= = : 4 S = - > 4 . ¢ = : 4 = P- { — 7 4 =o 2 —-4 pow ae -_ oo . “= > « ~< cad q r 2. — >» “= - a = hw = = “5 - —- - ——— > : — _ ee ~~ ae =— —= - - _=- - ~ - = = x = 7 vs — a ae — 7 . ~—— aS a = _— _ = i bi c i, = a ~4 25 \ ya : 5 y — : a ml :- - — - . = —— a -- > ~ : . ; : —— — : ait —_—_-—_——- a = — a — -# ~ = = - ae ~ . <- - ~ - -- = “ i. = . s =o aa “ . » ws ’ ris, 4 a —— ta 2 ~ % - < . a =~ 4 = . - = : < — ae cr —— —_ ia ke ~ = = - : ——= : The Rural Science Series EpItep sy L. H. BAILEY PLANT-BREEDING The Wural Science Series Tue Sor. Hing. Tur SprayYING OF Pruants. Lodeman. MILK AND ITs Propucts. Wing. Enlarged and Revised. Tue FertTILITy OF THE LAND. Roberts. Tue PrincreLes OF Fruit-crowinc. Bailey. 20th Edition, Revised. Busn-Fruits. Card. FerTILIzZERS. Voorhees. THe PRINCIPLES OF AGRICULTURE. Bailey. 15th Edition, Revised. IRRIGATION AND DRAINAGE. Sing. Tue FarmstHEAp. Roberts. Ruravt WeattTH AND WELFARE. Fairchild. THE PRINCIPLES OF VEGETABLE-GARDENING. Bailey. Farm Pouttry. Watson. Enlarged and Revised. Tue Freepinc oF ANIMALS. Jordan. THe FarMer’s Bustness Hanpsook. Roberts. Tue Diseases OF ANIMALS. Mayo. Tue Horse. Loberts. How to CHoosE A Farm. Hunt. ForaGeE Crops. Voorhees. BACTERIA IN RELATION TO CountTRY LiFe. Lipman. Tue Nursery-Book. Bailey. PLANT-BREEDING. Bailey and Gilbert. Revised. Tue Forcine-pook. Bailey. THe Prunine-Book. bailey. FRUIT-GROWING IN ARID ReGions. Paddock and Whipple. Rurat HyGiEne. Ogden. Dry-FARMING. Widésoe. Law FOR THE AMERICAN FARMER. (Green. Farm Boys anp Girits. McKeever. Tue TRAINING AND BREAKING OF Horses. Harper. SHEEP-FARMING IN NortH AMERICA. Craig. CoOPERATION IN AGRICULTURE. Powell. Tue Farm Woop.ot. Cheyney and Wentling. HovusenHoip Insects. Herrick. PLANT-BREEDING | BY; 3 AILEY | abd be NEW EDITION REVISED BY ARTHUR W.GILBERT, Pu.D. PROFESSOR OF PLANT-BREEDING IN THE NEW YORK STATE COLLEGE OF AGRICULTURE AT CORNELL UNIVERSITY New Work THE MACMILLAN COMPANY 1915 All rights reserved CopyrRiaHtT, 1895, 1906, By L. H. BAILEY. Set up and electrotyped. Published December, 1895. Reprinted April, 1896; August, October, 1897; March, 1902; March, 1904. Fourth edition, with additions, April, 1906; April, 1907; July, 1908; August, 1910; February, 1912; October, 1913. New ReEvIsED EpITION, ENTIRELY RESET. CopyrigHtT, 1915, By THE MACMILLAN COMPANY. Set up and electrotyped. Published February, 1915. Norwood ¥ress J. §. Cushing Co. — Berwick & Smith Co. Norwood, Mass., U.S.A. K2¢ FEB 11.1915 ©cia393605 FA.49 } ‘ HISTORY Tuis book had its beginning in a lecture that I gave twenty-three years ago (December 1, 1891) before the Mas- sachusetts State Board of Agriculture, in Boston, on “ Cross- Breeding and Hybridizing” ; and this lecture, in turn, was the outgrowth of one given in 1885 and soon afterwards published. Under the same title, but with a bibliography added, the Boston lecture was published as a pamphlet in 1892, and placed on sale, by the Rural Publishing Company of New York, as one of the Rural Library Series. It com- prised forty-four pages, and sold for 40 cents. In the sum- mer of 1895, I gave two addresses on variation and the origination of domestic varieties of plants under the auspices of the American Society for the Extension of University Teaching at the University of Pennsylvania. In the mean- time, I had been teaching the subject to my classes in horticulture in Cornell University. In the latter part of 1895, I put together these materials in book form, and hay- ing no short descriptive title I used the word or compound “ Plant-Breeding.” Of this work, the Massachusetts leec- ture comprised Chapter II, and the Philadelphia lectures Chapters I and III. The bibliography was not included. Chapter IV comprised “ Borrowed opinions” from the writings of Verlot, Carriere, and Focke. Carriére’s work on “Production et Fixation des Variétes dans les Vege- taux” had been translated, with a view to publication, as early as 1886. The book, “ Plant-Breeding,” was translated V vl History into the French by J. M. and E. Harraca, and published in Paris in 1901 as “ La Production des Plantes.” Having been thrice reprinted, the second edition was issued in 1902, although, through an inadvertence, it was not so marked on the title-page. Few text-changes were made, but the bibliography was included. Early in 1904 the third edition was issued. The bibli- ography was extended, and some changes were made in the text; but the principal departure was a new Chapter IV, from which the old “ Borrowed opinions” were omitted, and “Recent opinions” were substituted, comprising a dis- cussion of the work of de Vries, Mendel, and others, and a statement of the current tendencies of American plant- breeding practice. “In the eight years since this book was sent to the printer,” it was stated in the preface to the third edition, “there have been great changes in our attitude toward most of the fundamental questions that are dis- cussed in its pages. In fact, these years may be said to have marked a transition between two habits of thought in respect to the means of the evolution of plants, — from the points of view held by Darwin and the older writers to those arising from definite experimental studies in species and varieties. We have not given up the old nor wholly accepted the new, but it is certain that our outlook is shift-— ing. So far as practical plant-breeding is involved, the changing attitude is concerned chiefly with discussions of the nature of varieties and the nature of hybridization.” It was declared that ‘the time cannot be far distant when the subject of plant-breeding will be rewritten from a new point of view.” In 1906, the fourth edition appeared, with a new chapter on “Current plant-breeding practice”; and the book had History vil grown from the 293 pages of the original edition to 483 pages. This edition was translated into the Japanese by D. Karashima, and published in 1907. We now come to the present edition. The book has been made over by Dr. Gilbert, who has rewritten some of it and who has added all the new material, and in whose hands I have been glad to place it. My work in this edition has been only editorial. A considerable part of the old work has been preserved, whether wisely or not will be the occasion for different opinions. It has seemed to be desirable to retain something of a former point of view while at the same time expressing the applications of the work in the method and the language of the day. Con- siderable use has been made of the work of others, as is apparent in the pages. The Open Court Publishing Com- pany has loaned illustrations from the important work of de Vries, and pictures have been taken from the Yearbooks of the United States Department of Agriculture. All these aids we are glad to acknowledge. These new investigations have taken us far from the point of view of Darwin, in which the original editions of the book were founded. I doubt whether the students receiving their instruction to-day, with all their abounding facilities and opportunities, have any such feeling for a master-spirit as we had in those days when the studies of Darwin had given a new meaning to nature, when there were still a few naturalists left, and when the glow of his writings was warm in every person’s work. To one coming out of a plant-growing relationship, the masterful works of Darwin had introduced order, and the forms of cultivated plants had been made worthy of serious study. This inter- est was further stimulated by the writings of Wallace and Vill History others. All these writings were fascinating to read. How to produce new forms of vegetation seized some of us with irresistible power. The literature has now become complex and difficult, with considerable gain, no doubt, in a closer acquaintance with the subject, and a nearer approach to the ultimate truth; but the charm of the simple literature is largely buried, and I fear that much of our interest is now expressed in the discussion of methods and in disputing about the reasons. Yet we are accumulating knowledge, and after a time we shall come back to clarity and to a simplicity that the layman can use. LH. BAILEY: IruAca’,. Ni Y, December 1, 1914. TABLE OF CONTENTS CHAPTER I PAGES THe Fact AND PHILOSOPHY OF VARIATION ; ; ; 1-138 The fact of individuality, 2— variation and adapta- tion, 7 — species-formation, 8 — conception of unit char- acters, 9 — differences between plants and animals with regard to general association of parts and their methods of reproduction, 10 — bud-variation and bud-varieties, 11. CHAPTER II THe Causes oF INDIVIDUAL DIFFERENCES . : : ‘ 13-30 Fortuitous variation, 14— action of natural selection on variation, 14—sex as a factor in the variation of plants, 15 — physical environment and variation, 16— do external influences produce permanent effects in plants, 17 — natal and post-natal variations, 18 —con- ception of biotypes, 19— variation in food supply, 20 —variation in climate, 22—food supply in different branches, 23 — what cultivation is, 24 — variation in cli- mate, 25 — man’s control over climate as a means of making plants vary, 27——change of seed, 28 — bud- variation, 29 — struggle for life a cause of variation, 30. CHAPTER III THe CHOICE AND FIxaTION OF VARIATIONS : . ; 34-40 What is a variety, 35 —adaptation in nature, 87 — artificial selection, 37—bud selection, 39 — variation and selection not entirely within man’s control, 39. ix x Table of Contents CHAPTER IV PAGES THE MEASUREMENT OF VARIATION. : : : E 41-51 The science of biometry, 41 — type, 48 — biometrical expression of variability, 43— mode, 44 — modal coefti- cient, 45— mean, 45—use of mean, 46 — mathematical expression of variability, 47 — average deviation, 47 — standard deviation, 48 — coefficient of variability, 49 — probable error, 50 — use of statistical methods, 51. CHAPTER: V MutTATIONS . : : : : ; ‘ : : 52-91 Evolutionary theories of Darwin and de Vries, 52 — differences between fluctuating variations and mutations, 54 —history of mutation, 55—history of the appear- ance of double flowers, 56 — de Vries’ experiment with cenotheras, 59— analytical table of seedlings (after de Vries), 68 — how the mutants were produced in the gar- den, 71— mutating strains of O. Lamarkiana, 72 — de Vries’ laws of mutability of the evening-primroses, 72 — frequency of occurrence of mutations, 79 — spontaneous occurrence of new elementary species in the wild state, 80 — spontaneous occurrence of new elementary species and varieties under cultivation, 80 — experimental study of the origin of mutations, 84— experiments in the pro- duction of double flowers, 86— what do new characters come from, 90 — can mutations be produced artificially, 90 — economic significance of mutations, 90. CHAPTER VI THE PHILOSOPHY OF THE CROSSING OF PLANTS, CONSIDERED IN REFERENCE TO THEIR IMPROVEMENT UNDER CULTIVATION . : : : d a , ; 92-148 The struggle for life, 92— survival of the most fit, 98 — flexibility as an aid to survival, 93 — causes of varia- bility, 94— origin and function of sex, 95 — effects of Table of Contents crossing on the species, 97—the limits of crossing, 97 —swamping effects of inter-crossing, 98 — what deter- mines the limits of crossing, 98 —the limits of crossing tend to preserve the identity of species, 99 — the refusal to cross, the result of natural selection, 100—for the production of useful hybrids, do not have the parents too diverse, 101 — function of the cross, 101—rarity of natural hybrids, 102 — change of seed and crossing, 103 —results from change of stock, 105—crossing from standpoint of plant improvement, 108 — understanding of terms, 108—history of plant hybrids, 110— what plants can be hybridized, 111—vigor as a result of crossing, 112 — Darwin’s experiments with morning- glories, 114 — Darwin’s results with other plants, 115 — increased vigor in other crosses, 115 — three factors, 117 —-the outright production of new varieties, 118— how to overcome antipathy to crossing, 121 — variability of hybrids, 122 —characteristics of crosses, 128 — difficul- ties in making successful crosses, 125 — hybridization and asexual propagation, 125 —in-breeding, 127 — expe- rience with egg-plants and squashes, 128 — influence of sex on hybrids, 188— uncertainties of pollination, 140 —graft hybrids, 142-—the case of Cytisus Adami, 142 — Winkler’s Solanum graft-hybrids, 146—are these real graft-hybrids, 147. CHAPTER VII HEREDITY Heredity studied collectively, 149 — the coefficient of heredity, 152 — notation, 153 — conception of unit char- acters, 154— knowledge of heredity has come through experimental breeding, 154—rediscovery of Mendel’s work by de Vries and others, 155 — Mendel’s experi- ments, 157 —explanation of mendelian results, 166 — explanation of diagram, 171 — Mendel’s results with the offspring of hybrids in which several differentiating char- Xl PAGES Xl Table of Contents acters are associated, 171— Mendel’s iaw of inheritance of unit characters (table), 175 — results in F) with com- plete dominance in every character-pair (table 1), 176 — results involving three pairs of characters (trihybrid), 177 —incomplete dominance, 179—presence and ab- sence hypothesis, 181— examples of mendelian inherit- ance due to the presence and absence of a single unit, 181 — mendelian inheritance of color, 185 — white flowers in F, from red x cream, 187 —the ratio 9:3: 4, 188 — colored forms from white x white and the 9:7 ratio, 188 — Emerson’s experiments with beans, 189 — absence factors, 192 — mutations resulting from mendelian segre- gation and recombination, 195— mutations which men- delize are constant, 193—mendelism in wheat, 194— mendelism summarized, 200 — application to plant- breeding, 202 — the probable limits of mendelism in the production of new varieties, 204 —conclusion, 208. CHAPTER VIII How Domestic VARIETIES ORIGINATE Indeterminate varieties, 209 — plant-breeding, 212 — plant-breeding by selection, 218—rules for breeding plants, 222 — specific examples, 253 — the dewberry and blackberry, 255 — the apple, 255 — beans, 260 — cannas, 265 —the cabbage family, 267 —the chrysanthemum, 267. CHAPTER IX POLLINATION: OR How To Cross PLANTS . The structure of the flower, 270— manipulating the flowers, 281. CHAPTER X THE ForwaRD MOVEMENT IN PLANT-BREEDING . Systematic improvement of plants, 295—the plant- breeder should aim toward definite ideals, 297 — plant PAGES 209-269 270-293 294-323 Table of Contents improvement a serious business, 298—the results of plant-breeding effort, 299 —state plant-breeding associ- ations, 300— other plant-breeding associations, 304 — commercial breeding agencies, 308 — work of the council of grain exchanges, 310— United States Department of Agriculture and state experiment stations, 310 — work of the state agricultural experiment stations, 314 —in- struction in plant-breeding in the United States, 321 — Luther Burbank, 321. APPENDIX A GLOSSARY OF TECHNICAL PLANT-BREEDING TERMS , APPENDIX B PLANT-BREEDING Books APPENDIX C List OF PERIODICALS CONTAINING BREEDING LITERATURE APPENDIX D BIBLIOGRAPHY APPENDIX E LABORATORY EXERCISES : : : , Exercise 1 — Field study of variations by abs an herbarium of variations . Exercise 2— The statistical seks of. lees aa variability Exercise 3 — Eaeesittign Exercise 4— Statistical study of pares fiden different trees Exercise 5 — “Statistical eee of Teepiesies at different trees xill PAGES 325-327 328-31 302-554 335-393 394-467 394-399 399-412 412-420 420 420-423 X1V Table of Contents Exercise 6 — Statistical study of the quantity of grapes from different grape vines Exercise 7 — Study of VantiOn in rested specimens of ragweed or some plant showing many different types Exercise 8 — Study of bud variation and reversions in ferns Exercise os Study of he morphology of different kinds of flowers Exercise 10— "Technigue of ches cross- pnlhuation of plants Exercise 11 — Emberolosieal arias front aides shows ing cell division at different stages, chromosomes, pollen mother cells, development of the embryo sac, etc. Exercise 12— Study of pollen germination and fecundation i Exercise 13 = Practiced in the cross- pollinanon of ap- ples, pears, peaches, plums, etc. ; : Exercise 14 — Studies of mendelian inherifante Exercise 15— A study of mendelian characters in timothy and oats Exercise 16 — Mendelian neoblewie Exercise 17 — Ear-to-row test with corn Exercise 18 — Corn judging Exercise 19 — Statistical study of ears ‘of corn Exercise Tee of correlations of characters in corn Exercise 21 — Gore poccian a iaborene ste Exercise 22 — A study in potato selection . Exercise 23 — Study of citrus hybrids : Exercise 24 — Study of the results of the plant- sono tests of wheat, oats, cabbage, onions, or any crop where data are available ; ‘ é Exercise 25 — Studies of en of baeties come wheat, apples, plums, grapes, etc. Exercise 26 — Field trip to experimental Seale Exercise 27 — Working plans for practical breeding experiments PAGES 425 423 425-424 424-426 426-428 428 428 429 429-435 435-438 438-445 445-447 447-448 448-449 449-450 450-452 452-457 457-458 458 458 458-459 459 LIST OF ILLUSTRATIONS FIGURE 1. Variation in heads of timothy 2. Two seedling timothy plants, growing side iF sie sowie a common kind and degree of difference 3. A productive timothy plant . 4, A timothy plant that runs much to seed ; 5. A timothy plant that runs almost wholly to leaf . 6. Couch or quack grass, showing means of asexual propaga- tion by underground root stalks 7. Orange hawkweed 8. A frequency curve illustrating the distr ibasion of the height of the pea plants 9. Variations in statures of Gingihera dejiella, tant aa Hnothera Lamarkiana, its parent . 10. Variations in the amount of sugar in 40,000 beets 11. Chelidonium majus 12. Chelidoniwm laciniatum 3. Anemone coronaria, piele™naieanad ford 14. Anemone coronaria, semi-double-flowered form 15. Anemone coronaria var. florepleno 16. Hugo de Vries 17. nothera Lamarkiana ated Gnoihera RenciiG in Bas 18. Gnothera Lamarkiana. Curve exhibiting variations in the length of fruits of 568 plants . 19. nothera lata —@nothera Lamarkiana epectheta dante 20. A, spike with almost ripe fruits of Hnothera gigas, a mutant species; B, the same of (nothera Lamarkiana, its parent form 21. The cage in Professor de vevies? Benetinent Sanien: pWorinl corn and various species of Gnothera XV 53 63 66 XVl1 List of Illustrations FIGURE 22. Cupid sweet pea (photo by Beal) . 23. Linaria vulgaris — peloric flowers 24. Linaria vulgaris peloria 25. Antirrhinum majus : 26. Chrysanthemum segetum pishin : 27. Chrysanthemum inodorum plenissimum : : 28. Ancestral generations of Chrysanthemum segetum plenum 29. A, Chrysanthemum segetum; B, Chrysanthemum segetum grandiforium (after purification) . : 30. Extreme variability in the shape of the leaves of hy brid pop- pies. Second generation from a cross between the Bride variety of the Opium poppy and the Oriental poppy 31. Inbred corn plants, showing lessened vigor of growth (adapted from Yearbook) 32. Hybrid walnut and parents 33. A hybrid walnut (Juglans californica fenay: ronenag double the height of ordinary trees 34. Variation in hybrid pineapples 35. Variation in hybrid squashes 36. Hybrid citrange and its parents, Pantivis er a) trifoliata and common sweet orange : 37. Hybrid tangelo and its parents, pomelo and baer ine). 58. Samson tangelo (adapted from Yearbook) 59. Citranges (hybrid of orange and Poncirus (citrus) trifoliata) 40. Teosinte and its hybrids with Indian corn ‘ , 41. Cytisus Adami 42. Cytisus Adami 43. Mendelism in maize 44. Diagrammatic See Peer of Mendel's ES 45. Hybrid carnation between a single and a burster, sub wine intermediacy . 46. Fowls’ combs ; 47. Three generations of hybrid ores 48. Mendelism in tomatoes . : _49. Pride of Georgia, a good short- eanie eoitane 50. Select Jones improved cotton with uniform long Reale 51. Improving the tomato List of Illustrations XVll FIGURE PAGE 52. Crop averages in corn breeding for high and for low protein. Results of twelve generations. (Ill. Exp. Sta.) . . 216 53. Fruit of wild elderberry : ; ou 54. Fruit of a cultivated variety of the Siterberes ‘yetaael ap- peared as a variation from the wild form ‘ 218 55. Field of wilt-resistant watermelons, growing free from diac on infected land (from tae : ; . . 219 56. Disease resistance in cowpeas : 220 57. Improved types of lettuce and the varieties Poi which ace were developed ; E ‘ : : ; é $i 2St 58. Wild cabbage : . : , : : - : .. 240 59. Curled kale . : : : : . : ’ : is AR 60. Collard . ; ; , z é : : : . 22 61. Brussels sprouts. ‘ ; ‘ : ; , ¢ . 248 62. Savoy cabbage 2, a ; : : : : ; . 244 63. Cabbage shapes. ; : : ; . 245 64. Swede turnip, kohl-rabi, and Gaaiiflowe a : ; . 248 65. Wild form of Chrysanthemum morifolium . s ; . 249 66. Wild form of Chrysanthemum indicum : : : . 250 67. Pompon anemone type . i ; 2 ; 3 : . 251 68. Single type . : ‘ ; i ; ; . 252 69. Type of pompon ahepeecatheriain ; : : : . . 253 70. Japanese anemone type P : ! : , ‘ . 256 71. The small and regular anemone type . : ‘ , a ee 72. A pompon chrysanthemum . : : , : . 258 73. Type of Japanese incurved chry Sausthocaiin . 259 74. Japanese anemone chrysanthemum when fully See less . 262 75. New type with short stem . : ! 2 : : . 263 76. Incurved type : é Z : A 3 : q . 264 ((.. Hairy type. . é : : 2 : : : : . 267 78. Japanese type . ; : : é ; ’ . . 268 79. Reflexed type : ‘ : : : ‘ : . 269 80. Bellflower . : ‘ . : : : ; . 270 81. Flower of white lily : , 4 : ; , ees fi 82. Flower of greenhouse Se odbetiaia : ‘ f : . 272 83. Flower of night-blooming cereus . : F . > 28 84. Flower of the shrubby hibiscus ( Hibiscus nia ‘ . 204 XV List of Illustrations FIGURE 85. Bugbane (Cimicifuga racemosa) 86. Blossom of flowering raspberry (Rubus baa 87. Squash flowers of each sex . 88. Flowers of clematis (Clematis ainiiana’. 89. Tobacco flowers, showing the parts of the flower, a paul ready to be emasculated, and an emasculated subject . 90. Zinnia flowers 91. Instruments used in aallnntine flow ers 92. Ladle for pollinating house tomatoes 93. Bag for covering the flowers 94. Fuchsias, showing the stamens and nistila, Goa a ‘Gall feaay to be emasculated . 95. Fuchsia flower emasculated 96. Fuchsia flower tied up after emasculation 97. Tomato and quince 98. Pollinating kit 99. Pollinating kit 100. Main building of Seed icentantion: aiices of Sw edish Cae pany (photo by Newman) 101. Gardens at Luther Burbank’s : 102. Some of Burbank’s frames and garden hada 105. Spineless and spine-bearing cacti at Burbank’s : 104. A specimen herbarium sheet, showing variations in the leaves of the mulberry . ‘ 105. A specimen herbarium sheet, showing dimerence hare een two leaves of the horse radish 106. A specimen herbarium sheet, showing variations in eaves of the Persian lilac 107. A specimen herbarium sheet, aaae ea ntnine in ewer of the blackberry . 108. A common form of ragweed 109. Another form of ragweed 110. Demonstration of allelomorphism and of EGninleks Aatataiee 111. Demonstration of presence and absence hypothesis and of intermediacy . A : 112.. Demonstration of the presence oe an inhibitor rabie : Explanation of so-called ‘‘dominance and absence”’ . The Rural Science Series EpItTep By L. H. BAILEY PLANT-BREEDING venti Pas <5" q : > on ha ne ee hcl PLANT-BREEDING CHAPTHe I THE FACT AND PHILOSOPHY OF VARIATION THERE is no one fact connected with agriculture that more greatly interests all persons than the existence of numerous varieties of plants that seem to satisfy every need of the gardener. Whence came all this multitude of forms? What are the methods employed in securing them’? Are they merely isolated facts or phenomena of gardening, or have they some relation to the broader phases of the evolution of the forms of life? These are some of the questions that occur to every reflective mind when it contemplates an attractive garden, but they are questions that seem never to be answered. Whatever attempt the gardener may make at answer- ing them is either obscured by an effort to define what a variety is, or else it consists in simply reciting how a few given varieties came to be known. But there must be some method of arriving at a conception of the ways whereby the varieties of fruits and flowers and other culti- vated plants have originated. If there is no such method, then the origination of these varieties must follow no law, and the discussion of the whole subject is fruitless. But we have every confidence in the consecutive uniform- B 1 2 Plant-Breeding ity of the operations of nature, and it were strange if some underlying principle of the unfolding or progression of plant-life does not dominate the origin of the varied and innumerable varieties which, from time unknown, have responded to the touch of the cultivator. Let us first, therefore, make a broad survey of the subject in a philosophical spirit, and later, discuss the more specific instances of the origination of varieties. The fact of individuality. — There is universal difference in nature. No two living things are counterparts, for no two are born alike or into exactly the same conditions and experiences. Every living object has individuality; that is, there is something about it that enables the acute observer to distinguish it from all other objects, even of the same class or species. Every plant in a row of lettuce is different from every other plant, and the gardener, when transplanting them, selects out, almost uncon- sciously, some plants that please him and others that do not. Every apple tree in an orchard of a thousand Baldwins is unlike every other one, perhaps in size or shape, or possibly in the vigor of growth or the kind of fruit it bears. Persons who buy apples for export know that fruit from certain regions stands the shipments better than the same variety from other regions ; and if one were to go into the orchards where these apples are grown, he would find the owner still further refining the problem by talking about the merits of individual trees in his orchard. If one were to make the effort, he would find that it is possible to distinguish differences between every two spears of grass in a meadow, or every two heads of wheat in a grain-field., The Fact and Philosophy of Variation 3 In timothy, one of the commonest of our grasses, a casual observer may find differences in the length, shape, and color of heads; tendency of some plants to produce asexual leaves in the head; form of base of the head; My ft kn Seay iene . af Ate, wage Ce x i *, * Fic. 1. — Variation in heads of timothy. length, width, and color of leaves; erect or drooping character of the leaves; susceptibility of the leaves and stems to rust; period of blooming; habit of growth of plant, — erect or decumbent; few or many culms to the plant; ability to recover after cutting; quantity of seed Plant-Breeding a common kind and degree of difference. ing ide, show le bys SiC S . , growing Fic. 2. — Two seedling timothy plants 5 The Fact and Philosophy of Variation Fic. 3. — A productive timothy plant. Similar differences may be found in any group of plantsif the group is suffi- ciently studied. 1-5). produced, and others (Figs. 6 Plant-Breeding Fig. 4. — A timothy plant that runs much to seed. Variation and adaptation. — All this is equivalent to saying that plants are infinitely variable. The ultimate The Fact and Philosophy of Variation 7 causes of all this variation are beyond the purposes of the present discussion, but it must be evident, to the reflective mind, that these differences are a means of adapting the innumerable individuals to every little difference or Fic. 5. —A timothy plant that runs almost wholly to leaf. advantage in the environment in which they live. And if the result of variation is better adaption to the physical conditions of life, then the same forces must have been present in the circumstances which determined the birth of the individual. This change in environment may be 8 Plant-Breeding the cause of much of the variation in plants, since differ- ences in plants were positively injurious if it were possible for the conditions of environment to be the same. Species-formation. —If no two plants are anywhere alike, then it is not strange if now and then some de- ‘parture, more marked than common, isnamed and becomes a garden variety. We have been taught to feel that plants are essentially stable and inelastic, and that any departure from the type is an exception and calls for im- mediate explanation. The fact is, however, that plants are essentially unstable and plastic, and that variation between the individuals must everywhere be expected. This erroneous notion of the stability of organisms comes of our habit of studying what we call species. We set for ourselves a type of plant or animal, and group about it all those individuals that are more like this type than they are like any other, and this group we name a species. Nowadays, the species is regarded as nothing more than a convenient and arbitrary expression for classifying our knowledge of the forms of life, but the older naturalists conceived that the species is the real entity or unit in nature, and we have not yet wholly outgrown the habit of mind which was born of that fallacy. Nature knows little about species; she is concerned with the individual, the ultimate complete and working unit. This individual she molds and fits into the opportunities of environment, and each individual tends to become the more unlike its birthmates the more the environments of the various in- dividuals are unlike. We must consider, therefore, as a fundamental concep- tion to the discussion of the general subject before us, the The Fact and Philosophy of Variation 9 importance of the individual plant, rather than the im- portance of the species; for thereby we put ourselves as nearly as possible in sympathetic attitude with nature, and, resting upon the ultimate object of her concern, we are able to understand what may be conceived to be her motive in working out the problem of life: Recall the fact that the whole tendency of contemporary civilization, in soci- ology and religion, is to deal with the individual person and not with the mass. The present-day method of study- ing the evolution of plants and animals is essentially an- alytical. As the chemist attempts to discover the smallest units from which the substances of nature have been built up, so the student of biology and evolution is seeking for the smallest heritable units of which plants and animals are composed. This is only an unconscious feeling after natural methods of solving the most complex of problems, for it is exactly the means to which every organic thing has been subjected from the beginning. Conception of unit-characters.— The student of evolution now conceives animals and plants to be composed of what he terms “unit-characters,” analogous, roughly, to the atoms of the chemist. These are the smallest heritable units that a plant or animal may possess. Any distinct entity that can be traced from one generation to another, such as the presence or absence of pubescence on the leaves or stems, the height of the plant, whether dwarf or tall, the color of the flower or fruits, and very many others are now known as unit-characters. The more any group of plants is studied, the more definite and distinct these unit-characters become. The time may come when the gardener, from long experience, shall become acquainted 10 Plant-Breeding with these qualities, so that he may synthetically put many units together by crossing and produce new varieties _almost at will. Differences between plants and animals with regard to general association of parts and their methods of reproduction. — Unit-characters are nature’s blocks, which she uses to build up plants and animals into various shapes for dif- ferent purposes. These combinations of units when added together in proper extent and proportion consti- tute the plant and animal as we know it, the ultimate living and working organism, with power of growth and reproduction. In looking for the ultimate working unit, individuality or personality in nature, we must make a broad distinction between the animal and the plant. Every higher animal is itself a working unit; it is one. It has a more or less definite span of life, and every part and organ contributes a certain indispensable part to the life and personality. of the organism. No part is capable of propagating itself independently of the sex-organs of the animal, nor is it capable of developing sex-organs of its own. If any part is removed, the animal is maimed and perhaps it dies. The plant, on the contrary, has no definite or distinct autonomy. Most plants live an indefinite existence, dependent very closely upon the immediate conditions in which they grow. Every part or branch of the plant lives largely for itself, it is capable of propagating and multi- plying itself when removed from the parent or the colony of branches of which it is a member, and it develops sex- organs and other individual features of its own. If any branch is removed, the tree or plant does not necessarily The Fact and Philosophy of Variation 11 suffer; in fact, the remaining branches usually profit by the removal, a fact which shows that there is a competi- tion, or struggle for existence, between the different branches or elements of the plant. The whole theory and practice of pruning rests upon the fact of the individual unlikenesses of the branches; and the unlikenesses are of the same kind and often of the same degree as those that exist between different plants grown from seeds. Bud-variation and bud-varieties. —'The branches of a Crawford peach tree, for example, differ amongst them- selves-in size, shape, vigor, productiveness, and season of maturity, much the same as any two or more separate Crawford trees, or any number of trees of other varieties, differ the one from the others. If any one of these branches or buds is removed and is grown into an inde- pendent tree, a person could not tell — if he were ignorant of its history — whether this tree were derived from a branch or a seed. This proves that there is no essential unlikeness between branches and independent plants, ex- cept the mere accident that one grows upon another branch or plant whilst the other grows in the ground. But the branch may be severed and grown in the ground, and the seedling may be pulled up and grafted on the tree, and no one can distinguish the different origins of the two. And then, as a matter of fact, a very large proportion of our culti- vated plants are not distinct plants at all, in the sense of being different creations from seeds, but are simply the result of the division of branches of one original plant or branch. All the fruit trees of any one variety are obtained from the dividing up and multiplication of the branches of the first or original tree. 12 Plant-Breeding The reader is curious to know how this original tree came to be, and this we may find out before we are done; but for the present, let it be said that it is equally possible for it to have come from a seed, or to have sprung from a branch which some person had noticed to be very dif- ferent from the associated branches in the tree-top. In other words, the ultimate unit or individual of variation is the bud and the bit of wood or tissue to which it is attached; for every bud, like every seed, produces an offspring that can be distinguished from every other offspring whatsoever. CHAPTER II THE CAUSES OF INDIVIDUAL DIFFERENCES WE have now gone back to the starting-point, to that unit with which nature begins to make her initial differ- ences or individualities ; that is, to the point where varia- tions arise. This point is the bud and the seed, — one sexless, or the offspring of one parent; the other sexual, or the offspring of two parents. Now, inasmuch as the horticultural variety is only a well-marked variation which the gardener has chanced to notice and to propagate, it follows that the only logical method of determining how garden varieties originate is to discover the means by which plants in general vary or differ one from another. There is probably no one fact of organic nature concern- ing the origin of which modern philosophers are so much divided as the causes or reasons for the beginnings of variations or differences. It seems to be an inscrutable problem, and it would be useless, therefore, for us to attempt to discover these ultimate forces in the present book. Still, we must give them sufficient thought to enable us to satisfy our minds as to how far these variations may be produced by man; and, in doing this, we must discover at least the underlying philosophy of plant variation. It is the nature of organisms to be unlike their parents and their birthmates. Why? 13 14 Plant-Breeding Fortuitous variation. — It will probably never be pos- sible to refer every variation to a distinct cause, for it is probable that some of them have no antecedent. If we conceive of the forms of life as having been created with characters exactly uniform from generation to generation, then we should be led to look for a distinct occasion or cause for every departure from the type; but we know, as has already been pointed out, that heredity by its very nature is not so exact as to carry over every attribute, and no other, of the parent to the offspring. Plasticity is a part of the essential constitution of all organic beings. There is perhaps no inherent tendency in organisms towards any ultimate or predetermined completion of forms, as the older naturalists supposed, but simply a laxity or indefiniteness of constitution which is expressed in numberless minor differences in individuals. That is, some variation may be simply fortuitous, an inevitable result of the inherent plasticity of organisms, and it may have no immediate inciting cause. Action of natural selection on variation. — If we were to assume that every minor difference is the result of some immediate cause, then we should expect every individual plant or animal to fill some niche, to satisfy some need, to produce the definite effect for which the cause stands. But it is apparent to one who contemplates the operations of nature that very many — certainly more than half — of the organisms which are born are not useful to the per- petuity of the species and very soon perish. From these fortuitous variations nature selects, to be sure, many individuals to be the parents of other generations because they chance to be fitted to live, but this does not affect The Causes of Individual Differences 15 the methods or reasons of their origin. It is possible that, whilst many of these mere individual differences have no direct and immediate cause, they may still be the result of -a devious line of antecedent causes long since so much diffused and modified that they will remain forever un- recognizable; but even so, the fact still remains that these present differences or variations may be purposeless, and it is quite as well to say that they exist because it is a part of the organic constitution of living things that un- like produces unlike. Sex as a factor in the variation of plants. — All plants have the faculty, either potential or expressed, of propagat- ing themselves by means of buds, or asexual parts. This is obviously the cheapest and most direct possible method of propagation for many-membered plants, since it re- quires no special reproductive organization and energy, and, as only one parent is concerned in it, there is none of the risk of failure that obtains in any mode of propaga- tion in which two parents must find each other and form a union. There must be some reason, therefore, for the existence of such a costly mechanism as sex aside from its use as a mere means of propagation. It may be said that sex exists because it 1s a means of more rapid multiplication than bud-propagation, but such is not necessarily the fact. Many plants produce buds as freely as they produce seeds; and then, if mere multipli- cation were the only destiny of the plant, bud-production would no doubt have greatly increased to have met the demand for new generations. The chief reason for the existence of sex in the vegetable world seems to be the need for a constant rejuvenation and modification of the 16 Plant-Breeding offspring by uniting the features of two individuals into one. There thus arises from every sexual union a number of new or different forms from which nature may select the best, — that is, those best fitted to live in the condi- tions in which they chance to be placed. But whilst sex is undoubtedly one of the most potent sources of pres- ent unlikenesses, it is not necessarily an original cause of individual differences, since the two parties to any sexual con- tract must be unlike before they can produce unlike. When once the initial unlikenesses were established, every new sexual union must produce new combinations, so that now, when every new form, from whatever source it appears, comes into existence, there are other intimately related forms with which it may cross. This state of things has existed to a greater or less degree from the moment sex first appeared, so that the organic world is now endlessly varied as the result of a most complex ancestry. Physical environment and variation. — Every phase and condition of physical circumstances, which are not ab- solutely prohibitive of plant life, have plants which thrive in them. Every soil and climate, every degree of humidity, hills, swamps, and ponds, — every place is filled with plants. Even the trunks and branches of trees support other plants, as epiphytes and parasites. That is, plants have adapted themselves to every physical environment ; or, to turn the proposition around, every physical en- vironment produces adaptive changes in plants. There are those, like Weismann and his adherents, who contend, from purely speculative reasons, that these changes do not become hereditary or permanent until they have in- ~_ The Causes of Individual Differences bri fluenced a certain physiological substance which is assumed to reside in the reproductive regions of the organisms, and that all those changes which have not yet reached this germ-plasm are, therefore, lost, or die with the or- ganisms. Do external influences produce permanent effects in plants? —It is not necessary to discuss here the intri- cate arguments in the time-honored controversy of the permanent inheritance of external modifications. Such violent modifications as traumatic injury do not affect its germ cells and are not inherited. But it is the common experience of gardeners that the modifications of the envi- ronment of plants, such as changing food supply or changing seed from one environment to another, produce changes which eventually become hereditary. Whether these changes of environment act directly upon the germ-plasm to produce the change or whether they stimulate a ger- minal change which was otherwise latent, is a question which long and patient experimentation must decide. Certain it is, that plants have gone through a profound modification and it is easy to believe that environment has played no little part in these changes. Weismann teaches that ‘acquired characters,” or those variations which first appear in the life-time of the indi- vidual because of the influences of environment, are lost, because they have not yet affected the reproductive sub- stances ; but if these characters are induced by the effect of impinging environment during two or more generations, they may come to be so persistent that the plant cannot throw them off, and they become, thereby, a part of the hereditary and non-negotiable property of the species. Cc 18 Plant-Breeding Now, it is apparent that in one or another of the genera- tions which are thus acted upon by the environment, there must be a beginning towards the fixing or hereditable permanency of the new forms, and we might as well assume that this beginning takes place in the first genera- tion as in the last, since there can be no proof that it does not take place in either one. The tendency towards fixity, if it exists at all, undoubtedly originates at the very time that the variation itself originates, and it is only sophistry to assume that the form appears at one time and the tendency towards permanency at another time. Since plants fit themselves into their circumstances by means of adaptive variations, we must conclude that all adaptive variations have the power of persisting, upon occasion. All these remarks, whilst somewhat abstruse, have a most important bearing on the philosophy of the origin of garden varieties, because they show, first that changes in the conditions in which plants grow introduce modifi- cations in the plants themselves, and second, that wher- ever any modification occurs it is probable that it may be fixed and perpetuated. Natal and post-natal variations. — It is necessary at this point that we distinguish between natal and post-natal variations, —that is, between those variations which are born with-plants, and those which appear, as a result of environment, after the plant has begun to grow. It is commonly assumed that the form and general characters of the plant are already determined in the seed, but a moment’s reflection will show that this is far from the truth. One may sow a hundred selected peas, for example, The Causes of Individual Differences 19 all of which may be alike in every discernible character. If these are planted in a space of a foot apart, it will be found, after two or three weeks, that some individuals are outstripping the others, although all of them came up equally well and were at first practically indistinguishable. This means that, because of a little advantage in food or moisture, or other circumstances, some plants have ob- tained the mastery and are crowding out the less fortunate ones. The theory and practice of agriculture rests on the fact that plants can be modified greatly by the condi- tions in which they grow, after they have become thor- oughly established in the soil. Plants may start equal, but differ widely at the harvest; and this difference may be controlled to a nicety by the cultivator. Every farmer is confident, also, that the best results for the succeeding year are to be got only when he selects seeds from the best that he has been able to produce this year. So, given uniformity or equality at the start, the operator molds the individual plants largely at his will. Conception of biotypes. — Most varieties are not as uniform as would at first appear. = 4451.8 (SfV) pedtols n 286 Mean, = 15.5 inches. Use of mean. — The mean gives a good average value of the character and is often more useful than the mode in expressing type. The breeder must use his judgment The Measurement of Variation 47 as to which should be used in each case, the mean or the mode. Mathematical expression of variability. — After the average or mean of any group of plants has been deter- mined, it is desirable to know the amount of deviation of the different individuals from the mean. This determina- tion gives a concrete expression which is an index of the amount of variability exhibited. This variability is ex- pressed as the average deviation or the standard deviation. The latter is ordinarily employed by mathematicians. Average deviation. — The average deviation is deter- mined by obtaining, first of all, the amount which each class varies from the mean and multiplying each deviation by the number of individuals concerned. For example, the column D is obtained by finding the difference between the mean, 15.5, and the variations in column V: thus in the first case the difference between 5.8 and 15.5 is — 9.7 while farther down column V we find 16.3, which is greater than the mean, giving us a value of 0.8 in column D. Now, if there were the same number of individuals in each class, the average deviation could be found by adding up the deviations in column D, and dividing by the total number of individuals in column f, but there is one indi- vidual deviating — 9.7 while there are 43 deviating 0.8 and 18 deviating 5.3, and so forth. In order to overcome this the deviations are multiplied by the number of in- dividuals giving the column fD. The sum of this column divided by the total number of individuals gives the average deviation. This is an index of variability. The average deviation is expressed by the following formula : — 48 Plant-Breeding 2 Df. n Average deviation = Standard deviation. — The operations for finding the standard deviation are the same as for the average devia- tion except that the deviations in column D are squared before multiplying by the frequency numbers (f), thus giving the columns D? and D?f respectively. The sum of the latter divided by the total number of individuals and the square root of the result extracted gives the standard deviation. This can be expressed by the follow- ing formula : — 5 ‘ go 27: n The details of determining the average and standard deviation are as follows : — V f D {D Diane Df 5.8 i — 9.7 9.70 94.09 94.09 eee 4 — 8.2 32.80 67.24 268.96 8.8 6 — 6.7 40.20 44.89 269.34 10.3 29 es 150.80 27.04 784.16 11.8 30 — 3.7 111.00 13.69 410.70 133) ov — 2.2 81.40 4.84 179.08 14.8 39 — 0.7 27.30 0.49 19.11 16.3 43 0.8 34.40 0.64 25.2 17.8 34 De 78.20 5.29 179.86 19.3 26 3.8 98.80 14.44 375.44 20.8 18 oo 95.40 28.09 505.62 apes 8 6.8 |. 54.40 46.24 369.92 23.8 5 8.3 41.50 68.89 Holt 25.0 Z 9.8 19.60 96.04 192.08 26.8 2 chess 22.60 127.69 200ioo 28.3 il 12.8 12.80 163.84 163.84 29.8 1 14.3 14.30 204.49 204.49 n = 286 925.20 | >=4851.31 The Measurement of Variation 49 Average deviation = —— = 3.24 inches. Standard deviation, (o) = (ee = Coefficient of variability. — The average deviation or standard deviation as outlined above is always determined in the denomination of the unit in which the plant is measured ; if it is height of plant in inches, the deviation will be in inches and so forth. This prohibits the careful comparison of the deviations of different plants or parts of a plant because some deviations may be in pounds or others in inches, and hence they will not be directly comparable. It is desirable, therefore, to have an abstract expression so that the relative amount of variability of one class of organs may be directly compared with the variability of another. This is called the coefficient of variability. It is found by dividing the standard deviation by the mean. Thus an abstract number is found which expresses the variability. In our case the standard deviation = 4.1 inches and the mean = 15.5 inches, so that 4.1 Te .264 = 26.4 % = the coefficient of variability. If the coefficient of variability of the weight of the plants ‘had to be determined and was found to be, say, .384, it would follow at once that the height of the plant was considerably more variable than the weight. The coefficient of variability may be expressed as follows : — E 50 Plant-Breeding Oo Of uw’ 100. Probable error.1— It is obvious that these mathematical expressions of type and variability will be modified some- what by the number of individuals measured. The greater the number of individuals employed, the less the error. These differences which arise from the fewness of individuals employed is known as the probable error. It is expressed by a pair of divergences (+ /), the one above and the other below the actual value found, and indicates that the chances are even that the true value lies somewhere between the value found plus the error and the value minus the error. For example, the probable error of the mean in the problem here cited is + .016 and is found by the formula given below. This means that 1 Formule for probable errors : — Biiene. = Serer as standard deviation ere 67452 n number of individuals E standard deviation = + .6745 standard deviation OE V2 number of individuals + .6745 V2n E coefficient of variability = + .6745 = coefficient of variability 2 X number of individuals SES (G7/45) == V2 But when C is greater than 10% use the formula EC = + 6745 © [1 ee Vi2i 100 Nie The Measurement of Variation ol the true mean is probably somewhere between 15.5 + .016 and 15.5 — .016 or between 15.516 and 15.484. The size of the error is generally indicative of the number of the individuals employed and the general dependability of the work. Use of statistical methods. — The use of statistical methods enables the breeder to express quite accurately the amount of variability which would otherwise be expressed with considerable difficulty. It enables him also to keep an accurate record of his work from year to year and affords him a convenient method of comparing one year’s crop with another. It will be seen later that statistical methods may also be employed to express correlation and extent of inherit- ance. ( CHAR EER MUTATIONS THERE is endless dissimilarity in nature. No two plants and no two animals are exactly alike. There are more plants and animals than can find a place in which to live and thrive. There results a struggle for existence. Those animals or plants which, by virtue of the individual differences or peculiarities, are best fitted to the condi- tions in which they are placed, survive in this struggle for existence. They are “selected to live.” Those that survive, propagate their peculiarities. By virtue of continued variation, and of continued selection along a certain line, the peculiarities may become augmented ; finally the gulf of separation from the parental stem becomes great, and what we call a new species has origi- nated. Evolutionary theories of Darwin and de Vries. — This, in epitome, is the philosophy of Darwin in respect to evolu- tion of organic forms. It contains the well-known postu- late of natural selection, the principle that we know as Darwinism. This principle has had more adherents than any other hypothesis of the process of evolution. All recent hypotheses in some way relate to it. A number of them modify it, and some dispute it. The most pro- nounced counter-hypothesis is also the newest. It is that 52 Mutations 53 of Professor de Vries, botanist, of Amsterdam, Holland, who denies that natural selection is competent to produce species, or that organic ascent is the product of small differences gradually enlarging into great ones. According to de Vries’ view, species-characters arise suddenly, or all at once, and they are ordinarily stable from the moment they arise. mold ee ica! CON Fic. 9.— Variations in statures of (nothera nanella ee a mutant, and @nothera Lamarkiana (right), its parent. (£nothera nanella : Rangel 7—35em.s: Mi. 22.81 = 1 .02\em.s- oa; 7.26 == 0:72 ems: C- V., 31.84 + 3.16 per cent. Mnothera Lamarkiana: Range, 77—96 cm. ; Mes 88:68! 1055 em. sor 4.76) 0139 ent C. Vi. o:a0 = 044 per cent. 5 Za 10-15 16-20 20-25 «26-30 80-35 De Vries conceives that variations, or differences, are of two general categories: (1) Variations proper, or small, fluctuating, unstable differences peculiar to the individual (only partially transmitted to offspring); and (2) muta- tions, or differences that are usually of marked character, appear suddenly and without transition to other forms and are at once the starting-points of new species or races. Variations proper may be due to the immediate environ- 54 Plant-Breeding ment in which the plant lives. The mutations arise from causes yet unknown, although these causes are considered to be physiological. Probably many so-called mutations are hybrids and hence not mutations in the strictest sense. Differences between fluctuating variations and mutations : — 1. Fluctuating variations are very common and are to be found in all plants and animals. Mutations occur intermediately and are rare. 2. Fluctuating variations are thought not to be trans- mitted. Muta- tions are trans- mitted. 3. Fluctuating variations — pre- sent a series of differences which may be plotted on a frequency curve and obey the laws of chance. Muta- tions or saltatory variations do not obey the laws of MS 1 125 13 135 % HS 1S 18S 16 GS 17 125 18 ae chance, and Png Fig. 10.— Variations in the amount of sugar not be plotted in 40,000 beets. the form of a frequency curve. 4. Fluctuating variations do not lead to a new perma- nent mean of the race. Mutations cause a new mean to be +A —__ Mutations . 55 formed, around which is grouped a new series of fluctuating variations, forming a frequency curve. (See Fig. 9.) 5. In a fluctuating variation no new unit characters are added. The same char- acters are merely found in greater or less quan- tity or number (Fig. 10). Where a mutation oc- curs, new unit charac- ters are added or old ones lost. 6. Fluctuating vari- ations represent indi- viduals or parts of them. Mutations represent groups of individuals. In fluctuating vari- ations, the small differ- ences are grouped around what may be called a “center of fluc- tuation,’”’ which is the mean of the frequency curve. When a mutation is formed, a new center of fluctuation is established around a new mean. History of mutation. — The first mutation was recorded in 1590. In the garden of Sprenger, an apothecary of Heidelberg, was found a peculiar form of Chelidoniwm majus. The new form appeared suddenly and without intermediates from a lot of plants which had been culti- vated for many years. This mutant had “leaves cut into Fic. 11. — Chelidonium majus. 56 Plant-Breeding narrow lobes with almost linear tips, and the petals were also cut up.’”’ The new species has been constant since the first, and follows Mendel’s law when crossed with C. majus, its par- ent. (See Figs. 11 and 12.) The “word “mutation”’ was first used in 1650 by Dr. Thomas Browne, in _ his book ‘‘ Pseudo- doxia Epidem- Vicia: Sino erks quotes from Book VI, Chap- ter. X, “Of ethe Blackness of Ne- groes,”’ as fol- lows :— “We may say that men become black in the same Fie. 12.— Chelidonium laciniatum. , Coupled. pet uma wee back to the year 1855, when it suddenly arose from ordinary seed in a garden at Lyons. Carriére reported that from this one plant all double races and varieties of petunias have been derived by natural and partly by artificial crosses, and he added that likewise other species were known at that time to produce new double varieties rapidly. Geoffroy St. Hilaire, about 1825, expressed his belief in saltatory variations as a means of evolution. He thought that evolution does not take place entirely by Mie ale NY Mutations 59 the slow changes advocated by Lamark. His ideas were theoretical, however, and at that time were not borne out by experimental evidence. Darwin recognized the appearance of sudden variations of a marked character, such as is seen in the origin of large-crested Polish fowls and short-legged Ancon sheep. He thought that these new and strange forms would be lost soon by intercrossing and, being rare, that they pos- sessed no value. He held that the slow accumulation of minute fluctuating variations was the important factor in evolution. De Vries’ experiment with enotheras. — De Vries became convinced long ago that Darwin’s theory of the origin of species through ac- | cumulation of minute changes was not the only means of creating new types. He determined to produce mutations ex- perimentally, if possible. His results in the forma- tion of a new variety of the corn marigold will be described later. After making preliminary ex- periments with some Fic. 16. — Hugo de Vries. hundred species, de Vries finally decided upon nothera Lamarkiana as the most suitable form to use (Figs. 17 and 18). “Only one of my tests met with expectations. This species proved to be in a state of mutation, producing new elementary forms 60 Plant-Breeding continually, and it soon became the chief member of my experimental garden. It was one of the evening prim- roses.” This G. Lamarkiana was found to produce a large number of mutants, both when growing wild and under cultivation. The Gt. Lamarkiana plants which became the basis of Fig. 17. — @nothera Lamarkiana and @nothera nanella in bloom. future experiments were found growing wild in a field at Hilversum, near Amsterdam, Holland. Little is known of its history except that it is a native of America. It has not been found growing wild in America in recent years, although there seems to be evidence that it was seen and collected in the Southern States in the last century. The near relatives of @/. muricata, which were very common in the sandy regions of Holland, are very stable; de Vries Mutations 61 found no appreciable change in them, although he watched them for more than forty years. Lamark’s evening-primrose is grown in Europe as a cul- _ tivated plant, used principally for ornamental planting. It seeds abundantly and some of the plants have escaped cultivation. Groups of plants are found growing wild in many places. These wild plants remain in groups rather than being widely scattered, suggesting a definite hes SW 1) i © 2 & a2 29 & 2S 26 27 28 29 30 3) 3239 déMm. Fie. 18.— Enothera Lamarkiana. Curve exhibiting variations in the length of fruits of 568 plants. The dotted line is that given by Quetelet-Galton Law. origin for each group. CM. Lamarkiana is described as a “stately plant with a stout stem, attaining often a height of 1.6 meters and more. When not crowded, the main stem is surrounded by a large circle of smaller branches, growing upwards from its base so as often to form a dense bush. These branches in their turn have numerous lateral branches. Most of them are crowded with flowers in summer, which regularly succeed each other, leaving behind them long spikes of young fruits. The pace are 62 Plant-Breeding large and of a bright yellow color, attracting immediate attention, even at a distance. They open towards evening, as the name indicates, and are pollinated by bumble-bees and moths. On bright days their duration is confined to one evening, but during cloudy weather they may still be found open on the following morning. Con- trary to their congeners, they are dependent on visiting Insects for pollination. “In . Lamarkiana no self-fertilization takes place. The stigmas are above the anthers in the bud, and as the style increases in length at the time of the opening of the corolla, they are elevated above the anthers and do not receive the pollen. Ordinarily the flowers remained sterile if not visited by insects or pollinated by myself, although rare instances of self-fertilization were seen.” (. Lamarkiana is a biennial, producing rosettes in the first year and stems in the second year. This species was found to be variable in all periods of its life cycle, — in the seedlings, the rosettes, and the stems. De Vries pursued three methods in obtaining his muta- tions :— 1. Observations and studies of the plants while growing in the wild state in the fields. 2. Some of the plants were removed from the wild state and placed under cultivation. Many of the plants were self-fertilized and their seed sown under controlled con- ditions. By this method several mutants were found which were too weak to withstand the competition of field conditions. 3. Repetition of the sowing process for several genera- tions, leading to the production of new forms. Mutations 63 De Vries divided the new types of plants into five groups, classified as follows :— 1. Retrograde varieties with ‘negative attributes, —G. levifolia, A. brevistylis, and GE. nanella (Figs. 17 and 19). Fig. 19. — Cnothera lata (left), CGnothera Lamarkiana (middle), nothera nanella (right). 2. Progressive elementary species possessing new characters, and appearing as vigorous as the parent plant, CH. gigas and CZ. rubrinervis. 64 Plant-Breeding 3. Progressive elementary species, which are weaker than the parent species, Gi. albida and C!. oblonga. 4. Organically incomplete forms, @. lata (Fig. 19). 5. Fertile but inconstant species forms, GZ. scintillans and (. elliptica. The new species and varieties may be described as follows :— Group I, retrograde varieties, which have lost some of the characters possessed by the parent, 2’. Lamarkiana : — (LZ. levifolia is easily distinguished from its parent, CE. Lamarkiana, by having smooth, bright leaves, without undulations. These leaves are narrower and more slender than in Lamarkiana and the flowers of the brighter yellow. This variety was constant from seed, showing no reversion. It is a strong-growing plant and perfectly fertile. (H. brevistylis is a short-styled form. The ovary of this plant is abnormally situated and is not conducive to proper fertilization. The ovary is reached by only a few pollen tubes and fertilization must be incomplete. The few seeds that are obtained reproduce this type without reversion to Lamarkiana. (:. brevistylis may be dis- tinguished from the other forms before blossoming as the buds are much shorter and thicker than in the other species. The presence of leaves more rounded at the tip also distinguishes this form from others before flowering. (EL. nanella is a dwarf form, attaining often only one- fourth the height of the other types. ‘The flowers on this dwarf form are as large as upon Lamarkiana, which is a striking feature. The size of the leaves is proportionate to the height of the plant, but retain the same form as the Mutations 65 parent species. The stems are unbranched and very brittle. C. nanella is frequently produced as a mutation and is absolutely constant (Figs. 17 and 19). Group II, progressive elementary species, possessing new characters : — @. gigas is a giant form which is much larger in every respect than its parent, except in height. The stems are much larger; internodes are shorter and the leaves more numerous than the parent species (CZ. Lamarkiana). The flower-buds are large and closely crowded on the spike, and when the flowers open, they make a beautiful appearance (Fig. 20) . (. rubrinervis is characterized by the red veins and red streaks on the fruits. This plant is as tall as &. gigas, but a little more slender. A feature of this type is the brittleness of the leaves and stems, especially in the annual individuals, of which many are found. Many of these mutants may be recognized before the adult stage has been reached, for example, at about the age of two months. The leaves of @. gigas are broad, of a deep green, the blade sharply cut off from the stalk, all of the rosettes becoming stout and crowded with leaves. In @. rubrinervis, on the contrary, the leaves are thin, of a paler green, and with a silvery white surface ; the blades are in the form of an ellipse, acute at the apex, and gradually narrowing into the petiole. Both of these species are quite constant and do not revert to @. Lamarkiana. However, other mutants have sprung from these two species, especially from rubrinervis, which is produced in greater numbers from Berea than is gigas. F Fic. 20.— A, spike with almost ripe fruits of @nothera gigas, a mutant species; B, the same of @nothera Lamarkiana, its parent form. 66 Mutations 67 Group III, progressive elementary species which make a very weak growth : — (. albida has whitish, narrow leaves, apparently in- capable of producing sufficient quantities of organic food, and hence are very weak. These plants are not suffi- ciently robust to withstand competition in the field and require transplanting into rich soil in pots in order to allow them to live through the first year so that they can produce seed the second year. When these seeds are planted they produce individuals true to type. (. oblongaisasmall plant about half the size of Lamark- zana and may be grown either as an annual or as a bien- nial. It is characterized by its narrow leaves, which are fleshy and of a bright green color. Another striking feature of this type is the presence of numerous little capsules covering the axis of the spike after the fading away of the petals. CM. oblonga is very constant if grown from pure seed. The forms already described are relatively very con- stant and never revert to the parent form. Contrasted with these constant forms, de Vries found several incon- stant types as follows : — Group IV, organically incomplete types :— (E’. lata is characterized by the fact that only pistillate flowers are formed. The anthers seem to be robust, but they are dry, wrinkled, and nearly devoid of contents. It is a low plant with very dense and luxuriant, but brittle, foliage. It has bright yellow flowers which open only partially and remain wrinkled throughout the flowering time. (. lata may be recognized by its seedlings, which have leaves of a nearly orbicular shape and are very 68 « Plant-Breeding sharply set off against the stalk. The mature plant has broad sinuate leaves with rounded tips, which are often crowded together on the summits of the stems and branches to form rosettes. CM. lata may be considered a true mutation, and when crossed with GZ’. Lamarkiana, the progeny of the second generation segregates into mendelian proportions, lata being recessive (Fig. 19). Group V, perfectly fertile but inconstant species :— (EZ. scintillans is characterized by the production of deep green leaves with smooth, shiny surfaces, “glisten- ing in the sunshine.” The plants are smaller and less branched than the parental type. C. scintillans is a very inconstant form; from the seeds which are produced in great numbers, there results not only scintillans, but Lamarkiana, oblonga, lata, and nanella, with a predomi- nance of the parental Lamarkiana. In regard to its in- stability, de Vries says, ‘‘The instability seems to be a constant quality, although the words themselves are at first sight contradictory. I mean to convey the con- ception that the degree of instability remains unchanged during the successive generations.” (EL. elliptica is a very rare form both in the wild state and in cultivation. It is characterized by having narrow elliptical leaves and elliptical petals. ANALYTICAL TABLE OF SEEDLINGS (After de Vries) I. Leaves stalked. A. Leaves of the same breadth or broader.) — 1. Of the same breadth and shape, not to be distinguished as seedlings. 1 “(than in Lamarkiana)’’ as also in the other analytical tables. a. b. Cc Mutations 2. Broader, pointed, with many erumples. 3. Broader, rounded at the tip with very deep crumples, a. b. edge incurved. . Leaves narrower. 1. Broadest in the middle. a. Very long with long stalks, with narrow veins, almost smooth. b. 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J., Mendelian Inheritance in Prunus Hybrids. A. B. A. Rep. 7: 214-227, fig. 1912. Bracn, 8S. A., Report of the Committee on Breeding Tree and Vine Fruits. A. B. A. Rep. 7: 218. 1912. Bruuinc, JoHn, Breeding Experiments with Forage Plants in Florida. A. B. A. Rep. 8: 488-440. 1912. Breuuinc, JoHn, Selection in Pure Lines. Am. Breed. Mag. 3: 311-312. 1912. BuarincHEeM, L., Les problemes de biologie appliquée examines dans la quatrieme conference internationale de genetique. Revue Scientifique, 50: 50: 265-269. 1912. BrartnerD, E., Violet Hybrids between Species of the Palmata Group. Torrey Bot. Club Bull. 39: 85-97, 3 pls. 1912. Burrt-Davy, J., Observations on the Inheritance of Char- acters in Zea Mays. Roy. Soc. South Africa Trans. 2: 261-270. 1912. CasttE, W. E., The Inconstancy of Unit-Characters. Am. Nat. 46: 352-362. 1912. CHristizE, W., Untersuchungen wber alte norwegische Hafersorten. Fihlings landw. Zeitung: 297. 1912. CockErRELL, T. D. A., The Red Sunflower. Pop. Sci. 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Dorsry, M. J., Variation in the Floral Structures of Vitis. Torrey Bot..Club Bull. 39: 37-52, 3 pl. 1912. Dorsry, M. J., Variation Studies of the Venation Angles and Leaf Dimensions in Vitis. A. B. A. Rep. 7: 227-250, fig. 1912. East, E. M., A Study of Hybrids between Nicotiana Bigelourr and N. quadrivalvis. Bot. Gaz. 538: 2438-248, 4 figs. 1912. East, E. M., and Hays, H. K., Inheritance in Maize. Conn: Agr; Exp. Sta. Bull: 167: s387"pp.); 25 pls 2 Rey in Zeitsch. f. indukt. Abst.- u. Vererb. 6: 1938-196. 1912. East, E. M., Inheritance of Color in the Aleurone Cells of Maize. Am. Nat. 46: 363-365. 1912. East, E. M., The Application of Biological Principles to Plant Breeding. In Heredity and Eugenics, pp. 113- 138, fig. 1912. East, E. M., The Mendelian Notation as a Description of Physiological Facts. Am. Nat. 46: 633-655, 1 tab. 1912. Fintow, R. S., and Burxiu, J. 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W., A Mendelian Study of Tomatoes. 3168.0 SON wee oe = 6 cok G95. see ds = 764.5 (oo eee, kk = 874.5 BOLO: ES aE 50 500 18970.0 18970.0 = 37.94 cm. 500 We would get exactly the same result if we arranged the bean plants, in order of size, in a single line, placing them end to end, and then divided the total length of this line by 500, the number of individuals in it. : Average deviation. — One way of expressing variability is to find out by how much, on the average, any individual in the population deviates from the mean, the constant thus secured being termed the average deviation. This is ascertained as follows: the amount by which each class differs from the mean, or in other words, the deviation from the mean (designated by D) is multiplied by the frequency of the corresponding class, and then-the sum of these products is divided by the total 1The Greek letter capital ‘“‘sigma’’ (2) indicates that the sum of a series of values is to be taken. The total number of individuals measured is designated by n. Appendix E 405 number of individuals. The formula for the operation is Df. n Thus in our problem it would be found as shown in the table sao V f D Df Te aay: 28.44 113.76 WS. be 18.44 1327.68 29.5 x 169 8.44 1426.36 39.5 425 1.56 195.00 Ags oe Gt 11.56 739.84 BOR oe. an 21.56 819.28 Boel ae 31.56 347.16 BO ered 41.56 457.16 S95 % 2 6 51.56 309.36 5735.60 5735.60 _ 44.4712 em. 500 Of course, the deviations below the mean (28.44, 18.44, 8.44) are negative quantities, those above (1.56, 11.56, 21.56, 31.56, 41.56, 51.56) positive, but inasmuch as we are here concerned only with deviation from type, we are correct in neglecting these signs, and using the arithmetic sum, and not the algebraic. We would secure the same result if we went along our line of bean plants spoken of above with an average or mean indi- vidual as a measure, added up the lengths by which each one missed of being an average individual, and then divided this total by 500, the number of individuals measured. Clearly this would give the amount by which, on the average, each individual missed of being the mean or the average individual. Standard deviation. — Another constant expressing departure from type, and one which is preferred by biometricians on mathe- matical grounds, is standard deviation, designated by the Greek letter small ‘‘sigma”’ (a). It is found by squaring the deviations from the mean before multiplying by the frequencies, dividing the summation of these products by the number of individuals, 406 Plant-Breeding and then extracting the square root of the quotient. The formula is : — oe Dey C= = le V f Vf D Df D? Df 5-14 | 38.0 28.44 113.76 808.8336 3235.3344 15-24 72 1404.0 18.44 1327.68 340.0336 24482.4192 25-34 169 4985.5 8.44 1426.36 71.2336 12038.4784 35-44 125 4937.5. 1.56 195.00 2.4336 304.2000 45-54 64 £3168.0 11.56 739.84 133.6336 8552.5504 50-64 «=938 =. 2261.0 °21.56 819.28 464.8336 17663.6768 65-74 11 764.5 31.56 347.16 996.0336 10956.3696 15-84 =11 874.5 41.56 457.16 1727.2336 18999.5696 85-94 6 537.0 51.56 309.36 2658.4336 —_15950.6016 500 =18970.0 5735.60 112183.2000 M = 37.94 cm. Av. Dev. = 11.4712 cm. ao = 14.9789 cm. Performing the operations indicated by this formula, we find the standard deviation in our problem to be 112183.2000 = 14. 500 9789 em The squaring of the deviations has the effect of exaggerating the departures of the extremes, and thus the standard deviation is always greater than the average deviation, so that the two are not comparable. For the practical breeder the one is just as good as the other and whether he employs the average devia- tion or the standard deviation is of little practical importance so long as he is consistent in the use of one to the total exclu- sion of the other in the same piece of work. Finding the mean and the standard deviation by the ‘ short method.”’ — Where large numbers are used, the derivation of the mean and the standard deviation by the method presented Appendix E 407 above is a long and laborious process, in which the liability to error is great. A much shorter, simpler, and at the same time more accurate method has been devised. This consists in mak- ing a guess at the mean (designated by G@), and indicating the difference between each class value and this guess in a column marked (V—G). Each of these differences is then multiplied by the corresponding frequency and the algebraic sum of the total negative differences and the total positive differences is found. This is the total amount by which our guess missed the mean for the whole population, and hence we should divide this quantity by n to find the average amount by which we missed our guess. If this amount, which is called the ‘‘correction,”’ is positive, then our guess has been too low by that amount, and it is to be added to the guess. On the other hand, if it is negative, then our guess has been too high, and it is to be diminished by this amount. The formula for this procedure is : — correetion (c) = (Algebraic) 2J6V—@) n M=GeHte. LENGTH oF PLants (SHORT METHOD) V Ih (V—G) f(V—-G) f(V-—G)? 5-14 4 cay Ane Gear's 3600 15-24 72 Boge ato 28800 25-34 169 10... +1690 —3250 16900 35-44 125 0 0 0 45-54 64 10 640 6400 55-64 38 20 760 15200 65-74 1 30 330) 9900 75-84 af 40 440 17600 85-94 a 50) 300 2470-15000 500 Sum = _780 113400 Pig sell Ura C2 = 2.4336 408 Plant-Breeding M = 39.5 — 1.56 = 37.94 cm. c= 4 113400 _ 9 4336 = V224.3604 = 14.9789 cm. 500 14.9785 ~ 14.9785 _ 39 4g og. 37,94 7 In our problem, the mean as determined by this method, as shown in the accompanying table, is exactly the same as was found by the long method, 37.94 cm. We would have secured the same result if, after a casual in- spection of the line of bean plants spoken of above, we guessed that the mean was 39.5, and taking an individual of this length as a measure, we found the total amount which the short ones lack of being equal in length to the assumed mean, or the guess, and likewise the total amount which the long ones exceed the guess. The algebraic sum of these two amounts would be the total amount by which our guess missed of being the true mean, and since 500 individuals were measured, the average amount by which we missed on each individual would be found by dividing this sum by 500. Our assumed length would then be corrected by this amount, just as above. If we had guessed that the mean was 37.94, and went through the same process, then the sum of the negative differences would have exactly counterbalanced the sum of the positive differences, since our guess in this case coincides with the true mean. It would have made no difference whatever had we made our guess at 9.5. Indeed, this would have the advantage that minus signs would be eliminated and thus a frequent source of error removed, since students are prone to forget the algebraic signs. On the other hand, larger numbers would be involved. In finding the standard deviation by the short method, the elements of the (V—G) column are squared before multiplying by the corresponding class frequencies. The sum of these prod- Appendix E 409 ducts is then divided by n, just as in the long method. In find- ing the mean a certain correction was applied to the guess. Now, since we are here dealing with squares, we must apply as a correction the square of the correction found previously ; but unlike the previous procedure, this square of the correction is always subtracted from the quotient found as stated above. (All this has been proven mathematically correct, but the proof is beyond the scope of this study.) The square root is then found as before. The formula for deriving the standard deviation by this method is: — es haeegns n Using this method, we find the standard deviation to be exactly the same as before, as shown in the table above and the following calculations : — 5 =) 118400 (— 1.56)? = 14.9789 em. A further considerable shortening of the short method can be employed when the class values differ by amounts other than unity or a simple multiple of it, such as 10. In such a case the class differences are to be treated as unity and a correction made at the end of the calculation. The modified formule are: M=G + (c X True Difference between Classes). o = | (e- e | x True Difference. The short method, because of its simplicity and its labor- saving features, recommends itself for general use. It is also slightly more accurate than the long method because no deci- ‘mals are dropped until the very end of the calculation. Coefficient of variability. — Standard deviation, as a measure 410 Plant-Breeding of variability, allows of comparison only between similar organ- isms or parts, between such characters as are measured in the same denomination, as tubers with tubers, or height measured in inches with height in inches. This is because it is not an absolute, or abstract constant, but really represents a certain number of feet, pounds, centimeters, or what not. And just as we cannot compare 5 pounds with 5 inches mathematically, so we cannot compare standard deviation in inches with that in pounds. An undenominational abstract constant that will allow of com- paring diverse variabilities, let us say, height with thickness, or pounds with inches, is designated as the coefficient of variability. It is found by dividing the standard deviation by the mean. The formula is ae < 100 and itissymbolized by C. Itis really only the standard deviation measured in terms of the mean. For our beans the coefficient of variability for length is .3948 or since it is usually read as percentage, 39.48 %. This constant is now comparable with any other coefficient of variability for what- ever character or in whatever denomination it may have been measured. Thus we can compare the variability in the length of beans in millimeters with their variability in breadth meas- ured in millimeters or inches, or with height in men or sugar content in beets, if we wish. Probable error. — Probable error does not mean the amount of error that an investigator is likely to make in his experiments or measurements. It means that if he would measure another random sample of a population similar in size and character to the sample he had measured before, the chances are even that the mean for the new sample would lie somewhere between the limits denoted by the probable error. Thus, the mean as to length of plants for our beans is 37.94 em. with a probable error of + .4518. This means that the mean for the new population would not be greater than 37.9400 + .4518 = 38.3918 cm., or Appendix EH All less than 37.94 — .4518 = 37.4882 cm., but would fall some- where in between these two limiting values. It is symbolized by E with the initial of the constant to which it belongs attached in smaller case type. Thus, the symbol for the probable error of the standard deviation is E,; of the mean, Hy; of the co- efficient of variability, E¢. The probable errors are based upon certain relations between the standard deviation and the number of individuals. The greater the number of individuals, the smaller will be the prob- able error. In short, the probable error will indicate how much confidence we can place in our constant, and should always accompany the latter. It is really a part of the constant. In finding the probable errors the constant .6745 is used. This has been derived mathematically and is used by all biom- etricians in the same way. The following formule will show how the various probable errors can be found : — E (G745 =: SBE vi Bs = -- .6745 Sere V2n oa 10% or less.! v2 ae eae A + .6745 an 1+ 123 where C is greater than 10 %.! Our completed constants for length of bean plants are then as follows: — M = 37.9400 + .4518 cm. o = 14.9789 + .3195 cm. C=3948 + .96%. 1In these equations the value of Cin per cent is to be used. The prob- able error will come out as a percentage. 412 Plant-Breeding In the accompanying table the constants for the number of pods borne on these plants are likewise determined by the short method. Note that the column (V—G)? is entirely omitted, a short cut which is another considerable time saver. Instead, — the elements of column f(V—G) are simply multiplied by the cor- responding elements of the (V—G) column since f(V—G) times (V-G) equals f(V—G)?. NuMBER oF Pops (SHorRT MertuHop) \ vi J (V—-G) f(V-G) Ce Gye 5-14 16 —2(0) — 320 6400 15-24 140 —10 ae US Tae ie) 14000 25-34 169 0 O 35-44 115 10 1150 11500 45-54 40 20 ret) 16000 55-64 12 30 360 10800 65-74 3) 40 200 SO00 75-84 3 50 150 + 2660 7500 500 Sum = 940 74200 940 c =— = 1.88 eC = 3.5344 500 Mode = 29.5 ~ Modal Coefficient = 38.36 % M = 29.5 + 1.88 = 31.38 + .3631 (pods). : By Oe 3.5344 = 12.0360 + .2568 (pods). 500 _ 12.0360 ~ 3836 = 38.36 + .93 %. 31.38 ted EXERCISE 3 Correlation Certain characters in organisms tend to appear together and the inference is that they are causally connected, that is, Appendix H 413 one is the cause of the other or else both are dependent upon the same cause. Two phenomena are causally connected if any one of the ~ following four cases is true: — (1) If, when the first is present, the second is invariably present also. (2) If, when the first increases in amount, the second also in- variably increases a proportional amount. (3) If, when the first is absent, the second is invariably absent also. (4) If, when the first decreases in amount, the second also invariably decreases a proportional amount. Because a fixed or absolute relationship exists in each of the four cases the correlation between the two phenomena is said to be perfect, but in the first two cases it is positive in nature, in the second two negative in nature. If absolutely no relation existed between the two phenomena, the correlation would be zero. Now, in the bean problem used in the preceding exercise, it might be asked, ‘‘Is there any fixed relation between the length of plant and its number of pods?”’ Suppose, for example, that if on selecting a plant from the whole lot, it was found to be a long one, could we then say, on this information only, that it will be found to bear a great number of pods? If so, we are assum- ing that some relation exists between the two characters. Let us, for the sake of illustration, suppose that each bean plant bears one pod for every centimeter in length. Because in this case there exists a fixed or absolute relationship, the corre- lation is said to be perfect, and is expressed by 100 %, or more usually simply by unity (1). Now, suppose, however, that on selecting 300 plants averag- ing 80 cm. in length, we find the first 100 plants to bear an average of 50 pods per plant, the second 25 pods, and the third 10, it is clear that if we select one more plant at random and 414 Plant-Breeding measure it to be 80 cm. also, we could no more predict the number of pods it bears than if we had not.measured it at all. Here, then, we say there is no relationship whatever between length of plant and number of pods, or, in other words, the cor- relation is 0. Now suppose a third case, in which we find that invariably the longest plant bears the fewest pods, and the shortest the most. Here we could say the relationship is fixed or absolute too, but in an opposite, or negative manner, and accordingly, the correlation would be expressed by — 1. But now turning back to the first supposition, where it was assumed that one pod was borne for each centimeter length, suppose that the relationship were not so definite. Suppose that one pod occurs not for every centimeter, but sometimes for a little more than a centimeter, sometimes for a little less; then the relationship, though not absolute, is high, and the degree to which this relationship approaches the perfect 100 % relation- ship will express the correlation between the two characters. The correlation coefficient, in other words, would fall between 0 and + 1. We rarely find characters or organs in an organism to be absolutely related; usually they are associated in a more or less intermediate degree, somewhere between 0 and + 1, or 0 and — 1. The degree to which they are associated, or corre- lated, if it can be determined in an exact manner and expressed by a mathematical constant, should be an index of the degree for which one is the cause of the other, or the probability of finding the other when we know the first is present. This may be of importance sometimes to the breeder because some easily seen character may be responsible for, or indicative of, the presence of a desired, but unseen character. Thus a certain shaped kernel of corn (one with a large germ) is known to run high in oil content, one with large endosperm high in starch. To select kernels with large germs is much easier than to analyze Appendix E 415 many ears by chemical methods. Or if, after a relation had been established, we could safely choose the longest or tallest bean plants right in the field and know that they will bear the greatest number of pods, it would be of great advantage to the breeder. Now, an exact determination of the degree of correlation can be obtained by the biometrical method. Let us follow the pro- cess step by step, using our bean data. First of all, we take our data for the two characters for which we wish to find the correlation, length of plant, and number of pods. Our original observations will be somewhat as follows : — No. oF OBSERVATION (or PLant) LENGTH OF PLANT IN Co. No. or Pops 1 27 32 2 46 Q7 3 18 | 45 etc. etc. etc. In finding the constants — mean, standard deviation, etc., for each of these characters, the observations for length and those for number of pods were distributed in separate tables. Now, however, we distribute both sets of observations on one table, in what are known as arrays of a correlation table. (See Table 1.) For example, the first observation tabulated above would fall in the vertical array 25-34, as regards length, and in the 25-34 horizontal array, as regards number of pods. The second observation would fall in the 5th column (vertical array 45-54) and in the third row (horizontal array 25-34). Thus each vertical array would be a frequency distribution of length of plant with respect to number of pods, and each 416 Plant-Breeding horizontal array would be a distribution of number of pods with respect to length of plant. But if we add up all the fre- quencies along each horizontal array, we will get the frequency distribution with respect to the number of pods and it will be exactly the same as that found in the preceding exercise (see table on p. 404); likewise, if we add up the frequencies in the vertical arrays, we will get the frequency distribution with respect to length of plants. The various steps by means of which the constants for length of plant and those for number of pods were obtained were given in the preceding exercise and need no repetition. They are here secured by the “short method” and are given in the correlation table. We are here concerned with the finding of the constant which will express the degree of correlation between these two characters. The only new feature of this correlation table, aside from the method in which the observations are distributed, is the column marked 3P. Kach element of this column represents the total deviation (from the assumed mean, or guess) of the individuals in each array with respect to both length of plant and number of pods. Thus, taking the first horizontal array, the 5-14 class as regards number of pods, we wish to find how much the in- dividuals in this class deviate from the assumed mean for length of plants. It is found as follows : — 3 individuals each deviated by — 30 = — 90 9 individuals each deviated by — 20 = — 180 3 individuals each deviated by — 10 = — 30 — 300 1 individual deviated by + 20 = 20 + 20 Algebraic Sum = — 280 All the individuals in this array deviate from the assumed mean for length of plants by the algebraic sum of the total minus deviations and the total plus deviations, which is — 280, as indicated. But each individual in this array with respect to Appendix E 417 length deviated by — 20 from the assumed mean with respect to number of pods, and hence we must multiply — 280 by — 20 to find the total deviation from both assumed means and this gives us + 5600. All the elements in the =P column are secured in exactly the same way. The third element is zero, since the deviation from the assumed mean for number of pods is zero in this case. The fourth element comes out a minus quantity according to the following calculation: — 1 x —30 = — 30 18 x10 = 180 11 x — 20 = — 220 5 x 20 = 100 42 x —10 = — 420 2x30 = 60 oo xX = ) Ls 405 =~ 40 — 670 a eo = 108 480 — 670 + 480 = — 190 x 10 = — 1900. The algebraic signs for each quantity must be carefully ob- served throughout the calculations. Finally, the algebraic sum of all the elements in the SP column is determined.! This will give us the grand total deviation from both assumed means for all the individuals, and hence to find the deviation for each individual we must divide by 500. Per- 33100 0) = 66.20. Now all along we have been working from an assumed mean, or guess, and we must apply a correction, which, mathematicians tell us, must be the product of the correction for length by that forming the operation we get 1 The elements of the 2P column can be obtained by finding the total deviation of each vertical array with respect to number of pods and multiplying by the deviation of that array with respect to length, instead of vice versa. The elements will be different, but their sum will be exactly the same by either method. 25 Plant-Breeding 418 aye) G6E spog jo aquinn See ea ee eee See eo eee Ena RSET ENE eae eee Rees oY Te Weeaee (O9E0'S1) (68L6°F1) _ 5 MSE ese = = = = = = = : oe ane 00g 1} + | (9¢'T (S8'T)] = Oolee = x is a % 86’ F 9E'8E %96 °F 8h'6E= 0 |S] SO = = spod g9¢z° F 09€0'ZI ‘WH G6IE’ F LZ8L6FI = 2 | | a spod [¢9§° F SEIE ‘“WISICh + FelZE= W - a as, Prec es 98'S = wO w _ rot) “I for) D> "— 88'T OPES Oe alle Oe SoU re ot so Sele Meare Spog ‘ON qysu0T | | | = on HS ou) no an ee bo Je) A ; =) (=n) S (=) (=) (=) j=) (>) (jo) Ou (=) ron feos — =) = - oo D> wo > = OOTEE O0CEL OF6 OOM fs = G0 a on © S ee 0008 oosz | 009% ogt o¢ |e | e 7S-¢2 OO8F 0008 00% OF G j SG I £1-S9 0099 OO8OT 09g og ZI I ‘6 I ¢ I & if £9-S¢ 000¢ O0009T 008 OZ OF I ¢ I 9 ¢ els Ol I $S-CF O06I— | OOSTT OSII OL Gy ra I jG c SI CG: Bip Croat elect lee ies 0 0 0 691 F Z FI GGa) eGr 16S ean PE-GS OOO0T OOOFT | OGZI— OOFI— | OI— | OFT I 9 ZI Of NeP7Gn Ze C-SI 009¢ 00F9 Oz — | OZ— | OL I g 6 © IFS dz x(D-A) § ()-A) 3 D-A J} || F6-G8 | F8-GZ | $2-C9 | F9-Gs | $9-CF | FF-SE | FE-CS | FZ-ST|FI-G| A "md ¢'6Z = D ‘Ud UI JURT JO 4VsUIT sadog 40 uaaWON X INVIG JO HLONGT NOILVIEUOD I WIidVvL Appendix E 419 for number of pods. This product is always subtracted from the quotient of a 66.20 — (1.88 x — 1.56) = 69.1328. Now this corrected deviation must be secured in terms of the standard deviations for each character, and hence this quantity 69.1328 is to be divided by the product of both standard devia- tions :— 9 69.1328 — 3835. 14.9789 x 12.0360 — We have now finally arrived at our correlation coefficient, designated universally by the letter 7, the formula for the deter- mination of which is as follows : — >P SS er ee Correlation Coefficient (7) = GO; G2 Like all other constants the correlation coefficient must be accompanied by its probable error, the formula for the finding of which is as follows : — wy? res .6745 iPS 7) vn Solving this for our correlation coefficient, we find the prob- able error to be + .0257. The amount of confidence which can be placed in the corre- lation coefficient depends upon the size of its probable error largely. Biometricians say that in order to be of much value, the coefficient must be from five to ten times as great as its probable error. But whether the coefficient shows a high, low, or intermediate degree of correlation between the two charac- ters measured depends entirely upon its position with reference to its two limits, 0 and +1 or 0 and — 1. According to the 420 Plant-Breeding size of r found for the data used in our problem, the correlation existing between the length of plant and its number of pods is not great. EXERCISE 4 Statistical Study of Apples from Different Trees Object. —'To study the individuality of fruit trees. Materials. — Apples representing the total product of different trees; scales; calipers. Fill in the following form for each tree. Plot curves repre- senting the entire population of trees. | | NAME OF VARIETY | Tree no. Age of tree Condition of tree Total number of apples Number of marketable apples Total weight of apples Weight of marketable apples Average width of 50 apples Average length of 50 apples COLOR) 259 ey TAME oes tr ee ie eve Any other noticeable differences EXERCISE 5 Statistical Study of Branches of Different Trees Object. — To continue the study as outlined in Exercise 4, to test the individuality of trees. Materials. — Fruit trees of different kinds, preferably dwarf trees; tapes. Measure the new growth of various parts of each tree and of different trees. Plot curves of each tree and of all of the trees Appendix EK 421 Fig. 108. — A common form of ragweed, 422 Plant-Breeding Fic. 109.— Another form of ragweed. Appendix E 423 as a population, to show graphically the extent of bud variation present. EXERCISE 6 Statistical Study of the Quantity of Grapes from Different Grape Vines Use the same general method as in Exercise 4. EXERCISE 7 Study of Variation in Pressed Specimens of Ragweed or Some Plant showing Many Different Types Object. — Careful study of the large and small variations among different biotypes of ragweed (Ambrosia artemisiifolia). Materials. — Specimens of many different types of the above plant or any species of plant which is rich in biotypes. These specimens should be carefully pressed and mounted. (See Figs. 108 and 109.) Have each student make detail drawings to show minute differences. EXERCISE 8 Study of Bud Variations and Reversions in Ferns Object. — To determine the nature and amount of reversion from the parental type, and if possible to find some cause for the same. Material. — Obtain specimens of the sword fern (Nephrolepis exaltata) and Boston fern (Nephrolepis bostoniensis) and as many of the other ferns named below as possible. Study the trueness to type of each variety and any reversions which they may contain. Draw typical specimens. The following is the history, according to Cogswell, of some of the fern varieties. This is not a complete list but gives an idea of the origin of a few common horticultural varie- ties. 424 Plant-Breeding INTRO- DUCED IN SPORT OF (about) | nephrolepis Nephrolepis bostoniensis. . . . . 1880 | exaltata (sword fern) Nephrolepis Pierson. 37.04... 5°. 1903 | bostoniensis Nephrolepis elegantissima . .. . 1904 | Piersonii Nephrolepis ‘Scotti; (1). we ee 1904 | bostoniensis Nephrolepis; Barrowsil ~=2" 24) 2aey <. 1905 | Piersonii Nephrolepis Whitmaniti .. . . . 1906 | Barrowsii Nephrolepis todeaoides 4° 3 0. 1907 | Whitmanii Nephrolepis superbissima . . . . 1908 | Scottii Nephrolepis’*Scholzehi 2°02" .64 0 s.4 1909 | Scottii Nephrolepis Pruessnér,- 2 9. « -:... 1909 | Whitmanii Nephrolepis magnifica . . . : 1908 | Whitmanii Nephrolepis elegantissima compac ta : 1909 | elegantissima EXERCISE 9 Study of the Morphology of Different Kinds of Flowers Object. — To acquaint the student with floral parts and their functions. To determine the proper condition of the buds and flowers for emasculation, crossing, etc. Material. — Buds and flowers of various kinds and in different stages of development; microscope or hand lens; set of dis- secting instruments. The material should represent different natural families or orders. Have the students make careful drawings of the floral organs, of various types of flowers. Take special care to distinguish the stamens and pistils. The following outline by Dr. M. J. Dorsey may be found helpful in this exercise : — Appendix E 425 Stupy or FLowers (prerequisite to crossing) _ Flower — Non-essential organs — Calyx — composed of sepals. Corolla —composed of petals. Essential organs — Pistil — | carpels. a, style; b, stigma; c, ovary { placenta. ovules. Stamens — composed of { loculus or cell. a, filament; 6, anther pollen. Degree of cross-relationship. — 1. Self- or close-fertilization. (Occurring in perfect or her- maphrodite flowers.) 2. Cross-fertilization. (Between individuals of same species or variety.) 3. Hybridization. (Between species and sometimes between varieties which are very distinct.) Causes of sterility. — 1. Stamens and pistils maturing at different times. (Di- chogamy.) ' 2. Lack of affinity between pollen and stigma. 3. Scanty or insufficient pollen. 4. Lack of viability of pollen. Relative position between stigma and anthers. — 1. Stigma and anthers the same height. 2. Stigma above anthers. 3. Stigma below anthers. 426 Plant-Breeding Relative maturity of pistil and anthers. — 1. Both maturing at same time. 2. Stigma matures first — protogyny. 3. Anthers mature first — protandry. Methods of pollination. — 1. Insects. 2. Wind. 3. Water. 4. Self-pollination. Types of plants in regard to sex. — 1. Moncecious (both sexes on same plant). 2. Dicecious (each sex on different individuals within the species or variety). 3. Polygamous (perfect and imperfect flowers on the same plant). Types of flowers in regard to sex. — 1. Imperfect (1) Staminate — bearing only stamens. (2) Pistillate — bearing only pistils. 2. Perfect or hermaphroditic — bearing both stamens and pistils. Determine the following : — (a) Number of parts of flower. — a, sepals; b, petals; c, stamens; d, pistils. (b) Type of flower — perfect (hermaphrodite) or imperfect. (c) Relative position of stigma and anthers. (d) Relative maturity of pollen and stigma. (e) Is the flower pollinated by insects, wind, or selfed? (f) Draw the essential organs and label each part. EXERCISE 10 Technique of the Cross-pollination of Plants This exercise may be carried out in the winter in a green- house or conducted in the fall and spring out of doors, where Appendix E 427 additional expense is not involved in growing the plants under glass. The following suggestive directions may be given to each student : — Materials. —1. Instruments: tweezers; scalpel; small, sharp- pointed scissors, hand lens, etc. 2. For covering flowers: Manila bags, waxed paper bags, cheese cloth, etc. Wire labels, stringed tags, fine copper wire or twine cut into short lengths may be used to fasten the bags. Preliminary study of plant. — Before attempting to cross plants, it is necessary to know the structure of the flower to be used. To do this (A) locate all parts — sepals, petals, anthers, filaments, stigma, style, ovary; (8) determine whether the flowers are perfect or imperfect; (C) learn to recognize the “ripe” or receptive condition of the stigma and pollen. Technique. — (A) Emasculation. (Unnecessary where stamens and pistils are borne on different flowers.) For crossing purposes select flowers in which the anthers have not opened. Re- move the anthers with tweezers or scalpel, taking care not to injure the stigma. It may be necessary to remove part or all of the petals in some flowers in order to get at the anthers, but it is best to remove only the anthers, if possible. (B) Bagging. After the anthers have been removed, the flower should then be covered with some material, as a manila or oil paper bag, to prevent the entrance of foreign pollen. When the stigma is receptive, remove the covering, pollinate with the desired pollen of known purity, and im- mediately cover again, leaving cover on until fertilization has taken place — as indicated by withered or brownish stigma. It is desirable to remove the covering when the cross has “‘set.”’ 428 Plant-Breeding (C) The record. The record should include a description of each parent, giving particular attention to the contrasted characters. Colors may be recorded by comparing with a standard color chart. The female parent should always be mentioned first. The record on the label should include | variety name or number of each parent, date of emascula- tion, and pollination. (Name of worker can also be placed on the label.) As far as possible reciprocal crosses should be made. EXERCISE 11 Embryological Studies from Slides showing Cell Division at Dif- ferent Stages, Chromosomes, Pollen Mother-cells, Development of the Embryo-sac, etc. Provide each student with a high-power microscope and mi- croscopic slides mentioned above. Careful drawings of each slide should be made. EXERCISE 12 Study of Pollen Germination and Fecundation Materials. — Fresh and preserved flowers showing structure of carpels in cross and long section; microscopic slides showing growth and penetration of pollen tubes into ovary, fecundation, etc. For study of germinating pollen, fresh pollen may be germinated in sugar solutions of various strengths mounted in the cells of hanging-drop slides. If this is done at the beginning of the practicum, the germinated pollen will be ready for ex- amination before the end of the period. Careful drawings of all stages observed should be made. The drawings should show all the differences in the length and size of the pollen tube in various degrees of concentration of the sugar solutions. Note also the effect of temperature and other external influences upon germination. Appendix EH 429 EXERCISE 13 Practice in the Cross-pollination of Apples, Pears, Peaches, Plums, ete. To be carried on in the spring, when the trees are in bloom. For general methods of procedure, see Exercise 10. EXERCISE 14 Purpose. —To teach the Laws of Probability ; dominance and recessiveness; segregation and recombination; presence and absence hypothesis; inhibitory factors; complementary factors; inversed ratios, ete. Materials. — Coins, wrinkled and smooth peas, bath yellow and green in equal numbers for two character pairs; yellow and white kernels of both dent and flint corn ; a pack of playing cards; and chemicals. Program. — The instructor should take special care to make clear the significance of each step in the exercise and their con- crete application to problems of plant-breeding and genetics. 1. The Law of Probability is taught by tossing coins. Each student should toss one coin for 2 or 3 minutes and record the number of times it falls head, and the number of times tail. Then the total for the whole class is summed up. It will be found that the latter count, including more tosses, approaches the theoretical ratio much more nearly. This should be ex- plained by the instructor. 2. Then in the same way two coins may be tossed by each student. He now records heads; heads and tails; tails. The application of this law in the formation of gametes should be made clear by the instructor. 3. Now the material may be changed by way of illustration. Peas or corn comprising two allelomorphs may be used for this exercise. They are mixed together in equal numbers in a bag 430 Plant-Breeding and each student draws blindly from the bag one seed at a time, recording his draw. This exercise illustrates segregation and the formation of gametic cells. 4. Now each student may remove simultaneously one pea from each of two bags, and lay them down side by side to illus- trate the mating of gametes in an F, hybrid and the subsequent recombination of characters. He should record only the domi- nant characters present in each pair taken and his record will show the phenotypes of his F, hybrids. 5. The same principles can be illustrated by the use of a pack of playing cards. Draw at random two cards at a time. Record each combination observed. Two blacks coming simultaneously represent a homozygous black individual; a black and a red represent a heterozygous form appearing as black, two reds represent a pure recessive. For illustrating the combination of two character pairs, four cards may be drawn at a time. 6. Some simple chemical reactions ! afford an excellent series of demonstrations illustrating the main features of Mendelism. The following apparatus and chemicals are required : — 4 500 ce. flasks 3 dozen test tubes 1 100 ce. flask 4 small funnels for burettes 1 100 ec. graduate 1 iron stand and clamps 4 50 ee. burettes 3 test tube racks 1 2 ce. pipette 1 pipette dropper 500 ce. 10% ep. NH.OH 500 ce. 5% ep. HCl 500 ce. 25% ep. NH,OH 100 ce. 2% litmus powder 500 ec. 10% ep. HCl solution 10 ce. phenolphthalein While the burettes are not absolutely necessary, they will greatly facilitate the demonstrations. The solutions are to be made up beforehand by the instructor, who should try some pre- 1 This portion of the exercise is based on an article by G. H. Shull, ‘“A4 Simple Chemical Device for illustrating Mendelian Inheritance,” Plant World, 12: 145-153, 1909. Appendix EH 431 DTEMONITAATINN =D ALLELLLMYF YIM AND GF CIM LETE DTOMNANCE | ou Lae, mn Lameles Fi LYGQeES 7 Z7 St S 4 SS Ger & | Y GS] C+ QI q ¥ Pee q q Fig. 110. 432 Plant-Breeding DEMONSTHATION GF FAESENLE ANT AGSENME HYPOTHES/S ANT GF INTEFIMEDALY A SHEE. O27, Lameles Fi ZyGOIrS AA SS Wd Hig Geral Appendix KH 433 liminary experiments to see whether or not the strengths of ‘the solutions are correct. They may have to be varied slightly. The contents of each test tube representing a gamete (labeled in the accompanying figures) are given below. In order to secure the simple 3:1 or 1:3 ratio in F», eight test tubes representing the gametes of F; are necessary in each case. It is of course impossible. to represent the phenomenon of segregation in F by using the test tube labeled F;. The instructor will have to explain that after segregation the gametes are exactly the same in nature as those of the original parents of the cross, and that the hybrid F; now forms gametes similar to those of both parents, in equal numbers. (a) Demonstration of Allelomorphism and of Complete Dominance (Fig. 110). D contains 10 ee. 10% HCl + 2 ec. litmus solution. R contains 10 ee. 10% NH4OH + 2 ce. litmus solution. The dominance of blue over red can be shown by substituting 5% HCl for the 10 %. (b) Demonstration of the Presence and Absence Hypothesis and of Intermediacy (Fig. 111a). A contains 10 ee. 10% NH,OH + 2 drops Phenolphthalein. a contains 10 ec. 5% ACI. (c) Demonstration of Complementary Factors (Fig. 111b). A eontains 10 ce. 10% NH,O8H. B eontains 10 ec. H,0 + 2 drops phenolphthalein. Dominance of a character has usually been taken to be indica- tive of the presence of a positive factor determining that char- acter. But in some eases the absence of a factor, e.g. cases of awnlessness in wheat, or hornlessness in cattle, seems to be dominant over its presence. To say that the absence of a thing, in other words a purely negative condition, is dominant over its 2F 434 Plant-Breeding TIEMONITHATIIN, GF THE FPHESENLE GF AN IMNEITO? § FALTO A a DAME/ES | [ a8 t , BG 2? Appendix E 435 presence seems an absurdity. However, to make the facts consistent with the presence and absence hypothesis, two expla- nations are offered. One consists in assuming the presence of a positive inhibitory factor, which prevents the production of the character concerned. The other consists in assuming that one “dose ’’ of the factor concerned is insufficient to produce the result, hence in its simplex or heterozygous condition, the char- acter determined by the factor fails to appear, and it is only when the factor is in the duplex or positively homozygous con- dition that it does appear. The first of these explanations is embodied under demonstration (d). The last is embodied under the demonstration entitled ‘Explanation of So-called ‘Dominance of Absence.’ ” (d) Demonstration of the Presence of an Inhibitory Factor (Fig. 112). A contains 10 ec. 2.54% NHsOH +2 drops phenolphthalein. Ai equals A +5 ce. 10% HCl. (e) Explanation of So-called ‘Dominance of Absence” (Fig. 113). A contains 10 ce. 10% NH,OH +6 drops phenolphthalein. a contains 10 ee. 10% ACI. After the zygotes of F, are obtained, in this last demonstration, the instructor should add 10 cc. — 10% NH,OH to each Aa zygote of F. to show that another “dose” of factor A will now produce the result. EXERCISE 15 A Study of Mendelian Characters in Timothy and Oats Purpose. — To afford the student concrete illustrations of Mendel’s laws; to find unit characters in plants and to see their segregation and recombination. Materials, — Mature timothy plants of various strains, com- 436 Plant-Breeding EXPLANATION QF SO-LALLEQ TIOMNANEE GF AGSENEL”’ 2 Aa Cae | LAG a DATES Fo Z2yG0lrs — a ee ime. i: iL j— JI Wives ably Appendix E 437 prising as great a variety of unit characters as possible. A small bundle of stems for each student containing samples from different plants. Photographs and mounted specimens. Varieties of oats comprising various unit characters that may be readily distinguished in hybrid plants, such as black and white grains, side and panicled types of inflorescence; also bearded and beardless varieties of wheat or barley. Specimen plants of parent types should be available for inspection, also specimens of the F; plants. A large number of F; plants resulting from each cross studied should be available for examination by the class. Program. — 1. The instructor should first explain the purpose of the afternoon’s exercise and outline the order of procedure. Unit characters are to be studied and illustrated with timothy and oats or barley. Dominance, recessiveness (or presence and absence), segregation, and recombination can be illustrated here. 2. At this occasion a talk may well be given on artificial crossing of small cereals for the purpose of creating new varieties. The instructor may describe the inflorescence of the oat plant, and the technique of making crosses in these plants. He should illustrate the talk with charts and with diagrams made on the blackboard. 3. Mounted specimens of oat types together with the F, and F, progeny resulting from their crossing may be handed around for examination by the class. If enough mounts are available, the specimens may be drawn and described by each student. 4. Composite samples of timothy should be handed to each student. He should study them to see what diversity of unit characters can be found there, in the nature of differentiating botanical characters. A list should be made of all the unit characters observed. Drawings of timothy heads may help to train his observation and fix the idea. 5. A large progeny of F, oat plants should be distributed among the class after the parent types have been shown and their differentiating characters discussed. The class may now examine 438 Plant-Breeding the plants given to them, and sort out the segregated characters. When sorting has been completed, the counts for the whole class may be ascertained. It should serve to illustrate the expected theoretical mendelian ratio. Remarks.— Timothy affords very good material for this prac- ticum, especially when bundled and mounted specimens, together with photographs, are available. Oats exhibit excellently contrasted unit characters, but expe- rience shows them rather poorly adapted for class study, except when mounted specimens are used. The reasons for this are : — 1. Side and panicled characters — the specimens are often pressed out of shape, due to drying and storing, and are, therefore, difficult to distinguish. 2. Color. — Black oats crossed with white give oats of inter- mediate color which are often difficult to distinguish from black. White and yellow are impossible of being distinguished by the inexperienced student. Moreover, color in oat hulls varies greatly with the seasonal conditions under which it was grown. 3. Plants are likely to become broken up in handling, thus spoiling the count when mendelian ratios are expected. The first two of these objections can be obviated by using mounted specimens. Other characters such as naked, hulled, awned, and awnless can be illustrated in this way. Probably a better exer- cise would be given by substituting corn for oats. EXERCISE 16 Mendelian Problems Purpose. — To enable students to become familiar with what might be called the mechanics of mendelism by working out mendelian problems by the method of squares. Problem. — Given: Two pairs of contrasted characters — Tall vine (7), dwarf vine (t); Yellow seeds (Y), green seeds (y). Tallness and yellowness are completely dominant characters. Appendix E » 439 1. What gametes will be formed by an F, hybrid individual from the cross between tall, green and dwarf, yellow ? 2. How many offspring will it be necessary to grow in order to allow every combination to appear in the second generation ? 3. How many genotypes will there be? How many phenotypes will appear? In what ratio will the phenotypes appear? How many pure dominant individuals? How many pure recessive individuals? If the combination T Xt gave plants of medium height ion a tall plant with yellow seeds is crossed with a dwarf plant with green seeds, how many genotypes will appear in F.? How many phenotypes? In what ratio? Illustrative problems. — The following problems may be studied by way of illustration. These are taken from actual cases with the tomato, but will apply in principle to other plants, by sub- stituting other unit characters : — Problem 1.— Tall, homozygous (7) x dwarf, homozygous (t) = Tt; F, F, gametes = T';t Be eee ee F, selfed = POLLEN-GRAINS fig 's Te ft tT EGG-cCELLS t Ws tt 440 > Plant-Breeding Phenotypes (visible types) (2%) = 3 TT; 1 tt. Genotypes (actual types) (8%) =1T7T; 2 Tt; 1 tt. Problem 2. — Heterozygous Tall (Tt) x homozygous dwarf (tt). Whenever a plant which is already heterozygous is used as a parent, its gametes will become segregated during their formation, and when the crossing takes place more than one kind of progeny will be produced. In this case the female parent will produce two kinds of egg cells, namely, tall and dwarf. Graphically, this cross may be represented as follows : — PoLLEN GRAINS t t Eae CELLs The male parent is pure dwarf, therefore all of the pollen grains will represent dwarfness only. Phenotypes = 2 Tt; 2 tt. Genotypes = 2 Tt; 2 tt. If the female parent were crossed with a homozygous tall instead of a dwarf, the visible types the first year after crossing would all appear the same (tall) instead of two kinds as above. There would be Phenotypes = 4 TT. Genotypes =2T7T; 2 Tt. Appendix E 441 Problem 3. — The cases which have been considered hitherto show perfect dominance of one unit over another. This is not always the ease. It frequently happens that the first generation hybrid is intermediate between the two parents, and in the second gen- eration the heterozygote forms differ from either homozygous form. Thus when large, round tomatoes are crossed with small, plum-shaped ones, the F; hybrid is intermediate between the parents. If ZL represents largeness and (/) small, plum-shaped, then F, hybrids (ZI) will not be the sameas (LL), but will be distinctly different. The formule previously given, 2”, 3", etc., will not hold in cases of incomplete dominance. This will be more fully explained later. Large (LZ) X small, plum-shaped (lt) = Ll, an intermediate type of fruit. F, gametes = L, l. F, selfed = PoLLEN GRAINS L l L LL a Eaa CE.LLs l Ei ll Phenotypes = 1 LL; 2L1; 1 ll Genotypes =1 LL; 211; 1 ll. Problem 4. — Intermediate (Zl) x Large, round (LL) 442 Plant-Breeding PoLLEN GRAINS L L ip LL LL Eee CELLS | l Ll Li Phenotypes = 2 LL; 2 Ll. Genotypes =2 LL; 2 Lil. Problem 5. — Tall, smooth (Th) x dwarf, Hairy (tH) = Tall, Hairy (TtHh) Pvcametes: = i Ph tid 5 tie. F,selfed = PoLLEN GRAINS TOT: Th vee th Shak Th Eca@ CELLS Appendix E 443 Phenotypes (2") = 9 TH; 3 Th: 3 he Ra a fe Genotypes (3") = 1TTHH,1TThh, 1 ttHH, 1 tthh, 2 TTHh, 2 ttHh, 2 Tthh, 2 TtHH, and 4 TtHh. ~ Problem 6. — Tall (Heter)! smooth (Tth) x dwarf, Hairy (tH). Female gametes = Th, th. Male gametes = ?¢H. PoLLEN GRAINS tH Th TtHh Eaea CEs th ttHh It will be seen that two types are produced the first year after crossing instead of the one where pure parents are used. Segre- gation takes place immediately in the female parent because of its hybridity, and two kinds of gametes will be produced. In order to get a comparison with the F, when pure parents are crossed, it is necessary to self both types as follows : — (a) TtHh produces gametes as follows, Th, Th, tH, th. These are the same as in problem 5 and hence the resulting plants will be: — Phenotypes = 9 TH, 3 Th, 3tH, 1 th. Genotypes = 1 7TTHH, 1 FThh, 1 tHHA, 1 tthh, 2 TTHh, 2 tHh, 2 Tthh, 2 TtHH, and 4 TtHh. (6) ttHh produces the following gametes: tH, th. <2 1! ister’! is used ‘for short in place of heterozygote, similarly ‘“‘homo” is used for homozygote. 444 Plant-Breeding POLLEN GRAINS tH th tH Eaa@ CELLS th tt tt Hh hh Phenotypes = ttHH, tthh. Genotypes = ttHH, 2 ttHh, 1 tthh. Problem 7.— Tall, large-round (7L) x dwarf, small plum-shaped (tl) = Tall intermediate (TtLl). Hy eametes = TD: Tle ue sil: POLLEN GRAINS TL ia tL tl Ri CELE | Pr U Ti TtLl Taner Tl UIC INN A IEE: HT by5 Ttll Eaa CELLS ; = iL TOT | REEL (tLL ttLl tl TtLl | Till (tL tll It must be remembered in this problem that we have incom- | plete dominance in one allelomorphic pair, therefore the number of visible types is different than in cases where both units exhibit dominance. Appendix E 445 Phenotypes = 3 TTLL, 6 TTLI, 3 TTI, 1 t#LL, 2 ttLil, 1 till. Genotypes = 1 7TLL, 1 TTU, 1 ULL, 1 tll, 2 TTL, 2 Tiil, 2 Till, 2 wLl, and 4 TtLi. What visible types would be produced if incomplete dominance occurred in both characters? Problem 8. — Self-fertilize-Tall, intermediate (77TZI1). This is a pure tall, hence all of its progeny will be tall. POLLEN GRAINS TL Tl TL Vi i TELL Eae Cr.LLs Ei f BES BST TTI pe Ani sSsmiliotneies vend Phenotypes = 1 TTLL, 2 TTL, 1 TTuw. Genotypes = 1 7TIl, 2 TTL, 1 TTUl. EXERCISE 17 Ear-to-Row Test with Corn Field Practicum Purpose. — To demonstrate to the student the method of testing out the transmitting power of individual plants; to show him how a breeding plot should be arranged for corn; to teach him how to harvest the corn and make notes on which to base his selections. A practical demonstration of the method of pure line selection. Materials. — For each student a sack for holding ears, wired tags and strings for tying sacks, and sheets for taking data. A wooden rack with spikes for drying ears of corn. Grocery scales for weighing the ears from each row. 446 Plant-Breeding Data SHEET FOR CORN SELECTION (Kar-to-Row Method) Mark Dent (+); mark Flint (V). No. of row Total no. of hills Total no. of stalks No. barren stalks Total no. of ears Total wt. of ears No. mature ears Wt. mature ears No. immature ears Wt. immature ears Percentage mature ears Percentage immature ears Choose 10 of the best-looking ears from one row on which to take the following data :— Wt. of ears Length of ears Circumference ! of ears No. of rows per ear Wt. of shelled corn Wt. of cob A field plot planted by the ear-to-row method, saving unused half of each ear for comparison with its progeny. It should contain two or more rows, as space permits, for each student. Each row should contain 50 hills. The rows should be planted 1 Circumference should be measured at a point about 3 of the distance from the butt toward the tip. Appendix E 447 and cultivated under regular field conditions. Two buffer rows should be planted completely around the plot. These should be cut and discarded before the interior rows of the plot are studied. Their purpose and use should be explained to the class. Program. — After the instructor has explained the purpose of the practicum, and the manner of procedure for the afternoon, the class may be taken to the field. Each student should have one or two rows for himself. Students may be permitted to work in pairs, if desirable. Careful and detailed notes should be made on each row and recorded on data sheets provided for that purpose. The corn may be taken back to the laboratory for weighing. Statistics for the whole plot should then be compiled, so that the individuality of different rows can be compared. The student should select 10 of the best ears from each of his rows and put them on the drying rack provided. These ears are to be used later for a study in the laboratory. EXERCISE 18 Corn-judging Students of plant-breeding should be trained to have a critical judgment of agricultural and horticultural plants. Exercises in comparative judging are the best way to attain this end. Utility should be kept constantly in mind. Details of corn judging will not be given here; they are too well known to need emphasis. For the East, both dent and flint varieties should be used. The ears which are judged in this exercise may be the ones the student himself has previously harvested from the ear-to-row plot. The best ten ears should be used for Exercise 19, which should always accompany exer- cise 18. Object. — To encourage critical judgment of corn and, by the same means, of other crops. 448 Plant-Breeding Materials. — Ten ears of different races and types of corn to each student; tape, scales, charts, etc. Each student should score a sample of flint corn according to the following score card : — New England Flint Points Maturity and seed condition . . . Release ayy te one 20 Uniformity (or eee of single ears) DNL Tire a OTS 15 Kernels<)47 i oo c.8 Bea a a eae ho! cae Oe 15 Weight of ear . . eRe RSiirs Itc! Soh ines eerie nC aNe 10 Length and proportion Sap te ea ete Ge eae hae iene WEEE, 10 Maps. ies. SPUN AIMS CANE ean Woesiag eC ett 5 BuGtSs: ae: Sat Daa ah bik OE eg cA 10 Sulci (space between rows). Ate Rati irl Biliran 10 GOLOE AO We ne Bg ena ee ae yc ge ed alam ae Mega ae ee) 4G 21] pec gM Se Re AAT er Sey ce wc I 100 EXERCISE 19 Statistical Study of Ears of Corn This should accompany or follow Exercise 18. Object. — (a) To study critically and statistically the various parts of ears of corn. (6) To work up these data by biometrical methods, drawing curves, and ascertaining mean, standard deviation, coefficient of variability, etc., for the various parts of the ear. (c) To illustrate testing for germination. Materials. — Each student should be given the same ears of corn which he had for Exercise 18; tapes, scales, etc. The following form should be filled in by each student : — Notes. — This should not be merely a mechanical process, but the student should give each step very careful thought. These tables are given to assist in organizing the student’s method and his thinking, but not to replace them. Do not study the method but the plants. Consider carefully the significance of each step. Appendix E 449 STUDY OF CORN Variety: Dent, flint, sweet, pop. (Underline.) Where grown (a) Length of ear in em. (b) Cireumference of ear in em. (3 butt to tip) (c) Weight of ear (d) Number of rows (e) Cireumference of cob (4 butt to tip) (f) Weight of shelled corn (g) Weight of cob (h) Percentage of shelled corn (¢) Total number of kernels (j) Average weight of kernel (k) Width of kernels in em. (taken at ran- dom) ; (1) Compute average width (m) Length of 50 kernels in em. (taken at random) (n) Compute average length EXERCISE 20 Study of Correlations of Characters in Corn Use the same data as employed in Exercises 17 and 19. Make correlation tables by accepted biometrical methods of such characters as length and circumference; length and number of grains; weight and number of grains; length and weight ; etc. Work out correlation coefficients. Object. — To find out if certain characters are associated so that a measurement of one will give an indication of the other. Materials. — Data from Exercises 17 and 19; cross-section paper. are! 450 Plant-Breeding EXERCISE 21 Corn Selection — Laboratory Study Purpose. —To give the student an understanding of the qualities that constitute a good ear of corn; to teach the bene- fits and dangers of cross-pollination. Material. — For each student: 1 tape measure; 1 scalpel; 1 hand lens; 10 ears of corn selected from a row in breeding plot; samples of various types and colors of corn. These should have been shelled and soaked in water for 24 hours pre- vious to this laboratory period in order to render them easy to dissect. Cobs of corn bearing mixed kernels to illustrate zenia ; scales; data sheets; germinator. Program. — The instructor should first explain the purpose of the practicum and outline the afternoon’s work. He should explain the structure of a kernel of corn, calling attention to the difference between the various types of corn and the ad- vantage of certain shaped kernels. Fecundation should be thoroughly discussed, and its effect in causing zenia. Illustrate with diagrams, charts, and specimens. Discuss the dangers of mixing varieties by close planting. The danger of close fertilization and the stimulus resulting from cross-fertilization should also be discussed. The advantage and manner of making germination tests should be explained. The student should remove 6 kernels from each ear and place them in the germinator to be examined later, at which time he should record the percentage of germination. Questions and problems concerning zenia printed on the outline sheet should be answered in a written report. Laboratory Directions for Corn Study 1. Complete taking data on 10 ears of corn. Compare with remnant half of parent ear. From your data select the best 3 ears for breeding purposes. Appendix H 451 2. Remove 6 kernels from each ear for germination test, along a spiral line from 1 inch of butt to near the top, revolving the ear twice. 3. Draw a typical kernel. (a) Face aspect. (b) Side aspect. 4. Make and draw longisections through the middle line both ways of the kernel, showing the following structures: — (a) Mass of starch or endosperm. (b) Crescent-shaped body, the germ or scutellum near the smaller end of the grain. (c) Remaining portion of embryo lying in the depression between scutellum and seed-coat. (d) In sample kernels where does color lie, in the pericarp, aleurone layer, or endosperm ? (e) Note relative amount and position of starchy and horny endosperm in 1. flint kernel, 2. dent kernel, 3. pop-corn kernel, 4. sweet-corn kernel. 5. How would an F;, kernel of corn appear in a cross between 4 g white sugar x yellow flint? yellow flint xX white sugar? white flint X purple flint? purple flint x white flint? red sweet X purple flint? purple sweet x red flint ? Dominant Characters. — Colored over white. Yellow over non-yellow. 452 Plant-Breeding Red pericarps may conceal purple aleurone. Purple in aleurone over red in aleurone. Starchy over non-starchy. EXERCISE 22 A Study in Potato Selection Purpose. — 1. To teach the essential characteristics of a good tuber and a good tuber-line. 2. To teach the principles of selection by a study of variability in pure tuber-lines. 3. To demonstrate the tuber-unit method of potato selection. 4. To study variability by means of biometrical data, and the interpretation of constants and curves derived therefrom. 5. To fix in mind how the hills of different weights look. 6. To calculate the theoretical weights per acre when given certain weights per hill. First Exercise Materials. — Printed directions and sheets for recording data. Manila paper bags, size 12, for containing product of each hill. Cloth bags for carrying a number of these small bags when filled. A breeding plot planted by the 4-hill tuber-unit method, that is, each four hills having the same progeny-number should come from the same mother tuber, and they should be planted and staked so that the progeny of each hill and unit can be distinguished. This plot should be planted in good soil and given excellent care throughout the season as its usefulness to the class will depend entirely on the condition of the crop at harvest time. The rows and tuber-units should be labeled carefully and accu- ° rately in a convenient way, so that they may be made an object lesson in record-keeping. 453 Appendix EH 454 Plant-Breeding Enough hills should be provided so that each student may have for himself several tuber-units. Five to ten units to each student will be enough if the student is required to observe and compare a large number as they lie in the field. The complete data for the whole field should be compiled by the class as a whole, and distributed to each student for a comparative study. Program. — Just prior to the exercise, each hill should be dug carefully and the tubers replaced where they grew, but exposed to sight, especial care being taken that no labels be mis- placed nor lost. The class may then be taken to the field. The instructor should explain the purpose of the exercise, the principles of pure-line selection as illustrated here, and the method of planting a potato-breeding plot by the tuber-unit method. He should give careful instructions for the after- noon’s work. The class may then examine and compare the units as they lie exposed in the rows. The instructor should point out such differences as occur. A certain number of tuber- units should then be assigned to each student, and he should be required to take data from these units, as directed on the printed sheets provided. Such data-taking as involves the use of apparatus will necessarily have to be postponed until the following period, when it can be done in the laboratory. Each student should carefully preserve his tubers properly labeled for the next laboratory exercise. Second Exercise Materials. — Data taken in Exercise 1; the tubers collected in Exercise 1; scales; paper plates (6 for each student). Program. — The instructor should first outline the afternoon’s work. He should explain the qualities that constitute a good tuber; also how that ideal form, size, and color differ in various varieties. He should explain a score-card. The students may now proceed to finish taking the data on the tubers that they collected at the previous laboratory period. Appendix EH 455 When the data are complete, they can all be summed up for each tuber-unit and the units compared. Each student should next make out a score-card embodying the points of his ideal unit, and score his units by it. The instructor may now give out a score-card by which the whole class may score their units alike. Make up hills weighing 3, 1, 14, 2, 3, and 4 pounds, and draw them natural size. Compute the yield per acre from the above weights per hill, assuming the hills to be planted in rows 3 feet apart and 18 inches apart in the rows. One bushel weighs 60 pounds. Directions for Report on Potato Selection 1. Distribute the data for the number of tubers per hill into classes. 2. Determine the mode, modal coefficient, mean, standard deviation, coefficient of variability, and their probable errors for the number of tubers per hill. 3. Determine the mode, mean, standard deviation, and co- efficient of variability for the number of marketable tubers per hill, weight of tubers per hill, and weight of marketable tubers per hill. 4. Draw Quetelet curve, showing frequency distributions for number of tubers per hill, number of marketable tubers per hill, weight of tubers per hill, and weight of marketable tubers per hill. 5. Distribute into classes the data for the number of tubers per four-hill-unit, number of marketable tubers per four-hill- unit, weight of tubers per four-hill-unit, and weight of market- able tubers per four-hill-unit. 6. Draw Quetelet curves, showing frequency distributions for number of tubers per four-hill-unit, number of marketable tubers per four-hill-unit, weight of tubers per four-hill-unit, and weight of marketable tubers per four-hill-unit. 456 Plant-Breeding 7. Make a transmission curve from the data on the accom- panying sheet. Which progeny units would you select for breed- ing purposes? How do you account for the apparent discrep- ancies which occur, such as the cases where the offspring give a very different yield from their parents ? 8. Taking into account the number of tubers per hill, weight of tubers per hill, number of marketable tubers per hill, and weight of marketable tubers per hill, select the best 25 four- hill-units. Tabulate these, giving their progeny number and data for number of tubers per four-hill-unit, number of market- able tubers per four-hill-unit, weight of tubers per four-hill-unit, and weight of marketable tubers per four-hill-unit. 9. Give briefly your reasons for selecting the above four-hill- units. Draw Galton curves for these 25 four-hill-units, showing variation in the number of marketable tubers per four-hill-unit and weight of marketable tubers per four-hill-unit. 10. Determine the possible yield of marketable tubers from an acre of the highest and lowest yielding of the 150 four-hill- units, also for the highest and lowest and for the average of the 25 selected units. 11. Give a short summary of results as shown by the con- stants and curves and their bearing on your final selection. 12. Give direction for starting a potato breeding-plot.! Potato Data for making a Transmission Curve The following data have been obtained by the method out- lined above. They represent the weights in grams of parent hills and the average weight of their corresponding progeny. The parent hills have been listed in the order of their weight from lowest to highest (forming a Galton curve). 1 Reference: H. J. Webber, ‘‘Plant Breeding for Farmers.’’ New York Agr. Exp. Sta., Cornell University, Ithaca, N. Y., Bull. 251: 162-171, 1908. Appendix E 457 Nos PARENTS PROGENY || Nos. PARENTS PROGENY 1 1077 1463 26 1588 1454 2 1106 1080 eae 47 1588 1615 3 1106 1240 28 1616 1175 4 1361 1881 29 1616 1575 5 1361 837 30 1644 1775 6 1361 1136 31 1644 1807 Z 1361 1536 32 1644 1917 8 1361 1605 33 1758 2250 9 1361 1660 | 4 1814 1660 10 1361 1800 39 1871 1275 11 1361 1895 Lek oo 1871 1: 80 12 1389 1972 Lala SN 1871 1665 13 1418 1696 WORE cs: 1871 1688 14 1418 1904 le ao 1871 1750 15 1471 1440 fay AO 1874 1555 16 1474 1086 41 1874 1861 Lig 1474 1215 42 1874 1889 18 1474 1480 43 1928 1440 19 1531 (ee: 44 1928 1481 20 15a8 1294 45 1928 1620 21 1531 1574 46 1928 1982 22 1531 1725 eae: 274 1984 1575 23 1531 1755 he 48 2041 1236 24 1588 1320 | 49 2041 1880 25 1588 1365 one ses) 2098 2365 EXERCISE 23 Study of Citrus Hybrids Object. — (a) To study the possibility of obtaining valuable kinds of citrus fruits by means of hybridization. (b) To study the structure of citrus hybrids as compared with their parents. (c) To study the economic value of these hybrids. Materials. — Obtain from some of the extreme southern ex- 458 Plant-Breeding periment stations, or from nurserymen or growers, samples of citrus hybrids, such as citranges, tangelos, and the like, and samples of Citrus trifoliata. Purchase oranges, lemons, grape- fruits, and tangerines from the fruit stores. Provide also for each student, or group of students, a glass, spoon, sugar, and water. Compare the hybrids with their parents, with special reference to the following points : — (a) Fruit — size, shape, color, amount of juice, quality of juice, condition of segments, etc. (b) Trees (if branches or photos are available) — size, shape, branching, kind of leaves, etc. (c) General — length of season, resistance to cold, ete. Squeeze out the juice from several fruits, add sugar and water, and test the adaptability for beverage and other economic purposes. EXERCISE 24 Study of the Results of the Plant-to-Row Tests of Wheat, Oats, Cabbage, Onions, or any Crop where Data are Available EXERCISE 25 Studies of Origin of Varieties — Corn, Wheat, Apples, Plums, Grapes, Etc. Literature study of the history of varieties. Methods em- ployed to originate varieties should be carefully noted. EXERCISE 26 Field Trip to Experimental Grounds Most experiment stations have plant-breeding experiments under way, and if a fall inspection of the plats would be in- structive to students, they should be taken on such a trip early Appendix HK 459 in the fall and required to make careful notes, to be written up later in the form of a report. EXERCISE 27 Working Plans for Practical Breeding Experiments Object. —'To familiarize the student with field methods of breeding plants. Outline for Timothy Breeding First Year. — Select 10 heads of timothy and grow 50 plants from each. 100 ft. 10 rows. 4O ft 500 plants in 10 rows 100 ft. ; long. Plants 2 ft. apart in the rows. Second Year. — Cultivate. Third Year. — Choose several of the best plants from the best two rows, and the one best plant from each of the other rows — 14 or 15 in all. With the seed from these, plant a “test plat,”’ and plow up the original seedling plat. 60 ft. 15 rows. 60 ft. Rows 4 ft. apart — plants 2 ft. apart in the rows. Fourth Year. — Cultivate the test plat. Fifth Year. — Choose 2 or 3 or more of the best rows and save separately the seed from each. Plow up the remainder of the rows and plant to vegetables. 460 Plant-Breeding 60 ft. 4 selected rows. Plant }% acre multiplication plat from each select row. 60 ft. Seed them broadcast at the rate of 16 pounds per acre. Remainder of the plat utilized for vegetables. Sixth Year. — Use seed from multiplication plats to plant a fairly large-sized field. | Continue selection of seedlings, if de- sired, from select rows according to above scheme. Outline for Selective Breeding of Timothy First Year. 1. Manner of procuring seed from starting a selec- tion. — When timothy is ripening, go over a field and choose a number of good ripe seed-heads from tall, robust culms which appear to come from good plants. Also look for exceptionally good plants from along the roadsides and fences, and whenever they are found, preserve good heads for seed. Choose good seed- heads from at least 10 or 12 of these good plants. Thresh the seed from these heads, keeping the seeds from each plant sepa- rate, and sow them immediately. No time should be lost. 2. Planting the seed. — The seed should be planted early in August. Take small boxes about 2 feet long by 13 feet wide and 4 inches deep; fill them with good soil from some locality where there has been no timothy and thus where there is little likelihood of timothy seed being in the soil. Pack the soil down slightly in the box and smooth off the top, removing all lumps. Plant the seed in the boxes in short rows, placing the rows about 2 to 24 inches apart. In planting the seed open shallow furrows in the soil and sow the seed by hand, arranging so that the seed will be only very lightly covered. Sow the seed as thinly as possible in the rows and thin out later so that the plants will Appendix E 461 stand about 1 inch apart. Sow enough seed in rows of sufficient length, so that when properly thinned there will remain about 300 plants. If thinned to 1 inch apart, this will require rows aggregating 25 feet long. Be careful to keep the seeds from each head or plant separate from one another and plainly labeled. After the seed is sown, water the seed boxes carefully, using a fine spray, in order to prevent washing the seed out. A good method is to cover the soil with an open mesh cloth, such as cheese cloth, and sprinkle the water on this until the soil is thoroughly wet.. Then place the seed box in the shade in a moist place, such as the north side of the house. It is a good practice to keep the boxes covered with paper or glass, until the young plants begin to appear. It is important to keep them moist at all times. When the young plants are well up, thin them to about one inch apart in the rows, leaving the strongest plants. The plants should be kept in boxes until about the 20th of September, when they should be planted in the field. About a ‘week before transplanting they should be gradually exposed to the full sunlight in order to harden them up. At this time each plant should have 2 or 3 leaves, 3 or 4 inches long. 3. Transplanting into the field. — Choose a place in the field where the plants may remain for at least two years without being disturbed. Set the plants two feet apart in rows that are four feet apart. By this method the greater part of the cultivation can be done with a horse cultivator. In transplant- ing the seedlings from the boxes, a time must be chosen shortly after a rain, when the soil is well moistened. The plants should be set out about the 20th of September, if possible, so that they may become well rooted before winter comes on. It may be necessary to hoe them before winter, but this is not likely if the land is well prepared before planting. If 10 heads were originally chosen and 50 plants are grown from each head, there should be 10 rows 100 feet long, which would occupy a piece of land 40 x 100 feet. 462 Plant-Breeding 4. Second Year. Cultivating the seedlings. —In the spring the seedlings must be cleaned out very early before they are hidden by other grasses. The cultivation and hoeing must be done at sufficient intervals to keep the ground free from weeds and in good condition. These plants will produce a few culms each the first summer, which should be cut as soon as they have bloomed, in order that the strength shall go into the general growth. Do not attempt to select the best plants the first season. A safe judgment cannot be rendered until the second season. 5. Third Year. Selecting the best plants. — When the plants reach the stage for cutting in the second summer, that is, when they are in full bloom, the final selection of the best individuals can be made. Examine each row critically in order to determine which head or heads have given the best progeny as a whole. If any one or two rows are markedly superior to the others, choose several of the best plants in each of these rows. Also, choose the one best plant in each of the other rows. 6. Testing the selected plants as clonal varieties. — In order to make a further test of the 14 or 15 best plants, choose another uniform plat of fairly good soil between the 5th and 20th of Septem- ber and prepare for planting an area of slightly over 60 feet square. This plat should be located at some distance from any other timothy, preferably 200 to 300 feet. Dig up each selected plant; divide it into slips or clons and plant this new plat with them as before, in rows 4 feet apart. Plant one row with slips from each selected plant, placing the plants 2 feet apart in the rows. Transplant about 30 slips from each of the selected plants, so there will be a single row from each about 60 feet long. This plat may be designated as “the clonal test plat.” As soon as this clonal test plat is planted from the selected plants, the seedling test plat may be plowed up and used for other purposes. . 7. Fourth Year. Cultivation of ‘‘clonal test plat.’ — The Appendix EH 463 clonal test plat should be cultivated and hoed sufficiently to keep the weeds down and to allow the full development of the plants. 8. Fifth Year. Selecting the best clonal rows. — When the plants are well headed and are about to begin blooming, the final examination can be made. Go over each row carefully, and examine it with reference to yield and desirability of type, and select the superior row or rows. It will be best to retain at least 2 or 3 of the best rows; or more, if there is but little difference in them. Good early-maturing and late-maturing rows should be retained if both are present in the test plat. When this selection has been made, cut the crop on the dis- carded rows immediately so that the pollen from these dis- carded rows will not contaminate, by cross-fertilization, the seed which is being developed in the selected rows. At any con- venient time these discarded rows may be dug up and the space filled with new plants grown from cuttings of the chosen plants. By a little care and cultivation these select rows can be retained 5 or 6 years as a source of supply of seed of a superior kind. As the rows of selected types begin to run out, or become impure by ordinary timothy plants around them, or by other grasses erowing in the clumps, other or more extended clonal rows could be planted from them. 9. The multiplication plat. —'The seed from the select rows of the clonal test plat should be sown in the early fall, sometimes before the 15th of September in broadcast plats, as large as the amount of seed obtained will permit. Sow these plats, at the rate of about 16 pounds to the acre. _ There should be enough seed from each row to plant about § acre. Sixth Year. —The seed from these broadcast multiplication plats can be utilized the next year to plant a fairly large field which, if desired, may be harvested for seed to plant still larger areas. These plats may be utilized for seed for several years before they run out. 464 Plant-Breeding 10. Continuation of the selection. — If the farmer has in mind the continuous selection of his seed, with the view of selling his seed as improved seed, he should plant small samples of seed from each of the selected rows in the clonal test plat. Their treatment and subsequent selection should be a repetition of the original scheme outlined above.! General Directions and Questions for Report on Corn Breeding Suppose you buy a farm of 200 acres on which are growing the following crops: potatoes, corn, timothy, and one of the three cereals, wheat, oats, or barley. There are 50 acres of pasture and woodland. You wish to continue growing these same crops, and at the same time to improve them by a scheme of selective breeding. Plan the arrangement of fields and breed- ing plots for the first 6 years, using the following directions. Timothy breeding plots should be 200 to 300 feet from any other timothy. Corn plots 1200 feet from any other corn. (Why?) Each year should be planned separately, using maps and diagrams, but should be included in a definite six-year scheme. Observe proper rotations for crops where desirable. 1. In selecting plants for breeding purposes, why do we choose individual plants? 2. In breeding work, why do we test out the selected individ- uals by breeding each one separately ? | 3. Why is it most satisfactory for the breeder to work with plants that are self-fertilized ? 4. Why do we plant border rows around breeding plots? 5. Why do we detassel alternate halves of adjacent rows in corn breeding plots? 1 For more detailed directions for timothy breeding, see Webber, H. J., ‘*Production of New and Improved Varieties of Timothy.’ Cornell University Agr. Exp. Sta. Bull. 313, 1912. Appendix E 465 6. Why should corn breeding plots be isolated? What is a safe distance? 7. Why should timothy breeding plots be isolated? Whatisa safe distance? 8. Is it necessary to isolate breeding plots of the small cereals? 9. In selection work, what three rules should the breeder follow who understands the principles of pure-line breeding? Scheme for Potato Breeding Plots! First Year. — Choose 500 good tubers. Plant them in a breeding plot by the tuber-unit method. Rows should be 3 feet apart, hills 1} feet apart in the rows. At harvest time choose the best 50 units. Save the best 10 from each of these units for planting a breeding plot the next year. Second Year. — Plant the selected tubers in a breeding plot as in the first year. At harvest time discard all poor units. Select the best 50 units. Save 10 of the best tubers from each of these units for planting the third year’s breeding plot. Use the rest for planting a field crop the next year. Third Year. — Use these 500 tubers to plant a breeding plot. Plant your field crop with the remaining choice tubers. How 1 For details of the following schemes read Cornell University Exp. Sta. Bull. 251, ‘‘ Plant Breeding for Farmers,’’ 1908 ; also Bull. 313, ‘‘ The Production and Improvement of New Varieties of Timothy.” For cotton breeding, see Webber, H. J., ‘‘Improvement of Cotton by Seed Selection,’’ U. S. Department of Agr. Yearbook, 1902, pp. 365- 386. 16.5 ft. = 1 rod; 160.0 sq. rd. = 1 acre. Plant: Corn, 8-12 qt. per acre; Oats, 2~3 bu. per acre; Wheat, 2-3 bu. per acre; Barley, 2-3 bu. peracre; Potatoes, 12—15 bu. per acre; Timothy, 6-8 qt. or 16 lb. per acre. Standard weights: Corn, 1 bu. = 70 lb. shelled, or 56 lb. on cob; Oats, 1 bu. = 32 lb.; Wheat, 1 bu. = 60 lb.; Barley, 1 bu. = 48 lb.; Potatoes, 1 bu. = 601lb.; Timothy, 1 bu. = 45 lb. Average yield per acre in United States for 1902: Corn, 20.2 bu. ; Wheat, £5.95 buy.; moe 37.4 bu.; Barley, 50.4 bu.; Potatoes, 113.4 bu. H 466 Plant-Breeding~ large a field can be planted if the yield has been at the rate of 200 bushels per acre? Fourth and Subsequent Years. — Continue this same scheme, constantly discarding the poor units and selecting the best for breeding. Estimate how large your breeding plot should be in order to supply a 5-acre field with seed in the third year, supposing the yield from your selected units to be the same as the average yield given by the 25 best selected units in your former report, 1.e. about 370 bu. per acre. Scheme for Corn Breeding Plots All corn breeding and increase plots should be at least 1200 feet from any other corn. Why? First Year. — Select from the field 100 ears. From these choose the best 50 for planting a breeding plot the next year. Second Year. — From these 50 ears, plant a breeding plot by the ear-to-row method. Rows should be 4 feet apart, hills 3 feet apart in the row, each row to contain 100 hills. Surround the breeding plot with 2 or more border rows planted with seed from the unused select ears. Why? Detassel alternate halves of adjacent rows. Why? Select from the best 10 or 12 rows 50 to 100 of the best ears, choosing the best 50 for the next year’s breeding plot. Save the seed from the other best-yielding rows for an increase plot, or the general field. Third Year. — Plant your breeding plot as before, with the best selected 50 ears. With the other selected ears plant an increase plot or general field. Select as before the best 50 ears from the breeding plot for the next year’s breeding plot, saving the remainder for a new increase plot. Save ears from this year’s increase plot for planting next year’s field. Fourth and Subsequent Years. — As before, plant your breed- ing plot, increase plot, and field, using a continuous and pro- gressive scheme of selection. Appendix E 467 Scheme for Wheat Breeding Plots First Year. — Choose 100 fine heads for starting your improve- ment work. Second Year. — Plant seed from these select plants in short rows by the plant-to-row method. Space the rows 1 foot apart. Select a few rows, say twenty, to furnish seed for a breeding plot in the third year. Third Year. — Plant seed from each of these select rows in a breeding plot. Do not mix the seed from different rows. Plant as many 17 foot rows in each plot as the amount of seed saved will permit. This is at the rate of 1} bushels per acre. The rows should be 1 foot apart. Fourth Year. — Find average yield of progeny rows that came from the selected rows of the third year. Select several of the best strains which may yield about 24 bu. per acre. With this seed plant increase plots from each kind of seed. Save seed from 2 or 3 of the best yielding plots for more extensive trials in the 5th year. The rest of the seed can be used for planting a field. Make new selections of heads in the fields and repeat the whole program as before. There may be many more valuable types in the fields that can thus be isolated. Fifth Year. — Test out your select strains and choose one or two of the best for increase plots and for planting your field. Plant the field this year with seed from last year’s increase plot and from the test rows. Scheme for Oat or Barley Breeding Plots The principles of selection and methods of breeding these cereals are the same as for wheat. INDEX Absence tactors, 192. Acquired characters, 17. Adami, M., 145. Adams fund, 314. Adam's laburnum, 142. Adaptation, 7, 37, 106. Alfalfa, 313. Alkali resistance, 313. Allelomorph, 325. Allen, Dr., 314, 315. American Seed Trade Association, 309. Anemone coronaria, 57, 58. Animals, breeding, 217. Anthers, 276. Anthocyanin, 186. Antirrhinum (see snapdragon). Apples, 212, 255, 295; hybrid, 235. Arthur, 228, 239. Artificial selection, 37. Asexual propagation and hybridi- zation, 125. Asparagus, 313. Associations, plant-breeding, Atavism, 211, 231. Average deviation, 47. 300. Barker, E. E., 394. Bartel, T. C., 254. Barteldes, 264. Bateson, 155, 183, 187, 192. Beans, 260; Emerson’s experiments with, 189. Bibliography, 335. Biometry, 41, 325. Biotypes, conception of, 19. Blackberries, hybrid, 136. Blackberry, 253. Books, plant-breeding, 328. Braun, Alexander, 20. ‘‘Breaking the type,” 22, 219. Breeding periodicals, 332. Breeding plants, rules for, 222. Broughton, Mr., 91. Browne, Dr. Thomas, 56. Bruant, 237. Brunella vulgaris, 80. Brussels sprouts, 243. Budd, Professor, 258. Buds, methods of emasculation, 291. Bud-selection, 39, 242. Bud-sports, 210, 241. Bud-variation, 11, 29. Bud-varieties, 242. Burbank, 112, 321. Burpee, 264. Burr, ‘‘Field and Garden Vege- tables,’’ 295. Cabbage, evolution of, 267; savoy, 244; shapes, 245; wild, 240. Camerarius, 110. Canadian Seed Growers’ Associa- tion, 304. Cannas, 237, 265. Capsella Heegeri, 80. Carex, little natural crossing in, 103: Carnation, 179. Carriére, 58, 223, 239, 296. Castle, 180. Cauliflower, 248. Cavalier, wheat, origin of, 91. 469 470 Cereals, disease-resistant, 313. Change, of seed, 28 ; of stock, results from, 105, 107. Chelidonium, 55, 56. Cherries, hybrid, 235. Chimera, 146, 148. Chromoplasts, 186. Chromosome, 325. : Chrysanthemum, 251, 252, 2538, 256, 257, 258, 259, 262, 263, 264, 267, 268, 269; carinatum, 226; indicum, 250; tnodorum plenis- simum, 87 ; morifolium, 249 ; sege- tum, 86, 89; segetum plenum, 86, 88. Citranges, 132, 312. Citrus trifoliata, 312. Climate, as factor in variation, 25, 26; man’s control over, 27. Coefficient of heredity, 152; of va- riability, 49. Collard, 242. Color, mendelian inheritance of, 185. Commercial breeding agencies, 308. Composit, 223. Compositous flowers, 279. Corn breeding, 216. Correns, 155. Cotton, 213; 214, 312.313: Council of grain exchanges, 310. County agent, the, 310. Cowpeas, disease resistance, 220. Cross, function of, 101, 230. Crosses, characteristics of, 123. Crossing, a means not an end, 232; and change of seed, 103; effects on the species, 97; from stand- point of plant improvement, 108 ; how to overcome antipathy to, 121; limits of, 97,98, 99; process of, 281; refusal result of natural selection, 100; vigor as result of, ee Lass. Crossing animals, 216. Crossing plants, philosophy of, 92. Crozy, 237. Index Cucumber pollinations, 141. Cultivation, philosophy of, 24. Cupid sweet pea, 77. Curled kale, 241. Cytisus Adami, 142, 145. Darwin, 20, 34, 52, 59, 73, 105, 107, 111, 113, 209, 240, 242, 244, 296, 307. Dates, 313. Davenport, C. B., 183. Davenport, E., 149. Davis, Bradley Moore, 318. Deviation, average, 47 ; standard, 48. de Vries, Hugo, 52, 53, 59, 62, 63, U2 CO, e, 1055 LO ao: Dewberry, 253. Dihybridism, 171. Dicecious flowers, 278. Disease resistance, 219, 220, 313. Dominance, 165; incomplete, 179. Dominant characters, 325. Dorsey, M. J., 424. Double flowers, experiments in production of, 86; history of appearance of, 56. Downing’s ‘Fruits and Fruit Trees,’ 295. Draba, 73. Drought-resistant plants, 313. Duggar, B. M., 318. Duplex, 325. Durum wheat, 313. Ear-to-row, 308. East, E. M., 318. Eckford, 237. Egg-plant, 128, 141. Egyptian cotton, 313. Elderberry, 217, 218. Elementary species, 63, 80. Emasculation, 282. Emerson, 189. Environment as a cause of varia- tion, 16, 216: Epistatic, 325. Index Error, probable, 50. Evening-primrose (see QCinothera). Evening-primroses, laws of muta- bility of, 72. Factor hypothesis, 326. Fairchild, Thomas, 110. Fertilization, 270. Flowers, structure of, 270. Fluctuating variations and muta- tions, 54. Focke, 232. Food supply, as cause of variation, 20, 21; of different branches, 23. Frequency curve, 42. Fultz wheat, origin of, 91. Galton curve, 326. Gametes, 168, 326. Garden varieties, origin of, 18. Gartner, (C. &., 110; 111. Genetics, 326. Genotype, 326. Germ-plasm, action of environ- ment upon, 17. Gibb, 258. Gideon, Peter M., 233. Gladiolus, 237. Glossary, 325. Gmelin, J. G., 110. Goff, 228, 229. Gold Coin wheat, origin of, 91. Gourds, 140. Graft-hybrids, 142. Grain exchanges, council, 310. Grapes, 212, 235; hybrid, 133. Gray, Asa, 35. Green, Ira W., 91. Hallock & Son, 247. Harper, R. A., 318. Head-to-row, 308. Helianthemum, 73. Henderson, 264. Heredity, 149; coefficient of, 152. ; studied collectively, 149. Aga Heterozygote, 326. History of mutation, 55. Homozygote, 326. Hopetown wheat, origin of, 91. Hurst, 192. Husk-tomato pollination, 141. Hybridization and asexual prop- agation, 125. Hybridized, what plants can be, I ke Hybrids, 326 ; history of, 110 ; defini- tion of, 108; influence of sex on, 138; production of, 101; vari- ability of, 122. Hyper-chimera, 148. Hypostatic, 326. Ideal, 220. Illinois Seed Corn Breeders’ Associa- tion, 303. Immature seeds, 228. Implements of pollination, 292. Improvement of plants, systematic, 295. In-breeding, 127. Indeterminate varieties, 209. Individuality, fact of, 2. Individual selection, 308. Inhibitor, 180. Inter-crossing, swamping effects of, 98. Ipomeeas, 229. Kinshu rice, 313. Knight, Thomas Andrew, 110. Kohl-rabi, 248. Kolreuter, J. G., 110. Kumerle, J. W., 265. Laboratory exercises, 394. Lamark, 59. Lemoine, 237. Lettuce, improvement in, 221. Linaria vulgaris (see toad-flax). Linaria vulgaris peloria, 84. Linnezus, 110, 138. 472 Locke, 180. Lupines, 231. Maize, 224. Mass selection, 307. Mean, 45; use of, 46. Measurement of, 41. Mendel, 155. Mendelian inheritance of color, 185. Mendelian ratio, 179. Mendelism, application to plant- breeding, 202, 225 ; in wheat, 194; limits of, in the production of new varieties, 204; of tomatoes; 203; summarized, 200. Mendel’s experiments, 156. Mendel’s law, explanation of, 158. Methodical selection, 307. Minnesota Field Crop Growers’ As- sociation, 303. Mirabilis, 112. Modal coefficient, 45. Mode, 44. Moncecious flowers, 277. Monotypic genera, 224. Moore, Jacob, 235. Morning-glories, Darwin’s experi- ments with, 114. Morse & Company, 77. Morus multicaulis, 299. Munson, Professor, 117, 235. Munting, Abraham, 57. Mutability, laws of, with evening- primroses, 72. Mutants, how produced garden, 71. Mutation, history of, 55; first use of word, 56. Mutations, 40, 52, 326; economic significance of, 90; and fluctua- tions, 54; can they be produced artificially ? 200 ; examples of, 76; experimental study of origin of, 84 ; frequency of occurrence of, 79 ; mutations resulting from men- delian segregation and recombi- in the Index nation, 198; mutations which mendelize are constant, 193. Natal and post-natal variations, 18. Natural hybrids, rarity of, 102. Natural selection, 34, 93; as cause of variation, 14. Navel oranges, 313. Nectarines, 241. New York Plant Breeders’ Associa- tion, 304. Nicotiana pollinations, 142. Nilsson, Professor, 304. Nulliplex, 326. Oats, Swedish select, 313. CGncthera albida, 63, 67, 71, 74; analytical table of seedlings, 68-69; brevistylis, 63, 64, 71, 74; de Vries’ experiments with, 59; elliptica, 64, 68, 71, 74; gigas, 63, 65, 66, 71, 74; levifolia, 63, 64, 71, 74; Lamarkiana, 59, 61, 64,71; 74 > \hlata-64 or 74; muricata, 60; nanella, 63, 64, 71, 74; oblonga, 63,. 67, 71, 74; rubrinervis, 63, 65, 71, 74; scintillans, 64, 68, 71, 74; variations in stature of, 53. Ohio Plant Breeders’ Association, 304. Olives, drought-resistant, 313. Ononis repens, 80. Organs, essential, 274. Orton, 313. Palmer, Asa, 264. Peaches, 212. Peas, Mendel’s experiments with, Lome Pedigree culture, 308. Pelargoniums, 237. Peloric toad-flax, 79. Pepino pollination, 141. Pepper pollinations, 141. Peppers, 222. Index Perennial plants, 241. Periclinal chimera, 148. Periodicals, breeding, 332. Phenotype, 327. Physalis, 104. Pineapple hybrids, variation of, 123. Pistils, 27 Pf. Plant-breeding: associations, state, 300; books, 328; by selection, 218; defined, 212; forward movement in, 294; instruction, 32> Iaboratory, U.S.’ Dept: Agri., 311; projects, 315; use of term, 296. Plant improvement a serious busi- ness, 298. Plant introductions, Sue: Plants, differences compared with animals, 10. Plant-to-row, 308. Plateation, 397; defined, 327. Plums, 212, 294. Pollen, 280. Pollen storage, 289. Pollination, 270; process of cross, 281, 289; uncertainties of, 140. Poncirus trifoliata, 312. Population, 41. Potatoes, 241. Presence-and-absence 181. Pride Butte wheat, origin of, 91. - Probabilities, theorem of, 169. Probable error, 50. Punnett, 183, 184. division of, hypothesis, Quetelet curve, 44. Radishes, division of, 239. Raspberries, hybrid, 235. Recessive characters, 327. Recessiveness, 165. Regel, cited, 295. Reproduction, difference between plants and animals, 10. 473 Retrograde varieties, 65. Rogers’ grape hybrids, 235. Roguing, 251. Russian apples, 212, 258, 295. Savoy cabbage, 244. Score card, use of, 236. Sea Island cotton, 312. Sectional chimera, 148. Seed, change of, 28. Segregation, 327. Selection, accumulative, 209; ar- tificial, 37, 248; individual, 308; mass, 307; methodical; 307; plant-breeding by, 218. Sex, a factor in variation, 15, 215; influence on hybrids, 138; origin and function of, 95. Shirley poppy, 76. Shull, 190, 318.° Simplex, 327. Snapdragon, 83. Snyder blackberry, 255. Solanaceous plants, 222. Solanum darwinianum, 147; Gart- nerianum, 147 ; graft-hybrids, 146 ; kélreuterianum, 147 ; proteus, 147 ; tubingense, 146. Somatic, 327. Species, definition, 8. Species-formation, 8. Spencer, 105. Spillman, 180, 194. Sport, 39. Sprenger, 55. Squares, method of, 169. Squashes, 128, 140. Stamens, 271. State experiment stations, 310. State plant-breeding associations, 302. Statistical methods (see biometry). St. Hilaire, Geoffroy, 58. Stout, A. B., 318. Struggle for life, a cause of varia- tion, 30. 474 Sturtevant, 228. Sugar beets, variation in amount of sugar in, 54. Swede turnip, 248. Swedish Seed Association, 304. Swedish select oats, 313. Swingle, Walter, 312. Systematic improvements of plants, 295. Tangelo, 133, 312. Teas’ Weeping mulberry, 233. Teosinte, 137. Thomson, 149. Thymus vulgaris, 80. Timothy, variability of, 3. Toad-flax, 79, 81, 82. Tobacco pollinations, 142. Lomato, 215, 222. 228; 244, 246: ignotum, 246; pollinations, 141. Trihybrid, 177. Tschermak, 155, 188. Tuber-unit, 308. Type, 43. Unit-characters, 9, 154. United States Dept. Agri., 310. Uses, breeding for specific, 224. Variability, biometrical expression of, 43, 47; coefficient of, 49. Variation, action of natural selec- tion upon, 14; and adaptation, 7 ; causes of, 13, 30, 94; caused by environment; caused by _ sex differences, 15; in climate, 25; choice and fixation of, 34; de Vries’ classification, 53; fluctuat- ing, 54; in food supply, 20;| Index measurement of, 41; natal and post-natal, 18. Varieties, ‘‘coming true,”’ 210, 211; how they originate, 209; inde- terminate, 209; non-uniformity of, 19; outright production of, by. crossing, 118; retrograde, 63 ; spontaneous appearance in wild state, 79. Variety, what is it? 35. Verlot, 244, 296. Vigor as result of crossing, 112, 115. Vilmorin, 226, 230, 231, 269. Waitisael 22. Vries, de, Hugo (sce de Vries). Walker, Ernest, 243. Wallace, 105, 123. Watermelons, wilt-resistant, 219. Wealthy apple, 233. Webber, 133, 156, 312. Weismann, 16, 17. Wheat, Durum, 313. Wheatland fife wheat, origin of, 91. Wheat-rye hybrid, 136. Wier, DBa-2338: Wild cabbage, 240. Wilks, Rev. W., 76. Willis, 117. Wilson, strawberry, 248. 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