®{je ^. ^. ^iU IHtkarg Jfnrtlj Carolina ^iale Cnllegc 6b555 --™'SSk«""»««« soisiir" Date Due 1 .'.:.' i.--i. ' ' ^5;>:r"^ ■> \ ,, "• ^9/fov:;. .■^ . * . ^ Oct 5 '3: OcilB^ * ^b.^l"'^* jNlt'4? i n 1981 L. B. Cat. No. II37 4 10018 TEXT-BOOK OF POMOLOGY ^\)c Hural tH^crt^llBoofe Series; Edited by L. H. BAILEY Carleton: The Small Grains. B. M. Duggar: The Physiology of Plant Production. J. F. Duggar: Southern Field Crops. Fisk: The Book of Ice-Cream. Gay: Breeds of Live-Stock. Gay: Principles and Practice of Judging Live-Stock. Goff: Principles of Plant Culture. Gourley: Text-Book of Pomology. Guthrie: The Book of Butter. Harper: Animal Husbandry for Schools. Harris and Stewart: The Principles of Agronomy. Hitchcock: Text-Book of Grasses. Jeffery: Text-Book of Land Drainage. Jordan.: Feeding of Animals, Revised. Livingston: Field Crop Production. Lyon: Soils and Fertilizers. Lyon, Fippin and Buckman: Soils; Their Properties and Management. Mann: Beginnings in Agriculture. Montgomery: The Corn Crops. Morgan: Field Crops for the Cotton- Belt. Mumford: The Breeding of Animals. Piper: Forage Plants and their Culture. Sampson: Effective Farming. Smith: Agricultural Meteorology. Thorn and Fisk: The Book of Cheese. Warren: Elements of Agriculture. Warren: Farm Management. Wheeler: Manure and Fertilizers. White: Principles of Floriculture. Widtsoe: Principles of Irrigation Prac- tice. TEXT-BOOK OF POMOLOGY BY J. H. GOURLEY, M. S. HORTICULTURIST, OHIO AGRICULTURAL EXPERIMENT STATION FORMERLY PROFESSOR OF HORTICULTURE NEW HAMPSHIRE COLLEGE 5^pm fork THE MACMILLAN COMPANY 1923 All rights reserved \S\(^ Copyright, 1922 By the MACMILLAN COMPANY Set up and electrotyped. Published August, 1922. Printed in the United States of America LIBRARY M C. state College PREFACE The purpose of this book is to present the experimental and investigational bases of fruit-growing on the physiological side, omitting consideration of the systematic botany and taxonomy as well as of pathology. Pomology has here- tofore been approached mostly from the orchard-practice side, born of the experience of cultivators. Gradually the underlying physiological and chemical reasons for the suc- cess of these practices are being uncovered. It is on these rational bases that college teaching must henceforth largely rest. In the preparation of the present volume, it is assumed that the student is familiar with the more common orchard prac- tices, which statement will explain the omission of much in- formational material. It has been apparent for some time that much of the experimental results which have been ac- cumulating from year to year should be collected into con- venient form for students, for it should be the purpose of the student to study (not merely read) the science on which present-day practices in fruit-production are based. It may seem to some persons that we have here gone far afield for much of the material, but the more careful work of recent years has made use of nearly all the sciences in attempting to solve the problems. It is doubtless true that the advance which agricultural education is making in secondary schools will force the col- legiate work into a still more advanced position and much of the material formerly used with satisfaction will give place to more technical and scientific matter. This means, on the one hand, that the college class-room work will lie more 10018 VI PREFACE in underlying principles than in practices, and on the other, that the laboratory and the supervised summer instruction will become still more practical; and this we believe will meet with the approval of the best informed fruit-growers as well as educators. In the preparation of this book, the author has drawn freely from the work of others. He has also invited several of his colleagues to make suggestion and criticism of parts of the manuscript. However, in no case was the final copy submitted and, therefore, any errors that may occur devolve entirely on the author. He is particularly indebted to Dr. E. J. Kraus who offered many helpful suggestions and as- sisted in the interpretation of some of the experimental work. Similarly, Dr. F. E. Bear assisted with Chapters VIII and IX, and Dr. M. J. Dorsey with Chapter XIII. Others who read portions of the manuscript were Drs. W. H. Chandler, J. K. Shaw, H. R. KraybiU and Prof. W. Paddock. To James Macfarlane and J. L. Hayman thanks are due for their kindness in preparing several of the drawings. Wooster, Ohio, J. H. GoURLEY. April 1, 1922. TABLE OF CONTENTS (Numbers in the text refer to paragraphs) CHAPTER I PAGES The Composition of Fruits 1-18 Composition of apple leaves, 1; Composition of apple fruit, 2; Ash of fruits, 3; Forms of sugar in fruits, 4; Sugar- content of ripe fruit juices, 5; The essential oils, 6; Quality in apples, 7; The effect of location on quality, 8; Composi- tion of fruits grown on irrigated and non-irrigated land, 9; Chemical changes in the growing apple, 10; Composition of apples in common storage, 11; Changes in composition of the peach during growth and ripening, 12; Ripening process in pears, 13. CHAPTER II The Buds of Fruit-Trees 19-33 Buds defined, 14; Gross structure, 15; Classification of buds, 16; Leaf-buds, 17; Fruit-buds, 18; Flower-buds, 19; Simple buds, 20; Mixed buds, 21; Terminal and lateral buds, 22; Latent buds, 23; Adventitious buds, 24; Col- lateral buds, 25; Leaf-scars, 26; Fruit-spurs, 27; Fruiting of the apple, 28; Fruiting of the pear, 29; Fruiting of the peach, 30; Fruiting of the cherry, 31 ; Fruiting of the plum, 32; Fruiting of the apricot, 33; Fruiting of the quince, 34; Fruiting of the grape, 35. CHAPTER III The Differentiation of Flower-Buds 34-49 The apple, 36; Sepals, 37; Petals, 38; Stamens, 39; Car- pels, 40; The peach, plum and cherry, 41; Inflorescence, 42; The flowering branch, 43; Vascular anatomy, 44; The carpellary system, 45; Comparative morphology of fruits, 46. CHAPTER IV Factors which Influence Fruit-Bud Formation 50-73 Vegetative and reproductive processes, 47; The periodic TABLE OF CONTENTS PAGES idea, 48; Theory of specific constructive materials, 49; Reserve food, 50; Carbohydrates, nitrogen-complexes and moisture, 51; Relation of these materials to flowering of plants, 52; Relation of leaf area to flowering, 53; Effect of leaves on parts immediately surrounding them, 54; Horti- cultural practices that influence fruit-bud formation, 55; Cultural practices, 56; Pruning, 57; Ringing, 58; Stripping, 59; Bending, 60; Dwarfing, 61; Thinning, 62; Individual- ity, 63; Climate, 64; Plants threatened by death, 65; Light, 66; Biennial bearing, 67. CHAPTER V Pruning 74-101 Definition, 68; Objects of pruning, 69; Shape or form of the tree, 70; The type of tree to be developed, 71; Obtain- ing the ideal, 72; Fruiting system of the tree, 73; Effect of pruning on size and development of trees, 74; Effect of pruning on early bearing, 75; Effect of the unequal cut, 76; Heading-back versus thinning-out, 77; Detailed response of young trees, 78; Relation of pruning to nutrition, 79; Theoretical considerations, 80; When to prune, 81; Prun- ing at planting time, 82; Pruning young versus mature trees, 83; Salient features in pruning mature trees, 84; Renovation pruning, 85; Summer pruning, 86. CHAPTER VI 'he Thinning of Fruit 102-123 Definition, 87; History of thinning, 88; Philosophy of thinning, 89; Fruit production exhaustive, 90; Dependence of fruits on foliage immediately surrounding it, 91; Ob- jects of thinning, 92; To increase the size of the fruit, 93; Thinning to improve color, 94; Quality improved by thinning, 95; Thinning to prevent breaking of limbs, 96; Thinning to reduce disease and insect injury, 97; Thinning to maintain the vigor of the trees, 98; Thinning to secure more regular bearing, 99; Thinning to decrease the labor of handling excessive crops of small fruit, 100; The effect of thinning on the total crop, 101 ; When to thin, 102; The June drop, 103; How to thin, 104; Distance to thin, 105; Cost of thinning versus returns, 106; Thinning the peach, 107; Thinning the plum, 108; Thinning the pear, 109; Thinning the grape, 110. TABLE OF COX TENTS ix CHAPTER VII PAGES Orchard Soils 124-141 Factors involved, 111; Soils defined, 112; Soil classifica- tion, 113; Soils and subsoils, 114; Mechanical analysis of fruit soils, 115; Orchard soils, 116; Chemical nature of fruit soils, 117; Soil color, 118; Limestone soils, 119; Alka- line soils ,120; Drainage, 121; Organic matter, 122; Adap- tation of fruit to soil types, 123. CHAPTER VIII Cultural Methods in Orchards 142-178 Systems of cultivation, 124; Terms defined, 125; Sod culture, 126; Grass mulch, 127; Production of mulch ma- terial, 128; Clean cultivation, 129; Tillage and cover-crop system, 130; Cover-crops, 131; Nitrification, 132; Value of cover-crops in California, 133; Effects of cultural methods on the soil, 134; Effect of moisture, 135; Effect of tempera- ture, 136; Nitrates, 137; Is nitrification retarded under sod? 138; The toxic theory, 139; Effect of cultural systems on the growth of the trees, 140; Leaf area, 141; The Wo- burn experiments, 142; Yield of fruit, 143; Sod, tillage and mulch for the apple, 144; Cultivation for the peach, 145; Fall plowing the orchard, 146; Use of explosives for tillage purposes, 147. CHAPTER IX Fertilizers and Manures pqR the Orchard 179-217 Criticisms of orchard experiments, 148; Fertility re- moved by fruit-trees, 149; Fruit-trees essentially different from other crops, 150; Amount of food materials found in plants not a guide, 151; Analysis of the soil as a guide to fertilizing, 152; Necessity of fertilizing orchards, 153; Fer- tilizing tilled and non-tilled apple orchards, 154; Moisture and fertility intimately related, 155; Relative importance of the different essential elements, 156; Organic versus in- organic fertilizers, 157; Value of nitrogen, 158; Nitrate of soda, 159; Sulfate of ammonia, 160; Time of application, 161; Phosphorus, 162; Acid phosphate, 163; Potash, 164; Muriate versus sulfate of potash, 165; Hardwood-ashes, 166; Common salt, 167; Animal manures in the orchard, 168. Experiments in Uyililled Orchards: The Massachusetts experiment, 169; The Ohio experiments, 170; The Penn- sylvania experiments, 171; New Hampshire experiments, X TABLE OF CONTENTS PAGES 172. Experiments in Tilled Orchards: The Woburn experi- ment, 173; The New York experiments, 174; The New Hampshire experiments, 175; The Maine experiment, 176; The Oregon experiments, 177; West Virgmia experiment, 178; The Pennsylvania experiments, 179; The Ohio ex- periments, ISO; Results compared, 181. Other Results of Fertilizing: Color of fruit, 182; FertiHzing the peach, 183; Effect of fertihzing on regular bearing, 184; AppHcation of fertihzers, 185; Size of fruit, 186; Summary, 187. CHAPTER X The Relation of Climate to Pomology 218-253 Terms defined, 188; Rekition of weather to the fruit crops, 189; Temperature, 190; Rainfall, 191; Spring frosts, 192; Winds, 193; Sunshine, 194; Hail, 195; Continental versus marine climates, 196; Mountain versus valley cli- mates, 197; Climate of United States, 198; Climatic prov- inces of the United States, 199; The Eastern province, 200; The Gulf province, 201; The Plains province, 202; The Plateau province, 203; The Pacific province, 204; Natural guides to horticultural practices, 205; Bioclimatic law of latitude, longitude, and altitude, 206; Species adaptation, 207; Temperatures which injure setting of fruits, 208; Averting injury from frosts and freezes, 209; Effect of climate on the floral structure, 210; The effect of climate on development of fruit, 211; Climatic factors which delimit the geographical distribution of fruits, 212; Specific requirements for certain varieties, 213. Pheno- logical Studies: The physiological constant, 214; The blooming season, 215; Comparative blooming dates, 216; Duration of blooming period, 217; Period of ripening of hardy fruits, 218; Relation between blooming and ripen- ing, 219; Form for recording phenological data, 220. CHAPTER XI Winter Injury 254-281 Bud injury, 221; Injury to the woody parts above ground, 222; The killing of the terminals, 223; Killing of patches, 224; Crotch injury, 225; Collar-rot, 226; Frost- cracks, 227; "Black heart," 228; Sun-scald, 229; Root- kiUing, 230; How freezing kills, 231; Hardiness of different tissues, 232; Rest-period, 233. Factors Involved in Freezing: TABLE OF CONTENTS xL PAGES Maturity, 234; Sap concentration, 235; Rate of freezing a factor, 236; Protection of bud-scales, 237; Relation of crop the preceding season, 238; Correlation of wood structure and hardiness, 239; Influence of type of soil, 240; Proxim- ity to bodies of water, 241; Topography of land, 242; Winds, 243. Orchard Practices: Cultivation, 244; Pruning, 245; Protecting trees and buds, 246; Securing hardier fruits, 247; Treatment of frozen trees, 248; Variation in hardiness of fruits, 249; Hardy and tender varieties, 250; The grape, 251. CHAPTER XII Pollination and the Sterility Problem 282-310 Investigations in pollination, 252; Causes of unfruitful- ness, 253; Development of pollen, 254; Germination of the pollen, 255; Longevity and viability of pollen, 256; Length of receptive condition of the stigma, 257; Fertilization, 258; Cross-pollination, 259; Means of effecting cross- pollination, 260; Nature's methods of avoiding self- pollination, 261; Effect of cross-pollination on the fruit, 262; Effect of seed-bearing on the fruit, 263; Artificial pollination, 264. The Sterility Problem: Definition of terms, 265; Sterility not a constant factor, 266; Causes of sterility, 267; The cherry, 268; The almond, 269; The grape, 270; The plum, 271; The peach, 272; The quince, 273; The apple, 274; The pear, 275. CHAPTER XIII The Origin and Improvement of Fruit 311-338 Theory of Van Mons, 276; Work of Knight, 277; Selec- tion as a means of securing new fruits, 278; Mass-selec- tion, 279; Line-selection, 280; Clonal-selection, 281; Bud- selection, 282; Individuality of fruit-trees, 283; Results of selecting bud variations, 284; Plant introduction, 285; Chance seedlings, 286; Work in Canada, 287; Work of Peter Gideon and other pioneers in the United States, 288; Hansen hybrids, 289; Burbank's work, 290; Inheri- tance of characters in the apple, 291; The heterozygous nature of fruits, 292; Pedigreed nursery stock, 293; Graft- hybrids, 294; Breeding the grape, 295; Inheritance of self- sterility in grapes, 296; The inheritance of sex in the grape, 297; Rogers' hybrids, 298; Breeding disease-resistant fruits, 299; Stocks for pears, 300; Stock for grapes, 301. xii TABLE OF CONTENTS CHAPTER XIV Propagation and Fruit-Stocks 339-355 Handling the seed and stock, 302; The more common fruit-stocks, 303; Apple stocks, 304; Pear stocks, 305; Quince stocks, 306; Peach stocks, 307; Plum stocks, 308; Cherry stocks, 309; Quarantine measures, 310; Importa- tions of stock, 311; Fruit-trees on their own roots, 312; Re- lation of cion and stock, 313. Propagation of Fruit-Trees: Mound-layerage, 314; cuttings, 315; Grafting and budding, 316; Tongue-graft or whip-graft, 317; Budding, 318; June- budding, 319; Double-working of apple trees, 320. CHAPTER XV Storage of Fruit 356-369 Definition, 321; History of storage, 322; Types of stor- age, 323 ; The function of storage, 324 ; Factors influencing the keeping quality of fruit, 325; Maturity of fruit, 326; Effect of over-maturity, 327; Effect of delayed storage, 328; The storage temi)erature, 329; Influence of a fruit wrapper, 330; Influence of cultural conditions, 331; Type of package for storage, 332; The shrinkage of fruit in stor- age, 333; Apple-scald, 334; Pre-cooling, 335; Methods of pre-cooling, 336. LIST OF ILLUSTRATIONS PLATES FACING PAGE I. a, Showing reduction in flowering, elongation of internodes, and increased area to a leaf due to shading, b, Showing effect of shading a peach tree 38 II. a, An open-headed apple tree, b, A two-story apple tree with sets of scaffolds too close together 78 III. a, Dwarf apple trees trained in a horizontal cordon, espalier pear trees on wall to rear, b, A type of central leader that could now be developed either into a two or a three- story tree, c, An unpruned apple tree that has developed as a central leader, d, A two-story tree with four branches at each scaffold 116 IV. Six-year-old sour cherry trees, a, Unpruned; 6, moderately pruned; c, heavily pruned; d, summer pruned 154 V. a, Fruit from an unthinned Baldwin apple tree, b, Fruit from a thinned Baldwin tree. (Courtesy Ohio Exp. Sta.) 198 \l. In the background is shown the effect of acid phosphate on the natural growth of clover in the Ohio experiments. (After F. H. Ballon, Ohio Agr. Exp. Sta. Bull. 301) 246 VII. a, Trees grown permanently in sod. b, Trees grown under the gra.ss-mulch system, c, The tillage-cover-crop sys- tem used in this orchard. (Ind. Agr. Exp. Sta.) 298 VIII. o, The twig terminals of these Baldwin apple trees were killed in winter of 1917-18. b, A winter-injured peach tree that was not cut back 348 FIGURES PAGB 1. Curves showing the average chemical changes in the growing apple (Bigelow, W. D., H. C. Gore and B. J. Howard, U. S. Dept. Agr. Bur. Chem. Bull. 94) 11 2. Curves showing chemical changes in Rhode Island Greening apple in common storage. (Bigelow, W. D., H. C. Gore, and B. J. Howard, U. S. Dept. Agr. Bur. Chem. Bull. 94) 13 3. Fruit production and two axillary shoots, all arising from a single fruit-bud. (Rome) 22 4. Short spurs of apple bearing tenninal fruit-buds 25 5. Axillary and terminal fruit-bud formation in the apple 27 xiii xiv LIST OF ILLUSTRATIONS FIGURES PAGE 6. The beginning of a fruit-spur system in the apple 27 7. A flower-cluster base that has produced a fruit-bud and a long shoot. (Rome apple) 28 8. Branched fruit-spur system of the apple 28 9. Axillary fruit-bud formation in the pear 29 10. A vigorous fruit-spur of the pear 30 1 1 . Fruiting habit of the peach 30 12. Fruiting habit of the sour cherry. A strongly vegetative type 32 13. Floral diagram of the apple. (After E. J. Kraus, Ore. Agr. Exp. Sta. Research Bull. 1, part 1) 35 14. Early stages of fruit-bud differentiation in the apple. (After E. J. Kraus, Ore. Agr. Exp. Sta. Research Bull. 1, part 1). . 36 15. Diagram indicating positions of four flower primordia 37 16. Diagrammatic representation of origin of calyx primordia on edge of torus 37 17. Diagram showing development of the apple. (After E. J. Kraus, Ore. Agr. Exp. Sta. Bull. 1, part 1) 42 18. Diagrammatic drawing of an apple inflorescence or peduncle from which arise the pedicelled flowers. (After C. A. Black, N. H. Agr. Exp. Sta. Tech. Bull. 10) 43 19. Showing parts of a flowering branch 43 20. A, medium lengthwise section of a mature apple; B, cross-sec- tion of same. (From Robbins, Botany of Crop Plants, by permission of P. Blakiston's Sons Co.) 46 21. Diagram illustrating distribution of bundles in the torus and pedicel apex. (After E. J. Kraus and G. S. Ralston. Ore. Agr. Exp. Sta. Bull. 138) 47 22. Diagram to illustrate the hypotheses involved in Classes I, II, III, and IV 56 23. Diagrammatic representation of arrangement of scaffold limbs in pruning 76 24. Showing the type of growth that commonly follows the cutting of the terminal : 89 25. Showing a type of growth that follows when the terminal is not removed. The buds which give rise to shoots are usually not confined to the terminal ones 90 26. A graphic representation of the cycle of nitrogen through the plant and the soil. (After M. A. Bachtel, Ohio Agr. CgII. Ext. Bull, Vol. 8, No. 1, 1912) 151 LIST OF ILLUSTRATIONS xv FIGURES PAGE 27. Curves showing the maximum soil temperatures under the dif- ferent soil treatments in an orchard. (After Woodbury, Noyes and Oskamp, Ind. Agr. Exp. Sta. Bull. 205) 158 28. Curves showing the relative formation of nitrates under sod, tillage, and tillage cover-crop systems of orcharding. Parts per million dry soil 161 29. Row of trees to left was fertilized with 5 pounds nitrate of soda to each tree. The one to right untreated 200 30. Apple tree injured by hail storm. Note abrasions of bark and partial defoliation 225 31. Length of growing season in different parts of the United States. (After Henry) 229 32. Isophanal map of North America. (After Hopkins) 236 33. Map showing the boundaries of the Michigan fruit-belt. (After Seeley) 241 34. Fruit-bud of sour cherry. Left, flower bud alive; right, flower- bud killed 255 35. Winter injury on trunk of a Baldwin apple tree 256 36. Diagram of a simple pistil as seen in lengthwise section, show- ing a single ovule just prior to fertilization. (From Robbins' Botany of Crop Plants, by permission of P. Blakiston's Sons Co.) 290 37. French crab, imported apple seedling. (From Bailey, The Nur- sery Manual, by permission Macmillan Co.) 341 38. The tongue or whip-graft of apple 352 39. Shield-budding. (From Bailey, The Nursery Manual, by per- mission Macmillan Co.) 353 40. Method of double-working the apple 354 TEXT-BOOK OF POMOLOGY CHAPTER I THE COMPOSITION OF FRUITS For convenience, the composition of the common fruits may be divided into three phases: (1) composition of the tree, (2) composition of the fruits, and (3) the changes in the ripening process and in storage. Unfortunately, there is not as great uniformity of opinion among the chemists in regard to the composition of fruits as might be wished for, yet many experimental data are available and are valua])le for the present purpose. Different chemical methods in analysis and widely varjdng material account in part for the results and therefore for the difference of opinion. While it is not possible here to consider the analysis of all the fruits, some of the more important ones maj'- be used for illustration. Table I COMPOSITiON OP WOOD AND LEAVES OF TREES POUNDS IN 100 (percentage) ^ Wood Nitrogen Apple 0.50 Phosphoric Acid P2O5 0.15 Potash K2O ..0.25 Leaves 1.00 Pear .0.15... ..0.35 Wood 0.30 .0.10... ..0.25 Leaves 0.70 Peach .0.12... ..0.40 Wood 0.43 .0.10... ..0.22 Leaves 0.90 .0.15... ..0.60 'iVan Slyke, York, 1912. L. L. Fertilizers and Crops. 1 Orange Judd Cc )., New 2 POMOLOGY 1. Composition of apple leaves. — The net loss in fertility from orchard lands is somewhat reduced by the return of the leaves to the soil. True, a portion of them is blown from the orchard and hence it would not be entirely accurate to assume that the land received an annual fertilization of the full amount of the leaves produced. Thompson ^ has shown the amount of fertility represented in the fall of leaves for a period of nine years as follows: Table II POUNDS OF PLANT-FOOD TO THE YEARS OF AGE ACRE USED IN GROWING (after THOMPSON) FREES TO NINE Peach trees Apple trees P2O5 N K2O P2O5 N K2O Total plant-food taken up by trees in 9 years Total plant-food re- turned to the soil by leaves, etc Total plant-food re- tained in trees at the 9th growing season. . . 50.83 23.16 27.67 215.90 127.93 87.97 2.37.60 177.42 60.18 9.26 2.53 6.73 2S.10 12.84 15.26 27.22 12.97 14.25 "The net loss in soil fertility in growing an orchard to nine years of age is represented by the plant-food retained in the trees at the end of the ninth growing season. This table [given above] is based on the assumption that the leaves have not blown away, but have decayed on the land. The peach trees at nine years of age had reached their maximum size. The apple trees were only about one-fifth to one-eighth their maximum size, but the results indicate that an acre of mature apple trees would take from the soil about the same amount of plant-food as an acre of mature 1 Thompson, R. C. Ark. Agr. Exp. Sta. Tech. BuU. 123. THE COMPOSITION OF FRUITS peach trees. In other words, the approximate total loss of plant-foods in growing an acre of apple trees to their maxi- mum size would be five to eight times the amount shown in the table. This would make the total loss of fertility in growing an acre of peach or apple trees to maturity approxi- mately equivalent to the plant-food contained in 10 bushels of corn. This is surprisingly small and shows very clearly that soil exhaustion hi orcharding is almost entireh^ due to the removal of plant-food in the fruit crop." Shutt ^ has determined the analysis of the leaves of several standard varieties of apples in terms of composition of the ash, as follows: Table III COMPOSITION OF APPLE LEAVES (AFTER SHUTT) Composition of Percentage composition of important ash constit^lents Nitrogen Average of five varieties 3 1 P 1 1 S ll Nitrogen in organic matter Taken May 25 Taken Sept. 20 72.36 60.71 2.5..31 35.83 2..33 3.46 10.47 5.82 10.82 11.63 17.40 27.91 9.77 4.81 1.07 1.14 1.49 1.41 2.94 2.48 From these data it will ])e seen that apple leaves, when practically mature, contain 35.83 per cent organic matter which may be returned to the soil, and that there is 2.48 per cent of nitrogen in the organic matter. Of the ash, 5.82 per cent is phosphoric acid and 11.63 per cent is potash, or the relation of these two ingredients in the mature leaves is 2 to 1. Thus it will be seen that there is twice as great a demand on the soil for potash as phosphoric acid so far as the leaves are concerned. As will be seen later, the ratio is still greater in the ash of the fruit since there is six times as much potash as phosphoric acid present there. 1 Shutt, F. T. The chemistry of the apple. Ann. Rept. Can. Dept. Agr. Ottawa. 1894. 4 POMOLOGY There are no important differences between the ash of the separate varieties of apples, although some variations occur. 2. Composition of apple fruit. — The degree of ripeness, the variety, and the place where grown affect the chemical composition of apples. In general, they contain from 75 to 85 per cent of water, 82 to 84 per cent being rather com- mon. The total solids will be from 10 to 18 per cent of the whole, 75 per cent of which is sugar or aUied carbohydrates, and about half a per cent each is fat and protein.^ These vary markedly, depending on the variety. Malic acid is the predominating organic acid in apples and may run from .15 per cent to more than 1 per cent. Essential oils are also present and are responsible in no small degree for the flavor of the fruit, but they are not easily handled by the chemist and only recently have they been separated and expressed in terms of percentage of the fruit. Table IV COMPOSITION OF NORMAL MATURE FRUIT OF RED ASTRACHAN APPLE (adopted from CULPEPPER, FOSTER AND CALDWELL) ^ Analyst Sources of fruit Total Ash Acidity Crude Reduc- ing Cane Pro- solids malic fiber sugar sugar tein Per Per Per Per Per Per Per cent cent cent cent cent cent cent Browne . . State College, Pa. 15.30 0.37 1.038 6.67 3.53 Jones & Non-irrigated Colver orchard, Idaho 18.10 .94.57 6 98 2.15 0.288 Jones & Irrigated orchard, Colver Idaho 14.73 .890 6,08 2.91 .560 Culpepper, Foster & Auburn, Ala. 12.94 .2548 .9288 2.10 .574 4.960 .245 Caldwell 3. Ash of fruits. — According to Colby,^ apples and pears withdraw less mineral matter from the soil than do ^ Culpepper, C. W., A. C. Foster, and J. S. Caldwell, Jour. Agr. Res. 7: 17-40. 1916. 2 Colby, G. E. Ann. Rept. Calif. Agr. Exp. Sta. 1897-98. pp. 143- 148. THE COMPOSITION OF FRUITS 5 many other orchard fruits, averaging .264 to .250 per cent of ash in the whole fruit, while prunes averaged .480; plums, .535; apricots, .508; oranges, .432; lemons, .526; cherries, .482; and grapes, .500 per cent of ash. The ash of apples averages over one-half of potash, not unlike the other fruits; however, the analysis shows rather more variation for ash than has usually been noticed in the fruits in general. The same remark may be made as to variation in quantity of P2 O5, the next largest and most important ingredient. But, on the average, this amount is found to be much like that in the ash of oranges, figs, and apricots, which contain upwards of 12 per cent of phos- phoric acid; as against 21.24 per cent for the grape, 15.1 for cheny, and 14.1 of phosphoric acid for the prune. There is about 4 per cent lime in the ash of apple, and a similar amount in the ash of cherries, apricots, prunes, and grapes. The ash of oranges and lemons contains about five times as much as that of the apple. Colby, in speaking of fruits grown under California con- ditions, says, "The figures found for apples (and pears) are, on the whole, so much smaller than those which have been obtained for the other ordinary orchard fruits, that it would seem safe to conclude that here fertilizers will not be necessary for apple crops for many years to come. However, the figures do indicate that the first need will be for a nitrog- enous fertilizer. Along with this need will come that for a phosphatic fertilizer. There is no reason to supply potash to apple orchards for a great many years to come. " 4. Forms of sugar in fruits. — There is not absolute uni- formity in the method of expressing the sugar-content of fruits. In general, however, two kinds of sugar are present, sucrose and invert or reducing sugars. The sucrose is mainly cane-sugar (C12H22O11), while the invert sugars or dextrose group (C6H22O11) consist of glucose (dextrose), "6 POMOLOGY and levulose (fructose). The invert sugars are formed during the ripening process of fruits and result from the union of one molecule of water and one of sucrose, as follows: Sucrose Levulose Dextrose C12H22O11+H2O = C6H12O6 + C6H12O6 Strictly speaking, invert sugar contains equal parts tf levulose and dextrose, as can be seen by the above formula, while reducing sugars include levulose or dextrose alone or combined in varying proportions, and may include other reducing sugars and even reducing substances not sugars.^ This situation has led to some laxity in use of terms and usually the sugars are stated as sucrose and invert or reducing sugars. 5. Sugar-content of ripe fruit juices. — Thompson and Whittier have determined the percentage of sugars in ripe fruit juices by means of polarized light, as they question the value of determinations made by specific gravity on unknown solutions. Their work showed that levulose is the dominant sugar in apples, pears, quinces, and three of the grapes, and far exceeds the dextrose in the apples, pears, and quinces. With the plum and one variety of grape, the dextrose exceeds the levulose, but only in the plum does it far exceed it and in this case it is lower than the sucrose. Sucrose is the principal sugar in peaches and plums. 6. The essential oils. — Power and Chesnut ^ described the oil of apples as follows: "The essential oil, as extracted by means of ether from a concentrated distillate of either ordinary apple parings or those of the crab apple, is at ordinary temperatures a yellowish, somewhat viscid liquid, 1 Thompson, F., and A. C. Whittier. Proc. Soc. Hort. Sci. 1912. pp. 16-21. 2 Power, F. B., and V. K. Chesnut. Jour. Amer. Chem. Soc. 42: No. 7. THE COMPOSITION OF FRUITS 7 becoming much darker on keeping. When shghtly cooled it forms a concrete mass, due to the separation of small ocicular crystals, which consist of a paraffin hydro-carbon. It possesses in a high degree the characteristic, fragrant odor of fresh apples. Besides the esters mentioned, it has been found to contain, Ipy, specific tests, small amounts of ac- . H^f ^ etaldehyde and furfural. ■/ The jaeld of oil from the parings of the Ben Davis apple was 0.0035 per cent, and that from the more odorous crab apple 0.0043 per cent, which cor- responds to about 0.0007 and 0.0013 per cent respectiv^ely of the entire ripe fruit. " The esters referred to above are "the amyl esters of formic, acetic, and caproic acids, with a veiy small amount of the capiylic ester and a considerable proportion of ac- etaldehyde. " Amyl valerate, which is usually referred to as "apple oil," has not been identified as present in the apple. 7. Quality in apples. — As mentioned above, certain components of the apple give it flavor or eating quality. The term is used rather loosely in pomology, referring sometimes to the dessert quality, sometimes to the cooking property, and again to shipping and market quality. Shaw ^ has analyzed apple varieties to determine the ingredients which are associated with dessert quality, and the two apples used for illustrating high and low quality are the Grimes and Ben Davis. The following figures show the relative amounts of the important ingredients, each being the average of eleven determinations. 1 Shaw, J. K. Proc. Amer. Soc. Hort. Sci. 1912. p. 29. j;5^^€HrtA^'"^ y^-i V ^jy. POMOLOGY Table V ANALYSIS OF A HIGH AND A LOW QUALITY APPLE (AFTER SHAw) Water Total solids Sol- uble solids Insol- uble solids Reduc- ing sugars invert Sucrose Total sugars Acid as malic Ben Davis Grimes. . . 84.32 82.12 15.66 17.88 12.59 15.18 3.07 2.70 6.91 8.77 2.95 4.30 9.86 13.00 .44 .45 From these figures it is seen that the high-quahty apple has a much larger percentage of total solids, and when it is remembered that upwards of 75 per cent of the total solids are sugars, it will be seen that the Grimes is much to be preferred. (In this case, the Ben Davis has about 62 per cent and the Grimes 72 per cent of sugar in the total solids.) While sucrose is a valuable form of sugar in fruit, it has been shown previously that levulose is dominant in the apple. The relation of acid to sugar is important for high quality, for here is secured the sprightlincss which usually is associated with a dessert apple, although this depends on the taste of the individual. Shaw found from .1 to .2 per cent in sweet apples to nearly 1 per cent or possibly more in very acid sorts. The ratio of acid to total sugars varies from about one to one-hundredth in sweet apples to one to eight-hun- dredths in very acid sorts. The flavoring or essential oils which have been discussed are also of great importance in quality, "It appears then that high table quality in apples depends on (1) good texture which is accompanied by a low content of insoluble solids, (2) an abundance of sugars, especially sucrose, (3) an amount of acid sufficient to blend agreeably with the sugars but not excessive and (4) an abundance of pleasant and agreeable flavoring oils. " THE COMPOSITION OF FRUITS 9 8. The effect of location on quality. — While it is recog- nized that there is a niarketl difference in quality of fruit depending on where it is grown, there is not much data showing the chemical analysis of such fruits. Colby ^ has shown the effect of location on quality of fruit, particularly for the conditions which obtain in California. Apples which were grown at a high elevation averaged higher in both sugars and acids, which makes the best combination for a dessert apple. Those raised at elevations (4000 to 5000 feet) analyzed as high as 15 per cent sugar and .55 per cent acid in the juice, while those from lower levels (50-150 feet) analyzed about 2 to 4 per cent lower in sugars and as low as .16 and .17 per cent acid (in terms of sulfuric acid, SO3). Eastern apples, according to data cited, analyzed from 10.42 per cent sugar (Baldwin) to 11.36 per cent (Rhode Island Greening) in the juice. European grown fruits showed a still lower sugar-content, averaging 7.22 per cent. 9. Composition of fruits grown on irrigated and non- irrigated land. — The statement has not infrequently been made that fruits grown under irrigation are "flat" or insipid in flavor and are less able to withstand shipment and rough handling than fruit raised on non-irrigated land. To deter- mine whether there is any essential difference in composition, chemical analyses were made by Jones and Colver ^ of various fruits so grown. The results indicate that "From a general survey of analytical results, it may fairly be said that fruits in general manifest a well-defined tendency to elaborate greater percentages of total solids or dry matter, conse- quently of sugar, acid, and crude protein, when grown in non-irrigated sections. With comparatively few exceptions, 1 Colby, G. E. Rept. Calif. Agr. Exp. Sta. 1897-98. p. 14.3. ^ Jones, J. S., and C. W. Colver. The composition of irrigated and non-irrigated fruits. Idaho Agr. Exp. Sta. Bull. 75. 1912, 10 POMOLOGY however, no marked difference between irrigated and non- irrigated fruits in actual food or market value should be charged to differences in composition." 10. Chemical changes in the growing apple. ^ — Only data for winter apples will be included here, since the same general processes go on with smnmer varieties; the information, however, is not so satisfactory owing to the uneven ripening of the latter. This work was carried on with Ben Davis, Huntsman, and Winter Paradise. The curves (Fig. 1) show in a striking way the chemical changes which occurred throughout the season, from June 16 until November 5. Using total sohds as a basis, it will be seen that starch increases until the latter part of July when it has reached its maximum, then it begins to decline constantly but does not entirely disappear. The sucrose curve is almost the exact reverse of the starch. This form of sugar starts with a low percentage and continues low until the middle or latter part of July, when, through the conversion of starch into sugar, it begins to rise and continues until the fruit is ripe. On the date of the first examination of these varieties, June 16, the content of sucrose based on total solids was 4 per cent, and at the last examination, on November 4, it amounted to 25.4 per cent of the total solid content of the apple, the rate of increase being apparently no greater before the maximum content of the starch than afterwards. Unlike the smnmer apples which had been examined, the percentage of invert sugar here increased from the date of the first examination to approximately the date of the last, so that even in percentage composition the amount of invert sugar did not reach its maximum until the fruit was mature. In all three of the varieties of winter apples studied, the 1 Data and comments are taken from work of Bigelow, W. D., H. C. Gore, and B. J. Howard. U. S. Dept. Agr. Bur. Chem. Bull. 94. 1905. s?- '^ / J 1, ; 1 5 ^ > c ? 'O 1 ( \ ) / / / CO 1 \ 1 )\ / !Q \ \ \ \ / \ / ^ P ^\ / 1 ' i > coy to . 8 "/ \ .^ ^ " l\ 1 s \ I 5 1 % 1 \ ^ - \ \ \ 1 "^ \ \\ r \ \ w \ / R ? 2^, ^ ) c ' ^ '. ^ \\\ :\: 1/ " 2 1 12 POMOLOGY percentage of malic acid decreased from the first examination to the full maturity of the fruit. The percentage of total sugar estimated as invert sugar increased steadily from the first examination to full maturity. It is notable that after the maximum content of starch is reached, the percentage of starch and invert sugar taken together remains approxi- mately constant. More recently Thatcher^ has shown that the only enzymes which were found to participate in the changes in the carbo- hydrates of apples during the ripening process were the oxidases. 11. Composition of apples in common storage. — It is of interest to follow the ripening process as it occurs after the fruit is picked and placed in storage. The work of Bigelow et al.," Browne^ and Kulisch,'* are in substantial agreement, although performed under widely differing conditions. Bigelow's work with Rhode Island Greening apple illus- trates this ripening process, the apples having been picked between October 6 and November 7. The curves in Fig. 2 show graphically the progress of the ripening. By referring to them it will be noted that there was 13 per cent of sucrose on August 25, at the time the experiment was begun, and it increased rapidly until November 7 when it reached its maximum 30 per cent. The sucrose then rapidly disappeared until February 11 when the experiment was discontinued, at which time it was 6 per cent. It is of particular interest to note that the starch declined rapidly from August 25 until November 7 when it entirely disappeared, this being the same date when the sucrose reached its maximum. Here 1 Thatcher, R. W. Enzyms of apples and their relation to the ripen- ing process. Jour. Agr. Res. 5^: 1915: 103-116. ^ Loc. cit. ^ Browne, C. A., Jr. Penn. State Dept. Agr. Bull. 58. ^Kulisch.S. Landw. Jahrb. 1892. 21:871. THE COMPOSITION OF FRUITS 13 again is evidence that the starch is transformed into sugars as the ripen- ing proceeds. The malic acid also continues to behave as it did during the growth and development of the fruit. There is a gradual disap- pearance through- out the storage period. Invert sugars, unlike the starch and sucrose, con- tinue to increase throughout the ex- periment, being as high as 62 per cent in Februaiy. They gain rapidly as the sucrose disappears, indicating the transformation. The total content of sugar (calculated Fig. 2.— Curves show- ing chemical changes in Rhode Island Greening apple in common storage. % . _.,d.^''/o.. __ 1 r6- pn ' \ , y^ »~, ^^^^-^ f.-'' ,. \ G8= ' 7^ J ^^- -A 9f- ^1 (1 A 36 — / J' f r / / / «- A / 36- j^ ^ X ^ 1 se, Z8- 26- / \ Z4- n- A f V % :k\ / \ 14 ^y^^ IX- \ \ 8^\^ =>l.i5c/d a.iTnal/c \ 4- — s 30 & is 2a a /a z& a /a^a a ia\2a 7 /? 27 p \ |■"W/.9a^. Oct Nov, Iftc ■ '']?A...,.9rl^r'^f>.\ 14 POMOLOGY as invert sugar) increased from the first examination to the date of the disappearance of the starch. After this date the curve, representing the total sugar as invert, merges with that indicating the total carbohydrates as invert sugar. In the Rhode Island Greening, the total carbohydrate content decreased to some extent after the disappearance of the starch. This latter was not true, however, of some other varieties studied. 12. Changes in composition of the peach during growth and ripening.^ — In determining the chemical changes which take place in the growing peach, the fruit was selected at the following times for analysis: (1) after the June drop, (2) when the stone hardens, (3) when market ripe, and (4) when fully ripe. The varieties used were Triumph, Rivers, Early Crawford, Stump, Elberta, Orange Smock, and Heath Cling. The following data illustrate the marked changes in com- position between the early stages of growth and when the peach is fully ripe : Table VI COMPOSITION OF PEACHES AT DIFFERENT STAGES OF GROWTH COMPOSITION OF WHOLE FRUIT (AFTER BIGELOW AND GORE) Average of six varieties Stage of growth June drop Stone hardened Market ripe Weight of peach Grams 9.51 16.75 73.59 Per rent 64.55 71.54 92.49 Per cent 32.50 25.82 6.86 Per cent 2.94 2.89 .65 Total solids in flesh stone kernel Per. cent 14.77 16.97 14.04 Per cent 9.37 27 . 35 66.94 Per cent 7.. 54 44.78 ANALYSI.S OF FLESH Stage of growth Sucrose by reduction Reducing Acid as sulfuric Ash Average of six varieties June drop stone hardened Market ripe .18 1 . 57 5.70 2.71 2.26 1.98 .28 .34 . 56 .75 .68 .40 1 After Bigelow, W. D., and H. C. Gore. U. S. Dept. Agr. Bur. Chem. Bull. 97. 1905. THE COMPOSITION OF FRUITS 15 Between the time of the June drop and market ripeness, the peaches increased in weight nearly eight times. During the same time the percentage of flesh in the peach in- creased less than one-half, while that of the stone decreased from 32.5 to 6.86 and that of the kernel from 2.94 to 0.65 per cent. The percentage of solids of the flesh remains fairly con- stant during the life history of the peach; that is, the increase in solids is fairly proportional to that in water. This is shown by the fact that the percentage of solids did not greatly change from the time of the June drop to the period at which the peaches were considered market ripe. On the other hand, in the same period the stone changed greatly m its nature. As it became harder and more mature, the percentage of water materially decreased and that of solids increased from 9.37 at the period of the June drop to 66.94 when the peaches were market ripe. The solid content of the kernel in- creased from 6.89 to 44.78 per cent. At the same time, it should be noted that the percentage of solids in the kernel did not materially increase until after the hardening of the stone. By examining the analysis of the flesh, it will be seen that, unlike the apple, the reducing sugars decreased as the ripen- ing proceeded. The same was also true of the percentage of nitrogenous substances in all their forms calculated as total protein, albuminoids and amido bodies, and also of ash. On the other hand, the percentage of sucrose and of acids increased from the beginning to the end of the ex- periment. Analyses were also made to determine the changes which take place between what is termed "market ripe" and "full ripe" and the following data present the findings dur- ing this stage: 16 POMOLOGY Table VII ANALYSIS OF FLESH OF THE PEACH (AFTER BIGELOW AND GORE) /Su- Re- Total crose Marc 1 ducing sugar bij re- Acid sugar invert duction 2.91 2.20 7.97 6.23 .53 2.30 2.27 9.13 7.36 .48 Ash Average . Market ripe Full ripe While not indicated in the table, there was not much change in the percentage of flesh, stone, and kernel. There is some increase in the percentage of sugar, while that of marc and acid decreased slightly. It may also be pointed out that, comparing the composition of the flesh of the peach with that of the apple, there is practically no starch in the former (only at the veiy beginning), while the latter is quite high in starch until later in its development. 13. Ripening process in pears. — The pear is unique in its requirements for proper ripening. While many other fruits may be picked when ready for use or when "hard" ripe in order to lengthen their keeping, the pear must be picked much earlier relatively in order to allow the ripening process to proceed off the tree. This produces a fruit of much higher quality for all purposes than when it ripens entirely on the tree. Hence a study of the changes which occur in ripening is of more than ordinaiy interest, and the work of Magness ^ may be cited in this connection. Fruit which had been produced in three of the principal pear-growing sections of the Pacific Coast and picked at ^ This term applies to the total insoluble matter of the flesh of the peach, including the skin. 2 Magness, J. R. Investigations in the ripening and storage of Bart- lett pears. Jour. Agr. Res. 19: 473-500. 8 fig. 1920. THE COMPOSITION OF FRUITS 17 intervals from early summer until after the commercial picking season, were analyzed within a few days after pick- ing and after being in storage one and one-half to three and one-half months at temperatures of 70, 40, and 30 degrees F. Both sugars and acids were determined as well as the alco- hol-insoluble, acid-hydrolyzable reducing materials. Like the apple which has already been studied, the Bartlett pear increased in total sugar from early suimner until after the close of the commercial picking season. The increase in the latter part of the season is mainly due to an accumu- lation of sucrose, while the earlier increase is due mainly to reducing sugar. It will be remembered that the winter apples showed their greatest increase in sucrose also during the latter part of their development, although the invert sugars in- creased in the apple throughout the ripening process of the fruit. Further, "A distinct relationship was found between the total amount of sugar present in the ripe fruit and the tem- perature of the storage at which it had been held from the time of removing from the tree until ripe. Pears ripened at 70° F. contained the highc^st percentage of sugar; those ripened at 40° possessed the lowest total sugar content, and those held at 30° for from 6 to 14 weeks and then ripened at room temperature were intermediate in amount of total sugar. There was no marked relation between temperature of storage and relative amount of sucrose and reducing sugar." It is further observed that, " It seems well established, therefore, that the highest amount of sugar will be secured by holding the fruit at optimum temperature for ripening. "Percentage of titratable acid in the fruit tended to de- crease in fruit from the California sections as the season advanced, while it tended to increase in that from Oregon and Washington. There was an increase in acid between the 18 POMOLOGY time of picking and the time of full ripening of the fruit when held at 70° F. There was much less acid in fruit ripened at 40° than in that ripened at 70°, and still less in fruit that had been held at 30°. The acid content of fruit that was allowed to become well matured on the tree remained nearly con- stant during storage." Since there was always a greater amount of acid in fruit which was removed and ripened at 70° F. than when the fruit was picked from the tree, it be- comes " of interest especially in connection with the question of whether fruit acids are synthesized in the fruit itself or whether they are carried to the fruit from the leaves. The fact that there is an increase in the acid between the time the fruit is removed from the tree and the time of its becoming ripe is evidence that there is an actual synthesis of acid in the fruit itself. "There was a progressive reduction in the alcohol-insol- uble, acid-hydrolyzable reducing material as the season advanced, not only in the fruit fresh from the tree, but also in the same fruit after ripening. There is a marked reduction in these substances between the time when the fruit is first picked and the time when the same fruit becomes ripe. "The percentage of total solids is lowest at about the opening of the commercial season. This tends to increase with the accumulation of sugar in the late-picked lots." CHAPTER II THE BUDS OF FRUIT-TREES An accurate knowledge of the "bud system" of the several kinds of fruit-trees is of first importance and should be thoroughly understood by the student before attempting to leam the art and principles of pruning. The intelligent fruit-grower observes the "set" of fruit-buds and their condition as a guide to the response of the trees to cultural treatment; he likewise examines them in the more tender varieties to determine the percentage of live buds in early spring. Similarly, in many other ways the buds afford an index to the functioning of the tree. The consideration of buds naturally divides itself into three phases: (1) the location of the buds on the tree, and the "bud system" in the different kinds of fruits; (2) the time and details of differentiation of the flower-buds; and (3) the factors that influence the formation of flower-buds. Although the study of the location of the buds on the tree is no longer a matter of intricate research, yet it requires accurate observation in the field or laboratory, for there is much still to be learned concerning the relative economic value of buds located or developed in different parts of the tree, or of a branch or spur system. For example, it has been observed that in some varieties of the peach and cheny, the fruit-buds are more hardy when they are borne on short growths which are located throughout the inner area of the tree, while in others the reverse seems to be true. Buds in certain positions also are more likely to mature and the fruits will color better or have other advantages over those borne elsewhere on the tree. 19 20 POMOLOGY 14. Buds defined. — Buds are undeveloped shoots or branches, whether their content be of a leafy or floral nature or both. The closed, scaly, resting buds of fruit-trees represent a provision of the plant to protect the tender growing points or partially developed flowers and carry them over a relatively inactive period. This provision is in contrast to the "naked" buds of many tropical trees and shrubs, where climatic conditions do not require a winter resting period, and yet even in the tropical plants a period of rest of greater or less duration does exist. It might be added here also that sometimes there are several such periods of rest, followed by activity, known often as "flushes" of growth. Some northern plants also produce naked buds (as niost herbs, Kalmia, etc.). Buds have also been de- scribed as the free extremities of branches or incipient branches.^ 15. Gross structure. — The buds of all the common fruits are covered with overlapping scales which are, morphologi- cally, specialized leaves. The bud-scales are accompanied in some cases with a mat of soft hairs (pubescence) and some- times with more or less resinous material of a water-proof nature. Within these scales are the partially developed leaves, flowers or both, depending on the bud in question, and the axis on which they are borne. From the time the buds are initiated in the summer (or autumn) previous, until they open, there is a progressive development, some activity going on even during the milder weather of midwinter. Frequently the exact number of leaves which a shoot will bear are present in the bud, but this is not always the case, for vigorous shoots may develop additional ones during the season. Particularly is this true with the peach, plum, and apricot, and probably to some extent with most fruit-trees. Likewise the size which the leaves will attain is determined 1 Halsted, B. D. Memoirs: Torrey Bot. Club, 2: Sept. 1890. THE BUDS OF FRUIT-TREES 21 by the "growing conditions" of the season in which they expand, and the reserves carried over from the previous years. However, an increased length of shoots may be due to an elongation of the intemodes, such as occurs when a tree is stimulated just previous to or while the growth is being made, or if the tree is shaded during the period of growth (the latter constituting a lack of light stimulus). 16. Classification of buds.— Unfortunately there is some conf\ision in the terminology relative to the classification of buds. This variance in nomenclature by horticultural writers is due to an effort to use terms that are self-explana- toiy, relating to position of the bud, its structural contents, or to what it will give rise. The following terms as here de- fined will 1)0 used throughout this discussion. 17. Leaf-buds. — A "leaf-bud" contains the rudiments of a leafy branch, which may develop into a shoot or a spur. As pointed out above, the development of parts within the leaf-bud does not necessarily predetermine the length of the shoot or the number of leaves it will bear. Probably such is the case, however, with the short spurs. The term "branch" bud is frequently employed in horticultural writings to describe the same type of bud and has some advantages in clarity, but is scarcely more accurate than "leaf" bud. "Wood" bud is also used by some writers, but is less desirable and still less descriptive. 18. Fruit-buds. — A fruit-bud contains the unexpanded parts of the flowers. The term "inflorescence bud" would be more descriptive but does not follow usage. It may com- prise one or more individual flowers and perhaps also leaves or bracts, depending on the kind of fruit-tree. In the apple and pear, the fruit-bud usually contains one or more axillary leaf-buds also as well as the enfolding leaves. That is, the blossom buds of these fruits are "mixed," and when they have opened and fully expanded, a close examination usually re- 22 POMOLOGY veals a "secondary" growth arising from the axil of one or more of the leaves. This secondary growth may develop into a shoot of several inches in length or into a spur; generally it is short, often- times merely a bud. Usually it is terminated by a leaf -bud, but if the blossoms fail to "set," a fruit-bud is often formed. In fact, it is by no means rare for a fruit-bud to form on this shoot even though one or more fruits are de- veloping. (See Fig. 3.) 19. Flower-buds.— A flower-bud is one of the individuals of the flower- cluster, inside or outside of the fruit- bud. 20. Simple buds. — A simple bud contains either the unexpanded leaves or flowers, but not both. The term usually refers, however, to the fruit- bud. The peach, plum, and cherry have simple buds, but the latter may contain rather prominent leafy bracts also. 21. Mixed buds. — A mixed bud contains both flowers and leaves; hence it always refers to the fruit-bud. The apple and pear have mixed buds. The fruit-buds of the apple and pear are usually larger, plumper, and less pointed than the leaf-buds, but this is by no means universal. In the Baldwin and many other apples, for example, it is almost Fig. 3.-Fruit pro- duction and two axillary shoots, all arising from a single fruit- bud. (Rome.) THE BUDS OF FRUIT-TREES 23 if not quite impossible to distinguish the fruit-buds in the winter without dissecting them. Also, different varieties have to some extent fruit-buds which are characteristic in some particular, such as color, shape, size, or the degree to which they are appressed to the shoot. 22. Terminal and lateral buds. — All buds of necessity must be bonie either terminally on the end of a shoot, in which case they are called "terminal" (or apical), or on the sides of the shoot, when they are known as "lateral buds." The latter regularly occur within the axil of a leaf and are termed "axillaiy buds," although at times some lateral buds are adventitious. If more than one leaf-scar is found at the base of a bud, it must be considered terminal though on an exceedingly short shoot, and not an axillary bud. Frequently, a very close examination is necessary to dis- tinguish between an axillary and a terminal bud on an exceedingly short spur. On the other hand, not all buds which appear to terminate a shoot or branch are terminal, for, as in the case of many plums and the apricot, no true terminal bud is formed but the distal bud is axillaiy. 23. Latent buds. — A latent bud may remain dormant, or fail to expand, for more than one year and then through some impetus or stimulation start into growth. There are a large number of latent buds on fruit-trees, and if this were not true so many shoots would develop that many would perish for lack of light, nutrition, and other factors. Often these donnant or latent buds are overgrown or out- grown by the surrounding tissues, but remain alive. Thus, many apparently adventitious shoots really arise from latent buds. 24. Adventitious buds, as mentioned above, arise in ab- normal or unusual places. They arise on both roots and branches, especially if the parts above are removed or injured. After severe pnming operations, it is a common 24A POMOLOGY ^jSci^ence for adventitious buds to arise from the smooth T)afe of the large limbs below or from the healing tissue about wound. It is also common for such buds to form and evelop branches below a ringed portion of the trunk or limb. 25. Collateral buds. — Buds may occur singly or in groups of two, three, or more side by side, in which latter case they are said to be collateral, as with the peach and some kinds of plums. 26. Leaf-scars are of some importance in studying buds. The}^ are the former places of attachment of the leaves and should be distinguished from those of the bud-scales, as the latter scars are sometimes rather conspicuous early in the growing season. In the larger leaf-scars of the apple, the points of separation of three vascular bundles can be seen. As an axillaiy fruit-bud opens, a cleavage plane or "crack" usually occurs in the tissue between the vascular bundles, but this should not deceive the observer into believing each bundle to represent a separate leaf-scar. 27. Fruit-spurs. — The term "fruit-spur" as commonly used in pomological literature designates a short shoot that produces flowers and fruit, in contradistinction to the longer shoots of the tree. Probably no clear-cut distinc- tion can be drawn between these spurs and the other vege- tative growths of the tree, since a fruit-spur may become highly vegetative and develop into a large branch. Like- wise also a short growth or spur may continue growth for many years without producing flowers or fruits. The general term "spur," however, is of service to distinguish the short growths which are common on fruit-trees and upon which much of the fruit is borne. In the cases of the plum, the cheriy, and the peach, when they produce spurs, the fruit-buds are bonie laterally, whereas the terminal or distal bud of the spur generally is a leaf-bud, and the elongation of THE BUDS OF FRUIT-TREES 25 the spur is, therefore, continued in a straight line, of- some- times the spur perishes entirely. With the apple and the pear, on the other hand, a leaf-bud may ! end the growing axis, in which case further elongation in a straight line is possible. But when fruit-buds are pro- duced they are usually terminal, whether the axis which bears them is long or short, so that further elon- gation of the spur is forced out of a straight line through the devel- opment of lateral buds, which may be produced below the fruit-bud, but as a rule are devel- oped from axillaiy leaf -buds which have their origins within the fruit- bud itself, as is discussed above, short or several inches long. This secondary growth is of prime importance in the maintenance of the fruit-spur, although when the spur is very weak it may not develop. The power of continuing Fig. 4. — Short spurs of apple bearing termi- nal fruit-buds. TF = terminal fruit-bud. Such growths may be 26 POMOLOGY growth or development in the short spur, especially after it becomes old, is apparently centered largely in the terminal bud, whether this is a leaf- or flower-bud.^ 28. Fruiting of the apple. — The development of spurs in the apple can be seen in Fig. 4. Several are already short fruit-spurs and others may or may not develop from the short tenninal spurs which have produced only a leaf-bud at the terminus. In this case, all the lateral buds and the terminal one on the one-year growth are leaf-buds; on the two-year wood there are four fruit- and five leaf-buds shown in the drawing; and on the three-year wood are four fruit- and two leaf-buds, indicating that none of them behaved in their second year as occurred above, for no flowers were produced on the spurs before. This, then, may be con- sidered one type of fruit-spur formation on the apple. Since they are yet unbranched, they may be termed "sim- ple spurs." In Fig. 5 is shown a second type of fruiting habit of the apple. In this case, the one-year wood has produced both a tenninal and axillary (or lateral) fruit-buds. They can be clearly distinguished by their size. This type of flowering is very connnon with the apple and pear. This is a case of fruit-bud formation without a spur being first developed, for only one leaf subtended these buds and hence they are, by definition, axillaiy. The student should make close observations, however, for it is not unusual to find a very- short spur (sessile) on the one-year wood, having produced only two or three leaves, and hence a fruit-bud in such a ' The author observed for several years the results of "disbudding" spurs by partridge or grouse {Bonasa umhellus, L.). The terminal buds of the short spurs were broken off throughout certain trees in an orchard and the question arose as to how long it would be before the spurs were again sufficiently developed to produce fruit-buds. The results were rather uniform in that about 80 per cent of these spurs died. THE BUDS OF FRUIT-TREES 27 case in the strict sense would be terminal and not axillaiy. Some varieties of apples yield amiual crops, because the fruit in one of the years is pro- duced largely from axil- TF Fig. 6. — The beginning of a fruit-spur system in the apple. TF Fig. 5. — Axillary and terminal fruit bud formation in the apple. TF = terminal fruit-bud; AF = axillary fruit-bud. lary fruit- buds on the one-year old wood. Such varieties as the Jonathan, Wealthy, and 28 POMOLOGY Missouri Pippin produce axillary fruit-buds freely. The short spurs in Fig. 5 are homologous to those in Fig. 4. A third type or rather an advanced stage of spur formation is seen in Fig. 6. In this case, a terminal fruit- bud was formed in 1918 and two secondary shoots arose in 1919 from the cluster base (a), both of which produced fruit-buds. In 1920 the fruit- buds expanded and developed a cluster base at b and bb, and they gave rise to one short secondary growth at c which is a leaf -bud, and two secondary growths at cc and c'c', both of which were leaf- buds although from their size they might have been mistaken for fruit-buds. Thus there is the be- ginning of a "compound spur system" (probably a fruit-spur system) . The Rome Beauty produces a large num- Cn ber of its fruit-buds tenninally, i. e., on the ends of rather long shoots. In fact, this is the characteristic method of production in that variety. Usually the same spur would not fruit annually, but every second or third year, depending on the vigor of the tree. If the his- tory of the branches is traced back on the tree, it will be found that the branch (or spur system) con- FiG.7.— A flower- tinues to elongate and the place cluster base where the flowers or fruits were that has pro- borne is gradually overgrown and ^ tZ'lTl the branch appears straight, ^,^ ,^_,^, long shoot. rather than angular as m the fruit-spur system (Rome apple.) case of the short branched of the apple. Tf THE BUDS OF FRUIT-TREES 29 TF spur system, such as is illustrated in Fig. 8. In Fig. 7 is seen the beginning of the spur systems of the Rome. What may be termed a typical compound spur for many apple varieties is shown in Fig. 8. Such a spur may continue bearing fruit from its several units for manj^ years. 29. Fruiting of the pear. — This fruit is closely related to the apple botanically and it forms its fruit-buds in much the same positions. The fruit-bud is usually termi- nal on a spur, although terminal ones on long shoots or even water-sprouts are fairly _ T common. Fig. 9 shows a shoot of pear which has produced a terminal fruit-bud and three axillary ones, while in Fig. 10 is seen a vigorous fruit-spur on which three terminal fruit-buds appear and also one axillary. 30. Fruiting of the peach. — The peach differs from the apple and pear because fruit-buds occur freely on the vigorous, often much branched, one-year-old wood, which also produces the vegetative exten- sion of the tree. It will be remembered that the one-year-old temiinal shoots of the apple yield a veiy small portion of the fruit-buds only and very frequently none. The lateral shoots on the one-year-old wood of the peach may be rather short (less than ^'^ o _ a -'ll one to three inches long) and because of fruit-bud forma- their length may be termed spurs. Such tion in the pear, spurs are frequently very fruitful, and the fruit-buds produced on them may be more hardy than those on the more rampant growth of other branches or trees. Also 30 POMOLOGY short spur-like growths are frequently found on the older branches or trunk of the peach tree. These spurs arise from latent or adventitious buds, frequently at the place where a shoot or branch has died or been removed. These spurs are often fruitful and may perish after one year's growth or may continue a short unbranched growth from a terminal leaf -bud Fig. 10.— a vig- orous fruit- spur of the pear. lS/6 for two, three, or more years, but usually they are not long-lived. The peach fur- ther differs from the apple and pear in the number of buds that may stand at a node. Any of the following conditions may be found at a node on the one-year wood of the peach, and sometimes all of them on a single shoot: 1. A single leaf -bud. 2. An axillary fruit-bud. 3. A leaf-bud and fruit-bud in the axil of a single leaf. 4. Two fruit-buds with a leaf -bud between them or to one side of them in the axil of a single leaf, or with a leaf Fig. 11.— Fruit- ing habit of the peach. THE BUDS OF FRUIT-TREES 31 subtending each bud, or on a very short sessile spur. 5. Two fruit-buds in the axil of a single leaf, 6. Three fruit-buds in the axil of a single leaf. 7. A fruit-bud between two leaf-buds. The fruit-buds of the peach are usually large in comparison with the leaf-buds and are also pubescent. They are simple, comprising as a rule only one flower-bud, but in some cases they may contain two. As a rule, a weak or short branch bears only single fruit-buds, while the double or triple ones are bonie mostly on the stronger growth. A branch may be so strongly vegetative, however, that no fruit-buds are produced. Fig. 11 illustrates the fruiting wood of the peach. 31. Fniiting of the cherry.^ — Like the other stone-fruits, the sweet cherry bears from axillaiy fruit-buds. They are formed both on the terminal growth, more particular!}^ near its base, and on short spurs which are found, character- istically, on the older wood. The terminal buds of both branches and spurs are leaf-buds, with the result that their growth is in a straight line, in contrast to the apple and pear. Whipple states that the sweet cherry spurs will be alternat- ing in their bearing if the trees are not well cared for and properly pruned. The sour cherry forms its fruit-buds in practically the same positions as does the sweet cheriy. At times all the axillar}^ buds on the new growth are fruit-buds, which results in a naked branch the following season. The tenninal ones, however, are leaf -buds and hence they continue the growth of the spurs and branches and furnish a leaf area to support the developing fruit below. Fig. 12 shows one type of fruiting wood of the sour cheriy. 1 Whipple, O. B. The pruning of stone fruit trees. Better Fruit. Nov., 1917. Pruning the sweet cherry. Better Fruit, Dec, 1918. 32 POMOLOGY 32. Fruiting of the plum. — It is necessary to divide the plums into groups according to species, as follows: Prunus domestica, P. salicina, and the American species. All, however, bear only- simple buds, al- though bracts may appear when the buds open. The Domestica plums often develop a well- defined system of fruit- spurs in which the terminal bud is a leaf-bud (rarely a fruit-bud) . Fruit-buds are axillary both on the one-year- old terminal growth of the tree and on the one-year- old wood of the spur. They are usually borne singly, but it is not uncommon to find two or perhaps three coordinately in the axil of a sin- gle leaf. The bud itself may con- tain one, two, or three flower-buds (the number being somewhat characteristic for the variety) which may open before, with, or after the leaves appear. The spur under some conditions may terminate in a thorn rather than in a leaf-bud. The Japanese plums, Prunus salicina, produce axillary fruit-buds only. They are borne on the new wood either singly or in pairs with a leaf -bud between them, or in clusters. Fig. 12.— Fruiting habit of the sour cherry. A strongly veg- etative type. THE BUDS OF FRUIT-TREES 33 They also are bonie singly or in clusters on short spurs on the older growth, and such spurs may also be produced on the new growth. The American species of plum are much the same as the P. salicina in fruiting habits. 33. Fruiting of the apricot. — The fruiting habit of the apricot is practicallj^ the same as that of the peach. The fruit- buds are boilie singly, or in pairs on the new growth with a leaf-bud between them, or on short spurs on the older growth. There is no true terminal bud, but what appears so is a true lateral bud and it continues the growth of the branch. The cluster of fruit-buds on the new growth is bome in the axil of a single leaf instead, as may occur at times with the peach, each bud in the axil of a leaf. Spurs are formed more frequently with the apricot than with the peach. 34. Fruiting of the quince. — This fruit differs from the apple in the behavior of its over-wintering fruit-buds, in the fact that the terminal bud which contains the flower makes a short leafy growth of one to several inches and the simple (or single) flower is then unfolded. The fruit-buds are usually produced on short shoots (spurs) which become branched somewhat after the mamier of an apple spur. Axillaiy flower-buds may also occur abundantly on the one-year-old terminal shoots. 35. Fruiting of the grape. — This fruit also produces over- wintering mixed buds l)onie laterally on canes of one year. The flowers occur from lateral buds on the one-year wood. " All species except Vitis Lahrusca average two inflorescences to the cane but the last-named species, at least in some of its subdivisions, may bear from three to six inflorescences, each of course in the place of a tendril opposite a leaf." (Hedrick.) CHAPTER III THE DIFFERENTIATION OF FLOWER-BUDS Before studying the factors that influence the formation of flovver-butls in fruit-trees, the morphological changes which take place in bud formation from the earliest stages to com- pletion should be well understood. This has been worked over by several horticulturists^ and descriptions of the stages of development are available for the apple, pear, peach, plum, cheriy, and some other fruits. It has long been recognized that in the deciduous tree- fruits, generally, the flower-buds are more or less well devel- oped the season previous to their unfolding, although the details of their formation have been worked out but recently. As late as 1899, Goff wrote, "no systematic investigation seems to have before been made that gives us any definite knowledge as to the time when the development of the flowers actually begins, the rate at which it progresses, or the period through which it continues, in any of our fruit bearing plants." The broader details of the differentiation and develop- ment of the various floral structures and organs have been carefully outlined for the apple. The course of development is similar for the pear, and is broadly the same for the drupa- ceous tree-fruits, except that in the latter the receptacle, or 1 Goff, E. S. 17th and 18th Ann. Rept. Wis. Agr. Exp. Sta. 1899- 1900. Waldron, L. R. N. D. Agr. Exp. Sta. Rept. 10: 31-39. 1899. Quaintance, A. L. Ga. Agr. Exp. Sta. Rept. 13: 349-351. 1900. Drinkard, A. W. Ann. Rept. Va. Poly. Inst. 1909 and 1910. Kraus, E. J. Ore. Agr. Exp. Sta. Res. Bull. 1. part 1. 1913. Bradford, F. C. Ore. Agr. Exp. Sta. Res. Bull. 1. part 2. 1915. 34 THE DIFFERENTIATION OF FLOWER-BUDS 35 calyx-cup as it is sometimes called, and the carpel or carpels, are not so intimately united during development as they are in the pomaceous types. While there is considei-able diver- sity in morphology among the various wild species, the cultivated varieties are readily placed in one group or the other. The apple, therefore, may well serve as a basis for following out the sequence of developmental changes which take place in the differentiation of the fruit-bud and floral parts in the more common deciduous tree-fruits. 36. The apple. — Just prior to the differentiation of the parts of the flower-bud, it is not possible to distinguish between those growing points from which flower primordia will be de- veloped and those which will remain as vegetative growing points. Each shows a smooth rounded crown of meristematic tissue more or less in- closed by the beginnings of leaves or bud-scales. As the season progresses, the axis from which a flower-bud .,, , , 1 11 1 r Fig. 13. — Floral diagram will develop gradually becomes dis- f fh • i tinguishable through what appears to be a thickening or more broadly rounding or flattening- out of the growing apex or the crown (growing point), and soon thereafter the contour of this crown becomes slightly irregular or papillatcd, due to several new growing points becoming organized, which now proceed to develop into new axes (the individual flower primordia) and on these in turn growing points give rise to the individual floral parts and tissues. The development of the floral parts is acropetal, wliich means that they are differentiated in the same sequence as they occur in the fully developed flower. (See Fig. 13.) Thus their order of development is as follows: calyx (sepals), corolla (petals), stamens and pistils (carpels). As the pistils 36 POMOLOGY develop, the ovarian cavity is formed and upon the placentae of the latter the ovules are borne. (Fig. 14.) As the tip of the axis enlarges, the protuberances which arise spirally below it develop into individual flowers, al- though one or two leaf-buds are also differentiated slightly below the lowermost flower of the cluster. Fig. 14. — Early stages of fruit-bud differentiation in the apple, a, grow- ing axis; b, incipient lateral flower-bud; c, beginning of a bract in the axil of which a flower-bud may develop; d, a bract or leaf; e, surrounding bracts and bud scales;/, vascular bundles; g, pith. The further development of an individual flower-bud of the group may be considered as representative of the others in the cluster. When the central flower-bud is readily recogni- zable, it appears as a very short, stocky, conical mass, the apex of which is flattened except at the center where there is a small slightly convex elevation or knob, much as indicated in Fig. 15. A section through the bud would reveal a region of actively dividing cells near the upper surface, especially THE DIFFERENTIATION OF FLOWER-BUDS 37 toward the outer edge and a short way down the sides of the cone or cyhnder-Uke growth. The tissue beneath these embryonic regions is differentiated into pith cells and vas- cular bundles, and inclosing all is the epidermis. 37. Sepals. — A rapid multiplication of the cells at the outer edge of the near upper surface of the bud results in the formation of a slightly elevated ridge, the torus or receptacle. (See Fig. 16.) Growth takes place more rapidly at five points ca\yx priTTiordia eoLge of Fig. 16. — Diagramma- FiG. 15. — Diagram tic representation of indicating positions origin of calyx pri- of four flower pri- mordia on edge of mordia. torus. about equally spaced on this ridge, and thus the primordia of the sepals are begun. Because of the increase in number and size of the cells below and between the calyx primordia, the torus or recep- tacle of the flower continues development, particularly toward the outer edge, with the result that this outer portion is arched up and the calyx-lobes are elevated along on top of it. The petals, stamens, and carpels arise from the concave side of the toi-us, and the meristematic tissue out of which the primordia of these organs are finally differentiated exists as a sort of lining beneath the epidermis of the cup-like torus. As development continues, the sepals enlarge and become inclined toward one another at the apex, until they interlap and form a tent-like structure over the depression below them. When the period of winter rest arrives, these parts 38 POMOLOGY are structurally the most advanced of any within the flower- bud. 38. Petals. — Almost as soon as the primordia of the sepals are formed, those of the petals appear, the latter in a cycle within and alternating with the former.^ "Development is less rapid than in the case of the sepals but each outgrowth gradually assumes a thin scale-like appearance, more or less sickle-shaped in longitudinal section, and narrowly attached at the base. Each petal finally assumes an acute angle with the calyx and together they roof over the cup-shaped torus." 39. Stamens. — -" Directly after, or in some instances even at the same time that the primordia of the petals are being laid down, those for the stamens appear. They occur in three cycles. Those of the outermost cycle, directly within the petals, are laid down first, though they are immediately followed by the other two, in fact in some cases all three apparently form at the same time though the outermost cycle always develops the most rapidly. The outermost cycle arises so near to the primordia of the petals that in some sections they appear almost if not quite connected, though as a rule they are veiy distinct. This cycle consists of five pairs of primordia, each primordium appearing at first as a blunt, broad protuberance scarcely to be distinguished from a petal primordium. The middle and innermost cycles each consist of but five primordia. It is a difficult matter to decide whether there are actually three or but two cycles of stamens inasmuch as the two inner cycles are extremely close together. From an examination of many sections and dissections, however, the conclusion that there are actually three, seems to be well founded. The young stamen rapidly assumes a distinctly bi-lobed appearance; the basal lobe is short and slender while the apical broadens out, and it in turn becomes 1 The following quotations are from E. J. Kraus, Ore. Agr. Exp. Sta. Res. Bull. 1, part 1. 1913. .^K ^1 A E^'«^:^LiM^BK t# i M i / r ^M^I^SOt'- ®^ ^ m. s L r ^^^ ^ ^ f 1 ifs.^ N w ^ ^ :;^ f- 1? 13 1014 1.9 Id Height in ft., 1,915 Wid'h in ft., 1915 Diam. trunk, una Average total length of growth in feet Heavy pruning 4.41 10.25 41.53 84.08 101.74 7.57 5.17 2.17 Light pruning 5.58 15.51 34 . 33 99 . 39 224 89 10.79 G , 85 2.91 The same observation has been made with regard to bear- ing trees. ^ After twelve years' work with dwarf apples (the trees were then fifteen years old), they were lifted and weighed, with the following observations : "Those which had not been primed at all were 20 per cent heavier than those which had been moderately pruned, while those which had been hard-pruned were 16 per cent lighter . . . thus pruning not only doesn't increase the actual size of the tree, but it results in less new wood being formed." Tufts - shows that there is a definite correlation between trunk circumference and the weight of both top and root development of two-year-old black walnut and almond seedlings. Also that the average increase in circumference of severely pruned apricot, cherry, peach, pear, and plum during four seasons was 8.9 centimeters, moderately pruned 10 9, and lightly pruned 12.3. The latter developed stockier and stronger branches and made greater development than heavily pruned trees. Gardner ^ also points out that unpruned young trees, on the average, increased in size as rapidly or more so than either dormant or summer pruned ones. 1 Bedford and Pickering. Woburn Exp. Fruit Farm, 7th Rept. 2 Tufts, W. P. Calif. Agr. Exp. Sta. Bull. 313. 1919. 3 Ore. Agr. Exp. Sta. Bull. 139. Pages 3-45. 1916. 1907. PRUNING 81 Chandler ^ reports on young apple and peach trees of different ages with the same general results as above indi- cated, and the data from the one-year old nursery stock may be taken as typical of the results. The trees were selected carefulty as to uniformity of size and a part of them had their opening buds removed from the trunks to a height of about 18 inches, while the remainder were untreated. At the end of the season, the following data were obtained : Table X ON PRUNING ONE-YEAR-OLD DELICIOUS TREES (aPTER CHANDLER) Treahucnt Number of trees Ave. number of leaves, Oct. 19 Wt. of tops, grams, Oct. 19 Wt. of roots, grams, Oct. 19 Pruned Unpruncd. . . . 16 14 149 272 168.2 236.6 24.0 33.2 Reference has been made to sufficient experiments to indicate the status of the subject at this time, and while it would seem that practically all pruning is a dwarfing process, it should not prejudice the student against the necessity of such training of the young tree or pruning of the old one as is necessary for the securing of a well-balanced and fruitful individual. 75. Effect of pruning on early bearing. — Of still greater importance to the orchardist is whether heavy pruning of young trees will hasten or delay their coming into commercial bearing. In this connection it must be remembered that blossoming does not necessarilj^ mean fruit production. In general, it seems well established that the less pruning, the sooner a tree will form fruit-spurs and fruit-buds and es- tablish the bearing habit. It does not necessarily follow ^ Proc. Amer. Soc. Hort. Sci. 1919. 82 POMOLOGY that heavy pruning may not be conducive to greater fruit production on an older tree, as is pointed out in paragraph 79. This idea is not new but has frequently been mentioned by early writers. In 1768, Hitt wrote as follows: "If there are two apple, pear, plum or cherry trees, equal in health and strength, at one year old after grafting, let them remain some years after in the same stations . . . and one of them be pruned, and the other not, but suffered to grow in a shape quite rude and natural, the latter will produce fruit much earlier than the other, though, perhaps, its branches will not be in so regular a position as those of the former; hence it may be reasonably inferred that premature pruning a healthy, strong standard, in what manner soever, before blossoming, will keep it longer back from a bearing state than it would be were it left unpruned." ^ This effect of pruning on early bearing is shown by work at Woburn on dwarf apple trees. Records for twelve years were reported in three periods, wherein the yield of moderately pruned trees was given a value of 100 and the other treat- ments compared with it, as follows : Table XI EFFECT OF PRUNING ON EARLY BEARING (wOBURN) Id 5 yrs. 2d 5 yrs. 12th year Heavy pruning . . . Moderate pruning Light pruning. . . . No pruning 75 100 90 220 50 100 150 200 100 145 275 Similar results were obtained by Alderman and Auchter with young trees just coming into bearing, as shown by the following data: ' Hitt, Thomas. A Treatise of Fruit Trees. 3d Ed. London, 1768. PRUNING 83 Table XII EFFECT OF PRUNING ON EARLY BEARING (AFTER ALDERMAN AND AUCIITER) Type of pruning Bloom clusters to a tree, 1914 Fruits to a tree, 1914 Bloom clusters to a tree, 1915 Fruits to a tree, 1915 Percent- age fruit- buds to a tree, 1916 No. Wt., lbs. .14 3. -4 15.5 2 2.0 1.86 40.00 175.00 .7 12.2 24. .25 3.35 6. 04 3.7 Moderate Light 20. 38. In these experiments, more mature trees were also treated with the result that the heaviest pruned yielded more fruit than the lightly pruned ones. However, the trees were reported as in poor condition (making only four inches of terminal growth) and hence the data are not considered so relial^le as in the cases of younger trees. 76. Effect of the unequal cut. — A common weakness in the framework of the tree is a sharp-angled crotch or fork wherein one branch of the fork is about equal to the other in size. This produces a condition which is likely later to result in a poor type of development and a breaking of the tree. This can be avoided by the "unequal cut"; that is, by not cutting back the two branches of such a fork equally, but by making one decidedly shorter than the other so as to suppress its development and make it subordinate to the longer one which becomes a leader. By this method, a much stronger tree can be built. On first thought this principle would not seem to be in harmony with the obsei-ved fact — which is discussed later— that there is a stimulation to vigorous growth at the point where the cut is made. An explanation seems available, however, to account at least in part for the effect of the vni- equal cut. The case is at once different from one in which 84 POMOLOGY the entire top of the tree is pruned. When only a few shoots are cut back, there is no measurable unbalancing of the root system and top of tree and, therefore, no excessive supply of water and soil nutrients, for the other branches of the tree will make use of any additional amount. As a result, no special stimulation is manifest and the branch which was pruned is reduced in size in comparison with its former rate of growth. The following experiment may be cited on this point: ^ A shoot of equal length was chosen for observation on a number of three-year-old nursery trees. This shoot was cut back one-third its length in all cases, but with half the trees under observation all the other branches were likewise pruned back. The answer to the question here involved will depend on whether the selected shoots will respond similarly on both blocks of trees. The following data show that, if the remainder of the tree is pruned, the selected shoot makes a much greater growth than if it is the only one which is cut: Table XIII NURSERY STAYMAN WINESAP, 1919 (AFTER CHANDLER) Treatment Number of trees Ave. twig length, inches, before pruning, May 23, 1919 Ave. twig length, inches, after priming, May 23, 1919 Inches of new growth from each pruned twig, Sept. 20, 1919 Tree pruned . . Tree unpruned 30 30 29.2 29.2 9.9 9.9 32.0 9.9 77. Heading-back versus thinning-out. — In discussing the effect of pruning on the size and development of trees, no differentiation was made between types, but rather the 1 Chandler, W. H. Proc. Amer. Soc. Hort. Sci. 1919. pp. 88-101. PRUNING 85 general bulk pruning was treated, consisting in both head- ing-back and thiiming-out of the young trees. The effects of these two types of pruning on the branch growth and the development of fruit-spurs may now be studied to advantage. Heading-back refers to the cutting of the shoot or branch, removing the terminal growing point and a certain number of the lateral buds or shoots nearest the end of the branch. Thimiing-out, on the other hand, means the removal of surplus branches or shoots without any heading-back proc- ess. The effects of these two types of pruning are different and should be carefully examined. The experiments of Gardner ^ in Oregon were so arranged that the responses to these two types of pruning could be studied in detail. They show in general that thinning-out is more favorable to fruitfulness than heading-back, al- though both practices would be included in orchard oper- ations. The general response from the total or bulk pruning was not entirely in accord with the experiments cited above, in discussing the effect of pruning on size of tree, but varieties varied to a considerable degree. With Grimes on Doucin roots it made little difference whether a shoot was left un- pruned or was headed-back lightly or severely, the subse- quent units of growth the following season being about the same. The number of shoots resulting if a branch was severely headed-back would, however, be fewer than if lightly headed-back or left unpruned. With the varieties Esopus, Rome, and Gano, on the other hand, heavy pruning checked their growth. These latter statements refer to the effect of pruning on the subsequent size of the tree and are not to be confused with those in regard to the development of spurs and fruit-buds when trees are headed-back or thimied-out. ' Ore. Agr. Exp. Sta. Bull. 139. pp. 3-^5. 86 POMOLOGY With all the trees in the experiments, heading-back resulted in a decrease in the number of fruit-spurs to which the individual shoot gave rise, this being more marked with increase in the severity of the heading. In other words, fruit-spur formation on the individual shoot was correlated with its length after rather than before the pruning. A statistical study of the two types of pruning as applied to Grimes, Gano, Rome, and Esopus seemed to warrant the following conclusions: 1. A general heading-back of the shoots of a tree acted as a stimulus to new growth. The amount of the stimulus varied considerably with variety. 2. An equally severe thinning acted as a check to new growth, but this also varied somewhat with variety. 3. Heading-back resulted in a more marked check to fruit-spur formation than did equally severe thinning-out, with such varieties as Grimes and Esopus. The reduction was not so marked with Gano and Rome, as they bear a large percentage of their fruit-buds laterally on the new, terminal shoots, especially when young. 4. Thimiing-out increased the production of fruit-spurs, as compared with equally severe heading. On the other hand, heading generally augmented the production of ter- minal fruit-buds on the few shoots. In some varieties, thinning was accompanied by a greater production of lateral fruit-buds on shoots than equally severe heading; in other varieties, the reverse was the case. In general, thinning- out tends to increase flower and fruit production, while the heading-back is likely to decrease those functions. These two types of pruning are further considered in detail as they a]5ply to young trees. 78. Detailed response of young trees. — As is described and discussed above, thinning-out refers to the removal of a portion of the limbs, branches or shoots in order to "open PRUNING 87 up " the tree and is essentially different from heading-back, inasmuch as the ends of shoots or branches are not cut off. As a result, the terminal bud continues the growth of the branches and the lateral buds usually develop into branches or spurs or remain dormant. Gardner has calculated on this basis that of 100 shoots bearing ten lateral buds each and also a terminal bud in this case, a light thinning out (30 per cent) would leave 770 buds— 700 lateral and 70 terminal. It was then assumed that from these 70 shoots "we obtain 140 shoots and 490 spurs, leaving 140 dormant buds," which is considered not far from what would actually be obtained. From a heavy thinning-out (60 per cent) of this same number of shoots there would be 40 untouched ones. These would probably behave in much the same manner as the branches on the lightly thinned tree. ''Were this the case the result would be eighty new shoots (forty from the terminal buds and forty from as many lateral buds), about three hundred twenty spurs, and forty dormant buds. The individual spurs would be thicker and more vigorous in appearance, but probably the proportion of buds to develop into fruit-spurs would remain about the same." Thus a light thinning-out gives more shoots and fruit-spurs than a heavy one. The results of this estimate, based on extensive observation and experiment, are summarized in Table XIV. 88 POMOLOGY Table XIV PROBABLE RESULTS FROM DIFFERENT METHODS OF PRUNING ONE HUN- DRED SHOOTS, EACH HAVING TEN EQUALLY SPACED LATERAL BUDS (AFTER GARDNER) 11 11 11 il Number terminal buds left 700 200 300 200 400 250 150 50 70 700 140 490 140 40 400 Number new shoots formed Number spurs formed 80 320 Number buds remaining dormant . . . 40 Not only is it concluded that thinning-out has a beneficial effect on fruit-spur development, but also on their vitality and longevity. The trees that are headed back have a strong development of new shoots, mostly on the outside and top of the tree and, as a result, the spurs on the inside suffer and become non-productive, if indeed they do not die. On the other hand, thinning-out tends to strengthen the spurs already formed as well as to develop new ones. 79. Relation of pruning to nutrition. — That the relation of the stored food materials and the soil nutrients and moisture may be profoundly affected by pruning as well as by cultural practices has been emphasized by Kraus and Kraybill. Any one of four sets of conditions may be en- countered, similar to those described in Chapter IV. 1. A marked reduction in or limitation of carbohydrates, even though there were an abundance of available moisture and nitrates, would result in a depressed vegetative condition as well as a reduction in blooming and fruit production. This condition would result from heavy pruning as well as lack of photosynthetic activity, and, therefore, additional \J PRUNING 89 pruning would have a tendency to restrict furt.her the growth activity. 2. An abundance of moisture, nitrates, and carbohydrates would result in rapid vegetative extension. Under these conditions, it is probable that more time would be required to manifest a dwarfing of the tree by pruning than when one or more were lacking. 3. The ideal situation would exist if there were present or available a moderate Init ample ft f amount of nitrogen, together with carbohy- ^\ ' drates, in case the latter are synthesized in excess \^ of the quantities utilized in vegetative exten- sion, that is, an ample reserve food supply would be present within the tree. The result would be a good growth and a rather free de- ^ J / velopment of reproductive parts. It is sug- gested that pruning may or may not be needed, but usually some is required. Pruning would fur- nish a ready practical means of regulating the nitrogen-moistiu'e-carbohydratc relation. 4. A fourth condition is frequently encountered in old neglected orchards or with trees damaged in such a way as to approximate girdling. In such cases, there is usually a depressed vegetative con- dition, the trees bearing small light-colored leaves, and they may or may not produce abundant blossoms which are not likely to "set" well. Fre- quently such trees contain carbohydrates in excess, as compared with the availal)le nitrate nitrogen, or moisture, or both. In order to effect a Fig. 24. balance and induce vigorous growth and bios- Showing the type soms capable of setting fruit, either of two ^qj^^^q^i rj!, procedures might be followed but preferably jo^^g ^^^ cutting both. Top-pruning would reduce the total of the terminal. 90 POMOLOGY An excess of either vigorous growth 80. Theoretical importance on must have as ground a body based largely on biochemical, and analyses, and with bulky to handle mation comes or postulates now relative carbohydrates and hence increase the relative pro- portion of moisture and nitrogen; or the application of a quickly available form of nitrogen, such as nitrate of soda or sulfate of ammonia, would produce the desired result, treatment would push the tree into and again reduce flowering. considerations. — Any theory of pruning its back- of facts chemical, physical plants as as fruit-trees such infor- slowly. The speculations available can scarcely be tenned theories, but recent work is in material advance of the former "philosophy" expressed on the suliject and the near future will undoubtedly reveal much of fact that is now lacking. Commonplace as pruning seems, it is a singular practice. It might at first thought be likened to the thinning of plants which are growing very close together, and yet it is funda- mentally different because the various parts of the tree possess a single or common root system. Again, the branches of a tree seem, in many ways, to be independent units, yet they are members of a single whole. However, all the different parts are usually not so placed as to be favorable to high-grade fruit production or Fig. 25.— Showing a type of growth that follows when the ter- minal is not removed. The buds which give rise to shoots are us- ually not confined to the terminal ones. PRUNING 91 for the strongest mechanical structure. If this dense growth is allowed to develop unchecked, it will result in an excess shading of certain parts with a resultant condition that might be loosely called starvation, followed by a dying of the branches. If limbs or branches are removed, it is common knowl- edge that certain shoots are likely to develop which would otherwise remain as latent buds, and especially there is a stimulation or increased cellular activity near the point where the cut has been made. This response on the part of the tree is a type of regeneration — a provision through which some organisms replace lost parts — which leads to the point here involved : why or how does the plant manifest this increased activity near the point of injury? See Figs. 24 and 25. One theory commonly accepted is that a reduction in the number of growing points and cambial area would make available to the remaining parts an increased amount of the tree's reserve food supply, from which at least the initial growth is made. With this increased food supply, the opening buds would make a much greater growth than would have been possible had no growing points been re- moved. A second theory would account for the growth response following pruning by assigning the cause more particularly to the increase in amount of moisture and mineral nutrients, particularly nitrogen, to carbohydrates that are made available to the parts remaining. That is, it is due to a disturbance in the balance of the materials within the tree. These two views may be considered briefly together. In the first place, it is well known that a fruit-tree usually manufactures more food material than is utilized in the various phases of growth, including the production of the crop. The unused portion is translocated downward through- 92 POMOLOGY out the whole tree and remains in the cells of the storage tissues; it is termed "reserve material" because it can be used later in growth. Secondly, the amount and form in which the reserves occur in the parts of the tree vary at different times of the year, and one year with another. The following table illustrates this point by showing the amounts of dry matter, starch, and saccharose at time buds are swelling, in case- of a seven-year-old Bismark apple tree that has been growing in sod for four years. Table XV amounts op dry matter, starch, and saccharose in seven-year- old apple tree at time buds are swelling (after chandler) Part of tree Pounds Pounds Pounds dnj wgt. starch saccharose 3.15 0.98 .12 21.00 6.72 .17 15.13 5.14 .11 14.15 5.43 .28 6,49 2.37 .06 1-year twigs. . Older branches Trunk Large roots . . . Small roots . . . . Furthermore, it is significant in this connection to note that the reserves seem to be lower in the tree in spring and early summer when growth is very active than at other seasons, indicating that they are utilized in growth. It should also be recalled that growth activities are going on within the tree before leaves or blossoms are put forth. The following data would seem to establish this conception so far as the soluble materials are concerned. According to Chandler, the freezing point of the sap seems to be a fair measure of the amount of soluble carbon compounds present at different seasons: PRUNING 93 Table XVI FREEZING POINT DEPRESSION OF BARK SAP OF ELBERTA WILD SWEET CHERRY TWIGS (AFTER CHANDLER) PEACH AND Elberta peach Wild sweet cherry 1916 Freezing point de- pression, °C Moisture per- centage Freezing point de- pression, °C Moisture per- centage March 25 3.010 2.096 1.880 1.378 1.540 1.810 2.158 2.230 2.233 2.567 59.2 62.0 54.6 2.255 1.485 1.295 1.120 0.985 1.553 1.730 1.763 2.563 At3iil 17 May 3 May 10 60.1 June 19 July 6 August 17 61.4 October 5 December 29 54.3 According to Price/ the starch also is practically ex- hausted in the early growing season in all parts of the tree above the ground. If these statements are accepted, according to the first theory there should be no stimulation if the pruning is done at the beginning of the growing season. Chandler has shown, however, that it makes no difference whether the pruning is performed during the growing season or in late spring, so far as growth response is con- cerned. Hence this evidence would weaken the first theory and the latter calls for more careful attention. From. what has been said, it would seem evident that any pruning whatsoever would reduce the total amount of re- serves available for future growth. However, top-pruning will also reduce the future leaf area that is to maintain the 1 Price, W. A. Ohio Jour. Sci., Vol. 16. pp. 356-359. 1916. 94 POMOLOGY synthesis of the tree and hence profoundly disturb its re- lation with the amount of soil-moisture and nutrients taken up by the undisturbed root system. To what extent a reduction in the top of the tree will affect the amount of water and mineral nutrients absorbed by the roots can- not be stated definitely at this time, but certainly each growing point remaining must receive a greater supply than had no pruning been practiced. This, then, would seem to account in part for the apparent stimulation to growth which takes place. Critical observation has shown that heavy pruning will result in dwarfing of a tree, as already noted. This is ex- plained on the grounds that fewer growing points must necessarily produce less total linear growth and hence less weight and, therefore, the top of the tree is somewhat re- duced. This dwarfing in the top will react on the root system and it will become restricted. 81. When to prune. — ^Divergent views have been held as to the best time to prune fruit-trees, but careful obser- vations are bringing about more unity of opinion. An old adage says ''Prune when the knife is sharp," but another admonishes not to prune frozen trees and not to prune when the sap is "running"; so the layman has been left somewhat confused. Little actual experimental work has been done along these lines but much experience may dic- tate practice. From an experiment with apple trees con- ducted in Minnesota, where the winter temperatures are low, it is concluded that no difference in the healing of the wounds resulted whether the cutting was in fall, midwinter when the trees were frozen, or in the spring.^ With hardy fruits it is not uncommon to prune at any time during the dormant season, but preferably in late winter or early spring. With the grape, peach, and other fruits hable to winter in- 1 Brierley, W. G. Proc. Amer. Soc. Hort. Sci. 1919. p. 102. PRUNING 95 juiy, it is best to delay pruning until severe freezing weather is past. In Oregon it was observed that whether apples were pruned in November, i. e., just at leaf fall, December, or March (when buds were sweUing), the results were iden- tical. The amount and type of pruning was far more im- ]iorta-nt than ihc tunc. 82. Pruning at planting time. — Since the balance between tlio root system and top is disturbed when trees are dug for transplanting, it becomes desirable to prune the tree at planthig time. Occasionally a block of trees is seen that was not pruned when planted and the result is a number of small growths on the long slender branches, making it al- most impossible to prune with any satisfaction at a later period. Unless the moisture conditions are very favorable, many of such unpruned trees are likely to suffer perma- nent damage. Dr. Warder once said that the hole for a tree should be as big as the orchard. If his advice is taken, the soil well prepared and the hole made large, it is possible to plant without reducing the root system more than is done in dig- ging the trees. There appears to be no virtue in reducing the roots to mere stubs unless they are broken or mangled, diseased, or seriously dried out. Long weak roots should, of course, be made to conform to the others in length for convenience in handling. The first new growth of the tree is made from the reserve material within it, but as soon as the leaves appear they require moisture for functioning. Therefore, the reduction in leaf surface through pruning gives the roots an opportunity to develop a new area of root-hairs more nearly proportional to the leaf surfaces which are instrumental in absorbing the soil-moisture. Some extensive tests were made at the Woburn Fruit Fann to determine the effect of careless planting on the after growth of the trees. The results were surprising in most 96 POMOLOGY respects, as they showed that trees carelessly planted and the soil rammed about the roots produced a greater growth than those set in the "orthodox" way. No injurious effect resulted from planting trees with mangled or broken roots, provided a reasonable portion of the root system was left intact. Neither did the huddling of the roots into a small hole have any apparent effect. The conclusion is drawn that trimming of the roots is altogether unimportant, the omis- sion having sometimes one effect and sometimes another.^ 83. Pruning young versus mature trees. — The problem of pruning the yomig tree is essentially different from that of pruning the mature one so far as purpose is concerned, but the basic principles remain the same. In the first place, the great essential is properly to select the future scaffold branches and prune consistently to develop the type of tree selected as the ideal. The first three or four years of the apple and pear and the first two years of the peach tree rep- resent the formative or vegetative period in which the chief aim of the grower should be to develop a well-formed speci- men, regardless of fruit-spurs or buds. The tree then enters a period when it is desirable to consider the growth of fruit- ing wood, and with the apple and pear it means a cessation of a systematic cutting back of the terminals and usually as little pruning as possible. This, of course, does not mean that small rubbing branches and water-sprouts should not be removed or that a long rangy branch should not be sup- The tree next passes into the period of fruitage when the type of pruning will develop very largely into a thinning- out process with the apple and pear but also heading-back with the peach. As trees of the former fruits become older and larger, it will often be desirable also to head-back some ^ Bedford, Duke of, and Spencer Pickering. Science and Fruit Growing. London, 1919. Ch. 4 and 5. PRUNING 97 of the longest and highest branches, depending on the vari- ety, distance of planting, and other conditions of locality and preference. The cherry as well as the peach should be kept pruned to an open tree as the spurs and shoots will be more fruitful and the branches more vigorous. The same practice should also be followed with the plum. 84. Salient features in pruning mature trees.— The fol- lowing points should be borne in mind by the pruner in han- dling mature trees: 1. Remove all dead branches, also diseased or injured parts in order to safeguard the remaining portions of the tree. Some exceptions to this may be noted in case of such a disease as black-rot canker {Sphceropsis malorum) if it is abundant through the tree. If all diseased limbs were re- moved, little of the tree would remain, hence the practice is to remove only such limbs as show evidence of decline. 2. Open up the tree. If the tree has become too thick and ''bushy," it will be necessary to remove a portion of the limbs or a weakening of the fruit-spurs will result and fruit inferior in size, color, and quality will be produced. Rubbing limbs should be cut off, and long rangy ones that are out of proportion should be headed-back. 3. Avoid the removal of fruit-spurs. This is paramount, and a thorough understanding of the way a tree bears its fruit must be one of the basic guides in the removal of branches. There are times when it is desirable to remove some of the spurs, or portions of the individual spur, in order to improve those that remain. 4. Stubs are to be avoided. In removing limbs or branches, no matter how small, they should be cut close to the trunk or adjoining branch to which they are attached. This is not so important with the peach as with the apple, owing to the strong growth of the former which will more quickly envelope a small stub. 98 POMOLOGY 5. As a rule, it is desirable to remove the "suckers" or "water-sprouts " that may arise throughout the tree. Strong sucker growth along the main limb may be an evidence of decline in the branch and the outer extremities may be robbed of vitality if they are allowed to develop. On the other hand, it is often desirable to retain a portion for re- placing limbs. In such a case, it is usually desirable to head them back and treat in about the same way as a young tree. 85. Renovation pruning. — The dehorning of apple trees or the cutting back of one-third, one-half or even more of the tops of old trees, leaving naked branches from which to grow a new top, has had its advocates. This procedure re- quires great caution, for it is not unconmion to find that trees subnormal in vitality may have their death hastened by such a practice, although for the first two or three years the operation appears successful. It is usually better to cut back a portion of the tree at a time and always cut to a side branch rather than trust to the outgrowth of "suckers" or water-sprouts. Such trees should be stimulated by til- lage or the application of manures or fertilizers as a safe- guard against injury. The peach, on the other hand, may be headed-back severely with comparative impunity. Branches may often be developed in desirable places on an old tree by making use of water-sprouts which arise in those places. These sprouts may come into bearing in about three years and are handled in pruning in much the same way as a young tree. 86. Summer pruning. — As dormant pruning has been widely advocated to induce vigorous wood growth, so sum- mer pruning has been recommended to encourage fruit- fulness. The practice is an old one and has commonly been credited as a means of bringing tardy bearers into fruiting. There is veiy little experimental evidence on which to base this teaching, but it is well entrenched in the literature. PRUNING 99 The value of the practice seems to depend on the variety, soil, climate, time, and particularly the type of pruning (of which there are veiy many), and doubtless on the internal condition of the tree. It is true that summer pruning will often decrease vegetative growth, but it does not necessarily follow that fruitfulness accompanies such enfeebled growth. Some experiments have been conducted to detennine the value of this practice, but it scarcely seems possible as yet to hannonize the views held by different investigators on its value, but certainly it is pernicious at times. Doubtless the difficulty is due to the different methods employed and to the vaiying influence exerted on the materials manufac- tured and stored. Some have practiced both a thinning- out and heading-back of the branches relatively early or late in any given season, while others have merely pinched the tips of the branches. The results must, therefore, vary accordingly. For eastern conditions the consensus of opinion seems to be that summer pruning is not a desirable practice, as the trees are enfeebled and the effects on bearing are doubt- ful, often negative, and frequently the yield is decreased. In England where dwarf trees are rather widely grown, there is some difference of opinion on its value, ^ but the growers are more favorable to summer pinching if any treatment is to be given. However, Bedford and Picker- ing - report after ten years' work that "Summer pruning, shaping, or pinching, seem to have been followed by no good results in the case of our trees, rather the reverse; and we should not, therefore, recommend such treatment." Dickens ^ reports a successful use of summer pruning 1 Gardener's Chronicle. 3d Series, Vol. 41, pp. 400-40.3; 406-407. 1907. Jour. Royal Hort. Soc, Vol. 33, Part 2, pp. 487-499. 1908. ^Woburn Expt. Fruit Farm, 5th Rcpt. 1905. » Dickens, A. Kans. Agr. Exp. Sta. Bull. 136. 1906. 100 POMOLOGY with ten-year-old apple trees that had not previously fruited. The extent of the results reported, however, are scarcely sufficient to justify the practice. Batchelor and Goodspeed ^ conducted pruning inves- tigations with the Jonathan and Gano apples. The trees were five j^ears old when the work started and it was con- tinued for four years. The winter-pruned trees averaged 1055 pounds to a tree for the four years as compared with 937 pounds from the summer-pruned trees, or a loss for the period of 257 boxes to the acre. Thus the summer pruning resulted in less fruit rather than more in this experiment, but whether the reduction is due to a lessened area of fruit- bearing wood removed by the sununer pruning, or to an actual depression of fruit-bud formation is not clear. Drinkard,- working with dwarf apple trees, found that: "Summer pruning of branches of the tree the latter part of June, when fruit-buds normally begin to show differentia- tion, checked wood growth the year in which the pruning was done, and greatly stimulated the formation of fruit- buds, as was shown by the bloom and crop of fruit the fol- lowing year." The foliage of these trees was reduced 50 per cent by the pruning and as a result the "trees made very short growth in annual shoots." Summer pruning has been advocated by Lewis for west- ern conditions, for young trees of non-bearing age in order to produce a development of laterals and to gain practically one season by the operation.^ The pinching or pruning should be done rather early in the season, or as soon as the rampant growth can be observed, which will be about the mid- dle of June under Oregon conditions. The pruning would 1 Batchelor, L. D., and W. E. Goodspeed. Utah Agr. Exp. Sta. Bull. 140. 1915. 2 Drinkard, A. W. Jr. Va. Agr. Exp. Sta. Tech. Bull. 5. 1915. 3 Ore. Agr. Exp. Sta. Bull. 130. 1915. PRUNING 101 be much the same as for the following sprhig, althougli the trees may also need some thinning-out again and perhaps some cutting back the following season at the time of dor- mant pruning. The object of summer pruning for these young trees is to balance up the tree and to avoid heavy dor- mant pruning rather than to induce fruitfulness. Trees just reaching bearing age (four to seven years) are sometimes sunnner-pruned to induce fruitfulness and hence the time for the operation is later in the season, about the middle of July, or when the terminal bud begins to form. The cutting is again made where it is desired to force out new laterals and has a tendency on some varieties to bring about fruiting the following season. When this work is done properly, it is claimed that veiy little secondaiy growth will take place and practically no devitalizing effect will result to the trees, as is often the case under the conditions of the East. Vincent ^ reports that in a four years ' experiment in Idaho with summer pruning, the results are not entirely consist- ent. With Wagener the increase in yield amounted to HI per cent, with the Grimes 52.8, Jonathan 2.4, and Rome 1.6 per cent. The color of the fruit from the summer-pruned trees was superior. 1 Vincent, C. C. Idaho Agr. Exp. Sta. Bull. 84. 1915. CHAPTER VI THE THINNING OF FRUIT Thinning of fruit is an established orchard practice at the present time. It has long since passed the experimental stage. However, many successful commercial growers do not include it among their operations because its necessity has not been so apparent as has that of pruning or spraying. The western growers have been pioneers in this work from a commercial standpoint probably because their practice of packing fruit in small packages, notably the standard box, has made thinning not only necessary but profitable. The present tendency is for all fruit-producing states to have a packing and grading law, and when this is accomplished the thinning of fruit will doubtless become still more general. 87. Definition. — By thinning is meant the removal of a portion of the crop of fruit from the trees shortly after the June drop (/. e., soon after it has set) to prevent over- bearing. 88. History of thinning. — The practice of thinning fruit is by no means modern, but like many other agricultural operations, no definite time or place seems recorded as its origin. The pomological writers for many years have men- tioned it as desirable and have urged its use. In his "Trea- tise of Fruit Trees" published in London (1768), Thomas Hitt says, "When there is too great a quantity of fruit suffered to remain upon any part of a tree, it is not so good as if there were only a proper quantity left on; and some- times a tree becomes weak by bearing too plentifully. . . . "Fruits are thinned the best either with a very narrow- 102 THE THINNING OF FRUIT 103 pointed penknife or scissors ; for by nipping them off with the thumb and forefinger, those designed to be left on are often displaced, as also the young branches and leaves .... "Though I advise to thin fruit at different times, yet it should not be done later than the month of May; for if they are suffered to grow pretty large they rob one another, and none should be left on so near together as to touch before they be full grown; for they are apt to throw each other off or at least to spoil their shapes. Besides, they never come to the size they would otherwise do, and large fruit when ripe is always the best flavored. ..." Many of the same ideas have been repeated in subsequent works on fruit-culture, some writers enlarging and elaborating on these views. Two or three points are practically always mentioned by the early as well as modern writers, such as: the value of the practice to increase the size and appearance of the fruit; as a means of bringing about annual bearing; and to prevent the breaking of trees from overbearing. 89. Philosophy of thinning. — The theory of thinning is very simple, a theory that is paralleled in many branches of agriculture. The farmer thins his corn, the gardener his carrots and beets, the florist disbuds his carnations, chrysan- themums, and many other plants, and the forester thins his stand of timber, all for the same general purpose of allowing the remaining plants or parts ample room and food for development, or in other words to relieve the struggle for existence. For the same reason the fruit-grower also removes a portion of his fruit when it sets too heavily. It is natural for every plant to reproduce itself, for two of the fundamental laws in plant and animal life are nutri- tion and reproduction. Fruit-trees, however, very often set a great many more fruits than the}^ can properly mature. This distributes the moisture and food materials in so many channels that it results in small and inferior fruit. In this 104 POMOLOGY connection must be considered the characteristics of certain varieties, for it is well known that some heavy bearers are not apparently injured by their large crops, and conversely some light bearers never so utilize their energies as to produce heavy yields. 90. Fruit production exhaustive.^ — It is an exhaustive process for plants to produce pollen and seeds. The more the tree can be relieved of seed production and not sacrifice the crop, the more it is helped to balance up its life processes, namely: wood growth, crop production, fruit- and leaf-bud formation, and the laying up of reserve materials. Green ^ has shown that asparagus plants which fruit do not produce as large 'Hips" for cutting in the spring as those that are barren. While this is not entirely relevant, it illustrates the principle involved : Table XVII ASPARAGUS.- -product from fifty plants each, male and female (after green) Product from fifty male plants Product from fifty female plants First period 10 days ounces 37 104 266 203 ounces 21 Second period, 10 days 68 164 154 610 407 "This shows a gain of the male over the female plants of seventy-six per cent for the first period and a fraction less than fifty per cent for the whole season. " 1 Green, W. J. Bull. Ohio Agr. Exp. Sta. Vol. Ill, No. 9, 1890, p. 242. THE THINNING OF FRUIT 105 Green ^ also suggests that the varieties of imperfect flowering strawberries are more productive than the perfect flowering sorts because of the latter's exhaustion in pollen production. Later- the Ohio Station reported as follows: "The average yield from each eighteen foot row of perfect varieties (139 varieties) was 5.47 quarts, and from each row of the same length of imperfect varieties (66 varieties) was 7.19 quarts. There are some high-yielding perfect flowered varieties, and some among the imperfect that give low yields; but it is generally recognized as a fact that the former, as a class, are less proHfic than the latter." Fletcher,^ however, states that while this probably is correct if applied to a grand average of all pistillate and staminate varieties, it is not true when individual varieties are considered. "For all practical purposes staminate and pistillate varieties arc equally prolific." So this evidence from other plants would seem to add weight to the theory that fruit production is an exhaustive process in the economy of the plant. 91. Dependence of fruit on foliage immediately surround- ing it. — The amount of elaborated food manufactured liy the tree is governed by the area of healthy foliage that it possesses. And, furtheraiore, each fruit depends largely on the leaves in rather close proximity to it. Therefore, because only one side of the tree or one branch is heavily loaded, it does not obviate the need of thinning that part. 92. Objects of thinning. — The objects of thinning fruit may be summarized as follows : 1. To increase the size, color, quality, and uniformity of the fruit. 1 Green, W. J. Bull. Ohio Agr. Exp. Sta., Vol. Ill, No. 7, 1890, p. 221. 2/6id., Bull. 236(1912). 3 Fletcher, S. W. Strawberry-Growing, p. 130. New York, 1917. 106 POMOLOGY 2. To prevent the breaking of the limbs. 3. To reduce disease and insect injury to the fruit. 4. To maintain the vigor of the trees. 5. To secure more regular bearing. 6. To decrease the labor of handling the crop. 93. To increase the size of the fruit. — Probably the greatest advantage of thinning is the increase in the size of the remaining fruits and this is well borne out by experi- mental evidence. In fact, practically all data are expressed in terms of percentage of large and small fruits from the thinned and unthinned trees, and the amount of each. It is true, of course, that the increase in size will depend on several factors, especially the amount of fruit which has set. It is seldom that a heavily laden tree will not show a marked increase in size of fruit, if it is thinned sufficiently early and enough is removed. Disappointment is likely to result if a grower has his first experience in thinning a tree that is carrying but a moderate crop. The age and vigor of the trees are also important factors determining the amount of fruit an individual tree can carry through to maturity. The varietal factor again plays an important part, as does the cultural treatment. The following tables are fairly representative of the influence of thinning apples on the size of the remaining fruit: THE THINNING OF FRUIT 107 Table XVIII THINNING APPLES All imperfect fruits were removed and all others thinned to not than four inches apart. Yield to a tree for three years (after beach) Treatment Barrel fruit No. 1 No. 2 Total Baldwin Thinned. . Bu. 39 2 Per cent 75 . 5 ()0.9 80.8 79.4 Bu. 12.7 24.1 7.2 7.3 Per cent 24.5 39.1 19.2 20.0 Bu. 51 9 Unthinned Greening Thinned 37.5 30.2 28.1 01.6 37 4 Unthinned 35.4 Table XIX THINNING apples IN AN OHIO ORCHARD. (after ballou) ROME BEAUTY Tree No. 1. Unthinned. Number of apples set and matured on tree 4376 No. of apples picked Weight, pounds Bushels Per- centage of grade Firsts 1750 1950 670 488 390 134 9.76 7.8 2.68 48 22 Seconds Defective and small 38.53 13.24 4376 1012 20.24 108 POMOLOGY Table XIX — Continued ROME BEAUTY Tree No. 2. Thinned to 8 inches apart. Number of apples set 4178; number taken off, 771 No. of apples picked Weight, pounds Bushels Per- centage of grade Firsts 2656 445 306 3407 830 99 68 16.6 1.98 1.36 S3 24 Seconds Defective and small 9.92 6.82 997 19.94 Table XX thinning apples in a new hampshire orchard. baldwin (after gourley) Original number of apples After thinning Per cent No.l Per cent No. 2 Per cent culls 1. Unthinned tree. . . . 2. Thinned tree 3. Thinned tree 4. Thinned tree 5. Thinned tree 6. Unthinned tree .... Average for unthinned 4055 3453 3350 3130 3895 2938 2415 2061 1760 2277 16 58 82 79 71 48 32 72 78 • 40 16 19 26 43 60 25 4 1 .6 1 1 7 5 Average for thinned trees —1 Auchter - says, "In thinning bearing Ben Davis trees in 1914 it was found that the apples on the unthinned trees were 2 Auchter, E. C. W. Va. Agr. Exp. Sta. Bull. 162. 1917. THE THINNING OF FRUIT 109 so small that 65.7 per cent of the crop was less than 23^ inches in diameter, 34.1 per cent of the crop was between 2}4: and 2^ inches and practically none was above 2^ inches. In contrast to this, the crop from those trees thinned six to seven inches apart had only 13.6 per cent of the fruit less than 23<4 inches, while 71.6 per cent was between 23-i and 2% inches, and 14.6 per cent was more than 2% inches. Although there were nearly 2000 more apples per tree on the unthinned trees at picking time, still due to their small size, they produced less than one-half as great a total market- able quantity." The following average results of several experiments on thinning apples are tabulated and may be considered as fairly representative of the increase in size from thinning: 10 experiments, 100 trees. 8 varieties, Baldwin, Greening, Stark, Ben Davis, Rambo, Rome, Winesap, Jonathan. 5 states. Nova Scotia, New Hampshire, New York, Ohio, Colorado. Table XXI EFFECT OF THINNING ON SIZE OF FRUIT Per cent No. 1 Per cent No. 2 Per cent Culls Unthinned Thinned 43 71 Unthinned 45 Thinned 23 Unthinned 6 Thinned 3 94. Thinning to improve color. — ^An increase in color is one of the usual results of thinning. In most experiments the color of the fruits (especially on peaches and apples) has been increased, although it must be seen to be appreciated. In an unpubHshed experiment conducted by the author with Grimes Golden apples, the size was not so materially affected as was the color. Practically every apple was a fancy "box" grade, having developed a rich golden color and a 110 POMOLOGY pink blush on one cheek, as compared with the check trees on which nearly all the fruit was a little undersized, of a greenish color, and had no evidence of the pink check. 95. Quality improved by thinning. — Quality is more difficult to define and tabulate, but the unanimous report of experimenters and orchardists is that the enlarged and highly colored fruit is better in quality than the smaller and poorer specimens. 96. Thinning to prevent breaking of limbs. — No one who has been observing orchards for a period of years has failed to notice the appalling breaking of limbs as a result of over- bearing. Some trees and even orchards are so ruined after some exceptionally heavy crop that they never regain in form and symmetry what they lose in one season from lack of proper pruning and thinning. The use of props is also much reduced or entirely obviated in an orchard that has been well thinned. 97. Thinning to reduce disease and insect injury. — In thinning the fruit, any that have been injured by insect stings or early attacks of fungus, as well as ill shaped speci- mens, would be removed. In the case of peaches and plums, the amount of such disease as brown-rot is much reduced when the fruit does not hang so close together and also the spray solutions can better cover the entire surface of each specimen. In the case of the apple, there would be less opportunity for the second brood codhn-moth to find an entrance if no two fruits touch. Thus the instances might 1)6 multiplied of greater injury from insect and disease if the fruit is not thinned. 98. Thinning to maintain the vigor of the trees. — It is difficult to present experimental evidence directly on this problem, but it has been the experience and observation of fruit-growers for many years that a tree (especially a young one) which bears an excessive crop of fruit may be perma- THE THINNING OF FRUIT 111 nently injured as a result or may at least require several years again to bear fruit in quantity. This difficulty may be obviated by nature through a lack of setting of the blossoms and indeed this is connnon, notably with peach trees just reaching the bearing age. However, when a natural abscis- sion does not take place, it is desirable to thin the fruit. It would probably be difficult to cite a season when the above principle was so evident as after the winter of 1917- 18. Winter-injury was common throughout the northern poi-tions of the country and the testimony of a vast number of growers was that the trees that bore heavily in 1917 suffered the greatest injury from the following winter and many were killed outright. Hence not only young but also mature trees may have their vigor maintained by judicious and sj^stematic thinning. 99. Thinning to secure more regular bearing applies more particularly to the poach than to the other tree-fruits. In experiments with mature apple trees, the results have usually been negative. This is explained on the grounds that the fruit-ljuds have started to differentiate as such before the thinning and hence it can have no effect. Writers have, however, often urged that annual bearing was one of the greatest advantages to l)e gained by thinning. This seems most reasonable, and the teachings of plant physiology woukl give it some support. Just why the peach should be so responsive in this direction and the apple be unaffected is not clear unless it is due to a longer period of fruit-bud formation and type of bearing. Walker reports as follows in regard to the peach: ^ ''The trees on which the first lot (which had been thinned) grew had a strong set of fruit buds for the next season's crop; the trees on which the second lot (unthinned) grew were scarcely able to live." 1 Walker, E. Ark. Agr. Exp. Sta. Bull. 79. 1903. 112 POMOLOGY The same observation is made by Gould ^ who says: "The effect on the tree (peach) of wise thinning extends far beyond the current crop, for it is a mortgage on future crops if the tree is seriously depleted by overbearing." With the apple, however, the evidence is not satisfactory and usually the statements are general and without sufficient experimental evidence. It is possible that thinning younger trees may promote annual bearing, but there is no satisfac- tory evidence to present on this point. It is probable that growers may be inclined to credit one practice with the results obtained when several factors are involved, and thus 'prejudiced statements arise. Downing's writings ranked high in the pomological litera- ture of a half a century ago, and his statement may be cited as fairly typical of others. "When half the fruit is thinned out in a young state, leaving only a moderate crop, the apple, like other fruit trees, will bear every year, as it will also if the soil is kept in high condition. The bearing year of an apple tree, or a whole orchard, may be changed by picking off the fruit when the trees show good crops, allowing it to remain only in the alternate seasons which we wish to make the bearing year." - Against this statement of Downing the work of Beach ^ must be considered, in which after four years' investigation he says, "It will not, on mature, well established trees, materially influence the regularity of production or the amount of fruit setting for subsequent crops. The profit, if there be any, must come from the crop thinned." Also, Auchter ^ after five years' work on this subject, "while final 1 Gould, H. P. Peach-Growing, p. 299, New York, 1918. Rural Science Series. 2 Downing, A. J. Fruits and Fruit Trees of America, p. 63. 1900. ^ Beach, S. A. Loco cit. * Auchter, E. C. Loco cit. THE THINNING OF FRUIT 113 conclusions are not attempted, results indicate that thinning does not influence subsequent crops nor cause trees, naturally biennial in bearing habit, to bear a crop each year." The author also has reported that "Trees which were thinned to twelve inches apart produced no more blossoms the following spring than did the unthinned trees which had borne an excessive crop." ^ 100. Thinning to decrease the labor of handling exces- sive crops of small fruit is of considerable consequence from a commercial standpoint. The work of picking and handling a crop in which a considerable proportion of the fruit is small or below a standard merchantable grade is not economical. That this labor can be appreciably reduced is established in the foregoing paragraj^hs. 101. The effect of thinning on the total crop. — As in- dicated by data previously cited, not infrequently the total crop from a tree from which half the fruit has been removed will be as great as from an unthinned tree carrying practically the same amount of fruit as was originally on the thinned one. This of course is possible because of the increased size of the remaining fruit. Often the crop is reduced in total yield and in some cases it results in actual loss. Perhaps the experience of the workman is the only safeguard in deter- mining how much fruit should be removed, and even he will err in judgment at times. Excerpts from experiments conducted in several states show the range of variation in this regard and fairly repre- sent the situation. It is presumed that the trees in any given experiment are similar in size and amount of total fruit originally set. 1 Gourley, J. H. N. H. Agr. Exp. Sta. Tech. BuU. 9. 1915. 114 POMOLOGY Table XXII RELATION OF THINNING VERSUS NON-THINNING TO THE TOTAL CROP Average a tree, lbs. Colo. Unthinned 2 trees 843 Thinned 8 trees 610 Utah Unthinned 4 trees 254 Thinned 4 trees 269 Ohio Unthinned 6 trees 924 Thinned 9 trees 954 W. Va. Unthinned 3 trees (young) 159 Thinned 10 trees (young) 116 Unthinned 1 tree 664 Thinned 1 tree 648 Unthinned 1 tree 670 Thinned 1 tree 468 Unthinned 1 tree 534 Thinned 1 tree 528 Average unthinned trees 578 lbs. Average thinned trees 513 " The average difference in these particular experiments is 65 pounds or about 13^ bushels to a tree in favor of the unthinned tree. While no set of figures could be accepted as representing the exact relation of thinning to the total crop, as no two experiments would be alike since so many factors are involved, yet they are indicative of what might be ex- pected. Although these figures show that the total crop may be somewhat reduced, they must be viewed in the light of the discussion under size of fruit and it must be realized that the economic value of the crop is very likely to be higher from the thinned trees. 102. When to thin. — The time for thinning will vary with the variety, season, latitude, and possibly other factors. THE THINNING OF FRUIT 115 As a rule, the sooner the thinning is done after the June drop, the better will be the results. The apples will be nearly an inch in diameter at that time, some varieties larger and some smaller. This will be the middle of June with peaches and plums, and the last of June to the middle of July (depending on the locality), with apples and pears. When the season is late, it is advisable to begin the work before the June drop is quite over or it will be delayed until late in July in the northern latitudes. When the work is left until late in the season, the beneficial results are often reduced. The reasons for thinning about the time of June drop are : 1. The size will be increased to a greater extent. 2. The development of seeds and " pits" drains the energies of the tree. 3. If done before that time, it is probable that many fruits which were thinned would not have set, thus wasting labor and causing too great a distance be- tween fruits after the natural abscission has taken place. It is the experience of most growers that if thinning is delayed until late in the season, the size of fruit is not per- ceptibly increased. The author has seen distinct evidences of this on several occasions, especially with the apple. In order to establish that early thinning lessens the drain on the resources of the tree, a chemical analysis of the seeds and pits early in the season and later must be considered. As already referred to in Chapter I, Bigelow and Gore ^ report on the composition of the Triumph, Rivers, Early Crawford, Elberta, Heath, and Smock varieties of the peach, at three periods in the development of the fruit. First, immediately after the time of the June drop; second, when the stone had hardened; and third, when the fruit was • Bigelow, W. D., and H. C, Gore. U. S. Dept. Agr. Bur. Chem. Bull. 97. 1905. 116 POMOLOGY ripe for picking. The average composition of these varieties is shown in the following table : Table XXIII AVERAGE COMPOSITION OF SIX VARIETIES OF PEACHES AT DIFFERENT STAGES OF GROWTH (AFTER BIGELOW AND GORE) State of growth Weight of Total solids in Peach Flesh Stone Kernel Flesh Stone Kernel June drop Stone hardened. . Market ripe Grams 9.51 16.75 73.59 % 64.55 71.54 92.49 % 32.50 25.82 6.86 % 2.94 2.89 0.65 7o 14.77 16.97 14.04 % 9.37 27.35 66.94 % 6.89 7.54 44.78 Gould's ^ comments on this table interpret the problem in its relation to earl}^ thinning: "The most important feature of this table from the standpoint of thinning is in showing the rapid rate of increase of the solids in the stones while passing from the June drop stage to the hardening stage. The first analyses of the stone-hardened stage were made June 23 and 28, depending on the variety. During the period of fifteen to twenty days, the percentage of solids in the stones nearly trebled. The fact is also brought out that though the average weight of the pit (stone and kernel combined) is only 7 per cent of the weight of the whole fruit, the total solids in the pits comprise more than 25 per cent of the total solids in the whole fruit. " It is well to observe also that solids in the flesh remained fairly constant throughout the development of the fruit, the variation ranging from a total of 14 to about 17 per cent, a difference of only 3 per cent, while the solids in the stones constantly increased from about 9.3 per cent at 1 Gould, H. P. Loco cit. '^vs^& «»**-^*»V' -^ -^^#:*^i^«^^^ Plate III. — a, Dwarf ajiplc trees trained in a horizontal cordon, es- palier pear trees on wall to rear, b, A tj-pe of central leader that could now be developed either into a two- or a three-story tree, c, An unpruned apple tree that has developed as a central leader; recently the top has been removed, d, A two-story tree with four branches at each scaffold; the leader may now be removed. THE THINNING OF FRUIT 117 the June drop period to nearly 67 per cent at the market ripe period. "These figures, therefore, furnish a scientific basis for early thiiming, also for the frequent observation that the development of a large number of pits makes a heavy de- mand for plant food." Experience dictates the item listed mider 3 and it re- quires no further explanation. Some . writers suggest that the trees should be thinned twice or thrice, the first time after the June drop, the second about the middle of August, and the third about three weeks before picking, because the operator is not likely to thin sufficiently the first time over the trees. Doubtless it will seem necessary, especially to the begimier, to go over the trees at least twice in order to secure best results, but this is not likely to be possible on large scale orcharding. With some early varieties such as the Yellow Transpar- ent, it may be desirable to allow all the fruits to develop for a while and gradually thin the crop by making several pick- ings. The apples can be sold when quite small as this va- riety is merchantable when only a third or half grown. 103. The June drop referred to above is a natural ab- scission of the fruit which occurs at the time the permanent fruits are setting. That is, many fruits will start to develop and later fall. The explanation usually offered for this oc- currence is that the fruit is imperfectly pollinated; or it has been injured by insect or fungus disease; or the struggle for existence that may operate against a portion of the fruits in a cluster. Often it is greatly increased by adverse weather conditions at bloom time. Usually the central blos- som in a cluster opens first and when the fruit is set remains on the tree. Peach- and plum-growers need no further evidence than they already possess that the curculio is responsible for a 118 POMOLOGY large part of the drop many seasons. If the larva works into the soft pit the fruit drops very soon, while if it enters only into the flesh the fruit may develop for a time and then show color as if ripening and drop to the ground. In some sections, the apple-scab fungus causes a serious non-setting of fruit and early dropping. The fungus girdles the tender stems and prevents the development of the crop. 104. How to thin. — In the operation of thinning the apple and pear, the surplus may be removed by holding the cluster or spur and carefully and quickly giving the fruit an upward twist. A special type of shears is on the market that is convenient in cutting the stems, but usually the op- erator prefers to thin by hand. With the plum and peach, the operation is still simpler — just pick off the surplus fruits with the thumb and forefinger. Rakes and poles sometimes used to remove the surplus are not to be recommended, al- though such an operation is much cheaper. The objection is that no discrimination can be made between good and poor fruits. Shaking the tree is also a poor way to accom- plish the desired results. The most outstanding warning that can be given is to avoid breaking the fruit-spurs. Va- rieties vary in the ease with which they are thinned. The Rome apple, for example, because of the long stems, can be removed very rapidly, while the York is difficult and slow to work because of the short stems and ease with which the spurs are broken. It should be recognized that considerable thimiing may result when the trees are pruned, but with such fruits as bear their entire crop from axillary buds, additional thin- ning must be practiced. 105. Distance to thin. — No definite rule can be given for the distance apart that fruit should be thinned. Usually apples should be from five to eight inches apart and peaches from four to six inches. Beach recommends that apples be THE THINNING OF FRUIT 119 thinned to three times the diameter of the largest fruits at maturity while Wickson suggests that two and a half times the diameter of the fruit desired would be the proper dis- tance. Herrick found it desirable to thin Winesap to nine or ten inches apart for the best results. Of course, the smaller the fruit, the more it should be thinned, and conversely the larger the fruit by nature the less it should be thinned, except to prevent the breaking of branches. In some regions, the recommendation is to remove all fruit from alternate spurs in order to bring about annual bearing. In all cases the thimiing should be uniform and the work thoroughly done as the operation progresses, to insure satisfactoiy results. 106. Cost of thinning versus returns. — The task of thinning a large orchard of mature trees when they have set a heavy crop of fruit seems formidable and the question naturally arises as to whether it will pay. However, if the cost is computed to a tree basis or to a still smaller unit, the barrel or box, it will not seem impracticable. It will de- pend, of course, largely on how the fruit is to be handled. The cost of thimiing reduces itself to a question of time since no particular apparatus is necessary, and this will depend on the size and shape of the tree, the variety, and the person doing the work. Since the factors are so variable in this regard, it is diffi- cult to average conditions, but the following cases are cited : New Hampshire. Trees 35 years old. Average 4^ hours to a tree in one case (4 trees). Average 2yi hours to a tree in another case (4 trees). New York. Average 33^^ hours to a tree (4 mature trees), Ohio. Trees 17 years old; 1% to 2^ hours to a tree. West Virginia. Middle-aged trees bearing 4 to 6 barrels to the tree. Average 2 to 3 hours to a tree. Colorado. Average a little less than 3 hours to a tree. 120 POMOLOGY Hence, if it requires from two to three hours to thin a tree, the cost can readily be computed. It is obviously unfair to charge all the cost against thin- ning, since the same apples would have to be picked in the fall and at a greater expense, and also it would require more handling of inferior fruit and greater grading expense than when thinning is practiced. 107. Thinning the peach. — Peach trees are much inclined to heavy bearing and, as a result, the trees often suffer dam- age and the fruit runs small. This heavy bearing is largely due to the nature of the fruiting wood. Although a part of the fruit-buds may be removed by pruning, many more fruits are frequently suffered to remain than the tree can properly mature. "There is perhaps no other operation concerning the desirability of which there is a inore complete oneness of opinion among peach-growers than in regard to thimiing when the trees are overloaded." ^ The principles involved in peach thinning are covered in the treatment preceding. Close ^ reports on thinning the peach with decided re- sults in increasing the size of the fruit. The trees were five years old (Elberta) and in vigorous condition. He classi- fies his thinning as follows: " Common thimiing means that at maturity the fruit should be four inches apart; 'me- dium' means six inches apart, and 'severe' eight inches apart when ripe." He also thinned part of the trees early and others late: 1 Gould, H. P. Loco cit. 2 Close, C. P. Ann. Rept. Del. Agr. Exp. Sta. 1902. p. 89. THE THINNING OF FRUIT 121 Table XXIV record of ripe fruit from thinned and unthinned trees (after close) Kind of thinning Fancy, ^ per cent Firsts,^ per cent 48 51 60 80 47 SO 73 49 Early common Early medium 47 39 20 Late common Late medium Late severe 50 20 26 108. Thinning the plum. — Experience has differed in the advantages secured by thinning plums. In some places very good results were obtained in increasing the size of the fruit, while in others the increase was almost nothing. Some varieties fruit so heavily, however, that it would be well to thin to prevent the trees from breaking and to re- duce disease and insect injuries. Garcia 's ^ work showed that definite results were ob- tained by thinning plums to six inches apart and to a less extent to three inches. The trees thinned to six inches pro- duced on the average 84.1 per cent of first-grade fruit, those to three inches 77.6 per cent, and the unthimied trees 50.5 per cent: ' Fancy, above 2J^ inches in diameter. 2 First grade, 21^ inches or slightly less in diameter. 3 Garcia, F. New Mexico Agr. Exp. Sta. Bull. 39. 1901. 122 POMOLOGY Table XXV THINNING THE PLUM (AFTER GARCIA) Name Distance thinned in inches Percentage of first-class fruit Percentage of second-class fruit Wild Goose. Clyman . Tragedy . Yellow Egg . 3 None 3 None 6 3 None 3 None 75.7 70.1 67.4 93.4 85.9 53.7 86.4 96.9 53.7 81.1 57.5 27.5 24.2 28.8 32.5 6.5 14. 46.2 13.5 3. 46.2 15.9 30.6 53. On the other hand, Powell reports on thinning trees of the Burbank and Poole's Pride varieties, neither of which was a financial success. It cost ten cents a tree to thin the former and fifteen cents for the latter. "There was some difference in the size of fruit in favor of the thinned trees (Poole's Pride), but the difference was surprisingly small. However, the unthinned trees suffered very heavily from broken branches the latter part of the summer which did not occur with the thinned trees. As far as the crop was concerned the thinning was not a financial success." 109. Thinning the pear. — Not many data are available on the thinning of pears, but there is no reason to suppose that they would not respond if the trees had set a heavy THE THINNING OF FRUIT 123 crop. Powell ^ records an experiment with Kieffer pears in whicli trees, eight years of age, were thinned. The trees had set full and the fruits were removed so that no two were closer than six inches. As a result, 83 per cent of the thimied pears and 61 per cent of the check pears were of the No. 1 grade. 110. Thinning the grape. — Husmann ^ says: "It will sometimes be necessaiy to thin the grape, in order to more thoroughly develop the remaining bunches. The best thinning is the reduction of bunches and bearing shoots, at the first sunnner-pruning. If the nmnber of bunches on each fruit-bearing branch is reduced to two, it will do no injury, but make them so much more heavy and perfect." Bioletti ^ reconnnends thinning the grape in California as follows: "This excessive compactness can be pre- vented by thinning before the berries are one-third grown. Thinning, moreover, increases the size of the berries, hastens ripening, promotes coloring, and lessens some forms of sunburn. . . .The bunches are thinned at any time after the berries have set and before they have reached one-third their mature size. No bunches are removed, but only a certain proportion of the berries of each bunch. The number of lierries to be removed will depend upon how compact the unthhmed bunches usually become. In general it will vary from one-third to one-half of the total number. ..." This, it will be noted, refers to the European grape (Vitis vinifem) as grown in California, and the same recommenda- tions follow when V. vim f era is grown under glass in the East. > PoweU, G. H. Del. Agr. Exp. Sta. 12th Ann. Rept. 1900. p. 140. - Husmann, George. American Grape Growing and Wine Making. 1883. 3 Bioletti, F. T. Stand. Cyc. of Hort. III. p. 1385. CHAPTER VII ORCHARD SOILS Students of every phase of plant production, from, the extreme specialist in the greenhouse to the extensive grower of field crops, find a common interest in a study and under- standing of the soil. The most casual observation shows that soils vary in their nature or physical make-up and that plants flourish differently on the types. Researches during the past quarter of a century have added greatly to the knowledge of this subject and have opened up numer- ous new phases which must be considered by the student of soil science. It is not possible nor desirable, however, to enter into a full discussion of the properties of soils in this connection, but a brief outline of the types that commonly occur in the fruit regions should be reviewed. 111. Factors involved. — It is of course true that several factors must enter into consideration when selecting an orchard site. The location of the land as regards market conditions is of such great practical importance that a less valuable soil may be chosen in order to meet this re- quirement. Also the elevation in order to obviate frosts must be considered. An otherwise good slope may be so "seepy " owing to the geological formation that its use for orcharding is prohibitive without drainage. Also the pre- vious treatment of the land and the supply of humus and calcareous material may greatly affect the desirability of the land for fruit-growing. Aside from these features, how- ever, the mechanical or physical make-up of the soil is fundamental and worthy of careful study. Fortunately 124 ORCHARD SOILS 125 most fruit-trees will flourish over a rather wide range of soil types but some are better than others and some types are to be avoided entirely. The classification of soils accord- ing to the usual standard should, therefore, be considered first. 112. Soil defined. — Soil has been described as "the broken and weathered fragments of rock that cover in a thin layer the solid part of the earth and that furnish the foothold and, in part, the sustenance for plant life." ^ An understanding of the soil has involved a many-sided and complex investigation, for soils vaiy in an almost infinite number of ways and the adaptation of various kinds of plants to a given soil is far from constant. These conditions involve on the student of pomology a necessity for study of soil conditions as a basis for orchard production. 113. Soil classification. — As regards origin, soils are classed as either "sedentary " or "transported," depending on their geological histoiy. Soils are composed of minute particles of the various minerals of which the rocks of the earth are made up and the fineness with which they are ground, together with the proportionate mixture of these particles, gives a basis for classification. The method of arriving at this information is called a mechanical analysis. Four general groups of soil particles are recognized in agriculture as a basis of classification: sand, silt, clay, and humus. The size of the particles composing each of these series has been standardized by the United States Bureau of Soils as follows: Coarse sand 1/25 to 1/50 of an inch in diameter. Medium sand 1/50 to l/lOO " " " " Fine sand l/lOO to 1/250 " " " " Very fine sand 1/250 to 1/500 " " " " 1 Lyon, Fippin, Buckman. Soils, Their Properties and Manage- ment. New York, 1915. Rural Text-Book Series. 126 POMOLOGY Silt 1/500 to 1/2000 of an inch in diameter. Fine silt 1/2000 to 1/5000 " " '' " Clay 1/5000 to 1/250,000 '' " " " Sand is a valuable component of an orchard soil, although in itself it does not contain plant-food, since the sand par- ticles are largely quartz which weathers very slowly. It is of value because it lightens the soil, gives it natural drainage and has a tendency to make it warm. Clay is composed of very small particles, microscopic in size, and forms to a considerable extent the body of the soil. It is derived from various rocks and carries considerable of the mineral elements of plant-food. The colloids of the soil, which have recently received considerable attention, are associated with the finer clay particles. If clay is present in abundance, the soil will diy badly, shrink, and crack during very dry periods. On the other hand, clay causes the soil to be heavy and difficult to work when wet. Silt is much the same as clay in its character but the particles are intermediate in size between the sands and clay. A soil containing large amounts of silt is usually moderately rich, well adapted to the growing of the grain crops. Humus is a term given to decomposed vegetation and is of signal value in increasing the water-holding capacity of a soil and in causing it to be mellow and easy to work. This term is often used loosely or incorrectly, since vegetation plowed into the soil does not become humus until it is thoroughly decayed. The humic acids produced during decay contribute materially to the setting free of plant- food m'aterials in the soil. The term loam is used to describe a soil made up of a combination of sand, silt, and clay and it is further defined by the predominance of one or the other, as sandy loam, silt loam, or clay loam. The fruit-grower is interested in ORCHARD SOILS 127 the various loam soils, depending on the kind and variety of fruit grown. When the clay and silt particles predominate, only the fine grades of sand are usually present. If the silt grade is most abundant, the soil is a silt loam. If clay is greatest in amount, the soil is a clay loam. And if the exceedingly fine clay particles constitute more than 30 per cent of the soil mass, the type is a clay, the other 70 per cent being primarily of silt and very fine sand. A soil containing as nuich as 50 per cent clay is very "heavy," while those con- taining 60 to 70 per cent, as at Medford, Oregon, are ex- ceedingly stiff and hard to work.-^ 114. Soils and subsoils. — Most soils consist of a surface layer which is more fertile and usually darker colored than those l>ing beneath it. It may be veiy shallow or a foot to many feet in thickness. This surface soil determines the richness of the land, since the roots of most crops penetrate but little below it. Its fertility is due to the larger amounts of organic matter and the accumulation of the more readily available plant-foods, together with the activity of the beneficial soil flora. The subsoil, or that which Ues im- mediately beneath the surface, is of great importance to the fruit-grower and its character may vaiy from a sand to an impervious clay known as hardpan. The tree roots should have a wide range and penetrate the subsoil with ease as well as be free from standing water. While the subsoil must not be too well drained and devoid of plant- food, yet an open gravelly loam is usually considered best. If this does not obtain, it may be necessary to tile drain and plow or break up the subsoil for best results. The time to solve this problem or rather to avoid difficulty is when the orchard land is selected. The necessity for good depth of subsoil cannot be empha- 1 Wilder, H. J. U. S. Dept. Agr. Bull. 140. 1915. 128 POMOLOGY sized too strongly. This applies to every variety of apple or other tree-fruit and to every type of soil. Shallow soils should be assiduously avoided for orchard purposes wherever they occur. The presence of unbroken rock, large ledges, or hardpan within three feet of the surface should be con- sidered prohibitive. A soil depth of at least six feet should be insisted on wherever possible and an even greater depth is highly desirable. Most of the fruit sections in America contain some soils adapted to fruit-growing and others that give indifferent or poor results. Not infrequently the nature of the subsoil is the cause of the failures, for it must be remembered that trees are comparatively deep-rooted. While many sections might be taken for illustration, the extensive fruit region known as the "Ozarks" may be cited or a certain part of it which lies in the Arkansas Valley. Three types of subsoils are found through that general sec- tion. The good fruit subsoils vary from dark brown to a light reddish brown in color and are formed from broken granite. The deposit of this material varies from a few inches to several feet in depth, holds moisture well, but also drains well, and hence is good fruit land. Another type is a gravel subsoil which leaches badly and is likely to suffer in dry weather unless irrigated. A third type, on which many orchards have been inadvertently set, consists of the finest of soil particles and hence affords poor drainage. The roots seem unable to penetrate this soil and the trees suffer from droughts, root-rot, and widespread winter-injury. Inciden- tally, much of the difficulty can be avoided if alfalfa is planted, as the roots of this plant penetrate the subsoil. 115. Mechanical analysis of fruit soils. — The texture of a few typical fruit soils may now be exammed. No one type of soil is essential, since fortunately most fruit-trees have a fairly wide range of adaptability, but it will be seen ORCHARD SOILS 129 that in general the loam or gravelly soils when underlaid by- one not too heavy are frequently best adapted to fruit- growing. The kind and variety of fruit to be grown must be considered in determining whether the heavier or lighter types of soils should be selected. The light sandy soils are ideal to work, but they do not hold the soluble plant-foods so well and are likely to suffer in times of drought. In western New York, the apple soils are a little heavier than those in many other sections. The trees attain very large size and give high yields. In Niagara County, which l)roduces a large amount of fruit, the Dunkirk loam is typi- cal of the best fruit-soils. "Besides general crops, a very large acreage of this type (of soil) is devoted to fruit pro- duction. Throughout the county it (the Dunkirk loam) is distinguished by the prevalence of apple orchards. In the southern part the small area may almost universally be recognized by the presence and condition of the orchards. The trees have made a good growth and are regular in form and thrifty in appearance. While other types may pro- duce good apples, the opinion of a large number of apple buyers and packers is that apples grown on this soil are of superior flavor, color, and keeping quality. . . While the peach thrives on a soil much lighter than is suitable for the apple, it is said by a number of practical men that on this soil is obtained fruit superior in flavor, color, and keeping quality. Pears, plums, and quinces are grown and west of Lockport there is a large acreage of grapes."^ The following table gives the mechanical analysis of this soil: 1 U. S. Bureau SoUs. 1906. 130 POMOLOGY Table XXVI DUNKIRK LOAM, NIAGARA COUNTY, NEW YORK Fine gravel Coarse sand Medium snnd Fine sand Very fine sand Silt Clay Soil Subsoil 0.9 .0 4.2 1.7 3.3 1.4 6.4 5.5 13.5 4.3 52.9 54.9 18.4 32.1 In Ontario County, which is also in the fruit belt of west- ern New York, the best fruit is grown on the Ontario loam which is somewhat lighter and has the following mechanical analysis: Table XXVII ONTARIO LOAM, ONTARIO COUNTY, NEW YORK Fine gravel Coarse sand Medium- sand Fine sand Very fine sand Silt Clay Soil 1.0 1.1 3.0 4.0 4.5 5.4 12,8 14.5 14.6 19.0 47.5 39.6 16 1 Subsoil 16.3 Fort Valley is the center of the peach industry of Georgia and one of the best known peach sections of the coun- try. The soils best adapted to the production of this fruit are the Orangeburg sandy loam and the Orangeburg fine sandy loam. The fruit grown on these soils is superior to that on any of the other soils of that area. The latter is ranked as the best peach soil of the whole Gulf Coastal Plain region, owing to "the inherent characteristics of the soil itself and to the elevated and well drained posi- tion it normally occupies." Elberta is the variety typically grown. ORCHARD SOILS 131 Table XXVIII ORANGEBURG SANDY LOAM Fine gravel Coarse sand Medium sand Fine sand Very fine sand Silt Clatj Soil Subsoil 1.90 .52 6.90 3.42 6.68 4.44 27.10 21.86 40.40 29.56 10.28 9.00 6. 28 30.50 In comparison with the Ughter types, the very heavy dark soils of the Rogue River Valley near Medford, Oregon, on which the pear is being grown very extensively, should be considered. A number of types of soil occur in the valley and foothills which are adapted to the growing of pears and apples, the Phoenix clay adobe being one of the heavier kinds. Some of the most valuable orchards in the valley are on this soil. Table XXIX PHCENIX CLAY ADOBE Fine gravel Coarse sand Medium sand Fi7ie sand Very fine sand sat Clay Soil 0.9 2.4 2.2 4.1 5.7 21.4 63.1 This soil is 12 inches to six feet or more in depth, of a dark reddish brown to nearly black, sticky, and of a pronounced adobe structure. The soil in the Hood River (Oregon) district is much lighter and well adapted to apples. It is essentially a loam with a high percentage of very fine sand. The subsoil is much the same in character except in places where it be- comes very compact and not suited to orcharding. 132 POMOLOGY Table XXX HOOD SILT LOAM Fine gravel Coarse sand Medium sand Fine sand Very fine sand Silt Clay Soil 0.4 .1 2.4 .8 4.8 1.9 9.6 7.8 20.3 26.6 48.8 42.8 13.6 Subsoil 19.8 From these examples it will be seen that there is a rather wide range of fruit soils, although as a rule those which ap- proximate the following analysis are best adapted to most fruits : Per cent Aggregate of all sands 20-50 Silt 20-50 Clay 10-30 Hall and Russell give the following as an ideal fruit soil: Per cent Fine gravel 1.0 Coarse sand 6.8 Fine sand 42.0 Silt 23.3 Fine silt 7.3 Clay 10.9 116. Orchard soils. — Since an orchard soil is judged more from its mechanical make-up than from its chemical constitution, it may be well to define further the types best adapted to the several fruits. It is impossible to state within narrow limits just what may be termed an orchard soil. Indeed, perhaps a fourth or a third of the arable land of this country might be used with considerable success for orchard- ing if other factors were favorable. While analyses have been given of a few typical orchard soils, the list might be ORCHARD SOILS 133 greatl.y extended. In a very general way the following are usually requisites: (1) The soil should be sufficiently retentive of moisture so that the trees and crop will not suffer from lack of water throughout the growing season, or else irrigation should be available. (2) Fruit soils should usually be of a rather open nature so that ample drainage is provided; the texture being porous and friable. (3) The soil should not be low in organic matter. (4) Extremes of acidity and alkalinity should be avoided. (5) A depth of not less than six feet is highly desirable. The apple in general thrives on an open gravelly or light clay loam, although it succeeds on both heavy and quite light soils. Varieties differ in their requirements. Pears as a class prefer a heavier type of soil than the apple, but the "adobe" soils of southern Oregon represent an ex- treme rather than the usual type. On a heavy silt or clay loam they are at their best. The peach and cherry prefer a gravelly or heavy sandy loam, but in some sections the soil runs to a heavier type, even approaching a clay. The one requisite in all cases is good drainage. The domestica plums should be grown on a moderately rich loamy soil, and the salicina varieties on a somewhat lighter type. Much has been said in literature regarding the value of stony land for orchard purposes. This idea doubtless has its origin in the fact that well-drained soils are preferable and also that orchards are frequently successful on stony or rocky hillsides. There can be no virtue in such land other than the fact that an abundance of stones may give ample drainage and produce a loose type of soil and per- haps that a quantity of stones may serve as a mulch 134 POMOLOGY and conserve moisture. If a stony soil is selected, and it frequently is very satisfactory, it should be fertile and productive. 117. Chemical nature of fruit soils. — It is generally agreed that the mechanical make-up or texture of the soil is even more important than its fertility, since it is more difficult to change materially. However, it is a mistaken notion that the poorest soils should be selected for fruit- trees. This is true in spite of the fact that some kinds of fruit can usually be grown on the poorer soils with more success than most agricultural crops. It must also be rec- ognized that it is not entirely the percentage of mineral ele- ments m the soil in available form that makes for its fer- tility, but of great importance are the organic or humus content and its consequent soil flora together with a proper water relation and the absence of toxic materials or "unsan- itary" conditions. A chemical analysis of agricultural soils shows that the following elements are usually present: Silicon, aluminum, iron, phosphorus, calcium, magnesium, sodium, and potas- sium. Sulfur and chlorine are also found in small quan- tities. The nitrogen of the soil, which is so important to plant growth, is almost entirely in the form of organic mat- ter, although the soil-air contains small amounts of the at- mospheric nitrogen and also more or less ammonia. Nitro- gen occurs in mineral form in some places or is obtained by manufacture and purchased as nitrate of soda, potassium nitrate, and sulfate of anmionia for agricultural purposes. If the silicon, alummum, and sodium are eliminated as un- essential plant-foods, it leaves but 15 per cent of the soil as the source of the mineral constitutents of plants. 118. Soil color. — While the question of soil color may be over-emphasized, nevertheless certain characteristics are correlated with it. A dark color usually indicates the ORCHARD SOILS 135 presence of considerable percentage of organic material and this is usually associated with a rich soil. The Porters black loam of Virginia and the Phoenix adobe clay of Medford, Oregon, are examples of black soils espe- cially valuable for fruit-growing. Most fruit soils are not so dark in color. A reddish or yellowish soil usually indicates the presence of a large amount of oxidized iron. Some of the clays are very red as also are some of the soils derived from sandstone formation. Some of these are rich and productive, but ordinarily the red color would not indicate a well aerated and rich soil. 119. Limestone soils. — ^The question as to whether lime- stone soils are preferable for fruit is frequently raised. In order to form an opinion, the function of lime in the soil may be briefly reviewed. The function of lime in the soil is two-fold: (1) to prevent "sourness" and neutralize the aluminum com- pounds; and (2) to flocculate clay soils and tend to hold to- gether the sandy ones. Lime is looked on as a soil "im- prover" but it is of course a plant-food, for it is present in the ash of all plants and has a definite function to perform. However, it is rarely necessary to apply it for that purpose since all soils contain some calcium oxide. The exact per- centage of lime necessaiy varies with the nature of the soil and hence is relative. "The greater the clay percentage in a soil, the more lime carbonate it must contain in order to possess the advantages of a calcareous soil ; and that while in sandy lands lime growth may follow the presence of only .10 per cent of lime, in heavy clay soils not less than about .6 percent should be present to bring about the same re- sult." ^ The adaptation of plants to soils is a well-known phenom- enon and one which has frequently guided the agricultur- 1 Hilgard, E. W. Soils, p. 369. New York. 1906. 136 POMOLOGY ist in determining cultural requirements. Some plants are distinctly "lime-loving," such as most of the legumes (alfalfa, clovers), others are equally "acid-loving," as the Heath family and the chestnut (Castanea dentata), while others are cosmopolitan so far as the soil requirement is concerned. Among the fruits, the following are adapted to sour soils: blueberry, cranberry, strawberiy, blackbeny, and red and blackcap raspberries; while the currant is listed as injured by sour soils. ^ It would seem from observation that most fruit-trees, especially the apple, stand on middle ground so far as the lime requirement is concerned. They are neither distinctly hme- nor acid-loving (as these terms are commonly used) but flourish in both types until the dis- tinctly alkaline soils are reached on the one hand and the bog soils on the other. There is a popular belief that the apple does best on a limestone soil, but this would be diffi- cult to establish. The idea doubtless has its source in the fact that a limestone soil is frequently fertile and that many very fine orchards happen to be located in limestone dis- tricts. As a matter of fact, the non-calcareous soils are often preferred, even when either would be available. This is particularly true for the peach. Thus it is difficult to find evidence to answer this question in the affirmative since the eye does not detect any out- standing differences and, generally speaking, fruit-trees do as well in the non-calcareous regions as in the limestone areas. It would seem that Hilgard has put the matter too strongly so far as orchard fruits are concerned when he says, "The abundant fruiting of oaks on such lands as compared with the same species on non-calcareous soils is a matter of common note in the Mississippi Valley states; and the same is true of other trees, and of herbaceous plants as well." ^ 1 Lyon, Fippin, Buckman. Soils, p. 384. New York. 1915. ^Loco cit. p. 503. ORCHARD SOILS 137 There is also little evidence in this countiy to show that the application of lime to orchard land has any appreciable effect on the trees or the quality of the fruit. Its effect in increasing the growth of cover-crops on certain soils is quite another question and must at once be recognized. Indirectly this may bring about an increase in the growth and yield of the trees as is discussed in a later chapter. 120. Alkaline soils. — An alkali soil is one which is strongly impregnated with various salts, such as sulfate, chlorid, and carbonate of sodium, magnesium sulfate, cal- cium sulfate, calcium chlorid, and others. In some sections Table XXXI ALKALI IN SOILS OF ORCHARDS (AFTER LOUGHBRIDGE) Percentage in soil. Total Trees Condition sulfate carbonate chlorid Apples Red Bietigheimer Good .101 Duchess Poor .146 Jonathan Poor .041 Apricots Good .063 Affected .246 Peaches Best .070 Poor .106 Poor .160 Pears Best .131 Poor .261 Plums Very poor .165 138 POMOLOGY of the country, this type of soil constitutes a serious handi- cap to fruit-growing as well as to the production of other crops. Fruit plants vary considerably in their suscepti- bility to alkali conditions. Loughbridge ^ has made a care- ful study of this problem as shown in the table on page 137. "The (apple) tree is quite sensitive to alkali salts, and their effects on the foliage of the tree were veiy marked. The Jonathan seems to be more sensitive than the Duchess." The other fruits observed showed that when the trees are affected by alkali soil conditions, the newer Hmbs are more or less bare except for a tuft of leaves on the terminal, the leaves are small, yellowish or blackish in appearance, and the trees are barren of fruit. Observations and data cited show that "the suscepti- bility of the wine (grape) varies according to variety, and that while some are tolerant of very large amounts of car- bonate of soda and common salt, others succumb to the effect of far less of each." Hilgard ^ says, in discussing deciduous orchard trees, "Of these, strangely enough, the almond seems to resist best. The peach is more sensitive, the apricot does fairly well. Plum trees are nearly as resistant as peaches, but sometimes suddenly begin to fail when beginning to bear; the fruit appears normal on the outside for a time, but the pit fails to form, being sometimes flattened out like a piece of pasteboard; and the fruit fails to mature. Apples are rather sensitive; pears considerably less so, doing well even when the outside bark around the root crown is blackened by alkali. The olive is quite resistant, the fig less so." 121. Drainage. — As stated in paragraph 114, the natural drainage of the orchard land is of the greatest importance in maintaining a healthy and long-lived tree. If the soil is 1 Loughbridge, R. H. Calif. Agr. Exp. Sta. Bull. 133. 1901. 2 Calif. Agr. Exp. Sta. Bull. 128. 1900. ORCHARD SOILS 139 not naturally well drained, aitificial drainage may be very desirable if not necessaiy. While kinds and varieties of fruit will vary in their susceptibility to "wet feet," yet prac- tically all fruit-trees do poorly if the land is regularly soggy or springy during any extended period of the growing season. When artificial drainage is resorted to, the depth of the tiles and the distance apart the lines are placed will vary with the nature of the soil and the amount of water which must be drained. In a heavy soil the lines of tile are com- monly placed at 2 to 23^2 feet deep, and about 2 rods apart, while in a sandy or gravelly soil the depth would be greater — from 3 to 33^ feet. That is, the more open the soil the greater the distance the drainage water may be drawn. 122. Organic matter. — Probably any system of perma- nent agriculture should involve the returning to the soil of a plant residue or vegetative matter. This seems fundamental because investigation has entirely established the existence of a large soil flora and the necessity of bacterial action for the continuous availability of plant-food materials. A soil veiy low in organic matter is usually of poor tilth and sup- ports a stunted tree growth. Also the returning of vegeta- tion, especially legumes, to the soil maintains a much better supply of nitrates than when the soil receives "clean" til- lage or is entirely untilled. Many orchard soils are mate- rially improved in texture by plowing in a rank or heavy growing crop. This may be replaced after a few years by a nitrogenous crop. The student should appreciate, however, that it is often a long and expensive process to reconstruct a soil devoid of humus, or a heavy intractable clay into one which is well adapted to orcharding. From an economic standpoint, it is better to select soil that is already adapted to the crop to be grown and then by reasonable amendments maintain its fertility. 140 POMOLOGY 123. Adaptation of fruit to soil types. — As indicated in a foregoing paragraph, there is in nature a definite adap- tation of given plants to certain soils, some preferring an acid soil, others a calcareous one, some a wet soil, others an arid one. The different kinds of fruit-trees also manifest to a less degree some soil preferences, or rather they thrive better on one kind than on another. The knowledge in regard to varietal adaptation to soils is not extensive, although certain outstanding cases have been repeatedly observed. The work of Wilder ^ along this line is the most complete in American literature. The previous conception that the Baldwin apple thrives best on a rather light type of orchard land is confirmed by his observations. The subsoil should be somewhat heavier but not so clayey as to be termed stiff. The Rhode Island Greening, on the other hand, produces better fruit if the soil is of a heavy silty loam or light silty clay loam, under- lain by silty clay loam. The soil should be moderately rich in organic matter and retain sufficient moisture to be classed as a moist soil and yet must not be poorly drained. The "blushed" Greening is produced on soil which ap- proaches more nearly the Baldwin type. The Northern Spy is veiy exacting in regard to the type of soil on which it does best and the one suited to it seems to be a medium loam underlain by a heavy loam or light clay loam, i. e., a soil as heavy as can be selected without incurring danger of inferior drainage. Much the same type of soil is desirable for the Wagener. The heavier of the Baldwin soils is recommended for the Mcintosh but if experience is to be taken as a guide, this variety must be considered rather more cosmopolitan than many others, for it is successfully grown on soils ranging from rather light to fairly heavy and even on those which are not very well drained. Much the 1 See Wilder, H. J. Loco cit. ORCHARD SOILS 141 same is true of the Stayman. The Tompkins King, Graven- stein, and Ben Davis do well on an open-textured rather than a fine loam, with subsoil of the same or only slightly heavier texture. For peach varieties the following soil types have been suggested: Champion succeeds best on soils of only me- dium productivity, but they should be deep and well drained. Medium to heavy friable sandy loams, underlain by mate- rial not heavier than a friable loam and preferably a heavy sandy loam, are veiy desirable. Carman and Mountain Rose succeed best on soils somewhat less pervious than the Champion, yet deep and well drained. The Elberta and the Belle prefer stronger soils than the Carman and the Mountain Rose. Loams, silty loams, and silt loams, with subsoils of similar material seem best to meet these require- ments. For Late Crawford, a fairly strong soil, such as a light porous loam somewhat less retentive of moisture than the heaviest of the Elberta soils, is desirable. Some of the early varieties, such as Greensboro, are less sensitive to shallow soil conditions than the sorts mentioned above. CHAPTER VIII CULTURAL METHODS IN ORCHARDS The kinds of fruits vary in their requirements as regards culture, some bring tolerant of widely different methods while others are specific. Varieties also differ in this regard, some requiring thorough and annual cultivation while others may produce a satisfactory growth and yield with less stimulation. In general, however, it may be said that fruit-trees are vigorous and productive largely in proportion to the soil treatment that they receive. Young orchards in particular suffer readily from lack of good growing con- ditions and hence delayed bearing of commercial crops is the result. Older trees, while more tolerant of neglect, owing to the greater ramification of their root systems and also because of their greater reserve food materials will, nevertheless, usually respond readily to good soil treatment. Unfortunately, authorities do not entirely agree as to the best methods of orchard culture. Certainly there is no one best system for all orchards under all conditions. How- ever there are principles underlying the cultural problems which should guide the student in deciding what system to use. While the use of manures and artificial fertilizers is inti- mately related to cultural problems, a full discussion of them must be considered later, except as general statements require mention. 124. Systems of cultivation. — Broadly speaking, two general systems of cultivation are followed in orchard practice, one in which the land or a part of it is tilled and 142 CULTURAL METHODS IN ORCHARDS 143 the other in which the land remains permanently in sod. A number of variations of both these methods are in use. If a grower has achieved success with one or the other, he often becomes prejudiced against the other systems. 125. Terms defined. — Sod culture describes any system of soil management wherein the trees are grown in sod without tillage of any kind, or without mulching the trees with litter. The grass may remain without cutting or it may be cut and removed from the orchard or left lying on the ground. If the grass or litter is insufficient at least partially to kill out the growth beneath the trees, it must still be termed sod culture. This system, like all the fol- lowing, may or may not involve the use of manure or arti- ficial fertilizers and pasturing with stock. The grass mulch system consists in placing a mulch of litter (grass, straw, hay, corn-stalks, or other material) beneath the trees, usually extending it a little beyond the drip of the branches. As the trees become large, material must be brought in from outside the orchard in order properly to mulch them. A cleared or bare area should be maintained immediately about the tree trunks as a fire break and to lessen injury from rodents. Cleaii tillage involves the plowing or disking of the land in the late fall or spring and tilling at intervals of about two weeks throughout the early summer, usualty until the first or middle of July. After tillage is stopped, the ground lies bare until the following spring, hence no vegetation is turned into the soil. The tillage and cover-crops system is similar to the former, but in addition to the tillage a cover-crop is sown at the time of the last cultivation and the crop is plowed under in the late fall or spring. Instead of sowing a crop, the land may be allowed to grow up to weeds. Inter-cropping, which is often followed in young orchards, refers to the growing of any crop (usually a culti- vated one) between the tree rows for the purpose of harvest- 144 POMOLOGY ing it and thus utilizing more fully the land not yet occupied by the trees. The system of alternate-row cultivation is in use in some regions and involves the tillage and perhaps cropping of every other " land " or area between alternate rows of trees. 126. Sod culture. — In the first half or perhaps three- quarters of the nineteenth century, the prevailing prac- tice in this country was to grow fruit-trees in sod land and along fence-rows; especially was this true of the apple. This was before the western orchard sections had come into existence and before the rise of commercial orchard mg in the East. In the last quarter of the past century, the culti- vation of orchards, wherever possible, was advocated by the progressive growers. Both experiment and experience in this country prove that sod culture is the poorest way of handling an orchard, although there are some outstanding cases to the contrary.^ The chief objection to the sod system is that, on the average, fruit-trees do not thrive so well as when they are at least partially cultivated, as is shown by the growth of trees, color, size, and amount of foliage, and yield of fruit. This objection may be entirely or partially overcome, how- ever, by proper fertilization and mulching with litter. The reasons for these effects on the trees are discussed later. On the other hand, certain advantages of growing trees in grass land may be cited as follows: 1. It prevents the >vashing and erosion of the soil. This is not so true in New England and other northern sections, because the ground is likely to be frozen during the so-called "soft " weather in winter or early spring that occurs farther south. 1 The student should not confuse sod culture and grass mulch, for they are distinct systems if properly carried out, although it is not uncom- mon to find a mulch system soon degenerate into a sod culture, and thus they may be confusing. CULTURAL METHODS IN ORCHARDS 145 2. The color of the fruit is usually higher and, therefore, it has greater commercial value than when grown under cultivation. Not all varieties are affected alike, however, for some will develop a high color under tillage, 3. The land is in better condition for spring operations than when it has been plowed. This applies particularly to heav}^ soils which do not drain readily. Also there may be less winter-mjury in the sod orchard, 4. The dropped fruit is of higher market value. 5. Land too rocky to plow or to permit tillage may be ulitized by following some type of the sod system. 6. The expense of caring for the soil is reduced to little or nothing, in some cases only the loss of the land for pas- turage and many times not that, 127. Grass mulch. — This method of handling an orchard is an attempt to follow nature and allow litter to accumulate in increasing proportion beneath the trees and thus conserve moisture and add plant-food to the soil. It seems to have been worked out simultaneously by F, P, Vergon of Delaware, Ohio, and Grant Hitchings of Syracuse, New York. Both of their orchards are commercially successful and many have emulated the practice. As stated in the definition, the mulch system is limited to the practice of placing sufficient mulch about the trees partially or entirely to kill out the growth of grass beneath them. This would not include the practice of mowing the grass of the orchard and letting it lie where it falls, although a partial mulch is thus accumulated after a few years, but the grass still grows beneath the trees and thus the evil effects of it are not obviated. This latter system has been termed the "sod mulch" to distinguish it from grass mulch. After the mulch system has been maintained for a few years, the soil beneath the mulch becomes loose and friable, 146 POMOLOGY retains moisture, is cooler in summer and freezes less in winter, and nitrates may be more abundant than when trees are grown in sod, but this latter is not always true. The growth of the trees is usually vigorous, the foliage abundant, and the yield much improved as compared with sod-grown trees. Under most conditions, it is desirable to add artificial fertilizers or animal manures, but somethnes this does not appear necessary. It is usually desirable to plow the land before setting the trees. It may then be seeded down and the mulch system put in operation. When conditions will permit, it is still better to cultivate the orchard for four to six years. How- ever, some very successful orchards have been planted in grass land that had not been previously plowed for a nvunber of years and no ill effects appeared after the system had been followed for a long period of time. Its success under such conditions may be largely attributed to an abundant supply of moisture. The great difficulty is that neglect may result .and the orchard soon show ill effects, as indicated by sparser foliage, smaller and yellowish leaves, and small fruits. If faithfully prosecuted, however, it is a practical system of orchard management, and well adapted to many conditions. On hillsides that wash badly it is not desirable to plow much and yet the sod system is not desirable; hence the mulch finds a very desirable use. The same may be said of rocky land. Under many such conditions, it is not a question whether grass mulch is as good as cultivation but whether it is better than nothing. The mulch system is perhaps better adapted to the apple than other fruits, although the pear, quince, and small-fruits may be grown in this way. Under few conditions should the peach, cherry, or plum be so treated, as the results of tillage methods produce much better results and longer-lived trees. CULTURAL METHODS IN ORCHARDS 147 Among the precautions to be observed with mulched trees are: 1. Protection from mice, rabbits, and other rodents. The trees should be safeguarded by either a mechanical device or by means of a protective wash, but the former is much more reliable. Rodents are more likely to do damage in a mulch or sod orchard than in a cultivated one because of the harboring places. 2. Fire is another ever-present danger and provision should be made for firebreaks by having a bare space between the bole of the tree and the mulching material. On a young tree this area should be about a foot in radius and as the tree becomes older it should gradually be increased to three feet. A mound of coal cinders about the tree is also advis- able for this same purpose. 128. Production of mulch material. — One of the problems in a large grass mulch orchard is to secure sufficient material for mulching. As much as possible is secured in the orchard, but as the trees become older the amount available becomes less. In some sections oats and wheat stubble is mowed about two or three weeks following the cutting of the grain and in this way a large amount of material is secured. Others procure hay, straw, or the like for the purpose. One of the striking results secured by the Ohio Experi- ment Station ^ was the effect of fertilizers on the increased growth of grass in the orchard, which solved the mulch prob- lem. It was found that when acid phosphate was used, alone or in combination with potash, a striking increase in growth of the clovers resulted without any seeding whatever. When nitrogen was used alone or in combination, the clovers were crowded out by the timothy, blue-grass, red-top, and in some cases orchard-grass, which took possession of the land. iBallou, F. H. Ohio Agr. Exp. Sta. Bull. 301. 1916. Also Bull 339. 1920. p. 16. .4 148 ^5 5^ POMOLOGY (^f^p^SJgSrVI.) The following figures show the results ob- iea*m one orchard: 1^» Table XXXII RESULTS OF FERTILIZERS ON YIELD OF MULCH (AFTER BALLOU) Annual fertilizer treatment to an acre Yield Kind of grass Acid phosphate, 350 lbs lbs. 2,716 2,884 3,458 840 Acid phosphate, 350 lbs. ; muriate of potash, 175 lbs Red clover Acid phosphate, 350 lbs. ; muriate of potash, 175 lbs. ; nitrate of soda, 350 lbs Timothy, red- top, blue-grass, orchard-grass. Poverty-grass, weeds Unfertilized 129. Clean cultivation has never been widely used in the eastern United States, but in sections of the Northwest and in California it has been followed extensively. The danger of clean tillage seems to be in its ultimate effect on the soil itself. Especially is this true in sections in which there is a long growing season and the summer sun is intense.^ In the West it has been found that shade or cover-crops are desirable to shade the ground, thus protecting the soil flora and also maintaining the organic matter in the soil. While this system may and often does give satisfactory results for a period of years, it is likely to end in a premature decline of the trees and a decrease in size of the fruit. This would depend on the climate, the nature of the soil, and its fertility. 130. Tillage and cover-crop system. — From the stand- point of growth and yield of the trees, this system doubtless ' Paddock, W., and O. B. Whipple. Fruit-Growing in Arid Regions. New York. 1910. Ch. 11. CULTURAL METHODS IN ORCHARDS 149 stands preeminent for most orchard lands in this country. Except for economic reasons or because of topography of land or nature of its surface, it would usually be safe to follow this practice. While the chief benefits of tillage are to the soil itself, yet certain orchard pests are better controlled when grass or weeds do not occupy the land between the trees. Rodents and some of the injurious diseases and insects are less prevalent in a cultivated orchard, for the stirring of the ground desti'oys their natural harboring places. Weeds like- wise are kept under control, avoiding a loss of soil-moisture and plant -food materials to the trees. Tillage benefits the soil for orchard production in the following ways: 1. Maintains a better medium for the more desirable soil flora. 2. Increases nitrification. 3. Makes more available the plant-food materials of the soil. 4. Creates and preserves a surface mulch which conserves moisture.^ 131. Cover-crops. — This term was first used in this con- nection by L. H. Bailey in 1893 in Bulletin 61 of the New York (Coraell) Experiment Station. It has its origin from the fact that such crops are planted in middle or late sum- mer and are designed to make a cover over the land as well as a winter protection and to recover from the soil surplus moisture, as well as readily available plant-food materials and thus augment the maturity of the trees; also to pro- duce on the land itself a green-manure crop for main- taining fertility. The value of cover-crops in an orchard has been ques- tioned by some authorities on the grounds that no special benefit could be observed where they had been used. This 1 See also Bailey, L. H. Principles of Fruit-Growing. 20th Ed. p. 76. 1915. 150 POMOLOGY is one of the oldest practices in agriculture and it would in- deed be unfortunate to advocate the discontinuance of it unless there is adequate data to warrant the position. This the author beUeves is not the case, but rather that in the past few years it has been demonstrated beyond question that the practice is valuable both in the orchard and on the farm. To test the soil for the presence of organic matter (carbon) and to find an immaterial gain where abundant organic matter has been returned to the soil for a long pe- riod of time is hardly sufficient evidence on which to rest the case. It is of more value to the orchardist to know that where clean tillage has been followed in both citrus and de- ciduous orchards, the soil failed properly to support the trees within a relatively short time. When cover-crops were again included in the orchard management, the trees be- came vigorous and productive, even without the use of fer- tilizers. As is pointed out elsewhere, the hotter the climate and the longer the season, the quicker will the humus and also- the nitrogen disappear from the soil through tillage methods. True, there may not be sufficient material raised to main- tain an increasing ratio of organic matter as the trees be- come mature and shade a large portion of the ground. Then outside material may be resorted to, to supplement the loss. Hence the present teaching must be that abundant cover- crops are the safest way of preventing depletion of the soil where tillage methods are followed. 132. Nitrification. — The student should not confuse the two groups of bacteria that have to do with the nitrogen transformations in the soil. Where legumes are grown, the symbiotic organisms living in the nodules on the roots fix nitrogen of the soil-air and leave it behind in combined forms in their remains and in the tissues of the host. Among the organisms concerned in the decay of legumes as well as of other plants are those which break down the complex CULTURAL METHODS IN ORCHARDS 151 nitrogen compounds and change the nitrogen to avaihible forms. This process is known as nitrification, and the nitro- gen which the legume organisms took from the air is not available to other plants until these nitrifying organisms have had an opportunity to do their work. Incidentally it should be mentioned that there are other groups of ni- trogen-fixing organisms in the soil capable of taking nitrogen from the soil-air in considerable quantities when supplied Nitrogen as Nifrate Nitrogen as /Immcm/a \__Nifragen as 1 Part of Plant Nitrogen as Organic Matter Fig. 26. — A graphic representation of the cycle of nitrogen through the plant and the soil. with an abundance of phosphate, limestone, and organic matter. These organisms are not related to legumes but are present in all normal soils. The nitrogen left be- hind in their bodies also becomes available to plants in the process of nitrification. The nitrification process is graph- ically illustrated in Fig. 26. 133. Value of cover-crops in California.— In semi-arid regions, such as are found within the agricultural section of California, there is a notable deficiency in the organic mat- 152 POMOLOGY ter of the soil, and, as has ah-eady been pointed out, where there is a lack of organic matter there is also likely to be a lack of nitrogen. Under those conditions, legumes proved to be far superior for green-manures as evidenced by their effect on the succeeding crops. The yield of a number of crops following legume green-manures when compared with those following non-legumes showed the following in- creases: An average increase with potatoes of 39 per cent; with com, 45; with cabbage, 44; with sugar-beets, 43 per cent, respectively. Legumes alone gave as good or better results than non-leguminous green-manure crops plus an annual application of 540 pounds of nitrate of soda to the acre. Of more direct interest in this connection is the measur- able effect of green-manuring on citrus fruit-trees. The trees on plots where legumes have been turned in annually were superior in every way to those similarly fertilized but where no leguminous green-manure crops had been used. Green-manuring resulted in a 30 per cent increase in size of tree and a 68 per cent increase in yield at the age of ten years. ^ 134. Effects of the cultural methods on the soil. — Before examining the effect of these cultural systems on the trees, it would be well to follow the investigations as they affect the soil itself. While the student must consult works on soil science for a fuller treatment of this subject, yet some reference to it is necessary in order to secure a basis for the cultural methods used in orchards. It is axiomatic that an abundance of available inorganic plant-food materials and moisture will give a better devel- opment of the trees and production of fruit than when these are deficient at the critical period of development. It is, of course, equally detrimental to have excesses of moisture 1 Mertz, W. M. Calif. Agr. Exp. Sta. Bull. 292. 1918. CULTURAL METHODS L\ ORCHARDS 153 and in some instances of plant-food materials, and this should be avoided. 135. Effect of moisture. — Hilgard,^ in discussing the effect of moisture on crop production, says: "Production is almost directly proportional to rainfall during the period of active vegetation." In studying the moisture relation, it is important to consider the type of soil. A clay by its nature holds more moisture than a light soil, so that when a heavy soil contains 12 per cent of moisture, a light one under the same conditions may only have about 7 to 9 per cent, and the consequent effect on the trees would be as det- rimental under the one as under the other condition, be- cause of the factor of availability. It has usually been ob- served that the soil-moisture in an orchard standing in sod is less than when the soil is tilled, but under some condi- tions this has not held true. Woodbuiy ^ shows from an orchard experiment that moisture was less under sod culture than under tillage. "During the season of 1913 and 1914 we have a positive indication of the effects of different treatments on soil mois- ture. In both of these seasons, the rain-fall during the ac- tive growing period of the trees (May, June, and July) was considerably below the five-year average for those months. Inasmuch as the cultural practices are conservation meas- ures, preventing the loss of water after it enters the soil, it is largely in such dry periods that the value of certain sys- tems of management in conserving soil moisture are made manifest. "In both of these years, during the month of June, the upland plots either where the grass was cut and let lie or piled under the trees, were low in soil moisture. Where an adequate mulch was maintained on the surface of the soil 1 Soils, p. 193. 2 Purdue Agr. Exp. Sta. Bull. 205. 1917. 154 POMOLOGY either through the agency of cultivation or by a heavy straw covering, the percentage of moisture was more than twice that in straight grass land." Table XXXIII MOISTURE (total) IN SOIL (AFTER WOODBURY ET AL.) Straw Clean culture cover-crop mulch, grass cut, Grass cut, let lie Grass cut, piled let lie A B C D E F per cent per cent per cent per cent per cent per cent 1913 Apr. 29... . 18.9 19.1 19.2 19.6 18.5 19.5 June 17. . . . 14.6 15.0 18.8 7.2 6.1 6.5 Sept. 4 14.0 13.8 15.6 9.4 9.4 9.4 Nov. 25 20.4 20.1 21.3 21.2 20.3 20.2 1914 May 6.... 19.9 19.8 22.2 21.6 20.0 21.0 June 17.. .. 15.3 15.0 17.6 6.5 6.1 6.0 Aug. 13... . 11.4 10.4 10.9 7.2 7.1 7.9 Nov. 25 14.3 14.7 18.6 16.1 15.9 17.3 Data obtained at the New York State Experiment Sta- tion are in accord with those cited from Indiana. The soil in the latter experiment is described as follows: "The char- acter of the soil changes somewhat with the topographical outlines of the orchard. On the ridge and high ground the soil is a fertile Dunkirk sandy loam to a depth of nine or ten inches, underlain by a compact sandy subsoil. In the depression the type changes to a dark colored Dunkirk loam, ten to twelve inches deep, and underlain by a veiy fine com- pact sand." ^ 1 N. Y. [GenevaJ Agr. Exp. Sta. Bull. 314. 1909. JI^R^ H Plate IV. — Six-year old sour cherry trees, o, Unpruned; h, moderately pruned; c, heavily pruned; d, summer pruned. CULTURAL METHODS IN ORCHARDS 155 It is concluded from an experiment in the above orchard that, "The results of 120 moisture determinations in the Auchter orcliard show that the differences in tree growth and crop in the two plots of this experiment are mainly due to differences in moisture, the tilled plot having most mois- ture. As a consequence of the reduced water supply in the sod plot, there is a reduced food supply, for it is only through the medium of free water that plants can take in food. Analyses show that the difference between the actual amount of plant food in the two plots are veiy small." Table XXXIV MOISTURE TO THE ACRE IN TILLED AND SOD PLOTS (aFTER HEDRICK) Soil, depth Plot 1907 1908 Amount of moist are Amount of moisture 1-6 in Tillage Sod Per cent 12.20 7.30 Per cent 14.04 10.06 1-12 in Difference Tillage Sod 4.90 11.53 6.52 3.98 13.57 9.37 Diffprenrc 5.01 4.20 Thus, from these figures, it is concluded that moisture is the limiting factor in fruit production and tree growth in this orchard. On the other hand, the New Hampshire Station ^ de- scribes an orchard in which moisture was as abundant in the sod plot as in the adjoining tilled one, and hence was not 1 N. H. Agr. Exp. Sta. Tech. BuU. 11. 1916. 156 POMOLOGY the limiting factor. This condition is not the usual one, however, although the same conditions obtained in southern Illinois. The average difference in favor of the sod plot is shown below. Table XXXV SUMMARY OF MOISTURE DETERMINATIONS AVERAGE TO A PLOT. PERCENTAGE Surface soil Y'ear Plot 1, sod Plot 4, tillage Plot 5, tillage with cover-crops 1913 1914 .... 16.02 18.87 25.63 20.48 13.69 13.39 19.29 16.45 14.20 15.03 1915 20.82 1916 21.31 Average 20.25 15.70 17.84 Subsoil 1913 1914 1915 10.98 14.14 14.26 14.82 9.06 9.78 14.03 12.74 8.93 10.26 13.33 1916 13.24 Average 13.55 11.40 11.44 Much the same results were obtained at the Woburn Ex- perimental Fruit Farms (England), as indicated in the fol- lowing summary of the data: CULTURAL METHODS IN ORCHARDS 157 Table XXXVI SUMMARY OP MOISTURE DETERMINATIONS (wOBURN) UPPER 9 INCHES Date Tilled soil Grassed soil Average Plot 13 Plot U Plot IS Plot IB Plot 16 Plot 17 diff. 1907 B.Aug. 7.. C. Aug. 16. . P. Aug. 27 . . 13.50 12.54 11.30 13.95 12.54 11.79 12.13 10.20 11.40 14.30 10.00 12.73 14,86 9.75 11.43 17.76 12.15 11.05 +2.45 —1,13 +0.24 Mean 1910 B. Sept. 9 1910 Sept. 9. . . 12.45 13.25 Farmers A 14.60 12.76 12.15 12.60 12.74 Farmers B 13.03 13,82 11.24 12.38 12.34 14.07 A 19,70 12.01 12.67 14.72 14.84 B 13.72 16.71 13.54 15.73 +0.52 +2.10 +2,89 136. Effect of temperature. — The temperature of the surface soil can be affected somewhat by the soil treatment and the nature of the soil covering. To what extent a few degrees difference in temperature may affect the activity of the soil flora cannot be stated definitely, but it is possible that the effects are greater than the small differences of temperature would indicate. Many factors are involved in affecting the soil temperature, but the greatest are the temperature of the air and the absorption of the sun's rays. (Fig. 27). The .work of Bouyoucos^ shows that a difference of as much as five degrees of temperature may obtain between a soil which is tilled and one which lies bare or is in sod. The following table shows the data as a monthly average: 1 Bouyoucos, G. J. Mich. Agr. Exp. Sta. Tech. Bull. 17. 1913. Fig. 27. — Curves showing the maximum soil temperatur under the different soil treatments in an orchard. CULTURAL METHODS IN ORCHARDS 159 Table XXXVII AVERAGE MONTHLY TEMPERATURE OF UNCULTIVATED, CULTIVATED, AND SOD LAND. (after WOODBURY, NOYES AND OSKAMP) 7Ya7/(e of Uncultivated Cultivated Sod month 7" 20" 7" 20" 7" 20" December January February March April 34.5°F 27.73 30.73 31.81 42.24 36.62°F 34.84°F 27.79 29.42 30.60 39.63 54.12 64.4 70.04 66.24 62.80 50.46 39.50 35.94°F 30.92 30.06 30.67 37.10 50.88 60.64 66.61 63.75 61.84 50.90 41.27 34.38°F 29.22 30.07 30.81 41.93 37.07°F May 65.25 71.09 66.60 63.48 50.24 39.77 62.00 66.94 63.80 61.90 50.89 41.20 61.97 65.55 63.39 59.60 48.46 39.85 July 64 August September October November 63.74 61.40 52.43 45.07 Orchard experiments confirm these figures as shown by the followmg data: Table XXXVIII SOIL TEMPERATURE IN TILLED AND SODDED LAND. N. Y. STATE EXP. STA. DAILY JUNE 28 TO JULY 29 Depth of 6 inches Depth of 12 inches 7 a. in. 6 p. m. 7 a. m. 6 p. m. Sod Tilled Sod Tilled Sod Tilled Sod Tilled 66.3 67.4 71. 73.3 64.5 66.6 65.4 67.2 This work has been repeated in orchards under the va- rious systems of soil management with much the same re- 160 POMOLOGY suits. In one orchard ^ in which these observations were made, it was found that the soil temperature was lowest un- der the heaviest vegetation and highest under clean tillage during the summer and the reverse in winter; also the heav- ier the vegetation, the cooler the soil during the summer and the warmer in the winter. The following figures show the effect of the soil treatment during the growing season: Table XXXIX AVERAGE SOIL TEMPERATURE TILLED AND COVER-CROP PLOTS AT 8 INCHES. N. H. EXP. STA. Monthly average, April to September. Records made at 2 p. rn. daily April . . . May. . . June. . . July. . . Aug . . . . Sept . . . Average Sod Tilled 38.3 43.0 52.3 55.5 59.3 61.1 66.8 69.7 66.6 69.6 61.9 64.5 57.5 60.5 42.5 54.7 57.9 65.7 65.2 61.1 57.8 The depth of freezing in these same plots is shown at a time when the soil was supposedly frozen to the greatest depth of the winter. Table XL depth of freezing IN INCHES Sod Bare 16 Light cover- crop Heavier cover-crops, especially in last three plots Cover-crop Cover-crop Cover-crop Cover-crop Cover-crop 12 15 12 10 8 7 7 N. H. Agr. Exp. Sta. Tech. Bull. 12. 1917. CULTURAL METHODS IN ORCHARDS 161 In another investigation ^ it was found that the "clean cultivation with cover-crop and the straw mulch occupy the extreme positions in soil temperature behavior." The bare soil will respond very quickly to a change in the air temperature, rising rapidly during warm weather and con- versely showing the lowest temperature in the winter. By examining Fig. 27 it will be seen how closely the soil temper- ature follows that of the air. (Maximum air temperature.) ,J ^ ^ V ^ o. Z 1 O) ly responsible for the amount of bloom and hence for the possibilities of a crop of fruit. Therefore, it becomes of the first importance to study the cultural treat- ments that are most likely to give a maximum crop, so long as this is not inconsistent with the health and vigor of the trees. A fundamental principle established by all the experi- mental evidence at hand may be stated as follows: The growth of the tree and yield of fruit proceed in the same di- rection and are not antagonistic. This of course is within reasonable limits, for a point may be reached when the growth is so excessive as to suppress flower-bud fonnation. An extreme of such a condition is reported from the tropics.^ "Of our apple trees it is well known that in warm insular climates they grow into magnificent foliage trees, but re- main unproductive." In keeping with this principle, it may be said that the above data on the growth of the trees applies with much the same force to the yield. In regard to jneld no one sys- tem is always best, but the one most suitable to the condi- tions should be adopted. As seen above, the purposes of adopting a cultural sys- tem are to conserve sufficient moisture for maximum re- sults, to increase nitrification in the soil, and to set free plant- food materials, as well as to control weed growth. This, interpreted in terms of the plant, results in increased growth and fruitfulness. 144. Sod, tillage, and mulch for the apple. — The work with the apple shows that, as a rule, the trees growing in sod land are lower in yield and the fruit smaller but higher in ' Sorauer, P. A Treatise on Physiology of Plants, p. 222. 174 POMOLOGY color than when cultivated. If the trees are in sod mulch, the yield is somewhat higher than in sod alone, although as a rule fertilizers or manures are necessary to obtain best results. Some of the best-known experiments in this country have been conducted by the New York Experiment Station and have been referred to in the discussion of "growth." To recapitulate and state in more detail: The experiment was conducted as follows (Auchter orchard). The soil was a fertile Dunkirk loam, about ten inches in depth and under- laid by a sandy subsoil. The orchard of nine and one-half acres of Baldwin trees was divided in half in the first five years, so that 118 were left in sod and 121 under tillage. In the second five-year period, the orchard was divided into quarters so that one quarter was in sod for ten years and another in tillage for ten years, a third quarter was in sod for five years and under tillage the latter five years, while the other fourth was in tillage the first five years and in sod five years. While potash and phosphoric acid were used for the first three years in this experiment, no results were noted where they were applied and this fact need not come into the present discussion. The plot which was tilled for ten consecutive years re- sulted in an average yield to a tree of 4.29 barrels; the plot in sod for ten years yielded 2.54 barrels to the tree; the plot which was tilled for five years and in sod five years averaged for the second five-year period 2 barrels to the tree; while the plot which was first in sod for five years and then tilled for five, gave an average of 5.17 barrels during the second period. These figures are very striking and emphasize the value of tillage under the conditions of this orchard. Another experiment by the New York Experiment Sta- tion was conducted for a ten-year period to determine the value of tillage and mulch in an apple orchard (Hitchings orchard). In this case, the land was deep, fertile, and well CULTURAL METHODS L\ ORCHARDS 175 supplied with moisture, which factors favor the mulch sys- tem of orcharding. At the end of the period, the four vari- eties (Alexander, Fameuse, Northern Spy, and Wealthy) averaged 3.18 bushels of apples to the tree on the tillage block and 3.95 bushels on the sod mulch plot. The Pemisylvania experiments show the same general results in yield as in growth. The statement of Stewart is that "In general the mulch treatment, reinforced by out- side materials, has been most efficient in improving the yield, growth, and average size of fruit in orchards up to about 20 years of age. In older orchards, it has been sur- passed slightly by tillage and cover-crops, unless accom- jianied by adequate fertilization. It has also been most efficient in conserving moisture, in all cases that have been determined." Table LI INFLUENCE OF CULTURAL TREATMENTS ON THE YIELD OF TREES AVERAGE ANNUAL YIELD TO THE ACRE (aFTER STEWART) Varielies ^1 It i i! 1 '^ a. II 1 1 Jonathan York, Gano, Ben Davis 1902 1907-1915 40 Bu. 78.4 Bu. 85.7 Bu. 152.6 Bu. 78.1 Smokehouse, StajTiian 1901 1908-1915 40 127.9 147.5 43.7 Baldwin, Northern Spy 1873 1907-1915 40 398.0 385.2 The New Hampshire experiments show again the value of tillage over sod culture of the trees. The conclusions 176 POMOLOGY from the work are as follows: The trees growing in sod have not yielded sufficiently well to warrant the use of the land for orcharding. Tillage every other year resulted in decided benefit to the trees. Clean cultivation, without the use of green-crops, has proved successful in the recla- mation of a run-down orchard, increasing the yield nearly 100 per cent. It has shown evidence, however, that it could not be continued for a long period of time as the trees were not quite so vigorous at the end of a ten-year period as at the completion of the first five years. Tillage with cover- crops has proved to be a slightly better system than clean tillage alone. For yields of these plots see page 206. 145. Cultivation for the peach. — What has been said in regard to tillage applies with particular force to the peach. In fact, it is doubtful whether the peach will ever do as well under any other system as under cultivation. Most soil experiments with this fruit include fertilizers and are hence treated in the next chapter. Ralston ^ cites some work however, confirming the value of tillage for the peach. There were 288 trees to the plot equally divided between Early Crawford and Elberta. The trees were planted in 1 9 1 1 and the data taken 1915-17, inclusive. The soil is described as a ''very poor Cecil Clay which contains an abundance of small pebbles and a small amount of loose shale, and is fairly uni- form throughout." Table LII results of cultural treatments YIELD OF FRUIT IN POUNDS TO A TREE FOR 3 YEARS. (AFTER RALSTON) Intense cultivation (7 to 9 times annually) Commercial cultivation {3 to 4 times annually) Sod {in sod since spring of 1913) 1,943 lbs. 1,285 lbs. 712 lbs. Ralston, G. S. 23d Ann. Kept. Va. Hort. See. 1918. CULTURAL METHODS LY ORCHARDS 177 146. Fall plowing the orchard. — If the orchard can be safely plowed in the fall, it will result in a saving of time in the spring when a great demand exists for teams and men. This practice has been put to the test in many of the fruit- growing regions and without resultant injuiy to the trees. Fall plowing can be followed in both the North and South, and with tender fruits such as the peach as well as with the apple provided the soil will not erode. The land is usually allowed to lie in the rough (without harrowing) over winter and is harrow(Hl down in the spring. 147. Use of explosives for tillage purposes.^ — Much has recently been written in regard to the use of explosives in the planting of young trees and also in the tillage of mature ones. The experimental work on this subject is not exten- sive, although these agencies have been extensively used both as demonstrations and in conmiercial work. That a well-developed, extensive root system is correlated with a vigorous productive top of a fruit-tree goes without saying, and the theory of the use of explosives for this pur- pose is well founded. Whether such extraordinaiy means are necessaiy will depend on the nature of the soil, for if it is hard and impervious, rocky or underlaid with hard-pan or other resistant material, the use of an explosive should be most helpful. There is, however, no virtue in the use of dynamite other than what is gained by a better mechanical soil condition, or else in the cost of the operation. The soil should not be wet at the time of the operation or a pot-hole is likely to be blown out which makes a basin for water and is hence more harmful than other methods. It is usually advisable to blow the holes some time before setting in order to allow the soil to settle; othei-wise, the trees are likely to sink a few inches which is quite undesirable. > "The Use of Explosives in the Tillage of Trees." Pub. by Institute of Makers of Explosives, New York. 1918. 178 POMOLOGY Farley ^ conducted some experiments with peaches in which he fomid that there was usually an increase in growth of the trees during the first summer when they were planted with dynamite as compared with trees set in the usual way. In one experiment this increase was not maintained during the second and third season. "The crop of peaches pro- duced by the New Brunswick and Vineland trees during the third summer show a noticeable advantage in favor of dynamiting in the case of the variety Carman, the only variety which produced what could be termed a profitable crop." In general, however, he concludes, that, "The results of our experiments indicate that in the majority of cases the increased growth and fruit production recorded on dyna- mited trees is not great enough to make up for the increased cost and danger involved in planting. Furthermore, the use of dynamite is not recommended for tree planting on those soils that are naturally adapted to orcharding." 1 Farley, A. J. Proc. Amer. Soc. Hort. Sci. 1914. CHAPTER IX FERTILIZERS AND MANURES FOR THE ORCHARD The supplying of artificial plant-food materials to fruit- trees introduces a problem on which there is some differ- ence of opinion among authorities. However, much exper- imental evidence is available and in many sections the results of proper fertilization can be predicted with consider- able certainty. The original conceptions of this problem were based largely on the findings of the chemists, for it seemed logical to conclude that the elements found in the plant and its products in greatest amounts were the ones to return to the soil in like proportions. This doctrine led the horticulturists somewhat astray for a time, for valuable as it is, such a theory does not take into consideration the mechanical or physical condition of the soil or the impor- tant role of micro-organisms to soil fertility and the asso- ciated factors of heat, moisture, and soil sanitation. Obvi- ouslj^, the amount of artificial "feeding" that trees will require depends basicly on the original or native fertility of the soil together with its physical condition and mois- ture-content. Hence a wide variation in the practical re- sults of fertilizing orchards is to be anticipated, especially in the relative length of time that will be necessary to pro- duce like results. The problem should be studied from the standpoint of several generations of trees on the same land, yet the longest experiments have been in p-rogress scarcely a quarter of a century. 148. Criticisms of orchard experiments. — The field tests of orchard fertilizing have been seriously criticised 179 180 POMOLOGY from several points of view, viz. : (1) The soil in some of the experimental orchards has been exceedingly variable and yet no account has been taken of that fact in recording the ef- fects of the various fertilizer treatments. (2) Fruit-trees, particularly large apple trees, vary exceedingly in the size of the crop they produce, and averages for any given plot may be misleading. (3) When buffer rows have not been maintained between the plots, there has not infrequently been cross feeding which would seriously modify the re- sults. (4) Missing trees in an orchard may give certain advantages to those adjacent to the open spaces, and also diseased or subnormal individuals may not give a repre- sentative result of the treatments used in an orchard. (5) Differences of topography which may give an advantage to certain plots over others because of unequal frost action and drainage have often played a large part in results se- cured, without allowances being made for the inequalities, often without mention of them. (6) Unwarranted con- clusions have been drawn of the value of a single element by subtracting the performance of a two-element plot from that of a three-element plot. Many other suggestions or criticisms might be enumerated, all of which would be jus- tifiable in critically examining this problem. Without question it is more difficult to select uniform conditions for an orchard experiment than for field tests of the farm crops, and the available data are open to criticism on many grounds. Nevertheless, this field work has been a valuable, if not a necessary, forerumier of the more tech- nical studies of a physiological nature that must follow. A number of valuable economic questions have already been settled and much of the previous confusion in regard to or- chard fertilization has been cleared up. 149. Fertility removed by fruit-trees. — Proceeding from a chemical view-point, the amount of fertility removed by FERTILIZERS AND MANURES FOR THE ORCHARD 181 fruit-trees from the soil will give a basis on which to study the plant-food requirements of an orchard. Such modifica- tions as are suggested in the introductory paragraph will be considered later. There are marked variations in the analyses reported by chemists, due probably to a difference in methods and to the varying material analyzed. In order to obtain a satisfactoiy set of figures, Stewart has averaged a large number of analyses of the apple that were made in both America and Europe and reports them in the form of percentage of diy matter, instead of on the basis of ash constituents as they are given in Chapter I. The following table summarizes this information: Table LIII the composition of apple wood, leaves, and fruit Plant Dry Nitrogen Phos. acid Potash Lime Magnesia Iron part stance (N) (P2O5) (K2O) (CaO) (MgO) (Fes-Oa) Pet. Pet. Pet. Pet. Pet. Pet. Pet. Wood . 52.25 .62 .20 .36 1,6 .24 .03 Leaves 34.45 2.15 .44 1.34 2.48 .75 .125 Fruit. . 15.39 .43 .17 1.10 .08 .09 .02 The same writer has made a comparison of the total draft of an apple and a wheat crop to the acre, assuming vigor- ous and productive plants in each case. Such a collation is of interest, for it has usually been assumed that the apple makes a lighter draft on the soil in comparison with a grain crop. Table LIV compares the plant-food materials util- ized by the two crops. 182 POMOLOGY Table LIV relative amounts of plant-food materials removed by apples and wheat IN POUNDS TO THE ACRE ANNUALLY, BASED ON THE INDICATED IN TABLE LIII COMPOSITION Wood Leaves Fruit Apple (total) Wheat grain Wheat (total) Estimated annual weights Lbs. 3,500 11.3 3.6 6.6 29.1 4.4 0.5 Lbs. 3,500 25.6 5.3 15.9 29.5 8.9 1.5 Lbs. 24,500 16.2 6.4 41.5 3.0 3.4 0.8 Lbs. 31,500 53.1 15.3 64.0 61.6 16.7 2.8 Lbs. 1,500 30.0 10.0 9.8 0.84 3.0 Lbs. 4,200 43.7 15.8 26.8 8.0 6.1 Nitrogen (N) Phosphoric acid (PaOs) Potash (K2O) Lime (CaO) Magnesia (MgO) Iron (FeaOs) . . . Van Slyke has summarized his data for the several tree- fruits and observes that the quantity of nitrogen and pot- ash is about the same in any one kind of tree, while the amount of phosphoric acid is only about one-fourth that of the other two materials.^ Nitrogen 30 to 75 pounds Phosphoric acid 7 " 18 " Potash 33 " 72 " Calcium oxide (lime) 38 "114 " However, the amounts used by different kinds of fruit- trees vary greatly, as is shown by the table on opposite page. According to studies by Thompson,^ "fruit-trees demand plant food more nearly in the proportion in which it exists in the soil than does com or almost any other crop." ^ Fertilizers and Crops. New York. 1912. 2 Thompson, R. C. Ark. Agr. Exp. Sta. Bull. 123 (Tech.). 1916. FERTILIZERS AND MANURES FOR THE ORCHARD 183 Table LV amount of mineral plant-food material used to the acre (after VAN SLYKE) Variety Apple. . Peach. . Pear. . . Plum. . Quince . Number of trees Nitrogen (N) to the acre lbs. 35 51.5 120 74.5 120 29.5 120 29.5 240 45.5 Phosphoric acid (P^Os) lbs. 14.0 18.0 7.0 8.5 15.5 Potash Lime (K,0) (CaO) lbs. lbs. 55.0 57.0 72.0 114.0 33.0 38.0 38.0 41.0 57.0 65.5 Magnesia (MgO) lbs. 23 35 11 13 19 150. Fruit-trees essentially different from other crops. — It must be recognized in dealing with the fertility problem that fruit-trees are essentially different from other crops because of their greater root area and the fact that a large part of the roots may be found in the subsoil. This means that the soil will support a fruit-tree better than a plant with a restricted root system. Also the orchard occupies the land for many years, and hence the problem is different from that in which a rotation of crops is practiced. The situation is also more complex because of the material that is returned to the soil from the leaves. 151. Amount of food materials found in plants not a guide. — The relative amounts of the various "essential" elements in the tissues of the plant cannot be taken as an actual guide, because the soil may contain an abundance of the element which would seem to be most necessary to apply. This is particularly conspicuous with regard to pot- ash. According to the data, the tree uses four times as much potash and nitrogen as phosphoric acid. It is usual to find that most fruit soils are relatively rich in potash which ap- pears to become available sufficiently rapidly by good tillage 184 POMOLOGY methods. Therefore, instead of being first, potash usually is of the least importance of the three. Similarly nothing in the analysis indicates that nitrogen is usually of first importance, yet this is commonly preeminent. Furthermore, it must be recognized that more food may be taken into the plant than is necessary for complete functioning, if such material is present in the soil in abundance and in an available form. Jordan ^ conducted a series of experiments with such crops as barley, peas, tomatoes, tobacco, buckwheat, rape, and turnips, and concludes that "the results secured indi- cate that what a grain crop contains of certain elements is not necessarily to be regarded as a measure of what must be supplied in order to meet the needs for maximum growth." 152. Analysis of the soil as a guide to fertilizing.— The question naturally arises as to whether a chemical analysis of the soil would be a guide to the fertilizing of the orchard, and if so, what element in particular should be applied and at what probable rate. While it would seem but reasonable to make the assumption that such is the case, yet experience shows that the plants' requirements can be only roughly ap- proximated in this way and that errors will often result if dependence is placed in such a procedure. While it is true that trees on poor impoverished land will usually be notable for their paucity of both growth and yield, yet if the physical condition of the soil is congenial, a good growth may be secured out of all proportion to what would be expected from ordinary farm crops on the same soil. This is doubtless accounted for at least in part by the greater feeding area of the root systems of fruit-trees. 153. Necessity of fertilizing orchards. — Whether it is necessary to fertihze an orchard is a question not easily answered, since so many factors are involved. The prob- ' N. Y. Agr. Exp. Sta. Bull. 360, 1913, also F. R. Pemper, R. I. Agr. Exp. Sta. Bull. 169. 1917. FERTILIZERS AND MANURES FOR THE ORCHARD 185 lem should be viewed without prejudice from the stand- point of discovering any limiting factor to maximum results. If insufficient plant-food is available, this situation should be sensed as soon as possible and the condition relieved. It will depend, however, on the kind of trees, the soil, the system of culture followed, the age of the trees, and finally on the results of these conditions as manifested in the trees themselves. This is not so unsatisfactory as it at first seems. An experienced grower should have a sufficiently accurate knowledge of what the possibilities of trees are, to determine whether they need additional fertility. In general, the stone-fruits, particular^ the peach, should be fertilized each year after they come into bearing. The apple and pear, when grown in the sod or mulch system, should usually be fertilized. However, exceptions will present themselves; and when these fruits are well tilled they may continue for many years without need for additional plant-food materials, unless they are inter-cropped. When trees are nob making an av- erage terminal growth of at least several inches (6 to 12), when the foliage is not a rich green color and held well into the fall, and when they are not bearing good crops practi- cally every year, it would be well to introduce additional fertility either in the form of artificial fertilizers or manures or both. However, the varietal factor enters here strongly; also it should be determined whether the orchard is well drained and free from other conditions known to be inju- rious. All this, of course, means that in the case of doubt the only definite answer can be obtained by the local test. If a response is secured by any of the fertilizer elements or a combination of them, their use should at once be extended to the remainder of the orchard. Under many conditions, very large financial returns may be secured from the use of fertilizers; it is not wise to delay applying them until such marked results are secured as on some of the impoverished 186 POMOLOGY soils, but rather to maintain continuously a vigorous con- dition of the trees. 154. Fertilizing tilled and non-tilled apple orchards. — The source of much error in studying the fertiUzer problem in the apple orchard hes in a failure to recognize the all but universal experience in fertilizing a tilled and a sodded plan- tation. The fundamental or underlying reasons for this difference lie in the effects of stirring the soil on its nitrate and moisture-content. As a general rule, a well-cultivated apple orchard (including the use of cover-crops) will respond slowly to the use of chemical fertilizers, and one which is not tilled will give prompt returns. An outstanding ex- ception is in the impoverished soils of southern Ohio where the fertilizers gave as great and as prompt results in tilled as in sod orchards. The author believes this is of such im- portance that the fertilization of tilled and untilled orchards are considered separately. 155. Moisture and fertility intimately related. — Moisture is of first importance in the proper growth and develop- ment of plant and fruit, and when it is lacking the elements of fertility are not available. If the soil is too dry at a crit- ical period, the fohage suffers and the fruit is small and of poor quality. On the other hand, too much water in the soil is equally serious, resulting in stunted growth, yellow foli- age, and eventually death of the trees. Of the ten or more chemical elements that enter into the composition of the plant, only four are likely to require special attention in the way of amendments to the soil. These are nitrogen, phos- phorus, potassium, and calcium. Of these most of the cal- cium (lime) remains in the wood and leaves, while a large proportion of the potassium (potash) finds its way to the leaves and fruit. 156. Relative importance of the different essential elements. — While each of these so-called essential elements FERTILIZERS AND MANURES FOR THE ORCHARD 187 is necessary for tree growth, the relative necessity of their appUcation to the soil will depend on the amount already available and the quantity taken up by any given kind of plant. There has been much misunderstanding and erroneous teaching regarding this question in pomology. However, the field experiments have done much to clear up the situa- tion, although there is still a lack of conclusive information. 157. Organic versus inorganic fertilizers. — In compar- ative tests on the use of organic fertilizers, such as dried blood, tankage, and cotton-seed meal, and such inorganic materials as nitrate of soda, acid phosphate, basic slag, and nmriate or sulfate of potash, the conclusion is reached that the inorganic materials are usually to be preferred. In an Ohio experiment ^ two orchards badly in need of nitrogen show the following results as a five-year average in pounds of fruit to a tree: Table LVI comparative valxje op inorganic and organic forms of fertilizer (after ballou) Application to a tree 1st orchard 2d orchard 5 pounds nitrate of soda 5 pounds acid phosphate 2H pounds muriate of potash Lbs. 205.8 Lbs. 317.6 5 pounds tankage 5 pounds bone-meal 23/2 pounds muriate of potash Lbs. 93.8 Lbs. 1G3.9 158. Value of nitrogen. — One of the most outstanding results of the various fertilizer experiments conducted throughout the country is the importance of applying ni- 1 Ohio Agr. Exp. Sta. BuU. 30L 1916. 188 POMOLOGY trogen in a soluble form when an orchard is low in vitality. Such a treatment is of much more importance to an or- chard which is not tilled since it has been shown that the soil nitrates are likely to be greatly reduced under those cir- cmnstances. This, of course, will depend on the conditions of the soil and perhaps on the climate, for some notable cases are on record in which an application of nitrogen to a culti- vated orchard gave immediate and striking results. If an orchard experiment is continued for a very long period, the time is likely to come when nitrogen may be applied with profit whatever the cultural system followed. In point of efficiency in maintaining the growth and yield of the trees, nitrogen stands alone among the artificial fer- tilizers. 159. Nitrate of soda. — This carrier of nitrogen is more commonly used than any other because of its solubility. The results are usually prompt and marked. When this fertilizer is used alone, it often gives as good results for the first few years as when in combination with carriers of phos- phoric acid and potash. However, over a series of years, a complete fertihzer is considered best. The amount nec- essary varies with the age of the trees, their condition, and the type of soil involved. Nitrate of soda is also used as a special "stimulant" for trees that are sub-normal as a result of injury, having been employed with success on winter- injured trees, those hurt by fire or other agencies. For mature apple trees, the usual application is from 4 to 6 pounds to a tree or approximately 150 to 200 pounds to an acre. Smaller trees receive proportionately less unless the application is made over the entire orchard surface. For the peach, an application of 2}^ to ^Yz pounds to a tree is usually sufficient. 160. Sulfate of ammonia is also a readily available form of nitrogen and from a knowledge of its effects on other FERTILIZERS AND MANURES FOR THE ORCHARD 189 crops, it would seem to be adapted to orchard use. Unfor- tunately, sufficient data are not as yet available to warrant a definite statement of its value, but in demonstration tests the results have fully equaled those of nitrate of soda. Rei- mer ^ used sulfate of ammonia in an experiment with Winter Nelis pears in the Rogue River Valley, Oregon, and finds that "The plot which received 5 pounds of sulfate of am- monia produced a notable increase in yield, almost equaling the yield produced by 10 pounds of nitrate of soda. The 5 pounds of sulfate of anmionia contains as much nitro- gen as 63^2 pounds of nitrate of soda." Other experimental work in Oregon with both the peach and apple demonstrate that this material is of increasing importance in orchard work. With certain of the field crops, however, it has been found that this source of nitrogen is not quite equal to the same units of nitrogen in nitrate of soda. Also the chemi- cal changes which take place will ultimately exhaust the bases of the soil unless the land is well supplied with cal- cium or else lime is applied to offset the loss. 161. Time of application. — So far as is now known, the quickly available forms of fertilizers should be applied not later than blossom time to secure the best results, and it is convenient to add all materials at the same time whether they are readily soluble in water or not. They may be broadcast on top of the grass or mulch or sown with a fer- tilizer drill in the case of a tilled orchard. There seems to be some definite evidence to show that an application of nitrate of soda about two weeks before the blossoms open will greatly stimulate the "set" of fruits of the apple, this being particularly noticeable on weak trees. This seems to have been reported first by Ballon - from work in southern Ohio. An orchard of twenty-year-old Rome » Ore. Agr. Exp. Sta. Bull. 166. 1920. - Ohio Agr. Exp. Sta. Bull. 301. 1916. 190 POMOLOGY apples which had produced but one crop of fruit because of its extremely low vitality, was fertilized in part about the middle of April. ''The trees bloomed rather uniformly over the entire orchard, but the blossoms were unusually small and apparently lacking in vitality. However, after the petals of the blossoms had fallen, the little apples on the fertilized plots where nitrate of soda had been included clung to the fruit spurs and began to grow in a perfectly normal manner, while most of the embryo fruits on the ad- joining unfertilized plots withered and dropped from the tree just as the apples had been doing throughout the past life of the orchard." At picking time of this first year one row of eight trees which was fertiUzed with a 5-5 nitrate- phosphate combination produced twenty-one barrels of fruit, while the adjoining untreated row yielded nine barrels. The same effect of an early application of nitrate on the set of blossoms is reported by Lewis. He finds that as a result they secured a higher percentage of ''set," an imme- diate change in character of foliage, and a stimulation of wood growth. 162. Phosphorus is rather low in many soils and in animal manures, but is required in less amounts by fruit- trees than either nitrogen or potassium (in the relation of 4N, 1 P2O5, 4K2O) as was seen above. However, the data in regard to this element are rather unsatisfactory and in- consistent in the orchard experiments. It would seem to rank next to nitrogen in its requirement as an amendment to the soil, although when applied alone the results are frequently meager or negative. An exception is found in certain sections where phosphoric acid has had a positive result in encouraging the growth of clov^er in a sod orchard (see Ohio experiments) which in turn is beneficial to the soil. 163. Acid phosphate. — As a carrier of phosphoric acid, this material seems to give the most satisfactory results FERTILIZERS AND MANURES FOR THE ORCHARD 191 because of its availability. It is commonly used at the rate of 350 to 400 pounds to the acre. Both floats and basic slag have been used in orchard ex- periments with vaiying results, but neither has been so effi- cient as acid phosphate. Bone-meal has not proved valu- able in securing results within a reasonable length of time and it is not so widely used in orchards as formerly. 164. Potash is used by fruit-trees in relatively large amounts. This led to the earlier teachings that potash was the first essential in fertilizing fruit-trees. This theoiy ignored the fact that many fruit soils are comparatively rich in potash and hence obviated the necessity of adding it in an artificial form. The statements that potash fertilizers make better color, better shipping quality and flavor of fruits are without apparent foundation in experimental results. When potash is applied alone or in combination, the data show few instances in which outstanding results are secured from it. 165. Muriate versus sulfate of potash. — Some differ- ence of opinion exists as to the relative value of muriate and sulfate of potash for orchard use. Both have given satisfactoiy results where there was need for a potash fer- tilizer. Therefore, since the muriate is cheaper, it would seem good practice to apply it until further research shows a superiority of the sulfate. 166. Hardwood-ashes. — Wood-ashes have long been used for fruit-trees and were highly valued a half century ago, but their scarcity at the present time has greatly re- stricted their use. Wood-ashes will vaiy markedly in their composition; if they are unleached they will analyze about 4 to 6 per cent potash, 1.5 to 2 phosphoric acid, and 25 to 30 per cent lime. Potash salts have largely replaced wood- ashes as a source of potassium in orchard fertilization. 167. Common salt. — Sodium chloride has been advo- 192 POMOLOGY cated for orchards (at the rate of about 150 pounds to the acre) to release the potash in the soil and thus furnish the trees with that element. Since potash is not often the limiting factor, this practice is not of importance to the orchardist. Some such reaction as the following is believed to take place in the soil: NaCl -h KAlSiaOs = NaAlSisOg + KCl. 168. Animal manures in the orchard. — In several of the fertilizer experiments already cited, the value of manure for the orchard has been shown. When it is used on a sodded or mulched orchard, it not only furnishes plant-food but, what is often quite as valuable, it conserves the moisture. As a top dressing in a sod orchard it is slower acting, how- ever, and on the whole less effective than nitrate of soda, when nitrogen is badly needed. In a tilled orchard it is valuable as a source of organic matter as well as of plant- food. That the experimental results from its use are variable is shown by results in two orchards which seemed similar.^ In one was obtained an aiuiual cash gain to the acre for five years of $20.75, while in another the gain was $110.75, or $2.00 an acre less than the adjoining plot treated with ni- trate of soda alone. Unfortunately, these data are not given in terms of yield. From work conducted in Pennsylvania ^ • it is reported that ''in ten similar experiments, the gains from stable ma- nure in both tilled and unfilled treatments have averaged 79.3 bushels per acre annually, while those from commer- cial fertilizer averaged 73.0 bushels. In five cases involving tillage, however, the gains from the fertilizer have averaged 99.6 bushels per acre annually, while those from the manure 1 Ohio Agr. Exp. Sta. Bull. 301. 1916. 2 Penn. Agr. Exp. Sta. Bull. 141. 1916. FERTILIZERS AND MANURES FOR THE ORCHARD 193 have averaged only 83.4 bushels. In general, therefore, the manure has surpassed the fertilizer on untilled trees and has been surpassed by it on those receiving tillage. The extra mulching effect of the manures has doubtless contrib- uted to this result." EXPERIMENTS IN UNTILLED ORCHARDS As stated in the foregoing paragraphs, the most marked results from fertilizing have been secured in orchards that are not cultivated, and some typical cases may be cited to show the results attained. 169. The Massachusetts experiment.^ — In Massachu- setts a fertilizer test was conducted in an orchard of Graven- stein, Baldwin, Roxbuiy Russet, and Rhode Island Green- ing apples for a period of fifteen years. Three trees of each of these varieties were included to a plot. They were planted in 1890 and cultivated for five years. From 1895 until 1910, the trees were in sod, and the following list of treat- ments together with the total yield of fruit for this period summarizes the results: Table LVII RESULTS OF ORCHARD FERTILIZATION MASSACHUSETTS. (aFTER BROOKS) Plot Fertilizer Annual rate to the acre — pounds Total yield for 15 years — pounds 1 20,000 2,000 600 200 600 400 24,934 2 Wood-ashes 12,841 3 Nothing 3,940 4 Bone-meal 14,453 5 Bone-meal Low-grade sulfate of potash 21,863 Mass. Agr. Exp. Sta., 22d Ann. Rept., Part 2. 1910. 194 POMOLOGY This experiment shows the superiority of any of the treat- ments over the untreated plot. The striking point, in the Hght of later investigations, is the absence of an application of quickly available nitrogen for this orchard. The manure has given outstanding results in yield and growth, no doubt due to the supply of nitrogen it carried as well as to the organic matter added to the soil. Brooks states that too much manure was used, for the trees made too heavy a growth and the fruit was green and coarse. This is a com- mon experience when trees are over-fertilized with animal manures. Perhaps the most outstanding result of this ex- periment is the apparent superiority of the low-grade sul- fate of potash, which contains a large amount of magnesia, over the bone-meal-muriate-of-potash treatment. The dif- ferences in the two plots may have been due to the pres- ence of magnesium as the sulfate or chlorid or to the sul- fur itself in the sulfates of potassium and magnesium, but the cause or causes for the difference in behavior have not been clearly established. The effect of wood-ashes, which contain about 1 to 2 per cent of phosphoric acid (P2O5) and 4 to 6 per cent of potash (K2O), is of interest since the com- mon recommendation of the older horticulturists was to use wood-ashes for fruit-trees. 170. The Ohio experiments. — Further light is thrown on this problem by the Ohio experiments in which a mulch is usually included. This work was conducted in the southern part of the state on land low in native fertility, and where the surface soil is very thin, usually supporting a cover of poverty-grass {Danthonia spicata) and weeds. The land washes or erodes badly and hence it is not deemed wise to cultivate it. This experiment gave immediate results when nitrogen was used alone or in combination with fertilizers carrying phosphoric acid or potash. The beneficial effects continued FERTILIZERS AND MANURES FOR THE ORCHARD 195 each year, and clenionstrated beyond question that the first and most important need for these orchards was a qaickly available form of nitrogen. Nitrate of soda proved to be the bftst carrier of nitrogen. When phosphoric acid was used in combination with nitrate of soda or in a complete fertilizer, there was little or no evidence that it was a Umit- ing factor, although the soil is naturally low in phosphorus. However, it proved of great value in securing a stand of better grasses as is discussed in connection with producing mulch material. Neither did potash have any apparent effect in increasing the vigor or yield of the trees during the five-year test. These conclusions are supported by the following summaiy of the data: Table LVIII average yield to a tree in 3 orchards of rome beauty apples, 22-25 years old.l grass-mulch 5-year average. (after ballou) Treatment ^ 1st 2d Orchard Orchard Lbs. Lbs. 69.9 124.1 315.6 296.3 205.8 317.6 93.8 163.9 214.2 96.0 133.7 100.1 124.1 3d Orchard Checks Nitrate N it rate — phosphorus — potash . Duphcate Tankage — bone — potash Nitrate — phosphorus Potash Manure Lbs. 122.6 378.9 348.4 315.9 1 Loc. oil. 2 The followino; amounts of fertilizer were u-sed in each case: Nitrate of soda, 5 lbs. Acid phosphate, 5 lbs. Muriate of potash 2^/^ lbs. Stable manure 250 lbs. Tankage 5 lbs. Bone 5 lbs. 196 POMOLOGY In a later report,^ an additional experiment is recorded which confirms the earlier findings on the type of soil in southern Ohio. Other features of interest are also included. In 1914, a twenty-year-old orchard of Rome Beauty and Ben Davis apples which were very low in vitality and en- tirely non-productive was secured for the purpose of exper- imentation. Two rows of twelve trees each constituted a plot, the one having the fertilizer distributed in a circle beneath the tree, and the other having it applied over the entire tree square ("all-over method"). A check or buffer row was maintained between each two plots. Half the or- chard was cultivated and a cover-crop sown amiually, and the other half was put under the grass-mulch system, the fertilizer treatments being the same on both sections. There was no material difference in yield between the "circle" and the "all-over," method of distributing the fertilizer,, but the latter encouraged a strong growth of vegetation for mulching purposes. The conclusions of this experiment are striking in several particulars, notably in showing that fertilizer will produce equally prompt and valuable results in both tilled and mulched orchards in that section, an end not secured, under a number of other conditions, as discussed later in this chap- ter. Also tillage alone will not suffice to produce maximum crops on the soil in question. If the unfertilized grass-mulch plot is taken as the check, the following increases obtain for a five-year average: 1 Ohio Agr. Exp. Sta. Bull. 339. 1920. FERTILIZERS AND MANURES FOR THE ORCHARD 197 Table LIX results from fertilizing tilled and mulched orchards — southern ohio. (adapted from ballou and lewis) Percentage Average yield to the acre, increase 5-yr. period Barrels Grass mulch— unfertilized 37.6 Cultivation — cover-crops unfertilized 41 53.2 Grass mulch — fertilized 100 75.4 Cultivation— cover-crops fertilized 95 73.5 The more complete data are given in the following table: Table LX effect of fertilization on tilled and grass-mulch orchard — ohio. (after BALLOU AND LEWIS) Row No. Cultivated plot Nitrate of soda, 5 lbs. on tree circle Nitrate of soda, 5 lbs. on tree square No fertilizer Nitrate of soda, 5 lbs. ; acid phosphate, 5 lbs. on tree circle Nitrate of soda, 5 lbs. ; acid phosphate, 5 lbs. on tree square No fertilizer Nitrate of soda, 5 lbs. ; acid phosphate, 5 lbs. ; muri- ate of potash, 5 lbs. on tree circle Nitrate of soda, 5 lbs. ; acid phosphate, 5 lbs. ; muri- ate of potash, 5 lbs. on tree square Totals for cultivated plot 5-year average, 1914-18 Lbs. 3,220.1 3,017.2 2,270.8 3,081.6 2,950.6 2,308.0 2,935.7 3,407.5 23,191.3 198 POMOLOGY Table LX — Continued. Row No. Grass-mulch plot Nitrate of soda, 5 lbs. on tree circle Nitrate of soda, 5 lbs. on tree square No fertilizer Nitrate of soda, 5 lbs. ; acid phosphate, 5 lbs. on tree circle Nitrate of soda, 5 lbs. ; acid phosphate, 5 lbs. on tree square No fertilizer Nitrate of soda, 5 lbs.; acid phosphate, 5 lbs.; muri- ate of potash, 5 lbs. on tree circle Nitrate of soda, 5 lbs. ; acid phosphate, 5 lbs. ; muri- ate of potash, 5 lbs. on tree square Totals for grass-mulch plot 22,970 . 3 5-year average 1914-18 Lbs. 2,817.9 2,295.5 1,503.7 3,799.7 3,641.3 1,773.5 3,287.6 3,851.1 171. The Pennsylvania experiments ^ confirm the above results in general, with some modifications. Again nitro- gen has proved the most important element in increas- ing the growth and yield of apple trees in sod, although the other elements have seemed to be of greater importance here than in the Ohio work. In a summary statement Stew- art says, "The addition of phosphorus or potassium to ni- trogen applications has usually given larger returns than nitrogen alone. The nitrogen and phosphorus combina- tion has produced an average increase over the normal yields in two experiments of 265 and 308 bushels per acre amiually during 9- and 10-year periods. This combination is also proving important in one of the experiments in young or- chards. In at least three of the other bearing orchards. Loc. cit. Plate \'. — a, Kiiut ivom :in unthiiiiuHl liukhviii aiii)l(' iroo; 7 Inishels No. 1 fruit imd 17 ])ushels No. 2 fruit, b, Fruit from a thinned Baldwin tree; 19 bushels No. 1 fruit and 1)^ bushels No. 2 fruit. FERTILIZERS AND MANURES FOR THE ORCHARD 199 however, the addition of phosphorus has resulted in no im- portant benefit." Also, "Potash has increased the yields materially in three of the experiments in bearing orchards and apparently has shown some value in increasing the size of the fruit. It has also apparently had an injurious effect in two of the eight experiments. It would seem advisable therefore, to defer its general use in any particular orchard until definite evidence of its value. is secured." Manure has usually had a beneficial effect, although it is slower acting than nitrate of soda. These conclusions are supported by the following data: Table LXI 10-year summary of results in fertilizing apple orchards in pennsylvania. yield to the acre in bushels (after stewart) Treatment Trees in sod or grass mulch Baldwin, mature orchard York, Baldwin, mature orchard Bu. 228 488.6 450.9 291.8 479.9 519. Bu. Ill Nitrogen and phosphoric acid Nitrogen and potash as muriate Phosphorus and potash as muriate Phosphorus and potash as sulfate Nitrogen, phosphorus, and potash Nitrogen 486.1 318.2 113.1 91.3 292.2 186 2 405.1 The kind and amounts of fertilizer commonly used in the Pennsylvania experiments are shown in table on page 200. 200 POMOLOGY Table LXII AMOUNT OF FERTILIZER TO THE ACRE FOR BEARING TREES (after STEWART) Nitrogen Phosphoric acid Potash SO lbs. (N) 50 lbs. (P2O5) 25 to 50 lbs. (K2O) Carried in: Carried in: Carried in: 100 lbs. nitrate of soda 350 lbs. acid phosphate 50 to 100 lbs. muriate and or in of potash 150 lbs. dried blood 200 lbs. bone-meal or in or in or in 100 to 200 lbs. of low- 150 lbs. ammonium sulfate 300 lbs. basic slag grafle sulfate 172. New Hampshire experiments. — In order to de- termine to what extent the results from grass-mulch or- chards could be duplicated under the conditions existing Fig. 29. — Row of trees to l(^ft were fertilized with 5 pounds nitrate of soda each. Those to right were untreated. in New Hampshire, a test was arranged in a mature Bald- win orchard which was producing low yields. It had not been cultivated for several years, the grass being cut for hay and removed annually. The results secured by the treat- ments were quite similar to those obtained from the exper- iments just reviewed and demonstrate that the grass-mulch FERTILIZERS AND MANURES FOR THE ORCHARD 201 system of orcharding has wide apphcation. Table LXIII gives the treatments and the results secured for three years. Table LXIII YIELD OF BALDWIN APPLES IN A RENOVATED ORCHARD (nEW HAMPSHIRE) ALL TREES MULCHED WITH 200 POUNDS SWAMP HAY TO A TREE YIELD A ROW (8 TREES) IN BARRELS Row \o. Treatment 1916 Barrels 1917 Barrels i 1918 Barrels Average 3 years Barrels to the acre 1 7 lbs. basic slag to a tree . . 13.50 4.50 31.3 16.43 71.75 2 5 lbs. nitrate of soda 20.63 5.33 27.8 17,92 77.35 3 3 lbs. sulfate of potash 13.92 3.29 19.2 12.13 52.85 4 Check 9.48 3.30 24.1 35 . 36 12.29 53.55 5 28.88 6.97 23.73 103 60 5 lbs. nitrate soda 6 5 lbs. acid phosphate 3 lbs. sulfate potash 8.91 4.50 35.60 16.33 71.40 7 7.52 2.90 19.04 9.82 43.05 3 lbs. sulfate potash 8 Check 12.42 2.89 10.32 10.54 45.85 9 5 lbs. nitrate soda 3 lbs. sulfate pota.sh 21.08 4.51 20.24 15.27 66.85 10 5 lbs. acid phosphate 4.76 2.46 16.0 7.74 33.95 Ave. check rows, 4 and 8 10.95 3.09 20.21 11.41 49.70 Ave. nitrogen rows, 2, 5, 9 23.53 5.60 27.80 18.97 82.73 Ave. potash and phosphoric acid rows, 1, 3, 6, 7, 10... 9.72 3.53 24.23 12.49 54.60 EXPERIMENTS IN TILLED ORCHARDS It has been stated that a cultivated apple orchard usually responds much more slowly to the use of fertilizers than a sodded or mulched one, although there are conditions in which the response is as himiediate as in the latter case. While the former cases predominate, some standard experi- ments will be cited in which the trees have not responded to fertilization and others in which results were obtained. 1 Computed in part from total yield, approximately correct. 202 POMOLOGY 173. The Wobum experiment.^— At the Woburn Ex- perimental Fruit Farm (England), a cultivated orchard was treated annually for fourteen years and at the completion of the work the following conclusion was drawn: "Neither moderate nor heavy dressings of dung or artificial fertilizers, nor of both combined, had any appreciable effect on any feature of the trees nor on the crops from them. The total effect did not amount to 5 per cent and even that effect was doubtful. The only exception was in the case of nitrate ap- plied in the early summer which in several seasons produced a good effect." Later Pickering reports the following:^ "The results ob- tained at Ridgmont during twenty-two years lead to the conclusion that the apple trees which have been dressed every year throughout that period with various dressings of artificial or natural manure have shown no appreciable advantage over similar trees which received no dressing whatever. Whilst this, however, has been the case with dwarf and standard apple trees, and also mixed with plan- tations of apples, pears, and plums, the reverse has proved to be the case with bush fruits, such as currants, goose- berries, and raspberries: those which were left umnanured have been practically exterminated, whilst those which were manured flourished. But the manure which was essential in these cases was a bulky organic manure, such as dung, since artificial manures p'roduced but little more effect than no manure at all." 174. The New York experiments. — Hedrick reports on a twelve-year experiment ^ in a mature orchard in New York, showing that neither lime, potash, nor phosphoric acid had any practical effect on the growth or yield of the trees. 1 Woburn Expt. Fruit, Farm. 4th and 5th Rept. 1904-05. 2 Science and Fruit Growing. London. 1919. pp. 89-90. 3 N. Y. Agr. Exp. Sta. Bull. 289. 1907. FERTILIZERS AND MANURES FOR THE ORCHARD 203 The varieties involved were Baldwin, Fall Pippin, Rhode Island Greening, Roxbury Russet, and Northern Spy. Clean culture was followed annually until August 1, when a cover-crop of oats, barley, or clover was sown. Wood-ashes were applied at the rate of 100 pounds to a tree and also in the last seven years 83^ pounds of acid phosphate to a tree. The conclusion drawn is that: "The returns obtained in this twelve-year experiment are negative from a practical standpoint. The experiment shows that it is not profitable to apply potash, phosphoric acid, or lime to the soil of this orchard. Fifty-seven years of orchard cropping has not reduced this soil to the condition where it needs a 'complete' fertilizer, yet the leguminous cover crops plowed under in the orchard have usually produced beneficial effects the same or the next season. . . . An interesting fact is that both treated and untreated plots increased mark- edly in yield from 1893 to 1904. The probable explanation is that prior to 1893 the orchard was in sod but during the experiment it was kept under cultivation and grew more productive under the treatment." In another experiment ^ conducted in a younger orchard, a similar lack of response from the use of fertilizers is reported after fifteen years' work. The variety was Rome Beauty top-worked on Ben Davis. The following results were se- cured from the treatments: I N. Y. Agr. Exp. Sta. Bull. 339. 1911. 204 POMOLOGY Table LXIV YIELD AND GROWTH FROM FERTILIZER TREATMENTS (AFTER HEDRICK) Treatment Average yield to a tree, 7-yr. average Average diameter of trunk at end of experiment (1910) Stable manure Acid phosphate Muriate of potash Acid phosphate Muriate of potash 415.15 12.66 7.26 12.6 7.26 12.60 3.67 12.84 92.25 Lbs. 90.47 87.57 103.34 99.10 92.25 In. 6.26 5.98 6.35 Nitrate of soda 6.18 Check 6.14 It will be seen from these data that the fertilizers have resulted in practically no increases in growth or yield of the trees. Neither was there a difference in the uniformity of the crops or in the maturity, keeping quality, texture, or flavor of the fruit. It is recorded that the size of the apples was slightly increased by the treatments and that the foli- age was greener during the last season of the experiment where nitrogen had been applied. But the conclusion was drawn that "The trees in this experiment would have been practically as well off had not an ounce of fertilizer been ap- plied to them." After twenty years' work in this same orchard, the con- clusions are drawn that, "In general there are so many in- conclusive or contradictory results that no conclusion of practical value can be drawn from the yields. Heavy appli- cations of nitrogen in a complete fertilizer and in manure have not increased tree growth. When the costs are con- FERTILIZERS AND MANURES FOR THE ORCHARD 205 sidered, certain plats have given increases sufficient to equal the costs, or even to show a profit, but in other plats the same plant food elements have shown a financial loss." ^ 175. The New Hampshire experiments.— A somewhat similar experiment - was conducted by the New Hampshire Station. The orchard, which consisted of about 300 mature Baldwin trees, was situated on a light soil. It was found, after ten years, that the use of a complete fertilizer had de- cidedly increased the growth of the trees and that after the sixth year a better general appearance and darker green color was evident. This is in contrast with the New York experiment involving a heavier and richer soil, where such a difference was nol evident until the fifteenth year. How- ever, after twelve years' treatment, the fertilized plots failed to respond in yield of frint, as they had made very- slight gains and in some cases none over the first stimulus of the cultivation. An increase in size of the fruit, however, was distinctly noticeable, especially in the plot receiving the following treatment high in potash: 2 pounds nitrate of soda, 10 pounds sulfate of potash, and 8}^ pounds acid phos- phate to a tree (Plot 10). It was observed, however, that an increase in yield of fruit was to be expected in the near future because of the greater size of trees, and hence bearing surface. This is in accord with much of the work con- ducted in well-tilled orchards, some requiring, however, much longer to show the need of artificial "feeding" than others. In fact, some may never reach the point at which it would be economical to apply fertiUzers. The following table shows not only the effect of the fertilizers but also other cul- tural treatments as discussed in the previous chapter: 1 Hedrick, U. P., and R. D. Anthony. Twenty years of fertilizers in an apple orchard. N. Y. (Geneva) Agr. Exp. Sta. Bull. 460. 1919. 2 Gourley, J. H. Sod, tillage and fertilizers for the apple orchard. A ten-year summary. N. H. Agr. Exp. Sta. Bull. 190. 1919. 206 POMOLOGY Table LXV average annual yield to the acre in bushels (1909-1918) Plot 1 Sod 99 4 Clean tillage 191 5 Tillage cover-crops 196 6 To the acre: 70 lbs. nitrate 245 lbs. basic slag 188 140 lbs. sul. potash 7 To the acre: 70 lbs. nitrate 298 lbs. acid phos 154 140 lbs. sul. potash 8 To the acre: ' 70 lbs. nitrate 695 lbs. acid phos 145 140 lbs. sul. potash 9 To the acre: 210 lbs. nitrate 298 lbs. acid phos 160 140 lbs. sul. potash 10 To the acre: 70 lbs. nitrate 298 lbs. acid phos 176 350 lbs. sul. potash 176. The Maine experiment. — Much the same result has been obtained in the Maine experiments. A mature Ben Davis orchard of 400 trees was divided into three plots and the following treatments given: Plot A has had no fertilizer since 1912; plot B has received amiually since 1912, 500 pounds to the acre of a fertilizer carrying 4 per cent ni- trogen, 8 per cent available phosphoric acid, and 7 per cent potash; plot C has been given annually since 1912, 1000 pounds to the acre of a 4-8-7 fertilizer. For three years prior to 1912 the entire orchard was cultivated and fertilized at the rate of 1000 pounds to the acre of a 4-8-7 fertilizer FERTILIZERS AND MANURES FOR THE ORCHARD 207 which of course comphcates the matter but the results after eight years may be summarized as follows: "Exact records of yields and measurements of growth have been taken since the experiment was begun. No differences that could be attributed to the additional nitrogen (or other ingredients) in the fertilizer have been noticed." ^ 177. The Oregon experiments. — An interesting example of the influence of commercial fertilizers on a cultivated orchard of bearing apple trees is shown by the work of Lewis and Brown in Oregon.- The soils were exhausted by continual clean cultivation without the use of green- crops to maintain the supply of organic matter. Neither was irrigation practiced in order to supply the necessary moisture. As a result, the soils "lacked water-holding capacity, they baked or puddled early, and on hillsides were given to ero- sion." Two years' work demonstrated that no response of a practical nature could be expected from the use of potash or phosphoric acid, but when nitrogen was supplied the ef- fect was immediate. This would seem to be a special case in which the soil had reached the point of exhaustion of available nitrogen, and hence would no longer support the trees satisfactorily. Even though all these soils were cul- tivated frequently and part of them continually, the appli- cation of nitrogenous fertilizer gave as quick returns as when it is added to a run-down sodded orchard. The appar- ent exception here to the general premise in this text is prob- ably largely explained by the authors of the work as follows: "We are all familiar with the fact that shade crops induce bacterial action and by liberating nitrogen, stimulate tree growth. There are many evidences to show that alfalfa, left pennanently in the orchard, does not stimulate wood growth as rapidly as where placed in a shorter rotation with 1 Me. Agr. Exp. Sta. Bull. 236, 260. 2 Rept. 1916. Hood River Branch Exp. Sta., p. 37. 208 POMOLOGY clean tillage. The same rule to some extent applies to clover. In the former case, miless receiving an abmidance of water, often not the case, and care such as renovation and cultiva- tion in its somewhat unnatural environment, this shade crop does not make its best growth, and becomes soddy, a condition not only inimical to its own welfare, but to that of the trees as well. On the other hand, when organic matter such as clover or alfalfa is turned under frequently, say once in every three or four years, and followed by clean tillage, disintegration of organic matter and bacterial action are greatly accelerated, inducing great vigor of tree, especially in ' off ' years when the crop is light." It is, therefore, recog- nized that on the soils in question the nitrate was applied as a special measure and gave excellent results, but that such a treatment would probably not have been necessary had a better system of soil management been followed. It should also be stated in this connection that alfalfa may remain in the orchard for a period of years when properly handled without injury to the trees. The data in Tal)le LXVI give a summary of this work. 178. West Virginia experiment.^ — The experiments con- ducted in the Ohio Valley on impoverished soils, which were under cultivation, corroborates the results secured in southern Ohio. Nitrogen proved to be of first importance in obtaining a vigorous growth of trees and maximum yield of fruit. When phosphorus was used in connection with nitrogen, the results were somewhat greater than was se- cured from the latter alone, but the chief value of the phos- phorus seems to have been in promoting a greater growth of cover-crops and sod coverings. Potash apparently gave no response in these orchards. lAlderman, W. H., and H. L. Crane. W. Va. Agr. Exp. Sta. Bull. 174. 1920. FERTILIZERS AND MANURES FOR THE ORCHARD 209 Table LXVI results on spitzenburg apple trees from use of nitrate of soda (after LEWIS AND BROWN) Orchard > Plot I'uuiids to n tree. Nitrate of xoda Treatment, 3-yr. ave. to a tree 1914-1916. Ave. ter- minal growth. 1914 1915 Yield loose boxes 1914-1916 1 1. a 5.2 5.2 Clover 8.4 20.1 2. b 5.2 5.2 Green-manure 7.8 17.1 3. c 5.2 5.2 " " 5.3 16.1 4. No ferti izer Check 3 1 19.9 2 1. a 6.75 C.75 Alfalfa sod 8.8 15.4 2. b 6.75 6.7.5 9.2 8.4 3. c 6.75 6.75 11.8 14.7 4. No fertilizer Cheek 2.9 5.2 Lbs. nitrate to a tree 3 1. 7.3 16.1 11.7 No treatment 5.0 13.44 9.9 3. None 8.56 4.1 4. 3.0 12.61 14.1 4 1. 7.3 6.08 17.4 2 5.0 4.72 20.1 3. None 1.77 4.7 4. 3.0 5.78 17.7 In cultivated orchards in the eastern part of West Virginia where the soil is more fertile, the response from fertiliza- tion was practically negligible after eight years' work. 179. The Pennsylvania experiments.— The Pennsyl- vania Station - reports a set of experiments in tilled or- chards which is not in harmony with several of the others considered. It was found that under the conditions of their experiments, both manure and artificial fertilizers have given as good results in a cultivated as in a sod orchard. "In six cases with tillage, the gains from commercial ferti- 1 Orchards Nos. 1 and 2. a. Fertilizer broadcast on ground. b. Fertilizer sprayed on ground as liquid. c. Fertilizer sprayed on ground and tree as liquid. Orchards Nos. 3 and 4. Treatment began in 1916. All broadcast on ground. 2 Penn. Agr. Exp. Sta. Bull. 153. 210 POMOLOGY lizer have averaged 90.3 bushels per acre, and only 69.1 bush- els in the six corresponding cases without. Tillage, there- fore, has increased the efficiency of the fertilization in most cases. There were several important exceptions, however, and tillage excesses, either in depth or frequency, may actu- ally reduce the gains from fertilization." These conclu- sions are supported with the following data: Table LXVII ten-year summary of results in fertilizing tilled apple orchards (after STEWART) Treatment York, Stayman, Young orchard Ave. of checks Nitrogen and phosphorus Nitrogen and potash Phosphorus and muriate Phosphorus and sulfate Nitrogen, phosphorus, and potash. Nitrogen Manure 225.7 279.1 350.4 292.4 293.4 298.5 236.8 304.2 180. The Ohio experiments. — A discussion of these experiments was included under the section on "untilled orchards," since a comparative statement in that place seemed more desirable. 181. Results compared. — It is confusing to find such contradictory statements from a similar type of experiment, but the student should understand that it is the duty of the experimenter to report faithfully the results of his work without prejudice in regard to the results. When it becomes evident that the worker is endeavoring to prove instead of to find out something, the interpretation of his work is weakened proportionately. FERTILIZERS AND MANURES FOR THE ORCHARD 211 It is possible that the difference in results is due largely to the organic matter in the soil. In a climate where the season is long and the suramer heat intense, cultivation would "bum out" the organic matter or source of nitrogen much more quickly than where the opposite conditions obtain. Also a soil already devoid of organic material would probably produce the same results. It is at least worthy of notice that three of the experiments here consid- ered in which fertilizers in a cultivated apple orchard were very slow in producing results were in the North (Maine, New Hampshire, and New York). OTHER RESULTS OF FERTILIZING 182. Color of fruit. — In general, it may be stated that no fertilizer combination yet tried will increase the color of fruit appreciably. In some apple experiments there seemed to be a slight advantage to color from potash but not suffi- cient to warrant its use for this purpose. Alderman ^ gave double and triple applications of potash to plots of peaches and reports that there is "absolutely no effect upon color of fruit, a fact which indicates the worthlessness of this material as a coloring agent." In the case of a number of crops, phosphoric acid will hasten maturity, but this has not been observed with the apple. It has not infrequently been stated that iron salts will heighten the red color of fruits, and several well-planned experiments have been prosecuted to determine this point. At the Woburn Experimental Fruit Farm ^ where such a test was made, it was concluded after twenty-two years' work that where 2.8 grains of iron sulfate to a square meter or a similar amount of manganese sulfate was used, no ef- fect had been noticed on fruit color with the exception of 1 W. Va. Asr. Exp. Sta. Bull. 150. 1915. 2 Woburn Exp. Fruit Farm. 16th Rept. 1917. 212 POMOLOGY one year, and this was attributed to chance. Conversely, tillage or the use of nitrogen fertilizers or manure commoaly cause a profusion of foliage which shades the fruit and re- duces coloring; it also delays maturity and hence may lessen the red color of fruit. In other words, the development of color in fruit is largely dependent on maturity and the free action of sunlight. If fruits are bagged while green, they will not develop red color unless the bag itself is translucent to the extent of letting some light pass through when some proportionate color will develop.^ Where fogs occur and the intensity of the light is decreased, the color of the fruit is lower, and the converse holds true. 183. Fertilizing the peach. — It is not necessary to consider separately the fertilization of tilled and untilled peach orchards, since rarely is this fruit grown without cul- tivation. The outstanding fact to be considered here is that, unlike the cultivated apple orchard, the peach will usually respond readily to proper fertilization, particularly after the trees reach bearing age. Chemical data show that the peach is a heavy feeder and removes large quantities of plant-food from the soil. It is particularly striking that this fruit removes nitrogen and potash in great excess over phosphorus. This fact is well illustrated in Table LXVIII adapted from Alderman: ^ Since it has been shown that the peach uses large quan- tities of the soil ingredients in comparison with most other fruits, it might be anticipated that it should require rather heavy fertilization for best results. That the growth of the trees and yield of fruit are affected by proper fertilizing is shown by the following condensed table of the results se- cured by the West Virginia Experiment Station: 1 Blake, M. A. Rept. Soc. Hort. Sci. 1913. 2 W. Va. Agr. Exp. Sta. Bull. 150. 1915. FERTILIZERS AND MANURES FOR THE ORCHARD 213 Table LXVIII plant-food removed to the acre a year by the peach Nitrogen Phosphoric acid Potash New Jersey (173 trees) 64 lbs. 75 " 69.5" IS lbs. 18 " 18 " 40 lbs. New York (120 trees) 72 " Average 56 " Nitrate of soda 463 167o acid phosphate 112.5 Muriate of potash 112 Table LXIX EFFECT OF FERTILIZERS ON PEACH TREES (ADAPTED FROM ALDERMAN) Treatment ' ^ ^"7 1, 'SS^ ^^ e e -^5 1? ^ ^ ^ Lbs. to the tree Percent Sq. in. 69.95 80.6 4.28 71.93 75.5 4.26 72.06 74.0 4.06 49.48 58.0 2.63 42.42 57.9 2.89 82.29 76.0 4.12 82.09 75.2 4.39 82.59 76.2 4.26 60.82 64.4 3.26 ^ i Nitrogen and phosphoric acid . Nitrogen and potassium Complete C 'heck Potash and acid phosphate. . . Complete Complete with double potash. Complete with potash tripled. Lime Inches 16.1 14.47 15.0 8.16 7.28 14.40 15.59 15.0 7.84 ■ N = 200 lbs. nitrate of soda to the acre. P205 = 335 lbs. acid phosphate (16%) to the acre. K = 135 lbs. muriate of potash to the acre. 214 POMOLOGY The above experiment with bearing peach trees was con- ducted for four years. The soil in question was a shale loam and "low in fertihty," and each plot contained twenty trees of Carman and Waddell varieties. As a result of the treat- ments with nitrate of soda, the annual growth of the trees was double that of the untreated ones. The yield was nearly doubled also by the use of nitrogen but it delayed maturity by several days, which in some cases was advantageous from a commercial standpoint. Neither the element phosphorus nor potassium produced any beneficial effects and some in- jurious consequences followed the use of the latter. The influence of lime could not be definitely determined and was regarded as largely negative, although the produc- tion was somewhat increased. The trees which did not receive nitrogen produced fruit of higher color, but the cause was attributed to the extra sunshine which reached the fruit, owing to the sparse and sickly foilage. It is commonly stated that a limestone soil is markedly better than a non-calcareous one, but this statement is open to question, depending on what shall be considered such a soil and what is to be grown. Fruit-trees use lime in considerable quantities and would not thrive if the supply of carbonate of lime in the soil was veiy low, any more than other plants. However, as indicated before, it is not neces- sary to have a so-called limestone soil for the production of any of the common fruits. It is claimed that the "stone" fruits require more lime than the pome-fruit, although data are lacking to establish this statement. Lewis ^ reports that his work with lime on stone-fruits has given no benefits to the trees. On the other hand, lime seems to have been of some benefit to peach trees in the "Eastern Pan-handle" of West Virginia but no effect was noticed on the fruit itself. 1 Ore. Agr. Exp. Sta. Bull. 166. 1920. FERTILIZERS AND MANURES FOR THE ORCHARD 215 It is of course well established that lime will increase ni- trification in the soil, but orchard experiments, and many are on record, do not show much benefit from its use. The inter- crops and cover-crops, on the other hand, may require it and as soon as this can be determined, lime should ])e applied. 184. Effect of fertilizing on regular bearing. — It is usually found that, unless weather or other external causes interfere, fruit-trees that respond to tillage, fertilizer, or both will be more regular in their bearing than those that are somewhat below normal. It has been observed that well- fertilized trees are noticeably more productive in a season unfavorable for setting fruit or following a severe winter than untreated individuals.^ 185. Application of fertilizers.— When fertilizers are ai)])lied to a mulched or sodded orchard, they are merely broadcasted on the mulch or over the entire orchard area as the case may be, and the succeeding rains dissolve and carry them into the soil. This is usually done about the time the blossoms are ready to open, although in the case of nitrate of soda it may be applied earlier. When fertilizers arc added to a tilled orchard, they are usually applied after it is .plowed and perhaps harrowed once in the spring, thus incorporating them with the soil early in the growing season. 186. Size of fruit is influenced largely by the amount which a tree has set. Good cultural methods will increase the size provided they do not result in an overload of the trees, in which case the size may not be maintained. Ferti- lizers, especially those containing a liberal amount of potash, seem to have some effect in increasing size. Whenever moisture is well maintained, the size is increased. Manure will often produce excessively large and coarse fmits. Yomig trees are likelj^ to produce over-sized fruit, even to the point of losing some of the normal characteristics of 1 N. J. Agr. E.\p. Sta. Ann. Kept. 1884-94. 216 POMOLOGY the variety. Thinning has a greater effect on increasing size on a heavily ladened tree than any other practice. 187. Summary.^ — The following statements summarize the general conclusions which may be drawn from the fore^ going discussion: 1. The most fundamental difficulty in interpreting the experiments in orchard fertilization is due to failure to recognize whether or not an orchard is tilled. 2. Apple orchards in sod or grass mulch usually require fertilization to maintain the growth and yield of the trees. 3. Orchards which are being well cultivated, involving the use of some cover-crop, are likely to respond rather slowly to the use of chemical fertilizers, and when such bene- fit appears it is usually first seen in growth rather than in yield. 4. The length of time which an orchard under cultiva- tion can be operated without supplying additional fertility will depend on the initial fertility of the soil. 5. Nitrogen is likely to be the first limiting factor so far as soil fertility is concerned. This one element is likely to give as good results for a few years as a complete fertilizer, although on some soils the latter would be more desirable in the end. 6. This element (nitrogen) then may be supplied in either of two ways, by the use of the plow and harrow or from the fertilizer bag. 7. A peach orchard (which should always be cultivated) will respond generously to the use of fertilizers unless it is for the first two or three years after planting. 8. Red color of fruit is apparently not affected except adversely by fertilizing. 9. Size of fruit is variously affected by fertilizing. A 1 Author's statement. Proc. N. Y. State Hort. Soc, 2nd Ann. Meet- ing. 1920. pp. 92-93. FERTILIZERS AND MANURES FOR THE ORCHARD 217 veiy heavy crop, due to the treatment, may result in a de- crease in the size of the individual fruits, or if a moderate crop is produced the fruits may be markedly increased in size. Potash appears to be of some importance in increasing size. 10. An orchard which is inter-cropped should usually be manured or fertilized. 11. So far as apple trees are concerned, the addition of lime is rarely necessaiy, but it may be veiy desirable for the cover- or inter-crop grown. Peach trees have occasionally responded to applications of hme. 12. Inorganic forms of artificial fertilizers seem to give prompter results than the organic ones. 13. Yield and growth go "hand in hand" and are not antagonistic. 14. An early application of nitrogen (in a quickly avail- able form) will often stimulate the "set" of fruit the same season and hence give immediate results. CHAPTER X THE RELATION OF CLIMATE TO POMOLOGY The relation of climate to horticulture and agriculture is very intimate and is almost the ultimate determinant of what shall be grown. The orchardist feels that he has reached the frontier of his knowledge and ingenuity in at- tempting to combat the elements and overcome their devas- tating effects. Other factors, of course, determine where and what crops can be grown, but climate becomes the ac- tual determinant as the northern and southern limits for special crops are reached. While the forester studies the climatic conditions best adapted to certain types of tree growth and then does his planting accordingly, the horticulturist must consider the climatic peculiarities and causes of failure and then deter- mine means of overcoming them. It is also true that insect and disease pests are more abundant and more destructive some seasons than others, owing to favorable weather con- ditions, and the grower must accordingly modify his plans to combat them successfully. 188. Terms defined. — Climate has been defined as the average condition of the atmosphere, while weather denotes a single occurrence, or event, in the series of conditions that make up climate. The climate of a place is, then, in a sense its average weather. Phenology is the science of the rela- tions between chmate and periodic biological phenomena, such as the flowering, leafing, and fruiting of plants. The particular natural phenomena constituting climate that are of special interest in this connection are, tem- perature, rainfall, wind, sunlight, frost, hail, and humidity. 218 THE RELATION OF CLIMATE TO POMOLOGY 219 189. Relation of weather to the fruit crops. — The weather may specifically affect the fruit crop for any given season in two general ways: (1) it may govern largely the poten- tial possibilities of the trees to form fruit-buds; and (2) it may partially or entirely destroy the buds, blossoms, or crop in the process of development. These effects of weather on the fruit-crop may be subdivided as follows: (a) the nature of the growing season may be favorable or unfavor- able to a set of fruit-buds for the ensuing setation and the total effect of the warmth of the air nuist be observed in studjdng it. There is a minimum and maxumim temperature, below or above which the plant does not function, and there is for each kind an optimum tem- perature at which it grows or functions best. The minimum for most higher plants is around 40° to 43° F. and the maxi- mum is from 85° to 114° F., while the optima range from 75° to 85° F., depending in all cases on the species in ques- tion. Since the various phases of the plants ' functions may have different optima and since it is also difficult to define closely these terms, the above temperatures should be con- sidered as applying particularly to the more manifest growth activities. The student of pomology is interested in both the temperatures of the growing season and those of winter, 220 POMOLOGY for much damage may occur from too low or too high tem- peratures during the winter rest. The latter are treated in Chapter XL Many fruit sections are accmnulating data on which fu- ture plantings may be based with greater intelligence. The mean amiual temperature or the mean of the 365 successive daily means is a figure of importance for any given place, as is also the mean temperature of the hottest six weeks. The annual mean is frequently computed from the twelve monthly means which is practically the same as when calculated on the daily basis. The average dates of the last frost in spring and the first frost in autumn are also of great im- portance to the pomologist and vegetable-gardener. From these figures is calculated the average number of days free from frost at any particular point, and hence the length of the average growing season. The total temperature necessaiy for the development of plants or for the accomplishment of any phase of their growth has been a question of interesting speculation for many years and has resulted in an attempt to secure the "physiological constant" for a plant, which is discussed in a later paragraph. The general temperature conditions for the larger regions of this countiy are indicated in paragraph 198. From the standpoint of the pollination and "setting" of fruit, temperature is of vital importance and this is treated more fully in connection with pollination of fruits (Chapter XII). Aside from actual injury to the floral parts, partic- ularly the pistils from frosts and low temperatures, the development of the pollen-tube may be checked materially when the temperature falls below 50° F. The bees are not active much below 65° F. and hence the opportunity for pollination of the flowers is greatly reduced when the tem- perature remains constantly below that point during the period of blossoming. THE RELATION OF CLIMATE TO POMOLOGY 221 191. Rainfall. — The rainfall situation is indicated for the larger districts under paragraph 199. Most sections are likely to suffer at times from droughty conditions but a large part of the United States is well supplied with rainfall. The distribution of the rainfall throughout the twelve months has much to do with its efficacy in crop production, for even though a heavy annual rainfall is recorded for a region, it will avail little if a large proportion of it falls in the non-growing period. Rain at the blossoming period of fruit-trees is particularly injurious to the crop from both direct and indirect causes. It is primarily injurious because it prevents pollination, es- pecially when the rain is accompanied by cold weather and gales of wind. Injury to the floral parts may result from such weather conditions, but more particularly the insects instrumental in effecting pollination are not active. In the twenty-five years between 1881 to 1905, inclusive, Hedrick reports fourteen seasons in which rain or snow at blossom time was destructive or partially so to the fruit crop in some sections of New York state. ^ The effect of such inclement weather is probably more pronounced with self-sterile varieties of fruits than with the self-fertile ones. According to the investigations of Dorsey, rain operates against poUination and fruit-setting by causing the anthers to close or by preventing them from opening, but it does not burst the pollen-grains nor kill them. Neither does rain wash pollen from the stigmas to any great extent as has been reported, since there is a strong adhesive action between stigmas and pollen. In general, however, no fac- tors of weather are so effective in preventing the setting of fruit as rain and low temperatures.- 1 N. Y. (Geneva) Agr. Exp. Sta. Bull. 407. 1915. -Dorsey, M. J. Relation of weather to fruitfulness in the plum. Jour. Agr. Res., Vol. 17, No. 3. 1919. 222 POMOLOGY 192. Spring frosts. — Frosts in autumn are of some economic importance to the pomologist, but those occurring in the spring are usually much more disastrous to the fruit crop, and are considered here more in detail. The destruc- tion of blossoms and hence the prospective crop by spring frosts either locally or over rather large areas is a common occurrence and one of the most ruinous phases of fruit-growing. The United States Weather Bureau distinguishes three types of frost, based on the degree or severity of it, namely: "light," "heavy," and "killing." The latter two are usu- ally distinguished by the extent of injury to vegetation rather than to the actual amount of deposit. The term "killing frost" is described as one which is generally de- structive to the staple products of the locality. Vegetation may also be damaged by low temperature without an actual deposit of frost, a condition due usually to cloudiness. The probable dates of killing frosts for any locality are a valu- able guide to the fruit-grower and gardener and some maps have been prepared by the Weather Bureau showing the dates of the last killing frosts in spring for the different re- gions of the United States. The same sort of map is given for the last killing frosts in the fall and for the average num- ber of days without killing frosts.^ These maps are based on a very large number of records from many regular and cooperative stations of the Weather Bureau. There is great irregularity in the dates of the last frosts in the spring and the first ones in the fall for any given place, and usually the arithmetical average of these dates is used in construct- ing the maps but such a date entails a large amount of risk, one year with another. On the other hand, if the latest frost date recorded in the spring and the.earhest in the fall ' Reed, William Gardner. Frosts and the growing season. U. S. Dept. Agr. Off. Farm Manag. 1918. THE RELATION OF CLIMATE TO POMOLOGY 223 are used for calculating crop risks, then many years the grower limits his season much more than would have been necessaiy. While a fruit-grower may attempt to determine places that are safe for fruits by computing the average date of the last killing frost, yet it must be expected that in the most favorable locations there will occasionally be de- structive frosts. For New York state Hedrick has recorded a surprising frequency of frost damage in the fruit-growing regions, stating that "Fruits were injured at blossoming time by frosts in thirteen out of the twenty-five years under consideration." ^ Frost injuiy may take the form of russeting the fruit, occurring either in bands, in patches about the basin or cavity, or in spots on the surface of the skin. It may also cause blistering of the young leaves when they first expand, in which case they do not fully develop and often fall prematurely. In addition to the destruction of the pistils and ovaries of the flowers, the stems may be injured and the flower-cluster base may also be discolored, which oftr>n results in a heavy drop of the fruit. 193. Winds. — Heavy winds also play a part in the weather conditions that affect fruit-growing. They are by no means such destructive agents as temperature and rain- fall maj^ be, but they may reduce the number of blossoms which set fruit and prove ruinous to the crop as it approaches the hai-vesting season. Just as rain or humid conditions may prevent bees and other pollen-carrying insects from working during the blossoming season, so winds may also greatly reduce their activity and consequently reduce pol- 1 N. Y. (Geneva) Agr. Exp. Sta. Bull. 299. See also Wilson, W. M. Frosts in New York. N. Y. (Coniell) Agr. Exp. Sta. Bull. 31G. 1912. U. S. Dept. Agr. Farmers' Bull. 1096. 1920. Paddock, Wendell, and Orville B. Whipple. Fruit-Growing in Arid Regions. New York, 1910. 224 POMOLOGY lination. To what extent the floral parts, particularly the stigniatic fluid, of fruits in general are affected by the dry- ing action of wind cannot be stated definitely, but in the plum Dorsey noted that dehiscence was quickened as a re- sult of wind action and petals dropped earlier, but a drying of the stigmatic fluid was more critical late in the receptive period than in the earlier stage. The effect of wind on the maturing crop of fruit is a con- stant source of economic loss, as more or less fruit is blown from the trees every year and some seasons it assumes se- rious proportions. Windbreaks and close planting of trees on the windward side are often used to reduce the damage. Winds, in some sections, cause young trees to grow one- sided and to lean to the leeward, but it would be difl^cult to estimate the actual damage which results. One of the most serious effects of wind in fruit-growing is that encountered during the spraying (or dusting) sea- son. Not infrequently that work must be delayed on ac- count of high winds until the fruit crop is jeopardized. 194. Sunshine.- — Just as rain is the most unfavorable element in preventing the pollination and setting of fruit blossoms, so conversely is sunshine most favorable to its setting, especially when accompanied by a relatively low percentage of humidity. This condition affords the best opportunity for the agencies of pollination and also the growth of the pollen-tube. When the period of blossoming is bright, the flowers are usually in bloom for a shorter period, as would be expected. The absence of sunshine does not mean, however, that pollination may not take place freely. Sunlight is of first importance, of course, for the growth of plants in general and in the development and coloring of the fruit. 195. Hail usually occurs during the summer and may cause serious loss in the orchard as well as to farm crops. THE RELATION OF CLIMATE TO POMOLOGY 225 The hail marks on the fruit injure its selHng quahty and indeed may break open the skin, thus encouraging rapid deterioration. In some sections it is not un- common to find an entire fruit crop de- stroyed. (Fig 30). Serious injury may also occur to the tree itself, the healed scars often resembling some- what the work of the tree cricket (Oecanthus sp.) or cicada (Tibicen septendecim). 196. Continental ver- sus marine climates. — The climate of the in- terior of the northern sections of the United States and Canada is nnich more severe than is the marine climate on the same parallel. This difference is pri- marily due to the fact that the specific heat of water is much higher than the materials of which the earth's sur- FiG. 30. — Apple tree injured by hail storm. Note abrasions of bark and partial defoliation. 226 POMOLOGY face is composed. According to Hann,^ if the specific heats of equal weights of water and dry soil are compared, the latter would be 0.2 of the former, but when equal volumes are com- pared, the specific heat of the land is about O.G that of water. In other words, if equal quantities of heat are received by equal areas of land and of water, the land will have its temperature increased almost twice as much as the water. Therefore, this slowness with which water takes up and gives up its heat accounts for the more equable temperature of land adjacent to large bodies of water, particularly on the leeward side. The more exposed the land area is to the influence of ocean winds, the more uniform is its tempera- ture. The case cited later of the western section of the state of Michigan illustrates this fact as it pertains to pomology. Just as marine climates are more equable, so continental climates are characterized by a great range of tempera- ture. 197. Mountain versus valley climates. — One of the teach- ings that has become axiomatic in fruit-growing is to plant orchards on elevations and avoid valleys, coves, or other places where the movement of the air is restricted. This doctrine is based on the fact that the cold air drains from the high lands into the valleys and often results in damage to the crops in the latter places when those on the higher elevations may escape injury. Other factors, such as hu- midity of the atmosphere, also play an important part in the behavior of plants in valleys and on mountains. In general, a climate characterized by low humidity and bright sun- shine throughout the growing season will usually produce a fruit which has a clear skin and is comparatively free from such diseases as scab and sooty fungus. Such a climatic ' Hann, Dr. Julius. Handbook of Climatology. Eng. Trans. The Macmillan Cpmpany, New York. 1903. THE RELATION OF CLIMATE TO POMOLOGY 227 condition usually obtains at high altitudes and the reverse in valleys. High altitudes, especially in the East, may be humid and, therefore, the greater freedom from disease would not be found as indicated in the above statement. Aside from the presence of large bodies of water, no factor is so potent in causing differences in climate along any par- allel of latitude as elevation above sea level. The facts here would seem to be contradictoiy, for there is a vertical decrease of temperature with the increase in elevation, amounting to about 1° F. for every 300 feet. The amount of decrease of temperature will vary with the latitude, exposure, season, and local conditions. But what is termed "inversions of temperature" occur in clear cool nights up to a certain elevation which results in the higher lands being warmer than the valleys. According to Hann,^ "This increase of temperature upward reaches alti- tudes of at least 300 m., and is rapid in the lower strata, but slower farther up." In this country the effects of these inversions of temperature are experienced at practically all elevations at which fruit is grown, except as noted elsewhere, in certain canyons in the western United States. The occurrence of the colder temperatures in valleys is explained by the fact that there is a radiation of heat from the earth during the night and as a result the earth is cooled. The stratum of air which lies next to the earth is cooled, and, as cold air is heavier than warm, it results in its flowing downward, and the warmer air of the valley rising. Air will also lie in strata of somewhat equal temperatures, which phenomenon is experienced in traveling over undulating country, particularly at night. As a result of the above facts, it is frequently noted that fruit blossoms (and other vegetation) are injured or destroyed at lower elevations and those higher up escape damage. Even the blossoms on the 1 Loc. cit., p. 252. 228 POMOLOGY lower part of a tree may be entirely destroyed and those above be unhurt and develop a crop. Paddock and Whipple discuss fruit-growing at high alti- tudes as follows: "In a few favored locaUties peaches are successfully grown at an altitude above 6000 feet. But on the Eastern slope of the (Rocky) mountains no peaches are grown commercially without winter protection where the altitude is only 5000 feet. ... In general it may be said that as a rule, fruit cannot be grown to any extent at an altitude much above 5000 feet, and at this height much depends on the protection afforded by the moun- tains." 198. Climate of United States. — Due to the extent of territory comprised within the United States, there is a great variety of climate, from the Arctic region on the northwest to the semi-tropical climate of the south; yet the great pro- portion of this country lies within the temperate zone. However, as has been shown by Henry, ^ a great difference exists in the length of the growing season as latitude and ele- vation are changed and that this can be reduced to defi- nite laws will be seen later. The map in Fig. 31 shows this variation from a five months' season in the North to a twelve month in the South. Such a condition makes evident that climate will limit fruit-growing in certain sections except as artificial means and certain cultural practices are employed that will overcome the natural barriers. Any statistical statement of meteorological data would be too extensive for use here, but the student should fa- miliarize himself with local conditions. The extremes of rain- fall and temperature will serve to emphasize the wide diver- sity within the borders of the United States. These data may best be examined in connection with the several so- called climatic provinces of the United States. 'Henry, A.J. Weather Bur. Bull. Q. Washington, D. C. 1906. THE RELATION OF CLIMATE TO POMOLOGY 229 199. Climatic provinces of the United States.^ — While chmate frequently vai'ies inarkecUy within comparatively short distances, yet there are several grand divisions within REGIONS. BASED ON PERIODS OF GROWTH AND REST' Per.od of Veget-ation ■""" V^ ^^::^ SMonths '^^ 7 Months, . ^^ May-October.. 6Mon(h3 ^riz'j^:'''''' ^^^ Apr.l-Octobcr 7 Months ipr-a November -March ''^ S Months ^* Apr.l-Nove Tiber 6 Months QHJ December-March 4Montti3 March-November 9 Months ^a December -February 5 Months February - November OT5i December -Oanuary 10 Months "'^ 2 Months ' rebruary-Ded ember f-r;^ January II Months ^—^ 1 Month January -December 12 Months ^ No Period of Rest Fig. 31.— Length of growing season in different parts of the United States. the country which represent regions of similar climate. These have been described as "climatic provinces," being five in number. The largest, or Eastern, extends from the 1 Adapted from Ward, Robert DeC. The essential characteristics of U. S. climates. Sci. Month., Vol. II, No. 6. Dec, 1920. See also Bailey, L. H. Principles of Fruit-Growing, New York. 2Cth Ed. 1915. p. 11. 230 POMOLOGY eastern margin of the Great Plains, which roughly coin- cides with the 20-inch annual rainfall line and also with the 100th meridian, to the Atlantic Ocean, and southward nearly to the Gulf of Mexico. The strip bordering on the Gulf may be set apart as a subordinate district, the Gulf province. The Plains province includes the Great Plains proper, and extends westward to the Rocky Mountains. Between the Rocky Mountains and the Sierra Nevada-Cascade ranges comes the Plateau province. The Pacific slope constitutes a natural climatic region which may be called the Pacific province. ''The differences between north and south, resulting from differences in latitude, suggest a further subdivision of the Plains, Plateau, and Pacific provinces into northern and southern sections. Similarly, the Gulf province occupies the more southern latitudes of the Eastern province." 200. The Eastern province. — This extensive area is characterized by great uniformity in its climatic conditions and weather types. Over most of it the seasons are strongly contrasted. The summers are very warm and the winters cold. The rainfall is abundant or at least sufficient for agri- culture and nowhere in this district is there permanent ne- cessity of irrigation. There are only relatively slight and unimportant differences of topography, the whole area be- ing freely open from Canada on the north to the Atlantic Ocean on the east, and to the Gulf of Mexico on the south. In January, the isotherms over the eastern United States are very closely crowded together. The temperature then decreases northward at the rate of 2.7° F. in each degree of latitude, both on the Atlantic coast and in the Mississippi Val- ley, which is an extraordinarily rapid temperature-gradient. There is, however, much less difference of temperature be- tween South and North in summer. It becomes 1.1° along the eastern coast and 0.7° in the Mississippi Valley. THE RELATION OF CLIMATE TO POMOLOGY 231 The temperature conditions have been briefly generahzed as follows: Table LXX temperature conditions of the eastern province District Mean annual Jan. July Abs. mux. Abs. min. N S 40° 65°-70° 5°-10° 50°-55°+ 65° 80°+ 100°-105° 105° -40° to —50° zero- 10° The average dates of first and last frost, broadly gener- alized, are as follows: Table LXXI length of growing season, eastern province District Last Spring Fii'st Autumn Average length of growing season N S After June 1 (extreme N) Before March 1 Sept. (extreme N) November 3-4 months 7 months and over As indicated above, the rainfall is usually sufficient for vegetation over this province and well distributed through- out the year. Disregarding local areas on the mountains, the amiual rainfall is greatest (50+ inches) towards the Gulf, and on the South Atlantic coast and decreases from about 40-45 inches over much of the north and central Atlan- tic coast and Ohio Valley to 30-40 inches over the prairies and 20 inches at about the 100th meridian. 201. The Gulf province.— Over the southern tier of states bordering on the Oulf of Mexico, the temperatures are higher; the winters are much milder; the summers are 232 POMOLOGY longer and hotter; the rainfall is heavier; and there is a late summer or early autumn maximum. 202. The Plains province. — The essential difference be- tween the climate of the Great Plains and that of the East- em province is not so much one of general temperature conditions as of rainfall. The similarity of temperature may be seen by comparing the summary below with that given under the Eastern province. Table LXXII temperature conditions of the plains province District Mean annual January July Abs. max. Ahs. min. N S 40° 65° 0°-10° 40°-50° 65°-70° 80°-85° 105°-110° 110° —50° to —60° zero As compared with the eastern states, the Plains have larger diurnal ranges of temperature; more abundant sun- shine; drier air; greater evaporation; smaller rain probabil- ity; less rain; more wind. The contrast in rainfall between the Eastern and Plains provinces is striking. From a 20-inch rainfall on the eastern margin of the Plains, it decreases to below 15 inches on the western margin, and where the rain- fall is below 20 inches it is insufficient for successful agricul- ture, and irrigation must be practiced. 203. The Plateau province is a great interior region of very diversified topography. It has a wide range of moun- tain, high plateau, and arid lowland climate, superposed on and causing local modifications of the general dry continen- tal climate of the province as a whole. The outstanding characteristic is the small rainfall, which, however, shows marked increase with altitude. With the exception of local areas in the mountains, the mean annual rainfall is every- where less than 20 inches; it is mostly below 10 inches, and THE RELATION OF CLIMATE TO POMOLOGY 233 over no insignificant portion of tiie Southwest it is even be- low 5 inches. 204. The Pacific province. — Over the narrow Pacific coastal belt climati(; conditions are quite unlike those else- where in the country, and in many respects resemble those of northwestern and western Europe, including the Medi- terranean area. The wide range of latitude between north and south, together with the vaiying topographic controls and the differences of exposure to the ocean influences, ex- plain the great variety of climate in this province. These range from those of the rainy and densely forested slopes of Washington to those of semi-arid southern California; from those of the lowlands to the snow-covered mountain tops; from the cool sununer of the coast to the hot summers of the Great Valley. The climate, in general, is mild and equa- ble, with slight diurnal and seasonal ranges. The following table summarizes, in a very general way, the essential temperature characteristics of the Pacific prov- ince: Table LXXIII rEMPERATURE CONDITIONS OF THE PACIFIC PROVINCE District Mean amiual Jan. July Abs. max. Abs. min. N S 50°-55° 65° ± 35°-40° 50°-55° 60°-65°+ 65°-75°+ 95°-105° 110°-115° 10°- 0° 20°-10° The rainfall is heavy (over 100 inches) on the northwest- em coast of Washington, and decreases rapidly to the south, to about 10 inches in the San Joaquin Valley. 205. Natural guides to horticultural practices.— From earliest times the grower of crops has made use of certain natural guides to determine when he would plant and har- vest his crops as well as for other activities about the farm. Such an expression as "it is time to plant com when white 234 POMOLOGY oak leaves are the size of squirrels' ears" is familiar. Others use the time of the arrival or migration of certain birds, the unfolding of the leaves or flowering of certain plants, or the appearance of certain insects as an index to farm and or- chard practice. Such a method, if well observed, should be a veiy accurate guide, as it represents the sum of all the complex factors involved and no instrument can do this. 206. Bioclimatic law of latitude, longitude, and altitude.^ — A large number of observations made at many points and over a period of years has resulted in the deduc- tion of a set of laws in regard to the response of plant and animal life to climate. Howard reports the following laws: 1. The periodical phenomena of plants and animals are in response to the influence of all the complex factors and elements of the climate as controlled, primarily, by the mo- tions of the earth and its position relative to the influences of solar radiation. 2. The variations in the climate and consequent varia- tions in the geographical distribution and periodical activi- ties of the plants and animals of a continent are controlled by the modifying influences of topography, oceans, lakes, large rivers, and of other regional and local conditions, and the amount and character of daylight, sunshine, rain, snow, humidity, and other elements and factors of a general and local nature. 3. There is a tendency toward a constant rate of variation in the climatic and biological conditions of a continent as a whole in direct proportion to variation in geographical posi- tion as defined by the three geographical coordinates, lati- tude, longitude, and altitude. lU. S. Dept. Agr. Monthly Weather Review. Suppl. No. 9, 1918. A. D. Hopkins. Periodical events and natural law as guides to agricul- tural research and practice. THE RELATION OF CLIMATE TO POMOLOGY 235 4. Other conditions being equal, the variation in the time of occurrence of a given periocUcal event in hfe activity in temperate North America is at the general average rate of 4 days to each 1 degree of latitude, 5 degrees of longitude, and 400 feet of altitude, later northward, eastward and up- ward ill the spring and early summer, and the reverse in late suimiier and autumn. 5. Owing to the fact that all conditions are never exactly equal in two or more biological or climatic regions of the continent, and rarely alike in two or more places within the same region or locality, there are always departures from the theoretical time constant. 6. The departures, in number of days from a theoretical time constant, are in direct relation to the intensity of the controlling influences. Therefore, the constant, as expressed in the time coordinates of the law, is a measure of the inten- sity of the influences. Fig. 32 shows the working of this law as adapted to North America. "Taking base maps of North America and of the major and minor political divisions, parallel lines (des- ignated as isophanes ^) are drawn on them to define, accord- ing to the bioclimatic law, theoretical lines and zones of equal phenomena as to time of occurrence and equal biocli- matic conditions, at the same level."- "The isophanes, instead of following the parallels of north latitude in North America, proceed from the Atlan- tic to the Pacific in a northwestward curve at the rate of 1 degree of latitude to 5 degrees of longitude (Fig. 32), so * Isophane. In phenology, an isochrone of the first blossoming of a specified plant. Isochrone. Phenological isochrone is a line drawn between points at which plants of the same species attain the same degree of de- velopment simultaneously. (Standard Dictionary.) ^ For full explanation, see original text. 23G POMOLOGY that they serve as a diagrammatic expression of the average rate of four days' variation for 1 degree of latitude and 5 Fig. 32. — Isophanal map of North America. degrees of longitude. Therefore one of these lines across the continent at any given level of land surface represents the THE RELATION OF CLIMATE TO POMOLOGY 237 same average phenological constant date of a seasonal event and the same average climatic and biological conditions." In other words, if 1 degree of latitude is assumed to be equal to about 70 miles and 1 degree of longitude equal to 50 miles, then, other things being equal, there are 4 days variation for eveiy 70 miles north or south and for every 250 miles east or west from a given point, and for every 400 feet altitude. Or if any given isophane is followed, there would be no variation in time of occurrence of the nat- ural phenomena. Variations from these rules will occur, depending on such modifying influences as are mentioned in rule 2. A fuller appreciation of this subject means that spray cal- endars must be made up for conditions of similar climatic conditions; a study of insect and disease control must con- sider the local conditions; and so for many agricultural prac- tices and researches. 207. Species adaptation. — It is not a settled question as to liow far a species native to one set of climatic condi- tions can become adapted to an entirely different climate. That is, can a plant from a warm region gradually become acclimated to a cold one and hence secure hardier strains or races of tender plants? Can a plant which requires a moist growing season gradually become adapted to xero- phytic conditions or vice versa? These questions are of great importance in the science of pomology and much difference of opinion is recorded in literature. It is now usually ac- cepted, however, that a plant is not gradually changed to suit its enviroimient but that it is necessaiy to secure indi- viduals which possess the character desired and from this stock so breed a new strain as to combine other desirable qualities. At least this would seem to be the shortest and surest method of securing better fruits for extreme condi- tions of soil and climate. 238 POMOLOGY It is, of course, well known that a given variety or species becomes somewhat adapted to the length of growing sea- son in widely differing sections of the country, but this is not to be interpreted as meaning that a variety of peach, apple, or other fruit having the capacity to withstand a cer- tain minimum degree of temperature may be acclimated to a still lower one by adaptation. The work of Whitten, Dorsey, Macoun, and others show adaptation within certain limits. 208. Temperatures which injure setting of fruits. — It is well known, as stated above, that frosts destroy fruit blos- soms frequently, but it is also true that injury may occur without apparently killing the tender tissues. The after effects of the latter are seen in the heavy fall of fruit during about three weeks following the blossom period. The following figures give the temperatures at which the various fruits may be injured at blossom time: Table LXXIV temperatures which injure setting of fruits ^ Fruits In bud In blossom In selling fruit Degrees F Degrees F Degrees F Almonds 28 27 30 22-29 31 29 28 30 28 28 28 30 29 31 28-30 31 30 29 31 28 28 28 30 30 Apricots Cherries Grapes Peaches Pears Plums Strawberries Raspberries 32 28-30 30 30 29 31 28 28 Blackberries 28 ' See West, Frank L., and N. E. Edlefsen. Freezing of fruit buds. Jour. Agr. Res., Vol. 20, No. 8. 1921. THE RELATION OF CLIMATE TO POMOLOGY 239 Several factors determine at what temperature such in- jury occurs, for it is well known that it is not consistent. The amount of moisture in the atmosphere at the time of frost is conmionly cited as of the greatest importance, the greater tlic humidity the less likely will there be injuiy. Also the individuality of the plant may enter into the problem. West and Edlefsen conmient as follows in regard to this phenomenon: "The fact that the same branch of buds will on one occasion experience 27° F. with 25 per cent injuiy and on another occasion take the same temperature with no injuiy is no doubt due to the fact that the juice is con- tained in capillaiy cells and supercooling results — that is, the buds are cooled below the freezing point of the juice without the freezing taking place. The great difficulty of killing all the buds even at extremely low temperatures is due to the same cause together with the fact that the cell sap may be very concentrated. Differences in the hardi- ness of the different kinds of buds and also of the same buds at different stages of development is due to differences in quality and concentration of the cell sap." It is easy to overestimate the damage at the time of the low temperatures, for no means are available for determin- ing the extent of injuiy unless the floral parts (usually the pistils first) are blackened or withered. Orchards in which the blossoms seemed entirely destroyed may still set a fair crop of fruit. 209. Averting injury from frosts and freezes.^ — Attempts are sometimes made to avert injuiy to the fruit crop from spring frosts by various devices. Whitten ^ whitewashed peach trees to delay their blossoming, with some success. The principle made use of here is that a white surface will ' See papers on frosts and frost protection in U. S. U. S. Dept. Agr. The Monthly Weather Review, 42: 562-592. 1914. 2 Mo. Agr. Exp. Sta. Bull. 38. 1897. 240 POMOLOGY reflect light and heat, while a dark one absorbs it. Thus the whitewashed trees were delayed a few days in their time of blooming. He also shifted the resting period later in the winter by later tillage and accomplished similar results. The heating and smudging of orchards are also used rather extensively in some sections to ward off frosts and hold the heat radiated from the earth. Laying trees and vines down during the winter and cov- ering with earth or other material is also practiced to a lim- ited extent, as well as baling trees up with straw or fodder. The important factor here, however, is the proper loca- tion of the orchard. As indicated previously, high lands are more immune to frosts than low ones, so that there is a free movement of air and a drain of the cold air to lower levels; also coves or pockets should be avoided. The slope of the land is of some importance, particularly as the south- ern limits of fruit-growing are approached, and also with fruits that respond quickly to warm spells of weather oc- curring early in the season. The southern and southeastern slopes absorb more heat and hence trees often blossom some- what earlier here than on the northern exposures. It is easy to overestimate the value that can be gained by such a selection, however. The following figures indicate the proportional amount of heat received to a unit area by different slopes on June 21, at the 42d parallel north latitude:^ 20° Southerly slope = 106 Level = 100 20° Northerly slope = 81 One of the best known and in some respects most unique cases of the effect of water on climate is seen in the Michi- gan "fruit-belt." This is a strip of land from ten to twenty 1 After Lyon, Fippin, and Buckman. Soils. New York. 1915. p. 318. THE RELATION OF CLIMATE TO POMOLOGY 241 miles in width along the west side of the state from the In- diana line nearly to the Straits of Mackinaw. The southern boundary of this belt is about 42° N. latitude while the i jL..^ J DELTA Fig. 33. — Map showing the boundaries of the Michigan fruit-belt. northern boundary is almost 46°, and in this belt are exten- sively grown such tender fruits as the peach and cherry. The accompanying map ^ (Fig. 33) shows the boundaries 1 After Seely, adapted from Taft. Commercial cherry culture. Proc. Amer. Pom. Soc. 1917. p. 107. 242 POMOLOGY of the fruit-belt and indicates the isothermal lines as they locate the last killing frosts of the spring. The tempered effect along this littoral region is due to the prevailing winds passing over Lake Michigan during most of the winter and spring months. In the spring the winds are kept continually cool in passing over the lakes and hence prevent unseason- able advancement of the fruit-buds in April and May which results in disastrous effects in unprotected regions. On the other hand, the winter winds that leave the Wiscon- sin shore at a temperature of thirty to forty degrees below zero arrive on the Michigan side at a temperature of little if any below zero, since the waters of the lake rarely freeze over and are connnonly some three to five degrees above the freezing point. While a minimum range of ten to fifteen degrees below zero may be recorded along the northern sec- tion of this "belt," it may be thirty or forty degrees below zero in the north-central counties of the state. 210. Effect of climate on the floral structure. — Climate may have a veiy definite effect on the floral structure and more particularly on the vitality of the parts of the flower. A long and serious controversy was waged in the early his- tory of strawberiy-growing in this country (1850-70) on the sexual characters of this fruit. In some sections cer- tain varieties were perfect flowering and in others the same kinds were imperfect. That the climate had affected them in this way was later discovered. The same is true with the strawberry grown in eastern United States and in Eng- land, where in the latter place the mild, humid climate some- times causes imperfect flowering sorts to become perfect. The Bartlett pear, which is usually self-sterile, is reported by Garcia to be sufficiently self-fertile to insure fair crops of fruit in New Mexico. Likewise in California it was found that the Bartlett is self-sterile on the high elevations and partially self-fertile in the valleys. THE RELATION OF CLIMATE TO POMOLOGY 243 211. The effect of climate on development of fruit. — Shaw ^ luis shown that the variation in apple varieties is due to three principal causes: (1) cultural practices, (2) soil variation, (3) climate. Of the climatic influences, he places temperature as the most potent. From his researches he draws the following significant conclusions: (1) "Variation in form in the Ben Davis, and probabl}^ in other sorts as well, is due principally to the tem- peratm-e during a period of about two or three weeks fol- lowing blossoming. The lower the temperature the more elongated the apple. This elongation is seen in apples grown near large bodies of water, which lower the temperature at this season of the year, and in seasons where the tempera- ture is low owing to seasonal fluctations. This influence is also seen in the form of apples in different parts of the tree. Those in the lower north portion are more elongated than those from the warmer, upper south portion. " (2) " Sea- sonal temperature affects the size of apples, a cool season resulting in smaller fruit. This is marked only in full sea- son varieties, and is especially noticeable in the more north- erly portions of their distribution. On the other hand, in the extreme south a variety is apt to be smaller than when grown in a somewhat cooler climate." 212. Climatic factors which delimit the geographical distribution of fruits. — As pointed out earlier in the chap- ter, climatic factors limit the growing of deciduous fruits as the northern and southern boundaries of the temperate zone are approached. These factors are defined by Shaw as follows: "The northern limit of apple-growing is fixed by the minimum winter temperature, and the southern limit by the heat of the hottest part of summer, occurring usually in July or August. "The attainment of the highest quality, appearance and 1 Mass. Agr. Exp. Sta. 22nd Ann. Rept. 1910. 23rd Ann. Rept. 1911. 244 POMOLOGY keeping quality is very largely dependent on the warmth and length of the growing season. This may be measured with fair satisfaction for the apple-growing regions of North America by an average of the mean temperatures for the months of March to September, inclusive. This is called the mean summer temperature, and gives tempera- tures ranging from 52° to 72° F. "The factors determining the mean suimner temperature in a given orchard are (1) latitude, (2) elevation, (3) site and aspect, (4) soil, (5) culture, (6) prevailing winds, (7) sunshine. ''A departure of over 2° from the optimum mean for a given variety will result in less desirable fruit, though this may not be marked in short season varieties. "A summer mean too low for a variety results in (1) greater acidity, (2) increased insoluble solids, (3) greater astringency, (4) less coloration, (5) decreased size, (6) scalding in storage. "A summer mean too high for a variety results in (1) uneven ripening, (2) premature dropping, (3) rotting on the trees, (4) poor keeping quality, (5) lack of flavor, (6) 'mealiness,' (7) less intense color, (8) decreased size." 213. Specific requirements for certain varieties.^ — It seems to be established, as above stated, that a variet}^ of fruit has a certain optimum temperature at which it thrives best, but this has not been determined for all varieties. Win- slow ^ has contributed some interesting figures on the length of growing season required by some varieties of apples grown in the Northwest. The "length of growing season" is described by him as the number of days between killing frosts, or more accurately the period during which the mean temperature is over 43° F. He also uses the number of "heat units" during the growing season as a guide in the 1 Winslow, R. M. Amer. Soc. Hort. Sci. 1914. THE RELATION OF CLIMATE TO POMOLOGY 245 selection of a suitable location for the different varieties. The heat units for each month are determined by multipl}^- ing the number of days in the month by the mean monthl}' temperature. In this way, the sum total of heat during the season is expressed in heat units or given an index. The "hottest six weeks" are also made use of, since this period is considered a guide to the intensity of the summer heat.' Such varieties of apples as the Yellow Newtown and Esopus (Spitzenburg) are conspicuously limited in their range of successful production. In only a few localities are they at their best, while in other places well adapted to many va- rieties these two are of low quality and unreliable in their behavior. Winslow shows that the Yellow Newtown requires a climate possessing a long growing season, a high mean summer temperature, a high total of heat units for the sea- son, and it prefers a humid district where irrigation, if needed at all, is only supplementary. It is pointed out that other districts having similar conditions are adapted to the production of this variety, but if they depart much from them, the results are unsatisfactory. The Esopus is similar in its climatic requirements to the Yellow Newtown, with the exception that irrigation sec- tions are equally well adapted to its culture. Likewise the Winesap, which is at its best in compara- tively few sections, such as the Piedmont region of Virginia and the Wenatchee and Yakima valleys of Washington, re- ^ See also Merriam, C. H. Laws of temperature control of the geo- graphic distribution of terrestrial animals and plants. Nat. Geogr. Mag., VI, 1894, 220-238. The formula used for determining the hottest six weeks is: "multiply the monthly mean temperature of the hottest month by 3, add the mean temperature of the next hottest month and divide the total by 4." Example: If August monthly mean temperature is 68° and July 66°, then: — ^— = 67.5° temperature of the six hottest weeks. 246 POMOLOGY quires a long growing season witli a high summer tempera- ture. SHght departures from these requirements are at once manifest in a smaller size and poorer color. Figures for these more conspicuous examples are quoted: Table LXXV LENGTH OF GROWING SEASON FOR YELLOW NEWTOWN, ESOPUS, AND WINESAP APPLES (AFTER WINSLOW) Length of grouring season Total heat units Hottest six weeks Yellow Newtown days 240 270 13,750-15,700 F. 67.5°-70.7° irrigated sections Winesap 230-240 13 700 70.7° PHENOLOGICAL STUDIES The student will find a profitable field of study in observ- ing the relation between climate and certain periodic phe- nomena of fruit-trees, such as time of blooming and ripening of fruits. 214. The physiological constant.^ — There have been a number of attempts to calculate the total amount of heat or temperature necessary for a plant to function and go iWaugh, F. A. Vt. Agr. Exp. Sta. 11th Ann. Kept. 1897-98. pp. 263-272. I. Lamb, G. N. A calendar of the leafing, flowering, and seeding of the common trees of the Eastern U. S. II. Smith, J. Warren. Phenological dates and meterological data recorded by Thomas Mikesell between 1873 and 1912 at Wauseon, Ohio. U. S. Dept. Agr. Weather Bur. Suppl. 2. 1915. I ' ■'; -J. V/ .iruViy>"tt.''^'srqBiiwwawg^' Plate VI. — In the background is shown the effect of acid pliospliate on the natural growth of clover in the Ohio experiments. THE RELATION OF CLIMATE TO POMOLOGY 247 through its natural phenomena, such as blossoming, putting out leaves, and the like. The formulation of such laws is not surprising, and they were at first widely accepted ; how- ever, there are several fundamental objections to them. Hoffmann suggested that the time of bloom, as well as the other natural phenomena in the seasonal development of the tree, is dependent on the sum total of heat available to the plant up to that event. His zero point was arbitrarily fixed at the first of January after which he took the sum of the daily maximum positive temperatures (above 32° F.) of a thermometer exposed to the sun up to the beginning of the event. In this way, he accounted to a large extent for the difference in time of blooming of different seasons. De CandoUe and others have fixed the temperature at which the plant becomes active at 43° F. (6° C.) instead of 32° F., but even this ignores the well-established fact that plants have different optimum temperatures. It also may be assumed that the separate phases of the plant activities may have different optima. Furthermore, it has been pointed out that the buds of the tree may be much further advanced when they enter the winter condition some seasons than others, due to the sea- sonal variations. This would probably modify the total amount of heat necessaiy for blossoming the ensuing sea- son. Hence, it seems impractical to lay down any physio- logical constant for plants. 215. The blooming season. — As indicated above, fruit- trees of any given variety do not bloom at exactly the same time year after year, but may be a few days earlier or later than the average, depending largely on the character of the season. In an "early" season, they will bloom earlier and in a later season the blooming will be retarded. In addition to the total temperature available, other factors must also play a part in causing the difference, such as the intensity of 248 POMOLOGY heat at any given time in causing the blossoms to open; the age and vigor of the trees; the moisture factor; and also the character of the previous season and winter. Also winter- injured buds, if not entirely killed, are likely to open later than normal ones. Hedrick also points out that "In some seasons a species or variety may bloom a little before leaves burst forth; in others, leaf and flower come out simultane- ously and in still others leafing precedes blooming. In south- ern climates the tendency in several fruits is to bloom before they leaf, while in the north the same fruit will leaf and bloom together with the first wave of summer weather." He also states that varieties of hardy fruits vary in the rel- ative time at which they bloom. Some seasons one variety will bloom first and another year the order is reversed. As pointed out previously, the location has a definite in- fluence on blooming time, as proximity to large bodies of water which retard the blooming on the leeward side of such water; the slope of a hill which manifests a difference in temperature in the early season; and lastly but most impor- tant, the latitude and altitude. 216. Comparative blooming dates. — In order to com- pare the relative time at which the several fruits are most likely to begin to bloom, the following figures for New York state may be cited :^ 1 See also Utah Agr. Exp. Sta. Bull. 128. 1913. Vt. Agr. Exp. Sta., nth Ann. Kept. 1897-98. pi^. 248-2.57. Jour. Royal Hort. Soc. 36: 548-564. 1910-11. 37:350-361. 1911-12. THE RELATION OF CLIMATE TO POMOLOGY 249 Table LXXVI VE DATES OP BLOOM OF THE MORE COMMOl Sweet cherries May 1 Pears May 2 European plums Japanese pluma Hybrid pluma May 3 Currants Apples Sour cherries May 4 ' Hybrid cherries Gooseberries Peaches May 5 Crab-apples May 6 Native plums May? Strawberries May 16 Blackberries Dewberries May 31 Black raspberries Red raspberries June 1 Hybrid raspberries June 7 Grapes June 14 217, Duration of blooming period. — It is a common ob- servation that fruit-trees are in blossom longer some seasons than others. This is due to the weather conditions at the time of bloom, cold and damp prolonging the period of flores- cence and bright sunny days reducing it. The following data ^ will serve to illustrate this : 1 N. Y. Agr. Exp. Sta. Bull. 407. See also Vt. Agr. Exp. Sta., 11th Ann. Rept. 1897-98. p. 250. 250 POMOLOGY Table LXXVII BLOOMING RECORDS FOR PERIOD OF THREE TO FIVE YEARS AT GENEVA, N. Y. (AFTER HEDRICK) Ave. period of bloom Shortest period Longest period 12 7 18 Pears 10 5 15 Peaches 10 6 16 6 4 8 8 5 11 Grapes 20 19 21 European plums Varieties vary greatly, from middle of April to second week in May; in bloom from one to three weeks Salicina plums In bloom from 4 to 8 days Native plums Season the latter part of that of Domesticas Gooseberries 10 9 12 8 7 9 24 20 27 Red, yellow, and hybrid raspberries . , . 14 14 15 Black raspberries 7 6 9 Strawberries 17 11 26 THE RELATION OF CLIMATE TO POMOLOGY 251 218. Period of ripening of hardy fruits. — A distinction must be made between tlie time when winter fruit is picked from the tree and when it is "eating ripe." This difference does not obtain for summer varieties of fruit, for they are usually ready to use at the time of picking. The earlier fruits also are likely to show a variation in time of maturity which may necessitate several pickings. The same hypoth- esis considered under blossoming has also been applied to ripening of fruit, namely, Hoffman's theoiy of a thermal constant. Here again latitude, soil, and site are all factors that influence the ripening period. An extensive list of the common fruits has been prepared by Hedrick * which gives the time of ripening of each. 219. Relation between blooming and ripening. — Whether there is a correlation betw{>en time of blooming and ripening is a question of considerable practical as well as academic importance and several conflicting views have been held in regard to it. The large amount of data collected by Hedrick permits a general statement, although many exceptions may be cited. He says, "It requires only a cursory comparison of the data in the two bulletins to show that there are no correlations between blooming time and ripening time of fruits." From data secured from Hedrick 's "Peaches of New York," Norton ^ has prepared the following table, which shows lack of a definite correlation: 1 N. Y. Agr. Exp. Sta. Bull. 408. 1915. 2 Norton, J. B. S. Proc. Amer. Soc. Hort. Sci. 1918. 252 POMOLOGY Table LXXVIII relation op the blooming and ripening period of the peach Ripening period Blooming 'period Very early Early Medium Late Very late Total 1 1 Early 3 4 13 3 2 25 Medium . . . . 3 15 53 43 15 129 Late 1 1 6 7 5 20 Very late 1 1 2 4 Totals 7 20 74 54 24 179 220. Form for recording phenological data. — The fol- lowing form is recommended by Hopkins ^ as adapted to the use of the orchardist for recording phenological data: Phenological records Year. . Locality Latitude. or isophane Station No. Species: Pyrus Mains County Longitude or pheno-meridian Observer Common name: Apple State Altitude Slope Species, variety, or number a b c d e f 9 h i Ben Davis Grimes Golden . . . . Lac. cit. THE RELATION OF CLIMATE TO POMOLOGY 253 The spaces with letters a to i for the name or designa- tion of the seasonal events as given in the following lists for the different types of plants, and the blank spaces below the designated events are for the date of occurrence. a. First buds opening. b. First leaves unfolding. c. First flowers open. d. First flowers falling. e. First winter-buds forming. f. First seed or ripe fruit. g. First leaves coloring, h. First leaves falling. i. Other data. CHAPTER XI WINTER INJURY For convenience, the kinds of winter injury to fruit-trees may be grouped into three general classes: (1) bud injury, (2) injury of the woody parts above ground, and (3) root injury. 221. Bud injury. — While many factors are involved in winter-killing of plants or their parts, the conditions under which the buds are killed may be roughly placed in the three following categories: (1) when buds go into the winter in an innnature condition and low temperatures occur early in the winter (December); (2) when mature buds are sub- jected to such low temperatures during the winter that their tissues are killed; and (3) when unseasonably warm weather in winter or early spring is followed by very low temperature. Of the tissues of the fruit-buds the pistils and ovaries are the most tender and are frequently killed when the other parts remain unhurt. Such blossoms may expand, espe- cially' if the injury occurs just prior to blossoming time, but of course they can produce no fruit. ^ If the entire bud is killed, the tissues throughout turn brown and the bud dries and falls from the tree in the spring in the case of most of the stone-fruits, or it may persist for a time with the apple and pear as shown in Plate VIII a. Not all varieties of fruit that are tender in the bud are also tender in wood, as may be illustrated by the Elberta peach, but generally this is true. Winter-killing of the fniit-buds of the apple is rare, but 1 Bailey, L. H. Principles of Fruit-Growing. 20th Ed. p. 306. 254 WINTER INJURY 255 has been reported by Whipple ^ as occurring in Montana. In such cases, the axiUaiy leaf-bud will continue the growth of the spur and, before the growing season is over, it is diffi- cult to observe that flower-buds had been formed. Like the apple, the fruit-buds of the pear are not likely to be injured, but the spur itself may be killed with the con- sequent destruction of the fruit-bud. As a rule, the more commonly grown varieties of the sour cheriy are hardy in buds as far north as central New Eng- land, except in veiy extreme win- ters or when low temperatures follow after the buds have swollen. On the other hand, Macoun - re- ports that in the fruit-growing sections of Canada the cherry, like the European and Japanese plums, is injured more or less eveiy winter when not protected 1)}' some body of water. Similar injuiy to the buds of early Rich- mond cherries was reported in Wisconsin after the winter of 1917-18.3 (Fig. 34). The sweet cherry is much less reliable than the sour cherry; in fact it is not much more hardy than the peach. Varieties of the plum vary widely in their hardiness. Many of the American species (such as Prunus nigra) are very hardy, while others are not. Some varieties of P. salicina, such as the Burbank, also are reasonably hardy 1 ^\^lipple, O. B. Mont. Agr. Exp. Sta. Bull. 91. 1912. 2 Canada Exp. Farm, Kept. 1907-08. pp. 110-116. ' Proc. Soc. Hort. Sci. 15th Kept. 1918. p. 32. Fig. 34. — Fruit-bud of sour cherry. Left, flower-bud alive; right, flower-bud killed. 256 POMOLOGY in the northern latitudes. The European plums, while not tender, are usually not so hardy as other species and are not widely grown so far north as New England and Canada, although this again is somewhat a varietal character- istic. The buds of the peach are the most tender of any of the tree- fruits commonly grown in the northern United States. Varie- ties vary markedly and no def- l^fe S^^^^H^^^I inite point of injury can be •* -■ ai^H^H^^H stated, but a temperature from 18° to 20° F. below zero is likely to destroy all the fruit-buds and hence the crop. 222. Injury to the woody parts above ground. — While a loss of the fruit-buds is a serious eco- nomic factor, the injury that may occur to the tree itself is more destructive in its nature. Winter injuiy to fruit-trees may take sevei-al forms, some being rather characteristic of one sec- tion and some of another or all forms may occur in a given region. The following are the more important types of such injury: killing of the terminal growth of the shoots; killing of patches of tissue on the limbs or body of the tree; crotch injury; "black heart"; collar-rot; frost-cracks; frost-cankers; and sun-scald. 223. The killing of the terminals on many kinds of fruit- trees, even the more hardy ones, is common in a severe win- FiG. 35. — Winter injury on trunk of a Baldwin apple ■tree. WINTER INJURY 257 ter. This is particularly true if the growth has continued late and has not matured well the previous season.^ It may also be due to an inherent tenderness of the varieties. The result of this injury is much the same as from cutting or shearing back the terminal growth; that is, the uninjured buds nearest the terminal will make a longer growth than if no injuiy had occurred, while the more proximal ones are likely to remain dormant. 224. Killing of patches or areas of bark on the Umbs and trunk is also a common type of injury. This will first ap- pear as a sunken area which eventually dries and cracks. It is thought that considerable of the black-rot canker (Sphccropsis malorum, Peck) so common on the apple in some sections is due to the entrance of disease spores through openings in the bark caused by the splitting or drying out of the dead areas. This type of injuiy may also take the form of frost-cankers. (Fig. 35). Large dead areas on the trunks of the older trees are also conunon in the more northern sections, particularly on Bald- win and King apple trees. This injury is occasioned by much the same set of conditions as produced the dead areas on the smaller branches. It is somewhat more serious, how- ever, for there is opportunity to remove an injured branch but it is difficult to repair damage to the trunk. The bark in this case will loosen and come off. Unlike sun-scald this injuiy does not occur on any particular side of the tree. 225. Crotch injury is characterized by a kilHng of the tissues in the forks or crotches of both large and small branches. The injury may be restricted to a small area or it may be more extensive. Many varieties of apple may be af- fected, such as Ben Davis, Baldwin, Rhode Island Green- ing, and even Northern Spy. Several theories have been ^ Emerson, R. A. The relation of early maturity to hardiness in trees. Nebr. Agr. Exp. Sta. 19th Ann. Rept. 1906. p. 101-110. 258 POMOLOGY propos9d to account for crotch injury, such as drying out, occurrences of ice at these points, and immaturity of the wood. The latter, according to Chandler,^ is the principal if not the only factor involved. The last tissue formed and hence the most tender is near the base of the branches (crotches) and near the bottom of the trunk of the tree. This tissue becomes more hardy or mature as the season advances. Hence, if veiy low temperatures occur early in the winter, this tissue is the first that is injured. If the pre- vious growing season is short and the tree as a whole goes into winter in an innnature condition, the damage is enhanced. 226. Collar-rot or injury is an affection of fruit-trees localized at the crown or "collar." The injury may extend down on to the larger roots and also some distance up the trunk and it frequently encircles the base of the tree, result- ing in its death. Such varieties of apple as the Grimes, Grav- enstein, and King are particularly susceptible and for this reason they are often top-worked on to resistant sorts. The cause has been variously attributed to arsenical poison- ing,2 parasitic organisms, and to freezing. Grossenbacher has shown that the primaiy injury takes place in the winter in connection with severe freezing weather and hence that fungi are not the chief cause but are the agencies of decay following the winter injury. Chandler has also pointed out that blight {Bacillus amylovorus) is not the cause of collar-rot since the result of "body bUght" is a tightening of the bark when it dies, which is the opposite phenomenon of true collar-rot. The latter also holds that collar-rot is doubtless due to direct freezing to death from the low temperature and frequently to a rapid lowering of 1 Chandler, W. H. Mo. Agr. Exp. Sta. Res. Bull. 8. 1913. 2 Headden, W. P. Colo. Agr. Exp. Sta. Bull. 131. 1908. Grossen- bacher, J. G. N. Y. (Geneva) Exp. Sta. Tech. Bull. 12 and 23. 1909 and 1912. WINTER INJURY 259 the temperature, and not to a tearing of the tissue or drying out as described by Grossenbacher. That excessive alkali soils and arsenical poisoning are pri- mary factors in collar-rot has also been generally abandoned through the work of Headden ^ and Ball " in the first case and Ball ^ and his associates in the second. The view was held by Headden that large quantities of arsenic were found in trees suffering from collar-rot, but the fact that normal trees also often contained fairly large quan- tities of arsenic, that collar-rot occurred in orchards which had never been sprayed, and that herbaceous plants were growing about crown-rotted trees, caused this view to be abandoned for the one of freezing. 227. Frost-cracks or the splitting of bark or trunks of trees often accompanies other forms of winter injuiy. These cracks may extend up the entire length of the trunk and follow up one or more of the main branches for some distance, or they may be only a few inches in length. They may open as much as two centimeters or may be merely visible lines, but in any event they will draw together or clos(» after the severe weather is over. 228. " Black heart " is a common result of low tempera- tures and consists in the killing of the sap-wood and pith, although the cambium remains alive. As a result, the tree continues growth and rapidly forms a new layer of sap-wood within and bark without. Nursery trees are frequently "black hearted," particularly pears, and they may make a Note :— Following the winter of 1917-18 the author inspected several orchards of Ben Davis trees in the state of Maine in which the damage took the form of crotch injury almost entirely and while the trees were partly alive they were entirely beyond hope of repair. 1 Headden, W. P. Colo. Agr. Exp. Sta. Bull. 157. 1910. 2Ball, E. D. Jour. Econ. Ent. 2: 142-48. 1909. 3 Ball, E. D. el al. Jour. Econ. Ent. 3: 187-97. 1910. 260 POMOLOGY stunted growth or soon recover, depending on the extent of the injury and on the growing conditions immediately following planting. Mature trees in some sections are often "black hearted" throughout their lives with no apparent incapacity. 229. Sun-scald is manifest by a dead area on the south- west (sun-exposed) side of the trunk of the tree. This dam- age, unlike the other forms discussed above, occurs late in the winter when days of bright sunshine follow cold nights. The cause has usually been assigned to a starting of growth or sap movement on the side of the tree exposed to the sun which activity is inmiediately followed by severe freezing. However, Chandler does not credit this view from his work with winter injury but suggests that the tissue is warmed by the sun until the temperature nearly reaches the freezing point when a sudden drop will cause the tissue to ''freeze to death." ^ 230. Root-killing. — -This form of injury is likely to be general during a severe winter when the ground is bare. It is well known that bare ground will freeze much deeper than when the surface is protected by some sort of cover, but no cover of vegetation is equivalent to a deep snowfall which lies on the ground throughout the winter." Such hardy va- rieties as Mcintosh and Wealthy will be root-killed as readily as the more tender sorts, like Baldwin and Wagener, in a snowless winter, although the trunks and branches of the latter varieties would show severe injury while none might appear on the hardy sorts. Chandler has shown that the roots are the tenderest part of the tree, and that the portions nearest the crown are the most resistant, while the smaller remote rootlets are the most ' See also Mix, A. J. Sun-scald of fruit-trees a type of winter injury. Cornell Univ. Agr. Exp. Sta. Bull. 382. 1910. 2 Neb. Agr. Exp. Sta. Bull. 79, 92. 1903, 1906. WINTER INJURY 261 tender. From his experiments he concludes that apple roots will be killed at about —3° C. in summer when they are ten- derest and at about -12° C. in late winter with rapid freez- ing, this varying somewhat with conditions. He also shows that French crab stock is less hardy in the roots than the cion-roots of such varieties as Ben Davis; that "Marianna plum roots are more hardy than Myrobolan roots, and IVIah- aleb cheriy roots seem slightly more hardly than Mazzard roots." 231. How freezing kills. — A distinction is made between the loss of fruit crops by ''killing frosts" and by "freezing." The latter is here considered in studying the destruction of the tissues of fruit-trees. It is generally accepted that the freezing to death of plant tissues does not take place unless ice crystals are formed within the plant from water that has been withdrawn from the cells. While ice crystals may form within the cells themselves when the temperature falls veiy rapidly, the above method is much the more com- mon. It was formerly considered that much less injury w'ould result if thawing of the tissue was gradual so that the cells could again take up the moisture, assuming, of course, that the cells had not been ruptured in the process of freez- ing. Later investigators ^ have, however, shown that the rate of thawing has nothing to do with the killing of the tis- sue, except with ripe apples and pears, lettuce, and the leaves of Agave americana, but that the killing occurs when a sufficiently low temperature is reached. "Frozen to death" is a technical phrase describing plant tissues that have been subjected to a certain temperature at which death of their cells occurs. Such tissues present a brown, water-soaked appearance shortly after they thaw and evaporation is much more rapid than from living tissue. ' Miiller-Thurgau, Chandler, et al Mo. Agr. Exp. Sta. Res. Bull- S. p. 150. 262 POMOLOGY 232. Hardiness of different tissues. — As has been in- dicated above, the different tissues of a fruit-tree vary in hardiness, and they also change at different seasons of the year. It has been shown that when the trees are in a young growing condition, the cambium, young cortex, and sap-wood cells are the tenderest while the pith in young twigs is the first to be killed in mature trees followed by browning in the sap-wood and the outer or old cells of the cortex. The nota- ble point here is that cambium is most tender in the grow- ing plant but relatively hardy when it is in winter condition. This observation can sometimes be made with peach trees after a severe winter when a cross-section of the limbs or trunk will often look so brown or black that little or no hope could be entertained for saving them. The cambium may start into growth in the spring, however, and soon a new layer of sap-wood is formed, which begins functioning, and re- covery of the tree takes place. The fruit-buds of the peach are recorded to be about as hardy as the cortex, cambium, and sap-wood of the twigs in the latter part of summer, but during the winter they are the most tender of all the tissues above ground with the pos- sible exception of the pith cells. Usually the leaf-buds are more hardy than the fruit-buds, but instances are on rec- ord in which the leaf-buds and part of the sap-wood of the peach have been killed or badly injured while a portion of the fruit-buds have survived and produced, even in the ab- sence of leaves.^ This is explained on the basis of lack of maturity of the wood tissue, while the fruit-buds reached maturity before the freezing occurred. 233. Rest-period. — That perhaps all plants have a more or less definite rest-period has been well established by a number of writers, notably Klebs in Germany and Whit- 1 Chandler, W. H. hoc. cit. p. 224. Paddock, W. Soc. Hort. Sci. 1918. p. 30. WINTER INJURY 263 ten ^ and Howard - in this country. This phenomenon can be observed with different varieties of the same kind of fruit by the early swelling of buds and time of starting into growth. For the more southern peach-growing sections that are in the danger belt for spring frosts, the length of the rest-period becomes of serious importance, for the more forward vari- eties are most likely to be lost from freezes and frosts. In order to shift the resting-period to later in the winter, a series of experiments were conducted by Whitten to cause the trees to enter their rest-period at a later time and hence make them correspondingly later in awakening from this state. By means of late cultivation, it was possible to delay the rest-period and as a result the trees were a few days later in blossoming than was the case under normal conditions. FACTORS INVOLVED IN FREEZING 234. Maturity. — Reference has already been made to the importance of having the tissues well matured if injury from low temperatures is to be avoided. It has been estab- lished experimentally ^ as well as by extensive observation that maturity is the most important single factor involved. While the nature of the season is beyond the control of man, certain horticultural practices should be followed in order to bring about as great a degree of maturity as possible. These will be considered later. It has been observed that the hardiest varieties mature early in the season. Macoun has studied the effect of winter on a large number of plants at Ottawa, Canada, for a period of twenty-two years, having under his obsei-vation over 3000 species and varieties, many of which kill back more or 1 Whitten, J. C. Mo. Agr. Exp. Sta. Bull. 38. 1897. 2 Howard, W. L. Mo. Agr. Exp. Sta. Res. Bull. 1. 1910. ' Neb. Agr. Exp. Sta. Bull. 79 and 92. 1903, 1906. Ohio Agr. Exp. Sta. Bull. 192. 1908. N. Y. (Geneva) Agr. Exp. Sta. Bull. 269. 1905. 264 POMOLOGY less every year. All those which kill back more or less regu- larly are native to regions having a longer growing season than that at Ottawa and hence they mature too late there and the wood is not thoroughly ripened. He, therefore, con- cludes that a tree or shrub which will withstand a test win- ter at Ottawa must ripen its wood early. ^ Not only do the more mature trees exhibit greater hardiness, but they also become more hardy as the winter advances until they again respond to growing conditions as spring approaches. While writers have connnonly assigned the reason for lack of hardi- ness to a higher moisture-content of the tissue, Chandler has shown that, with the exception of the cambium, the tis- sue contains as much moisture later in the winter when it is more hardy as when it enters the dormant period. "It would seem highly probable that, except in the case of cam- bium, the additional hardiness acquired by the different tissues of the tree as they pass into Avinter, is due to a change in the protoplasm such that it can withstand the great loss of water rather than a change in the percentage of moisture or in sap concentration. It is also possible that changes in the sap solute that lower its eutectic point may occur and that these may increase the resistance to cold by holding water unfrozen to protect the protoplasm from too com- plete desiccation at lower temperatures." An additional point of evidence that maturity and growth conditions the previous season affect the resistance of trees to cold, is the observation that trees having their foliage injured or destroyed by insects or spray burning suffer seri- ous killing of the wood. Also the inner surface of branches which possess less foliage is nearly always more tender than the exposed sides. ^ 1 Proc. Amer. Soc. Hort. Sci. 1912. p. 59. 2 Proc. Amer. Soc. Hort. Soc. 15th Rept. 1918. p. 18. Card, F. W. Bush-Fruits. Macmillan Co., Rev. Ed., 1917. p. 56. WINTER INJURY 265 235. Sap concentration. — The work of Chandler on the relation of sap concentration to the freezing of plant tissue is particularly important. The experiments of Miiller-Thur- gau and Molisch had previously shown conclusively that practically all the formation of ice ciystals takes place in the intercellular spaces and only rarely (due to very rapid freezing) in the cells themselves. Furthermore, if the proto- plasm or membrane surrounding it fails to give up its Avater, the freezing point is thereby lowered or, in other words, a protection is afforded. They also observed that tissue could be super-cooled, just as a liquid, to a lower temperature than that at which ice would normally form in the intercellular spaces, and be raised again without ice formation and hence without injuiy. Chandler has shown that if the sap concentration could be doubled it would inhibit the loss of water, for twice as much would l)e held in the protoplasm "at any given temperature below the freezing point, but above the eutectic point ^ of the solute," as a protection against freezing. Extensive experiments were conducted with various kinds of herba- ceous and woody plants and their fruits and leaves to de- termine whether lowering their sap concentration would lower their freezing point. The sap concentration was low- ered by placing the plants in or by watering with solutions of various salts, sugars, or glycerine. The freezing point of the sap was then determined and reported in the terms of "depression," which means "the number of degrees centi- grade below zero at which, with no supercooling, ice forma- tion begins in the sap." The following table (after Chandler) illustrates how uni- i"By the eutectic point is meant the temperature at which the substance in soUition crystallizes out. At that temperature there would be at the same time ice, crystals of solute, and unfrozen solutions," 266 POMOLOGY versally the lowering of the sap concentration (from any cause) has lowered the freezing point: Table LXXIX relation of sap concentration to freezing young fruits Depression Cherries fresh from tree Cherries from twigs with ends in glycerine sixteen hours. . Cherries wilted five hours Peaches fresh from tree Peaches from twigs with ends in glycerine sixteen hours . . Peaches wilted five hours Apples from twigs with ends in glycerine thirty hours. . . . Apples from twigs with ends in water thirty hours Apples from twigs with ends in cane sugar thirty hours. . . Apples from twigs with ends in glycerine forty-eight hourt- 0.905 1.180 1,075 0.965 1.230 1.085 1.408 1.335 1.530 1.417 Thus it will be seen from these data that wherever the sap concentration of young fruits has been lessened, the temperature at which it will freeze has been reduced also. The same results were secured with the leaves and tender shoots of trees and with more succulent plants such as corn and tomato. Furthermore, it was shown that the sap con- centration of shaded plants is lower (i. e., not so dense) than that of unshaded ones and hence they kill at a higher temperature. However, all of these researches were con- ducted with succulent plants, and not with woody tissue in the dormant or resting-period. WINTER INJURY 267 Table LXXX data showing influence of shading on the killing of tissue (aftek chandler) Material Treatment Date Temper- °C.i Number of plants Percent- age all killed Percentage total leaf area killed Depres- sion Early Harvest apple twig and leaves Shaded June 28 — i 39 0.0 3o.9 1.975 do. Not shaded June 28 — i 42 0.0 0.8 2.438 do. Shaded June 28 —5 47 34.0 70.0 1.975 do. Not shaded June 28 —5 50 0.0 48.5 2.438 In order to deternihie whether such tissue could also be influenced in like mamier by appljnng fertilizers, a heavy application of potassium chlorid (500 pounds to the acre) was made to peach orchards in different locations over a period of four years. No difference appeared, however, in the amount of winter-killing of the wood, hardiness of the fruit-buds, or of the bloom when spring frosts occurred. However, on determining the sap concentration of twigs from these treated trees, no difference appeared; hence, accord- ing to the previous observations with other plants, no differ- ence in hardiness could be expected. The suggestion is made that if it were possible to increase the sap concentration by the use of fertihzers, some difference in hardiness of the blooms would be anticipated. 236. Rate of freezing a factor. — Very conclusive data are available to establish that a rapid fall in temperature is much more injurious than a gradual one, either with tissue after the sap is flowing or when it is entirely donnant; par- ticularly is this true with the buds. It has also been shown ^ To convert centigrade and Fahrenheit temperatures: F. — 32 Degrees — — - — = Degrees C. 1 .8 Degrees C. X 1.8 + 32 = Degrees F. 268 POMOLOGY that a rapid fall of temperature near the freezing point is more harmful than near the point at which the tissue is killed and this fact is applied as a possible explanation of "sun-scald" of apple trees. The following excerpts from Chandler's data illustrate this: Table LXXXI the effect of slow and rapid lowering of temperature on the killing of plant tissue Kind of buds Date Niwibcr buds Percent, killed Number buds Percent, killed Slowly to —18° C. Rapidly to —13.5° C. Rice's seedling peach Elberta peach Jonathan apple Montmorency cherry Chabot plum Mar. 22 Mar. 22 Mar. 22 Mar. 22 Mar. 22 138 100 34 176 236 44.2 88.0 64.7 58.5 78.3 154 85 33 184 183 51.9 92.9 75.7 62.5 86.8 When twigs of the apple, peach, cherry, and plum were exposed to a temperature which gradually fell to — 18° C, the killing was about the same as when it fell rapidly to — 13.5° C. These with other data show conclusively that both buds and wood are more surely injured if the tempera- ture drops rapidly than slowly, even though it does not go so low in the rapidly frozen tissues. 237. Protection of bud scales. — It has usually been assumed that the bud scales afford protection from cold as well as prevent loss of moisture from or entrance of water into the buds. However, this has not held true experi- mentally ^ for buds which had their scales removed were not frozen any quicker or at a higher temperature than were 1 Wiegand, K. M. Bot. Gaz., Vol. 41, pp. 373-424. WINTER INJURY 269 such buds with their scales. This work was done with peaches only, and they were treated on different dates from February 26 to March 12. The temperature was reduced to various points from — 10° C. to —22.5° C. with the follow- ing average results: Total number of buds, scales off, 4430, 51.0 per cent killed; total number of buds, scales on, 5078, 68.5 per cent killed. 238. Relation of crop the preceding season. — It has been observed in various sections of the country that trees which fruit heaviest are most likely to be injured by very low temperatures the winter immediately following. This ob- servation was repeatedly reported after the severe winter of 1917-18. Macoun describes a row of Wealthy apple trees (21 years old) at Ottawa that behaved in this way. Of fourteen trees, the eight which bore a medium to heavy crop in 1917 were killed or badly injured, while the six bearing either a light crop or none at all came through the winter in good condi- tion.^ In New York state and in New England it was noted that hardy varieties of the apple were killed more readily than such tender sorts as the Baldwin, if the former had set a heavy crop the preceding season while the latter had not. This result was earlier indicated when it was shown that well thinned peach trees seemed to be more resistant than unthinned ones which bore a heavy crop: ^ average per- centage of peach buds killed, tree thinned, 35.4; average percentage of peach buds killed, trees not thinned, 51.4. 239. Correlation of wood structure and hardiness. — Various attempts have been made to discover any correla- 1 Proc. Amer. Soc. Hort. Sci. 1918. p. 17. ^ Mo. Agr. Exp. Sta. Bull. 74. 1907. 270 POMOLOGY tion that might exist between the wood structure or other morphological characters and the hardiness of plants. Hal- sted ^ made a special investigation and reported that "No constant difference in all structures probably exists among apple twigs by means of which one sort may be umnistak- ably distinguished from all others. Much less is there any point in minute structure invariably present with those sorts which are classed as hardy and absent from tender vari- eties. Maturity of twigs is a condition of successful win- tering, and therefore the so-called hardy sorts are quite sure to finish their seasons' growth before autumn frosts arrive." More recently Beach and Allen ^ conducted some exten- sive investigations on this problem, and observed a large number of plant characters of hardy and tender varieties of fruits. In general, no outstanding and consistent correla- tions could be found, but they report that "The hardier varieties on the average had a slightly lower moisture con- tent than the more tender varieties," also "Large, thick petals are correlated with hardiness, although the converse of this is not always true." 240. Influence of type of soil. — Inasmuch as the type of soil materially influences the maturity of the trees, this factor becomes one of importance in studying winter injury. In general, a soil that is heavy and inclined to be wet will delay maturity and hence, other things being equal, there would usually be more winter injury on such a soil than on one of a lighter nature. This is particularly true of the sub- soil, as indicated in Chapter VII. Bouyoucos ^ has shown that a heavy soil contains more moisture and will not freeze so deeply as a lighter one, although a sand or gravel will 1 Halsted, B. D. Iowa Agr. Exp. Sta. Bull. 4. 1889. Mem. Torrey Bot. Club, 2: 1, 26. 2 Iowa Agr. Exp. Sta. Res. Bull. 21. 1915. 3 Bouyoucos, G. J. Mich. Agr. Exp. Sta. Tech. Bull. 26, 1916. WINTER INJURY 271 fluctuate more with the air temperature than the heavy soil because of the difference in specific heat.^ Hedrick - reports on the experience of Michigan and New York growers with the peach. In the first case the growers, al- most without exception, considered a sandy, gravelly, or stony soil much more favorable to peach-growing and that peach trees are more hardy in such a soil than in a heavy one. Bouyoucos investigated the depth and rate of freezing of the following types of soil: gravel, sand, loam, clay, and peat. It was found that "they all froze about the same time in the upper 6 inches, but in the spring they thawed and warmed up at different rates. This was attributed to their different specific heats and to the downward and upward trend of air temperature in the fall and spring respectively. The gravel and sand thawed first, followed by clay 1 day later, loam 2 days later, and peat 10 days later. After they were entirely thawed out all the types of soil had almost the same temperature from then on throughout the summer, autumn, and winter." He further shows, however, that if very cold weather is experienced early in the winter without any fluctuations in temperature, the light soil freezes deeper than the heavy ones, thus giving an advantage to higher moisture-content in such a case. In New York state, however, the growers would not distinguish between a heavy and a light soil so far as winter injur}'- is concerned, provided the heavy soil is "warm and dr}^" In both states the growers preferred a gravelly subsoil in order to secure a hardy tree. ^ There would seem to be a discrepancy between this statement and the one following by Heth-ick, but this is probably explained by the fact that trees growing on clay soil usually mature later and hence are more subject to injury in the tops. If the injurj^ occurred in the roots rather than in the tops, it would be much worse in the sandy soil. 2 Hedrick, U. P. Trans. Mass. Hort. See. 1919. 272 POMOLOGY As to the moisture of the soil, Hedrick reports that "Either extreme of moisture — excessive wetness or excessive dryness — gives favorable conditions for winter-killing. A wet soil is conducive to sappiness in the tree and also freezes deeply." It was also reported that a very dry soil failed to furnish the trees with sufficient moisture during winter and the buds and twigs died out and serious winter-killing followed.^ 241. Proximity to bodies of water. — The proximity of an orchard to a large body of water has a greater effect on the frost injury in the spring than on winter injury. How- ever, an effect on the latter is not infrequently noted. A conspicuous example of this is seen in the fruit sections bor- dering on the various lakes. "The distance to which the influence of a body of water will extend inland depends upon the volume of water, its temperature relative to that of the land, the area of its free surface, the slope of its shores, and the prevailing winds. The influence of Lake Michigan, mainly because of the gentle slope of its eastern shore, ex- tends nearly halfway across the state of Michigan, while the influence of Lake Erie, because of the abrupt rise of its eastern shore, extends inland only a few miles." " Many examples could be noted of peach orchards favor- ably located near lakes that are injured only in the most severe winters, while sections within a few miles frequently suffer a loss of the crop in whole or in part. However, the vagaries of winter injury seem endless, and many instances might also be cited where such an influence has not been noted. ^ 1 See also Paddock, W. Colo. Agr. Exp. Sta. Bull. 142. 1909. p. 11. 2 Standard Cyclo. Hort., Bailey. Vol. 3, p. 1284. (W. M. Wilson.) ^ For several years the author noticed the difference in date of bloom- ing of apple trees near the Atlantic coast line of New Hampshire and inland, showing a decided retarding effect of the cold winds of spring WINTER INJURY 273 242. Topography of land. — While it would seem patent to all careful observers that low lands suffer much oftener from frosts and freezes than the higher elevations, yet many orchards are located unfavorably in this regard. While the average temperature of the air decreases at the rate of 1° F. for each 300 feet of elevation above sea level, yet it does not follow that more injuiy from low temperatures occurs at the higher elevations. The disturbing factor of wind and the fact that cold air will settle and flow down hill accounts for the apparent contradiction. Here again, or- chards located on high elevations are sometimes injured more than those at lower levels during severe winters; however, the reverse of this is true on the average. Frost pockets, coves, and flat low lying lands are to be avoided for orcharding. In some of the western fruit sections, the reverse of this principle holds true, owing to special conditions. In some of the narrow river canyons, the fruit-trees suffer less from injury in the winter and from spring frosts and ripen their fruit from one to two weeks earlier than those planted on the land along the "rim rock" or at a distance from the can- yon. This phenomenon is explained by the fact that the rocks of the canj^on walls hold the heat, are dark colored and hence absorb a maximum of the sun's rays, and that there is a "draw" of air down the canyon that wards off frosty conditions. 243. Winds. — While winds play an important role in frost prevention, they also are a factor in augmenting win- on the coast. Yet in the severe winter of 1917-18, the effect of the water was insufficient to prevent the winter-killing of a well-cared-for young orchard within sight of the open water. The slope was a gentle one to the coast line, yet such hardy varieties as Wealthy and Mcintosh were killed as readily as the tender ones, such as Baldwin and Wagener. The ground was bare at the time of the low temperature in December, and hence the root-killing was extensive. 274 POMOLOGY ter injury in some sections. Frequently high wind velocity will accompany low temperatures and if the soil is not well protected by a covering of snow or of vegetation, it will diy out to the point at which root injury is extensive. The twigs and buds may also be injured to a greater extent under such conditions, and it is connnonly supposed that their tissues are directly dried out by the action of the wind. It is more probable, however, that these tissues experience a drying to death due to the water supply being shut off by the freezing of the roots. ORCHARD PRACTICES 244. Cultivation.^ — As indicated above, the chief factor in hardiness of fruit-trees is their maturity before going into winter condition. Therefore, in sections in which winter injury is likely to occur, the orchard practices should be such as to obtain a good growth and yet allow the wood and buds to mature before winter. In a cultivated orchard the tillage should stop by the first or middle of July in most dis- tricts (except when it is an advantage to delay the rest- period). A cover-crop should also be sown at the time of the last cultivation as it has a twofold function in relation to winter injury, (1) by sei^ving to withdraw any excess mois- ture in the soil and hence aid in maturity of the trees; and (2) by acting as a mulch to prevent such deep freezing, and al- ternate freezing and thawing as would occur if the land were bare. Emerson ^ and others note the effects of various cover-crops on depth of freezing in orchards. They show that in a season of snowfall corn or cane is a good crop for the orchard as it holds the snow to good advantage, while in a season of no snow such crops as mat down well will af- ford the greatest protection. 1 Neb. Agr. Exp. Sta. Bull. 92. 1906. WINTER INJURY Table LXXXII DEPTH OF FREEZING (AFTER EMERSON) 275 vVo snow Heavy snow Depth of snow Depth of freezing Cornstalks 17 in. 18 in. G in. Clean cultivation 19 " 2 " 24 " Oats 12 " 12 " 12 " Millet 12 " 12 " 15 " 245. Pruning. — Not much can be said in regard to the relation of pruning to winter injuiy except what has already been stated, namely, that practices which maintain a strong vigorous tree and yet permit normal maturity are likely to reduce danger from winter injury. At the Missouri Experiment Station it was found that the vigor and rela- tively late growth caused by stimulation of peach trees would have some effect in reducing bud injury in the spring. This was due to the shifting of the rest-period to later in the season, as indicated before. "In Missouri nearly every winter warm weather starts the buds into growth more or less. Fruit-buds on trees that have made a vigorous growth, caused by reasonably severe heading back or by cultivation, are the less liable to winter injury." ^ If, however, the injuiy has taken place, it becomes im- portant to prune judiciously if the best response is to be obtained. If peach trees have been severely frozen in the wood, it is best to give them a moderate pruning. If such trees are severely pruned (leaving only bases of the main limbs), they are very likely to be killed, but if the same trees 1 Mo. Agr. Exp. Sta. BuU. 74. 276 POMOLOGY are moderately pruned, experience shows that the maximum number can be saved. ^ (See Plate VIII b.) 246. Protecting trees and buds. — Various efforts have been made to protect tender trees and their buds during the winter, with some degree of success. Such precautions are of special value in sections in which growth is likely to be excited by premature warm spells, followed by low tem- peratures. When the wood or buds are likely to be frozen during the winter season while they are entirely dormant, the only prac- tice that seems efficient is to layer the vines or trees entirely, and this is not often feasible. Some peach orchardists do, however, cut the roots on one side of the tree, pull it down into a trench and cover it with soil, which has prevented injury. Entire grape vineyards are also laid down and cov- ered with soil, with success." Baling the trees with hay, straw, or other material has also been practiced with success, but is not generally recom- mended. Chief among the experimental efforts to coat the trees and buds with a protective material is the work of Whitten.^ He observed that the chief damage to the peach in Mis- souri resulted from killing after the trees had been started into premature growth from unseasonable weather in the winter or early spring. As a means to prevent the swelling of the buds, the following treatment was given: "During the winter a row of peach trees, running diagonally across the orchard, so as to embrace several varieties, was whitened by spraying with a lime white wash. These trees had been set only two years and had but few fruit-buds. Four older 1 Mo. Agr. Exp. Sta. Bull. 55. 1902. ^Hedrick, U. P. Proc. Amer. Pom. Soc, 35 Bienn. Rept. 1917. p. 48. 3 Whitten, J. C. Mo. Agr. Exp. Sta. Bull. 38. 1897. WINTER INJURY 277 trees, in various parts of the grounds, were also whitened." The following table gives the results on time of blooming: Table LXXXIII effect of whitewashing peach trees to delay bloom (after whitten) Varu'ty TreulmeHt First flower Full bloom Last bloom Health Cling Whitened Not April 13 " 11 April 21 " IS April 29 " 27 Wonderful Whitened Not " 14 " 11 " 22 " 18 " 29 " 25 Rivers Early Whitened Not " 13 " 9 " 21 " 29 " 27 Silver Medal Whitened Not " 13 " 7 " 18 " 13 " 28 " 21 As a more striking effect of the winter on the treated and untreated trees, it is recorded that 80 per cent of whitened buds passed the winter safely when only 20 per cent of the unwhitened ones were unharmed. A very interesting set of experiments was conducted to illustrate the difference in absorption of heat between white and colored material. Thermometers were covered with various colored cloth and whitewash and exposed in the orchard and on the side of a building. When the sun was not shining the thennometers registered much the same, but when the sunlight was intense marked differences oc- curred. "At one time, during bright sunshine a difference of 21 degrees was recorded between the white covered and the purple covered thermometers. A difference of 10 to 15 degrees was frequently noted between these two. This is sufficient to indicate that we might expect considerable dif- 278 POMOLOGY ference in the growth and time of flowering of whitened and unwhitened peach trees." 247. Securing hardier fruits. — A discussion of breeding hardier fruits is included in the general subject of breeding (Chapter XIII), but a statement in regard to the acclimati- zation of plants is apropos at this point. There is a lack of unity of opinion on this point, although it has been discussed for many years a,nd many observations have been recorded. It seems unlikely that individuals of a tender species will manifest any permanent character for hardiness when such plants are removed to a colder climate. While an occasional individual may be more resistant to cold than its companions of the same origin, the enviromnent may be different or some other cause operating which would not be permanent. To at- tempt to select biotypes showing this hardy character would be a slow process with the weight of evidence against its suc- cess. The better procedure to follow would be to breed such tender species with hardy "relatives" and select individuals exhibiting the desirable qualities of both parents. Hence it is practically useless to attempt to find a particularly hardy Baldwin apple or Crawford peach tree from which to prop- agate a strain that will withstand the northern winters where these varieties are unreliable. 248. Treatment of frozen trees. — Great care must be exercised in treating trees which have been frozen or the injury may be extended rather than reduced. As indicated previously, the pruning given winter-injured trees calls for moderation and the operation should not be hastened but rather delayed until the probable injury can be determined. Some seasons the peach is so injured that the buds are de- layed in starting; this calls for careful observation lest live wood be cut away and the tree umiecessarily reduced. In addition to proper pruning, it is also advantageous to apply a quickly available form of nitrogen, such as nitrate WINTER INJURY 279 of soda or sulfate of ammonia, as a means of stimulating growth. Thorough cultivation should, of course, be followed when conditions permit. Special repair work may also be necessary, such as bridge- grafting and cleaning and disinfection of the wounds.^ 249. Variation in hardiness of fruits. — While the vari- eties within any given kind of fruit vary widely in hardiness, yet there is a rather marked difference between species and genera of the common fruits. The apples as a class are the most hard}'' of the commonly grown tree-fruits, followed by the American plums, Japanese plum, sour cheriy, European plum, pear, sweet cheriy, apricot, and peach. It is true that the currant and gooseberry and certain species of Amer- ican plums are more hardy than the apples. There is so much variation in different localities and in different sea- sons, however, that such a classification cannot be con- sistent. 250. Hardy and tender varieties, — As with the different s])ocies and genera, so the varieties of fruits are variable in hardiness, depending on a multitude of conditions.^ The following lists are an attempt to rate some of the more com- monly grown varieties, the hardiest being in the first column and those in the other columns decreasingly hardy. 1 Purdue Univ. Agr. Exp. Sta. Circ. 87. 1918. - XI. S. Dept. Agr. Bur. Plant Ind. Bull. 151. 1909. Fruits recom- mended by the American Pomological Society for cultivation in the various sections of U. S. and Canada. 280 POMOLOGY RELATIVE HARDINESS OF SOME COMMON VARIETIES OF FRUIT APPLE (hardiness IN WOOD) 1 2 3 4 5 Hibernal Wealthy Northern Spy Ben Davis Baldwin Ontario Fameuse Red Canada Gano R. I. Greening Mcintosh Delicious Rome Jonathan King Oldenburg N. W Wagener Hubbardston Tolman Greening Twenty Ounce Gravenstein Yellow Wolf River Grimes Fall Pippin Transparent Winesap Stayman Red Astra- Pewaukee York Imperial Black GiUi- chan flower Haas Malinda Patten Greening peaoh (hardiness in bud) 1 2 3 4 Crosby Champion Elberta (hardy Crawford (early Rochester Georgia (Belle of) in wood) and late) Hill's ChiU Carman St. Johns Chairs Choice Gold Drop Waddell Mt. Rose Niagara Wager Alton Foster J. H. Hale Stevens Rareripe Ray Surprise Greensboro Hiley Salway Lemon Free Kalamazoo Reeves Fitzgerald Bernard Triumph Smock Fox Seedling CHERRY (hardiness IN WOOD) Windsor Eugenia May Duke Late Duke Early Richmond Tartarian English Morello Ostheim Vladimir Montmorency Reine Hortense Schmidt Governor Wood WIXTER IX JURY 281 PEAR (hardiness IN WOOD) 1 2 Flemish Beauty Angouleme Anjou Bartlett Sheldon Bosc Seckel Clairgeau Tyson KieflFer Longworth Clapp Favorite Winter Nelis Orel 251. The grape. — With the grape as with other fruits the chief factor affecting its harcUness is maturity. Glad- win ^ shows that the length of the growing season has a de- cided effect on the subsequent wintering of the vines. Not only does a longer growing season permit greater maturity of the canes and an increased thickness of the cell-walls of the wood tissue, but it also permits the ripening of the fruit which bears a correlation to the maturity of the canes. He says, "Our observations during the years 1915-16 indicate quite clearly that until an actual freeze occurs the vine ex- tends its energies to maturation of its fmit at the expense of wood maturity; and if the umnpe fmit be allowed to hang throughout the fall, wood maturity is not nearly so complete as when the fruit is picked some time previous to a freeze." It is also pointed out that the incipient floral parts within the complex bud of the grape may be destroyed by low tem- peratures and hence result in an "off year." This is often erroneously accredited to a hea\^ crop the previous season having robbed the buds of sufficient nutrient material to pennit fruit-buds to form. The application of such fertilizing materials as nitrogen, phosphorus, and potassimn had no appreciable effect on the killing of grape vines. 1 N. Y. Agr. Exp. Sta. Bull. 433. 1917. CHAPTER XII POLLINATION AND THE STERILITY PROBLEM The sexual relation of plants and the union of male and female elements to the proper development of fruits have been known since ancient times, but it is only within the past quarter of a century that marked progress has been made in understanding the causes of these phenomena and many of them are not yet fully apprehended. In studying the effect of pollination on the setting of orchard fruits, one should keep in mind that two points are involved: first, the importance of pollinization in effecting the development of fruits even though no actual fertilization takes place; and second, that as a result of such pollination there may be fertilization and development of the embryo, resulting in viable seed capable of producing new progeny. From the standpoint of the breeder, the latter is paramount (i. e., the production of fertile seeds), but the orchardist is concerned primarily with the former of the two results. The vegetable- grower, on the other hand, may be interested in the pro- duction of viable seed, depending on the crop involved, and with the nut-grower, it likewise becomes a matter of practical importance. 252. Investigations in pollination. — Centuries prior to the Christian era, the peoples of Egypt and Mesopotamia were cultivating dioecious plants for food and practicing artificial pollination of the fig and date palm.^ However, the first scientific investigation of this problem was not forth- coming until A. D. 1694 when Camerarius proved that fer- 1 Johnson, D. S. Sexuality in plants. Jour. Heredity, 6: 3-16. 1915. 282 POLLINATION AND STERILITY 283 tile seeds are not produced if the pollen or male element is lacking or unavailable when the flowers are in bloom. This has later been observed for angiosperms in general. Other subsequent investigators made contributions on this prob- lem, but the work of Sprengel of Germany (1793) marked an epoch when he published "The Secret of Nature in the Form and Fertilization of Flowers Discovered." His con- temporary in England, Thomas Andrew Knight, published a number of articles bearing on the pollination question and, as a matter of fact, almost discovered "Mendelism," and he announced as a law that "in no plant does self-fertiliza- tion occur for an unlimited immber of generations." This idea found its great culmination in Darwin's work when he said "nature abhors self-fertilization." And yet notwith- standing the wide application which this principle may have, it is by no means universal. Wheat, for example, is self- fertile, likewise peach varieties in general, the cleistogamous flowers of violet never open, the tomato is regularly self- fertilized, and so with many other plants. In this country a great impetus was given to a careful study of the inter-relations of varieties of any kind of fruit in an orchard plantation by the works of Beach, ^ Waite,- and Waugh.^ The problems of pollination incident to the setting of fruit will be considered in this connection, but the study of cross-pollination for the purpose of producing new varieties will be discussed in the next chapter. 253. Causes of unfruitfulness. — Many diverse reasons or causes must be given for the failure of trees to produce fruit. Some cases of barrenness still lack explanation. The ' Beach, S. A. Rept. N. Y. State Agr. Exp. Sta. 1892, '94, '95, '98, '99, 1900, '02. nVaite, M.S. U. S. Dept. Agr., Div. Veg. Path. Bull. 5. 1894. 3 Waugh, F. A. Rept. Vt. Agr. Exp. Sta. 1896, '97, '98, 1900. 284 POMOLOGY following may be listed as the more common causes: failure of fruit-buds to develop; lack of vigor or excessive vigor re- sulting in the dropping of the expanded flowers; winter in- jury to the floral parts; frost at blossoming time resulting in injury to flowers or inactivity of pollen-cany ing insects and the consequent lack of pollination; lack of "affinity" between varieties (self- or inter-sterility); defective pollen or embryo sacs; or hybridity, the causes of which are not understood. Some of these factors are treated elsewhere and only the various problems having to do with pollination and sterility will be considered at this time. 254. Development of pollen.^ — The pollen produced within the anther-sacs of the stamens contains the male ele- ment of the reproductive system of flowering plants. A brief statement of the development of the pollen will more clearly introduce the problems encountered in a study of pollination. A sufficient similarity exists between the several tree-fruits that all need not be considered. The stamens, as indicated in Chapter III, originate as an outgrowth from the torus, differentiating in their devel- opment into filaments and anthers. The anthers consist essentially of four lobes of pollen-forming tissue which, on further development, become differentiated as four sacs or locules, each of which contains the pollen-grains, one sac corresponding to each lobe. In the early development of the anther, the sporogenous tissue is first seen within each lobe, and surrounding the future ''pollen-making" tissue is a layer of cells known as the tapetum. The cells within the tapetum become the mother cells which, on further di- 1 See Sandsten, E. P. Wis. Agr. Exp. Sta. Res. Bull. 4. 1909. Kraus, E. J. Ore. Agr. Exp. Sta. Res. Bull. 1, Part 1. 1913. Dorsey, M. J. Minn. Agr. Exp. Sta. Bull. 144. 1914. Black, C. A. N. H. Agr. Exp. Sta. Tech. Bull. 10. 1916. POLLINATION AND STERILITY 285 vision (reduction division) , become the microspores or pollen- grains. Usually the anthers are partially developed prior to winter of the season before the blossom opens. If the development has gone sufficiently far in the autumn so' that the first division of the cells in spring is the reduction division, then they are in the pollen mother cell stage at that time. However, they may or may not have reached that point in the autumn. When growth is resumed in the spring, cell division becomes active and pollen-grains are eventually formed. The pollen-grains are unicellular and are known botanically as microspores, each one finally devel- oping two male gametes. The pollen-grain has a covering of two layers, the outer of which in some plants is frequently oily, gelatinous, or possessing minute projections useful in aid- ing in its distribution. This latter adaptation, however, is not encountered with common fruits. When "ripe" or mature, the anthers dehisce or expose the pollen-grains and on trans- fer to a receptive stigma, the latter germinate, as later de- scribed. If conditions are favorable and the two tissues are "congenial," fertiUzation takes place. A similar development occurs with grape pollen as for pol- len in general. It has been shown that a fundamental de- fect may occur in its development which accounts for ste- rility in the grape as is described later. 255. Germination of the pollen. — The condition of the stigma when it becomes receptive or at the time of pollination should next receive attention. The stigmatic surface just prior to the receptive period has a velvety papillose appear- ance which is readily distinguished from the moist often viscid condition when it is receptive. When the pollen- grains reach the receptive stigma, they are surrounded by the stigmatic fluid which has been secreted and in which the pollen gemiinates. It has been shown that sunshine had little or no effect on 286 POMOLOGY the germination of apple and plum pollen, or on the rate of growth of the pollen-tube. These tests refer to the artifi- ficial germination of pollen-grains in various media. It is well known that blossoms will be fertilized and the petals fall much more quickly in bright than in cloudy weather. The following data support the above conclusions in regard to germination : Table LXXXIV percentage of germination and rate of growth of pollen in SUNSHINE AND CLOUDINESS (aFTER SANDSTEN) Primus americana Apple (Pyrus Mains) Primus domestica Temperature, degrees C 34 31 33 33 32 33 32' 30' 331 70 68 69 71 68 69 62 60 64 72 67 70 70 70 68 60 59 65 The rate of growth of the pollen-tube appears to be read- ily affected by low temperature and, therefore, actual fer- tilization may be delayed some seasons more than others by several days. Sandsten reported that "Under favorable conditions it requires nine to thirty-two hours for the pollen tube of apples, plums, and cherries to reach the ovary when placed on the stigma or in the germinating medium. Cherry pollen requires a little over 12 hours. Two or three bright days at the time of full bloom is sufficient for the setting of the fruit." Dorsey questions these observations in regard to the plum and thinks the time would be greater, as much as eight to ten days under some conditions. Goff has shown that "Plum pollen does not germinate at temperatures below 40° F., and even at temperatures as high as 51° F. that there is slow pollen tube growth." ' Medium, a 3 per cent cane-sugar solution. POLLINATION AND STERILITY 287 256. Longevity and viability of pollen. — At present there is considerable difference of opinion in regard to tlie lengtli of time pollen remains viable. One investigator ^ records interesting observations on the longevity of pollen secured from widely different sources, namely, Washington (state), Tennessee, Missouri, and Mimiesota. Part of the samples were on the road four to five daj^s but arrived in "perfect condition." Germination tests on its arrival showed all samples to be practically normal. It was then placed in the laboratoiy in a temperature ranging from 10° to 18° C, and tests were made each month for six months with the exception of the last, which was eight months after its arrival. The following data show the results of this test: Table LXXXV LONGEVITY OF APPLE AND PLUM POLLEN. (AFTER SANDSTEN) First Lois germt- tuition Second Third Fourth Fifth Sixth Seventh Per Per Per Per Per Per Per cent cent cent cent cent cent cent 1 Apple 47 43 44 38 39 38 12 Plum 53 52 42 35 30 18 2 Apple 58 57 50 43 38 33 10 Plum 54 48 38 26 21 11 3 Apple 42 46 40 38 39 19 5 Plum 60 48 42 25 18 2 4 Ai)pIo 56 51 52 40 23 28 8 Plum 50 47 38 20 12 Sandsten, E. P. Wis. Agr. Exp. Sta. Tech. Bull. 4. 1909. 288 POMOLOGY The work of Crandall,^ however, indicates that apple pol- len may not remain viable so long as indicated by Sandsten. After observations for three seasons, he shows that when pollen was used that varied in age from one to eleven days, "The percentages indicate no definite relation between age of pollen and success obtained. . . . Apple pollen one month old has been tested several times in drop cultures, but no germination took place." He quotes Pfundt as finding that the pollen of Pijrus Mains (presumably the wild apple of Europe) retained its vitality in diy air for thirty-eight days and when preserved over sulfuric acid, for seventy days. "Records at the Illinois station contain no evidence of du- ration of vitality beyond the fairly successful use of pollen of Mains mains when eleven days old." Another investi- gator reports that a few pollen-grains of apple germinated after nearly three months and of pear after two months, but no tests were made after longer periods than these.^ Sweet cherry pollen also has a reasonably long period in which it is viable, as germination tests showed it to be in as good condition three weeks after it was gathered and dried as when it was first collected.^ Further data show that pollen is not injured by a temper- ature ranging from 25° to 55° C, if it be dry, but "at a tem- perature of 40 to 50 degrees C, in a saturated atmosphere, the pollen grains burst open due to the rapid inhibition of water and the number of bursted pollen grains increased as the temperature increased. Freezing temperatures ranging from — 1.5 to — 1 degree C. were not seriously injurious to the pol- len of apple, pear, and plum while less than 50 per cent of iCrandall, C. S. The vitality of pollen. Soc. Hort. Sci. 1912. pp. 121-130. 2 Adams, J. Germination of the pollen grains of apple and other fruit trees. Bot. Gaz. 61:131-147. 1916. 3 Ore. Agr. Exp. Sta. Bull. 116. 1913. POLLINATION AND STERILITY 289 peach and apricot pollen grains were killed by this tempera- ture." The lack of cultivation and fertility in orchards greatly injures the production and fertility of pollen. From these investigations it can be seen that the pollen of the apple, plum, peach, and cheriy, (and it can be added for other fruits as well) will remain viable throughout the period of blooming and probal:)ly for a much longer time if kept \mder ordinary conditions of temperature and humidity. 257. Length of receptive condition of the stigma. — In contrast to the surprisingly long time that pollen is viable and capable of germination and to the untoward conditions that it can withstand, the ]iistils are most delicate and of short duration. They are readily susceptible to mechanical injury as well as to damage from inclement weather. There is some question as to whether a stigma has more than one period of active secretion; in some cases there is only one, while other observers have held that more than one occurs. The pistils are sensitive to cold and are often injured when other floral parts are unhurt. Frosts or drying winds may cause a loss of the whole or a part of the fruit crop if they occur when the blossoms are open. Waugh ^ found that the stigmas of plums are receptive "From four to six days if pollen is withheld and conditions are favorable. If pollen is abundant they are almost im- mediately pollinated and cease to be receptive." Dorsey found that "under normal conditions, the plum stigma re- mains receptive for a maximum period of about one week, but usually from four to six days." 258. Fertilization. — The process of fertilization may be briefly stated in this connection since the whole problem of fertility and sterility of orchard fruits is intimately associa- ted with it. When the pollen-grain or microspore is formed, it possesses two nuclei, one known as the tube (vegetative) 1 Vt. Agr. Exp. Sta. 11th Ann. Rept. 1897-1898. p. 258. 290 POMOLOGY nucleus and the other the generative nucleus. When the pollen-grain germinates the latter nucleus divides, forming two sperm or male nuclei. As the pollen-tube grows down the style of the pistil, the male nuclei as well as the tube nucleus continue to approach the embiyo sac in which are the ovules. Here the tip of the tube enters the micropyl and dis- charges the two nuclei into the em- bryo sac so that fusion may take place, one with the egg or female nucleus and the other with the primaiy pericarp^_^ pollen tube synergids e^g nucleus nucellus embryo sac - - ' ' polar nuclei*-' anti podals -^"-'^ Fig. 36. — Diagram of a simple pistil as seen in lengthwise section, showing a single ovule just prior to fertilization. , outer Integument sperm nucleus, inner Integumen Hence it is seen that two ferti- lizations take place, one hav- ing to do with the origin of a new seed (ovule) and the other with the devel- opment of the endosperm or food-storage tissue surrounding the germ within the seed. As is well known from a study of an immediate cross between field and sweet com, there is an effect on the endosperm of the first or immediate generation. This effect may be seen in the condition of the kernel, i. e., when it is wrinkled or smooth or in the color of the endosperm or in both. In a study of sterility of the common fruits (as well as many other plants), it will be seen that not infrequently the endosperm will develop but the embryo will perish, a phenomenon termed embiyo abortion. (Fig. 36.) POLLINATION AND STERILITY 291 259. Cross-pollination. — The experiments of Waite and many subsequent workers have shown that, with many- kinds and varieties of fruits, it is necessary to have a trans- fer of pollen from one variety to another in order to insure fertilization and the setting of fruit. This transfer between varieties, instead of from the stamens to the pistils of the same flower, has come to be known as cross-pollination in contradistinction to self-pollination. That cross-pollina- tion should be the rule with many fruits will be shown later. In selecting a pollinizer, the chief concern is to choose a variety that possesses the following characteristics: 1. It must blossom at the same time and preferably at the same age as the variety which is to be pollinated. 2. It must be inter-fertile with it. 3. Should be a standard variety, i. e., be of high value for the purpose grown. 4. Should \)c a good ]wllon-producer. 260. Means of effecting cross-pollination. — Two agencies have usually been considered instrumental in the transfer of pollen: wind and insects. Experimental work and exten- sive observation, however, have shown that wind is of little or no importance with the tree-fruits, the nuts being ex- cepted. Insects play a most vital part in pollinating the blossoms. Chief among the insects are the bees, particu- larly the honey bees. Nature has provided for the visitation of insects in a most conspicuous way. Students of nature, particularly Darwin and his followers, are in full agreement that the insects are attracted by the bright or showy flowers and by the nectar secreted at the basal parts, thus bringing about the transfer of the pollen-grains which adhere to them, from flower to flower. When the flowers are so constructed as to permit pollination by the wind, they are said to be anomophilous 292 POMOLOGY and when insect pollination is the rule, they are called en- tomophilous. 261. Nature's methods of avoiding self-pollination.^ Several means have been developed in nature to prevent self-pollination. Not all of these obtain with fruit-trees but several are very effective. The chief devices among flowering plants are: 1. Special devices or contrivances of the flower which ensure cross-pollination when insects enter the flower. Or- chids exhibit these adaptations to a greater degree than any other group. 2. Difference in time of maturity of the stamens and pis- tils. This phenomenon is called dichogamy. When they mature simultaneously, it is homogamy. When the stamens precede the pistils in maturity, it is termed proterandrous, and if the reverse they are said to be proterogynous. 3. Even though flowers may exhibit homogamy, the relative position of the pistils and stamens or their rela- tive lengths may be such as to prevent self-pollination. Such a condition is termed kerkogamy (dimorphous of Darwin). 4. Separation of sexes. With most fruits the flowers are perfect, i. e., possess both stamens and pistils, but with some forms this condition does not exist. The strawberry is par- ticularly notorious in this regard, as some varieties possess perfect flowers and others have pistillate flowers only, while others which are perfect have more or less abortive and hence worthless stamens. The grape also exhibits the same set of conditions. That cross-pollination is necessary under such circumstances appears evident. 262. Effect of cross-pollination on the fruit. — Entirely aside from the results of cross-fertilization on the off- spring, the horticulturist is interested in any effect cross- pollination would have on the somatic tissue of the fruit POLLINATION AND STERILITY 293 which immediately develops. The experiments seem to es- tablish rather thoroughly that the color or markings of a fruit are not affected by the pollen used in fertilization, and neither is the flavor, quality, acidity, or "sweetness." That some of these characteristics are materially changed is sometimes reported but they do not seem to be well authen- ticated; at least such changes have not been observed under controlled conditions. Careful observations have been made to determine whether color of fruit could be modified by the pollen parent. The conclusion is reached that color in the innnediate cross is not directly influenced by the kind of pollen used, since any such effect must be found within the seed (endosperm) and there is no opportunity for an influ- ence on the fleshy portion. It is not uncommon to see fruits in which the color shows distinct "banding." This has been explained as a somatic segregation of the characters for color, permitting a more or less independent manifestation of them. The several colors may appear as bands more or less parallel or a band of but one color surrounded by the normal color. ^ The results reported in regard to size and shape, however, are not in harmony. It is possible that under varying con- ditions the outcome may be different. Fletcher ^ states that his investigations (mostly with apples and pears) show that there is "no immediate effect of pollen, and no differences obviously due to mutual affinity. The cross-fertilized fruits have averaged about the same in size, shape, color, and quality regardless of the pollen used." Wicks ^ comes to a similar conclusion from his studies with the apple. He ^ For further details see Kraus, E. J. "Bud variation in relation to fruit markings." Biennial Crop Pest and Horticultural Report. 1911-12. Ore. Agr. Exp. Sta. 2 Va. Agr. Exp. Sta. Ann. Kept. 1909-10. pp. 213, 224. »Ark. Agr. Exp. Sta. Bull. 143 (Technical). 1918. 294 POMOLOGY says, "No influence of the male pollen of any variety can be detected on size, color, shape and quality of the female parent." Alderman,'^ on the other hand, shows a decided benefit from cross-pollination of the apple over blossoms which were "selfed" or crossed with pollen from a tree of the same va- riety. A summary of his results in weight of fruit as affected by pollination is here given: Rome Beauty cross Gain over selfed 27 . 8 per cent York Imperial cross Gain over selfed 42 . 7 per cent Likewise, Lewis and Vincent found an improvement in size of the apple from cross-fertilization. These latter observations are in line with the original in- vestigations of Waite. He observed, among other things, that the self-fertilized Bartlett pears which he secured weighed on an average 100.4 grams, while the cross-fertil- ized pears averaged 145.2 grams each. 263. Effect of seed-bearing on the fruit. — It is a fact of considerable interest that there is commonly a correlation between the weight of seed and that of fruit. This of course loses force in the case of parthenocarpic fruits, since prac- tically no seeds are developed. Not only is there a correla- tion in regard to size but also it is not uncommon to find a lack of full development in a portion of an apple or pear where no seeds have matured within the adhering carpel or carpels, thus giving somewhat one-sided fruits. This phe- nomenon is of wide application and may often be seen, for example, on examining a bean pod in which one or more ovules did not develop, resulting in a hardened constricture or other evidence of lack of development of the parts im- mediately surrounding the abortive ovules. In such cases, there is a lack of stimulation of the surrounding parts and, 1 Proc. Amer. Soc. Hort. Sci., 14th Rept. 1917. pp. 94-101. POLLINATION AND STERILITY 295 as no development of the seeds takes place, the fleshy or surrounding parts usually fail to develop also. Not only is there an influence on the size of the fruit, but the number of seeds that has developed may also affect the quality, the more seeds the higher the quality. A striking case is that of the Japanese persinunon (Diospyros Kaki) ^ which develops many parthenocarpic fruits, but whether pollination is useful as a stimulation is not known. The fruits which develop seeds manifest a richer and better fla- vor than the seedless ones, and also other marked charac- teristics obtain. The seedless fruits are larger in size, of a smoother texture and usually ripen later than those devel- oping seeds. Outstanding is the effect of the seeds on the color of the flesh. When seeds develop, the flesh is dark in color and light when seedless. Heinicke records the relation between size of apples and the number of seeds that has developed. The following fruits of Fallawater apples were produced on spurs of equal vigor.- Number of seeds Weight grains of fruit 3 16.84 5 18.72 8 23.15 9 24.02 11 29.40 264. Artificial pollination. — The artificial pollination of common deciduous fruit blossoms is not practiced except for experimental piu'poses or the production of new varieties. Perhaps the nearest approach to any intervention by man is the occasional practice of placing flowering branches of plums or cherries in jars of water and hanging them in a 1 Hume, H. H. Proc. Soc. Hort. Sci. 1913. pp. 88-93. - Factors influencing the ab.scission of flowers and partially developed fruits of the apple. Proc. Amer. Soc. Hort. Sci. 1916. 296 POMOLOGY tree of a self-sterile variety, thus affording insects an op- portunity to effect cross-pollination. When poUination is to be practiced artificially, for exper- imental purposes or for securing new varieties, it is usual to protect the essential parts of the flowers in order to assure accuracy. The blossoms which are to be used as the female parent are inclosed prior to the opening of the petals. The blossoms from which the pollen is to be secured are also pro- tected in order to prevent a mixture with foreign pollen, by insects, or other agency. This covering is usually a paper bag, either manila paper or a translucent, paraffined bag be- ing employed. A question has been raised occasionally as to whether an abnormal condition would not be produced in this way and thus reduce the possibilities of success. How- ever, when coverings of cheese-cloth or other material allow- ing a passage of air have been used, no increase in efficiency has been noted. Others have covered the entire areas with a frame of muslin and either hand-pollinated the flowers or, in case the study is one of self-sterility, bees have been in- cluded. Such an equipment has some advantages, but the percentage of set is not greater than by the bag method. In manipulating the flowers, it is customary to cover the blossoms just before they are ready to expand and expose the essential parts. If the purpose is cross-fertilization, the stamens (and often petals) are removed at time of bagging, before pollen has been exposed, so that danger of self-pollin- ation is eliminated. It has been demonstrated that the re- moval of the sepals as well as the petals and stamens has no injurious effect in securing a perfect functioning of the pistils, if carefully done. When the work is performed by a novice or very hurriedly, it is doubtful whether this proce- dure is best, since fruits may be deformed by careless ma- nipulation and many stigmas are often badly injured. The pollen from another tree is frequently collected in a glass POLLINATION AND STERILITY 297 vial and applied with a camel's-hair brush or the finger. Others pick the flowers and brush the anthers over the pis- tils of the female parent. THE STERILITY PROBLEM When it is recognized that many varieties of fruit exhibit self-sterility, inter-sterility, and self-barrenness, and hence require cross-pollination with some other variety, the sub- ject becomes one of great economic importance. There is considerable variation of opinion in regard to the ultimate causes of sterility, and consideration here can well be con- fined to some of the established facts which closely pertain to pomology. 265. Definition of terms. — Self-sterility refers to the inability of a plant to develop fertile seeds when the pistil is pollinated with pollen from its own flower or from one of the same variety of fruit. Other meanings are given to it, such as lack of development of any fruit at all when the flower is self-pollinated. It must be understood that such a condition does not mean that either 'the pistils or stamens are defective but merely that fertilization does not take place, even though the pollen may germinate on the stigma, as often occurs; or if fertilization does take place, the young embiyo does not complete its development. The ultimate reason for this phenomenon is not clear, but the phrase "lack of affinity" has been given to it. In other cases, the pollen may be defective and hence cause self-sterility, or the embryo sacs may be defective. Self-fertility, on the other hand, refers to the ability of a plant to produce genninable seeds when its pistils are pol- linated from the same flower, tree, or variety, i. e., in the fertilization of the ovule, the male gametes were not derived from another variety or species. Varieties are said to be inter-sterile when certain ones fail 298 POMOLOGY to fertilize one another, but are readily fertilized by the pol- len of a still different variety. These various phenomena must not be confused with the condition that exists in the case of imperfect flowers, such as with some of the strawberries. Here there is an actual lack of one of the essential organs (stamens). The term morphological self-sterility may be applied to this case, which is not infrequent with other fruits such as the grape and mulberry. It has been shown that self-sterility is a heritable char- acter but that it may be modified by changing the environ- ment. Fvn-ther, a tobacco plant which is ordinarily self-sterile may become partially fertile and produce a few seeds at the end of a flowering period and under conditions adverse to vegetative growth . ^ While not particularly related to the sterility problem, the term parthenocarpy may here be defined. This indicates fruits which develop wholly independently of any pollination of the stigmas or fertilization of the ovules. The term refers to the development of fruit structures other than the seeds. This phenomenon is not uncommon with the apple and pear.- Another case of interest and quite unlike the above is when the flesh of the fruit develops only if pollination of the stigmas has taken place. Fertilization may or may not fol- low pollination, but if so there is an abortion of the embiyos at a more or less advanced stage and hence no viable seeds develop. Thus, finally, all fruit-trees are classed as either barren or fruitful, and if the former they are always sterile, whereas lEast, E. M., and J. B. Park. Studies on self -sterility. Genetics, 2:505-609. 1917. 2 See Kraus, E. J., and H. R. Kraybill. Ore. Agr. Exp. Sta. Bull. 149. pp. 6-11. Also Sturtevant, E. Lewis. Seedless fruits. Mem. Torrey Bot. Club, Vol. I, No. 4, 1890. Plate \'1I. — a. Trees grown permanently in sod. b. Trees grown under the grass mulch system, c. The tillage-cover-crop system used in this orchard. POLLINATION AND STERILITY 299 the latter may be sterile or fertile depending on the seed relationship. 266. Sterility not a constant factor. — Since the time of Darwin it has been known that self-fertility and -sterility of varieties of fruit may not be a constant characteristic, but that it may vary with the age of the trees, health and vigor, climate, general ecological conditions, and the like. This led to many disputes and apparent misstatements until the dual behavior of a variety was disclosed. The same tree may be self-sterile at one time and self-fertile at another. Vincent ^ reviews this question and calls attention to the case of the Yellow Newtown apple which is listed as self-ster- ile in one place and self-fertile in another, while the same variation is recorded for the Rhode Island Greening and Grimes Golden. Garcia reports the Bartlett pear as self- fertile in New Mexico while most other observers record it as quite self-sterile. Gardner ^ reports a similar variation with sweet cherries in different parts of Oregon. 267. Causes of sterility. — Kraus ^ divides the causes of sterility into two general groups: (1) morphological and (2) physiological. Several of the causes belonging to the first group are rather well known, while those of the second are more complicated and intangible. Among the more im- portant of the former may be listed the following: (1) a lack of germinability of pollen which in some cases may amount to as much as 1 to 100 per cent; (2) imperfect pollen or pollen in which some of the structures have degenerated; (3) more complete abortive pollen as occurs with some of the parthenocarpic fruits; (4) imperfection of the ovules which is frequent in many kinds of fruit ; (5) a physical impossibil- ity of self-fertilization as with dioecious plants; (6) various 1 Better Fruit, Feb., 1920. 2 Ore. Agr. Exp. Sta. Bull. 116. ^ The self -sterility problem. Jour. Heredity, Dec. 1915. 300 POMOLOGY modifications of perfect flowers which prevent self-pollina- tion; and (7) the possible case of the inability of the pollen- tube to grow sufficiently long to reach the ovaiy. Among the physiological causes the following may be included: (1) possible lack of nourishment of the pollen- tube in the case of some pistils; (2) negative chemotactic ac- tion, although this is not known to occur with fruits; (3) pos- sible toxic effect of the stigmatic fluid on the pollen or vice-versa (investigations tend to disprove this with the fruits) ; lack of fertilization; lack of development of the embryo after fertilization may have taken place. It might also be added that hybridity frequently results in entire sterility (heterosis). In studying the causes of self-sterility, it has been observed that there is a slow growth of the pollen- tube which results in a lack of fertilization, as with the Rome Beauty apple ^ and also with the tobacco.- In the latter case, it was noted that the pollen germinates as freely on the stigmas of flowers of the same plant as those of other kinds with which they are compatible. After germination, however, the pollen-tubes on selfed flowers grow so slowly that decay of the flower occurs before fertilization can be effected. 268. The cherry. — One of the most interesting cases of sterility that has developed in American pomology is that of the cheriy. It had been known for some time that vari- eties of the sweet cherry in particular were inclined to be self-sterile and were not parthenocarpic, but it later devel- oped not only that the sweet cherry was practically always self-sterile as grown in Oregon, but also that several of the standard varieties were inter-sterile. This appears to be a clear case of "lack of affinity" be- tween certain varieties and is not due to any lack of germin- iRnight, L. I. Proc. Amer. Soc. Hort. Sci. 1917. pp. 101-105. 2 East, E. M., and J. B. Park. Genetics, 3: 353-366. 1918. POLLINATION AND STERILITY 301 ability of the pollen or to defective pistils, as was demon- strated by careful tests. ^ The three varieties notoriously inter-sterile are Bing, Lambert, and Napoleon, and mixed plantings of them will give little or no fruit unless they are within the range of influence of some other variety that is inter-fertilo with them. Of those studied, the Black Repub- lican, Black Tartarian, and Waterhouse seemed to be the most efficient pollinizers for this group. While not entirely germane to the sterility problem, it is of interest to note that some members of the Duke group of cherries and also some varieties of the sour cherries (P. Cerasus) are capable of fertilizing some of the Bigarreaus. The sour cherries are usually credited with being self-fertile but there would seem to be many exceptions to this state- ment. 269. The almond. — Tufts ^ has shown that all the com- mon varieties of almonds grown in California are self-sterile to a large extent and certain of them are inter-sterile. The honey bee is considered the best pollinating agent for the almond. 270. The grape. — The first important work in this countrj^ on the sterility problem of the grape was that of Beach, although Goff had previously shown that the variety Concord would set fruit as well when the clusters were cov- ered with a bag as when left open. Beach found that "Cul- tivated American grapes show remarkable differences in the degree of self-sterility of different varieties. Many of them fruit perfectly of themselves. Others form no fruit when cross-pollination with other varieties is prevented. Most varieties are found between these two extremes, being neither fully self-fertile nor completely self-sterile." After 1 Gardner, V. R. Ore. Agr. Exp. Sta. Bull. 116. 191.3. - Tufts, W. F. Almond pollination. Calif. Agr. Exp. Sta. Bull. 306. 1919. 302 POMOLOGY testing 169 cultivated varieties (and many seedlings), he classified them as follows: Class I. — Self-fertile varieties having perfect clusters or clusters varying from perfect to somewhat loose, 38 vari- eties (21.8%). Class II. — Self -fertile varieties having clusters loose but marketable, 66 varieties (39.0%). Class III. — Varieties which are so imperfectly self-fertile that the self-fertilized clusters are generally too loose to be marketable, 28 varieties (16.5%). Class IV.— Self-sterile varieties, 37 varieties (21.8%). He also noted that varieties with short or recurved stamens are always self-sterile or nearly so. The explanation offered at that time for sterility was "a lack of affinity between the pollen and pistils of the same variety." ^ Dorsey - illustrates the method of testing sterility from the work of Beach as follows: ''When 143 clusters of Brighton were covered with bags and self -pollinated, the average rating of the clusters formed, counting 100 as a perfect cluster, was approximately one, and when thirty-two clusters distributed among eight other varieties were pollinated with Brighton pollen, the average rating was three, showing Brighton, for those varieties used, as well as for itself, to be a poor poUenizer. On the other hand, when 116 clusters of the Catawba were selfed, the av- erage rating on the same basis as above was eighty-six, as compared with one in Brighton. When the thirty-three clusters of eight other varieties were pollinated with pollen from Catawba, the average rating was sixty-seven, showing a marked difference between the Brighton pollen and the Catawba pollen when used either in selfing or crossing." 1 N. Y. Agr. Exp. Sta. Bull. 157. 1898. 2 Dorsey, M. J. Jour. Heredity, 6: 1915. p. 243. Minn. Agr. Exp. Sta. Bull. 144. 1914. POLLINATION AND STERILITY 303 It has been shown ^ that a marked difference in appearance exists between the dry pollen of self-fertile and self-sterile grape varieties. The former or normal pollen is oblong in outline with slightly flattened ends, while the latter is quite irregular and folded, and fails to genninate when placed in a nutrient solution. Dorsey has shown that the development of the pollen in self-sterile varieties of the grape is normal "up to the forma- tion of the microspores, but here a degeneration takes place which renders the pollen grains (microspores) sterile." A careful study of the pollen produced by those varieties which bagging tests have shown to be more or less self-sterile, show that the generative nucleus and, in some cases, also the vege- tative nucleus, degenerate. Such degeneration precludes the possibility of nomial functioning in eveiy pollen-grain where it occurs. Sterile pollen in the grape, then, is due to de- generation in the generative nucleus. He has also shown that "the genn spores are not formed in pollen borne by the reflexed type of stamen." To sunnnarize the causes and correlations in the sterility of the grape, the following statements seem warranted from present knowledge: 1. Self-sterility in the grape is due to defective pollen and not to the pistils. 2. "All varieties tested set fruit when potent pollen was used, which shows that the pistils are normal." 3. Potent pollen can be distinguished from impotent by its shape when diy. 4. Impotent pollen is correlated with the reflexed type of stamens. 5. The defective pollen is due to an abortion of the gen- erative nucleus. These studies lead to one veiy practical reconr.uenda- ' Booth, N. O. N. Y. State Agr. Exp. Sta. Bull. 224, 291-302. 1902. 304 POMOLOGY tion, viz., mixed plantings of the grape will be more fruitful than those of one variety only, 271. The plum. — Some of the most extensive investi- gations on the self-sterility problem have been with the plmn, notably by Bailey/ Waugh,- Hendrickson,^ and Dorsey.^ There is a general tendency throughout the plum species to self-sterility but there are many exceptions, as would be anticipated from a knowledge of the problem. The salicina (Japanese) varieties are as a rule self-sterile and self-barren. The Climax is the only one of several kinds observed by Hendrickson to be self-fertile in California. He also reported that, in general, the early blooming Japanese varieties such as Combination, Kelsey, and Satsuma, are scanty pollen- producers and not effective poUinizers, while the later blos- soming sorts such as Burbank, Wickson, Climax, Sultan, and Abundance produce pollen abundantly and are effective pollinizers. Varieties of the native American species of plums vary- in regard to the sterility character but are much inclined to be self-sterile, as is notable in the case of the Wild Goose which is perhaps more generally grown than any other single kind. They are for the most part fully inter-fertile, however, so that one given variety will pollinate any other, providing the two bloom at the same time.'' Waugh has shown that in the P. americana group the pistils are frequently defec- tive, averaging 21.2 per cent in the trees studies. The an- thers are also defective in some cases but not so frequently as the pistils. In some cases, the anthers mature before the 1 Bailey, L. H. Cornell Agr. Exp. Sta. Bull. 52, 106, 139, 175. 2 Waugh, F. A. Vt. Agr. Exp. Sta. Ann. Rept. 1897-98, 1898-99. 3 Hendrickson, A. H. Plum pollination. Calif. Agr. Exp. Sta. BuU. 310. 1919. ^ Dorsey, E. J. Jour. Agr. Res. 17: No. 3, 1919. ^Waugh, F. A. Standard Cycl. Hort. V: 2719. (1916.) POLLINATION AND STERILITY 305 pistils are receptive (proterandrous), while in other cases the pistils mature before the pollen is ripe for pollination (proterogynous). It is true, however, as has been stated, that the Japan- ese and American plums are generally inter-fertile both within their respective species and also in hybridizing be- tween the species. P. americana is less inclined to hybridize than some other species of American plums. The Domestica plums (European species) are variable, some varieties being self-fertile and others self-sterile,^ but as a class they may be considered inter-fruitful.- They are, however, largely inter-sfcerile with Japanese and American plums but may be inter-fertile to some degree, as indicated by Hendrickson.^ He has shown also that the French prune is abundantly self-fertile in California if bees are present to work over the blossoms, but that the Imperial prune is very much less so. His work with these varieties well illustrates the value of the common honey bee as an agent in prune pollin- ation.^ The following data which he obtained are self- explanatoiy: 1 Bailey, L. H. Principles of Fruit-Growing, 20th Ed. p. 158. 1915. 2 Marshall, Roy E. Proc. Amer. Soc. Hort. Sci. 1919. p. 42. 3 Hendrickson, A. H. Proc. Amer. Soc. Hort. Sci. 1919. p. 50. * As an interesting side light on the application of these pollination studies, the following excerpt is quoted from W. L. Howard, letter, dated March 11, 1920. "Our investigations in the Santa Clara Valley, zarried on for five years, showed that bees are an important factor in prune pollination. Before our investigations were started, bee men paid the fruit growers from 50c to .$1.00 an acre for the privilege of pasturing their bees in the orchards during the blooming season. Since our ex- perimental findings were published, three years ago, there has been a complete change in the situation. This sea.son bee men have been able to rent every hive they have to fruit growers for from S2.00 to $3.00 per hive, depending upon whether they are bunched in one place or scattered over the orchard." 306 POMOLOGY Table LXXXVI BEHAVIOR OF FRENCH PRUNE TREES WITH AND WITHOUT CROSS-POLLINATION (AFTER HENDRICKSON) 1916 1917 Per cent Per cent 3.5 13.2 Set on trees from which bees were excluded 1.04 0.43 FRENCH PRUNE Set on trees inclosed with bees and with an Imperial prune tree 18,05 15.5 Set on tree inclosed with bees 19.4 Average orchard set 7.2 7.2 Set on trees from which bees were excluded 0.0 0.34 IMPERIAL PRUNE Set on trees inclosed with bees and with French prune 1.7 7.9 Set on trees inclosed with bees alone 3.02 In many cas3s of experimentation, plums have been more highly inter-fruitful than inter-fertile, some producing fruits which contained abortive seeds. 272. The peach. — Unhke practically all other fruits, the peach, as a rule, is quite self-fertile and capable of set- ting and maturing a crop when self- or close-pollinated. Fletcher reports, "The results of hand-pollinating 2939 Gold Drop peach blossoms in 1906 showed no benefit to this variety from cross-pollination with St. Johns, Late Cran- ford, or Lewis; the self-fertilized fruits were perhaps a trifle superior." All experiments confirm this work in general and the recommendation that peaches of one variety may be planted in a solid block is standard, although growers frequently feel that they prefer to mix them somewhat. POLLINATION AND STERILITY 307 273. The quince is reported by Waite to be nearly as fruitful when self-pollinated as when cross-pollinated. 274. The apple. — As a class, the apple is inclined to be self-sterile although a number of varieties are known to be at least partially self -fertile. In contrast with the grape, the sterility is, according to Kraus, "due almost wholly to em- bryo abortion," and Knight ^ says also to lack of pollen- tube growth. From a practical standpoint, it is always bet- ter to have mixed plantings than a solid block of one variety, although the latter may be successful under some conditions. Waugh worked with eighteen varieties of apple commonly grown in New England and reported them all to be practi- cally self-sterile. Out of 258(3 blossoms covered, only three apples set, or l/lO of 1 per cent. Lewis and Vincent reported that of eighty-seven varieties tested, fifty-nine were self-sterile, fifteen self-fertile, and thir- teen partially self-fertile." Waite states that "The varieties of apples are more in- clined to be sterile to their own pollen than the pears. With the former, in the great majority of cases, no fruit resulted from self-pollination." Alderman ^ investigated the Rome Beauty, York Impe- rial, and Wagener for a period of three years, with the follow- ing results: iProc. Soc. Hort. Sci. 1917. 2 Ore. Agr. Exp. Sta. Bull. 104. 1909. 3 Loc. cit. 308 POMOLOGY Table LXXXVII effect of cross-pollination on the set of fruit (after alderman) Number Fruits Per cent blooms set set 16,826 168 .99 20,587 702 3.41 21,742 129 .59 25,775 2,137 8.29 3,407 43 1.26 6,993 611 8.73 Rome Beauty, not crossed . Rome Beauty, crossed York Imperial, not crossed York Imperial, crossed . . . . Wagener, not crossed Wagener, crossed Here it will be seen that the set of fruit was materially increased by crossing. The percentage of set was increased with the Rome three and a half times, with the York four- teen, and with the Wagener seven times. In addition, the weight of the Rome was increased nearly 28 per cent and the York 42.7 per cent over the size of the self-pollinated fruits. 275. The pear. — Since many varieties of pears are self- sterile and probably because of the influence of the work of Waite,^ considerable attention has been given to a study of this fruit. Bailey ^ says "Many of the varieties of pears are infertile with themselves: they need the pollen of other va- rieties to cause them to set fruit freely. Probably any va- riety will fertilize any other variety in case the two bloom simultaneously." Waite showed that out of thirty-six va- rieties tested, twenty-two were self-sterile, but called partic- ular attention to the sterility of the Kieffer. Fletcher ^ has shown that "unsatisfactory results may be expected from planting either Bartlett or Kieffer in large blocks, so that cross-pollination by insects is not general. ' Loc. cit. 2 Standard Cycl. Hort. V: 2506. 3 Va. Agr. Exp. Sta. Ann. Rept. 1909-10. pp. 213-224. POLLINATION AND STERILITY 309 Anjou, Lawrence, Duchess, and Kieffer are satisfactoiy va- rieties for planting with Bartlett so far as pollination is con- cerned. Some years Kieffer does not blossom simultaneously with Bartlett, but usually the blossoms overlap sufficiently. Le Conte, Garber, Lawrence, Bartlett, Duchess, Anjou, and Clairgeau are satisfactoiy varieties for planting with Kief- fer, so far as pollination is concerned. Some seasons the latter five varieties do not blossom simultaneously with Kieffer, but usually the blossoming seasons overlap suffi- ciently." He obtained the following results under Virginia condi- tions: Table LXXXVIII RESULTS OF SELF- AND CROSS-POLLINATION OF BARTLETT PEAR (aTER FLETCHER) PoUi7iations Average amount of blossoms set Average weight of mature fruit, ounces Bartlett X Bartlett " X Kieffer " X Anjou 1 in 513 1 in 10 1 in 7 1 in 9 1 in 10 2.00 3.00 3.75 3.50 " X Angoulerae (Duchess) 3.50 In Califoniia the Bartlett is grown very extensively and, in spite of the advice given to the growers to inter-plant with other varieties, there are large blocks planted alone. As a result of this situation, some experiments were con- ducted during 1916-18 by Tufts ^ to determine the status of the sterility (barrenness) of this variety in California and to detennine the best poUinizers, if such are necessary. It was found that the Bartlett is to a limited degree self- sterile under valley conditions, but entirely so in the foot- * Tufts, H. P. Calif. Agr. Exp. Sta. BuU. 307. 1919. 310 POMOLOGY hills. Hence it is advisable to inter-plant with one or more varieties for cross-pollination purposes. These experiments showed that the Angouleme, Anjou, Clairgeau, Cornice, Dana Hovey, Easter, Howell, and Winter Nelis will all pol- linate the Bartlett successfully. It was also learned that no cases of inter-sterility existed between the varieties studied and, therefore, any which blooms with the Bartlett will be a suitable pollinizer. Also, there does not appear to l^e the same tendency to fall at the June drop if cross-pollination has taken place. CHAPTER XIII THE ORIGIN AND IMPROVEMENT OF FRUIT In a study of the vast number of fruit varieties now grown in America, the fortuitous nature of their origin is impres- sive. The larger part of the varieties of apples planted in this country originated here, but the histoiy of many is ob- scure and only a veiy few came into existence as the result of direct breeding. This statement is true in large part for the other fruits also, in contrast to such other horticultural crops as flowers, ornamentals, and vegetables. Some work- ers have devoted their hves to the production of new fruits, but not until comparatively recent times have practical re- sults of much consequence been secured through breeding. The histoiy of the activities of man in the origin and es- tablishment of American pomology is highly interesting, much of it being available in the writings of Bailey. The outstanding difficulties in the production of new fruits by breeding or in the study of the laws of inheritance as they pertain to fruit-trees are: (a) the length of time required to secure the fruit of a new generation; (b) the small number of individuals that can be handled in such work with the larger tree-fruits; and (c) self-sterility, which is often en- countered in lines of attack. The first great stimulus to the breeding of fruits came from the conspicuous work of Van Mons in Belgium and Knight in England. The theories and work of these men should be perpetuated in our literature. 276. Theory of Van Mons. — Jean Baptiste Van Mons was a celebrated chemist of Belgium (1765-1842) who became 311 312 POMOLOGY interested in the improvement of fruits, particularly the pear. He placed himself in the unfortunate position of conceiving a theoiy and setting about to prove it. How- ever, in so doing, he greatly stimulated the science of plant- breeding; and although his theory was without foundation, the net result of his work is a landmark in the progress of the origination of new varieties of fruits. His theory, in brief, may be summarized as follows:^ All fine fruits are artificial products; the aim of nature, in a wild state, being only a healthy vigorous tree, and perfect seeds for continuing the species. It is the object of cultivation, therefore, to subdue or enfeeble this excess of vegetation; to lessen the coarseness of the tree; to diminish the size of the seeds; and to refine the quality and increase the size of the flesh or pulp. There is a tendency for fruit-trees to return, by means of their seed, to a wild state, and such a tendency is more marked in old trees than in young ones. Hence, the older a tree is the nearer will the seedlings raised from it approach a wild state, although they will never return entirely to it. Therefore, in order to secure superior varieties, the seed from young trees only should be selected, as these are in a state of amelioration. Again, there is a certain limit to perfection in fruits. When this point is reached, as in the finest varieties, the next generation will be more likely to produce poor fruit, than that from seeds of an indifferent sort in the course of amelioration. In following out this theory, Van Mons began with seeds from inferior sorts and sowed a new generation as soon as fruit could be procured from the last sown, continuing this process year after year. "To sow, to re-sow, to sow again, 1 Van Mons, J. B. Arbres Fruitiers. 1835-36. Downing, A. J. Fruits and Fruit Trees of America. 1900. pp. 5-7. Bailey, L. H. The Survival of the Unlike, pp. 141-151. 1897. ORIGIN AND IMPROVEMENT OF FRUIT 313 to sow perpetually; in short to do nothing but sow is the practice to be pursued and which cannot be departed from." He concluded that pears require the longest time to attain perfection, and he cari'ied the process with this fruit through five generations. Apples, he found, needed but four races, and peaches, cherries, plums, and other stone-fruits were brought to perfection in three successive reproductions from the seed. ''Van Mons' work, which was largely confined to pears, was begun in 1785. Thirty years later, in 1823, when he had commenced distributing scions freely throughout the world, he had 80,000 seedling trees in his nursery. At this time his first catalog was issued and in it 1050 pears were mentioned by name or number. Of this list 405 were his own creation and 200 of them had been considered worthy of naming, among them being some of the varieties still raised the world over, including Diel, Bosc, Colmar, Manning's Elizabeth, and many others of equal merit. "Probably no worker with plants has ever given to the world so clear a demonstration of the value of selection as Van Mons; and this demonstration is worth all the efforts put forth, even though this was made in the attempt to prove another and, as is now believed, erroneous doctrine." ^ 277. Work of Knight.— Thomas Andrew Knight (1759- 1838) was the first practical and scientific breeder of fruits. Bailey describes him as a man "who in the variety, accuracy, significance and candor of his experiments stands to the present day without a rival amongst horticulturists." He conducted experiments which are still standard in plant physiology and horticulture. Knight avoided the error of Van Mons, that of having a theory to prove, but devoted himself to a study of nature • Munson, M. W. Plant breeding in its relation to American pomology. Maine Agr. Exp. Sta. Bull. 132. 1906. 314 POMOLOGY and to the results of his manipulation of plants. Van Mons worked entirely along the line of selection of the best from each generation, but Knight was the first actually to cross- breed fruits in order to secure better varieties. That his conception of the problem was different from that of Van Mons and far in advance of it is shown from the following statement (1806) : "New varieties of species of fruit will gen- erally be better obtained by introducing the farina of one variety of fruit into the blossoms of another, than by prop- agating any from a single kind." His investigations in- cluded apples, pears, plums, peaches, nectarines, cherries, and strawberries, and he produced several varieties of each which were standard in their day. Hence to this early worker is owed the beginning of real progress in the improve- ment of fruits and the methods to be employed in securing them. Knight spent considerable time in studying the dura- tion of varieties of fruit. This work, while not entirely ger- mane to the present subject, is worth recording, although it is not now accepted. His theory may be briefly smnmarized as follows: The life of a variety of fruit is about as long as the life of the original tree which produced it; cions or buds taken from the tree will not come into bearing until the original tree bears fruit; and all trees propagated from the parent will die soon after the death of the original tree. Or, in other words, the life of a variety is about as long as the natural life of the tree which produced it. This, then, is a brief statement of two of the most inter- esting personalities in horticulture. It will be instructive to contrast their views with some of the more modem theories in the breeding of horticultural plants. 278. Selection as a means of securing new fruits. — The voluntary act of selection must enter into every method of securing new or improved varieties of fruits. It refers to ORIGIN AND IMPROVEMENT OF FRUIT 315 the individual choosing of forms that meet the ideal of the person conducting the work and has been unconsciously prac- ticed by man in all stages of civilization since the time he began to cultivate plants and to domesticate animals. With plants commonly grown from seed, such as grains and vege- tables, this method of improvement has found wide usage and has been claimed by some to be the only means neces- sary. This belief is founded on the principle of variation, and on the fact that all possible genetic combinations may occur in natural crosses. With fruit-trees, however, selection as a method of plant improvement has been given less at- tention, as fruits are reproduced asexually. Every Baldwin apple or Elberta peach tree is a part of the original tree which was a chance seedling. Such being the case, there remain but two methods of selection with fruits: namely, of bud sports or mutations, and of new forms that have come from seed. The latter may properly be subdivided into three phases: (1) a choice of trees that are chance seedlings, in the origin of which man has played no part; (2) a selection of the superior trees from a miscellaneous lot of seeds sown; and (3) a selection of trees which result from flowers crossed or hybridized by the grower. First, it must be recognized that man has nothing what- ever to do with the occurrence of the superior individual or variety under the first two methods of selection, but rather he "finds" it. On the other hand, through crossing or hybridizing, new forms may be secured by the combination of desirable characters within one plant, or by "breaking the type" or causing the original plant to vary. The chief methods of selection commonly used in im- proving plants are: (1) mass; (2) line; and (3) clonal selec- tion. The method will of necessity depend on the object in view and the nature of the material used in breeding. 316 POMOLOGY The terms "mass selection" and "line selection" cannot properly be applied to the methods employed in obtaining new fruits. They refer to securing an improved variety in plants that are propagated sexually (i. e., by seed), where an effort is made in each generation to obtain individuals that will be superior to the original form, 279. Mass-selection refers to the choice of several superior individuals from which seed would be sown en masse, no effort being made to keep the progeny from any single plant separate; and from the new individuals which arise, the superior ones would again be selected, until a strain or race is secured which is superior to the original stock. Such a process has never been undertaken with fruit-trees, since it is not necessary for a variety to be homozygous in order to propagate it asexually or for it to have superior fruit characteristics. The term mass-selection may be applied in a broad way to the method used by Van Mons and to that of Burbank. Seeds selected from one or more trees (themselves heterozy- gous) are planted in order to secure a large number of new individuals. From these new forms the superior ones are selected, usually after they come into fruiting, and are prop- agated as new varieties with no further selection. 280. Line-selection has no special application to fruits because, as yet, no one has tried to secure a race or variety which will come true from seed, as is necessary with the common farm and garden crops. With the latter plants, the term refers to a line of progeny derived originally from one individual. 281. Clonal-selection. — The term " clonal-selection " ap- plies only to plants which are propagated asexually, hence to fruit-trees. Clones have been defined as "groups of culti- vated plants the different individuals of which are simply transplanted parts of the same individual, the reproduction ORIGIN AND IMPROVEMENT OF FRUIT 317 being by the use of vegetative parts such as bulbs, tubers, buds, grafts, cuttings, runners, and the hke. The various sorts of apples, . . . commonly denominated varieties in a more restricted sense would be clons. Clons of apples, pears, strawberries, and the like, do not propagate true to seed, while this is one of the most importaat characters of races and strains of wheat, corn and others." (Webber.) Hence, any selection for propagation of superior trees of any of the fruits would properly be termed "clonal-selection." Thus, a tree which appears different from others in a planta- tion or is superior to them, as being a regular or heavj^ bearer, having better color, quality, or size of fruit, or being particu- larly hardy , might be selected for the purpose of propagating a desirable variation within the clone. The temi "strain" is commonly used in referring to such differences.^ 282. Bud-selection, as commonly used in horticultural literature, refers to the selection of a bud or branch which shows a superiority over or difference from the remainder of the tree. Instead of the whole tree being the unit of variation, the individual bud is the unit atid is so selected. Before dis- cussing the improvement of fruits by clonal- or bud-selection, it should be determined whether such variations occur within the tree-fruits. The data refer to deciduous fruit- trees for the most part, although the bud variations which have been reported for citrus fruits are so conspicuous that they are mentioned in this connection. 283. Individuality of fruit-trees. — It is well known that many plants have given rise to bud-sports or mutations, particularly under high cultivation, such as greenhouse roses and carnations. Here such variations as the occurrence of a pink rose on a plant producing white ones or a change in form of the flower have been so distinct as to be unmistak- ^ Babcock and Clausen. Genetics in Relation to Agriculture. McGraw-Hill Co., New York. 1916. 318 POMOLOGY able. With fruit-trees it has been more difficult to determine between variations due to environment and not of a per- manent character and those which are true bud-sports. The following data are presented to show that decided va- riations do occur between fruit-trees of the same variety (clones) and between branches of the same tree, but whether they are due to internal or external causes is not determined. It is assumed that the trees are always comparable and that there is no apparent external cause for the variation. Table LXXXIX the variations in yield of bearing apple trees as reported by several experimental stations in america New York ' exp. Trees, sta. numbers Total yield for 10 years, bushels Ratio 2 and 6 246.5 137.2 179 6 1 and 4 100.0 Canada ' Tolal yield for 14 years, gallons 4 trees 477.94 165.50 288 4 trees 100.0 Maine ^ Total yield for 5 years, barrels 10 trees 157.9 38 415.5 10 trees 100 Stewart, J. P. Penn. Agr. Exp. Sta. Ann. Rapt. 1911. ORIGIN AND IMPROVEMENT OF FRUIT 319 Table LXXXIX— Con/inue(Z New Hampshire ^ Tree Total yield for 6 poimds years, No. 3 4432 1527 515 860 269 No. 15 100 No. 278 Group D No. 280 4204 6817 591 711 1153 No. 281 100 It will be seen from this table that there are conspicuous differences in yield of seperate trees or sets of trees in the same orchard. The time covered by these records is sufficient to eliminate short-time differences. Such variations in yield have an important economic bearing and some of the out- standing instances of attempts to improve fruits by bud- selection may be noted. 284. Results of selecting bud variations. — If the data are granted to prove that decided variations occur between trees and their branches and that they are consistent year after year, then the question arises as to whether such varia- tions are permanent in nature (mutants) or whether they are due to some undetermined local condition (fluctuating varia- tions) and hence are not transmissible by asexual propaga- tion. Unfortunately, sufficient work has not yet been done to establish this point definitely, but most of the evidence for deciduous fruit-trees warrants the conclusion that such variations cannot usually be propagated (asexually) and hence the burden of proof lies with those who make such 1 Gourley, J. H. N. H. Agr. Exp. Sta. Tech. BuU. 9. 1915. See also Gardner, V. R. Bud selection with special reference to the apple and strawberry. Mo. Agr. Exp. Sta. Res. Bull. 39. 1920. 320 POMOLOGY claims. There are a few cases, however, which indicate the origin of new varieties in this way, although for the most part they represent an increase or change in color, as varia- tion of other characteristics is not common. Among apples, the Banks is recorded as a bud-sport of the Gravenstein, differing from the latter in being more highly colored, less ribbed, more regular in shape, and a little smaller in size. Other sports of the Gravenstein have been reported in Europe and in this country. Two bud-sports are credited to the Twenty Ounce apple — Collamer and Hitch- ings. The former bears fruits less mottled and striped, more highly colored and more regular in shape. The twigs of Collamer trees are more deeply tinged with red than are those of Twenty Ounce. Hitchings also produces more highly colored fruit than its parent. The same sort of muta- tion has been recorded in several places for Rome Beauty, the fruit of the new forms being a solid dark red, smaller, and quite regular in size. Red Russet is another bud-sport which originated in New Hampshire as a variation of Baldwin. This is the only au- thentic variation of the Baldwin which has been propagated, although it varies widely in different localities. Dorsey ^ describes an "improved Duchess" apple which seems to be a bud mutation, although conclusive evidence cannot be produced. The new form is identical with the old in all characters except color, which is much brighter and redder. Trees propagated from the red type retain the character, and this seems to add another to the list of fruits originating as bud mutations. Another interesting case of a bud-sport or mutation de- scribed by Shamel ^ is an improved French prune. This iDorsey, M. J. Jour. Heredity, Dec, 1917. p. 565. 2 Shamel, A. D. Origin of a new and improved French prune variety. Jour. Heredity, Nov., 1919. pp. 339-343. ORIGIN AND IMPROVEMENT OF FRUIT 321 variety is grown more largely in California than any other, but the small size has been a matter of concern, and many efforts have been made to improve it. Leonard Coates, a nurseryman and fruit-grower of Morganhill, California, ob- served a branch of a French prune tree that produced fruit of large size. Grafts of it were inserted into peach stock and the new form was found to be identical with that of the original branch. Extensive tests were made to deter- mine its value, and so successful do they appear that it is believed it may prove to be "the most valuable addition to the commercial prune varieties ever introduced ia America." There are no known cases of bud variations of the cherry, and only four mutations of the peach out of 2181 varieties described by Hedrick in "The Peaches of New York." Knight records the case of a Yellow Magnum Bonum plum, one branch of which bore red Magnum Bonum fruits.' A Coes Golden Drop is reported by Powell as producing a branch which bears red fruit. An Isabella grape vineyard, in California, is said to have produced several mutating vines which bore fruit superior in quality to the mother plants, and that have been propagated under the name "Pierce." The Golden Queen raspberry originated as a sport from Cuthbert, formerly called Queen of the Market, and was introduced to public notice by J. T. Lovett, Little Silver, New Jersey. The occurrence of nectarines as bud-sports on peach trees is, of course, common and has been observed by horticultur- ists for a long time. Whitten took cions from a high- and low-yielding Ben Davis tree in 1895 and has observed trees propagated from them until 1917. He says: "Summing up the results for the entire period of years since the trees came into bearing 1 Munson, W. M. Loc. cil. 322 POMOLOGY there is no significant difference between the total yield of the trees of high yielding parents and low yielding parents." ^ Stewart ^ reports an experiment in which trees showing marked variation in yield and color were propagated and planted for observation. At the time of his report, however, no progress had been made which would indicate that such superiority had been transmitted, thus again pointing to the conclusion that the differences were due to environment. Macoun ^ also propagated some trees which showed marked variation in yield, amounting to 100 and 200 per cent difference, and records were kept on the yields from the trees. However, no decided evidence is at hand after they have produced three crops to substantiate any claim that they will be superior in bearing. Extensive observations have been made in recent years of bud variation of orange, lemon, and grapefruit trees by Shamel ^ and others. These fruits, particularly certain va- rieties, are found to be in a very variable condition, and bud- sports are frequently observed with a number of the char- acters of both tree and fruit. In recording the performance of the trees, such characters are observed as : habits of growth of the trees; characteristics of the bloom; season and amount of production of fruit; size, shape, and color of fruit; texture, thickness, and appearance of the rind; amount and quality of the juice; and other tree and fruit characteristics. Shamel states in regard to lemon trees that "The produc- tive strains in every case known, produce a higher percent- age of first-grade commercial lemons than the unproductive 1 Whitten, J. C. Mo. Agr. Exp. Sta. Bull. 163. p. 55. 1919. 2 Stewart, J. P. Penn. Agr. Exp. Sta. Bull. 134. 3 Macoun, W. Dominion Exp. Farmers Bull. 86. 1916. * Shamel, A. D. Bud variation in lemons. Jour. Heredity, Feb., 1917. Lemon orchard from buds of single selected tree. Jour. Heredity, Nov., 1918. ORIGIN AXD IMPROVEMENT OF FRUIT 323 strains. For example, about 80 per cent of the crop of tree of the productive strain of the Eureka variety in the per- formance record plots has been of the best grade, while the unproductive strains have produced only about 20 per cent of the best grade of fruit." This statement does not refer to orchards which have been propagated from superior trees, but rather to superior trees under observation in orchards. However, several citrus orchards are now in bearing in Cali- fornia which have been propagated from superior trees or branches, and according to their records give distinct promise of ]ierpetuating the desirable characters of the parent trees. 285. Plant introduction. — In colonial times it was not surprising to find that many European fruits were introduced into America regardless of their adaptability. As a result there were many failures,^ and not until seedlings of these as well as of native sorts began to appear were valuable American fruits secured. The entire history of American pomology is inti- mately associated with that of the introduction of foreign fruits. England, continental Europe, Siberia, Japan, and China have all made contributions to the present catalogue of fruits. Perhaps the most interesting chapter in the history of fruit introductions is that dealing with the effort to secure hartly fruits from Russia. These fruits, which were intro- duced during the 70's and 80's of the last century, were heralded as the solution of apple-growing in the cold parts of the United States and Canada. Enthusiasm ran high for several years, but at the present time few of the varieties so introduced are considered valuable and the chief interest lies in using their seedlings for hardy stock on which to work other sorts and also for producing new varieties either from seedlings or from crosses. 1 Bailey, L. H. Survival of the Unlike. Macmillan Co., New York. 2nd E(i. 1896. Evolution of Our Native Fruits. Macmillan Co., New York. 1898. 324 POMOLOGY 286. Chance seedlings. — It is well known that the larger number of varieties of the tree-fruits originated as chance seedlings and were discovered and introduced into cultiva- tion by some observer and admirer of them. Hedrick and Wellington ^ review this matter in regard to the apple and say that "of the 3000 or more varieties which have been described, nearly all, as their histories show, have come from chance seedlings." Beach describes 698 varieties in "The Apples of New York" and of these "no case is recorded of a variety known to have come from a self-fertilized seed." Even the seed parent is given for only thirty-nine varieties in all, while the seed and pollen parent is known certainly for only one (Ontario). Both parents are named for the Pewaukee and Gideon, but in each case one of the parents is guessed. Seventy-one are listed as coming from chance seedlings, i. e., from seed sown without knowledge of either parent or from natural seedlings. The origin of 517 of the 698 varieties is unknown. However, progress is being made and several new varieties, produced by breeding, are about to be introduced from some of the experiment stations. Table XC origin of the common fruits Both parents One parent knoivn known 2(?) 39 20 61 74 57 49 108 37 214 182 479 Neither parent known Originated as bud sport Total Apple . Cherry Grape . Plum. . Peach . 588 (?) 1064 72 542 1765 4 1 K?) 4031 633 1145 203 700 2181 4862 1 Hedrick, U. P., and Wellington, R. An experiment in breeding apples. N. Y. (Geneva) State Exp. Sta. Bull. 350. 1912. ORIGIN AND IMPROVEMENT OF FRUIT 325 For cherries, Hedrick has searched the Uterature and finds that httle is known in regard to their origin. The histories of the varieties described in "The Cherries of New- York" show that nearly all of them have come from chance seedlings. No case is recorded of a variety known to have come from self-fertilized seed. The seed parent is given for sixty-one of 1145 varieties. The seed and pollen parents of twenty of the cherries described are given. Of these, sixteen are hybrids originating with N. E. Hansen, of South Dakota, leaving but four sorts the parents of which were known before the recent work of Hansen. Cherries arising from seed sown without knowledge of either parent or from natural seedlings are put down as chance seedlings. Of these there are 147. The origin of 1064 of the varieties described by Hedrick is unknown. In "The Peaches of New York," Hedrick describes 2181 varieties of peaches, no one of which is known to have come from a self-fertilized seed. The seed parent is given for 214 varieties; the seed and pollen parents for 37 varieties. Of chance seedlings, sorts from seed with neither parent known, there are 161. The origin of 1765 out of a total of 2181 varieties described is unknown. 287. Work in Canada.^ — The low winter temperatures and the relatively short growing season in many parts of Canada have made it necessary to secure varieties of fruits which would be adapted to such climatic conditions. It, therefore, devolved on the earlier workers in that countiy either to introduce or to originate new varieties, as standard commercial sorts were not sufficiently hardy. 1 Macoun, W. T. The apple in Canada. Dom. Canada Dept. Agr. Bull. 86. 1916. Apple breeding in Canada. Proc. Amer. Pom. Soc. 1917. pp. 11-27. Saunders, Win. Hardy apples for Canadian North- west. Central Exp. Farms. Bull. 68. 1911. Macoun, W. T. Apple breeding in Canada. Amer. Breed. Assoc, Vol. 8, 1911. pp. 479-487. •326 POMOLOGY Great credit is due the amateur and professional horti- culturists of Canada for the results of their efforts along this line. Not only have they produced varieties of apples which are hardy in sections where previously no fruit could be grown, but they have also arrived at some conclusions which will be of value to future plant-breeders. The Central Experimental Farms, where most of the work is conducted, are located at Ottawa, but there are also several substations at various points in the Dominion. At Ottawa, 734 named varieties of apples have been tested as well as many unnamed seedlings; also 160 Russian sorts, though many which were at first thought to be different have proved to be identical. The first recorded apple breeding in Canada seems to be that of Charles Arnold, of Paris, Ontario. He made several crosses between Northern Spy and Wagener and exhibited eighteen of the cross-bred apples in Boston in 1873. One of these apples, which was named Ontario, has attained some commercial importance. In 1869 Francis Peabody Sharp, of Upper Woodstock, New Brunswick, began some crossing with apples, having as his object the production of an apple of extreme hardiness and productivity. He used as parents the New Brunswicker — either Oldenburg or very similar to it — and Fameuse (as the male). Several of his crosses have been propagated, but Crimson Beauty is doubtless the best known and is most widely distributed commercially. The first extensive work in growing seedling trees was begun in 1890 by William Saunders when an orchard of about three thousand seedling trees was planted. The seed from which these trees were grown came from north of Riga, Russia. About fifty of them began to bear in 1897. "The number of trees was gradually reduced by winter-killing, by fire-blight, or were removed on account of weak growth and ORIGIN AND IMPROVEMENT OF FRUIT 327 inferior quality. All but a few of those which fruited were as good as the named varieties of Russian apples." Again in 1898 a large number of seedling trees was planted by Macoun. The seeds were taken from varieties of standard quality, such as Mcintosh, St. Lawrence, Fameuse, Wealthy, Gano, and Northern Spy. Excellent results were obtained, and in 1916 he reported that "During the past twelve years, 1211 of these seedling varieties have fruited, and of these, 83.30 per cent were of marketable size (medium to large) and only 3.95 per cent were small or crab-like. Of the 1211 varieties, there have been 378 considered so promising that they are being propagated for further test and 99 of the best have been named." Some of the hardiest of his apples have fruited as far north as latitude 58°, at Fort Vermilion on Peace River. In addition to this work, a somewhat different procedure was followed by Macoun in 1910. Seed was saved of the hardiest Russian apples, including Transparent, Charlamoff, Oldenburg, Tetofsky, and Hibernal. The seedling trees were sent to the prairie provinces, where the winters are particu- larly severe, and planted in nurseiy rows. After three years, any that survived the winter were transplanted to an orchard for further trial, and in this way the hardiest trees were selected and those producing worthy fruit were retained for propagation. Special work is also being conducted with crossing and hybridizing apples. Preliminary studies are being made on the transmission of fruit characters as a basis for future investigation. This work in crossing was begun by William Saunders about 1894. He introduced the berried crab {Pyrus hnccata) from Russia several years before; and after deter- mining its hardiness he made crosses between that species and many of the best and hardiest sorts of apples (P. Mains) grown in Ontario. In 1896 he used another hardy wild 328 POMOLOGY crab, known as P. prunifolia, in his crosses. The best hy- brids obtained from these crosses with P. haccata and P. prunifolia were again crossed with the large fruited P. Mains and thus he introduced a second quota of "blood" of the larger varieties. Several of these second crosses are now fruiting and are promising sorts. From the work in Canada the following conclusions are reached in regard to originating new varieties of apples: 1. To produce a hardy apple where no apples have yet been hardy: (a) cross the apple with the wild Siberian crab (Pijriis haccata) ; (b) sow seeds of apples which have ripened in a climate as nearly similar as possible. 2. To produce a hardy long-keeping apple of good quality: sow seeds of long-keeping varieties of good quality of which both parents are long-keeping. 3. To produce an apple having certain characteristics, as regards hardiness, vigor, and productiveness of tree, and quality, size, and appearance of fruit: sow seeds of varieties having most of the characteristics desired. 4. In cross-breeding apples where quality is an important factor, as it should be in most places, cross two varieties which are both good or very good in quality. It has been the experience at Ottawa that in crossing a variety of good quality with one inferior, the crosses will nearly always bear fruit of a quality inferior to that of the better parent. 288. Work of Peter Gideon and other pioneers in the United States. — The name of Peter Gideon will always be associated with the early struggles to produce an apple which would be of good quality and hardy enough to with- stand the severe climate of the Upper Mississippi Valley. His work continued for more than thirty years, in which time he grew thousands of seedlings of apple, peach, plum, and cherry, and shortly before his death (1899) he wrote that of all these thousands of seedlings and named varieties ORIGIN AND IMPROVEMENT OF FRUIT 329 of fruits tested, "only two trees remain." "One of these, the Wealthy, grown from a cherry-crab seed, obtained from Albert Emerson, of Bangor, Maine, of whom I obtained scions at the same time, from which I grew the Duchess, Blue Peannain, and the cheriy-crab, all of which, combined, were the foundation of Minnesota horticulture, that to-day is the pride and hope of the Northwest." ^ "Thus far it has taken from three to five hundred seedlings to give us one first-class apple, and from seed taken from the best apples we had." Patten, Watrous, and others of Iowa and the Central West also contributed much of the foundation work in securing hardy fruits for the prairie states. 289. Hansen hybrids. — N. E. Hansen of South Dakota has effected many inter-specific combinations between Prunus Besseyi, the western sand cherry, as one parent and varieties of P. salicina or P. Munsoniana as the other; and other combinations have also been made. In these "Hansen hybrids" a new tyi^e of plum has come into use in the North- west. While these sand cheriy crosses have been experi- mented with for some time, the success of the variety "Com- pass" cherry has added impetus to the movement. While the saad cherry is one of the parents of these crosses, they in reality are not cherries but plums. One of the outstanding characteristics of these hybrids is the profuse early fruiting habit. They often bear at three years of age and as they grow best in bush form and fruit on the terminal shoots, winter-killing affects them less. Under the prairie conditions of the Upper Mississippi Valley in the United States and Canada, varieties like Sapa, Opata, Etopa, Wakapa, and Okiya have been a boon to the homesteader. These fruits rot easily and cannot be shipped for long distances, but for ' Some doubt exists in regard to the source of the seed which procUiced the Wealthy apple, as is reported in Minn. Hort. 1917. p. 85. 330 POMOLOGY home use they have filled a need in regions where other plums could not be grown. This tribe is of special interest also because of its hybrid origin and suggests the promise to new regions which such combinations may have. From this work of Hansen, the Northwest has profited by varieties of many fruits and his work shows clearly what can be accomplished in horticulture by breeding. 290. Burbank's work. — The life and work of Luther Burbank of Santa Rosa, California, has been a great stimulus to plant-breeding. This is doubtless due to the great novelty of his creations and to the extent of his work. He has ever held in mind the production of fruits and other plants which would be of the greatest use and economic value and has held as secondaiy the accumulation of scientific data. Perhaps pomology has profited more from his introduction of Japanese plums, and the seedlings and hybrids which he has obtained from them, than from any other achievement. He has succeeded in hybridizing diverse forms of fruits, some valuable for commercial purposes and others as novelties. 291. Inheritance of characters in the apple. — One of the few definite experiments in breeding apples, which has thrown some light on the inheritance of characters, is the one con- ducted by Hedrick and Wellington.^ The results not only throw light on some of the laws of inheritance of apples but also furnish some practical results in the way of promising new varieties. There were 148 crosses made between standard varieties in 1898 and 1899. The seedling trees began fruiting in 1908 but the grafts from them four years earlier. Crosses were made between Ben Davis, as the female parent, and Esopus, Green Newtown, Jonathan, Mcintosh, and Mother; between Esopus as the female and Ben Davis and Jonathan; Mcin- tosh and Lawver; Ralls and Northern Spy; Rome and North- ^ Loc. cil. ORIGIN AND IMPROVEMENT OF FRUIT 331 ern Spy; and Sutton and Northern Spy. Some of the im- portant observations by the authors as a result of the work are as follows: (1) These crosses strikingly contradict the idea that seedling apples (of cultivated sorts) revert to the wild prototype. (2) The stimulus of hybridity is very marked in the vigor of the crosses under consideration. (3) The behavior of some of the crosses strongly suggests that apples may be "preponent" in one or more of their characters. Other conclusions which bear on the laws of inheritance are: In color of skin, the fruits in which yellow predominates over red seem from the data to be in a heterozygous condition for yellow and red. The fruits in which red predominates are either homozygous or heterozygous. The pure yellows are homozygous. The data favor the supposition that so far as size and shape are concerned, these characters are inherited practically as intermediates. While all the varieties were sub-acid, the progeny indicate strongly that crosses of these sub-acid varieties break up in the proportion of three sour apples to one sweet one. 292. The heterozygous nature of fruits. — If an individual plant is pure or homozygous for any one or all of its charac- ters, then all of the sexual gametes produced by it would, if the plant is self -fertilized, produce progeny which are alike. Thus, if a Grimes Golden apple were homozygous for all of its characters when self-fertilized, all the seedling trees produced would be practically identical with the parent. Such a condition does not exist, however, for the seeds of a self-fertilized apple tree will produce a motley array of prog- eny, varjing in color, form, quality, and tree characters. Therefore, all of the common varieties are heterozygous and may be regarded as the Fi generation of previous crosses. 332 POMOLOGY It so happens, however, that it makes no practical difference whether fruit varieties are homozygous or heterozygous since a valuable new kind is propagated asexually and hence has little opportunity to break up, or lose its type. Therefore, it is unnecessary in breeding fruits to take this into considera- tion and in crosses between heterozygous parents the re- combination of characters takes place in the Fi. This being the case, new combinations can be obtained from which to select desirable fruiting types without selfing individuals and encountering sterility or the great reduction in vigor which so often happens. 293. Pedigreed nursery stock. — Following the usage of the animal-breeders, certain nurserymen have adopted the term "pedigreed" to designate fruit-trees which have been propagated from a tree of known behavior or superior worth. This, of course, carries with it the idea that such trees will be better producers, have better color and quality, or have some other merit which individuals of the same variety selected at random would not possess. It must be remembered that animal-breeders always refer to a new individual produced by the union of sex cells while the nurseiyman refers to the same identical tree which has been increased by asexual propagation. Therefore, unless a true mutation occurs, the varying forms of a fruit variety will not be transmitted by vegetative propagation. Owing to the failure of practically all the experiments in the eastern United States to secure a superior strain of trees by prop- agating from a high producer or othenvise superior plant, there is a distinct prejudice among horticulturists to the use of the term ''pedigreed" trees. On the other hand, the cases cited from California show that many true bud-sports do occur in that state, and Coit has adopted the use of a better term to designate trees propagated from these mutants in the phrase "recorded trees." ORIGIN AND IMPROVEMENT OF FRUIT 333 Nurseiymen and fruit-growers will continue to search for superior strains of the old varieties and it cannot now be stated with absolute assurance that some success will not crown their efforts. 294. Graft-hybrids^ represent one of the most interesting phenomena that occurs in nature. They remained unex- plained for centuries although many of them had been ob- served. A graft-hybrid may be defined as the combination of the stock and cion tissues into a form which is intermediate between the two. The explanation for these queer ''freaks" or chimeras was not clear until they had been produced artificially. It appears that either there is a mingling of the tissues at the point of contact of the graft or else that an adventitious bud arises where the callous has formed, which partakes of both tissues. The result is either a pcriclinal chimera in which one tissue envelops the other (the hand-in- glovc type) or a sectorial chimera in which the two tissues occur side by side on the same stem, leaf, or flower, yet each retains its independent form. In at least one case, the number of chromosomes in the graft-hybrid is the same as if the hybrid were sexual in nature, thus being a true hybrid. An apple called Sweet and Sour, which is described in "The Apples of New York" and is occasionally seen, is probably a graft-hybrid. The apple is somewhat ribbed and this ribbed portion is green while the part between is yellowish. The flesh beneath the green skin is distinctly acid, while that under the j^ellowish skin is mildly sub-acid or sweetish. 295. Breeding the grape. — The early varieties of Amer- ican grapes wcr(> s(>cdlings of merit derived principally from Vitis Labrusca. The early efforts to grow the European * Popenoe, Paul. Plant chimeras. Jour. Heredity, Vol. 5, p. 521. Dec, 1914. Ca.stle, W. E. An apple chimera. Jour. Heredity, Vol. 5, pp. 200-202. 1914. 334 POMOLOGY grape (F. vinifera) in eastern United States failed utterly, but on the Pacific Coast they have been successful since the early Mission days. Recently Hedrick has succeeded in establishing V. vinifera in New York state where several are proving capable of withstanding the climate except that some winter protection must be given. In general, the breeding work that has been done with grapes, covering the period since the introduction of the Isabella (1816) and Catawba (1823) up to the present time, is one of the most valuable chapters in the history of breeding fruits in this country. 296. Inheritance of self-sterility in grapes. — It will be recalled that grape varieties differ in regard to the structure of their flowers. They are classified as (1) true hermaphro- dites, (2) hermaphrodites functioning as females, owing to completely or partially abortive pollen, and (3) pure males with the pistils absent or rudimentary. There are also two distinct types of stamens among these classes: (1) those which are upright, and such varieties are practically always self-fertile ; and (2) those which are reflexed or bent backward and downward which are self-sterile. Of the 132 important commercial varieties of the grape described in "The Grapes of New York," Dorsey (1909) shows that 95 have upright stamens and 37 reflexed. The question arises as to whether this character of the stamens will behave as a unit character or, in other words, whether self-sterility can be eliminated by breeding. 297. The inheritance of sex in the grape. — In the grape the flower type has such an important economic bearing that considerable attention has been given to the inheritance of flower type or sex. Since the wild vines are dioecious for the most part, the question has often been raised as to the origin of the perfect or hermaphrodite flower type such as is found in Concord. Some recent investigations have thrown ORIGIN AND IMPROVEMENT OF FRUIT 335 light on this question. When the data of Hedrick and Anthony ^ are presented according to the formula by Valleau, the following ratios are obtained: Table XCI flower types and ratios obtained in grape crosses Formula of the genetic con.flilulion Flower types of the progeny IMrentis Hermaphrodite Female Male types Upright X Upright Upright selfetl (same FH xFH FHxFH FFxFF FFxFH FF X FF GF X FM 180 673 16 207 94 7 47 1.52 16 206 73 6 9 3.8 : 1 Reflexed x Reflexed .... Reflexed x Upright Upright x Reflexed (cro.ss not made) Reflexed selfod Upright X Wikl male . . . 1 : 1 1 : 1 1.2 : 1 1:1:2 The apijearance of the large number of hermaphrodite seedlings in these crosses is of great importance to grape- growers, because it is possible to select seedlings which will be self -fertile. In crosses made between varieties of another species, Vitis rot imdi folia, Detjen - presents data which throw some light on the first appearance of the hermaphrodite flower in a dioecious species. This is epochal in southern grape-growing because it had heretofore been necessary to grow unproduc- tive male vines in vineyards in order to secure proper pollination. His evidence is so clear cut on this point that some of it will be included here in a condensed form for the convenience of the student : 1 Hedrick, U. P., and Anthony, R. D. Inheritance of certain char- acters of grapes. Jour. Agr. Res. 4: 315-330. 1915; also N. Y. State Agr. Exp. Sta. Bull. Tech. 45. Valleau, W. D. Inheritance of sex in the grape. Amer. Nat. 50: 554-564. 1916. - Detjen, L. R. Inheritance of sex in Vitis rotundifolia. N. C. Agr. Exp. Sta. Tech. BuU. 12. 1917. 336 POMOLOGY Table XCII FLOWER TYPES AND RATIOS OBTAINED IN CROSSES IN Vitis TOtundifoUa Flower type Cross Hermaphrodites Females Males Female x male . . 348 197 79 1420 461 228 74 1509 Scuppernong x Hope Thomas x Hope James x Hope The great contrast in the number of hermaphrodite vines bearing flowers with upright stamens when Hope is taken as a pollen parent and when male vines are so used is out- standing. Hope was found in the wild in 1910 and differs from the typical male vine in that it has a partially developed pistil. Its genetic constitution is shown by its behavior in crosses in which it is seen to be decidedly different from others of its kind. In the instances cited here, there is an excellent illustra- tion of the solution of the commercial problem of sterility in the grape by breeding. Contributions like these to the knowledge of horticultural plants will have a far reaching influence on practice. 298. Rogers' hybrids. — The work of Rogers in hybridiz- ing the native American grape with the European is epochal in the histoiy as well as in the commercial status of the grape. Rogers conducted his breeding work at Salem, Massa- chusetts, during the early 1850's. As a result of hybridizing large-fruited Labrusca grapes with the Black Hamburg and White Chasselas, both vinifera varieties, he secured about 150 seedling plants but only raised 45 to maturity. They were tested by himself and others, being known by numbers, from 1 to 45, but several were later named for persons of note in science or for other attainments, as well as for counties ORIGIN AND IMPROVEMENT OF FRUIT 337 and towns of Massachusetts. The named varieties which are now grown commercially are Goethe, Massasoit, Wilder, Lindley, Gaertner, Agawam, Merrimac, Requa, Aminia, Essex, Bariy, and Herbert. These grapes are of exception- ally high quality, combining the richness of the European with the general type of the American grape; but unfortu- nately these hybrids are usually somewhat deficient in vigor, hardiness of root or vine, self-fertility or pi'oductiveness. 299. Breeding disease-resistant fruits. — Most of the definitely plamied experiments in breeding of deciduous fruit-trees in the United States and Canada have had as their purpose the securing of hardier varieties. Of equal importance to the orchardists of the large fruit regions of this country is the problem of securing fruits resistant to such diseases as blight {Bacillus amylovorus), peach yellows, and the like, and breeding seems to be the ray of hope to these breeders. The selection of disease-resistant individuals would be the first means of attacking this problem, since man}^ other kinds of plants have produced disease-resistant strains, as for example, flax, cotton, and melons. In these genera, however, there is a new sexual generation each year, which affords an opportunity for variation that does not obtain within a clone. It, therefore, remains for the breeder to combine a variety or species which is immune to the trouble in question with a variety of commercial importance subject to it. Thus, if a Bartlett subject to blight is crossed or hybridized with a blight-free pear, there is a possibility of obtaining a fruit as valuable as the Bartlett but with the "factor" for blighting absent. This possibility rests on the assumption that disease-resistance or susceptibihty is a unit character and thus jiermits of recombination. 300. Stocks for pears. — According to the findings of Reimer, the following species of pear are quite blight- resistant: Pyrus sinensis, P. ovoidea, and P. Pashia {vario- 338 POMOLOGY losa). While he records that P. betulcefolia is somewhat susceptible to blight in Oregon, it has been remarkably free in South Dakota where it has been grown for twenty years, and in the trial plots at Washington, D, C, Pyrus Calleryana is a recently described species of pear native to China which is veiy promising as a stock. Hence, if a variety of high quality can be produced by hybridizing P. communis (from which all the commonly grown pears originated) with one of the hardy, blight-resistant species, the solution to one of the most serious problems in pomology would be at hand. Hansen has crossed P. sinensis and P. betulcefolia with several of the best cultivated pears (P. communis) and dis- tributed thirty-nine promising sorts throughout several states for trial. It is hoped that they may prove to be the basis of pear breeding to secure valuable varieties immune to blight.^ 301. Stock for grapes. — What appears to be a clear case of the Mendelian behavior of disease-resistance is seen in the work of Rasmuson ^ who attempted to secure varieties of V. vinifera which would be immune to the great scourge of phylloxera. He made crosses between certain American species and V. vinifera, and also crosses between different varieties of V. vinifera. In studying the F2 generation of these crosses, he found that the vinifera crosses yielded off- spring susceptible to the disease while crosses between the American species and vinifera yielded varieties part of which were resistant and part susceptible, but the latter were in the minority. The fact that disease-resistance proved to be dominant and susceptibility recessive in the progeny of this latter set of crosses, bodes well for the future. 1 Reimer, F. C. Proc. Amer. Pom. Soc. 1915. Hansen, N. E. S. D. Agr. Exp. Sta. Bull. 159. 1915. Galloway, B. T. Jour. Heredity, Vol. 9. Jan., 1920. 2E.S.R. 36:537. CHAPTER XIV PROPAGATION AND FRUIT-STOCKS Since most of the tree-fruits do not come ''true" from seed, it is necessary to provide a root or stock on which to bud or graft them. The term "fruit-stocks," therefore, re- fers to the seedhngs on which are "worked" varieties of the tree-fruits, nuts, and sometimes grapes. This is in distinction to "cion" which refers to the piece of wood of the desired variety introduced on the seedling stock. The entire fruit-stock situation is not well worked out, as miscellaneous seedlings of unknown genetic constitution are used.^ The seedlings, however, have given very good results, and the improvements that could be made by a more intelligent selection of material must remain a con- jecture. Certainly as regards hardiness, disease, and insect resistance, improvements of note could be accomplished. Already something has been undertaken and the proper organization for a further extension of this work is now in existence. However, as referred to later, the relation of stock and cion is only meagerly understood. 302. Handling the seed and stock. — After the fruit-seeds have been collected in the fall, they are assembled at the nurseries, either at foreign points or in this country, where they are properly handled for the raising of seedling stock. Apple seed is secured by washing pomace obtained at cider mills and it is then dried in the open air. The seed is then stratified in sand until early spring. The apple seed will ^See Chapter XIII. 340 POMOLOGY usually begin to sprout rather early in the spring, when it should be sown in a well prepared, deep, rich soil. This is important in order to produce straight long roots, as these are superior for propagation purposes. The seed is sown in rows four feet apart and the seedlings should be cultivated thoroughly throughout the summer. After the leaves have dropped in the fall, the little trees are dug, a part of the tops removed (leaving about six inches of the stem), the plants tied in bundles, and the bundles packed in boxes of green sawdust, sand, or other material in which they may be kept reasonably moist and cool. Such seedling roots are known as apple "stock." 303. The more common fruit-stocks.— The stock used for propagating a fruit must be "congenial," that is, the cion must be capable of making a good union and growth on such stock. A number of unusual combinations can be made, but the more common are here listed : Apple — French crab; Vermont crab; Minnesota crab; Virginia crab; and for dwarfing, Paradise and Doucin. Pear — French pear seed; Japan pear; Kieffer seed collected in eastern United States. For dwarfing, Angers or other quince. Quince — from cuttings, stools, or mound-layering; and seed (to a limited extent). Peach — seeds of wild or standard varieties, usually se- cured in this country. •Plum — seedlings of Primus domestica; St. Julien; myro- bolan (P. cerasifera) ; and sometimes P. americana. The peach may be used for plum stock when the latter is to be grown on light soils. For dwarfing myrobolan, also mira- bella (a form of P. cerasifera), and several forms of the native plums. Cherry — Mazzard cherry (P. avium); P. Mahaleb and P. pennsylvanica to some extent. PROPAGATION AND FRUIT- STOCKS 341 304. Apple stocks. — A change or adaptation of the nursery-stock situation is taking place, owing to the partial exclusion of stock formerly imported from foreign countries. However, the following are in use at present, as indicated above. French crab {Pijrus Mains, Limi.) is most commonly used for the apple, whether the seedlings are grown in France and then im- ported to the United States, or whether the seed is imported and the stock grown in this country. It is estimated that about 40 per cent of the apple stock used in this country is imported from France at the present time. (See Fig. 37.) Howard ^ answers the question as to what French stock is by quoting a French nurseiyman, as follows: "The crab apple seed comes from Pijrus Malus, Linn. {Mains communis, DC.) which is simply a natural apple. This is a cider apple. Although there are numerous grafted varieties none but the cider apple is used from which to procure seed. Occasionally small quantities of seeds from grafted varieties may become mixed with the crab seed but thisp^^ 37 -French makes the latter less valuable as such seeds ^rab, imported do not give satisfactory results for the pro- apple seedling. duction of seedlings. ''The apples from which we get our seed are used for cider-making purposes. Seed collectors go to the mills and to the fanns and wash the pomace that is left after the juice has been pressed out and the seed thus secured are dried in the open air. "Small quantities of apple seed come from Germany and 1 Howard, W. L. Plant propagation. Pub. by Univ. of Mo. 1914. 342 POMOLOGY even Russia and Austria, but France is known to be the one great exporter of tiiis seed. Apple seedlings are sold by dealers in Holland and the industry seems to have grown there during the last few years although the Dutch seedlings are much inferior to the French. "The grower generally receives his apple seed in January, places it in a veiy sheltered spot — often in a stable — thor- oughly mixed with damp river sand. The sand is kept moist and occasionallj'' the mixture of sand and seeds is stirred. When the seeds begin to swell — which will be in about four weeks — ^they are either placed in cold beds for transplanting or sown directly in the field. In three or four weeks they begin to come up. By soaking in lukewarm water before planting the seeds may be caused to germinate quicker, but I consider it to be better to follow the more natural plan and not force the seeds. "We never use ice. A few growers soak the seed for a period of two days at the most, but this practice is far from being common and is resorted to only when the season is advanced and it seems necessary to hurry the germination." Vermont crab stock is raised from seed collected at the cider mills of New England. In the past it was obtained largely from the pomace of seedling apples which abounded in the rough pastures, around stone walls, and even in the woods. There was also mixed with the "wild" apples, fruit of grafted varieties, often of poor grade. However, the fact that the seedling apples and uncared-for orchards of New England are rapidly passing out makes this stock of no great consequence in the trade. Virginia and Minnesota crabs are grown from seed col- lected at the cider mills in these states and in the past were used to a considerable extent, but at present the French crab stock has largely replaced them. For dwarfing, the Paradise and Doucin stocks have long PROPAGATION AND FRUIT-STOCKS 343 been employed. The usual understanding has been that the former produced a ''full dwarf" tree and the latter a "half dwarf"; however, there seems to be much confusion in re- gard to these terms. ''The original significant distinction betwixt the true Paradise or dwarfing apple stock and the true crab or free growing stock, had imperceptibly changed to a distinction in method of propagation, all those apple stocks which were raised vegetatively (from layers) being known as 'Paradise,' and those raised sexually (from seed) being known as 'Crab.' " ^ The work of Hatton shows that in a lot of seedlings from crab and "Paradise" stock, there will be in each both surface and deep-rooted plaiits. It also indicates that in lots of Paradise stock collected at various places in England and on the Continent, there were " 17 distinct types, easily distinguishable botanically, and varying in health and vigour of growth from the very dwarf French Paradise, which on our soil dies out with apple canker in a few years, through intermediate types such as the Doucin, moderate and sturdy in growth and precocious in cropping, to the veiy vigorous forms of Paradise, which have a vigour and robustness of growth previously supposed to belong only to ' crabs.' " Such is the situation in regard to apple stocks and much experimenting remains to be done before a uniform type is secured. 305. Pear stocks. — For the propagation of the pear the seedlings are usually obtained from France (Mayenne Prov- ince) where pear cider is made in quantity and hence the ])omace is available. Probably 80 per cent of the pear seed- lings used in this country are imported. The seedlings are grown in France as disease frequently ruins the crop when the seed is imported and an attempt made to grow them here. ^ Hatton, R. G. Results of researches on fruit tree stocks at East Mailing. Jour. Pomology, Vol. 2, No. 1. 1920. 344 POMOLOGY The pears collected for this purpose are the native Pyrus communis of Europe, fully 90 per cent being worked on this stock. Japanese sand pears, Pyrus serotina, are also em- ployed to some extent and are believed by some nurserymen to be superior to the French pear stock. In France this con- tention finds no support, as nurserymen there think the Japanese stock is quite inferior. This stock is secured di- rectly from Japan or the seedlings are first grown in France. Kieffer pear seed is also used to a limited extent in this country, the seed being obtained from canning factories in the eastern United States. It will be remembered that the Kieffer has as one of its parents the Japanese sand pear, the other being the Bartlett. 306. Quince stocks. — The fruit-bearing quinces (Cy~ donia ohlonga) are commonly grown on their own roots, i. e., from cuttings or by mound-layering. When worked on to another stock, the French Angers quince is most frequently used. This Angers stock is grown from cuttings, or by mound-layering or, more rarely, from the seed. In rare cases, the desired varieties of quince are root-grafted on the apple or pear and the original stock is cut away when the tree is moved to its permanent place in the orchard. 307. Peach stocks. — In the eastern United States, peaches are budded on stocks grown in this country. The pits are obtained from either seedling trees or standard varieties, but the former are usually preferred as more trees can be grown to a given measure of pits and the trees are supposed to be hardier. Pits produced the current season give a higher percentage of germination and are, therefore, selected. The plum (St. Julien and myrobalan) is sometimes used for the peach, es- pecially in the South and on wet or heavy land. Pits ob- tained in China are being investigated in regard to their desirability as stock bat have not yet come into use. PROPAGATION AND FRUIT-STOCKS 345 308. Plum stocks. — In Europe and to some extent in this country, the plum is propagated by suckers which arise freely from the roots of several of the species. To make use of such suckers, the tree must of course be on its own roots. Mound-layering and root-cuttings are also employed to some extent with the plum and in all of the above cases obtaining a stock is not a problem. When plums are worked on other stocks, the species must be considered. P. domestica is usually worked on seedlings of the same species, the stocks being largely imported. The mj^robalan (P. cerasifera) is chiefly used for plums because of its cheapness and because it makes a good union with all varieties; 80 per cent of this stock is imported. For colder regions, P. americana stocks are preferred. For light soils the peach is often taken as a plum stock. Mariamia (probably a hybrid form of myro- balan and some native plum of the Wild Goose type), St. Julien, apricot, and almond are also used as stock for the plum. For dwarfing, the myrobalan stock is employed as is also the mirabelle (also a form of P. cerasifera), the P. americana, P. Munsoniana, and P. angustifolia. 309. Cherry stocks. — Like the plum, the cherry will grow readily from root-cuttings, but it is usually budded on the seedling stock. The stock most commonly used is the Mazzard, a hardy and vigorous variety of the common sweet cherry (Prunus avium). This tree occurs along roadsides in the Central West and the seed is obtained in this country to some extent, but probably 90 per cent of the cheriy stock is imported. The sour cherries are frequently worked on the Mahaleb (Prunus Mahaleb) in this country as it makes a congenial stock and the seedlings are relatively cheap. The Morella cherries are worked on the Mahaleb stock, al- though Morella seedlings are sometimes used to a limited extent. P. pumila and P. Besseyi are listed as promising for dwarfing the cherry. 346 POMOLOGY 310. Quarantine measures. — For a period of years it had become evident that some measure should be taken to stop the introduction of foreign disease and insect pests which were annually finding their way to this country on nursery stock and other plants and plant products. As a result, a Plant Quarantine Act was passed by Congress on August 20, 1912, under authority of which the United States Depart- ment of Agriculture has, from time to time, issued various quarantine rulings which restricted or prohibited the im- portation of certain plants and plant products found to be infested with noxious diseases and insects. The ruling which particularly affected the nursery and florist business, and which was strongly protested by special interests, was known as Quarantine 37, and was issued November 18, 1918. This measure, together with later interpretations and rulings thereon, provides that: "Stocks, cuttings, cions, and buds of fruits for propaga- tion" and "seeds of fruit, . . . may be imported from coun- tries which maintain inspection, under permit upon com- pliance with these regulations, but, where a particular purpose is specified, for that purpose and no other. . . . Im- portations of nursery stock and other plants and seeds speci- fied in this regulation, from countries not maintaining in- spection, may be made under permit upon compliance with these regulations in limited quantities for experimental pur- poses only, but this limitation shall not apply to tree seeds." ^ From this ruling it will be seen that fruit-stocks for prop- agating purposes are still admitted into the United States, but possibly the time may come when all such stocks must be grown here. 311. Importations of stock. — While no restriction was placed on the entiy of fruit-stocks, the impression went out 1 U. S. Dept. Agr. Off. of Sec'y- Notice of Quarantine 37. Aug. 1, 1921. Item 2, Regulation 3. PROPAGATION AND FRUIT-STOCKS 347 that there was a faUing off of the importations. This was largely due to scarcity of stock in Europe, as a result of war conditions, together with a prohibitive price placed on this stock. The following figures are enlightening on the large amount of stock imported, following the establishment of quarantine measures by the United States Government: Table XCIII importation of fruit-stocks, july 1, 1919, to june 30, 1920 number of plants Counlru of origin Apple Plum Cherry Quince Pear Persir7i- mon Un- classified England France Holland .... Italy Japan 1,825,000 103,000 707.S00 2,808,720 758,800 500 1,107,900 500 24,200 459,900 300 Total 1,928,000 707,800 2,S()8,720 7.59.300 1,108,400 24,200 400,200 312. Fruit-trees on their own roots. — Since the fruit- tree above ground is of the variety tlesired, and a part or all of the root system is of seedling origin, it can be seen that considerable variation may be expected among the trees of any given variety. No two of the seedlings used as stock are alike (genetically) and they may vaiy markedly in vigor of growth, susceptibility to disease and insect pest, as well as in hardiness. It is well known to what extent a dwarfing stock may influence the cion part, but the smaller differences arc not readily observed in the standard trees. In Australia, New Zealand, South Africa, and to some extent in California, it is recognized that Northern Spy roots are more resistant to injuiy by woolly aphis (Schizoneura lanigera) than are the ordinary crab roots and hence are finding wide usage. Some varieties are more resistant to crown-gall {Bacterium tume- faciens) than are others, and this is doubtless true also of other diseases, pointing to an important field of endeavor 348 POMOLOGY for the future. In the prairie section of the northern United States and Canada, one of the serious problems in fruit- growing is the damage done to the roots of the trees by low temperature, and hence it is important to secure stock which is most resistant to cold. The first problem is the securing of own-rooted trees. Apples do not root readily from stem-cuttings and this proc- ess cannot be used commercially with the present Imowledge of the subject. Root-cuttings, however, can be planted with success, and the method is employed commercially to some extent. The most common process of securing own-rooted trees is by the "long cion — short root" method, also known as the "nurse-root" method. Advantage is taken of the fact that deeply planted root-grafted trees will often send out roots from the cion, and later (after two seasons) the trees are dug and the stock portion removed. There seems to be great variation in the ability of varieties to form roots. Shaw ^ made trials of over 150 different varieties and species to measure their rooting ability. There was a variation of rooting from to practically 100 per cent. A few of those exhibiting a high percentage of rooting are: Arkansas (77), Bailey Sweet (95), Sweet Bough (98), Fameuse (80), Opales- cent (89), Primate (92), and Westfield (83). Some exhibiting a low percentage of rooting may also be cited: Bethel (0), Black GiUiflower (6), Ensee (6), Ingram (2), Jeffris (3), Lady (3), Ortley (2), Paradise Winter Sweet (2), Red Canada (2), Tolman (3), and Yellow Belleflower (3). It cannot be stated at present with much definiteness just what factors influence certain varieties to root freely from cions and others to root very poorly. The following are suggested as entering into the problem: a correlation between hardness of wood and rooting ability, the softer the wood the higher 1 Shaw, J. K. Mass. Agr. Exp. Sta. Bull. 190. 1919. Plate VIII. — a, The twig terminals of these Baldwin apple trees were killed in winter of 1917-18. b, A winter-injured peach tree that was not cut back. PROPAGATION AND FRUIT-STOCKS 349 the proportion rooting from the cion; fertile, well-drained, sandy loam, soils offer the best conditions for securing a high percentage of rooting trees; there seems to be a relation between the varietal ability to produce roots from the cion and the thickness of the cambium layer during the dormant season. 313. Relation of cion and stock. — Little has been added to the literature on this subject during recent years other than that already mentioned. It has commonly been con- sidered that each part, i. e., stock and cion, maintained its own individuality with such exceptions as when dwarf trees were produced by working on slow-growing stock. It was argued that the trees and fruit in an orchard of Baldwin apples, for example, were always practically the same, allow- ing a reasonable amount of natural or continuous variation, and such other differences as could easily be traced to environ- ment factors. Additional exceptions were noted occasionally, such as the effect of a given variety on the root system as could be seen clearly when the trees were dug from the nursery; and a tendency of an individual tree to be more prolific, earlier or later in bearing than was usual for the variety. The question may now be raised as to whether the relation of stock and cion is not more important than previously sup- posed, and whether the whole problem of congenial stocks for fruit varieties may not need investigation. PROPAGATION OF FRUIT-TREES In the foregoing paragraphs it is apparent that most of the tree-fruits are grown on a foreign root system, i. e., the root parts are of seedling origin, largely for the reason that fruit-trees do not "come true " from seed. It is not the prov- ince of this text to deal in detail with the practice or manipu- lation of the processes used in general plant propagation, 350 POMOLOGY but a brief review of budding and grafting of fruit-trees is germane to the general treatment. Layerage. — Layerage consists in taking advantage of the habit of certain plants to throw out roots from decumbent shoots and runners. Portions of the stems or branches are artificially placed in contact with the ground, either by fasten- ing them on the surface or by covering with soil. Fruit-trees are not propagated in this way with the exception of a few by what is known as "mound-layering." On the other hand, strawberries, grapes, raspberries, gooseberries, and many ornamentals are propagated by different forms of layerage. 314. Mound-layerage is so termed because the soil is mounded about the base of shrubs or other plants which will throw out roots from the stems when in contact with the soil. The several rooted portions are then severed from the mother plant and thus begin an independent existence. The quince, gooseberry, and several forms of the Paradise apple arc propagated in this way. 315. Cuttings. — ^None of the commonly grown tree- fruits is propagated by means of stem-cuttings, with the exception of quinces which are handled to some extent in this way. A number of attempts have been made to prop- agate the apple by cuttings but none has as yet succeeded, although they may be rooted from the cion by the nurse-root method as previously described. The apple cuttings will frequently form a callus, but such activity does not favor root development. Plums (Marianna) are occasionally grown from cuttings as are also the quince and persimmon. The grape and currant are most commonly propagated by means of cuttings. Climate exerts considerable influence on the tendency of plants to develop from cuttings, the moist warm southern sections being much the more favorable. Root-cuttings are commonly used in propagating such fruits as have a natural tendency to sucker or send up shoots from PROPAGATION AND FRUIT-STOCKS 351 the roots. The blackberry, Japanese quince, and to some extent the peach, cherr^'^, apple, and pear may be propagated b}^ root-cuttings. 316. Grafting and budding. — The arts of grafting and budding are indispensable to the fruit industiy, since prac- tically all the tree-fruits are propagated in this way. Both processes involve the introduction of a portion of one plant into or onto the living or actively vegetative portion of another. In the former, a piece of the woody shoot bearing one or more buds is used, while in the latter one butl only is removed from the mother plant and introduced beneath the bark and in contact with the cambium of the "stock." Grafting is usually done in early spring just prior to or during the active period of growth, or in the case of root-grafting (bench-grafting) in the winter period. It is usually desirable for the cion material to be in a dormant condition when the union is made, although it is not necessarily fatal to have the buds of the cion l)eginiiing to open. 317. Tongue-graft or whip-graft. — For the propagation of nursery trees the tongue- or whip-graft is most commonly used, and the work is performed in the winter. The one- or two-year-old seedling trees are dug in the fall and stored where they can be kept cool, reasonably moist, and donnant. In Januaiy or Februaiy the grafting is done in-doors, which gives it the name bench-grafting. To produce what the nurseiyman calls "whole-root" trees, the entire seedling root is used, trimming off branching or superfluous parts, and the cion is inserted into the crown of the root. For "piece-root " grafts the seedling roots are divided into several pieces, about 3 or 4 inches long, thus securing several trees from one root. Both the cion and root are severed with a long oblique cut and an incision is made into the center of these surfaces so that the "tongue" of the cion will enter into the incision of the root, thus allowing the cambium areas to come into con- 352 POMOLOGY tact. It is not necessary but desirable that the cion and stock be of the same diameter. After the two portions are inserted, they are bomid tightly together with waxed string or raffia and the wounded areas covered with waxed tape to prevent the entrance of disease until the wounds are calloused. These grafts are then stored in sand or sawdust until early spring when they are planted in loose fer- tile soil. Such plants are allowed to remain in the nurseiy row for one or two years, when they are dug and are ready to put on the market. The apple and pear are often root- grafted, although "budded" trees of all kinds are becoming more popular. (Fig. 38.) 318. Budding is practiced entirely with the "stone or drupe" fruits in the East, and a large part of the pome-fruits are also propagated in this way at present. The fact that the budded tree has the advan- tage of the entire root system of the seed- ling, and that the likelihood of crown-gall is reduced by this method, has made it Fig. 38. — The popular with the trade, tongue- or whip- The essential . difference between grafting graft of apple. ^^^ budding, in producing nursery trees, is craft ) "'^ " " merely that one bud instead of several is introduced into the stock. The work is usually done in the latter part of summer while the bark is still loose and will "work readily." A "bud-stick" is cut from the variety desired and a shield-shaped portion of the bark is cut away from the shoot, including a bud in the center. The leaves are removed as soon as the " stick" is cut, leaving a small portion of the petiole to be used as a "handle" in placing the bud into the bark of the stock. A T-shaped PROPAGATION AND FRUIT-STOCKS 353 incision is made into the bark of the seedling tree an inch or two above the ground, on the north side of the tree so that the bud will be shielded from the sun. The amateur usually inserts two or three, one superimposed above the other, so that he may have several chances of securing a "catch." One only is retained when growth starts in the spring. Fig. 39. — Shield-budding. The bud tied; new growth of bud tied to stock (the following spring); stub completely removed. After inserting the bud, it is tied into place with raffia or cotton string, although the former is preferable. (Fig. 39.) After the bud has grown tight, which will be within two weeks if at all, the stricture is cut if it has not already loosened. The bud remains dormant until spring when it begins growth just as any other bud on the tree. The top of the seedling is 354 POMOLOGY then removed, usually a few inches above the bud so that the rapidly growing shoot may be loosely tied to the stub to prevent breakage. Later the stub is removed to within a half inch above the shoot. If the tree makes a growth of three to six feet the first year, it is usually dug in the fall and stored for spring delivery to the trade, but with the apple and pear they are frequently allowed to grow two years in the nursery row before being sold. The peach should always be dug at the end of the first year. 319. " June-budding " differs from the usual method in that "bud-sticks" are kept over winter, usually on ice, until seedling trees have made sufficient size by June or early July to allow of budding. The bud of the previous year is inserted into this rapidly growing stock, which soon starts into growth and the top is then removed. This gives a "one-year-old" tree the first season, thus saving a year's time. This practice is fol- lowed in the South, more especially with the peach. 320. Double-working of apple trees. — To Fig. 40 -Method g^^^j^ certain of the troubles affecting the of double-work- ing the apple. crowns and trunks of apple trees, such as collar-rot and winter-in juiy, a method of reworking nursery trees with varieties known to be subject to these troubles has come into rather com- mon use. Trees of hardy or resistant varieties are secured, among which may be mentioned Northern Spy, Tolman Sweet, or even Ben Davis for some purposes. Two- or three-year-old trees are preferred, if they are in good condition and have well-developed root systems. These are set in the orchard PROPAGATION AND FRUIT-STOCKS 355 in the usual way and allowed to grow a season in order to become well established. Before the next growing season begins, they are cut off about 20 to 24 inches from the ground line and grafted to the desired variety. If the cions are carefully gathered and labeled, there is the additional certainty of having the va- rieties true to name; in fact the double-working is sometimes done for this purpose. A single cion 6 to 8 inches in length is used, and in order to promote healing over of the stub with the least resultant weakness or deformity, the stock may be cut obliquely rather than square, with the cion inserted in a cleft at the top of the cut, as indicated by Fig. 40. Ordinaiy grafting-wax may be used to cover the wound but the work is facilitated by the use of waxed tape, which also gives better support to the cion until union takes place, and is more easily applied if the work must be done in cool weather. The nurseiy trees may be worked immediately after set- ting, but the chances of success seem to be greater if they are first allowed to become established in their permanent location. CHAPTER XV STORAGE OF FRUIT A great industry has been developed since the advent of the cold storage plant and it has become a large factor in handling the country's fruit crop. The details of its com- mercial importance and economic value will not be canvassed in this text, but rather the effect of storage on the fruit itself. 321. Definition. — Storage developments during the past quarter of a century represent a most valuable contribution of science in making perishable products available over a relatively long period of time. As used in this connection, storage usually refers to cool or cold storage of products and may be defined as the means by which perishable products are maintained at a temperature sufficiently low to arrest disease and the natural physiological and chemical processes of ul- timate maturity and decay, yet not sufficiently low to injure the tissue or quahty of the materials stored. 322. History^ of storage.^ — The idea of prolonging the season of fruits and other food products by the means of low temperatures is by no means modem. Meyer reports cold-storage methods applied to fruits in remote parts of China, wholly out of touch with civilization. He states that the Chinese have practiced cold storage for centuries." The earliest efforts along this line were to use the natural caves or artificial cellars where a fairly uniform temperature from 50° to 60° F. can be maintained at all seasons. Successful 1 We are indebted to "Practical Cold Storage" by Madison Cooper, Nickerson and Collins Co., 1914, for important parts of this account. - Stubenrauch, A. V. Storage and refrigeration of fruits and vege- tables. Standard Cyclo. Hort., Vol. VI, p. 3245. 366 STORAGE OF FRUIT 357 experimental refrigeration by mechanical means was ac- complished as early as the middle of the eighteenth century, but no successful conmiercial application of cold storage was evolved until after the invention of Lowe's carbonic acid machine in 1867. The present growth of the industiy, how- ever, is due to the invention of the ammonia compression machine by Carl Linde in 1875. The process was first ex- tensively applied to the preservation of meats, fish, and the like, but as early as 1881 the Mechanical Refrigerating Com- pany of Boston opened a cold-storage warehouse, which marks the beginning of mechanical refrigeration as applied to horticultural products. The use of natural ice for refrigerating purposes does not seem to have come into general use until comparatively modern times. The first large ice-house for the storage of natural ice was built in 1805. At first the ice was packed about the articles to be preserved, much as is done at present in shipping fish and oysters. Later a chest or box was used in which the ice was stored in one end and the products in the other, but such an arrangement lacked any means for securing a circulation of air. Later improvements in the design of storage-rooms called for the storage of the ice over- head with shafts allowing for a circulation of air, which added greatly to the success of this type of refrigeration. 323. Types of storage. — As can be inferred from the fore- going, there are two general types or systems of storage: (1) common, and (2) cold storage. The common, or non- refrigeration storage, refers to some system by which reason- ably low temperatures can be maintained, either by locating the rooms in a cellar, thus utilizing the low natural tempera- ture of the earth, or by the use of air currents to keep a room at the temperature of the out-door air. The cold storage has been evolved from the early efforts at refrigeration and involves the cooling of the storage-rooms 358 POMOLOGY by artificial agencies, either ice or mechanical means being used. 324. The function of storage. — It must be recognized that a fruit is a living organism and life processes continue until disintegration takes place. In common with many other organic products, the higher the temperature the more rapid is the disintegration and, therefore, the func- tion of storage is to delay the ripening process in a tempera- ture ^hat will not injure the fruit. It is also designed to retard the development of diseases with which the fruit may be affected, but it cannot entirely prevent their growth. Much depends on the condition of the fruit when it enters storage as to how long and how well it will keep. If the fruit is over-ripe, has been bruised, or is covered with rot spores, the low temperature may retard but cannot prevent its premature decay. ^ 325. Factors influencing the keeping quality of fruit. — The following factors have been outlined by Powell as af- fecting the keeping quality of fruit after it has been placed in cold storage: (1) the maturity of the fruit when picked; (2) the promptness with which it is placed in storage; (3) the temperature at which it is stored, as well as the uniform- ity of this temperature; (4) influence of a first wrapper; (5) the cultural conditions under which the fruit was pro- duced; and (6) the type of package in which it is stored. These factors will be treated separately. 326. Maturity of fruit. — In considering the keeping quality of fruit, it must of course be recognized that this is first of all a varietal characteristic (a unit character), just as much as color and size. Also the condition of the fruit when it enters storage will determine whether or not it can be kept for the maximum time for the variety. Numerous 1 Powell, G. Harold, and S. H. Fulton. The apple in cold storage. U. S. Dept. Agr. Bur. Plant Ind. Bull. 48. 1903. STORAGE OF FRUIT 359 tests have been made to determine at what stage of maturity a fruit will keep best in storage. It is well known that an under-ripe apple will wilt and shrivel and an over-ripe one will decay rather rapidly even when put in storage. It then remains to determine what is the best time for storing in order to secure the maximum keeping quality. This stage has been detennined as "hard ripe," i. e., when the apple has developed full size and good color for the variety. If the fruit is left on the trees until the highest color is developed, it will often be to the detriment of the keeping quality. The proper time for picking is usually associated with a browning of the seeds, but this is not always a reliable guide. An exception to this rule is noted when apples are grown on young rapidly growing trees. Such fruit is likely to be overgrown, and under such conditions the apples will usually keep better if picked before fully grown. In general, as will be seen later, light colored apples scald worse in storage than do well-colored ones. The following striking results were secured by the Department of Agriculture ^ which demon- strate the value of storing mature fruit only. The variety used in this test was the Rome Beauty, which by nature is a long keeper, but subject to scald if conditions are favorable for it. The immature pickings of fruit were made during the last two weeks of September and the mature pickings from October 2 to 20. 1 Ramsey, H. J., A. W. INIcKay, E. L. Markell, and H. S. Bird. U. S. Dept. Agr. Bull. 587. 1917. 360 POMOLOGY Table XCIV keeping quality of mature versus immature fruit: rome beauty ' four-year average. (after ramsey, markell, mckay and bird) Bad scald Decay At with- drawal 10 daijs later At with- drawal 10 days later First withdrawal, January 8-12 Mature 0.0 1.7 49.9 0.0 0.1 1 Immature 6 Second withdrawal, February 16-19 Mature 0.0 20.5 5.4 70.5 0.0 0.0 2 Immature Third withdrawal, March 31-April 2 1.0 48.9 10.4 81.5 0.0 0.2 1 6 9.8 Fourth withdrawal. May 4-11 Mature 3.5 58.9 17.8 81.6 0.1 0.4 2.7 18 327. Effect of over-maturity. — As mentioned before, it is very detrimental to the keeping quality of fruit to allow it to remain on the tree after it is ready to harvest, i. e., hard ripe, or to delay placing it in storage immediately after it is picked. 8ome conclusive experiments have been conducted 1 Percentage bad scald and decay at withdrawal from storage, and after a holding period of ten days under market conditions. Time in storage at first withdrawal, 3J^ months; second, middle of February; third, late March; and fourth. May. STORAGE OF FRUIT 361 by the United States Department of Agriculture which point to the necessity for storage before the fruit is over-mature if the best results are to be secured. The chief storage troubles from over-maturity are physiological and fungous decays. The following data are taken from work with the Esopus: Table XCV effect of over-maturity. esopus. • ^after ramsey, et al.) Decmj At unthdrawal 10 days later First withdrawal, January 12, 1914 First pick 0.0 2.3 1 3 2 3 Second withdrawal, February 19, 1914 9.1 1.3 Second pick 25.0 Third withdrawal, April 1, 1914 First pick 1.3 4.0 2.7 Second pick . . 2G.0 Fourth withdrawal, May 4, 1914 First pick 2.7 14.0 6.7 36.0 At the second withdrawal, February 19, which is some- what later than the usual commercial storage limit for this 1 Percentage physiological and fungous decay at withdrawal from storage, and after a ten-day holding period under market conditions. The first pick was made September 25, stored September 26, 1913. The second pick was October 10 and stored October 11, 1913. 362 POMOLOGY variety, the first picking was free from decay oi' other storage troubles, while the latter picking had developed 9.1 per cent decay. After being held outside for ten days, approximating the usual length of time from storage to consumption, the decay in the late picking increased to 25 per cent. The first picking developed only 1.3 per cent in the same period. The later inspections are well past the commercial limit for the variety, and the decay is correspondingly heavier, though still consistently less in the first picking. 328. Effect of delayed storage. — As has been seen, it is important to have fruit at the proper stage of maturity when picked, but it is also important that it be stored immediately or its keeping is impaired correspondingly. In the experi- ments here referred to, the fruit was picked at the height of the season for the variety and a portion stored in a ware- house in a temperature but little below that of the outside air. Other lots of the same fruit were immediately placed in cold storage. In studying the tabulated results, it should be added that the fruit immediately stored "was always brighter, less yellow, and usually firmer than the delayed." It will depend much on the season as to the extent of damage which results from delay in storage. Table XCVI IMMEDIATE VERSUS DELAYED STORAGE FOUR-YEAR AVERAGE. JONATHAN. (AFTER RAMSEY, ET AL.) Condition First icith- drawal, Jan. 9-12 Second with- drawal, Feb. 16-29 Third with- drawal. Mar. 27- April 2 Foxirth icith- drawal, May S-14 Imm. Dd. Imm. Del. Imm. Del. Imm. Del. Bad scald At withdrawal 10 days later 1.0 1.2 4.0 7.3 .3 1.2 0.1 8 4 6.7 90 n 8.5 14.7 6.8 12.2 21.5 35.8 13.1 17.5 17.9 27.0 7.8 12.0 33.8 46 4 Decay At withdrawal 10 days later 4.6 10.3 10 1 12 7 13.0 17 STORAGE OF FRUIT 363 329. The storage temperature. — The difficulty under many conditions is to secure a uniform temperature for the storing of fruits. This is an important phase of the problem, since fluctuating temperatures are harmful. The exact temperature which is best will depend somewhat on the fruit, the variety, the length of time the fruit is to be stored, and perhaps some other factors. In general, however, the minimum temperature given for a variety of fruit is to be preferred to a few degrees above, if the maximum keeping is to be secured. Powell's experiments indicate that a tem- perature of 31° or 32° F. is best for the apple since the rots, molds, and other diseases were retarded to a much greater extent than at 35° to 36° F. Cooper, however, states that a temperature of 30° F. is better than any degree above that, and 29° F. is practicable and advisable for long-period storing of the better keeping varieties. To store safely at 29° to 30° F. it is necessary that a forced circulation of air be employed. In cooling the fruit down to the final canying temperature, the refrigeration must not be applied too sud- denly. Table XCVII STORAGE TEMPERATURE FOR FRUITS. (aFTER COOPER) Apples Oranges Lemons Plums Pears Peaches Grapes Berries, fresh (few days only^ Currants " " " 30°-31° F. 32°-35° F. 38°-50° 32° 32°-33'' 32° 36° 40° 32° 330. Influence of a fruit wrapper. — If each individual fruit is wrapped in paper before placing in the package, its 364 POMOLOGY life will be extended beyond that of unwrapped fruits. This has been particularly tested with apples, since they have a long period of storage. The wrapper affects the keeping qualities in several different ways: it retards the ripening processes; it prevents the transfer of rot from one apple to another; it protects against bruising and the discoloration that maj^ result from improper packing or rough handling; it checks transpiration; and in general adds to its commer- cial value. (Powell.) A striking difference in the keeping quality of wrapped and unwrapped fruit is shown in the following table: Table XCVIII amount of decayed fruit, april 29, in bushel packages (after POWELL AND FULTON) Variety Unwrapped Per cent Baker Dickenson Mcintosh Mcintosh (second lot) Northern Spy Wagener Wealthy 4.3.0 15.0 32.0 52.0 63.0 60.0 Several different types of wrappers were used in these experiments — tissue, parchment, waxed or paraffin, and un- printed news — but no important difference was observed except with the parchment, on which mold developed freely at 36° F. but only slightly at 32° F. A double wrapper proved more efficient in retarding ripen- ing and transpiration than a single one. STORAGE OF FRUIT 365 Greene * found a considerable variation in the value of wrappers but states that they will extend the cold storage season from two weeks to several months, according to variety of fruit. He concludes, however, that they "are out of the question excepting where apples are packed in boxes or where packed for special purposes in barrels." Much the same results are recorded in a later report on this experiment.- 331. Influence of cultural conditions. — It is well known to those who grow, store, and sell fruit that any given variety will vary somewhat in its keeping quality, depending on where it is grown and on the particular season. Apple buyers become very discriminating after they are acquainted with fruit districts. Fruit raised on young trees, on low land, and on very light soils is likely to have a poorer keeping quality than fruit grown under the opposite conditions. However, it is difficult to determine the keeping quality of the product from any given orchard except by trial, for no definite rules can be laid down which will have wide ap- plication. 332. Type of package for storage. — The usual types of package for storage arc the standard apple barrel and the standard bushel box. Other packages are coming into use, such as the paper carton package of varying capacity, the basket and the Boston bushel box. The barrel is used for the great bulk of the apples grown in the eastern United States but it is not entirely satisfactory, for it requires a longer time for the fruit throughout this package to cool than is true with a smaller one. It is not convenient to handle and consider- able bruising occurs incident to proper packing. There is > Greene, L. Cold storage for Iowa grown apples. Iowa Agr. Exp. Sta. Bull. 144. 1913. 2 Whitehouse, W. E. Cold storage for Iowa apples. Iowa Agr. E.\p. Sta. Bull. 192. 1919. 366 POMOLOGY some difference of opinion in regard to an open and a closed package. The recent investigation on scald of apples shows that aeration of the fruit is important in preventing the trouble, which would argue for a somewhat open package. On the other hand, a slatted or otherwise open package often results in a shriveling of the fmit which is veiy serious with some varieties. 333. The shrinkage of fruit in storage. — As indicated before, the fruit in storage continues a life process which results in certain changes and losses through respiration. By far the greatest loss in weight, however, takes place through loss of moisture which amounts to about 10 per cent of the weight of fruit for a season. The diy-skinned and russet apples lose moisture much more rapidly than the oily-skinned ones. The Roxbury Russet, Spitzenburg, and Jonathan shrivel readily in storage unless the humidity is kept to nearly 85 per cent. 334. Apple-scald. — The development of scald is one of the serious problems to be dealt with in the storage of apples. Scald has been defined as a "superficial browning" of the skin which does not extend deep into the flesh but detracts from the appearance of the fruit and reduces its commercial value. A number of experiments have been conducted to deter- mine its cause and how it might be prevented, and as a result the following general conclusions have been drawn: 1. The cause of scald is apparently an abnormal respiratory condition. The disease can be readily produced artificially by storing under conditions of restricted aeration, and no scald can be produced on apples that are well aerated. The small amount of scald that usually develops in cellar and air-cooled storage-houses appears to be explained by the important role that aeration plays in the development of the disease. STORAGE OF FRUIT 367 2. Humidity apparently has no effect on the development of the disease, according to Brooks, Cooley, and Fisher, '^ while Whitehouse found that the drier the storage-rooms the less the scald. 3. All experiments showed that scald will dovc^lop more rapidly as the temperature increases. Powell and Fulton found that scald appeared to a much greater extent if apples were stored at 36° F. than at 32° F., although both lots were stored immediately after picking. Brooks and Cooley found a consistent difference in favor of the lower tempera- ture in the prevention of scald. Scald developed rapidly at 50° F. during the third month of storage, whereas it was four months before it appeared at 41° F., and five months at 32°. 4. Apple-scald has been more serious on green than on ripe fruit, but it develops more rapidly on the latter. All investigators have laid emphasis on this point as the most important so far as the fruit itself is concerned. " Immature fruit scalds readily in storage. Whatever the variety of apijles under consideration, it is in the best condition for cokl storage when it has reached prime maturity for picking, is well colored, hard-ripe, and neither immature nor over- mature." 5. Wrapping apples in paper delays the appearance of scald during storage. 335. Pre-cooling.'- — It has been determined that fruit will cany better and keep longer if it is cooled immediately after it is picked from the tree and before going into cold storage or refrigerated cars. This is particularly true of citrus fruits and such soft kinds as peaches. Experiments by the United States Department of Agri- culture have shown that it requires wann fniit from three to 1 Jour. Agr. Res. 18: 4. 1919. 2 Practical Cold Storage. Madison Cooper. Second Ed. 368 POMOLOGY four days to reach a temperature of 45° F. when it is placed in a refrigerator car, and that the fruit was not uniformily cooled, the top of the car being from 10° to 25° higher in temperature than the floor and near the ice bunkers. Such fruit arrives at its destination in poor condition and hence entails heavy losses to the shippers. The greater part of these losses can be saved by pre-cooling, providing the fruit is in good condition and well handled. 336. Methods of pre-cooling. — Two general methods are used to effect the pre-cooling of the fruit: (1) the car pre- cooling, and (2) the warehouse pre-cooling. The first con- sists in loading the fruit in a car ready for shipment and then attaching a cold air duct or chute to the trap doors into which ice is loaded into the bunkers or even to the doors of the car. A fan forces the circulation of the air through the car and the warmer air back into a room where it is again cooled and continued through the system of circula- tion. This method seems to be favored by transportation companies but it is objected to by the warehouse men be- cause the fruit is lowered in temperature so quickly that injury to its quality results. The temperature has been lowered from 80° or 90° F. — the outside temperature — to 35° or 40° F. in one to three hours. Another objection is that space must be left between packages and, therefore, by the warehouse method from 25 to 50 per cent more fruit can be loaded in a car. Neither is the car of fruit cooled so uniformily as by the other method. In the warehouse method, the boxes of fruit are placed in warehouse rooms similar to those of a cold storage plant and the temperature is lowered to the point desired for shipping the fruit. The boxes are frequently handled on endless belts. This system seems to be gaining in favor, al- though the whole practice of pre-cooling is relatively new and is not fully established. STORAGE OF FRUIT 369 It has been suggested that if refrigerator cars were so built as to be as well insulated as a modern cold storage room, it would not be necessary to ice cars in a ten-day haul in summer weather, if they were pre-cooled. nOPERTY WMART Af. C. State College INDEX Acid phosphate, 190 Adaptation of fruit to soil types, 140 of plants to soil, 135 of species, 237 Agave americana, 261 Alderman, W. H., 294, 307 mentioned, 212 quoted, 60, 79, 82 Alfalfa in the orchard, 208 Alkaline soils, 137 Allen, F. W., quoted, 270 Alternate-row cultivation, 144 American plums, 33 Analysis of apple tree, 92 of plant as a guide to fertiliza- tion, 183 of soil as a guide to fertiliza- tion, 184 Anomophilous flowers, 291 Anthony, R. D., 335 Apple oil, 7 scab, 118 scald, 366 seed for stock, 339 stocks, 340, 341 Apples at high elevations, 9 at low elevations, 9 quality in, 7 Application of fertilizers, 215 Arnold, Charles, 326 Arsenical poisoning of trees, 259 Artificial pollination, 295 Ash of apple leaves, 3 of fruits, 4 Auchter, E. C, quoted, 66, 79, 82, 108, 112 Averting injury from frosts, 239 Bacillus amylovorus, 258, 337 Bactenum liimefaciens, 347 Bailey, L. H., 304, 308, 311, 313 mentioned, 149 Ball, E. D., mentioned, 259 Ballou, F. H., mentioned, 189 Bartlett pear in California, 309 self-sterile, 309 Batchelor, L. D., mentioned, 100 Beach, S. A., 283, 301 mentioned, 118 quoted, 112, 270, 324 Bedford, Duke of, mentioned, 166 quoted, 74, 99 Bending branches to induce fruit- fulness, 67 Berry, 49 Biennial bearing, Tl Bigelow, W. D., et al, 12 referred to, 115 Biociimatic law of latitude, longi- tude and altitude, 234 Bioletti, F. T., quoted, 123 Bizzell, J. A., mentioned, 162 Black, C. A., 42 Black-heart, 259 Blooming dates, 248 period, duration of, 249 season, 247 Bonasa wnhellus, 26 Bone-meal, 191 Boston bushel box, 365 Bouyoucos, G. J., mentioned, 157, 270, 271 Breaking limbs prevented by thinning, 110 Brooks, Charles, 367 Brooks, W. P., mentioned, 194 371 372 INDEX Brown, G. G., mentioned, 207 Browne, C. A., Jr., 12 Budding, 351, 352 Bud injury, 254 scales as a protection, 268 selection, 317 sports, 320 Buds, advantage of position, 19 adventitious-, 23 axillary-, 23 branch-, 21 classification of, 21 collateral, 24 defined, 20 flower-, 21 fruit-, 21 gross structure of, 20 latent-, 23 lateral-, 23 leaf-, 21 mixed-, 22 simple-, 22 terminal-, 23 wood-, 21 Burbank, Luther, 316, 330 Camerarius, J., 282 Canada, fruit-breeding in, 325 Canyons, effect on frost injury, 273 Carbohydrates, 54 relation to flowering of plants, 56 Careless planting, 95 Carpellary system, 47 Castanea dentata, 136 Central leader tree, 77 Chance seedlings, 324 Chandler, W. H., 81 mentioned 92, 93, 258, 260, 264, 265 Changes in composition of peach during growth and ripening, 14 Chemical changes in the growing apple, 10 nature of fruit soils, 134 Cherry stocks, 340, 345 Chesnut, V. K., quoted, 6 Chimeras, 333 Cion, 339 Citrus, bud-variation of, 322 fruit-trees, 152 Clay soU, 126 Clean tillage, 143, 148 Chmate defined, 218 effect on fruitfulness, 69 effect on development of fruit, 243 effect on the floral structure, 242 of United States, 228 Chmatic provinces of United States, 229 Clonal-selection, 316 Close, C. P., mentioned, 120 Cluster base, 44 Coates, Leonard, 321 Coit, J. E., 332 Colby, G. E., 4, 5, 9 Cold storage, 357 Collar-rot, 258 Color of fruit, 211 improved by thinning, 109 Colver, C. W., 9 Common salt as a fertilizer, 191 storage, 357 Comparative morphology of fruits, 48 Composition of apple fruit, 4 of apple leaves, 2 of apples at high elevations, 9 of apples at low elevation, 9 of apples in common storage, 12 of fruits on irrigated land, 9 of wood and leaves of apple, 1 of wood and leaves of peach, 1 of wood and leaves of pear, 1 Continental chmates, 225 Cooley, J. S., 367 Cooper, Madison, 363 INDEX 373 Correlation between wood struc- ture and hardiness, 269 of trunk and twig measure- ments, 168 Cost of thinning, 119 Cover-crops, 149 in California, 151 Crandall, C. S., quoted, 288 Criticisms of fertilizer experi- ments, 179 Cross-pollination, 291 effect on fruits, 292 Crotch injury, 257 Cultivation and winter injur}', 274 Cultural practices, 61 Cuttings, 350 Cydonia oblonga, 43, 344 Danthonia spicata, 194 Darwin, Charles, 283, 291, 292, 299 De Candolle, A., mentioned, 247 Dehorning apple trees, 98 Delayed open center tree, 77 storage, effect of, 362 Delaying blossoming, 239 Depression, 265 Depth of freezing in an orchard, 160 Detjen, L. R., 335 Devitalizing of trees due to root- pruning, 64 Dichogamj', 292 Dickens, A., mentioned, 99 Differentiation of apple-buds, 35 carpels, 39 cherry-buds, 41 flower-buds, 34 peach-buds, 41 petals, 38 plum-buds, 41 sepals, 37 stamens, 38 Diospyros Kaki, 295 Disbudding, 26 Disease reduced by thinning, 110 -resistance dominant, 338 -resistant fruits, 337 Distance to thin, 118 Dorsey, M. J., 221 224 mentioned 238, 286, 320, 304, 303, 302 Double-working of trees, 354 Doucin stock, 342 Downing, A. J., quoted 112, Dniinago, 138 Drinkard, A. W., Jr., 64, 65, 67 mentioned, 100 Drupe, 48 Dutch seedlmg apples, 342 Dwarfing fruit-trees, 68 of trees, explanation of, 94 the cherry, 345 DjTiamite, its use in orchards, 177 Eastern climatic province, 230 Edlefsen, N. E., quoted, 239 Effect of cultural methods on yield of fruit, 173, 174 of leaves on parts surrounding, 60 of location on quality, 9 ■ of moisture on the soil, 153 of preceeding crop on winter injury, 269 of pruning on early bearing, 81 of pruning on size and develop- ment of tree, 78 of seed-beanng on fruit, 294 of sod on an orchard, 171 of soil covering on temperature, 157, 160 of thinning on total crop, 113 of tillage on nitrification, 162 of tillage on tree growth, 166, 168, 171 Elevations suitable for fruit-grow- ing, 228 Emb\TO abortion, 290 Emerson, Albert, quoted 329 374 INDEX Emerson, R. A., mentioned 274 Entomophilous, 292 Essential oils, 6 Eutectic point, 264, 265 Explosives for tillage purposes, 177 Exposure for fruit-trees, 240 Fall plowing of orchards, 177 Farley, A. J., quoted, 178 Fertility removed by fruit-trees, 180 Fertilization, process of, 289 Fertilizer experiments, 193, 194, 198, 200, 202, 203, 205, 206, 207, 208, 209 Fertilizing the peach, 212 Fire danger in orchards, 147 Fisher, D. F., 367 Fletcher, S. W., quoted, 105, 293, 306, 308 Flowering-branch, 43 Fortuitous nature of fruits, 311 Freezing point of sap, 93 French stock defined, 341 Frost-cracks, 259 Frost injury, character of, 223 to fruits, 238 "Frozen to death," 261 Frozen trees, treatment of, 278 Fruiting of the apple, 26 apricot, 33 cherry, 31 grape, 33 peach, 29 pear, 29 plum, 32 quince, 33 Fruiting system of tree, 78 Fruit juices, sugar-content of, 6 production exhaustive, 104 seeds for stock, handling of, 339 soils of the Ozark region, 128 soils of western New York, 129 -spurs, 24; vitality of, 88 -stocks, 339 Fruit, wrapper, influence of, 363 Fulton, S. H., 367 Garcia, F., 299 mentioned, 121, 242 Gardner, V. R., 80, 85, 87, 299 quoted, 68 Geographical distribution of fruits 243 Gideon, Peter, 328 Gladwin, F. E., quoted, 281 Goff, E. S., 34, 42, 301 quoted, 286 Goodspeed, W. E., quoted, 100 Gore, H. C. referred, to 115 Gould, H. P., quoted, 112, 116 Graft hybrids, 333 Grafting, 351 Grape breeding, 333 hardiness of, 281 Grass mulch, 143, 145 Green, W. J., quoted, 104, 105 Greene, L. 365 Grossenbacher, J. G., mentioned, 258, 259 Guides to horticultural practices, 233 Gulf chmatic province, 231 Hail, 224 Hall, A. D., mentioned, 123 Halsted, B. D., quoted, 270 Hann, Juhus, 226, 227 Hansen, N. E., 325, 329, 330, 338 hybrids, 329 Hardiness of different tissues, 262 Hardwood-ashes, 191, 203 Hardy fruits, 279 securing, 278 Headden, W. P., mentioned, 259 Heading-back versus thinning-out, 84 Heat units, 244 Hedrick, U. P., 68 INDEX 375 Hcdrick, mentioned 166, 202, 221, 223, 251, 271 quoted, 33, 248, 272, 324, 330, 334, 335 Heinicke, A. J., 295 Hendrickson, A. H., 304, 305 Henry, A. J., mentioned, 228 Herrick, R. S., mentioned, 119 Heterosis, 300 Heterozygous nature of fruits, 331 Hilgard, E. W., quoted 136, 138, 153 History of thinning, 102 Hitchings, Grant, mentioned, 145 Hitt, Thomas, quoted, 82, 102 Hoffmann, G. F., mentioned, 247 Homogamy, 292 Honey bee as a pollinator, 291, 301, 305 Hopkins, A. D., mentioned, 252 Hottest six weeks, 245 Howard, W. L., 341 mentioned 263 Howe, G. H., 65 How freezing kills, 261 to thin, 118 Humus, 126 Husmann, George C, 67 quoted, 123 Ideal form of tree, 78 Immediate effect of nitrogen fer- tilizers, 189, 207 Importation of stock, 346 Individuality, 317 of trees, 69 Inflorescence, 42 Inheritance in the apple, 330 Insects and pollination, 291 injury reduced by thinning, 110 Inter-cropping, 143 Inter-fertility of plums, 305 Inter-sterility of almond, 301 of cherry, 300 Inversions of temperature, 227 Iron salts, 211 Isochrone defined, 235 Isophane defined, 235 Japanese plums, 32 Jones, C. H., 60 Jones, J. S., 9 Jordan, W. H., quoted, 184 Jost, L., quoted 51, 52, 53, 54 June-budtling, 354 drop, 117 Keeping quality, influence of cultural conditions on, 365 of fruit, factors influencing, 358 Kerkogamy, 292 Klebs, G., nu'iitioned, 262 Knight, L. 1., 307 Knight, Thomas Andrew, 282, 311,313, 321 Kraus, E., 57, 62, 299, 307 mentioned 88 quoted 38, 39, 40, 41 Kraybill, H. R., 57, 62, 88 Kulisch, 8., 12 Layerage, 350 Leaf area of apple trees, 170 -scars, 24 Length of growing season, 244 Lewis C. I., 294, 307 mentioned 100, 190, 207, 214 Light, its effect on fruit-bud formation, 70 Lime for stone-fruits, 214 its application to orchard lands, 137 its function in the soil, 135 Limestone soils, 135 Line-selection, 316 Loughbridge, R. H., quoted, 138 Lovett, J. T., 321 Lyon, T. L., mentioned, 162, quoted 165 376 INDEX Macoun, W. T. mentioned 238, 255, 263, 269, 322 quoted 327 Magness, J. R., 16, 60 quoted 17, 18 Malus communis, 341 mains, 288 Manures for the orchard, 192, 194, 202 Marine climates, 225 Mass-selection, 316 Maturity of fruit, 358 of tissues, 263 Mazzard cherry, 345 Mechanical analysis of fruit sods, 129 Merchandizing apples removed by thinning, 177 Michigan fruit-belt, 241 Minnesota crab stock, 342 Modified leader tree, 77 Moisture, 54 Molisch, H., 265 Mound-layerage, 350 Mountain climates, 226 Miiller-Thurgau, H., 265 Myer, F. N., 356 Necessity of fertilizing orchards, 184 Nectarines as bud-sports, 321 Nitrate of soda, 188 Nitrates in orchard soils, 161, 162, 164 retarded under sod, 164 Nitrification, 150 Nitrogen-complexes, 54 Norton, J. B. S., mentioned, 251 Nut, 49 Objects of thinning, 105 OecaiUhus, sp., 225 Open-headed tree, 77 Optima temperatures for plants, 219 Orchard site, 124 soils, 132 Organic matter in apple leaves, 3 of orchard soils, 139 Organic versus inorganic fertili- zers, 187 Origm of apple varieties, 324 of cherry varieties, 324 of peach varieties, 325 Over-maturity, effect of, 360 Own-rooted trees, 347 Pacific climatic province, 233 Paddock, W., quoted, 228 Paradise stock, 342 Parthenocarpy defined, 298 Patten, C. G., 329 Peach, changes in composition, 14 stocks, 340, 344 Pears, ripening process in, 16 stocks, 337, 340, 343 varieties inter-fertile, 308 Pedicel, 44 Pedigreed nursery stock, 332 Peduncle, 44 Periodic idea, 52 Pfundt, M., 288 Phenology defined, 218 Phosphorous, 190, 198, 208 Ph3'lloxera-free grapes, 338 Physiological constant, 246 Pickering, Spencer, U. 99 mentioned, 166 quoted, 74, 202 Piece-root trees, 351 Pistils injured by cold, 289 Plains climatic province, 232 Plant introduction, 323 Quarantine Act, 346 Plants threatened by death, 69 Plateau climatic province, 232 Plum stocks, 340, 345 Pollen development, 284 germination, 285 longevity, 287 INDEX 377 Pollen, tube-growth, 286, 290 viability, 287 Pollination investigations, 282 Pome, 48 Potash, 191, 199, 208,211 Poultry in the orchard, 62 Powell, G. H., 321 quoted, 122, 123, 358, 363, 364, 367 Power, F. R., quoted, 6 Precautions relative to mulched trees, 147 Pre-cooling, 367 methods of, 368 Price W. A., mentioned, 93 Production of nuilch material, 147 Protection of trees in winter, 276 Proteranflrous, 292 Proterogynous, 292 Pruning, 63 and winter injury, 275 definition, 75 frozen trees, 94 mature trees, 97 objects of, 75 relation to nutrition, 88 root-, 63 summer-, 63 tree at planting time, 95 young trees, 96 Prunus americaiia, 304, 305, 340, 345 anguslifolia, 345 avium, 340, 345 Besscyi, 329, 345 cerasifera, 340, 345 Cerasus, 301 domestica, 32, 340, 345 horlulana, 42 Mahaleb, 340, 345 Munsoniana, 329, 345 pennsylvanica, 340 pumiln, 345 salicina, 32, 304, 329 serotina, 43 Prunus, virginiana, 44 Purpose of tillage, 173 Pyramidal formed tree, 77, 78 Pijrus baccata, 327, 328 hdulcpfolia, 338 Calleryana, 338 communis, 42, 338, 344 Malus, 42, 288, 327, 328, 341 ovoidea, 337 Pashia, (variolosa) 337 prunifolia, 327 serotina, 344 sinensis, 337, 338 Quality in apples, 7 of fruit improved by thinning, 109 Quarantine against stocks, 346 Quince stocks, 340, 344 Rainfall 221, 231, 233 Ralston, G. S., mentioned, 176 Rapid fall of temperature, 268 Rate of freezing, 267 Receptive condition of stigma, 289 Regular bearing, 1 1 1 effect of fertilizers on, 215 Reimer, F. C, 337 quoted, 189 Relation between blooming and ripening, 251 of air to soil temperature, 138 of cion and stock, 349 of leaf area to flowering, 59 of stock and cion, 339 Relative fertility needs of fruit- trees and farm crops, 183 Renovation pruning, 98 Reserve food, 53 Response of young trees to prun- ing, 86 Rest period, 240, 262 Ringing, 64 explanation of effects of, 65 378 INDEX Ripening period of fruits, 251 process in pears, 16 Roberts, R. H., 72 Rogers, E. S., 336 Rogers' hybrids, 336 Root-killing, 260 Russell, E. J. mentioned, 132 Russian fruits, 323, 326 Sachs, Julius Von, 52, 53 Sand for orchard soils, 126 Sandsten, E. P., quoted, 286, 288 Sap concentration, 265 Saunders, William, 326, 327 Scale axis, 43 Schizoneura lanigera, 347 Selection, methods of, 314 Self-fertility, defined, 297 Self-pollination, 292 Self-steriHty, defined, 297 in grapes, inheritance of, 334 of almond, 301 of apple, 307 of grape, 301 of peach, 306 of pear, 308 of plum, 304 of quince, 307 Sex in the grape, inheritance of, 334 Sexual relation of plants, 282, 292 Shamel, A. D., 320, 322 Shape or form of the tree, 76 Sharp, Francis Peabody, 326 Shaw, J. K., 7, 348 quoted, 8, 243 Shutt, F. T., 3 Size of fruit, 215 for thinning, 115 increased by thinning, 106 Sod culture, 143, 144 mulch, 145 Soil classification, 125 color, 134 defined. 125 Soil, for apple, 133 for apple varieties, 140, 141 for cherry, 133 for peach, 130, 133, for peach varieties, 141 for pear, 131, 133 for plum, 133 for Rhode Island Greening apple, 140 type and depth of freezing, 270 type and hardiness, 270 Sorauer, P., 53 Sour soils, 136 Sphceropsis jnalorurn, 97, 257 Sprengel, C. C, 282 Spring frosts, 222 Sterility, causes of, 299 not constant, 299 physiological causes of, 300 Stewart, J. P., 322 mentioned, 181 quoted, 175, 198 Stigmatic surface, 285 Stocks for grapes, 338 Stony soils for orchards, 133 Storage, defined, 356 function of, 358 history of, 356 shrinkage of fruit in, 366 temperature, 363 type of package for, 365 Stripping trees, 67 Structure of apple leaves, 170 Subsoil, 127 Sugar-content of ripe fruit juices, 6 Sugars in fruits, 5 Sulfate of ammonia, 188 Summer pruning, 99 Sun-scald, 260, 268 Sunshine, 224 Temperature, 219, 230 mean summer, 244 of bare and tilled soil, 157 INDEX 379 Temperatures injurious to pollen, 288 which injure setting of fruits, 238 Tender fruits, 279 Thatcher, R. W., 12 Theory of Knight, 314 of pruning, 90 of thinning, 103 of Van Mons, 312, 316 Thinning, definition, 102 fruit, 68 the grape, 123 the peach, 120 the pear, 122 the plum, 121 Thompson, F., 6 Thompson, R. C, 2 quoted, 182 Tibicen septendecim, 225 Tillage and cover-crops, 143, 149 of peach orchards, 176 systems, 142 Time to apply fertilizers, 189 to prune, 94 Tongue-graft, 351 Topography of land, 273 Top-pruning, 89 Toxic theory, 165, 171, 172 Tufts, W. P., 80, 301, 309 Two-story tree, 77, 78 Type of tree, 76 Under-vegetative trees, 62 Unequal cut, 83 Unfruitfulness, causes of, 283 Unfruitful trees, 62 Valleau, W. D., 335 Valley climates, 226 Value of fertilizers in tilletl and non-tilled orchards, of nitrogen for the orchard, 187 Van Mons, Jean Baptiste, 311 Van Slyke, L. L., mentioned, 182 Variation in hardiness, 279 Vascular anatomy, 44 Vase-shaped tree, 77 Vegetative and reproductive pro- cesses, 50 axis, 44 Vergon, F. P., mentioned, 145 Vermont crab stock, 342 Vigor of trees maintained by thinning, 110 Vincent, C. C, 294, 299, 307 mentioned, 101 Virginia crab stock, 342 Vitis Lahrusca, 33, 333 rotundijolia, 335 mnifera, 123, 334, 338 Waite, M. S., 283, 291, 294, 307, 308 Walker, E., quoted. 111 Warden, John A., mentioned, 95 Water-sprouts, 59, 98 Watrous, C. L., 329 Waugh, F. A., 283, 289, 304, 307 Weather, its relation to fruit crops, 219 Webber, H. J., quoted, 317 Wellington, R., quoted, 324, 330 West, Frank L., quoted, 239 When to thin, 114 Whip-graft, 351 Whipple, O. B., mentioned, 255 quoted, 228 Whitehouse, W. E., 367 Whitewashing trees, 276 Whitten, J. C, mentioned, 238, 239, 262, 263, 276 quoted, 321 Whittier, A. C, 6 Whole-root trees, 351 Wicks, W. H., mentioned, 293 Wickson, E. J., mentioned, 119 Wilder, H. J., mentioned, 140 Windbreaks. 224 380 INDEX Winds, 223, 231 and freezing, 273 Winslow, R. M., mentioned, 245 Winter injury. 111 and bodies of water, 272 due to heavy cropping, 269 Winter injury to woody parts, 256 Woburn Fruit Farm, 95 244, Woodbury, C. G., mentioned, 162 quoted, 153, 167 Yellow Newtown apple, require- ments for, 245