®Ifg §. p, pm pkarg Qft5 Date Due ^'M. BORROWE R-s Ny/ 0kMi^ -y ^ EXPERIMENTS WITH PLANTS i f^y^-' EXPERIMENTS WITH PLANTS W-.^jF V.ioSTERHOUT, Ph.D. ASSISTANT PROFESSOR OF BOTANY IN HARVARD rXIVERSITY EIGHTH EDITIOy Nehi fork THE MACMILLAN COMPANY LONDON: MACMILLAN & CO., Ltd. 1917 yiil rights reserved 0~b-< Copyright, 1905 By the MACMILLAN COMPANY Set up and electrotyped April, 1905 Reprinted August, 1905, June, 1906, February, 1908, June, 1910, January, 1911, June, 1912, December, 1917 Mount piraaant ^rraa J. Horace McFarland Company Harrisburg, Pa, o^^ .^tv PREFACE BY L. H. BAILEY My plan for a series of popular botanical texts contemplated three books, —"Lessons with Plants," primarily for the teacher; "Botany," for the school; and "Experiments with Plants," to suggest and ex- plain simple ways by which the pupil could be set at the working out of real problems in the growth and behavior of plants. The first two books have appeared. When I was working on the third, I chanced to visit the laboratory of Mr. Osterhout at the University of California, at a time when he was instructing a class of teachers. I saw at once that he was better fitted than I to write the book; and, finding that he was contem- plating a similar text, I gave up my enterprise and offered him the title of the proposed volume. It was at first intended that I collaborate in the preparation of the book, but insistent duties have interposed, and I have given it no personal attention; moreover, I did not feel that I could add to its usefulness; and again, a book made by two persons working so far apart, and one of them not now actively engaged in teaching, would be likely to lack homogeneity. The introduction of laboratory work has been the great contribution of natural science to pedagogy. The laboratory sets the pupil at work with a personal and concrete problem; it develops the creative and active Vi PREFACE BY L. H. BAILEY faculties, rather than the receptive; it asks the pupil what he has found out, rather than what he remembers. The school is now reaching out to the larger problems of the environment, and to the affairs of men; for it is to touch life at every point. In this movement the labora- tory is concerned ; consequently, the laboratory is de- veloping away from mere object -teaching and mere piece-work, into a vital and genuine touch with phe- nomena as they occur under wholly natural or normal conditions; and there is also a tendency toward the development of simple apparatus, in order that the pupil in even the humblest school may be reached. We now see that object-lesson teaching with natural history objects, and the giving of information about nature, are not nature -study: we must study the objects and phe- nomena in their natural relations. The schools are now ready for this point of view. They are growing plants in windows when they have no laboratories adapted to the purpose; some of them are establishing school-gar- dens; they are appropriating the adjacent fields; and they are even drawing on private gardens and farms. The ideal plant teaching, it seems to me, begins always with function and essential life relations, even with young children. I like the titles of Professor Oster- hout's chapters, — the "work" of roots and leaves and flowers; and I am glad that he relates the subject to the affairs of men by including a discussion of plant- breeding. College of Agriculture L. H. BAILEY. Cornell University, Ithaca, N. Y. INTRODUCTION The numerous questions which young people ask about plants are best answered by themselves. No other method gives vital knowledge so quickly and satisfactorily; in no other way is a real grasp of the subject obtained. To put them in the way of doing this so far as possible is the object of this book. To this end familiar plants have been chosen, familiar utensils used in the construction of apparatus and the conditions simplified as far as may be. The book may be used by both teacher and pupil : the order of topics may be followed or not, as seems best under the circumstances. In order that the knowledge gained in the classroom and out of it may be organized, notes should be kept: but the note -taking should not be made a burden. The following outline of work has been found suc- cessful. 1. The Question: this, it may be said, should be a real one in which the class as a whole takes an inter- est, not a formal affair in the nature of an imposed task, (vu) Vlil INTRODUCTION 2. The Method: i. e., how the question is to be answered, by observation or by experiment. In the latter case a simple sketch of the apparatus should be made. 3. The Material: i. e., what plants are to be used, how many and in what condition. 4. Times of observation of the experiment, e. g., every hour, every day, etc. 5. Precautions AND sources of error: these should be discussed as fully as possible before starting the experiment. Such discussion provokes thought, criti- cism and lively interest. Never foi^get to have control experiments. 6. Results: these should be presented concisely and clearly, in tabular form when possible. 7. Conclusions: distinguish between what is proven and what is indicated or rendered probable. Dis- cordant results should be given full consideration : they often suggest a new experiment or a repetition under modified conditions. 8. Practical Applications and Belated MaTTERs: under this head the general .knowledge and the mis- cellaneous observations of the class may be organized in a definite and useful way. Information should be obtained from farmers, gardeners and other practical men, the discussion of which will often provoke new questions and experiments. Notes may be made under each of' these heads. INTRODUCTION IX It is advisable to use a separate loose sheet for each question or experiment. The drawings should be inked with India ink; this can be done outside the class room: a drawing ^^w is not necessary — any good fino pen will do. A single bottle of India ink will supply a class, as very little is used. Where each experiment is to be done by each indi- vidual, a laboratory is necessary: where each is to be done by a group or section of the class, only a limited space is needed : where each is done by the class as a whole, a single shelf in front of a window and a drawer beneath to hold the utensils will suffice. For most of the experiments such plants have been sug- gested as will grow even with poor light and under discouraging conditions. This is an especially impor- tant consideration, in view of the fact that the average schoolroom is a very poor place to grow plants. While the microscopic work suggested is of the simplest kind, it may often be necessary to restrict it to demonstrations only or to omit it altogether. The principle involved is the thing of prime impor- tance in all the experiments. Exact quantitative results are not necessary, nor is it desirable at this stage to spend much time or effort in trying to obtain them. It may be added that practically all the experiments have been successfully tried in the schools, many of them in the lower grades. X I-^ TliOD rc TION It gives me much pleasure to make acknowledge- ment for helpful criticisms to Prof. W. A. Setchell, Prof. L. H. Bailey, Prof. R. A. Harper, and Prof. E. W. Hilgard. For Figs. 88a and 151 I am indebted to Prof. R. H. Loughridge; for Figs. 35 and 36 to Prof. L. H. Bailey; for Fig. 148a to Mr. C. K. Tuttle; for Fig. 103 to Mr. N. L. Gardner; for Figs. 23a, 201 and 202 to Mr. L. E. Hunt; for Figs. 92, 93, and 94 to Prof. E. W. Hilgard; for Figs. 231 to 236 and 240 to 245 to Mr. Luther Burbank, and for Figs. 249, 250, 252 and 253 to Prof. Hugo de Vries. A few figures have been redrawn from English or European sources. The line drawings are, with few exceptions, the work of Mr. H. N. Bagley, and the photographs, except as noted above, are by Mr. B. F. White. Berkeley, Cal. W. J. V. OSTERHOUT. January, 1905. CONTENTS CHAPTER PAGE Introduction v I. The Awakening of the Seed 1 II. Getting Established 89 III. The Work up Roots 87 IV. The Work of Leaves 163 V. The Work of Stems 224 VI. The Work op Flowers 286 VII. The Work of Fruits 312 VIII. How Plants are Influenced by Their Surroundings . . 326 IX. Plants Which Cause Decay, Fermentation and Disease . 361 X. Making New Kinds of Plants 406 Index 455 (xi) LIST OF ILLUSTRATIONS FIG. PAGB 1 Horse-bean 1 2 Horse-bean opened 1 3 Castor-bean 2 4 Castor-bean opened 2 5 Corn 3 6 Corn cut lengthwise 3 7 Sunflower seed 3 8 Sunflower seed opened 3 9 Peanut 4 10 Peanut opened 4 11 Arrangement for keeping: seeds on ice 5 12 A bottle containing seeds, filled with water and corked air-tight 5 13 A method of determining whether air-dry seeds contain water 7 14 A bean placed in water, showing successive stages in the process of wrinkling 8 15 A method of determining whether openings exist in the seed-covers .... 8 16 An arrangement for holding seeds while under water 9 17 A home-made balance constructed of umbrella wire 13 18 A modification of the balance 14 19 A method of keeping seeds half-submerged, in order to discover how the water enters 15 20 Seed-covers floating on water 16 21 Modification of the experiment shown in Fig. 20 19 22 Scarlet Runner Bean opened, showing the pocket into which the caulicle fits 20 23 Seeds half-submerged in wet sand, to determine how the water enters. . 21 23a Three rows of corn planted at the same time, each grain being half- buried in the moist soil 22 24 "Walnut divided in half, showing the wick-like central strand 23 25 Seeds placed in a saturated atmosphere 26 26 Another method of keeping seeds in a saturated atmosphere 27 27 Method of maintaining a saturated atmosphere and a constant water- level 27 28 Method of testing the permeability of the seed-cover to air 30 (xiii) XIV LIST OF TLFATSTEATIONS FIG. PAGE 29 Seeds on wet sand with different amounts of aii' at their disposal 33 30 Apparatus for determining whether germinating seeds produce carbon dioxide 34 31 Method of measuring the amount of carbon dioxide produced by ger- minating seeds 34 32 Method of measuring the temperature of germinating seeds 36 33 Method of determining whetlier air exists in the soil 37 34 Apparatus for determining how deep seeds should be planted 39 35 A planting stick 40 30 Screens for seed-beds 41 37 Method for testing the permeability of the seed -cover to heat 42 38 Arrangement for testing the swelling power of a single seed 49 39 Arrangement for testing the swelling power of a mass of seeds 51 40 Apparatus for demonstrating that swelling seeds exert pressure 53 41 Bottle broken by swelling seeds 54 42 Germination of Squash 54 43 Later stage of germination of Squash 54 44 Squash seeds arranged for germination experiment 55 45 Germinating Cocoanut cut lengthwise 57 46 Buckeye cut open 58 47 Buckeye. Plumule emerging from between elongated stalks of seed- leaves ' 59 48 Buckeye. A later stage 59 49 Buckeye. A still later stage 60 50 Scarlet Runner Bean germinating 00 51 Apparatus for demonstrating that osmosis exerts pressure 61 52 Apparatus for measuring pressure due to osmosis 62 53 Section of a bit of the seed-leaf of the Horse-bean 65 54 Water-bath 67 55 Filaree seeds burrowing into cotton 70 56 Corn making its way above ground 71 57 Bean getting above ground 71 58 Castor-bean twisting itself into a loop 72 59 Apparatus for measuring the force of the upwai'd growth of the plant. . 73 60 Modification of apparatus shown in Fig. 59 74 61 Arrangement for weighting an upward-growing stem 75 62 Modification of arrangement shown in Fig. 61 75 63 Bean with stem marked to determine region of greatest growth 77 64 Contrivance for marking stems in manner shown in Fig. 63 78 65 Scarlet Runner Bean with top (terminal bud ) removed 79 (i6 Radish seedlings growing upward along the glass side of a box 79 67 Sunflower seedlings penetrating the soil 80 68 Squash seedlings endeavoring to penetrate the soil 81 LIST OF ILLUSTRATIONS XV wo. PAGE 69 Apparatus for deterniiiiing how much force the root exerts in growing downward 82 70 Apparatus for determining force of growth of a root 84 71 Root marked in order to determine the region of greatest growth 85 72 Plant attached to support ready to have root cut off 87 73 Seeds pinned to corks which are floating on water 88 74 Seeds arranged with caulicles resting on mercury 89 75 Arrangement for causing germinating seeds to revolve slowly 91 76 Water-wheel for making germinating seeds revolve rapidly 93 77 Arrangement for testing effect of moisture on direction of growth of roots 95 78 Arrangement to test behavior of roots in moist air 90 79 Arrangement for ascertaining whether roots grow in the direction of moisture 96 80 Apparatus for observing behavior of roots as they encounter obstacles. 97 81 Apparatus designed to test behavior of side roots under the influence of gravity 98 82 Modification of apparatus shown in Fig. 80 99 83 Radish seedlings showing root-hairs 100 84 Root-hairs of Radish 101 85 Cutting of Wandering Jew in water, showing root-hairs 102 86 Apparatus for measuring rate of evaporation from a saturated soil 114 87 Method of supplying water to apparatus shown in Fig. 86 114 88 Four lamp-chimneys filled with soil for the purpose of studying tlie evaporation 115 88rt New growth on cultivated and uncultivated Apricot trees 11(1 89 Diagram of fairly dry soil showing relations of root-hair to surround- ing particles lli> 90 Cross-section of a root as it grows in the soil 120 91 Artificial root-hair 123 92 Diagram to illustrate effect of ideal plowing ]2(i 93 Part of furrow slice (of Fig. 92) magnified to show floccules or soil- crumbs ; 127 94 A single soil-crumb magnified 128 95 A still for making distilled water ];!7 96 The result of a water culture of Wandering Jew 140 97 Apparatus to determine whether the root excretes acid 143 98 Tubercles on roots of Clover 149 99 Two Scarlet Runner Beans of the same age, from one of which the seed-leaves were removed shortly after germination 163 100 Germinating Date 180 101 Leaf of English Ivy deprived of starch and placed in water 182 102 Arrangement for excluding light from a part of the leaf 182 XVI LIST OF ILLUSTRATIONS FIG. PAGE 103 Two lots of Squash seedlings of the same age, one grown in light, the other in darkness 184 104 A seedling of Castor-bean 186 105 Apparatus for the decomposition of starch 186 106 Air-pump 187 107 Details of piston of air-pump 188 108 Air-pump witb automatic arrangement to prevent piston from slipping back 190 109 Details of piston of air-pump 190, 110 Arrangement for investigating the' power of a leaf to "restore" air which has been " vitiated " by a burning candle 191 111 Arrangement for collecting gas given off bj' a water-plant in sunlight 192 112 Apparatus for growing a leaf in air deprived of carbon dioxide 193 113 Section of leaf of common wild Yellow Mustard 198 114 Section of leaf of Iris 199 115 A single chlorophyll grain 201 116 A single cell of a leaf with chlorophyll grains 202 117 Arrangement for determining whether leaves give off water vapor.... 203 118 Method of inserting a leaf-stalk air-tight in a rubber stopper 205 119 Apparatus for measuring transpiration of a leaf 206 120 Diagram showing in section and surface view the form and position of guard-cells when closed and open 208 121 Guard-cells and neighboring cells of epidermis 209 122 Artificial stoma and guard-cells 210 123 Modification of part of apparatus shown in Fig. 122 211 124 Acacia leaf, night or sleep position 218 125 Acacia leaf, day position 218 126 Leaf mosaic of Ivy Geranium 219 127 Leaf mosaic of Chestnut 219 128 Upright branch of Periwinkle 220 129 Same branch seen from above 220 130 Horizontal (trailing) branch from same plant 221 131 Diagram of cross-section of Squash stem 224 132 Corn-stalk 225 133 Stem of Squash (microscopic structure) 227 134 Cross-section of a bundle of Corn 231 135 Oak branch ( microscopic structure ) 232 136 Bordered pit, cut in half 234 137 Simple pit, cut in half 234 138 Pine branch (microscopic structure) 236 139 Method of injecting a twig by means of the air-pump 237 140 Arrangement for forcing water through a branch 238 141 Modification of arrangement shown in Fig. 140 240 LIST OF ILLUSTRATIONS ^yil FIG, PAGE 142 Method of measuring the amount of bleeding from a stump (root pres- sure) 243 142a Buttress formed on the lower side of a branch 248 143 Terminal part of a growing branch showing the three regions of growth 249 144 Bud of Brussels Sprouts cut lengthwise 250 145 Portion of tree trunk near a burl 262 146 Diagram showing eftect of weight applied to end of a beam 265 147 Diagram of a girder 266 148 Diagram showing the g'rder-like arrangement of strengthening tissues in a Bulrush 267 149 Cross-section of a portion of a Cabbage leaf 237 150 Collenchyma 268 151 Clematis climbing on an evergreen 271 152 Behavior of a strip of flower-stalk of Dandelion in water 273 153 Branch of English Ivy 275 154 Method of investigating lenticels 279 155 Method of investigating entrance of air into stem by way of stomata 280 156 Method of investigating entrance of air into stem by way of stomata and lenticels 281 157 Willow twig suspended in a saturated atmosphere 281 158 Apparatus for supplying air in a constant stream to an aquarium 283 159 Arrangement for supplying carbon dioxide to plants growing in water 284 160 Arrangement for growing water-plants in contact with a bubble of carbon dioxide or air ... 285 161 Cherry blossom cut open to show the parts of the flower 288 162 Ovary (seed-case) of Oat, with feathery style 290 163 Branch of the style of Oat, with germinating pollen-grain 290 164 Embryo sac of a Lily 291 165 Hanging drop arrangement for the cultivation of pollen-grains 293 166 Flowers of Gaillardia cut open 303 167 Flower of Iris, showing how the stigma removes pollen from the bee, etc. 304 168 Flowers of Partridge berry cut open 305 169 Flowers of Sage cut open 306 170 Fruit of Squirting Cucumber in the act of expelling the seeds 321 171 Clematis fruit, which flies by means of the feathery style 322 172 Linden fruit, which flies by means of a wing-like bract 322 173 Hop fruit, which flies by means of a bract 323 1 74 Maple keys, which fly by means of a wing 323 175 Burdock head 323 176 Fruit of Bur Clover 324 177 Fruit of Beggar's-ticks 324 178 Fruit of Clotbur 324 179 Potato which had been allowed to sprout and grow on a dry table 327 Xviii LIST OF ILLUSTRATIONS FIG. PAGE 180 Potato showing the effect of light and dryness on growth 328 181 Sprout of Prickly Pear grown in the dark 329 182 A spherical Cactus 331 183 Branch of Cytisus 332 184 Stems of Callitriche in cross-section 333 185 Epidermis of Holly 334 186 Waxy covering of Sugar Cane 334 187 Hairs of Wormwood or Sage Brush 334 188 Hairs of Mullein 335 189 Cross-section of stem of Water-polygonum grown in dry soil 335 190 Cross-section of stem of Water-polygonum grown in water 335 191 Upper epidermis of Water-polygonum 336 1 92 Cross-section of a leaf of Oleander 337 193 Arrowhead, showing effect of submersion on leaves 337 194 Cross-section of the ribbon-shaped leaves of Arrowhead 338 195 Leaves of Water-buttercup (water-leaf and air-leaf) 339 196 Lower epidermis of Water-polygonum 340 197 Leaves of Dandelion, normal and in saturated atmosphere 342 198 Gorse, normal and in saturated atmosphere 343 199 Leaves of Prickly Lettuce (sun- and shade-leaves) 344 200 Beech leaves (sun- and shade-leaves) 345 201 The effect of wind on the growth of a tree trunk' 348 202 Shows how branches are stunted and killed on the windward side 349 203 The result of having branches mainly on one side (as in preceding figure ) 350 204 Branch of Ivy Geranium 354 205 Different kinds of bacteria 362 206 Steam sterilizer 363 207 Tumbler containing a slice of boiled potato 365 208 A scraping from a potato culture 367 209 Funnel with neck removed so as to fit into a tumbler 369 210 Flat bottle containing gelatin (for "plate culture ") 370 211 Chart showing the distribution of cholera cases in the Hamburg epi- demic of 1892 373 212 Stab cultures in gelatin 375 213 Yeast-cells budding 390 214 Black Mould of bread 391 215 Same beginning to show spores at the edges of the bread 392 216 More advanced stage of spore formation 393 217 Portion of the mycelium 394 218 Black Mould of bread showing manner in which mycelium sends out root-like branches at short intervals 395 219 A single spore case of the Black Mould of bread 395 LIST OF ILLCSTIiATIOyS XIX 220 Formation of zygosi»ores of tlie Black Mould of bread .'{90 221 Green Mould of cheese 397 222 Spore of Corn-Smut germinating 398 223 Spore of Corn-Smut producing conidia 399 224 Summer Spores, or uredospores of the Black Stem Rust of Wheat 402 225 Autumn spores, or teleutospores of the Black Stem Rust of Wheat 402 22G Summer spores of the Black Stem Rust of Wheat, germinating on a Wheat leaf and sending the germ tubes through the stomata 402 227 Autumn spores of the Black Stem Rust of Wheat producing conidia . . 403 228 Section of Barberrj- leaf showing Rust 403 229 Cluster-cup of Black Stem Rust of Wheat 404 230 Perithecium of the common Mildew of the Lilac 407 231 Increased size due to hybridization (without selection) 411 232 Increased size due to selection (without crossing) 411 233 Improved Beach Plum 413 234 Branch of Improved Beach Plum 414 235 The Plumcot, a cross between the Plum and the Apricot 415 236 The Stoneless Plum and its parents 416 237 Curve of variation 418 238 Assymmetrical curve of variation 419 239 Double curve of variation 419 240 Shasta Daisy and its American parent 423 241 Shasta Daisy, variations 424 242 Shasta Daisy, double 425 243 Variation in leaves of hybrid Blackberries 426 244 Variation in stems of hybrid Blackberries 427 245 Variation in leaves of hybrid Poppies 429 246 Plum blossom, with anthers and petals removed 431 247 Flowers of Lamarck's Evening Primrose 444 248 Lamarck's and Dwarf Evening Primrose 445 249 Leaves of Lamarck's and Broad Evening Primrose 446 250 Seedlings of Lamarck's, Pale and Broad Evening Primrose 447 251 Four-, five- and seven-leaved Clover 448 252 Ten-leaved Clover 449 253 Atavistic Clover 449 EXPERIMENTS WITH PLANTS CHAPTER I THE AWAKENING OF THE SEED What is a seed ? Study as types of seeds the Horse- bean (or Other large bean), the Castor-bean and Corn. The Hokse-bean. — Examine some dry and some soaked Horse-beans. Notice the shape and appearance (color, mark- ings, surface, etc.) of the seed. The large black scar (hilum) at the end of the seed (Fig. 1) is the place of attachment to the pod. Remove the cover, notice its texture, thickness, etc. ; is the c __ pi Horse-bean; the scai (hilum) at (A). 2. Horse-bean opened, show- ing the two seedleaves(sO. the caiilicle (c) and the plu- mule (jtl). cover everywhere closely applied to the germ? Within the cover are two thickened halves, the seed-leaves (Fig. 2,5/) attached to a short rod-like body, the cau- licle (c) , at one end of which is a cluster of very small leaves, called the plumule (^Z), which may be easily studied with a hand- lens, or (1) EXPERIMEXTS WITH PLANTS even with the naked eye : these develop into foliage leaves. The seed-leaves, caulicle and plumule together, make up the germ or embryo plant. The seed of the Horse-bean, therefore, consists of an embryo plant provided with a cover. The Castor-bean.^ — The seed somewhat resembles a beetle in shape and color. Its scar (hilum) is covered Vi ea 3. Castor-bean; at {ca) the car- uncle, a spongy body which absorbs water diiring ger- mination; the scar (hihim) is concealed by it. 4. Castor- bean opened, showing endosperm (e), caulicle (c). seed-leaves (si) and caruncle (ca). by a spongy body (the caruncle. Fig. 3, ca) . ' The cover has a very different texture from that of the Horse- bean cover and fits loosely. The seed-leaves (Fig. 4) are thin and delicate in appearance, with prominent veins ; the caulicle and plumule are much smaller than in the Horse-bean. Outside the seed-leaves is a white oily substance which surrounds the germ but is not attached to it: it is called endosperm (Fig. 4, e) . The Corn.— Both dry and soaked grains should be used. In the Corn (Fig. 5) the seed-case adheres to the seed and forms the outer layer of the seed --cover, ^ This i.s poisonous and should not be eaten. THE AWAKENING OF THE SEED 5. Corn, the germ is located at [g) . 6. Corn cut lengthwise, showing caulicle (c) , plu- mule {pD, seed leaf (0 and endosperm (e). which is thin, transparent and fits snugly. If we cut through the grain, as shown in Fig. 6, we see the germ, consisting of a single seed- leaf {I) with cau- licle, plumule and a «/. large mass of en- dosperm, which in Sugar Corn is clear ^ and sugary, while in ordinary Corn it is hard and yellow on the outside, but floury toward the center. in some plants the seed is covered only by the seed- coat (the skin of the bean is such a seed -coat), while in others it is covered by the seed-coat plus a part of the seed-case (the seed- case corresponds to the pod of the bean) ; the seed- case may be con- solidated with the seed-coat, as in the Corn, or be separate from it, as in the Sunflower (Figs. 7 and 8), Peanut (Figs. 9 and 10), Walnut (Fig. 24), Peach, etc. When the seed- case, or any part of it, remains 8. SunHower seed opened, showing attached to the seed the whole "r^-ieLt^lso"""'' ^'^ "^ Sunflower seed. EXPERIMENTS WITH PLANTS is called a fruit, but for convenience we may speak of it as a seed; its covering we may call a seed-cover, whether it be a simple seed- coat or some- thing more. Obtain all the seeds you can which are large enough for study (including those of common fruits, flowers, cereals, etc.), com- pare them carefully with the types we have just studied: discover the germ in each one 9. Peauut. and study it with especial care. As the result of this comparison, we may con- clude that a seed is an embryo plant provided with a cover, and in some cases with endosperm: before germination it is in a sleeping or dormant condition. What is needed to awaken the seed ? Many persons will say that water and warmth are necessary. Place some seeds in moist sawdust in a place warm enough to ensure germi- nation. The sawdust should be merely moist (not so wet that water can be squeezed out of it by the hand) , and may be placed in boxes, pots or cans, which must have holes provided in the bottom for drainage: plant the seeds about an inch deep. Place some seeds of the same kind on ice, as shown 10. Peanut opened showing can- licle (c). plumule ipl) and seed- leaf {sLh THE A WAKENING OF THE SEED in Fig. 11. Obtain a box measuring about eighteen inches each way, place it in a larger box, and fill the space between the boxes with dry sawdust; place the ice in the inner box and surround it with dry saw- dust; enclose the soaked seeds in a piece of mosquito netting (to prevent losing them) and place them on the ice; cover them with moist sawdust (the melting ice will keep it continually moist) . Fifteen pounds of ice will last several days under these conditions. Place other seeds of the same sort under water: it suffices to simply put the seeds in a bottle, which is then submerged in water and tightly corked while under water, taking care to exclude all air-bubbles. Vaseline may be smeared over the cork to make it air-tight (Fig. 12). Air may be expelled from the water by boiling it for several minutes just before using, but 11. Arrangement for keeping seeds on ice: the spare between the boxes is tilled with sawdust, which also surrounds the ice. 12. A bottle con- taining seeds, filled with water and corked air- tight, to test the power of seeds to germinate with- out air. 6 uxpiJRiMEyrs with plants this is ill most cases unnecessary. It is advisable to wire the cork firmly in place, since a certain amount of gas is given off by the seeds, which may force it out of the bottle. For this, as well as for subsequent experiments on seeds, it is well to select kinds which germinate quickly, such as Horse-bean, Lima Bean (or other kinds of beans). Sunflower, Pea, Lupine, Radish, Squash, Wheat and Corn. It will appear from this experiment that the seed needs a sufficient amount of water, air and warmth, in order to grow. Every need of the plant presents a prohlem for the plant to solve. Some plants supply their needs in what seems to be the best possible way, while others adopt methods which appear much less efficient. We may say that the plant solves its prob- lem well or ill, though in so speaking we do not mean to imply that the plant thinks or consciously adapts means to ends, since we are convinced that this can- not be the case. The problems which plants are called upon to solve are very numerous, and the penalty of solving them poorly is to die, or be crowded out by more successful competitors. In studying the plant, we should try first of all to discover its needs and then try to think out for ourselves in each case the best solution of the problem involved. Let us consider first the problem of tvater. How much water does the embryo plant require, and how THE AWAKENING OF THE SEED is it obtained ! Do seeds in their ordinary dry condi- tion contain water? We may answer this question by placing some seeds in one end of a glass tube (a test- tube is most convenient, but any glass tube a few inches long will answer; a tin cup covered with a piece of glass answers every purpose) and heat- ing the end where the seeds are placed (Fij 13) . If moisture is present it will be driven off and condense in drops toward the cooler end, which should be left open.^ Explain the popping of Pop -corn. The amount of moisture in the seed greatly affects its preserva- tion (see page 45). How does the seed absorb water ? Place in water a lot of seeds of the same kind, as nearly alike as possible in size, shape and color, keep- ing other similar seeds dry for comparison. An interest- ing series for study is the Pea, Lima Bean, Castor- bean, Filbert (or some other nut). Radish, Flax or Quince. Observe constantly for half an hour, and after 1 If no moisture can be detected by this method, weigh out three or four ounces of seeds, heat them for some time in an oven or wherever they will not be scorched, and reweigh. Any loss of weight is due to moisture driven off by the heat. By heating on a water-bath (Fig. 54) untilthey cease losing weight, the exact percentage of moisture may be ascertained by dividing the loss in weight by the original weight. 8 EXPERIMENTS mTH PLANTS that at frequent intervals. Notice whether soaking af- fects the size, color or texture. Does the cover wrinkle: 14. A Bean placed in water, showing successive stages in the process of wrinkling; the wrinkling indicates where the water enters and how it spreads inside the cover. if so, where does the wrinkling commence, and in what direction does it progress? (See Fig. 14.) Does this in- dicate where water first enters the seed ? What causes the wrinkles ? Why do they disappear after a time ? Do the covers appear to hinder the water from being ab- sorbed by the germ? Consider the appar- ently water -proof covers of the Castor- bean, Buckeye, etc. Would it not be an obvious advantage to have openings in the cover through which the water might enter more rapidly? Are ~^^^ there such openings 15. A method of determining whether openings exist in • j.< QPPd-rOvei**; ^ the seed-covers. ^■^ LilC 0CCU-I./UVCI0 . THE AWAKENING OF THE SEED 9 Place the seeds in water and heat (Fig. 15) ; stir the water to remove the bubbles that form on the seeds; keep the seeds submerged; if necessary, hold them under water by a piece of glass or wire netting or by placing them in a wire spring (see Fig. 16) . Do you find openings: how many and where located I Test as many seeds as you can in this way. (The Squash, Walnut, Pecan and Brazil-nut give striking results; the Castor-bean is apt to be somewhat puzzling; the Filbert seems to have a good many openings; do they pass t h r O U 2" h the ^^' ^^ arrangement for holding seeds while under water. shell into the cavity?) Many seed -covers become cracked in the course of time ; distinguish between such cracks, which may occur anywhere, and openings which occur constantly in the same place. ^ If any of the seeds do not yield bubbles when placed in warm water it does not necessarily mean that there is no opening; it may simply denote a lack of air in the seed. Such seeds may be further tested by soaking thoroughly, wiping the surface dry and squeez- ing to see where water is pressed out. Or, in the ease of nuts, etc., any part of the shell where an 1 Where the cover consists of an outer and an inner part (i. e., seed-coat proper plus the seed-case), as in the Walnut. Pecan and Filbert, the outer por- tion is of principal interest but the inner one may also be tested after the outer is removed. The shell of the Brazil-nut is a true seed-coat. 10 JSXPERIMENTS WITH PLANTS opening is suspected to exist may be sealed to the end of a tube, which should then be placed under water and blown into forcibly (see page 31). We may also place the seeds in an air-pump and exhaust (see page 187). Does most of the water enter through these open- ings ? One way to find out is to stop up the opening, then submerge the seed and note how much the ab- sorption of water is thereby hindered (as compared with untreated seeds which are submerged at the same time). A good substance for closing the opening is rubber cement (the kinds used for repairing bicycle tires are good and easily obtainable) , or melted rubber applied hot (prepared by melting good black rubber in a spoon) ; if the latter is used, place whiting or flour on the surface of the rubber (after it is applied to the seed) to prevent it from sticking to other ob- jects. Try to cover the opening only: it is difficult, however, to avoid covering at the same time the adja- cent portions of the seed. Thus, in the case of the Horse-bean, the scar is apt to get covered. Since this is apparently more porous than the rest of the cover, it may be that it admits water readily; hence in covering it we are perhaps introducing an error. This may be offset if we cover an equal area (includ- ing the scar) in the control seeds (i. e., those which do not have the openings covered) without interfer- ing with the opening. THl^J AWAKENING OF THE SEED 11 Weigh both sets of seeds (i. e., the control and the others; there should be at least twenty in each set), treat them with rubber or cement, and weigh again. Before proceeding with the experiment, test the seeds to see if the openings are stopped. Place some untreated seeds in water (the control seeds must not be used for this) , and heat until bubbles begin to issue from the openings of all of them; then place the treated seeds in the warm water; if no bubbles issue from them we may consider it fairly certain that they are satisfactorily^ closed; the heat must not be too great or too prolonged, as it may in that case soften the rubber so that the expanding air inside may force an opening. Should any of the sealed seeds yield bubbles, it is better to throw all the sealed seeds away and prepare a fresh lot, until you succeed in getting them all air-tight. Submerge all the seeds in cold water (the wire spring shown in Fig. 16 is useful for keeping them under water; the seeds may be placed in it and weighed, together with the spring, thus making it un- necessary to handle them separately) . Remove the seeds at frequent intervals, dry them on the surface and weigh both sets, to see which is absorbing water more rapidly. Any seeds with cracks in the covers must, of course, be rejected. At the end of the experiment, place the seeds again in warm water, to 12 EXPERIMENTS WITH PLANTS discover if any cracks have been formed which might admit water and so vitiate the results. It is interesting to calculate the percentage of water absorbed and make a comparison after various periods of immersion. The followinof will serve to illustrate the method: — Twenty-five Scarlet Runner Beans sealed Twenty- five Scarlet Runner Beans unsealed Weight be- fore treat- ment witli i-ubber. 31.0 grams 29.5 grams Weiglit after treatment with rubber. Submerged in water 15 niinuies. Wt. 32.0 grams 32.34 30.8 grams 31. G2 Gain. 0.34 0.82 Per cent gain. 1.1 2.8 Submerged in water '6b minutes. Submergpd in water (iO niinuies. Submerged in water 1; Submerged in water yo mhiuies. j| 15 huurs. 1 1 P^"- Wt. 1 Gain. 1 cent 1 i gain. Wt. Gain. Per cent gain. Wt. Gain. Per cent gain. Wt. Gain. Per cent gain. 33.30 32.8 1.30 2.0 4.2 6 8 34.45 .35.2 2.45 4.4 7.9 15. 35.69 39.68 3.69 8.88 11.9 30.1 72.71 24.21 41.91 78.1 142.1 After soaking fifteen minutes, the weight of the sealed lot was 32.34 grams; subtract from this the weight before soaking (32), which gives the gain (0.34 grams) ; divide this by the original weight be- fore treating with rubber (31 grams) to get the gain in per cent. In this case an area on the unsealed seeds was covered with rubber so as to equal the amount covered on the sealed seeds. THIS AWAKENING OF TEE SEED 13 The experiment may be repeated in a different form by placing the seeds in moist sawdust instead of in water. Care must be taken that none of the rubber is removed in manipulating the seeds. This experiment requires a balance. If you have none at hand you should make one for yourself. The 17. A home-made balance constructed of ximbrella wire; it can be made sensitive to a tenth of a gram. arms of the balance should be of equal length. Why ? Try the effect of both equal and unequal arms. The pans should be attached at equal distances from the pivot. A very good balance is easily and quickly made of umbrella- wire, as shown in Fig. 17. The long rib is used for the arm of the balance, the short rib for the support. The rivet is taken out and a fine 14 EXPERIMENTS WITH PLANTS needle substituted for it; the varnish is burned off or scraped away. The upright piece is firmly wedged in a hole bored in a small block of wood (see Fig. 17). The pans are made of tin covers, attached with silk thread. Their weights may be equalized by trimming the edges or by attach- ing a little sealing-wax to them; when balanced they should hang about an inch and a half above the table. Another kind of sup- port, made by fixing two short glass tubes to a strip of wood (by means of sealing-wax) is shown in Fig. 18. When the balance is set up, test it carefully; first get the pans to balance; then put weights in both pans until they balance; then exchange the weights; if the balance is properly made they should still balance; failure to do so shows that the pans are not of equal weight, or are not attached at equal distances from the pivot. An inaccuracy in the balance will not vitiate your results for comparative purposes if you always put the weights in the same pan. Why? If you cannot obtain weights, make some of lead (to correspond with a druggist's; the metric system is much more convenient than the ordinary apothe- caries' weight). THE A WAKE^NING OF THE SEED 15 It would appear that considerable water enters through the opening, the amount being different in different kinds of seeds. The question may be raised Does all the water enter in this way? If, in the ex- periment just concluded, the openings were securely stopped, it would seem that we must, in many cases at least, answer negatively. However, all doubt on this point may be removed by partially submerging the seeds without allowing the opening to come in contact with the water. A very convenient way is to place the seeds in sand which is kept saturated with water (see Fig. 23) : for keeping the sand satu- rated, the device shown in Fig. 27 may be used. Or we may cut in a cork notches large enough to receive the seeds; after wedging them firmly in place, put the cork in water (Fig. 19). If water now enters the seed it must be through the cover itself, since the opening is not in con- tact with the water. Large, flat corks are best; if necessary they may be obtained at drug- stores. (Cork soles or the cork strips used by entomologists are good.) Flat pieces of wood will serve in place of cork. This experiment may be 19. A method of keeping seeds half-submerged, in order to discover how the water enters. 16 EXPERIMENTS WITH PLANTS carried on by weighing in the same way as in the previous one, and will afford interesting results for comparison. What seed-covers admit water most readily? We may make a satisfactory test by splitting the covers of dry seeds in halves, removing the germ and allow- 20. Seed-covers Hoating on water, each containing a few sugar crystals, whicli, by dissolving, indicate the rapidity of osmosis; controls on the glass strip. ing the dry covers to float like boats on the surface of the water (see Fig. 20). Into each put a few crys- tals of sugar, the dissolving of which will indicate how rapidly water is absorbed through the cover. On a dry piece of glass, near the surface of the water but not in contact with it, place other boats contain- ing sugar crystals, to see whether the sugar can absorb enough moisture from the air (or from the cover) to dissolve. In making the boats, we must take care THE A WAKENING OF THE SEED 17 that there are no openmgs or cracks through which water can enter; be careful that no water enters the boat at the rim. To imitate natural conditions more closely, place some boats on the surface of moist soil, pressing them down firmly. Test as many kinds of seed as possible. Does the germ (or endosperm) possess the power to draw water through the cover as the sugar does ? Repeat the experiment, substituting the ordinary seed- content (either a part or the whole) for the sugar: be sure that it is in close contact with the cover.' Weigh it at the beginning of the experiment, and repeat the weighing at frequent intervals to discover how much water it has absorbed. Notice also whether it softens or appears moist. The sugar, when placed in the boats as described above, seems to have the power to draw the water through the seed- cover; but if sugar were dissolved in the water on which the boats are floating, would it not exert a counter-attraction, and tend to prevent the water from being drawn^ up through the seed- cover? Prepare some boats (all from the same kind of seed-cover) ; place sugar in them and float some on pure water, others on a thick syrup made of sugar and water. Many other substances besides sugar have a strong attraction for water: the germ contains 1 The sugar is spoken of as drawing or attracting the water in a popular sense only. 18 EXPERIMENTS WITH PLANTS substances of this sort (salts, starch, sugar, etc.), and we suppose that the seed owes to them its power to absorb water. Now we have just found, in the experi- ment with sugar in the boats, that water is absorbed more rapidly than syrup. Is it so in the case of the seed ? Place weighed lots of seed of the same kind in water, in syrup and in a very strong solution of com- mon salt (dissolve as much salt as you can in the water). After a day or so remove the seeds, dry them on the surface and weigh. Can you make the solution strong enough to prevent all absorption I Rinse the seeds in water and plant them in moist sawdust, to see whether the sugar or salt have injured them in any way. Do you think that the seeds will germinate in sea- water ? If this cannot be obtained it can be made artificially by dissolving about 3% per cent of sea- salt (obtainable at grocers' and druggists') or common salt in water (4% drams of salt to a pint or 3X grams to 100 cc. of water). The seeds may be placed in the apparatus shown in Fig. 25, but cotton soaked in the sea- water is to be substituted for the wire netting. Are the seeds of plants which inhabit the seashore able to germinate in sea- water ? How is it with alkali soils in this respect ? In the boat experiments just described, we are struck with the fact that water appears to come through the cover only where the sugar or germ is in THE A WAKENING OF THE SEED 19 contact with it. Is this really the case, or does the water conae through elsewhere, but so slowly that it evaporates as rapidly as it reaches the inner surface of the cover ? Repeat the experiment as follows : Prepare the boats as before, and seal them to strips of glass by means of sealing-wax, as shown in Fig. 21. Smear the rim of the boat with hot sealing-wax, in 21. Modification of the experiment shown in Fig. 20. vert it on the glass and run a hot piece of wire around the rim until a tight joint is secured. Place the glass (boats down) on a tumbler, and carefully pour in water until it touches the boats; do not let it touch the glass strip. If water enters the boats, moisture will collect in drops. Let some of the boats so treated stand near by but not in contact with water, as a control experiment. If, as appears to be the case, the water does not come through the seed-cover except where the germ (or endosperm) is in contact with the cover (and 20 EXPERIMENTS WITH PLANTS draws it through), it would seem advisable to have as much contact as possible. Some seeds have the cover closely applied to the germ so as to be in contact everywhere; others (Peanut, Filbert, etc.), wiiere the seed-contents are loose inside the cover, have a small amount of contact; investigate this point in as many seeds as you can. In some seeds the cover separates in places from the germ when the seed is placed in water, so that the amount of contact is diminished; subsequently the cover becomes closely stretched over the germ ; in what seeds does this happen ? It would seem that the portion of the germ which is in immediate contact with the opening must receive water more quickly and in larger quantities than other parts more remote. Do you usually find the caulicle near the opening?^ Does the caulicle usually swell and grow more quickly than other por- tions of the seed ? Do you consider its position advanta- geous ? Notice the pocket around the caulicle in the Beans (Fig. 22), Pea, Buckeye (Fig. 46), etc. Do you think this might help to draw up water (by capillarity) and retain it, so keeping the caulicle moist? 22 Scarlet Runner Bean opened, showing tlie pocket into which the caulicle fits. 1 Examine particularly the Peach, Plum, Cherry, Walnut, Pecan, etc. THE A WAKENING OF THE SEED 21 Not only is it important that the germ should be in contact with the cover, but also that the cover should be in close contact with the soil. Hence the 23. Seeds half-submerged in wet sand, to determine how the water enters. necessity of rolling the soil to pack it firmly about the seeds as practiced by farmers, and "firming" the soil about the seeds as practiced by gardeners, i. e., by covering the seeds and then treading on them or by pressing down the soil with a board. Since the opening is so important, it may be that its position with reference to the soil may be impor- tant when the seed lies on the surface. On the sur- face of the soil in some pots (or boxes) place some seeds, one-third with the opening up, one-third with the opening down, one -third flat on the soil (see Fig. 23). Press all seeds firmly into the soil, so that each one is just half- buried. Which germinate first ? Corn gives very striking results (Fig. 23 a). Does the nat- ural position of the seed on the soil usually bring the opening in contact with the earth ? Do you see any 22 EXPERIMENTS WITH PLANTS advantage in having the seed flattened ? In a flat- tened seed, what is the best position for the opening ? Where is the opening usually found in a flattened seed? What course does the water take after entering the seed ? Perhaps the best way to trace the path of the water is by dissolving some coloring matter in it. Eosin (obtainable as Eosin Pink, one of the Diamond \ 23a Three idws of Corn planted at the same time, each grain being half-buried in the moist soil: those in the first row were placed flat on the surface; those in the second row with tlie pointed end upward; those in the last row with the pointed end downward. THE AWAKENING OF THE SEED 23 Dyes, at drug- stores) or ordinary red ink answers ad- mirably. Dissolve enough in water to make it bright red, and then submerge the seeds in the solution; it is well to use a good many seeds and to remove some every few minutes and take off the covers to see how far the water has penetrated. ^ Do you find that the water penetrates first at the opening ? In what direction does it spread inside the seed? What external indications do you see of this in the Bean (Fig. 14)? Trace it with especial care in the Walnut and Pecan. Although in these nuts the contact between the germ and the cover is small, yet this is offset by an absorb- ent, wick- like, central strand which takes up water directly from the opening and from which water spreads out into the broad partitions which are in con- tact with the folds and surfaces of the germ; the caulicle lies at the end of the fibrous, wick -like strand (Fig. 24). We shall probably find that the coloring matter will not penetrate into the germ, although the water does; the method is only trustworthy as showing the 1 The seed should be washed and wiped with a cloth to remove the dye. Eosin stains may be removed from hands and colorless fabric by Javelle water (obtainable at druggists') or by bleaching powder (obtainable at grocers' J. Walnut divided in half, showing the wick-like, cen- tral strand (s) by which the water travels through the seed to the caulicle and the broad absorbent plates by means of which it spreads. 24 EXPERIMENTS WITH PLANTS path of the water to and around the germ and endo- sperm, but not into it. In most of the thick covers (Filbert, Walnut, Pecan, Peach, etc.) we shall find that the water pur- sues special paths in the tissue of the cover. - These represent the paths which the sap took while the fruit was still attached to the plant. It will prove interest- ing to obtain young fruits of various kinds and place the cut surface of the stem in eosin solution, to trace the path taken by the sap. It may prove interesting to raise the question. Is not the seed-cover (in spite of the opening) a serious hindrance in absorbing water? We may answer this by removing the covers from some seeds and placing them in water (together with the untreated seeds for comparison). Select ten lots of seeds (twelve in each lot) free from cracks, etc. Remove the covers from one lot and then weigh each lot separately. Sub- merge them all in water, keeping the different lots separate. After half an hour remove one of the untreated lots; take off the covers and weigh. Let the covers stand until "air- dry," and then weigh them. Deduct this weight from the original weight of this particular lot; this will give us approximately the original weight of the seed-contents (i.e., the seed minus its covers). We now know approximately how much the seed - contents weighed at the start, also how much they have gained. We may compare :}^<>'* THE A WA KENINO OF TEE SEED 25 this with the gain of the seeds which were deprived of their covers at the start. After another half an hour, remove another lot and weigh; repeat this each half- hour. Any seeds may be used; it would seem desirable to test some which have thin covers (Bean, etc.) and some which have thick covers (Filbert, Peach, etc.). If you can obtain seeds of the Moonfiower, Mexican Morning-glory or Lupine, the weighing will be un- necessary; the results will be sufficiently striking to the eye to leave no room for doubt. Nurserymen recognize that the covers of many seeds (e. g.. Peach pits, etc.) are a hindrance to germination, and before planting them usually crack the cover; other seeds have the covering cut by a knife or file, while still others are mixed with sand and rubbed or pounded. Acacia seeds are boiled for ^YQ or ten minutes, which aids the penetration of water through the hard coat and makes a difference of months in the germination, while some kinds are placed in boiling water and allowed to cool slowly.^ How much water is necessary for germination? We may get an approximate answer to this question by taking several pots of the same size, filling them with dry sand and placing in each twelve seeds (the same sort in each pot). Water the pots regularly, giving to No. 1 a very small quantity of water each time, ' The heat may have an important stimulating effect. 26 EXPERIMENTS WITH PLANTS to No. 2 twice as much as to No. 1, to No. 3 twice as much as to No. 2, and so on. Another method is to use fruit -jars (one -quart or two-quart), placing the seeds on the bottom of the jar and covering them with half an inch of sand. Add different quantities of water to the different jars, and screw on the tops tightly. Whichever method be used, it is interesting to determine the amount of water in the seed at the stage when the cau- licle begins to protrude. This may be ascertained by weigh- ing the seed and then drying it (on a water-bath; see Fig. 54) until it ceases to lose weight; dividing the loss in weight by the weight of the undried seed will give the percentage. The determination is especially in- teresting in the case of the seeds which germinate with the minimum amount of moisture. It often happens that a seed has little or no water at its disposal except the moisture of the air. Unless it can absorb this in sufficient quantities, it cannot germinate. Seeds placed in a saturated atmosphere. THE A WAKENING OF THE SEED 27 Another method of keeping seeds in a saturated atmosphere. The question may be raised, Can seeds absorb enough water from moist air alone to enable them to ger- minate? This may be an- swered by placing some seeds in a saturated atmosphere for a time. Place the seeds in a fruit-jar, supported on a piece of wire netting, as shown in Fig. 25. Place a little water in the bottom of the jar and screw the cover on tight. Drops of condensed mois- ture are not apt to fall on the seeds when a fruit- jar is used, but should this happen start the experiment over again, protecting the seeds by a small inverted cone of wire net- ting or a small glass funnel. The apparatus shown in Fig. 26 may also be used: vaseline i« ncoH fr. mol^ck on ^^- '^^^^^^ ^f maintaining a saturated atmosphere lb USea to maKe an ^nd a constant water-level. 28 liXPElilMENTS WITH PLANTS air-tight joint with the glass cover. The apparatus shown in Fig. 27 is very convenient for this purpose: the inverted bottle has a cork in the sides of which two grooves are cut, so that as soon as the water sinks below the mouth of the bottle air enters through the grooves and water runs out until the level rises and closes the grooves: the water-level thus remains almost constant. As the experiment is to last for some time, it is advisable to take precautions against the growth of mould. Place the seeds in a tumbler and set them in a jar or pail in the bottom of which is a little forma- lin: cover the pail so as to confine the formalin vapor, and let it stand five or six hours. Control seeds (treated in the same way) should be planted in moist earth or sawdust. The experiment should be continued two or three months if necessary. The percentage of moisture in the seeds may be determined at the beginning and again at the end of the experiment, to see how much moisture they have absorbed and also the minimum amount which will enable the seed to germinate. The power to absorb water from moist air may be of great practical importance in storing seeds, etc., since if kept in a damp place they may easily germi- nate or decay. Of especial interest, in considering the absorption of water, are the mucilaginous covers of Flax, Quince, THE AWAKENING OF THE SEED 29 Radish, Squash, etc. Such covers can absorb a large amount of water even in a passing shower and hold it after the surrounding earth is again dry. Many seeds have spongy covers which act in much the same way, as, for example, the Walnut, Hickory, Almond (in which cases the spongy cover is usually removed before the nuts come to market). Nasturtiums, etc. The Walnut (Fig. 24), Hickory and Pecan have a central, wick -like strand of absorptive tissufe which conveys the water directly to the germ, over the sur- face of which it is spread out in a thin layer by means of thin plates of absorptive tissue. In the grasses and grain-plants the seeds are surrounded by parts of the flower (the "chaff"), which assist greatly in soak- ing up and retaining moisture, while the pulp of soft fruits and berries serves the same purpose. In the Castor- bean (Fig. 3) the large, spongy outgrowth at one end (caruncle) serves the same purpose, as can be shown by planting Castoi -beans dt-'prived of the caruncle alongside of unmutilated ones; its position is such that the water passes from it directly through the opening to the radicle, and it will be noticed that the germ is attached to the cover only at this one point. We have now found out something about how the seed gets water, and we can see clearly that, while the need is the same in all cases, the means adopted by different plants to supply this need are various; in other words, the same problem is solved in a variety 30 EXPERIMENTS WITH PLANTS of ways. Perhaps we cannot say in all eases which solution is the best: certainly, in absorbing water the thinnest and most permeable cover is the best, but whether such a cover would in all cases furnish suf- ficient protection to the seed before germination we cannot tell without a special study of that question. We know that, besides water, air is needed. How does the germ get air ? Does air pass readily through the seed -cover? We may find out by sealing the cover (air-tight) to one end of a glass tube, filling the tube with water and inverting it, as shown in Fig. 28, in a glass of water, taking care not to admit any air into the tube; the water should be boiled just before using, in order to expel the air. To seal the tube to the cover, smear the end of the tube liberally with hot sealing-wax; remove the super- fluous wax from the interior of the tube, press the end of the tube firmly against the cover (which must be free from cracks or openings), and run a hot wire around it until a tight joint is secured; allow the wax 28. Method of testing the permeability of the seed-cover to air. THE A WAKE XI NO OF THE SEED 31 to harden, then test the joint by placing the sealed end of the tube under water and blowing into it forcibly. The weight of the water- column tends to draw air through the cover. If any air enters it will appear as a bubble at the top of the tube; should this happen, empty the tube and test the joint as before by blow- ing forcibly. If no leak is detected, refill the tube and invert it as before. Test different sorts of seeds, especially those whose covers seem most porous and permeable to air. It should be remembered that in this case we are testing a seed -cover which is in con- stant contact with water; peihaps in a dry condition it would admit more air. This may be tested by fill- ing the tube only partly full, so as to leave a large air- bubble at the top of the tube; mark its limit exactly on a piece of paper pasted on the outside of the tube; the entrance of air can then be detected by the increase in the size of the bubble. We may, if we wish, avoid any contact of water with the cover, by sealing on a cover, warming the tube well and placing the unsealed end in water ; as the air in the tube cools, water will be drawn in. Which of these tln^ee methods approximates closest to the condition of the cover during germination ? Does air enter the seed through the openings? You may test this matter by closing the openings of seeds which have been previously thoroughly soaked (in order to ensure a sufficient supply of water for 32 EXPERIMENTS WITH PLANTS germination) and placing them in an atmosphere satu- rated with water (to prevent them from losing any water), together with untreated seeds as control. The openings may be closed and tested as described on page 10. The seeds may be placed on wire netting, in a fruit- jar containing water, as shown in Fig. 25 (the cover must be tightly screw^ed on) . At least a dozen seeds should be treated and the same number used as a control. The precautions against mould mentioned on page 28 should be observed. Set the jar in a place warm enough to promote germination. If the seed depends largely upon the opening for the admis- sion of air, we shall expect to find the germination of the treated seeds noticeably delayed. How much air is necessary for germination? We may get an approximate idea by taking six bottles of the same size and filling them to various heights with moist sand, as shown in Fig. 29 (the first, one- sixth full; the second, two-sixths, etc.). To exclude air from the sand, the bottle may be first filled with water and the dry sand slowly poured into it to the desired height; the superfluous water may then be poured off. The seeds (well soaked) may then be put in (the same number in each bottle), the cork may then be pushed down below the rim and sealed air-tight with vaseline or sealing-wax. A closer approximation to the correct amount could easily be made if the experi- TnE AWAKENING OF THE SEED 33 ment were to be repeated and the bottles filled more nearly to the right degree at the start. We may vary the experiment by dispensing with the sand and simply filling up the bottles to various heights with soaked seeds. The fact that so much air is necessary seems to indicate that some part of the air is changed (or 29. Seeds on wet sand with different amounts of air at their disposal. "used up") by the seeds. Let us see if this is so. After two or three days, cautiously remove the cork from one of the bottles (.containing about five -sixths air) and immediately lower a lighted match into it; or, better still, take a tall bottle or jar, place a layer (an inch or so deep) of seeds in the bottom, stopper tightly, allow it to stand a day or so and test with lighted match. If the match goes out, it indicates that the oxveen of the air has united with some other 34 EXPElUMKXTt^ WITH PLANTS substance so that it no longer supports combustion. We may now pour a little lime-water into the jar, replace the stopper and shake vigor- ously. (Lime-water is prepared by placing a little unslaked lime in a metal dish or pail, filling the pail with water and allowing it to stand for a day; the water should then be filtered through filter- paper or through a cotton plug in the neck of a funnel.) If the lime-water turns milky, it indicates that the oxygen has united with the carbon of the plant to form carbon diox- ide, a gas familiar to us as soda- water gas. Arrange an experiment, as shown in Fig. 30, by placing a vial of clear lime - water surrounded by soaked seeds in a jar and stop- pering loosely. As a control, use a similar arrangement without the seeds. We may make use of the fact that car- bon dioxide is readily absorbed by lye to perform a further ex- periment. Arrange two bottles 31. Method of measuring the amount (pint or half -pint), as sliown ^L^'S^'',°.?„/St fhet^^w '^ in Fig. 31, by fitting them with J.^,'?)" "' *''°"'"' " "^ 30. Apparatus for deterniin- ing whether germinating seeds produce carbon diox- ide, the vial is filled with lime-water. (.Seen in sec- tion.) THE AWAKENING OF THE SEED 35 rubber stoppers or cork stoppers which have been soaked in melted paraffin (obtainable at grocers' ; we may also obtain it in the form of paraffin candles). Pierce the stoppers with closely fittiDg glass tubes long enough to reach nearly to the bottom of the bottle. Place seeds in one bottle to the depth of an inch; leave the other bottle empty. Support both in an inverted position (by means of clothes-pins and rubber bands or wire, as shown in the figure), allow- ing the tubes to dip into a strong solution of lye. As the carbon dioxide is formed it will be absorbed by the lye, which will rise in the tube and thus indicate the amount produced. When carbon unites with oxygen we say that it burns. Whether we burn wood, coal, oil or alcohol, the principal combustible substance is the carbon, which, by uniting with the oxygen, produces carbon dioxide and sets free heat. The heat of our bodies is due to the same process of burning and the carbon dioxide is given off in the breath, as is easily shown by placing one end of a tube under lime-water and blowing into it. The carbon of the body burns, but it does so very slowly. In the seed the process is still slower. The slight degree of heat set free can be meas- ured by carefully comparing two thermometers (by placing them side by side in water at various tempera- tures and comparing their readings) and then arranging them as shown in Fig. 32. One tumbler is filled with 36 EXPERT ME XTS WITU PLANTS soaked seeds, the other with moist cotton (to make the conditions equal so far as evaporation is concerned), and a piece of cardboard is laid over the top. The thermometers are inserted to equal depths and read- ings are taken every fifteen minutes. A difference of more than a degree is not to be expected in most cases and it is often less than this. The tumblers must not be placed in the sunlight. How do seeds get air under ground? Does the soil contain air? Fill a bottle just half-way to the neck with the soil to be tested; place a thin layer of wet THE AWAKENING OF THIS HEED 37 I V: 33. Method of determining whether air exists in the soil. mM soil on top of it and tamp it down well with the blunt end of a lead-pencil; fill the bottle to the neck with water so that the spaces occupied with water and soil are about equal (the tamped-down layer is to prev^ent the water from penetrating the soil before we are ready). Insert a cork pierced with a wire (as. shown in Fig. 33) and force the wire down so as to puncture the tamped layer (move it from side to side if necessary until the air begins to bubble up) . When the air has all risen, we can tell approximately how much was contained in the soil. When the method is under- stood, we may dispense with the cork and tamped-down layer and proceed as follows : Take two bot- tles of the same inside diameter; fill both to the same height (half-full or less), one with water, the other with the soil to be tested; pour the soil slowly into the bottle containing water. If the soil contains no air it should cause the level of the water to rise to just twice the height at which it stood originally; the amount by which it fails to do this measures the amount of air in the soil. The result depends somewhat on how tightly the soil was 38 j^xPEiiiMKyrs with plasts packed in the bottle at first. The natural condition of the soil could be more closely simulated by forcing a tin cylinder (a tin can with the bottom removed would do) into the soil (using a rotary mo- tion) , measuring the cylinder of soil so obtained and pouring it slowly and carefully into an equal bulk of water. The deeper the seed lies in the soil, the less will be the circulation of air about it. A constant renewal of air is necessary, as we have already learned. The question naturally comes up, How does the depth at which the seed is buried affect germination ? One way of finding out is by means of a box, with one side of glass, in which seeds may be planted at different depths, as shown in Fig. 34. A convenient way of making such a box is to prepare the sides (as shown in the figure) and then make saw cuts in them to receive the glass, which is then easily removed when- ever necessary. A wooden strip for the bottom and another for the side (to give rigidity) complete the box. Both sides may be of glass, or one of glass and the other of wood. A box an inch wide at the top, with sides a foot square, is of very convenient size. The joints may be made air-tight by means of putty. In planting the seeds, the box should be tilted and a row of seeds placed directly on the glass; earth should then be pressed down on them; another row of seeds should then be planted, and so on until the THE A WAKENING OF THE SEED 39 top is reached. The box should then be filled with earth and the last row of seeds planted on the top. The soil should be kept moderately moist and at a temperature favorable to germination. The seeds are now under approximately the same conditions as exist in the soil; as we go deeper we find more water, less air (and less circulation of air) and less warmth (in our apparatus the lower layers of soil are apt to be warmer than is naturally the case). Our experiment indicates that there is a certain depth where the three needs of the germinating seed are best provided for. Various mechanical devices are in use for planting seeds at uniform depths in the soil (e. g., corn-plant- 34. Apparatus for determining how deep seeds sliould be planted 40 EXPERIMENTS WITH PLANTS ers, etc.). In sowing seed in the garden, the simplest and most effective way is to press a board edgewise into the soil to the right depth, place the seeds in the depression, fill it with earth and pack it A planting stick, to secure uniform depth fil'^lly by prCSSing thC in planting seeds. j^^^g^^.^^ ^^^^ ^^^^ ||.^ ^ board such as is shown in Fig. 35 may be used to secure a uniform depth. The circulation of air in the soil will depend on the way in which it is packed in the box, on the condition of the surface (whether a crust forms or not), on the kind of soil used and on the amount of moisture in the soil. It will be found worth while to vary the conditions by filling one box with sand, another with clay and another with a mixture of equal parts of sand and old loam, which makes a very excellent soil for seeds. Water the boxes equally throughout the ex- periment. Gardeners always recognize the necessity for "good drainage" (i. e., proper circulation of air in the soil), and secure it in a variety of ways. The seeds are usually sown in shallow boxes, porous earthen dishes, or in ordinary pots, in which case a layer of pebbles or pieces of broken pots is placed in the bot- tom. The surface of the soil is protected from baking (which forms a crust) by a cover of sawdust or litter, or by being shaded; the shade is also of value in THE AWAKENING OF THE SEED 41 protecting the seeds from drying. A screen made of lath or brush, as shown in Fig. 36, affords an excel- lent means of shading a seed-bed; a screen of muslin cloth is very commonly used. The quality of the soil should be carefully attended to. It should be of such consistency that it will pack firmly around the seeds but will not bake into a hard crust: a mixture of sand and good garden loam in equal quantities usually makes a good soil for this pur- pose. In some cases moss or cocoanut fiber is used instead of soil. Very small seeds are sown on the surface of the soil, which has been sifted and then carefully smoothed. They must then be protected against drying up by a glass frame placed over them, or sometimes by a board laid over them: after they have germinated. 36. Screens for seed-beds; a brush screen on the left, a lath screen on the right. the board is replaced by a piece of glass raised an inch or so above the soil. In some cases such seeds are covered with fine moss. In sowing grass seeds for lawns, it is very desirable to cover the seeds with stable manure or straw. Such a covering not only keeps the seeds from 42 EXPERIMENTS WITH PLANTS drying up but prevents them from being washed away in watering. In watering small seeds where no such covering is used, a cloth may be laid over them or water may be applied to the soil from below (by set- f{ ! ? i- / ? later stage. growtli ? Do you fiiid anything similar (id b:XPEIiIMENTS WITH PLANTS in the Bean, Pea or other seeds'? (See Fig. 22.) The surprising amount of force developed by swelling seeds is ob- viously connected with the absorp- tion of water, by means of which they increase in size. It is very easy to construct an apparatus in which the absorption of water will generate pressure just as it does in the seed. For this purpose we take a piece of glass tubing about one -sixteenth of an inch in diameter (in- side), or a little larger; smooth one end by heat- ing in a flame until it 49. Buckeye, a stm later stage. fuses slightly, and when it has cooled stretch over it a piece of ox -bladder or heavy parchment paper (ob- tainable of druggists). Hold the piece of bladder stretched like a drum -head across the mouth of the tube, and let an assistant wind it tightly clear to the tube's mouth with ordinary cotton twine; tie it 50. Scarlet Runner Bean witll a SqUarC kuot aud Ict it SOak germinating; the cover « , -, •, - i, • "u split across. for several hours, during which THE AWAKENING OF THE SEED 61 J the twine will shorten and make a tight joint. It is well to prepare several tubes, since some are sure to work better than others. Place in each tube a strong syrup (a solution of sugar in water) , stand them in a tumbler of water, mark the height of the liquid in each tube, and leave them over night. In the morning it will be found that the sugar has absorbed water through the membrane and that the liquid has risen in the tube. Choose the one which shows the greatest rise, for future experiments. To demonstrate that the absorption of water can produce pressure, it suffices to fill the tube completely full of syrup, invert in a tumbler of syrup and tie on a piece of sheet rubber (such as toy balloons are made of) , holding the end under the syrup all the time so as to exclude air. The rubber should be tied on in the same way as the bladder. The tube may now be rinsed in water and then placed in water as before (see Fig. 51). In a day or so the rubber will become tightly stretched, showing that pressure has been generated. In order to estimate how much pressure is produced, we may proceed as follows: Remove the rubber and fill the tube to within 51. Apparatus for demon- strating that osmosis ex- erts pres- sure. 62 UXPhJBfMhWTS WITH PLaXTS an inch and a halt' of the top with fresh syrup. Fit a small rubber cork to the tube and push it down about half an inch into the tube; insert a needle at one side of the cork, so as to allow^ the compressed air to escape and restore the normal pressure. Withdraw the needle and carefully dry out tlie inside of the tube above the cork. Melt some sealing-wax in a spoon, and pour it slowly into the tube until it runs over. With a hot knife smear it over the outside as far down as the cork, so as to close the tube air-tight (see Fig. 52) . Obtain or prepare a strip of paper ruled in fine divisions (millimeters or twenty -fourths of an inch, if possible), and gum it to the upper part of the tube for the purpose of measuring the length of the air- column in the tube. Place the tube in water, note the length of the air -column, and observe it fre- quently during the experiment. The amount of pressure produced in the tube can be easily calculated from the amount of com- pression which the air undergoes. The for- mula for the calculation is : 52. Apparat\is for measur- ing the pres- sure due to osmosis. Lenjjth of air-eoluran at start = Pressure at finish, Length of air-oolnmn at finish Pressure at start. Thus, if the colunm measure one inch at THE A WAKENIXG OF THE SKED 63 the start and oiio-lialf inch at the finish the equation Avill be 1 = Pressure at finish. % 15 pounds per square inch. whence thirty pounds per square inch equals pressure at finish The results are approximate only and will vary according to the charactei* of the membrane, the strength of the syrup, etc., and cannot be regarded as indicating what the same solution would do with a different kind of membrane (such as is to be found in the plant, for example) , but the pressure is clearly demonstrated and one method of measuring it illus- trated. In our apparatus the sugar attracts^ the water with considerable force so as to generate the pressure we have observed; we believe the pressure manifested by swelling seeds to be generated in much the same way, by substances within the seed (sugar, proteids, etc.) which attract water with considerable force. We have already learned that if we add water - attracting substances, such as sugar or salt, to the water in which the seeds are submerged, these substances exert a counter - attraction which hinders or prevents the absorption of water by substances within the seed. We may even withdraw water from the seed by plac- ing it in a sufficiently strong solution of salt or sugar. ' This expression is used onlj' for the purpose of describing the fact in popular language. 64 EXPERIMENTS WITH PLANTS Carefully weigh and measure a dry seed, place it in water for twenty -four hours, and then measure it again. Now place it in a very strong solution of salt or sugar until it returns to its original weight, and remeasure. Does it return to its original volume ? After the seed has grown for a time it is not possi- ble to shrink it back (by means of strong solutions or by drying) to its original volume, even if we suc- ceed in bringing it back to its original weight. The growth has become fixed, or "set." The seed is com- posed of very small chambers or cells (as may be easily seen by examining the broken surface of a Horse-bean seed-leaf with a hand-lens), each of which, like our apparatus, contains substances which absorb water and so generate pressure by which the walls of the chamber are distended (just as was the rubber fastened to the end of the tube in our apparatus). The rubber returns to its original size as soon as the pressure ceases. The stretched walls of the cells behave in the same way at first, but after a time they are strengthened and reinforced by the deposit of more material; when this has occurred the pressure may be removed and, while they will collapse to a cer- tain extent, they will not shrink back to their original size. The growth may then be said to be "set." We may ascertain when this occurs by the method described above. The explanation which has been given of the THE AWAKENING OF THE SEED 65 growth of the seed applies to the growth of all parts of the plant at all stages of development. We may cut off an inch from the tip of the root or stem and, after measuring and weighing it, place it in water, where it will continue to grow: we may then deter- 53. Section of a bit of the seed-leaf of the Horse-bean, showing cells filled with starch-grains {st), the protoplasm ipr) lying between them, the nuclei (/i) and the cell- walls [cw). mine when the growth has "set" by the method which we have just used for the seed. To get a better idea of the appearance of the cells, we may proceed as follows : Holding a well - soaked seed-leaf of the Horse-bean in the left hand, cut thin sections with a sharp razor held in the right; cut slowly with a drawing cut, place the sections in water and select the thinnest ones, even though they be very small pieces. Place them on a glass slide in a drop of water, cover with a cover- glass and examine under the microscrope. Fig. 53 shows the appear- 66 JilXPPyh'IM hWTS WI TII PLA XTS aiiee of the cells uiuler the microscope. Each cell has a cell -wall {cw) composed of cellulose, a firm substance almost identical in nature with ordinary paper or cotton or linen cloth. Within this firm cell- wall is the living substance or protoplasm (j)r), soft and jelly-like in consistency, which can be made clearly visible if we place the sections in weak eosin solution. It takes up the eosin rapidly and becomes deep red in color, leaving unstained the cell-wall and the starch - grains {st)^ which are the white glistening bodies embedded in the protoplasm. If we place some sections in iodine (see page IG-t) the starch-grains become bluish black and the protoplasm yellow. If we place other sections in safranin solution until they are deeply stained and then rinse in alcohol until they fade to a deep pink, we shall find in each cell a small, deeply stained body called the nucleus {n) ; this can be more easily seen in the outermost row of cells (where there are no starch-grains to obscure it), and still more easily in sections of the caulicle. Every living cell contains protoplasm and a nucleus, and is usually surrounded by a cell-wall. The living substance (protoplasm) of the cells is the source of all their activities. It may be killed in a variety of ways; e. g., by heat, poisons, etc. It then behaves very differently to what it does when alive. We may kill some seeds to see how this affects their power of growth. The most convenient way to THE AWAKENING OF THE SEED 67 kill the seeds in a dry condition is by heating them. To avoid scorching them, we may put them on a water-bath consisting of two tin-cups, as shown in Fig. 54. Water is placed in the lower cup, the seeds are placed in the upper one and covered, and the appara- tus placed on a stove. After the water has boiled for about an hour, the seeds should be removed and tested by the methods previously used for live seeds (some should be placed in moist sawdust to see if they are really dead). How does the pressure generated by dead seeds compare with that produced by living ones I To what extent do they "grow"! Does ^^ the growth become "set"? We may, as the result of these experiments, distin- guish two stages of growth, a temporary and a perma- nent. The temporary stage lasts until the cell -wall has been sufficiently reinforced by new material to prevent it from collapsing when water is withdrawn. Cut off an inch from the tip of a root and of a 54. Water-bath. QS EXPERIMENTS WITH PLANTS stem, kill it with boiling water, place in water and observe whether there is any growth, i. e., increase of weight or length, and whether such growth "sets." Inasmuch as wood and many other substances derived from plants (and animals) possess the prop- erty of swelling up in water, even when dead, it may be interesting to compare them with seeds in this respect. Test the swelling power of dead, dry wood in the same apparatus which you have used for seeds. How much w^ater does the wood absorb ? Wood has the power of taking moisture from the air to such an extent that it has been used to foretell changes in the weather by means of thin strips, which warp in opposite directions as the air grows moister or drier. A very important practical question is, whether wood swells equally in all directions. Draw two lines ten inches long on a piece of dry plank, — one with the grain, the other at right angles to it. Keep the piece of wood under water for two or three weeks, and then remeasure. Find out something about the behavior of different kinds of wood in shrinking, warping, etc., and the practical bearings of these facts. These experiments will serve to give clear ideas about certain physical aspects of growth which are of very general application. CHAPTER II GETTING ESTABLISHED Do seeds germinate better on the surface of the ground, or when buried in the soil ? Experiment with several kinds of seeds both in the laboratory and out- of-doors. The amount of moisture in the soil has a great deal to do with the matter and should be taken account of in arranging the experiments. What seeds, if any, do you find out-of-doors germinating success- fully on the surface of the soil ? How do seeds get buried in the soil? Find out all you can about the agencies which help to bury seeds, including wind, rain and running water, which cover the seeds with earth and mud; cracks and fissures in the earth into which the seeds fall ; burrowing animals and insects, such as gophers, ground-squirrels, wood- chucks, earthworms and ants, which bury seeds acci- dentally while burrowing, or carry them to underground storehouses; blue jays (and perhaps other birds) , wdiich are known to store seeds by burying them in the ground; and various animals w^iich trample the seeds into soft earth or mud. How deeply are seeds buried by these agencies ? From (69) 70 EXPEniMFJXTS wrrn plants a field long fallow, from the margin of a stream and from the edge of a wood take successive layers of earth (each an inch in depth) from the surface down to six or seven inches deep. Let these be placed in separate boxes and watered, in order to find out how 5"). Filaree seeds hnrvowiiig into cotton. many seeds capable of germination are contained in each layer. Some seeds are carefully buried by the parent- plants; the Peanut is one of these; by all means, watch this process if possible. As the flower- stalks lengthen they bend downward and bury the Peanuts beneath the o^round. GETTING ESTABLISHED 71 Some seeds bury themselves. The Filaree, Foxtail and Wild Oats have seeds of this kind. If you can obtain these, place them on the sur- face of moist soil (a rough, uneven surface is best) , and water them oc- casionally. How do the "clocks" assist in burying the Filaree? In order to see them work to best ad- vantage, they should be placed (seed end down) on moist cotton (see Fig. 55). The seeds of the garden Geranium (or Pelargonium) act in the same way, but to a very slight degree as compared with the Filaree. Buried seeds, which escape from their coverings only to find themselves imprisoned under ground, have before them the problem of get- ting their stems up into the air and light ; which plants seem to achieve this most easily? Notice the Corn (Fig. 56), which seems to pierce the soil with ease by means of its sharp bod- kin of firmly rolled leaves; the Scar- let Runner (Fig. 57) seems clumsy by comparison, ramming its crooked , i? •! 1 xi 1 J.1 '1 -1 57. Bean getting above stem forcibly through the soil and ground. 56. Corn making its way- above ground. 72 EXPERIMENTS WITH PLANTS often lifting up a good -sized lump of earth on emerg- ing; the Castor-bean doubles and twists (Fig. 58), like an athlete straining every muscle ; why does it have so much trouble? Does the growth of the seed-leaves while still underground account for it ? Suppose we re- move all hindrances from the Castor-bean; will the stem still form the characteristic "loop"? Allow some to germinate on the surface of the soil, or, better, in a flower -saucer which has been boiled (since Castor -beans are very apt to mould). Cover this with a piece of glass which has been boiled in water or rinsed in two per cent forma- lin. Remove the coats from a part of the seeds, so that they may be freed from all hindrances which might cause the formation of the "loop." Place some with the caulicle downward, others with the caulicle upward. Try the same experiment with other seeds which form a "loop." What part of the plant forms the "loop" in the Onion ? What plants do not form a "loop" ? (Notice especially Corn and Grasses.) How much opposition can the stem overcome in forc- ing its way upward? We may test this by means of the apparatus shown in Fig. 59. Find two bottles 58. Castor- bean twist- ing itself into a loop in its efforts to pull the seed-leaves out of the ground. GETTING ESTABLISHED 73 (about one inch in diameter) , one of which fits inside the other; cut off the smaller one as shown in the figure and make a spiral spring of the same diameter. (The spring is easily made by winding a piece of brass wire, about No. 18, closely and evenly around a spool.) In a piece of board (which should be about an inch thick) bore a hole large enough to snugly fit the larger bottle. Support this by two blocks (as shown in the figure) , so that it may hold the bottle in a vertical position. Allow the plant to grow up into the smaller bottle and press up- ward against the spring: put a little cotton- in the bottle as a cushion for the plant to press against. A suitable weight (about two pounds) must be placed on the ap- paratus ; sufficient earth should be removed at the bottom of the bottle to allow access of air. Each day mark on the outside of the larger bottle the height to which the inner bottle has been raised (a strip of paper gummed to the outer bottle • n X? i.1 • \ "VT71 ^^- -Apparatus for measuring the force Will serve for this). When of the upward growth of the plaut. 74 EXPERIMENTS WITH PLANTS the plant can compress the spring no further, remove it, invert the bottles, substitute for the inner bottle a larger one of the same diameter, and pour shot into it until the spring is compres- sed to the same point as it was by the plant. The weight of this bottle with the con- tained shot, plus the weight of the inner bottle and cotton (since the plant raised these in addition to compressing the spring) , will give the pres- sure exerted by the plant: if we divide this by the area of the cross -section of the stem just back of the crook we shall obtain the number of pounds pressure to the square inch. Thus, in one case the plant exerted a pressure of one pound. The diameter of the stem just back of the crook was one -eighth inch. The equation is Modification of tlie apparatus shown in Fig. 59. 1 pound =1 = ^R' 3.1416 X {-h) 2 81.5 pounds per square inch. It is interesting to note, in this connection, that the pressure of steam in the boilers of ordinary sta- GETTING ESTABLISHED 75 61. An arrangement for weighting an upward-growing stem. tiouary engines does not usually exceed eighty pounds per square inch. If a spring is not at hand we may use in place of it a bottle filled with shot, as shown in Fig. 60. A simple method of test- ing the force of the upward growth of the stem is by pre- paring a strainer, as shown in Fig. 61, by thrusting the finger upward through the bottom. The plant is allowed to grow up into the cone thus formed and receives both air and light; shot may be poured into the strainer until the plant can no longer lift the weight. As it is some- what difficult to bal- ance the load, we may use for this pur- pose the apparatus shown in Fig. 6l2. Three stout wire nails, about five inches long, are driven through holes previously bored in a board so as to be as nearly vertical as • I 1 rrii 62. Modification of the arrangement shown possible. They are inFig.ei. 76 KXPElilMENTS WITH PLAJSTS SO placed that the strainer slips down easily between them. Pieces of glass tubing about an inch long are attached by sealing- w^ax to the sides of the strainer in the manner shown in the figure. (This is most easily done by attaching lumps of wax to the tubes, placing them on the nails and then heating the strainer at the proper points. On placing it in position the wax will adhere to it.) They should be large enough to slip easily over the upright guides. A hole large enough to receive a small flower -pot is now bored in the board and two upright side -pieces nailed on so as to prevent the pot from resting its weight on the table. The strainer should slide on the guides with a minimum amount of friction. It must be remembered that if we prevent the stem from bending (e. g., by enclosing it in plaster of Paris), it will probably exert a much greater pressure. Tne amount which is registered by any of these methods is only a very rough approximation and is, as a rule, much smaller than w^iat the plant can exert. We must not be too hasty in thinking the limit of weight has been reached; for, after w^aiting a week or so, the plant will sometimes begin to lift a load which seemed at first too heavy for it. Plants sometimes come up through soil which is extremely hard. It is interesting to watch the be- havior of the plants in a very hard, resistant soil. Observe all the cases you can. Plant some Beans GETTING ESTABLISHED 11 about four inches deep and pack clayey soil firmly upon them. How long before they appear above ground ? Do they come up through the cracks (espe- cially at the sides), or not? Sometimes they lift up the whole mass of earth as a solid cake and thrust it out of the pot. After witnessing a feat of this sort we are more ready to believe the tales about mushrooms which lift flagstones and the like. In what part of the stem is the force developed which makes these feats pos- sible? Bend a piece of wire (about three inches long) into a V, and connect the ends by a fine thread (a single strand taken from a silk thread) so that the latter will be stretched taut; moisten this with India ink ; hold a cardboard scale (or ruler) against the stem and mark the stem at intervals of exactly one- eighth of an inch by touching it with the inked thread ; stems devoid of hairs are most easily marked (Fig. 63). The growth of the stem will cause the ink marks to separate, and the degree of separation will indicate the place of most rapid growth. Where is the region of most rapid growth? How long does the growth continue most rapid in this particular re- gion ? How long does this region continue to lengthen ? How much of the stem is growing at a given instant ? 63. Bean with the stem marked, in order to deter- mine the region of greatest growth. 78 KX PERI ME NTS WITH PLANTS Stems and other parts of plants may be quickly and evenly marked by means of the apparatus shown in Fig. 64. It consists of a small spool (such as is used for silk twist) with threads at regular intervals; it revolves on a small wire handle. The spool is first notched at regular distances in the following manner: Two knife-blades are fastened together (by clamps or strong spring clothes-pins) with a strip of wood (about one -twenty -fourth of an inch thick) between them. The double knife is then pressed against the two flanges of the spool, so as to make simultaneously two cuts in each. One blade is then inserted in a cut and the knife again pressed down so as to make a fresh cut. By proceeding in this way, all the cuts will be the same distance apart. A small piece of glass tubing is secured (by means of sealing-wax) in the center of the spool, and the thread is firmly wound upon it in a manner shown in the figure. A piece of wire, inserted in the glass tubing and then bent and twisted as shown in the figure, serves as a handle. The thread may be inked by rolling the spool over a pad (made by wrapping any absor- bent cloth around a stick) saturated with India ink. 64. Contrivauce for marking stems in the manner shown in Fig. 63. GETTING ESTABLISHED l^i By means of this apparatus any part of the plant, even if bent or crooked, may be instantly marked and with much greater accuracy than if done in the usual way. In place of a spool we may use two small notched wheels (obtainable of watchmakers) soldered together on a small piece of wire. What protects the delicate tip of the stem as it is driven forcibly through the soil ? Compare the devices by which the Corn (Fig. 56) and Scarlet Runner (Fig. 57) protect the tip. What hap- pens if the tip is injured % Remove it and see (compare Fig. 65). Do new branches arise ? When I Where % In 65^ Scarlet Runner ^l^g^|. ^^^^^_ Bean with top (ter- minal bud) removed. tloU do thcy grow I Is this the direc- tion which branches nor- mally take I What advan- tage in this direction of growth ? What happens if a stem meets an obstacle which it cannot push aside? Plant some seeds two or three ee. Radish seedlings growing upward 1-1 . . . -1 along the glass side of a box toward mCneS deep against tne obstacles placed in their path. go EXPERIMENTS WITH PLANTS glass sides of a box, such as is shown in Fig. QQ. As the stems begin to grow up along the glass, fasten small blocks of wood to the glass (by means of sealing- wax) directly in their paths. Let some of the blocks have several holes (about one-fourth of an inch in diameter) bored in them, to see whether the plant wdli find these and grow up through them. Do you see how plants find the crevices in concrete and brick side- walks and come up through them I Does the position of the caulicle make any difference in the time it takes the plant to get above ground? 67. Sunflower seedlings penetrating the soil. Plant (about an inch deep) an equal number of seeds of the same kind (at least ninety in all),. some with the caulicle up, some with the caulicle down, some with the caulicle at one side. Keep them all under the same conditions (as regards depth, moisture, warmth, etc.), preferably all in the same box. Which appear first above ground ? Let us see what happens to the seed wdiich lies on the surface of the soil. Its first problem is to get its root down into the ground. Have you ever noticed what difficulty some seeds have in doing this ? GETTING ESTABLISHED 81 Place on the surface of quite moist soil seeds of Mustard, Morning-glory, Wheat, Squash, Sunflower, Onion, Lima Bean and Horse-bean. Notice how the roots of the lighter seeds, in trying to penetrate the soil, raise the seeds up and even turn them over, and how the root -hairs and rootlets anchor these light 68. Squash seedlings endeavoring to penetrate the soil. seeds to the soil so that the roots finally penetrate it (Fig. 67). This is more noticeable when the soil is hard or firmly packed down. Fig. 68 shows the various somersaults performed by Squash seeds which were all originally placed flat on the surface of the soil. How much force can the root exert in boring its way into the soil? The contrivance shown in Fig. 69 may be used to answer this question. It consists 82 EXPKinMKyrs with plants of a stndent-laiup chimney (sizo No. 1) containing several corks (small enough to slide easily in the chimney) fastened together end to end by means of sealing- wax. In the enlarged base of the chim- ney a large cork or wooden disk is fitted, through which passes a clothes-pin of the sort indicated in the figure. Through the wire coil in the clothes-pin passes a wire nail, which is firmly held in place by two wire loops, which are securely fast- ened to the narrow neck of the chimney; another wire is passed around the chim- ney just below the nail, to hold the wire loops in position. A stopper is inserted in the end of the chimney and water poured in. A Horse-bean with a caulicle about a quarter of an inch long is inserted in the clothes-pin, which is then firmly wedged into the cork (a small wooden wedge may be used if necessary), and placed in such a position that the tip of the caulicle rests in a small excavation in the center of the topmost cork. If the pressure of the cork float is so great as to break or injure the root, stick a pin into the topmost cork in such a way as to temporarily remove the pressure from the i9. Apparatus for determining how much t'orf'e tlie root exerts in growing down- ward. The rnoT denre.sses the cork float. I GETTING ESTABLISHED 83 caulicle; the caulicle will soon gi'ow down and press against the cork. The amount of pressure may be reg- ulated by the amount of water placed in the chimney. The wire nail is now passed through the two wire loops and the coil of wire in the clothes-pin. The clothes- pin is now firmly held at two points, and may be wedged if necessary. The seed should be surrounded by moist cotton, and grooves should be cut in the edge of the cork to admit air. On a strip of paper gummed to the outside of the chimney marks should be made from time to time to indicate the position of the float. When the plant can depress it no farther, the force exerted should be measured by removing the clothes-pin, etc., and depressing the float (by means of a bottle filled with shot) to the lowest mark recorded on the gummed slip. The pressure per square inch may then be calculated, as in the case of the stem, by finding the diameter of the root just back of the tip. Another simple appai'atus may be arranged to test the pressure of the root, as shown in Fig. 70. It con- sists of a tube filled with earth, into which the root is allowed to grow, and a larger tube into which this fits ; the larger tube contains a wire spring, which is com- pressed by the growth of the root. The larger tube may be one -fourth of an inch in diameter: the smaller tube should slide easily inside it; its edges should be smoothed in a flame. It is well to break 84 EXPERIMENTS WITH PLANTS off the pointed end a little so as to allow a small open- ing for drainage; to prevent the root from growing through this opening, close it wdth a piece of gravel. The spring should be of such a stiffness that an ounce will compress it about an inch. Such a spring is easily made by winding a brass wire closely and evenly on a round stick (about one-eighth of an inch in diameter) . Se- cure the tubes with wire (or elastic bands) to a strip of wood, as shown in the figure; pin the seed to this strip and clamp a small piece of wood above for it to press against; the clothes-pin which secures the piece of wood also serves to secure the whole apparatus to a tumbler filled with water. Arrange a strip of cotton, as shown in the figure, to keep the seed moist; take care, however, that the soil in wiiich the root grows is not kept too moist, since in that case it will probably rot. As the root grows it forces the tube downward, compressing the spring; when it comes to a standstill, remove the root (but not the earth) from the inner tube and place 70. Apparatus for determining the force of growth of a root by means of a spring. GETTING ESTABLISHED 85 Upon the latter a funnel closed at the bottom with a stopper; into this pour shot until the spring is com- pressed to the same point as it was at the end of the experiment. The weight of the funnel with the con- tained shot gives the pressure exerted by the root. By preventing the root from bending, as suggested on page 76, we could obtain much larger pressures. Such a condition of things would occur naturally only in a very firm soil. Another way to roughly test the power of the root to penetrate the soil is to use a box with a bottom of wire netting (the meshes being about five-eighths of an inch square) . On the netting place cloths of various thicknesses, tin-foil, slices of potato, or anything else that the class may suggest. Fill the box with earth and plant the seeds ; it may be easily observed if the roots are able to penetrate any of these objects; for this purpose hang the box at a convenient height. What part of the root develops the energy necessary for such strong growth ? Eemove some roots which are growing in moist air (as shown in Fig. 78). Mark them in the same way as you have 71. Root marked in already marked the stem (Fig. 71). theTeii'onof^^ea"^ Remove only one root at a time, mark *^* e^owth. it and place it as quickly as possible in water, where it will continue to grow. Strong roots, such as those 86 j!]XPEIiIMEXTS WITH PLANTS of the Horse-bean, Lima Bean, Buckeye, or the roots of an Onion bulb are best for this experiment. In what region is the most rapid growth ? How long does it continue in this particular place! To what region does it then move? When the root forces its way into the soil so ener- getically, what protects the delicate tip from injury? Notice the protective cap which covers the end of the root. Roots of Wandering Jew grown in water (Fig. 85), caulicles of Sunflower, Squash, etc., show this cap well. Can you find it in other plants ? Use a lens if necessary. Why is the tip the most tender and delicate part of the root ? Why can it not be strength- ened by tough woody fiber ? Would such fiber prevent growth? Would it be an advantage to locate the growing region elsewhere than at the tip ? What would happen to the side roots and root-hairs (which are firmly fastened in the soil) if the growing region were above, instead of below, them ? What happens if the tip is injured? Remove the tips from tap-roots growing in water; do new roots appear ? Where do they arise ? In what direction do they grow I What advantage in this peculiar direction of growth ! CHAPTER III THE WORK OF ROOTS What is the function of the root? Find six healthy plants of about the same height. By an oblique cut sever the main roots of three of these about half an inch below ground, disturbing the earth as little as possible. It will be necessary to support the plants by tying them to a stick thrust into the soil (Fig. 72). This calls attention to one important function of the root, namely, to anchor the plant in the soil\ What sort of root is best adapted to anchor the plant firmly, a straight, deep root or a shallow, spreading one ? What plants are hardest to pull up ! Ex- plain why this is so. What kinds of trees are most easily uprooted ; wh}^ ? Examine the injured plants every day and note any abnormal symptoms. Notice 1 The roots of Carrot, Bulbous Buttercup and many other plants (especially such as grow in crevices of rocks, or such as hug the ground) contract when full grown and pull the plant down some distan?e into the soil. The tips 'of many Blackberry vines, which take root in contact with the soil, are soon drawn beneath the surface by the con- traction of the roots. iMake observatiojis on this point. What advantage in this action of the root ? 2. Plant attached to support ready to liave tlie root cut off. (87) 88 EXPERIMENTS WITH PLANTS any changes in the color, shape or position of leaves and other parts. What do you think these indicate ? Allow some uninjured plants to go un watered for a time ; do they show the same symptoms ? What does this indicate as to the work of the root ? In what direction should the main root grow, to do its work most effectively? Does the main root always grow straight down? Pin soaked seeds on corks in various positions (see Fig. 73), and allow the corks to float on water; pin the seeds in such a position that they will remain partly submerged; cover the dish with a piece of glass. Put some soaked seeds in various positions on the surface of moist soil and cover with an inverted tumbler, or place them in a pot half full of soil and lay a piece of glass on the top, to keep the air moist. If the roots bend downward, change the position of the seeds so that they point upward or lie horizontally. Do they begin to grow down- 73. Seeds pinned to corks -which are floating on water. ward again ? Why does the main root persist in doing this, no matter in what position it is placed? The idea has been advanced that the tip of the root, being not very rigid, droops downward of its own weight and that THE WORK OF ROOTS 89 this starts the growth in the right direction. This idea may be tested by a very simple experiment. In a small saucer, place some mercury; fasten two or three clothes-pins to the side of the dish (Fig. 74) ; to these pin germinating seeds (Peas are especially good) with perfectly straight caulicles about half an inch long; let the caulicles, especially at the - - _ 74. Seeds arranged with their caulicles tip, rest on tne SUriaCe OI resting on mercury, •which is covered the mercury. Pour in with a mtie water. enough water to partially submerge the seed. If, now, the root -tip bends downward into the mercury, over- coming its resistance, the idea that it droops of its own weight cannot be correct. If the mercury is not clean it may kill the root, since mercury salts are poisonous ; it is well, therefore, to first clean the mercury with a little cotton wool, and afterwards with running water. In place of mercury we may use gelatine (one part of gelatine dissolved in five of water), in which case no water is to be placed in the dish, but it should be covered with a piece of glass to prevent the roots from drying up. What starts the root in the right direction? Is it light, moisture, air, warmth, food or gravity ? We may test the first five simultaneously by a very simple experiment. Fill a box (having a bottom of wire 90 EXPERIMENTS WITH PLANTS netting) to one-half its depth with damp sawdust; on this lay the seeds, well soaked, and add enough saw- dust (equally damp with the first) to fill the box even with the top. On top of this put several layers of well-soaked cloth or blotting paper, and keep this wet during the experiment; let the edges press closely against the box. Hang the box up so that the under side may be easily observed. Air, light and warmth now come mostly from below instead of mostly from above, while moisture, ordinarily more abundant be- low the seed, is now about equally abundant above and below, and the same is true of any food the moisture contains. Since the sawdust is alike in depth above and below, it cannot influence the roots to rn-ow in one direction more than in another. If, now, the roots grow downward (and the stems upward) it must be in obedience to some influence other than these. Perhaps this is gravity : How can we test this sug- gestion? What would happen if we should make the force of gravity of no effect by placing the seeds on a revolving w^heel? If the wheel turns always at the same rate, each side of the root will in its turn be underneath for a short time, but no side more than another. So when all sides are equally affected by the downward pull of gravity, will it influence the root to grow in any one direction more than in another ? We may use the apparatus shown in Fig. 75 to answer THE WOBK OF BOOTS 91 this question. The essential parts are an ordinary clock and a small tub (of wood or, better, of wood fiber) , with two holes to admit a stiff wire or knitting- needle. The wire should be bent at one end and wired to the minute-hand of the clock. In order to prevent the minute-hand from slipping, it may be necessary to fasten it to its axle with a little solder or Arrangement for causing germinating seeds to revolve slowly. sealing-wax. Short bits of glass tubing are inserted in the holes in the tub, to act as bearings. The ger- minating seeds are to be pinned to corks impaled on the wire; the roots should point in various differ- ent directions; pour sufficient water into the tub so that the seeds dip in it each time they revolve; cover the tub with a piece of glass, place over this a piece of cardboard or cloth to exclude ight. and set the 92 EXPERIMENTS WIIH PLANTS clock going. The roots grow well under these con- ditions; do they continue to grow in different direc- tions, or do all assume the same direction?^ Does this (in connection with the previous experiments) indicate that it is gravity which causes all roots, under ordi- nary circumstances, to assume the same direction? How do the stems behave ? It seems at first rather puzzling to conclude that gravity, which causes roots to grow downward, also causes stems to grow upward; but there seems to be no escape from such a conclusion. We may now go a step further and substitute an- other force for that of gravity. This we may do by making the wheel revolve more rapidly. If a piece of wire is bent around the spoke of a wheel, so as to form a loose ring, and one spins the wheel, the ring will be hurled to the rim by a force commonly called centrifugal force. If the wheel be turned rapidly enough, the centrifugal force will be much greater than the force of gravity. Will a seed ]'evolving rapidly on such a wheel direct its roots in accordance with the centrifugal force? To test this, we may construct a water-wheel as shown in Fig. 76. Cut out of thin sheet zinc a circular piece six inches in diameter. Have this cut to allow the insertion of corks, as shown 1 It may happen that the root will grow on perfectly straight in the direc- tion given to it when fastened to the cork, or it may bend as the result of in- jury, influence of moiiture, light, etc. If such bendings do not occur in the control experiment (which should be made) it indicates that the directive force ■which prevents such bendings, and causes all the roots to grow in the same direction in the control experiment, has been nullified by the revolving wheel THE WORK OF BOOTS 93 in the figure. Let the flaps made by cutting remain in place. Fix round, flat corks in the cut places, and bend the flaps so as to support the corks as firmly as possible. For the axle use a knitting needle, impaling two rubber stoppers upon it, one on each side of the zinc disk, to hold the latter in place. They should press firmly against the disk, to insure its turning with the axle. The two up- right wooden sup- ports fastened to a block of wood are pierced by holes just large enough to admit the small glass tubes in which the axle rests. Each of these is closed at the end, to keep the axle from slipping too far. We place the apparatus in a sink, and attach a rubber tube to a faucet. At the end of this tube is a piece of glass tubing drawn to a point. The manner in which this is supported is shown in the figure. It should be wedged firmly in place by wooden wedges, and be so directed that the stream will strike the wheel just at its rim. The stream must be powerful Water-wheel for the purpose of making germinating seeds revolve rapidly. 94 EXPEBIMEXTS WJTff PLANTS enough to make the wheel revolve rapidly (two or three times a second). A piece of cloth must be put over and around it, like a tent, to confine the flying drops. Germinating seeds (preferably Peas) should be pinned to the corks on the sides not struck by the stream of water. In the course of a day or so, pro- vided the wheel is turning rapidly enough, we shall expect to see the roots all bending away from the cen- ter of the wheel and growing straight out in the direc- tion of the radius, while, on the other hand, the stems grow straight in, pointing toward the center of the wheel. Let us see what will happen if we place the ap- paratus on its side so that the wheel revolves horizon- tally. If the plants have become inconveniently large we may replace them by fresh ones with caulicles about an inch long. Two forces now act on the plants, — the centrifugal force and that of gravity. The roots take up an intermediate position, growing away from the center of the wheel as before, but also obliquely downward; the stems grow in the opposite direction. These experiments lead us to think that when root and stem issue from the seed, gravity determines the direction in which they grow: we can therefore under- stand how the seed, whether above ground or below, unerringly sends its stem and root in the right direc- tion. We can readily see that this is an important matter for the plant, for the quicker it gets its stem TJIJ^J WOBK OF BOOTS 95 above ground into the light and air and its root down into the soil the better will be its chances of living through this period of its life, which is more critical and more beset with dangers than any other. We can also see that in this connection gravity is the best guide the plant could have, since it is more constant and uniform than any other — the only one, in fact, that is absolutely constant. What happens if the root in its downward course meets with a dry region? When seeds are grown in damp sawdust, in a box provided with a bottom of wire netting, as described on page 90, how do the roots be- have as they grow down through the netting into the dry air I Often we see them turn upward, as in Fig. 77. Is this be- cause they try to avoid air, light, etc., or are they attracted by something in the sawdust? We may test this by arranging the ex- periment as fol- lows: Fill a tumbler one-third full of water and tie a piece of cheese-cloth over the top; on this put damp sawdust, and in the sawdust place several soaked seeds ; invert another tumbler over the whole, as shown in 77. Arrangement for testing the effect of moisture on the direction of growth of roots. 96 EXPERIMENTS WITH PLANTS Fig. 78. Do the roots, on emerging from the sawdust, turn back to it? The air now contains much more moisture than before, but in other respects there is no essential change. It would seem that in the first instance they turned back because the air was so dry, or, in other words, were attracted by the water in the sawdust. As a matter of fact, we know that tree roots find (and fill up more or less completely) cisterns and drains which are three hun- dred feet or more distant from the tree; in many towns there exist ordinances prohibiting the main- tenance of certain trees within a hundred feet of a sewer. In the above experiments the roots are not under perfectly natural conditions; we may approach these more nearly by the ar- rangement shown in Fig. 79. In the middle of a box of earth place a flower- pot, the hole of _ . • T, .1, which has been tightly 79. Arrangement for ascertaining whether *=" •^ rL';;:,\l"ls«f.l7wl;":atr.wMeh dosed by a rubber or ?Ku.''S«otiTew.r ""'" ""° cork stopper or by seal- 78. Arrangement to test the behavior of roots in moist air. (Sectional view). ^^--^^^^-^ 'f4:-: 1 TEE WORK OF BOOTS 97 ing-wax. Let the earth be reasonably moist when the seeds (well soaked) are placed m it, but do not water it further except by pouring water into the flower-pot, from which it will diffuse through the soil. After a few days examine the roots, to see what direction they have taken. What is the greatest distance from the flower-pot at which the direction of growth of the roots is aifectedf By using a shallow box (about one and one-half inches deep), with a glass bottom, and plac- ing the earth directly on the glass, we can watch the growth of the roots without disturbing them; but, since the glass affords no drainage, very little water may be used , else the soil will become so saturated with moisture as to spoil the experiment. The re- sult will depend partly on the amount of water present and partly on whether the roots are growing in sand, clay or sawdust. What direction should the side roots take to explore the soil most effectively for moisture ? glass side (see 80. Apparatus for observing the behavior of roots as they encounter obstacles. In a box with a sloping Fig. 80), filled with moist soil, place several seeds with caulicles (about an inch long) pointing straight downwards. Mark on the 98 EX PERT ME NTS M'TTH PLANTS glass '-■ the direction which seems to you most advan- tageous for the main roots and side roots and the rootlets which spring from the latter ; begin the marking directly over one (or more) of the roots. Ex- clude light com- pletely by covering the glass with card- board or cloth. What direction do the side roots have when they burst out of the main root? Do they after- ward change this M . A ■ , . . . .X. V. u ■ , -A direction ? I f s o , Apparatus designed to test the Dehavior of side ' roots under the influence of gravitj'. -^ hen? Do VOU think they solve the problem of direction in the best way? Are they guided in the direction they take by light, heat, moisture, food or gravity? Light has been care- fully excluded. If it were heat, moisture or food that guided them, we should expect to find adjacent side 1 A mixture of glue and whiting put on with a brush is excellent for mark- ing ; white paint will do, but dries more slowly; yellow pencils for marking glass are good. THE WOliK OF BOOTS 99 roots turning in the same direction, instead of which they radiate in all directions from the main root; and not only so, but roots from neighboring plants cross each other growing in opposite directions. Is it, then, gravity ? We may test this very simply. When the side roots have grown some distance, tip up the box, as in Fig. 81. Carefully mark on the glass the position of each side root; mark with especial care the position of the tips. Leave the box undisturbed and make daily observations. Do the side roots change their direction I Do the rootlets which spring from them change theirs ? As we watch the roots growing along inside the glass, we may occasionally see them encounter small sticks or stones or other ob- stacles; what do they do then? Obstacles may be pro- vided in abundance by fastening small pebbles or blocks of wood to the glass with sealing-wax before put- ting the soil in the box (Fig. 80) , or to the sides of a glass funnel (as in Fig. 82). Do ''' -^^-^f •-'-'.' "^/^---^p^-atus c5 y . j_^w shown in Fig. SO. 100 EXPERIMENTS WITH PLANTS the roots diverge from their course more than is ab- solutely necessary to avoid the obstacles? Do they resume their original course as soon as they have passed the obstacles ? Study, as far as is practicable, the rootlets which spring from the side roots in the same way in which - ^v > !> . ^^me- ' '*'^^Tw*\*^i< r v.* .*r 83. Radish seedlings grown on moist sand, showing root-hairs. you have studied the main root and the side roots. From the main root, the side roots and the rootlets, spring root-hairs; these can be seen in great profusion if we sow Radish seeds on moist earth in a pan_ (Figs. 83 and 84), and cover it with a piece of glass to retain the moisture. Sometimes the roots become covered with mould, w^hich may at first be mistaken for root- hairs. The best way to obviate this is to obtain clean seed; if this is not possible, rinse the dry seeds (^ 102 KXPKNTMhJyrSl W fTH PLANTS a few moments in five per cent formalin and- then rinse in clean water; heat the moist earth in the pan (which should be covered during the operation) so that it steams for ten or fifteen min- utes; allow it to cool and then place the seeds upon it. While the root- hairs are growing, the glass cover should not be disturbed. Does the amount of moisture affect the luxuriance of growth of the root- hairs? Use a series of pans, with the soil varying from wet to fairly dry. The seeds should be well soaked when placed in the pans; the moisture in each pan can be regu- lated by lifting the glass cover so as to permit greater or less circulation of air. What is the use of the root- hairs ? The absorptive surface of the root is increased many fold by the root- _____ _ _ hairs. The long, feathery root-hairs 85. Cutting of Wander- whlcll dcVClOD OU tllC rOOtS of CUt- ing Jew in water, show- ^ ing root -hairs which tlugs of thc Waudcriug Jew placed increase the absorbing ^ <-" -^ surface from fifty to \^ watcr (Fig. 85) iucrcasc the root seventy -five times; in \ r> / :;?£ce'°wT.ho"rrZl surface from fifty to seventy - five S:wr,'h"avetb: times; to get so much surface with- taTameVer,"""'*" out the devlce of root-hairs eacli THE WORK OF ROOTS 103 root would have to be from fifty to seventy- five times thicker, i. e., from an inch up to five or six inches in diameter. How do the roots (and especially root-hairs) manage the absorption of water from the soil? Do they find themselves surrounded by water ? Tie over the bottom of a lamp-chimney (a student-lamp chimney, size No. 1 is very good) a piece of cheese-cloth ; fill the chim- ney with soil that is moist enough to allow good plant- growth, and place it in a pan. Pour water into the pan and notice its rise in the soil. Are the spaces between the soil -particles filled with air or with water at the beginning of the experiment ? Take some more moist soil, and spread it out on a thin layer on a piece of paper. Notice the glistening appearance of each particle; as the soil dries this disappears and the particles become dull in appearance; why? If fine gravel is used, the whole process is very easily seen. It appears, then, that in moist soil the water is in the form of thin films around each particle and the spaces between these particles are filled with air; only in wet soil are these spaces more or less filled with water. In order to understand how the root absorbs water from the soil, we must understand what the soil is. Let us, therefore, take up the question, Of what is the soil composed?^ Take a handful of earth, rub it up iSee King: "The Soil." 104 EXPEBIMENTS WITH PLANTS well in water to form a paste. Place it in a fruit- jar, fill the jar with water, fasten the cover on, shake the jar well for some time, and then allow it to stand until the soil settles to the bottom. Examine the soil after it has settled. The coarse material on the bottom is sand^ above this is finer material consisting mostlj^ of clay^ the finest particles of which remain in suspension in the water, making it turbid. On the top of the water floats a little vegetable matter which in its de- composed state is called Immns, These three constitu- ents of the soil have very different properties, which should be clearly understood, since the entire fertility of the land depends on a proper admixture of these constituents. A more complete separation may be effected by first skimming off the vegetable matter, then shaking up the soil again in water and pouring the turbid water through a cloth. Continue the process until the clay is all removed : the sand will remain in the bottom of the jar. A still better separation may be effected by siphoning water from a pail through a piece of rubber tubing into a tumbler (with vertical sides) which contains earth (this should be constantly stirred with a pencil during the passage of the current) ; the current may be regulated by compressing the rubber tubing; the overflow from the tumbler should be caught in a second tumbler, of larger size, placed beneath the first. Beginning with a weak current, the finest particles will be carried over into the second THE WORK OF ROOTS 105 tumbler. When this has been accomplished and the water runs clear, remove the second tumbler, substi- tute another, and increase the strength of the current. By continuing in this way the soil may be separated into numerous portions, in each of which the size of the particles will be confined within certain limits. The time which the particles require for settling in these various portions is of importance. Make notes on this point. Sand. — Sand is made up of larger particles than clay, as may easily be seen in the experiments just described : the diameter of the particles ranges from .00004 inch to .001 inch and larger. Sandy soils are usually called "light" because they are more easy to work, although a cubic foot of dry sand weighs one hundred and five to one hundred and ten pounds, while a cubic foot of dry clay weighs only seventy to eighty pounds. Test this statement. They are more open, more porous, warmer and drier than clay soils. Pure sand contains practi- cally no plant -food ; it comes from quartz rocks ; the purest sand consists of practically nothing but particles of quartz which have a very characteristic appearance under the microscope. In order to examine sand micro- scopically, breathe on a slide, place a little sand on it and then turn it up edgewise so that all the sand falls off, with the exception of a few .scattered grains which adhere to it. Examine in the ordinary way with the aid of the mirror, giving a bright background, and also 106 UXPEBIMAWTS WITH PLANTS without the mirror, giving a dark background: use the low power of the microscope. Clay. — Clay is mostly made up of particles less than .00004 inch in diameter ; the particles have a tendency to cling together and become cemented with sand-parti- cles so as to form aggregate particles, or soil-crumbs, which may be of much larger size than the particles of sand. A clay soil, therefore, varies greatly in charac- ter, depending upon the degree of aggregation of its particles and its content of sand. In drying, clay tends to form a hard, compact mass which plant-roots cannot penetrate. When it becomes wet it is apt to assume a greasy, sticky texture,^ impervious to water and im- penetrable to plant-roots. In this state it may be further compacted by chemical agents, by kneading or by pressure, to form Jiardpan, which is really soil re- verting to rock. Hardpan may also be formed of com- pacted gravel. Clay lands are usually said to be heavy, stiff and cold : the first two terms refer to the fact that they are difficult to work, the last to the fact that they contain more water than sandy soils. Clay is usually the part of the soil richest in plant -food : it results from the decomposition of rocks containing feldspar. Examine some dry powdered clay under the microscope: do you find aggregate particles? are the particles of different colors? Find out what you can about them. 1 How do the properties of burnt clay differ from those of unburnt clay ? Why 1 Why does burning clay land improve it ? How is the operation carried out? THE WO UK OF h'OOTS 107 The experienced eye easily distinguishes between the particles of hornblende (which are black) , those of mica (which are brownish) and those of quartz and feldspar, which are both of light color but differ in form. Humus. — Examine a little leaf- mold: can you make out its nature? Place some of it under the microscope: place some on a red-hot shovel for some minutes : what change takes place ? Perform the same experiment with some dark colored soil : does it change color ? The simplest way to remove all the humus from a soil is to burn it thoroughly ; we then find that the dark color of the soil is due entirely to the humus. The fact that humus burns so readily recalls the origin of peat and coal, which are formed from humus: find out what you can about this. Humus gives to the soil a loose, open texture such as we see in leaf- mold ; it makes the land "mellow" and gives it "heart"; it retains an extra- ordinary amount of water (up to nearly twice its own weight) and is rich in plant-food. It often accumulates in forests to considerable depths. In ordinary soils hu- mus is present to the depth of three or four feet (i. e., the depths to which the roots ordinarily penetrate), and this part of the soil has a looser texture and darker color than the underlying subsoil, which is devoid of humus. By a proper admixture of humus, sand and clay we can obtain a soil of any desired consistency or texture and of any grade of fertility. The gardener does this 108 EXPERIMENTS WITH PLANTS extensively, the farmer to a lesser degree. The gar- dener has various mixtures for various purposes: for plants requiring much water he makes a clay loam (loam is a soil containing about equal parts of sand and clay mixed with humus: a clay loam contains more clay than sand, a sandy loam more sand than clay) . For plants which require but little water, such as Cacti, he makes a sandy loam: for Ferns he uses a soil composed very largely of humus. For young plants he makes an open, porous soil, which he re- places by a heavier soil as they grow older. In this way he succeeds in raising from a small pot of soil as large a plant as the farmer ordinarily produces by the use of a thousand times as much earth. The farmer is much more restricted in this respect, but he mixes humus with the soil by plowing in straw, stable ma- nure or green plants: he also adds ashes, clay or sand to the soil when necessary. What kind of soil is best for cuttings? Why? Which crops need a lignt soil; which a heavy soil? Classify the soils of your region according to the following scheme: Sand 80 to 100 per cent sand Sandy loam 60 to 80 ** " Loam 40 to 60 " " Clay loam 20 to 40 " *' Clay Oto 20 The red or yellow color of soils is due to the iron in them: the black color to humus. Point out any differ- TEE WORK OF BOOTS 109 erences you can in the crops borne by the different kinds of soils in your region. Examine the different soils with the microscope (as described above) : find out all you can about their composition and method of formation. How is soil formed? Wherever there are rocks, soil is being formed. Most rocks tend to break 'Up until they are completely changed to soil. Among the agencies which bring this about may be mentioned: (1) The mechanical action of moving water, ice and wind; (2) changes of temperature; (3) the chemical action of air and water; (4) the action of plants and animals. Find out what you can about these agencies.^ Study the weathering of rocks in your vicinity, also of building materials (including stone, brick, cement and mortar) ; which kind of building material weathers most rapidly? Why? On hillsides and mountains the soil can be seen in the act of originating from the rock which lies beneath it; such soil is said to be formed in place. In valleys, on the other hand, we find soil which has been transported from the hills or mountains by ice (drift soils) or water (alluvial soils) . Moving water always carries some soil with it, and later on de- posits it as the current slows down. This can be seen in any stream or in the little rivulets which are formed ^Consult Bailey: "Principles of Agriculture," Chapter I; Johnson: "How Crops Feed," Chapter II; Gaye: "The Great World's Farm," Chapters I to VII; King: "The Soil," Chapter I; any good text-book of Physical Geography; Darwin: "The Formation of Vegetable Moiald Through the Action of Worms.*" 110 EXPEHIMEyTS WITH PLANTS everywhere during rains. To study it more carefully, we may construct a trough about twelve feet long, a foot wide at the bottom, with sides six inches high. This is best made in three sections, each four feet long, fastened together end to end by strong hinges, so that they may be inclined at different angles. The lowest section should be level, the next iiiclined at an angle of fifteen or twenty degrees, the next at an angle of twenty -five to thirty -five degrees. Line the trough throughout its entire length with a piece of oilcloth twelve feet long and two feet wide: at the lower end gather up the oilcloth and tie it firmly to a piece of hose, which will serve to carrj^ off the waste water. Leave the lowest section empty; fill the next section with sand; fill the highest section with clay (placed in the trough in a dry, powdered condition) or a mixture of clay and sand (the clay should be pulverized and mixed with the sand while dry) . Attach a piece of rubber tubing to the faucet and allow a small stream of water to trickle down the entire length of the trough. The clay (or mixture) in the upper part of the trough will behave in the same way as rock (only the action will ])e much more rapid), and will show" clearly how rock is sculptured by running water; how masses of it become detached and fall off, and how as these are carried down stream they lose their sharp edges (this occurs especially where the clay overlaps the sand). If different layers of clay (or mixture) are THJ^J WORK OF JfOOrS 111 colored by earth colors (obtainable at a paint store) and placed over one another and then compressed or moulded so as to form folds like those of rock (syn- clines and anticlines), and placed in the upper sec- tion, we shall be able to see clearly how the water wears its way down through different layers of rock (the layers may be made of different hardness by mix- ing in' more or less sand so as to imitate harder and softer rock layers). In the second section we shall see landslides,^ terraces, meanders, oxbows, bubbling springs (where an obstacle occurs), and all the other features of stream action. In the third section we shall see alluvial fans and cones, deltas, beaches, the deposit of coarse materials near shore, and of finer materials further out and all the features of lake and ocean for- mations. Now that we have learned something of the nature of the soil, let us investigate further the manner in which it retains the soil -water. What becomes of the rain water which falls on the soil ? Fill a box about eighteen inches square and four inches deep with sand. On the surface of this place a layer of wet clay; smooth it carefully so as to leave no cracks and bring it down over the outside edges of the box so as to completely cover the sand. Place a quart of water in an ordinary garden sprinkler and slowly sprinkle it on the surface of the clay. Collect iln regard to all these features, consult any of the standard elementary text-books of Physical Geograpliy. 112 EXPERIMENTS WITH PLANTS the water by means of a piece of oilcloth about three feet square placed beneath the box. How rapidly does the water run off? How much remains behind? Place a layer of moist cotton batting, about an inch thick (sawdust or sphagnum moss such as florists use may be employed) on the surface of the clay, and repeat the experiment. Remove the clay from the sand and re- peat the experiment, with and without the cotton. In this experiment the cotton represents a covering of vegetation on the soil: such a covering retains the water in precisely the same way as the cotton. Com- pare as well as you can by observation the amounts of rain which run off from the surfaces of the following: Clay soil without covering. Sandy soil without covering. Soil with a covering of turf. Soil with a covering of tall weeds or other plants. Soil with a covering of shrubs or trees. It is believed that the floods of our great rivers, such as the Mississippi, could be wholly averted by preserving the forests at the headwaters. Find out the annual damage of these floods. This represents the interest on the sum which could be profitably invested in preserving these forests. What does this sum amount to ? If you live in a region where damage by flood occurs, make a similar estimate for your own region. When it is not feasible to reforest these areas, the natural growth of shrubs and undergrowth should be THE WORK OF ROOTS 113 encouraged by preventing fires, keeping out sheep, etc.^ Such a cover not only prevents floods, but it prevents the washing away of the soil on hillsides and slopes : the damage to good farm land from this source may assume enormous proportions and . it is exceedingly^ difficult ever to remedy it or restore the land so ruined. The water which runs off without penetrating the soil is called the runoff : that which soaks into the soil is known as the percolating water. For convenience we sometimes divide tlie soil -water into three kinds : (1) free water, which flows under the influence of gravity and percolates down through the soil ; (2) capillary water, which is held in the capillary spaces or pores of the soil and is not influenced by gravity but moves upwai'd or in any direction where the soil is becoming drier ; (3) hygroscopic water, which is so firmly held as a film around each par- ticle that it does not move about like the capillary water but can be re- moved only by heating to the boiling point of water, when it passes off as steam : the driest of "air- dry" soils contains considerable hygroscopic water. In what kind of soil is percolation most rapid ; in what kind of soil is water retained longest after a rain ? Fill two chimneys as described above — one with clay, the other with sand; put them in separate pans. Pour an equal quantity of water into each chimney, taking care that none runs over; through which does the water run more rapidly I Why ? Which kind of soil 1 Consult Roth, "First Book of Forestry," pp. 202-209: also Tunmey, « Relation of Forests to Stream Flow," Year-Book of the U. S. Dept. of Agricul- ture for 1903. 114 EXPi':uiMi':xTs with plants 3. Apparatus for measuring the rate of evapo- ration from a satui-ated soil. has the larg'er pai'tiek'.s; the hirger spaces; does this explain the matter! An inch of rain is said to pene- trate four inches in clayey soil and six to eight inches in sandy soil. What do you think of this statement ? Does air in the soil hinder percolation ? What becomes of the rain-water which percolates down through the soil ; is any of it drawn back up again as the surface dries? Prepare a bent tube as shown in Fig. ^Q^ one arm being about eighteen inches long and the other about four inches. Push a little wet cotton nearly to the bottom of the longer arm; fill this with clay; fill the longer arm of a similar tube with sand. Attach a funnel, as shown in Fig. 87, and pom- water upon the soil in each tube until the shorter arm of the tube is partly filled; when it stops rising, remove the funnel and pour a few drops of oil on the surface of the water in the shorter arm of the tube, to prevent evaporation. Mark accurately on a strip of paper gummed to the tube the height of the water -column (it should be about the same in botli 8?. Method of supplying . , . Ti> j^i j^ n ^^ ' 2.^ water to the apparatus tubes). It the water tails m the shown in Fig. so. THi: WORK OF ROOTS 115 shorter arm, it shows that some of the water which has run down through the soil is being drawn up again. In which tube does this take place more rapidly ? Is it hastened by putting the tubes in the sun? Explain. It often happens that a bed of gravel lies from three to six feet below the surface of the soil ; how does this affect the upward move- ment of water in the soil ? Place a little gravel in the tube and note the effect. To retain the moisture in the soil, the farmer re- sorts to cultivation and mulching, i. e., placing on the surface of the soil something (straw, dead leaves, stable manure, etc.) to prevent evapora- tion. Take four student-lamp chimneys (Fig. 88), cork them securely at the bottom and fill them with good moist soil (which should be previously well mixed so as to be uniform throughout) . On the top of the soil in one, place a layer of dry sawdust four inches deep (a) ; in another place a similar layer of sifted dry soil not packed down (/>) ; in another plant Wheat (c), and leave the last as a control {d) . Weigh each of them, and repeat the weighing at intervals 88. Four lamp-chiiinieys filled with soil for the purpose of studying the rate of evap- oration from the surface: (a) surface covered with a mulch of sawdust; (ft) surface tilled; (c)surface planted; {d) control. 116 EXPERIMENTS WITH PLANTS of a week. Which loses the most water; the least? Explain. The result of cultivating the soil is to keep a layer of loose, dry soil on top, which acts like the saw- dust in preventing evaporation, by reason of the fact that its large capillary spaces cannot take the water from the smaller spaces of the underlying soil. This is further illustrated by the fact that a dry brick will take water from a moist sponge, but a dry sponge will not take up water from a moist brick: it may be said that the surface crust energetically draws the water away from the underlying soil, just as a brick will suck a sponge dry. It is often noticed that where the soil has been well tilled every wagon-track or footprint remains moist after the soil around has become dry, and weeds spring up noticeably in such places owing to the 88a. New growth on Apricot trees growing side by side. Above, the cultivated; below, the uncultivated, fact that the com- pressed soil maintains TEE WORK OF ROOTS 117 capillary connection with the moist earth below. How a surface layer of loose, dry soil conserves moisture is well seen in Fig. ^^a^ which shows the new growth, during one summer, of two trees side by side under the same conditions, except that in one case the ground was cultivated while in the other it was not. The loose, dry layer of earth, known as the surface mulch, must be maintained by cultivating the surface as often as it becomes baked into a crust. The surface mulch not only prevents evaporation but it admits air (which is excluded by the crust) . It prevents the soil from cooling oif quickly at night and keeps it from freezing deeply in winter (snow acts as a mulch) . It also prevents rain from running off the surface. In view of these facts, the advice "Water your garden with the rake" becomes important: i.e., as soon as the water has sunk into the ground go over it with a rake and break up the surface crust so as to foi-m a mulch. (What connection is there between evaporation from the soil and the formation of dew ? Invert a small tumbler on the surface of moist soil and leave it over night. Are you able to find any dew on the glass the next morning? Why is dew ordinarily formed only at night and more copiously in absence of wind or clouds?) Is all of the rain-water which soaks down through the soil drawn back up again ? How are springs formed? How deep must we go before we find wet 118 H^XPERIMENTS WITH PLANTS soil, i. e., soil in which the spaces are filled with water instead of air I This level is called the water- table; does the height of water in a well indicate this point reliably ? From how great a depth is the water drawn up by the soil ? Get a glass tube about six feet long, or make one by joining together short lengths by means of rubber tubing. Fill this with clay (dried and pulverized), and place the lower end in water; it may be several weeks before the water stops rising. Clay lifts further than sand, because the spaces between the particles are smaller, but it cannot apparently lift more than six feet.^ This means that practically all water which sinks five or six feet below the roots of a plant is permanently lost to that plant. Moist soil draws up water more rapidly than dry, but can lift it no higher. Find out what you can about the height of the water-table in your vicinity at various seasons of the year; does it follow exactly the elevations and depres- sions of the surface of the land ? How many feet does it rise and fall yearly ? What is the ideal depth for the water-table? Does the rise of the water-table in spring help to thaw out the ground ? From these experiments it appears that in soil which is moist and in good condition for growing plants (but not wet) the water exists in the form of iThe finest silt may lift water as high as ten feet: this necessarily occupies a very long time. THE WORK OF BOOTS 119 drops which are held in the angles between adjacent soil - particles (see Fig. 89, which represents a fairly dry soil) ; it also forms a very thin film on the surface of each particle. The re- maining space is filled with air. The water causes the soil -particles to adhere to each other, just as two glass plates do when wet. or the hairs of a brush dipped in w^ater. We may picture- the relations of the root-hairs to the soil -particles by the aid of Fig. 90, in which the soil -particles (sp) are represented as surrounded by water, as shown by the contour lines ; this represents a wet soil containing the maximum amount of water in which plants can grow. Here and there air- bubbles (a) occur which furnish the root with oxygen. The root-hairs absorb water whenever they come into con- tact with it ; this causes more water to flow from neighboring particles not actually in contact with the root -hair. In this way each root-hair drains a con- siderable extent of territory. The absorbed water Diagram of a fairly dry soil, showing the relations of a root-hair (rh) to the surrounding soil -particles (sp) . The water (iv) is held in the form of small drops (menisci) between the angles of adjacent particles; the water also forms a very thin film on the surface of each particle, as well as on the surface of the root-hair. The remaining space is oc- cupied by air (a). Cross-section of a root, as it grows in the soil, showing the relations of the root-liairs (rh) to the soil-particles (sp) and the air-spaces (a): this soil is represented as containing the maximum amount of water compatible with good plant-giowth. Whenever a root-hair absorbs water, more flows toward It from the surrounding region; a single root -hair is thus enabled to drain a considerable area. The water absorbed by the root-hairs passes throngh the loose outer rind or cortex of the root to the wood-cells (shown as four groups of thick-walled cells in the center of the root); alternating with the four groups of wood-fells, are four groups of thin-walled bast, while m the center is pith. THE WORK OF ROOTS 121 passes through the root-han* and the soft outer part (rind or cortex) of the root to the woody strands in the center (shown in the figure as four groups of thick-walled cells), and by means of these up into the stem. (The four groups of thin -walled tissues alter- nating with the wood are the bast; in the center, surrounded by the wood and bast, is the pith.) Do the root-hairs attach themselves closely to the particles? Place some well- soaked seeds (Radish seed is especially good) on the surface of fine, moist gravel in a pan; over this lay a piece of glass to retain moisture. In two or three days the roots will be covered by a thick felt of glistening, white root-hairs. As they come into contact with the particles of gravel they become firmly attached to them. When this has happened, lift the seeds; are the attached particles lifted with them; how large a pebble can be lifted in this way; when the pieces are too large to be lifted does the root -hair loosen its hold or does it break, leaving a portion attached to the particle ? What conclusion do you draw as to the closeness and firmness of the attachment ? In dry soil the water exists in the form of innumer- able little reservoirs, which must be tapped by the root -hairs. To remove the water some force must bo used, for the water adheres quite firmly to the soil- particles. Not only must the reservoir be tapped but the water must be drawn forciblv from it. How does 122 EXPEEIMENTS WITH PLANTS the root-hair pull the water away from the particles ? It would seem that there must be substauees in the root -hair wliicli attract water, just as the sugar draws the water through a Wahiut-shell or bladder (pages 16 and 61) . In some roots we can taste sugar (Carrot, Parsnip, Beets, etc.); by applying chemical tests we find in all roots sugar or other substances capable of attracting water. It appears, then, that the root-hair, which is a long, closed sack (as you may easily see with a good hand-lens or with the low power of a com- pound microscope), contains substances w^hicli attract water. We can easily make an artificial root-hair ^ of any sort of membrane which will allow water to pass through but retain the sugar inside; such are ox- or pig-bladder or parchment paper; perhaps the most convenient is the membrane which lines an egg-shell; empty the contents of the e^g through a small hole at one end ; jilace the shell in a tumbler and cover with weak acid or vinegar; place another tumbler inside the first, to keep the egg submerged. When the shell is dissolved away, fasten the membrane to a glass tube (about one-fourth of an inch in diameter), as shown in Fig. 91; three or four turns of tightly wound string (or, better, of elastic band) fasten it satisfactorily.^ 1 Artificial root-hairs may be made by hollowing out Carro^^s. using an en- tire eg^, etc., but it seems better to eliminate all living parts from the appa- ratus, that the pui'ely physical features may be emphasized. 2 It is well to prepare several tubes and then choose the one which gives the best results on trial. TIU] WO UK OF BOOTS 123 Place it under water, and blow gently into the tube to make sure there are no leaks. Pour into the tube enough strong syrup (sugar and water) to fill it to f a point a little above the membrane. Sub- merge the membrane in water, and mark the height at which the syrup stands. If, now, this artificial root- hair absorbs water, we can detect it by the rise of fluid in the tube. How rapidly does it rise ? How far will it rise? As we have already learned (pages 61 to 63), the absorption of water generates pressure inside the (closed) arti- ficial root -hair. In the real root-hair pressure is generated in the same way. What happens if we now extract water from the artificial root-hair by submerging it in a stronger syrup than that which is inside of it f Pour sugar into the tumbler and stir it un- til a very strong syrup is formed; what happens to the liquid in the tube? Try the same experhnent with the root-hairs; have some seedlings with good root- hairs growing in water; add sugar to the water until a strong syrup is formed. The stiffness of the root-hairs is due ap- parently (like the stiffness of an inflated balloon or bicycle tire) to the pressure inside; this pressure is 91. Artificial root -hair, made of tlie mem- l)raiie whicli lines an egg-sliell. 124 EXPERIMENTS WITH PLANTS due to the absorption of water; when we draw this water out, the root-hairs collapse. Just as in the ease of the seed (see page 18), the presence of water- attracting substances (e. g., salts, etc.) in the soil- water hinders absorption by the root; this is the case along the seashore where the water is brackish and in alkali soils. In order that the roots may be able to explore the soil freely and absorb water from it, it must be in the proper physical condition or, to use a more common term, it should be mellow, i.e., of a loose, friable texture. The physical condition of the soil is" known as tilth. How may the soil be kept in good tilth! This in- volves two things: (1) keeping the soil-crumbs of the proper size, (2) keeping up the circulation of air in the soil. 1. The size of the soil-crumbs is of the greatest im- portance. If they are too large, the surface exposed to the action of the roots is relatively small. Suppose chat by tillage we break them up so that they are only one -tenth of their original diameter, we thereby in- crease the surface available to the roots ten times and multiply the possibilities of plant-growth accordingly. Soil composed of too large crumbs not only allows the rain-water to leach through too rapidly, but is unable to lift it up again to any great extent from the water- table. THE WOBK OF ROOTS 125 If, on the other hand, the crumbs are too small, the soil becomes impervious to water and wholly unfit for plant-growth: this is the case with the finest clays or puddled clay soils. As already explained, the surface mulch of larger- sized crumbs produced by cultivation conserves the moisture of the soil by preventing surface evaporation. 2. The air in the soil is kept in slow but constant circulation by the fluctuations of barometric pressure by which it is alternately forced into the soil and sucked out again: this phenomenon is sometimes so pronounced that the air, escaping from the lower strata of soil and rushing up through wells, produces a loud noise, causing them to be known as "whistling wells." But, despite this, it is necessary to stir the soil frequently in order to admit air if we wish to get the best results from crops. The great importance of air as an agent which promotes chemical changes in ' the soil is now becoming better understood: this point will be discussed later. The necessity for a supply of air may be strikingly shown by placing a potted plant in a pail of water so that the water-level stands a little above the top of the pot. Note the appearance of the plant from day to day. Alfalfa fields, if flooded for two or three days in summer time, turn yellow and the plants die. Note the effects of flooding on meadows or trees whenever an opportunity occurs. A crust on the surface of the soil 126 j!:xpEKiMEyTs wite plants excludes air. Paved streets and sidewalks often cause injury to trees by preventing access of air; for this reason it is better to leave an open space about them and aerate the soil by frequent cultivation. We fre- quently see Willows and other trees on the banks of streams living with their roots completely submerged in water or in saturated soil ; this seems at first glance to be in contradiction to what we have just learned about 92. Diagram to illustrate the effect of ideal plowing. The compactness of the soil is indicated by the density of the shading. Before plowing, there is a compact surface crust («), below which the soil grows less compact as we go deeper; after plowing, this compact muss is broken up into a loose, friable mass of soil-criambs, or floccules, with a consequent increase in the bulk of the furrow-slice {fs)\ compacted plow sole at (pi). (After Hilgard.) the necessity for a supply of air for the roots. In this case, however, the roots are in running water and are able to make use of the small but continually renewed supply of air which it contains. Where the soil is satu- rated with water, without free circulation, the air-sui)ply is quickly exhausted. Not only are the roots unable to breathe but chemical processes injurious to the plant are set up in the soil. Plowing and surface tillage are the principal means used to secure good tilth. The result of ideal plowing is shown in Fig. 92, in which the density or compact- ness of the soil is indicated by the density of the THJ^ WORK OF BOOTS 12 shading (the dots ai-c not intended to represent indi- vidual soil-particles or aggregations) . At {s) is the surface-crust, which may become very hard by the baking of the sun and the beating of rain upon it, as well as by the deposit of salts which are left behind as the water evaporates. In soils where such salts are very abundant (alkali soils) they form a whitish deposit on the surface. This action of salts may be very clearly illustrated by placing a little strong eosin solu- tion or a little table salt in the bottom of a tumbler and then filling the tumbler with wet sand and allow- ing it to stand in the sun for a few days. As we go deeper the soil becomes less compact (as indicated in the figure) until a certain depth is reached, when it begins to grow more compact as the subsoil is approached. The plow removes a slice of soil and inverts it; in ideal plowing the in- verted portion (called the furrow slice, /s) is left in a loose, friable condition. On examining it, we find it broken up into small rounded masses (soil- crumbs, or floccules), as shown in Fig. 93. Each one of these masses is made up of a number of small soil -particles, as shown in Fig. 94, which repre- 93. Part of furrow slice (of Fig. 92) magnified to show floccules. or soil-crumbs. 128 EXPERIMENTS WITH PLANTS sents a single soil -crumb greatly magnified. The particles are held together by the water {iv) , just as are two plates of glass or the hairs of a brush when wetted. If the brush be dry or submerged in water the hairs tend to fall apart; the same is true of the soil-particles. At the same time that the soil is broken up it is mixed with air. It will be noticed that the surface of the plowed land is much higher than that of the nnplowed: there has been a noticeable increase of bulk due to the spaces between the soil- crumbs formed by tillage. These spaces are filled with air, so that the increase in bulk represents the amount of air which has been mixed into the soil in the plowing. Surface tillage is accomplished by the harrowing which follows plowing, and also by placing the plants in rows several inches apart and running a cultivator between them. This serves the triple purpose of destroying weeds, breaking up and aerating the soil, and maintaining a surface mulch. It is important not to till the soil when it is too wet, since in that case the tendency is to break up the soil -crumbs into their constituent soil -particles, which A single soil -crumb magni- fied to show the soil-particles of which it is composed; the particles are held together by the water (iv), just as are the hairs of a brush when wetted. The white spaces between the particles represent air. THE WOBK OF ROOTS 129 results in the formation of a pasty mass impervious to water, as can be easily seen by kneading a little wet clay. Such a soil is called a puddled soil, and its properties are illustrated in the making of reservoirs, the bottoms of w^hich are sometimes lined with wet clay, which is then kneaded by driving sheep into the enclosure: the result is a layer which is water-tight. To a certain extent, puddling of the soil is caused by the beating action of rain, as well as by baking in the sun and the deposition of salts by evaporation. (Mulches prevent this action; so also does a covering of plants, which explains why the soil of meadows, natural pastures, woodlands, etc., remains in good tilth.) It is interesting to note that puddling may also be caused by tilling the soil when it is too dry, the effect being to reduce it to a fine powder, which forms a pasty mass on becoming wet. Puddled soil is improved by mixing manure, burnt clay, straw, coal ashes or sand with it. Try an experi- ment to test this. The addition of lime is also beneficial, since it tends to form floccules (see page 152). The texture of the soil is more important than its richness, and it is almost useless to apply manures to soil which is in poor tilth: tillage is of more importance than manuring.^ 1 See King : "The Soil," and "Irrigation and Drainage": Bailey : "Princi- ples of Agriculture," Chaps. II, III and IV. See articles in the Ycar-Book of the U. S. Dept. of Agriculture, for 1894 by Whitney, Galloway and Woods; for 1895 by Whitney ; for 1900 by Briggs ; for 1903 by King. 130 EXPEIUMKXTS WITH PLANTS How much water should the soil contain to give the best results in growing plants ? Take five tumblers, fill them with soil: add to the first 15 cc. of water each day: to the second, half as much ; to the third, half as much as to the second, etc. Plant the same number of Wheat-grains (or other seed) in each. After two or three weeks a great difference will be noticed: those which receive too much water will not grow, on account of lack of air ; those which receive too little will suffer from drought. Somewhere between will be the happy medium where the plants grow best. What per cent of water does this soil contain ! We may ascertain by weighing a sample of the soil and then drying it in an oven and weighing again. For practical purposes we may turn the ques- tion around and ask. How much air should the soil con- tain ? A simple method of answering this is to insert a small tube to the bottom of the soil, connect it with a funnel and then pour in water (from a receptacle containing a measured quantity of water) until the water stands level with the surface of the soil. Since the water displaces the air in the soil we may consider that the volume of water poured into the soil represents approximately the amount of air it contained : this may be easily compared with the volume of the soil. In watering gardens and potted plants, and in iri-i- gation on a larger scale, it is important to know how much water to apply. The greatest ignorance prevails in this respect. One irrigator will use ten times as THE WOIiK OF HOOTS 131 much water as another on the same land and for the same crop ; house-plants are more often killed by in- judicious watering* than by any other cause. The greatest harm is done by over -irrigation, which not only drowns the roots but ruins the soil -tilth. When- ever it is possible, irrigation should be done by means of underground pipes or drains : these deliver both water and air to the roots precisely where they are needed, and, if a good surface mulch be maintained, there is almost no loss by evaporation. This method is especially adapted to greenhouses and intensive horti- culture generally. It is stated that by this system, as practiced in the open, only a twentieth part of the or- dinary amount of water needs to be given and the tilth of the soil is kept in the best condition, while the sur- face of the land is left free for tillage. The amount of water which the soil should contain to give the best results will vary somewhat, according to circumstances (some plants require much more than others) . In general the soil should not contain more than 60 per cent of its water-holding capacity, i. e., at least two-fifths of the spaces should be occupied by air. The water- holding capacity of a soil may be deter- mined by saturating it with water, draining off the surplus, weighing a portion of it and then drying it on a water- bath to constant weight. The loss in weight divided by the dry weight gives the percentage of water (i. e.., water- holding capacity of the soil). 132 EXPERIMENTS WITH PLANTS Compare the water- holding capacity of sand, clay and humus (leaf-mold). Air reaches the roots of potted plants not only from above but also through the sides of the pot. How permeable the latter is to air may be tested by cementing a piece of it to a glass tube and proceed- ing as in the experiment shown in Fig. 28, or by sim- ply placing a piece in an air-pump (see page 187) and exhausting. The outside of a pot should be washed occasionally to keep it clean and porous, so that air may enter it freely. To retain in good condition the soil in which potted plants are grown, they should not be watered too often, but, w^hen water is given, it should be applied copi- ously (preferably by submerging the entire pot in a pail of water) . A good rule is to water about once a week in this way and to delay watering in any case until the pot sounds hollow on being tapped. The frequent application of a little water merely wets the top layer of soil, leaving the bottom dry. On the other hand, too much water deprives the roots of air and causes them to decay. Devise an experi- ment to determine in the case of some house plants how much water should be given. How may the soil moisture be regulated ? We may answer this question by reviewing what has already been said. (1) Moisture may be decreased by under- ground drains or by plowing land without subsequently TEL' WORK OF BOOTS 133 making a surface mulch, in which case it soon dries out; (2) moisture may be increased by a surface mulch which hinders the rain-water from running off and largely prevents loss by subsequent evaporation ; by keeping the soil in good tilth; by the addition of humus ; by artificial application of water. Other things being equal, the yield of a crop is di- rectly proportional to the amount of water it receives within the limits mentioned above. ^ How thoroughly do roots explore the soil for mois- ture? This may be investigated by carefully re- moving the earth in successive layers, or, better still, digging a trench around the plant and lifting out a large ball of earth, which should be carefully washed away by means of a hose. The roots of Corn, Barley, etc., examined in this way show a dense mat extending downward three or four feet. In a root- system of this kind we find practically every cubic inch of the soil explored by one or more (sometimes by very many) roots: a conservative estimate of the extent of the root- system of four well -developed Corn plants gave an aggregate length of over a mile of roots, not count- ing root-hairs. The estimate was made by calculating the number of cubic inches of soil (the roots occupied a cube of earth a little less than three and one -half iSee Bailey, "Principles of Acrrieulture"; King, "The Soil" and "Irrigation and Drainage"; also articles in the Year-Book of the U. S. Dept. of Agriculture for 1895 by Taft; for 1898 by Briggs; for 1900 by Johnson and Stannard; for 1902 by Beals. 134 EXPERIMENTS WITH PLANTS feet on a side) , which were thoroughly explored by the roots, and assuming each cubic inch of earth to contain only one linear inch of root. The entire root -system of a Squash vine was found by actual measurement to be over fifteen miles in length (not counting root- hairs), and of this length the major part must have been produced at the rate of 1,000 feet per day. The spread of the root is, in general, about the same as the spread of the branches. Thus the "feed- ing roots " (the fine, branching roots which do most of the absorbing) of a tree are largely located beneath the tips of the branches where the drip of the rain and dew falls directly upon them; and the same is true to a great extent of shrubs and herbaceous plants. With these general facts in mind, it will be of interest to investigate a few special cases, especially of trees or crops common in your region. It will also be of interest to examine the behavior of the roots of potted plants. As a rule, the roots of ordinary crops do not pene- trate the soil to a depth of more than three or four feet, but in dry regions they may penetrate ten or twelve feet (or more) into the soil in the search for moisture; in consequence of this they are enabled to withstand long periods of drought. Alfalfa grown in dry soil may penetrate more than twice as deep as this. Some crops. Grasses, etc., are known as "sur- face feeders." Such are often grown in orchards, etc., THE WORK OF BOOTS 135 since they do not interfere with the deeper roots of the trees. (Monocotyledons are mostly shallow -rooted, be- cause the roots spread out near the top.) Others, for the opposite reason, are known as "deep feeders." It is of the greatest importance to take these facts into account in hoeing and cultivating the soil: the deeper the roots the deeper should be tlie plowing and subse- quent cultivation. It is of importance to know that by proper irrigation it is possible to control the growth of the roots so as to cause them to grow deep or near the surface: the more the soil is saturated with water the nearer the surface will the roots stay, on account of their need of air. Where there is a long dry season the water-table sinks steadily: if the crop is planted early enough the roots follow the water-table down and so maintain themselves, but if planted two or three days too late they are unable to do so and the plants perish. What crops stand drought best ? Are they deep-rooted plants? Cake of Roots. — When roots become sickly, water sparingly; place the plant in a cool, shady place, sprinkle the leaves from time to time and, if necessary, prune off some of the leaves and branches. Under these circumstances the plant will need little water (for reasons, see page 212) and the roots will have an opportunity to recover. In repotting plants, invert the pot and tap smartly until the ball of earth is loosened. On removing the pot, 136 EXPERIMENTS WITE PLANTS a perfect felt of roots will usually be found next the pot. These should be removed, since they are sure to be injured in any case and their subsequent decay may affect the rest of the root. Remove the outer part of the ball of earth (which has become compact and sour) , hold the plant with the left hand at the proper height in the new pot, and with the right hand pack the fresh earth about the roots. The pot may then be immersed in water until bubbles cease to rise. Trees which are intended for transplanting should have the roots confined to a small space by transplant- ing and root- pruning once a year. Trees with spread- ing roots may be treated as follows: Some time before the tree is to be transplanted a trench is dug about it and filled with good earth. From their cut-off ends the roots will send out new rootlets into this earth. When this is accomplished the tree, with its ball of earth, may be pulled over and then raised by a suit- able tackle, and transported. (In addition to these precautions, it is important in transplanting trees to see that the points of the compass remain in the same relation to the tree in its new position, i. e., that the north side shall remain the north side after transplant- ing; for reasons, see page 220.) The water contained in the soil dissolves out from it mineral substances (such as the salt, which is con- stantly carried to the sea, and the lime, which is de- posited in boilers, tea-kettles, etc.). Are these mineral THE WORK OF BOOTS 137 matters absorbed by the plant ? We may easily answer this question by burning the plant, since whatever remains after thorough burning represents mineral matters which have been absorbed by the plant. We first dry the plant thoroughly in the sun or in an oven ; we then break it into small pieces, place them on a small iron shovel and heat it red-hot. Continue the heating until the ash becomes white, or nearly so, on cooling. If we weigh the plant before and after drying, and also the ash left after burning, we shall know approxi- mately how much water, how much cellulose (see page QQ) or woody fiber (the combustible part) , and how much mineral matter it con- tains. Is the absorbed mineral matter of use to the plant ? In order to deprive the plant of its supply of mineral mat- ter, we must furnish it with distilled water instead of or- T i TTT 1 95. A still t'(u- making distilled water: dmary water. We may ob- it consists of two pans and a cake- tain distilled water by means *^" ^^" ""^ graniteware or tinware). of the apparatus shown in Fig. 95. It consists of two pans and a cake-tin, the central cone of which has been shortened to the proper length by making vertical cuts with a pair of stout shears and then bend- ing back the flaps as shown in the figure. Water is 138 EXPERIMENTS WITH PL A XT S placed in the lower and upper pans and the whole apparatus set on a stove. When the water in the lower pan boils the steam rises until it strikes the under surface of the upper pan, which is kept cool by the water in it. The steam condenses in drops and collects in the cake- tin. It is desirable to use graniteware utensils for this apparatus, but tinw^are is equally good so long as it is kept bright and free from rust. Distilled water may be made in this apparatus at the rate of over a quart an hour. The cost of the whole apparatus need not exceed half a dollar. The purity of distilled water (like that of "rain- water) depends on the fact that when water evaporates it leaves behind any substances w^hich may be dis- solved in it. (We may use, if necessary, freshly col- lected rain-water in place of distilled water.) Wheat may be recommended for this experiment. Place the seeds in boxes of sawdust; water one with distilled water; the other w^ith pond-, river- or tap- w^ater (giving the same amounts to each). We may also grow the plants directly in water. For this pur- pose slips (about eight inches long) of the Wandering Jew or Inch Plant (Tradescantia) may be recom- mended. The slips are placed in fruit -jars contain- ing about two quarts of water, and placed where they will receive about the same amount of light as is needed by ordinary house -plants. We may carry the THU WORK OF ROOTS 139 experiment further and add to the tap-water various mineral substances, to stimulate the growth of the plant. Saltpeter and bone superphosphate (one ounce of each dissolved in three quarts of water) may be used in this way. Experiments carried out in this way have shown that the mineral matters indispensa- ble to the plant consist of four bases and four acids. hases : Th e acids : Potash Nitric Lime Phosphoric Magnesium Sulphuric Iron Carbonic (from the air If we dissolve in distilled water all the above sub- stances (except carbonic acid) , plants may be grown in it until they flower and fruit and produce perfect seeds; but if we omit any of the elements involved (except carbonic acid) , the plant soon stops growing and fails to flower or fruit. (Carbonic acid is neces- sary to the plant but is absorbed from the air, as we shall see later.) Fig. 96 shows the result of such an ex- periment made with the Wandering Jew or Inch Plant. All these substances must exist in the soil in order that the plant may thrive, and they must not only exist there but be soluble in the soil-water. The car- bonic acid of the soil is of great service to the j)lant, since it dissolves many substances which would other- wise remain undissolved. If, for instance, we add to lime-water (which has been filtered clear) a little soda- 140 EXPEBIMENTS WITH PLANTS water (i. e., water highly charged with carbonic acid; it is bottled under pressure and sold as "plain soda"), we shall get a milky precipitate or sediment of car- bonate of lime (due to the union of lime and carbonic 96. The result of a (five weeks) water culture of Wandering Jew: the one marked "full quota" had all the indispensable food- substances dissolved in the water; each of the others lacked one element. acid). On adding more soda-water, the milky ap- pearance vanishes and the water becomes clear, owing to the fact that the carbonate of lime has been dis- solved by the excess of carbonic acid. If we now heat this clear water, the excess of carbonic acid will be driven off (as shown by the constant and rapid THE WORK OF BOOTS 141 rising of bubbles) , and the milkiness will reappear as the carbonate of lime separates out in solid particles. This experiment may also be performed by stirring up fine marble dust or whiting (both of which consist of carbonate of lime) in a little water, pouring off a little of the milky fluid into two separate tumblers and adding to one a considerable quantity of tap -water, to the other the same quantity of soda-water. Cover each tumbler with a piece of glass and set them aside, to see in which the carbonate of lime will dissolve first. Since carbonate of lime is the principal constituent of marble and limestone, we can readily understand how these rocks are dissolved by water containing carbonic acid and also why they are deposited on vessels in which such water is boiled. The carbonic acid in soil -water comes mostly from the decay of animal and plant re- mains. It dissolves not only limestone, etc., but practi- cally all other minerals which the plant uses as food. We have already learned (page 34) that seeds give off carbonic acid ; if the root also has this property it must be of very great advantage to it in dissolving the plant-food immediately around it. Does the root give off carbonic acid ? We may test this by growing roots in lime-water. Fill two similar bottles with lime-water (filtered through filter paper or cotton wool) , and cut in the cork of each a notch large enough to receive the stem of a seedling plant two or .three inches long (Peas, Beans, etc., grown in sawdust answer excel- 142 EXPElilMENTS WITH PLANTS lently).- Place the seedling in the bottle so as to sub- merge the roots, and tuck a little cotton around the stem of the plant where it passes through the cork. Arrange the second bottle in the same way, but put no plant in it; simply fill the notch in the cork with cotton. If, now, the roots give off carbonic acid we shall expect to find the lime-water in which they are submerged turning milky after a time, while that in the control bottle remains clear (or shows a slight degree of milkiness due to the carbonic acid of the air). In order to get a better idea of the giving off of acid by the root, we should grow some roots in gela- tine to which litmus has been added. This very inter- esting experiment may be performed in a variety of ways. Some of the so-called "sparkling gelatines" used for cooking are preferable. Dissolve one part of gelatine in about five parts of water. This is most conveniently done by letting it soak in cold water over night and then putting it on a water-bath (see Figs. 51- and 206). When the gelatine is dissolved, add enough litmus dissolved in water ^ to give the gelatine a strong (reddish purple) color. Now add lime-water cau- tiously until the color changes to blue. The gelatine should now be filtered, as described on page 369, and should then be quite clear. Pour some of it into white saucers to the depth of a quarter of an inch; when it has "set," take some Peas (or other seeds, with straight 1 Obtainable at druggists'. THE WORK OF BOOTS 143 caulicles, about an inch long, and thrust the caulicles horizontally into the gelatine so that they are covered by it; arrange several seeds in a saucer in this man- ner, and then cover it with a piece of glass. If car- bonic (or other acid) is being given off by the root, we shall be able to detect it by the change in color (from blue to reddish) of the gelatine around it. The result will be most apparent if the color of the gelatine is as pronounced as possible without being strong enough to make it opaque. A still better method is to stop- per the neck of a small glass fun- nel at the lower end with a small cork, and then pour in the gela- tine until the neck is completely filled. A Pea with a straight caul- icle may then be placed in the fun- nel with the caulicle directed down- ward into the neck and submerged in the gelatine. The funnel should then be covered with a piece of glass, to retain moisture (Fig. 97), and may be conveniently supported in the manner shown in the figure. A simpler method is to use ordinary blue litmus paper, folded as for filtering and placed in a funnel, which is then filled with earth ^ in which seeds are App.iiJitiis to (letcniiiiie whether the root excretes acid; the root is growing in gehitine which has been colored bhie by the addi- tion of litmus. 1 The action of the soil on litmus paper must be tested, since sour soils will redden it. 144 EXPERIMENTS WITH PLANTS planted, as shown in Fig. 82. Water it until the roots have grown down along the litmus paper; then cease watering. In the course of a day or so the result should be plainly visible. This method, while sim- pler, is much less beautiful than the preceding. Another way for testing the roots for excretion of acids is to obtain a piece of polished marble, on which is placed a layer of moist sand about an inch deep, in which seeds are placed. As their roots come in contact with the marble they should, if they excrete enough acid and the time is sufficient (two to six weeks), produce a slight etching of the polished sur- face; if such etching occurs it may be made more striking to the eye by rubbing powdered graphite (obtained by scraping the lead of a pencil) on the mar- ble. It is often more convenient to use a seedling with a stout root (Bean, Scarlet Runner or Pea), which is laid directly on the polished marble, covered with wet filter paper which dips into a dish of water and is pressed down by laying a piece of glass over it. In place of marble we may use a mixture of equal parts of plaster of Paris (previously well heated) and whiting (or fine marble dust) rubbed up together in water and then poured out on a piece of glass and allowed to harden: if this be carefully removed from the glass the surface will have sufficient polish for the purpose. Roots are able to decompose even the hardest rocks, THE WOBK OF BOOTS 145 such as lava and basalt, though of course much more slowly than soft rocks, such as limestone, etc. Clay (which consists of alumina combined with silica and water) is of great service to the plant in "fixing" plant -foods. We may illustrate this by filling a lamp-chimney with clay or good garden soil (so firmly packed that the liquid takes an hour or so to run through) then pour in ammonia water at the top; the water will be deprived of the ammonia in passing through the soil and will come out at the bottom with- out any odor of ammonia. The ammonia has been "fixed" (principally by the compounds of alumina) in the soil so that it cannot be readily washed out by rain, etc. The same thing happens with dung liquor, phosphoric acid (fixed by lime and magnesia and, to a slight extent, by iron in the soil) or potash (for the last two, test with litmus paper) . The carbonic acid of the soil and the alumina and silica of the clay act, not as foods of the plant, but as servants w^hich store food; the clay (and likewise humus) "fixes" soluble food which would otherwise be washed out of the soil by the rain, the acids in the soil (carbonic acid, humus acids, etc.) render this "fixed" food soluble and available to the plant. The air which circulates in the soil is of immense import- ance in promoting chemical processes which prepare and set free plant-food of all kinds and especially nitrogen compounds (see pages 148 and 383) . Where the air sup- 146 EXPERIMENTS WITH PLANTS ply is deficient, tlie soil becomes sour by the accumu- lation of carbon dioxide and humous acids and the roots are killed; at the same time poisonous substances are formed which, if air were present, w^ould be converted into plant-food. Subsoils, when exposed to air, usually change color, an indication of chemical action. The soil is not only a sponge, from ivJiich the plant may obtain tvater, but also a storeJiouse of plant -food, and a laboratory in which plant-food is prepared and dissolved for the use of the plant. The amount of food in the soil depends partly on the kind of rock from which it is derived, partly on its "fixing" power, and partly on the kind and quantity of plants which grow upon it. In all these respects clay is superior to sand^; the rocks from which it comes are richer in food than the quartz from which sand is formed: it has greater "fixing" power than sand^ and produces a greater growth of plants whose decay enriches it still further: decay proceeds more slowly in clay than in sandy soils (since it is colder and wetter), and the products of decomposition are more fully fixed by it. For these reasons (and also because they contain more water) clay soils are richer in plant- food than sandy ^ soils. The best soil is a mixture of sand, clay and humus, which gives abun- dant food and good tilth. 1 The so-called "sand" of arid regions is as rich or richer than clay, since it comes from rocks rich Jn plant-food and is not leached by frequent rains. THE WOBK OF BOOTS 147 Even the best soil becomes exhausted of certam elements in time if crops are continuously removed from it. The deficient food elements must then be re- placed by fertilizers. The chief substances which it is necessary to replace in this way are nitrogen, phos- phoric acid, lime and potash. It is important to understand how best to supply these elements, since this knowledge often makes all the difference between successful and unsuccessful farming. How may nitrogen be supplied to the soil ? Manure piles smell strongly of ammonia gas (which contains over 80 per cent nitrogen), and manure is the most available source of nitrogen as fertilizer. In fresh ma- nure the nitrogen is mostly insoluble, but on stand- ing it decomposes (by the action of bacteria, see page 383) into soluble substances containing nitrogen and into ammonia gas and nitrogen gas. These gases will mostly escape into the air and be lost unless we mix soil with the manure so as to form compost: the soil absorbs the ammonia gas to a marked extent and it is then changed to soluble compounds of nitrogen.^ Air ' The absorption of ammonia gas by soil may be shown by filling a test- tube with mercury, closing with the finger and inverting in a dish of mercury so that it contains no air: now introduce ammonia gas by heating ammonia water in a flask, through the cork of which passes a tube to conduct the gas into the test-tube (heat at first long enousrh to drive out air); when the test- tube is full of gas, introduce a lump of dry clay from below: it will absorb the gas and the mercury will rise. In a control experiment use sand. Cottonseed oil may be used in place of mercury by wedging a lump of clay in the top of an ordinary tube, dipping the tube into a vessel of oil and then corking it at the top with a rubber cork in such a manner that the oil fills the tube nearly to the clay. Raise the tube and introdtice the gas as before. In each case use a control tube containing no soil. Decomposing humus also absorbs a good deal of ammonia gas. 148 EXPERIMENTS WITH PLANTS hastens decomposition, and if it is admitted too freely into the compost heap the gases will form more rap- idly than they can be absorbed: if, on the other hand, air is excluded, decomposition almost stops. Hence decomposition may be regulated by regulating the moisture and compactness of the heap. Since manure contains all the mineral constituents needed by the plant, it is by far the best fertilizer for general purposes. Another source of nitrogen is decomposing plants, such as leaf- mold, peat, etc. This is known as humus. It contains less soluble nitrogen than manure and decomposes more slowly. The humus in decom- posing forms ammonia and sets free acids which pro- mote the formation of soluble plant-food: these acids often change the color of the soil where it is in imme- diate contact with dead roots, etc. Humus may be ap- plied to the soil by plowing in straw, stubble, weeds or special crops grown for the purpose. Rapidly acting nitrogenous manures are urine, guano (manure of sea-birds), saltpeter and Chili salt- peter, all of which contain large amounts of nitrogen in soluble form. They are especially valuable as "forcing" manures and to tide a crop over a critical period. Experiments have shown that not more than one- half to one-third of the nitrogen applied as manure is recovered in the crop: the waste is due partly to the lilBBABT OF N. C. STATB C0LI>B€H5 TH£J WORK OF ROOTS 149 escape of ammonia and nitrogen gas and partly to the rain, which washes the soluble nitrogen compounds out of the soil. Some plants have the power of taking nitrogen 1 % ^ • -Y m 1 i"^ ¥ i m 7 V M i "7~TM M \I/J ^y 98. Tubercles on roots of Clover, from the air by means of the bacteria or minute plants which inhabit tubercles on the roots. Such plants are Clover (Fig. 98), Lupines, Beans and other mem- bers of the Pea family. A crop of Clover or Lupines plowed under and allowed to decay furnishes nitrogen 150 EXPERIMENTS WITH PLANTS to the soil: such crops are called green manures (see page 384). Certain other bacteria living free in the soil take nitrogen from the air and render it available to plants, while still others act on the humus and set free nitro- gen in soluble form (see pages 383 and 384) . Most forest trees have their roots covered with fungi (small colorless plants), which absorb and de- compose the humus in which such trees grow and render it available to the roots. How may phosphorus be supplied to the soil ? Phos- phorus as fertilizer is chiefly obtained from bones. If we soak a bone in muriatic acid it retains its form but becomes like gristle, because the mineral con- stituents are dissolved out: if, on the other hand, we burn it, it also retains its form but becomes brittle because the gristly substance has been burned away, leaving the earthy constituents, which consist of phos- phoric acid and lime. The burned bone may now be pulverized and spread on the land as fertilizer, where it is so very slowly dissolved by the carbonic, humous and other acids in the soil- water as to be scarcely at all available for absorption by the roots. By treating bone with sulphuric acid, we obtain what are known as superphosphates, which dissolve readily in water: when placed in the soil the superphosphates are changed back into the ordinary "insoluble" phos- phates, but they are divided into very fine particles THE WORK OF ROOTS 151 and distributed just where the roots can get at them instead of being in coarse particles on the surface, as is the case with ground bone, burnt bone, etc. Consequently the superphosphates give far better results than ordinary ground bone. Bone meal is usually ground bone, steamed to render it more soluble. It contains both the earthy and the gristly constituents (the latter contain nitro- gen), but on account of its greasiness decomposes slowly and dissolves very little. Bone-black is burnt bone; it contains practically no nitrogen. Certain kinds of slag and rocks rich in phosphoric acid are also used as fertilizers. How may lime be supplied to the soil ? Aside from the bones, we have as sources of lime, marl, marble, shells, land -plaster^ (also called plaster of Paris, gyp- sum and sulphate of lime), limy soils, etc. Lime acts much more quickly if burnt, since it then dissolves in water, while if air- slaked it is more slowly dissolved by the acids in the soil -water. The amount of lime in the soil can be judged by the condition of the well- or spring- water. If this contains much lime it is "hard" and deposits a scale (composed principally of lime) on the in sides of tea-kettles, boilers, etc. It may be softened for cooking purposes by boiling, or for washing purposes by adding soda (or other alkali). ^A story is told of Ben.i. Franklin, that he strewed fjypsum on a Clover field in such away that the words "This has been plastered" appeared conspicuonsly, owing to the more luxuriant growth where the gypsum was applied. 152 EXPERIMENTS WITH PLANTS It may also be softened by adding more lime (about one pint of lime-water to ten pints of hard water). Waters which readily redden litmus contain much lime. In addition to being itself a food, lime sets free potash in soluble condition from the insoluble com- pounds in which it is held, and increases the power of the soil to "fix" potash and phosphoric acid; lime greatly hastens the decomposition of humus and ma- nure, sweetens the sour soil by combinhig wdth acids and destroys many injurious insects and fungi. It improves the texture of the soil by flocculating clay. This may easily be shown by rubbing up clay in water and adding a little of this turbid water to lime-water (use distilled or rain-water as a control) . We may also mix burnt lime with clay and observe the effect on the mass when it hardens. How may potash be supplied to the soil ? Wood ashes contain large quantities of potash and constitute the best potash fertilizers. "Muriate" of potash (potas- sium chloride) and sulphate of potash are also used. Gypsum and lime set free soluble potash in the soil from insoluble compounds, as does also common salt. Crops may be, therefore, supplied with potash by ap- plying lime or gypsum to the soil, where the soil con- tains sufficient insoluble potash. Fertilizers which dissolve quickly when applied to the soil are much superior to those which decompose slowly (unless the cost is too great), since they give THE WOBK OF ROOTS 153 immediate results: the use of such fertilizers (e. g., guano and superphosphates) has revolutionized agri- culture and made high farming and intensive farming possible. For example, we now use from 100 to 200 pounds of superphosphates per acre where a hundred years ago 1,000 to 2,000 pounds of bone were used; i. e., for the same cost it is now possible to fertilize six to eight times as much land. When the soil is deficient in one constituent only, a small amount of fertilizer containing this constituent will give results out of all proportion to its cost.^ Hence it is important to know what elements of plant- food are lacking in the soil before attempting to enrich it. Chemical tests are useful, but in most cases the question is practically settled by applying fertilizers and noting the result. For the soil of our particular region we may arrange an experiment as follows: Lay out beds wherever convenient, or bring in the soil and place it in pots. On each bed or in each flower -pot place a single fertilizer or combination. We may use whatever is obtainable. A good series is General fertilizers: Special fertilizers: {a) Well-rotted stable manure (6) Chili saltpeter (c) Superphosphates {d) Wood ashes (e) Quicklime ^See Bailey: "Principles of Agrriculture," Chapters V and VI; King: "The Soil," Cliapter III; Roberts: "Fertility of the Land"; also articles in the Year- Book of the U. S. Dept. of Aericulture, for 1894 by Wiley and Webber; for 1895 by Snyder; for 1896 by Wiley; for 1898 by Means; for 1899 by Wiley; for 1901 by Woods; for 1902 by Holmes, Woods and McKenney. Lbs. per square yard, . 1 to IX • A to A- 2 4 to -A- . % to X .1% to 4 154 EXPElilAMt:NTS WITH PLANTS Lay out six beds a yard square;^ in each bed place a different fertilizer, working it well into the soil with a spade. The amount to be used may be deter- mined by finding the amount used per acre in practice and dividing this by 4,840 (the number of square yards per acre). The following will give an approximate idea of these amounts: Lbs. per acre. {a) Stable manure .... 5,000 ta 8,000 (&) Chili saltpeter .... 200 to 300 (c) Superphosphate .... 200 to 300 (d) Wood ashes 1,500 to 2,500 (e) Quicklime 8,000 to 20,000 The wood ashes used should be unleached ashes from cordwood (i. e., ordinary wood-stove ashes), in which case they contain about one pound of potashes in twelve of ashes: the rest consists chiefly of lime. If we wish to add potash without lime we may use commercial potashes, saleratus or pearl-ash at the rate of one thirty- sixth to one twenty-fourth pound per square yard: this should be dissolved in two or three gallons of water and applied in liquid form. Inasmuch as the amount needed varies greatly with the character of the. soil, it would be desirable to make a parallel series of three beds for each kind of ferti- lizer, using on one only half the amount given above, on another the given amount, and on the third half as much again as the given amount. In case there seems 1 These .should be separated from each other by an interval of several feel, to prevent the applied fertilizer from diffusing from one plot to another. 77//; woinc OF HOOTS 155 to be an injurious effect due to too mucli fertilizer, try the effect of giving it in two or three applications a few weeks apart. In each bed should be sown Wheat or some staple crop; the watering and other conditions should be alike for all the beds. The result is, of course, strictly valid only for the special soil and special kind of crop used, but if the soil be typical of the region and the crop a staple there the result will be of great value. Moreover, it will also have important general appli- cations. The following rapid method of soil-testing, used by Prof. R. H. Loughridge, of the California Experiment Station, enables one to make a test in half an hour which is sufficient for all practical purposes.^ Nitrogen and Humus. — To 1 part (by volume) of soil add 5 parts (by volume) of 10 per cent caustic potash; this is best done in a test- tube. Heat to boiling point and then set aside for five to ten minutes. If the liquid is black and opaque, it indicates abundant humus and nitro- gen: if the liquid allows light to pass through when held up at a window, the humus and nitrogen content is low; if the liquid is merely yellow, the content of these substances is very low. The test really tells us about the humus only, but, since in all except very arid regions the humus content is an accurate index of the nitrogen content, the test is of great value. Try this test on a soil rich in humus, such as leaf-mold or soil from a grove or forest; also on some sandy soil containing little humus. The color of the soil is a good indicator of the amount of humus it contains; the blacker it is the more humus in it. Phosphorus. — First prepare a standard of comparison as follows: Take about a pint of sand (as pure as possible) and pour on it about three times its volume of dilute hydrochloric acid, made in the propor- tion of one part of acid to four of water. Allow this to stand for an ^The necessary reagents are obtainable at drug stores. 156 EXPERIMENTS WITH PLANTS hour or so, stirring it up from time to time. Next place it in the sink and allow water to run through it for some time, until water, after being thoroughly stirred up with it, no longer gives any acid reaction to litmus. Spread the sand out to dry and when fairly dry take 25 grams for the experiment, setting the rest aside for subsequent tests. The sand thus treated has all the soluble plant- food washed out. We will now proceed to add to it definite amounts of plant-food in order that we may see what results these amounts give in our tests. A good conient of soluble^ phosphoric acid in the soil is one-tenth of one per cent. We will there- fore add this amount to the sand and make a test. To the 25 grams of sand add 5 cc. of % per cent phosphoric acid (made by dissolving one gram of solid phosphoric acid in 200 ec. of water) : this will give .025 gram in 25 grams of sand, or one-tenth of one per cent. Take two grams of the sand which has been moistened with the acid, burn it for five minutes on a red-hot shovel:^ place it in a test-tube and add 3 or 4 cc. of pure nitric acid; heat until it just begins to boil; add 2 or 3 cc. of water and filter. Allow 4 or 5 cc. of water to lun through the sand into the filtered liquid, in order to wash out the acid, and add to the filtered liquid an equal volume of a solution of molybdate of ammonia. (This is made by adding 10 grams of ammonium molybdate to 25 cc. of distilled water; then add 15 cc. of strong ammonia (chemically pure) and 150 grams nitric acid (chemically pure): keep warm and if a yellow precipi- tate occurs pour oflf the clear liquid for use.) Warm until it feels rather hot to the hand, then put it aside to settle. Pour off the clear liquid at the top and transfer the rest to a small funnel,^ the neck of which is not more than one-twelfth of an inch in diameter inside and whi exhales in twenty- four hours carbon dioxide amount- ing to about 1.2 per cent of his own weight, while some bacteria give off in the same length of time twice their own weight of carbon dioxide. It should be remembered that foods contain other combustible sub- stances besides carbon (e. g., hydrogen), and that the above figures leave out of account the energy liberated by burning these substances. They do not, therefore, indicate the total amount of energy set free, but only the principal part. By the method illustrated in Fig. 31, we can measure approximately the volume of carbon dioxide given off, and from this calculate the amount of energy set free from the carbon of the food in a given time. We may also find the weight of the carbon dioxide (one liter of carbon dioxide weighs about two grams) , and so calculate how far the energy set free would raise the organism if applied as mechanical energy. Make these calculations in the experiment described on page 34 (Fig. 31) . The experiment may be modi- fied by setting the bottle containing the seeds upright and bending the tube which passes through the stopper so as to make its free end dip into a vessel containing lye. The giving off of carbon dioxide is accompanied by the absorption of oxygen : this process is called respiration: it occurs in every living cell, since every such cell has need of energy to perform its work. 176 EXPERIMENTS WITH PLANTS In plants each cell probably absorbs its oxygen directly from the air, which penetrates all parts of the plant: in insects a somewhat similar method is found, in that branching tubes convey the air to all the viscera ; while in animals the air is conveyed to the lungs, absorbed by the moist membranes of the lung tissue, whereupon the oxygen combines with the red coloring matter (haemoglobin) of the blood, changing it from dark to bright red. The haemo- globin is carried to all parts of the body (principally in the arteries), where it gives up its oxygen to the various tissues and is thereby changed back to dark red and returns to the lungs (principally through the veins) for a fresh supply. While both plants and animals need all three kinds of food, i. e., proteids, fats and carbohydrates (sugars and starch), they require them in different propor- tions. In dietetics proteids are spoken of as flesh- or muscle -formers, while starch, sugars and fats are said to furnish fuel. This is not by any means true absolutely, but it is probably so in the main. The animal needs much more nitrogen-containing food (proteid) than the plant: the animal excretes large quantities of nitrogen (in the urine and feces), while the plant excretes none. It is interesting, in this con- nection, to compare the composition of the food con- tained in seeds with that contained in eggs. While the white of a hen's Qg^, for example, is almost pure THE WORK OF LEAVES 177 proteid, the yolk is largely fat and oil. The ^gg (minus the shell) contains about 14 per cent of pro- teid and 13 of fat; this is a higher percentage of proteid than most seeds possess, but Peas, Beans, etc., contain as much as 24 per cent of proteid: in oily seeds, fat may be present to the amount of 60 per cent. Of especial interest is the composition of Grains; as an example of these we may take Wheat. Moisten some ordinary Wheat flour with water and place it in a muslin bag. Allow a stream of water to run slowly through the bag while the dough is kneaded with the fingers. Collect the milky fluid which runs through the cloth: this contains the starch, which gradually settles to the bottom. When the starch is all removed there remains behind a mass which, from its glutinous consistency, is called gluten: this is the proteid of the Wheat (apply the proteid tests to it). It forms about 10 per cent of the flour, while the starch forms about 75 per cent. Take some grains of Wheat which have been suffi- ciently softened in water (a few minutes suffices in hot water) to. cut easily, and with a razor cut thin slices across the grain. Place some of these in a drop of water on a glass slide, cover with a cover- glass, and examine with the low power of the microscope. Re- move the cover -glass and add a drop of iodine solu- tion. Notice the blue-black color of the internal part 178 EXPERIMENTS WITH PLANTS of the gram and the intense brown or yellowish brown of the peripheral layer. Place another section on a slide, remove all superfluous moisture with blotting paper, and place upon it a drop of a saturated solution of cane-sugar in water. Then add a small drop of chemically pure sulphuric acid (by means of a pipette or medicine -dropper). Add a second drop of acid if necessary ; use no cover-glass ; be careful that no acid is spilled upon the microscope. Notice the bright red color of the peripheral layer; this indicates the pres- ence of proteid. The outer peripheral layer is much richer in proteid than the rest of the grain: owing to its dark color it is considered undesirable for flour and is separated from the rest of the grain in milling, forming the bran, so that ordinary Wheat flour consists of the internal part of the grain only. As the bran forms about one-fifth of the grain, this is a wasteful process. Whole Wheat flour contains the bran as well as the inner portion and is not only more nutritious but more easily digested and more healthful in other respects. Find out what you can about the process of milling and the use of flour in bread, etc.^ Note the great difference between the seed-leaves of the Horse-bean (Fig. 2) and the Castor-bean (Fig. 4). Can you explain this difference of structure on the 1 See Johnson, "Chemistry of Common Life," Chap. V ; Williams, "Chem- istry of Cookery," Chap. XH ; Williams and Fisher, "Theory and Practice of Cookery." Also an article by Snyder and Woods in the Year-Book of the U. S. Dept. of Agriculture, for 1903. THE WOBK OF LEAVES 179 ground of difference in function ? The Horse-bean seed- leaves are very thick and gorged with food; those of the Castor- bean are extremely thhi and contain prac- tically no food: on the contrary, the nutriment (en- dosperm) is packed around them and it is their task to absorb it. For this purpose they are closely and firmly attached to it and are provided with veins which help to convey the nutriment directly to the germ. As soon as germination begins they enlarge, and so increase their absorptive surface, and they continue to absorb the nutriment long after they have come above ground. When the food has entirely disappeared the husk falls away, leaving the seed- leaves free. The Corn has a seed-leaf (Fig. 6, I) which is both a storehouse and an absorbing organ ; it is the small white, shield- shaped portion of the germ which is closely applied to the starchy endosperm (the endo- sperm is shaded in the figure) . If Sugar Corn can be obtained, a drop of iodine will show that the endo- sperm contains little or no starch, while the seed-leaf is gorged with it. Remove the endosperm from ger- minating plants of Corn and Castor- bean, and com- pare their subsequent growth with that of uninjured control plants. What other familiar seeds have endosperm and ab- sorbent seed-leaves? Notice the curious seed-leaf of the Cocoanut (Fig. 45), which consists of a soft, 180 EXPERIMENTS WITH PLANTS 100. Germi- nating Date, showing the large absorb- ent seed-leaf (si). spongy mass, traversed by fibrous veins whioh convey the food. At first it is very small, but grows rapidly during germina- tion and soon fills the whole cavity. It ab- sorbs the milk and then the meat of the Cocoanut (both of these together make up the endosperm, which is partly solid and partly liquid) . Study also the germination of the Date (Fig. 100), which resembles that of the Cocoanut in the formation of a large absorbing organ. Between the seed-leaves and the next leaves produced by the plant, i. e., the foliage -leaves, there is a great contrast in appearance. Some of the differences be- tween the two, in the Horse-bean, are as follows : Seed-leaves Small Thick Pale yellow Underground Gradually grow smaller Fall off after a time Obscurely veined No stalk No stipules (appendages at base of stalk) Brittle ; not fibrous Opposite Foliage-leaves : Large Thin Bright green Above ground Gradually grow larger Remain on a long time Conspicuously veined Stalked Stipules present Tough and fibrous Alternate THE WORK OF LEAVES 181 Can you explain these differences of structure as due to differences in function ? What is the function of the foliage-leaves? Remove the foliage -leaves (a) from some young plants which have not yet exhausted the supply of food in their seed-leaves; {h) from some older plants in which this supply is exhausted and from which the seed-leaves have fallen away; in each case have control plants for comparison. Does the removal of the leaves check the growth? In which of the two cases {a) or {h) is this most apparent? Does the result indicate that the foliage-leaves, like the seed-leaves, nourish the plant ? Do the foliage-leaves, like the seed-leaves, contain food? Remove some foliage -leaves from a healthy, vigorous plant, preferably one which grows out of doors, with a good exposure to sunlight (a Nasturtium is excellent for this purpose). Remove some of the leaves at sundown. Boil them in water as soon as removed and place them in alcohol; let them remain in it until the green coloring matter is extracted. When this is accomplished (twelve to twenty-four hours is ususually sufficient), rinse in water, and place them in watery iodine solution. Do you find starch pi-esent? (The other tests mentioned on pages 164 and 165 may also be made ; the sugar test should be made on sap expressed from the fresh leaves; the test for oils and fats on leaves dried without being placed in alcohol.) 182 EXPERIMENTS WITH PLANTS Does this starch come from the supply stored up in the seed-leaves, or is it manufactured in the foliage-leaf? Keep a plant in darkness ^ until the leaves no longer give a starch test, then cut off several leaves and place them in tumblers of water; place one -half the number in sunlight and the other half in darkness; take care that the stalk (but not the blade) of the leaf dips under the water (Fig. 101). In two or three days test the leaves which have been in the light. Do you find any starch ? This starch must have been made hy the leaves after they were removed from the 'plant. Now test those which have been in darkness. Is the difference due to the absence of light? We may put this to a final test in a very simple way. Pin corks to the opposite sides of a leaf, as shown in Fig. 102, so as to completely exclude light from the covered portion; over an- other leaf put tin-foil so as to cover both sides, having first cut out letters or figures from the tin -foil on the upper surface; 101. Leaf of English Ivy deprived of starch and placed in water, to see if it can make starch when separated from the plant. 102. Arrange- ment for ex- cluding . light from a part of the leaf. ' The plant may be covered with a box or a cone made of pasteboard. THE WOBK OF LEA VES 183 The cork or tin -foil must not be applied so closely as to prevent the free circulation of air between it and the leaf. The leaves must not be removed from the plant and should be placed where they may obtain abundant sunlight; Nasturtium leaves may be recom- mended for this experiment. In two or three days test for starch. Now of what use is the starch in the foliage- leaves ? Is it absorbed by the plant, like the starch in the seed-leaves? If so, ought we not to find less starch in the leaves in the morning than at sundown (since the starch which is taken away from the leaf during the night cannot be replaced until it is again exposed to light)? Remove some leaves from a plant near sun- down and place them in alcohol ; early the next morn- ing remove some more leaves from the same plant and test both sets of leaves for starch. We may also make the experiment by cutting out a sample from a leaf £tt sundown, to be compared with a sample taken from the same leaf the next morning. Has the starch disap- peared ? Would it have done so had the leaves not been left on the plant! Repeat the experiment, but cut the leaves off and leave them over night in a tumbler of water (the stalks must dip well under the water) . It is now time to see whether we can answer the question, Why are the foliage-leaves and seed-leaves (of the Horse-bean) so different? You can see that it is of advantage to the plant to have the foliage -leaves re- 184 EXPERIMENTS WITH PLANTS main as long as possible on the plant. You can also see why they should have as large a surface as they can, since the more light they catch the more starch they can make. You can see, too, why the seed-leaves 103. Two lots of Squash seedlings of the same age. Those on the left were grown in the light, those on the right in the dark. need to be thick and bulky, so as to store up a great deal of starch. The reasons for the other differences in structure will become apparent as we go on. Perhaps you do not see why the foliage -leaves are green and the seed-leaves pale yellow. You will understand this if you put a few seeds into a pot containing soil or saw- dust and keep it entirely in the dark until the plants THE WORK OF LEAVES 185 are several inches high. The plants grow very tali and slender and the leaves are small and yellow, re- sembling the seed-leaves in color (Fig. 103). Put the plants in the light for a day or so. Test them for starch. Leave them in the light until they turn green. Then test again for starch. Does the result indicate that the green substance is necessary for making starch?^ It is this substance, called leaf-green, or chlorophyll, which is extracted by the alcohol when you test the leaves for starch. Usually it is not formed in darkness. Do you now see why the seed-leaves are not green ? Eemove some of the earth so as to expose them to the light. Do they turn green ? The seed-leaves and foliage -leaves are different be- cause they have different tasks to perform, and their structure must be adapted to the special kind of work they have to do. We may sum this up by saying, function determines structure. A good illustration of this is seen in the history of the Castor- bean seed-leaves. At first they are absorb- ing organs, pure and simple, and their structure is admirably adapted to the work they have in hand. Later, when they come to do the work of foliage-leaves, they grow much larger, thicker, tougher and more fibrous. They spread out above ground in a position to catch the light (Fig. 104), and their internal structure 1 Find out whether leaves variegated with white spots make starch in the colorless portions. 186 EXPERIMENTS WITH PLANTS w ) becomes greatly modified so as to be like that of foli- age-leaves. At the same time they acquire a green color and begin to manufactm-e starch. This principle is so general that we are justified in looking for similar structures wherever similar functions occur. Of what is starch made? We may get some indication of this by decom- posing starch by means of heat in the apparatus shown in Fig. 105. If a test-tube is not obtainable, use any piece of glass tubing (the thinner it is the less liable it is to crack) sealed at one end. Place the starch in it and heat slowly. When the starch begins to turn brown, water will col- lect on the sides of the tube ; this also takes place if we dry the starch to con- stant weight, at the tem- perature at which water boils, before beginning the experiment . The water must, therefore, result from the decomposition of the lo-,. Apparatus for the decomposition bt . ^ -r a 1 i. 4-1 sturch; the giises pass into a tumbler starch. It we conduct the of ume-water. 104. A seedling of Castor- bean, showing how the seed-leaves assume the form and function of foliage-leaves. THE WO UK OF LEAVES 187 gases over into lime-water, as shown in the figure, it will soon ])ecome milky. The starch, therefore, appears to break up into water and carbon di- oxide. What other substances may be formed we cannot determine with the means at our disposal, but these may be neglected, since chemical analysis shows that starch may be considered to result from the union of these two sub- stances. The question now arises, Is there any evidence that the plant makes starch by putting carbon dioxide and water to- gether ? We know from previous experi- ments that there is carbon dioxide in the air, since lime-water exposed to air soon forms a precipitate on the surface. We also know that the leaf is well supplied with water. Is it well supplied with air? The best way to answer this question is to place the leaf in an air-pump, which we may construct as shown in Fig. 106. A disk of rubber (leather or I'awhide may be used) is fitted to the inside of a student - lamp chimney (the larger size. No. 1, is preferable), and pushed down to the neck of the chimney. The 106. Air - pump made from a lampchim- ney, umbrella wire and rub- ber stopper. 188 JSXPEBIMENTS WITH PLANTS chimney is now inverted, the enlarged base is then carefully warmed and melted sealing-wax poured in to the depth of an inch or more. A slightly larger disk of rubber is now prepared by fitting a rubber stopper into the small end of the chimney and cutting a slice from it just above the chinniey's edge (leather may be used if rubber is not available). This rubber disk (r) is to be impaled on an um- brella wire, as shown in Fig. 107 (the larger of its surfaces is to be upper- most), and firmly supported on one side by a wooden disk {w) . The end ^ of a spool is excellent for this purpose ; it should be trimmed down to such dimensions that it will slip easily into the chimney. Below the wooden disk we place a little sealing-wax to keep it from slipping off ; above the rubber disk we also place sealing-wax, as shown in the figure. All the joints must be made air-tight with sealing-wax ; this is facilitated by filling the core of the spool with seal- ing-wax, sharpening the end of the wire, heating it and forcing it through the center of the rubber disk, and then through the core of the spool. We must not be discouraged by a few failures in constructing the apparatus, since, after a little practice, we shall be able 107. Details of piston of air-pump. THE WORK OF LEAVES 189 to make one successfully in a few minutes. When these arrangements are complete, apply vaseline to the edges of the rubber disk and mouth of the chimney (this precaution is important). Pour some water into the chimney and force the piston slowly down until the water stands half an inch or so above the piston; the rubber bends back as it is forced down, allowing the air to escape; when the piston is drawn upward the wooden disk prevents it from bending and so keeps the air from entering. Pull the piston back nearly to the top of the chimney and secure it by means of a clothes-pin, as shown in the figure; a lump of sealing-wax fastened to the wire above the clothes- pin prevents it from slipping back. Any leaks in the piston may now be detected by inverting the chimney; they may be stopped with sealing-wax if they occur in the joints; if the leak occurs around the edge of the rubber disk a larger one must be substituted. On the other hand, the trouble may result from having too large a rubber disk, in which case it will not lie flat and a smaller one must be substituted. In withdraw- ing the piston from the chimney, it is advisable to draw it out slowly, with a twisting motion. A somewhat more convenient form of piston may be made by a mechanic, after the plan shown in Fig. 108. It consists of a brass rod (about one-fourth of an inch thick), with a thread at the end carrying two nuts (Fig. 109, >^,w), a small washer (^^), and a brass 190 EXPERIMENTS WITH PLANTS disk {d) which supports the rubber disk (r) . It has the advantage of allowing a quick change of the rubber. Through a small hole about four inches above A -^. -n 109. Details of piston of the air - pump shown in Fig. 108: (r) rubber disk, (rf) metal disk, {iv) washer, («) nut. the rubber passes a stout piece of piano wire (or any steel wdre suitable for springs) , which is bent as shown in the figure and has its ends passed through an- other hole about an inch above the rubber. When the piston is drawn up, the wire springs out and prevents it from slipping back. When the apparatus is ready, place a leaf in the chimney and cover it with water. Force the piston down slowly until the water stands half an inch or so above it, and then pull it up and secure it in place. Does air issue from the leaf? If so. at what points? Notice especially whether more air issues from the upper or from the lower surface. Allow it to remain until all the air is drawn out, making another stroke with the piston if necessary. Notice the appearance of the leaf when injected with water. Explain its close resemblance to a leaf which has been boiled. If we prevent air from entering the leaf, how will it 108. Air • pump with a u t o - matic arrange- ment to pre- vent the pis- ton from slip- ping back. TRE WOh'K OF LEA VES 191 affect starch formation ? Keep a i)laiit in the dark until the leaves no longer give a good starch test. Remove the plant to the light and treat several of its leaves by covering both sides of a portion of the leaf with vase- line. Remove some of the untreated leaves from the plant, and place them in tumblers of water so that the stalk of the leaf and about half of the blade dip under water. Place all of the leaves where they will get abundant sunlight. In two or three days, test all the leaves for starch (removing them from the plant at sundown). Do you find starch in the portions from which air has been excluded ? Does the leaf decompose carbon dioxide? Invert a large bottle or fruit -jar, as shown in Fig. 110, over a lighted candle set in a cork floating on water. After a short time the candle goes out, indicat- ing that some of the oxygen of the air has been converted by burn- ing into water and car- l)on dioxide. Withdraw the candle by means of a string attached to it and introduce a leaf, the stalk of which passes through a hole in the center of a cork, as shown in the figure: do this without lifting the bottle above the surface of the water.. The experiment should be commenced in the 110. Arrangement for investigating the power of a leaf to " restore " air which has been "vitiated" by a burning candle. (Sec- tional view.) 192 EXPERIMENTS WITH PLANTS i morning and continued until near sundown (the leaf should receive sunshine in the meanwhile: prolong the experiment two days if necessary). We then lift the jar very carefully, so as not to admit any air, and introduce a lighted candle, as before. If it does not imme- diately go out, it indicates that some of the carbon dioxide has been absorbed by the leaf and decomposed, with the re- sult that oxygen is set free, so that further combustion is possi- ble. As a control use a bottle with no leaf in it. Chemical analysis shows that if carbon dioxide and water unite to form starch, oxygen must be given off, just as we have found in this ex- periment. Another way of testing this matter is shown in Fig. 111. A plant which naturally grows submerged in water is put into water in a glass jar and placed in sun- light. The gas evolved is col- lected in the funnel, which is 111. Arrangement for collecting the first filled with Watcr by SUb- ^^^uo^^.y...i.r.^l.niin ^^^^^^J^g ^^ aud COrkiug it THE WORK OF LEA VES 193 under water. When sufficient gas has collected, the cork is removed from the neck and a glowing splinter is quickly thrust into the neck. If it glows more brightly or bursts into flame, it indi- cates that the gas in the funnel is richer in oxygen than ordinary air, and, consequently, that the plant is giving off oxygen. These results, taken in connection with the fact that the formation of starch is prevented by depriving the leaf of air, make it highly probable that the leaf makes starch by causing car- bon dioxide and water to unite, accom- panied by the giving off of oxygen. It would lend greater certainty, how- ever, if we could deprive the leaf of carbon dioxide without at the same time depriving it of the other constitu- ents of air. We may do this by means of the apparatus shown in Fig. 112. fruit -jar is fitted with a stopper of cork or wood, through which passes a funnel filled with lumps of lye which will absorb the carbon dioxide from the air as it enters the bottle. On the bottom of the bottle we place some lumps of lye and a small bottle of water in which is a leaf of Nasturtium (or some other Jeaf which normally gives a good starch test) which has 112. Apparatus for growing a leaf in air deprived of car- bon dioxide: lumps of lye are placed in the funnel and on the bottom of the bottle. A bottle or M 194 EXPElilMEXTS WITH PLANTS been deprived of starch in tlie way previously described. Place the stopper in position and close all joints air- tight with vaseline. Prepare a control in which the lye is replaced by some indifferent substance, such as pebbles or broken glass. After a day or so of expo- sure to sunlight, test both leaves for starch. Has the leaf which is deprived of carbon dioxide (but not of the other constituents of the air) been able to make starch ? The leaves, by their power of giving off oxygen, "restore" foul air and make it fit for animals to breathe; this is especially noticeable in aquaria where, if a proper balance be struck between animal and vegetable life, the air contained in the water does not need to be renewed. Ordinary air contains about four- hundredths of one per cent carbon dioxide. It is calcu- lated that a square meter of ordinary leaf surface decomposes every hour in sunlight as much carbon dioxide as is contained in 1,000 liters of air. To offset this, carbon dioxide is continually poured into the air by combustion of all kinds as well as by the respira- tion of plants and animals. We have learned (pages 34 and 142) that roots and germinating seeds give off carbon dioxide just like animals. Leaves give off oxygen only in the sunlight. Do they give off carbon dioxide at other times, just as roots do ? We may easily investi- gate this by partly filling a bottle or jar wdth water, putting in as many leaves (with their stalks dipping in THJS WORK OF LEA VES 195 water) as it will conveniently hold, and then inserting a small vial partly filled with clear lime-water. Set the bottle away for a day or two in darkness. Prepare a control bottle in which no leaves are placed. Both bottles should be sealed air-tight. In which is more carbon dioxide produced, as shown by the lime-water test? As the result of this experiment we may say that in the dark a green plant behaves in regard to respiration like a colorless plant or an animal. There is a popular belief that plants are unhealth- ful in sick-rooms at night because they vitiate the air. As a matter of fact, it would take a very large number of plants to do as much harm in this respect as a single candle. Since the leaves have work to perform during the day, as well as during the night, we should expect to find the process of combustion going on then also, since it is this which furnishes energy to do work ; yet we have found that carbon dioxide is used up and oxygen produced by the leaves in daylight. Careful determina- tion of the relative amounts of the gases has shown that both processes take place simultaneously; the sunlight furnishes energy for the work of starch- making which results in the production of oxygen ; the combustion which results in the production of carbon dioxide furnishes energy for work of other kinds. Since the energy which is absorbed in the making of starch is all given out again when the starch is 196 JSXPEBIMENTS WITH PLANTS burned, it may be considered to be equal to the heat of combustion (or "fuel value" of starch) which is about 4.5 large Calories for every gram of dry starch. If we estimate that a square meter of leaf surface produces one gi-am of dry starch every hour in sunlight, it must in so doing absorb the energy of the sunlight to the extent of about 4.5 large Calories. But this amounts to only about one -half of one per cent of the total energy which falls upon it during that time in the form of sunshine. It should be noted that it is principally the red rays which bring about the chemical changes here considered, just as in the eye they, more than others, bring about the chemical changes which result in the sensation of sight, and for that reason appear much brighter to the eye than the blue rays. The latter, as is well known, are the ones which bring about the chemical changes in a photographic plate. What is the nature of the openings through which the air passes? With a sharp knife, make a shallow cut and tear off a small piece of the delicate, semi-trans- parent epidermis from the lower surface of the leaf,^ place it on a glass slide in a drop of water and cover with a thin cover- glass. Examine first with the low (one-half inch or two-third inch objective) and then with the high power (one-sixth inch or one-eighth inch objective) under a compound microscope. The epi- iThe best leaves for this purpose are those of a Lily (or any plant of the Lily family, e g., Hyacinth, Narcissus, etc.). Iris, a Grass (especially the Oat), Wandering Jew, Anemone, etc. THJi] WOMK OF LEA VES 197 dermis is then seen to be made up of a series of cells, all lying in one plane, with their edges closely joined except at certain points where openings exist (Figs. 113 and 114, s). Each opening (called a stoma, plural stomata) is surrounded by crescent-shaped cells called the guard-cells (r/). The openings are filled with air, giving them a dark appearance. Compare the num- ber of openings on the upper and the lower surfaces. Does it correspond with what you have already learned by means of the air-pump! Now let us examine the interior of the leaf.^ For this purpose roll a leaf tightly, hold the roll firmly be- tween the thumb and forefinger of the left hand, and with a sharp razor, moistened in water, cut the thin- nest possible slices across the leaf; the slices should be so thin as to appear almost or quite colorless. Transfer some of these with a wet camel's -hair brush to a drop of water on a slide, cover and examine as before. The epidermis of the upper surface (Fig. 113, e) appears as a nearly colorless row of cells. The function of the epidermis is to protect the leaf from drying up, as well as against the attacks of parasites, insect enemies, etc. For this reason its outer wall (cuticle, Fig. 114, c) is thickened and made water-proof (or almost so). Below the epidermis appear long, ^ The leaf of the common Yellow Mustard is chosen here because it is easy to obtain and easily prepared, while showing the parts of the leaf with great distinctness: leaves of Beet, Beech, etc., are excellent: any thin, tender leaf may be used. is 9 £l 1- 200 EXPERIMENTS WITH PLANTS cylindrical cells, like a lot of tubes standing on end, closely packed together. These cells (p, called the pali- sade cells from their resemblance to a palisade) contain a good deal of leaf -green, or chlorophyll, in the form of drops or granules (these are called chlorophyll granules, cliL gr.) thickly scattered upon the inner sur- faces of the walls of the cells. Below these is the spongy tissue {sp) ^ composed of loosely joined cells, with large air-spaces between them. Under the micro- scope the air- bubbles in these spaces have a dark appearance. Finally comes the lower epidermis, re- sembling the upper, but provided with abundant sto- mata, one of which is shown cut across at (s). Notice the opening with the two guard-cells, seen in section, and, just above the opening, a large air-chamber (a) which communicates with the air-spaces of the spongy tissue. The air, therefore, may penetrate through the stomata to the interior of the leaf, where a great ab- sorptive surface (many times greater than the external surface of the leaf) is spread out. As the cells of the leaf are full of liquid, this surface is constantly moist, and therefore in the best condition for absorbing carbon dioxide, just as the moist surfaces of the lung-cells are in condition to absorb oxygen. If these surfaces should become dry they would lose their power of absorbing gases almost entirely. • The leaf is, therefore, an absorbing organ, as well as the root: the one absorbs air- food (carbon dioxide), THE WORK OF LEAVES 201 the other soil- food (water and the substances dissolved m it) . These two kinds of raiv^ or crude food meet in the leaf, and there unite to form elaborated food, i. e., sugars, starch, fats, oils, proteids, etc. The leaf absorbs not only food, but energy, i. e., sunlight, which is needed to manufacture elaborated food. The absorption of light is the work of the green coloring matter, the chlorophyll, and especially of the palisade cells, which are on the upper side of the leaf, directly exposed to the light. If we examine a section of a leaf which exposes both sides equally to the light (such as Iris, Gladiolus, etc.), we find palisade cells on both surfaces (Fig. 114) . In many leaves there is but a single row of palisade cells, while in others we find a double row (Fig. 113) , which results in the more complete absoi'ption of light. The ability of leaves to absorb light is easily tested by making a tube (about an inch in diameter and twelve inches long) of card- board, directing it toward the light, placing a leaf over the end and looking through it. Find out how many thicknesses of leaf are necessary to absorb the light completely. Within the tiny chlorophyll gran- ules, the chlorophyll is scattered in the form of very minute drops (Fig. 115. a single ohiorophyii grain containing very 115), which arrangement enormously young starch-grains .-it ^' " '^ IS dotted to indicate the increases the absorptive surface of phyV Vs^'disVrfhiued Tn ,^^^ in t xi'i the form of very mi- the chlorophyll, and consequently its nute drops. 202 EXPERIMENTS WITH PLANTS ^^r ^^^s"^ efficiency. In order to do its Avork of starch-making, the chlorophyll must absorb rapidly large quantities of carbon dioxide, as well as large amounts of energy. The union of carbon dioxide and water under the influence of the absorbed energy (sunlight) produces grape-sugar, which is stored up in the form of starch, or else diffuses out into the cells and thence to the veins. The transfer to the veins is greatly assisted by the funnel-shaped collecting cells {col.) and the con- veying cells {conv. Figs. 113 and 114). If we examine (with the high power of the micro- scope) a section of a leaf which has been removed from the plant toward the close of the day, we find the chloro- phyll granules full of small white glistening bodies which turn dark when we place the section in iodine solution (Fig. 116). These are the small grains of starch, which have been formed by the union of carbon dioxide and water under the in- fluence of sunlight. During the night they are again changed to sugar, which travels along the veins down into the stem and root. This movement of sugar takes place during the day also, but the sugar is then manufactured faster than it can be 116. A single cell of a leaf with chlorophyll grains (c/ii.flrr), con- taining starch-grains [st. gr.) THJi] WONK OF LKA VES 203 carried away, and it is consequently stored up as starch. Every one has noticed that leaves removed from the plant quickly dry up unless placed in water. It would seem that they must lose water rapidly by evaporation. Is this normally the case when they are growing on the plant? Obtain two watch-crystals of about the same size (pieces of mica or glass may be used if the watch crystals are not obtainable) , and fasten them to opposite sides of a leaf by a piece of wire bent to form a clip, as shown in Fig. 117. Seal the joints between the leaf and the glass air - tight with vaseline (the leaf should not be removed from the plant and care should be taken not to injure it in any way) . If the leaf gives off water- vapor, it will condense in the form of drops inside the watch-crystal, especially when cooled. Examine the leaf from time to time and re- move to a cool place if necessary. Do you find that the leaf gives off water ? ^ From which side is more given off ? Is this the side on which the greater num- 117. Arrangement for determining whether a leaf gives off water vapor. 1 A more quick and accurate method i.s to cover the leaf with paper im- pregnated with cobalt chloride (4 to 5 per cent dissolved in water); this is dried over a lamp until it appears intensely blue. It is then placed on the leaf and covered with mica or glass held in place by a clip, as shown in Fig. 117. If water-vapor is escaping from the leaf the paper quickly assumes a reddish tint. 204 EXPERIMENTS WITH PLANTS ber of stomata occur (as shown by the air-pump or by microscopical examination) ? Does the water escape through the openings only? Select a plant in which there are very few stomata, or none, on the upper surface of the leaf (many species of Begonia, Holly, Willow, Poplar, Lilac, Tulip Tree, Mahonia, Oleander, Scarlet Eunner, etc.). After mak- ing sure, by testing with the air-pump or by examina- tion with the microscope, that the stomata are absent from the upper surface, remove several leaves from the plant and treat one lot by covering both the stalk and the lower surface of the leaf with vaseline or grafting- wax ; treat another lot by covering the stalk and the upper surface of the leaf ; treat a third lot by cover- ing the stalk and both surfaces of the leaf. Attach to each leaf a stout piece of thread (of about the same weight in each case), and weigh (taking care not to rub off any of the vaseline in the process) . Suspend the leaves by the attached pieces of thread, and re- weigh from time to time. Does it appear that much more water has escaped from the under surface than from the upper! Has there been any loss from the leaves which were entirely covered? If so, it indicates the amount of experimental error due to the incomplete sealing with vaseline, and this should be diminished as much as possible by any suitable means. (It must be remembered that unless care is taken some of the vaseline may rub off, or in a sunny place some may THE WOBK OF LEAVES 205 melt and run off if it is too thickly smeared on ; for this reason grafting- wax is better.) In examining the epidermis of leaves under the microscope, we find the stomata sometimes open and sometimes closed, as in Fig. 113. Since, as we have already found, all, or nearly all the water passes out through the stomata, we may judge whether they are open or closed by the amount of water the leaf gives off. This may be measured by the methods just described or by means of the apparatus shown in Fig. 119. A leaf is removed from the plant and slipped into a cork borer (just large enough to re- ceive it) , which has been previously forced through a rubber stopper, as shown in Fig. 118. On withdrawing the- cork borer, the leaf will be found firmly fixed in the rubber stopper. In this way a leaf or a stem may be quickly fixed air-tight in such a stopper without injury. A piece of small glass tubing, about fourteen inches long (the smaller the bore the better) , bent as shown r 118. Method of inserting a leaf-stalk air-tight in a rubber stopper. 206 EXPEBIMENTS WITH PLANTS in Fig. 119, is now forced through an opening in the stopper and the stopper is slowly forced into the neck of the bottle, w^hich is filled to the brim with water. Enough water will usually run into the tube during this operation to fill it completely; should this not happen, fill the tube with water before forcing the stopper into the bottle and keep the water from running out of the tube during the insertion by stopping one end with the finger. To test whether the stopper is tight, dry the joints and blow at the free end of the tube to see whether water can be forced out. If the joints are tight, set the apparatus in a cool, shady place, and let it stand until a little of the water has been absorbed by the leaf and a small bubble of air (one -fourth to one-half an inch long) has been drawn into the end of the tube. When this has occurred, dip the end of the tube into water, as shown in the figure, attach a ruler to the glass tube and, by means of a watch, time the progress of the bubble along the tube (which should rest in a horizontal position) . When the bub- 119. Apparatus for measuring the transpiration of a leaf and the degree in which it is affected by sunlight, wind, rolling the leaf, etc. THl!J WORK OF LEA VES 207 ble has passed into the bottle, admit another by raising the end of the tube above the water for a short time. When the rate of water absorption and evaporation (usually called transpiration) becomes fairly constant, transfer the apparatus to the sunlight and take observa- tions (make the experiment also with a leafy branch). If an increase in the rate of transpiration occurs in the sunlight, it may be attributed either to the opening of the stomata or to the increase in trans- piration (through the already open, or partly open, stomata) due to rise in temperature. In most cases both causes cooperate to increase the amount of tran- spiration. We can see why it is of advantage to the plant to have the stomata open in sunlight, since it is then that starch-making goes on, and if the openings of the leaf were closed the absorption of carbon dioxide would be impossible. We can also see why the more rapid evaporation of water which occurs when the stomata are open may be an advantage, since it leaves behind in the leaf mineral substances (just as' boil- ing water in a tea-kettle leaves behind a crust of lime and other mineral substances which are dissolved in the water) which, as we have already learned, are of value to the plant. The stomata usually close when the supply of water begins to run low, and we can readily see why this is advantageous, since otherwise the leaf would soon wilt, and may even do so in spite of the closing 208 EXPERIMENTS WITH PLANTS of the stomata, as we may observe on very hot days, and especially in hot dry winds. Place the apparatus out of doors in the wind (the hot- ter and drier the wind the better) , and observe the effect on the rate of evaporation. On the other h and, the sto- mata open as soon as favorable conditions for starch- making (i. e., the requisite supply of water, sunlight and warmth) return. The plant has in the stomata and guard -cells an automatic apparatus of great efficiency, yet wonder- fully simple, on whose proper working its very life depends. If we examine a stoma carefully, we see the two sausage -shaped guard- cells filled with green chlorophyll granules, while the surrounding epidermal cells have none. It is on this that their opening and closing depends. Under conditions favorable for starch- making, the guard- cells produce sugar, which 120. Diagram showing in section and surface view the form and position of the guard-cells when closed (heavy lines) and open (light lines). THE WORK OF LEAVES 209 draws water from the neighboring cells and causes the guard- cells to expand and open the stomata. When, on the other hand, unfavorable conditions come, the sugar -making ceases, and if the water supply begins to run low the guard- cells collapse and close the stomata. The manner in which the opening and closing is effected may be explained by reference to Fig. 120, which shows a stoma of Iris in both the closed and the open position. The guard- cell (as seen in cross- section, Fig. 121) has a thick wall on the side toward the stoma and a thin wall on the opposite side. According to mechanical laws, when such a structure expands from internal pressure (due to the absorption of water) the thinnest or weakest side must bulge outward, causing the cell to curve (as shown by the light lines in Fig. 120) . When the guard-cells expand, 121. Diagram of a stoma of Iris (seen in section) showing guard-cells and neighboring cells of epidermis. 210 EXPKBIME^TS WITH PLA.XTS 122. Artificial stoma and guard-cells. therefore, they curve away from each other, leaving the stoma open; when they collapse again, it closes. Various modifica- tions of this mode of action occur. The general relations of the guard -cells and surrounding cells may be seen in Fig. 121. If we tear off a strip of epidermis from a leaf of a Lily or Amaryllis and mount it on a slide in water, we shall (if the plant is well supplied with water and exposed to sunlight) probably find the stomata open : if now, we lift the cover -glass and intro- duce a drop or two of sugar or salt solu- tion, the water will be withdrawn from the guard- cells and they will at once collapse and close the stomata. The principle by which the stomata open and close may be illustrated by means of the model shown in Fig. 122. A piece of quarter -inch, thin -walled, black rubber tubing, which is not so old as to have lost its elasticity, is reinforced throughout its entire length, with the exception of half an inch in the middle, by a strip of elastic band (about one -eighth inch wide) firmly attached with rubber cement. It is then bent in the middle, as shown in the figure, so as to bring the reinforced walls facing THE WORK OF LEA VES 211 each other, and is secured at the bend by a clothes-pm. The free ends are connected to the arms of a glass U-tube which have been bent near together. The end of the U-tube is connected by a stout piece of rubber tubing with a bicycle pump. The connections are all tightly tied with twine or elastic bands, and air is pumped in. As the pressure increases, the outer, thin- ner walls of the rubber guard-cells bulge outward, causing them to curve and leave the stoma or space between them ppen ; when the pressure is released they collapse and close it. The degree of opening or closing is great or small accord- ing to the elasticity of the rubber, the rigidity of the reinforced wall, etc. If a U-tube is not at hand, use in place of it two short glass tubes inserted in a rubber stopper (enlarged a little at the end to prevent them from slipping out), as shown in Fig. 123; the cork is inserted in a piece of glass tubing, at the other end of which is a similar cork pierced with a glass tube which is connected with the pump. A wire may be passed over both stoppers to hold them firmly in place* The danger of drying up is the most serious with which the plant has to contend, and nothing affects the health of a plant so quickly as lack of water. Plants suffering from dryness show very character- nn ijl /\ 123. Modifica- tion of part of the appara- tus shown in Fig. 122. 212 EXPERIMENTS WITH PLANTS istic symptoms i. e., wilting, drooping and yellowing of the leaves, followed in time by the fall of the leaves, beginning usually with the oldest. In regard to the cause of the falling of leaves in autumn, see page 332. It is interesting to note that when the leaves fall away they leave a smooth scar ; this is due to the formation of a layer of loose cells just at the base of the stalk (as may be easily seen in a section under the microscope) . If leaves of the Kentucky Coffee Tree, Tree of Heaven (Ailanthus), Walnut or Ash are wrapped in a moist cloth and placed in the dark, this layer forms very rapidly (in the Coffee Tree within forty- eight hours), with the result that the leaflets fall off, leaving a clean scar. Is such a scar formed in most monocotyle- donous plants, such as Corn, Grasses, Lily, etc.? Plants which are suffering from drought should be watered, set in a cool, moist place and sprinkled with water. If the plant has suffered severely it may be necessary to remove some o\ the older leaves. Cut- flowers which have wilted may be placed in water and covered with a wet towel, when they will quickly revive. Leaves have various devices to protect themselves against the wilting due to heat and dryness. (What leaves remain fresh longest when removed from the plant for purposes of decoration? Why?) Some of these are obvious, and we may test them by means of the apparatus shown in Fig. 119. Roll the THE WORK OF LEA VES 213 leaf or fold it two or three times, after the fashion of a fan, and secure it by a rubber band. How does this affect the rate of transpiration ? Do you find devices of this kind among plants? Many Grasses (e. g.. Corn) roll up their leaves in the heat of the day or fold the stomatic surfaces together so as to diminish transpi- ration. Young leaves are far more easily injured by drying agencies than old ; they are nearly always rolled or folded (as they issue from the bud) in a manner that greatly reduces evaporation, and it will be noted that if one surface is more exposed than another it is the stomatic surface which is protected. Make obser- vations on this point: study especially the Tulip Tree, Canna, fruit trees, Maple, Ferns, etc. (see Gray's Les- sons, under vernation or aestivation). Many leaves are permanently rolled (Heath plants, etc.). Again, we may cover the leaf in our apparatus with cotton wool, pressed down tightly against the leaf by means of wire netting laid over it and held in place by clothes-pins. We may cover both sides of the leaf or the stomatic surface only, and may note the rate of evaporation in both sunlight and shade. Do you find coverings analogous to this on leaves? Study the leaves of the Dusty Miller, Horehound, Sage, Wormwood, Mullein, Cinquefoil, etc. Many leaves have a hairy covering during their youthful, sensitive period, but lose it as they grow older (Horse-chestnut, Beech, Service -berry. White Poplar, Pear, etc.). 214 EXPERIMJ^NTS WITH PLANTS We have already learned how a coat of vaseline stops evaporation from the leaf. Do you find leaves coated with water-proof substances, such as resins, gums, varnishes, wax, etc.? Notice especially the varnishes, gums, etc., on buds, which prevent them from drying up. Remove the scales, which are covered with var- nish, and note the result. Many leaves have a coat of varnish during their youthful period but dispense with it as they grow older and less sensitive, and the epi- dermis thickens (Cherry, Poplar, Birch, Alder, Peach, etc.). Take two leaves of the same size which are thickly coated with wax (the young horizontal leaves of Euca- lyptus are especially good) ; remove the wax fron one by rubbing with a soft cloth ; seal the cut surfaces with vaseline, place a leaf in each pan of the balance, and balance them by adding weights to the proper pan. Observe from time to time which is losing water more rapidly, as indicated by the rising of the pan. It will be noticed that leaves (Iris, Bamboo, Dusty Miller, Oxalis, Silver-leaved Poplar, Blackberry, etc.) which have a covering of hairs, wax, etc., have a glis- tening silvery appearance under water ; this is due to a layer of air which is held tenaciously. On dipping such leaves in water we find that the stomatic surface is so protected that it does not become wet; this is an advan- tage, since, if water penetrated into the stomata, it would completely prevent the passage of air and the THE WORK OF LEAVES 215 absorption of carbon dioxide. One of the great dan- gers to plants in the neighborhood of factories, etc., is the choking of the stomata with soot a,nd dust. Wherever there is much fine dust, plants suffer in this respect unless frequently washed by rain.^ House - plants are much benefitted by an occasional washing of the leaves with water. We can readily understand that it is an advantage to have the stomata placed on the under side of the leaf, since they are then better protected against dust, rain, direct exposure to the sun, etc., and this is the position in which they principally occur. Other devices for reducing evaporation that may be studied are the sinking of the stomata in pits (Olean- der) or channels (Cytisus, Broom, etc.), the reduction in the number of the stomata (universal in plants growing in dry situations), the reduction of leaf sur- face (in succulents, such as Hen -and -chickens. Live- forever, Ice Plant, etc.), dispensing with the leaves during a portion of the year (some Switch Plants), or complete and permanent loss of leaves (Cacti) . Obtain any leaves you can of these kinds, and test the amount of evaporation which goes on in them. For this purpose 1 Plants are sometimes injured when sprayed with oily liquids (to de- stroy insect pests), by the clogging of the stomata with oil. The result is that the leaves turn yellow and begin to drop off soon after the spraying occurs. The fumigation of plants with poisonous gases (to destroy insects) must be carried on at night when the stomata are closed. Otherwise the plant is killed. 216 EXPERIMENTS WITH PLANTS remove the leaf, weigh, seal the cut surface with vase- line or grafting wax and reweigh; expose the various leaves simultaneously to the same conditions for the same length of time (five or six hours in sunshine), and weigh again; divide the loss in weight (i. e., the difference between the results of the second and third weighings) by the original weight (results of the first weighing) to get the percentage of loss. Compare the percentages for the different leaves (e. g., a leaf of Squash with that of Hen -and -chickens). Plants which have adapted themselves to dry situ- ations have, as we have seen, a surprising ability to retain water. In all of the thick -leaved, fleshy plants, the so-called succulents, sufficient water is stored up in reservoirs (consisting of spongy colorless tissue) in the interior of the leaf to last from one season of rain to another, often for a period of months. Such is the case with the Hen -and -chickens. Live-forever, Ice Plant, etc. In many of these, gummy, mucilaginous substances or hygroscopic salts are present which hold the water tenaciously. Try the experiment of exposing on a piece of glass drops of pure water, together with drops of fluid expressed from such leaves or drops of a strong solution of salt, sugar or gum arable. Which is the first to completely evaporate? Along with modifications in structure go changes of position (e. g., from horizontal to vertical) which di- minish evaporation. Notice the vertically placed leaves TEE WORK OF LEAVES 217 of Iris, Gladiolus, Eucalyptus, Acacia, etc. Observe the behavior of Grasses in this respect. Many young leaves remain vertical until their epidermis becomes thick enough to prevent evaporation, when they change to the horizontal position. Note as mciny cases of this as you can. Many adult leaves change their horizontal position to the vertical one in the middle of hot summer days, when the light and heat are too in- tense. Study the familiar plants about you and find as many cases of this sort as you can. We have already learned (page 124) that plants may have their roots submerged in water and yet suf- fer from lack of it. This is because there are sub- stances in the water which attract it away from the plant. Try the experiment of placing leaves (or whole plants) with their stalks dipping in strong salt solu- tion. Plants in alkali lr.nds and along the seashore, where the water is brackish, suffer in this respect and consequently show the same devices to diminish evapo- ration as we find in plants of desert or semi- arid regions. While it is an advantage to have the leaf placed vertically when the sun's rays pour straight down, making the light and heat excessive, it will, under ordinary circumstances, be far better to have the leaf placed at right angles to the light, since in this posi- tion the leaf can absorb the maximum amount. The same leaves which in the excessive heat of midday 218 EXPERIMEXTS WITH PLANTS place themselves vertically (i. e., parallel to the light) will be found in the morning and afternoon with their faces perpendicular to the light; in this way they fol- low the sun all day, facing eastward in the morning and westward in the afternoon (plants of the Pea family, some Mallows, etc.) . What common plants do this? Study Clovers, Lupins, Melilotus, etc. Notice the cushion - like joints, or hinges, on which the leaves 124. Acacia leaf, night or sleep position. tum. Study the "sleep -position" of leaves at night in Oxalis, Clover, Acacia (Figs. 124 and 125), also in seed-leaves of Sunflower, Squash, etc. This position may be of advantage in reducing evapora- tion or in diminish- ing the loss of heat, or both. It may in many cases be produced artificially by putting the plants in dark- ness for a time dur- ing the day (Oxalis, Acacia, Clover, etc). ■^:^^' X2b. Acacia leaf, clay position. THE WORK OF LEA VES 219 The ability to turn toward the light must be extremely useful. Do all leaves have this power? Experi- ment with as many plants as you can, placing them before a window, or shading 126. Leaf mosaic of ivy Geranium. them on one side as they grow out-of-doors. Notice any cases where the plants grow near walls or are for any reason shaded on one side. Study especially climb- ing vines, like the En- glish Ivy, Boston Ivy, etc. Do the leaves in these plants seem to avoid shading each other? How do you explain this? When leaves cover over the available space so as to catch all of the light without interfer- ing with each other, their appearance sug- gests a mosaic (Figs. 126 and 127), and is 127. Leaf-mosaic of Chestnut. Called a leai-mOSaiC. 220 EXPERIMENTS WITH PLANTS ^^^^pp' What are the most perfect leaf- igt^T^ mosaics you can find? Notice the difference between the arrangement of leaves on hori- zontal and vertical shoots of the same plants (see Figs. 128, 129 and 130). Which arrangement re- quires the greatest bending and twisting of the leaves out of their original position? In what part of the leaf is the mechanism located by which these bending and twisting movements are accomplished? Study espe- cially in this respect the leaves of the Scarlet Eunner or other bean, and examine the cushion- like swelling at the base of the stalk of each leaf and leaflet. Inasmuch as a tree forms its branches and leaves with reference to the light, prevail- ing winds, etc., it follows that when it is transplanted its orientation should not be changed, i. e., the same side should be toward the north both before and after planting. 129. Appearance of the Study both trees and shrubs (the branch shown in rig. n ■, . n\xT 128 when viewed from smaller plants as well), to discover above. 128. Upright branch of Peri winkle ( Vinca). THE WOBK OF LEAVES 221 on which side their greatest development occurs and how this is affected by light. The leaf, more than any other part of the plant, needs protection against animals, ^^ insects and para- ^ sites. Devices for this purpose are found in great variety. Make a practical study of the following forms of protec- tion. ( a ) Prickles, spines, thorns, hairs, etc. These protective weap- ons are borne by both leaf and stem, and may be outgrowths from the surface (prickles of Rose and Thistle, stinging hairs of Nettle, which break off in the wound and discharge an irritating poison into it, hairs of Mullein, which are irritating to the mouth, etc.), or the spiny tip of the leaf (Thistle, Spanish Bayonet, etc.), or th6 teeth of the edge of the leaf KiO. Horizontal (trail- ing) branch from the same plant from ■which the upright branch shown in Figs. 128 and 129 was taken. 222 EXPERIMENTS WITH PLANTS (Sedges, Grasses, Holly, Century Plant), or the stip- ules of the leaf modified into thorns (Locust), or the whole transformed leaf (Barberry), or a transformed branch (Hawthorn, Honey Locust). {h) Bitter or poisonous substances. It would be very interesting to know how animals, both wild and domestic, learn to avoid poisonous plants. Many plants have a disagreeable or offensive odor which warns them away, as the Jimson Weed or Thorn Apple, and many others. Many have a disagreeable taste, e. g.. Poppies. But there are many others which to us have neither disagreeable taste nor odor, and yet are avoided by grazing animals of all kinds. In this respect their in- stincts are superior to ours. There are some poisonous plants, notably the "loco weeds," which are eaten by domestic animals and which produce dizziness, vertigo and insanity. It is stated on good authority that the loco habit may be taught by a single animal to a whole herd, and that an animal which has been appar- ently cured of the habit by treatment is never entirely trustworthy thereafter.^ In general, however, poisonous plants are avoided, and the same is true of many plants which are bitter or disagreeable without being poisonous (e. g., Worm- ' The annual loss from poisonous plants on the western stock ranges is aVjout $400,000. See the article by Chestnut, in the Year Book of the U. S. Department of Agriculture for 1900. TEE WO UK OF LEAVES 223 wood, Ragweed, Boueset, etc.). There can, therefore, be no doubt of the efficiency of this kind of protection. (c) Woody, leatliery texture, as in Rushes (or flinty, as in Horse-tails) , is a means of protecting many plants, a fact which is familiar to all. {d) Hugging the ground is a very successful device employed by plants, such as Knot-grass, Cinquefoil, Purslane ("Pusley"), Wild Strawberry, etc. CHAPTER V THE WORK OF STEMS The work of the stem and the work of the leaf are closely connected. We have learned that the leaf needs a constant supply of water; this is absorbed by the root, but in order to reach the leaves it must be conveyed upward through the stem. Where does the water travel in the stem? Cut olf a leafy branch (pref- erably of Squash, Sunflower or Geranium), and place the cut end in water in which enough eosin has been dissolved to give it a bright red color. Place it where the conditions are favorable for evaporation, and in an hour or so cut off the stem two or three inches from the lower end; if the liquid has risen in the stem trace it upward by means of successive cuts. Make a dia- gram showing the portion of the stem in which the colored liquid rises. If a Squash stem be used, the appearance when cut across resembles (224) 131. Diagram of cross-section of Squash stem: {str) strengthening fibers. I THE WORK OF STEMS 225 Fig. 131 in the essential points. In each of the angles of the stem is a large, fibrous bundle or strand; alter- nating with these are five bundles toward the center of the stem. The central portion of each bundle (the wood) is colored red by the fluid; on each side of the wood is a mass of softer tissue somewhat translucent (the soft bast), from the cut surfaces of which issue mucilaginous drops. Allow the branch to stand in the solution until the leaves become colored red, and then cut the stems lengthwise and trace the course of the bundles up through it and out into the leaves. Hold the leaf up to the light and notice the brauching of the bun- dles, or veins. Use a lens to follow the finer branches. Place a very young leaf, not over a quarter of an inch long, ^^^- ^""^ '^^^^ '^°'^: ' ^ ^ ' ing arrangement of on a glass slide in a drop of alcohol to fi^^^o^s bundles. which lye has been added, and allow it to bleach; rinse with water, mount on a slide in water, examine with the microscope and try to find the ends of the veins. Trace the bundles down into the root. Pull up some vigorous plants by the roots, cut off the ends of the roots, place the plants in eosin solution, and follow the path of the solution into the root and up into the stem. Make a diagram of the path of the solution in the root (see Fig. 90). Examine the Corn (Fig. 132), tracing the bundles up through the stem and out into the o 226 EXPEBIMENTS WITH PLANTS leaves* Bundles which group themselves into a circle in the stem and form a branching network in the leaves, as in the Squash, are characteristic of a great group of plants, the Dicotyledons (plants with two seed-leaves) ; a scattered arrangement of bundles in the stem, together with a parallel course in the leaves, as seen in the Corn, is characteristic of the great group of Monocotyledons (plants with one seed-leaf) . Place a small leafy branch of Oak, Hickory or some other hard wood in the solution, and follow the path of the liquid to the very extremity of the growing tip. At the very tip the wood is in separate bundles, as in the Squash, but as we follow it down toward the older part of the stem the separate bundles very soon coalesce to form a continuous ring of wood (and also of bast) . Take one of the Squash vines which has stood in the solution for some time, cut it square across, and from the cut surface take (with a sharp razor) sections (thin enough to be translucent but still fairly thick), and place them (without water or cover -glass) on a slide, and examine with the low power of the micro- scope. The fibrous bundles show the wood (i. e., the central portion of each bundle) colored red, with the uncolored bast lying on either side of it. Turning our attention to the wood, we see in it two large openings, the ducts (see Fig. 133). In tracing the colored fluid C/? OSS S £- C T / OA/ f^a/ndium uccd bast */> bast LONGfTUDi NAL S £ C T / O /V 133. Stem of 8quu«h: (rf) duct, (*rp) wood pH.-eiichvTna. (ir) trHcheid. (.*0 sieve-tube {sp) sieve-plate. Uc) comDanion eeU, {hp) bast parenchyma. 228 EXPERIMENTS WITH PLANTS up the stem, we notice that it travels much faster in these ducts than in the other parts of the wood. Between the ducts is a mass of smaller cells, which also become colored by the liquid after a time and which appear therefore to assist in conveying water. Having made out these points, we may take from the cut surface of the stem, by means of a razor moistened in water, the thinnest possible slices (when thin enough they are almost colorless and will sink in water ; in this way they may be separated from the thicker ones). Transfer them (by means of a camel's- hair brush dipped in water or the point of a knife) to a glass slide, and cover with a cover-glass. Examine first with the low and then with the high power of the compound microscope. Let us now cut the stem lengthwise in such a way as to divide a bundle lengthwise into two halves in a plane passing through the center of the stem. From one of the cut surfaces take sections (thin enough to be translucent), place them (without water or cover- glass) on a slide, and examine with the low power. We now see that the bundle consists of a mass of elon- gated tubes packed closely together, the central portion of which, the wood, is conspicuous by the red colora- tion due to the eosin ; the ducts are very conspicuous by reason of their large size. Let us now cut much thinner sections from a cut surface prepared in the same way, mount them in I TEE WOBK OF STEMS 229 water under a cover- glass and examine with the high power. We see that both the ducts (d, Fig. 133) and some of the smaller cells of the wood are covered with regular markings, round or elliptical in shape ; these are thin places in the walls called pits (jo, Fig. 138) through which water may pass readily from one cell to another. The smaller cells of the wood are of two kinds ; short cells with blunt ends (called wood paren- chyma, wp) , and longer cells with pointed ends (called tracheids, tr) ; these latter have thin walls with spiral or annular (i.e., ring-shaped) thickenings. The spiral and annular thickenings of the cell- wall are exceedingly useful to prevent the cells from being crushed by the pressure of the surrounding cells and so rendered use- less for the conveyance of water. As we follow the bundles up into the tip of the stem, we notice that the spiral and annular tracheids are the first elements of the wood to be formed, and that their structure allows them to stretch so as to keep pace with the growth in the length of the stem, since they are formed in the growing region of the stem near the tip. The thick-walled elements of the wood can stretch little or not at all, and they acquire their thick walls (and characteristic structure) in the region just below the growing portion of the stem where elongation has practically ceased (see page 249). Can you explain why the water rises so much more rapidly in the ducts than in the other cells ? Not only 230 EXPEKIMEXTS WITH PLANTS are they larger, but the water meets with no obstruc- tions ill passing through them, while in the smaller cells there are cross-walls at frequent intervals through which it must pass. Such cross -walls occur also in the ducts at an early stage of their development, but they are soon broken down and absorbed, and we find only remnants of them in the form of rings here and there on the walls of the ducts (as shown in Fig. 133). On comparing a fibrous bundle of the Corn (Fig. 134) with that of the Squash, we find also two large ducts {d, d) , together with (usually) an annular tra- cheid (a) and a spiral one {sp), beside which is a large air-space, the effect of a tear in the tissues caused by rapid growth; the rest of the wood consists of wood parenchyma {ivp) . Let us now investigate the wood of an Oak (or other hardwood tree such as Hickory, Chestnut, Ash, Acacia, etc.) and of a Pine (or other softwood tree such as Spruce, Cypress, Juniper, etc.) by first tracing the path of the water (by means of eosin solution) and then examining sections under the micro- scope. Cutting sections of woody stems presents certain mechanical difficulties, but these are easily overcome if we choose young stems (not more than two or three years old) and trim the surface to be cut until it is not more than an eighth of an inch in diameter. I cri/shed bast 134. Cross-section of a bundle of Corn: (d) duct, (a) annular tracheid (i. e.. with ring- shaped thickenings), {sp) spiral tracheid (i. e. with spiral thickenings), {wp) wood parenchyma, {si) sieve-tube, {cc) companion cell, {sir) strengthening fibers. sscr /oAf , . rind (of ccffex) €or. fi-^-'^^et^cc*!!^ rind (tr cortex) LONCtT UDI NAL ^£CT/ON 135. Oak branch: (cA;) cork, ice") cork cambium, {coV) collenchyma, ^cor.v) cortical parenchyma, {sir) strengthening cells, {cr) crystal-bearing cells, (6j)) bast paren- chyma, {sp) sieve -plate, (sO sieve -tube, (d) duct, {tr) tracheid, Kxvp) wood parenchyma, {st. wp) wood parenchyma containing starch, {mr) medullary ray, {I) lenticel. THE WORK OF STEMS 233 In the wood of the Oak (Fig. 135) we find the same elements as in the Squash, namely, ducts (o?), wood parenchyma {wp) ^ and long, pointed tracheids (^r), dovetailed together at the ends. Most of the tracheids in the Oak are pitted; tracheids with spiral or ring- shaped thickenings occur only in the innermost wood next to the pith. The wood parenchyma cells are usually distinguished by being filled with starch, so that by placing the section in iodine they stand out prominently; at the same time the medullary rays (mr), or silver grain of the wood, stand out unmis- takably by reason of their starch -content. Whether we look at the cross or the longitudinal section, the starch, by its dark coloration, forms a distinct pattern, which shows very clearly the course it travels from the outer green- celled tissue of the rind, inward through the narrow, ribbon-like medullary rays, and from them into the intersecting bands of wood parenchyma in which it travels freely up and down the stem. The form of the medullary rays (mr) is easily under- stood from the figure. They consist of cells elongated in the direction of the radius of the stem, and run from the rind (or cortex) through the bast into the wood, many of them reaching clear to the pith, to which they convey large quantities of starch. In the longi- tudinal section the cells of medullary rays are shown in surface view (i. e., not cut open), consequently we see the pits which occur in their walls; it is principally 234 EXPERIMENTS WITH PLANTS through these pits (which are openings in the wall closed by very delicate membranes) that the starch passes in the form of dis- solved grape- sugar from cell to cell. These pits occur on all the cell-walls 186. Bordered pit, cut in lialf (diagrammatic). of thc WOOd and are shown in the cross -section as dots in the cell- wall (for details see Fig. 136, which is a diagrammatic representation of one of these bordered pits cut through the center; a similar section of a simple pit is shown in Fig. 137) . These figures make it clear that the pits are nothing more than holes in the wall across which are stretched delicate membranes which allow water to pass through but prevent the passage of air- bubbles, starch grains, etc. On looking at a bordered pit, the narrowed entrance to the hole appears as a smaller circle within the larger one which corres- ponds to the diameter of the hole at its widest part. It is possible that 137. Simple pit, cut iu half (diagrammatic] THE WORK OF STEMS 235 air- bubbles, which would hinder the rise of the water, are trapped in these pits and so rendered harmless. The tracheids and wood parenchyma are also pitted so as to allow water and dissolved substances to pass readily from one to another. The great elongation of the tracheids especially fits them for conducting mate- rials lengthwise through the stem, while their dovetailed arrangement increases their surface-contact and so pro- motes the diffusion of liquid while at the same time it gives them great mechanical strength. Let us now in- vestigate in the same manner the wood of the Pine (Fig. 138). Here we find only tracheids. The only thing which resembles a duct is the resin duct {rd) , which does not convey water, but contains resin, scat- tered in irregular drops. The tracheids are large and are provided with very large bordered pits. Make a careful comparison of the wood of the Oak and the Pine. A very good way to study wood -cells is by isolating them. Place some rather thick longitudinal sections in a dish, add a few crystals of potassium chlorate, and pour in enough nitric acid to cover them. Set the mix- ture outside the window until fumes cease to come off, then wash the sections in water and tease out with needles, if necessary. The wood-cells will then have separated from each other and may be studied in their isolated condition ; in this way we may learn the length of the tracheids ; to ascertain the length of the ducts fa£ittJ€cd sprtnytt/ccd iast ^ ^ earn unt^ ^ ccr-p «1 1^1 I !v1IIIIJtJM 1111 III illl Ulvlli' Bf&a v / ^ ^ V4 ^'THm^iumhL, at sp \b^{*t>np^ M ^atl weed Spriny weed *^''^ — haSt LONaiTUDlNAL ^ECT/QN 138. Pine branch: {ck) cork, {cc) cork cambium, {col) collenchsmia, {cor.-p) cor* tical parenchyma, (rd) resin duct, {oh) old bast, {sp) sieve-plate, {si) sieve- tube, {bp) bast parenchyma, (p) pit, {mr) medullary ray. THE WOBK OF STEMS 237 we must employ another method. For this purpose we force one end of the stem through a hole in the center of a rubber stopper which fits into the air- pump in the manner shown in Fig. 139. If we now place the free end of the stem in water and withdraw the piston, water will be drawn up into the ducts. We must place in the fluid some coloring matter which cannot pass through the cell -wall; for this purpose we may use India ink or cinnabar rubbed up fine in water and filtered through filter paper so as to take out all the coarser particles. We now ex- haust for about half an hour, making as many strokes with the piston as necessary. If none of the coloring matter comes through, shorten the stem by cutting a piece off the end and proceed as before ; repeat this until the stem is short enough to permit the coloring matter to pass through.^ If we now remove the stem and cut it open, we can easily ascertain the length of the ducts, tracheids, etc., and whether there is open communication between them. We should suppose that water would travel faster in the open ducts than in the closed tracheids; the iThe liquid may also be forced into the stem by means of \h.e apparatus shown in Fig. 141. -k %. 139. Method of injecting a twig by means of the a i r • pump. 238 EXPERIMENTS WITH PLANTS r Oak would seem to have an advantage in this respect over the Pine. In order to compare their efficiency, cut a live branch of each about twelve inches long and as free from leaves or branches as possible. Remove the leaves and branches which are present, and connect the base of the branch by means of two or three feet of heavy white rubber tubing to a glass tube three or four feet long (the tube may be formed of several pieces joined together by rubber tubing) . Hold the tube upright with the branch hanging straight down, and fill it with water; compress the rubber tube several times to expel air. Place the branch upright and secure it by a clothes- pin in the position shown in Fig. 140 (which shows a slightly different arrange- ment from the one here described) . Con- nect the upper end with a piece of glass tubing (about six inches long), in which place a little water. Place a little oil on the top of the water in each of the tubes. Make the joints water-tight by winding with elas- (or with wire) ; close with sealing-wax any wounds made by the removal of leaves, branches, etc. The diameters and lengths of the branches should be as nearly alike as possible. The height of the water-column in the long tubes (measured from the 140. Arrange- ment for f orc- ing water through a branch. tic bands THE WOBK OF STEMS 239 level of the water in the short tube) should be the same in both cases. Mark carefully the height of the water- column in all the tubes at the begnming of the experiment, and at the end of twenty- four hours compare the amount of water that has run through the two stems, as indicated by the rise of the water- columns in the short tubes. In order to gain some idea of the energy required to force the water needed for transpiration through the stem in each of these trees, we may first ascertain the normal rate of flow and then the amount of energy required to force water through the branch at the same rate. Cut vigorous leafy branches, one of Oak and one of Pine, three or four feet long, and place them in Jars of water, on the surface of which we pour a little oil (cottonseed or olive) to prevent evaporation. Having done this, we weigh each jar with its contents and, after exposing it for twenty -four hours to conditions favorable to transpiration, weigh again. We now take a section of a lamp-chimney or of glass tubing, at least an inch in diameter, fit it at each end with a stopper of rubber or paraffined cork, and insert air-tight in one of these corks a glass tube (one-eighth to one-fourth inch in diameter), about three feet long. Now heat the tuoe and bend it till it comes in contact with the large tube (as shown in Fig. 141), and secure it firmly in this position by wire. 240 EXPERIMENTS WITH PLANTS 141. Modification of arrangement shown in Fig. 140. Trim away from the Pine branch all its leaves and twigs (the wounds made in so doing should be covered with sealing- wax), insert the base of the branch air- tight in the cork, fill the large tube brimful of water and insert the cork with its branch so as to exclude air as much as possible. Pass a wire over both corks, as shown in the figure, and secure it firmly. Attach a glass tube five or six inches long to the top of the branch, and pour mer- cury into the long tube until there is suffi- cient pressure to make water flow through the branch at the same rate as it flowed when intact (as shown by the weighing) . Perform the same experiment with the Oak branch.^ The same experiment may be per- formed by basing the comparison on the rapidity of rise of the sap as shown by eosin solution (instead of on the amount) . In this case two similar branches from the same tree should be compared, one being placed intact in eosin solution, the other stripped and connected with the tube as before, so as to force the eosin solution throu2:h it. 1 It is possible to perform the experiment on short twigs by pouring water instead of mercury into the long tube. THE WORK OF STEMS 241 It is of course impossible to estimate from the re- sults of the above experiment how much pressure is required to force water to the top of a Pine tree fifty or one hundred feet high, but we know that it must be a much greater amount than is needed to force it through a short branch such as we have used. We have at least found out that a powerful force is at work. Is the water raised by a force acting from above (i. 6., pulled up), or by a force acting from below (i. e., pushed up), or by both methods? As we have already learned, there is in the leafy branch a powerful force at work lifting the water, and this too when the branch is completely separated from the root. In this case the force must reside in the stem or in the leaves. Determine the amount and rapidity of sap -flow in a leafy branch, as compared with a similar branch deprived of its leaves (and with the wounds caused by their removal sealed with sealing-wax) . Does the result indicate that the force resides principally in the leaves? It would appear probable from this and other experi- ments Vvdiich have been made that the water is pulled up by a force acting from above. If this were the case it would create a partial vacuum in the ducts whenever the supply of water from the roots ran low. Do we find any evidence of such a state of things ? Allow a vigorous plant (Squash, Sunflower, etc.) to wilt slightly, thus showing that the supply of water from the root is running low. Now bring a part of the P 242 J^JXPl'Jh'IMJ^XTS WITH PLANTS steni under eosiii solution in a shallow pan, and cut the stem underneath the liquid by a quick, clean stroke of a sharp knife or scissors. After two or three min- utes, remove the stem and determine how far the eosin has penetrated. In what manner do the leaves exert this force ? We have already learned (page 122) that the root-hairs draw up water by reason of the water -attracting sub- stances which they contain. We determined the water- attracting power of the root- hairs by placing them in weak solution of salt or sugar and increasing the strength of the solution until it attracted water from them and they became flabby; we m.ay do the same with the leaves, and we then find that it takes a much stronger solution to attract water from them than from the root -hairs. If, then, the leaves are so much richer in water-attracting substances ^ than the root -hairs, the most probable explanation seems to be that they attract water from the root -hairs through the interven- ing cells and ducts, and so supply what they lose by evaporation. It is at present doubtful whether this explanation can account for the rise of sap for more than 150 to 200 feet.^ 1 The youngest leaves, which are richer in water-attracting substances than the old ones, are also the first to be colored when a short piece of stem is placed in eosin; this indicates that they attract water more powerfully than the older leaves. 2 Two factors which are little understood as yet must be reckoned with; the tensile strength of the water-column and the frictional resistance of the ducts, tracheids, etc. THJiJ WOBK OF STUMS 243 The fact that the run of sap commences in the spring before the leaves appear (as in the Sugar Maple, etc.) is apparently due to the formation at that time of large quantities of sugar and other water- attracting substances in the stem which draw up the water in large quantities. It is a matter of common observation that at certain times of the year many plants bleed (i. e., exude water) when cut or trimmed. Test some vigorous, well- watered plants in regard to this point (especially Squash, Sunflower, Dahlia, Begonia, Corn, etc.) by cutting off the plant near the ground and connecting the stump to a glass tube by means of a section of rubber tubing (see Fig. 142). Pour a little water in the tube and support it in an upright position. Place a little oil on the water and mark the height at which it stands. In favorable cases the water will rise in the tube; this is due to what is known as root- pres- sure; some observed cases of root- pressure show that it could, in cer- tain plants, under favorable circum- stances, raise the water manv feet; ' 142. Method of measuring but at the time of yeai* when ^^^ amount of bieea- " iug from a stump transpiration is greatest little or no (root pressure). 244 EXPERIMENTS WITH PLANTS root-pressure is, as a rule, observable. We may there- fore leave it out of account in this connection. The amount of water necessary to supply the leafy crown of a lar^e tree must be very large, and we might naturally suppose that all the wood of the trunk is employed in conveying it. It is often noticed, how- ever, that in old trees the heart- wood decays and leaves the trunk hollow without affecting the health of the tree. Moreover, on sawing off a tree or branch six or eight inches in diameter and placing the cut end in eosin solution, we find that the colored liquid does not rise in the inner portion of the wood but only in the outer. (In case this experiment is carried out, the tree may be removed from the solution and allowed to dry with its leaves on and will serve for years as demonstration material.) The cells of the interior portion of the wood are more or less stopped up with various substances, and appear more deeply colored than those of the outer portion; this inner portion is called the heart-wood^ and the outer the sap-wood. If water is prevented from traveling in the sap-wood, can it travel in the heart- wood instead ? We may answer this question by cutting a ring-shaped groove all around the tree or branch deep enough to go through the sap-wood and prevent the water from traveling in it. The wilting of the leaves will indicate the extent to which the water current is interfered with. No one who has seen this experiment carried THt: WORK OF STEMS 245 out can thoughtlessly destroy a tree by hacking it without realizing the injury he is inflicting. In connection with the study of wood and its struc- ture, take up as far as possible the practical aspects of the matter. What is meant by the seasoning of wood? What does this involve! How is it best accomplished? Why? Does the water escape principally through the sides or through the end of the log? What occurs if the end is painted or rendered water-proof? Does the wood crack less if allowed to season with the leaves on? What kinds of wood shrink most in drying? What kinds contain most water? ^ What determines the usefulness of a wood? What kinds of woods are used for the various parts of wagons? Why? Can you explain their peculiarities by a study of their cell structure? What woods growing in your region are useful in any way? Why? What woods last longest when exposed to the weather? What is the best treatment to preserve woods ?2 Learn how to read the history of a branch by the inspection of the scars on it.^ In some cases (e.g., Alder) this history can be read back many years. As the sap-wood grows older it changes into heart- 1 In regard to the absorption of water by wood, see pag:e 68. 2 See articles in the Year-Book of the U. S. Department of Agriculture for 1894 by Fernow; for 1896 by Roth; for 1903 by von Schrenk. On the manage- ment of forests, etc., see Roth: "First Book of Forestry"; Pinchot: "Primer of Forestry"; also articles in the Year-Book for 1895 by Fernow; for 1898 and 1899 by Pinchot. 3 See Bailey: "Lessons with Plants," p. 73 ff. 246 EXPJ-%x/ iry this part of the stem (called the -^J^^^^Ck) yfe=sl coUenchyma, Fig. 150) have these properties ; they are com- posed of cells thickened at the 150. CoUenchyma. comcrs ouly ; they are able to grow T3y absorbing nutriment through the thin places in their walls, and so keep pace with the growth of the stem. The rigidity of the growing parts is helped by the fact that the pith and internal tissues are com- pressed by the outer ones, which grow more slowly, and so set up strains (just as a spiral spring is more rigid if placed in a cloth bag which is too small for it) . Cut from the tip of a growing Elder stem (or stem of THE WORK OF STEMS 269 Grape Vine, Corn, Sunflower, Corn-stalk or any pithy stem) a piece at least a foot long, carefully remove a thin slice from the outer part of the stem and place it in water ; trim away everything from the pith, take a slice from it and place it in water beside the other. Both slices must be the full length of the piece of stem. Keep both slices under water, and examine at the end of twenty -four hours. Which has grown the more I A further illustration of this inequality of growth may be had by splitting a Dandelion stalk (see Fig. 152) lengthwise into four pieces and placing in water (other pithy or succulent stems or stalks may be treated in the same way) . The rigidity of the tip of the stem is also largely due to the fact that the cells are filled with water under pressure (just as in the case of the root -hair, see page 123), which renders them rigid. Cut off the tip of an herbaceous stem two or three inches in length, place it in a strong solution of salt or sugar for an hour or so. Explain the result. Place a wilted stem in the apparatus shown in Fig. 140 or 141, and force water into it under pressure. As a result of all these devices, the herbaceous stem is a model of strength, lightness and elasticity, serving its purpose perfectly; and we may say that this problem has been exceedingly well solved. In the case of tree trunks, the mere accumulation of woody material provides the necessary sti'ength; while 270 EXPERIMENTS WITH PLANTS in water-plants there is no problem of this sort, since the water supports them, and consequently we find them almost destitute of woody fiber. What plants get their leaves up into the sunlight with the greatest rapidity and the least outlay of material? Consider the twining and climbing plants in this connection (see Fig. 151) . The problem of climb- ing is one that has been solved by various plants in a great number of different ways, so that it would hardly seem possible to suggest other solutions than those actually found in nature. Beginning with the simplest cases, we have what we may call weaving 'plants^ which weave themselves in and out among the branches of other plants and cling by means of their branches and straight or slightly curved leaf -stalks or by means of hooks, spines, etc. As examples of this class of climbers, study the climbing Roses, Blackberry, Raspberry, Jasmine, etc. How does the plant behave when it first starts up from the ground ? Where does it begin to branch ! How does it reach or find the support ? How does it cling to it? Does it always prevent its leaves from being shaded by the plant which supports it ! Do you think that its stem seeks the light ? More special and elaborate adaptations for climbing are found in tendril -hearing plants. The leaf -stalk in many cases acts as a tendril, as in the Nasturtium, Clematis and the Potato vine; in other cases the leaf- 151. Clemiitis uu an evergreen (iu Califuriiij advantage of a climbing habit. 272 EXPERIMENTS WITH PLANTS blade, either in whole or in part, becomes transformed into a tendril, as in the Pea family ; in still other eases it is a branch which becomes a tendril (as shown by its position and development, or by the fact that it may occasionally bear leaves), as in the Squash, Pumpkin, Grrape-vine and Passion Flower. The last- mentioned plants have tendrils which are especially suitable for study. Find out all you can about the development of the tendrils and their behavior. Does the tendril always grow out straight at first ? How large must it be before it becomes sensitive to contact ? Does the tendril tend to swing around in a circle, as if seeking a support? How long does it take to make a complete circle? Does this depend some- what on the temperature? Does this movement seem to be performed by the tendril or by the stem on which it is borne ? How soon does the tendril coil after finding a support? Sticks of w^ood about the thickness of a lead - pencil fastened to upright pieces by a single nail so that they may be set at any angle are very convenient for experiments of this kind. The upright piece (a lath or portion of one) should be sharpened so as to be easily set in the ground. Is the tendril everywhere equally sensitive ? Can the tendril coil equally well regardless of the angle at which the support is set I How does it behave when the support is too large for it to coil around ? Do rain - drops falling on the tendril cause it to coil I THE WORK OF STEMS 273 A part of the shoot may be brought indoors and placed with the cut end in water, while a stream of water from the faucet is directed on it. Do you see any advantage in this behavior of tendrils ? Does the part of the tendril between the stem and the support coil ; if so, in what direction % Do you see any advantage in this coiling I Do the tendrils which find support grow stronger and more woody than those which do not ? What is the advantage of this I Why does the tendril coil? The best answer we can give to this question at present is that contact with a solid body arrests the growth of the contact side and promotes that of the opposite side. Why this is so we do not know. If we imitate the coiling of a tendril by cutting out a strip three or four inches 152. Behavior of a strip of liower-stalk of Dandelion, fastened at both ends and immersed in water (to show the reversal of coiling which occurs in tendrils). long from a Dandelion stalk (Fig. 152) and fastening the two ends by clothes-pins, we find on putting it in water that it shows the same reversal of the coils which is shown by a tendril which has fastened itself to a support ; it would seem that the reversal of the direction of the coiling is due to purely mechanical reasons, since the same result can be gotten with a twisted string. 274 JlJXPJfJJilJIJiWTS WITH FLAXTS Study also the tendrils of the Virginia Creeper or of the Boston Ivy (sometimes called Japanese Ivy). Why do they grow toward the wall I Bend back the tip of the vine so that the tendrils are directed away from the wall, and fasten it in this position. How do the tendrils (especially the newly formed ones) behave ? Is this due to the light ? Conduct some of the growing tips into boxes fastened on or near the wall, so that you can control the direction of the light as you please or exclude it altogether (if the plants are growing on a brick or stone wall the boxes may be simply wired to nails driven into the mortar be- tween the bricks or stones). How do the tips of the tendrils behave on touching the wall I If the little cushions by which the tendril attaches itself be in- jured or removed, can the tendril replace them? How long does it take a branch of the tendril to attach itself firmly? How much weight does it take to tear it loose when it has firmly attached itself? Attach a small box to it and pour shot into it until the tendril breaks loose from the support. In what direction do the main stem and the branches of these plants grow ? Is this direction due to gravity? Bend back and fasten some of the tips (of both main stems and branches) in a horizontal position and also pointing downward. Is the growth of the stem affected by light? Experiment on the stems by changing the direction of the light and by THE WORK OF STEMS :^/D excluding it altogether. Can you now explain why the tips of the st^ms press themselves to the wall? How do the main stem and branches behave when they reach the top of a wall? How do they behave when unable to attach themselves? The English Ivy climbs in the same manner as the Boston Ivy, but attaches itself by roots (Fig. 153) instead of by tendrils. Study its behavior carefully. The most interesting adaptations for climbing are found in the twining plants. The Morning-glory, Bindweed, Hop, Scarlet Runner, Pole Bean (or String Bean), Lima Bean or Sweet Potato may be studied as examples of this class of plants. How does the stem grow at first ? When does the tip begin to droop? Does it appear to swing around in a circle as if seeking a support ? As you look down on the stem from above, does the tip move like the hands of a watch (clock- wise) or in the opposite direction (counter- clockwise)? How large is the circle de- scribed by the tip ? How long does it require to make a revolution ? (Does the temperature affect the rate of the revolution?) How does the stem behave when it meets a support ? What is the size of the largest and the smallest support it can twine about ? Is it more advan- Branch of English Ivy. 276 EXPEBIMENTS WITH PLANTS tageous for it to twine up large stems or small ones (re- member that it must, in order to thrive, get its leaves above those of the plant on which it twines)? Does it twine best on a vertical or on an inclined support ? Can you see any advantage in this? Place the sup- port on which it is twining in a horizontal position; how does the plant behave? Does this make it ap- pear as though gravity were a cause of the twining ? Reverse a vertical support on which the plant has made several turns, so that the tip of the plant points downward ; how does the plant behave ? (For this experiment potted plants, with upright sticks set in the soil as supports, are very convenient, since it is only necessary to incline the pot or turn it upside down.) Does light affect the twining? Keep the plants in darkness, and observe the result. Are the turns of the stem equally steep at the tip and at the base ? Does this arrangement help to hold the plant in place by causing it to hug the support? Can the plant twine as well on a smooth support (e. g., a glass rod) as on a rough one (a branch or twig) ? How does the plant behave when it reaches the top of the support? What causes the plant to twine? The best answer we can give at present to this question is that the twining is due to the influence of gravity, which stimu- lates one side to grow more rapidly than the other. When the tip points north it is the west side which is THE WORK OF STUMS 277 stimulated in clockwise climbers, the east side in counter - clockwise climbers. Why gravity should stimulate the east side rather than the west (or vice versa) we do not know, any more than why it should stimulate the lower more than the upper side in so many cases. Many plants have underground stems (e. g., Iris, Ferns, etc.). Such stems are advantageous in many ways; the plant may die down in the fall and come up again from these stems in the spring (in such cases food is stored in them [Potato, etc.] which enables the plant to get a good start in the spring) ; they enable the plant to spread and take slow but sure possession of a great area (e. g., Horse-tail, Mints, Grasses, etc.); they are indispensable to the plant in sand-dunes and similar places, since they bind the soil together and keep it from blowing away.^ It is interesting to note that these underground stems, whose work is similar to that of the roots, closely resemble roots in their general appearance and are commonly mistaken for them. This affords another illustration of the fact that function determines form and structure. If we force underground stems to grow up into the light and air, they begin to function like ordinary stems and assume, in a measure, the ordinary appearance and structure of stems. ^ Plants which have this habit ai-e of great importance for binding the soil of dikes, levees, banks of canals, etc. 278 EXPEEIMJ^NTS ]VITH PLANTS The intimate connection between the work of the stem and that of the leaf, which we have had occasion to note frequently in this chapter, is further empha- sized by the fact that in most cases the stem (in the younger portions at least) contains chlorophyll and shares in the work of starch-making. Does the stem use up oxygen and produce carbon dioxide, as germinating seeds, roots and leaves do? Repeat the experiment described on page 194, using pieces of stems instead of leaves. How does the stem obtain the necessary supply of air for these processes? Do you find stomata in the epidermis ? Strip off a piece of the epidermis and examine it for stomata (as described on page 196). Examine also a thin section in water, and observe the bubbles of air between the cells (under the microscope they have a very characteristic dark appearance). Ex- amine an older part of the stem (where the color is no longer green) in the same way. Attach a bicycle pump to the stem by a short section of thick, white rubber tubing (which should be secured at the joints by elastic bands or wire), close the free end of the stem with sealing-wax, place the stem under water and pump air into it (Fig. 154). The openings, which are visible to the naked eye and which (in the Birch, Cherry, etc.) may become an inch or more long, are known as lenticels. A section through one THE WOBK OF STEMS 279 of them (Fig. 135, I) shows that it consists of a mass of loose cells which by their growth have ruptured the epidermis. This process always begins under one of the stomata, and a greatly enlarged opening is formed by tearing. The figure also shows that a layer of cork has been formed under the epidermis ; it is this which gives the brown color to the stem. The cork is a necessary protection to the stem, for, as it grows older, the epidermis falls off. When the stem gets still older the hark is formed; this consists of a mixture of cork, strengthening cells and the dead cells of the bast. The growth of the stem causes the bark to split and fissure, thus allowing air to enter. The lenticels are very clearly shown by sealing both ends of a short piece of stem with sealing-wax, placing it under water in the air-pump and exhaust- ing. In some cases merely placing the stem in hot water suffices. In order to see how readily air may travel down from the leaf into the stem, we may fix a leaf air- tight in a rubber stopper (as described on page 205), and fix this in a tul)e to which we fit a piston (con- structed as described on page 188) ; pour in a little 154. Method of investigating lenti- cels (air is pumped into the sub- merged stem by means of the bicycle pump). 280 EXPERIMENTS WITH PLANTS 155. Method of investigating the entrance of air into the stem by way of the stomata. water and exhaust the air (Fig. 155). Leaves of Geranium, Mag- nolia, Laurel, etc., may be recom- mended for this experiment. Having tried this experiment, perform the following: Fix a leaf or leafy branch air-tight in a cork and insert the latter into a bot- tle brimful of water so as to ex- clude air as much as possible (it will be necessary to insert the point of a knife beside the cork to let the water escape). Hang up the bottle in the sunlight (Fig. 156). The transpiration of the leaves will withdraw water from the bottle, causing a partial vacuum, with the result that air will be drawn in through the leaves and rise in bubbles from the cut end of the stem. The ex- periment shows clearly that the air and the water travel in differ- ent channels in the stem, so that they do not interfere with one another. In order to test how far the air penetrates and where it travels THE WORK OF STEMS 281 I in the stem, fix a short piece of stem air-tight in a cork and fit this in a lamp-chimney (as shown in Fig 139). Pour in water, and exhaust. Or force air through the stem by an arrangement similar to that shown in Fig. 141, in which case we may ob- serve with a hand - lens just where the air issues. It sometimes happens that in coating trees with tar to protect them from insects and fungi, they suffer severely from too liberal an application, wdiich deprives the stem of air. To determine the effect of ex- cluding air from the stem, we may take Willow cuttings and suspend them in moist air (see Fig. 157), by attaching them to a cork fitted into a lamp- chimney which stands in water. As the experiment is to last for several weeks, the constant level apparatus described on page 27 (Fig. 27) may be used. Let some of the cuttings be completely smeared over with vaseline, so as to en- 157. Willow twig tirely exclude air. Place all the cuttings STispendea in a •' *-• saturated atmos- ^^^^^^ favorable couditions of growth. 156. Method of investigating the entrance of air into the stem by way of the stomata and leuticels. 282 EXPERIMENTS WITH PLANTS When the untreated cuttings have put forth vigor- ous shoots, those with vaseline on them will probably show little or no development of shoots. Now care- fully wipe off the vaseline with a rag,- and then rub the stems well with dry sand and place them again in the chimney or set them in water, to see if they will grow. Cuttings and seeds sent long distances, especially to or from the tropics, are frequently ruined by start- ing to grow prematurely in transit. Of the three fac- tors which promote growth, namely, moisture, warmth and air- supply, the attempt is constantly made to control the first two, which is in most cases difficult or impossible, while the control of the air- supply, although" easily accomplished, has been neglected. Sealing up the plants in air-tight tins or packages has been tried, but this is far less effective than seal- ing each cutting by means of wax, paraffin or similar substances. This seems to promise a favorable field for experiment. How do the submerged portions of water-plants get air? When they have leaves which project above the water or float on its surface, they may receive a supply of air through them. Examine some plants of this sort (e. g., Pond Lilies, Arrowhead, etc.), and notice what enormous air- passages exist in them. Do these passages extend up into the leaves? Examine also swamp plants which have their roots in water or THE WORK OF STEMS 283 mud. In the case of plants which live entirely sub- merged it would seem that they must get their air from the water. Does water contain air? We have already gained some evidence on this point in our previous experiments. Place some tap- or spring - water in the air-pump, and exhaust. Are air- bubbles formed! Boil some of the water for half an hour, allow it to cool, place it in the air-pump, and exhaust. Are bubbles formed to the same extent as before ? Careful tests have shown that water may dissolve a large amount of air. It is this dissolved air in the water on which totally submerged plants depend for their supply. In order to grow water-plants successfully in aquaria, it is fre- quently necessary to furnish them with a constant supply of air. This may be done by means of the ap- paratus shown in Fig. 158. It con- sists of a long, vertical glass tube about one-eighth inch in diameter, widened a little at the top. When a drop of water falls into this from the siphon it will, if it strikes in the center, fill the 158. Apparatus for supplying air in a tube and then fall down, carry- constant stream to an aquarluna. ing the air before it (i. e., it acts like a piston). On arriving at the T-tube connection, the air passes over 284 EXPEMIMEJSTS WITH PLANTS into the aquarium, while the water falls straight down into a receptacle below. The water outlet tube must dip a little deeper under water than the air outlet tube ; otherwise the air, following the path of least resistance, will escape by the same outlet as the water. In order to keep the latter submerged to a constant depth, use a small jar as shown in the figure : the shallow^er the depth the greater the amount of air which will pass over, since enough drops must accumulate in the tube to overcome the pressure of the water at the outlet where it escapes. The drops should be made as large as possible and should strike the tube nearly in the center ; if the bore of the tube is too large the drop will not fill the cross -section and consequently will not act as a piston. In order to regulate the rate of flow of the siphon, it may be drawn out to a fine point (as shown in the figure), which can be broken off to the requisite degree and covered with cotton (held in place by an elastic band) to filter the water. A very successful way of growing algae and other water-plants is shown in Fig. 159. A jar or bottle is filled with water and inverted over water : carbon dioxide is conducted into it from a bottle containing fragments of marble (or marble dust or whiting), into which we slowly pour weak sulphuric acid by means of . Arrangement for supplj-inK carbon dioxide to plants growing in water. THE WORK OF STEMS 285 a funnel passing through the cork : a tube passing through the cork serves to conduct the carbon dioxide into the jar. A few moments must be allowed for the carbon dioxide to drive the air out of the bottle and tube; the tube should then be introduced into the jar and the evolution of gas continued until the jar is nearly filled with gas. Another method is to grow the algse in small tubs (of wood fiber) filled with water, keeping a huge bub- ble of carbon dioxide or air ^^^^.t^Tn^^St^^iSTb^^^^^^^^^ just below, them, as shown carbon dioxide or air. in Fig. 160. This bubble is kept in place by means of a net (made of cheese-cloth or mosquito netting) at- tached to a cii'cular hoop of small flexible lead-pipe (^), which rests on the bottom of the tub. The bubble may consist of air, or air blown from the lungs, or of carbon dioxide generated in the apparatus- shown in Fig. 159. The common method of placing aquatic animals and insects and aquaria in order to supply carbon dioxide is excluded for our purpose, for the reason that they feed on the algae. We may, however, place a well- developed cutting of Willow or Wandering Jew (Fig. 84) in the jar ; the carbon dioxide excreted from its roots will be a great stimulus to the algsB. CHAPTER VI THE WORK OF FLOWERS In preparation for flowering, the plant stores up a supply of food. How long does this take; what kind of food is stored, and where? Compare the behavior, in this respect, of plants which live for a year only (annuals), plants which live two years (biennials) and plants which live on from year to year (perenuials). Which method of preparation for flowering seems to you in general most effective I Find out what you can about the behavior of Cacti and the Century Plant. Study especially the different kinds of bulbous plants. Cut open the bulb of a Hyacinth, and notice the food stored for next spring's growth, and the flowers already formed and prepared to open at the earliest opportunity. The formation of flower -buds during the previous season would seem to be an advantage. Does this occur in most plants ? Open, and examine with a hand-lens the large winter-buds of the Horse-Chestnut, Buckeye, Hickory, Maple, Poplar, etc. Can you find any traces of flowers? In some cases the flower- buds may be recognized by their position ; for example, (286) THU WOBK OF F LOWERS 287 some Plums have a flower- bud on each side of the leaf- bud. As the new leaves come out in the spring, we find the three buds already formed in the axil of ea.ch leaf, and the flowers which are soon formed inside the flower- buds must wait a full year before opening. In the first stages of their formation the flowers may be too small to be seen (except with the microscope) ; we must not, therefore, be hasty in con- cluding that they are not yet present in any given case. Fruit - growers have thought it desirable to know the exact time when the flowers were formed in the bud, in order that they might try to control this process by irrigating and applying special fertilizers at the proper time. Learn what you can about these points . Examine some flower- buds which are just open- ing. Do you find an abundance of food in them and in the stems on which they are borne ? What kind of food predominates ? Is there a rapid consumption of food by the developing flowers f Repeat the experi- ment described on page 34, using flower- buds instead of seeds. (Buds of Composite flowers, e.g.. Sunflower, Dandelion, Daisy, etc., are especially good.) What does the result signify ? Can you detect any setting free of heat in the developing buds (see page 36) ? Of what use is the calyx, or green covering, of the flower-bud ? We may endeavor to answer this question by removing the calyx from the bud at as early a 288 EXPERIMENTS WITH PLANTS stage as possible in its development. The Passion Flower, Bindweed, CobsBa and other flowers where the calyx is large and inflated are especially well adapted to such experiments, but any large flower, such as the Poppy, Rose, etc., may be chosen. Re- move the calyx while the bud is still quite small, taking care not to injure the petals or other parts of the flower. It seems natural to suppose that the calyx protects the flower- bud against drying in the same way that the bud- scales protect the leaf- bud. What does the experiment show in regard to thisf Since pet- als are more easily injured than leaves by rain, frost, etc., even when the calyx is not removed, we should keep sharp watch to see whether the flowers deprived of calyx suffer more than the controls in these respects. Do you find that flowers which have been deprived of the calyx are able to develop normally? Does the sTKifMA result depend on how early the calyx is removed? Let us now look at the interior of the flower. If we cut open flowers of the ,«i n>, V, . . ^. Cherry, as shown in Fig. 161. Cherry blossom cut open, to snow •^ ' <=' the parts of the flower, 161^ WC fiud thC SCCd-CaSCS (or ovaries), containing the tiny seeds (or ovules). Surrounding the ovary are the anthers, or pollen-cases, mounted on short stalks, and containing a yellow dust, the pollen. THE WOBK OF FLOWERS 289 When the pollen is fully formed, the anthers open and allow it to escape. Of what use is the pollen? To answer this question, we may deprive the flower of pollen. For this purpose, choose flowers which are large enough to permit of the necessary manipulation; select unopened buds; carefully open them at the tip, and remove the anthers with a forceps, taking care not to injure the other parts of the flower. The flower is now deprived of all its pollen; but more pollen may be easily brought from neighboring flowers by the wind or by the bees (and other insects), which constantly fly from flower to flower. To prevent this, we may protect the flowers by covering them with small paper bags tied tightly on the stalk, so as to completely enclose the flower. Do flowers so treated form fruit! We must, in every case, have controls which set fruit, in order that we may know whether the experimental conditions are responsible for the lack of it. If the pollen is necessary for fruit -making we may next ask. How does it operate? We can see this most clearly if we examine the flower of some Grass or Grain. (Timothy is best for this purpose.) Examining a flower whose anthers have withered, we see what appears to be a tiny brush projecting from the flower. On removing the outer coverings of the flower with needles, we see the ovary (seed -case) with two brush -like styles or stigmas : on examining with a hand -lens we see that they are covered with pollen- 290 IJXPJ'Jh'fJflJXTS WITH PLANTS grains. Fig. 162 shows the appearance of these in the Oat. Placed in a drop of water on a slide, covered with a cover- glass and examined under the high power of the microscope, many of the pollen -grains are seen to be sending out long tubes (Fig. 163) which grow down along the brush -like style to- ward the ovary. What happens after that can be seen only 162. Ova^-y'ueed-case) of !» gOOd SCCtioUS, but Oat with feathery style. ^^y \^q dCSCrlbcd iu a few words. Inside the ovary lies (as you may see with a hand -lens) a tiny seed or ovule (Fig. 161). Within this is a mass of tissue, in the central cavity (embryo sac, Fig. 164) of which lies the Qgg. In the center of the eg^ is a nucleus. The pollen -tube approaches to within a short distance of the egg and opens at the end; a nucleus issues from it which unites with the nucleus of the Qgg^ so that the two form a single nucleus. The egg then begins to develop and eventually forms a tiny plant, with '''• sf ^Te "o f 'o S ,. , T , , n T • showing a pol- caulicle and leaves, such as we find m len-grain pushing out a long tube the ripened seed. ^^^\lV"iroik Unless the union of the nuclei takes o^S&lS! THE WOKK OF FTjOWEBS 291 place, the eg^ does not ordinarily develop; hence we see why pollen is necessary in order to set seed. If we examine various flowers with a hand- lens, we find the pol- len deposited in a par- ticular spot, which is provided with brushes, hairs or sticky sub- stances in order to retain it. This spot is called the stigma (see Fig. 161). What hap- pens if we remove the stigma ? Remove the stigma before the bud is open, being careful not to injure the other parts of the flower. Do not protect the flowers from insects, but rather assist pol- lination by placing pollen on the flower. Do you find that flow- 1G4. Embryo s;ic of ;i Lily, showing the iinion of the nucleus from the pollen-tube {pn) with the egg(e): the second pollen -tvibe nu<-leus (spn) xmites with two endosperm pro nuclei {nid), which nniltiply and form the endosperm: {ant) antipodal cells, (nr) nurse nuclei which help nurish the egg, etc., {p) pollen-tube. 292 EXPERIMENTS WITH PLANTS ers so treated are able to set seed? We must, of course, have unmutilated flowers (if possible on the same plant) for comparison, and it is important that we choose a plant whose flowers set seed freely. The effectiveness of the stigma in retaining pollen may be tested by dusting the flower with flour or any white powder and afterward endeavoring to blow it away. In the Monkey- flower the stigma has two lips which come together and hold the pollen firmly when it has been deposited. Touching the open lips with the point of a pencil will cause them to close at once. The silk of the Corn is practically a long stigma covered with projections to retain the pollen, which is carried by the wind: Wheat and Grasses generally have such stigmas, but they are much shorter and less conspicuous than in the Corn. It is the work of the stigma not only to capture and retain the pollen, but also to provide favorable con- ditions for its germination and to nourish it during the growth of the pollen -tube. The sticky substance on the stigma contains sugar (as you can easily ascertain by tasting or applying a chemical test), which serves the germinating pollen-grain for food. If we place pollen-graius in a drop of sugar solution of the right strength, we shall be able to observe their germination, which may, in some cases, take place in a few minutes (Willow, Sweet Pea). It is advisable to make up cane sugar solutions of 35 per cent, 10 per cent and 5 per THE WORK OF FLO WEBS 293 cent, and test pollen-grains of various species in each. The following may serve as a guide : 3 per cent, Tulip, Narcissus, Onion; 15 per cent, Sweet Pea, Nasturtium (Indian Cress) . A very convenient method is to take a glass or metal ring, or one cut out of wax (about one -half inch in diameter), and cement it to a glass -slide with vaseline: on this lay a cover-glass from the center of \ m ^^- — T^ — '^ \ d 165. Hanging drop arrangement for the cultivation of pollen-grains: («) slide, (c) cover-glass, (r) ring, {d) hanging dx'op. (Sectional view.) which hangs a drop of sugar solution containing the pollen (Fig. 165) ; seal this air-tight by means of vaseline. In each case, make control experiments by placing some of the pollen in rain-water (tap -water or spring- water may be used). In which medium does it grow best ? Vary the experiment by cutting off the tip of the stigma and placing it at one edge of the drop. Do the pollen-grains show any tendency to grow toward it?^ If so, it may help us to explain why the pollen-tubes grow down to the ovary. Presumably, in such cases, the stigma gives off substances which attract the pollen- 1 The fact that the pollen - tubes have a tendency to grow away from the air at the ed-\.-' ■•^^^v m ■1 181. Sprout of Prickly Pear grown iu the dark, showing leaf-like organs. 330 EXPERIMENTS WITH PLANTS leaves like ordinary plants and that their thickened, leafless stems have been brought about by the dry conditions under which they have lived, not directly as in the Potato, but by a long- continued process of change. We suppose that when the ancestors of the Cactus first came to live under drier conditions than they were accustomed to, some few of them were some- what better adapted to stand drought and so lived on and propagated themselves under the new conditions, while their fellows perished. Among the offspring of these plants the same thing happened ; those best fitted to the new conditions maintained themselves, while the others perished. In each succeeding generation the fittest^ survived and crowded out the less fit in the struggle for existence, the result being that in the course of time the plant became better and better fitted to its surroundings. In this way we suppose the vari- ous forms of Cacti to have developed to their present condition, this process of development being known as evolution. It will be seen from the illustration that evolution works by destroying the unfit ^ (thus giving the fit a better chance to develop), and results in bringing the plant into better and better harmony with its surroundings, or environment. The process of destroying the unfit and preserving the fit is called 1 Whether the fittest originated gradually or suddenly (by mutation) is dis- cussed in Chapter X. 2 This, it should be said, is not the sole method by which evolution works, but the only one of immediate importance in this connection. S01V PLANTS AliU INFLUENCED 331 "natural selection," and finds a close parallel in artifi- cial selection as practiced by man in adapting plants to his needs. All our farm and garden plants have been brought to their present condition largely by artificial selection.^ We believe that all the various kinds of plants and animals have reached their present condition by evolution and that evolution is still going on, though at a compara- tively slow rate. An examina- tion of plants which live in dry situations shows that they have the following charac- teristics.- (1) Reduced surface, obtained by suppression of leaves (complete or nearly so) . This is accompanied by thickening of stems in the Cacti (Fig. 182), some of which assume a spherical form, which gives a minimum surface. The Switch Plants, such as the Gorse (Fig. 198, a), Cytisus (Fig. 183), etc., assume the form of green, rod-like switches. 1 See Chapter X. 2 For experiments on this subject, see pages 215-218. 182. A spherical Cactus; a form which presents the minimum surface for evaporation with a maximum liulk for storage. 332 EXPERIMENTS WITH PLANTS The discarding of leaves in winter by deciduous trees and shrubs is an adaptation to the drought from which the plant suffers in winter, since the roots are then unable to absorb sufficient water to supply the leaves. We may test this by the following experiment : Take two vigorous plants growing in pots ; place one on ice (by means of the arrange- ment shown in Fig. 11) ; keep the other near it at normal tempera- ture; give both the usual quantity of water. Which plant wilts first? On continuing the experiment for a few days, it will be found tl^^:1ZJ:Z^Z that the plant on ice sheds its perform the work of leaves. |g^^^g (Begouia may bc rccoui- mended for this experiment). The fall of the leaf is preceded by the withdrawal of all nutriment from it and the formation of a layer of loose cells at the base of the stalk ; this layer finally breaks apart, leaving a clear, smooth scar (see page 212). The disorganization of the chloro- phyll gives rise to the gorgeous colors of autumnal foliage and, while not caused by frost, is hastened by it. Trees which retain their leaves in winter have various devices to restrict evaporation. Study in this 183. Branch of Cytisus (a switch EOW PLANTS ABE INFLUENCED 333 respect Pines, Spruces, Holly, etc. The branches are protected against evaporation by cork and bark ; the buds, by gums, varnishes, wax, hairs, etc. (see page 214). (2) Reduced surface obtained by having smaller leaves (Moor plants, Heaths, etc). (3) Eeduced air content obtained by diminishing 184. Steins of Callitriche in cross-section: (a) land form, (6) water form. Showing the larger air spaces in the latter. the size of the interior air-spaces (Callitriche, Fig. 184). (4) Reduced evaporation obtained by means of thickened epidermis, as seen in Cacti, Century Plant, Holly (Fig. 185), Oleander (Fig. 192), and most plants of dry situations. (5) Reduced evaporation obtained by means of coverings of wax (Sugar-cane, Fig. 186, Eucalyptus, Iris, Spruce), or hairs (Dusty Miller, Wormwood or 334 DXPEBIMENTS WITH PLANTS 185. Epidermis of Holly, with thick cuticle (c). 8age Brush [Fig. 1871, Mullein [Fig. 188], Jdive- finger, Immortelle, coverings of many winter -buds), or varnish and resin (cover- N^ ings of most winter- buds and many leaves when young; Cistus, Pines. 0000^( etc.). (6) Reduced evapora- tion obtained by rolling the leaves (Corn,i many Grasses) or keeping them in a vertical position (Eu- calyptus, Iris). (7) Storage of water (and food) in thickened leaves (Live-for-ever, Cen- tury Plant, Hen-and- chick- ens) , or in thickened stems 186. Waxy covering of Sugar Cane (in the (Cactl, Fig. 18*j, Ctc). The stored food and water are tempting to many animals, hence the Cacti are protected by sharp spines. The Century Plant is pro- tected by the sharp points of its leaves: form of rod-like outgrowths). 187. Hairs of Wormwood or Sage-brush. iSee page 213. HOW PLANTS ABE INFLUENCED 335 it goes on storing up food for several years, when it blooms and uses up the nutriment stored in the leaves, then dies. Hence the name, Century Plant, due to the popular belief that it blooms but once in a cen- tury. (8) More abundant woody fiber (see Pigs. 189' and 190) . (9) Longer palisade cells in the leaf (Fig. 194). (10) Reduction in number of stomata (Fig. 191) and sinking of the stomata in wells and depressions (Oleander, Fig. 192). All plants growing in dry situations show some of these characteristics, and many of them can be produced in 188. Hairs of Mullein. 190. Cross-section of stem of Water-polygonum grown in water; the fibrous bundles and strengthening tissue are shaded. 189. Cross-section of stem of Water-polygonum grown in dry soil; the fibrous bundles and strengthening tissue are shaded. 336 EXPERIMENTS WITH PLANTS any plant by growing it with a reduced amount of moisture. Make such experiments as you can on this point. Study every case you can^ and, if possible, make experiments, by growing the plants in pots (or plots) and regulating the amount of water given them. 191. Upper epidermis of Water-polygonum : UO from m leaf of a plant cultiviited under dry conditions, (.b) from the first leaf produced by such a plant after being placed in water, showing a larger number of stomata. It may seem surprising to find that many plants which grow in damp places show the features de- scribed above : such are plants growing in alkali soils, or along the seashore where the water is brackish. The explanation is that in these places there are substances in the water which hinder its absorption by the roots (see page 124). 1 Plants subject to the drying action of strong winds show these features excellently. HOW PLANTS A BIS INFLUENCED 337 192. Cross-section of a leaf of Ole- ander, showing the stomata (s) sunken in depressions, which are filled with hairs. Very different in appearance are the plants which inhabit streams and lakes, such as the Water-lily, Sjjatterdock, Ar- rowhead, etc., which are typical water-plants, with broad thin leaves, devoid of hairy cover- ings and provided with enor- mous air-spaces, especially in the leaf -stalk. These great air- spaces are necessary to convey air down to the roots and other submerged parts of the plant. The submerged leaves (and submerged parts) of water- plants obtain air from the water (see pages 193 and 283 for experiments) ; the leaves i/v are usually split up into fine divisions by which a greater surface is secured. Fig. 193 shows the behavior of the Arrowhead, which produces ribbon-like leaves under water and the characteristic Arrow- 193. Arrowhead, producing rlbbon-liUe leaves below the surface {w) of the head leaves above water. The S'TuS'eTSeTJirt'.'lhrr^dYel? figure also shows a heart- {Mtorr^s^a transition between the 338 EXPEBIMENTS WITH PL A XT S shaped leaf, a transition form between the two. Fig. 194 shows at (?)) a section of a submerged portion of a ribbon-like leaf, while at {a) is a section of a por- 194. Cross-section of the ribbon-shaped leaves of Arrowhead, (a) from a part of a leaf above the water, (6) from a part of a leaf below the surface, showing thinness, lack of cuticle and larger air-spaces. tion of a ribbon-like leaf which projected into the air. Fig. 195 {a) shows a submerged leaf (water - leaf) of the Water Buttercup, while beside it {!)) is another leaf which grew above the water (air- leaf) . The Water Buttercup presents a transition from a land -plant to a water-plant. If the water sinks, so that the sub- merged leaves are exposed to the air, they dry up and perish, while the air -leaves live on and the plant continues to flourish. We have good reason to believe that the water- plants (with the exception of certain groups of flow- MOW PLANTS AME INFLUENCED 339 erless plants) were originally land -plants which were forced by competition to take to the streams and lakes. Some of them still possess the power to live on land if the water falls away, while others can live only in water and quickly perish when left without it (Hornwort, Water-lily, Pondweed, etc.). The water-plants in general show exactly opposite features to those already enumerated as characteristic of desert -plants. They have a large exposed surface, thin cuticle, no waxes, varnishes, resins or hairs on the surface, a minimum amount of woody fiber, very large air-spaces and poorly developed palisade. 195. Leaves of the Water-buttercup: (a) water-leaf, (6) air-leaf. Stomata occur, as a rule, only on surfaces which are directly exposed to air (Fig. 196). Water-plants have usually a very poorly developed root- system : many of them have no roots at all, but float about on the water, sinking to the ])ottom on the 340 JiJXPElilMENTS WITH PLANTS approach of cold weather and rising to the surface again in the spring. Such plants, as a rule, have the custom of breaking up into pieces, each of which floats away and becomes a separate plant. A very interesting experiment may be made by growing the Water- hyacinth in soil instead of in water and observing the modifications it undergoes. We may also use the Water- polygonum for this experiment. 196. Lower epidermis of Water-polygonum; (a) from a submerged leaf, showing lack of stomata, {b) from an air-leaf produced by a plant growing in water. Water affects the size of every part of the plant noticeably, as may be seen by comparing plants grown in dry, sandy soil with the same species grown with abundant water (e. g., the weeds which come up in a garden as compared with those which grow in dry spots). The large wood -cells produced in the spring (spring wood), as contrasted with the fall wood, are another illustration of this (see page 247). A scion grafted 07i ROW PLANTS ABJ!] INFLUENCED 341 a stock which supplies it overabundantly with water forms a mass of large -celled wood- parenchyma in place of ordinary wood. It is often very noticeable that the leaves which are formed during a dry period are small and stunted, while those subsequently formed on the same branch during a rainy period may be four or five times as large. The roots of many plants branch in a peculiar, compact fashion when they grow in water (for example, the roots of trees when they enter a cistern or drain- pipe), hence the popular name, " water-roots." Very interesting results are obtained when we grow ordinar}^ land -plants in a saturated atmosphere, in the manner shown in Fig. 157. Select a bulb (or corm, tuber, etc.) which has begun to sprout: cut out a piece (two or three inches long) bearing a sprout at one end, place it in a dish, and cover it with a lamp-chimLey. Pour in some water, and cork the chimney, covering the cork with sealing-wax or vaseline. The air within the chimney will soon become saturated with moisture, and its influence on the growth of the plant can be readily observed. The tissue at the base, which is in contact with the water, will eventually decay; but this will not interfere with the growth of the sprout. The results of growing Dandelion leaves and Gorse in this way are shown in Figs. 197 and 198. Water seems to have a direct influence on the pro- 34'J iJXPJi'Ji'IMENTS WITH PLANTS duction of flowers and fruit. Land- plants growing in unusually moist situations run to stem and leaf, and produce flowers and fruit sparingly: on the contrary, when growing in unusually dry places, the same plants produce relatively more abun- dant flowers and fruit than usual . Such water- plants as are descended from land -plants are, as a rule, unable to flower or fruit under water (Water Plantain, Arrowhead, Hippuris, etc.). Gardeners induce plants to flower abundantly by digging a trench around the base of the \\\) trunk, and thereby cutting off numerous active roots: another method is to simply lay the roots bare. Cacti which are allowed to become somewhat dry and shrunken bear more freely. Bending and breaking the branches of fruit trees, which results in partially cutting off the water supply, is practiced for the purpose of causing trees to fruit. It also tends to make the fruit sweeter and of higher flavor. Fruit grown in the mountains (where it is dryer and the light stronger) is usually superior in these respects. Over- irrigation has a tendency to produce watery fruit which is neither very sweet nor highly flavored. ^ 197. Leaves of Dan- -pv 1 • • J 1 T 1 T delion drawn on -By knowing lust when and how much to the same scale: («) normal, (&) grown I See pages 318 and 319. SoyheT'^' '"*'" HOW PLANTS AMU INFLUENCED 343 irrigate, we may hope to control very largely both the quantity and quality of the crop. At present there is so much confusion in this regard that we may find one farmer using several times as much water as his neigh- bor for the same kind of crop grown under the same 198. Gorse: (a) leafy form, the result of growing in a saturated atmosphere, (6) normal (leafless) form, the branches transformed to spines. gene^-al conditions. In general, crops cannot be grown to advantage when the soil contains more than 50 to 60 per cent of the total amount it is capable of hold- ing. The study of irrigation is bound to be of increasing importance, since it is becoming evident that it will pay to irrigate, even in regions where the rainfall is now ordinarily regarded as amply sufficient for crops (see pages 130 and 131). 344 EXPERIMENTS WITH PLANTS Light. — The effect of light on the plant is ordinarily much the same as that of dryness. In fact, some of the effects of strong light are due to the increased trans- piration which it produces. In the case of the desert- plants, etc., the effects of the two are difficult to distinguish. There are, however, many effects of light which are independent and are manifested equally 199. Leaves of Prickly Lettuce seen in cross-section: (a) sun leaf, (6) shade leaf. well when the plant is grown in a saturated atmos- phere. Some plants (sun -plants) prefer the direct sun- shine, while others grow only in the shade (shade- plants). The latter (e. g., many Ferns, etc.) have leaves of paler color, relatively large and thin, and not well adapted to withstand direct sunlight : if exposed to it they soon die. Similar differences may be found in leaves growing on the same plant when, HOW PLANTS ABU INFLifENGED 345 as often happens, some of them are directly exposed to the sun while others are continuously shaded. Figs. 128 and 130 show two branches from the same plant : the one shown in Fig. 128 was well illuminated, while the one shown in Fig. 130 was shaded: there is . a corre- sponding difference in the size of the leaves. Fig. 199 shows the appear- ance of sections of sun- and shade - leaves of the Prickly Lettuce and Fig. 200 of sun- and shade -leaves of the Beech. Especially noticeable in the "sun-leaf'' are the longer palisade cells, the smaller air-spaces, the greater thickness of the leaf, and thicker cuticle or outer wall of the epidermal cells ; the number of stomata is also smaller. These effects are due partly to the liglit itself and partly to the dryness (or excessive evapo- ration) caused by the light, heat and wind. Leaves arrange themselves with reference to the direction of the light, and many follow the sun during the day (see page 217). Some plants, inhabitants of dry countries, place their leaves in a vertical position, thus avoiding the full effect of the light (see page 200. Beech leaves seen in cross-section: (a) sun leaf, (&) shade leaf. 346 EXPElilMENTS WITH PLANTS 217). The leaves of the compass plants are vertical and directed north and south. Many leaves tempora- rily assume a vertical position in very strong sunlight (see page 217), and it is noticeable that young leaves, which are more sensitive to the light than the older ones, usually assume this position. (Plants can be grown by electric light ; and this has proved profitable in forcing certain greenhouse crops in winter.) The trunks of trees may suffer from "sunscald," due to injury of the bark by the intense light and heat of the sun, or to the alternate thawing and freezing of the bark on the southwest side in late winter. The trouble may be obviated by shading the trunk with a screen of wire, boards, cornstalks, etc. Pruning often lets in too much light on the trunk, which suffers in consequence (this is especially noticeable in the Weeping Willow) . Very interesting results are obtained by growing- plants in darkness. To do this out-of-doors, it is only necessary to cover the plant with a section of stove- pipe, a wooden box or a barrel. Within doors the plant may be placed in a dark closet or box. Such plants (Figs. 103 and 180) have very long, slender stems (the nodes are far apart) ; they are pale in color, have little woody fiber, ^ and are consequently 1 This fact is taken advantage of in bleaching Asparagus, Celery and Rhubarb for market. The Celery is either "hilled up " or covered with gunny- sacks, or the light is excluded by means of boards : the leaf-stalks are thus bleached and rendered tender and succulent. The "laying," or lodging of Wheat is due to the shading of the lower portion of the stalk, which results in an insufficient production of woody fiber. now PLANTS ABE INFLU hJNCJiW 347 weak. The leaves^ (hi most plants) remain small and pale in color. Hairs and even prickles tend to dis- appear in darkness. It is well known that intense light causes a greater intensity of coloring of fruits, flowers and other colored parts of plants: this is especially noticeable in moun- tain regions. Compare the colors of flowers in shady woods with those in the sunlight of open meadows. Light also affects the abundance of flowers and fruit. Many plants bloom little or not at all in poor light, while in strong light they do so abundantly. This is noticeable in house -plants cultivated at a north or northeast window, as compared with those grown at a south window. The effect is due partly to the fact that with better light the leaves produce more food for the nourishment of the flowers and fruit, partly to the direct action of the light (and temperature) on the organs themselves. If possible, make experiments on this point. Some plants can be kept for years in healthy vegetative condition at an intensity of illumi- nation which is too low to permit them to blossom. Observe plants that are partially shaded (as by a house or hedge) , and note especially whether more blossoms are formed (blossoms formed on one side may, by twisting, appear on the other) on the side which is shaded or on the side which is exposed to the light. 1 In many Monocotyledons the leaves continue to grow in darkness. The scale-leaves of subterranean stems often develop into green forage-leaves if exposed to light (e. g., Hawkweeds). 348 EXPERIMENTS WITH PLANTS In making these observations, it will probably be noticed that many flowers grow toward the light and place themselves so as to receive it as directly as pos- sible. This has a useful purpose in making them much more conspicuous to insects. See page 298. Wind. — Every one is more or less familiar with the 201. The effect of wind on the growth of a tree trunk. effects of wind on plants. Near the seacoast, or on mountains, or wherever trees are exposed daily to strong wind, they show by their bent forms and curi- ous shapes its potent influence (Fig. 201). The dying of the branches on the windward side (Fig. 202) is due to the drying effect of the wind, which may in- crease transpiration as much as twentyfold (see page 208). Even moist winds may have a drying effect. It is interesting to observe how the one-sided develop- ment of leaves and branches affects the stem. This is HOW PLANTS ABE INFLUENCED 349 well shown in Fig. 203. It may be observed in vines, etc., which climb on walls. The effect of wind in drying up the blossoms of fruit trees, etc., is well known. For this reason, and also be- cause the winds lower the tempera- ture and do consid- erable damage to trees laden with ice and snow, the use of windbreaks is often indispensable. Food.— We have already learned (pages 137 to 162) that the kind of min- eral food th^ plant 1 receives affects its growth and general appearance . Thus, abundance of nitrogen ^ causes a particularly strong, 1 See articles by Riley and by Woods in the Year Book of the U. S. Depart- ment of Agriculture for 1901. 2 It is an interesting fact that abundant manuring with nitrogen, combined with abundant watering, very commonly produces "green flowers," i. e., flowers in which petals, stamens and even ovules are transformed into green leaf - like bodies. This happens frequently in garden Asters and other Compositae. In some cases this greening of the flowers is caused by the attacks of plant-lice 202. The effect of wind; branches stuiited and killed on the windward side. 350 EXPERIMENTS WITH PLANTS 203. How one-sided development of branches affects the trunk. (See Fig. 202). rank vegetative growth and imparts a deep green to the leaves, while phosphorus especially promotes the production of flowers and fruit. It is a well-known fact that starving a plant makes it flower and fruit m u c h earlier. De- priving it of water has the same effect (seepage 318). An excess of a particular substance in the soil may render it unfit for some plants, while others flourish in it. Thus, Asparagus svill stand so much salt that the weeds in an Aspara- gus bed may be killed by sprinkling on salt, while the Asparagus itself is not injured. Soil too alkalnie for ordinary crops will raise Sugar Beets and Alfalfa, while land too alkaline for these crops will grow Salt Bush, which makes good fodder. Peat Moss or Sphagnum is killed by a small amount of lime, while other Mosses flourish on lime- stone rocks and in water containing large quantities of dissolved lime. The presence or absence of lime usually has a marked effect on the flora. Some plants are known as lime loving, others as the reverse. IIO]V PLANTS ABE INFLUENCED 351 Some plants are found only in sour humus (either in wet humus, as Peat Mosses, Sundew, etc., or in dry humus, as Heath plants), while others are found only in "mild" humus (Dog's Mercury, Cow Wheat, etc.): some, indeed, are found only in a particular kind of humus, e. g., that of Conifers (Rattlesnake Plantain). Observe all you can in regard to the occurrence of plants in different kinds of soils. To a certain extent each kind of soil is characterized by certain plants. This has been noticed by prospectors, who have found that certain plants are found only where certain metals (e. g., zinc) abound. A fuller understanding of the kind of soil preferred by different plants ^ will not only enable us to better suit our crops to our land, but be of great assistance in determining the availability of hitherto uncultivated land for various crops. Not only the chemical, but more especially the physical character of the soil and of the subsoil (whether hard-pan or porous), is of importance in this connection. Find out what kind of land is considered most suitable for the various crops with which you are familiar. Try also to cultivate the ability to judge of the character of the land by the wild plants which grow on it. Such plants are indicators not only of the chemical and physical character of the soil, but also of the temperature and other important factors of climate. 1 The United States Department of Agriculture is now making soil surveys in various states, to determine what crops are best adapted to various soils. 352 EXPERIMENTS WITH PLANTS Heat. — At the beginning of tlie chapter it was re- marked that to give the plant too much of any of the things it requires is as bad as to give it too little. This is, perhaps, more strikingly seen in the case of heat than in other cases. We all know that too much heat quickly kills both animals and plants. On the other hand, if they have too little, they stop growing, and may die. In general, the less water the plant contains, the more resistant it is to cold. This is well shown by the behavior of greenhouse plants; excessive watering makes them over- sensitive to heat and cold (and light as well; such plants are liable to '■' sunscald"). Plants which have just been transplanted are said to be less sensitive to frost, since they contain less water. Frost does not injure buds in winter when they are compara- tively dry, but in spring, when they are full of sap, it kills them. Frost, during the period when sap is run- ning, causes the bark to adhere to the wood, and it does not again become separable until the return of milder weather. In such cases, the health of the tree may not always be affected; but the crop of fruit fails. Dry seeds which contain very little water (about 10 to 15 per cent)" stand extremes of temperature which would kill them if full of water. Seeds have been kept at the tempei^ature of liquid hydrogen (minus 238° C, or minus 396° F.) for some time, and carefully thawed out again, when they grew quite normally. HOW PLANTS ARE INFLUENCED 353 The way in which a frozen plant is thawed out makes a great difference. Allow some potatoes to freeze (they may be easily frozen in a water-tight can, sub- merged in a mixture of pounded ice and salt, or set in an ordinary ice-cream freezer). Place some of the frozen potatoes in water chilled by ice (but free from salt) , and let them stand until the water reaches room temperature. Place others at once in a warm place, so that they will thaw quickly. Frozen leaves (and other plant -tissues) have a peculiar transparent appearance on thawing ; the same thing occurs when they are boiled in water or injected with water in an air-pump (see page 190) ; in all these cases it results from the air-spaces becoming filled with water. It is supposed that when a plant is allowed to thaw rapidly this water evaporates and that the plant suffers injury, which might be avoided by slow thawing, which would permit the cells to again absorb the water which escapes from them into the air spaces during the freezing. The action of frost on the trunk may result in long splits in the trunk or in the killing of the ends of the branches, which soon turn black. The best treatment is to remove the injured portions by priming and to direct the energies of the tree to making new wood (prevent it from bearing fruit for a season) to replace that which is killed. Protection from frost is secured by covering the w 354 EXPKItlMEyrS WITH PLANTS plauts with a mulch, or, in the case of trees and shrubs, by bending them down (the roots must be cut in such a way as to permit this) on the approach of winter and covering them with straw or brushy Spraying or sprinkling with water at nightfall is a very effective means of protection ; this depends on the fact that moisture in the air prevents the radiation of heat and consequent cooling of the trees and soil ; it acts, so to speak, as a trap for the heat. Filling the air with dense smoke from bonfires of tar, resin or s i m i 1 a r substances answers the same pur- pose. The pale appearance of young leaves during cold weather, which is very noticeable in Winter Wheat, etc. (see Fig. 204 of the Ivy Geranium), is due to the fact that for the formation of chloro- 204. Branch of Ivy Genmium after a few days of cold weather; the young leaves have developed without being able to turn green. phyll a higher tempera- ture is required than for growth. The leaves con- sequently develop but cannot turn green. It is noticeable that some kinds of plants stand far 1 See an article by Galloway in the Year Book of the U. S. Department of Agriculture for 1895. BOW PLANTS ARiJ INFLUENCED 355 more cold than others (just as some kinds stand more water, light or alkali than others). Individual plants vary considerably in this respect : after a frost which kills most plants of a particular species it is often pos- sible to find one or two individuals which have sur- vived, not because of a more sheltered position but by reason of their greater hardiness. By preserving the seed of such plants and selecting seed from the hardi- est plants year after year, hardy varieties may be obtained. Of equal importance with hardiness in securing va- rieties for cold regions is the ability to ripen quickly (earliness). This may also be obtained by selection, as has happened in the case of Wheat in the United States; as a result the Wheat belt has moved steadily northward, especially in the last fifteen years. We have a record of one case in which a winter Wheat was in three years converted into a summer Wheat in this manner: conversely, in three years a summer Wheat was converted into a winter Wheat. The same thing is even more strikingly true of Corn, which on the plains of Santa Fe in South America requires six months to ripen, while in the Rainy Lake district of Lake Superior it ripens in two months and a half. This great change has all been accomplished by man. It has been found repeatedly in experiments that cuttings (of the same kind of plant) taken from a northern region and placed side by side with those of 356 EXPERIMENTS WITH PLANTS a southern region develop from fifteen to twenty days earlier than those which are accustomed to the warmer region. Early varieties of flowers, etc., are constantly imported from northern points. Temperature, more than anything else, determines what kinds of plants grow in a given region^. The tropics, the temperate and the arctic zones have each their characteristic vegetation. Plants which flourish in the tropics may be cultivated in the temperate zone (e. g.. Date Palm, Rubber Plant, etc.), but remain stunted and refuse to bear fruit. The study of the various zones to be found in a country is very important in determining what part is best adapted for various crops. ^ Wherever there are high mountains there are opportunities to study these zones to great advantage, since as we ascend the mountain we pass through successive zones. It will then be seen how much depends on exposure; i. e., the southern face of the mountain being so much w^armer than the northern, the zones will run higher, etc. The same may be seen in even a small hill or elevation. For this reason lAn interesting illustration of this is seen in the forests of the United States and Canada. As ws go northward from Florida we find, considering only good and well-watered soils, that the hardwood forest gradually diminishes, both in the number of trees and the number of kinds represented, until we come to the great pineries of the northern United States and Canada. Still further north these are succeeded by Birch, Willow and Alder: these gradually dim- inish northward until we roach the treeless wastes. 2 The " Crop Zones " of the United States are now being determined by the United States Biological Survey. HOW PLAINTS ABE INFLUENCED 357 the "lay of the land" is very important for plants. It often happens that one side of a valley yields good crops, while the opposite side is valueless for cultiva- tion. It is interesting to notice that during the day the hillside (especially the southern and southwesterly exposure) i^ warmer than the valley (except when a cold wind blows) ; the same is true at night, for the cold air, being heavier, sinks down into the valleys, so that they often have frost at night when the hill- sides above are exempt from it. Plants which grow in high altitudes have stunted stems with limbs densely branched or hugging the ground in the form of rosettes. These features have been produced experimentally to a certain extent by growing ordinary plants under favorable conditions by day and keeping them in an ice-house during the night. This imitates natural conditions, since the plants in question are comparatively warm during the day when the sun is shining, but cool off very rapidly after sunset and remain cold during the night. Normally the greatest growth takes place at night, hence chilling them at this time explains, in part at least, their stunted growth. Alpine plants have very commonly larger and brighter colored flowers, which are also richer in honey, so that the mountains are particularly good for bee-keepers. The foliage of these plants shows many 358 A'Xj'h'h'iMh'yrs with plants of the same devices for preventing evaporation which we have seen in desert plants : the strong light, rare- fied air and the constant winds tend to promote evaporation, while the coldness of the ground hinders absorption . Owing to the short time which such plants have for flowering and fruiting, they perform these opera- tions very rapidly, often in half the time needed by similar species in the lowlands. The plants of northern latitudes resemble alpine plants in most respects, and especially in the last- mentioned feature, i. e., early -flowering and fruiting. Gardeners take advantage of this to get early varie- ties by importing seed from northern regions. Some- times seed is sent to such regions to be grown until the desired earliness has been obtained. Of the plants familiar to you, which are most sensi- tive to cold? which are least sensitive ! Do you find differences in individual branches of the same tree in this respect? In view of the facts which we have just discussed, we may realize vividly that the life of every plant is a continual and delicate adjustment to its surroundings. Some plants possess the power of adjustment to a greater degree than others; but all must exercise it constantly in order to survive; and this is a funda- mental characteristic of all living organisms. We may illustrate this further by considering a tree. HOW PLANTS AKE INFLUENCED 359 It is a very exact index of its surroundings, so that a skilful woodsman knows at once, on looking at it, the conditions under which it has grown. The influence of light, water, prevailing winds, have all left their marks on it. Its position, with reference to the compass, can be told by examining it. For this reason, in transplant- ing a tree, we should be careful to set it so that the same side faces the north after, as before its removal. These facts serve to show that the form of the plant is largely determined by its surroundings. It may also be greatly changed by diseases, especially the attacks of fungi, to which are due the remarkable growths known as "witches' brooms," etc., as well as by in- sects, which not only cause the formation of all sorts of curious galls, but even in some cases produce the greening of flowers, in which the petals, anthers, etc., are transformed into green, leaf- like bodies. Moreover, the development of each part of the plant is influenced by that of every other, as is demonstrated every day by the experience of making cuttings and of pruning (see pages 79, ^^^ 257 and 263). If the tip of the main axis of a Pine be removed, the branches just below it begin to straighten up to take its place; one finally does so and the rest then fall back to their original positions; the one which becomes upright changes its structure and becomes like the tip of the main trunk whose place it takes, e. g., it becomes alike on all sides (and the intenuil structure changes. 360 EXPERIMENTS WITH PLANTS accordingly) instead of having an upper and a lower side (with a corresponding difference in internal struct- ure). The Potato furnishes another illustration; if the young tubers be cut off as they are forming, the tuber- forming material accumulates in the parts above ground and produces tubers in the branches; these are green and bear leaves. Try both these experiments, if possible. This influence of one part on another is called cor- relation. Numerous other illustrations might be given; it will suffice to mention the effect which the fertiliza- tion of the ovary has on surrounding parts (see page 309) . Experiments on this point may easily be made by removing the anthers in the bud and preventing pollination by paper bags. It is hoped that the facts set forth in this chapter will lead to experiments when practicable, and to con- stant observation of the experiments which are every- where spontaneously occurring in garden and field. CHAPTER IX PLANTS WHICH CAUSE DECAY, FERMENTATION AND DISEASE What is the cause of decay ? Formerly it was sup- posed to be due to some property residing in the organism itself ; our present knowledge is that it is due to plants called bacteria. Although too minute to be seen except with the microscope, they can neverthe- less be studied with the simplest apparatus. To beghi with, we may get an abundant growth of bacteria by putting a little hay in water and allowing it to stand a few days, when the bacteria will form a gelatinous film on the surface. On mounting a drop of this in water on a slide and examining it under the microscope, the bacteria appear as very small, glisten- ing bodies approaching in shape some of the forms shown in Fig. 205; very probably some of these will be in motion. This motion may be merely mechan- ical, i. e., a dancing motion such as any small particles (e. g., India ink or vermilion) show in a liquid, or it may be due to the activity of the bacteria, which move by means of whip-like protoplasmic projections (cilia). Pour off some of the liquid in which the bacteria are (361) 362 expj!:kiments with plants growing, strain it through a cloth, and fill five vials or bottles almost half full of it. Insert in the mouth of each vial (or bottle) a firm cotton plug made by [o. 205. Different kinds of bacteria: (a) spherical bacteria imbedded in a gelati- nous film which floats on the surface of the liquid, (6) rod-like forms, (c) bac- teria multiplying by division into two, {d) bacteria of lock-jaw (tetanus), with a spore at one end, ie) elongated rods, (/) rod-like forms dividing, {g) rod- like forms with a spore in each, (h) spiral forms. rolling the cotton into a firm roll just large enough to fit the vial. Place one of the bottles {a) in a warm place in the light, another {h) in a warm place in the dark, another (c) in a cool place (preferably on ice) PLANTS WHICFT OAirSi: DECAY 363 in the dark. Into the fourth bottle {d) put a drop of formalin, and place alongside of (b) . The fifth bot- tle {e) we will subject to the heat of steam. This is most conveniently done by placing the bottles in a pan and inverting another pan over it as a cover, or by means of the apparatus shown in Fig. 206. It consists of a pail (six to eight inches in diameter) and two pans, all preferably of graniteware (tin may be used) . One pan serves as a cover, while the other, which is pierced with holes, serves as a support. A little water is put into the pail, and it is then set on a stove or over a burner. The vials or other dishes are placed on the support, the cover is fitted on and the water is allowed to boil. When it has boiled for half an hour we remove the vials. This process is known as sterilizing (the apparatus is called a steam sterilizer). We place the sterilized vials in a warm place in the dark, and renew the sterilizing each day until they have been sterilized three days in succession. Examine all of the vials every day. In which does the most rapid growth of bacteria occur, as shown by the cloudiness of the liquid and the formation of a surface film? 206. Steam sterilizer, consist- ing of a pail, a pan for cover and a smaller pan pierced with holes as a sup- port (all should be of tin or agateware). (Sectional view.) 364 EXPERIMENTS WITH PLANTS Bacteria in general grow best at from 80° to 95° F. Below 40° F. and above 110° F. they make practically no growth. The temperature of ice fails to kill many kinds; even that of liquid air (minus 310° F.) does not kill all kinds. Bright light kills many kinds, while others are not much affected by it. Formalin is a good example of a disinfectant which kills the bacteria. (Disinfectants which kill the germs are called germicides, those which thoroughly check their growth or stop it are called antiseptics.) One part in 5,000 or 10,000 of water is said to be efficacious against many bacteria; articles may be disinfected by leaving them for a few hours in a closed box exposed to formalin vapor, or sulphur may be burned in any closed space with good results. Other chemical dis- infectants are chloride of lime, corrosive sublimate, carbolic acid, potassium permanganate, strong mineral acids, ete.^ The effect of sterilization is due to the fact that bac- teria in their ordinary or vegetative condition are killed by the heat of steam. Some of the bacteria found in iThe following will serve to indicate approximately the strength to be used : Carbolic acid 3 per cent or one tablespoonful of the ordinary solu- tion to a pint of water; lysol 1 to 2 per cent; copper sulphate 1 to 2 per cent; chloride of lime 3 per cent; potassium permanganate 1 to 2 per cent (useful as deodorizer also); corrosive sublimate one-tenth of 1 per cent; hydrogen peroxide nearly full strength; listerine full strength. Wounds should be well washed with disinfectant solution by means of a pipette and then covered with iodoform, or powdered boracic acid. PLANTS WHICH CAUSE DECAY 365 hay infusions produce resistant bodies known as spores (compare Fig. 205, g) which are not killed by this temperature. On standing a few hours the spores germinate and pass into the vegetative condition, when they may be killed by steam heat. Hence the value of sterilizing on three successive days. Ordinarily, however, one sterilization of half an hour answers every purpose. It was formerly supposed that the growth which occurs in infusions, etc., was due to spontaneous generation, i. e., to the origin of living organisms from lifeless matter. This view received confirma- tion from the fact that an infusion may be boiled and growth nevertheless occur. With the discov- ery of resistant spores and of the fact that after several sterilizations no growth occurs, the doc- trine of spontaneous generation was over- thrown. Let us now take three tumblers, place a slice of boiled potato in each, cover with cotton held in place by an elastic band as shown in Fig. 207 (or use 207. Tumbler containing a slice of boiled po- tato, closed by a cotton plug held in place by an elastic band. 366 EXPERIMENTS WITH PLANTS small tumblers and insert a cotton plug as in Fig. 212) and sterilize them all for half an hour. After they have cooled down again, remove the cotton from one {a), expose to the air for a minute and replace the cotton : to another (6), transfer a minute quantity of bacteria from the liquid by means of a needle J For this purpose we pass the needle back and forth several times through the flame, and when cool dip it into the liquid. We now lift the cotton at the edge and draw the needle once across the surface of the potato and at once replace the cotton. Leave the third tumbler (c) intact, as a control. Put all the tumblers away in a warm place in the dark and observe them daily. The bacteria in {a) come from the air ; many disease -producing bacteria (e. g., those of tuberculosis) are wafted about in the air; for this reason consumptives should take special precautions to avoid infecting the air. Do the spots of decay appear in {h) anywhere except along the needle track: do any appear in (c)? Does the potato beneath the spots alter in color, consistency, etc.? Scrape a bit of the potato from one of these spots, mount the scrap- ing in a drop of water, and examine under the micro- scope. The large, glistening bodies are starch grains, while the bacteria appear as minute bodies floating 1 This is prepared by heating the end of a glass rod in a flame until it fuses and then forcing into it a piece of fine steel (or platinum, if obtainable) wire about two inches long. PLANTS WHICH CAiSlJ DEC AT 367 208, about in the liquid (Fig. 208). Add a drop of iodine solution, and observe. Wo may get a good idea of the relative size of the bacteria by comparing them witii the starch - grains, which latter are too small to be distinctly visible to the naked eye but are easily seen with a hand- lens. Do you find that the spots on the potato differ in color, consistency, shape and gen- eral appearance? If so, they are, in all probability, due to different kinds of bacteria. In order to separate the various kinds, we may proceed as follows: Fill a vial half full of distilled water, and sterilize for half an hour. Then pass the needle through the flame two or three times ; when cool touch it to the spot from which a culture is desired, and stir it about in the vial. Remove the needle, sterilize in the flame, and then dip it in the vial again and touch it to a pre- viously sterilized slice of potato (arranged as before in a tumbler), at various points a little distance apart, and at once replace the cotton.^ If the amount of water used is sufficient, the bacteria will be so scattered that 1 During this operation the tumbler should be held nearly horizontal, to keep bacteria from falling upon the potato from the air. . A scraping from a potato culture, showing starch-grains and bacteria. A good way to get an idea of the size of bacteria is by comparing them with some well-known object, such as a starch-grain. 368 EXPERIMENTS WITH PLANTS each minute drop of the liquid will contain not more than one of them, so that whene\'er we touch the potato we shall deposit not more than one; hence each spot will be the result of the growth of a single bacterium: this is a pure colony: if we infect a sterilized potato (or other medium) from such a colony, so as to get only one kind of bacterium in the culture, we obtain a pure culture. It is interesting to consider, in connection with this mode of propagation, that, as long as an individual keeps on dividing, there can be no such thing as death from old age, since the parent is completely absorbed into the offspring. Bacteria are distinguished not so much by their forrn and general appearance under the microscope as by their behavior when grown on various substances, such as potato, gelatine, beef -broth, etc. They are classified largely according to the size, shape, consistency, color, etc., of the spots or colonies which they produce. One very interesting form, which may be easily recognized, appears frequently on potato and bread - cultures: it is bright red in color, and is of especial interest as causing the " bloody- bread" of the middle ages, which was believed to bleed miraculously. The bacteriological examination of water is so im- portant and at the same time so simple that we may well turn our attention to it. For this purpose we may prepare some nutrient gelatin as follows: Make some PLANTS WHICH CAUSE DECAY 369 beef- broth by heating a pound of chopped beef for half an hour (at about 65° C) in a pint of water. Strain it through a cloth, and add two ounces of gelatin (the " sparkling gelatin " used in cooking is preferable) , and let it soak over night. In the morning, heat in the sterilizer until dissolved, then add one-tenth ounce salt (best accomplished by adding one ounce salt to 100 c.c. of water, and taking 10 c.c. of this) and one -fifth ounce peptone (obtain- able at drug- stores; it may be omitted if necessary) , add a tablespoonful of molasses and finish by adding dilute lye or lime-water until the gelatin is slightly alkaline to litmus. Remove the neck from a funnel so that it will fit into a tumbler (Fig. 209), and filter the gelatin through filter paper or cotton, keeping the whole hot in the sterilizer during the process. If the gelatin does not appear clear, filter again, first beating in a little white of ^gg. It may then be placed in a bottle and, the neck be- ing plugged with cotton, sterilized. If necessary, re- peat this for three successive days, when it will keep indefinitely. (Each time the bottle is opened it must be sterilized again.) Now obtain several flat- sided bottles of the same size, and put into each sufficient gelatin to cover the side when the bottle is flat on the 209. Funnel with neck re- moved so as to fit into a tumbler: the whole is placed in the steri- lizer, in case gelatin is to be filtered hot. 210. Flat bottle containing gelatin: used for "plate cultures." 370 EXPERIMENTS WITH PLANTS table (Fig. 1210) . The same amount should be placed in each bottle; this is easily managed with a sterilized pipette or medicine -dropper. Wipe the mouth and neck of each bottle, and plug with cotton ; then sterilize and set aside for a day or two. If no bacterial growth appears, we may proceed. Warm the bottle just enough to liquefy the gelatin, remove the plug, and introduce (by means of a sterilized pi- pette or medicine -dropper) the same quantity of water (several drops) into each bottle (a separate sterilized pipette must be used for each) . Replace the plug, mix the contents by turning the bottle from side to side (do not allow gelatin to get on the plug) and place the bottle on its side in a dark place. Such cultures are called plate cultures," and they serve excellently to tell how many bacteria the water contains, since we may count the colonies which come from a given quantity of water (in this case we assume that each colony comes from a single bacterium). It is well, in making this experiment, to compare some' water from the drinking supply, some from a stagnant pond or pool and some from a barnyard. In the latter case we shall probably find bubbles of gas torming in the gelatin. This is an mdication of the PLANTS WHICH CAUSE DECAY 371 colon bacillus which is characteristic of animal excre- ment, and when found in water shows sewage contami- nation; such water should not be drunk without being boiled, and a sample should be taken to the health officer for examination. One fact which cannot help striking us in observing these cultures is the rapidity with which the bacteria grow. A single bacterium produces in forty-eight hours a spot or colony containing thousands on thousands. If we observe the bacteria in a hanging drop (see Fig. 165) under the microscope we can see the manner in which they multiply : it consists in simply dividing into two as shown in Fig. 205 (c). It has been observed that this division into two may occur as often as once every half -hour; if this rate could be maintained for twenty- four hours and none should die, we should have at the end of that time more than two hundred and eighty trillions of descendants from a single germ. It may be readily realized that even at a much less rapid rate of increase a few typhoid germs might soon infect a whole water supply. In the bacteriological examination of water, it is customary to count the bacteria by the method just described, and also to examine for the colon bacillus and for disease -producing bacteria, such as those of typhoid, cholera, etc. These are identified by their appearance in the cultures and under the microscope. It is important to know that typhoid may be con- 372 EXPERIMENTS WITH PLANTS tracted by eating raw oysters, which are frequently grown in water contaminated by sewage. Fig. 211 shows the distribution of cholera cases in the Hamburg epidemic of 1892. It will be noticed that, in the words of Professor Koch, "cholera went right up to the boundary of Altona and there stopped. In one street, which for a long way forms the boundary, there was cholera on the Hamburg side, whereas the Altona side was free from it." This is equally true when the boundary runs diagonally through a block. The ex- planation lay in the fact that while both cities used the same water supply (which received raw sewage from several towns) , Altona filtered the water carefully, while Hamburg did not. The filtration of water is a very simple process. It is passed through several feet of sand (sometimes mixed with charcoal) and a film soon forms on the sur- face of the sand which catches the bacteria. Such a film may be artificially produced, if necessary, by add- ing chemicals (e. g. alum) to the water without injur- ing it for drinking purposes. Every town or city water supply should be filtered; the cost is slight and the benefits very great. The small filters sold for house- hold use are for the most part highly injurious and serve only as breeding places for bacteria, owing to the fact that they cannot be properly cleaned. Let us now examine some milk. Fill three- vials half full of nutrient gelatin, plug, sterilize, and set 374 EXPERIMENTS WITH PLANTS aside for two or three days, and if no growth appears, proceed to roake a bacteriological examination of milk. For this purpose obtain some milk freshly drawn; some milk which has stood for from twelve to twenty - four hours, and some sour milk. Make so-called "stab cultures " by dipping the point of the sterilized needle into the milk, and then plunging it straight down through the center of the gelatin to the bottom; the needle must be sterilized in the flame after each stab. The plugs should be replaced at once, and the vials set aside. In which do you see the first signs of growth; in which is the growth most abundant; what do you conclude as to the relative number of bacteria in the three kinds of milk ? Stab cultures are especially interesting because some of the bacteria are placed deep in the gelatin w^here they are deprived of air, while others are left on the surface. Some kinds of bacteria die if deprived of air; other kinds die if exposed to the air, while there are still other kinds which can live under either condition. In a stab culture we have an opportunity to judge which of these classes of bacteria w^e have. Thus, a culture which grows like Fig. 212 (a), indicates the first class; if like Fig. 212 (&), the second class; if like Fig. 212 (c) , the third class (or a mixture of the first two). In order to determine whether bacteria use up oxygen and produce carbon dioxide, we may take an infusion PLANTS WHICH CAUSE DECAY 375 which is filled with bacteria, place it in a wide -mouthed bottle, and place in it a vial containing clear water, and stopper the larger bottle as shown in Fig. 30. As a control, use a similar arrangement with pure water in place of the infusion. A still better arrangement is kirn tllLl 212. Stab cultures in gelatin: (a) air-loving bacteria, (6) bacteria not able to grow in the presence of air, (c) bacteria which grow equally well with or without air. to repeat the experiment described on page 34, Fig. 31, using the infusion in place of the seeds. Wo may now place some milk in vials or bottles, close the mouths with cotton, and sterilize for ten minutes on three successive days. Open one bottle three days after the last sterilization, another a week later, and another two weeks later. Do you detect any 376 EXPERIMENTS WITH PLANTS sigD of souring ? It appears that the souring of milk is d):^^,_^ afterward taken 7n^;^^a up by botanists, who traced the connection care- fully and came to the conclu- sion that the cluster -cup was a necessary stage in the life- history of the 229. Cluster-cup (aecidium) of Black Stem Rust ot Wheat, n k t rv* fungus. A diffi- culty arose in the fact that the Eust prospers even when there are no Barberry bushes, and it is now known that, in some cases at least (e. g., in Australia) , the uredospores can live through the winter and infect the Wheat again in the spring. It is supposed, how- ever, that the teleutospores cannot infect Wheat, but only Barberry. The uredospores of the Black Stem Rust of the Wheat readily infect Barley, and vice versa; but it seems highly probable that they cannot infect Oats (nor vice versa) . The Black Stem Rust of Oats seems PLANTS WHICH CAUSE DECAY 405 to be a distiDct form, though it in every respect closely resembles that of the Wheat, and passes its cluster- cup stage on the Barberry. The same is probably true of the Black Stem Rust of the Rye: it does not appear to affect any other Grain. The Orange Leaf Rust of the Wheat is very similar in appearance to the Black Stem Rust; its cluster- cup stage is passed on Anchusa and Echium; the uredo lives over the winter in the United States. The Orange Leaf Rust of the Rye appears to be distinct from that of Wheat: its uredo lives over the winter in the southern states. The Crown Rust of Oats is found only on Oats. It resembles the Orange Leaf Rust of Wheat. Its cluster- cup stages are passed on Rhamnus. The method of observing the germination of the cluster -cup spores or the uredospores is simply to place perfectly fresh spores in a hanging drop of water. The teleutospores are to be treated in the same manner, only they must be preserved during the winter, for they will germinate only in the spring. These germination experiments may not always succeed, but they are worth trying. In order to make infections with uredospores, it is only necessary to grow some Wheat in pots during the summer; and when the leaves are three or four inches long, bring in a fresh leaf of Wheat which is well covered with uredospores, and tie two of the growing Wheat 406 EXPEBIMENTS WITH PLANTS leaves together, with the infected leaf between them, in such a way that there will be a close contact all along the leaf: this will ensui'e the uredo- spores reach- ing the growing leaves, and will prevent them from drying up. The moister the air is kept, the better; it may be well, therefore, to cover the plants with a paper bag (or, better still, with a bell-jar if available). The common Hollyhock Rust (found everywhere on Hollyhocks, the Round -leaved Mallow and other Mal- lows) is an example of a Rust which passes through its entire life- history on one kind of plant, thus con- trasting with the Rusts of Grain: it produces teleudo- spores only; they germinate readily in water and may be used for infection experiments (either by putting a drop of water containing the spores between two leaves tied together or by using the infected leaf in the manner described above) . The yearly loss from Grain Rusts in the United States is estimated at considerably more than $18,- 000,000. As an example of a Mildew we may study the com- mon Mildew of the Lilac. The mycelium appears on the surface of the leaf as a whitish covering (scrape off a little of this, mount it in a drop of weak alcohol and examine imder the microscope). After a time black specks, visible to the naked eye, appear here and there on the mycelium. Remove some of them and ex- amine under the microscope : they have the appearance PLANTS WHICH CAUSE DECAY 407 shown in Fig. 230. The long, branching appendages of the rounded black bodies are very characteristic. Press on the cover-glass with a rubber pencil -eraser until some of the black bodies are crushed; we may then see the spore- sacs, containing four or more spores. Mildews are very common on both wild and culti- vated plants and do a large amount of dam- age. They do not penetrate to any great extent into the leaf but absorb nUtri- 930. Penthecmm of the common Mildew of the Lilac; spore- TTIPnt bv mParm sacs (asci) issuing from an opening produce! by crushing. of short sucking organs which penetrate into the epidermal cells. Most of the loss from plant diseases is preventable by simple measures; among these are the following i^ (1) Spraying with chemicals (Bordeaux mixture, sulphur, etc.) which do not injure the plant. (2) Destruction of diseased plants or portions of them by burning; this of course destroys the spores. 1 Consult Ward: "Disease in Plants"; Lodeman: "The Spraying of Plants"; Ward: "Timber and Some of its Diseases"; Massee: "Text-book of Plant Diseases"; also articles in the Year-Book of the U. S. Department of Agriculture for 1895 by Waite and by Galloway and Woods; for 1896 by de Schweinitz and by Howard; for 1899 by Galloway; for 1900 by von Schrenk. 408 EXPERIMENTS WITH PLANTS Weeds, volunteer Grain, etc., along roadsides and in fence corners may harbor the disease, and hence should be kept down as much as possible. (3) Rotation of crops in the case of diseases which can live in the soil; this allows them to die out in the interval between crops. Plants with such diseases should be burned rather than plowed under. (4) Disinfection of seed, seed bins, thresher, etc. (5) Careful attention to wounds, cuts made in pruning, etc. These should be repeatedly painted with tar to prevent the entrance of disease. Among the books which may be consulted on the subject of the chapter are: Conn: "Story of Germ Life." "Bacteria, Yeast and Molds in the Home," "Agricultural Bacteriology;" Newman: "Bacteria," CHAPTER X^ MAKING NEW KINDS OF PLANTS 2 It was not long ago that the finest Tomatoes were so small, tasteless and full of seeds as to be utterly unfit to eat; at that time they were called "Love- apples" and were grown merely as curiosities. The splendid varieties of the present have all been made in a generation. All our cultivated fruits have been similarly im- proved. How this is done is well illustrated in the work of Mr. Luther Burbank on Plums. He began by carefully studying the various kinds of Plums obtain- able from this and other countries, with a view to finding out their individual peculiarities and possi- bilities of improvement. Then he crossed American, Japanese and European kinds together, and from the resulting mixture selected the best for further experi- ments, destroying the rest. The results have been 1 Indispensable for reading in connection with this chapter is "Plant Breeding," by L. H. Bailey. Both the second edition (1902) and the third edition (1904) should be at hand, since the former contains an interesting chapter omitted from the last edition. Also de Vries: "Plant Breeding," 2 Of the illustrations in this chapter I am indebted to Mr. Luther Burbank for Figs. 231 to 236 and 240 to 245, and to Professor Hugo de Vries for Figs. 247 to 252. (409) 410 EXPERIMENTS WITH PLANTS extraordinary: they may be briefly summed up as follows : 1. Every possible variety of coloring of skin and flesh has been obtained, from a pure golden yellow to deepest blood -red. Mottled and variegated forms have appeared in abundance. 2. The shapes vary as much as the colors. The ■'Apple Plum" has the size, shape and appearance of an apple: others are like an inverted pear, while all the intermediate shapes are represented. 3. The new flavors and aromas defy classification. While the Bartlett Plum tastes exactly like the Bartlett Pear, others suggest a banana, and all degrees of sweetness and acidity are found. Some have the aroma of pineapples, others of apples, and of certain kinds but a few are needed to fill a whole room with fragrance. 4. The sizes have been increased up to three inches long and two and one -half in diameter. That the hybrid may sometimes exceed either of the parents in size is well shown in Fig. 231. The parents are an American Plum (Primus Americana) shown on the right, and a Japanese Plum {Primus triflora) ^ shown on the left. Among the hybrids which appeared in the first generation of this cross, before any selection had taken place, was the one shown in the center of the figure. The Giant Prune, over two and one- half inches long, is another very interesting illustration MAKING NhJW KINDS OF PLANTS 411 of this point; it is a cross between the French Prune (shown in Fig. 1236) and the Pond Plum (a European Plum about one and three-quarter inches in length), a 231. Increased size iu Plums due to hybridization (without selection). Japanese parent on the left, American on the right, hybrid iu the center. Two-thirds natural size. and was brought to its present huge size by con- tinued selection: it therefore owes its size to crossing plus selection. Another offspring of the French Prune, called the Sugar Prune (Fig. 232), is not only much larger but ripens a month earlier and is even sweeter than the parent, running as high as about 24 per cent sugar, or practically one -fourth of the total weight of the fresh fruit. This was obtained simply by selection, no crossing having been done. These three instances illustrate very well the different ways of securing increased size. rr -r% n • • '->^-- Increased size in Plums due entirely to 0. l3y producing vane- selection (without crossing). French Prune . . 1 • 1 • i 1 (dried) on the left; Sugar Prune (dried) on ties which ripen a month the right. Two-thirUs natural size. 412 EXPERIMENTS WITH PLANTS before the earliest of the old varieties, and, on the other hand, varieties whioh last until December, the Plum season has been greatly prolonged. The impor- tance of early and late varieties is very great, since they enter the market without competition in their particular line. 6. Some varieties have been produced which seem to be unaffected by frost. Even though the petals and young leaves are frozen and killed, the stamens and pistils go on performing their functions and the trees bear a full crop of fruit. Other varieties have been obtained which are enormously productive even where the old varieties fail. Many of these begin to bear abundantly the third year from the seed when grafted upon trees of ordinary size; others have been bred to stand shipping for long distance. Some kinds have been secured which remain on the tree from six to nine weeks in hot weather without deterioration, thus possessing a great advantage over many of the older varieties which must be picked as soon as ripe. Some of these new Plums are accommodated to climates and conditions where the Plum has hitherto proved a failure. A notable instance of this is the Improved Beach Plum (Fig. 233), obtained by crossing the Beach Plum (Prunus maritima) with an American Plum {Primus Americana). The Beach Plum is a wild species growing along the coast as a low, spreading shrub, not more than three or four feet high, with a MAKING NEW KINDS OF PLANTS 413 very dull -colored, small, bitter fruit (see Fig. 233), utterly worthless except for preserving. It has the advantage of growing in all situations, thriving in dry sand or in the soggy soil of swamps, indifferent to cold and frost and wonderfully prolific. By crossing and selection, the good qualities of both parents have been retained and the bad ones 233. Improved Beach Plum in the tenter. The parents are: Beach Plum on the right, an American Plum on the left. Natural size. eliminated. The Improved Beach Plum, as it is called, bears so abundantly that the fruit almost conceals the wood, as may be readily seen from the photograph (Fig. 234) , which represents a branch three and a half feet long. The fruit is shown full size in Fig. 233. It is of a deep purple color, with white dots, with deep yellow flesh and a stone not larger than a cherry -pit. It is a delicious plum of unusually fine flavor, without a trace of the bitter taste of the Beach Plum. It is indifferent to frost, and grows and bears under the most trying conditions of soil and climate, and will 234. A branch of the Improved Beach Plum. (The fruit is shown natural size, in Fig. 233.) Less than one-eighth natural size. MAKING NEW KINDS OF PLANTS 415 produce abundantly where Plum culture has hitherto been impossible. An interesting departure has been made by crossing Plums with other fruits. A cross between the Plum and an evergreen Cherry has been made which promises most striking results. A still more re- markable cross is between the Plum and the Apricot, which Mr. Burbank succeeded in making, after making many trials, and which he has called the Plumcot (Fig. 235). This resembles an apricot but is more highly colored, with very fine silky down: the pit some- times resembles that of a plum, some- times that of an apricot: the leaf is 035. The pinmcot , t/tj ill pji cross between the mtermediate between the leaves 01 the pium and the Apri- cot. One - half nat- parents. The flavors are unique and ^»"ai size. varied and, taken all together, it is a most remark- able and delicious fruit. Not content with these achievements, he conceived the idea of producing a Stoneless Plum and Prune. Beginning with a small, unproductive variety, with fruit no larger than a cherry, but with a stone w^hich only partially covered the kernel, he crossed it care- fully with the French Prune and selected the progeny until a variety of new Plums were obtained, all of good size, good flavors and fine appearance, and all destitute of stones. In the center is no stone, but in its place a cavity within which lies a more 416 JSXPEBIMENTS WITH PLAN'lti or less well -developed seed. Some of the seeds are normal in size and shape, others more or less de- formed and abortive, while in a certain percentage seed and stone are both absent. Fie:. 236 shows, 236. The Stoneless Plum, lowet row; and parents, upper row. At the right in the lower row the StoneIes.s Plum, external appearance; in the middle the fruit cut open showing a normal seed with a cavity where the stone would ordinarily be; at the left, another frnit containing neither stone nor seed, the latter being represented by a shriveled remnant. In the upper row the parents: at the right the French Prune; at the left the Prunier sans Noyau. All natural size. in the middle of the lower row, one of these prunes cut across; in this a well -developed seed is present: on the left is shown another in which nothing remains of the seed save an abortive remnant. While Mr, Burbank believes it perfectly possible to breed out MAKING NEW KINDS OF PLANTS 417 the seed altogether, he does not consider it desirable to do so, for the reason that the seed adds flavor to the cooked prune. These astonishing results represent but a portion — indeed a minor portion — of the achievements of one man during a few years of work, and they afford an excellent illustration of the possibilities of plant- breeding. The method by which they have been brought about is simplicity itself: variation and selec- tion are the two processes which produce all these results. We may now examine them more in detail. It is a familiar fact that every plant shows some variation (since no two plants, or leaves even, are alike), and it has been discovered that variation obeys certain laws. It not only confines itself within certain limits, but there is a certain average form or type around which the variations group themselves. This may be made clear by means of a diagram. If we count the number of rays^ in a large quantity of daisies (the Common Ox-eye Daisy), we may find that it varies, let us say, from five to thirty- seven. If we sort them into piles, putting into the first pile all those with five petals, into the second all those with six, and so on, we shall find that the pile containing those with twenty -one petals is the largest. If, now, we string the daisies in each pile on an upright wire, so as to form vertical columns of them, we shall get I The rays are the white outer parts, usually called "petals." AA 418 EXPERIMENTS IV ITS PLANTS the series represented by the upright lines in Fig. 237. The highest pile is the one containing those with twenty- one rays, and the size of the piles decreases in both directions from this: those which contain daisies with five and thirty- seven rays are the smallest and represent the two extremes. When we draw a line over the tops of the piles, we get a curve of Zl U it 2S lb 27 26 i9 .10 0> 32.33 . 237. Curve of variation ; the result of sorting daisies into piles according to the number of rays they possess. very characteristic form. It has been found that, no matter what feature of an organism we study in this way, we get practically the same sort of curve (the only apparent exception being partial curves and double curves). This curve, therefore, becomes of great interest, especially as it is found that it can be expressed by a mathematical formula and that the variation obej^s certain mathematical laws. The mathematical, or statistical, study of variation has now become an important branch of biology. MAKING NEW KINDS OF PLANTS 419 It may be remarked that a curve like that shown in Fig. 238 would indicate that the species was evolving Z 17 18 19 » ai it 23 2t 25 2b 27 2a 29 JO 31 32 30 3« 35 3b 37 3839 40 -Jl ^^43 ■♦435 238. Asymmetrical curve of variation. in the direction of a larger number of rays, since it shows more individuals above than below the type in respect to the number of rays. A curve like that in 5 fo 7 8 9 10 11 U 13 t* 15 Ife ?7 18 )9 20 21 22 13Z1 25 ^li 27 28 29 3031 3^3J34J5 239. DoiTble c^^rve of variation. Fig. 239 would indicate a splitting up of the species into a form with thirteen and a form with twenty- one rays, 420 EXPERIMENTS WITE PLANTS The variations just discussed are the ordinary kind and may be called fluctuating variations (because they fluctuate around a mean, or average type) to distinguish them from sudden variations or sports (e. g., reversions and monstrosities), which are sudden and apparently lawless deviations from the type and only occur occasionally; fluctuating variations, on the other hand, occur everywhere and in all plants. A Peach tree occasionally produces a branch which bears only nectarines; this is called a sport. If the branch be cut off and used as a cutting it will produce a Nectarine tree. Occasionally a branch of this may produce peaches: this return to the original condition is termed atavism, or reversion, and is also apt to occur in plants which are not known to have originated as sports. When a sudden variation originates, as in this instance, from a single bud on a plant, it is called a "bud -variation." The various Moss Roses, many kinds of Chrysanthemums, many variegated plants, etc.,^ have originated in this way. The word sport is usually applied to bud -variations, but is not necessarily limited to them. It may be used for any kind of sudden variation. The term monstrosity is commonly used to designate a sudden variation which has the appearance of an abnormality or deformity; as, for example, when a stem becomes flattened and iSee Bailey: "Plant Breeding," first edition (1895) or second edition (1902), Lecture IV. (This lecture does not appear in the third edition , 1904.) MAKING NEW KINDS OF PLANTS 421 fan -like as in the Cockscomb, or when the edges of the leaf unite and cause it to assume the form of a pitcher, as happens not infrequently in various plants. Sadden variations may or may not come true to seed. The greatest importance is attributed to them by Professor de Yries, as will be seen later. Whoever wishes to improve plants must be on the alert to seize upon variations, whether they be of the ordinary fluctuating kind or sudden variations. Ordinarily only favorable ones will be preserved, but when these do not occur the plant- breeder may con- tinue to propagate the most variable individuals, hoping that in time favorable variations will occur. By varying the conditions of culture^ and climate (described in Chapter VIII), it is possible for the breeder to produce variations in the desired direction, or, as he says, "break the type." Some plants respond very readily to that treatment: others do not. In general, however, this is a tedious process and of very small value as compared with crossing. By crossing, the breeder can create almost endless variations and at the same time direct them in the desired channels. Crossing means the fertilization of a plant with pollen from a different variety or species. The result of the cross is called a hybrid.- 1 See an article by Webber in the Year - Book of the United States Department of Agriculture for 1896. 2 See Bailey: "Plant Breeding." See footnote on page 420. Also an article by Swingle and Webber in the Year -Book of the United States Department of Agriculture for 1897. 422 tiXPEBIMENTS WITH PLANTS The hybrid may resemble both parents and possess intermediate characters. This is the more usual con- dition, and may show itself as a mixing of the characters, as when a red flower crossed with a yellow one gives a spotted flower with red and yellow spots standing side by side; or it may result in a blending of characters, giving in this case a uniformly orange -colored flower; or, finally, we may have the characters both mixed and blended, giving orange- colored petals with red and yellow spots. The hybrid frequently resembles one parent much more than the other, sometimes showing the char- acters, of one parent only. It very frequently happens that the hybrid is of greater size and vigor than either of the parents. A good illustration of this is seen in Fig. 231. Another case in point is the Shasta Daisy (Fig. 240), which also shows how the qualities of diverse parents may be skilfully combined. It is the result of a cross between the common Field Daisy of the eastern United States ( chosen for its free - flowering habit ) , a European Daisy (chosen for its vigor and size), and a Japanese Daisy (chosen for the peculiar dazzling white luster of its petals). The hybrid proved larger than its parents and, by selection, flowers have been obtained which under good cultivation reach a diameter of six inches (see Fig. 240, which shows the Shasta and the American parent; the English and Japanese 240. The Shasta Daisy and one of its parents, the American Field Daisy. About one-half natural size. 341. Shasta Daisies, showing variatiou due to crossing. MAKING NEW KINDS OF PLANTS 425 parents are about the size of the American). Not only so, but the good qualities of the parents have all been retained and the bad ones eliminated. The hybrid is very hardy, blooms abundantly and con- tinues to blossom throughout the season (in California nearly all the year). The great white flowers stand up, each on a separate stalk, two to three feet long, making splendid cut -flowers, and remain fresh for two weeks after cutting. The petals have the peculiar whiteness and luster of the Japanese parent. More- over, the plants are perennial and bear more and more abundantly each season. Not content with mere increase in size and pro- ductiveness, the originator, Mr. Burbank, endeavored to obtain new forms of rays (or petals) . Among the hybrids which appeared were such forms as are illustrated in Fig. 241. By selection of these a number of different kinds of ex- ceeding beauty and interest have been secured, comparable --^2. Double Shasta Daisy. to the forms of Chrysanthemums. By continued selec- tion the double form shown in Fig. 242 was obtained. 24J. Variation iu leaves of hybrid Blackberries, all from the seed of one plant. MAKING XEW KINDS OF PLANTS 427 All these are propagated by cuttings, so that there is no trouble over iixation (see p. 433) . Thus in the short space of a few years a disagreeable weed has been transformed into a splendid ornament of the garden! Variation in stems of hybrid Blackberries, all from the seed of one plant. One of the most striking traits of hybrids is their tendency to vary widely. Figures 243 and 244, show- ing the variation in leaves and stems of Blackberry hybrids all raised from the seed of a single plant, will repay careful study (the colors of the stems are as variable as the forms) ; what points of difference can you distinguish in these specimens? The parent forms are not shown in this case, but in Fig. 245, illustrating the leaves of hybrids between the Oriental 428 EXPERIMENTS WITH PLANTS and the Opium Poppy (the two common garden sorts), one can trace clearly the influence of the parents and see how their characters combine to produce a great diversity of forms. These leaves I took from plants growing together in the same bed in Mr. Burbank's garden. Study the hybrids which are to be found in our gardens, especially the Pansies, Cannas, etc., and see whether they are variable. These, it should be remem- bered, have their variability reduced as much as possible by "fixing" before they are put on the market. Mr. Burbank's experience with Beans illustrates how the tendency to vary causes practical difficulties. On crossing the Cranberry Bean (which has red pods and white beans) with the Horticultural Pole Bean (which has red pods striped with white and red-and- white beans), a single seed was obtained: this was planted, and produced a plant having pods of mixed character but with all the beans black. When these were planted, an astonishing variety of plants appeared: some were Pole Beans running up twenty feet, others were Bush Beans; some spread out on the ground but a few inches in height; these latter in some cases produced pods taller than themselves. The variety of pods was bewildering, while the beans themselves represented in size, shape, color and mark- ings almost every known sort. Professor Bailey MAKING NEW KINDS OF PLANTS 429 records a similar experience with Squashes ^ in which the seeds of one plant gave one hundred and ten kinds distinct enough to be named and recognized. Such hybrids represent extremely variable types in which it is practically impossible to fix anything. 245. Hybrid Poppy leaves. At the left, a leaf of the Oriental Poppy; at the right, a leaf of the Opium Poppy; in the center a group of leaves of the hybrids. To successfully combine the qualities of different plants by crossing requires a rare degree of skill and judgment. It might seem, perhaps, as though it would be a comparatively simple matter to make all possible Plum crosses, for example, and select the best. But in practice it is found that the number of 1 Bailey: "Plant Breeding," third edition, 1904, p. 78. 430 EXPERIMENTS WITH PLANTS possible combinations is so great, and the results so bewilderingly varied, that short-cut methods must be used. In other words, the plant- breeder must be able to iadge beforehand what the result of crossing certain plants will be, in order not to waste time on profitless experiments. It is just here that the opportunity comes for the highest skill, based not only on empirical knowledge but on a profound insight into the laws of heredity and variation and a sound philosophy of nature. Moreover, there must be a clear-cut ideal present in the mind of the worker, toward which he persistently strives and from which he refuses to diverge even for the most promising side issues. He wields forces which at best are but partly understood; they manifest themselves in be- wildering variety: to hold persistently to a definite ideal is the surest path to success. There is no mystery in the method by which these crosses are made. Mr. Burbank's methods of pollina- ting Plums will serve to illustrate the matter. The flowers which are to furnish the pollen are carefully gathered a daj^ or so beforehand, -the pollen sifted out and kept in a cool place. The tree to which the pollen is to be applied is deprived of most of its blossoms, in order that the remainder may be sure to develop and that there may not be too many to look after properly. The blossoms which remain on the tree are prepared by cutting away the petals MAKING NEW KINDS OF PLANTS 431 with the attached anthers, as shown in Fig. 246. By comparing with Fig. 161, one can see just what part of the flower is removed. The pistils and stigmas are left exposed and uninjured. This is done before the buds are open. Mr. Burbank finds that the time when the hum of the bees is first heard in the trees is the best for pollination, as the stigma then seems to be in a receptive condition. The pollen is apjjlied by simply dipping the finger into it and touching it to the stigmas. The tree is then left to itself: the bees do not visit the flowers: the petals are not present to attract them, and there is no foothold for them should they come. So soms showing . the manner in there is little danger that any other pollen ^/g^'^t^V'Xe; will be brought. (Where it is important to ric\ed^sta- 1,1 . 1. l.^ n mens, are cut know the exact parentage, the flowers may away prepar- be covered with bags, as described on page nation. 289: for practical purposes this seems to be, as a rule, unnecessary.) The application of pollen may or may not result in the setting of fruit. If the parents are of very dissimilar species, fruit will not set at all: or it may do so occasionally, say once in a thousand times. Sometimes fruit appears to set, but on ripening it is found to contain no seeds: again, seeds are pro- duced which look well but are incapable of germina- 432 EXPEBIMENTS WITH PLANTS tion. Or the seeds may germinate, but the young plants prove so weak that they cannot be raised. Even in favorable cases not all the flowers yield seed, but if only a few good seeds are obtained it is sufficient for a start. ^ All the seeds from the tree are carefully saved and sown: as soon as they come up, the judgment of the breeder comes into play. From the foliage he is able to judge beforehand what the fruit will be, and so save needless time and trouble by preserving only the most promising. In order to make these fruit quickly, they are cut off near the ground when only a few inches high and grafted upon other trees, where they often proceed to flower the third year from the seed. When the blossoms appear, another important question must be decided. Shall they be pollinated with the pollen of a sister hybrid, or of one of the two parents, or of another variety? Here, again, comes the opportunity for the greatest skill and judgment, amounting in its highest manifestations to positive genius, and yielding in the brief space of a few years results which a lesser skill could not compass in a lifetime. A successful plant- breeder judges plant character as a great organizer judges human character, partly by evident signs, partly by an intuitive feeling for the more subtle differences iThe more difficult the cross the greater should be the number of plants used. Thus, Mr. Burbank has succeeded by using large numbers in crossing the Tobacco and the Petunia, a very difficult cross indeed. MAKING NEW KINDS OF PLANTS 433 which can hardly be defined in words and which may be completely hidden from the ordinary observer. When the fruit appears it is carefully examined, compared and tested : the seeds of the best are pre- served and the rest are destroyed : out of a thousand or more, only one or two may survive the rigid tests which are applied. The seeds of these are sown and the best again selected. This is continued indefinitely until a desirable variety is secured, or until it be- comes evident that no good results are to be expected: in that case the plants are all destroyed, and the work of years ends in nothing. It is very evident, therefore, that hybridization, with all its marvelous results, is but the beginning of plant- breeding. All that it does is to furnish variations. To seize upon these, even though they be slight, and divert them into the proper channels, to intensify the good and suppress the undesirable qualities, until the ideal is reached, is the task of selection. ^ When plants can be propagated by cuttings, grafts, bulbs or other vegetative parts ^ the ideal once achieved is easily maintained, for plants so propagated "come true," or, in other words, maintain the characters of the parent plant, with little variation. Far other- wise, however, with plants which are propagated by 1 See articles in the Year -Book of the United States Department or Agriculture for 1898, by Webber; for 1901, by Hays; for 1902, by Webber. 2 1. e., leaves, corras, rootstocks, roots, tubers, etc. BB 434 £XPEBI3fENTS WITH PLANTS seed; for, after selection has achieved the ideal, it has still the task of "fixing" it so that it will come true to seed. In order to. achieve our ideal, we have had to set in motion the tendency to variation, or, as we say, we have "broken the type." When the ideal is achieved, this same tendency which we have set in motion will destroy our ideal unless selection is able to suppress the tendency and so "fix the type," or, in other words, bring the plant again to a state of equilibrium. This we can do to a great extent, but not so fully that continued selection is unnecessary. And it often happens that, after an ideal is achieved, years elapse before it is sufficiently fixed to put it on the market. The great possibilities of selection are well illus- trated in the case of corn -breeding as carried on by Professors Hopkins and Shamel at the Illinois Experiment Station.^ At the same time, these ex- periments illustrate the great value of a thorough acquaintance with the plant and its possibilities, com- bined with a knowledge of the desirability of the various possible lines of improvement as shown by the demands of the market. Suppose you were to undertake the production of an improved variety of 1 See "Com Culture and Breeding," Thirteenth Report Kansas Board of Agriculture, XVHI, 785-817. Also Bulletin No. 82, Illinois Agricultural Experiment Station, 525-539. Also articles by Professor Shamel in the Cosmopolitan for May, 1903; by W. S. Harwocd in WorkVs Work for September, 1902, and by C. P. Hartley in Year - Book of the United States Department of Agriculture for 1902. MAKING NEW KINDS OF PLANTS 435 Corn. You would have before you the possibility of improving along any one of the following lines: 1. Increased yield. — In the ordinary corn-field one well -developed ear to a hill means a yield of about fifty-five bushels to the acre; two ears means over one hundred bushels, three ears over one hundred and fifty bushels. Now in Illinois, where a great corn- breeding movement is in progress, it was found that there are, on the average, more than two stalks to the hill, each capable of bearing a well -developed ear; yet the average yield is less than thirty bushels to the acre. The trouble is partly due to barren stalks, partly to poorly developed ears. Consequently an effort was made to improve the Corn in these respects. Now, it was found that a barren stalk produces more pollen than a productive one, since none of its strength goes to producing an ear: consequently it fertilizes a larger number of plants than the pollen from a productive stalk: the result is that the tendency to barrenness is consequently on the increase. Obvi- ously one thing to do was to go through the fields looking for barren stalks, and cutting off their tassels before the pollen was shed. In this way the per- centage of barren stalks was noticeably decreased. Another thing to be done was to select seed from the best ears. To do this properly requires skill and experience. Not only the size and shape of the ear but the manner in which it is filled out, especially at 436 EXPERIMENTS WITS PLANTS the end; the weight and color of the grain and of the cob; the number, size and shape of the kernels, and many other points must be considered. It is not sufficient to select the best ears: we must know which of the selected ears can transmit its good qualities in the highest degree; in other words, we must determine what is known as the hereditary percentage^ (i. e., the percentage of off- spring which inherit the desirable characters). For this purpose the kernels from each ear are sown by themselves in a separate row, so that the offspring of the different ears can be readily compared. The poor, or barren stalks, and the suckers are removed before the tassel appears. Since the pollen is carried by the wind for about a mile, it is an obvious advantage to have the field well separated from other fields likely to contaminate it. In the fall the seed for next year's crop is selected from the rows which, all things considered, give the best results. The results of this work may be illustrated by the experience of a farmer in southern Illinois who was induced to plant three hundred acres with improved Corn seed. These three hundred acres yielded thirty bushels per acre more than the fields planted with unimproved seed, or, in other words, gave about 1 The hereditary percentage is one of the most important matters in selection and is only too commonly lost sight of by breeders. MAKING NEW KINDS OF PLANTS 437 double crops. Now, as the cost of labor, etc., remains the same, whether improved or unimproved seed is planted, the gain is all clear profit. An increase of only ten bushels per acre in the yield of corn would mean an increase in our national wealth of over four hundred and eighty million dollars a year. 2. Quality. — A bushel of corn, weighing fifty-six pounds, contains approximately: 36 pounds dry starch, worth \% cents per pound. 7 pounds gluten, worth 1 cent per pound. 5 pounds bran or hull, worth % cent per pound. 4%" pounds germ, 40 per cent of which is oil, worth 5 cents per pound. 3X pounds water and soluble matter, worth cents per pound. Which one of these constituents shall we increase to improve the quality of the corn? We might en- deavor to increase the percentage of oil,' since this is the most valuable component. We must, however, first consider whether any one will pay a correspond- ingly higher price for corn containing more oil. As a matter of fact, a company which buys about fifty million bushels of corn per year offered to pay a higher price for corn containing a higher percentage of oil: an increase in oil of one pound per bushel would increase the price of corn five cents per bushel. The Illinois Experiment Station succeeded in increasing the amount of oil from 4.7 per cent to 1 The oil is valuable as a component of "artificial rubber" used for electrical purposes, and is of especial importance in view of the decrease of the world's supply of rubber. The oil is also used for lubricating: purposes, for adulterating olive-oil, as well as in the manufacture of soaps, paints, etc. 438 EXPERIMENTS WITH PLANTS nearly 7 per cent in six years. The method at first involved a rigid chemical analysis of the ears and selection of the best. Afterward it was found that for practical purposes the chemical analysis could be dispensed with: since the germ contains most of the oil, it is only necessary to select the kernels with the largest germs. On the other hand, Corn with a lower oil -content is wanted as a feed for hogs, since it produces harder, firmer bacon. So the Station pro- ceeded by selection to decrease the amount of oil to less than 2 per cent. It would, therefore, depend on market conditions whether w^e should try to increase or decrease the amount of oil in the corn. In the same way we should breed to increase the amount of protein if the corn is to be used for food, but to decrease it if the corn is to be used for starch. The Station workers were able to increase the pro- tein from 10.92 per cent to 16 per cent in about six years, and to decrease it to Q,QQ per cent in the same length of time. Here, again, it is found practicable for ordinary purposes to dispense wdth chemical analysis and select those kernels w^hich have the white, starchy part around the germ best or least developed, according to which is desired: this is possible be- cause the protein is almost all contained in the germ and in the horny outer part of the kernel, w^hile the starch is practically all in the white portion which lies between them. MAKING NEW KINDS OF PLANTS 439 3. Size, shape, color, etc. — Some of the points already mentioned might appropriately come under this head also: in addition, we may mention that the Station has increased the length of shank nearly two feet in five years' selection, and has been able to shorten or lengthen the ear, to increase or decrease the width of the ear and to raise or lower the position of the ears on the stalks. Further changes in the appearance of the Corn plant could be made almost indefinitely if they seemed desirable. The color of the kernel is of some importance; some markets demand golden yellow meal and others white: furthermore, manufacturers of white meal pre- fer white to red cobs, since debris from the latter is apt to color the meal. Hard kernels from which the germ readily separates are desired by hominy- makers. Large ears (one to a plant) are desirable when the corn is to be shucked by hand and shelled or sold for milling. Smaller ears (two or more to a stalk) are desirable where machinery is to be used and the ears fed to cattle. 4. Earliness, etc. — To obtain early varieties is, in general, a very difficult matter. Two things must be secured; first, hardiness, i. e., resistance to frost, sudden changes, etc.; second, the ability to ripen fruit in a shorter season. This is a difficult com- bination to obtain: nevertheless, the Corn -belt has moved rapidly northward in the last fifteen years. 440 EXPERIMENTS WITH PLANTS The original home of the Corn was in Central America, and it has moved all the way to Lake Superior, with the consequent gain in hardiness and ability to ripen quickly, as the result of selection by man. 5. Adaptation to peculiar regions or conditions. — There are thousands on thousands of acres of land where Corn cannot now be grown, simply because the soil contains too much alkali. Yet the same soil will grow Sugar Beets excellently. Why should it not be possible to breed a race of Corn tolerant of alkali? A race of Corn resistant to drought would also prove of great value. 6. Resistance to disease, etc. — An immense amount of damage is annually done by Corn - smut (see page 400) . Yet in the most badly infested fields some sound ears will be found. By careful selection of these a resistant variety might be obtained. Any one who should attempt the improvement of Corn on the old hit-and-miss principle might possibly stumble on good results, but the chances would be largely against him. To be sure of success, he must, after taking into account such considerations as those mentioned above, decide which particular line of im- provement is most feasible and most profitable, and, after formulating a definite ideal, work persistently toward it. The greater his skill and the more accurate his judgment the sooner will he accomplish his aim; in this work it is impossible to set any limits MAKING KUW KINDS OF PLANTS 441 to the results which are obtainable in the hands of a master. ^ From the standpoint of economics, plant- and animal -breeding is of the highest importance, since it adds, in a superlative degree, to the permanent wealth and increased material happiness of a nation. The work of our successful plant- and animal -breeders cannot be too highly estimated, and it is a pity that it so seldom results in much pecuniary gain to them- selves. Government work in this line has been totally incommensurate with the importance of the subject. The United States Government, however, has made a beginning by establishing a laboratory for plant - breeding. 2 The whole doctrine of plant- breeding is intimately connected with the question of the origin of species. Darwin, seeking an explanation of this question, took his cue from the experience of plant- and animal- breeders, and conceived that species may originate lEven in unskilled hands good results may often be obtained. For the remarkable achievements of Canadian school - children, see an article by George lies, "Teaching Farmers' Children on the Ground," in the Wo7'ld^s Work for May, 1903. 2 On the general subject of plant -breeding, see articles in the Year - Book of the United States Department of Agriculture for 1899, by Webber and Bessey; for 1901, by Hays (also those already referred to). Also the bibliography in Bailey's "Plant Breeding," also articles in Country Life in America for July, 1903, by Bailey; in The WorhVs Work for 1902 (Vol. II, p. 1209), by Bailey, and in the Sunset Magazine for December, 1901, February and April, 1902, by Wickson, and in the Century for March, 1907, by de Vries, See also de Vries: " Plant Breeding." 442 EXPERIMENTS WITH PLANTS in nature, just as forms originate in the garden, by the selection of ordinary fluctuating variation alone. In other words, an ordinary fluctuating variation may be so intensified by selection as to form a distinct mark of difference between the improved and the original form: when all the intermediate forms have perished, we have two species instead of one. Darwin^ believed that species originated in this way both in the garden and in nature (where the struggle for existence selects the fittest and destroys the rest), and that the species so formed remain distinct. Professor de Vries has recently called this view in question on the basis of some very remarkable experi- ments. ^ Selection cannot make new species, he declares, 1 Darwin likewise believed that species could originate by sudden varia- tion, but was inclined to lay less emphasis on this mode of origin. 2 In these experiments ( which have lasted over twenty years ) Professor de Vries has combined in brilliant fashion the special points of superiority of various methods. The plant - breeder has the advantage of being able to grow and judge large numbers of individuals in a limited space: of this he has made use. The animal - breeder in the most important cases keeps in a book a pedigree -record of each individual animal, its characters and those of its offspring. Professor de Vries has also done this in all the most important cases, giving a number to each bed, other numbers to each row in the bed, and also to each plant in every row. Thus, each plant receives a number, and a record is kept both of it and its offspring. In many cases the seeds of each separate plant were sown in separate beds, in order that the hereditary percentage might be clearly determined. Most careful precautions have been taken to prevent crossing, by enclosing the flowers in parchment paper bags. Finally, he has made extensive use of the statistical methods described above (p. 417) and thus discovered many important principles which would not otherwise have come to light. MAKING N-EW KINDS OF PLANTS 443 either in the garden or in nature; all selection can do is to temporarily intensify the selected character and increase the frequency of its occurrence: when selection ceases the percentage of frequency soon falls to the original figure and all becomes as it was before. Moreover, new species are not formed gradu- ally, as the selection theory demands, but they originate suddenly, fully formed and constant from the start, without any intermediates between them and their parent- species. As there are no intermediate forms, it is useless to search for such "missing links," for they never existed. This mode of origin of species, which he calls mutation^ he has observed year after year in his garden at the University of Amsterdam. It occurs in one of the Evening Primroses {G'Jnothera Lamarckiana, or Lamarck's Evening Primrose, Figs. 247 to 250), which each year produces several new species. These remain constant and perfectly distinct, and never produce intermediates between themselves and their parent- species. They originate without any of the means ordinarily considered necessary: no ex- tended lapse of time is demanded; no fluctuating variation, crossing or struggle for existence appear to enter directly into the matter. It is not to be supposed that this process can be observed in the majority of plants. The opponents of Darwin have already contended, on the ground of care- ful experimental evidence, that species, instead of MAKING NJUW KINDS OF PLANTS 445 being in a state of continual slow change, are con- stant. Professor de Vries, as the result of his own experiments, believes that species are constant except at certain mutation periods which may occur only at long intervals, perhaps of some hundreds of years. ^1 wSIk^^ IH^^^n ■ ■ -t l*^^ 5^J£« f 248. Lamarck's Evening Primrose at the riglit, and one of the new species wliich has arisen from it (Dwarf Evening Primrose) at the left. The bags are for the pur- pose of excluding insects from the flowers which are being artificially pollinated. Botanic Garden of the University of California. The differences between the new species and the parent form may be great or small: it does not matter which they are, if only they are fixed and constant. Fig. 248 shows a striking difference in appearance between the parent- species and one of the new ones. This difference cannot be overcome by culture; the tallest Dwarf Evening Primrose is always much smaller than the shortest Lamarck's Evening Primrose. 446 EXPERIMENTS WITH PLANTS In Fig. 249 is shown a leaf of Lamarck's Evening Primrose and also one of a new species which sprang from it, namely, the Broad Evening Piimrose {(Eno- thera lata). The latter leaf is not only somewhat shorter and broader, but is blunt in- stead of pointed at the tip. This was the first species to originate in Professor deVries' cultures. The seed of the Lamarck's Evening Primrose which he had gathered in an abandoned field and sown in his garden produced, the first season, among a large num- ber of ordinary plants, three which were distinctly differ- ent from the rest though closely similar to each other. They had broader, less pointed leaves, swollen buds and small fruits: the stems were noticeably small, weak and brittle: at the tips of the branches the young leaves and buds were collected in crowded rosettes so that the plants were at first called "round- heads." Most curious of all, these plants were entirely unable to produce good pollen. Such was the origin of the Broad Evening Primrose; and each subsequent year, as the seed of the Lamarck's Evening Piimrose Leaf of Lamarck's Evening Primrose on the right, and of Broad Evening Primrose on the left. MAKING NEW KINDS OF PLANTS U7 has been sown, the origm of the Broad Ev^ening Primrose from it has been observed. It is possible to identify this and other new species in the seedling stage. Fig. 250 shows the difference in the appear- ance of the seedlings of (Enothera Lamarckiana and Oenothera lata-, while the strikingly small and pale 250. Mutations obtained by sowing seed of Lamarck's Evening Primrose. TjT)ieal Lamarck's Evening Primrose on the left, Pale Evening Primrose in the middle, and Broad Evening Primrose on the right. leaves of (Enothera albida, another of the new species, contrasts with both the other two species. Most of the other new species (of which there are several) can be identified in the seedling stage; so that they can be early transplanted and isolated from each other. This greatly facilitates the handling of the specimens, and makes it possible to deal wath much larger numbers than would otherwise be the case. Professor de Yries' ideas may be well illustrated by means of his experiments on the Bed Clover. Every one knows that four- and five -leaved Clovers are found occasionally. Beginning with a plant which 448 EXPEBIMENTtS WITH PLANTS bore (in addition to tiie normal leaves) one four- leaf and one five -leaf, he sowed its seed and found that about half the resulting plants bore (in addition to normal leaves) four- and five-leaves. The best four plants were saved and their seed sown: this time 80 per cent of the offspring had the four- and five-leaves and a few six- and seven - leaves made their appear- ance. This process of selec- tion was continued until 2")!. Four-, five- and seven- . n n ii nc leaved Clover. practically all the onsprmg were of the new type (i. e., three- to seven- leaved, Fig. 251), or, in other words, the seed came true. One might suppose that it would now be possible to go on and make plants with eight-and nine-leaves. The attempt, however, proved fruitless. The limit of selec- tion was reached with seven, and it was im- possible to go beyond it. On the ground of many similar experiences, he comes to the conclusion that all plants have a limit which is quickly reached by selection, and here its power ends.^ The improved race is not a species: it has no constancy, and when left to itself quickly returns to the original type. 1 He believes that it is even possible to tell beforehand how much a plant can be improved by selection and where the limit will be MAKING NEW KINDS OF PLANTS 449 252. Ten-leaved Clover. There is a well-known freak or monstrosity occur- ring in many species of plants in which the leaf splits lengthwise more or less completely. This occm-s occasionally among the Eed Clover plants just described, and gives rise to leaves with higher numbers (four to fourteen). For example, a five- leaf may, by splitting, become a ten-leaf, such as is shown in Fig. 252. Professor de Vries believes that this is to be classed as a mon- strosity and is quite different from the four-, five-, six-, and seven-leaves just described, which are due to fluctuating variation and obey mathematical laws. It occurs rarely, appears and disappears suddenly, bears no constant relation to the whole number of leaves, and is to be classed as a sudden variation. Occasionally a Clover leaf is met with of the form shown in Fig. 253. It might at first sight be classified as one of the abnormalities just described. When we consider, how- ever, that the arrangement of the leaflet in two rows, one each side of the stalk, is the same as that possessed by the allies of the Clover and the arrangement which the ancestors of Clover itself probably had a long time ago, it seems prob- 253. Atavistic Clover leaf. cc 450 JEXPEBIMENTS WITH PLANTS able that it is a latent character, which has long lain dormant, but is now brought out by some unknown cause. This phenomenon is called atavism and the plant is called an atavist (see p. 420). If the seeds of such a plant are sown, probably few atavists or none at all will appear in the progeny. It is to be classed as a sudden variation. If, now, we should find a plant all of whose leaves showed an increased number, say nine, and all of whose descendants showed the same number coming perfectly true to seed, and kept this up without any need of selection, this would constitute a mutation.^ Such a plant has not been found, but Professor de Yries hopes it may occur, and is continuing his propagation of the Red Clover with this end in view. The example of Clover makes clear Professor de Vries' ideas as to the kinds of variation. We have, first, ordinary fluctuating variation (due partly or wholly to differences in nutrition caused by external conditions): second, sudden variations, e. g., mon- strosity, atavism, etc. (due to causes wholly unknown) ; if these should come true to seed they would be called mutations, otherwise not. A mutation is a sudden variation which comes true to seed, and he believes 1 This would constitute an extreme case. The mutation might, and probablj' would show fluctuating variation in the leaf numbers, so that not every leaf would be a nine -leaf but the type would be (for explana- tion of type see page 420), and this type would remain absolutely constant without selection. MAKING NEW KINDS OF PLANTS 451 that this alone can give rise to a new species. Further- more, he includes in mutation the effects of crossing: he believes that new species can arise from hybridiza- tion and that there are well-established instances of this. Professor de Vries does not deny the great value of selection for cultivated plants: he merely insists that the effect of selection is only temporary and soon ceases when selection stops. Each year the seedsman must carefully go through his beds and "rogue," i. e., remove the rogues or plants which do not come true to seed or which in any way fall short of the standard: only so can he keep the seed at all pure and true to type. And this is the best proof that he has not succeeded by selection in making a true species. Where he does get a constant form, Professor de Vries believes it is due to the selection of mutations which the seedsman does not distinguish from fluctuating variations. He believes that our garden varieties have mostly originated in this way, since he finds that most of those with which he has experimented are constant. The reason why they are not regarded as such is that they are usually grown side by side with the parent forms (or other nearly allied forms), so that crossing takes place and hybrid seeds are produced: these, when sown, give variable forms after the manner of hybrids, and much confusion results. His experience is that if a pure (i. e., not crossed) white variety of a 452 EXPERIMENTS WITH PLANTS normally colored flower be pollinated from its own flowers it will produce white flowers only and prove constant. Such varieties, he considers, are really species. Every one who has opportunity should be on the lookout for sudden variations, both in garden and field. Should one be found it should be kept under observation, protected from crossing by paper bags (as described on p. 289), and hand- pollinated. The seed should be saved and sown, in order to see whether it proves constant. Professor de Vries offers a satisfactory reply to the opponents of evolution, who contend, first, that species are constant and, second, that if evolution were going on we should be able to see the process. He says that species are constant except at mutation periods: moreover, evolution is going on and he has seen it, not once merely, but year after year in his garden: he has furnished seed to other botanic gardens in various parts of the world, and the same phenomena have been observed. The seed sown at the University of California produced about 8 per cent of mutations, which I have had the privilege of personally observing. Further, his theory makes it unnecessary to seek for a continuous series of "missing links," since it assumes that they never existed in such a series. His dis- coveries demonstrate conclusively that evolution can be studied experimentally in a manner hitherto unsus- MAKING NEW KINDS OF PLANTS 453 pected, and furthermore raise the important question whether we can control evolution and so produce species at will. Some experiments already made in this direction are very encouraging and open up a promising field of research.^ 1 In regard to the work of Professor de Vries, consult: de Vries, "On the Origin of Species," Popular Science Monthty, April, 1903; "My Primrose Experiments," Independent, Sept. 25, 1902; "On Hybridization," in Bailey's "Plant- Breeding" third edition, 1904, p. 189. Also Hubrecht, "Hugo de Vries' Theory of Mutations," Popular Science Monthly, July, 1904; MacDougal: "Professor de Vries' Experiments on the Origin of Species," Independent, Sept. 25, 1902; Lyle, "Plant -Making in a Dutch Garden," Everybody's Magazine for June, 1902; MacDougal: "Mutation in Plants," American Naturalist for 1903. INDEX Asterisk (*) denotes illustrations Abnormality, 420, 421, 449.* Absorption, due to osmosis, 17, 60, (i^, 64, 67, 122-124. of ammonia by soil, 145, 147. — carbon dioxide, 191,* 192.* 194. 195, 200, 202. — endosperm, 57,* 179, 180.* — light by leaf, 196, 201. — nitrogen by plants, 147, 149, 383, 384. soil, 145, 147-150, 383, 384. — organic substance from soil, 150. — oxygen, .33, 34,* 35, 175, 194, 195, 200, 287, 317, 388, 390. — phosphorus by soil, 145. — potash bj' soil, 145. — salts by plant, 136, 137, 161. — stored food, 57.* 164, 179, 180,* 183, 260. 287. 313. — water by root, 88, 102, 103, 119,* 120*- 123.* — — — — affected by temperature, 332. seeds, 6,* 7,* 8,* 9*-15,* 10-19,* 20.* 21,* 22,* 23,* 20,* 27.* soil. 111-114. wood, 68. — — affected by dissolved substances, 18, 124. 217, 336. force required for, 121-123,* 124. Acacia, protection of, against drying, 217. seeds of. boiling to hasten germination. 25. sleep position of leaf of, 218.* wood of, 230. Acanthus, protection of pollen by, 294. Acid, excreted by roots, 141-143,* 144, 145. in fruits, 315. — soil, 141, 143, 145. 146. Acid, acetic, manufacture of, 387. boraeic, as preservative, 380. carbonic, as plant-food, 139. — as solvent of plant-food, 139-145. — given off by root, 141, 142, 143.* 144. — source of, in soil, 141. — See, also, Cai-bon Dioxide, carbolic, as disinfectant, 364. fatty, 171. hydrochloric, 155, 157. lactic, 378-379. nitric, as plant-food, 139, 140.* — for isolating wood cells, 235. — test for proteids, 165. oxalic, a by-product in proteid formation 254. phosphoric, as plant-food, 139, 140.* salicylic, as preservative, 3S6. sulphuric, as plant-food, 139, 140. — in manufacture of superphosphates, 1.50. — as test for formalin, 377. proteids, 166, 178. Acer. See Maple. Aconitum. See Monkshood. Adaptation. 326-361. .Ecidiospores, 403.* Aerotropism, 89, 98, 135, 293. .(Esculus. See Buckeye and Horse Ohest nut. Estivation, pi-otection against drying by 213. Agave. See Century Plant. Ailanthus, leaf scar of, 212. Air affects direction of growth of i)ollen- tube, 293. affects direction of growth of root. 89, 98. 135. ;455) 456 INDEX Air, apparatus for supplying to aquaria, 283,* 285.* in fruit, 317. — leaf, 187-191, 198,* 199,* 200. — seed, 8,* 32, 33,* 34,* 35. . — - - how absorbed, 30,* 31, 32. — stem, how absorbed, 258, 278, 279,* 280.* 281,* 282. — soil, 36, 37,* 38, 39,* 40, 103, 119,* 120,* 124, 125, 128, 130, 132. amount best suited to plants, 130. — — promotes beneficial chemical changes, 125, 126, 145, 146. — water, 283. kept from roots by flooding, 125. sidewalks, 126. soil crust, 125. stem hy coatings of tar, 281. kills bacteria, 382. method of excluding, 5.* saturating with water vapor, 26,* 27 * lack of, effect on plant, 281,* 282. needed by fruit, 317. leaf, 191,* 192,* 193,* 194, 195. plants, 326. roots, 125, 126. seed, 5.* 6, 32, 33.* 34,* 35, 36, 37,* 38, 39,* 40. — for starch formation, 191. nitrogen of, used by plant, 149, 383-385. — taken from, by bacteria, 383-385. plant-food in, 139, 191,* 192,* 193,* 194, 195. "restored" by leaves, 191,* 192, 194, 195. trapped by pits of wood-cells, 235. "vitiated" by combustion, 191,* 192, 194. animals and plants, 194, 195. — . See Respiration. water vapor of, absorbed by seed, 26,* 27.* wood, 68. See, also. Carbon Dioxide, Oxygen, and Nitrogen. Air-pump, 187,* 188,* 189, 190, 353. Air-spaces, effect of light on, 345. larger in water plants, 339. Albumin. See Proteid. Alcanna, as test for fats and oils, 2.59. . Alcohol and lye for bleaching, 225. Alcohol, coagulates proteid, 254. dissolves chlorophyll, 181, 254. produced by yeast, 169, 390. use of, as mounting medium, .392. Alder, in northern latitudes, 356. leaf-scars of, 245. protection of, against drying, 214. Alfalfa, killed by flooding, 125. roots of, penetrate deeply, 134. Alinit, 384. Alisma. See Water Plantain. Alkali, black, 159. for softening water, 151. renders absorption difficult, 336. salts of, form crust, 127, 159. tolerated by some crops, 350. white, 159. Alkali soils, 127, 157-160. — reclamation of, 159, 160. — salts found in, 159. — tests for, 157, 158. Allium. See Onion. Alluvial fans. 111. Almond, cover of, retains water, 29. escape of, from seed-cover, 54. Alnus. See Alder. Alpine plants. See Plants, Alpine. Althaea. See Hollyhock. Altona, cholera epidemic of, 372, 373.* Alumina, as constituent of clay, 145. fixes plant-food, 145, 147. Amaryllis, stoma of, 210. Amelanchier. See Service Berry. American Grapes, protection of roots of, 162. Plum. See Plum. American. Ammonia, as reagent, 156. fixed by clay, 145, 147. produced by bacteria, 147, 149, 383. test for proteids, 165. Ammonium molybdate, 1,56. oxalate, 157. sulphate, action of plant on, 161. Ampelopsis. See Ivy, Boston. Amsterdam, University of, 443. Anagallis. See Poor-man's Weather-Glass. Ananassa. See Pineapple. Anchusa, Rust of, 405. Anemone, protection of pollen by, 295. stomata of, 196. INDEX 457 Animals, aid in soil formation, 109. avoid poisonous plants, 222. bury seeds, 69. combustion in, 35. decay of, 381. digestion in, 166-172. distribute seeds, 323-325. food needed by, 16-1, 176. give off carbon dioxide, 35. how supplied with oxygen, 176. protection against. See Protection. respii-ation of, 35. Annual rings, 247. Annuals, seed formation of, 314. Annular tracheids, 227,* 229, 230, 231.* Anthers, 288.* opening of, 289. transformed into leaf-like bodies, 359. withering of, 289. Antibacterial substances, 379. Anticlines, 111. Antipodal cells, 291.* Antirrhinum. See Snapdragon. Antiseptics, 364. Antitoxins, 378, 379. Ants bury seeds, 69. Apium. See Celerj'. Apple, effect of fertilization of, 309. epidermis of fruit of, 317. seed of distributed by birds, 325. stomata of fruit of, 317. Apple Plum. See Plum. Apple. Apricot crossed with Plum, 415.* Aquaria, balanced, 194. method of supplying air to, 283*, — — — carbon dioxide to, 284,* 285.* Arabs preserve Date pollen, 294. Arachis. See Peanut. Arid regions, richness of soil of, 146. Aristotle on the Fig. 310. Arrowhead, 337,* 338,* 342. air passages of, 282. Artemisia. See Wormwood. Arteries, 176. Ascent of sap, 224,* 225,* 226, 227*-2:il,* 232*-236,* 237,* 239, 240*-243, 258. Asexual reproduction liy spores, 302,* 305, 393, 394,* 395* 396,* 397.* 398,* 399,* 401. 402,* *03.* 404.* Asexual reproduction by vegetative parts, 433. Ash, leaf-scar of. 212. wood of. 230. Ash of plants, 137. Ashes as fertilizer, 152, 153, 154. benefit puddled soils, 129. Asparagus, bleaching of. 34^5. tolerates salt, 350. Aster, cross-pollination of, 304, green flowers of, 349. Atavism, 420, 449.* Atriplex. . See Salt Bush. Attachment of plant to soil, 87. — root -hairs to soil -particles, 119,* 120,* 121. Attraction of salts, etc., for water, 8. 124. 217, 336. Atwater on foods, 173. Australia, Rusts in, 404. Autumnal coloration. 332. Avena. See Oat. Bacteria, 361-389. air-hating, 374, 375, air-loving, 374, 375. behaviour of in cultures. 368. cannot live in plants. 378. classification of, 368. cultivation of, 361-365,* 366, 368-370. 374-375.* denitrifying, 383. disinfectants for. 364. effect of air on, 382, 383. heat on. 363, 364. light on, 304, 382. forms of, 361, 362.* immortality of, 368. nitrifying, 383-384. of air, 366, 367. — "bloody bread," 368. — cholera, 371. 372, 373,* 376. — of decay. 381-387. — diphtheria. 376. — hay, 361-365. — lockjaw, 362,* 378. — milk, 372-378, 381. — root tubercles, 384. 385. — scarlet fever, 376. 458 INDEX Bacteria of tuberculosis, 376. — typhoid, 371,376. — vinegar, 387. — water, 368. parasitic, 380. prepare nitrogen for the plant, 149,* 150, 383. propagation of, 362,* 371. pure cultures of, 367-368. respiration of, 374. saprophytic, 380. spores of, 362,* 365. Bagley, acknowledgement to, x. Bailey on agriculture, 109, 129, 133, 15^. — gardening. 249, 263. — plant-breeding, 409, 420, 421, 428, 441, 453. — pruning, 264. — study of branches, 245. Balance, method of making, 13.* 14.* Bamboo, protection of stomata by, 214. Barberry, protection of, against animals. 222. Rust of, 402, 403,* 404.* Bark, 262,* 279. binds stem, 248. formation of, 256. function of, 256, 333. protects against drying, 333. slitting of, to prevent binding, 248. softened to prevent binding, 248. stretching of, 247. Barley, pepsin in, 172. roots of, explore soil thoroughly, 133. Rust of. 404. seeds of, germinate while immature, 43, Smut of, 4U0-401. Bartlett Plum. See Plum, Bartlett. Barium hydrate, 158. Bast, 120,* 198,* 199,* 224,* 225, 226, 227,* 231,* 232,* 233, 236,* 254-257. Bast-ring, 226, 246. Beach Plum. See Plum, Beach. Beals on soil, 133. Beam, effect of strains on, 265. Bean, 77,* 141, 144. food in, 177. get'ing above ground of, 71,* 76, 77. path of water in the seed of, 8,* 23. Bean, pocket of seed of, 20.* root tubercles of, 149. Bean. See also Horse bean. Bean, Cranberry, hybrids of, 428. Bean, Horticultural Pole, hybrids of, 428. Bean, Lima, absorption of water by, 7. — germination of, 81, 85. — resting period of, 43. — twining of, 275. Bean, Pink, germination of, 51. Bean, Pole, twining of, 275. Bean, String, twining of, 275. Bean hybrids, 428. Beech, hairy covering of young leaf of, 213. — sun- and shade-leaves of, 345.* Beer, manufacture of, 169, 391. Bees, partial to certain colors, 298, 299. — power of scent of, 300. — visit but one kind of flower at a time, 299. — visual powers of, 300. Beet, sugar in, 122. self- vs. cross-pollination of, 302. Beet, Sugar, tolerates alkali, 350, 440. Beggar's-ticks, dispersal of seed of, 324.* Begonia, 332. root pressure of, 243. transpiration of, 204. Bending stem to increase fruit production. 318. Benzine, test for fats and oils, 165. Berberis. See Barberry. Bertholetia. See Brazil Nut. Berries, pulp of, retains water, 29. Bessey, on plant-breeding, 441. Beta. See Beet. Betula. See Birch. Bichromate of potassium. See Potassium bichromate. Biennials, flowering of, 286. seed formation of, 314. Bindweed, calyx of, 288. twining of, 275. Birch, contains fat in winter, 259. dispersal of seeds of, 321. in northern latitudes, 356. protection of, against drying, 214. lenticels of, 278. run of sap of, in spring, 259. INDEX 459 Birds bury seeds, 69. distribute seeds, 324, 325. Bird's-eye Maple, 262. Bitter taste as protection against animals, 222 223 Blackberi-y, climbing of, 270. contraction of root of, 87. protection of stomata by, 214. rooting at tip of, 87. Blackberry hybrids, 426,* 427.* Bleaching powder, 23. Bleeding of plants, 243.* Blood, coagulation of, 171. composition of, 171. in relation to oxygen, 176. Blue, preferred by bees, 298, 299. Blue rays cut out by potassium bichromate, 265. Blue jays bury seeds, 69. Bluestone. See Copper Sulphate. Blue Vitriol. See Copper Sulphate. Boilers, pressure in, 74. Boiler-scale, 151, Bone as fertilizer, 150, 151. 153. phosphorus from, 150. Bone-black as fertilizer, 151. Bone-meal as fertilizer, 151. Bone-superphosphate, 139, 150, 153, 154. Boneset, protection of, against animals, 223. Boracic acid. See Acid, Boracic. Bordeaux mixture, 407. Bordered pits, 227,* 232,* 234.* Borers, may promote fruit production, 319. Boston Ivy. See Ivy, Japanese. Bran. 178. Branch. See Stem. Brassica. See Brussels Sprouts, Cabbage, Mustard and Rape. Brazil nut, micropyle of, 8,* 9. Bread, 178. crust of, contains dextrin. 168. Mould. See Mould. Breaking stem to increase fruit production, 318, 319. Briggs, on soil, 129, 133. Brine, as preservative, 386, 387. Broom, protection of, against drying, 215. Brownian motion, 361. Brussels Sprouts, bud of, 250,* 251. Buckeye, flower-buds of, 286. fruit of, how supplied with food, 313. germination of, 58,* 59,* 60,* 85. pocket of seed of. 20, 58.* preparation for flowering of, 286. seed-cover of. 8. seed of, structure of, 58,* 59,* 60. See, also. Horse-chestnut. Buckwheat, germination, 47. self- vs. cross-pollination, 302. Buds, crystals in, 254. flowers of, 286-288. food in, 253. formed on roots, 249. latent, 262.* opening of, 25 1. protection of, against dryness, 213, 214. 251, 334. structure of, 250,* 251. Bud-scale, 288. function of, 214, 251. Bud variation. See Variation. Bulbs, propagation by, 433. storage of food in, 260, 261, 286. Bulrush, strengthening fibers of, 267.* Bundles. See Fibrous Bundles. Bur Clover. See Clover, Bur. Burbank, acknowledgement to, x, 409. work of. 409-411,* 412, 413,* 414* 415,* 416,* 417, 422, 423,* 424,* 425,* 426,* 427,* 428. 429* -432. Burdock, dispersal of seeds, 323.* Burs, 323.* Butter, emulsification of, 169, 170. preservation of, 386. Buttercup, contraction of root of, 87. water, 338, 339.* Butterflies, visual powers of, 300. Cabbage, self- vs. cross-pollination of, 302. strengthening fibers of leaf of, 267. Cactus, effect of water and darkness on, 329,* SrO. 331.* fruit of, production of, increased by dry- ness, 342. habit of. 329, 330, 331.* protection of, against animals, 334. dryness, 215, 333. storage of food in, 286. 460 INDEX Cactus, storage of water in. 334. soil needed by, 108. California, University of, 445,* 452. Callitriche, air-spaces, 333.* Callus, 249, 263. Calorie defined, 174. Calyx, 288.* work of, 287, 288. Cambium, 227,* 232,* 236.* 246-248. Cambium-ring, 246. Canada, forests of, 356. Canal banks protected by plants, 277. Cane, Sugar, protection of, against drying, 333, 334.* Cane-sugar, 165. Canna, protection of, against drying, 213. Canna hybrids, 428. Canning, 386. Capillary action of soil, 116. Caprification of Fig, 310, 311. Carbohydrates. See Starch and Sugar. Carbon, energy from, 173. Carbon dioxide, absorption of. by chloro- phyll, 202. leaf, 200. — apparatus for supplying to aquaria, 283,* 284,* 285.* — as constituent of starch, 186. — as measure of energy set free, 174, -— as plant-food, 139. — decomposed by leaf. 191,* 192,* 193,* 194, 195. — generation of, 284.* — in air, 187, 194. — measurement of, 34,* 175. — produced by leaves, 194, 195. Moulds, 394. root. 141, 142, 143,* 144. seeds, 6, 33, 34,* 35, Yeast, 390. — role of, in respiration. 175. — supply of, affects starch formation, 193.* — unites with water to form starch, 187, 193, 202. See, also. Acid, Carbonic, and Respiration. Carbonate of lime. See Lime carbonate. Carbonic acid. See Acid, Carbonic. Carex. See Sedge. Carrot, contraction of root, 87. for artificial root-hair, 122. storage of food in, 260, 313. sugar in, 122. Caruncle, 2. function of, 29. Carya. See Hickory, Pecan. Casein, 172, 377. Castanea. See Chestnut. Castor-bean, 1, 2.* absorption of water by, 7, 29. air reservoir of seed of, 42. cross-pollination of, 302. caruncle of. retains water, 29. endosperm of, function of, 179. getting above ground of, 72.* lipase in, 170, 171. micropyle of, 9. protection of pollen by, 295. resting period of seed of. 44. seed-cover of, 8. seed of, structure of, 29. seed leaf of, function of, 178, 179. 185 186.* self- vs. cross-pollination of. 302. Caulicle. 1,* 2,* 3.* 4.* direction of growth of, 59. pocket around, 20,* 58.* Celery, bleaching of, 346. Cell, antipodal, 291.* bast-, 120,* 198,* 199,* 224,* 225, 226, 227,* 231,* 232,* 233, 236,* 254-257. cambium, 227,* 231,* 232,* 236,* 246-248. chlorophyll granules in, 198.* 199,* 200, 201,* 2C2. collenchyma, 268.* crystals in. 232,* 254. division of, 227,* 232,* 236,* 246. 362.* 371. 390.* egg-, 290, 291.* epidermal, 198,* 199,* 334,* 335,* 336,* 337,* 338,* 340,* .344,* 345.* guard-, 198,* 199,* 200, 208,* 209,* 210,* 211.* 336,* 337,* 340,* 344,* 345.* hair-, 324,* 335,* 337.* in relation to growth, 64, 65,* 66-68. isolation of, 235. nucleus of, 65,* 66, 290, 291,* 311. osmosis in, 64. 123, 124, 208, 209. I INDEX 461 Cell parenchyma, of leaf. 198.* 199*-202.* 337,* 338,* 344,* 345.* seed, 65.* 66. stem. 227,* 231,* 232,* 233, 236,* 257. 258, 328, 333.* root, 120,* 121. pits in wall of, 227,* 229. 232.* 233, 234,* 235. protoplasm of, 65,* 66, 290, 291.* sclerenchyma, 224,* 225.* 2J7,* 231,* 232,* 236,* 266. 267,* 268. starch in. See Starch, strengthening, 224,* 225,* 227,* 231,* 232,* 236,* 266, 267,* 268. structure of, 65,* 66. water in, 64, 123, 124, 208, 209. wood-, 120,* 121, 198,* 199,* 224*-227,* 228-231,* 232*-234,* 235. 236*-237, 238*- 240,* 341. Cell-wall, 64, 65,* 66. Cellular structure. See Histology. Cellulose, 65,* 66. decomposition of, 381. Centrifugal force, effect of, on direction of growth of stem and root, 92, 93,* 94. Century Plant, protection of, against animals, 222, 334. — protection of, against drying by epider- mis. 333. — seed formation of, 314. — storage of food in, 260, 286. — storage of water in. 334, 335. Ceratophyllum. See Hornwort. Cereals in crop rotation, 160. Charcoal, 372. Checkerberry. See Partridge-berry. Cheese, 377. j Chemical action due to light, 182,* 184,* 185, ' 195, 196. 201, 316. 364, 382. | — in the plant, 166-177, 182-196, 253, 254, 258, 259, 314-316. soil, 125, 139-15'J. soil-formation, 109. — . See, also. Respiration. Chemotropism, 293, 294. Cherry, evergreen, 415. flavor of, 288.* lenticels of, 278. protection of, against drying, 214. Cherry, seeds of. distributed by birds. 325. Chestnut, on poisonous plants, 222. Chestnut, leaf mosaic of, 219.* protection of fruit of. 320. wood of, 230. Chicfcgo, sewage of, 382. Chickory, flowers of, attract bees, 299. protection of root of, 162. Chili saltpeter. See Sodium nitrate. Chloride of lime. See Lime chloride. Chloroform in testing for fats and oils, 165. Chlorophyll absorbs carbon dioxide, 202. cannot form in cold weather, 354. — darkness. 185. decomposition of. causes autumnal colors, 332. effect of light on. 184,* 185. function of, 185, 201. in stem. 278. Chlorophyll -granules, 198,* 199,* 200, 201, 202.* Cholera, 371-373,* 376, 380. Chrysanthemum, sports of, 420. Cichorium. See Chickory. Cinnabar, injection of wood with, 237. Cinque foil, hairy covering of leaf. 213, 334. protection of, against drying, 334. protection of, against animals, 223. Cistus, protection from drying, .334. Clay, burning of, 106. burned, benefits puddled soils, 129. composition of, i06, 107. fixes ammonia, 145, 147. — dung liquor, 145. — plant-foods, 145. flocculated by lime, 152. is impervious to water, 125. lifts water higlier than sand does. 118. microscopical examination of, 106. percolation in, 113. plant-food in, 106. properties of, 106. richer in plant-food than sand is, 146. size of particles of, 106. water-holding capacity of, 132. C'lay loam, 108. Clematis, climbing of, 270, 271.* dispersal of seeds of, .vl2.* 462 INDEX Climbing plants. 270, 271.* 272. 273,* 274, 275.* Clock, floral. 295. Clotbur, dispersal of seeds of, 324.* Clover, benefited by lime, 151.* in crop rotation. 160. leaves of, follow sun, 218. position of flowers of, 307. root tubercle of. 149.* sleep position of, 218. Clover, Bur, dispersal of seed of. 324.* Red. variation in, 448.* 449*- 450.* Cobffia, calyx of, 288. Cobalt chloride, as index of transpira- tion. 203. Cockle - bur. resting period of seed of, 44. Cocoanut, distribution of, by water, 325. endosperm of. function of, 57, 179, 180. germination of, .56, 57,* 58. structure of fruit of. 56. 57,* 58. Cocoanut oil. See Oil, cocoanut. Cocos. See Cocoanut. Cohn's solution, formula for, 398. Cold. See Heat. Collenchyma, 268.* Colon bacillus. 371. Color of autumn leaves, 332. — flowers, 297-300. — fruits, 316, 325 — fruits and flowers affected by light, 347. — night-blooming flowers, 300. preferred by insects, 298, 299, Color-contrast in flowers, 297, 298. Combustion, 35. as source of energy, 173. brought about by ferments, 173. Companion cells. 227.* 231.* 232,* 255. Comnass plants, 346. Composite family, cross - pollination of, 303.* — green flowers of. 349. Composition of soil, 103-109. — starch, 186,* 187. Compost, 147. 148. Conditions of growth, 252, 253. Conduction. See Stem, path of air, etc., in. Conidia, 399, 402, 403, Conifers, humus of. preferred by som* plants, 351. pollen of, carried by wind, 300. See, also. Pine. Conn, on bacteria, 408. Contagious diseases, 380. Contact-bed for sewage, 382. Contraction of root, 87. — wood, 68. Convolvulus. See Bindweed. Copper sulphate, 161. as a disinfectant, 364, 400, 401. Coreopsis, cross-pollination of. 304. Cork, 232,* 236,* 256. 279. protects against drying, 333. Cork-cambium. 232,* 236.* Corms, propagation by. 433. storage of food in. 260, 261. Corn, bran of, 437. breeding of, 355, 434-441. canning of, 386. cross-pollination of. 302. endosperm of, 3,* 179. fat in. 437. fibrous bundles of, 225.* 226,* 230, 231.* food in. 3,* 437. germ of, 3,* 437. germination of, 21. 22.* 47. 71.* 72. getting above ground of, 71.* in silo, 388. leaf-scar of, 212. oil of, 437. original home of. 440. pepsin in, 172. pollen of, carried by wind, 301. 436. protection of, against drying, 213, 334, tip of stem, 71,* 79. proteid in, 437. roots of, explore soil thoroughly, 133 strength of. 268. structure of. 268. root pressure of. 243. seed-leaf of. 3.* 179. self- vs. cross-pollination, 302. silk of, 292, 301. Smut of. See Smut of Corn. starch in, 3. 437. stem of. structure of, 225,* 230, 231 * rigidity of. 269. INDEX 463 Corn, stigma of, 292. 301. strengthening fibers of, 231,* 266 structure of grain of, 2, 3.* wandering of, 440. water in, 437. Xenia in, 311. Corn, Sugar, endosperm of, 3. — seed-leaf of, 179. Corolla. 288.* Correlation, 79,* 359. 360. Corrosive sublimate as disinfectant, 364. Cortex. See Rind. Corylus. See Filbert, Hazel. Cosmos, cross-pollination, 304. Cottonseed oil. See Oil, Cottonseed. Cotyledons. See Seed-leaves. Cover. See Seed cov* r. Cow Wheat loves mild humus, 351. Cowpox, 379. Cracks, seeds buried in, 69. Crataegus. See Hawthorn. Crocus, opening and closing of flower of, affected by heat, 296. storage of food in, 260. Crops, dependence on water supply, 133. green, in crop rotation, 160. rotation of, 160, 161. white, in crop rotation, 160. Cross-pollination, 301,302, 303,* 304,* 305,* 306.* Crossing, process of 430. 431,* 432. results of, 411,* 413.* 416,* 422,* 423,* 424,* 425,* 426,* 427,* 428, 429,* 434. species originate from, 451. utility of, 421. Crude food. See Food, Crude. Crust. See Soil crust. Cucumber, Squirting, dispersal of seed of, 321.* Cucurbita. See Pumpkin and Squash. Crystals, 232,* 254. Cultivation conserves soil moisture, 115,* 116,* 117, 125, 129, 133. should be adapted to depth of root, 135. Cupra-ammonia as light filter, 265. Currant, acid in, 315. Curve of variation. See Variation , Curve of. Cut. fever caused by, 262, 263. Cuticle, 197, 198,* 199,* 328. 334.* effect of light on, 345. of water plants, 339. Cuttings, correlation in, 359. fever in, 262, 263. propagation by, 433. regeneration in, 257. soil required by. 262. 263. transpiration of. 282. treatment of, 263. Cydonia. See Quince. Cypress, wood of. 230. Cytisus, 331, 332.* protection of, from drying, by sunken stomata, 215. See, also, Broom. Dahlia, root pressure, 243. Daily movements of flowers, 295-298. leaves, 218.* Daisy, cross-pollination of, 304. European, 422. Field, 422, 423.* Japanese, 422, 425. Ox-eye, variation in, 417, 418,* 419.* Shasta, 422, 423,* 424.* 425,* 427. hybrids, 422, 423,* 424,* 425,* 427. Dandelion, behavior of leaf of, 252. dispersal of seeds of, 322, 323. effect of saturated atmosphere on. 341, 342.* flowers of, arrangement of, 298. affected by light, 298. opening and closing of flowers of, affected by light, 295. protection of pollen by, 295. root by, 162. stalks of, tissue tensions in, 269, 273.* Darkness. See Light. Darwin, on orchid pollination, 307. — origin of species, 441, 442. — self- vs. cross-pollination, 301. — soil formation, 109. Date, germination of, 180.* fruiting of, 356. seed-leaf of, 180.* vitality of pollen of, 294. Daucus. See Carrot. Decay, 381-387. 464 INDEX Decomposition due to bacteria, 147, 148, 151, 381-187. of carbon dioxide by leaf, 191.* 192.* — rock by chemical action, etc., 144, 145. — starch by heat, 86,* 87. Deer-berry. See Partridge-berry. Deformity. 420, 421. Delphinium. See Larkspur. Deutzia, cross-pollination of, 303. Dew, formation of, 117. Dextrin, changed to grape sugar, 168. in bread crast, 168. formation of, 167, 168. Diastase, 166, 167. Dicotyledons, characterized, 226. Digestion in animals, 166-172. — plants, 166-172. Dikes, protected by plants, 277. Dioecious plants, 302. Diphtheria, 376, 380. Directive action of air, 89, 98, 135, 293. — — chemical substances, 293, 294. gravity, 88,* 89,* 90, 91,* 92, 93,* 94, 95, 98,* 99, 264, 277. 308. light, 264, 346. water, 95,* 96,* 97, 98. Diseases of plants, 397, 398,* 399,* 400, 401, 402,* 403,* 404-407,* 408.* damage done by, 400, 401, 406. prevention of, 400, 401, 407, 408. 440. Disinfectant, .364. Dispersal of seeds, 320-325. Distilling, 137,* 138. Distribution of seeds, 320-325. Dog's Mercury, loves mild humus, 351. Drought. See Dryness and Water. Drupes, protection against drying of seed of, 317. Drying, protection against. See Protection against drying. Dryness, effect of, on plant, 82, 211-217. 326, 327,* 328,* 329*-.331,* 332,* 333,* 334,* 335,* 336,* 337,* 338,* 339,* 340*- 342,* 343.* See, also. Water. Ducts, 224,* 226, 227,* 228, 229, 230. 231,* 232,* 233, 234.* length of, 236. 237.* Ducts, resin-, 235, 236.* ■water travels faster in, 228, 229, 230, 237. Dung liquor, fixed by clay, 145. Dust clogs stomata, 215 Dusty Miller, hairy covering of, 213. — protection of, against drying, 333. water, 214. Earliness, 355, 411, 412. Earth. See Soil. Earthworms bury seeds, 69. Eau de Javelle, 23. Echinocystis. See Cucumber, Squirting. Echium, Rust on, 405. Egg, ood in, 176, 177. of plants, 290. presei'vation of, 387. Elaborated food. See Food, Elaborated. Elasticity of stem, 269. Elder, flowers of, 298. pith of, 269. stem of, 268, 269. Electric light, 346. Elm, buds formed on roots of. 249. cross-pollination of, 303. Embryo. See Germ and Seed. Embryo-sac, 290, 291.* Endosperm, 2,* 3,* 4, :u* 179, 180.* absorption of, 57, ^^ 179, 180.* in Xenia, 311. Endosperm nucleus. 291,* 311. Energy absoi-bed from sunshine, 195, 196, 201. in foods, 173. in starch, 196. uses of, 173-175. Environment, effect of. on the plant, W'H'.- 360. Eosin, 22, 24, 66, 161, 224, 225, 228, 230. 24'J, 251. Eosin stains, how removed, 23. Epidermis of fruit, 317. of leaf, 197, 198,* 199,* 204, 205, 21!). 2i:{, 214. protects against drying, 333, 331.* Epilobium, dispersal of seeds, 323. Equisetum. See Horse-tail. Erodium.' See Filaree. Ether, test for fats and oils. 165. I INDEX 465 Etiolation, 184,* 185. 328,* 354.* Eucalyptus, protection of, against di-ying, 214, 217. 317, 333, 334. fruit of. 320. Eupatorium. See Boneset. European Plum See Plum, European. Evaporation. See Soil, Evaporation from, and Transpiration. Evening Primrose. See Primrose, Evening. Evolution, 330, 441-403. control of, 453. indicated by variation curve, 419.'*' Excentric growth, 348-350.* Excretions, nitrogen in, 176. poisonous character of, 378. Experimental morphology. See Plant, form of. Exposure, effect of, on fruit production, 319 External agents, 326-361. See, also. Air, Food, Gravity, Heat, Light, Water, Wind. Eye, effect of light on, 196. Fagopyrum. See Buckwheat. Fall wood, 232,* 236.* 247. Fascination, 420, 421. Fats, changed to starch, 259. decomposition of, 381. emulsification of, 169, 170. energy from, 173. formation of, 170, 201. in eggs, 177. —growing region, 253. — seeds, 165, 177. —trees, 259. saponification of, 170, 171. tests for, 165, 259. See, also. Oil. Feces contain waste nitrogen, 176. Fehling's solution, preparation of. 164, 1()5. Feldspar, 106. 107. Fermentation by bacteria, 380. —Yeast, 169. Ferments, 166. cause oxidation, 173. restore vitality of seeds, 44. Fernow, on forestry, 245. Ferns as shade plants, 344. Ferns, protection against drying, 213. rhizomes of, 277. soil needed by, 108. unrolling of leaf of, 252. Fertilization, 291,* 292.* after effect of, 309, 360. Fertilizers, 139-160. effect of, on fruit, 315. fruit production, 318. Fever caused by wounds, 262, 263, 388. Fibrin coagulation of, 171. for digestion experiments, 171, 172. Fibrous bundle, 198,* 199,* 224,* 225,* 226. 227,* 228, 230, 231,* 250,* 251, 317. effect of water on, 335.* Ficus. See Pig, Rubber Plant. Fig, flower structure of, 310. pollination of, 310, 311. Filaree, seeds of, bury themselves, 70,* 71. Filbert, absorption of water by, 7. openings in cover of, 9. path of water in cover of, 9, 24. Filtration of water, 372. Fire, protection against, by bark, 256. Fish, preservation of, 386. Fisher, on cookery, 178. Five-finger. See Cinquefoil. Flavor, affected by external conditions. 318, 319, 342. improvement of, by breeding, 413, 415. Flax, absorption of water by, 728. seed-cover of, holds water, 28. Flesh-forming foods, 176. Fleur-de-lis. See Iris. Flies carry disease, 380. prefer yellow, 299. Flinty texture protects against animals. 223. Floods, relation of, to forests, 112. Floral clock. See Clock, floral. Florida, forests of, 356. Flour, proteid in, 177. starch in, 177. Flower, attraction of insects for, 297-300. color-contrasts in, 298. color of, affected by light, 347. double, produced by breeding, 425.* effect of heat on, 296, 347. light on, 295-298, 347, 348. DD 466 INDEX FJower, effect of water on, 496, 342. foo.l needed by, 286, 287, formation of. 286, 287. improvement of, by breeding, 422, 423,* 424,* 425,* 427. injury of, 288. night blooming, 299, 300. opened by insects, 308. opening and closing of, 296, 297. platforms of, 309. production affected by heat, 347. light, 347. protection of, against drying, 288, insects, 308. water, 294, 295. position of, 30T, 308. respiration of, 287. sets free heat, 287. structure of, 288,* 290, 291.* work of, 28G-311. See, also. Anthers, Petals, Ovary and Ovule. Flower-buds, 286, 287. Flowering, preparation for, 286, 287. Food, as source of energy, 173, 176. — material for growth, 173. crude, 201, 136-162. digestion of, 166-172. effect on plant, 349-351. elaborated, 57^* 65,* 164, 169, 179. 180,* 183, 253. 254, 260, 278, 286, 287, 313. 314. energy in, how measured, 173. flesh- orming, 176. from the air. 200. — — soil, 201. how conveyed to fniits, 313. in buds, 253. — eggs. 176, 177. — leaves, 181. 332. — seeds, 57,* 65,* 164-180,* 437. — root, 122. 255, 260. — stem, 169, 243, 250, 253, 254-260, 286, 287, 313. 314. — soil, 146. lack of. promotes fruit production. 350. made soluble. 166-172. manufacture of. 182-203, 253, 254, 278. mineral. 136-162, Food, muscle-forming, 176. needed by fruits, 312-316. plant, 326. organic, absorbed from soil, 150. preservation of, 376, 377, 385-388, 397. required for growth, 253. storage of, in preparation for flowering, 260, 286, 287. stored, utilization of, 57,* 164, 179. 180.* 183, 260, 286, 287, 313. plant, dissolved by carbonic acid, 139-145. — fixed by clay, 145. — humus. 145, — set fi'ee by lime. 152. — raw. 136-162. 201. wandering of, 57.* 164, 169, 180, 183, 253, 254-257, 259, 260, 286. 287. 313. 314. Forage crops, time for cutting. 314. Forests, effect of heat on, 356. hiimus in. 107. prevent floods. 112. remain naturally in good tilth, 129. Forest, trees of. differ from isolated speci- mens. 261. Form of plant, effect of external agents on. See Plant, form of. Formalin, as disinfectant and preservative 28, 364, 377. 386, 401. test for, in milk, 377. Foxtail, seeds of, bury themselves, 71. Fragaria. See Strawberry. Franklin, on gypsum as fertilizer, 151. Fraxinus. See Ash. Freak, 420, 421. 440.* Freezing. See Heat. French Prune. See Prune. French. Frost. See Heat. Fruits, acid in, 315. air in, 317. air needed by, 317. air, how conveyed to, 317. attract animals. 324, 325, benefited by ringing, 257. effect of light on, 316, 347, — — water on, 342. wind on, 349. defi'^ition of, 4, 312. fat in, 314. epidermis of, 317, INDEX 467 Fniits. fibrous bundle in. 317. flavor of, increased by dryness and warmtli, 315. food needed by, 312-316. improvement of. by breeding, 409-411,* 412, 413.* 414,* 415,* 416,* 417. oil in, 314. path of food to, 313. water in, 24. pectin compounds in, 315. production of, methods of increasing, 318, 319, 342 protection of, 330. respiration of, 317. ripening of, 315, 316, 324, 325. starch in, 314. struggle for existence of, 312. stom."\ta of, 317. s icculent, require more water, 320. sugar in, 314. 411. method of increasing, 315. thinning of, 312. transpiration of, 317. water needed by, 316, 317. work of, 312-325. Yeasts on, 390. Fruit trees, buds on roots of, 249. — protection against drying, 213. Fuel value of foods, 173, 196. Fumigation of plants, 215. Function determines structure, 179, 185, 186.* • Fungi. 361-408. destroyed by lime, 152. rotation of crops, 160. on roots of trees, 150. protection against by bark, 256. callus, 263. Furrow-sliee, 126,* 127. Gaillardia. cross-pollination of, 303.* flower structure of, 303.* Galloway, on freezing, 354. — soil, 129. — plant diseases, 407. Galls. 359. Gai-dner, acknowledgment to, x. Gardner on plant breeding, 441. Gases, fumigation with, 215. Gases. See. also. Air, Carbon dioxide. Nitrogen, Oxygen. Gasolene, lest for fats and oils, 165. Gastric juice, 171. Gaye, on soil, 109. Gelatin for bacterial cultures, 368, 369, — mould cultures, 395 Generation, spontaneous, 365. Geotropism, 88.* 89,* 90, 91,* 92, 93,* 94, 95, 98,* 99, 264, 308. Geranium. See Herb Robert. Geranium, air passages in, 280. behaviour of seeds of, 71. flower of. position of. 307. stem of, 224. Geranium, Ivy, effect of cold on chloro- phyll, 354. — leaf mosaic of, 219. Germ, 1,* 2,* 3,* 4,* 20*, 56, 58.* contact of, with cover, 20. osmotic action of, 17. See, also. Seed. Germicide, 364. Germination. See Seed. Giant Prune. See Prune, Giant. Gibson, on pollination, 307. Girder, 266. Girdling increases fruit production, 257, 318. Gladiolus, leaf structure of, 201. protection of, against drying, 217. Glauber's salt in soil, 158. Gleditschia. See lioney Locust. Glucose. See Sugar. Gluten, 177, 178. 437. Glycerine for shrinking cells, 390. a product of saponification, 170, 171. Gnaphaliiim. See Immortelle. Goodyera. See Plantain, Rattlesnake. Gophers bury seeds, 69. Gorse, 331, 343.* effect of saturated atmosphere on, 341, 343.* Grafting. 248. 249, 433. Grains, chaff of, holds water, 29. conveyance of food to seeds of, 313, 314. growth at nodes of, 250. proteid in. 177. 468 INDEX Grains, starch in, 177. ovary of, 289. pollen of, 289. carried by wind, 300. stigma of, 289. style of. 289. time for cutting, 314. Grape attracts insects. 299. fruit production of, increased by bending, 318. girdling, 257. — of, stomata of, 317. pith of, 269. protection of pollen by, 295. root of, 162. self- sterility of, 309. stem of, 268. rigidity of, 269. tendrils of, 272. Grasses, are shallow-rooted, 134. chaff of, holds water, 29. germination of, 72. growth at nodes, 250. leaf scar of, 212. ovary of, 289. pollen of, 289. carried by wind. 300. position of leaves of, 217. protection of, against drying, 213, 334. — — — animals, 222. relation to light, 265. rhizome of, 277. stigma of, 289, 292. stomata of, 196. • style of, 389. Gravity, effect of. on direction of growth of root and stem. 88,* 89,* 90, 91,* 92, 93,* 94, 95, 98.* 99, 264. 276, 277. effect of, on direction of growth of dower and fruit, 308. Gravel stops rise of water in soil, 115. Gray, on aestivation, 213. Green flowers, cause of, 349, 359. — manures, 150, 384. — rays, partially cut out by potassium bichromate, 265. — rays partially cut out by cupra- ammonia, 265. Ground, See Soil- Ground-squirrels bury seeus, 69 Growth at nodes, 249, 250. correlations of, 79,* 359, 360. effect of heat on, 252, light on, 253. water on, 116,* 117, 252. food required for, 253. force of , in stem, 73,* 74,* 75,* 76.* root, 81, 82,* 83, 84,* 85. of leaves, inequalities of, 251. oxygen necessary for, 5. 6,* 32, 33,* 34,** 35, 36, 37,* 38, 39,* 40, 125. 126. 281.* 283, 326. region of differentiation, 229. in root, 85,* 86. stem, 77,* 78.* relation of, to osmosis, 64-68. temporary vs. permanent, 67. the three regions of, 249.* Guano as^a fertilizer, 148, 153. Guard-cell, 197, 198,* 199,* 200. 208,* 209," 210,* 211.* artificial, 210,* 211.* Gums lessen transpiration, 214, 216. 333. Gymnocladus. See Kentucky Coffee Tree. Gypsum. See Lime sulphate. Habit of plant, 264. Haemoglobin, 176. Hairs, absence of, from water plants, 339. effect of light on. 347. — protect against animUls, 221, 256, drying, 213, 214, 333, 334,* 3o5.* • water and dust, 215. Hamamelis. See Hazel, Witch. Hamburg, cholera epidemic of, 372, 373.* Hanging drop, 293,* 395, 405. Hardiness, 355, 412, 413. Hardpan, 106, 351. alkali, 159. Harper, acknowledgement to, x. Hartley, on plant-breeding, 434, 441. Harwood, on plant-breeding. 434. Hawkweeds, behavior of scale leaves, 347. Hawthorn, food in buds of, 253. protection of, 222. Hay, sweating of, 388. time for cutting, 314. Hays, on plant-breeding, 433, 441. INDEX 469 Hazel, pollen of, carried by wind, 300. starch in, during winter, 259. Hazel, Witch, dispersal of seeds, 321. Heart wood, 244, 245. Heat, as preservative, 386. effect of, on absorption by root, 332. bacteria, 363, 364. — — — direction of growth of stem and root, 88, 89. — — — evaporation, 115. flora, 351, 356. flower and fruit production, 347. — — — growth, 252. leaf, 345. Mould. 394. opening and closing of flowers, 296. effect of on plants, 352, 353, 354.* 355-358. transformation of fat into starch, 259. transpiration, 207. entrance of, into seed, 42, * 43. excessive, injurious, 352. of respiration, 35, 36*, 287. lack of, kills plants, 352-354. prevents chlorophyll formation. 354.* — — preserves foods, etc., 386. — — produces rosette form, 357. needed by plant, 326. — to awaken seed, 4, 5,* 6. set free by flowers, 287. seeds, 35, . 6.* Heath plants love sour humus, 351. protection of, against drying, 213, 333. Helianthus. See Sunflower. Heliotropism, 264. 346. Hemizonia. See Tarweed. Hen • and • chickens, protection of, against drying. 215. storage of water by, 334. transpiration of, 216. water reservoirs of, 215. Herb Robert, protection of pollen of, 295. Hereditary percentage, 436, 442. Heredity, 411,* 413,* 416,* 422, 423,* 424,* 425*, 426,* 427,* 428, 429,* 434, 436. 442. Hickory, flower-buds of, 286. path of water in. 226. Hickory, preparation for flowering of, 286 seed-cover of, holds water, 29. wood of, 230. Hieracium. See Hawkweed. Hilgard, acknowledgment to, x. — on soils, 126,* 160. Hilum. 1,* 2. as place for entrance of water, 10. Hippuris, 342. Histology of flower, 290,* 291.* — fungi, 395,* 396,* 397,* 399,* 402,* 403,* 404,* 407.* — leaf. 196-198.* 199*-201,* 202,* 208,* 209,* 333, 334,* 335,* 336.* 337,* 338,* 340,* 344,* 345,* 402,* 403,* 404.* — leaf-stalk, 212. — root, 120,* 121. — seed, 65,* 66, 67, 177, 178. — stem, 224*-227,* 228-230.* 231, 232,* 233, 234*-236,* 267,* 268,* 328. 333,* 334,* 335.* Holly, cuticle of. 334.* protection of. against animals, 222. drying, 333, 334.* transpiration of. 204. Hollyhock, rust of, 40fr. Holmes, on fertilizers, 153. Honey. See Nectar. Honey Locust, protection of. against ani- mals. 222. Honeysuckle family, cross - pollination of. 303. flower, position of, 307. Hop, cross-pollination of, 302. dispersal of seeds of, 322-323.* twining of, 275. Hopkins, work of, 434-439. Horehound, hairy covering of leaf, 213. Hornblende, 107. Hornwort, 339. Horse-beau, germination of, 81, 82,* 86. micropyle of, 10. seed of, stnieture of, 1,* 2. seed-leaf of, contrasted with foliage leaf 180-186. function of, 178, 179. microscopic structure of, 65,* 66. Horse-chestnut, flower-buds of, 286. hairy covering of leaf of, 213. 470 INDEX Horse-chestnut, preparation of, for flower- ing, 286. See, also, Bnckeye. Horse-t.'iil, protection of, against animals, 223. rhizome of, 277. House plants, care of, 132, 136. Houstonia, cross-pollination of, 305. Howard, on mosquitoes, 380. on plant diseases, 407. Hubrecht, on mutation, 453. Hugging the ground as protection against animals, 223. Humulus. See Hop. Humus, 104. as fertilizer, 148. colors soils, 107. fixes plant-food, 145. of forest, 107. plant-food found in, 107, 351. properties of, 107. retains water in soil, 132. 133. test for, 155. Hunn, on gardening, 249, 263. Hunt, acknowledgment to, x. Hyacinth, preparation of, for flowering, 286. stomata of, 196. storage of food in. 286, 313. water, 340. Hybrids, character of, 411,* 413,* 416,* 422, 423,* 424,* 425,* 426,* 427,* 428, 429,* 434. defined, 421. Hydrochloric acid. See Acid, Hydrochloric. Hydrogen, a product of decomposition of cellulose, 381. in foods, 175, peroxide as disinfectant, 364. Hydrolysis, 167. of starch, 167-169. Hydrotropism, 95,* 96,* 97, 98. Ice, method of using, 5.* role in soil-formation, 109. Ice Plant, protection of, against drying, 215. water reservoirs of, 216/- Hes, on plant-breeding, 441. Ilex. SeeHoUv. Illinois Experiment Station, plant-breed- ing at, 434-439. river, sewage of, 382. Immature seeds, germination of, 43. Immortality of bacteria, 368. Immortelle, protection of, against drying, 334. Immunity, 379. Impatiens. See Jewelweed. Improved Beach Plum. See Plum, Im- proved Beach. Inch Plant. See Wandering Jew. India Ink, injection of wood with, 237. Indigo rays cut out by potassium bichro- mate, 265. Infectious diseases, 380. Injury, effect on the plant of, 79.* 86, 263. Insects bury seeds, 69. destroyed by crop rotation, 160. lime, 152. how supplied with oxygen, 176. method of alighting at flower of, 307. open flowers, 308. partial to certain colors, 298. protection against, by bark, 256. — of flowers from, 308, 309. fruits from, 320. role of, in pollination, 289, 291. 297-311. trapped by plants, 172. unwelcome. 308. visual powers of, 300. Insectivorous plants, 172. Iodine solution, preparation of, 164. test for starch, 164, 367. .Iodoform as disinfectant, 364. Ipomcea. See Moonflower, Morning Glory and Sweet Potato. Iris, cross-pollination of. 304.* flower of, platform of, 307. sti-ucture of, 304.* leaf of, structure of, 199,* 201. protection of, against drying, 217, 333, 334. water, 214, 294. pollen, 294. rhizome of, 277. stomata of, 196, 199,* 208,* 209.* storage of food in, 260. 313. Iron, needed by plants, 139, Iron chloride, 171. INDEX 471 Irrigation. 130, 131, 135. effect of, on fruit. 343. Ivy, Boston. See Ivy, Japanese. Ivy. English, aerial roots of. 275.* — attracts insects, 299. — leaf-mosaic of. 219. — starch in leaf of. 182.* Ivy. Japanese, leaf -mosaic of, 219. — tendrils of, 274. Ivy Geranium. See Geranium, Ivy. Jam, process of making, 315. Japanese Ivy. See Ivy, Japanese. — Plum. See Plum, Japanese. Jasmine, climbing of, 270. Jasmine, Yellow, protection of root of, 161, 162. Javelle water, 23. Jelly, process of making, 315. Jewelweed, protection of pollen by, 294. Jimson Weed. See Thorn Apple. Johnson, on bread, 178. Johnson, on soil, 109, 133. Juglans. See Walnut. J uncus. See Rushes. Juniper, seed dispersal of. 325. wood of, 230. Kentucky Coffee Tree, leaf scar, 212. Kerner and Oliver, on pollination, 307. — — — protection of pollen, 294. King, on irrigation and soil, 109, 129, 133, 153. Knot-grass. See Polygonum. Laburnum, flower of, position of, 307. Lactic acid. See Acid, Lactic. Lactuca. See Lettuce. Land. See Soil. Land plants. See Plants, Land. Land plaster. See Lime sulphate. Landslides, experimental formation of, 111. Lappa. See Burdock. Larkspur n^eds light for germination, 47. Lateness, 412. Lathyrus. See Pea, Sweet. Laurel, air-passages of, 280. Leaf absorbs light, 201. air in, 187*-190. Leaf, air-spaces in. 198,* 199,* 338.* as absorbing organ, 200. as mulch, 115. arrangement of, 220,* 221.* benefited by washing, 215. absorbs carbon dioxide, 200. — oxygen, 194, 195. autumn, 332. bleaching of, with lye and alcohol, 225. coloj; of, in autumn, 332. compared to root, 200, 201. decomposes carbon dioxide, 191,* 192,* 193,* 194, 195. development of, 250,* 251. effect of cold on, 354.* dryness on, 345. freezing on, 353. heat on, 345. light on, 184, 185, 344.* 345,* 346, 347. water on, 341, 342,* 343.* wind on, 345. energy absorbed by, 196, 201. evaporation from. See Leaf, transpira- tion of. fall of, 212, 332. caused by spraying, 215. foliage, contrasted with seed-leaf, 180- 186. follows sun, 217, 218, 345. food in, 181. function of. 181-223. gives off carbon dioxide, 191.* 192,* 193,* 194, 195. hinge-like joints of, 218, 220. injured by fumigation and sprays, 215. internal structure of, 196-212 (198,* 199,* 201,* 202,* 208,* 209,* 210.* 211.* microscopic structure of, 196-198,* 199*- 201,* 202,* 208,* 209,* 333,* 334,* 335,* 336,* 337,* 338,* 340,* 344,* 345,* 402,* 403,* 404.* method of fixing air-tight in stopper, 205.* movements of , 217, 218.* 219,* 220.* 221.* of water plants, 337,* 338.* osmosis in, 242. position of, 216, 217, 218.* propagation by, 433. 472 INDEX Leaf, protection of. against animals by bit- ter taste. 222, 223. hairs, 221. — — hugging the ground, 223. poisonous substances, 222. prickles, 221. spines, 221, 334. teeth, 222, 334. texture. 223. thorns, 221. enwrapping, 251, 261. drying, by hairs, 213, 333, 334,* 335.* position, 217, 218.* reduction of surface, 215, 332, 342.* in number of stomata, 215, 235, 336.* — rolling, folding, etc., 213, 334. sunken stomata, 215, 335, 337.* thicker cuticle, 333, 334,* 337,* 338.* — — — — — water -proof substances, 214, 251, 333, 334.* water - retaining substan- ces, 216. raises sap, 242. respiration of, 194, 195. scale, 347. shade, 3^4,* 345.* sleep position of, 218.* starch formation in, 182-203 (182,* 184,* 186,* 191,* 192.* 193,* 198.* 199,* 201,* 202*). starch in. 181. 182.* 183. storage of food in, 260. strength of, how secured, 267.* sun. 344.* 345.* transpiration of. 203*- 206.* 207, 208,* 209,* 210,* 211*-218,* 317, 328, 348. turns toward light. 217-219. unequal growth of opposite sides of, 251. variegated, starch in. 185. veins of. 198,* 199,* 225, 267.* water, 337,* 338.* 339.* 340.* withdrawal of nutriment from, in au- tumn. 332. Leaf, work of, 163-285. See, also, Seed-leaf and Stomata. Leaf green. See Chlorophyll. Leaf-mold, 107. — capacity for holding water of, 132. — test for humus in, 155. Leaf-mosaic, 219. Leaf-scar, 212, 245, 332. Leathery texture protects against animals, 223. Lenticel, 232,* 278, 279.* Leontodon. See Dandelion. Lettuce, Prickly, sun- and shade-leaves of, 344.* Levees, protected by plants, 277. Life, length of, in plants, 286. Light, absorbed by leaves. 201. affects absorption of carbon dioxide. 207. chemical action caused by, 182 * 184,* 185 195, 196, 201, 316, 364, 382. kills bacteria, 364, 382. effect of, on chlorophyll, 184,* 185. color of fruit, 316. — — — direction of growth of plant, 264, 346. — — — evaporation from the soil, 115. eye, 196. flowers, 295, 296, 298, 308, 347, 348. form of plant, 184,* 185, 261, 327, 328,* 329,* 344,* 345*-348. fruit. 308. 342. 347. — fruit and flower production, 347. — — — germination, 47. growth. 253. leaves, 184,* 185, 217-219, 344,* 345,* 346. Mould, 394. portion of effective in heliotropism, 265. starch formation, 196. relation of, to self -pruning of trees, etc. 261. starch formation, 182,* 184,* 185, 201. stem, 264,346. ' stomata, 207-209. transpiration, 207. electric, for growing plants .346. needed by plants, 326. INDJUX 473 Light filter, 265. Lilac, food in buds of, 253. Mildew of, 406, 407.* starch in. during winter, 259. transpiration of, 204. Lilium. See Lily. Lily, embryo-sac of, 291,* leaf-scar of, 212. stomata of, 210. storage of food in, 313. Lily, Pond. See Lily, Water. Lily. Water, 282, 337. 339. Lima Bean. See Bean, Lima. Lime as fertilizer, 151, 153, 154. benefits puddled soil, 129. destroys insects and fungi, 152- effect of, on flora, 350. flocculates clay, 152. for softening water, 152. how supplied to soil, 151. needed by plants, 139. promotes decomposition, 152. sets free plant-food. 152. sweetens sour soil, 152. test for, 157. Lime carbonate, dissolved by cavbouic acid, 140. chloride as disinfectant, 364. oxalate, crystals, 232.* 254. sulphate, as fertilizer, 151. — etched by roots, 144. — for casts, 76. germination experiments, 44. water, 34, 139. Linden, change of fat to starch in, 259. dispersal of seeds of, 322.* fat of, in winter, 259. protection of pollen of, 294. LinnaBus, floral clock of. 295. Linum. S^e Flax. Lipase, 170. Liriodendron. See Tulip Tree. Listerine as disinfectant, 364. Live-f or-ever, protection of, against drying, 215. storage of food in, 260. — — water in, 334. water reservoirs of, 216. Loam, 108. Lockjaw, 328. 380. Loco weeds, 222. Locust, protection against animals, 222. Lodeman, on pruning, 264. — spraying, 407. Lonicera. See Honeysuckle. Loughridge, acknowledgment to, x. on soil testing, 155, 160. Lubbock, on pollination, 307. Lupine, dispei'sal of seeds of, 320. leaves of, follow sun, 218. root-tubercles of, 149, seed-covers of, hinder absorption, 25. Lupine, Yellow, visited by bees, 299. Lupinus. See Lupine. Lye absorbs carbon dioxide, 34. and alcohol for bleaching leaf, 225. softens bark, 248. Lyle, on plant-breeding, 453. MacDougal, on mutation. 453. Madia. See Tar-weed. Magnesium needed by plants, 139. Magnolia, air-passages of, 280. Mahonia, transpiration of, 204. Maize. See Corn. Malaria, 380. Mallow, leaf of, follows sun, 218. Rust of, 406. Mallow family, cross-pollination of, 303. Manure as general fertilizer, 148, 153. as mulch, 115. benefits puddled soils, 129. decomposition of, 383. green, 150, 384. nitrogen in, 147. Maple, bird's-eye, 262. dispersal of seeds of, 321, 322. 323.* flower-buds of. 286. food in buds of, 253. preparation of, for flowering, 286. protection of, against drying, 213. Maple, Sugar, run of sap of, in spring, 243. 259. Marble as fertilizer. 151. dissolved by carbonic acid, 141. etched by roots, 144. Marking, apparatus for, 78.* Marl as fertilizer, 151. 474 INDEX Marnibium. See Horehound. Marsh gas, 381, Massee, on plant diseases, 407. Material, economy of, in construction, 265. 266. McKenny, on fertilizers, 153. Meadows killed by flooding, 125. remain in good tilth, 129. Meanders, experimental formation of. 111, Means, on fertilizers, 153. Meat, preservation of, 385, 386. Medicago. See Alfalfa, Bur Clover. Medullary rays, 232,* 233, 258. Melampyrum. See Cow Wheat. Mclilotus, leaves of, follow sun, 218. Mentha. See Mint. Mercurialis. See Dog's Mercury. Mesembryanthemum. See Ice Plant. Metabolism. See Chemical action Iti plants. Mexican Morning-Glory. See Morning- Glory. Mexican. Microscopic structure. See Histology. Mildew, 406, 407.* Milk, action of f elements on, 172. as emulsion, 170. bacteria of, 372-378. souring of, 376. Mica, 107. Micropyle, 8,* 9. admits air, 30,* 31, 32. function of, 10-24. should be in contact with soil, 21,* 22.* Mignonette attracts insects, 299. Milling. 178. Milner, on foods, 173. Mimulus. See Monkey Flower. Mineral substances in soil, 136-160. Mint, rhizome of, 277. family, cross-pollination in, 303. Missing links, 443, 452. Mississippi, 382. Mitchella. See Partridge-berry. Moisture. See Water. Molasses, 369, 389. Molybdate of Ammonium. See Ammonium molybdate. Monkey Flower, stigma of, 292. Monkshood, protection of pollen of, 294. root, 161. Monocolytedons are mostly shallow-rooted. 135. behavior of leaves of, in dark, 347. characterized, 226. have no cambium, 228. ^lonoecioiis plants, 302. Monstrosity, 420, 421, 449.* Moon Flower, seed -cover of, hinders ab- sorption, 25. Moor plants, protection against drying, 333. Moors, absorption difficult in, 336. Moore, on bacteria, 384. Morphologj', experimental. See Plant, form of. Morning-Glory, germination of, 81. seed-cover of, hinders absorption, 25. self- vs. cross-pollination of, 301, 302. twining of, 275. Mexican, seed-cover of, hinders absorp- tion, 25. Moss Rose. See Rose, Moss. Moths visit night-blooming flowers, 300. visual powers of, 300. Mould, precautions against, 28, 72, 100, 102, 397. bread, 391,* 392,* 393,* 394,* 395,* 396.* green, 396, 397.* Movements of flowers, 296, 297. — leaves, 217, 218,* 219.* 220,* 221.* Mucor stolonifer, 391. Mulch for soil, 40, 115,* 116,* 117, 125, 129. 133, 135, 353. Mullein, hairy covering of leaf of, 213. protection of, against animals, 221. dryness, 334, 335.* Miiller, on pollination, 307. Mushroom, power of growth of, 77. Mustard, effect of light on flowers of, 298. germinati jn of, 8. Mustard family, cross-pollination in, 303. Mustard, Yellow, structure of leaf of, 196. 197, 198,* 200-202. Muscle-forming foods, 176. Mutation, 330, 442-444,* 445,* 446,* 447*-453. Mycelium, 392, 402. Nails used to promote fruit production, 319. Narcissus, pollen of, 293. starch formation in, 183, 191.* 193.* INDEX 475 Narcissus, stomata of, 196. Nasturtium, leaf-stalk of, acts as tendril, 270. pollen of, 293. Natural selection, 330, 331, 442-453. Nectar attracts insects, 300. protection of, 295. Nectarine, origin of, 420. Needs of plant, 326. Nepenthes, 172. Nerium. See Oleander. Nettle, pollen of, carried by wind, 300. protection of, against animals, 221. Newman, on bacteria, 408. Nicotiana. See Tobacco. Nightshade family, cross-pollination of, 303. Nitragin, 385. Nitrates, produced by bacteria, 383-385. Nitrate of potassium. See Potassium nitrate. Nitrate of silver. See Silver nitrate. Nitrate of soda. See Sodium nitrate. Nitric acid. See Acid, Nitric Nitrites produced by bacteria, 383-385. Nitrogen combines with starch to form proteids, 253. conserved by plants, 176. effect of, on plant, 349, 350. escapes from soil, 148, 149. how supplied to soil, 147, 148, 149,* 150. in air, 149, 383-385. — beans, 177. — eggs, 177. — peas, 177. — percolating water, 149. needed by animals, 176. plants, 139, 140,* 176. prepared for plant by bacteria, 149,* 150, 383-385. prepared for plant by fungi, 150. produced by bacteria, 383. promotes leaf-, rather than fruit-produc- tion, 318. selected by plant, 161. taken from air by bacteria, 383-385. some plants, 149. test for, in soils, 155. waste of, by animals, 176. Node, 327. Node, growth at, 249, 250. Notching, to increase fruit production, 318. Nucleus, 65,* 66, 290, 291,* 311. Nuphar. See Spatterdock. Nutrition. See Food. Nuts, absorp ion of water by, 7, 23,* 29. protection of, against drying, 317. seed of, 320. Nymphaea. See Lily, Water, Oak, cambium of, 232,* 246. fibrous bundle of, 226. food conveyed to fruit of, 313. latent buds of, 262. path of water in, 226, 230, 232,* 233, 234,* 235. pollen of, carried by wind, 300. starch in, 259. stem of, microscopic structure of, 232,* 233, 234,* 235, 246. wood of, compared with wood of Pine, 235, 238. Oat contains no pepsin, 172. germination of, 47. stomata of, 196. ovary of. 290.* pollen of, 290.* stigma of, 290.* style of. 290.* Oat, WiLl, seeds of, bury themselves, 71. Oat Rust, 4C4, 405. Oat-smut, 400-401. Odor attracts insects, 299, 300. CEnothera. See Primr^ se. Evening. Oil, emulsification of, 169, 170. energy from, 173. formation of, 201, in eggs, 177. — fruits, 314. — growing region, 253. — seeds, 165, 177, 437. injures leaf, 215. produced from starch, 314. saponification of, 170, 171. test for, 105, 259. See, also. Fat. Oil, C coanut, 169, 170. Oil, Corn, 437. Oil, Cottonseed, 147, 169, 170. 476 INDEX Oil. Olive, 169, 170, 171. Oily seeds, transformation of food in. 314, Oleander, protection of, against drj'ing, 215. 333, 337.* transpiration of, 204. Olive oil. See Oil, Olive. Onion, germination of, 47, 72, 81. pollen of, 293. roots of, 86. storage of food in, 313. Opening and closing of flowers. See Flower. Opium Poppy. See Poppy, Opium. Opuntia. See Prickly Pear. Orange rays cut out by cupra-ammonia, 265. Orchids, cross-pollination of, 306, 307, Orchis. See Orchids. Oriental Poppy. See Poppy, Oriental. Origin of species, 441-453. Osmosis, 122, 123,* 124. generates pressure, 60, 61,* 62.* in seed, 60, 63, 64, 67. makes stem rigid, 269. of leaves, 242. relation of, to growth, 64-68. through seed-cover, 16,* 17, 18, 19,* 20. Osmotic pres.sure, measurement of, 62,* 63. Ovary, 288,* 289, 290.* correlation of, 360. Ovule, 288,* 312. Oxalate of ammonium. See Ammonium oxalate. Oxalate of lime. See Lime oxalate. Oxalic acid. See Acid, Oxalic. Oxalis, dispersal of seeds of, 321. opening and closing of flowers of, 295. protection of, against water, 214. sleep position of leaf of, 218. Oxbows, experimental formation of, 111. Oxidation, as source of energy, 35, 173. brought about by ferments, 173. See, also. Combustion and Respiration. Oxygen, absorption of, 33, 34,* 35, 36, 175, 194, 195, 200, 287, 317, 388. 390. given off by leaf, 191,* 192,* 193,* 194, 195. how supplied to organisms, 176. needed for growth, 5,* 6, 32, 33,* 34,* 35, 36, 37,* 38, 39,* 40, 125, 126, 281.* 283. 326. See, also. Air. Papaver. See Poppy. Palisade cells, 198,* 199,* 200. 201. effect of light on, 345. poorly developed in water-plants, 339. Palms, pollen of, carried by wind, 300. Pancreas, 169. Pancreatic juice, 169-172. Pansy hybrids, 428. Parasitic bacteria, 380. Parenchyma of wounds, 319. See, also. Cell parenchyma, Bast paren- chyma and Wood parenchyma. Parental characters. See Heredity. Paris, plaster of. See Lime sulphate. Parsley family, flowers of, 298. Parsnip, flowers of, attract bees, 299. storage of food in, 313. sugar in, 122. Partridge -berry, cross -pollination of, 304. 305.* Passiflora. See Passion Flower. Passion Flower, 272. calyx of, 288. Pasteur's solution, formula of, 398. Pasteurization of milk, 377. Pastinaca. See Parsley. Pastures, remain in good tilth, 129. Paving, keeps air from roots, 126. Pea, 89, 141-144. absorption of water by seed of, 7. contains no pepsin, 172. cross-pollination of, 306. flower of, opened by bees, 308. platform of, 307. food in, 177. germination of, 47. leaves of, follow sun, 218. pocket of seed of, 20. protection of fruit of, 320. Pea, Sweet, pollen of, 292, 293. Pea family, cross-pollination in, 303, dispersal of seeds in, 321. protection of pollen in, 294. root-tubercles of, 149, 384. 385. tendrils of, 272. Peabody, on foods, 173. Peach, escape from seed-cover of, 5-1. protection of, against drying, 214, 317. fruit of. 320. INDEX 477 Peach, seed-cover of, 59. hinders absorption, 25. path of water in, 9, 24. sports of (Nectarine), 420. Peanut, air-reservoir of, 42. buries its seeds, 70. protection of fruit of, 320. structure of fruit of, 3, 4.* Pear, epidermis of fruit of, 317. hairy covering of leaf of, 213. self-sterility of, 309, stomata of, 317. Pear. Prickly, cross-pollination of, 306. effect of moisture and darkness on, 329. ■pearl ash, 154. Peat bogs, absorption difficult in, 217. Peat moss, killed by lime, 350. loves sour humus, 351. Pecan, escape from seed-covering of, 54. opening in seed-cover of, 8,* 9. path of water in seed-cover of, 9, 24. Pectin compounds in fruits, 315. Pelargonium, behavior of seeds of, 71. See Geranium. Penicillium, 396, 397.* Pepsin, 171, 172. Peptone, 369. Perennials, flowering of, 286. Periwinkle, leaf-arrangement of, 220,* 221.* Petals, color of, 297-300. injury of, 288. transformed into leaf -like bodies, 359. Petroselium. See Parsley. Petunia, crossed with tobacco, 432. Phaseolus. See Bean and Scarlet Runner. Phleum. See Timothy. Phoenix. See Date. Phlox, protection of pollen of, 294. Phosphoric acid. See Acid, Phosphoric. Phosphonis, effect of, on production of flowers and fruit, 318, 350. how supplied to soil, 150, 151. needed by plants, 139, 140.* obtained from bones, 150. test for, in soils, 155, 156. unites with starch in proteid formation, 254. Photosynthesis. See Starch -formation Phylloxera. 162. Physiography, experiments in, 103-160. Picea. See Spruce. Pinchot, on forestry, 245. Pine, cambium of. 236,* 246. correlation in, 359. cross-pollination of, 302. dispersal of seeds of, 321, 322. latent buds of, 262. pollen of, carried by wind, 300, .301. — — vesicles of, 301. protection of, against drying, 333, 334. friiit of, 320. wood of, compared with Oak wood, 235, 238. microscopic structure of, 235, 236.* Pine-apple, trypsin m, 172. Pink Bean. See Bean, Pink. Pink family, cross-pollination of, 303. Pitcher Plant, pepsin in, 172. Pith. 120,* 121, 269. Pits. 227 * 229. 232,* 233, 234,* 235. Plants, action of, in forming soil, 109. alpine, 357, 358. chemical action in, 1C6-177, 182-196, 253 254, 258. 2.59. 314-316. climbing, 270, 271,* 272, 273,* 274, 275.* decay of, 381. dicotyledonous, 226. diseases of, 397, 398,* 399,* 400, 401, 402,* 403,* 404-407,* 408. damage done by, 400, 401, 406. prevention of , 400, 401, 407, 408, 440. engineering principles illustrated in struc- ture of, 266, 267.* 268,* 269, 270. form of, effect of correlation on, 359. fungi on, 359. — light on, 184,* 185, 261, 327, 328,* 329,* 344,* 345*-348. form of. effect of water on, 326,* 327,* 328,* 329,* 330, 331,* 332,* .333,* 334,* 335.* 336.* 337,* 338,* 339,* 340,* 341, 342,* 343,* 344.* effect of wind on, 348,* 349,* 350.* food of. in soil, amount of, 146. dissolved by carbonic acid. ir9-145. fixed by clay and humus, 145. — — — — set fi'ce by lime, 152. — needed by, 164-176. 478 INDEX Plants, habit of. 264. has problems to solve, 6, 29, 260. how supplied with air. 176, 187*-190, 278, 279,* 280,* 281.* 282-285. injury of, 79.* 86.* 263. land vs. water, 3:58, 339,* 340, 342. length of life of, 286. monocotyledonous, 135, 226, 248, 347. moncecious, 302. needs of, 6, 326. poisonous, 222. selective action of, 161. strength of, how secured, 266, 267,* 268,* 269, 270. struggle of, for existence. See Struggle for existence, supply carbon dioxide to aquaria, 285. tendril bearing, 270-274. twining, 275, 276. water, characteristics of, 337,* 338,* 339,* 340*-342. weaving, 270. Plant-breeding, 331. 335, 409-411,* 412-413,* 414,*415,*416,*417,418,*419,*420-423,* 424,* 425,* 426,* 427,* 428, 429,* 430, 431*-444,* 445,* 446,* 447,* 448*, 449*- 453. Plant lice cause green flowers, 349. Phmtago. See Plantain. Plantain, cross-pollination of, 303. protection of pollen of, 295. Rattlesnake, prefers coniferous humus, 351. Water, 342. Planting stick, 40.* Plaster of Paris. See Lime sulphate. Platinum wire, 366. Plow sole, 126.* Plowing, 126,* 127,* 128,* 132. Plum, escape of, from seed, 54. flower of, 431.* improvement of, by breeding, 409-411,* 412, 413,* 414,* 415,* 416,* 417. pollination of, 430, 431.* self sterility of , 309. See, also. Prune. Plum, American, 409, 410, 411,* 412, 413.* Apple. 410. Bartlett, 410. Plum, Beach, 410. European, 409, 411. Improved Beach, 412, 413,* 414.* Japanese, 409, 410, 411. Pond, 411. Stoneless, 415, 416,* 417. Plumcot, 415.* Plumule, 1,* 2,* 3,* 4.* protection of, 71,* 72,* 79.* Pneumonia, 380. Pocket around caulicle, 20,* 58.* Pod, 3. Poisonous plants, 222. Pole Bean. See Bean Pole. Pollen, carried by insects, 289, 291, 297-3r . wind, 300, 301, 310. 311. effect of, 309, 311. exclusion of, 289. germination of, 290,* 292. 293,* 294. injured by rain, 294. protection of, 294, 295. use of, 289. vitality of, 294. Pollen-tube, 290,* 291.* attracted by stigma, 293, 294. grows away from air, 293. Pollination, 289-311, 430-431,* 435, 436. cross-, 301. effect on ovary, etc., 309. self-, 301. Polygonatum. See Solomon's Seal. Polygonum, protection of, against animals, 223. Water-, 335,* 336.* 340.* Pond Lily. See Lily, Water. Pond Plum. See Plum, Pond. Pondweed, 339. Poor -man's- weather-glass, behavior of flowers of, 295, 296. protection of pollen of, 295. Pop corn, 7. Poplar, buds formed on roots of, 249. cross-pollination of, 302. flower-buds of, 286. leaf of, hairy covering of, 213. pollen of, carried by wind, 300, preparation of, for flowering, 286. protection of, against drying, 214. — — — water, 214. INDEX 479 Poplar, transpiration of, 204. Poplar, White, haii-y covering, 213. Poppy, needs light for germination, 47. position of dowers of, 307. protection of, against animals, 222. Poppy, Opium, 427,* 428. Poppy, Oriental, 427,* 428. Poppy hybrids, 427-420.* Portulaca. See Purslane. Potamogeton. See Pondweed. Potash, as plant-food, 139, 140.* how supplied to soil, 152. increases fruit production, 318. needed by plants, 139, 140.* set free by lime, 152. Potassii^m, bichromate, as light filter, 265. chloi-ate, 235. nitrate, 139, 148, 153. permanganate, 364. Potato, correlation in, 360. cuticle of, 328. effect of freezing on, 353. light on, 327, 328.* water on, 326, 327,* 328,* 329, 330. eyes of, 200. for bacterial cultures, 365,* 366, 367,* 380. protection of pollen by, 295. starch in, 328. stem nature of tuber of, 260. storage of food by, 260, 297, 313. transpiration of, 328. Potato, Sweet, twining of, 275. Potato Vine, tendrils of, 270. Potentilla. See Cinquefoil. Powell, on praning, 264. Preservation of foods, 376, 377, 385-388, 397. Prickles, effect of light on, 347. protect against animals, 221, Prickly Lettuce. See Lettuce, Prickly. Prickly Pear. See Pear, Prickly, Primrose, cross-pollination of, 305. protection of pollen by, 294. Primrose, Evening, Broad, 446,* 447.* — Dwarf. 445.* — Lamarck's, mutations of, 443, 444,* 445,* 416, 447.* — Pale, 447.* Primula. See Primrose. Propagation. See Reproduction. Protection against animals, etc., by bark, 256. bitter taste, 222, 260, 320. — — — — concealment, 200, 320. — hairs, 221, 256, 200. — — — — hug ing the ground, 223. — — hard cos^erings, 320. — — — — poisonous substances, 162, 222. — — prickles, 221. spines, 221. 256. 260, 320, 331,* 334. suspension, 320. teeth of leaf, 222, 334. texture, 223. thorns, 221, 260. — cold, 353, 354. — drying by calyx, 288. — — — dispensing with leaves, 215, 331,* 332,* 343.* enwrapping leaves, 251, 261. hairy coverings, 213, 333, 334,* 335.* — — — position of leaves, 217, 218.* — — — reduction of leaf - surf ace, 215, 333, 342.* — — number of stomata, 215, 335, 336.* rolling and folding of leaf, 213, 334. sinkingof stomata, 215, 335,337.* storage of water, 331,* 334. thicker cuticle, 333, 334,* 337,* 338.* — — — water-proof substances, 214, 251. 333. 334.* water-retaining ^:ubstances, 216 — — — woody coverings, 317. — dust by hairs, 214. — fire by bark, 256. — fungi by bark, 256. callus. 263. — water by callus, 263. hairs, etc., 214. wax, 214. of plumule, 71,* 72.* 79.* — root, 161. 162. Proteids. decomposition of. 38L energy from, 173, 174. formation of. 201. 253, 254, 480 INDEX Proteids, in animals, 171, 172, 176. — Beans, 177. — bran, 178. — dietetics, 17G. — eggs, 176, 177. — flour, 177. — friiits, 314. — growing region, 253-259. — Peas, 177. — seeds, 165, 166, 314, 437. — Wheat, 177. 178. path of, in stem, 227* 231,* 232,* 236,* 254- 257. tests for, 165, 166. Protoplasm, 65,* 66, 291.* Prune. See Plum. Prune, French, 411,* 415, 416.* Giant, 410, 411. Stoneless, 415. 416,* 417. Sugar, 411.* Prunier, sans Noyau, 415, 416.* Pruning, 263, 346. correlation in, 359. of roots to increase fruit -production, 319. self-, 261. Prunus. See Almond, Apricot, Cherry, Peach, Plum and Prune. Ptyalin, 167. Puccinia. See Rust. Pumpkin, fruit of, 317. path of proteid in, 254. tendrils of, 272. Purslane, protection of, from animals, 223. Pusley. See Purslane. Putrefaction, 380. Pyrus. See Apple, Pear. Quaker Bonnets. See Houstonia. Quaker Ladies. See Houstonia. Quartz, 105, 107. Quercus. See Oak. Quince, absorption of water by seed of, 7, 28. branches of, twisted in layering, 314. seed-cover of, holds water, 28. Radish, absorption of water by seed of, 7, 28. germination of, 47. Ra:\ish, relation of, to light, 265 root-hairs of, 100,* 101,* 121. seed-cover of, holds water, 29. Ragweed, protection of, against animals, 223. Rain buries seeds, 69. percolation of, in soil, 111-118. puddles soil, 129. Ranunculus. See Buttercup. Rape, 314. Raphanus. See Radish. Raspberry, acid in fruit of, 315. climbing of, 270. Rattlesnake Plantain. See Plantain, Rat- tlesnake. Raw Food. See Food, Raw. Red rays cut out by cupra ammonia, 265. Regeneration dependent on oxygen, 281,* 282. in stem, 257. of root, 86. — stem, 79.* Reproduction by seed, 291,* 292.* — spores, 362,* 365, 393, 394,* 395,* 396.* 397,* 398,* 399,* 401, 402,* 403,* 404.* — vegetative parts, 433. Reseda. See Mignonette. Resins absent from water-plants, 339. protect against drying, 214. 334. Resistance to disease, 440. Respiration defined, 175. increased by wounds, 388. measurement of, 34,* 175. of animals, 35, 176, 194. — flowers, 287. — fruits, 317. — leaves, 194, 195. — Moulds, 394. — seeds, 33, 34.* 35, b3.* — Yeast, 390. Reversion, 420, 449,* 450. Rhamnus, Rust of, 405. Rheum. See Rhubarb. Rhizomes, function of, 277. propagation by, 433. resemble roots, 277. storage of food in, 260. Rhizopus nigricans, 391. Rhubarb, bleaching of, 346. INDEX 481 Rhubarb, protection of root of, 162. Ribes. See Currant. Rieinus. See Castor-bean. Riley on food of plant, 344. Rind, function of, 257. of root, 120,* 121. of stem, 224,* 225,* 232,* 233. 236.* starch in, 258, Ring, annual, 247. bast-226, 246. cambium— 246. woody, 226, 246. Ringing, 256, 257, 318, Ripening of fruits, 316. — seeds, 314. River water, plant-food in, 138. Rivers, self-purification of, 382, 383. Roberts, on fertilizers, 153. Robinia. See Locust. Rocks, decomposition of, 109, 144, 145. Roguing, 451. Rogues, 451. Rolling of leaf protects it against drj'ing, 213, 334. Root, aeration of, 36, 37,* 38, 39,* 40, 103, 119,* 120,* 124-126. 128, 130, 132. aerial, 275.* absorption of water by, 88. 102, 103, 119,* 120,* 121-123 * affected by heat, 332. salts, 124, 336. acid excreted by, 141-143,* 144, 145. anchors plant in soil, 87.* behavior of, to obbtacles, 99.* buds formed on, 249. care of, 135, 136. climbing, 275.* contraction of, 87. decomposes rocks, 144, 145. depth of penetration of, 134, 135. direction of growth of, influenced by air, 89, 98, 135. centrifugal force, 92.93,* 94. ■ food, 89, 98. gravity, 88,* 89.* 90, 91,* 92, 93.* 94, 95, 98,* 99. heat, 89, 98. water. 89, 95,* 96.* 97, 98. EE Root, effect of heat on, 332. water on the form of, 341. etches marble and plaster of Paris, 144. excretion by, 141-143,* 144, 145. exploration of soil by, 133-135. food in, 122, 125, 260. force of growth of, 81, 82,* 83, 84,* 85. fungi on, 150. gives off carbonic acid, 141-143,* 144. growing region of, 85,* 86. microscopic structure of, 120,* 121. 255. needs air, 125. of water-plants, 339. osmotic action of, 123, 124. path of water in, 120,* 121. penetration of soil by, 80.* 81.* propagation by, 433. protection of, 161, 162. proteids in, 255. pruning of, 136, 318. regeneration of, 86. resemblance of rhizome to, 277. selective action of, 161. shallow vs. deep, 87. storage of food in 260. strengthening fibers of, 120,* 267, 268. sugar in, 122. tip of, how protected, 86. — — result of injury to, 86. treatment of, to promote fruit produc- tion, 342. tubercles of, 49,* 384, 385. Root cap, 86. Root-hairs, absorb water by osmosis, 121 123,* 124, 242. effect of water on growth of, 102. method of obtaining, 100,* 101.* of radish, 100,* 101.* of Wandering Jew, 102.* relation to soil-particles, 119, 120, 121. turgidity of. 123. Root-pressure, 243,* 244. Root-stock. See Rhizome. Rosa. See Rose. Rose, calyx of, 288. climbing of, 270. protection of, against animals, 221. Rose, Moss, origin of, by bud variation,, 420. Rose, family, cross-pollination of, 303. 482 INDEX Rosette form as protection against ani- mals, 223. — of alpine plants, 357. Rotation of crops, lGO-161, 407, 408. Roth, on forestry, 113, 245. Rubber plant, 356. Rubus. See Blackberry, Raspberry. Runoff, 113. Rushes, protection of, against animals, 223. Russian Thistle, dispersal of seeds of, 322. Rust, Black Stem, of Grain, 401, 402,* 403,* 404,* 405. Crown, of Oats, 40.'). Hollyhock, 406. Orange Leaf, of Wheat, 405. Rye, germination of, 47. pepsin absent from, 172. Rust of, 405. Smut of, 400, 401. Saccharomyces. See Yeast. Sage, cross-pollination of, 305-306.* hairy covering of leaf of, 213. structure of flower of, 306,* 307. brush, protection of against drying, 334.* St. Louis, water supply of, 382. Saleratus^l54. Salicylic acid. See Acid, Salicylic. Salix. See Willow. Saliva, 166, 167. Salt, 161. as preservative, 385, 386. in osmosis, 18. in soil, test for, 158. sets free potash, 152. Salt Bush tolerates alkali, 350. Salt marshes, absorption difficult in, 217. Saltpeter. See Potassium nitrate. Chili. See Sodium nitrate. Salts in soil, 13G-1G0. — — fixation of, by soil, 145-147. form crust, 127, 129. — — hinder absorption, 18, 124, 217, 3:!f). needed by plant, 139, 140.* protect plant against dryness, 216. Salvia. See Sage. Sambucus See Elder. Sand, 104, 147. bound together by plants, 277. Sand, freed from plant-food, 155, 156. microscopical examination of, 105. percolation in, 113. plant-food in, 105, 146. power of, to lift water, 118. properties of, 105. water-holding capacity of, 132. Sandy loam, 108. soil for cuttings, 262. Sap, rise of, 224-245, 2.59 (224,* 225,* 227.* 231,* 232,* 234,* 236,* 237,* 238,* 240.* 243*). Sap wood, 244, 245. Saponification, 170, 171. Saprophj'tic bacteria, 380. Saunders, on pruning, 264. Scabiosa. See Scabious. Scabious, protection of pollen of, 295. Scale of boilers, 151. Scale, bud. See Bud scale. Scar. See Hilum. Scarlet avoided by bees, 298. Scarlet fever. 329, 376. Scarlet Runner, 144. absorption of water by seed of, 12. germination of, 59, 60.* getting above ground of, 71. protection of tip of stem of, 71,* 79. transpiration of, 204. twining of, 275. Scent. See Odor, von Schrenk, on woods, 245. — plant diseases, 407. de Schweinitz, on milk, 377. — plant diseases, 407. Scion, 248. Scirpus, strengthening fibers of, 267.* Sclerenchyma. See Cell, Sclerenchyma. Sea water, effect on germination of, 18. renders absorpti(Mi difficult, 336. Seasoning of wood, 245. Secale. See Rye. Sedges, protection of, against animals, 222. Sedum. See Live-for-ever. Seeds, air-dry, contain water, 7* air needed by, 30,* 31, 32,* 33, 36, 37,* 38. 39,* 40. burial of, in soil, 69, 70. carbon dioxide given off by, 6, 33, 34,* 35. INDEX 483 Seeds, catdicle of, 1,* 2,* 3.* 4.* 20,* 58.* chaflf of, holds water, 29. diastase in, 168, 1C9. dispersal of, by animals, 323,* 324,* 325. — — — mechanical contrivances, 320, 321.* water, 325. wind. 321, 322,* 323.* effect of extremes of temperature on, 352. embrj'o, 288, 312. embryo of. 1,* 2,* 3,* 4,* 20,* 56,* 58.* fat in, 165, 437. ferments in, 166-172. food conveyed to, 313, 314. — in, 65,* 164-180, 437. — transformed in, 314. force exerted by swelling of, 48, 49,* 50, 51,* 52, 53,* 54* germ of. See Seeds Embryo of. germination of, 1-86. affected by air, 5,* 6. — alkali soils, 18. depth of planting, 38, 39,* 40,* 41. drying, 47. heat, 5,* 6. light, 47. — — — — sea water, 18. water, 4, 6. on surface of soil, 69. quickness of, 46. getting above ground of, 71,* 72,* 73,* 74,* 75,* 76, 77,* 79.* — down into ground of, 80,* 81,* 82,* 83, 84,* 85,* 86.* heat set free by, 35. 36.* hilum of, 1,* 2. 10. immature, germination of, 43, lipase in, 170. micropyle of, 8,* 9. micr*^ scopic structure of, 65,* 66, 67, 177, 178. needs of, 4. oil in, 165, 437. osmotic action of, 17, 18, 60, 63, 64, 67. path of water in, 22, 23,* 24. penetration of soil by, 8C,* 81.* pocket around caulicle of, 20,* 58.* preservation of, 7, 28, 45, 46, 385. Seeds, proteid in, 437. pepsin in, 172. plumule of, 1,* 2,* 3.* 4,* 20,* 58,* 59.* proteids in, 105, 166. respiration of, 33 34,* 35, 36.* resting period of, 43, 44. restored by ferments, 44. ripening of, 314. starch in, 05,* 164, 437. structure of, 1,* 2,* 3,* 4.* 20,* 57,* 58,* 59,* 65,* 180.* struggle of, for existence, 312. sugar in, 164. 165. small, treatment of, 41, 42. testing of, 44, 45. tiansportation of, 282. trypsin in, 172. vitality of, 44. water in, 7,* 437. how obtained, 6-30 (7,* 8,* 9,* 15,* 19,* 20,* 21,* 22,* 23,* 26,* 27*). wrinkling of, in water, 8.* Seed-beds, screens for, 41.* soil for, 41. Seed-case, 3,* 4,* 288.* 289,* 290, 360. Seed-cover. 1,* 2,* 3,* 4,* 20, 21, 23,* 24. escape from, 48, 49,* 50, 51*-54,* 55 * 57,* 58,* .59.* 60,* 61,* 62,* 63.* function of. 47, 48. hinders absorption of air, 30,* 31, 32. heat. 42,* 43. water, 8,* 9*-15,* 16*-19,* 20. 21,* 22,* 23*-25. holds water, 28, 29. openings in, 8,* 9*-15,* 16*-19,* 20, 21," 22 * 23*-25. osmosis through, 16,* 17,* 18, 19,* 20. place of rupture of, 54, 58. Seed-leaves, 1,* 2,* 3.* 4,* 178, 179, 180.* contrasted with foliage-leaves, 180-186- function of, 163,* 164-179, 180.* number of, 226. Seedlings. See Seed. Selection, 331, 433-453. Self-pollination, 301, 302. Self-sterility, 309. Senecio. See Ragweed. Septic tank, 382. Serum, 171. 484 INDEX Service berry, hairy covering of leaf of, 213. Setchell, acknowledgement to, x. Sewage, purification of, 381, 382. Shade plants, 344. Shamel, work of, 434-439. Shells as fertilizer, 151. Shoot. See Stem. Sidewalks exclude air from roots. 126. Sieve tubes, 227,* 231,* 232,* 236,* 254, 255. Silage, 387, 388. Silica, 145. Silt, 118. Silver grain. See Medullary rays. Silver nitrate, 158. Simple pits, 227,* 232.* Size, increased by breeding, 410, 411,* 413,* 416,* 422, 423.* Sleep position of flowers, 294, 295. leaves, 218.* Smallpox, 379. Smut, 397-401. Smut of Corn, 397, 398,* 399,* 400, 440. Smut of Grain, 400-401. Smut, Stinking, 400. Snapdragon, flower of, opened by bees, 308. protection of pollen by, 294. Snow as mulch, 117. Snyder, on fertilizers, 153. — foods, 173, 178. Soap for soft?niug bark, 248. Soda for softening water, 151. in soils, test for, 158. Soda-water dissolves marble, etc., 141. Sodium chloride. See Salt. nitrate as fertilizer, 148, 153, 154. — plant selects nitric acid from, 161. sulphate in soils, 158. — test for. 158. Soil, absorption from, 103-162. affects the distribution of plants, 351. action of rain on, 111-113, 129. aeration of, 126. 128. air in, 36, 37.* 38. 39.* 40, 103, 119,* 120,* 124-126. 128, 130, 132. alkali, 157-159. alluvial, 109. as a laboratory for preparation of plant- food, 146. as a sponge, 146. Soil as a storehouse of plant-food, 146. burial of seeds in, 69, 70. capillary action of, 116. chemical action in, 144-153. classified, 108. clayey, 106. color of, 107, 108, 155. composition of, 104, 105. contact of, with seed, 21, crust of, 116, 117, 125, 126,* 127, 129. drainage of, 40. drift, 109. evaporation from, 115. exploration of, by roots, 133-135. formation of, 109, 110. heart of, 107. heat absorbed by, 43. — retained by, 43. humus in. 104, 107, 132, 133, 145, 148, 351 — — test for, 155. injured by over-irrigation, 131. tilling at wrong time, 129. lifts water. 114. lime supplied to, 151. — in. test for. 157. mechanical analysis of, 104. mellow, 107. mineral substances in. 136-160. nitrogen supplied to, 147-150. — in, test for, 155. of arid regions, 146. phosphorus supplied to, 150. — in. test for. 155. 156. physical condition of, 115,* 116,* 117,* 119,* 120,* 124, 125, 126,* 127,* 128,* 129-133, 384. potash supplied to, 152. plant food in, 136-160, 201. puddled. 125. 129. required by cuttings, etc., 108, 262. 263. salts in, 136-160. sandy. 105. saturated, 118. sour, sweetened by lime, 152. temperature of, 43. tests for, 155-160. texture of. See Soil, Physical condition of. tilth of. See Soil, Physical condition of. INDEX 485 Soil, transported, 109. washed away on slopes, 113. water-holding capacity of, 132, water of, 103. amount suited to plants, 130, 131. how absorbed, 111-113. 129. how regulated, 132, 133. Soil-crumbs, 124-127*, 128*. Soil-floccules, 126, 127,* 128. Soil-mulch, 115,* 116.* 117.* 125,* 129, 133. Soil-particles, 119.* 120,* 128 * Solomon's seal, storage of food in, 313. Sorrel, wood. See Oxalis. Spanish Bayonet, protection against ani- mals, 221. Spatterdock, 337. Species, origin of, 441-453. Sphagnum. See Peat Moss. Spines protect against animals. 221, 256, 260, 320. 331.* Spiral tracheids, 227,* 229, 230, 231.* Spongy tissue of leaf, 198,* 199,* 200. Spontaneous generation, 365. Spores of bacteria, 362,* 305. — Corn-Smut, 397, 398,* 399.* — Mildew, 407.* — Mould, 393, 394,* 395,* 396,* 397.* — Rusts, 401, 402,* 403,* 404.* Sport. See Variation, sudden. Spraying, 407. with oil injures leaf, 215. Spring, fat changed to starch in, 259. run of sap in, 243, 259. sugar changed to starch in, 259. Spring-wood, 232,* 236,* 247. Springs, formation of, 117. Spruce, protection against drying, 333. wood of, 230. Squash, cross-pollination of, 302. effect of light on, 184,* 185. fibrous bundles of, 224,* 226, 227.* fruit of, water conveyed to, 317. germination of. 54,* 55,* 56, 81.* micropyle of 8,* 9. path of proteid in, 224,* 227,* 254-256. water in, 224*-227,* 228-230. peg of, 54*-56. root-cap of, 86. root pressure of, 243. Squash, sap of, forces which raise, 241. seed-cover of, holds water, 29. seedlings of, 184,* 185. sleep position of seed-leaf of, 218. stem of, microscopic structure of, 224,* 226, 227,* 228, 229, 246. tendrils of, 272. transpiration of, 216. Squash hybrids, 429. Squaw-vine. See Partridge-berry, Squirrels, Ground, bury seeds, 69. Squirting Cucumber. See Cucumber, Squirting. Stannard, on soil, 133. Starch, absorption of, from leaves, 183, 258. as food, 164, 176. changed to fat, 253, 259. oil, 253, 314. sugar, 167-169. 258, 314, 391. conveyed to wood, 232,* 233. decomposition of, 186,* 187. digestion of, 166-169. disappears in darkness, 182,* 183. energy from, 176, 196. formation of, dependent on air supply. 191.* chlorophyll, 185. light, 182. in variegated leaves, 185. leaves, 182-203, (182,* 184,* 186,* 191,* 192,* 193.* 198,* 199,* 201,* 202*). stem, 278. fuel value of, 176, 196. in buds. 253. — chlorophyll grains, 201,* 202.* — cortex, 258. — flour, 177. — fruits, 314. — growing region, 253, 254. — leaf-cells, 202.* — medullary rays 232,* 233. 258. — potato, 328. — rind, 258. — seeds, 65,* 164, 314. 437. — wheat, 177, 178. — wood, 232,* 233, 257-259. path of, in stem, 169, 254, 257, 258, 313, 314. 486 INDEX Starch, role of, in proteid formation, 253. test for, 164. wandering of, 169. 183, 253, 254, 313. 314. Starch-grains, 65,* 66, 201.* 202.* 367.* Starch-trees. 259. Steam pressure in boilers. 74. Steapsin, 170. Steel wire, 366. Stem, air supply of, 278. 279,* 280,* 281.* 282. annual rings of, 232.* 236.* 247, 262.* bark of. 262,* 279. binding of, 248. — — formation of. 256. function of, 256. protects against dryness. 333. stretching of, 247. bast of, 120,* 224,* 225, 227.* 231,* 232,* 233, 236,* 254-257. behavior of, toward obstacles. 79,* 80. bending of, to increase fruit production, 318,342. binding of. 248. breaking, to increase fruit production, 318, 342. buttresses of, 247. 248. cambium of, 227,* 232,* 236* 246-248. chlorophyll of, 278. climbing, 270. 271,* 272, 273. 274. 275.* collenchyma of, 268. correlation in, 79 257, 359, 360. direction of growth of, affected by cen- trifugal force, 92, 93,* 94. gravity. 90, 91*. 92, 93*- 95. 264. light. 261 264. 270. wind. 348.* 349.* effect of frost o'n, 353. heat on, 346. light on, 220. 261. 346. 359. elasticity of, 269. epidermis of, 278. fat in. 253, 259. fibrous bundles of. 224*. 225*. 226, 227*- 231,* 2.32*-234,* 235, 236,* 246. 254-2.56. food in. 169, 243. 250. 253,-260, 286. 287, 313. 314. force of growth of, 73,* 74.* 75.* 76.* function of, 163-285. Stem, girdling, to increase fruit production. 257, 318. method of fixing air-tight in stopper, 205.* microscopic structure of, 224,* 225*-227* 232*-234*. 235. 236*. 246. 254-256. 267,* 268,* 328, 333,* 334,* 335.* notching, to increase fruit production, 318. one-sided development of, 349, 350.'' path of air in, 258, 278, 279,* 280,* 281,* 282. proteid in. 227. 231. 232,* 236,* 254- 257. starch in, 169. 254, 313, 314. sugar in. 259. water in, 224*, 225.* 226, 227*-231.* 232*-236,* 237,* 258. propagation by. 433. proteids in, 254-257. pruning of. 261-264. regeneration in, 257. — of. 79 * regions of growth of, 77,* 78. rigidity of. due to osmosis, 269. strengthening tissues, 224,* 231,* 232,* 236 * 267,* 268-270. tissue tension, 268, 269. rind of, 224,* 225.* 232,* 233. 236.* 257, 258. ringing of, 244. 25", 318. self-pruning of, 2C1. starch in, 169, 253, 254, 260, 313. 3U. —formed in, 278. storage of food in, 253, 257-260, 286, 287. strains of. due to wind, 265. strength of. how secured. 266. 267,* 268,* 269. 270. strengthening fibers of, 224,* 231,* 2.32,* 236,* 267,* 268. effect of water on, 335.* struggle among branches of. 261. 262. sugar in. 243, 250. 254. 259. sunscald of, 346. tendril-bearing, 270, 271,* 272, 273,* 274. tip of, how protected, 79.* structure of. 226, 250.* 251. twining, 275-277. twisting, to increase fruit production, 318, underground, 260. 277. weaving, 270. wood of, 224*-227*. 228-231*. 232*-234.* 235, 236*, 237*, 238*-240.* INDEX 487 Stem, work of. 163-285. See, also, Corm. Rhizome and Tuber. Sterility, self-, 309. Sterilizer, 363.* Stigma, 288-^-290,* 291, 292. Still. 137.* 138. Stinking Smut of Wheat, 400-401. Stock, in grafting, 248. Stomata. 196-198.* 199,* 203*-206,* 207, 208.* 209.* artificial. 210.* 211.* effect of light on, 207-209, 345. function of. 207. 208. mechanism of. 208,* 209,* 210,* 211.* occur principally on under side of leaf, 215. of fruit, 317. — water-plants, 339. protection of, against dust, 214. — — — water, 214. reduction In number of, as protection against drying, 215. 335, 3.36.* sunken, as protection against drying, 215, 335, 337.* Stoneless Plum- See Plum, S'oneless. Stoneless Prune. See Prune, Stoneless. Stopper, method of fixing leaf or stem air- tight in, 205.* Storage of food. See Food, Storage of. — water. See Water, Storage of. Strains in beams, 265. — stem, 265. Straw as mulch, 115. benefits puddled soils, 129. Strawberry, effect of fertilization on, 309. position of flower of, 307. protection of, from animals, 223. Strength in relation to material, 265. 266. Strengthening fibers. See Cell, Strengthen- ing. Structure, Cellular. See Histology. microscopic. See Histologj'. Struggle for existence, 6, 46, 261, 262, 312, 326, 330. String Bean. See Bean, String. Structure determined by function, 179, 186.* Style, 288.* 289, 290,* Sub-irrigation. 131. Sublimate, corrosive, as disinfectant, 364. Subsoil, 107, 146. Succulents, 215. Sugar as preservative, 386. cane, 165. changed to starch, 259. coagulates blood, 171. decomposition of. 381. fermentation of, 390. for yeast cultures, 389. formation of, 201. in fruits, 314, 315, 411. — growing region, 253, 254. — osmosis expei'iments, 16,* 17, 18, 19.* — roots, 122. — stems, 243, 250, 253, 254, 259. — seeds, 104, 165. — proteid test, 166, 178. — stigma, 292. produced from starch, 167-169, 258, 259, bl4, 391. role of. in proteid formation, 253, 254. test for, 164, 165. travels in cortex, 254, 257. — — wood in spring, 259. Sugar Beet. See Beet, Sugar. Sugar Cane. See Cane, Sugar. Sugar Corn. See Corn, Sugar. Sugar Maple. See Maple, Sugar. Sugar Prune. See Prune, Sugar. Sulphate of ammonium. See Ammonium sulphate. Sulphate of lime. See Lime sulphate. Sulphate of sodium. See Sodium sulphate. Sulphur as disinfectant. 364. as remedy for plant diseases, 407. in proteid formation, 253. needed by plants. 139, 140.* Sulphuric acid. See Acid, Sulphuric Sundew loves sour humus, 351. pepsin in, 172. Sunflower, cross-pollination of- '^O-l flowers of, 298. effect of light on, 298 germination of, 81. rise of sap in, 241. root cap of, 86. root pressure of, 243. seed of, 3.* 488 INDEX Sunflower, seed of, resting period of, 44. seed-leaf of, sleep position of, 218, stem of, 224, 269. Sunlight, See Light. Sunscald, 346. Superphosphate, 139, 150, 153, 154. Surface crust. See Soil, Crust of. Surface mulch. See Soil mulch. Sweet Pea. See Pea, Sweet. Sweet Potato. See Potato, Sweet. Swingle, on Date Palm, 294. — on Fig. 310. — Smuts, 400. — variation due to environment, 421. Switch Plants. 215, 331, 332,* 343.* Synergidae. 291.* Synclines, 111. Syringa. See Lilac. Taft, on soil, 133. Tar excludes air from stems, 281. Tarweed, dispersal of seeds of, 324. Teleutospores, 402.* Temperature. See Heat. Tendrils, 270. 271,* 272, 273,* 274. Terraces, experimental formation of. 111. Texture of soil. See Soil. Physical condi- tion of. Thigmotropism. 272. 273. 274. Thinning of fruit. 312. Thistle, dispersal of seeds of, 321, 322. protection of, against animals, 221. Thorn apple, protection against animals, 222, 320. Thorns protect against animals, 221. Thyme, visited by bees, 299. Thymus. See Thyme. Tilia. See Linden. Tillage. See Soil, Physical condition of. Tilletia. See Smut, Stinking. Timothy, flower of. 280. Tilth. See Soil, Physical condition of. Tissue. See Cell and Histology. Tobacco crossed with Petunia, 432. fermentation of, 388. Tomatoes, canning of, 386. immature seeds of, germinate, 43. improvement of, by breeding, 409. Touch-me-not. See Jewelweed. Toxins, 378, 379. TracheTd, 227,* 229, 230, 231.* 233, 234 * 235, 236.* Tradescantia. See Wandering Jew. Transpiration. 203* -205.* 206* -208.* 209,* 210,*2ll*-218,*3]7. 328. affected by enwrapping leaves. 251. 261. hairy coverings. 213. b33. 334.* 335.* light. 206.* 207. position of leaves, 217, 218.* reduction of leaf-surface, 215, 331.* 332.* 333, 342,* 343.* — in number of stomata, 215, 335. 336.* rolling and folding of leaf, 213, 334. sinking of stomata, 215, 335, 337.* thicker cuticle, 333. 334,* 337,* 338.* water -proof substances, 214, 251. 333, 334.* water-retaining substances, 216. wind. 208. 348. woody coverings, 317. Transplanting, 135, 136, 220, 359. Trees, buds on roots of, 249. effect of flooding on, 125. frost on, 352, 353. heat on. 346. light on, 220, 261, 346, 359. fat, 259. pruning of, 263, 264. roots of. 87. 125. 136. — — fungi on, 150. seed of, how preserved, 46. self-pruning of, 261. starch, 259. struggle among branches of, 261, 262. sunscald of, 346. transplanting of, 133, 220, 359. treatment of, to increase fruit produc- tion, 318. 319, 342. See. also. Forest and Stem. Tree of Heaven. See Ailanthus. Triticum. See Wheat. Tropaeolum. See Nasturtium. Trypsin, 171, 172. Tuber, propagation by, 433. stem nature of, 260. Tubercle bacteria, 149, 384, 385. Tuberculosis, 366, 376, 380. INDEX 489 Tulip, opening and closing of flowers of, 296. pollen of. 293. Tulip Tree, protection of, against dryness, 213. transpiration of, 204. Tumble weeds. 322. Tourney, on forests, 113. Turgidity, 123, 124, 209, 269. Turnip, storage of food in, 260, 313. Tuttle, acknowledgement to, x. Twinberry. See Partridge-berry. Twining plants, 275, 276. 277. Twisting to increase fruit production, 318, 319. Type, 420, 434, 450. Typhoid fever, 371, 376, 379, 380. Ulex. See Gorse. Ulmus. See Elm. Uredospores, 402.* Urtica See Nettle. Urine, 48. U. S. Biological Survey, 356. laboratory for plant-breeding, 441, Dept. of Agriculture, publications of, 113, 129, 133, 153, 160, 178, 222, 245, 264, 294. 310, 349, 354, 377. 384, 400, 407, 421, 433, 434, 441. soil surveys of, 351. forests of, 356. Ustilago. See Smut. Vaccination, 379. Variation, bud, 420. cause of, 421, 450. curve of. 417, 418,* 419.* due to crossing, 422, 424.* 426,* 427*-429,* 430, 434. environment, 326-360. fluctuating, 417. 418,* 419*-421, 442, 443, 448.* 449, 450. lack of, in vegetative propagation, 433. production of, 421. sudden, 420. 421. 442,' 443-445,* 446,* 447*- 449,* 450-453. • suppression of, 433-434. Varnish, absent from water-plants, 339. protects against drying, 214, 333, 334. Vegetable matter. See Humus. Veins of animals, 176. — leaf, 225. Verbascum. See Mullein. Vernation as protection against drying, 213. Vicia. See Horse Bean. Vinca, leaf arrangement of, 220,* 221.* Vinegar as preservative, 386. manufacture of, 387. Viola. See Violet. Violet, dispersal of seeds of, 321. protection of pollen of, 294. preferred by bees, 298. Violet rays cut out potassium bichromate 265. Virginia Creeper attracts insects, 299. tendrils of, 274. Vitis. See Grape. deVries, acknowledgement to, x. 409. on origin of species, 442-453. Waite, on plant diseases, 407. Walnut, cross-pollination of, 302. germination of. 59. leaf-scar of, 212. seed of, path of water in, 23,* 24. structure of, 3, 23,* 24,59. seed-cover of, escape from, 54. — — holds water, 29. openings in, 8,* 9. 23,* 29. Wandering Jew, 102,* 138. 139. 140.* growth of, at nodes, 250. root cap of, 86. root-hairs of, 102.* roots of, 102.* stomata of, 196. supplies carbon dioxide to aquaria, 285, Ward, on plant diseases, 407. Wasp, power of scent of, 300. vision of, 300. Water, absorption of, by root, 88, 102, 103, 119,* 120*-123.* 332.* seeds, 6, 7,* 8,* 9*-15,* 16-19.* 20,* 21,* 22,* 23.* 26.* 27.* wood. 68. affected by heat, 332. force required for, 121-123.* 124. hindered by dissolved salts, etc., 18, 124. 217. 336, seed-covers, 8-26. 490 INDEX Water, action of, on soil, 109-114,* 115*-119,* 120,* 129-133. amount of, in air-dry seed, 7.* • soil needed by plants, 130, 131. wood, 24b. needed for germination, 25, 26. as component of starch, 186. bacteria of, 368. buries seeds, 69. capillary, 113. decreasing, promotes fruit production, 319. distillation of, 137.* distributes seeds, 325. eflfect of, on direction of growth of roots, 89, 95,* 96,' 97, 98. form of plant. 326. 327,* 328,* 329.* .'530, 3."}1.* 332.* 333,* 334,* 335.* 3.36.* 337,* 338,* 339,* 340,* 341, 342,* 343.* growth. 116,* 117. 252. energy required to raise, in stem, 239, 210*-243.* evaporation of, from leaves. See Trans- piration. soil, 115. filtration of, 372. free, 113. haid, 151. hygroscopic, 113. injurious in stomata, 214, in seeds 7* in soil. 103, 111-135. how regulated, 132, 133. formation of, lJ9. lack of, effect on fruit of, 342. plant of. 88, 211-217, 326, 327,* 328.* .329*-331,* 3.12,* 333.* 3.34,* 335,* 336.* 3.J7.* 338,* 339,* 340*-342,* 343.* needed by fruit, 316, 317. pl.ant. 135, 211, 326. seed, 46. of ponds and rivers, plant-food in, 138. path of, in root, 120,* 121. seed, 8,* 22, 23,* 24. stem, 224,* 225,* 226, 227*-231,* 232'-236,*237,*244, 258. percolation of. in soil, 111-114,* 11.5-118. problem of obtaining, 6. Water, protection against, by callus, 263. hairs, 214. w.ix. 214. purification of, 382. rate of travel through wood of, 238,* 2.39 rise of, in soil, 114, 115. role of, in starch formation, 187, 193, 202. sea, 18. 124, 217, 336. storage of. in plants. 331,* 334. Water-bath, 67. Buttercup, 338, 339.* culture, 140.* glass, 387. hyacinth, 340. lily. 337. 339. — closing of flower of, 295. — protection of pollen of, 295. Plantain, 342. plants, characteristics of, .337,* 338,* 339,* 340*-342. polygonum, 335,* .336,* 340.* reservoirs in plants, 216. roots, 341. table, 118, 135. vapor, effect of, on opening and closing of flower, 296. plant, 341. — mfthod of keeping air saturated with, 26,* 27.* wheel, 93.* Wax, absent from water-plants, 339. protects against drying, 214, 333, 334.* water, 214. Weather, effect of, on growth, 252 Weaving plants, 270. Webber, on fertilizers, 153. — plant-breeding, 433, 441. — pruning, 264. — variation due to environment, 421. Weed, on pollination, 407. Weeds, destroyed by crop-rotation, ICU. harbor disease, 407. Weeping Willow. See Willow, Weeping. Wells, whistling, 125. Wheat, 130. 138, 155. early, how secured, 355. germination of, 47, 81. immature seeds of, 43. microscopical examination of, 177, 178. INDEX 491 Wheat, proteid in, 177. rust of, 401, 402,* 403,* 404.* 405. starch in. 177. stinking smut of, 400, 401. smut of, 400, 401. stigma of, 292. strength of stalk of, 267. structure of grain of, 178. Whistling wells, 125. White, acknowledgement to, x. White Poplar. See Poplar, White. Whiting. See Lime carbonate. Whitney, on soils, 129. Wickson, on plant-bi-eeding, 441. Wild Mustard. See Mustard. Wild. Wild Oat. See Oat, Wild. Wiley, on bacteria. 384. on soils, 153. Williams, on flour, 178. Willow, cross-pollination of, 302. cuttings of, need air, 281,* 282. in northern latitudes, 356. pollen of, 292. regeneration in, 257. roots of, 126. starch in, 259. supplies carbon dioxide to aquaria, 285. transpiration of, 204. Willow, Weeping, effect of light on, 346. Willow Herb, dispersal of seids of, 323. Wilted plants, treatment of, 212. Wind buries seeds, 69. carries pollen, 289, 300, 301. causes strains, 265. disperses seeds, 321-322. effect of, on fruit, 319. leaf, 345. plant, 348,* 349,* 350.* transpiration, 208, 348. loosens bark, 248. Witch Hazel. See Hazel, Witch. Witches' Brooms, 359. Wood. 120,* 121. 198,* 199,* 224*-227.* 228- 231,* 232*-234,* 235. 236*-237. 238*- 240,* 341. absorbs moisture from the air. 68. annual rings of, 247. decomposition ;f, 381. effect of water su.jply on. 335.* 340. Wood, energy needed to raise sap in. 239, 210,* 241. 242. 243.* fall. 232,* 236,* 247. force of swelling, 68. heart of, 214, 245. injection of, 237. preservation of. 245. rate of conduction of sap in. 238.* 239. resistance of, to weather, 245. sap, 214, 245. seasoning of, 245. sectioning of, 230. spring, 232,* 230. 217. shrinking of, 245. starch in, 257-259. sugar travels in, in spring, 259. swelling of. 68. usefulness of, 215. water in, 245. Wood Anemone. See Anemone, Wood. Wood-ashes as fertilizer, 152-154. Wood cells, method of isolating, 235. Woodchucks bury seeds, 69. Wood Sorrel. See Oxalis. Woodlands remain in good tilth, 129. Woo ly fiber, deficiency of, in water-plants 339, ring, formation of, 226. 246. texture protects against animals, 223. Woods, on fertilizers, 153. — flour, 173, 178. — food of plant. 349„ — plant diseases, 407. — pruning, 264. — soil, 129. Woolly coverings. See Hairs. Wormwood, protection of, against animals 2*^2 drying. 213, 333. 334.* Wounds, 319, cause fever, 388. treatment of, 171. Xanthium , See Cockbur, Clotbur. Xenia, 311. Yeast, 169. 389, 390.* 391. Yellow not liked by bees. 298-299. Yellow fever. 380. 492 INDEX Yellow Lupin. See Lupin, Yellow. Yellow Mustard. See Mustard, Yellow. Yield increased by breeding, 414,* 435-437. Yucca. See Spanish Bayonet. Zea. See Com. Zinc, 161. affects flora, 351. Zinnia, cross-pollination of, 304. Zygospores, 396.* BOTANY An elementary text for schools By L. H. BAILEY Professor of Horticulture in Cornell University With over 500 illustrations. Half Leather. i2mo. Si. ID, net "I hare examined the book with much -interest. It is easily seen that it is written with Professor Bailey's clearness and felicity of style,* and I think it, as a whole, one of the most charmingly and appropriately illustrated of modern botanical text-books. I expect it to prove a stimu- lating and very useful work." — Professor W. F. Ganong, Smith College. " It is the very best book that I have yet seen, and I shall take pleasure in using it in my class this year and in recommending it to others as occasion serves."— Herbert O. Clough, Albany Academy, Albany, N. Y. 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