments were made by Haberlandt in 1876 with four kinds of summer grain in which, on the ist and 15th of the months April, May and June, the seed was sown on a bed 3 sq. m. in size. The results may be summarized as follows : The amount of harvest in all sum- mer grains decreased more and more as the seeding was delayed. This was based first of all on the considerably weaker growth of the grain planted late and was most evident in the smaller number of fertile stems. A de- crease not only in the quantity, but also in the quality was very noticeable. The weight in straw increased with delayed sowing. In general the chafif and roots of the crop increased disproportionately to the weight of the grain. The quality of the grain itself also decreased greatly. Barley and oats from later sowings had a greater amount of chaff by weight; the smaller the in- dividual grains were, the greater this disproportion became. The later sowings were attacked to a greater extent by ergot, mildew, rust and especially by leaf lice. Besides this, up to the time of forming the blades, as well as blossoming and ripening, they required a greater amount of heat than did earlier sowings. Even the germinative power of the har- vested grain was affected and of a lowered quality in seed from plants of 1 Haberlandt, Pr., Die Beziehungen zwischen dem Zeitpunkt der Aussaat und der Ernte beim Sommergetreide. Oesterr. landw. Wochenbl. 1876, No. 3; 1877, No. 2. 2 Thiel, H., Ueber den Einfluss der Zeit der Aussaat auf die Entwicklung des Getreides. Ref. in Biederm. Centralbl. f. Agrikulturchemie. 1873, p. 47. 20 1 late sowings. In the first place, the percentage of germination was lower; in the second place, the grain from late sown and late harvested seed also recjuired a longer time for germination. From Haberlandt's earlier investi- gations in this line, showing a lesser development of grain in bulk as well as in absolute and specific weight, it is further seen that the amount of soil moisture alone is not the only cause of the difiference between late and early- sowing. In these experiments the plants had a sufficient water supply, from the beginning, and yet showed these different proportions. Thiel's experiments with late sowings were made at various times in the autumn. The time of harvesting for all the plants, even of widely different periods of sowing, was approximately the same, but very late sown seed had a very small yield so far as it remained alive at all. Indeed Thiel rightly calls attention here to the fact that late sown seed sprouted simultaneously with that sown earlier with corresponding spring weather, without, however, having had time to collect sufficient material for an abundant development as did the plants grown from seed sown earlier. Naturally the constitution of the seed plays a considerable role here. The older the seed, the more slowly the reserve substances are mobilized. With ripening and subsecjuent maturing, the amounts of sugar and amido nitrogen compounds decrease^ and do not become prominent again until germination. The more or less favorable sprouting of the seed depends on its age and the soil constitution. At this point we will insert the warning that no reliance should be placed on the results of other germinative tests, but one's own soil must be tested di- rectly as to its behavior with dift'erent seeds. Seed which keeps well, accord- ing to common germinating tests, may give poor results, especially in heavy soils and, conversely, a light soil may often help seed to make a good growth, which developed only a moderate quality in the germinating bed. Hiltner's" report, for example, on newly harvested rye, which had suffered from a thunder storm, showed that it grew well in some fields, but absolutely would not grow in heavy soil. In another case, rye, developing 97 per cent, seed- lings in a germinating test, molded almost entirely on one field, while in an adjacent one it gave normal growth. Souring of Seed. In the section on too deep sowing (p. 106) we have already considered the disadvantages to which seed is often exposed in heavy or in incrusted soils with a large water content. Even germinated seed has to struggle against difficulties due to physical constitution of the soil; viz., from an excess of water in heavy soils. Here is found also souring of seed, which, to be sure, can occur also in light soils, but has been obserx^ed usually only in heavy, tough soils. The souring is due to a decay of the roots which have been longer in contact with standing water, charged with organic substances. Most roots 1 Johannsen, W., Studier over Planternes periodiske Livs vttringer, I; cit. Bot. Jahresb. 1897, I, p. 143. 2 Hiltner, L., in Prakt. Blatter f. Pflanzenbau u. Pflanzenchutz, 1903, Part I. 202 withstand very well a continued contact wuth running or standing water, which is free from organic substances, as can be seen in the different water cultures. Here, however, all living or dead vegetable particles in the culture vessels are avoided, for the decomposing organic substances take up all the oxygen which is present in a small supply. The roots of the growing plant must be killed because of a scarcity of oxygen and excess of carbon dioxid. Also, under ordinary conditions, seeds can survive contact with water, lasting for weeks, if the temperature is low. Thus Feige^ states that wheat which had stood for 5 weeks under cold water at 5°C. still lived. On the other hand, wheat kept 8 weeks under water, the temperature of which in- creased to 7°C. had disappeared without leaving a trace. Corn, which had previously been healthy, withstood water at 3°C. for 4 or 5 weeks, but was injured somewhat more than the wheat mentioned above. In the same way, alfalfa and clover withstood standing in water better than did com. According to Kiihn, rye suffers especially from souring, while under the same conditions brome grass and others develop very luxuriantly. To this circumstance is due the erroneous belief, which even now occasionally appears, that rye can change into brome grass. According to our view, "Arrabbiaticcio" of wheat in Marengo and on the Roman Campagna be- longs under this head. Peglion'- explains the disease as a general deteriora- tion of the plants due to being overrun by the luxuriant growth of weeds, w^hich thrive better than the wheat on unsuitable soil. In Southern Italy the disease is called "calda fredda" and "secca moUa." The souring of the winter oil seeds, especially rape, is the most serious of all. From standing continually in water the roots decay from the tips backward so that in spring only the crown of the root and the leaf rosette remain. These appear to be healthy as long as the moist spring weather prevents their dr}'ing out, yet, as the season becomes dry, the plants turn brown very soon and may be drawn from the soil by one leaf. An investigation by E. Freiberg and A. Mayer" serves to explain the fact that under continued wet conditions the character of the vegetation changes, so that phenomena appear like the above mentioned predominance of brome grass when rye had been sown. This experiment proved that the roots of marsh plants need much less oxygen than those of cultivated plants. This proves, as might have been supposed from the ver}^ beginning, that the individual plant species make different demands on the oxygen of the soil and, accordingly, must adjust their habitat to existing conditions. From the result of the experiments, however, another conclusion may be drawn which may serve in general when judging the demands made by different plants on soil; viz., the amount of air needed by their root systems. It is found that the more oxygen the plant needs for respiration, the greater is its nitrogen content. Marsh plants show a strikingly low nitrogen content and 1 From Oesterr. landw. Wochenbl. cit. in Biedermann's Centralbl. 1877, p. 76. - Peglion, v., SuU' arrabbiaticcio e calda freddo. Annuar. d. R. Stazione di Patol. veget. Roma. Vol. I, 1901, p. 37. 3 Freiberg, E, und Mayer, A., Ueber die Atmungsgrofse bei Sumpf- und Wasser- pflanzen. Landwirtsch. Versuchsstationen 1879, p. 463. 203 have an open inner structure, permitting the storing of larger quantities of air within the body and suggesting the facihtation of internal respiration. Real water plants respire with a lesser intensity than land plants, as Bohm^ found in his experiments, by measuring in a hydrogen atmosphere the car- bon dioxid given off during internal combustion. Since it may be assumed that the amount of respiration is determined by the amount of protein burned in the plant's body, the oxygen needed by the root system will be greatest in cultivated plants, rich in nitrogen, and the most suitable soils will be those which most completely satisfy this need together with the other demands of the plant, i. e., rich field soil, which is loose or has been loosened. Those lands, therefore, which are repeatedly subjected to an oxygen scarcity, through the formation of crusts from rain action and the deposition of silt by floods, will have to be improved by corresponding changes in their physical structure. In the cases of souring, on the other hand, in which the air supply is not necessarily cut oft' by the physical constitution of the soil and in which only an excessive supply of water can fill the large interstices in the soil, we will have to turn to the removal of the water.. Here deep drainage or at least drainage canals 120 cm. deep, lowering the ground water level by this amount, are the most advisable precautionary regulations. The development of so deep a pervious layer is necessary because many Leguminoseae, like alfalfa, and sainfoin, with their deep growing main roots and fewer fibrous roots, are apt to die when they reach the ground water. Souring of Potted Plants. The souring of potted plants occurs chiefly when loamy or peaty soils are used. If the drainage hole of the flower pot is stopped up and excessive amounts of water given by some inexperienced laborer, the roots of the potted plants die completely, since they become brown and soft. The sour soil can be recognized at once by its characteristic odor. In this the process of decomposition of the abundantly present organic frag- ments, always contained in nutritive pot soils, takes place very differently. Probably acid compounds and also free acids are produced from the but imperfectly understood humus elements. If iron is present in the soil the tminjurious ferric salts can be reduced to the injurious ferrous ones, since, when the soil spaces are enlarged with water, a perceptible scarcity of oxygen must occur. The water is saturated with carbon dioxid from the secretions of the roots and also from the decomposition of the organic matters in the soil, and, with continued action, the carbon dioxid is sufficient to kill the plants. W. Wolf- proved experimentally that healthy plants, set in water contain- ing carbon dioxid, at once began to eliminate it in very greatly reduced quantities. The result is a wilting of the leaves which die later. 1 Bohm, Ueber die Respiration von Wasserpflanzen, Sitzungsber d. Kais. Akad. d. Wiss. zu Wien. 1875, May Number. 2 Tagebl. d. Naturf. Vers, zu Leipzig 1872, p. 209. ^o4 £ven if we cannot yet explain with certainty the mechanics of wilting which take place here (the explanation given by W. Wolf^ does not seem to be sufficient) we will, however, scarcely go astray in assuming that, as the result of the excessive accumulation of carbon dioxid in the soil water, the normal elimination by the roots of carbon dioxid, which is con- siderable in vigorously growing plants, is at once arrested. An unusually high gas pressure must therefore be produced within the plant, increasing to a positive pressure in the ducts and reducing their ability to conduct water to the aerial parts. The power of the ducts to conduct water will be decreased by the amount taken up by the negative pressure in the ducts. If thereby this conduction of water is weakened without corresponding re- duction of the use of water in the leaves, wilting results immediately. If the plants are placed in distilled water, as in Wolf's experiments, a normal appearance and normal functions again set in. The distilled water in this case is like a sponge, absorbing the carbon dioxid and other excretory pro- ducts of the roots. Finally the result is the same for the root, whether the carbon dioxid appears dissolved in water, or as a gas resulting from an insufficient soil absorption. For the aerial parts of the plant, however, conditions are differ- ent and it is very important whether they come in contact with water rich in carbon dioxid or in air containing the gas. At least Bohm's experiments- on the leaves of green land plants have emphasized this. He immersed leaves of different land plants under water containing carbon dioxid and found that the plant no longer gave oft' oxygen if the part concerned was prevented from surrounding itself with an atmosphere containing carbon dioxid which would cut it off from direct contact with the water. The results of excessive watering in pots with the drainage stopped and the consequent cessation of plant and soil activity are best determined by a microscopic comparison with the soil in a pot containing a healthy growing plant. What intense activity is found in the soil ! From the upper surface down to the bottom of the pot (in leaf and heath earth) are found fragments of leaves and stems, on which many kinds of the so-called mold forms with sterile mycelia, or with mature conidia, exercise their power of decomposition. According to the nature of the vegetable matter, Sepedon- ium (chrysospermumf), V erticillium ruherrimum, or P enicillium glaucum, Acremonium, Acrocylindrium, Cladosporium penicillioides, dift'erent kinds of Fusiarium and many others are found. On the upper surface often still other genera occur, especially the aerobic ones together with living diatoms and other forms of algae. The schizomycetes go deepest of all. Starch granules and bits of cytoplasm are found surrounded by colonies of rod bacteria radially arranged; colonies of bacteria have often been established also on fragments of crystals. All this active life is engaged in reducing the plant substance and favors the processes requiring oxygen, which we 1 Jahresber. f. Agrik.-Chemie, 1870-72, II, p. 134. 2 Anzeigen der Wien. Akad. d. Wiss., 1872, Nos. 24-25, p. 163. 205 term decomposition. All this active life will either be stopped, by closing the soil interstices with water, or be turned to those destructive phenomena of decay, decomposition in the absence of oxygen. Every soil has its my- cological as well as its bacterial flora, which decomposes the organic sub- stances. According to Oudemans and Koning^, these are approximately typical for definite kinds of soil. In potted plants it is safe to assume the beginning of stagnation when the upper surface of the soil is covered with a hard white or reddish colored lime crust, firmly attached to the edge of the pot. From the uncommonly large amount of carbon dioxid developed by the addition of acetic acid, it is evident that the incrustation of the uppermost soil layers in the pot, and at the edges, results especially from calcium carbonate. Magnesium carbonate is met with and also ferrous carbonate, which later through oxidation, produces as ferric hydrate dififerent colors in the crust. According to the microscopic examination, the characteristic swallow-tailed crs^stals of gypsum and the octahedrons of calcium oxalate, as well as the rhombic forms of calcium phosphate, soluble in acetic acid, occur. The presence of the last named salt can not always be demonstrated and never in large amounts. On the other hand, calcium carbonate and probably magnesium carbonate, together with very fine particles of quartz sand, make up the usual substances of the crusts, between which is per- ceptible at first an abundant fungous growth with a formation of conidia on the humus. The production of these crusts may be explained by the fact that the water, given in large quantities in watering, becomes charged with the carbon dioxid, abundantly produced by the process of decomposition within the soil interstices. Hence water is a splendid medium for dissolving the calcium carbonate present in the soil, the magnesia, the ferric phosphate, the ferric silicate, etc. The more quickly the superfluous water is drawn away by good drain- age in the pot, the less will the minerals be dissolved and washed away. On the other hand, if the water stands in the pot and once becomes charged with calcium, which is soluble in the form of calcium bi-carbonate, it can only be removed by evaporation from the saturated upper surface of the pot and, w^hen the pores of the pot are not closed by a green, slimy algal growth, this excessive water also evaporates slowly through its sides ; it leaves behind the dissolved substances. The pots "become coated." The calcium remains behind as calcium carbonate just as on the edge of a kettle in which water containing lime has been boiled. Thus the usefulness of the two processes, the frequent washing of the flower pots and the breaking up of the upper surface of the soil, is dem- onstrated. In the increasing desire to attain our ends by fertilization, different fertilizers are added to water soaked plants, but the main need, — sufficient 1 Oudemans, C. A. J., et Koning-, C. ,T., Prodrome d'une flora mycolog-ique obtenue de la terre humeuse du Spanderswoud etc. Extr. Archiv. neerland. ; cit. Z. f. Pflan- zenkr. 1903, p. 60. 206 aeration of the soil, — is overlooked. The plants have not improved with this treatment. The best results are obtained by transplanting when growth starts and the application of heat to the roots to stimulate growth. Eichhorn's^ investigations prove that fertilizing may be injurious rather than advantageous with acid soil, in the presence of free humus acid. He states that earths, rich in humus, which contained free humus acid, liberate the acids from solutions of neutral salts. The acidification thus produced is stronger than it would be without these salts and, therefore, fertilization with neutral salts will increase the acid in such soils. This happens with calcium phosphate or any phosphate where the phosphoric acid, or calcium phosphate, passes over into solution. The addition of neutral potassium salts, especially alkaline sulfates, favors decomposition. If tlie humus acid is combined with a base, such acidification does not take place. The addition of manure, liquid manure, etc., will act only disadvantageously with such chemical decomposition and is to be avoided as are marly earths. Injudicious Watering. The frequent dying of house plants makes necessary a reference to in- judicious watering. Excessive watering may be due to the fact that in- experienced people assume a lack of moisture in the soil as soon as the plant wilts. The fact that frequently, after watering, the plant becomes turgid during the course of the day gives weight to this assumption. If wilting follows this second turgidity, water is added until the plant is permanently wilted and the roots decay. Such conditions arise especially in the autumn when the more tender plants are put in conservatories with but little heat. The coldness of the soil then causes the wilting. We know from a number of cases cited by Sachs- that dififerent plants require definite temperatures for their roots to keep them working, i. e., taking up water. Tobacco and pumpkins wilt in a soil at 3° to 5°C. ; but if the same soil is warmed to 12° to i8°C., the root activity is re-established. In the examples cited above, when the previously watered, wilted plants become turgid during the day, this result is attributed to the influence of the watering. The real cause, however, was the diurnal rise in temperature of the air and of the soil, caused by the sun, whereby the roots were again stimulated to take up water. W^ith the coming of night and the corresponding fall in temperature below the limit at which the roots are still to take up water, the wilting is repeated. The plant can therefore die of thirst even when the soil is very moist, if the soil be too cold. On the other hand, in moist air, the plants can remain alive a long time with wholly decayed roots, as is shown by water cultures. This is also the reason wh)% in root diseases, symptoms of dis- turbance are noticeable in the aerial organs only at a late stage. Another cause of the wilting becomes noticeable in midsummer. If plants transpiring rapidly are exposed for some time to the hot sun and to 1 Landwirtsch, .TahrbiJcher 1877, p. 957. 2 Lehrbuch der Botanik, 1st. Ed., p. 559. 20/ currents of air, they begin to wilt in spite of sufficient soil moisture, because the quantity of water evaporating through the leaves cannot be replaced quickly enough by the root. To be sure, the supply of water will be in- creased as the temperature rises simultaneously with the increased sunshine. According to De Vries\, imbibition of the cell walls is increased and thereby their ability to conduct water, but the increased supply, nevertheless, cannot make good the loss through evaporation and the leaves must droop. If the pots are then watered, w'ithout having been tested, the earth will become sour. The same result is found in the so-called New Holland and Cape plants belonging to the families of the Epacrideae, Ericaceae, Papilionaceae, Rutaceae, etc. The loose, fine, sandy, but little decomposed earth, such as heath mould, cannot be pressed very firm into the pots, because the unde- composed pieces of roots and leaves form a very loose consistency ; with too heavy watering, however, the fine grains of sand and clay are first stirred up and then washed down so that only the long, loose fibrous elements re- main at the upper surface of the pot. These naturally retain but very little water and let it run down very quickly to the bottom of the pot. On this account the upper surface of the pot is always almost half dry. If now the gardener lets himself be led astray and waters the pots under such con- ditions, and if the pots have no good drainage, the very fine roots will decay. (It should be remarked in passing, that the so-called soured pots quite fre- quently show an alkaline reaction. I found with potted plants, whose roots had decayed, that moist red litmus paper turned blue as far as it lay upon the surface of the pot). As a means of overcoming this, transplanting into very sandy earth and sinking the soured plants in beds with warm soil has already been recom- mended. As a matter of course the roots must be cut back to the healthy part when transplanted. As a precautionary measure, the pots may be plunged into the ground and similar methods may be recommended. In doing this, how- ever, a stick or a piece of wood, turned like a cone, should be used to make a deep, funnel-like hole, whose upper edge is exactly the size of the edge of the pot. The pot then hangs in the hole. Below the pot the lower part of the conical hole forms a cavity and prevents the earth worms from crawling into the drainage hole in the pot and stopping it up. In flower pots stand- ing in a room, or on flower racks, the soil will not sour if only some little care is taken. The water content of the soil may be judged easily and com- paratively accurately by tapping the pot. If the earth is full of moisture, the water lies between the individual particles of soil and the sides of the pot and the sound resembles that of a dense mass ; when the amount of water is scanty, however, the pot rings hollow. According to the above, therefore, one should consider not only how much to water, but in what way potted plants should be watered. In order to avoid washing away the finest particles of clay and sand and thereby I Bot. Zeitung-. 1872, p. 781. 208 forming crusts, or choking the drainage of the pot, the water should never he poured quickly through the spout of the watering pot. In plants set in pots and sunken, a hose should be used, or, in pots set on forms in con- servatories, a slender and long spout, giving only a gentle stream of water. One should avoid holding the stream of water at the base of the stem, which is often entirely white as a result of incrustations of lime. Use of Saucers Under Pots. In house plants the use of saucers under pots is general. This saucer is necessary for preserving cleanliness on the window sill and on the flower table, but is usually injurious for the plants themselves. No matter whether the pots be watered from above or by soaking up water from the saucers, the soil will almost always take up too much water. Many plant lovers con- sider this condition advantageous. The result, however, is a choking of the roots at the bottom of the flower pot. The decay of the roots continues gradually upward and finally shows itself in the dying of the edges of the leaves. If these symptoms appear, the plant is, as a rule, lost to the ama- teur, but the gardener can often cure it. For the amateur, who has no warm bed at his disposal, we would recommend setting the sick plant in pure sand and placing it in a warm, half shady place. The Running out of Potatoes. In discussing the disadvantages of heavy soils, we should consider the point of view, repeatedly brought forward in practical circles, that our potatoes "run out," i. e., gradually lose their good qualities and degenerate. Some people would explain this by holding that, in the customary method of propagation by planting tubers, one really propagates asexually, without interruption, an individual once produced from seed and that, thereby, an organism so long lived must at last .show the weakened condition of old age. A proof of this is found in the retrogression in the starch content of our favorite older varieties as, for example, in the Daber potato. According to our point of view, the cause of the supposed running out lies in the lack of foresight of the agriculturalist in growing varieties on heavy soil which have been produced on light soil. We refer in this connection to Ehrenberg's work^ on the results of 15 years experiments at the "Deutsche Kartoffelkulturstation." The average yield of all the varieties grown seemed to increase constantly from 1889 to 1903. In regard to the "Daber" potato, the yields decreased only on heavy soil which is easily explained since in Daber a very light, dry, sandy soil predominates. If newly grown seed of this variety was planted in heavy close soil, it gave better results than the form which had been cultivated there for some time. The same new seed, however, planted in sandy soil, usually gave a poorer result when compared with the naturalized plant. We find 1 Ehrenberg, B., Der Abbau der Kartoffeln. Landw. Jahrb, Vol. XXXIII; cit. Centralbl. f. Agrikulturchemie, 1905, p. 235. PART III. MANUAL OF Plant Diseases BY PROF. DR. PAUL SORAUER Third Edition—Prof. Dr. Sorauer In Collaboration with Prof. Dr. G. Lindau And Dr. L. Reh Private Docent at the University Assistant in the Museum of Natural His'.ory of Berlin in Hamburg TRANSLATED BY FRANCES DORRANGE Volume I NON-PARASITIG DISEASES •BY PROF. DR. PAUL SORAUER BERLIN > WITH 208 ILLUSTRATIONS IN THE TEXT •i-e'-v 9.^ Copyrighted, 1915 By FRANCES DORRANCE ©CI.A401.187 THE RECORD PRESS Wilkes -Barre, Pa. MAY 29 1915 209 proof in these experiments that newly introduced seed retains at first the char- acter developed in the place where it has been bred. If, for instance, heavy soil reduces the starch content, the reduction does not take place in the first year with new seed and therefore this seed contains more starch than the native seed. On sandy soil, however, a variety has been bred which contained the largest amount of starch possible under the conditions. The newly intro- duced varieties with the peculiarities brought with them, however, had not as yet adjusted themselves sufficiently to these conditions and therefore gave a lesser yield. Exhaustion or degeneration will therefore take place only where a variety does not find the cultural conditions it requires. The cir- cumstances may be similar in all phenomena of supposed exhaustion or degeneration. Our cultural varieties are the products of breeding under very definite conditions of position, soil and weather, and are kept pure only if they again find conditions similar to those where they are grown. If it is desirable to make use of valuable peculiarities of any definite species in another locality, good results are obtained only by frequently renewing with seed from the native habitat or from habitats similarly situated. Sensitiveness of the Sweet Cherry. The complaint in different places that the sweet cherry every year suf- fers increasing injury from frost, the exudation of gum, attacks of fungi etc. is often due to the failure to observe the fact that the cherry does not like a heavy soil. This circumstance has been especially emphasized recently by Ewert^ and deserves to be repeatedly borne in mind by the fruit breeder. Naturally here also some cultural varieties are able to adapt themselves better to heavier soils, but in general the rule holds good that the sweet cherry likes a light, deep soil and flourishes especially well on alluvial sand and loose soils. The amount of nutrition in the soil is a far less decisive factor than its physical constitution, especially its granular condition. Often a scarcity of lime is given as the cause of poor growth, > which can be overcome by supplying lime. The improvement in growth, however, may not always be traced back to the nutritive action of the lime but to the change in the physical soil condition due to it, viz., greater friability and thereby increased aeration. Ewert's statements throw light on lime as a nutri- tive substance. He states that the sweet cherry flourishes even when the lime content is from 0.04 to 0.15 per cent. Soil with possibly 80 per cent, of easily washed away particles is not suited to the growth of cherries even with 40 to 45 per cent. CaCOg, if this is chiefly present in so fine a condition that it also can be washed away. The cherry is peculiarly sensitive to stand- ing water and it grows best in dry soil in open places. The Tan Disease. Trees standing on damp ground may show decreased growth, especially if their early growth was rapid. The older bark cracks or, after the outer- 1 Ewert, Das Gedeihen der Stifskirschen auf einigen in Oberschlesien hauflgen Bodenarten. Landw. Jahrb. 1902, Vol. XXXI, p. 129. 210 most cork layers have fallen off, blister-like or flat, warty swellings put in an appearance and later these have a diseased wooly outer surface. If the place becomes somewhat dry, a reddish yellow to a brownish yellow powder may be brushed off which in color resembles fresh tan bark. This may have given rise to the term "Tan Disease." In introducing the subject of this dis- ease into scientific discussion I have re- tained the name used by practical growers. The same process takes place also in roots and young branches. Young bran- ches with knotty tan pustules may be found in cherries. Up to the present this disease of the bark of the older trunk and roots has been observed most frequently in apples. Plums seldom suffer. Similar processes, resulting in the falling off of larger pieces of bark, have been found in elms and will be treated under growth disturbance due to marshy soils. In figure 23 is seen a piece from an apple root, natural size. Its bark has been broken open by cross-tears varying in size, the edges of which have been forced back ; the open places are covered with an ochre powder or (when first taken from the soil) with soft, moist, brown masses. Figure 24 represents a cross-section through such a callus place. We find the wood (c is the cambial zone) of a practically normal structure traversed by the medullary rays (m), most of which show no variation whatever. Only in some (m') it is notice- able that in the younger portions they be- gin to broaden, thereby causing a looser construction. This process of loosening, however, finds its evident expression only in the bark where the rows of medullary ray cells, beginning to separate from one another, form loops. While the younger inner bark, with its hard bast cords, still shows no change from a normal structure, the older layers (at left side of the illustration) display an impoverishment of the cell contents and some radial stretching (k'). This excessive elongation of the bark parenchyma becomes greater, the fur- ther toward the outside the cells lie, and it increases within the cork zone in such a way that the cells lying free on the outer surface take on a pouch- like form (s) and are only very loosely united with one another. Fig-. 23. Apple root with ruptured tan spots, natural size. (Orig.) ^It If the outer surface of the root dries off, the cell pouches shrink and, in the outer layers, are entirely separated from one another. Then a tan- colored, powdery mass forms which may be wiped away with the finger. Even the lamellae of plate cork (t) which are present at the edge in thick layers (of equal size, under normal conditions) and, graduall}^ dying back from the outside, fall away at the place of the tan disease, are also drawn into the process of loosening. These split off because some of the middle layers round off their cells and show a tendency to assume the structure of cork as will be described more fully later under the cherry. Fig. 24. Cross-section through a diseased spot in an apple root. (Tan disease.) (Orig.) If the outgrowth of the bark at the edge of the tan canker and the emp- tying of the cell have reached maturity, the well-known hourglass arrange- ment of plate cork layers occurs (f) which cut off the hypertrophied bark parenchyma, finally becoming cork, and it becomes an element of the bark scales. The cell elongation meantime advances laterally and further toward the inside. Thus at w we see the beginnings of this since the bark cells, normally elongated tangentially, are becoming square in cross-section and in- crease in number by division in order to round off more toward the diseased side, to become more open by enlargement of the intercellular spaces (r) and finally to pass over into the radial elongation which increases to pouch- 212 like outgrowths. By this advance of the process of over-elongation into constantly younger bark parenchyma layers, the activity of the root is finally exhausted at the place of the tan disease. The injury is not so intensive in the aerial axes Sometimes in larger trunks the phenomenon is not noticed until the bark is closely examined. It is then found that some bark scales stand out raggedly. If these are re- moved, which may be done very easily, it is observed that the outermost layers of the succulent bark tissue form irregular blister-like swellings which rupture later and decompose into dust-like masses which may be wiped away in dry weather. Figure 25 shows the fresh bark sur- face of an apple tree which has been laid bare by the removal of the outer bark scales. On this greenish brown, juicy surface hemispherical or elongated warty excrescences (a) appear very clearly. Figure 26 shows a cross-section through such a boil-like swelling in which, however, the wood, cambium and youngest inner bark have not been drawn. We recognize at the first glance the corres- pondence in structure with that of the tan spot of the root. At the lower part of the figure we find the bark parenchyma with three hard bast bundles of a normal arrangement and position, but close above these hard bast bun- dles is noticeable a change in position since the tangentially elongated bark cells, rich in chlorophyll, begin to increase in length radially (r), to divide and to be arranged in parallel lines broken by large intercellular spaces (i). The fact that this change in tissue must have taken place very early, at the time of pushing out from the cambium, is evident because the permanent tissue of the coUenchyma (cl) has developed only one layer within the tissue of the excrescence. The chief part of the swelling has come from the peri- pheral layers which have developed into ctishions (zv) of elongated, finally pouched cells (s), which have raised the plate-cork cell layers and finally split them. In explaining this phenomenon we must not forget that these tan places arise underneath the old bark scales, and, with a formation of full cork, finally become bark scales by suberization. Thus we find that the organization of the bark into constricted and constricting cell layers, as they alternate in the bark, has taken place in the young bark tissue, for we find that, in young fresh bark tissue, cross bands of plate-like cells, varying in structure and the Fig. 25. Piece of the bark from the trunk of an apple tree with the tan disease. a the calluses of the tan disease, b frag- ments of the dry bark scales covering the whole. (Orig.) 213 constitution of their walls, transverse in curves (np) the hypertrophied tis- sue, which, at the beginning, contains starch. This formal and functional organization of the bark parenchyma which determines the formation of the bark may be found also in other tree barks, but first occurs, so far as I have observed, in the older axes in which the bark parenchyma has been influenced by the pressure of the bark scales lying above it. On this account I have called these bands of tangential cells s Fig-. 26. Spot on the trunk of an apple tree with the tan disease, the letters in the text. (Orig.) Explanation of (np) "Pressure bands," which later suberize, often also developing plate cork cells and cutting off the bark scales. I have had opportunity to study the tan disease in young cherry branches in a wet summer on very vigorous young trees in a nursery. Figure 2y shows that on these cherry branches the outer bark had split or been torn open in broad, irregular stripes (e). An intense yellow ochre colored mass' (/) could be recognized at the ruptured spot, which, when tapped vigorously, gave off a powdery dust. The whole impression given by these branches was as if they had been very thickly covered with rust fungus. 214 The first indication of the disease occurred in July, when, among nor- mally growing trunks, the leaves of some specimens turned yellow and fell off. Nevertheless the terminal buds of the branches developed a vigorous August growth which held most of its foliage until fall. In September the outer bark covering split and the surface appeared like yellow ochre velvet beginning at the lowest part of the branch and decreasing in in- tensity toward the tip. Further, the fact is worthy of notice that practically only the luxuriantly growing wild trees appeared to be diseased. The phenomena of the tan were only sparsely noticeable in grafted trees. It was seen at once that branches, where they had re- tained their leaves, had only a few really torn spots in the bark, indeed only closed, warty excrescences, i. e. the younger stages of the disease. In the axils of two year and much older diseased trees, ruptured places in the bark (r) occurred less fre- quently. Usually the individual ■^ centres of disease appeared there in the form of ver}'- broad, very high yellow ochre cushions running crosswise. The investigation of these cus- hions and of the broad, ruptured, discolored surfaces on branches one year old showed at once marked correspondence with those on the older ones ; only it could not be seen that the lenticel cushions give off any dust. The discolored mas- ses were found to be light brown, cylindrical, wrinkled cork cells with rounded corners, which were broken off individually or in small groups. The branches, giving off this dust, seem with a few exceptions to be otherwise healthy, only their primary bark is very much broken by the considerable separation of the parenchyma cells. Places with loosened structure are found in the wood as well as in the bark. Cross bands of duct- less parenchyma wood may be noticed in the stages produced toward the Fig-. 27. One year old and two year old cherry branches with tan cushions between the split bark stripes. (Orig.) 215 middle of summer. These are filled full of starch, while the normally constructed wood, excepting the medullary rays, has none. Within these cross bands the medullary rays are broadened and have gummy spots. The beginnings of the tan formation are found close under the terminal buds of the topmost branches, where the epidermis is still uninjured, but is already underlaid with cork, possibly five layers thick. In places, this pro- tective layer, consisting of comparatively thick walled cells, corresponding to plate-cork, shows a change even in its first stages, so that the cells lying directly beneath the epidermis have developed into parallel rows of cylindri- cal, radially elongated; brown-walled, full-cork cells. There is present here, therefore, the character of lenticel growth which StahU has already de- scribed thoroughly for the cherry and which only differs from his descrip- tion in that here the full cork cushions are rarely produced under the stomata. It is seen that an extensive formation of full cork can take place in- dependently of the stomata in the development of a plate-cork layer, since several layers of lenticels are produced in which the cork formation ad- vances inward into the primary and, in fact, into the secondary bark. As the shoot of the current year becomes older, a second layer of plate- cork appears very normally, directly beneath the one first produced. It has been found just as thick (viz., 5 to 7 cells) as the first whose cells gradually collapse with the apparently lessened swelling and the browning of the walls. During this process the normal cork covering of the cherry trunk appears to be differentiated into two layers. The upper, older one is very dense, since the cells usually have so collapsed that their cavities are recognizable only as fine lines; this layer passes over gradually into the second, later formed cork layer. In the latter, the plate-like cells are very uniform and their wide lumina are filled wath a watery content or even with air. They border on a browned cell layer, with a clearly protoplasmic w^all lining, which, as cork cambium, assumes the continued formation of the cork layer occurring in places. When treated with sulfuric acid, the composition of the oldest, sunken, collapsed brown cork layer is easily recognizable, since the cells are often distended and show in places their original height and width, at times almost square in cross-section, while the full cork cells are not changed. With this treatment the layer, produced later, rounds out its youngest cork- cells into hemispheres after the cork cambium has been destroyed. In the formation of the many layers of lenticels, the development of such elements is repeated in the secondary cork layer underneath the first centres of full cork. The second case of lenticel formation, not connected with stomata, is illustrated in figure 28. This shows the cross-section of a new structure on 1 Stahl, Entwicklungsgeschichte und Anatomie der Lenticelle. Bot. Z. 1873, No. 36. 2l6 the barked cherry trunk. We must imagine that all the tissue here shown in the form of a callus covered with bark rests upon the old wood cylinder from which the bark has been removed. Since reference to the anatomical processes, leading to the formation of this new tissue on the exposed wood, is made in the chapter "Wounds" (bark wounds), we will mention here only the fact that, if at any given time the bark is removed from a tree, the newest cambium, thus exposed, begins to grow again and covers the wounded surface with a parenchymatous tissue layer. This parenchymatous covering is increased by the later appearance of a constant meristematic layer. The inner surface of this layer forms -TSt Fig. 28. Newly formed wood and bark body on the bark wound of a cherry trunk. The bark shows a lenticel excrescence. (Orig'.) normal cambium, which gives rise to woody tissues toward the centre and back towards the periphery. Figure 28 is a new structure several months old which, in the form of a broad wrinkled callus, has grown on the cambium of an experimentally barked sweet cherry trunk. The old wood of the barked trunk has been omitted in the drawing; it would join on at hp. The cambial zone (c) has sharply differentiated this tissue into wood and bark. The wood, where it rests on the old trunk, has a parenchymatous structure (hp) ; which later passes over into a vascular new wood (nh) forming libriform fibres. The structure of the bark is at first irregular and corresponds to the formation of wood which only gradually obtains its normal structure, for the hard bast bodies begin in the form of individual, short elements {hh) with wide lumina and only later grow out from the cambium as connected groups of elements {hh^) elongated like fibres^. The bark of the new structure has formed a protective cork layer in its peripheral parenchymatous layers which has gradually grown very thick. At first only plate cork was formed ; but later, in different places, full-cork masses {Ik) developed instead of the plate cork cells, splitting the covering {k) composed of the latter cells and pressing the cork cambium inward {kk) by their increase which extends further and further backward. The full cork began to form when the whole peeled surface, for the purpose of further investigation, was enclosed in a glass cylinder, partly filled with water. While this lenticel out-growth, produced from the phello- gen, was only slightly noticeable in those parts of the bark which remained in the air, it had developed an unusual luxuriance below the surface of the water. The tan disease of the cherry is therefore an abnormal increase of the normal lenticel formation. So many and such extensive full-cork cushions are produced close to one another that they unite, pushing off the epidermis in large connected tatters and appearing as uniform velvety surfaces cover- ing a large part of the branch. The outermost layers of the full cork cush- ions are so loose that the connection between the peripheral cells is broken by a slight blow when the air is dry ; this explains the discoloration and the dust flying from places affected with the tan disease, if the spots be touched or shaken vigorously. This scattering of the dust increases with the num- ber of full cork cells lying above one another and cushions composed of parallel rows of full cork, 20 cells deep, have been observed. In this case the process of elongation has included the entire thickness of the primary phelloderm so that the later formed, secondary full cork lies directly under- neath this, i. e., no separating plate cork layer is left between the different generations. The appearance of the tan disease will have to be traced to the super- abundance of water in the hark body. This local excess of water may be due, on the one hand, to supplying the roots abundantly with water, especially 1 Reference should be made in passing to the illustration of the beginnings of tuber gnarls not in any way whatever connected with the tan disease but shown in the drawing- at B. They are produced by a local accumulation of plastic material as, for example, the isolated wood in the bark of the new structures formed near the wounds of various trees (cherry, apple, pear and pine). At the centre of such wood formations with a spherical wart-like structure may be recognized one or more hard bast cells. The case in which hard bast cells (especially diseased ones) are overgrown by tissue is of very frequent occurrence in injuries of very different origin. This over- growth consists usually only of a covering of plate-like cork cells several layers thick. In some cases, however, instead of the rapidly transformed cork cambium, a persistently active cambial layer is formed which deposits wood elements toward the inside and bark elements toward the outside. Such a case is represented in the wart-like tissue excrescence (B) at (u') while at (u) in the left part of the figure (A) may be seen only a cork covering around one of the isolated hard bast cells first produced. The bark rays pass around these new structures on both sides as if around some foreign body. 2l8 those of vigorous individuals ; on the other, by the lessened transpiration of the bark because of greater humidity. Such conditions in the cherry lead to lenticel excrescences as is proved by experimentally producing an accum- ulation of full cork in parts of the bark kept under water and further by observing specimens naturally diseased. In this way it was discovered that the cork excrescences preferred the youngest, well-leaved internodes in which the bark formed folds. Such folds were produced, for example, in places where the vascular bundles of the leaf left the axial cylinder and pushed out the bark when passing into the petioles. Some other observations have been made showing that the decreased evaporation due to increased moisture favors lenticel formation. Thus Stapf ^, in his studies on the potato, mentions that stomata develop into lenti- cels if transpiration is arrested. Further, Haberlandt^ found that in the horizontal branches of different trees (the linden, elm, honey locust, etc.) the lenticels always occurred in greater numbers on the under side than on the upper side, although counting the stomata on both sides gave approxi- mately equal numbers. The under side of the branch, inclined toward the earth, will surely transpire less than the upper side, because of the greater proximity of the soil and the lesser supply of air. The tan cushions in plum trees are essentially similar to those observed in the cherry. As yet they have been observed only on old specimens with diseased roots. I have known of only the initial stages in apricots. In all varieties of stone fruits the cork excrescences were accompanied by marked processes of bark loosening which in part resulted in the shoving of the bast cords towards the outside. In young wood a weakly developed wood ring and a reduction of hard bast bundles to isolated wide bast cells, filled with a brownish-red gummy substance, w^as often noticed where the tan disease had not broken out. Traces of gummosis were present everywhere, and at times rich gum centres were found. In cherries, the especial sus- ceptibility of certain varieties to the tan disease may be recognized when different varieties are planted close to one another, as, for example, in the "black ox heart" and in "Winkler's white ox heart." All the cases which I have known originated on heavy soils or marshy meadows. The history of some cases showed that the diseased trees had been fertilized with stable manure or liquid manure. These statements in connection with the anatomical conditions lead me to explain the tan dis- ease as the result of an excessive w^ater supply from the soil. When trees are attacked during vigorous growth, they undergo such a disturbance that the evaporation from the top is not sufficient to remove the excess of water. The decreased leaf activity, or a partial loss of foliage due to atmospheric influences or to pruning, should receive especial consideration. These cork 1 Stapf, Beitrage zur Kenntnis des Einflusses geanderter Vegetationsbedingun- gen etc. Verh. d. Zool-Bot. Ges. Wien; cit. Bot. Jahresb., VI. Jahrg., Section I, p. 214. 2 Haberlandt, Beitrage zur Kenntnis der Lenticellen. Sitzungsber. d. Akad. d. Wiss. in Wien, Vol. LXXII, Section I. July No. 1875. 219 excrescences and phenomena of loosening of bark and wood occur also in healthy trees, with corresponding conditions in the place of growth, but in- crease in the tan disease to an extreme manifestation. The remedies are apparent, and extensive aeration of the soil chiefly promises success. The Girdling of the Red Beech. According to the description given by Th. Hartig^ the disease named in this heading, which I have not known from my own observation, should be included here. Hartig found in a beech grove, 20 years old, that many trunks, beginning about one to two metres above the ground and extending to the top of the tree, were surrounded at intervals of 30 to 100 cm. with an almost circular, somewhat spirally running roll as thick as a quill. These rolls were proved to be overgrowth phenomena in wounds caused originally by lenticel excrescences. The formation of cork had extended further and further backward into the bark until it reached the wood and for a year or two years the formation of wood was arrested at this point. No appreciable injury due to the disease, which occurs only in very well grown sapling groups and there especially on trunks of the first or second class, could be confirmed. Root Disease of the True Chestnut (Mai nero). This disease, very common in France, manifests itself, according to Delacroix-, most strikingly in damp, impenaous soil and in grafted trees. The leaves lose their dark green color and the branches begin to dry up at the tips. The nuts only partially ripen and remain in the burrs. Delacroix found that the mycorrhiza of the fine roots had changed, as if diseased, and had assumed, as he thinks, a parasitic character because the amount of humus was deficient. The mycelium then grows into the larger roots up to the base of the trunk and then, in the trunk, upward to the branches. A secretion containing tannic acid results from the injuries to the roots and trunk. In this weakened condition, the trees offer a suitable centre for in- fection by other parasites, as, for example, Polyporus sulfur eus and Armil- laria mellea as well as Sphaerella macidiformis. I include this disease at this point because of the results of a thorough investigation which I had an opportunity to make with material from Ren- nes. The explanatory letter sent by M. Crie stated that the dying branch- wood had an odor indicating fermentation if broken, or the bark removed, and he suspected a conversion of the tannin, whereby glucose and alcoholic fermentation took place. The pieces of branches sent were thickly covered with lichens and the leaves showed a browning which extended from the edge deep into the intercostal fields. 1 Hartig, Th., Vollstandige Naturgeschichte der forstlichen Kulturpflanzen, p. 211. Berlin 1852. 2 Delacroix, G., La maladie des chataigniers en France. Bull soc. mycol. de France XIII, 1897, p. 242. 220 The roots decided the matter. They had a rough appearance due to a great many black, hard cushions, differing in size and flattened into hemi- spheres, which covered the upper surface. If treated with a solution of caustic potash, when the tannin, occurring as a flocculent precipitate, turned a wine red to hrown, cross-sections show that the bark excrescences were covered by a normal cork layer. The primary bark had developed parenchymatous ex- crescences the cells of which, arranged in radiating rows, had polorless walls, apparently dissolving with difficulty in sulfuric acid, and had a very firm brown content. These bark excrescences were later cut off by an hourglass- like, plate cork lamella, distending the outer cork layer, and were forced out over the upper surface of the root as calluses by the subsequent growth of the inner bark. The healthy bark was filled with starch. In the material sent me the branches had only very sHghtly raised bark excresences, possibly ^ to >^ mm. broad, flattened and hemispherical. In them was found the beginning of a many layered lenticel excrescence such as had been observed in great numbers in the cherry with the tan disease. The constitution of the leaves, still remaining on the branches, had already indicated the diseased condition of the roots. They showed a browning and drying up of the parenchyma in the intercostal fields, extending from the edge toward the mid-rib. Finally, the parenchyma was green only in the immediate proximity of the ribs. The black, yellow-edged, roundish spots, scattered over the sick leaves and containing various fungi colonies, must be considered as secondary phenomena. The condition found in the branches in connection with the excrescences on the roots brings the disease, which has been termed "Mai nero," into the group of the tan diseases. Ac- cordingly, the choice of fibrous or good friable land which has a constant, abundant soil ventilation will be the best precaution against the disease. The Rootblight of Sugar and Fodder Beets. As rootblight we designate a disease of the tissues which can set in even when the young seedlings unfold their cotyledons or begin to open the first leaflets. A black spot appears on the stem below the seed leaves which spreads further toward the root end (less toward the cotyledons) and be- comes depressed. Even if the young seedling has not reached the upper surace of the soil, the first stages of the disease can be recognized. Vanha observed that the tissue becomes glassy before turning brown. The little plants begin to wilt and usually break at the diseased point. Death results at once. If the disease is limited to a small area on the hypocotyledon stem and the plant does not succumb, the depressed place will heal and a normal, later growth follows. Because the diseased place blackens and often shrinks to the size of a thread below the seed leaves the practical grower also calls the appearance "black leg" or the "threads." The same term is used as well in the blackening and softening of the hypocotyledons of cab- bage plants, which arise, however, from other conditions. 221 It is noteworthy that often great numbers of beet seedlings are diseased, and yet frequently perfectly healthy plants may be formed close to the dis- eased ones. It should be emphasized further that, when the disease develops at all it is found simultaneously in all parts of the field, and that, as a rule, iso- lated spots are not attacked in the middle of diseased fields. As the plants be- come older, the rootblight ceases. The healed plants usually, however, remain below the healthy ones in size and sugar content and show a tendency to- ward root splitting and other deformities. Stoklasa^ emphasizes the fact that all varieties are not equally susceptible to rootblight. The disease has been known since the increase in beet culture in the 30's of the last century and, according to Stift^, the discussion as to the cause of the phenomenon began in 1858 at the meeting of the beet sugar manufacturers of the Zollverein. At that time the opinion was expressed by practical growers that the trouble was due to the physical condition of the soil, i. e., a too great solidity of the soil. It was emphasized that root- blight was found only where the upper surface of the soil was hard and had not been loosened on which account a thorough cultivation and stirring were advisable. At the time scientists took up the question, the parasitic theory was already at the crest of its development. At first Julius Kiihn in 1859 gave expression to the opinion that the moss button beetle (Atomaria linearis Stephn.) attacked the plants, and, where it had eaten, the rootblight made its appearance. I have observed something similar^. The centipede and such animals were also cited as causes. This theory which prevailed for many years was first upset when Hellriegel found that the disease could be pro- duced without animal injury and in many cases came from the beet- seed. As a result he advised a soaking of the beet-seed for 20 hours in a one per cent, carbolic acid solution*. Karlson, at about the same time, ascribed the phenomenon to a special fungus and in this emphasized the fact that only weak specimens succumbed to rootblight. Seedlings from very good seed or those which were strengthened by an energetic growth, would not be overcome by the fungus carried in these seed balls (Scleranthus)^. The experiments in sterilizing with carbolic acid and with copper sulfate showed a decrease of the rootblight. In spite of the advantage due to ster- ilization, Karlson lays especial stress on the selection of especially strong seedlings and lays the responsibility for the spread of rootblight on our present cultural methods'', which aim only at obtaining large amounts of seed and neglect the quality. 1 Stoklasa, Jul., Wurzelbrand der Ziickerriibe. Central bl. f. Bakteriologie. Sec- tion II, 1898, p. 687. 2 Stift, Anton, Die Krankheiten der Zucl?:errube. Wien 1900. Verlag des Cen- tralver. f. Riibenzuckerindustrie. 3 Zeitschr. f. Pflanzenkr., 1892, p. 278. 4 Hellriegel, Ueber die Schadigung junger Riiben durch Wurzelbrand etc. Deutsche Zuckcrindustrie, Jahrg. XV, p. 745. Biedermann's Centralbl. 1S90. p. 647. 5 HoUrung also found a lesser degree of disease in sowing large beet seed balls (Scleranthus). Dritt. Jahresb. d. Versuclis.stat. f. Nematodenvertilgung. 1892. 6 Blatter fiir Zuckerriibenbau, 1900, No. 17. The theory of seed steriUzation was further developed by Wimmer, one of Hellriegel's collaborators. Of the different substances used in sterilizing, carbolic acid was proved to be the most advantageous and, in fact, when used in the one per cent, solution of "Aciduni carboHcum crudum lOO per cent. Pharm. Germ. II." To one part by weight of seed should be reckoned about 6 to 8 parts by weight of liquid. A warm water solution was proved favorable as well as a cold water solution^ While Wimmer left the question undecided as to the influence of the weather and the soil constitution Holdefleiss held to the theory that this and not parasitism caused rootblight. In soils favorable to the disease, he usually found an abundant amount of ferrous oxid, but comparatively little calcium. In this the tendency to choking with mud and incrustation of the soil are unmistakable and the discovery that rootblight was cured by abun- dant hoeing was in accordance with this. On this account Holdefleiss recommends, in addition to a continued, open condition of beet soils, a rich addition of burned (quick) lime (12 to 15 centner German per acre)- which is given with the best results to the first grown crops and not directly to the beet. Loges^ had good results from the addition of 7 cent, of quick-lime per acre. As a further contributory factor, Hollrung emphasizes a lower temper- ature and the fact that rootblight never extends above the surface of the soil to the aerial parts of the axis which are exposed to air currents. He asserts definitely that rootblight is brought about by physical and chemical causes making themselves felt in cold soil, impermeable to air currents. The theory that the soils, in which black leg of the beet occurs, are easily choked with mud and become hard is substantiated by Marek and Krawczynski. Ac- cording to Stift's statement (loc. cit. 10 to 20) in such a soil 77.25 per cent, fine sand was found. Opposed to these theories, shared by many other investigators, the par- asitic theory was still maintained and found its most active defender in Frank. Frank, with Kriiger, from 1892 on, made various experiments and determined that, besides the Pythium de Baryanum found by Lohde, and oc- curring in many diseases of seedling plants from very different genera, be- sides the Rhisoctonia violacea mentioned by Eidam, there was a specific beet fungus, Phoma Betae Frank, "which not only causes heart and dry rot of the mature beet, but also the rootblight of the young beet roots."'* Re- peated discoveries in field experiments, however, soon showed even this investigator that weather and soil conditions exert a decisive influence. "It is still undecided whether the seedling thereby becomes more susceptible to the fungus attack or whether this is not sufficiently explained by the fact that cold weather delays the growth and the plant remains unusually long 1 Hollrung, in Zeitschr. f. Riibenzuckerindustrie i. D. R. Vol. 46. Part 482. 2 1 Centner in German weights equals 50 kg-, or approximately 112 English pounds. 3 Bericht. d. Landw. Versuchsstation Posen. 1891. 4 Frank, A. B. Kampfbuch gegen die Schadlinge unserer Feldfriichte. Berlin, Paul Parey, 1897, p. 117. 223 in an immature condition which is especially susceptible to the disease, while seedlings forced by heat pass rapidly through the susceptible stage and thus escape the danger." In this explanation, after many modifications of Frank's original state- ment, is expressed the theory that besides this specific excitor of disease, Phoma, a definite degree of susceptibility of the beet seedling must exist for the production of rootblight. Sorauer held this point of view earlier since he proved that rootblight can exist without the presence of Phoma and that, instead of this, bacterial growth accompanies the disease. We owe the most thorough investigations of the bacteria of rootblight to Hiltner, whose recent studies we will consider with great thoroughness after sketching Stoklasa's theory. According to Stiff's statements (loc. cit. p. 17) Stoklasa admits that bacteria can produce rootblight in beets, and he considers the following species capable of doing so: — Bacillus subtilis, B. liquefaciens, B. fluore- scens liquefaciens, B. mesentericus vulgatus and B. mycoides; Linhardt de- clares the latter to be the essential cause of injury. Recently Pseudomonas campestris has been added to these. Stoklasa considers that the above men- tioned atmospheric and soil conditions produce a predisposition in the beet seedlings. He turned his attention especially to oxalic acid, normally formed by the life process of the plant as potassium oxalate. Soluble oxalates, which act as poisons, are transformed into an insoluble calcium oxalate, if calcium oxide can be taken from the soil by the root hairs. By thus neut- ralizing the oxalic acid its retarding action on the process of assimilation ceases and the plant recovers. If much nitric acid is present in the soil or is added in excess (strong fertilisation with nitrate of soda), an hastened de- velopment takes place at any rate, but at the same time the oxalic acid con- tent increases. In such a case, if the young beet plant cannot take up suf- ficient calcium, it becomes predisposed to rootblight. As already said, we owe the most thorough study of the relation of bac- teria to this disease to Hiltner and Peters^ These investigators made a number of experiments and found that there are soils which almost never show any rootblight and, conversely, there are others in which the disease al- most always appears. They concluded from this, that many soils are in a con- dition to lend a certain protective power and they perceive that this pro- tective peculiarity is the ability of the immunizing soil to provide the outer- most cell layers of the roots of the beet seedling with such micro-organisms as can prevent the penetration of fungi and bacteria producing rootblight. Hiltner and Peters call this protective sheath, which they had observed similarly in peas, "Bacteriorhiza." If its formation be prevented by steri- lizing the soil and killing the protective soil organisms, in case the seed had not been previously sterilized, the fungi and bacteria causing rootblight could enter the young seedlings and destroy them. 1 Hiltner, L,., and Peters, L., Untersuchungen liber die Keimling-sl^ranlcheiten der Zuelzer- und Runkelriiben. Arb. d. Biolog. Abt. f. Land-und Forstwirtsch. am Kais. G-esundheitsamt, Vol. IV, Part 3, 1D04, p. 207. 224 The words of Hiltner and Peters themselves best show how little the organisms per se are to be feared and how the chief cause of the disease is to be sought in the conditions making the plants susceptible. In speaking of the results of their experiments, they say (loc. cit. p. 249) "this result, how- ever, shows that the production of diseased seedlings in the seed bed presents a rather complicated phenomenon. This cannot be laid exclusively to the face (heretofore almost universally accepted) that parasitic fungi or bacteria ac- cumulate on the seed balls, then passing over to the roots, for these organ- isms in themselves cannot cause the diseased conditions of the beet. Only after the resistance of the roots has been weakened by the influence of cer- tain substances, viz., oxalates, can otherwise harmless parasites attack them." According to Hiltner's theory, the substances or circumstances predis- posing a plant to disease are produced by the decomposition of the tissue in the seed balls, either on the field as a result of unfavorable weather, or later in storage because of too great warmth. A work by Sigmund^ reports upon the advance given to the occurrence of rootblight by the fact that the micro-organisms especially concerned in it (Phoma and Bacillus mycoides) find certain organic compounds in the nutrient solution of the host. After he had emphasized the fact that the parasites are not able alone to increase the disease, he mentions that the number of diseased beet seedlings can be increased if glycocol, uric acid, asparagin, hippuric acid, leucin, etc., are found in the nutrient solutions of the micro-organisms named and the beet balls are soaked in this nutrient so- lution. In this important disease we have simply listed, first of all, the various theories and results of investigations as they have appeared from time to time, in order to show that with all observers, in spite of their very different points of view, one statement is found running through all their discussions like a red line, viz., the influence of the soil^ This influence shows itself most distinctly in heavy,. binding soils. It can make itself felt also on other soils if they are encrusted for any reason whatever. The prime factor under such conditions is the scarcity of oxygen. At present we cannot say defi- nitely what processes are started in the soil, seeds and the young plants. In the same way, no definite decision can be made as to whether rootblight is a constitutional disease, i. e. a deflection of the normal life functions leading to tissue decomposition, or a parasitic process, i. e. a process producing the same result but caused by the co-operation of micro-organisms. If, as we beUeve, in the majority of cases the latter should be granted, we must bear in mind emphatically the fact that these organisms, no matter whether fungi 1 Sigmund, Wilh. Beitrage zur Kenntnis des Wurzelbrandes der Riibe. Natur- wissensch, Zeitschr. f. Land- und Forstwirtschaft, 1905, p. 212. 2 Further material from practical sources may be found in the annual reports of the Special Committee for Plant Protection. (Jahresberichte des Sonderaus- schusses fiir Pflanzenschutz. Deutsch. Lnndw.- Gesellsch. 1892-1905). 225 or bacteria, can only destroy the seedlings where they have some predis- position to take up such organisms. This predisposition is the product of the soil in which they are grown under definite atmospheric conditions. Therefore, the soil condition is always the first cause affecting the as- similatory process and inducing rootblight. The question whether this affec- tion always takes place with an excess of free oxalic acid and whether the abundance of the acid acting poisonously is due to the formation of more acid by the plant body or that less acid is oxidized because of a scarcity of oxygen, may be left for later investigation. It is enough for our purpose to know that the disease is a result of a binding consistency of the soil under unfavorable atmospheric conditions, i. e. cold, wet weather. We will now return to the statements of practical workers, who, from the beginning, have insisted that the cause of rootblight lies in the condition of the soil. When citing these expressions, we come to the self-evident regulations for fighting it. Briem reports a case from the years 1904-1905^. On a newly broken field near Prague in 1904, with cold, wet weather, and a consequent slow growth, beets were extensively root blighted although until that time the phenomenon had been rare. Also, the beets did not revive completely until later. The same field in the following year, after a rich fertilizing with potassium, nitrates and phosphates, was again planted with commercial beets. As a result of the very wet, cold weather, the seed sprouted only at the end of two weeks (on the 24th. of April). It was. feared that, with the weakened growth resulting from the cold nights, rootblight would again set in. Fort- unately this did not happen and the warm days, coming at the beginning of May, soon caused the rapid, vigorous unfolding of the first pair of leaves. However, when, on the 20th of May, a violent rain had beaten the field down unusually hard so that water could only soak in very slowly, many seedlings showed the beginning of rootblight after five days. This example of the result of a sudden exclusion of the air from soil, beaten hard by rain, shows therefore that it is primarily advisable to'> keep the upper surface of the soil constantly open by cultivation. Secondarily, even if the soil contains lime, a further supply of quick lime must be given. The effect of the lime must not always be considered as a nutritive means, but as a mechanical one for improving the soil since it increases its friability. Superphosphate has given good results-. In fields liable to these conditions, increased attention should be given to the use of as vigorous seed as possible. If one wishes to sterihze the seed which, according to our theory, is of very little advantage^, a carbolic acid solution should be used. For the sterilization of one hundred and twelve pounds of beet seeds 1.5 k. carbolic 1 Briem, H., Wurzelbrandentdeckung und kein Ende. Blatter f. Zuckerriibenbau V. June 15, 1905. 2 Zeitschr. f. Pflanzenkrankh., 1896. p. 54 and p. 340. Landwirt, 1896, Nos. 15, 17, 21. Jahresber. d. Sonderausschusses f. Pflanzenschutz, 1902. 3 Hiltner in Mitteil. d. pflanzenphysiolog-. Versuchsstat. Tharand. Sachs, landw. Zeit. 1904, Nos. 16-18. 226 acid (Acidum carbolicum liquidum crudum loo %) or the more expensive, pure crystallized acid in 3 hi. water. To test the acid's desired solubiUty, 0.5 grams should be shaken thoroughly in one litre of water; this should dis- solve in from 5 to 10 minutes. When the sterilizing solution is ready, the seeds are poured into it and stirred about repeatedly and vigor- ously in the course of the next few hours. Then the seed is pressed down with weighted boards so that it remains entirely covered by the solution. After about 20 hours it is taken out and spread in a thin layer in an airy place and stirred often with a rake. As soon as it is sufficiently dry it can be planted with a drill, but it may lie for some time, when completely dry, without being injured. If it is desirable to use the sterilizing solution several times, it is neces- sary only to replace the liquid lost by pouring in the needed quantity of a stock solution. However, considering the cheapness of the material, it is well not to use the solution too often^. Instead of sterilization, the coating of the seed with calcium carbonate seems to us to be advantageous. But the main thing is to work the soil, for even the most carefully handled seed, found to be faultless in the germinating tests, can become dis- eased. Hiltner, in his above-mentioned work, gives some suggestions in this connection which are well worth consideration. Up to the present in trade, the quality of the seed has been tested according to its behavior in the seed bed, by means of a suitable method. It is now seen, that the number of diseased seedlings increases, the longer the seed is left in the seed bed. Ex- periments show tliat if, for example, the seedlings are taken from the sand seed bed on the 9th day, often more than ten times as many are found to be diseased as when taken out on the 6th day. To this it should be added that if the seeds lie close to each other the mutual infection is considerable. Be- sides this, the number of diseased seedUngs differs greatly, depending upon whether the seed was soaked or not and whether distilled water, water free from calcium, or water containing calcium, was used for the soaking. If finally it is taken into consideration that the constitution of the soil de- cides the subsequent behavior of the seedlings, it will be concluded that the methods at present used for judging of the quality of the seed give no pro- tection and no standard for beet seed. In order to obtain an insight into the germinating power, the best seeds will have to be tested in as many germi- nating seed beds as possible and with different methods-. The best germinat- ing results, however, in no way give a guarantee as to rootblight. This depends upon whether the micro-organisms present in the dried blossoms, containing the seeds, find an opportunity of so developing in the soil that they can attack the young seedlings. 1 Wilfarth, H., and Wimmer, G., Die Bekampfung' des Wurzelbrandes der Riiben durch Samenbeizung. Zeitschr. d. Vereins d. Deutschen Zuckerindustrie, Vol. 50, Part 529. 2 For the difference in germination of the seed treated in the same way but sown in sand and in soil, compare the reports by Marek in tlie year Book of the German Agricultural Society. (Jahrb. d. Deutsch. Landwirtsch. Ges. 1892.) ^27 Tropical Plants. In consideration of my standpoint, that in much of our cuhivation too little account is taken of the soil conditions, especially of its physical consti- tution, I think it necessary to refer also to the demands of tropical plants on the physical peculiarities of the cultivated land. In regard to tropical plants, I base my theory on the statements of Fesca^ who has often given his own experiences, and further, on the recent publications of the Biological Agri- cultural Institute at Amani-. As we shall see, in these injuries, as in those in temperate cHmates, phenomena are often involved which are due to scarcit)^ of oxygen mani- fested in heavy soil or in soils which have become compacted through culti- vation. Many plants in the tropics can develop accessory organs with a scar- city of oxygen, like the adventitious roots from the trunks of trees buried or covered with slime. The palms (Phoenix, Kentia, Chamaerops etc.) can develop root branches growing perpendicularly out of the soil which have a peculiar respiratory arrangement (Pneumathodes) ; this appears as a mealy coating extending backward for a certain distance from the tip of the root. This mealy condition is produced by the increase, enlargement and breaking up of the outer layers of the rootbark with a rupturing of the epidermis and an almost complete suppression of the schlerenchymatic ring. Jost^ deter- mined experimentally with Phoenix that these pneumathodes remain in the soil when it is well aerated, but, on the other hand, are raised above the sur- face of the pot if it is submerged in water. Similar arrangements were found also in Pandanus, Saccharum and Cyperus. Root-Rot of the Sugar Cane. Among the numerous diseases of sugar cane, root-rot plays a prominent part. In Java it is considered the worst enemy of sugar cane culture. Nat- urally growers have not failed to cite the micro-organisms (Vertlcillium. (Hypocrea) Sacchari, Cladosporium javanicum Wakker. Allentospora rad- icle ola, Wakker, Pythium etc.) colonizing on the diseased roots as its cause. Nevertheless Kamerling's'' recent experiments have now confirmed beyond all doubt the supposition that a constitutional disease is concerned here, 1 Fesca, Der Pflanzenbau in den Tropen und Subtropen. Berlin Siisserott. Vol. I, 1904. 2 As said above, the statements on the phenomena of disease in cultivated tropcal plants serve chiefly as proof of the necessary consideration of soil and at- mospheric conditions as a cause of disease. In the descriptions we can sum up the material more briefly since abundant literature easily makes possible special studies. Besides the magazines already mentioned, pp. 65 to 67, the recent publica- tions of the Usambara-Post furnish valuable material. "Der Pflanzer," Adviser for Tropial Agriculture" issued with the co-operation of the Biological Agricultural In- stitute, Amani, by the Usambara-Post, 1905. ("Der Pflanzer," Ratgeber fiir tropische Landwirtschaft unter Mitwirkung des Biologisch-Landwirtschaftlichen Institutes Amani, herausgageben durch die Usambara-Post, 1905.) 3 Jost, Ein Beitrag, zur Kenntnis der Atmungsorgane der Pflanzen. Bot. Zeit 1887, No. 37. * Kamerling, Z., Verslag van het Wortelrot-Oenderzoek, Soerabaia, 1903, 209 pages, with 19 Plates. 228 resulting from compacting the soil. Raciborski with Suringar^ has expressed the theory, earlier proved, that by transplanting sugar cane, which had suf- fered from this root disease, known as Dongkellanziekte , to other soil, the plants would become healthy. The disease occurs especially on heavy clay soils and manifests itself in Java, when at the beginning of the spring mon- soon the plants die with alarming rapidity after they have already shown for some time an abnormal branching of roots and also deformed root hairs. He investigated the soils in which the disease occurred and found that they did not have sufficient friability and easily became compacted. The permeabil- ity of the soil can be increased by supplying humus, since this, as also ferric hydroxide, or silicate rich in iron, favors the formation of friable soils. Since the humus is gradually lost by oxidation, care must also be taken to retain the porosity of the soil by a renewed supply of stable manure, rice straw or green fertilizer (compost). According to Wakker's- studies, many leaf spot diseases seem either directly produced by moisture in the soil (if of a parasitic nature) or favored by this moisture. Wakker found in the vicinity of Malang "a yellow streak- ed, banded disease," "rust," "ring spot disease," as well as the red and yellow- spot disease. While he considers the first named as a parasitic phenomenon favored by moisture, he explains the yellow spot disease, in which the leaves acquire somewhat elongated, greenish yellow spots running into one another, as a hereditary constitutional disease. Diseases of Cotton. The majority of the cotton diseases may be considered at present to be of parasitic origin, but I doubt if this will always remain the case. With the conviction that many of the micro-organisms already found are to be con- sidered parasites of weakness, naturally the first existing factor must be considered as decisive, viz., the disturbance in nutrition causing the weak- ness which first offers the possibility of infection by the fungus. This will have to be sought primarily in weather and soil conditions. Examples of disease, in which only the soil is considered as the cause in the rainy season, are reported by Vosseler^ from our East African col- onies. In 1904, in the district of Kelwa, there occurred a "browning of the stems," which produced greater damage in that region than all the other diseases which had appeared up to that time. Brownish black spots were produced in the bark below the tip of the main shoot, as a result of which followed the dying of this part as well as of the upper lateral shoots. The disease appeared, however, only on so-called sour soil. 1 Kamerling, Z., en Suringar, H., Oenderzoeking-en over onvoidoenden groei en ontijdig Afsterven van het riet als gevolg van wortelziekten. Mededeelingen van het Proefstation vor Suikerriet en West- Java, No. 48; cit. Zeitschr. f. Pflanzenkr., 1901, p. 274, and 1904, p. 88. 2 Wakker, J. H., De Bladzeikten te Malang. Archiev voor de Java-Suikerindus- trie, 1894. Aflevering 1. 3 Vossler, Zvs^ei Baunnvollkrankheiten. Immune Baumwollsorten. Mitteil. Biolog.-Landwirtsch. Institut Amani, 1904, No. 32. :229 The red spot disease of the leaves, occurring to a devastating extent along the whole coast, was a second phenomenon. A pale border appeared along the edge of the leaves ; the zone was distinctly cut off from the inner portions by a zigzag line. Dark red spots, or a uniform red coloration with which a deforming of the leaf surface was often connected, then appeared. The disappearance of this trouble with the appearance of drought indicates that the soil during the prevailing wet weather had unfavorably affected the growth of the cotton. Vosseler seems to suspect that the dreaded "wilt dis- ease" should be included among the chmatic diseases and refers in this to the possibility of producing immune races by growing plants from seed of healthy stock in diseased fields. According to Schellmann^, cotton cannot grow on stiff clay soils and sour humus soils. Castor Bean Cultures. Although Ricinus thrives in subtropical and even in temperate zones, according to Zimmermann-, it is extensively cultivated only in the tropics where it grows from sea level up to possibly 1600 m. The oily seeds are the desired crop. At any rate an abundant supply of nutriment is needed for Ricinus, since it makes very great demands on the soil. The plant also re- quires large amounts of water while growing. Later, however, the physical constitution of the soil has a determining value in the matter, since the plants do not thrive in all soils which, not well drained, remain constantly wet. These observations in the tropics correspond with our experience in growing Ricinus as a decorative plant. Only the plants develop well which have plenty of room and a porous soil, rich in nutriment. When grown in pots, to which much nutriment is added by fertilizing salts, the earth becomes encrusted and the plants remain small and weak. Tobacco. Very instructive examples of the determinative influence of the soil are furnished by Hunger's^ observations on the development of the Delhi- tobacco and its different behavior toward the "Mosaic Disease," which will be reported more fully in the section on enzymatic diseases. Hunger says that a soil of white clay in which much sand has been mixed, is the best for thin-leaved tobacco if the amount of precipitation is favorable, but at the same time this also favors most the abundant appear- ance of the mosaic disease in the form of the so-called "gay-head." Here, after topping, the plant gives the impression of having made too rapid growth; long internodes, a yellowish-green foliage, a great many lateral shoots, all of which are sickly. 1 Der Pflanzer, Usambara-Post, 1905, No. 1. Here also older literature. 2 Zimmerman, A., Die Ricinus-Kultur. Der Pflanzer, Ratgeber fiir tropische Landwirtscliaft unter Mitwirkung- des Biolog-isch-Landwirtsch. Institutes Amani, herausg. durch d. Usambara-Post 3 Zeitschr. f. Pflanzenkrankh. 1905, Part 5. Hunger, as Botanist at the experi- mental station for Dellii- Tobacco (VIII Abt. d. Bot. Gart. zu Buitenzorg) has had at his disposal most extensive material for observation. 2T,0 If the clay soil lacks sand, however, and becomes loamy, it is useless for tobacco culture. The roots of the plant develop scantily and are often deformed. The leaves are not of the right length and are of poor quality. The mosaic disease appears a week or two after transplanting. The red, atmospherically disintegrated soils of Ober-Langkat are pretty compact and here the plants are squatty ; the leaves standing close above one another are not especially thin while the mosaic disease occurs rarely. It only appears exceptionally on the shoots which, after topping, develop sparsely. On dark soils rich in humus, tobacco has an enormous, well-proportioned development ; the very large leaves are dark green and thin. The mosaic disease abounds. This disease scarcely, if ever, occurs on the peaty, porous, Paja soil, which has a high water-holding capacity. The enormous leaves almost never wilt in the soil containing much water, but are very thick and rich in oil; with fermentation they become dark colored and are therefore not very valuable. On fresh Paja soil the mosaic disease cannot be produced even by topping. Coffee. The tree, which of all our tropical plants deserves the most consider- ation, coffee, is extremely susceptible to soil conditions ; although droughts are not favorable and it likes best to grow in soil which even at a time of drought keeps fresh, yet it withstands drought much better than too much moisture. If, during the rainy season, it is covered with water for only a few days, it becomes irretrievably diseased. A sufficient capacity for water in the soil, combined with abundant aeration, is therefore its chief need. Freshly cleared forest soil is found to be especially favorable for its culti- vation. Black rust (swarte roest) and canker diseases (Natalkrebs and Java- krebs) (Djamoer oepas) with their diseased cambium are probably physiolo- gical disturbances introduced by unfavorable soil and atmospheric conditions and result later in fungus attack. The Liberian coffee is said to be less sus- ceptible to impervious soil than the Arabian, and flourishes where the latter fails^ The leaf disease described by Zimmermann as "Blorokziekte"- seems to me also to belong here. The leaves develop convex, yellow spots. Later, the epidermis ruptures on these spots and the cell contents turn brown. The trees in Java, to be sure, are not killed by this disease, but their fertility is greatly reduced. As the result of an excessive water supply, Zimmermann observed^ the so-called "little stars," occurring rarely in Coffea liberica and more frequently in C arahica; i.e. blossoms which open prematurely when incompletely developed and therefore remain sterile. The disease should 1 Delacroix, G., Les maladies et les ennemis des cafeiers. II 6dit. Paris, Chala- mel, 1900, p. 8. 2 Teysmannia 1901, p. 419. 3 Eenige Pathologische en Physiologische Waarneminger over Koffle. Mededee- lingen uit S'Lands Plantentuin, LXVII. 23t not be confused with the black discoloration of the blossom buds passing under the same name. These buds finally fall off unopened. Different kinds of root moulds have been described and considered as the cause of root-rof^. I think it will be necessary to study here the question whether parasitic fungous forms can attack the plant injuriously only when the roots have already been weakened by unfavorable nutritive conditions. Cocoa and Tea. Fesca says in regard to the cocoa tree "extremes of soil structure, poor sand, as well as tough clay, are not favorable to the cocoa tree. Rather it demands greater soil depth and freshness, without the necessity of enduring standing water, as well as greater humus and nutrition content, than does coffee." The same author, who himself has analyzed good tea soils in Japan, say of tea, that he found in a more compact soil, 30 to 40 per cent, of water as capillary water. Tea demands a sufficiently deep soil which is free from standing water, to which it is very sensitive. Here too a still little understood fungus is described as the cause of a root disease. It is said to result in the early death of the bushes, especially when growing on damp soil. Neverthe- less Fesca" assures us that he has never yet seen the disease on well aerated soils. We might also trace the diseases of young tea plants described by Zimmermann^ to an unfavorable place of growth, although a fungus bearing lobed haustoria has been observed at the disease centres. The leaves become flabby and discolored ; the stems turn brown at the base or higher up where the root seems healthy. Often only the leaves show brown spots, especially on the midrib. The fungi developed from the diseased parts of the stem (Nectrieae) could not produce the disease even in infection experiments. In dry weather the disease decreases considerably. Also transplanting the seedlings from the closely planted seed bed arrested the disease. If we have considered here with the greatest brevity the soil demands of our most impor- tant cultivated tropical plants, it must still be added that naturally the climate remains the decisive factor. Among these climatic factors especial attention must be given to humidity since the quality of the harvest often depends considerably upon this. In cocoa plantations in Kamerun, for instance, it may be observed that the quantitative production of the trees is unusually abundant, but the quality of the fruit is only mediocre as the result of great dampness. The trees also are short-lived here. Other Tropical Plants. Of grains. Maize requires, first of all, a deep, mellow soil free from standing water and cannot thrive on tough clay. Sorghum behaves similarly, but is still more sensitive to cold and dampness and, because of its deep root 1 Bolletirii del Institto Fisico-Geographico de Costa Rica, 1901. 2 Loc. cit., p. 273. 3 Zimmermann, Untersuchungren iiber tropische Pflanzenkrankheiten. Sonder- berichte iiber Lan- und Porstwirtschaft in Deutsch-Ostafrika, Vol. II, Part 1, 1904. 232 system, is very resistant to drought. This accounts for its growth on tropi- cal and subtropical steppes. The Negro or brush millet (Pennisetum spica- tum) is entirely unsuitable for firm soil, but is excellent for porous soils in dry localities. The other millet varieties behave similarly. The Leguminoseae, which are suitable for growth as a second crop be- cause of their usually short vegetative period, may, in the tropics and sub- tropics, acquire great importance not only as collectors of nitrogen and as an excellent nutritive substance, but are also valuable on account of their close shading of the soil, preventing it from hardening and'as soil loosening, green manuring plants. The plants make good growth in dry soils ; — accordingly . heavy soils, in regions with abundant precipitation, are not suitable for them. Busse^ has given more detailed studies of sorghum diseases and their rela- tions to atmospheric conditions. Of tuberous plants, the sweet potato requires about the same cultural conditions as our potato. The cassavas (Manniok) require deep, loose, dry soils, but rich in humus. The moisture-loving Maranta species, furnishing arrowroot, also requires looseness of the soil, on which account virgin soil is found to be less suitable because of its compactness. P2ven Taro, the tubers of the different Colocasia species, which requires a great deal of moisture, flourishes only when the soil is pervious. The same is true of the Yam, which is derived from different species of the genus Dioscora. In regard to poppy culture and the harvesting of opium, reference should be made to Braun's^ work, and in regard to rubber plants and especially the Liana, root and herbaceous rubber plants, to studies by Zimmermann^. Means for Overcoming the Disadvantages of Heavy Soils. Drainage. In this we have to take into consideration not only soils rich in clay, but also those sandy ones whose graular structure is so fine that they can become as closely compacted as clay soils. Of the practical means used to increase soil aeration, drainage deserves to be named primarily. It facilitates the exchange of air in the soil inter- stices as well as removing stagnant water accumulations after every rain. The drainage pipe acts as an apparatus for sucking up air. When the rain fills the soil, it forces out the air which has a less oxygen content than the atmosphere, but is richer in carbon dioxid. But since the rain is quickly soaked through the drains, air rich in oxygen streams just as quickly from the surface down into the pores increasing, thereby, the processes of oxida- tion in the soil and the activity of the roots and micro-organisms needing oxygen. The fear that drainage will impoverish the fields has rarely any founda- tion, since the numerous analyses of drain water show only slight traces of 1 Busse, Walter, Untersuchungen iiber die Krankheiten der Sorghum-Hirse. Arb. d. Biolog-. Abt. f. Land- u. Forstwirtschaft a. Kais. Gesundheitsamte, Vol. IV, Part 4. 1904. 2 Der Pflanzer, 1905, No. 11-12. 3 Ibid, Nos, 8-10. 233 potassium and ammonia as well as phosphoric acid, which had been ab- sorbed by the friable soil. Nitrates, because of their easy solubility, at any rate, are lost in larger amounts, but they are also partially washed away from undrained soil into the subsoil. Further, the soil capacity for heat, increasing with drainage, should not be underestimated as well as the improvement of the crop produced, of which it may be said in general that damp, and therefore cold, soil produces crops poorer in nutriment. The reason why damp soil is cold is evidenL from considering the fact that if water has a specific heat equal to one, the highest specific warmth ever shown by soil is only equal to 0.5 ; i. e. at most lialf that of water. If this water which is the hardest to warm is removed by drainage, the soil must become warmer. Previous to drainage, the soil remained cold until late in the spring, thus causing a later awakening of vegetation and a later germination of the seed. A cold place of growth is especially disturbing to young plants, since it holds development back in a developing phase, which is determinative for the whole later plant. The root system becomes poor, the appearance sick, and later favorable temper- ature conditions are not able to overcome the bad condition. One of Stock- hardt's^ experiments with winter r^'e may serve as an example. The ex- perimental plots differed in drainage and soil porosity. One plot was traversed at a slight depth by a drain possibly 2.5 cm. wide and in such a way that the pipe, bent at right angles at one end of the drain, opened like a chimney toward the upper surface of the soil. The soil of this plot, as well as that of the undrained one, was broken up 50 cm. deep, while a third plot was dug only 25 cm. deep and not drained. In corroboration of earlier results obtained with lupin, oats and the like, the harvest showed an ap- preciable excess on the drained lot, although the young plants showed no difference before spring. Reckoned per acre this crop amounted as follows : Grain Straw Totals and Chaff kg. kg. kg. Part I, drained and dug 50 cm. deep 539 1470 2009 Part II, undrained and dug 50 cm. deep 411 928.5 1339-5 Part III, undrained and dug 25 cm. deep 338 859.5 1 197-5 Grain content Nitrogen content per bu. of the grain Lot I. 40.80 kg. 2.18 per cent. Lot II. 39-85 kg. 1.83 " " Lot III. 37-70 kg. 1.83 " " Patz-, referring to the use of drainage for removing iron from newly broken soil, says, "usually iron is found directly under the surface of the soil and at the height of the usual ground water level. The ground water 1 Chemische Ackersmann, 1859, p. 232; 1861, p. 100; 1864, p. 22. 2 Hannoversche landw. Zeit. 1880, No. 45; cit. Biederm. Centralbl. f. Agrik.- Chemie, 1880, p. 911. 234 carries the iron upward and in many cases cements the sand grains in the soil at the usual height of the ground water level in such a way that often in laying a drain, a hard, stone-like, red soil is found. By laying drains cor- rectly and systematically, with the horizontal drains intersected at right angles by the absorbing drains, the latter having at least a depth of 1.2 m. and the distance between every two drains being kept 10 times the depth, the level of the ground water will be lowered to the depth of the drain and no more iron will be carried to the soil above the pipes. The iron already present in the soil will be dissolved by the atmospheric precipitation and led to the dainage pipes or it will remain in the soil as the non-injurious oxid." Working of the soil. Where there is no need of carrying away excessive water, furrowing and deep plowing, instead of drainage, will often serve the same end. In this care must be exercised if, with fertile, friable soil, there is a prospect of bringing a dead subsoil to the upper surface by the furrowing or plowing. In addition to fertilizing each time, the gradual deepening of the friable soil should take place at least over a period of several years. Since, with the deepening of the friable soil, the root surface becomes extended and, accordingly, an increased harvest. takes place with a greater utilization of the soil, an increased supply of manure is demanded with the increasing loosening of the soil. In soils inclined to crust, but otherwise not unfavorably constituted physically, hoeing and hilling suffice for increasing the soil aeration. This cultivation, which can scarcely be sufficiently recommended to the agricul- turist and the gardener, and which can be used in any soil, regulates the soil moisture. Some good, practical experiences as to the advantages of loosening the soil, may be found in the reports of the German Agricultural Society's special committee for the protection of plants (Landwirtschaft-Gesell- schaft). We will cite a single example which is supported by comparative experimental cultures. In Skollmen^ (East Prussia) Mentzel divided into two parts a field planted with mixed Swedish wheat, Epp wheat and Kas- tromer wheat, and kept one half of it loose by harrowing after every rain, — ^ i. e. by working with the narrow bladed cultivator, — but did not work the other half. Although its soil was better, the latter half yielded only 2160 kg. per acre, the former, however, 2650 kg. A green manure fertihzer turned over deep in light soils and super- ficially in heavy soils, acts in the same way as this loosening of the soil sur- face. By means of this green manure the capillary raising of the water from the underlyng soil layers especially is interrupted". On the one hand, the moisture is thus retained in the deeper layers of the lighter soil; on the other hand, in heavy, wet soils, a well aerated, friable surface is formed so 1 Jahresb. d. Sond.-Aussch. f. Pflanzenschutz. Arb. d. Deutsch. Landwirtsch.- Ges., Part 107, 1905, p. 64. 2 King, F. H., Tenth Annual Report of the Agric. Exper. Stat, of Wisconsin, 1884. p. 194. 235 that the seeds can germinate normally. The stronger, more sturdy plants, which have passed through the most critical germinative stages, are then better able to combat the soil moisture, which rises capillarily higher and more rapidly after the green manure has decomposed. Freezing. The loosening of heavy soils in winter through a suitable freezing is of the greatest importance in their cultivation. If we take into consideration that water, when converted into ice, expands about one- eleventh of its volume, it is evident that the more closely lying soil particles are forced apart by the ice crystals. Also, since rocks are covered with a network of fine cracks, into which the water gradually soaks, the frost is constantly decomposing them and in fact the effects are greater as the freezing and thawing alternate during the winter. Naturally the rapidity of the action will depend upon the composition of the soil, i. e. on its water content. The smaller this is, the more quickly and deeply the frost can penetrate. Therefore, heavy and humus soils will freeze and thaw most slowly. WoUny's^ experiments show the advantage accruing to the soil from the loosening action of the frost. He had two plots of land loosened up in the fall and left lying in open furrozvs, while a third was not worked. This plot and one of the two others were turned over in the spring while the third was worked only superficially. It was then proved that for the various plants cultivated, the yield was smaller from the plot which had not been left fallow in the fall, while the largest harvest was given by the one in which the open furrows froze during the winter and were broken up once more in the spring. Mulching. We now come to the advantage derived in heavy soils from the covering of the friable surface with litter, after having considered earlier the protection given light soils by such a covering. The greatest advantage is that the covering substance prevents the compacting of the soil particles since it takes up the force of the rain drops and, conducting the water slowly, spreads it over the surface of the soil, thereby keeping the friable surface more porous. In nurseries the seed also germinates more uniformly in covered beds. The weeds do not grow so vigorously and can be more easily and completely removed, since they root more superficially in the looser soils. The great air variations between day and night produce a heavy for- mation of dew in the porous covering material. This runs ofl: to the benefit of the underlying soil and increases its fertility. If bark is used to a depth of I to I ^ inches, it furnishes a covering for the seed beds in winter and, in the spring, a protection against the penetration of frost and the cracking of the soil. Seed and seedling beds should have water given them in June or July. In August the ground is harrowed and, in case the bark should then be covered too deeply, the exposed soil is covered with new bark. Snares for the control 1 Wollny, E., Ueber den Einfluss des Winterfrostes auf die Fruchtbarkeit der Ackererden. Biedei-mann's Centralbl. 1902, p. 301. 236 of the unevitable June bug are made of heaps of scattered, moist bark which heats itself. The June bugs lay their eggs in these heaps which later, with a part of the underlying earth, are put in a wagon and worked up with peat, or lignite, ashes, lime, plaster and organic refuse to a compost pile, which, after a year or two, kills the grubs. Harrowing. Harrowing is a process which should find mention here. Anderegg^ has published very noteworthy results of harrowing meadozvs. A meadow of uniform soil composition and mould was divided into four equally large lots. These yielded, — (i). Unharrowed and unfertilized 377 kg. hay (2). Unharrowed but fertilized 833 kg. hay (3). Harrowed but unfertilized 770 kg. hay (4). Harrowed and fertilized 1563 kg. hay Harrowing winter sown grains not only re-opens the encrusted soil, but also increase considerably the formation of young shoots. Director Con- radi^, however, justly points out the fact that the harrow is usuable only if the crust is not too thick and the soil not too binding. Also, if an encrusta- tion in spring may be foreseen, the seed must be more thickly sown since harrowing destroys plants and the sand is thinned. For that reason har- rowing is very useful occasionally in thinning the plants. The increased standing room for the plants left in place gives a greater supply of light to the basal nodes and starts the lateral shoots into a rapid growth and pre- vents their too rapid lignification when these buds obtain moisture from the earth heaped up by the harrowing. H the earth is not pulverized sufficiently by the harrow, the roller, and preferably a wheel roller, must be used in ad- dition. In the majority of cases the roller will have to follow the harrow, because binding soils are not made absolutely fine by the harrow, and also because it is desirable that the earth torn away from the base of the plants may be pressed back again. The best time for harrowing depends on the development of the plant and the water content of the soil. If the plants have grown too far or continuous dry weather prevails, the harrowing should be omitted or, in the latter case, should never be carried out without a subsquent rolling. A few words also might be pertinent here as to the significance of stones in the soil. In this connection, Wollny's^ experiments have shown that with a high, constant air temperature (during the warmer seasons) soil covered with stones and mixed with them is slightly warmer than is that free from stones. With a falhng temperature comes the reverse. During the daily minimum soil temperature, soil containing stones is for the most 1 Illustr. landw. Vereinsblatt, 1880; No. 8; cit. in Biederm. Centralbl. f. Agrik.- Chemie. 1880, p. 693. - From "Der Praktische Landwirt" in Fiihling-'s landw. Zeit., 1880, p. 151. 3 Wollny, Fuhling's landw. Zeit, 1880, p. 314. part colder than that free from stones, while during its maximum it is warmer. In regard to conditions of moisture, field soil covered with stones is found to be wetter during the warmer seasons than uncovered soil of otherwise similar composition. Soil covered with stones lets more water slip through than does one not so covered. The Use of Lime, Marl and Plaster. The importance of lime arises from its chemical action as a direct nutritive substance as well as from its properties, which change the mechan- ical constitution of the soil. Aside from favoring friability, it should be emphasized that the lime attacks the silicate in clay soils and sets free sol- uble potassium compounds. By its more rapid destruction of the organic substances, it causes a better decomposition of humus. In regard to the technique in using lime, it is advisable to keep burnt (quick) lime in baskets under water until no more air bubbles arise (possibly 3 to minutes) and then to heap up the pieces in layers. They decompose (slake) of themselves and the lime stone, which lost its carbon dioxid in the previous burning, now becomes the white powdery calcium hydroxid (Ca(OH)^,) and as such represents slaked lime, which is soluble in 730 parts of cold water, and only in 1300 parts of boiling water (lime water). 100 parts of quick lime correspond to 132 parts of slaked lime. The lime should be uniformly spread over the field in quiet weather by hand, or with a suitable shovel. It is well to spread it in the fall on the stubble and then to work it under the surface. If it is necessary to wait until spring, it must be spread as early as possible before seeding, as soon as the soil has dried. Smaller doses (750 kg. to 1500 kg. per hectare) repeated about every five years, are more advisable than a single heavy liming, because, in the latter, the decomposition of the humus is so violent that the subsequent increase in the harvest is at the cost of a later production. It is said in practice that fer- tility is difficult to maintain on a lime-stone soil, because organic matter dis- appears rapidly. Naturally the amount of lime depends upon the soil. Tough clay soil will bear most, while great care must be used with poor sandy soil. Soils which are lacking in organic matter or have water standing on them, may not be limed at all. The results which become evident most quickly are given by a humus soil poor in lime ; — Sorrel (Rumex acetosella) indicates a scarcity of lime. Lime will act here splendidly as a fertilizer. If local lime deposits be used, such as possibly meadow-lime or marl, or the so-called waste lime (gas lime, lime ooze, lime ash), it is distinctly ad- visable, before using it, to let the air pass through in order to decom- pose it, or still better, to let it freeze. When using waste lime one should convince oneself first of all, by a simple experiment, that no injurious sec- ondary action can take place. According to Hoffman's experiments^, it 1 Mitteilungen der Deutsch. Landwirstchafts-Ges. 1905, p. 367. 238 should also be taken into consideration that the more lime used, the less should fertilizing with potassium be neglected. In using stable manure, it is well to put the lime in the soil sometime before the manure is added. Bone meal should be avoided on soils containing lime. In the same way, it is not ad- visable to use ammonia and ammonia superphosphates together with lime. Pulverized quick lime should be used on binding, clayey soils ; lump or slaked lime on better loam soils. In regard to the need of lime by the different plants, IIofl"mann states that the Leguminoseae in general are distinguished as the most responsive to applications of lime, but that the Lupines and Serradella may be con- sidered as hostile to lime and sweet peas also do not like the direct use of lime or marl. In the use of marl also, the lime is the most active principle and hence it follows that a clayey soil, rich in humus, bears marling better than a poor sandy soil which in turn can be more benefited by a clay marl than by a lime or sand marl. The sometimes dreaded "impoverishment" from the use of marl will take place only if fertilizing with stable manure is delayed. The last is indispensable for all soils and especially for heavy ones in keeping the fields productive. No«mineral fertilizer can replace stable manure. The influence exerted by the lime contained in marl upon decomposition of the humus substances is illustrated very clearly by Petersen's^ experi- ments. He determined the amount of carbon dioxid produced in different soils by the process of decomposition with and without the addition of cal- cium carbonate. In using a heavy clay soil, known to be perfectly sterile, with 1.98 per cent, humus and 36 per cent, of its water holding capacity in water content, he obtained in 16 days 0.07 per cent, of the weight of the dry soil in carbon dioxid. On the other hand, the same soil under the same con- ditions with the addition of }^ per cent, of calcium carbonate, mixed in the clay as marl, yielded 0.20 per cent, carbon dioxid, or per liter of dry soil, without addition of lime, 0.9153 g. ; per liter of dry soil, with addition of ;^2 per cent, lime, 2.6167 g. A leaf mould with strongly acid reaction consisting of 58 per cent, humus and 30 per cent, of the absorptive capacity in temporary water con- tent, yielded after 16 days, without and with the addition of t per cent, cal- cium carbonate (when the earth still gave an acid reaction) : per liter of dry soil, without the lime addition, 0.891 1 g. COo ; per liter of dry soil, with the addition of i per cent, calcium carbonate, 3.386 g. COo. With the addition of 3 per cent, calcium carbonate, the soil yielded 5.3476 g. carbon dioxid, while the series of check experiments, free from lime, produced only 0.9664 g. COo. The addition of the lime, therefore, had caused 3 to 4 times as great a production of carbon dioxid, i. e., humus de- composition, as in the soil in an unmarled condition. Heiden, in Pommritz, summarizes thus the effect from the use of marl: The chemical action arises primarily from its content of calcium carbonate 1 Jahresbericht f. Agrik. 1870-72. Landwirtsch. Versuchsstationen, Vol. 13, p. 155. 239 and consists in the hastened decomposition of the organic elements of the soil, in the combining of the free acids so injurious to plant growth, in the conversion of ferrous oxid into ferric oxid, and in bringing about the ab- sorption of the basic nutritive substances by the soil. The bases are held in the soil as hydrated silicates and as the salts of humic acid. In the absorp- tion of the bases by the humus body, these must be present combined with carbon dioxid. The lime promotes the formation of carbonates. Further, the mineral elements of the soil are decomposed, whereby the basic nutritive substances are freed and made accessible to the- plant. Every marl does not suit every soil, — clay soils, where possible, must have a lime or sand marl. Aside from these indirect advantages, the direct effect of the use of marl is shown in the addition of potassium, soluble silicic acid, magnesia and phosphoric acid, which, together with lime, are present in every marl. A few words should be added here as to the use of plaster or gypsum. Franklin's words, — "This has been plastered," are well-known. He wrote this in plaster on a clover field in order to recommend to his countrymen the process which had been known with great advantage by the Romans (Knop, Kreislauf des Stofifes) and the Greeks. According to Knop's experi- ments and those of Deherain and Liebig, a solution of plaster in soils con- taining absorbed potassium, frees it in the form of sulfate, while the lime it- self is precipitated. The method of spreading the plaster on clover plants freshly covered with dew or rain, recommended by experience, is found to be advantageous, since a solution of plaster is formed on the moist plants; dripping from them, it acts at once in the immediate vicinity of the roots. It thus rapidly becomes of advantage to the bacterial flora, for Pichard's^ researches and those of others show that plaster and other sulfates (potas- sium and sodium) exercise a most favorable influence on the process of nitrification. Plaster should be used in an unburned state and indeed for clover and lupines from 2 to 5 centner per acre in the spring. Although the influence of calcium hydrate or carbonate, favoring de- composition, was discussed above, it must still be emphasized, that, as shown by Wollny's" work, this is only of value when the substance is already de- composed and contains humic acid, while the addition of calcium on unde- composed organic substances rather hinders decomposition. This is especially true for calcium sulfate (gypsum) which comes under consideration as a conservation material for animal manure. In a mixture of quartz sand (300 g.), powdered peat (5 g.), and 60 ccm. water, Wollny^ found Volumes CO, in 1000 Volumes Soil air — without the addition of gypsum with the addition of gypsum ■ 0.05 g. 0.1 g. CO. 3.194 3.029 2.713 1 Annales agronomiques X, p. 302. - WoUny, E., Die Zersetzung der organischen Stoffe etc. Heidelberg-, Carl Winter, 1897, pp. 133 ff. 3 Journal f. Landwirtschaft, 18S6, p. 263. 240 The addition of the plaster had accordingly reduced the loss in organic substances and also in nitrogen; i. e., had exercised an arresting influence on decomposition. The use of calcium compounds as a remedy against dis- eases, in which an excess of nitrogen comes under consideration, will be discussed under the individual cases of disease. 3. THE DISADVANTAGES OF MOOR SOILS. The Acids in the Soil. Ramann^ explains as moors, — the formation of more moist regions in temperate zones, in which soils poor in nutritive substances, with an acid reaction, are covered with dwarfed bushes, grasses, mosses and peat-moss (sphagnum), and also lichens. The humic acids* act freely here, and cause the acid reaction of the soil. Acids are formed by the decomposition of the organic substances in the soil to which fungi as well as bacteria surely contribute a share (Cepha- losporium, Trichoderma, etc., according to Koning^). Formic acid, acetic acid, butyric acid, etc., are produced which decompose rapidly in well aerated soils. Besides these, however, the humic substances also form the still little known crenic acid with its salts (crenates) which, widely dis- tributed in soils and water, form a yellow, strongly acid solution, drying to an amorphous mass. While its salts with alkalis and alkaline earths are soluble, its ferric oxid remains insoluble. With the entrance of air aprocrenic acid is produced from it, the salts of which are either in- soluble or dissolve with difficulty. A great influence on the weathering and the transportation of the accessible mineral salts may be ascribed to these acids and their compounds^. Raw humus, peat and other soil substances with a strong acid reaction lose only a part of their acids even after lying sometime exposed to the air. Since even well aerated forest soil often shows an acid reaction, it may be concluded that scant oxidation either does not cause the production of the soil acids, or only at times produces them. We must consider here also the work of definite bacteria in this acid for- mation. Free acids are often absent in good soils, but poorer moor soils are frequently rich in them and become even poorer because extensive leaching and weathering processes constantly take place, due to the free acids. 1 Ramann, Bodenkunde, 2nd. Edition. Jul. Springer. 1905. 2 Koning-, Arch, neerland. sc. ex. et nat. 1902 II, 9, p. 34. 3 Ramann, loc. cit. p. 144. * In the light of recent investigations on the nature of the organic matter of the soil it seems that we moist revise some of the older terminology. The term "humic acids" is rather to be regarded as a loose generic term applicable to a group of organic compounds found in the soil. — Vide: — Mulder, The Chemistry of Vegetable and Animal Physiology, trans, by From- berg, 1849. Schreiner, O. and Shorey, E. C, Bulletins 53, 74, and 88, Bureau of Soils, U. S. Department of Agriculture. Jodidi, S. L. .Tour. Amer. Chem. Soc. 34: 94. 1912; Jour. Franklin Inst. 175: 245. 1913. (Translator's note) 241 In regard to the sensitiveness of our cultivated plants to free acids, Ramann cites Maxwell's^ experiments with i-io and 1-50 per cent, solutions of citric acid. He found that all the Cruciferae were quickly destroyed, the Papilionaceae more slowly. Grain suffered greatly, only the pearl millet and maize could withstand it. Tolf made discoveries in regard to humic acids, according to which seedlings suffer in acid moor soils. In the acid moor, the diffusion of the salt solutions is sharply arrested. According to Reinitzer and Nikitinsk, pure humic acids are unsuitable for the nutrition of bacteria and fungi. On the other hand, most of the higher plants can endure a moderate amount of these acids. We discover from our cultures of Ericas, Azaleas, Rhododendrons and other Ericaceae in moor soil that a number of plants indeed seem directly adapted to acid soils. The dark colored humus parts consist preponderately of Humin and humic acid (Ulmin, according to Mulder). The humus substance must be considered as a mixture of closely related bodies with and without nitrogen, which can be separated into two groups according to their behavior with al- kalis. The brown humin substances, insoluble in the most diverse solvents, swell up in alkaline liquids and pass gradually over into humic acids. The humic acids (their chemical composition is insufficiently known), containing possibly 59 to 63 per cent. C, 4.4 to 4.6 per cent. H. and 35 to 36 per cent. O, are easily dissolved in alkalis and are re-precipitated from their solutions by stronger mineral acids. If they are withdrawn from acid soils (moor soils) with alkalis or ammonia and precipitated with hydrochloric acid, a voluminous, jelly-like substance is obtain which, in drying, forms a brown or black amorphous mass. The humic acids are separated from their solution, by freezing, in the form of a dark colored powder, which gradually passes over again into solution. Ramann emphasizes the fact that humic acids are somewhat soluble in pure water, but not in water containing salts. The salts of the alkalis and of ammonia with humic acids are sokible in water, but not those of the alkaline earths (calcium and magnesium). Yet the latter also seems to become soluble with an excess of acids. Calcium humate will decompose quickly into calcium carbonate which will combine into new masses of humic acids. On an average, the nitrogen content of humus substances is greater in dry regions than in moist ones. By the advancing decomposition, the nitro- gen, which in organic combinations is accessible to plants with difficulty, is carried over into compounds easily absorbed. Raw Humus. Humus is beneficial and indispensible only wdiere, in pure deposits or mixed with the mineral skeleton of the soil, it is exposed to constant aeration and to sufficient moisture. Its chief action on plant growth does not lie in its nutrient content or in the carbon dioxid formed by its decomposition of minerals, but in its physical properties. 1 Journ. Amer. Chem. Soc. 1898, 20, p. 103. 242 If humus is mixed with dense soils, they are loosened and made warmer and more easily worked. In sandy soils the humus acts as a hinder and in- creases the watef capacity, whereby the fluctuations in temperature become less marked. These favorable peculiarities, which arise from the mixing with mineral elements in the soil, disappear as soon as the humus is de- posited on the soil in impervious layers, i. e., is not broken up by abundant decomposition and the micro-organisms. In compact humus layers, the con- tent in free acids is almost always greater. The forest soils, which are most rapidly decomposed and worked up, are the best. In warm chmates the work progresses very quickly of itself. With a favorable humus decomposition, we find that in forest soils the porous forest debris, which forms the layers of litter, is not so thick and merges gradually into a friable, strongly decomposed, structureless humus layer. If in any region the factors contributing to decomposition are ab- sent, these layers of litter are retained, settle only gradually and become a firm, fibrous humus mass, which is deposited on the subsoil and remains more or less sharply separated from it. Such cases may be observed in poor sandy soils, especially those containing meadow ore. This process, in which therefore the organic substance acquires no earthy composition, will occur everywhere where conditions unfavorable to decomposition exist, — as, for example, when the air is excluded by water, or conversely, with too great drought in the hot seasons or in places exposed to constant strong winds. Our forest tracts, where heather (Calluna vulgaris), cranberries and huckleberries (Vaccinium) the pteris and aspidium brakes and the cushion- forming mosses grow, are most inclined to the formation of such fibrous and but shghtly earthy humus layers, the undecomposed elements of which are deposited in dense masses on the soil and in this way form the so-called "raw-humus." The upper layer of such raw-humus deposits still shows the interwoven structure of the plant debris, the lower layer, in which the plant parts are but slightly distinguishable from one another, has a fibrous dark humus substance interwoven with roots. In moist beech, pine and spruce tracts, such raw humus may become peat-like. Ramann (loc. cit. p. 162) states as his opinion of the change in the soil beneath a covering of raw humus, — that, besides the exclusion of air, the humic acids especially form the injurious factors. These act on the un- weathered silicate, decomposing it energetically, bringing into solution al- kalis and alkaline earths and, since at the same time the amount of acid solutions absorbed in the soil is slight, leaches the soil, i.e., the soluble sub- stances are carried down to greater depths. If raw humus lies on sandy soils, the grains of the uppermost layer appear to be strongly bleached and milk-white, the intermixed silicate rock is greatly weathered and usually transformed into white kaolin. The humus admixture still richly present on the upper surface decreases more and more from the top downwards so that 243 the soil becomes light gray in color and, because of this color, is called gray or lead sand. Below this Hght colored layer is found, sharply separated from it, a yellow to brownish looking soil, the deeper layers of which gradually be- come lighter. Here, the sand grains show mixtures of ferric-oxid or ferric hydrate. Then comes the white raw sand, still but little affected by weather- ing. The uppermost humus soil layer is found to be most weathered and the layer most impoverished by leaching. If the leaching of such an upper soil layer, under the influence of the raw humus deposited on it, be carried to a given stage, the action of the salts in the soil on the soluble humic acid must cease, the salts then remain in solution and can penetrate to the lower layers of the soil. If they come in contact here with soluble salts, they are precipi- tated and coat the separate soil grains with a structureless layer of organic substances. Under the microscope, I found the sand grains covered with brown, chart-like etchings. If this process keeps up, the precipitated or- ganic substances finally cement the separate sand grains into compacted layers below the lead sand, — meadozv-ore has been produced. 'Meadov/-Ore. According to Ramann's explanation of the production of meadow-ore, given in the previous section, this is a humus sand stone. It occurs in var- ious forms and first of all as "Branderde" or "Orterde," which has a white easily pulverized form and shows a large content of organic substances. This is formed in rich soils which are but little changed unfavorably. The real swamp ore is a firm, stone-like, hard mass, deposited on easily pulver- ized or loose soil layers, with a medium content of organic substances and a brown to black color. This is the form most widely distributed in North Germany (Liineburger moor). Besides this, there is a lighter brown swamp-ore which is ver}^ firm and tough and holds but small amounts of organic substances. This is the hardest form, offering the greatest resistance to a working of the soil and frequently occurring in great thickness. In judging the processes of leaching, an analysis taken by Graebner^ from Ramann's- work may be useful. The swamp ore soil in the Main Forestry District Hohenbriick in Pomerania contained in its different layers : — • (a) Lead sand, which was 15 to 20 cm. thick and contained 1.05 per cent, of organic substances^. Soluble in Residue insoluble in Hydrochloric acid. Hydrochloric acid. Potassium 0.0076 per cent, of the soil 0.618 (Sodium o.oiii " " " " " 0.167) Calcium o.oiio " " " " " 0.060 Magnesia 0.0026 " " " " " 0.020 (Manganous oxid 0.0032 " " " " " 0.060) Ferric oxid 0.0964 " " " " " 0.450 Aluminum oxid 0.0268 " " " " " 0.650 Phosphoric acid 0.0058 " " " " " 0.043 Total content except silicic acid. 0.1645 2.068 1 Paul Graebner, Handbuch der Heidekultur. Leipzig, Wilh. Engelmann. 1904, p. 194. 2 Die Waldstreu, Berlin, 1890, p. 30. 3 Ramann in his "Bodenkunde" 1905, p. 166, gives the same analysis without the elements enclosed in parantheses. 244 (b) Swamp ore, 5 to 8 cm. thick with 7.28 per cent, of organic sub- stances : Soluble in Residue insoluble in Hydrochloric acid. Hydrochloric acid. Potassium 0.0178 per cent, of the soil 0.754 (Sodium 0.0033 " " " " " 0.360) Calcium 0.0194 " " " " " 0.170 Magnesia 0.0137 " " " " " 0.028 (Manganous oxid 0.0044 " " " " " 0.047) Ferric oxid O.1936 " " " " " 0.690 Aluminum oxid 1.5266 " " " " " 2.320 Phosphoric acid 0.2956 0.042 Total mineral substances except silicic acid 2.0744 4-4^1 (c) The yellowish brown sand underlying the swamp ore: Soluble in Residue insoluble in Hydrochloric acid. Hydrochloric acid. Potassium 0.0085 per cent, of the soil 1.103 (Sodium 0.0213 " " " " " 0.528) Calcium 0.0254 " " " " " 0.225 Magnesia 0.0401 " " " " " 0.064 (Manganous oxid 0.0068 " " " " " 0.026) Ferric oxid 0.3448 " " " " " 0.760 Aluminum oxid 0.4000 " " " " " 3-2IO Phosphoric acid 0.0281 " " " " " 0.043 Total mineral substances except silicic acid 0.8750 5-959 We perceive from the above figures that, by leaching, the lead sand has not only lost in soluble substances, but that the greatest part of all the rock debris containing nutritive substances has been decomposed by weathering and being washed deeper down. It is therefore a fact that cer- tain soil layers in forests and in open moors (usually formed from such soil layers) become impoverished. This is very significant agriculturally if the impoverishment exceeds the supply of nutriment furnished by weathering and the annual rain fall. Meadow ore must be distinguished from the real swamp ore ; the for- mer is insoluble in an acid solution, such as hydrochloric acid, while the swamp ore is abundantly dissolved. Especially in humus moor soils, where the deposition of raw humus leads to the formation of swamp ore, do two chief injurious factors come under consideration : — the lack of oxygen due to the density of the soil and the content in humic acids. The processes taking place, with an exclusion of oxygen, have been considered in another place (for example, p. 99). We have here to take only the humic acids under consideration. Graebner pays the desired attention to this point^. Continuing Wolf's^ investigations on 1 Log. cit. p. 228. 2 Tagebl. Naturf, Vers., Leipzig, 1872. 245 the wilting of the leaves and their ultimate death, resulting from the de- tention of the plant roots in water excessively charged with carbon dioxid, Graebner cites Maxwell's experiments^ with citric acid and those of Tolf and Blank with humic acids, all of which lead to similar results. This is the place to record Ramann's statement as to the cause of retarded diflfusion in acid soils. Either the colloidal composition of the moor-substances can re- duce the capacity for diffusion and the colloidal substances are precipitated by neutralization with lime, or some direct action of the humic acids is present. If one thinks of the discoveries showing the influence exerted by slight acid increases on the protoplasm", whereby its currents are arrested, one must consider the direct action of the acid to be of the chief importance. Special proof already exists of the retarding of transpiration by acids (tar- taric, oxaHc, nitric and carbonic acids, etc.) and its hastening by alkalis (potassium, sodium, ammonia) ^ It can therefore be said, with Schimper, that plants in a strongly acid soil will suffer from physiological drought even in the presence of abundant water. To this must be added that the great power of humus to retain water makes the mechanical withdrawal of the water from the soil particles much more difficult for the roots than if in sandy soil. Plants are found to wilt in peaty soil or loam with a percentage of water sufficient to keep them perfectly fresh in sandy soils, as Sachs'* experiment has already shown. All these injuries due to the soil find expression most of all in the culti- vation of pines, which subject Graebner^ has treated with especial thorough- ness. He found in young pine plantations, which had grown tolerably well for some years, that the shoots formed in May at first developed normally, but, with the appearance of the summer drought, became grayish green in color. If the dry period continued, the shoots begin to curl, the needles of the previous year became blunt and brown and in many cases the little trees dried up in a few weeks. By digging in the soil, it was found that swamp ore had been formed below the roots or even around the still rather slender ones. To supplement his description, Graebner pictures in the figures here reproduced root development on swamp ore soils. We see in figure 29, that the strongest and longest roots are spread out not far below the surface of the soil and parallel to it, so that its nutrition must take place through the raw humus and the lead sand, which is poor in nutritive substances. Since root development is greater in solutions poor in nutritive substances than in concentrated solutions, this results in a wide reaching out of the root branches, which, in the present case, according to Graebner, seem several meters long and but little branched. The aerial axis, however, is scarcely a 1 Journ. Ann. Chem. Soc. XX (1898) p. 103. 2 Pfeffer, Pflanzenphysiologie II Vol. 1904, p. 798. 3 Pfeffer, Pflanzenphysiologie I Vol. p. 231. 4 Sachs, Handb. d. Exp.-Physiol. Leipzig-, 1865, p. 173. 5 Graebner, R., Handbuch der Heidekultur, Leipzig, 1904, W. Engelmann, p. 231. 246 meter high. Poverty in nutritive substances in combination with the lack of moisture, easily becoming great in lead sand, are the causes of an ultimate blighting at the tops. Figure 30 shows the root growth of an oak. The oak was planted after the layer of swamp ore had been broken through artificially. But this layer of swamp ore had later re-united and the portion of the root in g, nearly shut away from an air supply, had practically stopped growing. No mycor- rhiza, or scarcely any, could be found on this part of the root, Graebner attaches the fol- lowing significance to such phenomena. If the swamp ore is deposited below the roots, the earth lying above it is naturally exposed to great fluctuations in moisture, and in times of drought becomes so dry that the plants die from a lack of moisture. In cases of this kind, however, the plants forming their roots en- tirely in the lead sand, exhibit a very weak growth, grad- ually making itself evident by short, yellow needles. If the swamp ore, however, lies di- rectly around the roots, which are about as large as knitting needles, and have penetrated in to the better soil, it presses against them, causing knotty swellings. This takes place if the roots reach the better sub- soil through an" opening in the swamp ore layer. Such me- chanical constrictions disturb further root growth. The tree is therefore essentially dependent on the roots lying above the swamp ore layer. Growth and vital activity are normal during the spring dampness, but all activity stops if a hot summer dries out the soil. Graebner found the root lips shrivelling, turning to resin or dying entirely. In larger trees, with a renewal of moisture, time and material are necessary for new root growth. This loss in time and substance becomes evident in the growth of the aerial axis and, in combination with the results of the period of drought, causes in great part the weak growth of the moor pines. The plantations improve as soon as the fluctuations of moisture are less extreme. Fig 29. "A meadow ore pine" from the Lune- burger moor, grown after the formation of the meadow ore. r raw humus, b lead sand, o meadow ore. Below the meadow- ore the yellow sand begins. (After Graebner.) 247 Usually pines on high moor soil develop a very crooked form"^. Yet ihe seeds of these crippled pines, after the moor has been drained dry, grow into erect trunks. Schroter and Kirchner- also state that, on too wet places in the high moor, Pinus montana makes a reduced cripple growth ("Kusseln"), but recovers after the water has been drained fi:om the soil. Our pines form such ("Kusseln") also on wet meadows. In the cases I have observed, this form of growth was produced by the resinification of the terminal bvid of the main shoot, because of insect and fungus injury; there then develops below this bud a number of shoots which remain short (and in part some rosette shoots). Plgure 31 shows a pine 48 years old which came from the Liinebur- ger moor and which Dr. Graebner most kindly placed at my disposal. The height of the whole tree, — including the tops and measured from the root neck up, amounted to 74 cm. ; the length of the trunk up to the first branch, 39 cm. ; the girth of the trunk below the lowermost branch, 8 :3 cm. ; the average length of the needles, 2 cm. The foliage of the whole tree is very sparse. The needles have remained only on the latest shoots, all the older ones have fallen. The branches are greatly thickened in places and cracked open as a result of injury from frost. The perpendicularly growing tap root is 8 cm. long to its place of horizontal bending; the largest horizontal root branch, 18 cm. The branch growth is sparse and the branches have sharp angles (k) and often dead tips (a). These sharp angles or bow-like curves (k) arise because the branches and the main trunk have received one- sided, canker-like frost wounds to which correspond an increased wood for- mation and a stretching on the opposite side. Greater frost wounds, extend- ing over more than half the circumference of the axis, are found at / and /'. Fig-. 30. An oak from the Luneburgei- moor planted after the meadow ore had been broken through. The layer of meadow ore had closed later. r raw humus, b layer of sand 20 cm. thick, o meadow ore. g- yellow sand. (After Graebner.) 1 V. Sievers, Ueber die Vererbung von Wucksfehlern bei Pinus silvestris. Porstl.-naturwiss. Zeitschr. 1898. Part 5. 2 Lebengeschichte der Bliitenpfianzen Mitteleuropas, Part III, 1905. p. 222. 24B In figure 32 f on the main trunk is reproduced in natural size, in order to show that, like "open canker," the wounded surface consists of many very small, over-growth edges of different years which recede like terraces. In accordance with the paltry branch growth in figure 31, the root is also small ; it cannot follow its natural tendency to send its tap root downward Fig. 31. A moor pine with flatly extended roots from the Luneburger moor. (Orig.) a dead tips of branches, k parts of the branch which have grown out at sharp angles, k' parts of the branch curved like bows, / frost wound where the branch leaves the trunk, f frost wound m the form ot an open canker with a distinctly limited wood body, h roots which had grown against the layer of meadow ore. perpendicularly (compare figures 5 and 6, p. 95), but must extend its root branches in the upper soil layers and moss cushions. Part of the lowest root branches are partially bent upwards at a sharp angle, probably because they have met with a layer of swamp ore or some similar impenetrable body. In his study of the high moor of Augstumal in the Memel delta, Weber^ gives very interesting illustrations of the crippled forms of pines, corresponding to the Finns sihesfris f. turfosa, Willk. Here he describes also the crippled birches, v^hose roots, like those of the Scotch fir, always showr splen- didly developed mycorrhiza. The trunk, usually only a few centimetres thick, is most- ly bent and knarled, and covered below with a seamed hark, a very striking feature in such small trees. To this it should be added that these small birches usually only about 1.5 m, high form a well set top. On an average, the main root penetrates only 15 to 20 cm. in- to the soil, then bends to one side, to run parallel with the surface. The roots, spreading sidewards, attain to 3 to 4 times the length of the trunk. The vegetation on the high moor is best characterized by a specimen of Betula pubescens described by Weber". The upper trunk, which had white rot at the top, was 1.8 m. high; the wood from which the bark had been removed was possibly 34 mm. in diameter above the root neck and had 51 annual rings, the last eleven of which alto- gether were only 0.9 to 2.6 mm. wide. The little tree was just beginning to become blasted at the top and was overgrown for 30 cm. above the root neck with Sphagnum medium and >S. acutifolium. In cultivation, it is not only necessary to break through the swamp ore layer, but also to bring it up to the surface of the soil. In the air, it decomposes to a brown sand, which gradually becomes lighter in color be- cause the organic elements have weathered. Freezing the swamp ore hastens this process greatly. The decomposition usually takes place more quickly when the content in or- ganic substances is higher. Brown colored swamp ore (rich in humus) is usually de- composed in a year; on the other hand, the light colored (which is poor in humus) Fig-. 32. Canker-like, wounded place on the moor pine. c the (deepest lyiiier) wood centre, / edges of the wound rising like ter- races in which the most recent, j, are the most rolled back and the old bark, r, covering it, which is breaking loose in squarrous pieces, 7v dying, outer- most edge of the wound, / lichen growths. (Orig.) only after 2 to 4 years. 1 C. A. Weber Ueber die Veg^etation und Entstehung- des Hochmoors von Aug- stumal im Memeldelta, etc. Berlin. Paul Parey, 1902, pp. 40 ff. 2 Loc. cit. p. 47. 2$0 Poisoning of the Soil by Metallic Sulfur. In considering factors injurious to plant growth ferric sulfid as pyrites (and rhomboidally crystallized as markasit) must be noticed primarily since it is one of the most widespread precipitates produced in the formation of moors. Ferric sulfid is found less in moors themselves than in the imder- lying sand and on the line between the organic deposits and the subsoil. If pyrites weathers, there is produced by oxidation and absorption of water sul- furic ferrous oxid, — ferrous sulfate, copperas, and free sulfuric acid (FeS^-l- 70+H,0=FeSo,4-H2SOJ . The ferrous sulfate oxidizes with the formation of basic salts to ferric oxid. In the presence of sufficient amounts of calcium carbonate, calcium sulfate (gypsum) is produced. If ferrous carbonate occurs, it passes over into ferric oxid or ferric hydrate with the loss of carbon dioxid and the taking up of oxygen. As is well known, the ferric hydrates cause the yellow to brown color of the soils and are able to absorb gases (carbon dioxid, nit- rogen, etc.) to a very marked degree. Among them is the brown clay iron ore (limonite Feo[OH](;) which cements together the surrounding sand^ In moor regions, however, the layers containing pyrites are often not oxidized at all ; because of the presence of water and the strongly reducing action of the moor substance they cannot obtain any oxygen. The most disasterous effect of the iron sulfid is its inhibition of the com- bining of the bases present in the soil and the free sulfuric acid formed by weathering. As a rule, calcium carbonate is present in the soil, so that gyp- sum can be formed, often alum or magnesium sulfate are also produced. An excess of the last can act injuriously. When experimenting with an exces- sive supply of alum, I found spotted necrosis appearing in barley. However, if the bases are absent, the free sulfuric acid will act directly as a plant poison. If, in improving the soil, the layer containing the pyrites is brought to the surface, the soil will at first remain infertile. Minssen- shows that at times the upper layers of the moor also contain iron sulfid. In a sample from Silesia he found 7.286 per "cent, of the dry substance of the surface soil to be sulfuric acid, soluble in water, 3.940 per cent, ferrous sulfate and 3.346 per cent, free sulfuric acid and approximately twice as much in the deeper layers, aside from great masses of still un- weathered iron bisulfid. The top of the sulfate here analyzed was later re- moved 62 cm. deep, so that the lower layers richly impregnated with iron sul- fid were laid bare. The oxidation of the pyrites gave such large amounts of compounds injurious to vegetation that any agricultural use of the moor within a conceivable time seemed impossible. Such a case shows the neces- sity for the use of foresight in opening up lowland moors. 1 Ramann, Bodenkunde, 1905, p. 87. 2 Mitteilung'en d. Ver. z. Forderung- der Moorkultur im Deutsch. Reich, 1904. No. 1. The question as to the nijuriousness of the black colored water floimng on to the meadozvs from the alder bogs of forests has been treated in detail by Klien^. In one especial case which gave rise to complaints against the forestry commission, the water coming from the forest was viscid, brown and at times smelled bad. In 100,000 parts, it contained 31.28 parts organic sub- stances (humic acids, etc.) and 17.59 parts mineral substances, among others 7.81 parts calcareous earth, 3.07 parts ferric oxid, etc. The humic acids formed the injurious factor here. In similar cases it depends on the kind of soil overflowed by such bog water. It will be especially injurious if it flows over ferruginous soils or those with a clay subsoil, while a soil rich in lime can more easily withstand overflowing from the alder swamp, such as oc- curs in spring floods, because of the hastened decomposition of the hurhus, peculiar to such a soil. Nevertheless such water should be avoided for irri- gation and back water. The formation of ferruginous sand depends on the precipitation of fer- ric hydrate and iron silicates. Mixtures of ferric hydrates with varying amounts of ferric silicates and phosphates also give the so-called meado'di- ore. This combination occurs in moors, standing bodies of water and other places, where water containing iron comes in contact with the air, together with the co-operation of bacteria (iron bacteria according to Winogradski)-. One is inclined of late to lay stress on the co-operation of the micro-organ- isms'. Susceptibility to Frost of Moor Vegetation. In moor soils which have been brought under cultivation, their especial sensitiveness to frost as compared with other kinds of soil has been proved by repeated experiments. In this, important diflrerences are found if the moor soil has a sandy covering or if it is mixed with sand. Wollny* found in his experiments that the latter is more fertile than the former, in which the ground water was higher. Instead of the sand, a covering with clay has also been proved to be beneficial. In meadow cultivation when too much water has been removed, Fleischer"' recommends covering with sand, rich in feldspar, or loam, or clay to avoid too great drying out. Jungner" gives fur- ther examples from the province of Posen. In them moor fields which had not been covered with soil containing clay, showed also a second total freez- 1 Klien, Die nachteilisre Einwirkung- des aus Eller-Bruchen und Torfmooren kommenden schwarzen Wassers auf die Wiesen. Konigsberger land- und forst- wirtschaftliche Zeitung 1879, No. 28; cit. in Biedermann's Centralbl. f. Agrik- Chemie, 1880, p. 568. 2 Winogradski, Ueber Ei&enbakterien. Bot. Zeit. 1888, p. 260. 3 E. Roth, Die Moore der Scliweiz, unter Beriicksichtigung der gesannten Moor- frage. Leopoldina, 1905, No. 3, p. 34. 4 Wollny, Untersuchungen liber die Beeinflussung der physikalischen Eigen- schaften des Moorbodens durch Mischung und Bedecl1. II p. 141. 2 Chemisch-physiologiscne Untersurhungren iiber die Ernahrunsr der Pflanze von Knop and Dworzak. Aus Berichte d. Kgl. sachs. Gesellsch. d. Wissensch. vom 23. April, 1875. Cit. Jahresber. f. Agril^ulturchemie, 1875. p. 267. ^ Pag^noul, Sur le role exerce par les sels alcalin sur la veg-^tation de la b^'tter- ave et de la pomme de terra. Compt. Rend. 1875. Vol. LXXX, p. 1010. Fertilizing- experiments carried on for five years with chlorids showed for beets a fluctuation in contents from 1 to 50. In potatoes, the smallest yield in tubers coincided with the least amount of potassium carbonate in the ash but with the greatest amount of chlorides. 307 kAT Fi£ 40. Blossoming buckwheat plant grown in a normal nutrient solution. (After Nobbe.) Besides the probable increase in the transportability of the phos- phoric acid, it can be proved that chlorine has a favorable influence on the transference of the starch prepared in the leaves. According to Nobbe's experiments, the plant starving for chlorine continues to grow, exhibits a very dark green color and gives a considerable pro- duction of substances rich in carbo- hydrates, but sooner or later,^ — at any rate before the time of blos- soming, — there occurs a peculiar change in form and structure. Nobbe found the dark, abnormally fleshy leaves crammed full of starch (in oak and buckwheat) rolling up, becoming brittle and dropping. The stems and petioles seem puffed up, the intemodes of the stems always are shorter and many finally dry from the tips backward. If the plant reaches the blossoming stage, only scat- tered, unusually poor small fruits develop, despite the abundant starch material in the leaves. The effect of a lack of chlorine is best recognized by a comparison of a normal buckwheat plant with one grown with a lack of chlorine (figures 40 and 41). g. Lack of Iron AND "Jaun- dice" (Icter- us). The expres- s i o n s, "jaun- dice," "yelloiv- sickness, "white- l e a V e d n ess," "v art egation," 3o8 (b) "chlorosis," "alhication," "etiolation," are the most common names for the condition in which a leaf loses its green coloring matter in spots, or over the whole extent of its surface. The causes for this change in color are very different, but always represent a condition of weakness. In order to survey the manifold causes of the disease, we will endeavor to group them into I. Induced and non-transmissible conditions. (a). The discoloration attacks the whole surface of the leaf, which has matured in the light. After having been green in its young stages, the whole leaf assumes a yellowish, yellow to yellow- white color tone. Icterus or jaun- dice. Cause : usu- ally a lack of nu- tritive substances. The pale discol- oration is present in the young organ and the leaves re- main in a con- dition resembling youth until their p r e m a t ure end. Cause : lack of light and at times of heat (see these topics). Innate and transmis- sible conditions. Portions of the plant show yellow to pure white spots or stripes. Those plants suft'er especially in which pure white leaves appear near the ones spotted with green or all green. The spots have usually a sharp demarcation. White-leavedness, alhication, variegation, sometimes transmissible through seeds or by grafting. Cause : probably enzymatic dis- turbances (see these). Of course there are intermediate stages between the types named, since the individual causes often work together. ' In the present division we will examine only the icteric conditions and treat them under lack of iron because, since the investigations of the Gria\ father and son, it is customary to consider jaundice as caused especially by 2. Fif 41. Buckwheat plant grown in a solution free from chlorine. (After Nobbe.) 1 Gris, A., Ann. scienc. nat., 1875, VI ser. Vol. VII. p. 201. 309 a lack of iron. The authors named found jaundiced leaves turning green where painted with a soluble iron salt. A change to green may also be ob- served if the roots of such plants have a dilute iron solution at their disposal. The experiments on the efifectiveness of the iron solution were often re- peated; as, for example, by Knop^ and Sachs-, who observed in cultures of maize in nutrient solutions free from iron, that the plants remained green only as long as the reserve material from the seeds lasted. After this time, leaves developed which were green only at the tip and were already yellow at the base, until the next leaves appeared uniformly icteric. Similar dis- colorations, at first appearing in stripes, were found on mature plants which had developed normally at first, and then were placed in a nutrient solution free from iron. The blossoms then became sterile and the production in dry weight was considerably less. Frank^ observed that there occurred with a lack of iron an universally noticeable phenomenon of starvation, viz., the newly produced leaves exhausted the older ones, which lost their color and died. In icteric organs, the chlorophyll grains have a normal form, but their number and size is possibly smaller and their color pale. Although the chlorophyll pigment contains no iron*, the whole nutritive condition of the chlorophyll grain will become weakened by the lack of iron. But at first the chloroplast exists in a normal form which is not destroyed until later. In this lies the difference between the phenomena of starvation and enzymatic albication. In order not to be obliged to separate the phenomena whose similar symptoms lead to confusion, we will mention here icterus due to cold. We find in cold, wet seasons a gradual yellowing in most cultivated plants, which disappears of itself with a rise in temperature. Often in spring, the leaf points of our flowering bulbs are yellow when they push out of the earth and the young leaves push out gradually with a normal green color only as the weather becomes warmer. From this transitory jaundice must be distinguished the chronic form, in which the yellow leaves always remain yellow. This may be observed if sudden great cold affects the young cells and destroys the chloroplasts. Then, in place of these, are found only fine grained yellowish groups and at times also yellow drops. These cells do not recover later. At the place of transition to the parts of the leaves which, protected by the earth, have become green, colorless, swollen and also light green chlorophyll grains which later partly turn green may be found at the place of transition to the portions of the leaf, which, protected by the earth, have become green. 1 Knop (Jahresberichte f. Agriculturchemie, 1868-69, p. 288) obsei-\'ed in such experiments that the iron whicli got into the plant could not be proved in the cell sap, and, therefore, must be present in a combined form. In 1860 (Bot. Z. p. 357), Weiss and Wiesner determined that iron occurs only in insoluble compounds and in the contents of the older cells as well as in their walls. 2 Experimentalphysiolog-ie, p. 144. 3 Krankheiten der Pflanzen. 1895, I, p. 290. ■* Molisch, Die Pflanzen in ihren Beziehungen zum Disen. 1892, p. 81. 3TO With the action of sudden cold, lasting for several hours, Haberlandt^ found that a noticeable change occurred at a temperature of minus 4 to 6 degrees C. and only at minus 12 to 15 degrees C. does the destruction of the chlorophyll grains become complete (with the exception of those in ever- green plants). With the formation of vacuoles there was produced a dis- tortion of the form of the chloroplasts which were either passing over into the position along the side walls (apostrophe) or were rolled up in lumps. Of these the ones inclosing starch grains were destroyed more quickly than those without starch. In the leaves of Vicia odorata no difference could be perceived in the destruction of the chlorophyll, dependant upon the age of the leaf. We will touch upon this subject again under autumn coloring. A yellow leaved condition in spring is found often in pears growing in nurse- ries, as the after efifect of frost disturbances. The grape is very susceptible to icteris. Different factors have been recognized here as the cause. In the cases observed by Mach and Kiirmann- in the Tyrolean vineyards, the analyses of green and icteric vines, growing close together, showed: Water Content of the yellow leaves 77.97 per cent. Water Content of the green leaves 73.17 per cent. Based on dry weight, the green leaves possessed a higher percentage of organic substances and of nitrogen, but considerably less ash. The ash of the yellow leaves contained six times as much of the elements insoluble in hydrochloric acid as did that of the green leaves. On the other hand, there was less potassium in the former. Watering with liquid stable manure acted beneficially. A similar case is described by E. Schultz'\ The leaves and woody portion of the diseased vines contained only half as much potas- sium as those of the healthy plants, which were found, however, to be poorer in calcium and magnesium. Besides this icterus due to a lack of potassium, a jaundice of the grape, resulting from an excess of calcium, has been determined by numerous observations. It seems to me that the amount of calcium in itself is not the injurious factor, but chiefly the lack of potas- sium, since calcium soils, as a rule, are poor in potassium. We will return to this case in the section on the excess of calcium. Nitrogen starvation is also a frequent cause. This, differing from the phenomena due to a lack of other nutritive substances, does not manifeiit itself in the death of the plant in an early stage but only retards the growth and reduces all the organs to a minimum. The oft repeated experiments with the cultivation of non-leguminous plants in nutrient mixtures without the addition of nitrogen have shown that under otherwise favorable conditions, with certain races, a new min- 1 Haberlandt, tJber den Einfluss des Frostes auf die Chlorophyllkorner. Osterr. Bot. Zeit. Cit. Jahresbericht, 1876, p. 718. 2 Biedermann's Centralbl. 1877, p. 58. 3 Zeitschr. d. landwirtsch. Centralver. fiir das Grossherzog-tum Hessen. cit. Centralbl. f. Agrikulturchem. 1872, p. 99. 311 iature plant can be produced from a seed, developing even to the production of a few blossoms and new seeds. The entire nitrogen content of the whole plant, however, does not in this case equal that of the original seed. It is evident from this fact, firstly, that the plant is not in a condition to make use through its leaves of the nitrogen from the air in quantities worth mentioning; secondly, however, we perceive that nitrogenous substance stored up in the seed enables various individuals to run through their whole developmental cycles, that is to say, to perform all the life-processes, in a minimum compass. This demonstrates further that the nitrogen stored in the seeds is easily mobilizable and capable of transportation, indeed, that the same molecule may probably be utilized more than once for the same pur- pose in the construction of the cell cytoplasm. A consideration of the growth of plants, with a lack of nitrogen, indicates such a condition, for it is found that the lowermost leaves are exhausted to the amount of growth of the tip of the stem and begin to dry, beginning at the edge, or at the tip. In the rapid convertibility and capacity for transportation of the nitro- gen a lack of this nutritive substance occurs very rapidly and manifests itself in jaundice. In our cultures such cases can also occur, if the supply of nitrogen in the soil is still abundant but not in a form available for the special requirements of the definite plant under cultivation. The best ex- ample is found in our sugar beets, to which, besides stable manure, nitrogen is given chiefly in the form of Chile saltpetre. The frequent, very favor- able results of fertilizing various other cultivated plants with ammonium sulfate have now led to the use of this fertilizer in beet culture. But in a practical way these results have not been satisfactory, since the polarization of the beets was far from normal. In a thorough discussion of this point Hollrung^ Kriiger and Schneide- wind emphasize that the sugar beet is a pronounced nitrate plant, but since the ammonia is not converted so rapidly and directly to nitric acid by the micro-organisms of the soil, a lack of nitrogen compounds may occur and the beets suffer although enough nitrogen is present as ammonia. The phe- nomena of a yellow leaved condition may be due to the constitution of the nitrogen fertilizer which is unsuited to beets, although it may be suit- able for grain and potatoes. An older note has already pointed to the difference in effect secured according to the form of nitrogen provided. Analyses by Lagrauge- showed that in beets fertilized with ammonium sulfate, twice as great an ammonia content was demonstrable as in those fertilized with sodium nitrate. It is a well-known fact that a yellow color can be caused in beet leaves by drought alone, so that we need to cite only a very characteristic example. In 1896 (according to Troude^), the beets in France, especially in the northern part, suffered extensively from a yellow leaved condition. The 1 Hollrung, Inwieweit ist eine Diingung- mit schwefelsaurem Ammoniak geeig- net, bei den Zuckerriiben eine Schadigung hervorzurufen? Vortrag. Blatter fiir Zuckerriibenbau, 1906, p. 70. ^ Biedermann's Centralbl. 1876. I, p. 258. 3 Cit. Zeitschr. f. Pflanzenkrankh. 1897, p. 55. 312 phenomenon appeared in June after a longer period of intense drought and became widespread especially in sunny positions and on light soils, while regions with a damp, sea climate showed the disease only slightly. The sugar content of the slowly growing beet was from 2 to 3 per cent, less than that of healthy specimens. By a survey of the individual cases just cited, we are led to the con- viction that icterus is one of the most widespread symptoms of disturbed assimilation. No conclusion as to any definite cause has been furnished as yet, however, in the occurrence of jaundice. h. Changes Due to a Lack of Phosphorus and Sulfur. The distribution of phosphorus in the various parts of the plant, de- termined earlier by Ritthausen's macro-chemical studies, was proved later micro-chemically by Lilienfeld and Monti, as well as by Pollacci\ The last found that, in general, the cell walls are free from phosphorus while the proptoplasm, and especially the nucleus, with the chromatin bodies, con- tain this element in abundance. Among the aleurone bodies the crystalloides and globoids likewise contain phosphorus. The proteins depend especially on the amount of phosphoric acid at hand and a lack of it will make itself felt especially in the blossom buds and in the maturing of the seed. Accord- ing to Nobbe's cultural experiments-, phosphorus does not seem to play any part. in the formation of the chlorophyll pigment; — the foliage of oaks which had stood for three years in nutrient solutions, free from phosphoric acid, was still green. In other plants Nobbe ultimately observed that a deep orange red color appears in the leaves and petioles. There is no production of any new dry substance, or only a small amount. Moller' observed in die needles of his pine seedlings a blue-red- (dull violet) color due to a lack of phosphoric acid. In two-year old plants the violet color tended more to olive brown. In the reports on discoloration phenomena, which set in with a lack of various nutritive substances, the results obtained with one plant species cannot be applied to a different species, since discoloration is not every- where the same. In regard to phosphoric acid, I found that when plants of beets, peas, and seradella were grown without phosphoric acid they dried a gray green when they had previously been a faded green, but not yellow, while, with a lack of nitrogen, the same species turned a pure quince yellow. Nobbe found a somewhat better development with a lack of sulfur in the nutrient solution, yet his experimental plants scarcely attained half the normal height and the yellowish green leaf blades exhibited a correspond- ingly scanty development. The starch was scanty and small grained. Cell division was considerably impaired. The forming of fruit either did not take place, or only very scantily. 1 Pollacci, G., Sulla distribuzione del fosforo nei tessuti vegetal!. Malpighia. Vol. VIII. Cit. Zeitschr. f. Pflanzenkrankh. 1895, p. 299. 2 Dobner-Nobbe, Botanik fur Forstmanner. 4th Ed., p. 317. 3 Karenzerschelnung-en etc. Zeitschr. f. Forst- u. Jagdwesen, 1904, p. 7 45 313 i. Changes Due to a Lack of Oxygen. General Phenomena. It is to be assumed as well known that, with the cessation of the supply of oxygen, the protoplasmic currents gradually come to a standstill (oxygen rigor.) Kiihne^ observed that in an atmosphere of hydrogen the motion in the stamen hairs of Tradescantia virginica stopped after 15 to 20 minutes. Wortmann- found that the parts of plants in air free from oxygen respired at first exactly as much carbon-dioxid as those with an unimpaired supply. Later a difference made itself felt in favor of the latter plants. Like the gradual cessation of the cytoplasmic currents, this gradual retrogression in the amount of carbon-dioxid with the exclusion of oxygen (intramolecular respiration) indicates that the oxygen stored in the plant body is consumed at first. Death from suffocation, therefore, takes place slowly, especially since the green plant with sufficient illumination still decomposes carbon- dioxid and water and thus forms oxygen for some time. Bohm^ detected a small amount of oxygen in the volume of gas evolved when he enclosed the green leaves of land plants in an atmosphere of hydrogen with sufficient illumination. Aside from the cases which have been observed already in the divisions on "Loamy soils" and "Too deep planting of trees," we will consider a few occurrences of bad aeration as a result of closing the lumina of the ducts forming the main water system. Such stoppage is especially serious for the sap wood*. With Bohm^ we may picture to ourselves the process of aera- tion as follows : There is not only a difference in pressure between the outer air and the diluted air inside the ducts, but also a difference in con- stituents. The enclosed air will give up its oxygen in the respiratory pro- cesses more rapidly and take up the carbon-dioxid produced. This is either soaked up, by the filling of the ducts with water, and carried off in the rising sap current, or, since it penetrates the moist walls rather easily, is given out in a radial direction by diffusion. The new and necessary oxygen which -n lesser amounts may also enter through the roots with the air rich in oxygen, dissolved in the water, will, nevertheless, under normal conditions get into the plant mainly through transverse conduction. It diffuses more easily through moist walls than does the nitrogen of the air, because water absorbs it more abundantly than it does nitrogen. Since now the oxygen within the plant body is utilized most but is also most easily capable of moving from part to part, there results a prevailing dift'usion stream of oxygen from with- out inwards in each horizontal plane of a trunk. 1 Untersuchungen iiber das Protoplasma. 1864, p. 89 and p. 106. 2 Wortmann, tJber die Beziehungen der intramolekularen zur normalen At- mung. Inauguraldissertation, Wiirzburg, 1879. 3 Bohm, tJber di3 Respiration von Landpflanzen. Sitzungsber. d. Kais. Al^ad. d. Wissensch. in Wien, Vol. 67 (1873). 4 Elfving, tJber die Wasserleitung im Holze. Bot. Z. 1882, No. 42. 5 Bohm, J., tJber die Zusammensetzung der in den Zellen und Gefafsen des Holzes enthaltenen Luft. Landwirtsch. Versuchsstationen Vol. XXI, p. 373. 314 Wiesner^ made further observations on gas exchange. He shows that the periderm, the cork covering, is completely impermeable to air even with great differences in pressure. The exchange takes place only through the lenticels which are permeable even in winter. In wood free from ducts the equalization takes place through the cell walls, especially through the deli- cate pitted walls in which, besides the diffusion, absorption through the col- loidal walls comes into effect. In woody bodies, rich in ducts, transpiration and the penetration of gases through the ducts, functioning as capillary tubes, should also be taken into consideration. The equalization of the pressure takes place more quickly axially than transversely. The more turgid a parenchyma or wood cell is, the more slowly does the equalization of the pressure occur. This relation is reversed in the periderm cell. If it incurs the loss of its aqueous contents and is filled with air, whereby its wall becomes dry, the cell loses its permeability for gases. In parenchyma which conducts air, a part of the air flows through the intercellular passages during the equalization of the pressure, another part passes through the closed membranes and, indeed, most easily through the places which have remained unthickened. A statement by Mangin- throws light on the processes taking place in trees, with poor soil aeration. He found that the ducts in Ailanthus were filled with tyloses, and, in explaining the process, states that, correlative with a lack of air in the soil, a deficiency in the supply of air in the ducts takes place. Consequently the air in the ducts becomes diluted beyond the opti- mum and the tyloses of the adjacent cells push into the tube of the duct and, on their part, also hinder the conducting of water. In regard to the influence of a lack of oxygen on seeds, Bert's" investi- gations should be considered first of all, according to which germination progresses more slowly in a lesser air pressure. Many years ago Corti* observed that a dilution of the air had an arresting influence on the cyto- plasmic currents. Since, however, with a normal air pressure and only de- creased oxygen content, germination takes place more slowly and, con- versely, with a lowered air pressure but increased supply of oxygen the seeds germinate more rapidly, it is evident that even the partial pressure of the oxygen alone is a decisive factor. In the phenomena due to lack of oxygen, opportunity is again offered of pointing to the fact that sudden changes are more disturbing than gradual changes. Stich^ found that in an atmosphere poor in oxygen the normal respiratory quotient is recovered by decreasing the absolute amounts of oxy- 1 Wiesner, Versuch iiber den Ausgleich des Gasdruckes in den Geweben der Pflanzen. Sitz. d. Kais. Akad. d. Wissensch. zu Wien am 17 April, cit. in Oesterr. Bot. Zeit. 1879, p. 202. 2 Mangin, Influence de la rarefaction produite dans la tige sur la formation des thylles gommeuses. Compt. rend, 1901, II, p. 305. 3 Bert, Recherches experimentales sur I'influence que les changements dans la pression barometrique exercent sur les phenomenes de la vie. Compt. rend LXXVI et LXXVII. 4 Meyen, Pflanzenphysiologie, 1838, II, p. 224. 5 Stich, C, Die Atmung der Pflanzen bei verminderter Sauerstoffspannung und bei Verletzungen. Flora, 1891, p. 1. 315 gen and carbon-dioxid. With a gradual removal of oxygen, intramolecular respiration is aroused only with a considerably lower percentage of oxygen, than it is when the oxygen is suddenly decreased. The discovery that phenomena of suffocation occur also in seeds if their tissue is entirely filled with water is of great value to the practical worker. Usually when seeds are soaked they get the water necessary for germination 'vithout having all the air pressed out of the intercellular spaces. If, how- ever, the seeds are kept too long in water, decomposition sets in, in which often a distinct ordor of butyric acid, a result of bacterial decay, becomes very evident. In the same way experiments, like those of Just^, for example, show that when air has been removed by a pump from the tissues ordinarily containing air and the space filled with water, the percentage of germi- nation is very greatly reduced. When seeds have been put in layers on top of each other while damp, it is not the excess of water, which so quickly destroys the germinating power, but the excessive heating and formation of carbon-dioxid. Wiesner- found also that the carbon-dioxid is developed later than the heat. Hence its development is not the only source of heat ; this is to be sought also in the absorption of wat-er. The seed, coming in contact with water, con- denses it as it enters the tissues and thereby frees heat. That an excess of oxygen is just as injurious as a lack of it, is natural. Bert found that the oxidizing processes in plants are arrested by too high a tension of the oxygen. A mimosa died at 6 atmospheres in common air, hav- ing lost its irritability because of a lack of oxygen. If the air was made richer in oxygen, a pressure of 2 atmospheres was sufficient to cause death. The Brusone Disease of Rice. The unusually dreaded brusone disease which manifests itself by the appearance of rusty spots in the leaves together with a blackening and drooping of the blades, has often been the subject of earnest study, ever since Garovaglio in 1874 began investigating it. The majority of investi- gators considered the phenomenon parasitic. Some thought it necessary to assume bacteria to be its cause, and some held various fungi responsible, — among others, Piricularia Oryzae Br. et Cav. Recently, however, Brizi'' has made comparative cultural experiments from which it becomes evident that an exclusion of air from the roots in high temperatures in water cultures induces disease of the plants with the phenomena of the Brusone disease. With these experimental results agree very well the discoveries which have been made in Italy and Japan. It has been especially observed that the Brusone disease usually appears if com- pact, only slightly pervious soils are healed greatly and a rapid change of temperature sets in. There then follows an affection of the root which 1 Bot. Z. 1880, p. 143. 2 Landwirtsch. Versuchsstationen, 1872, No. 2, p. 133. 3 Brizi, U., Ricerche sulla malatti del riso detta Brusone. Ann. Instituto agrar. Ponti. 1905. Milano. Cit. Zeitschr, f. Pflanzenkrankh. 1906. 3i6 brings disease of blades in its train and only later do parasitic organisms infest the diseased parts. We consider Brizi's experiments as decisive and think that suffocation of the roots during high temperature, which greatly increases the leaf activ- ity, is the first impulse to the disease. The soil should be aerated at once. The Diseases of Gladioli. A phenomenon of disease, not rare in cultivating gladioli in heavy soils, or on pieces of ground with a lighter soil, but a higher ground water level in wet years, may be traced to a lack of oxygen. The disease manifests itself in the often sudden aeath of the plant at a time when the inflore- scence is already developed. At first the lower leaves seem marbled with yellow (noticeable at first only when the light falls through them). The chlorophyll bodies decompose and leave yellow drops which look like oil. While this process advances apparently in stripes between the veins in the aerial parts of the leaves, brown, depressed places are found on the leaf bases still below the soil which initiate a complete decomposition of the leaf parenchyma. No real weakening takes place, but the decomposition repre- sents a process of humification. Bacteria^ and often also fungi, small worms, m.ites, etc., are always found in these tissues which smell sour like humic acid. The aerial parts of the leaves dry quickly and become covered with black pits of Cladosporium and Altemaria. Despite the wealth of parasitic organisms present, the disease should not be characterized as parasitic, since the first stages, viz., the brown coloring of the ducts and of the parenchyma, lying close to them, are produced within the healthy tissue without the co-operation of such organisms. Later a number of the duct tubes are filled with a cloudy, brown mass which be- comes firm like gum. The latter phenomenon has been observed also in other plants, the roots of which were injured by continued moisture in the soil and the lack of oxygen thus produced artificially. Gladioli like a great deal of moisture in the soil but it should not be long continued. In dry years the mistake is often made of watering bulbs and tuberous plants every day. This is wrong, the excessive drying of the soil must be prevented by mulching with litter. k. Changes Due to a Lack of Carbon-Dioxid. Despite the small content of possibly 0.036 to 0.040 volume per cent, of carbon-dioxid, which the air^ possesses, while consisting of nearly 79 parts of nitrogen and 21 parts of oxygen, it suffices everywhere for a high rate of growth; if this important nutrient substance is entirely lacking, the other factors of growth are without value, even in a most favorable com- bination, as may be observed experimentally by placing vessels of caustic 1 According to Jolly's investigations (cit. in Forsch. a. d. Gebifte der Agrikul- turphysik. 1S79, p. 325) the oxygen content of the air varies not inconsiderably (between 20.53 and 20.86 per cent.). The largest oxygen content is found v^^ith a prevailing polar current and the least with a prevailing equatorial current. 317 potash under closed bell-jars. Corenwinder^ found that buds and young leaves do not develop further in air free from carbon-dioxid. In Bous- signault's- experiments two maize kernels developed into plants of which the dry weight itself and the carbon and oxygen contents were less than in the seed, while the nitrogen content was just as large. Hydrogen and ash had undergone a slight increase. Bohm^ found in leaves of the scarlet runner bean, cut ofif from the plant during growth, from which the starch had been removed by darkness, that these leaves not only formed roots from the petioles in full daylight and in an atmosphere containing carbon- dioxid, but also increased in breadth even if they were watered only with distilled water. On the other hand the seedlings of the scarlet runner bean grown in distilled water and exposed to the action of full daylight under bell-jars with caustic potash showed only an increase in length up to lO cm. while the stems shrivelled below the primordial leaves which as a rule were free from starch. Seedlings of the scarlet-runner bean which had been grown in garden soil rich in humus but were robbed of all but a small amount of their starch by weak illumination, did not form any new starch but went to pieces when later strongly illuminated in an atmosphere robbed of its carbon-dioxid. Therefore, the carbon-dioxid in the soil and the other favorable conditions for growing were of no value. Godlewski* found that the starch also disappeared in plants exposed to full daylight if the carbon- dioxid of the air was kept from them. A further insight into the method of growth of plants from which the carbon-dioxid of the air had been removed is given by my own experiments'"'. Young cabbage plants were left in a 0.5 per cent, nutrient solution, part under bell- jars with caustic potash, part under others without caustic potash and the remainder left free between the bell-jars. After ten days the har- vest yielded : — Bell-jars Bell-.iars Uncovered plants with Potash without Potash Plant No I. IT. III. IV. V. VI. VII. VIII. IX. Fresh weight of root and stem 0.457 0.367 0.414 0.470 0.175 0.2305 0.297 0.313 0.232 Fresh weif?ht of leaves . . 1.598 1.494 1.564 1.682 0.765 1.011 1.736 1.712 1.850 Upper leaf surface in square cm 50.6 47.5 50.1 47.3 25 4 26.6 50.4 54.1 37.1 Total dry weight 0.2755 0.2510 02.685 0.2760 0,0760 0.0985 0.1705 0.1740 0.1765 Percentage of the fresh weight in dry weight 13.4 13.5 13.5 12.8 8.4 7.9 8.1 8.6 8.4 Total evaporation in grams 69.3 74.4 82.5 75.0 27.4 34.4 43.1 40.4 43.3 Evaporation per gram dry weight 251.5 296.4 307.2 271.7 360.6 349.2 252.8 232.2 245.3 The table shows that the production in fresh and dry weight was the smallest under the bell-jars with potash. The absolute amount of evapora- 1 Recherches chimiques sur la vegetation. Fonctions des feuilles. Compt. rend, t. LXXXII, 1876, No. 20, p. 1159. 2 Boussingault, Vegetation du Mays, commence dans une atmosphere excempte d'acide carbonique. Compt. rend. Vol. LXXXII, No. 15, p. 788. n Bohm, in Sitzungsber. d. Wierner Akad. 1876, cit. Bot. Zeit. 1876. p. 808. * Bibliographische Berichte iiber die Publikationen der Akademie der Wissen- schaften in Kraukau. Part I, cit. Bot. Zeit. 1876, p. 828. 5 Sorauer. Studien liber Verdunstung. Forschungen auf dem Gebiete der Agrikulturphysik, Vol. Ill, Parts 4 and 5. tion is greater or less according to the amount of newly produced dry sub- stance ; it is smallest in the plants under the bell-jars with potash. Naturally the effect of the bell-jars, i. e., the humidity prevailing under them, is to be taken into consideration. This factor manifests itself, when compared with the uncovered specimens, by the lower percentage of dry weight in the plants, i. e., by a loose structure and longer petioles. If the specimens from the bell-jars containing pota.-h are compared only with those of the other bell-jars, the result is more certain. The lack of carbon-dioxid manifests itself most by the lessened total production, especially in the leaf apparatus; the upper surface is only about half as large. The most striking effect is the amount of evaporation, which is cal- culated per gram of dry substance present. This is greatest in the plants deprived of the carbon-dioxid supply. Th-e same condition is found in the calculation of the evaporation per square centimeter surface in the plants grown under both conditions. This fact should be associated with the re- sults of other experiments, according to which it is evident that the amount of evaporation increases also in plants which lack other nutritive substances. If, for example, plants from a normal favorable nutrient solution are placed in one of too low concentration, or in distilled water, evaporation is in- creased; it increases also in seedHngs after the removal of the organs con- taining reserve food, the cotyledons. It may be assumed that the plant must force itself to a greater transportation of water through its roots, i. e., to a greater one-sided kind of labor, in order to meet lesser amounts of re- serve substances contained in the solution due to their increased absorption by the roots from the surrounding soil. For practical work, the above investigations suggest an attempt to in- crease production by increasing the supply of carbon-dioxid. Experiments actually show that a much more rapid formation of starch is obtained by increasing the carbon-dioxid. In many plants an increase up to 6 to 8 per cent, was possible. Of course, a different absolute quantity of carbon-dioxid is necessary for each plant and in the same plant for every other combination of the vegetative factors in order to obtain an optimum production. The strengthening of the vegetative processes by the addition of carbon-dioxid manifests itself in the more compact growth and thicker leaves^ While previous experiments have taken up the results of a lack of car- bon-dioxid for the whole plant, Vochting- tested the behavior of various branches, which were left on the normally growing plant, but transferred to an atmosphere free from carbon-dioxid. It was found thereby that each branch and leaf must be maintained by its own work and that their life activity gradually dies away if this work is prevented by a lack of carbon dioxid. The plant can, indeed, develop further the branches in the atmos- phere free from carbon-dioxid, but the leaves on these branches are a faded 1 Feodoresoo, E., Einfluss der Kohlensaure auf Form und Struktur der Pflanzen. Cit. Centralbl. f. Agrikulturchemie, 1900, p. 137. 2 Vochting, H., tjber die Atahangig-keit de.s Laubblattes von senier Assimi- lationstatigkeit. Bot. Zeit. 1891, Nos. 8 and 9. 319 green and form no starch. They also do not recover, if the branch, is brought back to air containing carbon-dioxid, but go to pieces after a short lime. It thus becomes evident that each leaf has its independent existence and that any disturbance of it cannot be adjusted by the organism as a whole. The organ which has become functionless is thrown ofif from the body. B. EXCESS OF WATER AND NUTRITIVE SUBSTANCES, a. Excess of Water. MOISTURE. The phenomena of yellowing and decomposition connected with stag- nate water have been considered when discussing the disadvantages of heavy soils. We are thus concerned here only with proving by example, how an excess of water, like a lack of it, retards production. Thus Stahl- Schroeder's^ experiments with oats in sterile sea-sand to which the nutrient solution had been added, gave the following results. With the addition of water there were produced : % of the No. Weight of Weig-ht of Medium Phos- Nitro- entire water of 1000 Ivernels straw and length of Ash phoric g-en capacity ker- chaff the plants acid of the sand nels S g- cm. 7r % % 35 84 15.5 (calculated) 6.2 49 9 9 3.752 50 1723 21.6 73.9 102 2.933 1.444 2.915 70 2074 18.5 101.8 140 2.712 1.090 2.501 90 1S27 16.3 115.0 157 3,007 1.207 2.407 95 469 11.1 (calculated) 90.8 162 5.892 1.847 3.444 Thus only the vessels containing a medium amount of water yielded a good harvest in grains. With a larger water content, the harvest of grains fell, while the yield in straw increased. With a lack of water in the sand (35 per cent.) and with an excess (95 per cent.) none of the grains ripened. The poorer the growth of the plants, the greater their percentage of ash con- tent, and wealth of phosphoric acid and nitrogen. Clogging of Drain Tile. Wherever flat lying drains extend through the root systems of perennial plants, an unusually luxuriant root growth may stop up the drains. The long whip-like, very slender and comparatively thin roots lying side by side, like cords, in this way form mats ten or more meters long and as thick as the width of the drain allows. The most dangerous tree seems to be the wil- low for most of the drain mats seem to be formed by it, yet all plants may form similar root-growths and Magnus- once found, for example, the rhizome of the horse tail {Equisetum palustre, L.) growing very luxuriantly in such a mat. Cohn^ found a drain mat which came from a pipe laid 125 1 of. Biedermann's Centralbl. f. Agrikulturchem. 1905, Part 2. 2 Sitzungsber. d. Bot. Vereins vom 26 Mai, 1876. Vol. XVIII, p. 72. 3 Verh. d. schles, Gesellsch. f. vaterl. Kultur, 25 Oktober, 1883. 320 cm. deep and was formed entirely from the ramifications of the root of a single Equisetum from which a piece 12 meters long could be separated. Miiller-Thurgau experimented with roots from one plant, putting some in a nutrient solution, others in distilled water ; each experiment showed a stronger growth in the solution. These experiments showed that root growth increases locally when the roots reach places containing food sub- stances. If the drain mats return after removal, it is advisable to take out care- fully both trees and roots by uprooting and not by chopping down. If the trees must remain it is better (especially with double lines of drainage) to lower the surface laid pipes (as a rule between 80 to 90 cm.) to the level of the pipe system lying deeper (1.5 m.). Sprouted Grain. In the phenomena to be cited here which are connected with an excess of water, injury is caused either by the fact that water from outside acts mechanically on the tissues at an unsuitable time, or the water taken up by the roots cannot find utilization and be carried off in corresponding amounts. To the first group belongs grain sprouted on the field during the harvest because of rain. The disadvantage is the greater in this instance, since the sprouted kernels can neither be used for nutritive purposes nor are they suitable for seed. Of course the germinative capacity for subsequent use as seed decreases according to the amount the kernels have sprouted. Ehrhart^ found that the weakness and thus the mortality of the seedlings increased as their development had already advanced because of the pre- mature sprouting. We owe to Marcker and Kobus- thorough investigations of the changes in the seed due to sprouting. The former investigated barley, half of which was harvested uninjured, but the other half was left standing for almost 14 days, wet through by rain. The differences were shown by a determination of the elements soluble in water, for they amounted to the following in Sprouted and in zvell-harvestcd barley Soluble starch 1.17 per cent. 1.76 per cent. Dextrin 0.00 per cent. i.io per cent. Dextrose 4.92 per cent. 0.00 per cent. Maltose .7.32 per cent. 3.12 per cent. Other soluble substances... 5.23 per cent. 5.64 per cent. 18.64 per cent. 11.62 per cent. We thus see that the vigorous diastase action has resulted in a very abundant sugar formation from the starch and dextrin. The starch con- tent had fallen from 64.10 per cent, to 57.98 per cent., because of the sprouting. If the kernels are used for making starch, the great amount of 1 Deutsche landwirtsch. Presse, 1881, No. 76. 2 Aus Braunschweiger landw. Z., 1882, No. 22, cit. \n Biedermann's Centralbl. f. Agrikulturchemie, 1883, p. 326. 321 diastase would now presumably convert more starch into dextrin and sugar, when softened, and result in appreciable losses in manufacture. The great- est changes due to sprouting, however, are found in the nitrogen-containing elements of the grain. While especially the ammonia content had remained unchanged (nitric acid was not found in quantities worth mentioning in either of the two kinds of grain) the soluble proteins had decreased to a great extent, the insoluble to a lesser one. This decrease is explained by the relatively great increase of the amides. Thus, in sprouting, first the soluble proteins had been consumed in the formation of the amides and later even a part of the insoluble ones. Kobus arrived at the same results in his investigations of sprouted wheat, whose gluten content had decreased from 20 to 25 per cent. This fact explains the well-known loss in baking quality of a flour made from sprouted grain. The germinating capacity in the experiments carried out by Marcker had fallen from 98 per cent, to 45 per cent. It thus becomes evident how worth while are the great efforts which must be exerted in any case to make possible harvesting the grain while dry. Similar losses may befall other field crops as well, as, for example, lupines, rape, beet roots. The cases in which the seed germinates inside the fruit without being noticeable externally are interesting but not of importance agriculturally. I found such cases in pears, apples, melons, and pumpkins. Other observers found the same phenomena in oranges, as well as pumpkins, and indeed in other fruits also which had remained very long on the trees, and in that which had only colored late. Further statements on this subject may be found in the section on germination interrupted by drought. The Rupturing of Fleshy Part.s of Plants. Fleshy roots, stems and fruits frequently crack open in long periods of dampness. Among vegetables, kohlrabi, carrots and parsley suffer especially. Hallier^ proved that the rupturing is due to excessive water supply, for by hanging parsley roots in water he found after three days that all the part which was in the water had cracked open. Boussingault- observed the rupturing of cherries, mirabelle plums, pears, grapes, and blueberries after the fruits had hung in water. I obtained the same results by imbedding them in wet sand. Of herbaceous stems, those of rape crack open very freely shortly before the time of blossoming. The figure here given shows the change in a bean, which I had planted too deep in wet sand. In July, 1882, in Proskau. I found ruptured potato stems and Beta vulgaris roots. At that time a very rainy July had followed a dry spring after a small amount of winter moisture. The phenomenon was apparent at first on light places in the soil and in the best developed plants. I found similar cases in roses and in plum seedlings, which had been taken from the sand and 1 Hallier, E., Phytopatholog-ie, p. 87. - Compare Bot. Jahresbericht, 187.3, p. 253, 322 placed deeper in a nutrient solution than they had been in the sand. The base of the stem split in those specimens previously exposed to the air. In the souring of crops in fields planted with horse beans, peas, vetches, etc., the base of the stem is rup- tured at times above the places where the (rotted) roots arise, and it is found that a spongy, loose tissue protrudes from the torn place, as in the bean here illus- trated. All these phenomena have one characteristic in common —that they are initiated only when, after a considerable period of normal develop- ment, or still more after a previous dry period, an un- usual supply of water is given suddenly. If the plants are in contact with water from the beginning of their de- velopment, they adjust them- selves to their surroundings. The same adjustment can be observed especially in those varieties which develop in water as well as on dry land. Levakoffski's^ experiments on Epilohiutn hirsutum, Lycopus europaeus and Lythrum serve as examples. The compari- son of water and land speci- mens shows that in the water plants, two rows of colorless 1 Levakoffski. De I'influence de I'eau sur la croissance de la tige etc. Cit. Bot. Zeit. 1875, p. 696. Fig. 42. Bean plant split at the base as the result of excess of water. The torn place has scarred over. 323 cells, free from chlorophyll, 3 to 4 times as long as they are broad, exist between the cambium and the bark parenchyma which are not present in the land specimens. This difference becomes greater, when the older parts of the plant are compared with one another. Below the surface of the water these cell rows become a thick, lacunar tissue Epidermis and bark soon go to pieces here. The cells which form this special tissue are de- veloped from the cambium. The sudden excess of water, which causes the rupturing of part of the plant, destroys the equilibrium in the epidermis, or the cork layer present instead of the epidermis, and in the fleshy parenchyma body. Especially after previous periods of drought, the elements of the upper epidermis be- come thicker walled and less elastic and are not able to accommodate them- selves rapidly enough to the swelling inner tissue. If the rupturing takes place in succulent organs without any previous dry period, due to a long continued supply of water in damp surroundings, the torn places, as a rule, differ from those due to drought, in that, in the latter, the wounded surface turns to cork or is cut off by a new cork layer. In the former, on the other hand, the parenchyma cells, exposed by the rupture, remain thin walled, at times elongated into pouches and decaying easily. Boussingault found that the fruits lost sugar to this excessive water. This loss of sugar together with the increased absorption of water may explain the watery taste of the fruit after rainy weather. Some blossoms, left under water, also lost sugar. On the other hand, in sugar beets, rape, in the seedling roots of wheat, barley and maize no sugar was lost although the tissue was rich in sugar. There is a method of storing zvinter apples which is well worth recom- mending, viz., placing the fruit in layers in sand. If the sand is kept too moist, a large percentage of the fruit may lose in selling value because the skin ruptures. Miiller-Thurgau^ made similar observations in related experiments. After apples had lain eight months in boxes of earth he found the fruit was wet, some of it ruptured, some mealy, and its acid and sugar content much lower. The percentage of decaying apples was much less, however, than in fruit lying free in the cellar. The rupturing of fruits and vegetables, due to storage methods, can be overcome by supplying a dry, well ventilated place. In fruit on the tree, especially the egg plum which is very delicate, it is advisable in longer periods of rain to shake the water from the tops of the trees. Finally, attention must still be called to the fact that the tendency to rupture can also become hereditary. An observation of this was made with cucumbers". In forcing these, the owner always chose for his seed the finest specimens of a variety which ruptured easily, and observed that this bad condition manifested itself more abundantly and earlier from year to 1 Funfter Jahresb. d. deutsch-schweizerischen Versuchsstation zu. Wadensweil. Zurich, 1896. 2 Zeitschr. f. Pflanzenkrankh. 1899, p. 183. 324 year. He then planted half of his greenhouse with the forcing variety pre- viously used and the other half with an outdoor variety. The latter gave healthy fruit up to autumn, while the half planted with the first variety produced ruptured fruit from the beginning of May on. Such observations give hints well worth noticing when choosing seed of vegetables which tend to rupture. The Woolly Streaks in Apple Cores. In describing apple varieties the expression "The carpels of the cores rupture," is found stated here and there, as a characteristic of the variety. According to the illustration here given, a condition of membranous carpels is said to be indicated in which the inner walls of the core divisions are not uniformly smooth and solid, but show a surface crossed by streaks which Fig. 43. Cut apple, the coi-e of which shows woolly streaks (w). look white and woolly, and extend slantingly from the centre to the outside. The phenomenon occurs frequently and is considered to be normal,- — which deduction I do not care to hold to. Aside from the fact that under certain circumstances all the fruit in the same variety does not show such woolly streaks and that, in dilTerent years, it is developed to a different degree, even appearing in isolated cases in varieties which, as a rule, have a smooth core, the conditions found microscopically also prove splendidly the ab- normal nature of these streaks. If a carpel with such streaks is cut through, as shown in Fig. 43 at w, the appearance is found as given in Fig. 44. In this the side designated by K is the inner wall of the core, while F indicates the outer side bordering on the flesh of the fruit. In varieties of apples with smooth carpels, the inner lining of the core is formed only of such cell elements, as are shown 325 at p. These are very much elongated, extraordinarily thick-walled cells, traversed by many, frequently branched canals ; they turn yellow with chloriodid of zinc. Single layers of such cells may cross one another. Ac- cordingly, besides such cells seen in full length at p, the same horizontal section also exhibits parts of elements in cross-section q. It is evident that, because of the close arrangement of the cells on the one hand and because of their very strong walls on the other hand, a very great firmness is ob- tained in the core tissue, increased by the transverse course of the cells. It is evident further, that in fruits with a larger calyx depression, through which fungi may grow easily into the core, the spread of fungi, which pro- duce decay, is limited by the parchment-like, solid carpels. Rupturing- of the papery carpel or the apple, due to the excrescence tissue of a woolly streak. (Orig.) This protection from internal decay is destroyed by the woolly streaks (Fig. 43 W) for they consist of very loose tissue, which breaks through the solid walls. We see in Fig. 44 that these woolly streaks are formed of thick bunches of cell rows elongated like threads, which differ strikingly from the sur- rounding ones because of their thinner walls, and very gradually pass over into the tissue of the fruit {F), while others are quite sharply and suddenly cut off from the thick- walled cells {p) below the places in the core which have remained membranous. Only at the base of this bunch of threads do short, schlerenchymatous cells {sk) , isolated or lying beside one another in mats, recall the elements {p) to be found in the normal wall. Although these 326 thin-walled cell rows approximate more nearly tissue of the fruit in form and by the blue coloration from chloriodid of zinc, they still do not corres- pond to it entirely. The difference consists chiefly in a wart-like thickening of the cell wall iv which is most strongly developed in the outer cells of the thread bunch, but in the inner cells is often only weakly indicated and generally is not present at all in the schlerenchymatous elements. These cell wall thickenings which push outward and look like buttons, show, with the action of chloriodid of zinc either a pale blue color or remain uncolored, or even appear yellow. The latter case is found most distinctly in the very thick- walled cells (sk) in which the whole membrane is also colored yellow. Fig. 44, at the left, is a more strongly magnified section from a cell row of the bunch filament. It is seen here that the wart-like protuberances of the wall which I would also like to consider phenomena of the swelling of various points in a fine middle lamella, often have mushroom forms (kn)'^. Thus it should be assumed, that at the time of the chief swelling of the fruit, the tension of the tissues in the carpel has become so great, because of a sudden, great supply of water, that the connection in the membranous tissues is broken in stripes and loosened and the elements now freed from pressure, and not thick-walled, extend like pouches into the hollow of the core. Varieties inclined to have woolly streaks are especially easily exposed in damp years to the formation of moulds, i. e. phenomena of decay in the core. It is, therefore, advisable to use these fruits quickly. The Ring Disease of Hyacinth Bulbs. This disease is very serious for growers of hyacinth bulbs. It manifests itself by the browning and loosening up of a scale in the midst of healthy bulb layers. The decomposition of the tissue progresses from the neck of the bulb downwards into the bulb centre. If it reaches the latter, the bulb is as good as lost. The disease is often transmitted to the bulblets. All the diseased parts become covered with Penicillium, which here has actually taken on a parasitic character. The reason for the extremely rapid spread of the fungus is to be found in the change of the substratum which proves unusually favorable for it. Analyses show especially that the fresh, healthy substance of the ring-diseased bulb possesses more sugar than that of healthy specimens. The former resemble younger scales in contrast to the older ones. Since now a reduction of the sugar takes place with the increased ripeness of the bulbs, we shall have to conclude from the greater amount of sugar that diseased bulbs are less ripe. In fact it may now be proved that by their cultural methods our bulb- growers often run the risk of harvesting unripe bulbs. In taking up the bulbs, the grower sometimes does not wait until the leaves have completely dried up in summer. This holds good primarily where the hyacinths serve 1 The same or similar phenomena have been observed very recently by various scientists. I found them also in the hair-like cells, clothing the interior of beets which had become hollow; in the leaf parenchyma cells of fallen oat plants, etc. 327 as decorative plants in gardens and public places. There a bed of old liowers and slowly yellowing leaves is very unsightly. Consequently the bulbs are lifted and let ripen in another place. The resulting great injury to the root prematurely checks the vegetative growth of the bulbs. The leaves dry before they have lived out their life and their bases, i. e. the scales of the bulbs, remain immature and rich in sugar, thereby forming the desired centre for convenient infection by the fungus. In the large field-grown commercial bulbs, the supply of fertilizer enters into the question, since it is desirable to produce very strong bulbs in the shortest possible time. The fertilizer so lengthens the time of growth that many varieties have not finished growth at the fixed time of harvest. The leaves, still green, then possess in every case unique scales and during the storage of the harvested bulbs on the "bulb floors," up to the time of the autumn sales, Penicillium has ample time to attack the scales, which remain rich in sugar, and to destroy them. It is a matter of course that varieties ripening especially late will exhibit this bad condition and the growers, therefore, speak of "ring diseased races." The testing of the bulbs is accomplished by cutting superficially through the tip of the neck during the dormant period. If the cross-section shows a brown ring between the white scales of the bulbs, these bulbs should not be sold. Stock suffering from the ring disease can be cured by putting the bulbs in sandy soils, not freshly manured, with a deep lying ground water level, where, with scarcity of nutriment and moisture, they can ripen early. The fact still remains to be mentioned that a phenomenon has been con- fused with the real ring disease, which is very similar to it judging from its habit of growth\ The cause is known to be a nematode {Tylenchus Hyacinthi Pr.) which can wander into the scales from the leaves. In this disease, however, a gall-hke distension of the cells takes place, also the formation of cork walls like little islands and other differences, as has been described more in detail in the second edition of our manual. Springing of the Bark. In illustrating the ruptured bean plant (Fig. 42), we noticed that a soft tissue mass had protruded through the gaping split in the cracked stem. This is the new formation of bark tissue, which may be considered a re- action of the organ to the wound stimulus and the decreased tension. Other cases, however, occur in which matters are reversed, viz., that the increase of bark tissue is the primary process and the splitting, the secondary one. Such an increase in growth can arise from different causes. Hartig- con- siders one of these to be the increase in size caused by a sudden isolation of forest trees. He describes cases of hornbeams in a beech grove, where, 1 Journal de la Soc. nat. et centrale d'Horticulture de France. April, 1881. Sorauer, Zur Klarung- der Frage liber die Ringelkrankheit der Hyacinthen. Wiener illustrierte Gartenzeitung-, 1882. April number, p. 177. 2 Hartig, R., Das Zerspringen der Hainbuchenrinde nach plotzlicher Zuwachs- steigerung. Untersuch. forstbot. Inst. Vol. Ill, p. 141. 328 after isolation. — "the breast high growth, measuring 1.2 sq. cm. in cross- section, in a few years increased in cross-section growth to 13.7 cm. ann- ually^." The cork was split thereby in numerous places and resulted in a rupturing, indeed, in places it lifted the bark body from the wood-cylinder. Hartig found similar conditions in oaks and explained this by a greater soil activity, resulting from the isolation and increased action of light". Phenomena of this kind may be found also in other trees, especially in parks and gardens. Shedding of the Bark. Hartig describes a case in which the splitting of the bark is due to an increase in the normal growth. I observed a splitting and shedding of the bark from an ab- normal cell - elongation in the bark parenchyma. In 1904, I found in an avenue of elms a num- ber of trees standing side by side at the bases of which a great many pieces were perhaps as long as one's hand. Upon closer investiga- tion, loosely hanging strips of bark 25 to 50 cm. long were found on the lower end of the trunk, which could easily be removed. The trunk, thus exposed, was cov- ered with greenish tis- sue in spots which proved to be new for- mations of bark. The loosened pieces of bark (Fig. 45), exhibited on the inner side flat, light brown cushions irregularly distributed and differing in size and thickness. Having a spongy consistency, they easily gave way to the pressure of a finger-nail. Here and there, between them could be seen crater-like, harder, small protuberences. The upper surface of the cushion was smooth ; it was rough and sometimes woolly in places because of prominent, hair-like processes. The part of the bark remaining on the Fig. 45. Inner surface of a fallen piece of elm bark, with cushion-like, protruding tissue islands. (Orig.) 1 Lehrbuch der Pflanzenkrankh, 1900, p. 261. 3 Unters. Vol. I, 1880, p. 45. 329 tree appeared a yellowish green and juicy. It consisted of bark parenchyma, which had originated from a healthy cambium. The subjoined Fig. 4() pictures the bark about to 1^ be shed. At h is shown . 5^- the old wood ; at nh the last produced new wood ; g indicates ducts ; c the cambium. Next this lies the normal, young bark which gradually passes sp.- over towards the outside into the broken older bark. In reality the extent of loosened older bark is much greater in proportion to the normal young bark than is shown in the draw- ing, because of lack of space. The normal inner bark has a very regular structure, in which layers of porous bark parenchyma alternate regularly with flat bands of slender cells (/) which might be difTer- entiated as "wedge-cells." These slender cell bands would correspond to the "pressure wedges" men- tioned in connection witli the tan disease. The cells forming these wedges ap- pear in longitudinal section as long as in cross-section, nearly colorless, with pe- culiar, wide-meshed wall thickenings, looking like irregular wedges. The parenchymia lying between every two such thin, slen- der bands of wedge cells is proportionately large-celled, porous and rich in starch. Deposited in it are large, hard bast bundles, {h) with the rows of calcium oxalate crystals accompanying it (o) and the cells {si) containing mucilage. FiS'. 46. mst Elm bark with bark excrescence. (Orig.) 330 These alternating tissue layers are separated by broad curved medul- lary rays (mst) which even in the entirely healthy bark can exhibit a wavy course, but in the diseased bark may often be displaced and take a hori- zontal course. The sharp curvature is caused by the spreading apart of the parenchyma cells which, containing chlorophyll and lying between the slen- der bands of wedge cells, elongate into pouches, and for a long time contain a great deal of starch. They also press outward the hard bast bundles and the rows of oxalate crystals. This great layer of separation is covered by a plate cork layer extending irregularly into the tissue and often accompanied by full cork (t) and the suberized bark tissue cut ofif by it which belonged to the earlier period of growth (k). The cork layer often curves spherically into the pouch-like spongy tissue (sp) and forms the hard, crater-like points on the under side of the loosened bark scale, which were mentioned at the beginning of this description. The process of loosening the bark tatters is completed on the boundary between the hard tissue of the suberized cortex of the previous year, and the soft pouch-like parenchyma. The upper sur- face of the separating cushions appears woolly and rough, or smooth, according to whether the pouch-like parenchyma clings more or less strongly to the separating surface. In the elongation of the parenchyma these out-pushings differ from the tan disease in which cork excrescences are concerned essentially. von Tubeuf^ describes a case of the Weymuth pine very similar to that on Ulmus, only no shedding of the bark strips could be observed because of the smoothness of the bark. The pine was diseased and covered with cushions of Xanthoria parietina. Among these lichens were found blister- like processes, of which part appeared to be split and were produced by a distention of the bark tissue. The resin ducts were enlarged, the deeper bark parenchyma cells elongated into pouches and poor in chlorophyll. von Tubeuf's statement that he had produced very similar knob-like processes on a branch by wrapping it with cotton wadding which was kept constantly moist, warrants the assumption that, in the cases above described, we perceive the action of a local excess of water. The same kind of processes as these in the bark have been observed on roots also. vSome years ago a serious disease of the grapevine was re- ported from near Lindau". Its effects were similar to those caused by the rust fungus, but it could not be proved to be of parasitic origin. The part of the trunk beneath the soil and the older roots exhibited tears i to 3 cm. long from which protruded calluses, white at first but later turning a chocolate brown. The lateral roots near these calluses died. The calluses consisted of bark parenchyma cells abnormally lengthened radially and scarcely connected any longer. The American varieties, scattered among the diseased European vines, were found to be unaffected. As is well- 1 V. Tubeuf, Intumescenzenbildung: der Baumrinde unter Flechten. Naturw. Zeitschr. f. Land- u. Forstwirtsch. 1906, p. 60. 2 Kellermann im Jahresber. d. Sonderausschusses f. Pflanzenschutz. Arb. d. Deutsch. Landw.-Ges. 1892-93. 331 known, the extremely luxuriantly growing American vines consume much greater amounts of water. Tissue warts of this kind are much more abundant than is generally assumed and occur also on decorative plants^ They are reactions of the plant body to a wound stimulus or internal disturbances of equilibrium in the supply of water and nutritive substances. Watersprouts. By the term watersprouts, watershoots, or suckers, are understood ex- ceedingly vigorous foliage shoots with long internodes, which grow up perpendicularly from old branches or trunks. Often trunks covered with lichens are distinguished by abundant sucker formation. Since the suckers grow up into the crown of the tree, they produce wood, and, indeed, un- fruitful wood, at the very places which it is desirable to keep free from branches in order that sufficient light and air may reach -the inner part of the crown. It is not advisable, however, to remove the suckers, if the cause of their formation is not removed at the same time. In many cases the cause may be found in an impervious subsoil. The roots of the vigorous tree reach this impenetrable layer sooner or later, which not infrequently is a vein of closely cemented sand containing iron. The absorption of food stuffs is limited by this, the tree forms only short shoots and smaller leaves, but still bears fruit. In a warm and damp spring, when all trees make a strong foliage growth, the energy of the weakened tree also appears to be Increased by the favorable vegetative conditions. The strong upward force of the water causes the formation of adventitious buds or stimulates dor- mant buds, especially those not too far distant from the central trunk, since the upward force of the water and the nutrition is much more energetic in a perpendicular direction than in the more inclined position. Gardeners know how to turn this to use in growing plants on trellises. The horizontal branches on one side of the mam trunk, which are weaker than the corres- ponding ones on the other side, are held in a perpendicular position for a year. This treatment results in a much greater and more rapid growth and development. With the production of water shoots a gradually in- creasing inequality in nutrition sets in, at the expense of the older, more horizontal branches which now suffer from scarcity of nourishment. This explains the death of the tip twigs of older lateral branches which begins with the appearance of the water shoots. One part of the tree starves when some other part develops very luxuriantly. As has been said, it is scarcely advisable to remove the water sprouts during such a disturbance in the equilibrium of nutrition, rather, it is more advantageous in older trees to graft them with valuable varieties and, at the same time, to saw off a part of the older branches, so that the tree is thus rejuvenated. In places where the sub-soil cannot be opened up easily 1 Sorauer, P., tJber Rosenkrankeiten, Zeitschr. f. Pflanzenkrankh. 1898. p. 220. 332 the evil can be checked for a considerable number of years by using ferti- lizers at some distant from the trunk. The tree in its endeavors to reach the fertihzer develops a new vigorous root system. Young trees can be entirely cured by transplanting. It must also be emphasized that the formation of suckers disappears of itself from many trees after a few years. This is the case where such water sprouts have been induced by an excessive pruning of the tree or the sudden dressing of the trunks. In avenues of trees, or along streets with telephone wires, and in tree plantations, through which a street or railroad line has been cut, a strong development of suckers is found on the sides of the trees toward the street. In such cases large branches are often sim- ply chopped off on the side toward the street. Since the root system remains unimpaired, it pumps up just as much water as before the tree top had been reduced. By the removal of the branches, however, there is less consumption and consequently dor- mant buds are awakened M'hich mature into slen- der shoots, becoming water sprouts whose buds often sprout even in the year of their pro- duction. Th. Hartig^ has observed that these premature shoots de- velop no basal buds. If suckers are pro- Fit 47. Fasciated branch of Picea excelsa. The origfinnl band-like shoot iJ), in one year, has developed three siu:- cessive stages which sprout out from one another (J. .?. ■/). {a) Bud scales. (K natural size. After Nobbe.) Fig. 48. Cro.ss-section of the fasciated spruce branch. A through the upper part of the branch; B through the lower part : (a) bark with needle cushions; '^b) wood; (^i) pith. (Natural size. After Nobbe). duced by the sudden re- moval of large branches from the crown, their formation may be retarded by creating other diverting centers by scarification. In the spring pruning of branches, scarifying will, indeed, prevent the formation of the water shoots. In the same way, chopping into a vigorous root near the base of the trunk at the side where the tree crown has been greatly thinned out. will decrease the supply of water and prevent the sucker formation. 1 Vollstandige Naturgeschichte d. forstl. Kulturpflanzen, p. 176. o ^ '7 Union of Parts. We may likewise consider as due to local over-nutrition the con- dition arising when a cylindrical branch becomes broad and flattened. It then looks as if a number of branches had grown together; nevertheless, this is only rarely the case, for almost always only a single branch is in- volved which, by broadening its vegetative point, no longer has a vegetative cone at its apex, but a comb-like vegetative surfaced In the illustration of a spruce fasciation here given (Fig. 47) we recog- nize the fact that the broadened axis is a single unit, first by the continued Fig:. 49. Fasciation of AInus glutinosa. I /< natural size. After Nobhe). spiral position of the needles, especially at i and 2, and further in the cross- sections A and B (Fig. 48), of which the pith and wood form a single connected, uniform surface, and do not show any possible coalescence of many single adjacent rings, as must be the case where fasciation is produced by the coalescence of many branches originally separated. This theor^^ is not changed by a consideration of the fasciation of the alder (Fig. 49), in which, besides the unusuallv characteristic crook-like bending of the 1 iJber Pflanzen-Verbanderung-. Referat in Bot. Zeit. 1867, p. 232. 334 branches, resulting from a one-sided increase of growth, we can also per- ceive the splitting of cylindrical branches from the band bodies which occurs more frequently in deciduous trees. Thus the material for many axes, which can be isolated, lies accumulated in the fasciated stem, while the stem itself is a unit. We can speak only hypothetically as to the production of the fasci- ations, which are characterized as hypertrophies by the great increase of the leaves and cords of the leaf spurs. An axis, which fasciates later, must originally have suffered some arrestment. We have seen already in roots held fast between split rocks that pressure from two opposite sides may give the axis a band-like form. Under certain circumstances such a changed direction of growth may continue if the cause of arrestment itself has dis- appeared. Thus Treviranus cites an observation on the stem of Tecorna radicans which had become band-like from pressure against the wall, but still remained band-like, after it had grov/n far out over the wall. Here the branches, which developed further, also became band-like in places. Besides such lateral pressure, in other cases a transitory pressure from above may also probably cause a broadening of the vegetative point into a vegetative surface, and such pressure can possibly be produced by the ab- normal behavior of the bud scales (delayed loosening due to resinification, drying, etc.). In case no abnormal increase of pressure occurs, direct in- juries to the vegetive tip may cause the increase of the vegetable points. If the fasciation has once been produced, it can be propagated by cuttings ; even under certain circumstances it can be proved constant in the seed, as is seen in the favorite garden plant, cock's comb (Celosia cristata). The capacity for fasciation may be presupposed in all plants and actually observed cases have been reported in great numbers (150) by Masters^ As mentioned already, the fasciated growth produced by a band-like fasten- ing together of isolated axes, should be distinguished from real fasciation. T-opriore- has produced such cases artificially in roots. Compulsory Twisting (Spiralismus Mor.). A. Braun'' characterizes by the above name, those malformations of the stem which corsist of barrel-like distended places in which the grooves, extending down from the leaves and representing the vascular bundles be- longing to them, exhibit an extreme, spiral twisting. At times the barrel- like swelling is so great that the stem splits in the direction of the spiral twisting and divides into a number of spiral bands at these diseased places. Schimper has named this disturbance in growth "Strophomania." The ma- jority of cases are known in the families of the Dipsaceae, Compositae and the Rubiaceae. Single examples are described also, for the Labiates, 1 Masters. Vesretable Teratology, 1869, p. 20. (Compare Penzig- and the isolated cases in the Bot. Jahresberichten.) 2 Liopriore, G., Die Anatomie bandartig-er Wurzeln. Cit. Zeitschr. f. Pflanzen- krankheiten, 1904, p. 226. 3 Sitzungsberichte naturf. Freunde z. Berlin. Cit. Bot. Zeit. 1873, p. 11 and 20. 335 Scrophulariaceae, Cruciferae and, among monocotyledons, Asparagus, Lilium, Orchis, Triticum, etc., and also in Equisetum. We think it justifiable to consider the compulsory torsion- as a fasci- ation which has swollen up like a barrel. The cases have no agricultural significance. Differing from them is the increased spiral twisting of normally con- structed woody trunks, which we trace to an arrestment of the growth in length (usually resulting from a lack of water and nourishment). Dropsy (Oedema). a). In Small Fruits. Since the propagation of standard gooseberries and currants by budding on vigorous shoots of Rihes aureum has found wider distribution, there has been a great increase in the complaints of a disease of the stock which makes doubtful the success of the budding. This disease has been called "dropsy" by growers and consists in the appearance of closed bark tumors, i. e. of bark swellings entirely covered by the outermost cork layers, or of swellings rupturing later (Fig. 50 A). These swellings of the bark are sometimes small, but they may reach an extent of several centimeters. They are formed either on one side of the trunk or surrounding it, spreading into one another. They appear most abundantly on wood two or more years old, yet they can also occur in great numbers on branches one year old and directly cause their death, while the wood of the older branches may become diseased, to be sure, but does not directly die. When, as is the custom at present, Ribes is grafted indoors in the spring, rupturing tumors are found frequently directly below the place of budding. In such cases the bud does not grow. But in extreme cases the same kind of swellings may also be found further back from this place, on the trunk between every two buds, as wxll as near the buds or, rather, the branches already developed from them. Cases are observed in which the base of a shoot left standing on wood one or two years old, has swollen up like a barrel and is covered by loose, hanging strips of bark. The branch above this place is dead. As soon as the bark layer, which forms the outer skin of the branch and covers this fresh swelling, has split, the swollen place, pushing out from under it, exhibits a yellowish, spongy, soft, callus-like tissue-mass con- sisting of cells, elongated to pouches, very poor in contents but rich in water. (Fig. 50 5 s). This is the former normal bark of which the cells beginning in the region between every two groups of bast cells (Fig. 50 5 &) have elongated extraordinarily in the direction of the trunk's radius at the expense of their contents, otherwise rich in green coloring matter. They have partially separated from one another, and, by their constantly in- creasing extent, have finally ruptured the outermost oldest bark layers 336 (Fig. ^o B e k) which no longer participate in the changes and are sep- arated prematurely by the cork layers {k) from the tissue lying beneath them^. The full thickness of the bark is not always attacked by the pouch-like elongation ; in very severe cases, however, even the cells of the cambial region are deformed {c). The wood is no longer normal. Instead of normal mature wood, consisting of thick-walled, elongated wood cells and ducts, (•1 l(J 1 1 -^ ^ 1 ! 1' M 1 1 1 0A Fig-. 50. Dropsy in Ribes aureum. (Orig.) with cross walls broken through like ladders, a wood is produced, composed of short, broad, comparatively thin- walled, parenchymatous cells {h p) . The cross-section (Fig. 50 5) shows the transition of the healthy side of the branch (A'') into the dropsical side {W) ; h indicates the normal wood. At the time when the layer st was produced, the disease manifested itself in the 1 Compare Sorauer in "FreihofE's Deutsche Gartnerzeitung" August 1, 1880, and Goschke in Monatsschrift d. Ver. z. Beford. d. Gartenb, October, 1880, p. 451. 337 cambium and the result was that, from there down on the diseased side, parenchyma wood {h p) was formed wdiich at the left ended in a medullary ray (m). Still further towards the left, normal wood was produced at the same time. The same difference is found in the youngest bark parenchyma {t p). Because of the great radial elongation of the cells on the dropsical side (W) the hard bast cords {h) are pressed out like bows and the cell rows, containing calcium oxalate (o), which accompany the bast body, have also been correspondingly misplaced into steeply ascending, irregular rows. At chl are groups of parenchyma which have remained rich in chlorophyll. It is evident that this loose structure of the tissue, rich in water, which forms the swelling, has no great permanency. In dry places and with increasing dryness in the air, this tissue turns brown rapidly, shrivels, collapses and forms a soft, brown mass, part of which remains clinging to the wood, while part sticks to the outer bark tatters which roll back in times of drought and spread out, gaping, from one another. Such stems of such plants then have a rusty appearance and are best excluded from cultivation. Because of the ease with which such stock can be grown on strong soils, the loss from the disease would be less important, if it did not attack directly the potted specimens which have been budded and if the number of budded plants was not considerably decreased thereby. I am not of the opinion, often expressed in general practice, that an over-abundant feeding of the plant is to blame, but I think that an excess of water makes itself felt in some places on the axis. If there should be an accumulation of plastic food material here at the same time, it would manifest itself preferably by an abundant cell increase. But this is not the case. If the cells on the healthy and on the diseased sides are counted, only an insignificant preponderance is found on the side attacked. Accordingly, an abnormal cell elongation is chiefly concerned here. This is explained by the treatment of the Ribes stems during the preparation for budding. In order to obtain slender stems, growing tall rapidly, the other sprouts, produced at the sides, must be removed and even the lateral branches on the young stock must be cut back. If now the stock is well rooted, it will grow rapidly in the greenhouse and the buds, scantily present because of the earlier pruning, are still fur- ther decreased by the fact that the shoots developing from them are cut back or entirely removed. By cutting off the branches, the amount of water forced up by the water pressure is increased in the main axis and manifests itself in a pouch-like elongation of the younger bark cells and in the forma- tion of tumor swellings which finally rupture. My attempts to produce dropsy by abundant watering and the rapid ("crcing of well-rooted specimens in the greenhouse, together with a con- tinued removal of the developing lateral shoots, gave very favorable results. The disease will be prevented if the budded stock is not forced too rapidly and the sprouts from the bud are cutting back carefully, but not 338 entirely removed. Maurer^ has recommended the use of Ribes nigrum in- stead of R. aureiim for budding stock. However, I have also known of cases of excrescences on the axes of the black currant, especially after the transplanting- of such plants as tend to sterility. b). In Stone Fruit.s. It may be foreseen that, with the present methods of culture, phenom- ena similar to those observed with Ribes, will also appear in other vari- eties, for our fruit trees are becoming more and more delicate, due to the great increase in nutrition supplied them. The mass of the parenchy- matous branch substance increases constantly in comparison with the prosenchymatous tissues. Between unbudded, wild stock, and budded varieties there are considerable differences. Direct measurements have shown me that the branches of the cvdtivated varieties acquire a fleshier bark while the wood ring decreases considerably in thickness-. I have called this increasing tendency of our fruit trees to form soft, parenchy- matous tissues, storing up reserve substances, at the expense of the breadth of the wood ring, " parenchymatosis." In special cases this change in development acquires such extreme pre- ponderance that diseases arise. I observed such diseases especially in the fruit wood of pears which is often shortened up to barrel-like fleshy swell- ings ; growers call these "Fruchtkuchen." The morbid disturbance con- sists either in the shedding of the cork layers and outermost bark layers in shield-shaped pieces from the side of the branch, thus showing a greenish yellow callus-like tissue mass, or in the uplifting of the bark itself in stiff', crumbly scales, like rings extending almost around the whole branch, with similar changes in the tissues. In the latter case, all the branches found above such a place are dead. If the diseased condition manifests itself in a less luxuriantly developed fruit wood, which may be distinguished from the "Fruchtkuchen," as fruit spears, a complete casting of these twigs was often found resembling that of the normal dropping of the twigs observable every year in poplars. In the present abnormal dropping in pears, the exposed surface was not smooth but uneven and woolly, light colored, however, like the cross-section of healthy wood. A cross-section through a place in the branch which is found in the first stages of the disease, shows that the bark has developed strongly on one side, especially within the primar\^ bark. Its parenchym.a is thin-walled, vesiculated in places or pouch-like and extremely porous. A comparison of the pith in a branch which has split and in a healthy one of equal age shows that the former is one-third larger than the latter, while the wood ring is only one-third as wide. Significant structural differences are connected with these misproportions. While a healthy shoot shows 1 Der Obstgarten, 1879, p. 182. - Sorauer, P. Nachweis der Verweichlichung- unserer Obstbaume durch die Kultur. Zeitschr. f. Pflanzenkrankh. 1892, p. 66. 339 normal libriform fibres and an abvmdantly developed vascular system, the wood of the diseased branch is made up almost exclusively of parenchy- matous thin cells, between which the vascular cords are deposited. In normal trees, under certain circumstances, the weakness of the wood ring can be compensated for by schlerenchymatous elements in the bark\ The dropsical branches of pears differ from those of Ribes in that the wood body is also involved in the parenchymatosis and entirely broken up. By the rounding up and dilation of the wood cells, which have become par- enchymatous, the ducts are gradually curved, displaced and finally torn. Just as soon as the loosening process has affected the whole extent of a fruit spear, or a "Fruchtuchen," dropping follows. The diseased branches came from trellised trees in a well watered garden, richly fertilized with cow-manure. Even if such extreme cases are less frequent, yet the first stages, con- sisting of the widening and excrescence of the medullary rays and the pro- cesses of elongation in various groups of bark cells, are often observed. Swellings on the St. John's Bread Tree. Swellings often appear as a result of cell elongation and cell increase. Savastano- reports thus, for example, of the outgrowths on the branches of Ceratonia Siliqua. Conical outgrowths, rich in tannin, are found at the tips of the flower stalks, causing atrophy of the blossoms. In an earlier study^, he describes the production of larger swellings on the St. John's Bread tree. On normally developed fruit branches, in the beginning of the disease, the fruit falls in the first stages of development and the remaining basal part of the axial cone begins to swell. The repetition of this process in succeeding years produces a knotty swelling which can attain a very con- siderable size and a height of 6 to lo cm. The bark of this hypertrophied tip of the fruit twig is often seven times as thick as that on the normal fruiting wood and the wood itself consists of ductless wood parenchyma. In the almost pithy bark, the bast fibres have wider lumina and take an unusual course. The medullary rays are twisted, the wood ring is often bent. In the parenchyma, various cell groups with discolored walls and a gummy content are recognizable. From the beginning of the disease, the tannin content of the sweUing increases, causing a distinct disturbance in lignification. A case described by Vochting* in Kohlrabi plants may be mentioned here. If all the vegetative points were removed, the leaf cushions swelled to extensive structures. In the normal wood of the axis, as in the leaf cushions, the cambium developed thin-walled xylem elements. In similar 1 Pieters, A., The influence of fruit-bearing on the development of mechanical tissues in some fruit trees. Ann. of Bot. Vol. 10. London, 1896. P. 511. - Savastano, L., Tumori nei coni gemmarii del carubo. Boll. d. Society d. Naturalisti in Napoli. 1888. Vol. II, p. 247. 3 Savastano, L., Hypertrophie des cones a bourgeons (maladie de la loups) du Caroubier. Compt. rend. 12. Janv. 1885. 4 Vochting, H., Zur experimentellen Anatomie, cit. Bot. Jahresb. 1902. II, p. 300. 340 experiments with Helianthus annuus Vochting found little tubercles formed on the roots. I observed barrel-like thickenings of the sharply bent roots of sweet cherries. The swellings, described by Warburg^ in the branch canker of the kina tree on damp soils, may also represent such correlation phenomena. Retrogressive Metamorphosis (Phyllody). If the organs of a morphologically higher developmental stage seem transformed into those of a lower one, we speak of a retrogressive meta- morphosis. The change in the blossoming organs is pathologically of mo- ment only if the sexual apparatus, by changing into a group of vegetative organs, loses the purpose for which it was designed and thereby initiates sterility. These cases are listed under the group of phenomena caused by excess of water and nutriment, in accordance with the following theory. The development of the vegetable organism depends upon two factors, the con- stitution of the organic building materials and the way in which they are utilized. With the assumption that the first achievement of the organism, — assimilation, i. e., the formation of new dry substance, — takes place in a normal way, the development of the plant depends upon the way in which this organic building material is utilized. In this we recognize two directions which we will keep separate as the vegetative and the sexual generations. The latter is initiated usually by the appearance in the organism of an often clearly recognizable dormant period in the production of its vegetative apparatus. As a rule, new leaves are not formed at this time, the apical growth of the twigs stops. In place of this the process of the storage of reserve building material becomes conspicuous. We find this storage process initiated and favored by a decrease in the absorption of water with increasing light and heat. An increased con- centration of the cell sap is required, if the reserve substances, for ex- ample, are deposited in the form of starch. If such a concentration cannot be obtained under any circumstances whatever and the building substances remain in a diluted form, — for example, sugar, — only a slight impetus is necessary to start up vegetative activity. Thus, a certain antagonism pre- vails between the two developmental phases, which we may consider as transmissable adaptations to atmospheric conditions. After a cool wet period when the plant takes mineral substances from the soil and through the production of the leaves causes the chlorophyll apparatus to attain to its richest possible development, a warmer, drier period follows which makes possible the greatest amount of light. In this period the sexual organs are formed from the finished, plastic building materials prepared in the leaves and develop further, after a shorter or longer dormant period. 1 Warburg, O., Beitiag zur Kenntnis des Krebses der Kinabaume auf Java. Cit. Bot. Centralbl. 1888. Vol. XXXVI, p. 145. 341 The more the plastic material is worked up by the leaves, the more numerous and perfect are the sexual organs formed within this dormant period. The manner in which these primordial buds subsequently develop depends on the nature of their further nourishment. If influences make themselves felt which are necessary for the maturing of the vegetative organs, foliage leaves will develop and, indeed, either from the newly formed centres or from the already existing primordia of the sexual gene- ration. Thus "phyllody" takes place. From our experience in horticulture, we know that an abundant supply of nutritive substances with a simultaneous increase in warmth and mois- ture, usually at the time of a lesser light action, are conditions initiating and favoring the process of phyllody. This becomes especially apparent in the production of double flow'ers, in which the stamens are transformed into petals. Since this process can become hereditary, like all changes in the di- rection of growth, where conditions remain equal, and may be increased, it is evident that we will find examples in which the tendency to the retro- gression of the sexual organs into forms of morphologically lower develop- ment, has affected all parts of a flower, and then the whole blossom turns green. Of course, the influence of the soil is rarely the direct cause of phyllody. This is due rather to definite combinations of all the factors of growth, as already mentioned, and also occurs not infrequently as a correlation phe- nomenon resulting from the suppression of other processes of growth. Thus phyllody of individual flowers and inflorescences is produced by injuries to the vegetative axis and by vegetable and animal attacks (mites). For example, C. Kraus^ removed leaves from Helianthus annuus plants of differ- ent ages, leaving only the bracts of the blossom head. In the older plants the bracts curled back and enlarged prematurely. In the younger plants 25 per cent, showed an actual phyllody, since the bracts assumed, more or less, the form of foliage leaves. In my freezing experiments, I have often observed that the bud scales were transformed into herbaceous, leaf-like organs after the apical portion had been destroyed by frost. GoebeP obtained similar results by removing the leaves of young plants of Prunus Padus, Aesculus, Rosa, Syringa and Quercus, and then putting the plants into plaster casts. Teratology has classified the phenomena. The simplest case is "virescence," turning green, in which an organ of the flower retains its form in all essentials, but becomes green in color. As a rule, the organ be- comes fleshier with this appearance of the chlorophyll coloring matter. In the actual metamorphosis of the floral organs into leaves (phyllody, phyl- 1 Kraus, C, Untersuchungen liber kiinstliche Herbeifiihrung- der Verlaubuiig usw. durch abnorme Drucksteigerung-. Forsch. auf. d. Geb. d. Agrikulturphysik. ]S80, p. 32. 2 Goebel, Beitrage zur Moiphologie und Physiologie des Blattes. Bot. Zeit. 1880, p. 803. 342 lomorphosis) the organ also approaches the foliage leaf in form. Bracts become normal stem leaves, the sepals are replaced by actual foliage leaves, the petals become green and fleshy, the pistils become stamens (staminody) or the stamens and pistils assume the character of petals or green, fleshy leaf-like structures, as, for example, in the double cherry, the double Ranunculus, etc. In mignonette, through phyllody of the ovules, little leafy axes can be formed in the urn-like open ovule cases. In the favorite tub- erous Begonias, 1 found that the placentae had grown out of the ovule cases and the ovules carried over on to petal-like transformed branches of the pistil, etc. There are cases in which all the parts of a flower are transformed into small, uniformly green leaves, i. e., a complete green flozver condition (chloranthy) arises. One of the best examples of this is the green rose {Rosa chinensis, Jaqu.), received in its time with great enthusiasm, the transformation processes in which have been thoroughly described by Celakowsky\ I would like to introduce here also parthcnogensis, which various scientists have often proved recently to be of constant occurrence. Kirchner" saw in this an arrangement "which, differing from the much more wide- spread, spontaneous self-pollination, serves to assure the development of seed, capable of germination, in cases where, for any reason whatever pollination has become uncertain or difficult." Even those seed primordia can be assumed to be of a somatic character, in wdiich, at the time of the production of the embryo sacs, the reducing division is suppressed and the egg cell retains a vegetative character. In cryptogamic plants Apogamy corresponds to the process of phyllody in the phanerogams. Instead of the sexual products, vegetative organs appear here, as in Athyrium Filix fem'ma var. cristatum, Aspidium falcatum and Pteris cretica. It is said that in the last plant, no more female sexual organs are formed at all, but the young plant is produced from a vegetative sprout exactly on the places in the prothallium, where the archegonia m.ust have stood^. Such plants which "produce their young alive" (viviparous) furnish abundant material for propagation, just as, for example, the bulblets of many lilies, produced by the transformation of a flower. The Barrenness of the Hop. A special process of phyllody, of great agricultural significance, is the barrenness, the blindness, the fool's head formation of the hop. The names designate only dilTerent degrees of a malformation which begins with a simple, abnormal lengthening of the catkins and develops into the formation 1 Celakowsky, Beitrage zur morphologischen Deutung- des Staubgefafses. Pringsheims Jahrb. 1878, p. 124. 2 Kirchner, O., Parthenogenesis bei Bliitenpflanzen. Ber. d. Deutsch. Bot. Ges. 1904, Vol. XXII. Generalversammlungsheft. Here also a bibliography. a Noll in Straszburger's Lehrbuch der Bot. 1894, p. 243. 343 of fluttering, dark green inflorescences on which develop foliage leaves, difl^ering in size and varying in numbers. Fig. 51. Different transitional stages between the normal hop catkin and a leafy one. (Orig-.) Hop growers know that the cjuality of the hop decreases according to the increased length of the catkin and enlargment of the bracts. The de- velopment of the catkins, most advantageous for technical use, is a short, 344 compact form of the whole inflorescence and a short, broad form and papery, thin consistency of the bracts, as shown in the preceding Fig. 51, Nos. i and 2. Half of the leaves have been removed in No, 2, in order to show the short- ness of the joints in the catkin spindle. Nos. j and 4 show the abnormal excessive lengthening of the catkin, known among growers by the name "hrausche" hops, which must count as the first stage of phyllody. Such "brausche" hops are coarse, contain less substance, ripen somewhat later and have more herbaceous bracts. Beginning with this condition, the phenom- ena of phyllody increase up to the stage shown in No. 5. The green foli- aceous leaves, which here become visible, attain at times the size of a nor- mal leaf, h is the leaf blade which may be followed back into the petiole. At the base of this petiole stand the two green lateral leaflets {n,n) which in the present basal part of the catkin are very small, but increase in size up- ward. No. 6 is taken higher up on the inflorescence and shows the lateral leaflets {n,n) in a size equal to the other bracts, while the leaf body {h) is much smaller. The remaining bracts and protective leaves are seen at No. 5. Each one encloses a flower. The scale leaves, which exceed developmentally the other leaves and are developed only in the normal female inflorescence of the hop have the same bract-like constitution as do the protective leaves, so that the whole catkin seems composed of uniformly developed bracts. All the bracts are short lived and soon become dry skinned, when they lie over one another like tiles. The barrenness consists, therefore, of the development of the otherwise suppressed leaf blade between every two bract-like leaves. Wide exper- ience now shows that damp years^ and soils strongly manured with sub- stances containing nitrogen cause the more extensive appearance of the barrenness. Frequent summer rains, resulting in cloudy days, are often injurious, even without directly producing the disease. The cells of the leaf, as well as the axis, then elongate and even if favorable harvest weather occurs, the catkins ripen only superficially. They are brought into the storage rooms while containing much more water of vegetation, thereby causing a very rapid heating of the whole heap. Consequently, even in well- developed catkins, a rapid loss of the peculiar gloss and the light green color takes place, together with a considerable reduction in value of the whole harvest product. As a remedy for the barrenness, the removal or checking of the causes must be attempted, in case these are found in the soil in the form of excess of water or nitrogen. If the cause is cloudy, damp air, all means should be utihzed which further the greatest possible aeration and illumination of the hop-plantation. If nitrogen is present in the soil in excess, a subsequent fertilization with superphosphate is advisable. 1 Beobachtungen iiber die Kultur der Hopfenpflanze. Published by the Deut- «icher Hopfenbauverein, Jahrg. 1879-82. 345 Forked Growth of Vines. It may be noticed in various localities, that different varieties of vines assume a tendency to excessive branching and retain it hereditarily. The kind of false ramification appears as a forking of the vines and such dis- eased plants are usually little if at all productive. Rathay^ published the most thorough observations on this subject and corroborated these state- ments in lower Austria. The wine growers there, who call these branch- sick vines "Forks," or "Double tipped," state that the forked formation may commence in very different places. The vines which in adjacent groups usually begin showing this abnormal direction of growth, first develop scattered forked branches and in this way present a "spurious forking" as may be seen everywhere in luxuriant vineyards. This initial stage of the disease is not dangerous, since the plants frequently return to a normal growth. The danger begins with the spread of the disease over the whole plant. Correlated with this is the transmissibility of the disease. This has been demonstrated in cuttings and suckers of affected vines. No cause of this phenomenon can be given as yet with certainty. R.athay was convinced that parasites were not present. The opinions of practical workers disagree greatly. Some think that exhaustion of the soil by intensive grape culture is the cause, while others are of the opinion that a clogging of the soil due to heavy rain storms or to the working of the soil during and soon after rain has an injurious effect. In my opinion this disease is a phenomenon of turning green — vires- cence — i. e., a morbid increase of the vegetative development. Kaserer's- statements favor this hypothesis. He states that, the first evidences of the disease are found in the transformation of the covering bract of the tendrils into a small leaf, the most advanced stage in the trans- formation of all the tendrils into leafy shoots. In grape vines, the tendrils are axial organs, of which the development depends upon the amount and constitution of the organic building materials present. In younger vines they become herbaceous shoots, but in older ones develop into inflorescences at the lower buds. If all the tendrils are transformed into leafy shoots the vegetative development will predominate, a morbid condition. The building material present is wrongly utilized. The cell sap necessary for the formation of the sexual organs is not properly concentrated. Thus far it is possible to agree with Krasser', who speaks of a diseased condition of the protoplasm in certain regions as a cause of this "herbaceousness." If Krasser, referring to the works of Kober and Gaunersdorfer (1901) insists that no disturbances in conduction and no lack of nutritive sub- stances can be assumed as causes of the "herbaceousness," w^hich represents J Rathay, Emerich, tjber die in Nieder-Osterreich aJs "Gabler" oder "Zwiewip- fler" bekannten Reben. Klosterneuburg, 1883. 2 Kaserer, H., tJber die sogenannte Gablerkrankheit des Weinstocks, Mitteil. d. k. k. chemiscli-physiol. Versuchsstation Klosterneuburg-, 1902. Part 6. ' 3 Krasser, Fridolin, tJber eine eigentiimliche Erkrankung der Weinstocke. II, Jahresb. d. Ver. d. Vertreter d. ang-ewandten Botanik. 1905, p. 73. 346 only a metamorphosis of scattered buds into leaves, but that a very local affection of the cells of some buds is present, this does not upset at all our theory of phyllody. It is a matter of course that the formation of each organ takes place under definite nutritive conditions. That these change constantly and are the product of the momentary combination of all the factors of growth has been emphasized already in the introductory chapters of this edition. It is still far from possible to determine these combinations. For the present, we have only scattered observations on this subject, — that, for example, an excess of potassium and nitrogen in relation to the con- sumption of the other nutritive substances one-sidedly increases the vege- tative activity at the expense of the sexual development. An excess of water with a relatively scanty supply of light can in a similar way influence the direction of growth. We cannot determine how these disturbances in equilibrium are produced individually for the formation of each organ, whether momentary' arrestments in the absorption or transportation of the nutritive substances form the cause. We can, therefore, state only very generally that phyllody is produced by a preponderance of the direction of growth producing green leaves as against the mode of growth favoring the sexual organs. The so-called "changelings" or spurious f orkings, • are plants which are still partially fruitful. Among the conditions favoring the tendency to phyllody, Kaserer cites unfavorable positions on which drainage water collects from higher lying ground. Healthy plants set out in a group of affected plants are said to fork rapidly. Superphosphate seems to favor a return to fruitfulness. We consider the replacement of diseased plants by healthy ones of varieties which withstand a more abundant supply of water and heavier soils to be the most advisable mode of procedure. The so-called aggregations of forked plants might be improved by drainage and the addition of sand together with that of calcium phosphate. Falling of the Leaves. The falling of the leaves, the normal result of age^ is of pathological significance only because, under certain circumstances, it can appear prematurely. The causes which may lead to such premature dropping of organs are of different kinds, and extremes of weather may give rise to it. Ac- cordingly, the phenomena could be treated in different sections of this book. Nevertheless, we prefer to consider here the processes of loosening as a whole, because they are connected with changes in the tissues, in which in- creases of turgor occur decisively, after the organs, for any cause whatever, have become functionally weak. In regard to the falling of the leaves, for example, Wiesner- differentiates the falling of the leaves into a summer 1 Dingier, H., Versuche und Gedanken zum herbstlichen LaubfalL Ber. d. Deutschen Bot. Ges. Vol. XXIII (1905), p. 463. 2 Wiesner, Jul., Ber. d. Deutschen Bot. Ges. Vol. XXII (1904), p. 64, 316, 501. Vol. XXIII, p. 49. 347 falling, falling due to groivth, falling due to heat and falling due to frost. Pfeffer^ gives us an insight into the diversity of the causes. "Such a hasten- ing of the leaf-fall is brought about, for example, by insufficient illum- ination, also by an insufficient water provision and by too high a temperature. Not infrequently, however, a premature shedding of the leaves is caused especially by the sudden change of external conditions, which for perti- nent reasons concern fiirst of all the older leaves." As examples of the injurious influence of a sudden change in the amount of transpiration, Pfeffer cites the sudden loss of leaves in plants as soon as they are brought from the moist greenhouse air into a dry room. Sharp changes of temper- ature, illumination, etc., can act in the same way. V. Mohl- has studied the anatomical processes very thoroughly. The shedding of leaves is accomplished by the formation of a trans- verse parenchyma layer at the base of the petiole, as a rule within the leaf cushion, and, in fact, usually where the cork of the bark passes over into the epidermis of the petiole, and in the interior of the petiole tissue, which is produced by a special cell division. The cells of this layer separate from one another in one plane. V. Mohl calls the zone in which the layer of separation is formed, the "round-celled layer," because it consists of very short parenchymatous tissue, which toward the leaf body gradually passes over into the elongated cells of the petiole, but is sharply defined on the side toward the bark of the twig. In very many cases, a cork layer formed of plate-like cork cells, sep- arates the green bark of the branch, rich in chlorophyll and starch, from this short-celled parenchyma of the found-celled layer of the leaf cushion which usually contains no starch, and very little cholorophyll and turns brown at the base at the time of leaf fall. Schacht^ considers this cork sheet, which, at the sides, passes over into the inner cork layers of the bark, to be the cause of the shedding of the leaves. In fact, it may be assumed that if a cork layer be shoved in between the tissue of the bark and that of the petioles, the food supply of the leaf is impoverished and the leaf gradually goes to pieces. Nevertheless, the cork layer is not the cause of the leaf fall, for V. Mohl has shown that it is not formed in many plants which cast their leaves. Thus, for example, no cork layer can be found in ferns with deciduous fronds (Polypodium, Davallia) further, in Gingko biloba, Fagus silvatica, some varieties of oak, Ulmus campestris, Morus alba, Frax- inus excelsior, Syringa vulgaris, Atropa Belladonna, Liriodendron tulipifera, etc. On the other hand, the cork layer is formed in Populus canadensis and /'. dilotata, Alnus glutinosa, fuglans nigra. Daphne Mesereum, Sambucus racemosa. Viburnum Lantana, Lonicera alpigena, Vitis vinifera, Ampe- lopsis quinquefolia, Aesculus macrostachya, Pavia rubra and P. lutea, Acer 1 Pfeffer, Pflanzenphysiologie. II Edition, Vol. 2 (1904), p. 278. -' V. Mohl, Tiber die anatomischen Veranderumgen des Blattgelenkes, welche das Abfallen der Blatter herbeifiihren. Bot. Zeit. 1860, Ncs. 1 and 2. •i Schacht, Anatomie and Physiologie, II, 136. 348 platanoides, Prunus Padus, Rohinia Pseudacacia. The cork layer should, therefore, be considered only as a protective layer for the bark tissue ex- posed by the falHng of the leaf, often developed before the leaf has fallen. The real layer of separation, in fact, is formed above the cork layer in the almost isodiametric parenchyma of the round-celled layer, not in the brown-walled portion bordering directly on the cork, but in the adjacent healthy portion, of which the walls are light colored. There, shortly before the leaves fall, a zone is found running obliquely in front of the bud toward the outer side of the petiole and composed of young, delicate walled cells with intercellular spaces containing less air. Small starch grains are found in these cells which otherwise do not occur in the enlarged end of the petiole. In this newly formed tissue-zone, the cells separate from one another with- out tearing, but by rounding ofif, as Inmann^ has observed. One part re- mains attached to the petiole as it breaks off, the other to the leaf scar Avhere it soon dries up. The leaf-fall, accordingly, is a vital act, not a me- chanical one. Before the leaf falls, vascular bundles take no part in the changes undergone by the cell tissue of the swollen end of the petiole. These extend through the round celled layer and the cork layer without changing their organization, even without turning brown. The cleavage in these *^^kes place in a purely mechanical way after the split has extended through the parenchymatous tissue. In many plants (Nuphar, many monocotyledons, herbaceous ferns- ) in which there is no cork formation on the leaf scar, its outer dried cell layers pass over directly into the healthy bark parenchyma and are thrown off during later development. V. Bretfeld^ arrives at the conclusion that the process of abscission of the leaves is the same in monocotyledons and dicotyledons, only the shutting off of the abscission surface differs in different genera. An essential difference lies, however, in the time of the formation of the tissue zone in which the separating layer is produced. While in dicotyledons, the process of ab- scission is the product of living activity, taking place shortly before the leaves fall, this process in the tree-like monocotyledons, orchids and Aroideae is exhibited' as an act prepared by the primordia of a definite layer and advancing with the general tissue diff"erentiation. The loss of leaves occurring in conservator)^ plants of the her- baceous and bushy Begonias, of Cistus species and many Mytaceae and Leguminoseae from New Holland must be mentioned in discussing leaf fall due to an excess of water. The upward force of the sap is increased excessively by an abundant watering of the plants at the time of minimal' leaf activity. The cleavage surfaces of the falling leaves at times are very mealy, due to the loosened cells of the abscission surface. 1 Bot. Zeit. 1850, p. 198. 2 V. Mohl, tJber den Vernarbungsprozess bei der Pflanze. Bot. Zeit. 1849, p. 645. p. 645. 3 V. Bretfeld, tJber den Ablosung-sprozess saftig-er Pflanzenorgane Bot. Zeit. 1860, p. 273. 349 Leaf Casting Diseases. The leaf casting diseases form the most significant case of premature dropping of the leaves. We speak here in the plural, although it is custo- mary generally to call a sudden dropping of the needles of young pines "leaf casting." All plants can "cast their leaves" which are capable in any way of pushing off their dying leaf apparatus. The only concern, then, is whether the leaf body in its entirety suddenly becomes functionally weakened, or even functionless. It is only because it appears so uncom- monly abundantly among pines and is accompanied by severe results that the dropping of the pine needles is cited especially often for "Leaf Casting." This form of disease manifests itself most frequently and severely in seedlings two to four years old, the needles of which suddenly become I'rownish-yellow or brownish-red in the spring and fall after a short time. The considerable spread of this phenomenon dates only from the general change in the cultural methods; instead of sowing the seed and of the Femel management, the raising of plants in seed beds has been introduced. Since that time it has been observed that in the months from March to Mav, often within a few days, great areas of seedling plants look as if they had been burned. In this, however, it can be noticed that young plants protected by a not xtry close conifer forest, or one of mixed trees, or, in nurseries protected by trees of an earlier seeding, do not cast their needles, while exposed areas in the open or in enclosed places are extraordinarily at- tacked by the disease. Specimens with pruned roots suffer more than those with long, vigorous ones, while plants on wet soil suffer most intensely. Mountain plantations are less attacked than those on plains and a northern exposure seems to be almost entirely spared, while a southern or western one suffers greatly. The disease does not appear every year, but generally only after wet, cold winters with but little snow, and alternating sharp frosts. The plants cast their needles most extensively if dry springs, March and April, are distinguished by bright warm days followed by cold nights. Often the phenomenon occurs in stripes or spots. It has been observ'ed further, that plants protected from the noonday sun by neighboring woods, etc., general- ly did not become diseased. Plants in seed beds, which were left covered until after the time of spring frosts, did not cast their needles while ad- jacent, unprotected seedlings did so. Seedlings grown between older covered plants or between broom plants, even those protected by high grass, did not develop the disease, while others where the broom plants had been dug out in the spring were attacked. Ebermayer\ in explanation of these facts, states that observations of a forestr}' experimental station, made for several years, showed that in March and April the soil temperature down to ij4 rneters was scarcely more than 1 Ebermayer, Die physikalischen Einwirkungen des Waldes auf Luft und Boden etc. Resultate der forstl. Versuchsstat. in Bayern. Aschaffenburg-, 1873. Vol. I, p. 251. 350 5 degrees C, while the air temperature in the shade not infrequently was higher than 19 to 22 degrees C. Such differences in temperature between the air and the soil result directly in the excessive transpiration of the aerial parts of the plant, while the roots kept in a state of inactivity because of the cold soil, are incapable of taking up the soil water, or not to the amount necessary to replace the aerial loss. Thus the young pines dry up even when the soil is abundantly wet. The greater the difference between the soil and the air temperatures in direct sunlight, the more abundant and devastating is the leaf casting. On the other hand, the more frequently conditions arise which raise the soil temperature, such as warm spring rains, or which prevent a greater lowering of it, i. e. masses of long unmelted snow or of mulch, the less the disease appears. This lessening of the disease will take place also if the temper- ature of the air and the intensity of the sunlight are decreased as, for ex- ample, by a very cloudy sky, by a position on northern slopes, or under the protection of larger trees, high grasses or bushes, or by the artificial screening of the seed beds during the day. That older plants suffer less often from leaf casting is explained, in the first place, by the more strongly developed wood which in all plants may be considered as a water reservoir; in the second place, by a more abundantly developed, deeper reaching root system, which possesses more organs for absorption in its greater number of fibrous roots. Holzner^ has raised an objection to this theory. In leaf casting, dis- coloration appears within 2 to 3 days, while, in an actual process of dr)'ing, the pine needles redden only gradually. He considers the cause a direct effect of frost. It is a well established fact that frost will also cause leaf casting. Baudisch- protected seedlings by a brush covering one meter deep above the surface of the soil. The plants which had remained healthy until the protection had been removed then suffered from the April frosts. Many authors ascribe an injurious influence to autumn frosts^. The theory most generally accepted at present considers the disease to be para- sitic and, accordingly, recommends that it be treated with fungicides. Ac- cording to V. Tubeuf's* experiments, it cannot be doubted that there are also cases of parasitic leaf casting^. However, the fact must be taken into consideration, that the fungi of leaf casting are present in abundance on older pines, firs, spruces and larches, without calling forth the specific phenomena. Therefore, unless some conditions especially favorable for the much dreaded juvenile disease are present, it cannot become epidemic. 1 Holzner, Georg. Die Beobachtung-en iiber die Schtitte der Kiefer oder Fohre und die Winterfarbung- immergriiner Gewachse. Freising, 1877. Here bibliography of 145 studies on leaf casting. 2 Centralbl. f. d. ges. Forstwesen VII, 1S81, p. 362. 3 Alers in Centralbl. f. d. ges. Forstw. 1878, p. 132. Nordlinger ibid p. 389. Dammes and others, Jahrbuch d. schles. Forstvereins 1878, p. 40 ff. 4 V. Tubeuf, Studien uber die Schlittekrankheit der Kiefer. Arb. d. Biolog. Abt. am Kais. Gesundheitsamt. Part II, 1901. 5 Cf. Vol. II, p. 268. 351 All these statements as to the factors causing leaf casting agree in maintaining that the needles fall because they have become weakened functionally or still are normally weak as a result of the winter's rest.. Moreover, the abscission process depends upon the development of the cleav- age layer which presupposes living activity and an increased turgor. Thus, there arises an antagonism; the leaf organ is not at the time in a condition to function as a normal center of attraction and consumption. Because of its anatomical structure the basal part above the region of the subsequent cleavage can be excited and it is prematurely brought to the development of this cleavage layer by the increase in turgor, which arises in the spring due to exposure to the sun, or has been retained from the previous year, and finds no equalizaion since even the inactive lamina of the leaf do not take up the water from it. This disturbance in the equilibrium of the turgor distribution is the cause of all premature dropping of the leaves. In the special case of the pine leaf casting I think that the contrasts described by Ebermayer and, indeed, the sharp contrasts, represent the most frequent cause of the disease. Only in explaining it, I differ from him in so far that I accept as cause the winter's inactivity, evident also in the constitution of the chloroplasts, instead of the excessively increased evap- oration from the needles. Only the base of the needle is excited and de- velops the cleavage layer, which, as will be mentioned under petals, can, under certain circumstances, be produced in an extremely short time. I am of the opinion that the needle does not become dried out, but is put out of action by the cleavage layer. I would like to assume from the absolute scanty elimination of water by pines in winter, that a drying of the needles resulting from an excessively increased evaporation, is not the cause of the discoloration and falling of the needles. An experiment in a water culture of one year old seedlings showed me that a pine ceased its evaporation on the i/th of November despite following days with temperatures of + 3> 4. 7> 9 degrees C. Up to the 22nd of December they did not evaporate one gram more of water, although the root stood in water\ It can, therefore, scarcely be assumed that the spring temperature can, in a few days, cause a great loss of moisture, more particularly as the pine is a tree species which evap- orates the least of all-. Since the drying of the needles does not seem to me to be the cause of leaf casting, but rather a lack of equallization in the water supply, resulting from the sharp contrast between the needle surface, weakly assimilative, and its base, already active, I would like to believe the best preventative method to be the avoidance of such sharp contrasts: I, therefore, add the proposals made by Ebermayer : — A. Increase in soil temperature : ( i ) due to the prevention of too great cooling during the winter by means of leaf, brush or moss coverings; (2) 1 Sorauer, Studien iiber Verdunstung. Forschungen auf d. Gebiete der Agri- ;ulturphysik, Vol. Ill, Parts 4,& 5, p. 10. - V. Hohnel, loc. cit. Vol. II, p. 411, 352 by draining wet soils; (3) by loosening and mixing heavy soils with earths rich in humus, so that the warmth of the air can penetrate more easily. B. Lessening of sharp contrasts by shading: (i) by brushing the seed beds with evergreen boughs, which should not be removed on warm days ; (2) by making the seed beds in places which are protected on the south by tracts of trees. "In the restoration of pine woods, on the wliole, the most radical means consists in a return from the extensive clearing system to a plan of seeding, such that the young plants have the necessary protection from the direct sunlight in the overhead wood protection, but can still obtain as much light as is necessary for their vigorous development. The same end is attained by a slender fringe of trees running from N. E. to S. W., which are much used at present in the restoration of the pine tracts. In the cultivation of extensive clearings the shading can be obtained by a shelter growth of such plants as are favored by the habitat, — for example, by birches, etc., or by previous spruce plantations." "In cases, where no shelter growth can be arranged because of local conditions, the planting of seedlings is preferable (yearling plants with a good root system seem best suited for this), yet the first two cultural methods will much more surely attain the desired goal." Finally it is well to emphasize that every attention should be given to obtaining a good root system ; — accordingly, too thick seeding, heavy, un- broken soil, considerable injury in transplanting and the like are to be avoided. A leaf casting occurs also in older trees. The older needle bunches of plants standing on moor-soils in misty depressions, or found in localities subject to extreme frost, fall prematurely. But, in the autumn, these hang to the trees, turning yellow or drying up, and are thus distinguished from the seedlings specifically diseased with leaf casting. On heavy soils the pine always dies easily^. Leaf-Fall in House Plants. Among the most delicate of the house plants belong the azaleas, be- cause, as a rule, they suddenly drop their leaves in summer or in the autumn; the broom-like little tree then at best develops only a few pitiful flowers. Here too are concerned sharp contrasts occurring suddenly. Either the plants (usually set in moor soil) in summer are left too dry, and later watered very abundantly, or they are brought too suddenly into the warm house in the autumn. In both cases, the leaves are weak functionally and then their functioning is increasingly stimulated by the increased upward pressure of the water. If the transition is brought about gradually, the inac- tive leaf surfaces would have time to resume their normal action by a general slow increase in their turgidity and there would be no resultant injur}\ 1 Runnebaum, A.. Das Absterben und die Bewirtschaftungr der Kiefer im Stan- g-enholzalter usw. Zeitschr. f. Forst- u. Jag-dwesen, 1892, p. 43. 353 But, with the sudden upward pressure of the water, the basal region alone is stimulated, thus causing the development of the cleavage layer. In foliage Begonias, rubber plants, camelias and many others, the leaves begin to drop in .the autumn and winter. Here, the leaf is in a natural, dormant state. Abundant watering in a warm room causes an up- ward current of water which the leaves cannot utilize. Here are briefly a few of my own observations. A Begonia fuchsioi- des which had been forced through the winter in a warmer room, was brought at the end of March into an unheated, but sunny room. Within a few days it dropped all its leaves except the youngest ones. Libonia floribunda, which had been kept very cold, was suddenly brought into a greenhouse in December for forcing. The plants dropped all the older leaves, while plants remaining in the cold retained theirs. Some specimens of a double white fuchsia were brought into the house in the autumn in order to get early shoots for cuttings. Other specimens of the same variety were left in the cellar until the beginning of March. At this time the tips of all the plants were set as cuttings in a bench with 25 degrees C. soil heat. After a few days the cuttings, from the plants in the cellar, lost their leaves up to the very tips, while the others had not even lost the leaf at the cut surface. The tips of one branch, taken a few days later from a cellar plant, were placed in sand in the cellar, without any especial care and were found in May to have rooted, while the tips from the cellar plants had gone to pieces in the warm case. For house plants it may be recommended as a fundamental principle that the plants should be subjected gradually to other vegetative conditions, and the dormant period, upon which every vegetative plant enters, should not be interrupted by an increase in the supply of heat and moisture. The Dropping of the Flowering Organs. This process takes place in the same way as that of the leaves^ The composite axes of the inflorescences in Aesculus and Pavia are known to separate into their individual parts, which loosen from one another with smooth cleavage surfaces. In the same way, if many fruits are set, a num- ber of half-grown ones are often abscissed to a joint in the fruit stem. The staminate blossoms of the Cucurbitaceae are abscissed at the cleavage layer formed on the boundary between pedicel and blossom, those of Ricinus communis in a line of separation, produced at a joint lying in the lower part of the peduncle. The hermaphrodite blossoms of Hemerocallis fidva and H. flava, left unfertilized, are abscissed by a cleavage layer ex- tending under the base of the blossom through the upper part of the ped- uncle. The cells of the cleavage surface round up and separate from one another. 1 V. Mohl, H., tjber den Ablosung-sprozess saftiger Pflanzenorffane Bot. Zeit. 1860, p. 273. 354 In the same way a fully developed cleavage layer is found in the sepals of Papavcr somniferum, Liriodendron tulipifera, at the time they fall; in the falling parts of the calyx of Mirabilis Jalapa, Datura Stramonium; in the petals of Rosa canina, Papaver; in the single corolla of Lonicera Capri- folium, Rhododendron ponticum, Datura Stramonium; in the stamens of Lilium bulbiferum and L. IMartagon, Dictamnus Fraxinella, Liriodendron ; in the stigma of Lonicera Caprifolium, Mirabilis Jalapa and Lilium Martagon. In the majority of cases, the cells of the abscission layer contain no starch, or at least no more than does the surrounding tissue, while, in the leaves and thick sepals and petals of Liriodendron abundant starch is pres- ent. This lack of reserve nutriment is explained by the rapid formation of the cleavage layer in the blossoms, for which the momentarily transportable nutritive substance is sufficient. In the sepals of Papaver somniferum, the cleavage layer is produced in a single night, in the petals of single roses, in the hours of an afternoon. While cell increase seems to occur in the cleavage layer of leaves, it can hardly take place in the petals. The pro- cesses there visible consist only of a more abundant protoplasm, an in- creased porosity and mutual separation, due to a rounding up of the cells, and, at times, a pouch-like enlargement of the cells, whereby the cleavage layer looks velvety. The appearance of the cleavage layer is delayed as the organs are better nourished. The Shelling of the Grape Blossom. By the term "shelling" or "falling" the winegrower means the dropping of blossoms soon after blooming. In some regions the phenomenon returns annually while, in other localities, it appears only in isolated years, as, for example, in those when wet, cold weather destroys the blossoms. Accord- ing to Miiller-Thurgau's^ investigations, with a low temperature at the time of blossoming, the cells of the stigmas were beginning to turn brown even before the blossom sheaths fell, which indicated death or at least an extensive retarding of the process of pollination. Actually, on such stigmas the pollen grains did not develop pollen tubes at all, or only poorly. The dropping of the petal cap took place \Qvy slowly or was en- tirely suppressed. The ovule cases of such blossoms remained for some lime, often actually for a long time, but they scarcely enlarged at all. How- ever, since, according to Miiller's discoveries, ringing of the vines is usually beneficial, the low temperature cannot be the direct cause of the incompleted act of pollination and the failure to mature the seed. The dull, cool weather during blossoming is especially favorable for the growth of leafy shoots, which, on this account, require the material stored up for the development of the inflorescence, so that the nutrition is not sufficient for the blossoms. Such a starving of the blossom cluster and, consecjuently, a more or less 1 Miiller-Thurgau, tJber das Abfallen der Rebenbliiten und die Entstehung kernloser Traubenbeeren. Der Weinbau, 1883, No. 22. 355 extensive shelling of the blossoms will occur also with weather favorable for blooming, if abundant nitrogen is present in the soil, or if virgin soil with an abundant supply of nutrients and water is used for the cultivation of grapes, when the luxuriant development of the vegetative organs limits the further development of the sexual apparatus. In fact, Miiller gives examples of such cases and, at the same time, states his experience, viz., that sometimes fertilization has helped over- come the evil, and sometimes a long incision in the vine accomplishes the same end. Miiller also ascribes to the same causes the appearance of seedless grapes on the bunch, which, as a rule, is correlative with a partial shelling. The seedless grapes are larger than the unpoUinated seeded ones which, at times, remain on the bunch even until autumn. The seedless ones, however, are not as large as normal, seed bearing grapes, although, like them, they color and become sweet. Indeed, it is evident that they ripen earlier and become sweeter than the grapes with matured seeds. Since the seed primordia in the seedless grapes do not seem much larger than at the time of blossoming, it must be assumed that some dis- turbance had taken place at that time. It is probable that, in such cases, pollinization had taken place, but that either a temporary lack of suit- able nutritive substances, or some other disturbance, prevented the further development of the tgg cell. The stimulus, exercised by pollination on the walls of the ovule cases is present and the grape consequently develops. Since, however, it does not need to use up any of the nutritive substances flowing towards it in maturing the seeds, this grape at first exceeds develop- mentally the grapes containing seeds. Weighing seedless and seeded grapes proves that the seed, in maturing, functions as a centre of attraction for material. Miiller-Thurgau^ found that the weight of the fruit flesh of lOO berries of Riesling was Seedless With i Seed With 2 Seeds Normal, with 4 Seeds 25.0 g 58.2 g 77.2 g 112. g As examples of the differences in the material development, the results of an experiment by Miiller with Riesling may be cited here. 1000 berries on the 25th of September showed Seedless a weight of 208.9 ?,> sugar 10.63%, acid 18.2% Containing seeds ...a weight of 846.0 g, sugar (^.77%, acid 24.2% On the 1 2th of October Seedless a weight of 231.0 g, sugar 14.7%, acid 11.0% Containing seeds ....a weight of 898.7 g, sugar 12.3%, acid 15.7% In regard to the effect of ringing, an experiment showed that the non- ringed vines bore only unfertilized grapes, which fell soon, while the bear- 1 Mliller-Thurg-au, Einfliiss der Kerne auf die Ausbilding des Fruchtfleisches bei Traubenbeeren iind Kernobst. II. Jahresbericht d. Versuchs-stat. Wadensweil. Zurich, 1893, p. 52. 3S6 ing vines, which were ringed shortly before blossoming, furnished com- paratively long bunches with an extremely large number of seedless berries, between which were found only scattered normal ones. This formation of seedless grapes is a great injury, under our present conditions, since the prematurely ripe grapes shrivel before the general vintage until all the juice is lost, and drop off or decay; they, therefore, are wasted. If, on the other hand, this degeneration is increased, it may be termed an advantage. Probably our currants and Sultana raisins, among which only scattered berries with seeds are found, are the products of plants in which a seedless condition of the berries has become the rule. In other localities, cuttings of the currant grape are said to bear grapes with seeds. Eger^ gives some advice well worth considering. He studied the in- dividuality of different varieties of grapes from many points of view and found that certain plants of the same variety always ripen their berries earlier and that many, under otherwise similar conditions, show a lesser tendency to the falling of the bloom, which, especially in Riesling, is very considerable. Accordingly, in each nursery and vineyard those individuals should be labelled which are notable each year because of their favorable development, and only from these should cuttings be chosen for propagation. Other processes are found in our stone fruit trees when grown for trade. If the wood is thinned too much, i.e. too many leaf branches are cut away, in order to furnish light for the blossoms and young fruit, the buds, blossoms and young fruit may be dropped. By the sudden decrease of the evaporating leaf surfaces, an increased root pressure sets in for the other organs, which cannot take up the increased amount of water. Cleav- age of the abscission layer results. The dropping of the organs can natural- ly be initiated by other causes^. The Shedding of the Young Flower Clusters of Hyacinths. Many shipments of hyacinth bulbs from different growers have shown me that the shedding of complete but undeveloped flower clusters is not of rare occurrence. The uncolored, otherwise perfectly healthy flower clusters, still rather short, may be lifted from entirely healthy bulbs with fully de- veloped, often excessively elongated foliage. In the very luxuriant variety Baron Van Thuyll (originated in Holland) I found yellowish areas on otherwise normally developed leaves and these areas were shghtly swollen, even split here and there. The flower clusters were strong, perfectly healthy, perhaps 8 cm. in length, with an equally long, perfectly healthy, almost colorless stalk. The stalk had separated from the base of the bulb and the cells of the former were found to be swelled up more or less ascus-hke. This swelling 1 Eger, E., Untersuchungen liber die Methoden der Schadling-sbekampfung und iiber neue Vorschlage zu Kulturmafsreg-eln fiir den Weinbau, Berlin, P. Parey, 1905, p. 63. ■■i The Dropping- of the Buds of Peaches. Gard. Chron. XIII, 1893, p. 574. 357 could be traced back from the place of cleavage, to varying depths. The pro-cambial cells of the firo-vascular bundles were broadened like bladders. The ducts thus exposed were simply broken off and, like the other ex- posed surfaces, had absolutely uncolored walls at first. The separation begins to show itself in the rounding up and bending outward of scattered cells in the basal tissue of the flower stalk, usually at a short distance from the base of the bulb. Simultaneous with the begin- ning of this convexity a swelling of the membranes of these cells appears at the side where the curvature sets in. It is the striated middle lamella of the cell walls which swells. Also, the swelling does not take place uni- formly in the whole membranous layer, but in some places to a greater de- gree than in others, hence the swollen, stripe-like areas have a knotted course, in places showing constrictions, A bead-like irregular condition of the outer surface of the cell walls in the cells lying next the cleavage surface seems worthy of attention. The hemispherical, to nipple-shaped swellings correspond to those in the woolly stripes in the apple core and take on a pure golden yellow color with chlo- riodid of zinc while the rest of the membrane becomes intensely blue. This disturbance sets in if, when growth starts, the hyacinths bulbs are given at first too great warmth and too copious watering. The flower cluster, not yet beginning to elongate, cannot utilize or absorb the water brought to it by the increased root pressure. Thus an excess of water is accumulated at the base of the flower stalk, whose cells elongate and weaken their connection. A slower forcing of the hyacinth might prevent this condition. Twig Abscission. The small branches which, usually, together with their fully developed foliage, are cut off from the main axis by some organic process may be called abscissed twigs. This abscission takes place chiefly in the autumn, yet it has been observed in summer (July) and as in leaf casting we must take into consideration diff'erent causes for the same phenomenon. All trees do not show this peculiarity and even those in which it appears do not shed their branches every year\ nor do all of them do so. Young, vigorous trees often do not shed, while older specimens, or those standing on poor soil, in the autumn cover the ground underneath them with branches. The poplars- furnish the best known example. Their branches, often meters long, with their swollen, hemispherically rounded joint-like abscission surfaces, smooth and shining like velvet in damp weather, show most clearly that the branch is not loosened by a forcible tearing of its component parts, but by a separation of certain tissue zones preceded by internal organic processes. 1 Borkhausen, Forstbotanik I, p. 294. 2 K. Muller, Hal., Der Pflanzenstaat, p. 532, gives an illustration of this. 358 The abscissed branches of oaks^ should be mentioned. In spruces except for the twigs frequently found bitten off by squirrels", there are probably no actual abscissed twigs. Further, this phyllocladia, or loosening of the branches, has been ob- served in Xylophylla and Phyllocladus^, in all Dammara species and especially in Dammara aiistralis, according to A. Braun, in several Podo- carpus species, in Guajaceae, Piperaceae, many bushy Acanthaceae, in Laurus Camphora, Crassiila arborescens, Portulacaria afra, Taxodium disiichum^ , in Tilia"' in Uhnits pendula, Evonymus, Primus Padus, Erica, Salix^, etc. The trees partially owe their characteristic habit of growth to these abscissed twigs. But the process of freeing varies according to the habitat, weather and other agencies. Thus Rose, for example, emphasizes that, with continued drought, the branches fall more abundantly; in the majority of cases, side shoots are dropped, but many plants lose their tips as well. The last case is observed most frequently in young trees grown on fertile soil. Nordlinger*' emphasizes that predominantly the weakly grown branches are the ones shed. Just as we find the leaves falling in summer, we also find a summer abscission of the branches. Gymnocladus, Catalpa bignonioides, Gleditschia, Tilia and especially Ailanthus glandidosa exhibit the same formation of an abscission layer and the separation of the cells from one another as found in the case of fallen leaves. In young shoots of Ailanthus it may be ob- served that, besides the parenchyma, even the still unlignified cells of the vascular bundles are involved in the formation of the cleavage layer. No cork is developed at this time either near the abscission or in the upper surface of the bark of the branch. Hence we often find it affirmed that the process of abscission does not depend upon the formation of a cork layer and that this cork layer is to be considered only as a protective layer for the free-lying parenchyma appearing sometimes earlier (before the cleav- age), sometimes later. We owe very extensive investigations of twig abscission to v. Hohnel', who has included conifers especially in the scope of his work, and has come to the conclusion that, in them, one cannot speak of any twig abscission. 1 Th. Hartig, Naturgeschichte d. Forstl. Kulturpflanzen, p. 119. Pfeil, Deutsche Holzzucht, 1860, p. 136. Wigand, Der Baum, 1854, p. 67. Schacht, Der Baum, 1853, p. 305. Lehrbuch d. Anatomie usw., 1859, II, p. 19. 2 Ratzeburg, Waldverderbnis, I, 1866, p. 219 (Plate 2S, Fig. 3). Compare Beling and further Roth (tJber Abspriinge bei Fichten), Bot. Jahresbericht von Just, II, p. 968, 971, and v. Hohnel, Bot. Jahresb. VI, Gonnermann, tJber die Abbisse der Tannen and Fichten. Bot. Zeit. von v. Mohl and Schlechtendal, 1865, No. 34. Rosei Bot. Zeit. 1865, No. 41. ■i V. Mohl, tJber den Ablosungsprozess saftiger Pflanzenorgane Bot. Zeit. 1S60, p. 274 and 275. 4 Rose, tJber die "Abspriinge" der Baume. Bot. Zeit. 1865, p. 109 (No. 14). ^' V. Mohl, Dber den Ablosungs]>rozess saftiger Pflanzenorgane Bot. Zeit. 1860, p. 274 and 275. •! Nordlinger, Deutsche Forstbotanik. 1874, I, p. 199. "• V. Hohnel, tJber den Ablosungsvorgang der Zweige einiger Holzgewachse und seine anatomischen Ursachen. Mitteilungen aus dem forstlichen Versuchswesen Oesterreichs von v. Seckendorff, III, 1878, p. 255. Weitere Untersuchungen liber den Ablosungsvorgang von verholzten Zweigen. Bot. Centralbl. 1880, p. 177. 359 so long as the shedding of Hving, fresh and sappy branches is meant by it. In conifers, the branch to be shed first dies on the trunk, becoming yellow or brown ; it is shed in the usual way only after death, and a cork layer is always formed ; in this process, the wood breaks off at a definite place. The abscissed twigs of deciduous trees are shed in a living and sappy con- dition by means of a parenchyma zone traversing the thick wood but with- out the assistance of a cork layer. The age of normally abscissed twigs varies greatly. In Taxodium they are always one year old ; in Pinus strobus, always three years old ; in Piniis Larcicio, 2 to 7 year old ; in Pinus sihestris, 2 to 6 years old ; in Thuja occidentalis, 3 to 1 1 years old. It was stated at the outset that spruces and firs are said not to shed their branches. Nevertheless, I remember once having seen fresh spruce shoots with a dismembered surface resembling an articulation. In deciduous trees, it can be seen clearly that the twigs usually shed are those grown from lateral buds or adventitious eyes which are often weakly, and have grown only to short shoots. Only in poplars and willows and seldom in oaks are long shoots abundantly shed, and then only older ones (branches up to 6 years old). In rare cases the process is observed also in Primus Padus and Evonymus europaea, while in other trees usually one year old shoots alone are shed. Worthy of our attention is v. Hohnel's observation that the wood of Thuja occidentalis is weaker where the constriction will appear later, than at any other place. At the place which will later be the cleavage surface, ihe wood is greatly constricted. The parenchyma cells of the bark enlarge so that a considerable loosening is produced. In Thuja orientalis the fleshy branch cushion is lacking, and no regular shedding is found. Meehan^ found in Ampelopsis quinque folia that the basal internode remains stationary and, in the following year, produces new shoots, which in turn disarticulate with the occurrence of colder weather. The law formulated for leaf casting may be applied to abscissed twigs: — the centre of consumption, which here is the twig, for some reason, no longer forms' the normal centre of attraction for the undiminished flow of water and an excess of water accumulates accordingly in the basal zone which is still capable of reaction, and anatomically dift'erently constructed. Either the branches, from the beginning, have been more weakly set, or, because of an unfavorable habitat they do not develop so far or, in great summer drought, they have become prematurely ripe or they are rendered incapable of action by cold, etc. In a weak organ, the relative excess of water makes itself felt first at the base. If this organ develops, from the start, with the presence of a large water supply, no shedding takes place. Wet years exhibit little if any twig abscission. The theory held by fores- ters, that years with much twig abscission initiate good seed years, has its 1 Meehan, On disarticulating branches in Ampelopsis. From "Proceed, of the Americ. Acad, of Philadelphia." Part I, 1880, im Bot. Centralbl, 1880, p. 1005. 36o foundation in the fact that these are dry years, favoring the maturing of the blossom buds. Even if twig abscission is of Uttle practical importance in forestry, it is, however, of horticultural importance as a symptom. Especially in the autumn the stem parts of many greenhouse plants are abscissed, as in the bushy Begonias, Melastomaceae, Acanthaceae, etc. They are positive indications of excess of water, and the only means of prevention is to keep the plants dry, b. Increase of Food Concentration. Among the phenomena of disease to be discussed in this section, those must be considered in which an excess of water in the plant becomes mani- fest locally. In this the root activity is not necessarily increased, the accum- ulation of water is produced rather by a depression of the transpiratory activity of the leaves. Increase in turgor must set in in various organs, or parts of organs, by increased water supply, as has been proved artificially in severed leaves. Consequently, the fact remains to be considered here that the humidity of the air often co-operates decisively. Conversely, in other cases, in which an excess of nutrients is involved, attention should be called to the fact that this excess does not always presuppose an absolute accum- ulation in the soil, but also occurs when the solvent, i. e., the water, is temporarily present in too small an amount, thereby producing an injuriously high concentration of the soil solution. The demands made upon the soil solution by each species seem to differ according to the different quantitative proportions in which the various nutrients and other factors of growth participate in the production of one gram of dry weight of a species. In plants, for example, which require much potassium or nitrogen to produce their substance, a high percentage solution of these substances will be necessary for the root. The plants do not die, if the desired high concentration is not afforded them, but they change their mode of growth. They then require, as already proved, much more water just as if they must strive to obtain the necessary quantity of a certain nutrient by an increased absorption of the more dilute solution. In spite of the large quantity of water and substances otherwise offered, the production as a whole is small. A similar cessation of growth is found, if the plants are placed in a too concentrated soil solution. The absorption of water is relatively scanty; the amount of ash, however, large and the production in dry weight small. The excess then is taken up but not uti- lized, the mineral substances are simply deposited in the plant and may partially be leached out again by water. In water cultures with a high concentration of nutrients the short, gnarled root hairs are sometimes per- ceptibly covered with crystalline scales. Thus, for example, accumulations of saltpetre may take place in the plant if an excess of potassium nitrate is given. Emmerling^, by means of experiments, explains very acceptably 1 Emmerling, A., Beitrage zur Kenntnis der chemischen Vorgange in der Pflanze. Landwirtsch. Versuchsstationen, Vol. XXX, Part 2, 1884, p. 109. 36i the processes taking place. He shows that, exactly as with the use of cal- cium nitrate, potassium nitrate is decomposed by oxalic acid, even in very dilute solutions, in such a way that potassium oxalate and free nitric acid are produced, while oxalic acid does not act strongly on calcium carbonate, since it only coats it with an impervious, thin layer of calcium oxalate. If now the saltpetre in the soil is relatively great in proportion to the acid which a plant species can form, the saltpetre will be taken up, to be sure, but will be decomposed only proportionately to the oxalic acid present, and the free nitric acid is used in the formation of the proteins; the remaining saltpetre is deposited unchanged in the plant. In our cultivated plants the law certainly holds good, that they all re- quire the same nutrients but in different concentrations, and also that their capacity for enduring the accumulation of various substances is decisive for the success of the cultures. It should not be forgotten here, that neither the absolute amount of nutrients, which is borne without any injury, nor also the quantity of any nutrient proved to be the best (optimum) for pro- duction, represents absolutely fixed amounts for any definite plant. Rather, it should be assumed that the need for any definite nutrient changes con- stantly according to the combination in which the other vegetative factors are present at the moment. Thus, there is always a relative optimum and maximum for each vegetative factor. The mode of production and the product, — viz., the plant body, — change according to the momentary com- bination of the vegetative factors ; — thus morphological, anatomical, and chemical analyses give different values for each individual. Each change in concentration in the same nutrient mixture changes the method of growth and directly manifests itself, under certain circumstances, in the behavior of the root hairs, as stated by Stieler^ He found in the growing root hair, with each change in the solution, a change (thickening) of the membrane at the end of the root hair; — under certain circumstances, in fact, a cessation of growth occurs. In aqueous solutions of the electro- lytes, the root hairs in many plants form vesicular, irregular widenings, and can even crack open at the tip or (rarely) laterally. The non-electrolytes exercise an injurious influence, only if they have a poisonous effect or are present in too high a concentration, which causes plasmolysis. The ob- servation that concentrated magnesium compounds can be proved to act directly poisonously, is especially noteworthy. This cannot be observed for other nutritive salts even with high concentration. These investigations confirm my own observations, viz., that, in a highly concentrated nutrient solution, "gnarled or distended" root hairs appear, and thereby indicate that the plant has had to combat difficulties in absorbing its food. In regard to varieties of grain, the experiments indicate that oats, for example, can suffer from the amounts of nutrients which, for wheat, make 1 Stieler, G., Uber das Verhalten der Wurzelharchen gegen Losungen Disser- tation. Kiel 1903. Cit. Bot. Centralbl. v. Lotsy 1904, No. 47, p. 541. 362 possible only a full production. Thus oats often fail on parcels of land, which have gradually been too heavily fertilized. Measurements of the amount of transpiration show that in concentrated solutions, the plant needs less water, for the production of one gram dry weight, than it does in very dilute ones. From this it is evident that, up to a certain degree, fertilizing signifies a saving of water^. The structure and size of the root system is changed gradually by con- centration, corresponding to the change in the root hair, already mentioned. Schwarz's- experiments with pines demonstrated this very well. He found a gradual decrease in the extent of the roots of conifers with an increase of the nutrient content of the soil, as had already been determined for other plants. Here the relation between the aerial and underground axes was changed. While, in unfertilized sand, the weight of the root system of the pine seedlings was greater than that of the aerial parts, with an abun- dant supply of nutritive salts the weight of the root system amounted to only one-fifth that of the aerial axis. Even in cabbage plants, which have been gradually accustomed by cul- tivation to the highest admissible concentrations, an over-nutrition finally takes place and with it a retrogression in production. Thus kohlrabi plants were found to be especially susceptible to large additions of phosphorus, while they require high nitrogen and potassium fertilization, together with a corresponding addition of calcium^. Changes in Meadows. The method of improving sour and sandy meadows by fertilization, depends essentially on an increase of the nutrient concentration. The acid- loving grasses, or those of sterile soil, which withstand only w^eakly con- centrated solutions, then disappear and our good fodder grasses, demand- ing higher nutrient content and producing more nutritive substance are established. Very instructive experiments on permanent meadows are found in Lawes and Gilbert*. We will cite from them only one example, in order to show that those different grass species gradually prevail in those nutrient solutions, of which they can endure a higher concentration. With the stated fertilizers, the percentages of the various grass species in 100 hay plants were found as given in the following table. From this table of grasses, we see how the rapidly spreading Festuca duriuscula disappears on sterile sandy soil, if the concentration of the ni- trate solutions and the mineral substances increase simultaneously. Agrostis vulgaris and Anthoxanthum odoratmn behave similarly, while, conversely, 1 Sorauer, P., tJber Mifsernten bei Hafer. Oesterr. Landwirtsch Wochenblatt. Nos. 2, 3, 1888. 2 Schwarz, F., tJber den Einfluss des Wasser- und Nahrstoffgehaltes des Sand- bodens auf die Wurzelentwicklung von Pinus silvestris im ersten Jahr. Zeitschr. f. Porst-u Jagdwesen. January. 1892. 3 Otto, R., Vegetationsversuche mit Kohlrabi etc. Gartenflora, 1902, p. 393. 4 From "Journal of the Royal Agric. Soc. of England" and "Proceedings of the Royal Hort. Soc. 1870," cit. in Biedermann's Centralbl. 1876, II, p. 405. 363 the heavy feeding plants of our sewage disposal fields, Dactylis glomerata and Poa frk'ialis, during the five years over which the experiments extended (the results are given in the table), became more and more abundantly established on the parcels of land strongly fertilized with nitrogen, and crowded out the others. The grass of village streets, Brouius mollis, ap- peared in high percentages only when stable manure had been used, while Loiiiim pcrenne and Holcns lanatus were present everywhere, to be sure, yet spread but little where stable manure was abundantly used. Species of Grasses ^ -^ Festuca dnriuscula i3-04 Agrostis vulgaris 8.62 Lolium perenne 8.62 Holcns lanatus 4.97 Dactylis glomerata 1.76 Poa trivialis 1.50 Bromiis mollis 0.08 Anthoxanthum odoratum. 3.29 Among other interesting observations of these authors, is the one that the parcels of meadow land, which had remained unfertilized, exhibited great diversity in the families and species growing on them. The grass was short, stemless. and, at the time for cutting, comparatively very green. With mineral fertilizers, the Leguminoseae gained the upper hand, while, in the Gramineae, which, however, showed no especial prevailing genus, the tend- ency to the development of blossoms was more decided than on unfertilized land. Conversely, ammoniuM salts, given alone without other fertilizers, almost excluded the Leguminoseae, and the Gramineae, therefore, predomi- nated. Festuca and Agrostis reached their highest percentage, and Rumex, Carum and Achillea throve luxuriantly. If Chile saltpetre alone were used, the effect in general was the same as with ammoniutn salts ; nevertheless, among the grasses, Alopecurus pratensis was especially prevalent ; and a predominating tendency to leaf production also became noticeable in contrast to the development of the flower stems. Besides the somewhat better developing Leguminoseae, there was a lux- uriant development of the little useful Plantago, Centurea, Ranunculus and Taraxacum. The highest yield and the best development of the grasses was found with stable manure to which some fertilizer containing nitrogen had been >) CO d ^ £ Stable-] Manure tion onl ith um Salt Si .2 to tsi neral ai onium ilizers 'al and mmoniu lizers 0) s 3 C u £-S srtiliza mmon >.t< ith Mi Amm Fert Minei uble A Fert < £3 ■£fe fc < ^ Q '^ 21.42 12.00 2.98 0.79 0.22 0.19 21.29 2.76 11-55 9-15 1.38 0.78 3-39 3-03 11.89 8.60 2.59 2-73 9.68 4.86 11.06 8.82 2.17 2.01 2.27 2.79 5-04 23-58 4-85 16.86 1. 6 1 577 12.00 15-47 27-43 29-34 0.15 0.63 2.21 0-93 9.64 12.53 2.41 0.80 0.49 O.IO 0.19 0.06 1 By mineral fertilizers, the authors mean a mixture of super-phosphate with potassium, sodium and magnesium sulfates. 364 added. The Leguminoseae and other plants disappeared, having been over- grown by the grasses w^hich then ripen more easily than if they have only a nitrogen supply. Stable manure alone also yielded a considerable har- vest of Bromus mollis and Poa trivialis especially, with fewer Legumi- noseae, but it left much to be desired in the fineness and uniformtiy of the hay. If mossy meadows are brought under cultivation, the moss cannot en- dure a concentrated nutrient solution, or, at least, a high concentration of various nutrient salts which require still closer examination. This explains the disappearance of moss from meadows after they have been fertilized with potassium. The same behavior is found for the horsetail (Equisetum) which is said to disappear absolutely after the use of calcium chlorid, and seems, on this account, to be especially sensitive to high calcium concen- tration. In contrast to the extreme impoverishment of the meadows, manifested by a mossy vegetation, stands the over-powerful development of grass on the so-called rankly grozving places. There is an abundant nitrogen fertili- zation from the excretions of animals and its results are shown by a more luxuriant blade development. According to Weiske^, the plants had nearly twice as much protein but possibly ^ less of substances free from nitrogen, than the neighboring plants which had not been over-fertilized. Accord- ingly, the ash of the former contained more alkalis, magnesium and sulfuric acid. The plants on such rankly growing places, despite their greater volume, remained in an immature condition. With a greater spread of such over-fertilized places, these plants would become more injurious than bene- ficial. In this they resemble the condition on the sewage disposal beds. Sewage Disposal Beds. The increased use of sewage disposal beds near large cities requires special discussion of the injuries unavoidable in this practice. Ehrenberg- has recently published his experiences in regard to the Berlin sewage beds. Aside from the notably increased development of Plasmodiophora Brassicae, due to the rapidly repeated cultivation of species of cabbages, he reported also injuries due to animal parasites. Most of all occurred the extraordinary increase of Silpha atrafa, whereby great areas of beets were completely destroyed. The parasites found over-abundant nourish- ment in the decomposing organic substances of the liquid sewage and, in the dams and canals, lurking places where they were protected from cold and enemies. The great supply of nutrients also attracted the crows from long distances to the sewage beds on which seeds, as, for example, maize and wheat, were uprooted in whole rows. Rats were another pest. In addition to the damage done by animal and plant forms, the wind caused more damage here than on other fields. On the Berlin sewage beds 1 Annalen d. Landwirtsch. 1871. Wochenblatt, p. 310. 2 Ehrenberg, Paul, Einig-e Beobachtungen iiber Pflanzeiibeschadigungen durch Spiiljauchenberieselung. Zeitschr. f. Pflanzenkrankh. 1906. 365 a large number of fruit trees in full leaf were blown down, in spite of strong stakes, because the earth, which was wet through, did not support the roots sufficiently. This was especially noticeable if a part of the field, with the surrounding avenues of fruit trees, was flooded with liquid sewage. Sugar and fodder beets, carrots and similar roots irrigated during the growing season, could not withstand liquid sewage about their crowns for any length of time. In a few hours the leaves began to wilt and towards evening the petioles became limp. Grains, grass, legumes and other plants without fleshy roots did not react in this way. Probably the wilting is physiological since the scanty root fibers present on each fleshy root cannot draw enough water from the highly concentrated soil solution to make good the loss from evaporation. If the concentration of the soil solution was decreased by the absorption of the soil, the wilting disappeared. To avoid this, dams one meter wide were built, or the roots were hilled up as they grew and irrigated in the furrows thus produced. Attention has been called in another place to the change in the growth of grasses. On the Berlin sewage beds, Lolium italicum abounds and often is entirely killed if irrigated in winter. The softness of the grass, indicated by its easy decay, is also caused chiefly by an excess of nitrogen. On an average, in the years 1900 to 1902, a hectare of the Berlin sewage land received 800 to 1200 kg. Nitrogen^ In spite of the very sparse seeding and the widely separated planting the over- fed grain plants are usually inclined to lodge. I had an opportunity to study the process taking place in this lodging of oats on the Berlin sew- age beds-. In this, a peculiar softening of the leaf tissue, due to bacteria, was noticeable. Regarding the behavior of young seedlings with over- fertilization, I observed in barley, that, in comparison with the normally nourished plants, over- fertilized ones became a darker green, but were back- ward in growth. Then the tips of the leaves bore greyish yellow spots and finally turned entirely grey ; at this time a number of seedlings lodged. Soon after lodging, the part of the stalk above the bend began to dry. But while plants normally drying finally assume a straw color, only the lower leaves in this case became straw-colored and the upper ones dried to a hay green color. Of importance here is also the diseasing of the vascular bundles and the great predisposition of the plants to attacks of fungi•^ Besides the well-known delay in the ripening of grain on sewage fields. Ehrenberg also mentions the change in the proportion between the yield in straw and grain. In irrigated oats the proportion of grain to straw- was as I :3.33, in non-irrigated, as i :2.88. Such a "luxurious growth of strazv" gradually becomes typical, for seven newly grown varieties of barley gave an average proportion of grain 1 Backhaus, Landwirtschaftl. Versuche auf den Rieselg^utern der Stadt Berlin \m Jahre 1914. - Sorauer, P., Beitrag zur analomischen Analyse rauchbeschadig'ter Pflanzen. Landw. Jahrbiicher von Thiel., 1904, p. 593. 3 Loc. cit. p. 646. 366 to straw of i :i.75, while varieties grown for a long time on sewage beds, showed 1 :2.88. Wheat and rye behaved similarly. The amount to which ripening can be retarded in extreme cases, was found for red mountain wheat, which, sown on April 19th, ripened on irrigated fields on the 13th of September, but on non-irrigated, on August 24th. There was then a difference of 20 days. Mention is made in another place of the disadvantageous effect of chlorin compounds on the starch content of potatoes, and on other plants. The "coating ivith ooze and mud" is the most important injury in sew- age disposal beds. Liquid scivage contains, besides great quantities of sodium chlorid and other salts, many organic substances especially pieces of paper, coffee grounds and the like. Six investigations of Berlin sewage in 1902, gave on an average : Organic Substances 0.030 per cent. Potassium 0.006 per cent. Sodium 0.022 per cent. Sulfuric acid 0.006 per cent. Chlorin 0.020 per cent. The pieces of paper and the organic substances dry up on the beds into tough, thin, flat cakes, decomposing only with difficulty because of their fatty content. Soaked with salts and organic substances, these form the ooze, which acts detrimentally to the soil. The high content in salts will easily cause a leaching of the calcium through an exchange of bases. Analyses^ prove that, on sewage beds covered with ooze, calcium is actually carried off. The calcium content amounted in upper surface sub-soil Normal soil 0-i53 per cent. 0.031 per cent. The same soil, but covered with ooze. 0.122 per cent. 0.048 per cent. An application of calcium is, therefore, desirable in soils covered with ooze, since its action improves the soil physically. The disposal of the above mentioned papery flat cakes, which may choke young plants, especially grasses, will have to be undertaken first of all by harrowing, tearing and removing the rags. Nevertheless, in planting the fields, great quantities get on to the soil and liave an injurious effect. The enrichment in organic substances, due to the ooze, may be recognized from the loss when heated : Normal soil contained (in a friable condition) ... 1.994 per cent. The same soil, covered wath ooze 2.418 per cent. Vegetative experiments in pots shouted that an admixture of ooze always arrested growth, and an addition of quick lime did not overcome this re- tardation. The arrestment in development did not show itself in the ap- pearance of positive symptoms of disease, but only in the delayed sprouting 1 Backhaus, loc. cit. p. 69 and p. 114. 36/ of the seed and general depression in growth. The explanation of the phe- nomenon should be sought in the physical domain. The ooze which is very impervious to water and air, because of its closely cemented particles and its fatty content arrests the spread of the roots and greatly prevents the rise and fall of the water. The Scurvy Disease. Among the many forms of disease, of which the causes are not satisfactorily explained, scurvy should be included under the diseases due to material ex- cess. The reason for this is the frequent observation that after the addition of substances tend- ing to increase the alkalinity of a soil, scurvy usually appears in increased amounts. Scurvy or "scab" consists of flatly spread, cork colored bark-like spots formed on the fleshy under- ground root, or storage tu- ber. As long as such a bark- like cleft re- mains super- ficial the dis- ease is called "surface scur- vy." If, on the other hand, the injured places deepen rapid- ly becoming grooves or holes, the dis- ease is called "deep scurvy." In certain cases warty outgrowths appear on the wounded surface, and this condition has been distinguished as "knotted scurvy." Fi£ 52. Carrot diseased with deep scurvy, seen from the most diseased side of the root. Fig. .-1. /, /' and /-, vascular bundle rings arranged in terraces: g. holes in the tissue with tinder-like edges; k, tuberous parenchyma outgrowths on the carrot head, which may be indicated as the overgrowth tissue of the scurvy wound: s. initial stages of the scurvv which extend downward along the root groove (/H: ;-, outer edge of the scurvy hollow; c. its deepest part: Fig. B. Cross-section of tlie carrot near the center of the deep scurvy (c) .■ Vascular bundle rings destroyed by the scviryy /, /' and t- which extend outward like terraces from the deepest part of the wound; 1 shows the poor formation of the outer vascular rings. 368 Besides sugar and fodder beets, potatoes suffer most frequently : also roots of the Umbelliferae, such as celery, carrots, parsley, etc. ; more rarely the fleshy roots of cabbage plants. This condition is characterized by the destruction of the cork layers. For some time they are replaced again and again by the underlying tissues. Fig. 52 illustrates a sugar beet suffering from "zonal deep scurvy" or "girdle scurvy," the worst form of this disease. The beet is 7 to 8 cm. thick at its head, but is circular only at the top ; while on both sides where the roots grow, there is a considerable flattening which disappears again toward the lower end. The flattened sides are depressed like troughs and the centre of the trough is possibly 6 cm. away from the cut surface at the head of the beet. • The inner surface of the trough is wavy because, around the very deep centre, the dififerent layers of the beet flesh rise like terraces above one another towards the outer edge in more or less clearly defined zones. The consistency of the tissue at the edges of the trough is tindery, scurvy-like, i. e. fissured and the fissures traversed by tube-like passages, which initiate a fibrous decomposition of the substance. The passage-like fissures are lined with brown, corked, jagged pieces of tissue, whose sur- faces show a peculiarly grainy decomposition. In spite of the deep decom- position at the place attacked, we find that the beet retains the ability to react, for the edges of the various rings of vascular bundles, because of a new cell formation, curve out like ramparts after the injury. That the growth of the beet at the scurvy places may previously have been somewhat arrested is evident from the fact that, on the injured side of the beet as well as on the opposite side, the different tissue rings are smaller than on the other sides. If cross-sections of the diseased plants are treated with sulfuric acid, it is found that beneath the brown, dry, gradually de- composing tissue layers, which have turned to cork, the intercellular sub- stance of the apparently healthy root flesh assumes a yellowish, wine-red to bright carmine tone. Often some duct groups also seem to be provided with solid balls, or stoppers, which assume the same color when treated with sulfuric acid. Later the intercellular substance is found to be broken up and finally begins to decompose into a grainy slime. To the naked eye the whole process seems a form of dry decomposition. As already mentioned, this form of scurvy which extends so deep into the flesh of the beet, is less frequent. We usually find much flatter, bark- like fissures, occurring in circular areas, and often showing that they have appeared in a rather early developmental stage of the beet, but later have stopped spreading. It is worth noting that, in the zonal deep scurvy, the head of the beet does not seem to be attacked, but the disease becomes visible first at a certain distance below this, in the soil. In too deeply planted beets the first traces of scurvy are often found at the base of the petioles. Very similar phenomena are noticed also in potatoes, carrots, etc. In potatoes, it has been observed that the scurvy formation extends out from the lenticels. If we examine such a lenticel, we perceive without diffi- PART V. MANUAL OF Plant diseases BY PROF. DR. PAUL SORAUER Third Edition— Prof. Dr. Sorauer In Collaboration with Prof. Dr. G. Lindau And Dr. L. Reh Private Docent at the University Assistant in the Museum of Natural History of Berlin in Hamburg TRANSLATED BY FRANCES DORRANGE Volume I NON-PARASITIC DISEASES BY PROF. DR. PAUL SORAUER BERLIN WITH 208 ILLUSTRATIONS IN THE TEXT Copyrighted, 1916 By FRANCES DORRANCE t^ JAN -3 1917 ©CI,A448786 THE RECORD PRESS Wilkes-Bai-re, Pa. l/Wj V SB73) .56 3^9 culty how fit a point it is for parasitic attack. Here, under the skin, formed of plate-hke cork cells (k) (in the subjoined Fig. 53), we find the first stages of lenticel formation beneath the stomata in the form of irregu- lar cells, poor in contents (a). Since this cell formation extends further and further backwards and the cells first formed take up water, swell and rupture the corky cortex, a lenticel is produced which now gives rise to scurvy. From it the loosened cork cells (/) push out in the form of a whitist, moist meal. These cells decay, and the process of decay is con- tinued further inward so that the close pressed, still connected rows of immature cork cells (v) must be sought deeper and deeper in the interior of the tissue. Here the starch (st) disappears from the tissue surrounding the cork cells. Continued moisture will develop very similar conditions in Fig-. 53. Lentical formation on the potato skin. other underground parts of plants. In this process the cork mantel, which has previously acted as a protection, is seriously loosened and broken apart. The scurvy disease has recently been considered to be parasitic and usually is described as due to bacteria. Therefore, it is also treated in the second volume of this manuaP. But there it is emphasized, that the cause is ascribed to very different organisms, by some, to bacteria, and by some to fungi. On the one hand, it is stated that these organisms should be con- sidered as wound parasites, which cannot attack the uninjured cork layer (Kriiger), while, on the other hand, inoculation experiments on immature organs have been carried out successfully under special circumstances. (BoUey). It must also be added here that a great many practical experi- ments have determined beyond question that, as already mentioned, certain substances contained in the soils favor scurvy. This explains the possible 1 See Beet scurvy, p. 46 and Potato scab, p. 75. 370 connection of the scurvy disease with parasitic organisms, which, never- theless, are not specific scurvy organisms. It is much more probable that, in beet soils, saprophytic species, which are generally present, are able, be- cause of definite changes in the composition of the soil, to attack weakened, old beets, or tender young ones. The fact that the healthy vascular bundle rings are more slender where scurvy began, i. e., their growth in breadth has been retarded, proves that the beet has undergone arrestment during the time of the scurvy disease. Supported by Bolley's inoculation experiments^ which prove that beet scurvy and potato scab are due to similar causes, we will take up the main question, viz., what conditions have been determined practically as favoring or causing scurvy. It is Avell known among agriculturalists that marling the field results most frequently in an attack of potato scab. The yellow marl, which contains magnetic oxid (Fe., O4) is said to be the most dangerous. Frank has conducted cidtural experiments- to determine the problem. Scurvy is produced on unsterilized soil, but not on sterilized, even when loamy marl is added to it. As shown by experience, meadow ore. street sweepings, sewer muck, fresh animal manure, liquid manure and Chilean saltpetre all favor scurvy, which fact enforces the decision, that an alkaline reaction afifords the most favorable conditions for the development of scurvy organisms. Bolley^ also arrives at this conclusion. His experi- ments show that the scurvy bacteria which he used develop most rapidly on neutral or basic nutrient soils. Frank's comparative experiments prove that moisture acts favorably, and Bolley emphasizes the observation thnt light, sandy soils, as a rule, yield smooth tubers. Frank's results seem to contradict the observation that a good deal of scurvy can be found in some places in hot, dry years. These apparent contradictions are explained by Thaxter's investi- gations*. He distinguishes between organisms causing the deep scurvy and those causing superficial forms and emphasizes his conclusion that a '^eutral reaction seemed most favorable for the organism which he cultivated. Slight alkalinity, however, like slight acidity, seemed to have a retarding efi^ect. In his experiments young tubers were attacked at any place, older ones on wounded surfaces and especially on lenticels, while nearly ripe tubers were entirely free. All scurvy organisms, therefore, do not seem to require the same con- ditions. In common, however, they prefer lenticels and young organs with a delicate cork covering. In beets, the places where the rootlets arise are especially suitable as points of attack for the micro-organisms. These places become very much broken in wet soils, and this fact explains the assertion that moisture favors the development of scurvy diseases. Wet, 1 Bolley, H. Ij., A. disease of beets, identical with deep scab of potatoes. Gov. Agric. Exp." Stat. f. North Dakota. Bull. 4, 1891. 2 Kampfbuch gegen die Schadlinge unserer Feldfriichte. 1897, p. 177. 3 Zeitschr. f. Pflanzenkrankh. 1901. p. 43. 4 Thaxter, Roland, Tbe Potato Scab. Fourteenth Annual Report of the Con- necticut Agric. Exp. Stat. 1890. '371 heav}^ soils are aerated with difficultA' and if substances are present in the soil, which require large amounts of oxygen, they take it from the living plant when a sufficient amount is not found in the soil. Refuse, sewage, animal manure, ferrous oxid compounds, etc., must be considered as sub- stances which require a great deal of oxygen. We find examples where a piece of land fertilized with stable manure yielded scabby potatoes, while unfertilized land surrounding it yielded a crop free from scurvy^. However, in the decomposition of sewage and other animal refuse, injurious sulfur compounds are produced in the soil, which will naturally act poisonously on the root system and yet favor certain groups of bacteria. As soon as such processes set in, the scurvy bacteria, which prefer neutral or alkaline soil, will thrive. Such conditions may also be produced in clay soils in times of intensive beat and drought ; or they can be brought about by the addition of marl containing iron. In this way might be explained the appearance and often the annual repetition of the scurvy, which may appear after marling but does not always set in. All the above named factors favoring scurvy can actually develop it in certain cases and not in others. The good effect of lime, already observed in many cultural experiments-, may be explained by its characteristic flocculating action in heavy soil, with a conse- quent improvement in physical texture. The soil becomes warmer, more porous, more easily aerated, while the animal manure is more protected from unfavorable decomposition. The easily aerated sandy soils, which do not long" contain highly concentrated soil solutions, are usually free from scurvy. Therefore, the various substances, said to favor scurvy, are not injurious in themselves but only in certain combinations, which direct soil decomposition into unhealthy channels. We have been led to the point of view here expressed by our own experiments^, which were intended to answer the question, as to whether scurvv can be retained constantly in the soil and can spread there. The result was negative. In the two successive experimental years not only the tubers obtained from healthy seed, but, with a very few exceptions, even those originating from scabby potatoes were healthy. Thus it is clear that the condition of the seed does not necessarily determine that the scab dis- ease will be present in open land, and so the much recommended steriliza- tion is unnecessary. The recommendations for combatting the disease must be based on a change in the constitution of the soil and especially on the avoidance of substances which favor scurvy. In regard to the oft-asserted injuriousness of lime, my experiments have proved that tubers, some of which were brought directly in contact with the lime, remained perfectly smooth skinned and healthA^ Recentlv, substances have been introduced 1 Arb. d. D. Landw.-Ges. Jahresbericht d. Sonderausschusses f. Pflanzen- schutz 1904. 2 Kriig-er, Fr., Untersuchungen iiber den Giirtelschorf der Zuckerriiben. Zeit- schrift d. Ver. d. Deutsch. Zuckerindustrie. Nov. 1904. 3 Zeitschr. f. Pflanzenkrankh. 1S99, p. 182. 372 into trade which are said to increase the reaction of the soil (for example, sulfarin). In connection with scurvy diseases of edible roots, we would like to call attention also to similar phenomena on smooth barked young trees, which have not as yet been studied. Lindens, elms, oaks, etc., on certain kinds of soil (i. e. moor-soil) had round, rough splits in the bark, which increased greatly in extent adjacent to the adventitious buds or shoots. This bark scurvy is frequent near large cities, where the base of the tree is exposed to debris of all kinds. Another phenomenon found in barley and wheat, which should be in- cluded in this group, is "spotted necrosis," i. e., the appearance of deep, dark reddish brown, dying spots at the tip and along the edge of the grain leaves. Up to the present, I have found the disease most extensively in heavy, clayey, or moor soil, which had had abundant potassium fertilization and also in regions with a deposit of ashes. Progressive Metamorphosis. W'hile, in the cases already discussed in this chapter, we have empha- sized as the common characteristic of all the phenomena, the influence of unsuitable concentrations of the soil solution, because of which the plant suffers, we will now consider the cases in which the plastic building sub- stances have been increased out of proportion to their utilization. Here, too, an excessive supply of nutrients in the soil does not give rise necessarily to this condition, but, for various reasons, a disturbance in the equilibrium in the formative direction of the individual may occur, that is to say, a change in the utilization of the plastic food materials. Examples of this are those phenomena grouped under progressive metamorphosis, such as the transformation of leaf organs into a morpho- logically higher developmental form. Teratology classifies such transfor- mations under the heads "petalody'' and "pistillody," i. e., cases in which the calyx bracts become petal-like, or parts of the corolla assume the char- acter of the stamens, or the organs actually belonging to the androe- cium circle are changed into carpels. Numerous examples of peta- lody are furnished by the cultivated forms of our Primulae and Ranunculi. We find the best instances of pistillody in the poppy (Papaver sornni- ferum). Tn this plant, as in the dififerent varieties of cabbage, long con- tinued cultivation has so disturbed the morphological rules, that the organs tend to transformation. A most interesting case may be found in the poppy heads which, at the base, bear a circle of many small, woody primordia of smaller heads (stamens which have been changed into carpels). Tn double tuberous Begonias, tulips and other Tlliaceae, specimens are found in which the stamens have been transformed into carpels with seed primordia. Re- lated to this are the phenomena of the "cone malady" in conifers, especially in pines, as illustrated in Fig. 54. 373 In the majority of cases, the cones at the base of an annual shoot he close together and remain small- er than normal ones, but yield seeds capable of ger- mination. The production of such cones, instead of staminate flowers, points to a local excess of con- centrated, plastic food ma- terial. Borggreve^ has made a corroborative observa- tion. He found, the year after transplanting several spruces, possibly 15 years old, in the Botanical Gar- dens at Bonn, that the terminal shoot had been transformed into a pistil- late inflorescence. If an excess of plastic building substances partici- pates in this, so that the various leaf members of a blossom retain their form, but the axis is lengthened, we speak of the disunion of parts of the blossom normally united as aposta- sis. The calyx, for ex- ample, then appears sepa- rated from the corolla by a long internode, the cor- olla in turn from the stamens, etc. The most perfect form of over-nutrition of the blossoms is found in the so-called "Rose-Kings," i. e., in the roses in which a new blossom springs from the center of an older one. 1 Forstliche Blatter 18S0. Vol. 17, p. 245. Fiff. 54. Cone disease in the Scotch pine. (After Nobbe.) 374 or new blossoms appear laterally. A\'e term such cases proliferous shoot development {proliferation). Unusual buds arise inside of one blossom or of one inflorescence. Fig. 55. Sprouting- pears. Such buds sometimes develop into blossoms, sometimes into leafy shoots. If such an adventitious bud stands in the centre of a blossom, so that the axis of the flower appears to end in it and can be continued only by the development of this bud, we call such a proliferation diaphysis. If, on the other hand, the adventitious bud appears in the axil of any member of the inflorescence, or the bracts, the formative variation bears the name 375 of axillary proliferation, the appearance of buds within the flower (ecblastesis). Sprouts in the centre of the blossoms are more frequent than those in the axils, a circumstance probably connected with the fact, that all shoots, which form the direct continuation of the erect axis, obtain water and nutrition more easily than do lateral branches. In favor of this is also the very rare occurrence of proliferations in flowers which stand isolated in the axils of leaves. The doubling of blossoms in the Compositae consists, as is well-known, mostly in the change of the normally tubular labiate flowers into brightly colored ligulate flowers (ray florets). Proliferation in the Compositae has often been ob- served, when, instead of the separate florets, a whole head is produced at the base of the inflorescence. Thus Magnus' reports specimens of Bellis perennis which had numerous, stemmed secondary heads around the edge of its heads. The same phenomenon has been observed at times on Crepis biennis, L. as well as on Cirsium arvense Scop. Everywhere the individual florets were so developed that they had a more or less long stemmed axis, often provided with dry, mem- braneous leaflets and crowned by a small but perfect flower head. In fact, on the edge of each secondary head, tertiarv' heads and even heads of later orders may develop. Similarly sprouts from phanerogamic fruits are not rare. The best known examples are found in our pomaceous fruits and, of these, more often in pears than in apples. We give in Fig. 55 an illustration of sprouting pears, in which one or more secondary fruits develop on the primary fruit. This phenomenon may be explained by considering the fruits of our pomaceous fruit as twigs, of which the bark has developed extraordinarily. Usually, the tip of the twig ends in the carpels. These develop into a core and bear the seeds inside this core. The bark of the twig swells, depressing more and more the terminal blossom above the seed primordia and be- comes the flesh of the fruit by material changes and cell- elongation. As in tlie proliferation of the rose, a pear blossom may also develop a secondary blossom in its centre, in which the small axillary crown between the embryonic carpels elongates ; the carpels are pressed apart, or do not develop at all. This secondary blossom matures into a twig, sprouting from the firts pear. This develops a blossom at its tip or, without it, swells out like a top, thus producing a second pear on the first one. If these twigs do not develop sexual organs, 1 Sitzungsber d. Sitz. V. 28. Nov. Bot. Ver. d. Prov. Brandenburg XXI, 1879. Fig. 56. Larch cone with growth of the axis continued. (After Nobbe.) 376 the monstrous pears have no core. If the prohferous axis of the fruit divides, lateral, smaller pears sprout around the central one. In apples, the ability to sprout often extends only to some branches of the vascular bundles in the fruit. Then a knot swells out at the side and can increase to a small secondary fruit. If the lateral sprout develops and produces an actual bud, we find two cores lying diagonally above one another. This case bears great resemblance to double fruits which arise from the union of two separated, laterally placed embryonic flowers. A simple case is the development of a dormant leaf bud on the unthickencd part of the fruit, i. e., the stem. In conifers, prohferation is found in the continued growth of the cone axis into a needled branch; this may be found most often in larches (see Fig. 56). Among the phenomena in which an excess of plastic food material is manifest, belongs also the occurrence of leaves at places on the axis which normally should be leafless, Chorisis, and the increase of the leaf organs in a node {Doubling, Dedoublement) as also the multiplication of parts of a compound leaf (Pleophylly). The most common example of the last case is the four-leafed clover. Tammes\ in a recent study of this case, mentions that De Vries, by continued selection, has created a race, the in- dividuals of which possess four to seven leaves. This is also a very good example of the way in which phenomena of over-nutrition, once produced accidentally, may become hereditary. We referred to this point also in treating of fasciation. In the clover, individual veins and even the mid- rib seem more vigorous and are divided, at times extending even into the petiole. Then each part of the divided petiole bears leaflets at its tip. Pleophylly also deceases on the branches of the second, third and fourth order in which the supply of nutrients decreases in contrast to the first produced, vigorous axes. We find less striking examples in all plants. Leaves which display especially strongly developed leaf surfaces and then a forking of the different veins are found everywhere on the branches most favorably located for the supply of nutrition. Such luxuriantly developed forms are found most often in the so-called sprouting of the stock, i. e. sprouts growing from dormant and adventitious buds on the stumps of felled trees (for example, Populus and Morus). The size proportions usually far exceed the average and the leaf forms often vary from the type, even to unrecognizable forms. In these cases the newly produced shoots have the whole store of reserve substance of the tree stump at their disposal, which causes their enormously increased growth. As related phenomena we will also name here the witches-broom which we may pronounce a "twig -malady." The accumulation of the plastic food material in various places in the branch, which gradually seeks utilization 1 Tammes, Tine, Ein Beitrag zur Kenntnis von Trifolium pratense quinquefolium de Vries, Bot. Zeit. 1904, Part XI, p. 211. 377 in a proleptic bunched formation of branches may be produced, in the ma- jority of cases, by parasitic stimulation. As a rule, the abnormally formed axes deviate structurally from normal ones^. Further, there belongs here retrogression to the juvenile form- in trees which sprout vigorously after great injury. The so-called rosette shoots, as shown for a pine in Fig. 57, result from local over-nutrition, due to the fact that the trees have previously suffered very great loss of foliage (usually from the attacks of caterpillars). The mobilized building sub- stances, which have thus lost their province of nutrition, now stream toward the dormant buds, lying between the normal clusters of needles or more clearly recognizable in the form of weak whirls, and cause them to sprout. Instead of clusters of needles, simple broad, sword-like needles with serrate edges are then produced. In their axils, as shown in the figure, the normal short shoots (clusters of needles) may again be formed. If we consider these cases as a whole, we perceive at once a feature common to all. It is the excessive presence of build- ing material in one part of the axis. In- deed, by over-nutrition, organic sub- stances, actually newly formed by the leaf apparatus, are placed at the disposal of a part of the axis, or an accumulation of the structural material is produced pig. 57. Rosette shoot of a locally since the mobilized reserve sub- Scotch pine. stance does not find its normal utilization , ,, , f.u ■ , 111 the .ixils 01 the simple sword-hke needles due to some injury such as attacks of are shown the short shoots with double J J needles. (Enlar.ered.) (After Katzeburo.) caterpillers, pruning, storms, etc. If this excessive material reaches the existing primordial organ, it becomes manifest in the increased development of the normal form, or, within the compass of progressive metamorphosis, of other organic forms. If the structural substances reach a vegetative point, additional organs are formed. Each vegetative point is always the product of the food at its command. It retains its distinctive morphology only as long as the nutritive process re- mains the usual one. If the amount of structural material is increased, the vegetative point forms additional primordial organs, thus changing the laws of the leaf arrangement, determined by heredity. New normal, vegetative points may develop in the form of buds. There are, therefore, no steadfast characteristics in an organism and cultivation constantly changes the in- herited structural type. 1 Compare Zang-, Wilh., Untersuch. iiber die Entstehung- des Kiefernhexen- besens. Ber. d. Kg-1. Lehranstalt f. Weinbau usw. Geisenheim 1905, p. 235. Abun- dant material has been furnished recently in the Naturwiss. Zeitschr. f. Land- u. Forstwirtschaft. 2 Diels, L,., Jugendformen und Bliitenreife im Pflanzenreich. Berlin 1906. Gebr. Borntrager. 378 Pressure of the Buds (Blastomania A. Br.), In the preceding section the so-called "sprouting of tke stock" has been considered. The phenomena are observable everywhere where large trunks of poplars, oaks, beeches, chestnuts, etc., have been felled. On the cut sur- face of the stump a callus arises from the cambial zone and numerous ad- ventitious buds are formed on this. The various processes of propagation by "leaf-cuttings" of Begonias, Gesnerias, etc., show that new buds may be produced on the cut surfaces of herbaceous stems and leaves. The peculi- arity of "viviparity" should be presupposed as equally well-known, i. e., the development of new vegetative buds from an uninjured leaf blade during the normal course of development (Asplenium, Bryophyllum, etc.). Fre- quently observed, but abnormal cases, are similar formations of buds in Cardamine pratensis, Drosera intermedia^ Arahis pumila, etc. Duchartre found small leafy shoots growing out of leaves of Solanum Lycopersicum. Braun observed such excessive formation of adventitious buds on the leaves and especially on the stems of the cultivated forms of Calliopsis tinctoria. For example, he could count about 300 on a piece of stem possibly 20 cm- long'. Similar cases have also been observed on other plants-, and I found specimens of Pelargonium zonale and P. pcltatum with disc-like, fleshy outgrowths at the base of the stem which were entirely covered with little buds. Individual, more vigorous specimens developed to such a point that even very small leaves could be distinguished; the majority of the buds died because of mutual pressure. A similar fleshy cushion was formed by a Dahlia variabilis tuber which had been forced in a propagating case, in order to develop new eyes from the base of the stem. The shoots were cut off immediately for use as cuttings, whereupon the growing stum.ps de- veloped new lateral shoots from their basal buds, which became more and more numerous but increasingly weaker. In this way a herbaceous goitre gnarl was produced. The Goitre Gnarl of Trees. With the rarely occurring bud accumulation in herbaceous plants, above mentioned, there is naturally connected a formation of goitre gnarls in trees, which, with few exceptions, are produced when the growth in length of normal branch buds is prevented, thus inducing the sprouting of new lateral buds in their stead. The shoots from such buds stand closer, the nearer they are to the base of the branch from which they arise, because the internodes are shortest there. If the tip growth of such shoot primor- dia is limited by injury, or some other cause, such as mutual pressure, they again develop lateral shoots. The illustration from a trunk of Acer campestre in Fig. 58 gives a fine example of a goitre gnarl. After the noticeably thick bark had been 1 Braun. A., tJber abnorme Bildung- von Adventivknospen am krautartigen Stengel von Calliopsis tinctoria, Dec. Verh. d. Bot. Ver. d. Frov. Brandenburg, XII, p. 151. 2 Magnus, P., Verh. d. Bot. Ver. d. Prov. Brandenburg, XII, p. 161. 379 Fig-. 58. Peeled, gnarled growth of the maple. 38o removed, the wood showed the spike-like processes of the dead bud cones. The surface view is given at a; at b the cross-section of the spike-Hke wood cones with the medullar}' parencliyma indicated by the darker inner circles. Similar structures appear in very different tree genera and at will in places on the aerial axis as well as in the buds of the root stock, — ^but here more rarely. The places exposed by the removal of branches are especially preferred. Here the latent and adventitious buds, accumulated at the base of the branch, begin to develop into small shoots. The wood elements. Fig. 59. Formation of gnarls on the branches of Malus sinensis. (After Kissa.) Fig. 60. Cross-section through a gnarl cushion. It is seen that the central part of the individual spikes of the Knarl is produced by a broadening of the medullary ray of the branch axis. (After KisSA.) arising from the cambium of the trunk, take a serpentine course around the bud cones, because they are prevented by them from extending through the cambium. The plastic food material is, therefore, not conducted so readily towards the base of the trunk. But the economy of the tree suffers little, as the gnarled swelling usually occurs on one side of the axis, so that the opposite side lies free and remains constantly accessible for normal nutrition. Nevertheless, normal branch primordia may not always be assumed 'as the points of departure of gnarl formation. There are also cases in which the spikes of the gnarl arise from excrescences of the medullary rays. One 38i such case is treated in a study by Kissa^ on gnarl formation in Malus sinensis, which he conducted under my direction. Fig. 59 shows a branch of gnarl cushions, which have sprouted chiefly from the parenchymatous base of a small fruit shoot. In cross-section, it is seen that the conical spikes represent wood cylinders, of which the central tissues have arisen from broadened medul- lary rays. This kind of medullary ray (Fig. 60) is either primary or is produced only in a later annual ring. The wood layer of the spike is a continuation of the wood ring of the mother branch. As in a normal lateral axis, the spike of the gnarl is covered by its own bark and has also a well de- veloped cambial layer. Just like a normal branch, the spike of the gnarl ramifies (Fig. 60 hm') and lengthens by apical growth. But not one of these axes at any time bears the primordia of leaves or buds. The differentiation of the ' \ tissue of the spike of the gnarl takes place in the very first developmental stages inside the bark of the mother branch, which at first appears to be only swollen. This swelling is produced from the upward forcing of the bark by a num- ber of especially strongly de- veloped medullary rays, pro- vided with meristematic tips. By the further apical growth of these structures, the bark of the mother branch is finally ruptured and the spikes of the gnarl, covered with their own bark, now appear as independent structures. But growth in length soon ends since the bark cap and the underlying meristematic layer dry up. Instead of an apical growth, a basal, lateral sprouting now takes place in the difi:"erent gnarl spikes in the interior of the mother branch. In Fig. 60, the cross-section of a branch covered with gnarls, we see that the medullary rays forming the pith of the spikes are mostly primary, and, therefore, arise from the pith of the mother branch, sp indicates the Fi.E 61. Longitudinal section through the .spikes of a gnarl. (After Kissa.) 1 Kissa, N. W., Kropfmaserbildung bei Pirus Malus sinensis. Zeitschr. fur Pflanzenkrankh. 1900, p. 129. spike ; m, pith ; A, wood ; r^ bark ; c, cambium ; insf, medullary rays of the mother branch ; hm, wood layer ; rm, bark layer of the spike ; n, meristematic cap of the spike; hm', rm', wood and bark, of the lateral sprouts of the gnarl cone; h', second annual ring; h" , third annual ring. Fig. 6 1 is a highly magnified longitudinal section through a spike of a gnarl lying within the bark of the mother branch. Pli, indicates the phel- logen ; k, the cork layer ; Fc, the collenchymatically thickened cells ; Pr, the I)arenchyma of the primary bark of the mother branch, of which the inner- most layers begin to be filled with starch ; St, starcli ; .Ihp, dead layer of parenchyma cells of the primary branch bark ; M, meristematic tip of the spike; /J, cells of the wood layer of the gnarl cone with their pores (For) ; c, cambium ; B, bark of the spike. Therefore, the cone mantel (Abp), composed of the shaded ce-lls, forms the boundary between the spike primordia and the mother bark of the twig and may be clearly recognized as the axial cylinder, since the wood layer (A) is covered with its own bark tissue (B) while, between both, the cambial zone (c) becomes recognizable. The wood cylinder is composed chiefly of very porous parenchymatous wood (For). The bark tissue abounds in starch. The young spike is lengthened l)y the apical growth of its meristematic cap, and gradually compresses the adjoining cells of the mother bark into a yellowish layer (Abp). Above this dead cell layer, the mother bark is still per- fectly healthy and dies only if ruptured by the gnarl cone. In the above statements, we have paid special attention to the structure of the completed gnarl cone, and Vvill now turn to the processes of broadening the medullary rays, which initiate the formation of the gnarl cone. I have studied one such case in Ribes nigrum'^. Fig. 62 h shows the accumulated beady gnarls, up to one millimetre in height, which lie side by side, or partially over-lapping. In the cross-section, Fig. 63, is seen the radiation of the wood ring of the branch, in fan-like or feathery subdivisions, into the body of the gnarl which in this case is not conical, as in Malus sinensis, but resembles a spherical wart. Fig. 63 gives at B the longitudinal section, at A the cross-section of a gnarl wart. -D is the normal axis of the branch with its pith body (m) and wood ring (A), which now seems cleft by the excrescent medullary rays Fig. 62. Bead-like for- mation of gnarls in the black currant. 1 Sorauer, P., Krebs an Ribes nigrum. Zeitschr. f. Pflanzenkrankh. 1891, p. 77. 383 (mst). These medullary rays form the point of departure for the fan-like gnarl formations (sp) which, in later development, display a central wood body (kh) and a distant bark layer (r). A cross-section through the branch at such a warty place shows (Fig. 64) that the wart represents a conical outgrowth (k) of the inner bark, which has ruptured the outer bark layers, but is still covered by them, like lips (/). The edges of the lips are dead, and a m}-celium is usually foimd in the depressions. This grows out into the outer, browned and dying or already dead cells of the primary gnarl cone (p). If we trace back the excrescent tissue which, towards its base, possesses a wood layer com- posed of slender, reticulately thicken- ed vascular cells, passing over into the normal wood ring, it is found to be only a simple outgrowth of a medullary ray. Fig. 64 illustrates an advanced stage of the medullary ray outgrowth of a branch at the end of the first year (the year of its production) ; the left side still shov.s the normal bark structure; at ak are the suberized .1 Fig-. 63. of a Cri)ss-section through a part twig- covered with gnarls. Fig. G4. Cross-section through the bark of the black currant; healthy tissue at the left; at the right a continued outgrowth of the medullary rays. remnants of the outermost bark layers shed in the course of the year of its production, which contain scattered crystals of calcium oxalate. These remnants are still connected in places with the discolored, uninjured cork lamellae (gk) which enclose the twig, like a firm, uniform girdle. Below 3& the cork layer He the collenchymatically thickened bark layers (c o) ; these border on the parenchyma containing the chlorophyll (chl) which is seen separated into zones by tangential calcium oxalate bands (o, o\ o^). The normal bark of the healthy branches also not infrecjuently has tangential cavities along these bands of crystals, produced by the tearing of the cells which remain thin-walled and contain small deposits of calcium oxalate, so that some of the crystals appear to be lying free near the edges of the cavities. In the autumn of the first year, the phloem rays may be seen to extend as far as the first oxalate band (o). Adjacant to these rays, as is usually the case in our woody plants, the cambial zone (c) curves outward over the wood, and then in again, like a bow. This shows that the medullary ray assists in the radial extension of the axis, just as the pith cylinder itself causes the longitudinal stretching. On an average the normal medullary ray (m) retains, inside the bark, the number of cells last formed in the wood and its extension in the bark then depends only on the greater distension of the in- dividual cells. Near the excrescence, however, medullary rays are often found of which the cells have increased in number (in') but have kept essentially their radial, normal elongation. An ex- Fig. 65. Medullary ray in the first traordinary cell increase finally takes stages of tiie gnari formation. place in the ray of the excrescence and the cambial zone curves abruptly outward. This is best seen in the comparatively few cases in which the medullary rays begin with the formation unilaterally of excrescent tissue, as shown in Fig. 65. In this figure m indicates the cells of the medullary ray within the wood ; c the cambial zone wdiich at the right side rises towards the wood (A) and sinks back at the left side over the wood; nr is the normal side of the bark ray, which pushes against the thick-walled bark parenchyma (p) and, in caustic potash, is clearly differentiated from its surrounding tissue by its yellower color. At are indicated the very thin-walled small cell rows containing calcium oxalate; here, near the cambial zone, the walls of these cells show a peculiar granular consistency as an indication of their approaching decomposition. Such a granular, slimy decomposition of these cell bands and the movenient of the calcium deposits to the edges of the cavities thus produced is also found in the normal bark. On the excrescent side (wr) of the bark ray, of which, the cells turn a still darker yellow after treatment with caustic potash, than do those of the normal side, and not infrequently display a distinct knot-like swell- ing of the w^alls, the cambial zone turns abruptly outward (c') and indi- 385 cates that it will curve outward like a cap in the mature tissue of the excrescence. This conical elevation of the cambial zone is visible in Fig-. 64 wc. It forms also an apical region, which, however, does not lie at the outermost tip of the excrescence but always remains covered by bark tissue, which dies from the outside inward until it reaches the meristematic tip of the excrescence cone. The apical as well as the basal region of the meristematic zone of the gnarl cone begins to develop shoots in the following year. Successful sections, showing the full course of a medullary ray. demonstrate that the formation of the secondary axes takes place repeatedly in the same M^ay in which the primar}^ gnarl cone was produced, — viz., by the outgrowth of part of the medullary ray extending through the bark. If the structure of the internodes is traced from the spot already recognizable as the primordium of a gnarl towards the younger parts of the branch, a lack of uniformity in the structure of the medullary rays is seen in the very weakly developed wood ring of the axis. At the base of the buds of the current year in which the immature wood cylinder has only the spiral ducts of the pith crown and a few libriform fibres, together with scattered, reticulated or porous ducts, medullary rays may be found here and there which vary from the other rays in the somewhat greater width of the cells, the somewhat stronger refractive power of the cell walls, the distinct straight course and the further continuation in the bark. It is noteworthy here that the end of the phloem ray extending furthermost into the bark, unlike the other phloem rays, is not more slender than those behind it, but broader, in fact, the broadest of all the cells composing the ray. While, therefore, the normal medullary rays are conical, this one has turned its broadest base toward the periphery. This is the same tendency in growth, found in the older stages, which appear as distinct excrescence rays. Such a differentiation in the earliest stage shows how this goitre gnarl formation is prepared in the first juvenile phases of the axis. Besides the excrescences of the medullary rays, there are still other factors which distend the bark during the encysting of diseased tissue centres. We will return to these points in the section on the "tuber gnarls" which are best treated under the processes of wound healing. I had an opportunity to obser^^e in Primus Padus the formation of goitre gnarls, which branch like witches broom, and have found similar structures on gooseberries^ I also found warty gnarls, similar to those described in Ribes, in Cydonia vulgaris^. On gooseberry bushes near com- post heaps, I could later determine gnarl structures in a form similar to those in the black currant^ In a case in the red cherry currant, of which I heard only recently, long leafy shoots which had no mature buds on their leaf 1 Jahresbericht des Sonderausschusses fiir Pflanzenschutz. Arb. d. Deutsch. ■Landw.-Ges. 1898, p. 145. 2 Ibid. 1899, p. 188. 3 Ibid. 1900, p. 213. 386 axes, developed from a goitre-like gnarl-knot. At the places where the pith bridge in the branch node otherwise leads to the bud, either no meristematic layer was found or it remained covered by a bark cap and developed into a small gnarl spike. Instead of the apical bud, I found accumulations of spike primordia which, in the following year, became actual goitre gnarls from which sprouted weak, leafy branches, as in Acer and Tilia. So far as may be concluded from their description, the remarkable "cylindrical gnarls" (chichi, nipple) on Gingko Biloha may also be in- cluded under the goitre gnarls. According to Kenjiro Fujii^ these chichi or nipples are found to be cylindrical or spherical excrescences which, as a rule, grow down perpendicularly from older branches. Their size varies from the length of a finger to 2 meters, with a thickness of 30 cm. They resemble normal branches, on Mdiich all foliage is lacking. Having reached the soil, they strike root and then are able to develop leaves. Similar for- mations are said to occur on the roots. I have given a more thorough description to this form of the goitre gnarl formation, in which normal embryonic buds do not participate, be- cause it demonstrates the importance of the medullary ray tissue in a way which, as yet, has not received the slightest consideration. Frank- cites references, deserving attention, and also describes earlier observations on gnarl structures. In this, however, the chief concern is the explanation of the wavy course of the wood fibres in gnarled wood. We lay the chief weight on the causes, which lead to the broadening of the medullary rays. The form of goitre gnarl, last described, is only the extreme of a tendency to an excrescence of the medullary rays, which may lead to certain canker swellings. In them, however, processes are involved which are caused by wounds, while here we can ascertain internal disturbances in the equilibrium of the processes of growth, but no external ones. ■ We are concerned with local increases of pressure and turgor con- ditions brought about by the form of nutrition. Kny's^ investigations in this connection, give us the desired proof. He found, in the action of mechani- cal pressure, that, in the meristematic cells of the medullary rays, the di- vision walls take a dififerent direction and produce two-rowed medullary rays. In this instance, the results of mechanical pressure from outside, must, according to our conception of the matter, be afifected also by the mutual pressure of the tissues upon one another, caused by increase- in turgor. Since, however, turgor, — a sufficient water supply being pre- supposed,- — depends on the constitution of the cell contents, on the abundant presence of compounds which attract water, each increased supply of plastic food material will give rise to an increase in turgor and a change of the existing pressure conditions in the different tissue forms. 1 Kenjiro Fujii, On the nature and orig-in of so-called "chichi" (nipple) of Gingko biloba. Bot. Magazine. Vol. IX, No. 105. 2 Frank, A. B., Die Krankheiten der Pflanzen. 2d ed., Part 1, p. 82. 3 Knv, L,.. tJber den Einfluss von Druck und Zug usw. Pringsheims Jahrb. f. wiss. Bot. 1901. Vol, XXXVII, p. 55. 387 Such an increased supply of plastic food material is present, if some disturbance in the normal economy of the plant arises, due to the removal of certain centers of consumption. Goitre gnarl formation arises from the removal of branches necessitated by trimming the trunks and various other kinds of pruning. We find striking examples of this in lindens, poplars, maples, etc., planted along streets ; in an ever-increasing accumulation of buds at the places where branches have been removed. If such gnarl accum- uations occur at especially preferred places, well suited for the work of assimilation, some shoots from these gnarls gain the upperhand and ap- proximate water sprouts. c. Effect of an Excess of Nitrogen. As seen already, a disturbance in the formal development of the plant body by a local accumulation of the prepared building materials is. to be sure, of interest scientifically but has no great disadvantage agriculturally. Indeed, we actually find that the cultivation of such formal variations, as doubled flowers, is often intentionally increased. The conditions are very different, however, if the material processes are unequally affected by the raw materials. Here the question of fertilization comes primarily under consideration and disturbances are especially involved which are produced by an excess of nitrogen and an unequal increase of the supply of potassium. We have already mentioned the fact that the soil will be injuriously influenced physically by an over-abundant supply of soluble fertilizing salts. Even if the salts keep the soil damper, as long as sufficient atmospheric precipitation is present, yet they form a constant menace for the plants in time of drought, because a too highly concentrated soil solution may easily be produced, making more difficult the passage of the water into the plant roots^. This cannot fail to have some effect on the development of the plant. Gerneck's- work throws some light on this subject. He observed in Triticum that root hairs were formed more abundantly if Ca(NO:,)2 was added than if KNO^ was used. In feeding with nitrates, the blades and ears developed late, while, with chlorid and phosphate fertilization, they appeared early. With the latter method, the root cells appeared to be more thickened than with the former, in which the epidermal cells and the leaf schlerenchyma were also the least lignified. We will now discuss a few special cases. Over-Fertilized Seed. The erroneous theory that plants can be brought to unbounded per- fection by abundant fertilization has given rise to an endeavor to give seeds additional help by fertilizing them at the time of sowing. The seeds were either "candied," i. e. coated with a crust of nutrients, or they were soaked 1 Wollny, Ij., Untersuchungen liber den Einflus.s der Salze auf die Boden- feuchtigkeit. Vierteljahrsschr. d. Bayer. Landwirtschaftsrates 1899. Supplement p. 437. - Gerneck, R., tJber die Bedeutung- anorganischer Salze fiir die Entwicklung- und den Bau der hoheren Pflanzen. Gottinger Dissertation, cit. Just, ,Bot. Jahresber. 1902, II, p. 301. 388 in more or less concentrated nutrient solutions. The discovery was then made immediately, that such treatment assistance is often useless, and some- times injurious. Fertilization experiments with beets, made by Fremy and Deherain, throw some light on this point. They proved that ammonium sulfate and potassium salts have an injurious effect on the germinative process, and they also found that germination failed entirely, even with a concentration of 0.2 per cent. The results of soaking experiments made by Tautphous^ with beans, peas, maize, rape, rye and wheat proved that seeds soaked in distilled water germinated best of all and that the capacity for germination was the more reduced, the more concentrated the solutions (potassium chlo- rid. sodium chlorid, (commercial) sodium nitrate, potassium sulfate, potas- sium phosphate and calcium nitrate in a solution of 0.5 to 5 per cent.). Rape germinated in a 2 per cent, solution almost as well as in distilled water, while the other seeds were considerably impaired, even in a 0.5 per cent, solution. The development of the seedlings was considerably more lux- uriant in a 3 per cent, sodium chlorid solution than in distilled water. Fleischer- reports on an experiment made in East Prussia, in fertiliz- ing potato seed with kainit and superphosphates ; a considerable number did not sprout and at the time of harvesting were found unchanged in the soil. The analysis of these tubers gave a content of pure ash nearly twice as great as the average values given in Wolflf's ash analyses. In a thousand parts of dry weight the ungerminated tubers, compared with normal ones, contained potassium in the proportion of 37 to 22. While the calcium con- tent was almost the same in the diseased and normal tubers, the magnesium was apparently twice as great in the former ; the phosphoric acid almost double, and the chlorin content thirteen times as great as in the normal tubers. The sulfuric acid also increased to four times the amount in one thousand parts of dry weight, so that it is evident that exactly the elements of the kainit (potassium, sodium, magnesia, sulfuric acid and chlorin) had undergone an unusual increase in the ash of the unsprouted tubers. In the present case, the fertilizer was applied in the spring directly before the potatoes were planted, not sometime previous to planting, as prescribed in the directions for the use of kainit. In Fittbogen's" field experiments with oats, which had been mixed in a gruel of superphosphate before sowing, the plot sown with candied seed yielded less than did that with unfertilized seed. If, on the other hand, the superphosphate was diluted with sawdust, the yield was the heaviest of all. Probably the sulfuric acid hydrate which often appears, together with phosphoric acid hydrate, also acts injuriously in direct contact with the superphosphate. Briigmann'* also reports on the injurious action of fer- 1 Tautphfpus. v., Die Keimung- der Samen bei verschiedener BeschafCenheit derselben. cit. Bot. Jahresber. 1876, II, p. 117. 2 Beobachtungen liber den schadllchen Einflufs der Kainit- und Superphosphat- diingung- auf die Keimfahigkeit der Kartoffeln. Biederniann's Centralbl. 1880, p. 765. 3 Deutsche landwirtschaftl. Presse 1877, No. 81. 4 Hannover'sclie landwirtsch. Zeit. 1881, No. 12. 389 tiliers made soluble by sulfuric acid. This action was very evident in dry springs, and, in fact, on v^dieat as well as on other cultivated plants. In seeds, the injurious effect of the "candying" will be the less felt the longer the seed lies in the sojl, before sprouting, for then frequent rains can wash more of the fertilizing salt into the surrounding soil. This has been demonstrated in earlier experiments in Salzmunde\ Over-Fertilized Beets. Common experience with present intensive beet cultivation, shows that an increased nitrogen supply increases the harvest in bulk, but reduces the sugar content. For this reason we will give only one proof that shows the importance of the form in which the nitrogen is applied. PagnouP analyzed three beets, of which the first (H) had been watered several times with a solution of (commercial) nitrate of soda; the second (J) with ammonium sulfate; while the third (K) represented a normal beet, har- vested at the same time. H. J. K. The harvest weight amounted to 4i45g 26/Og ySsg Density of the sap amounted to 1.026 1.040 1.046 Percentage of sugar in the beet substance amounted to 3.9 6.3 8.3 CO2, and Chloral alkalies in 100 parts beet substance amounted to 1.991 0.924 0.814 The amount of these in 100 parts sugar is 28.0 14.6 9.8 It is evident that with nitrogen fertilization the amount of fresh sub- stance harvested has increased three and a half to five times that obtained with normal cultivation, but the sugar percentage has fallen to one-half. The comparison of the effect of the nitric nitrogen with that of am- moniacal nitrogen is especially interesting. Mention was made above that the latter gives rise to a considerably greater ammonium content in the beet substance. Miiller-Thurgau's recent experiments" show that the nitrogen fertiUzed plants have a heightened respiration, which may well be the result of a heightened conversion of cane sugar into the directly reducing sugar. On an average every 6 beets contained Sugar, directly reducing, Cane sugar Beets rich in nitrogen 0.34 per cent. 8.27 per cent. Beets poorer in nitrogen 0.04 per cent. 14-39 P^r cent. An idea of the processes which are initiated by a superabundant nitro- gen supply may be obtained from the statements of Pfeiffer-Wendessen*, 1 Jahresber. f. Agrikulturchemie 186.3, p. 60. ~ Annules agronomiques 1876, p. 321. 3 s. tJberdiingte Kartoffeln. p. 390. 4 Bericht liber die Genei^alversammlung d. landwirtschaftl. Centralver. f. d. Herzogtum Braunschweig. Blatter f. Zuckerrubenbau 1896, No. 8. 390 who is of the opinion that in any case the nitrogen is transformed into proteins, which, in combination with calcium, are decomposed into asparagin, glutamin and corresponding organic salts. These form soluble salts with calcium, which in turn are found again in the sugar extractives, etc. Schultze also characterizes the incompletely utilized, intermediary nitrogen compounds as essential constituents of the syrup which impair the crystal- lization of the sugar. In the plant itself, as in sugar manufacture, the com- pounds here named may retard the precipitation of the sugar, and thus explain the condition of unripeness and of small sugar content in the over- manured beets. Besides the delay in ripening, the beets do not keep well when stored in piles. Phosphoric acid improves the quality; the juice of beets, which had been over- fertilized with phosphoric acid and badly polarized, contained the fewest elements which prevent the crystallization of the sugar. Good and bad experimental results have been obtained from top dressing chiefly with Chile saltpetre. This condition is observed in almost all experiments. Besides the quantity used, the result depends also on the way in which the plant utilizes the fertilizer. This differs greatly according to the variety, the density of the soil, the way it is worked, the locality and the weather. Reference should be made to Kuntze-Delitsch's^ observations on top dressing. He found that the soil easily forms a crust, causing the young beets to die in spots because of a lack of oxygen, while the older ones develop poorly. In any case, fertilization with Chile saltpetre should be followed immediately by harrowing-. Opinions differ as to the advisability of using nitrogen fertilizers with seed beets. While it is asserted by some that the quality of the strain de- clines, Wilfarth^, on the strength of his experiments, contradicts this statement. Over-Fertilized Potatoes. The effects of over- fertilizing potatoes with nitrogenous fertilizers are the same as for beets. Miiller-Thurgau's^ results show for both that an abundant nitrogen fertilization causes a stronger leaf development with a greater chlorophyll content. At the same time, the formation of starch is impeded; the starch is more rapidly dissolved in the leaves, and smaller quantities are stored. The organs show a greater glycose content, the re- serve substances are more rapidly dissolved, the nitrogen compounds are more extensively transformed, while respiration is heightened and growth increased. A poorer keeping quality of the tubers is correlative with a lesser supply of reserve substances and their more rapid consumption in respiration. 3 cit. Zeitschr. f. Pflanzenkrankh. 1896, p. 310. 2 The action of the perchlorate in the use of Chile saltpetre will be discussed under the section on Injurious gases and liquids. 3 Wilfarth, H., Wirkt eine Stickstoffdungung der Samenriiben schadlich usw. Zeitschr. d. Ver. Deutsch. Zuckerindustrie. Vol. 50, Part 528, p. 59. ■1 Miiller-Thurgau, Dritter Jahresbericht des ptlanzenphysiol. Laboratoriums d. Versuchsstat. Wadensweil. Ziirich 1894, p. 52. 391 But an excess of nitrogen directly promotes decay, while that of calcium phosphate has an opposite effect. I planted in sandy soil, in alternating rows, pieces of healthy tubers from three varieties as different as possible and also pieces from tubers suffering from black dry rot^. This field was divided into two halves absolutely similarly planted, of which one was given large amounts of Chile saltpetre on all the rows, the other Thomas slag. In the healthy seed, in the half fertilized with Qiile saltpetre, the tubers sprouted very imperfectly while almost all the diseased seed had decayed. The results obtained in the plot fertilized with Thomas slag were directly opposite. There the diseased seed yielded very uniform healthy plants. In the last named plot, plants from healthy and diseased seed of all varieties developed shorter shoots with more highly colored foliage. They ripened more rapidly and the harvest was nearly twice as large as from the plot fertilized with Chile saltpetre-. With this might be associated also the phenomenon well-known in practical circles as iron spottedness or the multi-colored condition of pota- toes. Tubers outwardly normal have brown or brownish-gray places in their tissue in the fresh cross-section. In this, the rest of the flesh can be perfectly healthy and remain white, or, exposed to the air, may quickly assume a rusty red color. The spots originally discolored have brown, dead cell walls and many still contain starch. Often, and, in fact, when the cut surface subsequently turns red in the air, only traces of starch may be found in the diseased centres, but sugar is found instead. While some observers think the iron spottedness must be traced to an abundance of acid iron compounds in the soil, others are inclined to be- lieve dampness to be the cause. Many discoveries show, however, that heavy fertilization with stable manure caused the iron-spotted condition in certain varieties, which, in the same year, with chemical fertilization, re- mained healthy^. Tubers which turn red, when cut, are found most fre- quently where an abundant nitrogen fertilization is used. Hence one is justified in considering a multi-colored condition of the flesh to be an indi- cation of nitrogen over- fertilization. Tubers with iron spots, as a rule, yield healthy plants in the following year. Chile Saltpetre With Woody Plants. Janorschke* has investigated the phenomena of nitrogen fertilization without the addition of calcium and phosphoric acid. He found that plants with multi-colored leaves became greener for the first year or two. In dwarf fruits the branches continued to grow almost without interruption until August and even later, which thus prevented the setting of the blossom buds. Attention should also be called to the fact that the effect of the fertilizer 1 Zeitschr. f. Pflanzenkrankh. 1894, p. 12G, und 1895, p. 98. 2 Zeitsch. d. Landwirtschaftskammer f. d. Prov. Schlesien 1899. 3 s. Jahresberichte des Sonderausschusses fiir Pflanzenschutz, herausgegeben V. d. Deutsch. Landw.-Ges. 4 Zeitschr. d. Landwirtschaftskammer f. Schlesien 18S8, No. 34. 392 on trees does net make itself felt until the year following its application, but then has a continuous action up to the third year. From my own ex- periments, in which sewage was used, I consider the increased tendency of the fruit to decay, especially when it begins at the core, as well as the greater susceptibility to frost, to be the effect of a one-sided, excessive nitrogen fertilization. Calcium phosphate counteracts this evil. Experiments with apple trees, abundantly fertilized with saltpetre, showed that the fertilized trees suffered more from aphids than did unfertilized trees\ The foliage of Ailanthus glandulosa growing in well-fertilized positions became yellow and the branches blighted. On the cut surfaces of fresh branches Penicillium developed abundantly. The sugar content of the tissue at this place was very great. In orange plantations, fertilized trees tended to gummosis and the dis- ease called "Die-back" in Florida is traced directly to over-feeding with organic nitrogenous compounds. These orange trees are said also to be more susceptible to insect attacks". Over-Fertilization of Vegetables and Other Field Crops. Although our vegetables, as a whole, in their present form, are the product of a high degree of cultivation, and have adjusted themselves to abundant fertilization, we still often find cases of disease due to over- fertilization, especially where sezvage has been used. There is a perceptible increase of the easily oxidizable substances which turn brown in the air. In this case, the walls of the ducts turn brown and, not infrequently, some of the ducts are filled with an inky fluid. Bacterial decay occurs frequently in over-fertilized plants. Peas and other Leguminoseae withstand least of all an excess of nitrogen while increased adaptation is found in some Um- belliferae, as celery for example. But even here the favorable amount is often exceeded in sewage bed cultivation. If the cut surface of fleshy root tubers becomes rusty, the tubers as a rule have lost in flavor. The more advanced stage, frequently found in vegetables shown in the markets of large cities, consists of an increased sponginess of the tissue and a greater brown spottedncss. Such conditions and the bacterial decay, connected with them, manifest themselves in cabbage plants accustomed to nutrient solutions of the highest concentration. Under such conditions it is ad- visable to add calcium phosphate and to cultivate continuously. Owing to the increased use of rhubarb stalks as a spring sauce, the plants are being cultivated on sewage beds. In such plantations I observed cases where the unusually thick stems were absolutely insipid. Thus a scanty production, or a complete consumption of the organic acids, is con- nected with over- fertilization. In my opinion this regression in the amount 1 Fiinfter Jahresber. d. Grofsherzogl. Obstbauschule zu Friedberg i. d. W. 2 Webber, H., Fertilization of the soil, etc. Yearbook U. S, Depart. Agric. for 1894. Washington 1895, p. 193. 393 of acid associated zvith an excess of nitrogen may also be sought elsewhere and may be the cause of the rapid appearance of bacterial decay^ In the Cucurbitaceae (cucumbers and melons) a concentration of the nutrient solution, not dangerous in itself, can act injuriously if the temper- ature is continuously too low. In this case gum appears most abundantly on the iruit and connected with it a blackening of the ducts is also noticed. In tobacco culture, an excess of nitrogen manifests itself in coarser leaves and a larger nicotine content-. Mention has been made of the fact that sewage fertilization of grain may cause lodging and sterility. ExcESSivB Nitrogen Fertilization for Decorative Plants. Very numerous cases of this may be found. Besides fertilization with sewage and Chile saltpetre, or ammonium sulfate, horn shavings are ex- tensively used, especially for garden plants. Naturally we can cite only a few examples. 1 gave a few plants of Begonia semperflorens an excess of ammonium sulfate. Four days after fertilization the young shoots became discolored at the base and began to drop. The edges of the leaves began to show dirty green areas which later became brown and dried up. These were connected with the healthy tissue at the centre of the leaf by a more transparent transitional zone. In the sun, the wilting became more rapid. The pith and bark were found to be filled with masses of calcium oxalate ; the individual crystals were not as sharp as those in healthy speci- mens but more rounded like tubers. No starch was present in the diseased tissues and the chloroplastids were reduced to small angular grains. The ducts were frequently filled with a brown, granular content. The cell walls of all the tissues were brown. The contents of the epidermal cells of the leaves were brown and granular. Before the decomposition of the chlorophyll grains, brown drops were often found in the contents of the mesophyll cells. In Begonias, as well as in Pelargonium sonale, the leaves discolor and fall off easily wnen dried. I found an unusual number of calcium oxalate crystals in the pith and young bark of the axes of diseased plants. The stems of the Pelargoniums contained in general fewer and smaller starch grains. They were almost entirely lacking in the bark parenchyma, while, in the over- fertilized plants, they were present in abundance. This is an example of the same phenomenon observed in potatoes and beets, — i. e., a poverty in carbohydrates. A slight fertilization with Chile saltpetre, given to freshly rooted Pelar- gonium cuttings at first caused a very luxuriant growth. Later, because of frequent repetition, the efifects became serious; — the leaves drooped, and brown decayed areas appeared on the stem just above the leaf bud. In a a short time these spots encircled the entire stem. Then the leaves fell and 1 See Action of oxalic acid, p. 361. - Schellmann, W., Der Tabak und seine Nahrungsanspriiche. "Der Pflanzer." Herausg. Usambara-Post 1905, No. 5. 394 the whole aerial axis died back to a short stump. New, weak shoots then began to sprout. We have cited this example, in order to show that the effect of over-fertilization, although it takes place through the soil, does not make itself felt at first at the base of the axes but on the peripheral organs, the leaves. In comparative experiments with Fuchsia cuttings^, a continued fer- tilization with small amounts of ammonium sulfate resulted in a noticeable increase in growth and an enlargement of the leaves. The epidermal cells of the leaves had thinner walls and the wood ring of the branches made a weaker development. The starch content was smaller, the chlorophyll con- tent larger, the period of growth lengthened. When the fuchsias were protected from autumnal frosts, by being brought into a greenhouse, they had time to ripen normally, and the differences as compared with unfer- tilized plants disappeared. The fertilized ones had rather the advantage in a greater growth. Here we have a result such as is evident in growing fodder beets. The addition of large amounts of nitrogen retards the ripen- ing process. If the plants can reach maturity before frost, so that the leaves ripen normally, we obtain the desired results from fertilization, i. e., the production of greater amounts of material, with a normal supply of reserve substances. But, as a rule, the climatic conditions prevent the termination of growth and winter finds the organs in an immature condition. The disadvantage of harvesting insufficiently matured plants has been emphasized under "agricultural crops." Such plants have a greater tendency to decay. The same results were obtained with comparative fertilization experi- ments with Erica. The red blossoming varieties developed less vividly red or almost bluish red blossoms in the series of experiments with a one-sided nitrogen fertilization; their habit of growth was more drooping and the blossoms set less abundantly. The fertilized specimens suffered so greatly from Botrytis cinerea in winter that most of them died, while unfertilized plants of the same varieties from the same place came through the winter uninjured. Bluth- carried out an experiment which showed the effect of a highly concentrated solution of all the nutrient substances. The Ericas, in the second year of cultivation, were given continued supplies of a one- tenth per cent, solution of Wagner's nutrient salt. After ten to twelve days the leaves became a darker color and their growth stronger, but the plants showed a greater sensitiveness to the action of the sun and drought, in com- parison with many hundreds of unfertilized specimens of the same variety. The new lateral shoots of certain tender varieties (£. hiemalis, E. congesta, etc.) developed a drooping and often curved habit of growth. Hard needled varieties (£. hlanda, E. mediterranea, E. verticillata, E. mamniosa) retained their erect habit of growth but the buds set in a strikingly small 1 Sorauer, P., Einfluss einseitiger Stickstoffdungung-. Zeitschr. f. Pflanzen- krankheiten 1897, p. 287. 2 Zeitschr. f. Pflanzenkrankh. 1895, p. 186. 395 number, or not at all, while the branches continued growth. Here too, for the most part, the fertilized plants died during the winter from Botrytis. In other fertilization experiments, made with horn shavings on Ericas, there was a luxuriant leaf development at the expense of the blossom buds, but the fertilized plants, during the winter, showed no greater weakness. From the many instances which have come to my notice, I must state the frequent "failure of forced Lilies-of-the-V alley," as due to an excessive nitrogen fertilization. Chile saltpetre and ammonium sulfate are often used when the plants are grown for two years out of doors. The plants grow more luxuriantly and their very strong (mostly blue- tipped) "pips" (bud-cones) deceive the buyer; the formation of the in- florescences, however, is weak. Such plants force with great difficulty and frequently bear flower clusters in which some buds do not mature. Com- parative experiments made by Koopmann^ showed very interesting differ- ences in forcing. When kainit was used as a fertilizer in growing the plants, the flower clusters developed first and the leaves followed very slowly, — on the other hand, when ammonia was used the leaf growth w^as so luxuriant that the flower clusters were entirely hidden by the leaves. In general, potassium may be recommended as a fertilizer for Lilies-of-the- Valley. A. further injurious effect could be determined for Roses. I have be- fore me observations showing that tea roses, among others, Marfchal Niel and Nyphetos, grown indoors, drop their buds after heavy fertilization, or decay at the point where the calyx passes over into the stem. When dis- eased plants had been repotted in a sandy soil poor in nutrients, normal blossoms developed in the following year. I observed similar phenomena of decay in Bourbon and Remontant roses in the open after sewage fertiliza- tion. Here, an application of gypsum gradually decreased the disease. In other garden plants, even in ivy, I had opportunity to observe phe- nomena of decay after an excess of nitrogen (usually in the form of sewage fertilizers, liquid manure, Chile saltpetre and ammonium sulfate). In the majority of cases, I have recommended transplanting the plants into pure sand or a very sandy leaf loam for a year and have tried it myself repeatedly with good results. Leaf Curl of the Potato. We will include here this disease so well-known to potato growers and so often studied scientifically; the causes of which, however, are still un- known. The reason for considering leaf curl here is the deduction from my observations that diseased shoots show characteristic evidences of one- sided nitrogen fertiUzation. Direct results are not involved here, only the after effects in the following year. The parent tuber is either immature in a few eyes, or entirely so. In the following year a diseased condition de- velops in all of the shoots or only in some of them. This limitation of the 1 Zeitschr. f. Pflanzenkrankh. 1894, p. 314. 396 attack is to be emphasized, because, at times, up to the present, observers have emphasized especially that all the stems on a tuber become diseased, i. e.' that the cause of the disease must lie in the whole tuber, while my observations have shown beyond question that the diseased condition may be limited to a few eyes. According to Kiihn^, the disease appeared as an epidemic first in 1770 in England and in 1776 in Germany, causing extraordinary losses. The first symptom is the discoloration of the leaves which no longer have the fresh appearance of healthy plants. The main leaf stem is usually found bent downward or completely rolled up; the various leaflets are folded, curled here and there and covered with brown, usually longish spots. The latter extend as far as the main rib of the leaf and finally to the stem. At first only the superficial cells are brown, later the disease extends deeper into the tissue, even to the pith of the stem. This changes the consistency of the stem from a normal flexibility to a glassy brittleness. In addition, according to Schacht, sugar is found very abundantly in the diseased cells-. If such plants live until harvest time, they either set no tubers at all or only a very few. In the earlier literature, very different causes (including parasitic fungi) are given, as shown by reference to the previous edition of this manual. Newer theories may be found in Frank's^ study. He distinguishes a number of different forms of the disease and, agreeing with me, states that the very beginnings of the diseased condition do not show any fungous action. The cause of the death of the protoplasm in the various brown tissue centers is not known. Differing from my observations, however, Frank emphasizes "that all the shoots of a plant became sick simul- taneously*." In making more extensive cultural experiments, using several varieties, and directed especially to the study of leaf curl, I found that the phenom- ena of disease appeared initially only in one variety {Early Puritan). The diseased plants, scattered among the healthy ones, made only a third as much growth and showed the well-known characteristics, especially the breaking of the curled leaves. Small corky fissures were often found on the petioles. The first stages of the disease on the stems were found in one of the internodes below the surface of the soil, where a blackening of the duct walls could be determined. This characteristic can be traced back, radiating more or less deeply into the tuber which otherwise seems healthy. This shows that the tuber has not carried the disease to the shoot but, conversely. In the same way, the browning of the ducts radiates out from the diseased 1 Kiihn, Jul., Krankheiten d. Kulturgewachse. 1858, p. 200. — Ber. aus. d. physiolog. Laborat. d. landwirtsch. Instituts zu Halle. 1872, Part 1, p. 90. y Bericht an das Kgl. Landesokonomiekollegium liber die Kartoffelpflanze und und deren Krankheiten. 1854, p. 11. 3 Frank, A. B., Die pilzparasitaren Krankheiten der Pflanzen. Breslau 1896, p, 300. — Kampfbuch gegen die Schadlinge unserer Feldfruchte. Berlin, Parey, 1897, p. 217. 4 Kampfbuch p. 222, 397 stem node into the roots, produced at that point, and may be found in the whole part of the axis which is still green, up to the ribs of the last leaves. Especially striking is the sap turgescence in the apparently perfectly healthy parent tuber which exhibits some cells with large unconsumed starch grains. The groups of cells containing the starch lie scattered in the very turgescent parenchyma of the tubers, which shows scarcely any traces of solid cell contents, while the nuclei are large. It is further noteworthy that, just as healthy and diseased shoots may be produced from one tuber, the characteristics of disease on the same stem can often be restricted to definite areas. Healthy eyes may develop on diseased stems and diseased stems, are found in which only half of the vas- cular bundle ring is blackened. Thus, like other diseases connected with the discoloration of the ducts, leaf curl begins to manifest the first symptoms of disease at the periphery. The cuticle blackens most of all. The cell contents began to change color at first to a weak inky color, until the walls and contents have become uni- formly brown, after which the epidermal cell collapses. Where the epidermis borders on the coUenchymatous tissue, the dis- coloration advances in its walls. They become slightly yellowish at first, then reddish yellow (in some varieties a peculiar blood red), and finally brown. This discoloration of the walls, which seems to spread rapidly tangentially, recalls enzymatic activities. The further course of the disease diiifers in the difi^erent varieties, probably because the cell walls vary in construction, some being more loose- ly built, others more solidly. In F.arly Puritan it was observed that the browned cell walls could be attacked by a granular decay, in which small rod-like bacteria probably participated. In these cases the tissue disap- peared, while holes and depressions appeared in the bark tissue of the stem and mycelium was found. In Early Puritan the depressions deepened to the wood ring and, as the disease advanced, their pressure could be dem- onstrated even on the still green tips of the stems. The browning of the ducts, however, did not proceed from them ; it began at the base of the stem and spread only in the vascular system. At the torn places processes of healing often manifested themselves in the pouch-like elongation of the adjacent, healthy bark parenchyma cells. The statement given above, that the symptoms of disease do not uni- versally appear uniformly relates, for example, to the appearance of hrozvn specks on the uncurled leaves. However, in the petioles of these leaves there is exactly the same pale inky filling of the ducts which, in some cases, thickens to a grainy slime ; the walls of the ducts also are browned. The characteristics here described occur separately also in other plants with an excess of nitrogen. If these symptoms are compared with the re- sults of earlier observations, leaf curl may be described as follows. The diseased condition appears most luxuriantly and abundantly on tender early varieties. The harvested tubers are immature, being distinguished by a 398 smoother skin, a lower starch content and a considerably higher potassium content. They are also smaller in size and have a smaller dry weight. Under favorable conditions, healthy plants may often be grown from such tubers. Among the characteristics given, we have emphasized the length of the existence of the parent tuber, which remains turgid and retains starch, because Hiltner^ has recently described such a case belonging here and, in fact, a partial subsequent enlargement of the parent tuber. Different people have made the same observations. In Hiltner's case it was also observed that the plants produced from the turgid tuber developed no tubers below the soil, attached to the stolens, but bore them directly on the lower inter- nodes of the green stems. These stems, however, were only half as long as in normal plants and bore leaves, rolled together, which reminded Hiltner of leaf curl. He thinks that these processes are a result of the use of im- mature tubers for seed. These tubers, after developing the stem, had uti- lized in their own further growth the material obtained by the action of the leaves. Naturally too little organic substance remains for the tubers of the current year. If we accept Hiltner's theor}' as to the production of tubers which re- main turgid, we can infer that leaf curl results from the use of unsuitable seed. The tubers were not sufficiently matured in the previous year. This must also make itself felt in the full development of the individual eyes. While the majority of these had time to develop normally, some may have remained immature and have retained this character when sprouting in the following year. This will explain the fact that often only isolated shoots are found which show leaf curl. The characteristic of immaturity is the marked abundance of potassium and nitrogen compounds with a scanty deposition of carbohydrates as reserve substances. We find such conditions favored by the use of fresh manure with early varieties and drought stops the growth of the tubers prematurely. If an over-supply of nitrogenous compounds, not normally utilized, determines the appearance of leaf curl in the potato, the shrivelling disease of the mulberry tree, and other diseases, to be mentioned under "Enzymatic Diseases," then the symptoms of the blackening of the ducts and rapid bacterial infection, already found, may be explained easily. This theory is further supported by a study made by Appel-, who, under the name "Bacterial-ring disease/' describes the phenomena which often suggest leaf curl. He makes bacteria responsible for the ring disease and "indeed, as in black-leg, not one species alone but a few closely re- lated forms." "These bacteria are undoubtedly present normally in many soils " Influenced by these statements I should like to Include bacterial ring disease under those diseases in which a constitutional weak- ness in the plant and not a parasite determines the phenomenon and favors 1 Hiltner, L., Zur Frage des Abbaues der Kartoffeln. Prakt. Bl. f. Pflanzen- bau und Pflanzenschutz 1905, Pai't 12. 2 Appel, O., Die Bakterien-Ringkrankheit der Kartoffel. Flugrblatt 36 d. Kais. Biolog. Anst. Dahlem. 1906. 399 especially the spread of the bacterial infection. These conditions are simi- lar to those described as leaf curl, in which I likewise have observed decom- position of the tissue b)^ bacteria. It thus seems that we have before us a whole group of potato diseases, with the common characteristic that the ducts turn black. This may be traced to the fact that incompletely consumed nitrogenous compounds make their influence felt in an insufficient development of the carbohydrates. We must seek to overcome this condition to the best of our ability by fulfilling the requirements for a gradual, complete ripening of the tubers on the plant. d. Excess of Calcium and Magnesium. In addition to the observations on the use of lime as mentioned in earlier sections, we will emphasize here first of all Orth's^ warning that it should be supplied to the field in small, frequent doses rather than in one heavy application. Of course, an excess of calcium cannot be determined exactly by defi- nite figures, since the demand of each plant and each field is diflferent. Also, in adding the lime it does not depend at all on the absolute amount of cal- cium supplied but on the proportion to the other nutrients of which the calcium influences the solubility and capacity for transportation. Finally, the weather conditions at the time the lime is applied must be considered. Hofifmann-, from his broad experience, has given many warnings which are of utmost value practically. Calcium is injurious when used in large amounts on exhausted soils. On lighter, active soils, poor in humus, during dry springs, it loosens and dries the soil too much and disturbs the bacterial action. If it is used in the form of marl, it must first be well decomposed in the air, in order that possible injurious elements can be oxidized at the right time. Calcium acts detrimentally in continued drought, and also with stagnant water if it, in the form of so-called "water-lime," is mixed with a good amount of silicic acid, ferric oxide and clay. In wet weather, it be- comes as hard as cement. But even under normal conditions, calcium may be detrimental. We must not forget that, together with the desired efifect of decomposing organic substances, containing nitrogen, and of transforming the ammonia produced into calcium nitrate, ammoniacal compounds are set free. If ammonium nitrate or ammonium sulfate is mixed with calcium carbonate or phosphate, it produces the very soluble calcium chlorid and g\^psum and ammonium carbonate or phosphate. In Wagner's^ experiments (Darmstadt), the loss of nitrogen, produced by the volitalization of ammonia, was observed to be 30 per cent, of that in a fertilization with nitrate. The same losses are pro- duced very easily, if the soil is rich in calcium carbonate, if the ammonium 1 Orth, A.. Kalk- und Mergeldiing-ung-. Anleitung, im Auftrage d. Deutsch. Landw.-Ges. Berlin 1896. 2 Hoffmann, M., Diingungsversuche mit Kalk. Arb. d. D. Landw.-Ges. Part 106. 3 Zeitschr. der Landwirtschaftskammer f. d. Prov. Schlesien. 1904, p. 1683. 400 salt is only superficially worked in so that the sun and wind have abundant access to it. Then the free ammonium carbonate, produced by the trans- formation of the fixed ammonium sulfate, can be removed from the field very quickly. Sandy soils, which at the time are rich in calcium, are on this account not suited for an ammonia fertilization, especially not as a top dressing. This explains why quick lime should not be brought directly into contact with stable manure or other ammonium fertilizers. Besides these reactions, lime also acts on phosphoric acid. This action must not be underestimated. The action of the phosphoric acid on super- phosphate, which is soluble in water, is impaired by the simultaneous use Superphosphate Lime Ammonium sulfite Potassium Tliomas slag Stable manure and guano Kainit Chile Saltpetre Fig. CG. Diagrammatic repi-esentation of the favorable and unfavorable mutual relations of fertilizers to each other. of lime ; but not so much so as the phosphoric acid in Thomas slag, soluble in citric acid. The destructive efifect of lime on phosphoric acid is greatest when used with ground bone. It may be the place here to refer to the mutual relation of fertilizers in order to avoid using them in such a way as to impair their action. Instead of more lengthy descriptions we will reprint a figure borrowed from the "Practical Advisor in Fruit and Garden Culture," 1906, No. 17^ In this diagram, the thin connecting lines signify that the various kinds of fertilizers may always be mixed together. The fertilizers, which appear connected by double lines, may be mixed with one another only very shortly before spreading; while those fertihzers connected in the figure with thick lines may never be mixed together. 1 "Praktischen Ratgeber im Obst- und Gartcnbau." No. 17, 1906. 40I The poisonous effects of an excess of magnesium and the associated theory given by Loew, as to a definite quantitative relation between calcium and magnesium in the soil for obtaining good harvests, have been con- sidered already in the section on "Lack of Calcium" (p. 301). Recently Loew^ has supplemented his earlier statements by calling attention to the fact that the favorable quantitative relation between calcium and mag- nesium in the soil cannot always be fixed by definite figures. It changes as soon as the two bases are made accessible in different degrees for absorp- tion by the plant. Loew's theory is contradicted by experiments made by Meyer-. The emphatic fact here is that heavy additions of calcium as well as of magnesium can greatly impair the yield. Naturally the various plant species behave very dift'erently with the same fertilizer. Given the same quantity of magnesium, the grain and straw yield of oats was lessened, but that of rye was not decreased. GosseP, on the basis of his own experiments, also considers Loew's point of view to be incorrect, yet we think it, nevertheless, worth consider- ation. Too much faith must not be put in definite figures because each cultural experiment offers different conditions. A constant effort must be made to overcome the injurious effects of the magnesium compounds when- ever brought into the soil in great quantities in the fertilizer. Of first im- portance is the great quantity of magnesium chlorid spread on the field with the so-called "waste salts" which reduces the sugar content of beets, the starch content of potatoes, etc. An effort must be made to combine th'e non- absorbable chlorine with a base, especially calcium, so that it can be washed easily into the subsoil. Finally attention must be called to the fact that the same amount of calcium acts injuriously at one time and beneficially at another, according to whether it is added in the forms of calcium carbonate or calcium sulfate. Thus, for example, Suzuki*, found in vegetative experiments with moun- tain rice, that the yield was considerably reduced by an excessive ad- dition of calcium carbonate (the proportion of calcium to magnesium was as 3:1), even if phosphoric acid was present in an easily soluble form. On the other hand the addition of an equivalent amount of gypsum caused an unusual increase in the yield, especially of grain. From this experiment, however, it is evident that the injurious action of an excess of calcium is not always to be sought in a decrease in the looseness of the soil as compared with that found after the use of slightly soluble phosphoric compounds, but probably has its foundation also in the neutralization of the root acids. 1 Loew. O., and Aso, K., tjber verschiedene Grade der Aufnahmefahig-keit von Pflanzennahi-stoffen durch die Pflanzen. Bull. College of Agric. Tokyo. Imp. Univ. Vol. VI. No. 4, cit. Centralbl. f. Agrik.-Chemie 1905, p. 594. 2 Meyer, D., Untersuchungen iiber die Wirkung verschiedener Kalk- und Magnesiaformen. Landw. Jahrbticher Vol. XXXIII, 1904, p. 371. 3 Gossel, Fr., Bedeutung der Kalk- und Magnesiasalze fiir die Pflanzenernah- rung. Vortrag auf d. 75. Naturf. Vers. (s. Cliemikerz. 1903, No. 78). 4 Suzuki, S., tJber die schadliche "Wirkung einer zu starken Kalkung des Bodens. Bull. College of Agric. Tokyo, Imp. University. Vol. VI. cit. Centralbl. f. Agrik.-Chem. 1905, p. 588. 402 By neutralizing the acids of the plant routs the available phosphoric acid will not be so largely absorbed. The great difference between the action of calcium carbonate and that of gypsum is due to the fact that gypsum is taken up from the soil only so far as it is soluble in water (i. e. in the very sUghtest amounts), while the absorption of the carbonate by the plant depends upon the carbonic acid of the root. Excess of Calcium With Grapes. Since the introduction of grapes grown on budded American vines there have been very many complaints of Jaundice. The disease is de- scribed usually as "Chlorosis" ; but according to my conception it must be called "Icterus." Of course, the causes of the yellow condition of the foliage of grapes may differ very greatly, as in other plants. Very frequently, root decay, occurring with or without fungi, plays a role in heavy soils. Vitis Riparia and V. rupcstris, with their weaker root systems are especially sensitive to such soils, while varieties with strong roots (Jacquez, Herbemont, etc.), better adapt themselves^. American vines, however, are grown with great difficulty on soils containing a great deal of calcium in an easily soluble form and not rich in nutrients. In France it was possible to collect the greatest amount of information on this subject. Luedecke- repeats the results of soil investigations which the agricultural society of Cadillac undertook in 1890. The soil which showed no jaundice of the vines and that which showed jaundice contained No jaundice jaundice Phosphoric acid 0.07 per cent. 0.06 per cent. Potassium 0.39 per cent. 0.37 per cent. Calcium 1.81 per cent. i8-93 per cent. Ferric oxid 5.90 per cent. 3.02 per cent. Nitrogen o.io per cent. o.io per cent. The content of both soils in nitrogen, potassium and phosphoric acid, therefore, is about equal ; the ferric oxid percentage is high in both, but the calcium is nearly ten times as great in the soil producing jaundice. In the fertilization experiments undertaken with Chile saltpetre, ammonia, superphosphate, potassium chlorid, magnesium sulfate and iron sulfate (ferric sulfate), only the last gave any satisfactory results. In this ex- perimental plot, the vines formed a great many new roots. The same re- sults were again obtained under similar conditions on soils naturally rich in iron, in which, therefore, the favorable action of fertilization with iron sulfate cannot be ascribed to a previous lack of iron. 1 Eg-er, E., Untersuchungen liber die Metlioden der Schadlingsbekampfung usw. Berlin, Paul Parey, 1905. 2 Luedecke in Zeitschr. f. d. landw. Ver. d. Grossherz. Hessen 1892, No. 41, 1893, No. 2. 4<>3 Such results, proving that jaundice of the grape is due to a high calcium content are found^ frequently as are also observations as to the efifectiveness of the iron sulfate. The question now is, how to explain the injurious effects of calcium and the beneficial action of the so-called iron compounds. Luedecke found that the water coming from the lime soils of Rhenish Hessen has an alkaline reaction, and he found that with an addition of some iron salt (iron stilfate or ferric chlorid), the iron was precipitated. He, therefore, came to the conclusion that, since plants are able to take up iron only in a dissolved form, and since the alkaline water prevents its solution, the grape vines suffer from a lack of iron in spite of the great amount of it in the soil ; they, therefore, become icteric. Viala and Ravaz noticed the injurious action of lime in a neutralization of the cell sap of the roots". i Until we have the results of further experiments, we must be satisfied with the fact that large amounts of easily soluble calcium compounds will produce icterus of the grape, and that abundant additions of iron sulfate have often been found to be useful in combatting it. It is now of the first importance to consider that the affinity of the sulfuric acid of the iron com- pound for calcium is great and forms g^^psum which, only slightly soluble, is proved to be non-injurious, or even beneficial to growth. Eger=^ cites Oberlein-Beblenheim's experimental resuhs, showing that, on rich soils, fertilization with gA'psum considerably increases the yield. Since the addition of gypsum, made at the same time to poor soils, remains absolutely without result, the favorable action of the gypsum may probably be ascribed to its power of loosening up the soil. e. Excess of Potassium. Reference has been made already to the danger to soil constitution of a continued heavy potassium fertilization, and in this it was emphasized that lighter soils and moor soils responded more favorably to the addition of potassium. Recently, however. Hollrung has called attention to another disadvantage of all fertilization with mineral salts.— therefore, of potassium salts also. He refers to Hall's experiments, showing an absolute change in the water conditions in the soils. Hall determined (after 1866) the num- ber of days in one year in which drainage flowed from an unfertilized field, as contrasted with one constantly fertilized with Chile saltpetre. The longer the drainage flows, the more water is removed from the field. Al- though the results fluctuated in the several periods of five years each, which he compared, yet as a whole for the entire length of time, they indicated that in the "salted soils," larger amounts of water had passed into the drainage through the subsoil. This makes possible conclusions as to an unfavorable transformation of the soil. 1 See V. Babo and Mach, Handbuch des Weinbaues and der Kellerwirtschaft (s. Eger). 2 See Eger. 3 Loc. cit. p. 84. 404 The effect of potassium salts on the plant depends on the form of the fertilizing salt and the soil on which it is used^ The question arises here as to the part played by the accessory salts incorporated in the soil with the addition of potassium. At present, kainit and the 40 per cent, potas- sium salt are used more extensively, ^^^ith kainit, 3^4 cwt. should be used if one desires to add as much potassium as is present in one cwt. of 40 per cent, potassium salt. Among the accessory salts introduced in the kainit, sodium chlorid plays a prominent role. Besides this, magnesium sulfate and magnesium chlorid come under consideration. The individual plants behave very differently with sodium chlorid. Its effect on sugar beets is very good, but potatoes are very^ sensitive to it". The results with sugar beets, however, are rather deceptive. According to Aducco and AVohltmann's experiments, the amount of beet substance harvested is in- creased, but the quotient of purity and the sugar content are reduced. On account of the accessor}^ salts, Schneidewind and Ringleben^ tested raw potassium salts with different potassium compounds as contrasted with the highly concentrated forms. It was shown for a mixture of clover and grass, and for oats, sugar beets and potatoes, that kainit was superior to potassium chlorid and potassium sulfate, if sufficient amounts of calciimi carbonate were present. If these were lacking, opposite results were ob- tained. If the slightly soluble gypsum was used, instead of calcium car- bonate, kainit proved to be especially injurious for the mixture of clover and grass, but less so for oats. In potatoes the action was favorable if the soils were poor in potassium. With an increase of potassium, the effect of excess became evident, i. e. the starch content was lowered. Szollema^ found that the decrease of starch, effected by the chlorid, which is connected with a greater abundance of water, was somewhat greater in the varieties of potatoes naturally rich in starch than in those poor in starch. When plants are very sensitive to the chlorine compounds of the raw potassium salts, as, for example, kainit, the loss of potassium by its partial leaching from the soil during the autumn and winter, is really an advantage in so far as many of the dangerous accessory salts (sodium chlorid and magnesium chlorid), are washed out at the same time; therefore, while actually less potassium remains in the soil, it becomes more effective, be- cause it is in a purer form. This leaching of the potassium must be taken into consideration in soils with only small amounts of calcium and other such absorbents, as, for example, in light, sandy, and moor soils^ Concerning the disadvantageous eft'ects of potassium fertilization on cultivated plants, other than those already named, we will mention further 1 Blatter fiir Zuckerriibenbau 1905, p. 62. - Blatter fiir Zuckerriibenbau 1905, p. 89. 3 Schneidewind, W., and Ringleben, O., Die Wirkung- der Kalirohstoffe und der reinen Kalisalze bei ver.schiedenen Kalkformen. Landwirtsch. Jahrib. 1904. Vol. XXXIII, p. 353. ■4 Szollema, D., tJber den Einfluss von Chlor- und anderen in den Stassfurter Rohsalzen vorl-commenden Verbindung-en etc. cit. Centralbl. f. Agrikultur-Chemie 1901. p. 516. 5 Schneidewind, Auswaschen des Kalis im Winter, Zeit-schr. d. I^andwirtschafts- kammer f. Schlesien 1904. No. 14, p. 471. 405 the effect on Tobacco observed by Behrens\ His experiments showed that the water content of the leaves increased considerably if potassium sulfate was added to stable manure and that this hastened greatly the decay of the leaves which dry with difficulty in the air. This probably is con- nected with the increase in turgor observed by Copeland, which is due to potassium salts (Potash). Sodium salts (soda) did not show this physi- ological reaction-. The complaint of farmers that continued potassium fertilization re- duces fhc quality of pasture plants so that animals fed with such hay, grow thin, should be considered here. Even if the statement that this ex- cessive action occurs is still contestible, nevertheless it is true, that a de- crease in flavor has been observed in the hay from fields repeatedly fertilized with kainit, or with kainit and Thomas slag^. The injuries appearing in different field crops and fruit trees are gen- erally the result of an unexpedient use of potassium salts, a practice often followed by serious injurv'*. These will best be prevented by not using potassium in large amounts on heavy soils, by not spreading the salt with the seed, by repeated, smaller applications of potassium and (in plants especially sensitive to chlorine, as, for example, potatoes) by the use of the 40 per cent, potassium salt, and of other purified, highly concentrated com- pounds, instead of the commercial salts. The frequent use of potassium in small quantities is often beneficial because the calcium in the soil water, containing carbon dioxid, will be more easily leached out the more potassium salts are added to the soil, since the calcium is converted by them into soluble compounds. Hoffman^ recommends the use of a high per cent, commercial marl, where possible, and its application in at least 5 to y^A double centner*' per acre. If the soil is liable to become encrusted {"he baked"), at least 2^4 double centner of quick lime should be turned under superficially in the autumn and repeated possibly four years later. f. Excess of Phosphoric Acid. Injuries due to an excess of phosphoric acid are rare. They can only be expected where superphosphates are used abundantly, i. e. where some phosphoric acid, soluble in water, is present. The phosphoric acid of Thomas slag, soluble in citric acid, is less mobile. However, even the phos- phoric acid, soluble in water, passes over immediately into an insoluble form since the di-phosphates of calcium, magnesium, aluminum and iron formed in the soil, are dissolved only very slowly by the carbon dioxid of 1 Behrens, J., Weitere Beitrage zur Kenntnis der Tabakspflanze. Landw. Versuchsstationen 1899, p. 214. 2 Bot. Jahresber. 1897, I, p. 72. 3 Mitteilungen d. Deutsch. Landw. -Ges. vom 11. Marz 1905. •t Clausen, Resultate von Obstbaunadungungen. Landwirt.schaftl. Jahrbiicher Vol. XXXin. p. 939. 3 Hoffmann, M., Die Kalisalze. Anleitung. Herausg. v. d. Deutsch. Landw. Gesellsch. 3d ed., 1905. « A double centner equals 220 lbs. 4o6 the soil and the acid secretions of the roots. Injury from superphosphates is, therefore, to be feared even with heavy appUcations only on soils which are poor in calcium, iron and aluminum carbonates. There are only a small number of experiments on this subject. The careful investigations, made at the experimental station in Bernburg, on sugar beets^ fertilized with the monobasic calcium phosphate, i. e., excess of phosphoric acid soluble in water, have shown that the sugar content does not decrease and also that the amxounts of beet substance and non-sugar have remained the same as in normally fertilized beets. So far as my own experience goes, an excess of phosphoric acid may manifest itself in a shortening of the root system,— the usual result of culture in all highly concentrated solutions, and also in shortening the vegetative period with a premature ripening of the crop. The plants do not develop fully, the leaves turn yellow prematurely, and, accordingly, the yield is smaller than it would otherwise have been. g. Excess of Carbon Dioxid. Experiments on the effect of carbon dioxid content in the air and soil, greatly in excess of the normal, have led to contradictory results. While some observers have recognized only injurious effects, others report a satisfactory development. These apparent contradictions may be due to the fact that with carbon dioxid, as with all other nutritive substances, the effect depends upon how simultaneous the activity of all the other growth factors may be. The activity of the plants is generally adjusted to the small normal carbon dioxid content of the air-. They sometimes respond to a greater increase of carbon dioxid by arresting growth, sometimes by increasing it, depending upon whether the carbon dioxid increase occurs suddenly, or gradually, and whether the amount of light and warmth, water and nutrients permits the individual utilization of the increased amount of carbon dioxid. Godlewski" has substantiated this point of view by experiment. Our hot bed plants furnish abundant proof of the favorable affect. According to E. Demoussy's investigations*, this is due not only to an in- creased warmth, but actually also to an increase of the carbon dioxid in the air of hot beds, sometimes amounting to more than two thousandths parts. In comparative cultures, the air of the hot bed, which after careful testing showed no ammonia, had furnished nearly three times the harvested weight of plants grown in ordinary air under otherwise similar conditions. 1 See lecture by H. Roemer; cit. Blatter f. Zuckerrubenbau 1905, p. 229. 2 Brown, F., and. Escombe, F., Der Einfluss wechselnden Kohlensauregehaltes der Liuft auf' den photosynthetischen Prozess der Blatter und auf den Wachstums- modus der Pflanzen. — Farmer, J., & Chandler, S., tJber den Einfluss eines tJber- schusses von Kohlensaure in der Luft auf die Foiin und den inneren Bau der Pflanzen. Proceed. R. See. LXX. cit. Centralbl. f. Agrik.-Chemie 1903, p. 586. a s. Sachs, Arbeit, d. Bot. Instituts zu Wiirzburg. Part III. 4 Compt. rend, de I'Acad. d. sciences 1904. cit. Centralbl. f. Agrik.-Chemie 1904, Part 11, p. 745. 407 The fact that experiments in steriUzed soil, as contrasted with those in non-sterilized soil, resulted in much smaller amounts of yield, is ascribed by Demoussy to the killing of the micro-organisms which, by their activity, contribute to the decomposition of the carbon dioxid production. It is also probable that the growth of plants close to the ground is favored by the carbon dioxid constantly given off by the soil, since it has often been de- termined that air at the surface of the soil contains more than three ten thousandths carbon dioxid. In air in which the carbon dioxid has a tension five times above the normal, a great many different plants increased about possibly 60 per cent, more in weight than they did in ordinary air. These also blossomed earlier and more abundantly^. If plants, which naturally behave differently according to species and individuality, are no longer able to utilize the carbon dioxid given them, their life functions must cease. Kosaroff- distinguishes between a specific- ally injurious effect, and one due indirectly to the decrease of the partial pressure, or rather, the removal of oxygen. As a result of the depression of the transpiratory current, the plants wilt. Bohm^, like Saussure, ob- served that germination was retarded, in that with an increase of carbon dioxid, the roots and stems constantly became shorter and shorter. The chlorophyll formation and assimilation were considerably decreased. Neither can geotropism be perceived in articulated plants (Gramineae Commelinaceae, etc.) in a carbon dioxid atmosphere, nor may a stimulus, found in the air, initiate any bending*. Finally, when carbon dioxid begins to be excessive, the effect may first be beneficial, then later gradually harmful. Reference should be made here to the experimental results obtained by Brown and Farmer^. They observed that, with an increased carbon dioxid content in the air, all the parts containing chlorophyll became a darker green after 8 to 10 days, and the starch content increased, but the internodes became short and thick, the leaves rolled up even to the point of deformity, the flower buds dropped, or their primordia were not formed. Such conditions as are given in the experiment need scarcely ever be feared in practice. Such cases occur most frequently in hot beds where the manure, needed to raise the temperature of the beds, sets free too much carbon dioxid. This trouble may be overcome by proper ventilation, (even on frosty days.) 1 Demoussy, E., Sur la vegetation dans des atmospheres riches en acide car- bonique. Compt. rend. CXXXIX, p. 883. 2 Kosaroff, P., Die Wirkung der Kohlensaure auf den Wassertransport in den Pfianzen. Bot. Centralbl. 1900, Vol. 83, p. 138. 3 Sitzungsber. d. "Wiener Acad. 1873 vom 24. Juli. 4 Kohl, Die paratonischen Wachstumskriimmungen der Gelenkpflanzen. Bot. Zeit. LVIII, 1900, p. 1. 5 Lioc. cit. SECTION II. INJURIOUS ATMOSPHERIC INFLUENCES. CHAPTER IV. TOO DRY AIR. Injury to Buds. Although in house plants, for example, we have constantly met with the lack of sufficient atmospheric moisture as a factor in the production of the phenomena of disease, it has as yet been but very little taken into consideration. The direction in which continued great scarcity of atmospheric moisture makes itself felt may be seen from the peculiarities of the xerophytes. As an example of this, we will mention Grevillius\ He found in the plants of a treeless lime plateau a thickening of the epidermis and its wax coating, or, as a substitute for this, a great increase of pubescence. These char- acteristics are more marked in leaves near the top of the stem. The epi- dermal cells, in contrast to normal forms, usually have somewhat smaller lumina. The palisade cells are broader and more closely joined to one another, the intercellular spaces are smaller; the mechanical tissues in the branches and petioles are better developed, the pith less ; it has smaller cells but is richer in starch. These changes, in fact, occur almost always in con- nection with a great lack of moisture in the soil whereby it is hard to judge which is due to the dryness of the air alone and which to the excessive transpiration conditioned by it. However, we find various processes setting in when, with a sufficient supply of soil moisture, the air is constantly hot and dry ; these will have to be discussed here. They are in part phenomena of arrestment in the life of the buds or in the conditions of germination; in part disturbances in the mature leaves which lead to the falling of the leaves in summer. Two stages must be noticed in the life of the buds and the development of the young shoot after the bud has unfolded. If a considerable dry period 1 Grevillius, Morpholog-isch-anatomische Studien lib. d. xerophile Phanero- g'amen -Vegetation der Insel Oeland. Englers Jahrblicher 1897, XXIII, p. 24. 409 SSog sets in in the early spring when, as a rule, it is continued by a persistent East wind, the opening of the buds, dependant on the alternating action of sunshine and rain, will be delayed. The gummy masses in the bud scales of many varieties of trees, usually due to the gelatination of the tissue, must be softened by rain to facilitate the development of the buds, while the resin- ous and partially balsam-like products of this softening in the scales, warmed by the sunshine, give way at the same time to the pres- sure of the buds. In continued dry and windy, spring weather, the buds unfold more slowly because the necessary growth of the inner side of the scales is prevented so that they cannot turn back far enough. In the second kind of injury, the young tip of the shoot, just appearing, is suddenly exposed to the sharp rays of the sun and to very great evapora- tion in abnormally dry air, after the protecting scale has been thrown off. In order to understand this process, we give a few illustrations from Griiss^ In Fig. 67 is shown the cross-section ;;^^-^QC through the bud covering of the oak ; in Fig. 68, one through Pinus Mughiis. It is easy to distinguish the different scales firmly overlapping above the strongly developed epidermis of the outer side and, by comparing the two bud coverings, the increase of precautionary protection in the conifers is found to take place by means of the deposition of masses of resin (h). In the cross-section of the individual cov- ering scales it is noticed that their outer or, later, under side possesses especially strongly developed elements. In the pine, the epidermal cells have been very greatly thickened sclerenchymatically. The bud covering of the winter oak is composed of 8 separate scales, and its cell layers found underneath the epi- dermis are so strongly thickened that the lumina have almost disappeared. Fig-.67. Cross-section Fig.GS. Cross-section through the bud through the bud covering: of Quer- covering of Pinus cus sessili flora, Mughus, Scop. Sm. (After Griiss.) (After Griiss.) 1 Griiss, J., Beitrage zur Biologic der Knospe. schaftliche Bot. Vol. XXIII, Part 4, p. 637. Pringsheims Jahrib. f. wissen- 410 The summer oak, Quercus pedunculata, Ehrh. behaves somewhat differently. If, in the Spring, a basal growth increases the sclerotic elements, the cover- ing scales show a certain stiffness and remain longer attached to the growing shoot. They thus protect it longer from the dangerous fluctuations in tem- perature. The oak in the warmer Mediterranean countries, Quercus Ilex, L. hardly shows the sclerotic elements in its scantier bud coverings, and some- times they are entirely lacking. In this we are concerned with protection against the summer drought period and find it in the hairs, which develop from the epidermis, and also the cork layer, which develops from the sub- epidermal tissue. Before the leaves burst out from the bud, the scales, bent together like a roof, are simply small leaves reduced to stipules, but when the leaves break out, the under side grows further at the base, while the sclerotized outer side does not do so. Consequently the base of the scale, drying from the edges backward, become fleshy, cushion-like and, like a prop, presses the scale outward. This is the time of danger, since even the delicate vege- tative cone is exposed to the fluctuations of temperature, and almost with- out protection. This explains the internal ruptures made by the action of the frost, sometimes found in the spring^ and also the phenomena of shrinking from drought, resulting from constant sharp East winds. No matter in what way the protective apparatus of the bud scale is formed in the various species, whether from sclerotic cell layers or from cork layers, layers of hair or masses of resin, the fact holds good that this apparatus develops differently in different years, according to the weather and the amount of nutriment at the time of its formation, and, accordingly, is of different protective power in the following spring. If, for example, the summer has been moist and cloudy, the covering scales tend to develop- ment towards the nature of the green leaf and the cells become larger or less thickened. In spring they react more quickly to the increase of turgor of the tissue and separate from one another more quickly. Thus the grow- ing point is exposed prematurely to inclement spring weather, and so loses too rapidly the protection against its power of transpiration. This factor must not be underestimated, for Griiss reports- that, when he removed the strongly developed outer scales from an oak bud, he noticed that the bud was destroyed with great regularity, even if the temperature did not fall and there was present sufficient moisture. Also the inner, more dehcately walled coverings became dry since they were not accustomed to the increased transpiration. Uninjured buds kept under similar conditions (on cut twigs) developed further. Experiments with beech buds, from which the whole covering had been removed, showed that the young, exposed leaves kept fresh much longer than those of the oak. This is due to the pubescence of the young beech leaves, which protect them from too great transpiration and the con- 1 See chapter on the Action of Frost. 2 Loc. cit. p. 649. 411 sequent drying. This view is supported also by the observation of Griiss, that, in Aesculus Hippocastanum, the young leaves, known to be very thickly pubescent, will develop normally after the removal of the bud cover- ing. The effectiveness of the resin covering is seen from an example of Abies Pinsapo, Boiss. When the resin had been removed from the buds by carbon disulphid, they dried up. It may now be asked how such irregularities in the unfolding of the buds can be combatted practically. The formation of the bud covering cannot be influenced and the danger- ous fluctuations in temperature and atmospheric moisture in spring cannot be controlled. Nevertheless, we think a precautionary measure might in- deed be adopted in forestration in order to moderate the extremes of trans- piration. In the first place, the soil should retain its natural covering of moss or litter, since in this way the soil moisture is preserved, and a damp atmosphere made possible. Hence it might be advisable not to clear away all the leaves, etc. Finally, however, and especially in younger plantations, it might be advantageous to retain protective forests on the side of the tract exposed to the strong spring sun. Among such protective trees the rapid and loosely growing birch is especially useful. In garden plants, naturally, one can control conditions very much better. In this conne^ction, attention should be called for the present only to the fact that one should not attempt to replace the uniformly great loss from transpiration by increasing the water at the roots. That does not work well and plants are found to dry up which have an excess of water at the roots. The only natural means is artificial shading. Defoliation Due to Heat. Observation shows that every year from spring on the foliage falls from our deciduous trees. In city planting this is especially noticable in Acer Negundo and the slightly developed inflorescences of the linden show this almost at once, sometime before the "linden blooms." The process is less striking, but constantly present in other deciduous varieties. Wiesner^ gives this constant dropping of separate yellow leaves the special name of "the summer defoliation" and sees its cause in the changes in the sun's altitude. I think that other causes can also operate here, for, while the summer defoliation usually sets in predominately after the 21st of June, observations show that, for example, according to Wiesner's statements, in Acer Negundo, Acer Calif ornicum., and related species, the leaves first formed may be dropped even in May and at the beginning of June. As long as this loss of leaves is slight in comparison with the whole foliage of the tree, it has no pathological significance. Experiments have shown that it is a perfectly normal phenomenon for the leaves on a branch to complete their cycle of growth at different periods. Thus some would 1 Wiesner, Jul., tJber Laubfall infolge Sinkens des absoluten Lichtgenusses (Sommerlaubfall). Ber. d. D. Bot. Ges. 1904, p. 64. 412 fall earlier, some later. Those produced first in the spring are weak in their formation, being smaller and not so brightly colored; hence they soon reach their full development, Avhen their assimilation is arrested, as the stronger leaves, produced later, cut off their light. Then the tree frees itself of the organs incapable of working. However, the summer defoliation is to be considered as a phenomenon of disease when it becomes extensive and suddenly attacks the well develop- ed foliage in full sunhght. Late frosts and more often a continued period of drought, combined with great heat, are among the causes of summer defoliation. Wiesner distinguishes the latter form as "defoliation due to heat," clearly a result primarily of excessive transpiration with an unequal decrease in the supply of water in the trunk. I found examples of defoliation due to heat in the trees planted along the streets, especially among the lindens, in spite of abundant watering. From this it is evident that actually the dry air with abundant sunshine should be assumed to be the injurious factor. With deficient water supply in the soil alone the foliage dies from summer blight but usually remains hanging on the tree. The linden, despite its beauty, is not to be recommended as a street tree because of its especial sensitiveness. The summer linden shows earlier and more severe effects than the winter linden, and after the appearance of summer heat, almost without exception, is found covered with the fine webs of the weaving mite {Tetranychus telarius). In many trees aphids occur in immense quantities. After defoliation, from which only the tips of the branches are excepted, there is manifest a prematurely dormant period. As soon as the weather becomes cooler (or when the streets are abundantly watered during the hot period) a second growth appears in which the de- velopment of lateral buds can push off the hanging leaves (defoliation due to growth, according to Wiesner). In wet autumns the wood of this second growth does not ripen properly and is easily injured by the winter frosts. In order to avoid these conditions it is advisable to plant elms rather than lindens along the streets. If these conditions appear along avenues of older trees, v/hich cannot be replanted, the streets must be sprinkled as frequently as possible. Spraying under heavy pressure in the late evening may prove to be especially useful. I consider that consistently following this measure will prove the most effective prevention of vermin attacks. Honey Dew. According to observations made up to the present, a disease must be in- cluded here which has often^ been described under the name "honey dezi'" {Melligo, Melaeris, Ros mellis) and which has been traced to very different causes. This disease is characterized by the appearance of a sugary coating 1 Saccharogenesis diabetica; Unger. "Exanth. p. 3.— Honning- Dugen, Fabricius Kiobenh. 1774. — Le Givre, Adans, cit. bei Seetzen: Sistematarum generaliorum de morbis plantarum. Gottingae 1789. 413 on leaves, blossoms and young twigs of woody and herbaceous plants usually covering the outer surface of the organs, sometimes as a shining uniform varnish, sometimes in the form of yellowish tough drops. Meyen^ relates that for some time tlie theory expressed by Pliny was accepted, namely, that the honey dew was an actual falling from the air, occurring in the dog days especially and coating not only the plants, but even the clothing of men. T- Bauhin contradicts this theory and calls attention to the fact that only isolated plants or species in any region become diseased. After the excretion of a sweet sap from the anus or the abdominal tubes of the aphids had been observed, they were considered to be the cause of the dis- ease and at the time it was observed that aphids and honey dew were fre- quently found together. To this, however, was opposed first of all, the fact that the aphids usually occur on the under side of the leaf, the honey dew, chiefly on the upper side. However, this fact is no very certain proof since the aphids of the under side of the leaf can sprinkle the upper side of the leaf lying next below. But gradually the observations on honey dew- were increased on isolated outdoor and indoor plants on which no aphids could be found or upon which they did not appear until sometime later. Hartig's observation, made in 1834, is interesting in this connection. A rose plant, wdiich had not been taken from the house, secreted small drops on the under epidermis of the leaves from which the sugar was separated in rhomboidal or cubical crystals. Tn this the green color of the leaves changed to a grayish one, due to the disappearance of the chlorophyll in the mesophvll at the secreting places and to the appearance of clear drops in the cells. Treviranus", in the same way, frequently found such sugary secretions in the warm, continuously dry air out of doors as well as in greenhouses, on white poplars, lindens, orange trees, distils (Carduus arctioides) and cited still older observations by Lobel, Pena, Tournefort et al., according to wdiich honey dew occurs on olive trees, varieties of maple, walnuts, willows, elms and spruces. He, and later Meyen, were convinced that the drops containing sugar were secreted directly from the epidermal cells, to which the former observers also added that the stomata did not take part in this secretion. Further observations on honey dew occurring in very different plants, especially oaks, were furnished later by Gasparrini''. The honey dew on the linden has been chemically investigated by Boussingault and that on the grape cherry (Prunus Padus) by Zoller^ Boussingault found that the honey dew% collected at two different times, differed quantitatively in regard to the different substances; from which fact it is evident, that the secretion does not always have the same per- centage composition. But the nature of the substance seems to change also, for although Boussnigault found only cane sugar (48 to 55 per cent.), in- vert sugar (28 to 24 per cent.), and dextrin (22 to 19 per cent.), Langlois 1 Pflanzenpatholoj?ie, 1841, p. 217. 2 Phvsiologie der Gewilchse, 1838, Vol. II, Part I, p. 35-37. ■" Sopra la melata o trasudamento di aspetto goommoso etc. Bot. Zeit. 1864, p. 324. * Okonom. Fortschr. 1872, No. 2, p. 39. 414 also found mannit as one constitutent of the honey dew on the linden. Czapek^ collected the results of more recent observations. From this it may be concluded that the composition of the honey dew varies in different plants. A harmony of the theories as to the causes of the phenomenon has not been obtained as yet. While Biisg'en- studied carefully the aphid stings on plants, he proved that the animals secrete through the anus much larger amounts of honey dew (the secretions of the abdominal tubes are waxy) than is usually assumed, and, on this account, he concludes that real honey dew depends only on aphids. Bonnier^ made some experiments which showed an artificial production of honey dew without the intervention of the animals. Biisgen says the peculiarities of the cuticle allow neither an osmosis or distillation of sugar saps from the interior of the cell nor, as Wilson assumed, an osmotic withdrawal of liquids through drops of sugar to be found on the surface of the leaf, such as are formed by the excretion of the aphids. This statement, however, does not consider the fact that the smooth surface of the cuticle can become broken and that secretions in individual cases can find their Avay through the stomata. Bonnier's results prove the later case. Leaves which had been exposed to great differences in temperature (conifers, oaks, maples, etc.), showed under the microscope, when examined by direct illumination, the formation of nectar-like drops from the stomata when the light was sufficiently strong. My own observations confirm the occurrence of honey dew without the intervention of aphids. In one case T found an abundant formation of honey dew on the older leaves of pear seedlings grown in water cultures and exposed to the hot July sun. This observation showed that deficient soil water was not necessarily a factor. I believe that honey dew is produced if there is a sudden excessive increase of transpiration in strongly function- ing active leaves, caused by a strong light stimulus, and brings about too high a concentration of the cell sap. If the disturbance continues beyond a certain point, the leaf suffers permanently and falls prematurely. In another case the rain gradually washed the sugar coating away, which made possible an attack of the black fungi (sooty dew). The production of honey dew is not always dependent upon extreme and absolutely high temperatures and strong light stimuli, but sudden great contrasts as, for example, the sudden shock to an organism caused by an intense morning sun following a very cool night, which had suppressed its activity. Shading would be the best preventative measure and repeated sprinkling an effective remedy. 1 Czapek, Fr., Blochemie der Pflanzen. Jena. Gustav Fischer. 1905, Vol. I, p. 408. 2 Biisgen, M., Der Honigtau. Biolog. Studien an Pflanzen u. Pflanzenlau.sen. Sond. Biologisches Centralbl. Vol. XI, Nos. 7 and 8, 1891. 3 Bonnier, G., Sur la miellee des feuilles. Compt. rend. 1896, p. 335, cit. Zeit- RChrift f. Pflanzenkrankh. 1896, p. 347. 415 Probably the much dread Mafuta disease of the sorghum millet (Andropogon sorghum) in German East Africa belongs here. The word Mafuta means oil. Honey-like excretions are found on leaves and stems. These give rise to a sooty coating'' . Other plants also suffer especially in times of drought. Heart Rot and Dry Rot of Fodder and Sugar Beets^. The heart rot of the sugar beet should be considered as a phenomenon usually related to honey dew^. It is found usually in hot Julys in rainless periods and is characterized by the death of the heart leaves. These have not grown to half their normal size. The dying foliage suddenly becomes black. In severe attacks the whole leaf area dies, but, as a rule, the plants develop new foliage. In addition to the affection of the leaves, the body of the beet is attacked by a decomposition or dry rot. The beet, near its head end, has spots which can deepen as the tissues decompose, and finally destroy the beet. Of greater agricultural significance in this connection is the fact that a part of the non-reducing sugar disappears from the beet and another part is converted into reducing (grape) sugar". If the rainy weather sets in at the right time, the dead tissue can be thrown off through the formation of cork. If the healing process does not set in soon enough, so that a long con- tinued autumnal dampness can exercise its influence on the decayed places, the process of destruction of the beets, which are poorer in sugar, is also continued in the storage pits. Most observers are inclined to seek the cause of the trouble in fungi, since mycelium is often found in the diseased heart leaves*. Frank especially defended the fungi theory and wished to make two species re- sponsible for it : Phoma Betae, Frank^ and Fusarium heticola, Frank. It is certain, however, that the first stages of the disease of the heart leaves are without fungi and bacteria, and the parasites later, during damp weather, occasion an advance in the destruction of the tissue. However, when the beet plants are healthy, the fungi cannot attack them. Only when evapora- tion is sufficiently increased and the absorption of water sufficiently de- creased do the conditions arise which predispose the plants to attack by fungi. Practical workers state that the addition of lime also in the form of waste lime favors the attack of the disease. We have very instructive field experiments^ along these lines in which some areas were limed, and some not. Where lime was used, the beets were diseased, where there was none, the crop was healthy. 1 Busse, W., Weitere Untersuchungen liber die Mafuta-Krankheit der Sorghum- Hirse. Aus "Tropenpflanzer," cit. Zeitschr. f. Pflanzenkrankh. 1902, p. 82. 2 See Vol. II, p. 240. 3 Frank, A. B., Kampfbuch. 1897, p. 131. 4 Prillieux et Delacroix, Complement a I'etude de la maladie du coeur de la Betterave. Bull. Soc. mycologique. VII, 1891, p. 23. 5 syn. Phoma sphaerosperma, Rostr., Phoma Betae, Rostr., Phyllosticta tabifica, Prill, et Del. 6 Zeitschr. f. Pflanzenkrankh. 1895, p. 250, 1896, p. 339. 4i6 Also the location itself has often been found to favor the appearance of the disease, since on field ridges with a gravelly underground, or declivi- ties from v\^hich the water runs away quickly, often only dry rotted beets are produced. The different varieties are proved to be susceptible to different degrees ; the Vilmorin sugar beet is said to be especially sus- ceptible ; varieties with smooth leaves spread flat on the ground and long roots should be preferred in threatened regions^. Sasse-, as a result of his very thorough field experiments, states that vapor and deep cultivation prevent the outbreak of dry rot. Opinions vary greatly as to the influence of fertilization. In my opinion, the variation is explained by the varying action of the same fertilizer on different fields, and dependent on the weather. Fertilizers making the soils more porous, increasing their capacity for warmth and decreasing their power for re- taining water, tend to favor the development of dry rot ; this can occur with waste lime^. The same fertilizers are satisfactory^ in heavy soils. Fertiliza- tion with kainit has been most questioned. Tt is erbphasized that the soil will actually retain water better after fertilization with commercial manures, i. e. offer greater resistance to the influence of drought, and yet not infre- quently where kainit fertilization has been used, the first heart rot of the beets will be found. In my opinion there is a natural explanation for this phenomenon. Kainit tends to develop leaves extraordinarily ; hence, with a continued dry period, the extensive leaf area withdraws water very quickly from the root system, causing an injurious concentration of the cell sap. Analyses have shown that, with a high potassium content in the leaves, the dry rot appeared more marked, the smaller the proportion of phosphoric acid present. Therefore, the choice of land which dries quickly may be a preventa- tive measure for this disease. When the soil is light those materials, which heat the soil (lime, separator ooze) must not be given directly to the beets. With the appearance of dangerous droughts, one should decrease the drain- age since, ordinarily, it would not be practical to always water the crop. A further condition should be considered, namely, whether the evaporation of the plants can be reduced by removing the older leaves, or by shading with straw mulching. Faulty Development of the Blossoms. Much oftener than is generally supposed, great atmospheric dryness manifests itself in blossoms, especially double flowers. If specimens of the same species with single and with double blossoms in the same position be compared (fuchsias, petunias, tuberous begonias, roses, etc.), it will be observed without exception that the single blossoms develop more rapidly 1 Bartos, W., Einige Beobachtung^en iiber die Herz- unci Trockenfaule, cit. Centralbl. f. Bakteriologie 1899, p. 562. 2 Sasse, Otto, Einig-e Beobachtungen aus dem praktischen Betriebe betreffs Auftretens der Herz- oder Trockenfaule. Zeitschr. f. Pflanzenkrankh. 1894, p. 3.59. 3 Richter, W., tjber die Beziehungen des Scheideschlamms zum Auftreten der Herzfaule der Riiben. Zeitschr. f. Pflanzenkrankh. 1895, p. 51. 417 and quickly. The slower and more retarded dexelopment of double blooms may be traced to greater distribution of the water and nutritive substances conveyed through the petioles over a more considerable leaf area. The loss in transpiration, due to the increased number of petals, is greater and can in no way be replaced by supplying w ater to the roots. Consequently, the organs develop more quickly ; they become ripe prematurely and cease growing before the blossom has been completely developed. On this account half open blossoms often fall where there is great atmospheric dryness. This should not be confused with the dropping of the blossoms, due to excess of water. In the latter case it may often be observed that both the blossoms and peduncles fall. \\^ith excessive transpiration in a very dry atmosphere, the petals fall where they join the peduncle after having turned brown there. AMien, as is often attempted in greenhouses, an artificially moist atmos- phere is produced by abundant watering of entire plants, their condition is improved only if the flower pots stand on the soil, since the vaporizing dampness from the soil keeps the atmosphere constantly moist. But if the pots stand on wood, iron or stone, the blossoms shrivel up in spite of the watering and a Botrytis growth is found where the petals loosen. This leads consequently to erroneous conclusions since Botrytis diseases are usually accompanied by great atmospheric humidity. The double staminate blossoms of tuberous begonias fall in excessively dry air, and form one of the most striking examples of the difficulty. I observed this often in the dry summer of 1904 in places which had never had direct sunlight. That the falling of the petals was actually due to dry- ness of the air was shown l)y an experiment in which plants were used, which usually drop their blossoms at the time of opening. They retained and developed them, however, if placed over broad basins filled with water. The pistillate blooms always mature. The first indication that the staminate blossoms are going to fall is that the bud does not straighten up but remains drooping. AA'ith the hand lens a small brown ring may be seen at the union of the calyx and peduncle. There the young tissue is found to be deep brown, its walls and contents collapsed. At the calyx, the shrivelling and tearing of the tissue forms large holes until finally the petals hang only by a few shreds of tissue. In the individual petals, the vascular bundles also seem deeply browned even at the places which are still not discolored and apparently fresh. This drying of the base is really a pre- mature end of the life cycle, since the cell contains only scanty flakes of protoplasm. Near the dead tissue there is an abnormal accumulation of asymmetrically formed, separate crystals of calcium oxalate, as the final residue of the organic substances consumed in respiration. A second kind of defective blossom development, resulting from dry- ness, was observed in the Liliaceae and Amaryllideae. In these instances the perianth remained stuck together at the apices. Although the rest of the blossom was normally developed and colored, the tips of these perianths 4i8 turned yellow, sliivelled up and dried into a mass which finally crumbled. The injury is horticulturally of significance only when the blooms are forced and large individual blossoms are desired as in Lilium aureum, Liliuni longi- florum and Hippeastrum robustum, Dietr., etc. In that species which is known among gardners as Amaryllis Tettaui and is often grown as a house plant because it blooms freely, I observed more carefully the mechanics of opening and incomplete development dur- ing drought. The three outer tips of the brick red perianth begin to separate from one another at their base on the day before the blossoms are completely opened; hence the large conical flower bud first of all shows three shts. The tips of these three outer- most petals, however, remain stuck fast together even if the process of separation from one another is so hastened by the increased growth of the innerside of the perianth that this is curved outward like a pouch. In this convexity, which becomes constantly greater, lies a great elasticity which would be able to sep- arate the gummed tips from one another and, in normal cases, actually does tear them apart. The strength of this elastic power, produced by the basal epinasty of the perianth, is demonstrated if the still gummed apices of the three tips are cut off about forty-eight hours before the normal time of opening. Then, within lo minutes, the individual tips have separated 1.5 to 2 cm. from one another, i. e. the corolla has begun to open. The resistance offered to this strong elasticity arises from the fact that the green apices of the three outermost tips are anchored to a strong cone about 5 cm. long. Sometimes this cone is thimble shaped. There is a heavy growth on the underside of each tip which curves out like a ridge, and corresponds with a midrib, making a very fleshy growth on each tip. Fig. 69 shows three of the perianth tips, touching each other with their keel-like wedges (a). These wedges contain no vascular bundles. These lie {g) frequently in groups of 3 or 4 peripherally in the real laminal part. The individual laminal halves at both sides of the fleshy median ridges are curv^ed inward and touch the adjacent peripheral tip with their edges (r) ; U...4^- a Fig-. 69. Cross-section throug-h the apical region of a still closed blossom of Hippeastrum robustum. Explanation of the letters in the text. 419 these are green, while the fleshy cushions at the center (c) , containing the largest parenchyma cells, seem colorless. In contrast to the abundant small grained masses of starch in the rest of the tissue, the cushions display only a few large starch grains. The epidermis is normally flat walled at the outside of the peripheral tip, but, on the ventral side, at the beginning of the development of red coloring matter, shows a papillary outgrowth. Al- though this grew out to distinct pajjillae, mutually interlocking, like clogged wheels, on the cushion-like raised places (a), it shows scarcely any elongation on the flat laminal part. In this close interlocking of the papillae of the tip of one part of the perianth with those of the others may be seen the reason for anchoring these tips so firmly together. An elastic strain loosens the tips since these pai)illae grow rapidly to conical hairs, thus breaking the connection. In the cavities (h) which the outer petals leave free, lie the tips of the three inner ones, whose epidermis, however, develops papillae sooner than that of the outer ones. The mutual resistance of the out-growing papillae favors the separation of the inner tips of the perianth and, therefore, the blossoming. When the atmsophere is dry, the primordia of the papillae may still be found, but they do not develop into conical hairs ; hence the tips of the petals remain united and gradually shrivel up. House Plants. The typical picture of a house plant which meets our eye shows brown- ing and drying leaf tips. Where gas is burned, usually one is inclined to lay the blame on the gas. As a fact, the dryness of the air in the room is the cause and the condition is as marked in dwellings where gas is not used. The fact that plants, especially the so-called foliage plants, die after the tips become brown and dry, may be explained as due, not to the atmos- pheric dryness, but to the attempts of the grower to get greater moisture in the air by very frequent watering. However, the plants get no benefit from this increased supply of water. They can use more water and transpire it only when the tissue develops more abundantly, resulting in a more vigorous assimilation and a greater production of leaves. The dryness of the air, however, inhibits this very development of the leaves. When the foliage of tropical climates (many foliage Begonias, Hoflf- mannias, RuelHas, Marantes, etc.), are brought from the moist conservatory into a room of the same temperature, the development at once ceases. The older leaves begin to curl back; the younger ones roll up their edges and remain smaller than those previously formed. The apical growth of the shoots is retarded ; all processes of elongation are reduced. It is peculiar that with many plants (for example, many bushy Begonias) the blossoms, produced in dry air, either do not open at all or only incompletely, and finally fall off without having become diseased. This process may also be observed out of doors. The dormant period of the plant sets in more 4'20 quickly, and, when tlie new vegetative period begins, the development of the buds is retarded and often entirely prevented. With such activity in the parts above ground, the roots will rot if given too abundant water. Various methods have been proposed to overcome the injurious in- fluence of the dry air in the room, such as to spray frequently or to cover the plants at night with damp cheese cloth, etc. However, such methods have not proved sufficiently satisfactory. I obtained best results by using Wardian cases or by setting the plants over water. Recently flower tables have been used in which the plant stands on a zinc box filled with water, the top of which has been punctured full of holes. Through this, water vapor constantly rises between plants placed above it. Hard Seeds in the Leguminaceae. The hard-shelled condition of Leguminaceae seeds, not only those of the Papilionaceae, but also those of the Mimoseae and Caesalpiniaceae, can be considered as a natural protection against micro-organisms at a time in their development when they are most readily infested. All our wild grow- ing Papilionaceae exhibit the same constructive principle and the hard- seeded condition becomes dangerous only when it prevents germination. This hard-shelled condition arises from the special thickening of the palisade layer of the seed grain which, with its cuticle, forms the outer- most covering of the seed shell. These columnar palisade cells, lying very close to one another, show in cross-section strongly refractive cross lines (light lines) of an especially dense substance. The cell content contains those substances which cause the coloring of the seed shell and to which great importance is ascribed as substances protective against parasite at- tacks. Next to the palisade layer, described by Nobbe as the "hard layer," lies, on the under side, a layer of so-called hour-glass cells, next which are thin-walled cell layers with large intercellular spaces. These cells function especially in the swelling of seed. Corresponding to the gluten layer in grain seeds, we find in the majority of Leguminaceae seed, with the ex- ception of the Phaseoleae. Vicieae and a few other varieties, according to Harz\. the endosperm in the form of a hard, horny matter, which becomes slimy when placed in water. In the region of the scar, palisade cells and round hour-glass cells usually appear in two rows. In this instance we follow Hiltner's experiments-, which show that the hard-seeded condition preventing the rapid swelling of the seeds, naturally forms a protection against micro-organisms. Older lupine seeds, wdiich were not absolutely hard-shelled but swell up only wdth difficulty, were soaked in water. The seeds which swelled each day were laid separately in the germinating box. This showed that those lupine seeds which swelled most rapidly and hence w^ere not hard-shelled; almost always rotted, while 1 Landwirtschaftliche Samenkunde. - Hiltner, I^., Die Keimungsverhaltnisse der Leguminosensamen und ihre Beeinflussung durch Organismenwirkung. Arbeiten d. Biolog. Abteil. f. Land- u. Forstwirtsch. am Kaiserl. Gesundheitsamte. Vol. Ill, Part 1. Berlin 1902. 421 the percentage of g-ermination was higher in those seeds where the swell- ing hegan later; due to the higher percentage of hard seeds. It was concluded from experiments with eight year old clo\er seed which, on account of age, had already begun to grow dark, certain seeds having become brown and shrivelled, and which was sorted according to color, that the grains, which still had the appearance of completely fresh seed, gave the highest percentage of germination. Among the slightly dis- colored seeds, the brown ones germinated least and gave more than 90 per cent, of rotted grains. Among these seeds, a much larger percentage of the light-colored ones decayed than of tlie violet ones. This led to the deduction that the violet color of the seed covering offered a protection against bac- terial attack. The different percentages of hard-shelled seeds from a given variety over a period of several years, show the dependence of that condition on the weather. Hiltner, by drying the seed artificially at a temperature of 35°C., or over sulfuric acid, could increase the percentage of hard-shelled grain. This experiment showed the atmospheric condition required to pro- duce the undesired hard-shelled seeds. This condition, therefore, resembles glassiness of grain. As the process of drying during ripening is hastened, more hard-shelled seeds might be formed. In general practice, however, contradictory results are often found. In dry positions it was observed that the seeds of lupines, vetches, scarlet clover and the kidney vetch (anthyllis ) (W'indklee), in time become hard- shelled, while the finer clover seeds show rather the reverse. Hiltner's observation on artificially dried seeds explains this contradiction. The in- fluence producing an increased toughness of the shell in thick-walled seed aff"ects thin-walled seeds as well, but in them the shell splits, consequently increasing their small capacity for swelling; further Rodewald states that cold can decrease the hard-shelled condition of Leguminaceae seeds, \\'hen one realizes that hard seeds can lie for years in the soil without germinating and that those, even less capable of swelling, may germinate so late that they cause a second growth, it will be evident that the seed grower must control the formation of hard shells to eliminate them. In the course of years, many methods have been recommended. Thus, for example, the seed should be laid in a i to 2 per cent, solution of sodium carbonate, to dissolve the silicic acid in the shell. Again, simply sift out the hard-shelled seeds, since they are all somewhat smaller than the normal ones which will germinate. Again, treating the seeds with hot water has sometimes been successful, sometimes not. Dipping in boiling water for one minute was injurious, but was beneficial when the seed was emersed for five seconds only. This treatment, however, over so short a time, cannot be entrusted to laborers. Potassium permanganate, dilute sulfuric acid, an ammoniacal solution of copper sulfate, have been as unsuccessful as the sodium solutions. On the other hand, Hiltner found concentrated sulfuric acid to be successful. The sulfuric acid injured only tliose seeds which 422 had been damaged in threshing, even if the seed was left for sometime in the acid. Frequently, treatment with sulfuric acid for half an hour will be sufficient if the seeds have been thoroughly wet by stirring. When the treatment is completed the acid should be thoroughly washed ofif with clean water and then immediately with lime water for at least 5 to 20 minutes. Microscopic investigations of seed treated in this way showed that (in Acacia Lophanta) the sulfuric acid had removed not only the cuticle but also the greater part of the palisade cells and had stopped before reaching the "light line." Yet the seeds could swell in water only when the acid had penetrated the light line in some places^ Therefore, this cell layer, present in the seed shell of all the Leguminaceae, according to Mattirolo^, con- sisting of an especially dense cellulose, prevents the seeds from rapid ab- sorption and elimination of water. Connected with this innate hard-seeded condition is the hardening of the seed membrane during germination. With those seeds which, in germi- nation, pushed their cotyledons above the soil, the cap-like seed shell is gradually pushed off, if it has been retained until the moisture is absorbed and thus remains flexible. But if a hot, rainless period sets in suddenly, the cap dries on the cotyledons, preventing their development, as well as the breaking of the young stem. In case it is not destroyed, it is twisted to one side. Lopriore^ mentions here the germination of beans. I have ob- served similar phenomena in cucumbers, pumpkins, melons and the seeds of stone fruits. The retention of the dry, stony shell shows itself most de- structively in the seedlings of plums, peaches and other Amygdalaceae. Sprinkling of the seed bed in the evening is, therefore, a precaution which should not be omitted. 1 Hiltner und Kinzel, tJber die Ursachen und die Beseitigung' der Keimungs- hemmungen bei verschiedenen praktisch wichtigeren Samenarten. Naturwissensch. Zeitschr. f. Land- u. Forstwirtschaft 1906, p. 199. 2 La linea lucida nelle cellule malpighiane degli integumenti seminale. Torino 1885, cit. von Hiltner und Kinzel. 3 Berichte d. Deutch. Bot. Ges. 1904, Part 5, p. 307. CHAPTER V. EXCESSIVE HUMIDITY. The Mode of Growth With Continued Atmospheric Humidity. Older works have called attention to the fact that the structure and functions of individuals are altered by the influence of a high degree of atmospheric humidity in the same way as by the removal of light. Accord- ing to experiments of Vesque and Viet\ plants grown in moist air have longer, less branched roots, more delicate stems, leaves with longer petioles and smaller blades. The walls of the epidermal cells are less wavy; the cell rows of the mesophyll somewhat less numerous and without differ- entiation into palisade parenchyma. The whole tissue of the leaf grown in moist air is in every respect more uniform, while in dry air the difference between palisade and spongy parenchyma is clearly seen. The vascular bundles in the internodes are much more developed in dry air. This refers not only to the diameter of the whole bundle, to the number of ducts and their diameter, but especially to the hard bast fibres which may occur abundantly in dry air and be entirely lacking in moist air. Duval-Jouve- observed with grasses that dry, hot situations increased the development of the bast bundles, while, in moist places, this development is retarded. The authors named quote Rauwenhoff^ who describes etiolated plants in this way. In comparative experiments with dry and moist air, under light bell- glasses, as well as shaded ones, it was found that, in darkness but in dry air, the plants were less spindling than those grown in the light in moist air, from which it is concluded that the form of the etiolated plants is due chiefly to deficient transpiration. Brenner* expresses the same theory. In his experiments with Cras- sulae, he observed a tendency to decrease the succulency of the leaves in moist air, but to increase the upper surface. The cells of the stems were actually elongated. Wiesner^ also found that the leaves of Sempervivum 1 Vesque et Viet. Influence du Milieu sur les vegetaux. Annales des scienc. nat. Sixieme serie. Botanique t. XII, 1881, p. 167. 2 Botan. Jahresbericht 1875, p. 432. 3 Annal. d. scienc. nat. 6 ser. V, p. 267. 4 Brenner, W., U.ntersuchungen an einigen Fettpflanzen. Just's Bot. Jahresb. 1900, p. 306. ' ^ , ^ 5 Wiesner, Jul., Formveranderungen von Pflanzen bei Kultur in absolut feuchten Raumen. Ber. d. Deutsch. Bot. Ges. 1891, p. 46. 424 tcctorum considerably enlarged in an absolutely moist room and became markedly epinastic. The leaf rosettes were spread out because the inter- nodes developed further. W. Wollny^ found that a lessened thorn de- velopment occurs in normal leaves of Ulcx enropaeus as a result of con- tinued atmospheric humidity. He also observed, however, that the chloro- phyll content decreased as the leaves increased. According to Eberhardf', the number of chlorophyll grains is decreased if the stems become longer and the leaves larger. In a later work" this investigator summarizes his experiments as follows ; moist air combines a reduction in the thickness of leaves and stems with elongation. The formation of hairs is decreased, that of blossoms and fruit retarded. Epidermal, bark and pith cells become longer, the intercellular spaces greater, the number of secretion canals smaller and the development of the wood less noticeable. A smaller pro- duction of lateral roots is noticed. E. Wollny* also mentions that the time of blossoming and ripening is retarded and, by numerous experiments, strengthens the easily foreseen conclusion, viz., that the evaporation from plants and soil, under otherwise equal circumstances, is smaller, the greater the atmospheric humidity. It should be mentioned briefly in passing that in numerous cases abundant excretion of water takes place in the form of drops with the reduction of transpiration and by means of different devices in the various plants"'. We frequently find this in potted plants which in the fall are brought into un- heated greenhouses, when the leaves touch the rapidly cooling window- panes. Finally, I will mention the results of my own experiments''. In trees (pear) the whole new growth and also the different individual internodes and petioles were observed to be shorter in dry air, and the leaf blades more slender in moist air. In grains, the growth from seed was found to be somewhat less in dry air; the leaf number was also somewhat decreased, but the size of the individual leaves was increased longitudinally, while somewhat lessened in width. The same change in dimensions was also exhibited by the individual leaf cells. The influence of moist air elongated the leaf sheaths and also the individual blades, as well as the roots themselves, although the plants, even those exposed to dry air, stood in a nutrient solution. The fact that the substance as well as the form of the plants will be changed with varying humidity is to be surmised as a matter of course. In fact, my experiments show that in moist air a lesser amount of green 1 Wollny, W., Untersuchungen liber den Einfluss der Luftfeuchtigkeit auf das Wachstum der Pflanzen. Inaugural-Dissertation. Halle 1898. 2 Eberhardt, M., Action de I'air sec et de I'air humide sur les vegetaux. Compt. rend. 1900, t. 131, p. 114. 3 cit. Centralbl. f. Agrik.-Chem. 1904, Part 8. 4 Wollny, E., Untersuchungen tiber die Verdunstung und das Produktions- vermogen der Kulturpflanzen bei verschiedenem Feuchtigkeitsgehalt der Luft. Forsch. auf d. Geb. d. Agrikulturphysik Vol. XX, 1898, Part 5. 5 s. Dot. Jahresber. 25. Jahrg., Teil I, p. 76. Abh. von Nestler und Goebel. G Sorauer, Studien iiber Verdunstung. Forsch. auf d. Geb. d. Agrikulturphysik, Vol. III. Part 4-5, p. 55 ff. 425 matter was produced and that of this green matter, with plants in moist air, a large percentage occurred in the roots. In this, the aerial parts were richer in water. It was determined in regard to the functions, that evap- oration in moist air is absolutely less ; it is less also, however, per gram of green and dry matter produced, i. e. the plant in the production of one gram of material in moist air needs less water and this might occur because, under these circumstances, it produces it with few^ mineral substances. A further experiment with peas^ shows that the newly produced sub- stance has an actually lower percentage of ash. The increased amount of water taken up by the plant, because of the strong evaporation in dry air, results in the plant's taking up in a given unit of time only half as con- centrated a solution as it does with a weakened evaporation, when growing in moist air. These results explain sufficiently why plants in moist air frequently succumb more easily to disease than plants grown in dry air. The plants are weaker in growth, richer in water and poorer in ash. Nevertheless, we have no insight into the diversity of the organic elements in the plant body. It is very probable that plants grown in moist air are richer in sugar, poorer in starch, as well as richer in asparagin and poorer in actual protein. Influence of Moist Air on Plants Injured by Drought. It has been supposed that plants which have suffered from intense drought can be most quickly restored to their former activity if placed in a very moist atmosphere. The following experiment shows the danger of this procedure. Cherry seedlings, which survived a long drought in sand cultures, at once showed an adjustment to the lessened amount of w^ater supplied the roots. At first, without change of habit of growth, evaporation gradually decreased until the sand still contained possibly only 4 per cent, of the amount held when saturated. At this point the plants began to wilt, but, at the same time, evaporation ceased almost entirely. For example, at a temperature of 30°C. and abundant sunlight, a little plant which had formerly used daily about 8 g. water, evaporated only one decigram. After adding considerable water, the plant gradually increased the amount of evaporation. If, on the other hand, the drought continued too long, the leaves dried backward beginning at the tips, showing no discoloration. If now, after being watered, the plants were brought into moist air they did not recover as I had thought they would at first. Those under the bell jars containing dry air had elevated the upper mature leaves, and The partially dri'ed bases of the older leaves became turgid again ; evapor- ation again set in slowly. The gardener will find this observation of practical use in growing potted plants. Excessively dry plants after watering must not be changed in position. They must be somewhat shaded and they should not be placed in air practically saturated with moisture, since this will stop almost all activity. 1 Loc. cit. p. 79. 426 Cork Outgrowths. Cork is universally formed as normal tissue. It may increase abnorm- ally, forming an excrescence under special circumstances. Even the regular formation of cork may be observed in varying amounts in different seasons. Attention should be given to the usual bark pores with their rounded com- plementary cork cells separated by intercellular spaces. These cells, show- ing for some time a cellulose reaction, are steadily reproduced during the time of growth. In winter, when the exchange of gases in the dormant bark is at its minimum, the production of the complementary tissue is stopped. In the autumn a layer of normal cork is formed from the cambium layer instead of the roundish complementary cork cells. With the awaken- ing of bark activity in the spring, the cork cambium again forms comple- mentary cork, rupturing the winter covering layer of the lenticel, just as, when the first lenticels were formed, it had split the epidermis. The more moist the air becomes, the more frequently the elongating complementary cork cells which attract water are formed on the surface of the bark. The longish, mealy, white excrescences, which may be rubbed off, are well- known. They occur on the smooth barked trunks of cherries and alders in damp habitats when the atmospheric humidity is increased and the fohar transpiration decreases. At the base of the strong petioles of Juglans regia, Sambucus nigra, Ailanthus glandulosa, Paulowna imperialis and other trees, in the autumn, structures may be observed very similar to lenticels, only the cambium layer is missing (Stahl)\ Later research- has shown that cork cushions not only develop at the base of the petiole but, in many plants, at the veins of the under side of the leaf {Ficus slipulata) and finally also on the leaf-blades. Now, although this formation of cork on the leaf-blade is a phenom- enon almost as widely distributed as that on the stems with which it closely corresponds in structure and development, yet, in spite of the wide distribu- tion, there is no pathological significance in these formations. In these cork outgrowths of leaves, two types may be distinguished^, either the cork layer with its dividing walls and its usually one-layered phellogen lies parallel with the leaf surface in the same plane,- — when the cork excrescences are raised above the surface of the leaf in the form of warts ; or the cork layer and especially its phellogen lies in the form of hour- glass-like, depressed zones in the interior of the leaf and usually becomes deeper and deeper. Many plants have both forms on the same leaf. In contrast to the regularity of the appearance and production of stem cork, emphasis should be placed on the accidental appearance of cork excrescence on leaves. Aside from the fact that the two above mentioned types can begin on the same leaf, there are also transitions between the two types. In 1 Stahl, Entwicklungsgeschichte und Anatomie der Lenticellen. Bot. Zeit. 1873, No. 36. 2 Poulsen, Om Korkdannelse paa Blade. Kjobenhavn 1875. 3 Bachmann, tJber Korkwucherungen auf Blattern. Pringsheim's Jahrb. 1880, Vol. XII, Part 2, p. 191. 427 fact, the cork outgrowths can arise in the same leaf in different layers (they usually occur in the sub-epidermal layer) and can have a different develop- mental course (Bachmann). The external appearance of these cork formations on leaves, occurring on gymnosperms, monocotyledons, and dicotyledons, is very different. Sometimes there are small cones, sometimes sheets of cork, or strips of considerable extent. " At times the cork excrescences, however, lead to the formation of holes which penetrate through the whole leaf (Ilex. Zamia, Ruscus, Camellia axillaris, Peperomia obtusifolia. Eucalyptus Gunni and E. Globulus, etc.). This perforation begins as yellowish points. In leaves with large intercellular spaces the cork formation is preceded by a growth of the parenchyma cells, in such a way that the intercellular spaces are filled by outpushings of the cell walls. If the cells with somewhat thicker walls in the rows of cork cells are changed by repeated division, the cell walls lose their original thickness. Frequently also the cork cells undergo a subsequent elongation after they have split the epidermis; the outer ones are stretched first. • In Zamia integrifolia, brown stripes, running parallel with the veins, are found on leaflets, splitting later into pieces or tearing down the whole length. These stripes are cork tissue which are not produced sometime after the leaflets have been torn and, thereby, representing wound cork, but are structures formed even embryonically in the younger leaf. Cork ex- crescences appear on both sides of the older leaves of Dammara robusta, but especially on the upper side, remaining usually small and flat. When young, they form small round spots on the green leaf surface and later be- come brown, when they are raised like little mounds. Finally, the epidermis and the immediately adjacent cork layers rupture. In Araucaria Ciinning- hami and more rarely in A. Bidwilli, small cork mounds may be found on older leaves of the previous year which can coalesce into ridges. In Sciadopytis verticillata and Cryptomeria japonica small cork warts occur at times also on older leaves ; such structures may be recognized more fre- quently (but usually only on the underside) on the broad leaves of Sequoja sempervirens. In commercial horticulture, small point-like cork warts in Cyclamen persicum form a blemish as do also the chart-like etchings on the upper side of leaves of Pelargonium peltafum and in different kinds of foUage Begonias. These cork outgrov/ths appear, so far as observed, only in moist greenhouses and hot beds. Among the monocotyledons, Clivia Gardeni, Hook and Clivia nobilis, Lindl., Pandanus reflexus, Dichorisandra oxypetala, Billbergia iridifolia, Vanilla planifolia, and other orchids exhibit cork structures which penetrate into the leaf. The cork excrescences on the leaves do not occur in the same amount in all specimens, nor to equal extent on all the leaves of the same plant, nor are the appearances constant each year. It must be concluded from this that special conditions cause this development of cork structures. So far as experience shows, they are due to an excessive atmospheric 428 dampness with a continued excessive supply of water at the roots and a decreasing intensity of hght. An insight into the production of these phe- nomena may be found in the Cork Disease of the Cacti. This disease, often found in imported cacti, has become a constant source of anxiety for the European grower. It manifests itself in the different varieties of cactus, in the appearance of dry, papery places. These begin sometimes as raised yellow spots, or as spots remaining green and looking somewhat glassy. They widen out either into large cork colored surfaces, or become depressions which look like the scars of places injured by biting insects or animals. My special studies were first of all with Ccrcus flagelliformis. In severe cases the tips of the stems still seemed t Fig. 70. Piece of the trunk of a Phyllocartius which, on its under side, exhibits "cork excrescences in the form of warts, while, on the opposite side, the process of perforation is beginning-. fresh and green, but at a little distance back from the tip a zone of rust colored specks began, starting usually below a thorn cushion. The specks gradually united into a rusty surface which ruptured here and there. On the healthy part, the outer epidermal tissue consisted of two layers of irregularly 4 to 6 sided cells with thickened, heavily cutinized outer walls. Under this double layer was a single row of cells elongated tangentially and thickened like collenchyma. Then came the bark tissue containing chloro- phyll and an abundance of crystals of calcium oxalate. Cork had been formed in the outer epidermal cells of the rust spots on the stems. The cork cells were wall-like in some places, irregular in others, like a cap which finally ruptured on the crest, thus rupturing the outer wall of the upper epidermal layer. In other Cereus species, different sides of the stem seemed whitish and dry in wide stretches. Here cork layers formed in the epidermal cells in the angle of the stem; these were raised like papillae, while on the surface 429 of the stems they were warts. In young spots a change hi the bark par- enchyma was noticed. The outer cells were no longer distinctly collenchy- matic and tangentially elongated but rather were broadened radially, thin- walled, poor in chlorophyll and partially divided. Because of this structure, the bark cells forced the cork tissue outward, causing whitish blisters or warts. In Opuntia and Phyllocactus, the second variety of cork outgrowth is prevalent and is characterized by the formation of depressed places or by total perforation. Fig. 70 of a Phyllocactus illustrates both forms of cork excrescence. On the under side we see wart-like convexities, on the upper side the beginnings of perforation. A cross-section of the flat stem shows the fleshy bark beyond the vas- cular Inindle. In healthy places the bark is hlled with starch (st) and con- tains numerous slime cells (s), cal- cium oxalate crystals and glands (0). when the wart begins to form, the bark parenchyma, by utilizing the starch, stretches, divides and pushes out the epidermis. The peripheral tissues (i) , poor in contents, begin to die and a layer of flat cork cells (/) separates the (lead tissue containing many inter- cellular spaces filled with air from the still living succulent tissue. At this ])oint the progress of the disease stops and the stem seems covered with dry paper-like spots. If, however, there is no further removal of starch nor stretching of the bark parenchyma, and large particles die, the upper surface of the dead tissue finally ruptures, forming holes (/) which gradually be- come more and more depressed v/hile the flattened cork cells (t) are constantly formed, growing inward. At r the bark changed, giving rise to the cork formation. There the change occurred earliest and most intensively and advanced rapidly into the interior of the leaf. The process of cork formation is in itself a normal process in cacti when the stems reach a certain age. At the base of older stems there may be seen a formation of bark as in trees. The i)atliological feature is the for- mation of flat cork layers in the younger parts, at the expense of the bark. The cause may be found in the formation of tissue centers in the bark in which the cells elongate, while the starch breaks down and the cell contents are gradually impoverished. Fig. 71 shows the first change in the tissues, in the formation of bark types of cork excrescence. This illustrates a piece of bark from Phyllo- Fig. 71. First stage of a cork excrescence in Phyllocactus. 430 cactus with a spot dififerentiated from its healthy surroundings by a scarcely perceptible yellowish discoloration and a very slight convexity : e, indicates the epidermis ; I, the collenchyma-like thickened cells ; o, the crystals of calcium oxalate. The change begins close to the vessels i^g) in the delicate venation traversing the succulent parenchyma. The darker spots in the parenchyma indicate the chloroplasts, which are found there either in the normal position along the walls, or collected in large refractive drops of cell contents (o'). Probably as a result of an accumulation of destructive enzymes and an increase in acid content, the sheath cells of the vascular bundle {gs') and those even further away ii) become poorer in contents and elongate, thus causing the first evidences of disease. Thus an inner growth is produced which, if it advances nearer to the upper surface, starts the for- mation of cork. If the cells, extending further back into the inner bark, become impoverished, more and more cork will be formed. Since the cork tissue cannot elongate as the organ grows, it must be of necessity rupture, and thus forms superficial warts as the cork formation advances. Grooves are formed by the strain of the tissues growing with varying rapidity and these deepen until there is a complete perforation as in deep scurvy of potatoes. In order to control or eradicate this important disease of cacti, the water supply is lessened and air is given abundantly. Should there be a regular appearance of the disease covering several years, the plants must be kept dry even to shrivelling. Bitten or Perforated Leaves. In herbaceous plants, as also in trees in different localities, the leaves are often strongly perforated as if some animal had eaten away the tissue between the veins, without, however, finding any animal on whom the blame may be laid. Since the injuiy increases in intensity with time, ob- servers are more eager to find the cause. In extreme cases the injury is of such extent that the leaves appear like many paned windows, since only the network of veins remains together with a slight margin of leaf parenchyma. .Such leaves are often bent and twisted but do not die prematurely. The shoots themselves show no disease and frequently new sprouts with normal foliage develop in the axils of these perforated leaves. The most extreme case which I have had opportunity to observe was found in potatoes. The shoots of the plants at the beginning of July bore only perforated leaves (see Fig. ^2). Usually the lower leaves w^ere per- forated only in places, the upper ones w^ere split longitudinally in the areas between the veins and frequently parts of the edge were also destroyed. The younger leaves often had a feathery appearance since the different leaflets consisted only of the veins with a very slender margin. Between the perforations yellowish points were seen in the leaf-blade when held to the light. These proved to be the first stages of the process of suberization w^hich ended wdth the perforation of the leaf. The formation 431 of cork took place in the way described in the preceding general section. It was proved, however, to be a secondary phenomenon. The disease first manifested itself in the pale green color of the mesophyll usually near the finely anastomosing veins. This appeared more frequently in the palisade than in the spong}' parenchyma. In isolated cases, instead of becoming pale, the cell contents discolored to a brownish tone which was accom- panied by the suberization of the walls. The epidermis, in its changes, followed the mesophyll groups and small dead tissue centers were produced which did not change any further. In the group of cells forming the transparent places in the leaf because of the dissolution of the chlorophyll, an enlargement was seen on account Fig. 72. Potato leaf perforated as a result of a morbid formation of cork. of which the non-participating epidermis was pushed outward. A cork formation now set in among the enlarged mesophyll cells ; then these places broke out. By the advance of these processes backward into the flesh of the leaf, the cork centers were depressed to complete perforation. This can be understood easily since young leaves are affected. In their growth, these stretch all the tissues; since the tissues containing cork cannot stretch with the other tissue, they must tear. The process, therefore, is, in principle, that found on the stems of cacti. In other plants also, which show perforations of the leaves, the im- poverishment and enlargement of difi^erent cell groups may be recognized as the early stages and, on this account, naturally belong to the phenomena 43-' which will later be described as intumescences. The causes will also be taken up more in detail then. In the production of the perforations, individual nutrition plays a prominent part; for, in the same place of growth, specimens which seem almost eaten up, may be found near plants which remain untouched. At times, only isolated species suffer. Thus, for example, I found in groups of different species of maple only one single vigorously growing variety which was diseased, among other kinds developing noTmally. Formation of Cork on Fruits. The brown, dull, not infrequently scaley spots or lines on the smooth outer surface of apples and pears, the so-called rusty tracery is well-known. Some varieties show the phenomenon every year, so that it has been in- cluded in the general description of the species. They are formations of cork, which, as a rule, arise from the stomata. In some years the process be- comes abnormal in its appearance, so that not on]}' "the varieties with rust spots" have a |)artia] or entire cork-colored sur- face, but also the fruits of varieties usually remaining smooth-skinned are affected. Injuries to the epidermis when the fruit hrst swells are the cause of this phe- nomenon. In cases already known to me (apples, pears, plums, grapes), it could be proved that a light late frost had split the cuticle covering of the young fruit in innumerable small tears. Under these the fruit at once formed cork layers. In places the epidermal cells die and remain together with the first formed cork layers as scales on the rather dull, leather colored surface of the fruit. Whenever the corked places form a contiguous surface, the fruit in development does not swell uniformly, with the result that huge splits show on the fruit itself. The spores of Monilia especially enter these places and mummify the fruit. But these phenomena, in the strictest sense, do not belong here. They are connected with an excess of moisture only in so far as the splitting occurs the more easily, the more quickly the swelling of the fruit takes place with continued moisture. On the other hand, I would like to consider the appearance of cork warts on the stems of grapes as a process which becomes noticeable only in moist air. In Fig. 73 we see two grapes, the stems of which exhibit a browned rough surface due to the appearance of many cork-colored, closely distributed warts. The phenomenon occurs before the grapes have reached their normal size. Fi£ 73. Grapes with cork warts (W) on the fruit stem. microscopically small splits. PART VI. MANUAL OF Plant Diseases BY PROF. DR. PAUL SORAUER Third Edition—Prof. Dr. Sorauer In Collaboration with Prof. Dr. G. Lindau And Dr. L. Reh Private Docent at the University Assistant in the Museum of Natural History of Berlin in Hamburg TRANSLATED BY FRANCES DORRANGE Volume I NON-PARASITIC DISEASES BY PROF. DR. PAUL SORAUER BERLIN WITH 208 ILLUSTRATIONS IN THE TEXT Copyrighted. 1916 By FRANCES DORRANCE P'- JUL 1 1 1917 THE RECORD PRESS Wilkes-Barre, Pa. ©CU470231 433 The warts are developed most abundantly at the place where the grapes join the stem: large branches of the clusters usually remain smooth and, as a rule, only some grapes show the disease. This is unimportant in con- tinued dry weather, but with humidity makes for a development of parasites. If then a sharp dr}- period follows, some of the \er}' warted stems shrivel and the grapes as well. Fig. 74 shows a cross-section through a warty grape stem which exhibits the usual axillary structure and has some strikingly broad medullary rays (ms) which divide the wood ring (h). In the bark we notice a regular distribution of the hard bast groups (b) and in front of them the sieve elements (.v) with often thickly swollen walls. At o is indicated one of the abundant crystals of calcium' ox- alate. These occur at times as small glands, at times as raphides. The dififerent stages of the forma- tion of these corky warts are shown at JV. The wart-like ex- crescences, which resemble len- ticels. are produced by the radial enlargement of some of the par- enchyma cells lying immediately beneath the epidermis or some- what deeper; and the consequent outpushing of the outer skin. By an increase of this process, which does not preclude the dividing of the elongated cells, an accumu- lation of tissue is produced with a corky covering which finally be- comes brow^n and splits. By the increase of the bark parenchyma and the dying of the outermost brown corked elements the large warts are produced, the peripheral cell layers of which are pushed out from each other in a saucer-shaped form. A distinct cork cambium is formed connected with the dying bark of the outermost layers. This constantly extends deeper into the bark of the stem. If the weather continues to be cloudy, warm and damp, or if the grapes are too much hidden under the foliage, the conditions are ideal for the development of fungi among which may be noticed first of all Botrytis cinerea. The phenomenon is especially frequent in greenhouses, and here the close, moist atmosphere must be improved by ventilation and heat must be provided at the same time. If the warty grape stems are found out of doors, some of the foliage above the bunches of grapes must be removed and, after each rain, the water retained by the foliage carefully shaken off. 74. Cross -section through the warty fruit stem of a grape. (Orig.) 434 As a phenomenon related to cork excrescences, I once observed wings on young grape leaves. These appeared between the larger side veins on the leaf blade and were opposite each other like lips. These outgrowths (emergences) were a development of the blade usually forming over a vascular bundle. The chagrinisation (granulation) of the rose stem should be cited here in addition. As is well known, standard roses are laid flat through the winter and covered with brush or earth. At times in the spring when these are raised from the soil, the young bark stems, which should be smooth, are often found covered with small warts, many having, as a rule, a pale or brownish-red periphery. The warts are outgrowths of the lenticel. These begin below the stomata and force the guard cells apart. Mycelia may be proved to be present if the periphery is discolored. Yellow Spots (Aurigo). At times the leaves of monocotyledons, more than those of dicotyledons, are covered with yellow or reddish brown specks. This speckled condition begins at the tip. The specks usually shade through a pale green zone into the otherwise normally green leaf. Their number may be increased, since, as the disease progresses, small new specks are formed between the older ones. At times the tissues affected in the discoloration are forced out, which shows a clear transition to real intumescences^. This yellow spotting occurs especially in greenhouse and house plants, and among these, we find it most frequently in Dracaenae, palms and varie- ties of Pandanus. To illustrate the formation of these specks and show how, under certain circumstances, they increase until the leaf is perforated, I will cite some observations on Pandanus javanicus. The spots always begin in the part of a mesophyll lying between two veins. Toward the upper side of the leaf these cells resemble the palisade parenchyma, on the under side, spong)^ parenchyma, but in the centre they are very thin walled, approximately isodiametric, somewhat hexagonal, filled with a colorless watery content. From the innermost colorless tissue groups, the peripheral cells, i. e., those bordering on the mesophyll, containing chlorophyll, begin to stretch excessively toward the side of the least resistance, viz., toward the centre, whereby they frequently compress the central cells. Frequently the elon- gatioin takes place only in the cells arranged directly upward and downward, but not in the lateral ones of the thin-walled group, and a peculiar arrange- ment is thus produced. The central part of the tissue then consists of empty cells arranged radially, elongated like pouches, which often have become thick-walled by swelling, later browning and turning to cork. With increasing intensity, the spongy parenchyma is involved in this process of elongation with the dissolving of its chlorophyll body; its contents disinte- 1 Vol. 9, Part 5. 435 grate 'into a brown granular substance, and in this the yellow coloration becomes more intensive. The upper surface of the leaf is often raised like a wart when the tissue, rich in chlorophyll, is drawn into the abnormal process of elongation. Frequently the progress of the disease is stopped when the elongated cells become cork, then there are only yellow spots, recognizable when immature, indeed, only when the light falls through them. The whole centre of the disease may then be separated from the healthy tissue by a zone of actual cork cells. As the disease advances in severity even the cells of the vascular bundle sheath may be affected and show the characteristic elongation, browning and swelling until finally the elongating mesophyll cells rupture the epidermis above them. The processes already described under the phenomenon of perforation nov; follow. Diseases due to fungi and seemingly similar in outward appearances may easily be distinguished in Pandanus, since in them there is no elongation of the cells. In Dracaena rubra and Draco, the disease at times only disintegrates the chlorophyll of the inner cell groups ; here membranes are often seen with bead-like swollen places extending into the inner part of the cell. In studying Dracaena tndiz'isa, I observed an abundant formation of sugar in those tissues in which the chlorophyll had dissolved. This sugar did not occur in healthy tissues and disappeared from the diseased spots as soon as the walls began to turn brown and develop cork. Hence this yellow spotted condition seems in many cases to be an initial stage of real intumescence, in others, as in the Dracaena, it is usually a diseased condition without any sequelae and the temporary increase of sugar and the bead-like swellings of the walls point to causes which are similarly affective in the over-elongation of the cells. In practical treatment, one should realize that the plants exhibiting aurigo suffer from a supply of water which they cannot assimilate. The amount of water destroying the equilibrium need not be greater than that normally supplied, but, being given during the dormant period, the plant cannot utilize it and the external con- ditions are not such as could stimulate this absorption. The spots occur with great frequency in the autumn and winter when the plants are brought into a warm place. They then have sufficient heat, water and mineral nutrient substances, but the light is deficient. Hence the one-sided stimulus must be removed and the plant put in a cooler, dryer place where there is as much light as possible. Intumescences. The knot-like or pustule-like distensions of the tissue usually occurring in groups and which I have considered as "Intumescentia" have not been sufficiently studied by practical pathologists. They are most abundant in leaves but are not rare on the stems. However, as yet, the observation of intumescences on blossoms and fruits has been limited. The consideration of a specific case gives the best information as to the development of such structures, the value of which lies in their symptomatic 436 significance. In January, 1879, I observed specimens of Cassia tomentosa in a hothouse. I found the edges of leaflets on young shoots were curled under. This curhng seemed to be due to the increased growth of the upper side, which showed a pustule-like convexity. When these convexities were fewer and located along the mid-rib, the leaflet was less curled. If they were scattered abundantly and uniformly over the whole surface, the leaf seemed almost blistered. This cannot be said to be actually blistered, how- ever, because the convexity of the upper side corresponds to no equally great concavity of the underside. The swelling is conical, having, at first, the same color and dull upper surface as the rest of the leaf. Later the tip of the cone becomes light colored, more rigid and shiny. Still later the tip becomes yellow, broadens and finally ruptures (Fig. 75, se), if the whole leaflet has not already turned Fig-. 75. Leaf intumescences in Cassia tomentosa. (Orig.) yellow, the swelling now seems depressed in the centre, funnel-like, and turns brown. The phenomenon is due to a sporadic tube-like outgrowth of the upper palisade parenchyma (p). The inner side contains many chloroplasts closely packed together and, toward the spongy parenchyma, is provided with slender, slit-like intercellular spaces filled with air. With the appearance of swelling, the chloroplasts begin to disappear from the tip of the cell backward, a few of the cells become elongated; gradually the surrounding tissues are involved. More and more chlorophyll is dissolved as the elongation advances, so that finally the palisade cells, which have become tube-like, seem almost entirely colorless or are provided with a few small yellowish grains scattered throughout the whole cell lumen. With this elongation of the cells forcing up the epidermis there is a slight in- crease in width, which presses the cells very^ close against one another laterally, with only small intercellular spaces in the spongy parenchyma. As 437 soon as this pressure has ruptured the epidermis (e) at the highest point of the excrescence {^e) the ends of the paHsade parenchyma, which are now freed, swell up hke clubs (kp) and, turning brown, thicken their walls more or less farther back. The epidermal cells which are ruptured, and others in the same region, turn brown and partially collapse. The same swelling can also occur on the side of the leaf. In this case, the spongy parenchyma cells lying directly beneath the epidermis, covered with hairs (h) and otherwise usually isodiametric, become long and cylindrical. In various epidermal cells of the upper as well as the lower side of the leaf and in many of the parenchyma cells which have grown out like tubes, glycerin draws together in indi- vidual large glucose drops or many small ones. I found similar leaf distensions in Acacia longi folia and A. micro- botrya leaves specked with yellow and also on those normally green. Myrmecodia echinata is an ex- ample of the general appearance of intumescences with cork leaves. The leaves of this plant usually de- velop intumescences on the lower side, while the cork excrescences predominate on the upper side. In Fig 76 we perceive that actually both of the parencyma layers lying next to the epidermis participate in the formation of the delicate gland- like outgrowth of the tissue. The epidermis (c) (its stomata are un- changed) is raised up and ruptured where it joins the normal tissue. Strange to say, however, it appears to be still unbrowned and turgescent, i. e., still completely and sufficiently nourished like the tube-like mesophyll cells (a). I found that the excres- cences had dried up and had been cut ofT from the healthy parenchyma by the formation of the layer of flattened cork cells at their base (b) only when the leaf was well advanced in age. The partially blister-like, partially wart-like cork excrescences are most frequently found without intumescences. They are distributed irregularly over the whole leaf surface as rusty, sometimes silvery shining specks; the region of the mid-rib is most affected. The cork forms first within the epidermal cells, advancing thence into the mesophyll, attacking at first two adjoining layers of the hypoderm. Fig-. 76. Piece of a leaf of Myrmecodia echinata with a cork wart breaking out on the upper side and gland-like intu- mescence on the under side. (Orig.) 438 formed of four or five rows of colorless cells with very wide lumina but poor in contents (d). The underlying palisade parenchyma, extending into the hypoderm in the conical-Hke buttresses (e) is usually not affected, but, like the spongy parenchyma, poor in chlorophyll, often exhibits strongly refractive, often green colored drops in its cells where the cork is formed. Often such corky masses very greatly resemble certain fungous dis- eases as I have had opportunity to observe in Pelargonium zonale. The under sides of the leaves were covered with white cystopus-like masses, isolated or united into large groups. These were hemispherical cork excrescences, later separated from one another like fans and filled with air. They began with an enlargement of the spongy parenchyma, whereby all the intercellular spaces were filled up. The epidermis, as a rule, remained unchanged while the mesophyll cells adjoining it were elon- gated perpendicularly and were divided by cork walls, with a gradual loss of chlorophyll. The cork cells partially lost their parallel arrangement because of an irregular increase and were much distended until the epidermis ruptured. The epidermis, however, manifested its restraining influence by pressing upon the cork cells, so that their walls seemed crumpled. The process of elongation and suberization extended deeper and deeper into the mesophyll until at times the excrescence was four times as thick as the leaf. A brown, twisted mycelium (possibly a Cladisporium) grew into the stomata and later into the wound of the rupturing cork excrescence. Grapes are especially susceptible to intumescences and especially those plants taken from greenhouses into the open for early forcing. In addition to the excrescences on the leaves, little knots were formed on the stem of the grapes, and, since the structure of these dift'ered from the warts already described, they may be considered here more thoroughly. Fig. yy is a cross-section through such a knot. The vascular bundles, forming the wood-ring of the stem, are indicated by h, the pith by m; the hard bast by hh ; the abnormal change in the bark parenchyma extends to this point. This change is characterized by a distension of the parenchyma lying underneath the coUenchyma-like elements and an ultimate elongation, the cells of which have subsequently divided. Because of this over elon- gation the coUenchyma {c) is pressed together and, without previously having participated in the elongation, dies together with the epidermis. The normal epidermis may be recognized 2it e; k indicates the cork zone formed on the boundary of the dying tissue. The latter may not always be found, however. Often the dying tissue passes over imperceptibly into the very thin-walled, still living tissue which shows slight cork formation at the place of transition, eg indicates the normal collenchyma, occurring in groups and not in connected rings. The division and over-elongation of the bark parenchyma and the absence of cork excrescences distinguish these knot- like intumescences from the cork warts which, in an immature stage, resemble them greatly. 439 The intumescences on grape leaves have on the under side the form of iand-Hke elevations which often coalesce and are indicated on the upper leaf surface by yellowish and at times somewhat raised places. They are produced by tube-like outgrowths of the spongy parenchyma lying under the epidermis ; the cells of this spongy parenchyma are poor in solid con- tents and closely pressed against one another b}^ the distension. With their increasing over-elongation, the epidermis is browned and ruptured. In the beginning only the cells lying directly beneath the epidermis are affected, but usually, after the distension begins, the cell layer next below is attacked and it is usually this which later is most elongated and its cells not infrequently divided by cross walls. The cells forming the centre of the swelling are the longest and most slender and stand exactly perpendicular to the outer surface of the leaf, while those laterally adjacent are arranged Fig. 77. Part of a knot-like intumescence on the stem of a gi'ape. (Orig.) slantingly like a fan, decreasing in length, increasing in width. The presence of starch could not be proved. In the most extreme cases observed, all the cells of the mesophyll, up to the palisade parenchyma of the upper side, take part in this elongation. I did not observe, however, that the palisade parenchyma had been attacked. These intumescences are not infrequent in vineyards and cases may be found showing their cause most clearly. In the course of years material has come most abundantly to my hands. I quote from the report of the court gardener, Mr. Rose. He had a grape house planted with 14 vines; of these, six were Black Hamburgs (Blauer Frankenthaler), one of these was planted where the hot water pipe entered. Therefore, the temperature was higher and the humid- ity very great. This vine alone developed intumescences to such a degree that the under side of the leaves seemed almost felty. A Royal Muscardine vine 440 was planted on the opposite side of the greenhouse. The foUage of these two plants became intertwined as they grew into the upper part of the house. The Royal Muscardine plant had no trace of disease. These instances show how differently varieties behave in the same environment, and how individual diseases in the same variety may be explained. In regard to the dift'erent behavior of dift"erent vines, reference should be made to a study by Fr. Muth\ who observed the production of intu- mescences after spraying the leaves with copper compounds, while, for ex- ample, the early red Veltliner and Muscat St. Lauret show no sweUing. Morillon panache, Madeleine Angevine and the Blue Ox-eye were very greatly affected. In another similar case, Noack- found that the disease decreased when water was withheld. The occurrence above described does not correspond with the phe- nomena found on Ampelopsis hederacca". In this plant Tomaschek found bead-like structures on young branches, petioles and leaf veins, and espe- cially on the outer side of the side leaves. The beads were very small when the illumination w^as insufficient and dried up in the autumn. They were formed below the stomata even in the very young parts, since the cells surrounding one cavity grew down into it and forced up the epidermis by an increase in size. In the autumn and winter true lenticels with a cork formation were found, instead of these outgrowths. In addition to the instances already described and those to be men- tioned further on of disease manifesting itself on greenhouse plants, I will now report on the behavior of one of the Gramineae. On the island Riigen, among vigorously growing oats, plants were found showing abnormal growth. A cross-section of the lowest node, covered with dirt, is illustrated in Fig. 78. The centre of the node exhibits the well known irregular course of the vascular bundles (g) and the primordia of a root (w) ready to break through the distended bark of the node. In this bark covering r indicates the normally formed part, while at r' the subepi- dermal parenchyma cells are already beginning to elongate radially. The excessive elongation increases at j to a decidedly tube-like character and affects all layers of the bark near the root just coming through. This dis- tends the epidermis very greatly, and, as its cells do not take part in the process of elongation, it finally begins to separate in different places (c). The leaf blade at s shows an external injury from grazing cattle which extends deep into the node. The tissue is considerably browned, the vessels, as far as the middle of the node, are partially filled with gum. The 1 Muth, Fr. tjber die Beschadigung der Rebenblatter durch Kupferspritzmittel. Mittel. d. Deutsch. Weinbau-Vereins 1906. 2 Noack, Fr., Fine Treibhauskrankheit der Weinrebe. Gartenflora 1901, p. 619. 3 Tomaschek, tJber pathogene Emergenzen auf Ampelopsis hederacea. Osterr. Bot. Zeit. 1879, p. 87. 441 facts warrant considering this injury the exciting agent in the formation of intumescences. Other adjacent blades which have not been similarly injured, do not develop the excrescences. The assumption can be very easily made that, given an abundant supply of water and nutritive sub- stances, the turgescence in the stem would be great, while the evaporation from the node covered with soil would be slight and an injury from grazing cattle which would remove part of the tissue, would so increase the turgor that intumescences would be formed. I had already observed similar correlation phenomena in the action of copper sprays on potato leaves^ In vigorously growing varieties a number of leaves were found injured by the spray; near the dead spots in the tissue, the intumescences later appeared. Still other causes may have similar 9 r ,g Fig. 78. Intumescence on the lower node of an oat plant. results, since small warts have been observed on potato leaves when the copper solution had not been used-. Von Schrenck^ has reported more recent results in this connection. A few days after cabbage plants in green- houses had been sprayed with copper ammonium carbonate, pale knots, gradually becoming white, developed on the under side of the leaves. They proved to be intumescences. Unsprayed plants in the same house showed no eruptions. Spraying with weak solutions of copper chlorid, copper acetate, copper nitrate and copper sulphate did cause some distensions. Von Schrenk, however, considered these intumescences a reaction of the leaf tissue to the chemical stimulus of the poisons, not correlative phenomena. 1 Sorauer, P., Elnige Beobachtungen bei der Anwendung von Kupfermitteln gegen die Kartoffelkrankheit. Zeitschr. f. Pflanzenkrankh. 1893, p. 32. 2 Masters, Leaves of potatoes with warts. Gard. Chron. 1878, I, p. 802. 3 Schrenk, H. v., Intumescences formed as a result of chemical stimulation. Sixteenth ann. report Missouri Bot. Gard. May, 1905. 442 Here belongs the case which Haberlandt^ describes in a Liane, Cono- cephalus. He describes the formation of compensatory hydathodes, after the normal organs of the leaves have been poisoned. The extremely abundant nocturnal transpiration takes place at the base of the shallow depressions on the upper side of the leaf by means of sharply differentiated, epithemial hydathodes with water pores always lying over the juncture of vascular bundles. Where these organs had been poisoned by painting the leaf with a 0.5 per cent, alcoholic sublimate solution, small knots were Fig. 79. Stem of Lavetera trimestris — with intumescence. (Orig.) Fig. 80. Brancii of Acacia pendulata — witli intumescence. (Orig.) Fig. 81. Magnified section of Fig. SO. (Orig.) formed above the vascular bundles. Each morning large drops of water were found. on these places. These knots, which had assumed the function of the dead hydathodes, seemed to be composed of long, pouch-like cells, in the lower part divided by cross walls adjoining one another (without inter- cellular spaces). The club-like swollen ends separate from one another like a brush. They have been produced by the elongation of the conductive oarenchyma cells and often of the palisade cells and have broken through the epidermis. 1 Haberlandt in "Festchrift fur Schwendener," cit. in Naturwiss. Woclienschr. 1899, p. 287. 443 Fig. 79 shows the habit of growth of a piece of Lavatera trimestris stem with excrescences due to cell elongation. Fig. 80 shows the rup- tured bark of Acacia pcndxila, while Fig. 81 shows the same much more clearly because of its magnification. In Malope grandiflora and Lavatera trimestris, stems and branches were found bearing many long calhises on the side exposed to the sun. These were caused by considerable longitudinal and radial stretching of the bark and wood cells. If the callus is still young, the process usually sets in by a radial and still more marked tangential stretching, at the level of the primary hard bast bundles of the parenchyma cells containing chlorophyll and lying between two bundles : with this increase they are pushed outward Fig. 82. Cro.ss-section through a year old branch of Acacia pendula with intumescence. (1-433).) (Orig-.) like a bow. The mechanical ring appears to be broken because the bast bundles are pressed far apart and the collenchyma layers less developed. In large intumescences the broken places apparently extend deeper since the wood also changes its prosenchymatous elements and the cells of its medullary rays into a wide meshed parenchyma. Fig. 82 throws sufficient light on the processes concerned in the forma- tion of the moss-like collection of intumescences in Acacia pendula; m indicates the pith ; h the woodring ; c the cambium ; h the hard bast groups ; e the epidermis ; s the beginnings of elongation within the primary bark ; zv the bark parenchyma cells which have become tube-like and ascend in spirally parallel roM^s and, after breaking through the epidermis at w, separate from one another like sheaves. 1) Sorauer, P., tjber Intumescenzen. S. 458. Ber. d. Deutsch. Bot. Ge.s. 1899, Bd. XVII. 444 When the intumescence is highly developed, the over-elongation extends backward to the secondary bark, stretching the cells of the phloem rays (q). In fact, cases occur in which the woodring seems stimulated in those layers last formed because the outermost cambial layers are constructed of paren- chyma wood. As on the various kinds of Eucalyptus, the intumescences occur most frequently on the side of the branch turned toward the light, and often only then. After the explanation given these cases, a more thorough discussion is needed here. Fig. S3. Blossoms of Cymbidium Lowi with gland-like intumescence (a) on the tops of the perianth. (Orig.) Intumescences occur most rarely on blossom organs. I observed one such case in Cymbidium Lowi. The blossoms, normally large and otherwise well-developed, exhibited on the under side of the perianth, quince yellow or yellowish green, hemispherical bosses (Fig. 83a) ; exactly the same struc- tures could be found also on the ovaries. In an immature stage they had a smooth upper surface, later they cracked open in the apical region and became depressed like a funnel. In the older knots, the depression advanced to complete perforation of the perianth tip. For this reason the blossoms were unsalable. In Fig. 84, it may be seen that the cell layer found beneath 445 the epidermis (e) of the under side of one part of the perianth has devel- oped erect, club-Hke tubes, at first bent toward one another hke lopped trunks (s), which first had been held together by the brown-walled, swollen epidermis not afl:'ected by the stretching. After the epidermis had ruptured, the tubes, which were rather thick walled, deep brown and had lost their contents, separated from one another like sheaves. The process of the over-elongation gradually attacks the deeper and deeper lying parts of the cell and finally advances even directly to the upper epidermis (w). At this time the epidermis ruptures and the tips of the perianth tip^ become perforated. The first stages of the intumescences have been studied in the ovaries. The first symptoms are a localized change in the epidermal cells, the walls of which are yel- -^ lowish brown, and swollen. These cells extend over«the upper surface. Beneath these places Fig. 84. Cross-.section througrh an intumescence on the perianth of Cymbidium Lowi. Upper figure, young stage; lower figure, mature condition. (Orig.) O upper side. C under side, e epidermis, i- (upper figure) beKiniiiiiR of elongation of the sub-epidermal cells, J (lower figure) the rupturing of the chib-like over-eloug ited cells, g vascular bundled. zt> av.mced condition of perforation. the tissue is perfectly colorless, more closely pressed together and filled more abundantly with protoplasm and oily looking drops. In some of these places a radial stretching has already taken place, which increases up to a diagonal inclination and cross-division. The process gradually extends to the sur- rounding cells, especially to those lying directly beneath the epidermis. The elongating layer becomes strikingly thick-walled and turns cofifee brown, while the collapsing, swollen epidermis forms a light yellowish brown cap. The discoloration is accompanied by a process of suberization, and to this probably may be ascribed the fact that the cells, becoming brittle in the still 1 Sorauer, P., Intumescences an Bliiten. Ber. d. Deutsch. Bot. Ges. 1901. 19, p. 115. Vol. 446 incompletely developed organs affected during their elongation, rupture and crumble. This is the beginning of the funnel-like depression at the tip of the intumescence. Among fruit intumescences, I have most frequently observed the unripe pods of beans and peas and noticed that many varieties of fungi infested the pods. The fruits, especially when near the surface of the soil, seemed closely covered with warts and awakened the suspicion of a marked fungous infection, as may be seen in the pea-pod shown in Fig. 85. •In cross-section, it may be seen in different places, which still seem smooth to the naked eye, that some epidermal cells have already begun to elongate. These often lie directly beside the stomata, but without the cooperation of the stomata in producing intumescences. Gradu- ally the parenchyma cells lying below be- come elongated. The elongated elemerfts are often divided by cross-walls and form warts. However, these are first formed of rows of cells arranged like columns. These warts grow to a height of one millimeter ; later they become brown from the dying of the peri- pheral layers and, after the covering splits, the rows of cells spread out like a sheaf. Fig. 86 shows the greatest development. The normal wall of the pod is shown at fr; c indicates the epidermis ; P layers of the thick-\\alled partially intersecting elements of the inner parchment-like fruit membrane. In the centre of the outgrowth {w) the elongated columnarly arranged parenchyma cells, separating toward the outside, irregu- larly like a fan, are visible. The outermost peripheral zones, shaded in the drawing {z, z), indicate the moribund tissue. The walls of these collapsed parenchyma groups, often shrinking together in curling tips, seem yellow to brown and give the warts an earthy color. From the repeated splitting of the intumescences, which are often so close to one another that only a few normal epidermal cells separate them, the whole wall of the pod obtains in places a mossy outer surface. The parchment-like inner wall of the pod forms intumescences ; indeed this is. more frequently the case than on the outer wall. In some kinds of peas, with very pithy pods, white tissue felts resembling species of mold may be found almost every year on the firm, smooth inner surface. In one case in the intumescence tissue, I found numerous oospores which presum- ably had belonged to Peronospora Viciae. Fig-. 85. Pea-pods with gland- like raised outer surface. (Orig.) 447 mcr- '^:. f^ From the examples already cited it is evident that the intumescences may occur on all aerial organs of plants. They form one link in a chain of phenomena which in part commonly occur together and in part, in fact, overlap. We have described the simplest disturbances as "Aurigo ;" they are characterized by the impoverishment of some tissue groups in the interior of the leaf with a destruction of the chlorophyll apparatus, usually with the formation of carotin. As the chlorophyll disappears the cells are apt to become distended. They fill the intercellular spaces, thus exercising pressure on the surroundings ; they finally die as the cell walls become suberized. Such nests of over-elongated cells are also termed "internal intumescences." In real intumescences the processes of impoverishment and cell elongation begin in the peripheral layers of the organs and in fact usually in the sub-epidermal cell layers, more rarely in the epidermis itself. The process of over-elongation is less impeded here and frequently advances into the more deeply lying tis- sue layers, so that we find cases of intumescences be- ginning on the under side of the leaf and gradually including the whole meso- pliyll as far as the upper epidermis. If the forma- tion of cork sets in in the intumescence tissue, we find wart-like or pitted cork centres which can lead to the complete perforation of the leaf. On the trunk the intumescence manifests itself in the hypertrophy of the bark parenchyma which, in isolated enclosed centres, breaks out from the bark in the form of warts with a smooth or repeatedly split outer sur- face. If the processes of over-elongation are not restricted to small isolated centres but attack the parenchymatous tissue in large, connected surfaces, all the organs rupture, causing the condition which we have called "dropsy." Although the phenomena described here are related structurally, we have treated them separately because different conditions are the dominat- ing causes of different outbreaks. Many investigations have shown that an atmosphere heavily ladened with moisture is a decisive influence in causing intumescences. 'J^eferences to my work and that of other older investigators may be found in the bibliography of Kiister's^ "Pathological Anatomy." I will cite '' 'WS^'/ Fit 86. Cross-section throug-h the outer surface of pea-pods witli intumescences. (Orig-.) 1 Kiister, Ernst, Pathologische Anatomic. Jena 1903. Gustav Fischer. 448 here a few especially pertinent observations. Some of these consider the question of light on the production of an intumescence. In this connection Atkinson^ explains that increased turgescence in leaves will be produced by repressed transpiration if the greenhouses are poorly lighted. Actually, in many cases, I found intumescences in the autumn and winter, because of cool, cloudy weather, if the greenhouses had to be heated after the plants had been brought in from outside. Trotter- states directly that half darkness favors the formation of intumescences. Steiner'^ also made the same observation, but stated that they will form only in the first days of darkness, so that one may conjecture an after eifect of the former activity of the light. This author observed also in Ruellia and Aphelandra, that the plants with equal atmospheric humidity only formed intumescences for a few weeks and therefore had adjusted themselves to the high degree of moisture. That the abrupt transition from dry to moist air is actually the decisive factor is shown by the renewed formation of intumescences, when the plants, after having become adjusted to a dry atmosphere for three weeks are brought again into moist air. Steiner found that no intumescences are produced under water, as did Kiister* on poplar leaves which he had left floating on water or nutrient solutions and in darkness as well as in light. Only when the illumination was too great, this process was suppressed, probably as a result of increased transpiration. In contrast to this, Viala and Pacottet^, in describing intu- mescences on grape leaves in greenhouses, said they had determined by direct experiment that intumescences are produced by the action of the light in a moist atmosphere. They are produced only directly under glass. The Missouri Botanical Garden makes a similar report. The most thorough experimental studies are Miss Dale's''. She ob- served with Hibiscus vitif alius, that the yellow and red rays are especially effective in producing intumescences. Her experiments with potatoes are especially instructive in regard to the action of sudden changes in the vege- tative conditions. The plants were grown in a cold section of a greenhouse and then set in a warm house at a temperature of about 2i°C., under a brightly illuminated bell-glass. After 48 hours, the stem and the upper side of almost all the leaves were covered with masses of pale green raised spots. If the plants were then brought into dry air, the blisters shrivelled 1 Atkinson, G. F., Oedema of the tomato. Bull. Cornell AgTic. Exp. Station 1893, No. 53. -' Trotter, A., Intumescences fogliari di Ipomea Batatas. Annali di Botanica 1904, No. 1. •" Steiner, Rudolf, tjher Intumescenzen hei Ruelli formosa und Aphelandra Porteana. Ber. d. Deutsch. Bot. Ges. 1905, Vol. 23, p. 105. 4 Kiister, E., tjber experimentell erzeugte intumescenzen. Ber. der Deutsch. Bot. Ges. 1903, Vol. 21, p. 452. ^ Viala et Pacottet, Sur les verrues des feuilles de la vigne. Compt. rend. Acad. d. sciences 1904, No. 138. « Dale, E., Investigations on the abnormal outgrowths or intumescences on Hibiscus vitifolius. Phil. Trans. R. Soc. of London, ser. B. 1901, Vol. 194. — Dale, E., Further experiments and histological investigations on intumescences, with some observations on nuclear division in pathological tissues. Phil. Trans. R. Soc. of London 1906, ser. B. Vol. 198. 449 up to black spots or perforated the leaves. >If some leaves fell, when the the plants were kept longer under the moist conditions, a great cushion of intumescences was produced on the leaf scar which displayed similarity to the wound callus. Older plants under similar conditions did not develop intumescences as quickly, nor as abundantly, while very old leaves developed none. Pieces of leaves, laid in moist cotton, after possibly two days, were thickly covered with eruptions. Quickly growing plants react most easily to the stimulus of a sudden change in the amount of moisture. These observations support our theory that the formation of intumes- cences is the reaction of the organ to a stimulus due to a sudden increase of atmospheric moisture. Only the immature organ reacts. If older leaves, as we observed, for example, with Solanum Warsccwicsii, respond with a formation of intumescences after having been brought from the open air into a damp greenhouse, these are exceptional cases of a special excitability of the species. Such cases occur in various plant genera. My results differ from those of other investigators, since I always found that intumescences invariably developed as the result of an arrested assimi- lation due to an excess or deficiency of light. It always manifests itself, however, in the scanty formation of solid reserve substances, usually, in fact, those already formed become dissolved. In accord with Miss Dale's assump- tion, the variation in assimilation may be connected with the increase of the oxalic acid content in the cells showing in the abnormal increase in turgor. In the .same way, experiments with young leaves and pieces of leaves show how the root pressure may be eliminated. Different combinations of the vegetative factors may give rise to that deficient assimilation which shows itself in the formation of intumescences. In the greater number of cases falling under my observation, I find the cause to be an increase of heat and moisture given to a plant naturally dormant, or being forced to arrest its assimilation from external conditions. The following action throws light on inhibitory regulations. The Tubercle Disease of the Rubber Plant. On the under side of the leaves are found numerous abundant, very small, gland or tubercle-like, hemispherical swellings. These are produced by the pouch-like elongation (Fig. 87, int) of the cells of the leaf, which, in a normal condition, have the form and arrangement shown at the side of the picture marked m and, therefore, are separated by larger or smaller intercellular spaces (i). The morbidly elongated tissue (int) on the under side of the leaf thus approaches the normal leaf palisade parenchyma (p) which is provided with a three-fold epidermis (e). Of these three layers, the outermost is small-celled and provided with a very thick layer of cuticle. The innermost cell layer of the epidermis displays more thin-walled, com- paratively very broad cells (w), which form the so-called water-storage, protective layer. Isolated cells, enlarged like sacs, in this layer conceal 450 those peculiar grape-like clusters of cell substance incrusted with calcium (c) known as cystoliths. The close structure of the upper epidermis of the leaf must prevent the passage of air, while the lower epidermis is well fitted for this purpose. The spong}^ parenchyma shows large intercellular spaces (i), the enclosed air in which can pass out through the air chambers under the stomata (a) and the stomata (st) to the outside, making room for the freshly entering outer air. The conduction of water takes place through the leaf veins, one of wdiich is seen in section at (/ and shows at r the large ducts. The course 7ZE/ Fig-. 87. Cro.ss-section through a leaf tubercle of the rubber tree- of organized building substances, produced in the leaf and flowing down toward the trunk, is shown at sch, the sheath of the vascular bundle ; k indicates the place at which the cells begin to enlarge because of an excess- ively increased turgor, thus filling the intercellular spaces and forming, therefore, first of all, "internal intnmescences." The excessive water con- tent manifests itself still more in the peripheral tissite, since, exposed only to the pressure of the epidermis, its cells elongate into tubes and, together with the epidermis, can be pushed outw'ard (int). Actually, therefore, the tubercle disease of the rubber plant is a regular intumescence which belongs to the previous division. We have, how^ever, 451 isolated this phenomenon of disease, becavise it has an essentially practical significance in the cultivation of Fiscus as a market plant. The disease occurs less often in plants grown for sale than in home ornamental plants, where it may lead to a premature defoliation. My experi- ments prove that it is produced by giving excessive heat and water to plants when their growth has stopped and their transpiration lessened, thus stimu- lating them to renewed activity. T produced intumescences by keeping a rubber plant in a very^ hot room and giving it abundant water after it had made a vigorous summer growth and passed into the normal resting period, instead of the cooler, drier environment which it should naturally have had. Leaves fell immediately, while intumescences were formed on the younger ones. When the plant was put in a light, but cooler place, the leaves with the intumescences remained on the stem until the next summer, when the plant again grew nor- mally if somewhat more weakly. This kind of disease and its cure may be considered characteris- tic. The intumescences, therefore, are highly shj- nificant synipfoms of ab- normal turgidity in all plants. As soon as they show themselves, the plant must be put into a light, cooler environ- ment and given a de- creased water supply. The Skin Diseases of Hyacinths. Fie-. 88. Hj'acinth bulb infected with the pustules of the skin disease- (Orig.) s scales which have lost their srloss. fi formation of pustles, r dried edpe. k young- bulb. This phenomenon (Fig. 88) has not been considered, although it occurs very frequently. Normally the outer scale leaves are smooth, firmly enclose the bulb, and usually extend up to its neck. In this disease they are short and die back from the dying edges. Often such hyacinth bulbs crack open and are thickly covered with dry leaves, especially near the place torn. On the still fleshy outer parts of the bulb, colonies of the blue-green mold (Penicillium glaucum) frequently occur. The leaves standing isolated, or connected with one another, are flat- tened on the upper side and often many boil-like, swollen, yellow places appear. In the colored part also of normally dried bulb scales, they almost always show some mycelium. In cultures this is proved to belong to Penicillium. The tissue of such diseased places differs from that of normal 452 scales in its yellow, uncommonly brittle walls, breaking into sharply pointed pieces and in the wide Kmiina of the cells, while that of the healthy ones, with their somewhat swollen, thick, colorless walls, have sunk together until the lumen disappears. All traces of starch have disai>peared from the yellow-walled tissue, which sometimes traverses the scale, is suberized, and pushed up by the subsequently produced cork cells and from the colorless surrounding tissue. After the diseased, dry bulb scales have been removed, one notices that the still perfectly white, succulent scales, normally extending to the neck of the bulb, have begun to dry, beginning at the top. Here the tissue loses its natural smoothness and turgor, so that gradually the scale has a folded appearance, due to the collapse of the cells which lie betw^een the more prominent vascular bundles. Besides this, the edge usually becomes yel- lowish. At the same time, on the deeper parts of the fleshy, white places in the scales, glistening from turgidity, appear small, longish, glassy, trans- parent, yellowish spots, protruding slightly above the upper surface. These Figr. 89. Cross-section through a scale of a hyacinth infected with skin disease. (Orig.) increase in a few days and almost at once become more noticeable because of the yellowish juicy edge. Then, however, the change advances more slowly, since the outpushing occurs only gradually more distinctly and its centre becomes whitish with a dr)^ membrane and longitudinal folds ; with increasing age, the centre becomes depressed and finally the scale seems perforated. WHien treated with sulfuric acid the upper lamellae, lying directly beneath the cuticle (Fig. 89 /) of the somewhat thickened epidermal cells, swell up markedly and at times mycelium may be found in them. A cross-section through the diseased scale (Fig. 89) shows at h an older pustule and on the left of this a younger one. In the discolored epidermis, the walls are swollen and this process of swelling and suberization (vk) in the older leaves has already advanced through the whole thickness of the scale. Here the fleshy, starchless parenchyma, which at the beginning {p) was found to be still colorless and with a normal arrangement, has col- lapsed like cords and' formed hardened places with irregular openings {s). In the cells directly beneath the outpushed epidermis, there are no nuclei, while they are present in the next inner cells, but brown in color. In the epidermis, cork cells are produced, while the parenchyma lying beneath gives 453 the sugar reaction with the Trommer test. In this tissue, rich in sugar, the formation of cork advances and since the corked cells do not collapse, they rise gradually more and more above the other tissue of the bulb scales, the walls of which retain their cellulose reaction and collapse. Analyses give dry substance Healthy bulbs. Diseased bulbs. In the outer scales 34.6 per cent. 51.82 per cent. 36.7 per cent. 55.43 per cent. In the inner scales 22.4 " 33-50 " 32.6 " 40.16 " Thus the diseased bulbs are richer in dry substance, which is not strange since the process of drvdng of the outermost scales has advanced rather further in them. After the removal of all the brown colored scales, the sugar content (defined as grape sugar and reckoned on dry substance) is, Healthy bulbs. Diseased bulbs. In the outer scales 0.71 per cent. 0.82 per cent. In the inner scales 1.23 " 1.66 " That is, the bulbs are richer in sugar in the inner, younger scales than in the older- ones, and when diseased both the inner and outer scales are richer in sugar than those in a healthy condition. We thus obtain the same results as were found in the ringing disease. As a matter of fact, both diseases frequently occur simultaneously and these pustules, which may be termed intumescences, prove to be symptoms of a scantier ripening of the bulbs. This may be found even in very luxuriantly cracked specimens. It is self evident that Penicillium grows rapidly and frequently on such a medium. The skin disease therefore deserves great consideration as a symptom and indicates that bulbs should be grown in a sandy soil not too rich in humus nor too damp. The Glassy Condttion of Cacti. A diseased condition was observed in various cacti and studied more closely by me with Ccreus nycticalus Lk. This condition is characterized by the appearance of glassy places, later becoming black. In the more delicate Cereus varieties, a greater extension of this tissue change kills the part of the stem which lies above it. Death results either through a drying up of the blackened tissue, or w^ith the assistance of bacteria, through the appear- ance of a pulpy condition, when the outer skin may be loosened by a slight pressure of the fingers. If the centre of disease is limited to one side of the stem, this may be healed, leaving deeper cup-like wounds. The illustration on page 456, of the manner of growth, shows a piece of the stem of Cereus nycticalus blackened at the upper end and softened to a pulp. On this softened part, a strip of the outer skin has been loosened by a slanting pressure of the finger. At the base of the piece of the stem are found healed wounds which extend to the wood ring of the stem. 454 When examining badly diseased specimens, it is noticed that a number of glassy places occur like warts on the upper surface. The cross-section shows that while the outer part of the bark of this piece of stem is still dark green and normally constructed, the underlying bark layers lack chlorophyll and starch and have greatly enlarged cells which cause the warty excres- cence. In contrast to the usual intumescences in which an elongation of the sub-epidermal layers causes the warty outgrowths which often rupture, I have termed the abnormal enlargement of the cell centres lying deeply depressed in the tissue, "internal intumescences." In this, these phe- nomena are related to the yellow-spotted condition described above. Here the first stages of the disease are found in centres of cells poor in content, browning and turning to cork in the midst of green tissue ; only in cacti the stems are afifected, while in Pandanus the changes are found in the leaf. The cell aggregations, which usually increase only in one direction, collapse, while, especially in the bark of the cactus, the cells retaining thin, colored walls, are usually elongated into tubes and have a star-like arrange- ment. From these inner diseased tissue centres, the process of impoverish- ment and over-elongation of the bark parenchyma extends backward toward the wood-ring and laterally in the direction of the bark, constantly further around until a considerable part of the stem is browned or blackened. Finally the outermost cell layers are also attacked by the discoloration without the usual appearance of any over-elongation ; rather, the stem appears as black as ink, even to the naked eye. In the first stages of this disease, wdiile the tissue still has a glassy appear- ance, the process of blackening occurs almost immediately after the sections are made, indicating that even then there are large amounts of tannic acid, which unite with the iron of the knife. Since, however, the discoloration follows when the plants have been injured with a horn knife, or with a platinum spatula, the presence of a sensitive substance must be assumed that rapidly discolors in the presence of the oxygen of the air. But guaiacum tinctures alone, or with hydrogen peroxide, do not give a blue coloration. With litmus paper the whole bark parenchyma gives a sharp acid reaction. An accumulation of glucose may be considered as a factor which might begin the over-elongation of the cells ; for, after treating the section with the Trommer sugar test, cuprous oxid is very freely precipitated in the glassy tissue as a whole, and this precipitate is scantier toward the healthy tissue. The proportion of starch content is the reverse. In the most dis- eased tissue, it is nil, while the healthier surrounding tissue displays starch abundantly. The proportion of calcium oxalate is peculiar; it occurs usually abundantly in the slime passages. In healthy green bark tissue, this calcium oxalate occurs chiefly as raphides, while in the diseased parts it is found usually in short octahedrons and at times in large cylinders. Probably varving amounts of the water of crvstalization determine the form. 455 The upiier figure in illustration 90 shows the process of heahng. It is a cross-section through the branch with a depressed wound, which may be seen at the base of the picture, showing the habit of growth. M is the pith with its shme cells ; H, normal old wood ; R, bark. It is seen at the wound that the tissue atrophy originally included the whole bark {R). The wood cylinder (//), however, was not attacked. The edges of the bark wounds {zvr) died and were separated by a full cork layer {t) from the healthy bark parenchyma at the sides. In the remaining part of the bark, a new growth in thickness had set in, which manifested itself by forming the primordia of new hard bast strands {b'). The old hard bast near the wound was diseased and found shut in by a cork envelope. The whole tissue zone (fe'-^')had been formed anew subsequently, and indeed in those parts covered by the bark by means of a normal cambial activity, but at the wound itself by an increase of the youngest sap wood. For the wound destroyed the cambium, and accordingly the last formed cambial wood layer has started a renewed increase of cells and has formed callus-like tissue. The primordia of the vessels, which at the time of the deposition of the latest sap-wood had already become thick-walled, have, however, not taken part in the increase, but have been pushed outward passively by the newly formed callus. It is seen in this, that these primordia of the vessels {g'), which in the cross-section resemble the ducts {g) in the normal wood {H), now occur isolated in the callus tissue. The healing process becomes more exactly recognizable in the lower anatomical figure which represents a piece of tissue from around the hole in the upper cross-section. H again represents the old wood with some vessels {g). Where the elements, represented with thick walls, cease, is seen the most depressed part of the wound. On this remain the youngest elements of the sap wood, which had increased in size and number after the phenomena of decay had ceased. The immature sap wood, already differentiated, became .more porous and thin walled, and thus it happens that thin- walled vessels {g') may be found again in a delicate parenchyma wood. All the tissue indicated by (w) has been newly formed, its produc- tion corresponding with the new formation of bark on peeled trunks. The new tissue, developed from the callus, already exhibits some differentiation. This diff'erentiation indicates that the stem is about to form new bark where it w^as injured, for in the region directly in front of the thin-walled vessels {g'), we find the first parallel cell divisions indicating the formation of a new cambial zone. Besides these, the primordia of secondary hard bast (&') may be recognized, to be sure, even in parenchymatous tissue with a plastic content but not containing chloroplasts, which later becomes normal bark. This healing process, however, has only been obser\'ed when the plant had direct sunshine and fresh air in circulation. I have learned to recognize the disease as occurring in greenhouses and indeed in those where because they contain plants from warmer climates the air is enclosed and very moist. In one special case, the abundant ventilation in the greenhouse stopped the 457 Fig. 90. At the right .side of the figure, indicating the manner of growth, is a reduced piece of tlie .stem of Cereus nycticalus, which, blackened and softened at the tip, .shows a piece of tlie barlv loosened by pressure of the fingers. On its lower part are found deep bowl-like wounds which have been healed- The upper drawing of the structure shows a. cross-section of a bowl-like wound which is being healed. The lower drawing gives the new structures and tissue differentiations, which take place during the process of healing the wounds. (Orig.) M pith, H wood, R bark, g normally placed ducts, £•' displaced ducts, b groups of dead, hard bast of the outer bark, enclo.sed by bark, d' groups of young hard Viast of the outer bark, 'cvr dead edge of the wound of the older bark (A*). The old tissue is separated from the healthy tissue by a layer of plate- like cork cells (/). ?i' and >i new bark differentiated from the wound callus, disease, while in the following year, with the new planting of foliage plants and with accordingly increased humidity in the air, it reappeared to a great degree. For this reason, I would like to consider the phenomenon as a direct result of excessive humidity. Methods for checking this are self evident. In one case, besides the increased supply of light and air, the addition of plaster to the soil has proved advantageous. We have devoted considerable space to intumescences and related phenomena in order to point to their importance. Greenhouse plants are chiefly considered and repeated observations have shown that most numer- ous diseases may be traced to the act that the natural dormant period of the plant was not considered and the plants were stimulated to untimely and therefore abnormal growth, by a high degree of heat and moisture. CHAPTER VI. Fog. In temperate climates, complaint is rarely heard of injuries from fog. In the mountains, vegetation has adjusted itself to the abundant precipi- tation and the attempt has been made so far as possible to overcome the delay of ripening grains and of drying the remaining vegetable produce by cultural regulations. The so-called "fog holes" of the plains may also be "frost holes." These are distinguished by a vigorous lichen growth on the tree trunks. In warm regions, fog becomes a more important factor, causing damage to plants, since it actually favors the development of saprophytic and parasitic fungi. We find the greatest number of complaints in regions where cotton is grown and exhaustive descriptions have been sent from Egypt. David^ writes from the cotton experiment station at Zagazig that each October morning in lower Egypt, the soil is covered by heavy, thick vapors or low fogs. The first general result is that the bolls do not open because the carpophyles remain too tough. The foliage becomes covered with red spots, ascribed to the action of the sun on the dew drops, acting as lenses. The cotton fibres in the bolls decay and lose their value from the action of a black fungus. Besides cotton. Hibiscus esculantus and H. cannabinus also suffer; young maize plants as well. The irrigation with Nile water, its soaking through the land while the soil is fallow, makes it moist, dense and slimy or oozy. This physical characteristic is the chief factor which makes Egyptian fogs more disastrous than the English and mountain fogs. The sensitiveness of cotton is due to its special soil and climate needs. These are very thoroughly described in Oppel's'- special work. According to this, cotton as a low-land plant cannot endure a stony soil or any abrupt changes in temperature. In its time of growth, lasting six months, it requires i8° to 20°C. a medium heat and abundant moisture, but it is found to be very sensitive to continued rain. "A high degree of atmospheric warmth, a good deal of soil warmth, a clear sky during the day and abundant 1 David, Nebel und Erdausdiinstungen und ihr Einfluss auf agyptische Baum- wolle. Zeitschr. f. Pflanzenkrankh. 1897, p. 143. ' Oppel, Die Baumwolle nach Geschichte, Anbau, etc. Leipzig, cit. Bot Jahresber. 1902, I, p. 374. 459 dew at night are the chief conditions." After the blossoms open, dry warm weather must prevail. Sandy soil is especially suitable. In soils rich in humus the plant runs to foliage. Clay soil is absolutely unsuitable, since it does not let the water percolate through. However, examples of adaptation to the climate are known. Thus, Webber and Bessey^ report that cotton, when carried from the Bahamas to Georgia, did not thrive at first, but gradually adjusted itself to the temper- ate climate. However, fogs, even of the English variety, may become disastrous, especially near cities with many factories. P. W. Oliver-, upon the re- quest of the Royal Horticultural Society, has published the most extensive studies on London fog. The most troublesome admixture is the smoke, the elements of which coat not only the plants but window panes, etc., with a sooty covering. An analysis of this sooty covering shows : carbon 39-00 per cent. hydrocarbons 12.30 organic bases 2.00 sulfuric acid 4-33 hydrochloric acid 1.43 ammonia 1.37 Metallic iron and magnetic oxid 2.63 Silicate, iron oxide and other mineral substances. 31.24 The injuries to plants are usually only phenomena of discoloration. However, different plants are more susceptible ; hence the fog may cause the dropping of the leaves. In injuries of the first kind, leaf tips and edges become brown, but the remaining leaf surface is still capable of functioning (Pteris, Odontoglossus, etc.). The dropping of leaves with yellowing and browning, or even without any external signs of injury, is the most frequent result. Sulfuric acid is considered as the cause of the leaf destruction; in addition, Oliver ascribes as an injurious influence also metallic iron. In deciduous plants which remove all the starch from the leaves before they fall, the most important agent exciting abnormal leaf fall is sulfuric acid. PLxperiments determining a rapidly reduced transpiration show reactions similar to these from fog, if at the same time the light was decreased. I also ascribe the emptying of the cells to the lack of light, for with the action of the acid alone, I found in my experiments that the whole cell contents died quickly and were deposited on the wall. Of the tar compounds, pyridine was found in fog in especially large amounts. When exposed to vapors of this substance, the leaves became limp and a darker green. The cells were plasmolyzed; the cyptoplasm in the epidermis had turned brown, but the chlorophyll did not change. As a • 1 Yearljook of the Dept. of Agriculture, 1899, p. 463. 2 Oliver, F. W., On the effects of urban fog- upon cultivated plants. Journ. Hortic. Soc. Vol. 16, 1893; cit. Zeitschr. f. Pflanzenkrankh. 1893, p. 224, und Gard. Chron. 12, 1892, p. 21, 594, 648, etc. 460 rule, wherever a brown coloration occurred, tannin was found in the cells. The penetration of pyridine, like that of sulfuric acid, takes place chiefly through the stomata. Very similar effects were found also, due to sub- stances related to pyridine, such as picoline, lutidine, nicotine, thiophene, etc. Phenol attacks the foliage very vigorously in aqueous solution as also in the form of vapor, with strong plasmolysis and a brown 'coloration of the protoplasm and chloroplasts. The blossoms behaved very differently in relation to fog; at times they showed considerable difference in two varieties of the genus and, in fact, in different petals of the same blossoms. Tulips, hyacinths and narcissus were very resistant. It is interesting that, as a result of the lack of light connected with the fog, whereby assimilation, transpiration and respiration are repressed, a peculiar yellow-spotted condition often sets in. In this, there is an accumu- lation of the acid content (because, with the decreased respiration, less organic acids are burned) and an increase of turgescence connected with this seems to lead to cell elongation in the mesophyll (aurigo). Thus, in considering the eft"ect of fogs, we have to consider two injuri- ous factors, the decreased light and the action of the poisonous substances. This becomes the more dangerous the greater the plant's need of light. Plants adjusted to a lesser supply of light (ferns) are less sensitive. Only in greenhouses can the injurious effect of such fogs be lessened, and this has been done in England. Special purifying apparatus is made use of (fog annihilators), with which the air entering the greenhouse is passed over strongly absorbing substances (charcoal). For out of door planting only a choice of resistant species can come under consideration. CHAPTER VII. RAINSTORMS. The injurious effects of beating rains on the soil have already been mentioned. They pound the upper surface down or cover it with great quantities of silt. The immediate result is oxygen starvation for the roots. The mechanical effect of heavy rains on the plant itself is first to be con- sidered. There are many natural devices in plants which safeguard the leaves from the beating and tearing effects of heavy rains or the undue accumulation of water from long continued gentle rains. StahP and Jungner- have given a thorough presentation of these conditions and call attention to the formation of the tips and to the position and repeated division of the leaf surface, etc. The direct results of the rain are a decrease of transpiration and a great water absorption by the roots. They have been less considered. Here also the swelling of the wood of trees belongs. Fried rich's investigations^ show that a constant swelling of the tree trunk (aside from any direct growth) takes place during the night because with lessened transpiration, the tree swells, while in the daytime it shrinks. The differences will be most marked when the growth is rapid and the wood swells, especially when rain comes after considerable drought. Bark and periderm are less affected. Growth and swelling of the wood cylinder are regulated by the influence of atmos- pheric humidity on the tops of the trees. It is thus easily evident that smooth bark will crack in places because of the strong and sudden increase in swelling and growth. When the soil is rich and the atmospheric humidity great, these cracks may become open w^ounds. constantly increasing by bacterial infection. Rough places then arise on the bark of the young tree trunks. These may be observed, for example, in lindens, elms, ashes, maples, etc., near wet ditches and ponds. The influence of longer periods of rain manifests itself in herbaceous plants, even more than in woody ones, by cracks in fruit and stems. Among 1 Stahl, B., Regenfall und Blattgestalt. Ein Beitrag- zur Pflanzenbiologie. Annal. de Buitenzorg.; cit. Bot. Jahresber. 1893, 1, p. 49. - Jungner, J. R., Om regnblad, daggblad och snoblad. Bot. Not.; cit. Botan. Jahresber. 1893, p. 49. ^ Freidrich, Josef, tJber den Einfluss der Witterung auf den Baumzuwachs. Mitteil. iib. d. forstl. Versuchswesen Osterreichs. Wein 1897, Part 22. 462 our vegetative plants, the splitting of cucumbers is most important. The fruit suffered most of all, but sometimes the stems also cracked. Decreased temperature, accompanied by continued rain, not infrequently causes the total failure of harvests, since the cucumbers often show gummosis and are attacked by various black fungi. Long, cool rainy periods also cause a premature leaf fall, badly devel- oped heads in grain, a small amount of sugar and starch in beets, tubers, etc. Repeated showers have a very disastrous effect when they fall on blossoming fruit trees and during the setting of the seeds of field crops. In the first place, the insects, necessary for fertilization, cannot fly about so freely, and secondly, the anthers will not open so well, nor will the pollen grains stick so well on the stigma. Nevertheless, the theory that the increase of bacteria and fungi is always favored by periods of rain does not hold absolutely. Parasitic diseases usually increase only if the rain is accompanied by warmth. On the other hand, cold wet weather retards the growth of the most important parasites (rusts, false mildew, etc.). In tropical regions, however, rain storms usually favor the development of fungous diseases and, to give at least one example, we will mention Busse's obser\'ations\ He found that the Phytophthora decay on the cocoa fruits was especialy marked in rainy years. The amount of rain is not decisive but rather the character of the storm. Mighty gusts of rain seem to keep the fungus spores from settling on the smooth-shelled fruit ; but the softer, more frequent rains, easily producing stagnant moisture in the de- pressions in the soil and in the regions where the drainage is poor, have proved favorable for the fungi. Those regions suffer less to which the fresh sea breezes or some wind has unhindered access. Among cultivated plants in rainy seasons, the wind is a helpful agent in the struggle against parasites. This helpful agent has never been suffi- ciently credited for its work. The tops of trees should be freed of excessive water by frequent shaking. This should be done especially in closely planted orchards and in warm rainy periods. 1 Busse, W., Reisebericht der pflanzenpatholog^ischen Expedition d. kolonial- wirtschaftl. Komitees nach Westafrika. Tropenpflanzer 1905, p. 25. CHAPTER VIII. HAIL. All injuries from hail form wounds, with a consequent loss of sub- stance ; any chemical action as a result of the cold of the hailstones cannot be demonstrated ; only the mechanical blow which either tears away various parts of the tissue and, by drying, causes them to go to pieces, or slits the leaves and branches in knocking ofif more or less large pieces. The small piece of rye-blade, which is shown here, has been struck by hail at the points g, c and v, and shows the effects of the blows of the hail stones. In considering such a section after a hail storm which has not been severe enough to knock ofif the leaves, or heads, or to break the whole stalk, we find, as every' one knows, whitish or white spots on the green striped upper surface. The striping is produced by alternate dark green furrows and lighter colored lines. In cross-section, it is seen that these furrows consist of a soft bark parenchyma, containing chloroph)dl, while the lighter colored stripes are composed of thick-walled fibre-like cells (/>). These fibre strands stiffen the blade. The thicker their walls are, the more re- sistant the blade is and the less inclined to fall. In Fig. 91, the green parts are seen to be changed most. The cells at g appear uninjured; at 2 only dry cell walls are found, which are connected with one another by a scaiTolding-like structure. Toward the centre of the blade, however, there is green living tissue (m). Here, the blow of the hailstone has not destroyed the epidermis (^) at all,, but has bruised the more delicate bark parenchyma underlying it so that part of the cells have died. Only a few pieces of the cell walls of the former juicy bark tissue remain and, at this point the hail- stone has had such force that it has broken the thick-walled, tough epidermis at 0. Air has entered through this opening and this hail spot appears white to the naked eye, while at m a greenish tone may still be noticed. Similarly, the loss of tissue will take place in other parenchymatous parts of the plant and the assimilatory activity will fall according to the severity of this loss. Yet, this reduction of the life-activity may become of great influence only if the hail storm sets in at a time when vegetative growth has stopped and the plant has entered upon the reproductive period, when it withdraws the cytoplastic substance from the leaves. 464 C. Kraus' made his observations on barley and describes the effect of hail storms on the grain. He found many heads greatly bent backward and turned, since, after the buds had been hit by hailstones, they were so bruised that only the furthcrest developed could free their tips from the outermost leaf sheathing. ' Heads which had been hit directly were retarded in their whole development ; the kernels were lighter, not uniform and often tipped with black. The v.eight of the heads was about 38 per cent, of the normal, that of the grains about 43 per cent. Kraus found similar conditions in two unbearded wheats, in which, however, because of the absence of beards, the heads had worked their way more easily out of the uppermost leaf sheath. Accordingly the weight of heads of wheat struck by hail was only about Fig. 91. The effect of hail on a blade of rye. (Orig.) g healthy green tissue, z tissue injured by a hail-stone, ii adjoining healthy tissue, v completely destroyed bark of the blade with ruptured outer membrane (a), h parenchyma of the blade, b vascular buadle, p ropes of cells resembling bast fibres. 24 and 15 per cent, and the weight of the grains about 27 and 17 per cent, less than normal. When the hail storm occurs early in the year, i. e., perhaps in May, many shorter green glades bent at the base are found later between the ripening, upright ones covered with hail spots. The hailstone had probabl}' bent the plant and the blade required more time to straighten and this had delayed ripening. Wheat seems to be the most robust. I observed after a hail storm in June, 1905, that rye blades showed the injuries represented in Fig. 91, while in the corresponding cell groups of the wheat, the inner tissue was split by 1 Kraus, C, Wirkunj 1899, Nos. 14-15. von Hagelschlagen. Deutsche Landwirtschaftl.Presse 465 only one tear or was not injured. The epidermis was not torn, but only the walls and contents were browned. The heads were broken in a very charac- teristic way. Fig. 92 shows a slight breaking, with the axis making an obtuse angle (A). In the more severely injured heads, the axis was bent two or three times, and where bent was almost bare. Fig. 93 shows the construction of the axis where bent : g, ducts ; r, torn parenchyma ; "<', a vascular bundle, which has been killed. Laterally from this, at br, the tissue as a whole was a deep brown. Where other heads had been hit the epidermis was torn open ; the bordering tissue had collapsed, fallen to .pieces and turned brown. Some vascular bundles were found to be almost entirely isolated, since the torn or disintegrated parenchyma had cracked off. This might be a result of ten- sion, since later the still green heads continued their growth. The injuries vary very greatly according to the way the hailstones strike. Kraus's observation shows that after the hail- stone had struck the head before it had become rid of the leaf sheath, the beards remained where they were. Therefore, the head ap- peared bent like a bow. The injuries usually \\'cre at the points where the young heads are attached rather than in the internodes of the axes. Oats will endure severe injuries if the panicles are still enclosed in the upper leaf sheath when the hail storm strikes them. F'er- fectly sterile heads may be produced and the injury to the plants resembles that of thrip so much as to lead to confusion. In some years I have often found twisted barley heads due to the sucking of thrip. PuppeF has often studied tlie effect of mechanical blows and his illustrations are very helpful. For example, with a heavy smooth roller, he flattened a field of young winter rye which had not yet formed a blade. When the heads began to develop, they were deformed exactly as if they had been injured by hail. 1 Puppel, Max, Hagel- und Insektenschaden. 40 plates from original photographs. Fig. 92. Head of wheat broken by hail. The grains have fallen at the broken place, leaving it bare. (Orig.) 466 Wheat, hit by hail on the 4th of June, was pecuHaiiy injured. Besides the well known hail wounds, plants were found scattered throughout the field with a green appearance and almost empty heads. In July, the kernels present were still green and milky. The heads, as a whole appeared a light leather-brown, due to the discoloring of almost all the glumes. Among these were found short, fresh green tips which belonged to the sprouted small heads. These contained six to eight blossom primordia, not one of which had developed, and the uppermost showed only the beginnings of the anthers. The glumes were lancet-like, dark green and as soft as any herbaceous growth, so that a distinct transition to a foliage character was recognizable. In one case young plants had actually sprouted out of the base of some small heads. Behrens^ obsen-ed similar conditions in hops after a hail storm occur- ring on the first of July. Four weeks later the blossoming catkins opened Fig. 93. Cross-section through the stalk of the wheat head of the previous figure, at the place broken by hail (h). (Orig) and contained only leaflets. The author's experiments connect this trans- formation of the inflorescence actually with the destruction of the leaves by hail. On vines from which the leaves had been stripped, the so-called brausche hops grew (see p. 344), while on the stems on the same place which had not been stripped, catkins developed normally. In potatoes, it has been observed that injuries due to hail reduce the starch content of the tubers^ Injury to the pods may seriously affect rape. It is a matter of course that, in all cultivated herbaceous plants, the destruc- tion of the leaf must affect the yield — even to the loss of the harvest. It would he a mistake to remove foliage injured by hail. Experiments with cabbage plants showed that better heads were obtained when the injured foliage had been left than when it had been removed. 1 Zeitschr. f. Pflanzenkrankh. 1896, p. 111. 2 Jahresber. d. Sonderausschusses f. Pflanschutz 1903, p. 94. 467 Internal injuries in juicy fruits, caused by hail, are interesting. Fig. 94 shows a cross-section of a tomato fruit skin struck by hail. We notice at the left, the actual place hit, a hard, dry dark-brown excrescence, the blow of the hailstone did not destroy the epidermis (e). The more tender sub-epidermal tissue was fatally bruised and consequently turned brown and dried (t). As a result of the further process of swelling, the tissue of the still unripe fruit is torn and transformed to a hard cyst. Besides this injury, which is most strikingly noticeable, however, a second hard place is found in the juicy flesh of the fruit surrounding a vascular bundle ( / 1 1 i J Fig-. 100. Cross-section through a blighted spruce tip; from the Foi-estry Division of Starnberg. (After v. Tubeuf.) 1 Beobachtungen iiber elektrische Erscheinungen im "Walde. Naturwiss. Z. f. Land- u. Forstwirtsch. 1905, p. 308. 2 V. Tubeuf, Die Gipfeldiirre der Fichten. Naturwiss. Z. f. Land- u. Forst- wirtschaft. 1903, No. 1. Continuation ibid. No. 7, 8. widely distributed tip blight, appearing suddenly in many individuals, must be the result of electricity. The most important point to which the author himself calls attention is that lightning usually strikes below the top, injuring the trunk, but leaving the crown uninjured; in other observed cases whole trees have died, but never the crown alone. In discussing the objections of other pathologists who consider that this blight is due to beetles or leaf rolling caterpillars (Grapholitha pactolana)^, v. Tubeuf emphasizes the fact that the the trees show the characteristic symptoms of disease when the bark beetles are absent, and that these, attracted by the smell of turpentine, appear only secondarily. Some pines and larches behaved like the spruces. In spruces injured by lightning, the dead wood is found in the form of brown strips of bark, surrounded by cork, lying within the otherwise green and fresh bark, and below the dead tops. v. Tubeuf could not find this either in trees which had been broken off, bent or eaten off, nor in others which had been frozen or killed by insects. Further investigations- proved that the anatomical characteristics of top blighted spruces, are identical with those found in trees where lightning had produced extensive injuries. The main support of the theory, however, lies in the fact that v. Tubeuf and Zehnler^ by means of experimentally pro- duced sparks, were in a position to produce, on the living trunk, external appearances of top-blight as well as all the similar anatomical pathological phenomena, viz., the dead "bark-eyes" which are surrounded by a layer of white cork. So long, therefore, as it cannot be proved that other causes produce the same symptoms, we must hold to the fact that the kind of top blight described is a result of electrical discharges. These, in themselves, may be weak, but v. Tubeuf states that in his experiments with deciduous trees, and in his observations in the field, electrical injuries do not radiate far into the healthy tissue. In artificial electrical injury, the leaves died only to a certain point. In order to faciUtate the conception of electrical discharge, v. Tubeuf calls attention to the St. Elmo's fire* and has produced this experimentally. He refers in this to earlier experiments by Molisch^ Inspired by the ob- servations which Linnaeus' daughter and son had made on the effect of lightning on flowers, he produced a light cluster, i. e., a shiny but quiet electrical equalization. In V. Tubeuf's experiments, potted plants were insulated by being placed on a ball of wax. The soil was connected by a copper wire with one conductor of an induction machine and a wire was likewise fastened to the ball of the other conductor. As soon as the machine was set in motion the 1 See Moller in Zeitschr. f. Forst- u. Jagdwesen. 1904, Part S. 2 V. Tubeuf, tJber den anatomisch-pathologischen Refund bei gipfeldiirren NadelhtJlzern. Naturwiss. Z. f. Land- u. Forstwirtsch. 1903, No. 9, 10, 11. 3 V. Tubeuf u. Zehnder, tJber die pathologische Wirkung kunstlich erzeugter elektriseher Funkenstrome auf Leben u. Gesundheit der Nadelholzer. Sonder- 4 V. Tubeuf, Elmsfeuer-Versuche. Naturwiss. Z. f. Land- u. Forstwirtsch. 1905, Part 5. 5 Molisch, Leuchtende Pflanzen. Jena 1904, G. Fischer. 489 flower pot, together with the plant, was charged. "If the other wire is brought near the plant, a current of the positive and negative electricity is seen which had been separated in the two conductors and then in the two wires. The positive electricity flows out in the form of a light cluster, the negative appears like little beads of light on the tips." Experiments with spruces and pines proved that a considerable number of needle tips on a plant, negatively charged, gave out the electricity in the form of beads of light when approached by the positively charged wire. If, however, the plant is charged positively, the electricity flows from the tips of the needles without lighf^. It was observed in, tender plants that if the positively charged wire is held so high above the plant that there were no beads of light to be seen on the edge of the blossoms and that no sparks jumped over, no injurieg fol- lowed. If this precaution was not observed, after a few minutes the petioles and parts of the sprouts below them began to wilt. These appeared darkly glassy as after frost or injury. It should be deduced from these experi- ments, that quiet electrical discharges can not call forth a direct injury, but that such an injury is felt at once if a spark discharge takes place. Differences Between Lightning and Frost Wounds in Conifers. As yet, in v. Tubeuf's pubhshed results of his experiments, there is still lacking an illustration of the anatomic condition of the lightning traces which manifest themselves as eye-like spots in the bark. (See Fig. TOO.) Although in the works of CoUadon and R. Hartig, mentioned at the beginning of this section, we also find statements as to isolated, ring-hke traces of lightning, it still seems to me that further experiments must be made to demonstrate whether such injuries could not be produced by frost. My question has received added force since in deciduous trees I have ob- served similar phenomena round about bast groups which, lying near the eyes, had been injured by frost. In order to get reliable comparative material, I begged from v. Tubeuf specimens of his spruce, artificially struck by lightning, and produced frost wounds by exposing a healthy five year old pine (v. Tubeuf had also found characteristic lightning wounds in pines and larches) in May for a night to a temperature of y°C. below zero in a freezing cylinder. The tree, appar- ently uninjured when taken from the freezing apparatus, was observed at the end of the year. This delay was necessary in order to give it time to heal over possible inner injuries as must also have taken place with the lightning wounds. The pine showed inner injuries only in the bark on one side of the base of the trunk ; indeed, partly in the form of isolated dead cells with brown swollen contents in the middle of healthy parenchyma; partly in the form 1 tJber die Unterschiede in der Wirkung der positiven und negativen Elelv- trizitat. Compare Plowman, Electrotropism of roots. Americ. Journ. Sc. 1904. cit. Bot. Centralbl. 1905, No. 40, p. 342. 490 of larger dead cell groups which were enclosed by a living parenchyma wall, circular in form ; thereby they formed a figure resembling an eye (Fig. loi). In the centre of this eye-like figure frequently a depression was formed (h), which was lined by slightly l)rowned, at times almost colorless, cells (u). In comparing the pictures, which vary in each section, one became convinced that these cells, enclosing the cavity, corresponded to a resin canal lining and at times had been pushed out like vesicles into this cavity. This was bounded on the outside by a dead bark parenchyma (/>), with only rarely collapsed cells and usually of natural size, of which the contents and walls 77? ^.... .----~p Fig. 101. Pine, artificially frosted. (.Orig-.) - Isolated dead bark cells with brown homogeneous contents, h cavity in the dead heart of the tissue, u slightlv colored or almost colorless lining of the central cavity which, in structure and composition, exhibits clearlv the structure of the lining of a resin canal, /> brown bark parenchyma cells from the region of the resin canal, completely impregnated with resin, xe parenchyma elongated like plates and containing starch. ;/> normal bark parenchyma. were impregnated with resin. By clearing the sections, different groups of oxalates could be recognized in the dead parenchyma as well as cells with grains, which should be considered as starch impregnated with resin. This dead tissue was bounded on the outside by the above mentioned circular zone of plate-like cells, which in their arrangement resembled a cork overgrowth when treated with chloriodid of zinc, but gave a cellulose reaction in their walls and were often filled abundantly with starch and small drops of resin (r). This overgrowth of the dead tissue centre, which gave the eye-like appearance to the frost wound, often passed over into the normal bark par- enchyma (r/') which here and there left recognizable traces of starch. 491 Fig. I02 shows a cross-section through the bark of a small spruce trunk injured by artificial lightning. The trace of lightning (b) shows, first of all, a central brown strip-like kernel of swollen parenchyma. This kernel is surrounded by a broad, clear zone (k) which consists of radially arranged rows of ver}^ thin-walled, nearly empty cells, often containing air. Toward the outside, this zone adjoins a tissue ring (kk) of plate-like cells, rich in cyptoplasm, the walls of which give a cellulose reaction. These cells gradually pass over into the normal bark parenchyma (rp) with its large lumina. The resin ducts (g) lying outside the trace of lightning but pretty near to it, are, as a rule, uninjured ; the living cells at times projecting into the resin ducts are light-walled. This vesicular outpushing of the lin- ing cells is a normal phenomenon ; for in branches of healthy spruce in winter, resin canals are often found completely filled by tylose-like enlarge- ments of the lining cells. Resin ducts also occur isolated in the immediate proximity of a trace of lightning in wdiich the cells filling them are changed to brown, swollen, resinous masses. The dead tissue kernel in the centre of the lightning trace consists fre- quently only of dead bark parenchyma. Often, however, it can be noticed that some bast groups (h') have participated in this. The fact should be emphasized, that the dead parenchyma cells are often entirely collapsed and dried. In my opinion, the production of the light colored circular zones, composed of thin-walled cells with broad lumina which are found to be actual cork cells and constitute the difference from the frost wound, is due to the drying up of the cells. I conceive of the production of this difiference in the two forms of wounds as follows : The electric spark causes a rapid drying out of the dead tissue. Since this, like frost, does not cause any slowly spreading, subsequent death of the adjoining tissue, vigorous cells, capable of reacting, directly bound the dead tissue centres. A reaction to the wound stimulus sets in at once if the vegetative activity makes itself felt in the bark. The parenchyma around the dead tissue responds to the wound stimulus by cell elongation and increase. The cell groups dried by lightning, allow the sur- rounding cells to elongate greatly. The more rapidly the process takes place, the more material is used up. If this is not present in sufficient amounts only a formation of cork will take place and thus the fact is explained that after the electrical discharge the bark parenchyma surrounding the dried tissue must elongate and divide to fill out the large spaces ; then there is a formation of cork. When frost kills an area of tissue, lying in the bark parenchyma, at first no drying of the tissue takes place. The dead, swollen cells retain their size, and are still turgid. Also the pressure of the dying frost-injured tissue on the healthy surrounding tissue is not essentially increased. The sur- rounding cells have no incentive wdiatever to the great elongation and division which were necessary in the drying out of the lightning traces. Therefore, there will appear around the dead centre of the frost wound the -ir Fig". 102. Spruce, showing traces of artificial lightning-. (Orig.) b central portion of the trace of lightning in tlie bark parencliynia. // group of normal hard bast. A' group of bast enclosed by the lightening tiace, /• cork ring, kk the cell layer resemljling the cork cambium, jr resin canal in the healthy bark, from the normal lining of which some cells have curved outward like vesicles, gg resin canal, filled with resin, o oxalate crystals, st bark cells filled with starch, ip healthy bark parenchyma. <■ swollen tissue grovips in this bark parenchyma, sell bark scales. 493 new structure, produced as a result of the wound stimulus and in the form of a circular zone of scantier and smaller cells. The plastic food material, flowing toward these spots, cannot be longer used for cell increase, since the need has been met. It will therefore be laid down in the form of reserve substances. Hence the noticeable accumulation of starch directly about the frost wound. As a positive result of the investigation, it should be cited that in coni- fers a definite difference exists between artifically produced, eye-like wounds due to lightning and to frost. In wounds due to lightning the dead bark tissue dries rapidly and is then surrounded by a porous layer of cork which forms a light colored outer ring. In frost wounds, the dead cells in the interior of the bark parenchyma at first retain their former size. They are enclosed by a circular zone of newly formed cells; these do not develop a porous layer of cork, but rather form a slender parenchyma zone, with nar- row lumina, which usually is richer in reserve substances than the normal bark parenchyma. This zone, in a wound due to lightning, is formed next to the cork zone. These statements are corroborated by von Tubeuf's observation on the differences between wounds due to lightning and to frost. In injuries caused by lightning the ring of dead bark radiates into the healthy tissue in constantly widening bands, while similar phenomena in the injuries due to frost have not been observed in conifers up to the present. In regard to the theor}'^ of the action of lightning, the present observa- tions on the structure determine that the electric spark primarily produces a drying of the tissue. Injuries to Trees in Citie.s and Towns. With the increased use of electricity in cities, there is a serious menace which must be mentioned. Stone's investigations^ show that the alter- nating and the direct currents cause injuries by local burning. In dry weather, this is less to be feared, but becomes essentially greater when the bark is damp. The direct currents used by street car lines come under especial consideration here. Besides killing this tissue, the weaker currents also stimulate action. Both conditions should be closely examined. Dis- charges into the earth during thunder storms are more frequent, according to Stone's obsers'ations, than is usually supposed and they explain many injuries in the trees, which often are also mistreated by the inconsiderate cutting out of the branches in order to isolate the wires. Effect of Spray Lightning on Grapevines. Among Calladon's- numerous observations on the action of lightning, the statement is found that in a vineyard, the upper surface of the soil which had been struck by lightning presented a regular, sharply defined circle, the 1 Stone, G. E., Injuries to Shade Trees from Electricity. Hatch E'xper. Stat. Massachusetts Agric. Coll. Bull. 91. Amherst, 1903. , - Colladon, Daniel, Effects de la fouclre sur les arbres et les plantes ligneuses. Mem. de la soc. de phys. et d'histoire nat., de Geneve 1872, p. 548-53. 494 centre showing the strongest action. The vine leaves showed a number of spots, which at first appeared dark green and after several days turned brick red. In the younger sappy stems, especially the cambium had turned brown, while the wood was uninjured. In the injured tissues, the cell walls remain unchanged, but the protoplasm was contracted and killed. Rathay^ has described the same observation of the distribution of the effect of light- ning on numerous individuals and, after mentioning earlier cases, also refers to the fact that the same phenomenon of the spreading out of the lightning is observed in sheep herds, where likewise several individuals were always hit. Like Colladon, Rathay also observed that the leaves became red in varieties which showed a red autumnal coloring. All the ends of the branches died back. The process of the red coloration in leaves has already been determined by Wiesner and by me as a result of ringing and bending experiments. Rathay supplemented this by observing that the reddened leaves transpired much less than normally green ones. Leaves reddened after having been struck by the lightning, resembled, in all particulars as yet tested, those which turned red from ringing the branches and actually the injury from lightning resembled in many points mechanical girdling, since here the bark lying outside the cambium was killed. "The cambium of the parts struck by lightning remains alive and develops inside the dead tissue, toward the outside, a callus surrounded by wound cork and, toward the inside, a w'oodring which is separated from the older wood by a thin brown layer." The grapes on the vine struck by lightning dried up absolutely. We find in a work by Ravaz and Bonnet- different points of importance, showing parallelism between the effect of lightning on grapevines and on conifers. After calling attention to the fact that a place struck by lightning which was planted with 50 to 100 vines, showed that the strongest plants were much injured, it should be emphasized that, after being struck by lightning on the 20th of May, the tips of the shoots turned down toward the ground and dried up. The nodes remained green for some time, while the internodes looked almost scalded. The phenomenon of disease gradually decreased toward the bottom. Below the dried tips, the pith was torn in the injured young shoots and pressed against the woodring. The roots remained uninjured. Some weeks after having been struck, the injured internodes appeared a reddish brown, shrivelled and cracked longitudinally. The tears showed a scar tissue. The intermediary nodes were strikingly swollen. Where the tips had not been struck, the branches grew further, but had very short internodes. The young wood tissue appeared brown and its cells empty and with unthickened walls. The injured parts of the bark were enclosed by cork so as to form island-like structures (compare 1 Rathay, Emerich. fiber eine merkwurdig-e durch den Blitz an Vitis vinifera hervorgerufene Erscheinung. Denkschr. d. math.-naturwiss. Klasse d. kais. Akad. d. Wissensch. Wien 1891. Extensive bibliography here. 2 Ravaz, L. et Bonnet, Effects de la foudre sur la vigne. Extr. des annales de I'ecole nationale d'ag-ricult. de Montpellier; cit. Bot. Jahresb. 1900, II, p. 417. 495 Fig. 102). The cambium formed first an irregular tissue, whicli gradually passed o^•er into normal wood (compare Fig. 99). From these statements we arrive at the conclusion that lightning (like frost) also causes considerable injury by mechanical action and, in fact, as a result of sudden excessive differences in tension. The trunk reacts in a dift'erent degree according to its age when injured by lightning. Where the bark is not injured to its whole extent, the dead places are surrounded by a cork layer. If the young wood is not entirely killed but only compressed or torn, a parenchyma wood develops later, which slowly passes over into normal wood, so that false annual rings can be produced. All phenomena spread out gradually from the base of the trunk; that is, they finally disappear. It is a matter of course that micro-orga,nisms infest all wounds due to lightning and it is easily comprehensible that these cases have been described as parasitic diseases. An example is offered by "Gelivure" of the grape which has been described as bacteriosis, but, according to Ravaz and Bonnet, is nothing less than a wound caused by lightning and infested by bacteria'. Spray Lightning on Fields and Meadows. Steglich- observed one July a potato field which had been struck by lightning. The lightning hit in two places and the plants became yellow and died ; the stems seemed cracked open and perforated so that the walls of the wound appeared torn. V. Seelhorst" describes injuries to beets from lightning. In one case the place struck formed a circle about 15 m. in diameter. In the middle of the circle the beets were all killed. The leaves on the plants near the peri- phery were wilted and discolored. Often individual specimens slightly in- jured, stood between plants greatly injured. At times small cavities were noticeable in the beet, especialty in the head. In other cases, practical workers speak of discoloration and weakening of the heads of the beets and similar phenoniena ; nevertheless, secondary parasitic influence may have made itself felt here. Colladon'* also makes a report of a beet field struck by lightning. The leaves of injured plants were colored red, shrivelled or torn in places and the edges partially dried. In one potato field the ma- jority of the plants in the upthrown soil were found to be healthy; only in one place did the base of the potato stem seem torn and burned. In the place struck by lightning on a meadow, with a diameter of 6 m., the highest thistle tips were killed, while the lower parts and the grass remained healthy, although here and there the earth was found to have been torn up. To explain the circumstance that the condition of individuals hit on similarly planted bits of land always varies, Rathay cites photographs of 1 Ravaz, L. et' Bonnet, A., Les effets de la foudre et la g-elivure. Compt. rend. 1901, I, p. 805. ^ Jahrb. d. D. Landw.-Ges. 1892. 3 V. Seelhorst, Rubenbeschadigung- durch Blitz. D. Landw. Presse 1904, p. 515. * Loc. cit., p. 555. 49^ lightning showing that it usually is not a simple discharge between tw^o points, but is scattered and ends in many points. In addition to this, it should be emphasized that when grapevines are trained on wires, these spread the injurious effect over a greater area. V. Bezold's^ statements that, according to the statistics of the Fire In- surance Company in Bavaria, the danger from lightning had increased three- fold between 1833 and 1882, are especially significant. The extensive removal of forests and marsh drainage and the rapid increase of rails and electric wire conductors are supposed to play a part in this. Disadvantages in Electro-Culture. The attempts to use electricity directly in plant cultivation have fol- lowed three lines. In the first place, it was desired to increase the assimi- latory activity by illuminating with electric light ; in the second place it has been attempted to let an electric current pass through the earth by sinking two metal discs in the soil connected with some source of current ; in the third place, an attempt was made to cause the current to pass directly through the plant (or tree). As yet the results have been very contradictory, so that no decision has been reached. Great hope is set often on the influence of a silent elec- tric discharge. This takes place when, for example, a net of wires is laid over a field without touching the soil and one pole of an electrifying machine is connected with the wire and the other w'ith the soil. In such cases the plants act as conductors and through them, by means of the silent electric discharge, the electricity will stream out from the tip of the cultivated plants. Such a current must actually take place constantly in nature, since the soil exhibits an electric charge dift'ering from that in the layers of air lying above it. The best known experiments are those of Lemstrom" and Pringsheim^. Older works on experiments, in which the electrical current is conducted through the soil, had been collected and enlarged by Wollny*. The results of Pringsheim's experiments, in which the electricity was produced by a static electric machine, sound extremely favorable, since in potatoes, sugar beets, beans and straw-berries a quantitatively and quali- tatively better yield is obtained. Since, however, many unfavorable experi- ences exist, this field, for the present, should not be considered any further, as it is not sufficiently cleared up. However, Lowenherz'' work must be mentioned because it has been carried through with scientific exactness and opens up new points of view. . 1 V. Bezold. W.. ttber ziindende Blitze im Konigreich Bayern wahrend des Zeitraums 1833 bis 1882. Abh. d. Kgl. Bayer. Akad. d. Wiss. II. CI., Vol. XV. 2 L.emstrom, Elektrokultur. Translated by O. Pringsheim. Berlin 1902. W. Junk. 3 Pringsheim, Otto, Neue Elektrokulturversuche. Osterr. landw. Wochenbl 1904, No. 24; cit. Centralbl. f. Agrikulturch. 1905, Part 6. 4 Forschungen auf dem Gebiete der Agrikulturphysik. Vol. II, 1888, p. 88. 5 Liowenherz, Richard, Versuche iiber Elektrokultur. Z. f. Pflanzenkrankh. 1905, p. 137. 497 The experiments were made with ChevaHcr barley ; a direct current of electricity was used which was conducted through the soil. The grains were ver}' carefully sown, so that in half the experimental pots the seeds lay with their long axes parallel to the direction of the current, thus being traversed longitudinally by the current, while in the other pots, the grains were laid at right angles to the direction of the current. It was thus found that the different position of the grain in relation to the direction of the current resulted in a ver}^ unexpectedly great dift'erence in the effect of the electricity. With the strength of current used (0.015 to 0.030 amperes) an injury in the process of germination was universally noticeable, but it could always be recognized that the grains, which were traversed longitudinally, germin- ated less well than those through which the stream passed crosswise ; yet in the first named series, a difference was perceptible in the grains lying parallel with the direction of the current, inasmuch as those developed the most poorly in which the positive stream entered at the tip of the grain and left at the end where the embryo lies. If the direction of the current was reversed two or three times within the 24 hours, no difference in the results could be produced, but, if the current was changed two times per minute, such a difference became clearly evident. The grains laid perpendicular to the direction of the current sprouted just as well as seed not electrically treated. In those traversed longitudinally by electricity, the disadvantage manifested itself noticeably only in the fact that the grains germinated 12 to 24 hours later. This experiment, which deserves consideration, shows clearly that varied conditions must be taken into consideration in cultivation with electricity Supplementarily, the endeavor to .treat electrically the roots and oldeir wood of grapevines by currents of high voltage should be considered here^ At the request of the Imperial Agricultural Association at Moscow, experi- ments were introduced, incited by reports of combatting Phylloxera by elec- tric currents, in which experimental cases, containing roots and cuttings, were exposed for 10 minutes to an electrical discharge. Some roots were then treated with a spark discharge. It was found that currents of high voltage caused an earHer and more favorable development of the vines. Roots, however, which had been treated directly by being connected with the machine exhibited injuries, for the upper parts did not sprout. Sprouts appeared only on the subsoil nodes. 1 From a review of the "Weinlaube" 1904, No. 34; cit. Ccntralbl, fur Agri- kulturchemie 1905, p. 394, CHAPTER XL. LACK OF HEAT. A General Survey. Life Phenomena at Low Temperatures. The plant is much more dependent on the temperature of the air than on the temperature of the soil. Before the soil can follow the fluctuations in the warmth of the air, this has already awakened plant life and at times brought it to considerable development. The individual parts of the plant naturally do not respond to the fluctuations in the temperature equally quickly. While the warmth of leaves and thin stems, in the shortest possible time, increases or decreases, parallel with the temperature of the air, thick trunks will need considerably longer timei, more particularly since all plant tissues are poor conductors of heat. From this last circumstance it is evident that thick trunks are sometimes warmer than the surrounding air, sometimes cooler, and, in fact, are on an average cooler than the air in the daytime and warmer at night. But those parts of the plants which extend into the air are also cooler in the daytime. The cooling down of the leaves comes from their radiation of heat. This will be greater the greater the surface of the part in proportion to its bulk. Evaporation should also be taken into consideration as a further cause; it proceeds at the expense of the warmth of the plant part. These two causes explain the phenomenon that, on bright nights, the thermometer shows a temperature several degrees lower if it stands directly between densely growing plants with thin leaves, such as meadow grass, than is found in the air layer above them. If the temperature of the air itself approaches the freezing point of water, the parts of the plants may be cooled below zero degrees C. by their heat radi- ation and, as a result, die, or. at least, at times some of their functions are arrested. According to Sach's^ observations the chloroplasts of the firebean (Phaseolus midtiflorus) and maise (Zea Mays) cannot turn green if the temperature does not rise to at least 6 degrees C. Rape acts in the same 1 Lehrbuch III, p. 636. 499 way. The stone pine (Pimis Pinea) requires at least 7 degrees C. In Potamogeton, the breaking down of carbon dioxid is found first between 10 to 15 degrees C. ; on the other hand, in Valhsneria even above 6 degrees C, and in the leaves of the larch at 0.5 to 2.5 degrees C, and in meadow grass at 1.5 to 3.5 degrees C. The movement of the leaves of the sensitive plant (Mimosa pudica) first occurs when the temperature of the surrounding air exceeds 15 degrees. The difference in the amount of heat required by different plants is shown best by the obsen^ations made on the germination of seeds in ice. Uloth^ found, for example, that seeds of wheat and maple (Acer platanoides) germinated in ice and bored their way deep into the ice, which they melted by the heat developed during germination. The fine lateral roots of the wheat had traversed ice pieces one-eighth of a meter in thickness. Later experiments- showed the same observer that several of the Cruci ferae (Lapidium rudcrale and L. sativum, Sinapis alba and Brassica Napus), oats, barley and r\'e, as well as other grasses, had germinated in large percentages. In barley and oats the percentage of germination, however, was noticeably less than in wheat and rye. Of the Papilionaceae, 80 per cent, of the peas had germinated in the ice-cellar and 12 per cent, of the lentils; 60 per cent, of sown parsley seeds showed germination. Incited by these observations, Haberlandt^ later undertook further experiments with sowing the common agricultural seeds in cases which were kept constantly at a temperature of zero degrees to i degree C. by means of ice. After a month and a half, rye, hemp (Camelina sativa), red clover, alfalfa, vetches, peas, and bastard clover showed the beginnings of germination. After four months, how- ever, a further development of the little roots could be proved only for mustard, camelina (or gold of pleasure), bastard clover, red clover and alfalfa, while wheat, barley, oats, ray grass, buckwheat, beets, rape, poppy, white clover, beans, etc., did not reach germination. Of all the plants, alfalfa had strikingly proved most favorable. These results, in regard to grain varieties, stand in very marked con- tradiction to Uloth's conclusions and also to the results of experiments which Hellriegel* has published. Of all the plants tested, winter rye was proved decidedly to require the least heat. With an almost constant tem- perature of o degrees C. (within the six weeks period of the experiments the temperature only a few times slightly exceeded this, reaching i degree C), this plant developed its leaf and root apparatus perfectly normally. Winter wheat was proved to need somewhat more heat because of the small size of its germinating plants, and, agreeing with Uloth's results, to a still greater degree, barley and oats, which at o degrees C, only slightly devel- oped their rootlets, while unable to force the leaf cone out of the grain. At 1 Fiihlins's Neue landwirtsch. Z. 1871, p. 875. 2 Flora 1875, p. 266. 3 Wissenschaftl. praktische Untersuchung-en auf d. Gebiete d. Pflanzenbaues. Wien 1875, I, p. 109ff.. 117. 4 Beitragre zu den naturwissenschaftl. Oryndlagen des Ackerbaues. Braun- schweig, Vieweg 1883, p. 284-304. 500 2 degrees C, however, the elongation was quite perfect. Maize had not changed at 5 degrees C. and even at 8.7 degrees C. germinated very slowly and imperfectly. Vetches and rape seed had germinated at o degrees and exhibited a development of the seed leaves worth mentioning, while peas in greater numbers, and lupins and beans in smaller amounts, had elongated the root body, to be sure, but had not developed the aerial axillar}^ part. Of seeds which had germinated at 2 degrees C, flax was more sensitive than rape seed, which germinated at approximately o degrees, but did not advance developmentally or show growth worth mentioning until given a noticeably higher temperature (8.7 degrees C). Peas and clover were found to stand next to vetches. They put forth a root and leaf at an average temperature of 2 degrees C, while beans and lupins needed at least 3 degrees C. for this. Asparagus developed slowly at 2 degrees C. For the carrot, approxi- mately 3 degrees seemed to be necessary' for germination, and for the beet root about 5 degrees C. was needed. It is not necessary to state here in detail that naturally the length of time of germination increases in proportion to the amount of temperature variation from the optimum of germination, but attention might be called to the fact that such germination experiments with the lowest possible tem- perature could lead to the growing of varieties hardy to frost. In all the seeding experiments uneven germination is found. It may be possible that those seeds which have first germinated at such low temperatures give plants which have a lesser need of heat for all their life processes than do other individuals of the same groups. Kirchner's experiments^ show that not only the initial stages of ger- mination can take place normally at such low temperatures but also that a further growth in length is made possible. Kirchner found mustard, rye, wheat, peas and hemp growing, as seedlings, for some time at temperatures which lay but little above o degrees C. To be sure, plants with a greater need of heat still show some growth in length when carried over into a low temperature ; but this growth can be explained only as the gradual dying out of the oscillations of the energ}^ of growth obtained under earlier, more favorable conditions. Kerner- has observed with Alpine plants that they can even blossom at o degrees. The melting water trickling into the soil from the snow fields is able so to stimulate the life activity of such plants that the heat produced by their respiration is able to melt the ice crust when it is even 2 to 5 cm. thick, so that the green organs reach the open air (Soldanello). Autumn Coloration. The coloring of the leav^es in the autumn is not always the same for the same variety. It seems that the difference is caused by the habitat of the individual. In general two types can be distinguished ; either a perfectly 1 4. Vers, deutscher Naturforscher u. Arzte zu Salzburg, p. 75 d. Berichtes. 2 Berichte d. naturwissenschaftl.-mediz. Vereins zu Innsbruck, Sitzung vom 15. Mai 1873, cit. Bot. Z. 1873, p. 438. 501 normal process of yellowing is found, beginning at the edge of the leaf, and followed by the; drying of the tissue, toward the centre of the leaf, or the yellowing and drying do not follow parallel, but rather opposite paths, i. e., the process of turning yellow begins at the petioles and the larger veins and advances toward the periphery, so that the edge is colored last of all, while, nevertheless, the first to dry subsequently. I observed the last course espe- cially well in Acer platanoidcs, less constantly in Acer Pseudoplatanus. The middle surface showed an uniform brilliant quince yellow, while the peri- pheral zone was still green. With advanced lowering of the temperature, many leaves showed a turning brow'n and dying of the outermost edge of the still green part of the leaf periphery, while the yellow, middle field did not yet show any dead places in the tissue. This case can also occur with Tilia, and in fact usually on one side, .iince only half of the leaf shows the process. Nevertheless in the linden, the coloration, advancing, from the edge toward the centre, is more frequent. The investigations of numerous cases show that the irregularities of color- ation are connected with the irregular dying of the vascular bundles. The normal autolysis in the autumn sets in when the whole vascular bundle system of the roots has still retained its functioning and the dying back only begins at the finest ends of the nerves at the edge of the leaf. Then the leaf discolors and dries first along the edge ; the discoloration ad- vances gradually in the portions of the leaf between the smaller veins and finally also between the larger ones toward the midrib and the petiole. If, on the other hand, the functioning of the ducts is prematurely destroyed in the branch or in the petioles, which can be perceived from the browning of the vascular bundles, then the discoloration begins at the petiole, or the larger veins, and extends irregularly toward the periphery. The course of the dying back, due to continued summer drought, re- sembles the normal autumnal autolysis, inasmuch as the parts of the leaf receiving the least amount of water are the first to discolor. Besides the drying of the leaf edges, however, that of the middle region of the larger intercostal fields becomes more noticeable here, because these lie fartherest from the strongly developed conducting strands ; thus especially great de- mands are made upon them because of excess of light and heat. The autumn coloring begins with a change of the chlorophyll often accompanied by the appearance of a red coloring matter. At first a change in the position of the chloroplasts is noticed, and a tendency to unite. I found in the spruce that the individual chloroplasts form radiating processes which unite with those of the adjacent ones. The red coloration is condi- tioned by the presence of ferments and related bodies. Many evergreen plants turn a dirty brownish green. According to Kraus^ this coloring is produced as follows : fine grained protoplasmic masses, colored a bright reddish green to copper red, occur in the palisade parenchyma in place of 1 Kraus, tJber die winterliche Farbung immergriiner Gewachse. Sitzungsber. d. phys.-med. Soc. Erlangen; cit. in Oekonomische Forstchritte 1872, Nos. 1 u. 2. 502 the disappearing chloroplasts. The further the cells of the leaf flesh are separated from the brown upper surface, the more transitions are noticed from these reddened cytoplasmic masses to the normal chloroplasts. All these changed tissues may, in many cases, be brought back to the normal color, if cut branches are brought into a warm place. In this, how- ever, the intensity of the light is not increased, and this may explain why only a lowering of the temperature should, in general, be considered as the cause of the autumn coloring. A further proof lies in the fact that in the autumn natural ripening only the ripened places, i. e., the places most cooled down by heat radiation, change their color, while the parts inside the top of the tree and covered by the outer leaves, show no change. In regard to the change in the coloring matter of the chlorophyll, it has been proved by Frank^ and Wiesner- that the chlorophyll passes over into a substance which Pringsheim called "Hypochlorin"^. This is an oily body, usually dark colored, which is produced from chloroplasts by the action of anorganic and organic acids and finally crystallizes into needles or whip-like brown crystals. Tschirch* has proved that this hypochlorin is identical with the "Chlorophyllan" of Hoppe-Seyler and that it should be considered as the first product of the oxidation of the chlorophyll (and in fact of only one part of the raw chlorophyll, viz., the cyanophyll of G. Kraus). This product is formed of itself if a chlorophyll solution is left standing for some time^ Tschirch found that the formation of chlorophyllan or hypochlorin, increasing according to the amount of acid, could be proved (tytrimetri- cally, by means of normal alkali) in the parts of the plants. Besides water plants, there may be only a few plants, the cell sap of which does not have a marked acid reaction. In genera which contain little acid, the formation of the chlorophyllan will be small and the extract made from this will have to stand some time, while in strongly acid plants (Aesculus, Rumex) the oxidation proceeds so fast of itself that no purely green extract can be made, since it at once exhibits the peculiarities of the modified chlorophyll and, even when chilled, deposits chlorophyllan. It is worth mentioning, for our consideration, that according to Tschirch even carbon dioxid is able to change the chlorophyll into chlorophyllan. Also the tannic substances with which the red coloring matter is certainly related, will have to be reckoned among those bodies with an acid reaction which attack the chloroplasts. It is thus a question whence it comes that this discoloring influence of the acid cell sap makes itself felt in the chloro- plasts only in the autumn. This can be explained either because in the course of the summer so little free acid is available in proportion to the rest of the 1 Sitzungsber. d. Bot. Ver. d. Prov. Brandenburg XXIII, v. 24. Feb. 1882. 2 Bemerk. iiber d. Natur d. Hypochlorins. Bot. Centralbl. 1882, Vol. X, p. 260. 3 Untersuchungen iiber Lichtwirkung. Pringsheims Jahrbiicher 1880, Vol. XII. 4 Sitzungsber. d. Bot. Ver. d. Prov. Brandenburg XXIII, v. 28. April 1882. 5 Concentrated hydrochloric acid breaks down the chlorophyllan into a body dissolving in hydrochloric acid with a blue color, the "Phyllocyanin" of the authors, and a brown body insoluble in hydrochloric acid, but soluble in ether, the "Xanthin" of C. Kraus. (Tschirch, Untersuchungen iiber das Chlorophyll III. Ber. d. deutschen Bot. Ges. Vol. I, Parts 3 and 4; cit. Centralbl. 1883, Vol. XIV, No. 25, p. 356. 503 substances in the leaf cell that the chlorophyll used in the formation of the chlorophyllan is constantly and quickly replaced by the preponderant process of assimilation, in which case usually no yellow coloration of the chlorophyll body is noticeable, or the chlorophyll body may be protected by a substance which does not let the acid through, gradually losing this protection in the autumn. However, both processes might take pace and, according to the above experiments, this is most probable, Frank and Wiesner refer to the actual presencei of an arrangement in the chloroplasts which protects them against the attacks of the acid cell sap. They emphasize that the green grains lie imbedded in protoplasm which is impervious to acids. Tschirch has also mentioned that each chlorophyll grain is surrounded by a colorless cytoplasmic membrane (hyaloplasma- layer) which is especially easily proved in water plants, and in this way possesses a special protection against the acid cell sap. As the leaf cell approaches the end of its life in the autumn the proto- plasm is no longer very abundantly present. But even where it is still more abundant, it undergoes, in the cold of the autumn, a change (which may be overcome by heat), making it permeable to acids. Frank found that the yellow coloration, produced by the action of acid on the chloroplasts, had already occurred when they, together with the nucleus, lay closely imbedded in the cytoplasmic wall layer. Such a change in the diosmotic character- istics of the protoplasm of evergreen trees also makes possible the action of acids. The organic acids increase, however, in the autumnal leaf in this way, making easier leaf coloration. In regard to the red coloration, C. Kraus^ has proved that the Brenz- catechin (orthodihydroxbenzine) first found by Gorup-Besanez- in wood- bine occurs in all leaves which change color in the autumn even (so far as the partial investigation extended) in all leaves still growing vigorously. This substance turns green with ferric chlorid and a beautiful red with vege- table acids. The extracts of the leaves give the reactions of oxyphen acid, on which account the conclusion is pertinent that the red coloring matter in the young leaves and in those which have changed color in the autumn comes from the increased effect of the Brenz catechin, due to the increased action of the acid. Summarizing all that has been said previously we can consider the process of the autumnal change of color as a process of oxidation, increased m proportion to the process of assimilation and due to the effect of light. This acts very differently on the substances present in the cells of the various plants, so that the chlorophyllan is produced from the chlorophyll coloring matter and the leaf becomes yellow.^ If the Brenz catechin, which may be produced artificially from carbo-hydrates and probably is 1 tJber die Herbstfarbung der Blatter und die Bildung- der Pflanzensauren. Biedermanns Centralbl. 1874, I, p. 126. 2 Annalen der Chemie und Pharmacie 1872, Vol. CKXI, Parts 2 and 3. 3 The chlorophyllan extraction of leaves dead in the autumn shows the same "bandes accidentelles permanentes" as Chantard emphasized earlier (Centralbl. f. Agrikulturchemic 1874, p. 40). 504 present in opalescing drops, is changed into a red coloring matter by means of an autumnal abundant formation of acid, a reddening and yellowing of the leaves follow. The leaf turns brown, however, if on the other hand, there predominates the formation of brownish yellow masses observed by G. Kraus^ and Haberlandt- with the destruction of the form of chloroplasts, which masses C. Kraus considered as the products of oxidation and humi- faction of the carbo-hydrates and which, as I believe, can directly arise from the decomposition of the chloroplasts. The most frequent, but certainly not the only cause of the red color- ation, is the lowering of the temperature, whereby the action of the light becomes relatively excessive. It is not the absolute values of light and heat which are determinative here, but the relative ones, i. e., those coming under consideration in relation to one another. A lowering of the temperature reduces the process of chlorophyll form^ation, while it sustains in full activ- ity that of oxidation, which, forming Brenz catechin, requires more light^, and initiates the red coloration. If the activity of the chlorophyll apparatus is increased, i. e., more carbo-hydrates are formed, the accessible oxygen is no longer sufficient for so high a degree of oxidation and the process of red coloration is suppressed. If, however, the work of the chloropyll is arti- ficially retarded by a lack of nutriment and moisture, then the oxygen acces- sible in the cell can suffice to reoxydize to a high degree the material which has become more scanty; in this case the autumn color occurs even in summer. As has been mentioned already, I observed in August, wdth girdling experiments on Crataegus, that the autumn coloring occurred even during the intense heat of summer and that at times it was possible with somewhat more solid leaves to bring the tip of the leaf which had been left on the; tree to a bright red autumn change of color by breaking the midrib while the leaf base, lying below the sharp point of breaking, retained its normal deep green color. Besides this, in the course of the, summer, we find, in many plants, ihat the first formed leaves of the annual growth, which have quickly lived out their Hfe, assume their autumnal coloration in the heat of summer (Ampelopsis). Places on young red leaves, which have been covered, remain greener. We will take up these conditions again under "Defoliation due to frost." The winter preparation of evergreen plants will be taken up thoroughly in the section on "Theories as to the Nature of Frost Action." Frosting and Freezing to Death. In the literature on this subject, we find different conceptions of the term "freezing to death." Death which gradually sets in in a plant because it has not obtained the warmth necessary for carrying through its normal functions has been explained in part as freezing. On the other hand, only 1 Okonom. Fortschritte 1872. Nos. 1 and 2. ^ Biedermanns Centralbl. 3 876, II, p. 48. 3 Batalin. tJber die Einwirkung des Lichtes auf die Bildung des roten Plg- mentes. Acta Hort. Petrop. VI. 505 the death which occurs suddenly as a result of a lowering of temperature below the minimum boundary of heat requirement and which is connected, as a rule, with the formation of ice, may be considered as "freezing to death." We can best overcome this difference in the use of the terms if we consider the first injury, due to a lack of heat, as a "chronic injury" and sudden death as an "acute injury." Tender plants from the tropics, which in our greenhouses do not con- tinuously find the heat necessary for all their developmental phases, often furnish examples of chronic injury. Failures in the culture of Indian varieties of Anoectochilus and other tender-leafed orchids. Begonias, Ges- neraceae, Marantaceae, etc., are well known. I found their leaves becom- ing brow^n-specked, curling and dying if exposed for some time to a tem- perature of 3 degrees above zero to 5 degrees below zero\ In wet, cold years, open ground culture of melons, cucumbers, tobacco and beans became diseased when the lack of heat was prolonged. In acute injury, one is inclined involuntarily to ascribe it to the forma- tion of ice. That this in itself does not cause death is shown in many cases by our hardy plants, which often are frozen stiff and as brittle as glass and yet continue their growth after the frost has disappeared. Let us picture to ourselves the effect of the formation of ice in the tissue. If the temperature of the part of the plant has fallen to the freezing point or somewhat below it, small ice crystals are formed on the outside of the cell wall. These crystals, produced at first from the absorption water and later from the imbil)ition water of the cell wall, become constantly larger, since, at their base, more and more water from the mycellar inter- stices of the cell wall is changed to ice. Finally, all the fine ice prisms are united into an ice crust. The cell w^all has attempted to make up for the loss of water which it has undergone by taking up new amounts from the cell contents. Thus the protoplasmic body of the cell becomes poor in water, and material changes begin, which finally reach such an intensity that the equilibrium of the different mycellae of the cell wall and of the proto- plasm is permanently disturbed. They change in such a way that no more life activity is possible. The cell, killed by frost, thus shows that its walls offered no resistance to the pressure of the cell sap, gradually letting it flow away. In direct contact with the air, this passes over into decomposition and the cell itself collapses. The frozen part of the plant appears wilted and dried, or rapidly decays. The cell sap, passing out of it, — this initiates the decay, — presses through the mycellar interstices and not through any breaks in the cell wall which might have been produced by frost. Indeed in a frozen part of the plant the tissue can be blasted by the ice in different 1 Compare also Molisch, Hans, Das Erfi"ieren der Pflanzen bei Temperaturen iiber dem Eispunkte. Sep. Sitzungsber. d. K. Akad. d. Wiss. Wien. Mat.-naturw. Klasse, Vol. CV, sec. 1; cit. Z. f. Pfianzenkrankh. 1897, p. 23. 5o6 groups and, as frequently observed, the cells of the epidermis can be raised from the underlying parenchyma, while a rupturing of the individual cells, due to the freezing of the water, has as yet been rarely observed. There- fore, the theory formerly generally expressed and now frequently held by practical growers, that the frost kills the plants by rupturing the cells, has been given up as untenable. In the same plant the same degree of cold can be uninjurious at one time and fatal at another, according to whether thawing takes place gradu- ally or suddenly. This latter case may be observed if frozen leaves or herbaceous stems of soft-leaved plants are held in the warm hand. The places of contact frequently become black after thawing and die. We will return to these phenomena in the following. Rapid and violent changes in temperature within a scale above zero degrees C. also did not remain ineffective. Sachs^ has proved that each rapidly appearing rise or fall of temperature is followed by an increase or decrease of the rate of growth. While de Vries could observe no disad- vantageous results from such fluctuations, I found a dropping of the leaves in the most extreme cases, especially if the fluctuations took place in a scale which began several degrees under zero and rose considerably above zero. The same plants in fact die if a change of temperature is repeated several times within a short period, as shown by Goppert's experiments-. Milk- weed {Euphorbia Lathyris) was taken from a temperature of 4 degrees C. below zero into a room at 18 degrees C. The leaves, bent backward and against the stem, because of frost, were raised at once and assumed their normal horizontal position. The same process was found in a repetition of the experiments, which took place five times within two days. On the third day the raising of the leaves began to be less and after eight days the plants were dead. Here, therefore, the cause of death was the rejpeated action of slighter degrees of frost, while out of doors, and uncovered, they could qndure 10 to 12 degrees below zero for some time without bad effects. The same experiments gave similar results with many other plants. This ex- plains the observation in general practice that slighter degrees of cold in many places kill plants which, at the same time, in a place with more con- stant temperature, can endure much greater cold. Goppert also calls attention to another fact which may serve to explain the frequent contradictions in regard to the fatal action of slighter degrees of frost in those plants which usually defy greater cold. It depends espe- cially upon the conditions under which the plant may find itself at the time, as shown by the experiment with the common groundsel (Senecio vulgaris) and meadow grass (Poa annua). Pots of these plants, which had already withstood a temperature of 9 degrees below zero, were placed for 15 days in a greenhouse at 12 to 18 degrees C. above zero. After this time they froze at a temperature of 7 degrees below zero, while other examples of the same 1 Lehrbuch d. Bot., 3d ed., p. 638. 2 tJber die Warmeentwicklung in den Pflanzen usw. 1830, p. 62. 507 varieties, which had remained out of doors during this time, weire found absolutely uninjured by rapid thawing. The killed plants had been made more tender by the retention in the greenhouse. Kornicke^ also comes to the same conclusion in his observations that French varieties of grain, on an average, more often fall victim to frost than the varieties which originate from the provinces of Prussia and Silesia. The longer cultivation in a country with a mild winter has made the varieties less resistant. Under otherwise equal conditions, Haberlandt- found that the seed- lings of field beans, field vetches, carrots, barley, peas, rape, poppy, red clover, alfalfa and flax, grown in a greenhouse at 20 to 24 degrees C, were frozen to death even at 6 degrees C. below zero; rye and wheat at 10 to 12 degrees below zero, while plants of the same variety, grown at the same time in a cold frame, died only at 9 to 12 degrees below zero, and rye and wheat only at 20 to 24 degrees C. below zero. The plants and parts of plants whose growth has entered upon a dor- mant period, on an average, suffer less and it is well known that dried seeds survive uninjured many degrees below freezing, while they go to pieces in a germinating stage with much slighter frost. During the vegetative development the susceptibility to frost changes with the different phases of the cell life. In unfolding apple blossom buds, which had suffered from a spring frost, I found the youngest cells, richest in protoplasm, were not injured, but those somewhat older, in an energetic stage of elongation, had turned brown, while the still older parenchyma cells in turn seemed healthy. The cases, cited up to the present, show clearly the difficulty in giving definite thermometer degrees as fixed minimum and maximum boundaries for the developmental capacity of any species. Each plant is certainly con- nected with a definite scale of heat, but the boundary and optimum values may change, to a certain extent, according to the combination of the remain- ing vegetative factors, momentarily present, which earlier contributed to the construction of the individual. On the other hand, it must be maintained that in spite of all the vege- tative conditions, which increase susceptibility to frost, many plants (espe- cially numerous algae, mosses and Alpine plants) never show any damage from frost. We will have to explain this phenomenon by the fact that the need of heat of such plants is so small that the greatest reduction in tem- perature is generally insufficient to produce those molecular changes in the tissues which would prevent a reassumption of the normal life functions. Theories as to the Nature of Frost Action. After discussing the circumstances which modify the freezing of plant parts, we will consider the theories which have been formed as to the nature of frost action. 1 Annalen d. Landw.; cit. in Neue landw. Zeitung v. Fiihling 1871, Pai't 8, p. 586 ff. 2 Haberlandt, tJber die Widerstandsfahigkeit verschiedener Saaten. Wissensch. praktisch. Untersuchungen, Vol. I. 5o8 In this, the phenomena of crippling, due to chronic action of cold, no longer come under consideration ; for these phenomena are primarily normal functions which are only retarded grJidually by a lack of heat until life becomes extinct^ The matter is quite different in the acute cases where death follows immediately upon the cold. In the acute frost phenomena, the formation of ice becomes a consider- able factor. This does not occur, hov/ever, at the point where pure water freezes but only below o degrees C, because the cell sap represents a salt solution. Besides this, observations, of which those of Miiller-Thurgau" especially should be cited, show that ice is produced only after the freezing point has been exceeded to a certain degree, either to an excessive chilling or supercooling. As an example of how often the supercooling point lies considerably below the freezing point, a few statements of the above named investigators may serve as examples. In grapes, the freezing point (G) was found to be at 3.1 degrees C. below zero, the supercooUng point (U) at 6.7 to 7.8 degrees C. below zero; in apples and pears, 1.4 to 1.9 degrees C. below zero (G) and 2.1 to 5.1 degrees C. below zero (U) ; in potatoes i.o to 1.6 degrees C. below zero (G) and 2.8 to 5.6 degrees C. below zero (U), etc. The formation of ice occurs suddenly ; therefore, in cases where some supercooling has taken place, there follows a sudden change in temperature. Our hardy plants, which can still grow unimpaired after they have become brittle with ice, show that the formation of ice is fatal only for certain varieties. In other cases, however, it has been observed that parts of plants, under certain conditions, can be cooled down to a still lower temperature and remain alive, while, with lesser cold, but different conditions, they are frozen as soon as the formation of ice has taken place. This formation of ice, the process of which we have already described thoroughly, is now ascribed by Miiller-Thurgau^ and Molisch* to such a withdrawal of water from the cell, that the cell dies on this account. Ac- cording to this, death from frost would be a simple process of drying up. The investigators support their theoi-y by the physical process, that, in freezing swollen colloidal substances, pure w^ater will be cr>'stallized out, and the colloidal substance, thus gradually drying, becomes stiff. In contrast to the above theory, is the one we hold, that death from frost is no specific process of drying but should be sought in a molecular irre- parable destruction of the protoplasmic structure. This destruction is expressed mechanically as well as chemically. The destructive tempera- ture is specific for each variety, each individual, each part of the plant and each method of growth of any plant part, but is not directly connected with 1 Compare Kunisch, H., tJber die totliche Wirkung niederer Temperaturen auf die Pflanzen. Inauguraldissertation. Breslau 1880. — Sachs, Landw. Versuchs- stationen 1860, p. 196. 2 Landwirtscliaftl. Jahrbiicher 1886, p. 490. 3 Ix)C. cit., . 534. 4 Molische, tJber das Erfrieren der Pflanzen. Jena 1897. 509 the formation of ice, as was evident in the number of plants which, without injury, endure the formation of ice in their tissues. These plants are called "resistent to ice" and they freeze only if the parts, which have been frozen stiff, are cooled down below this specific minimum. This specific minimum is not fixed but rises with the amount of cell sap, i. e., death from cold occurs at a higher temperature and, conversely, a loss of water will cause an increase in resistance to all factors^ and therefore, with frost, will cause death only at a lower temperature. Mez- adds to these the following observations : Any aqueous solution of a substance must be cooled down below the freezing point of water before ice can be crystallized out. In dilute solutions, as they exist under normal circumstances in cell sap, the lowering of the freezing point is pro- portionate to the molecular concentration (Raoult's law^). Dalton's law in regard to the solution of osmotic substances which contain several sub- stances in solution, holds good here. According to it, the amount that the freezing point is lowered ec}uals the sum of those amounts which each sub- stance would produce of itself. Since now each cell in the same plant may have a content gradually diflfering from that of the other cells, the point of minimum cooling of the cell sap will be a constantly changing one. Since the composition of the cell sap within the latitude of the specific limits of all varieties of plants fluctu- ates according to the nutrition, it is easy to understand that the various individuals possess a different resistance. This also explains the different behavior of dry and juicy parts of plants. The fact that in seeds, which may be dried, death can result also from a removal of water is explained by Miiller and Molisch by the assumption that it takes place because of the sudden formation of ice in the supercooled plant, whereby the water is very rapidly removed. Pfefifer* opposes this hypothesis and his book contains a thorough treatment of the pertinent literature. Mez's studies, already mentioned, support Pfefifer, for his investigations led to the following results. The fall in temperature, indicating the end of crystallization, did not lie, in any of the objects tested, below 6 degrees C. below zero. (The experiments were made with petioles of Helleborus, Saxif raga and Strelitzia, with leaves of Sempervivum and sprouts of Opuntia, Asparagus, Begonia, Peperomia, etc.). "But the cell sap, capable of coagulation and not absorbed, stiffens be- tween o and 6 degrees C. below zero. Accordingly, at 30 degrees C. below zero, no greater dr)'ing of the protoplasm, resulting from the removal of water in the formation of ice, takes place than at 6 degrees C. below zero. A plant which always survives the formation of ice in its tissues, does not 1 Pfeffer, Pflanzenphysiologie, 2d ed., p. 315, note. 2 Mez, Carl, Neue Untersuchungen iiber das Erfrieren eisbestandiger Pflanzen. Sond. Flora Oder Allg-em. Bot. Z. 1905, Vol. 94, Part I. 3 Raoult's law: cit. Nerst, Theoretische Chemie, 4th ed. 1903, p. 152. 4 See the chapter on "Die TIrsachen des Erfrierens'' in "Pflanzenphysiologie," II. Vol., 1904, p. 314. 5IO die, therefore, as a result of the dying of the protoplasts, but of a coohng down below the specific minimum." We find in this a confirmation of our earlier standpoint, viz., no simple process of crystallizing out the water is caused by the action of the cold but a material disassociation. This action of the cold makes the life functions impossible. Besides these essentially mechanical processes, however, chem- ical decomposition often plays a part. This will be initiated sometimes by too great cooling, sometimes without it. Not every plant needs to be first cooled down in order to freeze, but it probably freezes more rapidly, i. e., is cooled down to a sub-minimum temperature, if the freezing occurs in association with supercooling. At least this is shown by Mez's experi- ments with pieces from the stem of Impaticns parviflora. We learn from these experiments how very much the supercooling depends upon the con- stitution of the cell sap. Gases, dissolved air, hinder or decrease super- cooling just as do emulsified oil. gum or plant mucilage. It is also found that pruned plant parts, cooled down in water, always freeze without any further reduction of temperature or, at least, without an essential one. It happens that plant stems, standing partially in water, are found to be frozen as far back as they extend into the air. Molisch tested the question experi- mentally by letting branches of Tradescantia zehrina lie half in water. During the night a temperature of 5 degrees C. below zero acted upon them. After a slow thawing in a cool room, the half of the sprouts which had been left in the air were found to be frozen, while the lower half, sticking in the ice, remained uninjured. The upper half, surrounded by air, will have been cooled down rapidly by supercooling and is thereby frozen. On the other hand, as far as the plants stood in water, the cooling down takes place slowly on account of the high specific warmth of the water, and the super- cooling will be hindered by the freezing water about the stem as well as by the ice in the tissues above the water, which have been frozen. An observ-ation made by Miiller-Thurgau, that in a heap of beets, the outer frozen roots protect the inner ones from freezing, calls attention to the specially favorable influence of the formation of ice. This point is emphasized by Mez, since he says in general that the transformation of the cell sap into a solid aggregate condition forthwith protects from too rapid radiation the energy still retained in the plant. The conducting of heat is ver>^ much lower in ice than in water in which the warmth is distributed by currents. The danger of freezing, i. e., the lowering of the temperature to the specific death-deahng minimum, can in part be promoted by secondary cir- cumstances and in part hindered by them. The decrease lies in the use of the specific heat of water ; this will be mentioned again in methods of pro- tection against frost and further in the formation of ice itself, which occurs at zero, or a very little below it, while death sets in only at lower tempera- tures or finally in a change of the cell sap, since a greater quantity of oil, gum and mucilage acts retardingly. 511 The increase of the danger of freezing to death exists in all conditions which hasten the appearance of a fatal supercooling. Thus, for example, the anatomical structure of the individual, depend- ing upon the vigor of nutrition, can influence this. In very luxuriant growth, the lumina of the cells and ducts are wider and the intercellular spaces larger. However, the wider the duct, the more the lowering of the freezing point is suppressed by capillarity. We find this fact emphasized by Bruijning\ He found that the extract of Taxus leaves, in narrow capillary tubes, has a freezing point of 8.8 degrees C. below zero, while the same extract in open reagent glasses freezes at 1.3 degrees below zero. Besides the greater amount of water in the tissues, the constitution of the air (amount of humidity contained) and its movement come under con- sideration. In the later connection, attention should be called to the wide- spread discovery that, in protected positions (in narrow valleys, fields sur- rounded by woods, etc.) plants freeze which would remain uninjured in regions accessible to the wind. In order to explain this circumstance, we will have to recall the fact that air in motion increases evaporation and thus concentrates the cell sap. With stronger evaporation the formation of ice will occur more quickly, whereby supercooling will be avoided, and, at the same time, protection of the remaining heat in the tissue will be brought about. In its prevention of supercooling by the superimposed ice, may be found the advantage of the "open furrow" for winter grain ; it retains snow much longer. Fog will also act as a protection. We find a recent example of this in the observations made by Thomas", who, in Thuringia, found that the foli- age of young beeches, on the heights covered with fogs was uninjured, while in the valleys it was brown and wilted as a result of frost. In this case, an evident boundary line could be found. In mountain forests, the covering of clouds is a protection against frost which one should not underestimate. We will now turn once again to the fact that in many cases a rapid thawing of frozen plant parts can bring about death, while a slow warming does not kill. The correctness of this assertion is often contested. If it is given as an universal rule, it seems inconclusive; but if it is limited to cer- tain cases, it certainly is of value. An older and very instructive example is given by Karsten^. A large shipment of tree ferns (Balantium) had to withstand 20 degrees below zero enroute. .Some of the plants, when they arrived, were put, in a still frozen condition, into a warm place and were killed, while almost all of those first thawed in cold water and then taken 1 Bruljning, F. F., Zur Kenntnis der Ursache des Frostschaden. Sond. Wollny's Forschungen auf dem Gebiete d. Agrikulturphys. 1896; cit. Centralbl. f. Agrikulturchemie 1898, p. 173. 2 Thomas, Fr., Scharfe Horizontalgrenze der Frostwirkung an Buchen. Thiir- inger Monatsblatter 1904, 12. Jahrg., No. 1. 3 tjber die Wirkung plotzlicher bedeutender Temperaturanderung usw. Bot. Z. 1861, No. 40. 512 into a cold place, remained alive. From this, it is evident that the rapid thawing and not the frost is the cause of death. Miiller-Thurgau has stated of ripe fruit and Molisch of the leaf of Agava americana, that these objects can be kept alive after moderate freez- ing, if thawed very slowly, but that they die when thawed rapidly. I pressed the surfaces of the frozen leaves of herbaceous Cinerarias between my finger tips. The plants, left in their places of growth, showed, after thawing, that only the places pressed with the fingers were killed. According to the discoveries of gardeners, it is only the tender-leaved, juicy spring blossoming plants, grown ' in greenhouses (Cinerarias, herbaceous Calceolarias, etc.), which, after a night of freezing, can be rescued by the longest possible retardation of the thawing. In plants perfectly resistant to ice, however, the rate of freezing and thawing seems to have but little influence on life. In explanation of the matter, two points should be taken into consid- eration. First, in rapid thawing, the same processes will be enacted which occur, for example, in the evaporation of fluid carbon dioxid whereby the formation of solid carbon dioxid takes place, as is well known. In rapid thawing, the warmth necessary for melting will be removed, not only from the surrounding air, but also from the deeper layers of this part of the plant, which are thereby cooled down still more. In such plants in which the critical point, i. e., the specific minimum, lies close below the freezing point, this removal of heat, increased by rapid thawing, can cause death. The second point to- be taken into consideration is that the cell wall, from which ice has been crystallized, cannot possibly soak up the great amounts of water which are produced suddenly by rapid thawing. The water remains in the intercellular spaces and evaporates there while the cell of the leaf is not able to regain the necessary turgid condition. From this comes the gardening method of protecting from the rising sun all plants which have suffered from late frosts. Let us consider finally the natural processes of the autumnal changes of material from the standpoint of Mez's theory as here discussed. When the plants prepare for winter, they collect the greatest possible amounts of reserve substances and reach the maximum at different times, according to their individuality. In Pimis austriaca, for example, Leclerc du Sablon^ found this maximum in May, but in the spindle tree (Evonymous Euro- peus), which sends out its shoots earlier, he found it in March; in decidu- ous trees the maximum is reached in the fall. In evergreen plants, the reserve carbo-hydrates remain abundant in the leaves-. Their activity seems reduced to a minimum, since their stomata are closed permanently. 1 Leclerc du Sablon, tjber die Reservekohlehydrate der Baume mit ausdauern- den Blattern. Compt. rend. 1905, p. 1608; cit. Centralbl. f. Agriculturchemie 1906, p. 322." — Pabricius, L., Untersuchungen iiber Starke- und Fettgehalt der Fichte usw. Naturwiss. Z. f. Land- u. Forstwirtschaft 1905, p. 137. 2 Simon, Der Bau des Holzkorpers sommer- und wintergriiner Gewachse usw. Ber d. D. Bot. Ges. 1902, p. 229. PART VII. MANUAL OF Plant Diseases BY PROF. DR. PAUL SORAUER Third Edition— Prof. Dr. Sorauer In Collaboration with Prof. Dr. G. Lindau ^nd Dr. L. Reh Private Decent at the University Assistant in the Museum of Natural History of Berlin in Hamburg TRANSLATED BY FRANCES DORRANGE Volume I NON-PARASITIC DISEASES BY PROF. DR. PAUL SORAUER BERLIN WITH 208 ILLUSTRATIONS IN THE TEXT Copyrighted, 1917 By FRANCES DORRANCE 6^- ©C!,A476180 SEP 20 1917 THE RECORD PRESS Wilkes-Barre, Pa. "^v^ \ 513 Thes€ reserve substances are protected so far as is possible against frost. Part of the starch wanders into the protected central portion of the trunk and branches (pith, medullary rays and parenchyma wood), and part is transverted into sugar or occurs instead as a fatty oil. In the needles of Alpine spruces, the substance of the chloroplasts is found to flow away and the cell content in winter forms a homogeneous cytoplasmic mass with abundant oil drops. Lidforss^ has proved this transformation for all the green cells of evergreen plants ; in the spring the starch is reformed. This removal of solid bodies from the cell with the appearance oi winter takes place, according to Mez, as an advantageous arrangement in |)lants resistant to freezing. He calls the fluid substances "thermally active," for, in crystallization, they set free heat. The solid elements, on the other hand, follow retardingly the temperature of the fluids ; they are "thermally passive" and absorb heat, since, with the formation of ice, the change of temperature from the point of supercooling towards zero, they must again give up this heat relatively rapidly. This circumstance acts in such a way that, with the accumulation of solid bodies in the cell, the melting point of the cell sap cannot be reached after supercooling has taken place. A great number of thermally passive elements consequently form a menace for the plant, while the fluid, thermally active bodies are proved advan- tageous as producers of heat. Profiting by the experiments of A. Fischer-, we will distinguish between oil trees and starch trees, according to whether they change their starch into oil or let it pass into the interior of their trunks and branches and convert it into sugar in the bark. The fatty oil of oil trees (conifers, birches), which we have learned to recognize from Jonescu as a protection against lightning, besides this peculiarity of preventing supercooling, like sugar, is thermally active, i. e., stores up heat to be given out in crystallization. The trees which transform all their starch into oil, conifers, may be fitted to survive a higher degree of cold than those in which a part of the starch is left free and becomes sugar only in the bark (the ma- jority of deciduous trees). This circumstance surely explains the phe- nomenon that conifers and birches extend farther up into cold regions. Disturbance due to Chilling. Cases occur in potted plants in greenhouses, in which the plants suffer when carried from one house to another, in case they are thus exposed to a temperature below zero degrees at times for only a few minutes. Practical gardeners maintain that the plants have "taken cold." Moebius^ has studied this statement very recently, and has been able to confirm the above assertion. For example, he took a Begonia metallica from a warm house, kept it one or two minutes out of doors in a tempera- ture of 5 degrees C. below zero and then put it again in its former place. 1 Lidforss, Zur Physiologie unci Biologic der wintergrunen Flora. Bot. Centralbl. 1896, p. 33. -• Jahrb. f. wiss. Bot. 1891, p. 155, cit. by PfefCer loc. cit., p. 137. 3 Mobius, M., Die Erkaltung der Pflanzen. Ber. d. D. Bot. Ges. 1907, Vol. XXV pt. 2, p. 67. 514 Even the same day, he noticed newly produced brown spots on some of the older leaves. Later these leaves got a "glassy, dark appearance, jiung down and dried up." The young leaves did not suffer. The same kind of discoloration and wilting phenomena were observed in other similar experiments and are in all essentials the characteristics which have been given by practical growers as a result of taking cold. Moebius emphasized that no formation of ice in the tissues can be concerned here. I can bring proof of this in an experiment which I made with Begonia anjyrusti(jma. A pot of this plant was taken from a warm house and put out of doors after the temperature had risen to 0.5 degrees C. Within a short time, I saw glassy spots appear on some leaves. According to the experimental results given in different places in the present chapter, I perceive in the wilting and glassiness of different leaves, with sharp falls in temperature the results of sudden differences in tension in the tissue. The contraction of the cells as a result of the excessive cool- ing will cause, in places, an outpressing of water into the intercellular spaces. Besides this, the difference in the different tissue forms united in the leaf organ makes itself felt. We will refer in this connection to the subsequent section on frost blisters where various elevations of the epidermis and loos- enings of the tissue are described. The practical grower at any rate should keep in mind the fact that, in transporting plants from warm houses, there is a possibility of taking cold, even if plants are exposed only a few minutes to a freezing temperature. Since a sharp change of temperature should be avoided, the wrapping of the pots with cloth or paper must be recommended for all cases. B. SPECIAL INSTANCES OF FROST ACTION. Turning Sweet of Potatoes. In the well-known phenomenon, that potatoes turn sweet when sub- jected to slight degrees of frost, Goppert^ and Einhof- had noticed that in- dividual differences make themselves felt. Under the same conditions only part of tlie tubers turned sweet and remained soft, while the others became hard. If the potatoes were brought quickly into considerable cold (about 10 degrees) the)^ were frozen, as a whole, without showing any formation of sugar. The turning sweet could not be observed except at temperatures which lay only a little below the freezing point. Miiller-Thurgau found that this change set in only in potatoes which had been taken from the soil at least a month earlier. It could not be produced in freshly harvested tubers. Probably similar phenomena led Payen^ to the conclusion that even before the action of the frost, the tubers, which showed the formation of sugar, might have started to grow again. 1 'Warmeentwicklung-, p. 38. - Neues allgem. Journ. f. Chemie. Berlin 1805, p. 473. 3 Cf. Czapek, Fr., Biochemie Uer Pflanzeen. Fischer, Jena, Part 1, p. 371. Here also notes on older literature. 515 The fact, established by EinhotT and Goppcrt, that potatoes freeze with greater degrees of cold without becoming sweet and that those which have become sweet remain soft, is explained simply by Miiller-Thurgau's^ experi- ments. He found that the potato tuber freezes only at 3 degrees C. below- zero. To be sure, its real freezing point lies possibly about i degree below zero, but the cell juices must first be cooled down to 2 to 3 degrees below freezing, i. e., be "supercooled," before the first ice crystals can be formed between the cells. Naturally, a lowering of the temperature from zero to 2 degrees below zero retards many life processes. Among these are two which come especially under consideration here; viz., the transversion of the starch into sugar and the utilization of the sugar. It may be assumed that the sugar from the protoplasm of the cell is partly used in respiration, partly during the period of growth in the regeneration of the cytoplasm and the starch reversion. Miiller-Thurgau- found, in fact, that potatoes which had become sweet after having been kept at a temperature of 20 to 30 degree C. had increased their starch content at the expense of the sugar. This had disappeared ; with a lowering of the temperature to o degrees and 2 degrees below zero, the process of respiration (and most probably also that of the regeneration of the protoplasm) decreases, while the transversion of the starch into sugar does not fall off so quickly. Consequently, the sugar accumulates in the tuber and becomes noticeable in the flavor. It amounts to about 2.5 per cent, of the fresh substance, yet comparatively wide fluctu- ations are found in difi^erent individuals of the same variety. A higher w^ater content in the tubers favors the turning sweet. This increase of sugar corresponds to the loss of starch yet, according to Czubata's'^ analyses, no corresponding proportion can be proved in the two processes. According to Czubata, a part of the protein passes over from tlie insoluble into the soluble condition during freezing. Muller assumes that the ferment here concerned increases with the lower temperature. If potatoes which have become sweet are left for some days in a room with a temperature of more than 10 degrees, respiration increases and the sugar is oxidized, i. e., the potatoes lose their sweetness and in this way again become usable for cooking. Other proposed means, as, for example, the leaching of the tubers with water, did not lead to any results. Besides this, however, it should be emphasized that one need not hesitate to use potatoes for seed which have become sweet. Such potatoes freeze only with a greater degree of cold than non-sweet tubers'*. I should like to add here supplementarily a statement made to me verbally that in Reinerz a cellar is said to exist in a cave in which potatoes become sweet even without the action of frost. This phenomenon is 1 Miiller-Thurgau, Ein Beitrag zur Kenntnis des Stoffwechsels in starkehal- tigen Pflanzenorganen. Botanisches Centralbl. 1882, No. 6. 2 Landwirtsch. .Tahrb. 1883, p. 807. ^ Czubata, Die chemischen Veranderungen der Kartoffee beim Frieren und Faulen. O.ster.-Ungar. Brennerei-Zeitung 1879; cit. in Biedermanns Centralbl. 1880, I, p. 472. i Muller-Thurgau, Landwirtsch. Jahrb. 1883, p. 826. 5i6 ascribed to a strong exhalation of carbon dioxid. I have not been able to prove experimentally an increase of sugar in the tubers, by a two days' retention in a carbon dioxid atmosphere. Nevertheless, it might be possible that some eifect would be noticeable after a lonja^er time. The statement gains probability from a work by Bachet^ and Savelle. according to which, by the use of carbon dioxid with a somewhat higher temperature and greater pressure, starch flour was rapidly turned into dextrine and grape sugar, espe- cially if the process of saccharification was facilitated by the addition of gluten. It can be assumed that, because of an abundant supply of carbon dioxid in the above mentioned case from Reinerz, natural respiration is repressed just as by a lower temperature and the process of sugar formation which, according to Miiller, can be proved up to a temperature of lo degrees has caused its slow accumulation. The production of saccharose during germination after an increase of temperature is proved by Mar- cacci's- experiments with slices of potato which had been dried in the sun and in an oven. In the sprouting tubers, saccharose is found in the young shoots and later in the leaves (probably due to the hydration of starch). It is evident from the above that the methods of using these potatoes, which in outward appearance are rarely distinguishable from healthy, non- sweet tubers, can in no way be applicable for frozen ones, i. e., those turned to ice. A tuber which has been frozen hard is dead and, in thawing, at once falls victim to a high degree of decomposition. It becomes soft and gives off water, while the cut surface turns brown at once, if not immedi- ately coated with acid. The skin separates quickly from the flesh, like a bladder, with a development of gas. The bark cells beneath the cork layer break apart because of the dissolution of the intercellular substance. The cytoplasm is brown and granular and drawn back from the cell wall; the protein crystalls are dark brown ; the cell sap is strongly acid. The Running to Seed of Beets. By this name are characterized those specimens of sugar beets and fod- der beets which set seed even in the first summer. In some years the phenom- enon occurs very frequently and disturbs the harvesting and use of the beet since the root is woodier than in the two-year-old beets. Opinions differ as to the cause of the phenomenon. They take two different points of view ; some make the constitution of the seed responsible for this, others, the atmospheric conditions and especially spring frosts. In consideration of the fact that actually in years when late frosts have attacked the young beet plants, unusually many may be found which have run to seed and, sup- ported by Aderhold's experiments with kohlrabi, to be mentioned later, we will give here the present cultural retrogression. From the abundant literature on sugar beets we will cite only one work, since it reports recent scientific in\estigations and makes brief references 1 After Compt. rend 1878; cit. in Biedermanns Centralbl. 1879, p. 544. - Marcacci, A., Sui prodotti della transformazione dell' amido, cit. Bot. Jahresb, 1891, I, p. 47. 517 to the older experiences. Andrlik and Mysik', on the ground of numerous analyses, have come to the conclusion that the weight of the seed-bearing tuber may sometimes be less than that of the normal tuber, at other times greater. The root of the. seed-bearing tuber is poorer in potassium, phos- phoric acid and sulfuric acid as well as ammonium nitrate and amido- nitrogen. The sap is purer. Of the organic substances formed by the seed-bearing beet, the sugar content amounted to only 45 to 50 per cent. ; in the normal beet 54 to 69 per cent. "The greater part of the organic sub- stance, free from sugar, is in the pith. i. e., in the elements forming the solid skeleton of the plant. * * * ." "The pith formation probably takes place at the expense of the sugar." We perceive that the beet plant has changed its inbred method of growth. Instead of storing, in the first year, only reserve substances in the root and making use of them in the following year for the formation of seed, it at once makes furthci use of the organic substances gained by the leaf apparatus. This circumstance points to the fact that the normal process in the cul- tivated beet, the uninterrupted formation of new leaves, has undergone some disturbance. The growth has ceased for some time, rather the beet has passed through a dormant period which would correspond to the winter rest of a normally ripened tuber. The newly mobilized reserve material is used here for the production of the inflorescence, just as in the normal case, after the arrestment of growth. It is conceivable that the late frosts may call forth such an arrestment. They will incite a greater formation of seed stems, the later in the year they occur and the more the subsequent weather favors inflorescence formation. If, however, the weather, follow- ing the frosty night, is especially favorable for the development of foliage, the elongation of the axis, already begun, can stop and the development of the root advance. In large sugar beet fields, as a rule, such seed-bearing beets and similar transitional forms are found. This inclination to the set- ting of seed can certainly be hereditary in the seed, possibly can be prepared in the seed of normal beets, if not sufhciently matured, i. e.. for example, if harvested before it is ripe, Aderhold- has furnished experimental proof of the formation of seed- bearing roots in Kohlrabi, as a result of frost action. He brought seedlings in pots into a freezing chamber for 8 to 10 hours and then placed them out with others which had been exposed to frost. In one experiment; he ob- tained, ior example, two seed-bearing roots from 18 untreated plants, while from the same number of specimens which, for 10 hours in May, had been exposed to a temperature of 2 to 6.5 degrees C. below zero, he had 7 seed- bearing plants. In both cases some Kohlrabi plants later overcame the impetus of frost action and formed a root body. 1 Schos.srii)ie unci normale Rtibe. Blatter f. d. Zuckerruben))au 1905, No. 24, p. 374. 2 Aderhold, R. uber da.s Sehie.ssen des Kohlrabis. Mitt. d. K. Biolog. Anst, 190(5, No. 2, p. 16. 5i8 It is well known that, in some years, such premature development of inflorescences occurs often in other plants, which form fleshy, storage organs (celery, carrots, radishes). It is very probable that not only frost action but also other processes of arrestment are effective here. Frosty Taste in Grapes. The processes which occur in the turning sweet of potatoes take place also in woody plants. In this connection, Pfeffer' mentions Fischer's inves- tigations- on the fluctuations between the starch and sugar in the so-called starch trees, such as the linden and birclv'. When branches are taken in winter from out of doors into a warm room, starch is formed in the bark parenchyma, within a few hours, and. in the cold, can again pass over into sugar. A similar formation of sugar, connected with the decrease of organic acids, is found to occur in grapes after the action of frost. Even when the main stem of immature clusters had been attacked by frost but was still green and the berries clear, a considerable decrease of acid and increase of the sugar content was founds An investigation on Riesling grapes of the decrease of acids in a plant which had been exposed from October 19 to November 9 to a temperature as low as 5 degrees C. proved an acid reduction of 4 per cent. Half ripe clusters, greatly injured by frost when cut ofl", showed from October i to 11, an acid loss of 4.5 per cent. The frosty taste, however, does not seem to be due alone to the increase of sugar and decrease of acid, but material compounds may perhaps diffuse from the stems of the grapes which the protoplasm of cells would not have let pass through, if there had been no frost action. Through these changes, the susceptibility of the grapes to the fungus of white rot may be increased, since Viala and Pacottet'' have shown that this fungus is able to infest only the berries which have a high sugar and a smaller acid content. The be- havior of l)lack rot is exactly the reverse. Changes in the Blossom Organs. In the action of frost, the permanent processes are sometimes chemical, sometimes mechanical. In the former it is difficult to decide in how far they are initiated by the freezing, or if they begin only with thawing. Thus for example. Gopperf^ has observed in the blossoms of Phajus and Calanthe that they turned blue when frozen. This change in color is explained by the fact that, through the action of the frost, the indicans, which* is abun- dant in the normally colorless cells, especially around the vascular buncjles, 1 Physiologie, 2d edition, I, p. 514. •^ Jahrb. f. d. wiss. Bot. 1891, v. XXII. :! tJber die Periodizitat der Stiirkezu- und abnahme in den Baumen. Compare Mer, E. in Bot., Jahresb. 1891, I, p. 46. ■i Biedermanns Centralbl. 1879, I, p. 233. •"' Viala, P. et Pacottet, Sur la culture du black-rot . Compt. rend. 1904, CXXXVIII.'p. 306. . c. ^, '•■ tJber Einwirkung des Frostes auf die Gewiichse., Sitzungsber. d. bchles. Ges. t. vaterl. Kultur 1874, cit. Bot. Zeit. 1875, p. 609. 519 is oxydized to indigo. Prillieux^ states that this change appears first with thawing. Other statements on the beha\ior of the coloring matter in blos- soms vary as greatly and it can only be said in general that the red coloring matter is one of the most resistant ; in fact, according to Goppert-, who has collected many observations on the color phenomena produced by frost, it can be increased in the leaves and blossoms with slight frost action. Most frequent, and therefore most important, are the disturbances in the blossoms of our fruit trees due to frost. For all practical purposes, the way the process of discoloration takes its course is immaterial. Scien- tifically, however, it may be of interest to become more exactly acquainted with the frost action. But since it is impossible to determine in natural spring frosts what are the first efiiects and what the subsequent changes, I have subjected apple blossoms to artificial frost. After a blossoming apple branch had been exposed for 2 hours to a temperature of 4 degree C. below zero, the investigation, carried on imme- diately after the removal of the freezing cylinder, showed that all the petals, and also some places in the leaves, had taken on a glassy consistency. Even after a few minutes (the air temperature was 11 degrees C.) a flabbiness and a turning brown began in the parts which had become glassy. The brown discoloration of the leaves, therefore, is not the direct effect of the cold but a phenomenon making itself felt first with thawing. The petals, with the natural reddish tinges on the under side, had brown veins and were spotted. The edges began at once to collapse and dry up. A cross-section showed that the discoloration was due less to the turning brown of the cell walls than to that of the cell content, since these excreted reddish yellow to brownish yellow solid masses deposited usually in the longitudinal axis of the cells and resembling carotin. The different cell layers of the petals behaved differently. The excreted yellow masses could be proved to be especially abundant beneath the colorless epidermis which had remained at its natural height. Besides this, the parenchyma cells which accompany the vascular bundles of the fine veins showed these excretions especially distinctly. This latter circumstance caused the venation of the fine petals to appear strikingly brown to the naked eye. With the rapidly advancing process of drying, the cells of the mesophyll collapsed, while the cells of the epidermis retained their natural size. Fig. 103 shows a part of a petal soon after it had been removed from the freezing cylinder. It shows the leaf still in its natural dimensions, with the large intercellular spaces (/) between the very thin walled cells of the flesh and with the unchanged epidermis (r). The discoloration, due to the yellowish brown contracted mass of the cell content {b) , is most intense near the vascular bundles (g) and in fact especially so on the under side of the leaf. In the vascular bundle the narrow spiral ducts have turned brown. 1 Bot. Zeit. 1871, No. 24.— Bull, de la Soc. hot de FVance 1872, p. 152. -' Kunisch, H. ttber die tr«dllche Wirkung- niederer Temperaturen auf die Pflanzen. Inauguialdissertation, p. 29. Breslau 1880. 520 The browning process took a diflerent course in the stamens. After they had been taken out of the freezing cyhnder they remained apparently unchanged, while the petals had already begun to wilt. Only later did the stamens become yellowish brown and the anthers a pale yellow. A cross- section through the stamens showed that the brown coloration was essen- tially conditioned by the epidermis which is rich in contents. To be sure, in all the tissues, the cell contents seemed contracted into drops or lumps and were brown, but the amount of substances in the inner cells was so scanty that the coloring of the whole tissue remained pale. The spiral ducts of the stamens, like those in the petals, had light brown walls. In the anthers, the discoloration depended likewise on the amount of cell contents. These were most abundant in the connective tissue and this consequently seemed most deeply brown, while the epidermis in the anthers themselves and the underlying fibre cells, arranged like palisades, had only very scanty, solid masses of contents and, therefore, seemed almost colorless. The rem- Fig. 103. Cross-section of a petal of the apple injured by artificial frost. nants of the ground tissue near the connective tissue were somewhat darker. The pistils showed the greatest injuries. They were a deep brown and bent when taken out of the freezing cylinder. At first no collapse of the tissue could be seen anywhere. The papillae of the stigma seemed stifl:" and filled with Ijrown cytoplasmic contents. As in a fresh condition, they still held fast the somewhat swollen and, therefore, differently formed pollen grains, filled with cloudy, uniform contents. In the pistil, as in the stamens, the peripheral layers were richest in content and, therefore, their contents and walls most deeply colored brown. Among the mechanical disturbances, tangential holes were observed here and there in the tissue of the pistil as in that of the stamens. They were partly produced by the loosening of the cells from one another, but also by the tearing of the cells themselves. The number and size of the holes in the tissue increased towards the bottom of the pubescent pistil, the hairs of which, poor in contents, showed a browning of the walls. Here the tissue at the base of the pistil widened into five diverging, bluntly conical 521 parenchyma groups, arranged with tlieir tips toward the centre, as the point of transition into the five carpels. Each of these displayed an epidermal covering and a parenchymatous inner Hesh. In the cross-section shown in Fig. 104, through the receptacle of the apple we see that the future flesh is already traversed by numerous, regularly arranged vascular bundles (g). The receptacle, covered with a firm epidermis (c), extends, toward the inner side, into five anchor-like branches (a). These are the five ovaries into which the pistil has widened. On their reflexed edges, which in the cross- section look like the flukes of an anchor (r), the seed-primordia are formed je^r Fig. 104. Cross-section thio«gh a young receptacle of the apple injured by frost. in the under part of the receptacle and get their nutrition through the vascu- lar bundles (gc). The seed cavities (sf) and the cavity left free in the centre (h) because the edges of the ovaries have not united, are lined with regular epidermis (e). The cells of the epidermis of the axillary side (br), as also within the fruit cup, are found to be richest in contents and, there- fore, most deeply browned, while the central, at first meristematic part of each ovary is only slightly discolored. A splitting of the tissue manifesting itself in the appearance of tan- gential holes (/), due to the separation of the collenchymatous layers (c) 522 from the inner flesh of the fruit (m) may be seen in the transitional zone from pistil to ovaries, even with a low magnification. It should be empha- sized that in thiS; as in the stamens, a tearing of the cells (c) actually takes place, while in the coarser tissues only the usual separation of the different cell layers is formed. These mechanical (listurl)ances which, as we shall see later, are so imjiortant in the vegetative organs, have a lesser influence in the blossoming organs. The inflorescences die because of the chemical change in the cell contents and drop more quickly if the tissue splits at the same time. The experi- mental results correspond to the phenomena after natural spring frosts. The dependence of the susceptibility upon the consti- tution of the cell sap may be perceived from the adjoining illustration of a young apple blossom severely frosted (Fig. 105 ). The shading, carried out only on one side in this and other drawings, holds good naturally for both halves. All the shaded parts indicate tis- sues with intercellular spaces, which clearly contain air. At r sugar may be proved by the glvcerin reaction. The crosses indicate the regions wdiere metabolism has already ad- vanced so far that abundant calcium oxalate is deposited. The rings (/) are intended to indicate the different places turned brown by frost ; all the younger, inner parts, rich in cvtoplasm, have remained healthy; the dark line is a vascular bundle. Here we should mention only supplementarily the fact that, besides the acute affects of cold already described, chronic disturbances in the life of the blossoms also occur which concern only the retarding of the normal life processes. The best known example might well be the suppression of the opening of the blossoms in Crocus vermis and Tulipa Gesnertana. Because Fis. lor,. Primordia of an apple flower bud injured by frost. 523 of the low temperature, no sufficiently strong growth of the inner side of the perianth leaves takes place, so that the bending out of these leaves and, therefore, blossoming is suppressed. The blossoms of Ornithogalum uuihcllatuin, Colchlcnm autumnale, Adonis vernalis and others, react simi- larly but more v\eakly. The processes in Mimosa pndica, Oxalis acetosella, etc., prove that even green leaves act thermostatically because of the influ- ence of lower temperatures. Material on this subject may also be found in the later sections which treat of the mechanical effects of frost. The Rust Ring.s in Fruit. The so-called rust rings appear as the result of slight injuries from frost in young fruits. By this are understood various formations of cork in the skin of the fruit, spreading, especially in the pomaceous fruits, in ring- like zones. In many varieties the appearance of cork-color etchings is a very normal process. Our Reinettes. for example, often possess star-like, small rusty spots. The so-called "netted Reinettes" have linear cork trac- ings on the outer skin of the fruit and often such cork formations obtain a surface-like extent, as, for example, in the French Reinettes, Parker's gray pippin, in the gray autumn butter pear, the medlar, etc. This condi- tion is morbid only when the phenomenon is very extensive in some years (for example, 1900) on many fruit varieties whicli otherwise remain smooth and when the formation of the cork covers the greater part of the fruit. The initial stages are found in early youth. It is evident after the appear- ance of very late May frosts that the contents of some groups of epidermal cells turn brown and the cells begin to die. Beneath such places plate cork is formed, and the dying epidermis becomes somewhat convex. During the swelling of the young, green fruit, the formation of cork advances further into the fruit flesh, producing considerable groups of parallel rows of cells arranged perpendicular to the upper surface. In a special case observed in "Amanli's butter pear" these cells, arranged in rows, appeared to the same extent as those in the epidermal cells ; they were found actually suberized, however, only in the peripheral layers while the light-colored, thick walls of the more deeply lying cells gave a cellulose reaction. The greater the new formation, the more the overlying, dying cell layers are separated and the outer surface of the fruit becomes rough and scaly. In flask-shaped pears the pouchy part of the fruit, bearing the blossom end, often appears to have rusty grayish scales, while the half toward the stem is smooth, and green. In other cases, a broad, cork-colored band is seen near the blossom end, etc. At times with this splitting of the waxy covering and dying of the epidermal cells is connected the development of the newly produced underlying tissue into stone cells. These appear later in circular aggregations on the outer surface of the fruit, so that the conditions are produced which we have described as "Lithiasis" (p. 170). ("Diel's butter pear," "Good Louise of Avranches"). Since such changes are usually 524 found on one side the growth of this cork-color side, containing the stone cells, is often retarded, thus producing deformed fruit. After I had succeeded in causing a splitting of the cuticle in tough leaves by the action of artificial frost, I did not hesitate to trace the injuries in the wax coat of young fruit to frost action, more particularly the forma- tion of such "rust rings" as had been observed only in years with late frosts. The pears, which are susceptible to frost, sufifer most abundantly and greatly, in fact usually on one side and at a certain height on the tree. The Behaviok of Oi.dkr Foliage With Acute Frost Action. During frost, changes in the chlorophyll grains are noticeable inasmuch as they usually round up into lumps in the cells which have become poor in sap. A chemical change of the chlorophyll coloring matter, due to the frost alone, is not assumed by the majority of investigators, so far as found in statements concerning frozen chlorophyll solutions. Wiesner founcP no difference in a chlorophyll solution in olive oil exposed to a temperature of 30 degrees C. below zero. On the other hand Kunisch- states that the alcoholic extract of chlorophyll from hyacinth leaves, frozen at 7 degrees below zero, was found to differ from that of leaves which had not been frozen. Often dull whitish spots are found in frozen leaves which can arise from ice accumulations crystallized out into the intercellular spaces. Hoffmann found in Ceratonia, Laurus and Camphora, a vesicular raising of the epidermis and called it a "frost blister-'. In heavy frost, the leaves which have been frozen through become as brittle as glass and transparent. When such leaves are thawed, the change in color depends upon whether the protoplasm of the cells has been killed or not. If it is dead, it becomes permeable to acids in the cell ; these penetrate to the chlorophyll grains, and cause their decomposition (the formation of chlorophyllan) : the cytoplasm turns brown ; the cell sap exudes rapidly; the leaf dries into a brittle, brown mass. Goppert*, who describes the various colorations of foliage leaves, also mentions an extremely strong weedy smell in frozen plants. In ferns the odor peculiar to the whole family is retained in frozen and dried speci- mens in an unusual intensity. In artificially frozen branches of the sweet cherry I noticed a decided odor of bitter almond. These phenomena are the result of the chemical changes which make themselves felt immediately and strongly during thawing. Fliickiger'^ has observed a different eft'ect in the frozen leaves of the cherry laurel. During distillation, these gave off an oil differing from that of the fresh leaves and no prussic acid, while leaves covered with ice, but not frozen, gave both substances under normal conditions. 1 Wiesner, Die natiirlichen Erscheinungen zum Schutze des Chlorophylls, etc. Festschrift d. k. k. zoolog.-bot. Ges. zvi Wien 1876, p. 23. 2 Kunisch, H., tjber die todliehe Wirkung- niedei'er Temperaturen auf die Pflanzen. Inauguraldissertation. Breslau 1880. 3 Kunisch, loc. cit. p. 22. 4 Goppert, tJber Einwirkung des Frostes auf die Gewachse. Sitzungsb. d. Schles. Ges. f. vaterl. Kultur 1874; cit. Bot. Z. 1875, p. 609. 5 The effect of intense cold on cherry-laurel; cit. Bot. Centralbl. 1880, p. 887. 525 It is important to refer here to the behavior of the mineral substances in leaves killed by frost, because we thus obtain an insight into the loss in substance caused by the destruction of the foliage in spring frosts. Schroeder's' analyses of red beech foliage which a May frost had killed and which, four weeks later, was examined in the dried condition, gave the following: In the frozen foliage, the whole nitrogen content (3.56 per cent.) of the fresh May leaves is found, while in the autumnal leaves, only about 1.33 per cent, remains, so that, therefore, almost three times as much nitrogen is lost for the plant from the loss of the May foliage as in that of the autumnal falling of the leaves. The dry substance gives 3.01 per cent, ash. Of this ash, 22 per cent, was phosphoric acid, i. e., as much as fresh May leaves, while the July leaves possess only 5 per cent. In May leaves about 30 per cent, of potassium was present normally ; in frozen ones, how- ever, only 5 per cent. Naturally very little calcium was present in the young foliage (6.78 per cent, in healthy foliage, 4.70 per cent, in frozen foliage) ; while the vegetating July leaves possessed three times as much (20.34 per cent.) the dead November leaves actually exhibited 37.60 per cent. In opposition to the opinion that foliage killed by spring frosts remains hanging on the trees, which thus gives its valuable mineral elements time to wander back into the trunk, reference should be made to Ramann's inves- tigations-. He proved that the foliage of the oak, spruce and fir, killed by cold, at first possessed the same composition as fresh foliage, when analyzed before a rain, but, during the rain, it underwent a very considerable change. Ramann found that, within ^2 hours, water withdrew not less than 19.219 per cent, of the whole ash of red beech leaves and actually 26.46 per cent, of the oak. This easy diffusibility of the ash elements should not be considered to be the result of later decomposition, as is proved by the fact that the greater amount had been leached out in the first 24 hours'; viz., in the beech 15.42 per cent.; in the oak, 19.66 per cent. These latter amounts gave in pure ash 11. 15 per cent, and of extraction for the trunk, 14.18 per cent, for the oak. The amount to which loss of the foliage injures the main body is shown in another difi:"erent work by .Schroeder' on "The migration of nitrogen and mineral elements during the first development of the spring growth." The exhaustion of phosphoric acid in the trunk during the production of the young growth is the greatest, namely, 46 per cent. ; then follows potassium, 2,2 per cent, of which is used up ; nitrogen and magnesium are removed from the trunk up to possibly 26 per cent. Before the end of this period, 12 per cent, calcium and 84 per cent, of the initial amount of silicic acid are added and replace the loss. Of the whole amount of nitrogen, potassium and 1 Schroeder. Untersuchung erfrorenen Buchenlaubes. Forstchemische u. pflan- zenphysiologische Untersuchungen. Part 1, 1878, Dresden, p. 87. 2 Ramann, Aschenanalysen erfrorener Blatter und Triebe. Bot. Centralbl. 1880, p. 1274. 3 loc. cit. p. 83. 526 phosphoric acid wandering into the young growth, possibly one-fifth comes from the trunk, and four-fifths from the root and soil. These figures favor the theory that the root-body, to a still higher degree than the trunk organs, gives up its reserve provision of nitrogen, phosphoric acid and potassium. Deficient Greening of Younger Leaves. A special form of the efifect of lower temperatures on the coloring of plant bodies is the remaining yellow of grozving organs due to the lack of temperatures necessary for turning green. Elving"^ found that etiolin was formed at temperatures which were still too low for the formation of chlorophyll in spindling seedlings, which, exposed for a short time to the light, became yellower than those left in the dark. When plants are uncov- ered in the early spring, numerous examples are found in which the etiolated shoots which had been produced under the cover, in spite of the at times abundant illumination, generally do not lose their yellow color or lose it only slowly and irregularly in spots. The most abundant examples were furnished by garden hyacinths. If these are uncovered too early in the spring and frost surprises the young leaf cones which are not yet green the leaves develop later a normal color but their young tips remain white or yellow. In the parts which appear yellow, we usually find the chloroplasts formed and arranged normally, i. e., along the free lying parts of the cell walls or those bordering intercellular passages (epistrophe), but the color- ing matter is only a more or less intensive yellow. In this stage, all possible transitions, up to the complete absence of the grains in the wholly bleached tip of the leaf, are found ; these are not. however, conditions due to disso- lution but are arrestment formations. In the whitest parts of the meso- phyll. the cells are filled with a watery cell sap which is traversed by cytoplasmic cords, without the deposition of any chlorophyll bodies in the cytoplasmic wall layer. In other cells of the yellowish parts, the differenti- ation of the contents extends to the primordia of the chloroplasts, but these appear more whitish, more tender, we might say, and at times, cloudier, less dense and less sharply defined. Normally formed, intensively green chloroplasts are finally found in the parts of the leaves which have grown out of the soil after frost action. At times the lack of green is connected with the presence of red coloring matter. Charguerard- furnishes an example ; he observed in Phalaris arundinacea picta, that the young leaf tips, with their well-known white stripes, appeared reddened by frost. The rose red coloring disappeared with warm weather. Schell" confirms the appear- ance of the red coloration with cold. In the spring he placed plants with red-colored, young leaves under three different temperatures and observed that the specimens kept in a room at 15 degrees C. became green within 1 Arbeiten d. Bot. Instituts zu Wurzburg, Vol. II, Part 3; cit. Bot. Centralbl. 1880, p. 835. - Revue liorticole, Paris 1874, p. 249. y Botanischer .Jahresbericht 1S7C, p. 717. 52? i8 hours, while those kept at 8.5 degrees C. turned green only after 5 days. The plants left out of doors, with a maximum temperature of about 4 degrees C. became green only after 20 days when the temperature of the air had risen. These observations favor my theory, that the red coloring is conditioned by the preponderance of a process of oxidation, connected with the action of light, over the process of assimilation. With equal amounts of light, a rise in temperature so increases assimilation that the process of turning green preponderates. To avoid a fixation of the morbid yellowish appearance of leaf tips, Ideached by frost, it is advisable to remove the winter co\'ering gradually, or, for the first few days, to spread a light layer of brush over the plants. Defoliation Duf. to Frost. The sudden falling of the foliage during and after the ai)i)earance of the first autumnal frost is only one form of the autumnal defoliation which should be designated death from senility (in contrast to the cases already described of abnormal defoliation after excessive heat, drought, lack of light, excess of moisture and other causes, producing a sudden loss of func- tion of the organ). The leaf has simply lived out its life. A normal death of this kind has the least disadvantageous results for the trunk which remains alive. From the senile leaf apparatus many plastic as well as important mineral substances gradually wander back into the trunk and are used again in the following period of growth. The retention of abundant amounts of organic structural substances and the leaching of easily soluble nutritive substances by rain are very disadAantageous in leaves which die in a juven- ile stage, since these are thus lost to the trunk. But both processes have but little significance when the leaves die of old age. In this case, as has recently been emphasized repeatedly by B. Schultze\ the assimilation of carbon dioxid may well be proved, up to the last moment, even if naturally with weakened power. Through the preponderance of the processes of decay over those of construction the leaf's supply of easily soluble proteins is especially impoverished, \\ith the increasing thickening and calcification of the membranes, the conducting of new nutritive substances becomes constantly more difticult, so that the demonstrable reduction- of nitrogen, phosphoric acid and potassium thus becomes explicable, even if no consid- erable process of retrogression is accepted. After all that has been said in earlier sections on the infiuence of position, soil constitution and w^eather, it is not necessary to emphasize here the fact that the life period of the leaves can be proved to be very difl^erent for the same species and that in this frost also acts on leaves which vary 1 Schultze, B., Studien liber die Stoffwandlung-en der Blatter von Acer Negundo L., 76 Versammlung d. Ges. Deutsch. Naturf. ; cit. Centraltal. f. Ag-rikulturchemie 1906, p. 35. - Fruwirth, C. and ZieLstoff, W., Die herbstliche RUckwanderung von Stoffen l)ei der Hopfenpflanze. Landw. Versuchsstat. 1901; cit. Bot„ Jahresb. 1901. Part 2, p. 161. 528 greatly in age. Accordingly the process of leaf fall is not always the same. The most usual case consists in the formation of a tissue zone at the base of the leaf which is a characteristic abscission layer. We repeat here the illustration of the autumnal abscission layer in the leaf of Acsculus Hippo-, castamim (cf. Fig. io6). The illustration gives a section made longitudin- ally through the joint at the base of the petiole, a is the bark parenchyma of the branch; b, the layer of plate-cork cells which remains when the petiole has fallen and thus forms a protection for the bark tissue ; c indicates the cells at the base of the petiole which at e pass over into the firmer paren- chyma of the broadened bases of the petioles, provided with abundant accu- mulations of calcium oxalate. Between c and e takes place the process of separation, since at d the cells round off and begin to separate from one another. If now the leverage of the leaf, moved by the wind, makes itself felt, the petioles break off at the loosened cell layer. Fig. 10(). Autumnul abscis.sion layer of a horse chestnut leaf. (After Dobner-Nobbe.) The riper the leaf is at the time of the final autumnal frost, the more easily it falls ; on this account, the old leaves of the branch are found to be the first ones broken off by the wind in the autumn. The greater the life energy and the quantity of plastic material, the more resistent the youthful leaf seems to frosts which are not killing frosts. If killing degrees of frost occur in the autumn at a time when the leaf has not yet sufficiently matured its abscission layer, i. e., the tree is still far distant from its dormant period, then the dead foliage remains on the branches over winter (beech and oak). The beeches in w^iich the foliage remains hanging often leaf out later in the spring than do normally matured specimens^. At the time of the first night frost, it is found in the early morning, if the frost still lies on the ground and even in windless weather, that, as soon as the sun comes up, the simple leaves of the trees break oft' and the leaflets of composite leaves fall from the common spindle, v. Mohl- found in such 1 dc Candolle, A., in Centralbl. f. Agrikulturchemie 187'J, I, p. 159. :; Bot. Zeitung- 1860, p. 16. 529 cases that the leaf scars of the fallen leaves, or those just about to be loosened, were covered, in a number of plants, by a thin layer of ice. Paul- ownia, for example, exhibited an especially thick ice crust. Often the leaves were still connected with their scar only by the ice crystals. These ice crystals had been formed in the abscission layer of the leaves. The columnal structure of the crystals, their cloudiness, produced above the vascular bundles by little air bubbles, and their arrangement, ending sharply with the boundary of the leaf scar, favor the view that no considerable masses of cell sap, which had possibly flowed out. have been frozen but that small particles of water pass through the cell walls exactly at the place where they are observed and are there stiffened to ice. The formation of ice may often occur very early and thereby cause, when thawing", the fall of leaves wdiich otherwise would have remained for some time on the tree and may even still be green. Besides this action of the ice lamellae, a premature autumnal defoliation may set in because the leaf is partially or entirely frozen; it, therefore, suddenly becomes function- less and is then ])ushed off. In autumnal defoliation the loosening of the leaf always takes place in the abscission layer which, according to Wiesner's observations\ does not always arise from a secondary meristem but is often found also as a rem- nant of the primary meristem. In other cases of leaf-fall the process of disarticulation can take place in different tissues. If the process of disarticulation within the layer of separation be con- sidered in general, the following modifications will be found, according to Wiesner-. So strong an osmotic pressure can be produced in the cells of the abscission layer that the tissues separate from one another, leaving smooth surfaces. This we find in defoliation which is the result of excess of water even where this excess arises from abundant watering after a long period of dryness. The phenomena of the dropping of the leaves of Azaleas, Ericas and New Holland plants, so well known to gardeners, after the drying of the root ball, belong here, as does also summer defoliation with the occurrence of rains after a long drought. According to Wiesner, in autumnal defoliation the macerating action of organic acids comes especially under consideration. He assumes that the surfaces of separation, in death from frost, as a result, have an acid reaction, and explains this by the fact that the frost kills the cytoplasm, thereby making it permeable to the acids which occur in the cell content and then act on the membranes. Oxalic acid may play a great part in this. The above-named investigator laid the stems of various plants in a 2.5 per cent, solution of oxalic acid and found that the leaves had loosened within a few days. The stems of plants which form abscission layers at the internodes also disarticulated within a short time. 1 Wiesner, Julius, Tiber Frostlaubfall nebst Bemerkung-en iiber die Mechanilt tier Blattablosunpr. Ber. d. D. Bot. Ges. 1905, Part 1, p. 49. - loc. cit. p. 54. 530 If llie leaf surface is injured by frost, but tlie part of the leaf lying below the abscission layer, i. e., the leaf stump, remains alive, the frozen part of the leaf will dry up, but the leaf base will be found intact and turgid. Between the leaf base and the dried part differences in tension must arise which lead to the loosening of the leaf body. Experiments made by Prunet^ show how quickly the parts injured by frost have dried up. A frozen vine branch with four leaves placed in water, evaporated 475 mgr. of water within two hours. In this, its loss in weight amounted to 14.46 per cent. Under the same conditions a similar branch, not injured by the cold, evaporated only 132 mgr. of water and, because of the absorption of water which had taken place simultaneously, increased its weight by 0.26 per cent. Wiesner has also shown experimentally how, in plants which retain their frozen foliage for some time, often for the winter, this may occasion- ally be based on a rapid drying. He took branches of Ligustrum ovalifoHnni with frozen leaves and placed them in a warm room in such a way that the sprouts could constantly soak up water. After 6 to 12 days, these dropped their leaves while the leaves of shoots not provided with water remained firmly attached. In cases occurring out of doors, where the dead foliage remains in place on the branches, the separation takes place only after the destruction of the tissue. The moldering of the membranes within the abscission layer will gradually advance so that the wind or some other mechanical cause finally brings about the breaking off of the leaf. In these moldering processes micro-organisms will doubtless cooperate. From what has been said, it is clear that the mechanics of separation in the autumnal senile defoliation, as well as in that due to frost, can often differ even in the same individual, according to the age of the leaves and the existing accessory circumstances. In many plants (grapes), besides the loosening of the w^hole leaf from the axis, the loosening of the leaf blade from the petiole also occurs. In other disturbances also, this region is especially susceptible and at times manifests its similarity to the base of the petiole through a similar discoloration. For example, in poplars, it can be observed that in the autumn the base and tip of the petiole become red while the remainder is yellow. The difference in the time when these processes set in in different indi- viduals, and in the same individual at different heights of the various branches, is connected with the physiological age of each leaf. The younger this is, the later it falls from the branch, under otherwise equal conditions, as Dingier- has determined, by pruning experiments. He observed a greater power of resistance in the young leaves, especially to autumn frosts. The young leaves of Carpinus Betidus did not freeze during frost periods, 1 Prunet, A., Sur les modifications de I'absorption et de la transpiration, qui surviennent dans les plantes atteintes par la g-elee. Compt. Rend. d. I'Acad. des Sciences 1892, II, p, 964. 2 Dingier, Hermann, Versuche und Gedanken zum herbstlichen Laubfall. Ber. d. D. Bot. Ges. 1905. Part 9, p. 463. 531 lasting all day, but older ones were affected and fnially died. I found similar conditions in plane trees in which the age of the tree made itself felt in the same way. In street trees, young specimens had been planted be- tween the older trees. Although they did not stand under the protection of the older trees, they still retained their considerably stronger foliage when most of that of the older trees lay on the ground. Behavior of Beet and Cabrage Plants in Frost. In storing sugar beets the loss of sugar, which occurs in the heaps because of the respiration of the beet body, can be decreased only by the lowest possible temperature'. In sugar beets which have been frozen, a raising of the sugar content was actually found when the water was frozen out. This has been reckoned by Ninger to be 0.39 per cent-. The new formation of saccharose which takes place during the process of freezing is no greater than the amount destroyed. Also the amount of nitrogenous substances and the proportion of proteins to non-proteins re- mains unchanged. So soon, however, as thawing begins, the latter appear to be increased at the expense of the former. The elements of the raw fibers (cellulose and related substances) become more soluble in acids and alkalis and in part also more soluble in water because of the freezing"'. In this an increase of non-sugar substances is produced in the sap. I observed in frozen beets partial swellings of the membranes which might be ex- plained as a visible expression of the chemical changes in the cellulose. .Strohmer and Stift found a striking increase in the acid content. The large sugar content, produced by the loss of water, and the conse- quently more concentrated cell sap will, however, retard the actual freezing of the beet body. Besides this, in the storage piles, the outer, frozen tubers will protect the inner ones from freezing. Miiller-Thurgau has referred to this especially and Mez* has explained it by the fact that the conversion of the cell saj) into a solid aggregate condition preserves the energy still present in the cell from too rapid dispersal. The conduction of warmth takes place much more slowly in ice than in water, where the warmth is distributed by radiation. The statements of market gardeners that brown cabbage (Brassica oleracea acephala) obtains its desired sweetness only after frost, may find adequate explanation in the accumulation of .sugar due to the low tempera- ture. According to the analyses made by Marker and Pagel'', an amount of sap equal to 68.66 per cent, of the remnants of the plant may be pressed 1 Heintz, Atnuing- der Riibenwuizeln. Zeitschrift d. Ver. f. d. Rlibenzuckerin- dustrie d. deutsch. Reiches 1873, v. XXIII; cit. Bot. Jahresb., I, p. 358. 2 Bot. Jahresber. 1880, p. 665. 3 Strohmer, F. und Stift, A., tlber den Einfluss des Gefrierens auf die Zusam- mensetzung- der Zuckerriibenwurzel. Osterr-Ung. Z. f. Zuclverindustrie und Land- wirtsch. 1904. Part 6. 4 Mez, Carl, Neue I^nter.suchungen liber das Erfrieren eisbestandiger Pflanzen. Sond. Flora od. Allgem. Bot. Zeit. 1905, p. 109. 5 Marker und Pa.ge1, tjber den Einfluss des Frostes auf Kohlpflanzen. Bieder- mann's Centralbl. 1877, v. XI, p. 263-66. 532 out from frozen cabbage plants while the same pressure gave only /-i per cent, sap in examples which had not been frozen. lOO ccm. of sap con- tained in frozen plants not frozen plants Dry substance 7.96 g 4.04 g Raw Ash ' 1.63 " 0.97 " Grape Sugar 4.17 " 1.41 Dextrin (?) 0.80 " 0.58 " Nitrogenous substances 0.80 " 0.51 Extractive substances free from nitrogen 0.50 " 0.54 This shows that the soluble elements in the sap have undergone a con- siderable increase and that, in this, grape sugar is especially concerned. Here, therefore, just as great a formation of sugar has been found as in the potato; Schmidt' states this to be 21.85 per cent. Frost Blisters. Frost blisters are of less significance agriculturally but certainly worthy of consideration scientifically because of the production of mechanical dis- turbances in the tissues inside the organs which remain alive. These mani- fest themselves in the appearance of usually small, blister-like places in the epidermis and at times also in the sub-epidermal layers which are raised from the thin-walled parenchyma of the leaf flesh or the tougher paren- chyma of the leaf veins. Instead of an extensive description, we will reproduce in Fig. 107 a cross-section- of the frost blister on an apple leaf. O indicates the upper side, U, the under side. M is the mid-rib, j> a larger lateral vein. In the mid-rib. the crescent-like wood body, with its numerous ducts {(j), forms the chief part. On the upper side adjoins a thin walled layer of parenchyma (m) free from chlorophyll, corresponding to the pith body of the axis. This parenchyma layer is covered by thick-walled collen- chymatous cells (c) ; these develop more abundantly, the larger the vein is. The collenchyma extends as firm wedges somewhat above the part of the leaf surface which consists only of leaf flesh. The leaf flesh shows the usual division into palisade parenchyma {p) and spongy parenchyma {sp). Of these layers, containing chlorophyll, the palisade parenchyma does not extend over the vascular bundles on the upper side but spreads out on both sides like a keel so that it terminates in a short cell layer {hr). This be- comes one layered, between the collenchyma and the parenchyma of the body of the vein. The spongy parenchyma, on the other hand, extends on the under side o\ er the body of the vascular bundle and forms the bark part of the vein in which, as in the bark of the branch, may be found oxalate crystals (o) arranged in crescent-like rows. The epidermis {e) covers the whole leaf uniformlv. 1 After Ritthuusen; cf. "Der Landwirt" 1875, p. 501. - Sorauer, P. Frostblatjen an BUltteni. Z. f. Pflanzenkrankh. l'J02, p. 44. 533 The mechanic.nl action of frost is sliown Iiere in the form typical for the majority of our plants since, on the upper side of the leaf, the collen- chyma tissue above the vascular bundle of the large vein is raised up from the parenchyma, thereby forming an opening (/'). On the under side of the leaf, the spongy parenchyma has been freed from the bark part of the vein on the scarps of the very prominent body of the vein so that cavities (h), containing air, are produced on both sides of the rib. The formation of the cavities is explained by the fact that the youthful, still hyponastic leaf, the edges of which are up-curled, from the action of frost, contracts at both sides of the mid-rib from above downward, as well as tangentially. If the up-curled, trough- like leaf contracts, the curling must become greater, i. e., the distension of the under side becomes stronger. This manifests itself in a pulling toward the raised edges (see the direction of the arrow in Fig". 107. Cross-section through a frost boil in .in npplo leaf. the ilkistration ). The tension is the greatest at the scarp of the vein and can, at times, lead to a splitting of the epidermis (c'). If thawing now takes place, the result of the action of the frost is the overlengthening of the tissue which has been strained, for the tissues are indeed distensible but not completely elastic. They do not regain their former size and arrangement. The lower epidermis, which has been most strained, elongates and no longer exercises on the spongy parenchyma, lying beneath it, the previous amount of pressure. The pressure in the epidermis is broken and the spongy parenchyma responds at once, elongat- ing into pouches. If, at the time of the greatest tension, the epidermis is torn apart, the over-elongated edges of the tear (e') form a crater-like opening toward which grow out the rows (/) of the spongy parenchyma which develop into threads. 534 We find further investigations of frost blisters in a work by NoackV, who comes to the conclusion that they are produced "because water from the cells is pressed into the intercellular spaces and there turns to ice so soon as the temperature falls to a certain degree below the freezing point, differ- ing for the different varieties of plants." The formation of ice crystals was found by Noack to be strongest at the place where later the separation of the epidermis becomes visible. We owe a recent study to Soleredef-. He observed in the leaves of Buxus the same hairy outgrowth of the meso- phyll cell rows that I had found in apples, cherries, apricots and have illus- trated in Fig. 107. Solereder has proved experimentally that this elongation of the cells of the leaf flesh is a secondary phenomenon occurring with an abundant supply of water. He removed the under side of the leaf and set the plants in a moist place. Cuticular warts were then produced on the cell membranes, similar to those which we have illustrated by the woolly stripes in apple cores (p. 324) and have observed also in the frost blisters of cherry leaves. The beginning of this hair-like elongation of the cells is found in the sheath of the vascular bundles, i. e., in places where the cork disease of the cactus (p. 429, Fig. 71) may be recognized as the initial point of the diseased processes of elongation. We find in this an experimental proof of our theory that the disturbances named may be traced back to excess of moisture. We will discuss later, in connection with other mechanical disturbances due to frost, the question whether the frost blisters were produced by the crystallized ice, or formed previously by a difl^erence in tension due to the cold, thus ofi^ering for the formation of ice the most convenient places of deposit. We will for the present only emphasize the fact that the holes in the tissue pictured in the apple leaf (on the upper side of the veins and below on their scarps) are a typical frost peculiarity found frequently in very dilferent leaves which also remain green during the winter. Comb-like Splitting of the Leaves. In some years with late frosts the phenomenon, in which the otherwise continuous surfaces of tree leaves often appear slit and thereby approach those forms which are characterized as "folia laciniata" may be found not infrequently. While, however, in commercial varieties, the slit leaf form is a condition fixed in the developmental course of the individual and may be transmitted by grafting, the slitting due to frost forms a transitory stage which, even in the same summer, may return to the normal leaf form. I had opportunity in the spring of 1903 to observe the very frequent occurrence of the phenomenon in Aescidus Hippocastanum^. The structure shown in Fig. 108 was restricted to the lowermost leaves of the shoot, i. e.. 1 Noack, Fr., tjber Frostblasen und ihre Entstehung. Z. f. Pflanzenkrankh. 190R. p. 29. 2 Solereder, H., tJber Frostblasen und Frostflecken an Blattern. Centralbl. f. Bakteriol. 2d Section, v. XII, 1904, No. 6-8. 3 Sorauer, P., Kammartige KastanienbUltter, Z. f. Pflanzenkrankh. 1903, p. 214. 535 those appearing first from the hud. C)n the same leaflet could he found all transitions from deep incisions extending as far as the mid-rih (Fig. io8f) to the normal undivided leaf surface (Fig. io8/). It was observed on those transitional ijlaces that exactly in the middle line of each intercostal field and spread between two parallel, lateral veins, occurred a lighter colored, transparent stripe along which the tissue was broken in places. (Fig. 108(7.) The edge of such a ruptured place, like the edge of the individual feathery Fig-. 108. Horse chestnut leaf, injured in the bud by frost, and toi-n, like the teeth of a eomli, during unfolding'. tips of the slits, often shows a some\^•hat yellowish, harder line, sometimes appearing a little callused. This callused edge consisted of plate cork cells, to which, on the outside, were not infrequently attached rags of dead meso- phyll cells. It is evident from this that the comb-like incisions had not been formed in the bud, but were produced later. In the above mentioned, transparent lines, of which the first are broken only in places, the mesophyll is found to be dead on the uninjured part. The cell content was still abundantly present but brown and collected in 536 balls. The vascular Inindles showed the well-known frost browning. The fact that exactly the midline of the intercostal fields is always the part injured by frost is explained by the peculiar folding of the leaf surfaces in the bud primordia. I found the same phenomena also in Acer Pscudoplatanus and some other thick-leaved varieties of maple ; in these, however, only in the form of irregular perforations. Laubert' observed a feathery slitting of the leaves of the birch and the white beech. Thomas- explains the slit condi- tion of the leaves chiefly as a result of the action of the wind. It has been known, ever since A. Braun and Caspary, that chestnut leaves can be per- forated and in places slit by the mutual rubbing of the leaf surfaces, but the phenomenon here described has nothing to do with the action of the wind. 1 have found the beginnings of the split leaf condition in little trees which had been brought into the house soon after the action of the frost". The Heaving of Seeds. Aside from the injuries which hardy herbaceous plants can sufifer from lying too long under a snow cover, because they are often suffocated, we have to take into consideration another phenomenon which becomes espe- cially disadvantageous for grains, i. e., the heaving of young plants. It is only the soils which contain a great deal of water which exhibit the heaving of seed by frost. After unsettled winter weather, when sharp frosts suddenly follow wet days in the early spring, a number of young [jlants with exposed roots are not infrequently found on the upper surface of the held. A part of the roots, to be sure, still touch the earth with their tips, and eke out for the seedlings a pitiful existence, while other rootlets, perfectly free, with torn tips, are exposed to drying wind and sun. The explanation of this occurrence is very pertinent here. The heavy soil retains large quantities of water; this freezes into long, needle-like crystals and thereby raises the upper layers of the soil, together with the young seed. If a part of the fine roots have already reached a considerable depth they are torn loose. In the subsequent thawing the soil can settle back in place, but not so the young plants. A repetition of the process finally brings the above result and may cause considerable loss if help is not brought quickly. The help consists mainly in the use of a heavy roller at a time when the soil has already dried to some extent. By pressing the sprouted seed, the lower nodes of the stem obtain protection and dampness enough to put out new adventitious roots and in this way gradually overcome the injury to the organs which hold them fast and nourish them. Especially in grain plants rolling acts beneficially and in damp spring weather strong blades will grow from plants which have thus been drawn out of the soil. 1 Laubert, R. Regelwidrige Kastenienblatter. Gartenflora, 52. Jahrg., 1903, Oktober. - Tliomas, Fr. Die meteorologischen Ursachen der Schlitzbliitterigkeit von Aesculus Hippocastanum. Mitt. d. Thuring. Bot. Ver. 1904, Part 19, p. 10. 3 cf. Z. f. PHanzenkrankh. 1905, p. 234, Note. 537 Draina^^e will naturally act as a precautionary method. A loosening of moor soil by raking it o\er with sand may also be proved favorable. Kiihn', in this connection, found that drill cultivation was also effective since all seeds were thus hoed in again. Between these seeds are produced thereby "small grooves into which the moisture chiefly passes and thus, under the conditions cited, an upraising of the soil is observed in the spaces between the ])lant rows, while the plant rows themselves remain untouched." Hedwig- recommends early sowing in order to obtain as abundant deep growing roots as possil)le and thereby to secure the plants more firmly in the soil. Ekkert'' recommends a surface sowing, but chiefly the growing of strong plants. In favoring this surface sowing, Ekkert seems to have been influenced by the statements of Count Pinto-Mettkau, who says that only seeds which lie deep are hea\ed out of the s