JOURNAL OF GENETICS CAMBRIDGE UNIVERSITY PRESS iLonion: FETTEE LANE, E.G. C. F. CLAY, Manager also H. K. Lewis, Gower Street and William Wesley and Son, 28, Essex Street, W.C. CfUinliurBl) : 100, PRINCES STREET Berlin: A. ASHER AND CO. Hetpjia: F. A. BROCKHAUS i^tto Sorfe : G. P. PUTNAM'S SONS Bombaa anJ dalculta: MACMILLAN AND CO., Ltd. All rights reserved w JOURNAL OF GENETICS EDITED BY W. BATESON, MA., F.R.S. DIRECTOR OF THE JOHN INNES HORTICULTURAL INSTITUTION AND R. C. PUNNETT, MA. PROFESSOR OF BIOLOGY IN THE UNIVERSITY OF CAMBRIDGE Volume I. 1910— 1911 Cambridge : at the University Press 191 1 Cambrtirge : PRINTED BY JOHN CLAY, M.A. AT THE UNIVERSITY PRESS QH A-51 MJGA- )lo CONTENTS. No. 1 (November, 1910) PAOE Frederick Keeble and Miss C. Pellew. White Flowered Varieties of Primula siiiensis ......... 1 Redcliffe N. Salaman. The Inheritance of Colour and other Characters in the Potato. (Plates I — XXIX, one coloured, and 2 Text-Figures) 7 Fkederick Keeble and Miss C. Pellew. The Mode of Inheritance of Stature and of Time of Flowering in Peas {Pisum sativum) . 47 E. R. Saunders. Studies in the Inheritance of Doubleness in Flowers. I. Pehinia. (Seven Figures) ..... 57 L. Doncaster and F. H. A. Marshall. The Etiects of one-sided Ovariotomy on the Sex of the OflFspring ..... 70 No. 2 (March, 1911) R. P. Gregory. Experiments with Primula sinensis. (Plates XXX— XXXII and 2 Text^Figures) 73 M. Wheldale. On the Formation of Anthocyanin . . .133 Florence M. Durham. Further Experiments on the Inheritance of Coat Colour in Mice 159 vi Contents No. 3 (August, 1911) PAGE L. DoNCASTBR. Some Stages in the Spermatogenesis of Abraxas Grossulariata and its Variety Lacticolor. (Plate XXXIII) . 179 W. Bateson and R. C, Punnett, The Inheritance of the Peculiar Pigmentation of the Silky Fowl. (4 Text-Figures) . . .185 H. M. Leake. Studies in Indian Cotton. (Plates XXXIV, XXXV, 4 Text-Figures and 2 Diagrams) ...... 205 Redcliffe N. Salaman. Heredity and the Jew, (Plates XXXVI — XXXIX, and 6 Text-Figures) 273 No. 4 (November, 1911) W. Bateson and R. C. Punnett. On Gametic Series involving Reduplication of Certain Terms. (Plate XL and 1 Text-Figure) 293 Edith R. Saunders. Further Experiments on the Inheritance of " Doubleness " and other Characters in Stocks. {2 Text-Figures) 303 L. DoNCASTER. Note on the Inheritance of Characters in which Dominance appears to be Influenced by Sex .... 377 Correction. On Plate XXXIV, to face p. 208, /or " Monopodial " read " Sympodial," arid for " Sympodial " read "Monopodial." Volume I NOVEMBER. 1910 No. 1 WHITE FLOWERED VARIETIES OF PRIMULA SINENSIS. By FREDERICK KEEBLE, Professor of Botany, University College, Reading ; AND Miss C. PELLEW, Research Student, Botanical Lahoraiory, University College, Reading. [It was intended that this paper should be published simultaneously with an extensive memoir by Mr R. P. Gregory on inheritance in Primula sinensis. Mr Gregory's paper is already in type ; but owing to its length and to delay incidental to preparation of the coloured Plates illustrating it, we have been obliged to hold it over for the next number of the Journal. — Edd.] White Flowered Varieties. White flowered varieties of Primula sinensis are of two kinds, one with red or reddish stems (coloured stems) and the other with green stems. Coloured stemmed whites, when crossed with a variety with coloured flowers, yield an Fi with white or tinged white flowers. Green stemmed whites, when similarly crossed, yield an F^ with coloured flowers. Since the white or tinged white ^1 plants give rise, on selfing, to white and coloured flowered plants in the proportion of three white to one coloured, it is inferred that the coloured stemmed whites carry the factors for colour, but that pigment formation is inhibited by the presence of a dominant white factor. Since, also, green stemmed whites give rise, when crossed with a colour variety, to a coloured -Pi, it is inferred that they lack the dominant white factor as well as one or more of the colour-factors. Jonm. of Qen. i 1 2 White Primula sinensis Thus, of white varieties of Primula sinensis hitherto investigated, those with coloured stems are "dominant whites," and those with green stems " recessive whites." One exception to this rule is already known : the green stemmed, white variety Pearl having been shown to be a dominant white. The purpose of this note is to record the existence of what appear to be exceptions to the rule of dominant white among coloured stemmed, white varieties. The evidence is based on the gametic behaviour of Snow King, a variety which has white flowers and dark red stems. Plants of Snow King, raised in 1908 from seed obtained from Messrs Barr, proved true to type, except for an occasional magenta flaking of the petals of a few plants. The variety again bred true to type in 1909. In 1 908, three plants of Snow King were used for crossing with the following coloured varieties : Reading Pink (pale pink flowers, green stem). Crimson King (dark red flowers, reddish stem). Pink Stellata (pale magenta flowers, reddish stem). A green stemmed variety with pink flowers a shade deeper than in Reading Pink, numbered 2 A. It should be remarked that, in green stemmed, coloured flowered varieties of P. sinensis, the deeper flower colours of the self-coloured types are not fully developed. Such plants however carry the factors for the deep colours ; for, when they are crossed with coloured stemmed varieties with pale coloured flowers, the deeper shades are fully developed in the coloured stemmed ofifspring. The Fi generations, obtained from the crosses between Snow King and the several plants enumerated above, were as follows : — Expt. No. Cross Description of f , plants 20-2 Snow King X Crimson King 1 10 tinged white : 9 magenta 52 Beading Pink X Snow King 1 5 ,, ,, : 3 ,, 200 Pink Stellata X Snow King 12 ,, ,, (nearly pure white) 2 A (Green stem x Snow King, flowers pink) 8 pale magenta A uniform F^ family of whites or tinged whites occurs in only one of these crosses. In No. 2 a, the F^ consists of coloured flowered plants and, in Nos. 20*2 and 52, it is composed of tinged whites and coloured in about equal proportions. 1 The same plant of Snow King was used in crosses 20-2 and 52. F. Kkeblk and C. Pellew 3 In order to investigate the meaning of these results which are in disaccord with those obtained hitherto with coloured stemmed whites, coloured and white tinged plants of the Fi generation were selfed, and the F, generation examined. The results were as follows: — F^ from coloured flowered F^ plants. Experiment No. 20*2, a magenta plant selfed. ^2. Observed 20 coloured : 8 white and flaked white. Calculated 21 „ 7 ^ 1 » <^ >? ••• >j jj n Experiment No. 52, two magenta plants selfed. F^. Observed 54 coloured : 19 white and flaked white. Calculated 55 „ 18 „ „ „ 3 1 i> ■•■ » » » Experiment No. 2 Al, two magenta plants selfed. F^. Observed 77 coloured : 22 white and flaked white. Calculated 74 „ 25 F, from tinged white F^ plants. Experiment No. 20*2, a tinged white selfed. F^. Observed 29 white and tinged white : 12 coloured. Calculated 33 „ „ „ 8 » ■*•" >» i> i> " » Experiment No. 52, two tinged whites selfed. F^. Observed 63 white and tinged white : 15 coloured. Calculated 63 „ „ „ 15 „ »» -'•" » »> » " »> Experiment No. 200'1, a white plant selfed. Fj. Observed 13 white : 9 coloured. Calculated 18 „ 4 »» 1" »> " i> In the F, from coloured plants, we obtain approximately 3 coloured : 1 white, and in the F^ from tinged white sister plants we have approxi- 1-8 4 White Primula sinensis raately 13 white (and tinged) : 3 coloured. A departure from the 13 : 3 ratio should be noted in Experiment 200*1 . This must be attributed to the fewness of the F^ plants grown, until more evidence can be obtained. It was noticeable that some of the white plants of F2 from white and coloured Fi, showed a considerable increase of flaking as compared with that observed in certain plants of Snow King. Among those flaked, white plants from coloured Fi plants, there occurred one or two plants bearing flowers with a very faintly tinged ground. Further investigations will, it is hoped, demonstrate the significance of these facts. On the basis of the numbers obtained in F^, we arrive at the following conclusions : — The plant of Snow King used in Experiment No. 200, which gives a tinged ^1, is homozygous (TTTT) for the domi- nant white factor. That used in Experiment No. 2 A, which gives a magenta ^1, is homozygous (ww) for the absence of the dominant white factor. Since the flowers of this plant are white, it lacks a colour factor. That is, its gametic constitution is cw. Since the stem is red, the loss of colour factor has regard only to the flower and not the stem. Writing Snow King cw and plant 2a, Cw, Fi = Ccw = coloured. The plant of Snow King used in Experiments Nos. 20*2 and 52 which give both coloured and tinged white in F^, is heterozygous (Ww) for the dominant white factor. Since the variety as a whole breeds true to whiteness, the heterozygous (Ww) plants must lack colour factors. Their gametic constitution is cWw. Snow King (cWw) x Crimson King or Reading Pink (Cw). Fi = Cc Ww, white or tinged white and Gcww, coloured. i^, = 9 CW, 3 cF, 3 C«;, 1 cw. F^ =lGw,2 Ccw, 1 cw. = 9 white + 3 white + 3 coloured + 1 white 3 coloured : 1 white. = 13 white : 3 coloured. In order to investigate further the nature of the factors necessary for the production of colour in Primula sinensis, plants of recessive white Snow King were crossed with the recessive white, green stemmed varieties of Ivy leaf (for a plant of which we are indebted to Mr Bate- son) and Snow-drift. F. Keeble and C. Pellew 5 From Ivy leaf x Snow King an /*, was obtained consisting of 4 flaked white on dark red stems, and 1 flaked white on reddish stem. Snow-drift by Snow King yielded an F^ consisting of 24 magenta flowered plants with reddish stems. Thus a fully coloured Fy is obtained as the result of a cross between two white flowered varieties. The F^ generation from these crosses has not yet been obtained. Table of Flotoer and Stem colour in F^ stem Flower coloor -^ ^ White "■^ Ko. of Expt >o. Dark and Pale plants not Reddish red Magenta Pink tinged pink flowered CrooH Fi family from (20-2-1 23 — — 14 3 6 — — \ Snow King magenta Fj plants 1 - — 5 — 3 — 2 — — X Fi family from ting- (20-2 -2 28 — — 3 6 17 — 2 Crimson King ed white Fi plant ( — — 15 — 3 — 12 — — ' (52-3 23 — — 10 7 6 — X 9 8 — 1 — — Fi families 2 2 — — from magenta 52 -5 27 17 1 8 1 Fi plants 7 6 — 1 I i - — — 7 — — 2 5 — ^ Reading Pink / 52-4 32 — — 7 2 23 — — Fj families — 9 14 — — 8 12 2 1 Snow King from magenta. F\ plants [52-6 15 — 3 1 14 2 — — ^ 5 — — *. I - — — 5 — — 4 — 1 J /2a1 21 — — 16 — 4 — — \ 5 5 Fg families from 2 magenta -\ Fi plants 2a5 39 6 30 1 9 4 2^x [ Snow King — — 8 5 — 3 — — — 21 — — 6 16 — , Fs family from f 200-2 17 7 — 10 — — I Pink Stellatax white Fi plant I — — 5 — 2 — 3 — — j Snow King THE INHERITANCE OF COLOUR AND OTHER CHARACTERS IN THE POTATO. By REDCLIFFE N. SALAMAN, M.D. Introduction. The experiments here described were begun in the spring of 1906 and are still being continued ; the work has been carried on in my garden at Barley in Hertfordshire. Although the subject material of this research was my own choice, at the time it was determined on I was quite ignorant of the very special advantages as well as disadvantages which the Potato offers for the Mendelian student. To Professor Bateson and Professor Punnett I owe a debt of gratitude for the encouragement they have always given me and the time they have so kindly devoted to examining and criticising my work. The potato plant as grown domestically in England is a perennial, that is to say, it is raised from tubers vegetatively year by year. Most of our varieties bear flowers, but only a very small proportion set seed ; this peculiarity will be considered more fully later, and has already been dealt with in detail (9) ^ The potato flower bears five anthers (sometimes six or seven) arranged in a cone through whose apex projects the stigma. The anthers dehisce at their distal extremities, the pollen, when there is any, falling on to the knob-shaped stigma which projects but a short distance beyond the cone's apex. When cross fertilizations are made, the flower which is to act as the female parent is emasculated before the bud is open while both anthers and stigma are still unripe. The flowers are borne as a cyme, on axial stalks, each bloom having a short stem about an inch long, and at a distance of half an inch ^ The nambera in brackets refer to the Bibliography. 8 Colour and other Characters in the Potato below the base of the flower there occurs a ring of cork. In all potatoes the flowers have a great tendency to separate at this point from their stems : the tendency is more marked in those flowers where the anthers are sterile. If such a flower is used as the female parent the chances of a successful cross fertilization are somewhat less good than if the fertilization is made on one with fertile anthers owing to this habit of separation. In all potato plants, however, when grown out in the open, successful fertilization, be it " selfing" or "crossing," is a hazardous undertaking, and I personally do not succeed in getting more than about "5 % of the individual flowers I handle to set seed. Once the ovary begins to swell there is little fear of separation taking place at the cork ring, indeed the stem gradually thickens and carries the berry late into the autumn. All my work has been carried on without placing the flowers in bags. The reasons for not adopting special precautions were that when bagged the flower invariably drops, that bees and the like never approach a potato flower though a small fly often lives in the bottom of the corolla, that the flower is constructed for self-fertilization, and that the quantity of pollen is so scanty as to render fertilization by the wind in the highest degree improbable. Each year I have sterilized a number of flowers and purposely left them unpollinated, in no instance has any fertilization taken place. In two instances out of some hundreds so treated the ovaries swelled till they attained a diameter of 3/16 in., but they contained no seed and dropped. Although the potato, owing to its scanty pollen, its frequent sterility, and its delicate flower, is not an ideal subject for Mendelian research, it does still off"er to the experimentalist one redeeming char- acter. An individual plant can always be "carried on " by means of its tubers into the next season's work, and whether it be for the sake of comparison or for the purposes of further fertilization this property is of the utmost service. The Scope of the Observations. Attention has been concentrated mainly on the heredity of characters of the tubers, for the haulm or foliage of the potato plant, though variable in habit of growth, size, shape, texture and colour, does not lend itself readily to this type of work. The foliage more especially is so variable in different parts of the same plant, whilst the differences between one type of foliage and another, however apparent, are so difiicult to define that except in one instance, which will be considered later in detail, I have not made out anything sufficiently definite. R N. Salaman 9 The colour of the stem is always correlated in some degree with that of the tuber, but whereas one meets with innumerable white- tubered plants, yet, as far as my experience goes, in all of these some colour may be found, if not in the stem, then in the shoot which emerges from the tuber in spring. Very definite Mendelian segregation of colour in the stem occurs when the black or deep purple pigment, such as is seen in " CJongo," is introduced, but in the case of the red- and white-tubered plants the quality of the pigment being constant, it is the quantity that varies and that is not readily to be measured. In one family of 100 seedlings I ascribed values to the colour as seen in the stem. The parent was a plant with a medium quantity of pigment in the stem. The degrees of pigmentation in the stems of the seedlings were divided into " strong," " medium," and " weak," and the numbers in each class bore to each other as nearly as possible the relation of 1 strong : 2 medium : 1 weak. The absence of distinct and definable gradations between the various degrees of colour, as well as the possible personal bias in the classifica- tion, is my reason for not publishing the results of the observations on colour in stem and foliage which were made in every individual plant during the four years' work covered by this paper. Observations on the colour of the flowers have been made, but only in the case of seedlings of the potato known as Lindsay's etuberosum has anything of interest been observed : a description of the phenomena in the flowers is given in the section dealing with this peculiar variety. Observations on the pollen have disclosed some interesting facts in connection with heredity of sterility and have confirmed East's (4) observation of the relation between amount and viability of pollens. The incidence of disease {Phytopthara infestans) has been closely watched, but only in the case of the Lindsay etuber, q.v., has anything definite been observed. The fact that there has been till now no really immune variety to work with has prevented any headway being made in this direction. The Material used. All the observations, excepting those dealing with the peculiar variety already described by Sutton (s), and known as Lindsay's etuberosum, have been made with ordinary domestic varieties. The most useful of all the potatoes employed has been Sutton's " Flourball," which indeed gives the key to the understanding of them all. The black pigment was introduced by the potato known as the " Congo," a potato which is of a deep blue-black both within and without and which is used domestically for salads. One variety which 10 Colour and other Characters in the Potato proved of value was a white kidney potato known as " Record." It was brought out by Messrs King, of Coggeshall, but it has entirely gone out of cultivation as far as could be ascertained, not only in England generally, but in my garden also, and my notes of its characters are unfortunately not very full. I give here a list of the domestic varieties I have used. In self and cross fertilization. A. Flourball (Sutton). Record (King). Congo. Reading Russet. Red Fir Apple. Queen of the Valley. Bohemian Pearl. Sole's Kidney. Early Regent. Prof. Maerker. S. etuberostim. B. For observations on pollen. Varieties in list A. Ringleader. Supreme. Dutch Cornwall. Peckover. The Dean. Purple Eyes. Up-to-Date. Duke of York. S. commersonii ^ S. tuberosum S. verrucosum S. maglia - species. Several other varieties were used in class A without success. Sterility of Anthers. Con tabescence. Darwin (3), in considering the origin of sterility, describes a con- dition not uncommonly found amongst plants of various families in which the anthers are more or less twisted up or aborted and contain no pollen. Darwin called this condition "contabescence," and described how it might be propagated by layers, cuttings, etc., and even by seed. Gaertner first observed the condition and described a similar change affecting the female organ (6), Bateson described in the Sweet Pea a similar phenomenon and found it recessive to fertile anthers (i). The potato " Record," which possesses no pollen in its anthers, was crossed by Sutton's " Flourball," which possesses abundant pollen : 20^ of the 32 F^ plants which bore flowers not one of which contained any 1 In 1910 26 of the i^^ plants flowered and they were all sterile. R N. Salaman 11 pollen. Two individuals of the F^ family were fertilized by a derivative of " Flourball A," very rich in pollen, and gave rise to 39 plants, 19 of which bore pollen and 20 bore none : the expectation on the assump- tion that sterility is dominant being here equality. In the "Congo" potato the anthers are entirely devoid of pollen, though they are not usually aborted or crippled. A plant of this variety was crossed by a " Flourball " seedling, and out of 18 ^^ plants which flowered, 8 had abundant pollen and 10 had none : here again the expectation was equality, " Congo " being heterozygous in sterility. Two F^ plants possessing abundant pollen were selfed, and of 44 plants examined, 41 possessed pollen and 3 possessed but a few grains of immature pollen. Why these plants should not have borne a fair quantity of pollen seeing that the F^ parents must have been recessives and should have bred true, it is not possible to say. All three examples came out of one family. A second cross with " Congo," viz. by " Reading Russet," gave only a small F^ family, three plants bearing flowers, two containing pollen, and one none. Similar results were obtained in the cross " Red Fir Apple " and " Reading Russet," F^ being part pollen producers, part sterile, whilst jP*, from the pollen bearing F^, gave 9' plants all pollen producers. The flower of the " Red Fir Apple " is heliotrope in colour and the anthers are aborted. " Queen of the Valley " has heliotrope flowers with sterile anthers. Crossed by " Flourball " one plant gave a series of F^ plants of which some bore pollen and others none, although exact notes as to their characters in this family were not taken. One of the F^ plants was crossed by a " Bohemian Pearl " seedling, and gave rise to a long line of pollen producers. The heredity of male sterility in the potato is obviously the converse of that described by Bateson in the Sweet Pea, for the condition here is distinctly dominant. Bateson found it partially coupled mth green axils in certain families. In the case of the potato, the only evidence of sterility being coupled with any other character was of a negative sort. Working with a large number of established varieties as well as with those plants which arose in the course of this work, I never found a plant possessing pale heliotrope flowers that had other than sterile and contabescent anthers, whilst those that were further tested proved ^ In 1910 22 more F- plants flowered and all possessed pollen in the anthers. 12 Colour and other Characters in the Potato to be heterozygous as regards sterility of anthers. No connection was observed between the condition of the male and female organs. The presence of pollen in the anther being as we have seen a recessive character, it is of some interest to note how it behaves in selfed families. Unfortunately these pollen observations were not begun till 1909, although the breeding experiments began in 1906. Still a good deal of information may be extracted from the early notes. Thus, in 1906, a red-tubered seedling derived from a "Flourball" plant in 1904, was "selfed," and gave rise to a large number of seedlings. One white-tubered plant {D) was reserved. From this a further generation was bred, and from this again another, so that in this case the family has been handed through five generations, and in all the anthers have had abundant pollen though the quality of the pollen was bad. Two other lines, A and 0, derived from " Flourball," have been bred through three and four generations respectively, and the recessive character, viz. presence of pollen in the anther, has remained true. The occurrence of spontaneous sterility, due to absence of pollen, has already been mentioned as having taken place in the F"^ generation of the family " Congo " x " Flourball " ; it has also been observed in some other families where it was unexpected, but in all these cases it has occurred in normal and not deformed or strictly " contabescent " anthers. It is possible that " contabescence " is not a simple character but that absence of pollen and deformity of anther are due to separate factors between which exists an intimate linking. The relations between quality and quantity of pollen and the shape of pollen in varieties and species of Solanum are discussed elsewhere (9). Heeedity of Characters in the Haulm. The difficulties in relation to haulm characters have already been adverted to ; although to experts constantly reviewing crops of well- grown varieties it becomes comparatively easy to diagnose a variety by the general appearance of the foliage, and by inspection to designate at once such and such a potato as an " Up-to-Date " variety, or a " Ringleader " type, and so forth, yet if one closely compares any two foliages, taking corresponding specimens from various parts of the plant, it will be found very difficult to describe any constant differentiating character between any two varieties; there are differences no doubt, R. N. Salaman 13 but they do not admit of such definition as to fit them for Mendelian analysis. The cross of " Red Fir Apple " and " Reading Russet " was made in 1906 for the purpose of tuber colour observations, and in 1909 a large family of some 120 individuals of F^ plants were raised. The " Red Fir Apple " has a somewhat distinctive foliage, the leaves are relatively small, ovate with sharp apices, peculiarly soft and silky to the touch, and, in addition, have a character which entirely distinguishes them from " Reading Russet " and most other varieties. The leaf has a peculiar twist in its axis, this twist being seen in all the upper leaves and often down to the lowest when the plant is 18 inches high or more. The condition of leaf twist here in question must be clearly distin- guished from that which occurs as a pathological condition in many varieties ; in such cases the plants are dwarfed, the stems shrunken, the axes of the branches very shortened, and the leaves on them crowded together. The individual leaves also are much twisted, crenate and small. In the "Red Fir Apple" the twist is less violent, it is not associated with crenation, and the plants are thoroughly healthy, vigorous and of good size. " Reading Russet " possesses a much coarser foliage, the leaves are big, broad, blunt, flat, smooth, hard and coarse ; the green colour is of a deeper shade than in " Red Fir Apple." The four F^ plants which were examined were intermediate as regards shape and texture of foliage, but resembled " Red Fir Apple " shape rather than " Reading Russet " ; no twist in the leaf axis was observed. In F- an analysis was made of the plant's foliage characters as seen in the table below. The characters taken are all leaf ones. " Reading Russet " shape. Broad and blunt leaf. „ „ texture. Few stiff hairs, glazed surface to leaf. " Red Fir Apple " shape. Ovate, sharp apex to leaf „ „ texture. Soft and silky. Twist. Twist in the axis of the leaf. Intermediate shape. Leaf shape neither " Reading Russet " nor " Fir Apple " in type, but re- sembling more closely the latter. „ texture. Softer than " Reading Russet " and harder thau " Fir Apple." 14 Colour and other Characters in the Potato Foliage of F"^ Generation. " Reading Russet " texture. " Reading Russet " shape 10 „ „ „ Intermediate shape 1 Intermediate texture. " Reading Russet " shape 4 „ „ Intermediate shape 40 " Fir Apple " shape 12 " Fir Apple " texture. Intermediate shape 9 „ " Fir Apple " shape 42 11 Total number of J^2 plants .... 118 Twist in leaf 27 In considering these figures it must be remembered that it is a matter not only of considerable difficulty to classify the living plants according to the shape and texture of their leaves, but that the personal element is paramount in such a classification. More particu- larly do such remarks apply to the consideration of texture and to the intermediate forms. Certain features, however, are readily and unmis- takably recognized ; these are the twist in the axis of the leaf and to a lesser degree " Reading Russet " shape. The intermediate form of leaf is much more like the " Fir Apple " leaf than the " Reading Russet," and the former may therefore be con- sidered dominant, whilst the twist in its leaf is recessive. If the " Reading Russet " shape and texture are recessive, then it should occur combined in the F^ family in the ratio of 1 : 15 and here it is 1 : 12. The twist in the leaf occurred 27 times out of 118, that is practically in the ratio of 1 : 3, and it was associated 23 times with the " Red Fir Apple" shape, the remaining four having intermediate shapes and none showing " Reading Russet " shape. Allowing again for the difficulty in distinguishing the intermediate form from " Fir Apple " shape and texture, it would seem to be a fact that this peculiar twist in the leaf is definitely linked up with the " Fir Apple " characters of shape and texture. None of the eleven plants possessing " Reading Russet " shape showed the slightest sign of a twist. The same consideration leads one to believe that " Reading Russet" texture is coupled up with "Reading Russet" shape; ten out of eleven times it is recorded as being so linked whilst the eleventh R. N. Salaman 15 time " Reading Russet " texture was united to intermediate shape, which might possibly be an error of observation. These observations demonstrate at least that such fleeting and difficult characters as leaf shape and texture in the potato segregate in the sexual generation. This year^ a fresh F^ family of this cross is being raised, and close attention will be paid to their foliage character. The Shape of the Tubers. No character seemed at first sight more elusive and less likely of solution in respect to its heredity than that of shape. Whenever I spoke to experts I was told that from the best " kidney " types you could pick out "rounds," and that exhibitors had won prizes both for " rounds " and for " kidneys " from one and the same potato. East (5) notes four cases where originally " long " tubered varieties produced as bud sports rounded tubers; in two cases these "round" tubers reproduced themselves vegetatively true to " roundness," while the other two relapsed in the following season. The oval varieties he notes as producing on single plants entire crops of very elongated tubers, which however did not grow true in subsequent years. My observations would lead me to think that these bud sports in " kidney " and oval potatoes are quite common and are to be explained by their heterozygous composition as regards " roundness." A frequent cause of trouble in dealing with the shapes of tubers is the nomenclature. The terms used to describe the diflferent shapes are sufficient for the purpose of the gardener, but they connote no scientific accuracy. Where the cylindrical potato ends and the kidney begins, where the latter ceases and the "pebble" starts, and where both merge into the round is a problem which it would be hopeless to attempt to solve by the mere classification of tubers. It is only by the isolation of a type and its fixation as pure when bred sexually that the problem can be solved. In describing the shape of a potato, two points can be regarded as 1 In 1910 out of 71 F2 seedlings on Ang. 3rd 6 showed the "Fir Apple" twist, on Aug. 23rd 14 had developed it. 16 Colour and other Characters in the Potato fixed, viz. the point from which the tubers grow out from the stolon, and the most distal point from that, which in 19 out of 20 cases coin- cides with the central of the crown of eyes at the distal end. It is from this eye that the earliest and strongest shoot grows out. The line between these two points is the long axis, the breadth and depth are respectively the greatest measurements in each direction measured at right angles to the long axis and to each other. Adopting the conventional terms for potato shapes, the names long, kidney, pebble, and round appear to have the following meanings : — A long potato is one in which the long axis is between \^ and 2| times the greatest breadth, and the depth is equal to the breadth. The ends are either blunt, as in the " Congo," giving the tuber a cylindrical appearance, or they are pointed as in B, Plate XXIV. A kidney potato is one in which the length is usually between 1^ times and twice the breadth, and the depth is considerably less than the breadth, giving the tubers a flattened appearance which is charac- teristic. The measurements of three specimens, unselected, of well- known " kidneys " are : — "Myatt's Ashleaf " : Length. Inches Breadth. Inches Depth. Incnes Ratio (1) (2) (3) 2, 3 2, 12/16 4/16 1, 1, 1, 9/16 7/16 7/16 1, 3/16 1, 3/16 1, 2/16 =44 : 25 : = 48:23: = 36:23: ;19 19 ;18 "Sutton's Ideal": (1) (2) (3) 2, 2, 2, 7/16 5/16 4/16 1, 1, 1, 8/16 10/16 7/16 1, 4/16 1, 4/16 1, 4/16 = 39 : 24 ; = 37 : 26 : = 36:23 :20 ;20 :20 "Table Talk": (1) (2) (3) 3, 3 3, 1/16 1/16 1, 2 1, 14/16 15/16 1, 6/16 1, 9/16 1, 8/16 = 49 : 30 : = 48 : 32 : = 49 : 31 : ;22 :25 :24 "Sir John Llewellyn' > . (1) (2) (3) 3 2, 2, 13/16 11/16 1, 1, 1, 10/16 10/16 13/16 1, 2/16 1, 4/16 1, 7/16 = 48 : 26 = 45 : 26 = 43 : 29 : 18 :20 :23 The Lapstone Potato is a bluntly elliptical or oval potato which is much broader than it is deep. The Pebble Shape. This term includes a vast number of rather irregularly shaped tubers — tubers for the most part obtusely elliptical and almost as broad as they are long. R. N. Salaman 17 Below are some typical specimens : — "Beading Basset," see Plate XXI. Length Breadth Depth RAtio (1) 2, 6/16 1, 15/16 1, 7/16 = 38 :31 23 (2) 1, 15/16 1, 12/16 1, 3/16 = 31 : 28 19 (3) 1, 15/16 1, 13/16 1, 8/16 = 31 :29 24 "Flourball," see Plate I. (1) 1, 15/16 2, 1/16 1, 8/16 = 31 : 33 .24 (2) 2, 3/16 2, 9/16 1, 13/16 = 35 : 41 29 Round Potatoes. The tubers are practically globular, as in " Wind- sor Castle." An examination of these different descriptions is enough, almost in itself, to convince one of their artificiality, but when one comes to close quarters with them by breeding various pure lines and by crossing, one is soon convinced of the fact. If Plate I, seedlings of " Flourball," be now examined, it will be seen that it is easy to pick out^ Longs Nos. 14, 48, 135. Kidneys „ 21, 87, 88, 123. Pebbles „ 74, 90, 91, 154, 179; but a close inspection shows a number of tubers which might be described as round, but which are not globular. They are short, and as deep as they are wide, such as Nos. 40, 89, 92, 112, 132, 138, 155, 156, 162, 185—10 individuals out of a total of 43. If now we turn to Plates II, III, IV, V we shall find a family of 100 individuals all bred from one of these peculiarly shaped tubers (A). The whole family present a striking uniformity of appearance and similarity to the parent. Exceptions, however, there are, and they are figured in full in Plates IV and V. Turning to these plates we see photographed all the available tubers from each of these individual plants, and it will be at once seen that each individual plant in Plate IV contains striking examples of this " round " type amongst its tubers. 1 It should be said that the representatives of the individual plants here shown are when there are ovals and others more resembhng "rounds" present on the same root, always the oval. The bias in favour of the "longs" as against the "rounds" has been purposely made in the composition of all the plates, in order that the recessive "round," when present, shall be free from the suggestion that it is only a variant form of the dominant "long." If therefore the effect to the eye be less convincing the deductions that are drawn rest on a firmer basis. Jonm. of Gen. i 8 18 Colour and other Characters in the Potato On Plate V, Nos. 67, 87, 91, 94, only further illustrate the fact that though certain tubers of a plant in this family may be more or less oval, yet other tubers on the same plant will be found to be of this peculiar " round " type. One exception, however, stands out, and this is No. 100, which is definitely unlike the parent type and all its 100 other sister plants. It is possible that it arose from a stray tuber and does not belong to this series at all — a view that has some plausibility, seeing that two years before " Flourball " seedlings were grown on this ground. Efforts are being made this year (1910) to obtain selfed seed from this plant. On Plate VI a further illustration {Q family) of this "round" type of potato is seen; it arose from a "Flourball" plant, but not the same one as the line A. Seed from four of these plants has been saved and a batch of seed- lings of G* were planted in October 1909 and hurried forward; on April 26, 1910, they were examined and all the seedlings bore tubers, varying from |^ to f in. diameter, true " rounds " in shape. Those of the Q^ seedlings which have formed tubers have also developed typically "round" ones\ It thus appears that there is a certain definite type of "round" potato that can be extracted from Sutton's " Flourball," and which can be bred sexually pure through at least two generations after having been isolated. Before following further the evidence as regards the heredity of this type and its behaviour when crossed with other types, it will be best to discuss more fully its shape and variations. The tuber shape, which is under consideration and which for the purposes of my work I have called "round," is to be found white, or coloured as red or black. No relation has in the course of this research been shown to exist between shape of any kind and the pigmentation either of haulm or tubers. The "round" tubers may be furnished either with "deep" or "fleet" eyes. It will be shown later that depth of the eye is itself a character inherited on Mendelian lines, and my experiments fail to show any relationship between depth of eye and shape of tuber. The size of the tuber is of course variable, but I have not found, however one may have 1 Aug. 29, 1910. Although the G family has not been completely harvested there is evidence that the G^ family consists of three "longs" to one "round," and that the G^ and G* families are pure to "roundness." R. N. Salaman 10 bred it, this type of " round " potato assuming large proportions ; few examples with a diameter over 2 inches occur, although oval and kidney from the same original parent stocks may be of large size and weight. A typical specimen of this " round " type is represented by the first tuber of G*, Plate VI. The tuber is apple-shaped, its upper or proximal end as well as its distal or crown end is depressed, and the height is less than either its width or its depth. The actual dimensions are : — Length Breadth Depth Ratio 1. 5/16 2, 2/16 1, 1/16 =21 : 34 : 17 One of the tubers of the parent A has the following measurements: — Length Breadth Depth Batlo 1, 5/16 2, 2/16 1, 1/16 =21 : 34 : 17 The most characteristic feature is the stumpiness of the tuber in relation to its breadth. Potatoes are raised commercially by the vegetative method, thus a crop of " Magnum Bonums " raised to-day should be regarded as merely an offshoot — a cutting so to speak — of a seedling raised some time before the year 1876. In other words the tens of thousands of tons which in the past 34 years have been grown of this stock are for scientific purposes merely replicas of a particular tuber of a particular individual, and hence the continuity through the intervening years of the variety's characters. Tubers that are grown by this vegetative means, within limits, reproduce themselves in their original shape more or less exactly, though I think, and hope to prove, that the degree to which a potato reproduces its shape vegetatively depends in large measure on its gametic constitution. It may therefore be confidently expected that whilst a crop raised from a typical "round" such as .4 by vegetative means will remain perfectly true to type (and this indeed has been proved in the case of A itself, by growing it in 1908 and 1909), a crop raised say from the fifth tuber of No. 67, Plate V, might produce tubers more or less uniform and unlike the type A. A family raised by seed from any of the individuals, however aberrant in shape, will probably produce a set of seedlings at least as uniform as the family A itself. The variation of this "round" type, if grown vegetatively, so far as my experience goes, is very slight or indeed none at all. The variations of the type as raised sexually by seed are slight but definite, being 8—2 20 Colour mul other Characters in the Potato towards greater length and approaching the pebble shape. In diagram the type and extreme variation may be represented as below : — Fig, 1, These drawings are tracings of sagittal sections of potatoes — the long and trans- verse axes are shown — the depth cannot be shown. Height and breadth are here represented, the depth being relatively great. The " round " type is not a potato that recommends itself for its beauty or its economic qualities as regards shape ; its merit is derived from the fact that there is very good reason to regard it as a gameti- cally pure type, and that " roundness " in the sense in which it has been used here is a simple Mendelian character. The further evidence in support of this thesis will appear as we proceed to discuss other shapes. A seedling of "Flourball" was selfed in 1906, and in 1907 a large number of seedlings were raised from it, one only of which was again selfed in 1907. The plant was carried forward by tubers to 1908, 1909 and 1910. In both 1907 and 1908 it produced seed, but in these two years only four plants came to maturity, and they produced the tubers numbered in Plate VII, D\ D\ 1908, D^ and D\ 1909. The seedlings from 1909 seed have not yet formed their tubers. The tubers of plant D are quite unlike the " rounds " of the A family, they are oval and more or less kidney-shaped. The offspring of these, only four in number (excluding the seedlings now growing), comprise distinct types. R N. Salaman 21 D*, 1908, a long pyriform tuber. D*, 1909, cylindrical tubers tending to kidney shape. />, 1908, oval or blunt kidney with a sister tuber nearer circular. jj , 1 juy ), ,, ,, » The numbers in this case are all too small to draw precise deduc- tions; all that can be said is that D does not represent a fixed type, that, on selfing, it gives both longs and ovals. In 1908 this same D was crossed by A, and on Plate VIII the family is shown, or rather two families, because two D plants (D' and D^) both grown from tubers of the original D of 1907 were fertilized by pollen of A. A glance at the plate is enough to show that one has here two types of tubers, the " round " that we have already discussed on the one hand, and a series of ovals and kidneys on [the other. The "rounds" are: Nos. 3, 4, 5, 8, 13, 14, 15, 16, 18, 19. 3, 6, 7, 8, 10, 12, 14, 18, 19, 20, 21, 22, 28. That is, 10 out of 19 in the first family, and 13 out of 30 in the second family. Total, 23 out of 49. One has, in other words, "rounds" and not "rounds" in practically equal numbers; and it must be remembered that one counts here only those as " rounds " which come well up to the standard already given for a typical " round " such as either A, G^ or G'. The result of this cross admits of a direct Mendelian interpretation, for inasmuch as A is pure to " roundness," D must be heterozygous in that character — a fact which was already strongly indicated before. And the " non-rounds " must be all heterozygous in shape. If now one examines more closely the " non-rounds," one sees that they are made up of good kidneys such as Nos. 1 {D^ x il), and 1, 4, 11 and 26 of (D^xA); of cylindricals, such as 5 and 23 (D* x J.), while the remainder are ovals and pebbles difficult to place, but which include among themselves abundant examples of the same shape as the parent D. The experiment therefore as portrayed in Plate VIII is capable of being interpreted as meaning, not only that an oval " pebble " such as shape D is heterozygous as to " roundness," but that a true kidney and a true cylindrical may also be heterozygous in the same degree. Further, if "roundness" (i.e. shortness of axis) is the one allelomorph here in action, then " non-roundness " or length is the other. Later evidence 22 Colour and other Characters in the Potato will be given proving that there is a tuber shape true to length, but before bringing this evidence forward it will be necessary to discuss a little further the nature of the kidney and the shapes which are heterozygous. Plate X shows a family derived from the cross of H^, a kidney whose origin will be described later, and the typical "round" A. The " rounds " can be picked out most readily. The typical " rounds " are : Nos. 4, 6, 7, 16, 17, 19, 22, 25, 26, 27, 29, 30, 34, 35, 36, 38, 39, 40, 42, 45, 49, i.e. 21 out of 44, practically half. A kidney potato of so typical a shape as H^ is therefore heterozygous in shape, and length, and must clearly be dominant to " roundness." Excellent specimens of kidneys occur in the family, and they must also be heterozygous. It is interesting to note that No. 46 is more or less cylindrical, and that it is heterozygous and probably a merely variant form of kidney. The hybrid nature, in regard to shape, of the kidney may be regarded as settled, that of the pebble follows as a necessity, but we have in support two sets of crosses. A pebble-tubered plant iT" was crossed by the same " round " A as has been used before (see Plate XI). H^'^ is a typical pebble tuber and another of the same root-crop can be seen on Plate IX. The family, consisting of 47 individuals, is seen at once to break up into two types, the " round " and the ovals of different degrees. The " rounds " : Nos. 1, 2, 3, 4, 10, 11, 13, 13a, 15, 17, 18, 19, 26a, 29, 31, 32, 33, 34, 40, 46, 48, 49. 22 out of 47 are all typical. Emerging from this union of pebble and "round" occur really good kidney tubers such as 26, 38 and 41, as good or better than those produced in the family H^ x A, where the parent was a typical kidney. The next cross, and perhaps the most convincing, is represented in Plate IX. It was made between a kidney potato, " Record " on the one hand, and the pebble-shaped " Flourball " on the other. The ofTspring number 32, of which Nos. 12, 13, 18, 21, 24, 25, 26, 30 are all typical "rounds"; i.e. 8 out of 32, or 1 : 4, the expected proportion R. N. Salaman 23 if both the kidney and tlie pebble-shaped parent are heterozygous as regards shape, i.e. " length," and amongst the dominants some are excellent kidneys, others pebbles. No. 3 is interesting because it shows on one and the same root a cylindrical potato and a pebble, a form which has just been shown to be heterozygous. The arguments and the evidence in support of them, as to the heredity of the tuber shapes have, so far, all turned on the fact that there exists a variety of " round " potato which is recessive and breeds true; at the same time all examples that have been so far brought forward contain directly "Flourball" blood. It might therefore be supposed that the whole structure of my contentions rest on this keystone — this " Flourball " derivative — and that if this latter be removed the ai-gument and deductions would fall to the ground. It becomes necessary, therefore, at this stage to describe an experi- ment entirely free from such an objection, at least as far as I am aware. A cross was made in 1906 between "Red Fir Apple" and " Reading Russet." " Reading Russet " is a pebble-shaped potato and " Red Fir Apple " a long cylindrical. F^ was not examined critically for shape; the note as to the 117 young seedlings raised in 1907 is that about one-quarter bore " round " tubers, of these only nine survived, and only five of them were reared in 1909. Four indi- viduals are shown in Plate XXI, and the fifth one, which was omitted, was a long-shaped tuber. On the whole the evidence is rather in favour of F^ being a mixture of " longs " and " rounds " in the propor- tion of 3 : 1, but of the F^ "rounds" we have no examples. The F^ generation, however, is represented by 120 individuals contained in the two families Z^<^' and D^*\ both derived from the selfing of a kidney-shaped F^ plant. The first family, D^*\ consists of 60 individuals; of these 52 are represented in Plate XXII, and of the eight missing, five were long and three " round." When the plate is examined, and still more the actual individuals, the " rounds," such as we have already become accustomed to, are to be found at once, and the following typical examples are seen, Nos. 1, 2, 22, 35, 37, 46, 47, 49, 61, 63 and 64, which in addi- tion to the three not figured, makes the total of 14 out of 60 or nearly 1 : 3. The second family, X'<*>, Plate XXIII, affords some very striking examples of typical "rounds" such as Nos. 6, 47, 52. The family contains 59 tuber-bearing individuals, and of these Nos. 6, 10, 17, 19. 22, 24, 29, 30, 33, 40, 47, 52, 54, 61 are typical "rounds," i.e. 14 out of 59 or 1 : 3. 24 Colour and other Characters in the Potato In the two families containing 119 tuber-bearing individuals, 29 are "round," that is 1 in 3, as would be expected in an F^ family from a heterozygous parent in which "roundness" was recessive. It remains now to consider the evidence bearing on the existence and nature of the dominant shape in its pure form. So far, it has been shown that length of tuber is dominant and that the degree of dominance is variable, i.e. the hybrid form is not constant, the heterozygous tubers varying from a long kidney to an ovoid. On Plates XXII and XXIII, amongst the long tubers are undoubtedly pure dominants, but which exactly they are, and how to distinguish them from the impure dominants with certainty nothing but breeding experiments could determine. It is, however, significant that by selecting those individuals whose tubers were the most uniformly long, it was found that out of the 119 members of the L family already described there were 34, or a little more than one-quarter, that could be picked out as being probably pure in respect to length. Fortunately better evidence is to hand in respect to individuals homozygous in the character of length. A potato, called "Sole's Kidney," yielded abundant seed in 1906, in 1907 several hundred seedlings were planted^ and they all came true to type, viz. a long attenuated kidney, see Plate XXVI. One of these seeded and 50 seedlings were raised in 1909, and every one of these were long kidney form, see Plate XXVI. It would seem, therefore, that this potato G, " Sole's Kidney," is a pure dominant as regards length. Another kidney, "Bohemian Pearl," was sown in 1907 and a very large number of seedlings (family B) raised ; these were not examined very critically in respect to size and shape, but were noted as being uniformly long and pyriform : one selfed naturally, and of the five seedlings raised three bore long tubers, and two bore oval tubers, Plate XXV. These ovals are distinctly flattened and are not " rounds." They have been grown in 1909 and have retained their shape. Had there been any appreciable number of oval or "round" tubers in the first batch of 300 seedlings raised in 1907 it would undoubtedly have been noted ; on the contrary, my own and my gardener's impression is that nothing but "longs" occurred. There is in my mind but very little doubt that the stock B is pure to length. Efforts are being made to self the oval tubered plants this season. 1 I was presented with several hundred of the seed of both these stocks by the Manager of the Cambridge University Farm. R. N. Salaman 25 In 1908 a cross was effected between a pebble-shaped tuber {Af, Plate XXIV) and a seedling of the family B carried on by tuber from 1907 ^ The issue of this union forms a striking example of the effect of crossing a heterozygous by a dominant long. The whole family of 39 individuals is without exception long or oval, and includes the most elegant kidney and one or two cylindricals, see Plate XXIV. In three experiments cylindrical potatoes were employed as the female parent. In the first " Red Fir Apple," a cylindrical, was crossed by " Reading Russet." There is good reason to believe that the F^ family really consisted of three " longs " and one " round," though the small number of survivors, viz. 11 in the first season, does not assist one to any definite conclusion. Those of the F^ family which survived 1909 are shown on Plate XXI. " Red Fir Apple," though long and cylindrical, is therefore in all probability heterozygous as regards length. It is of interest that, since it has been cultivated in my garden, it has become shorter and broader and less cylindrical; on the other hand "Congo," which was used in the second and third experiment, maintains its truly cylindrical shape. Plates XII and XXV. In the second experiment "Congo" was crossed by a "Flourball" seedling of 1906. The "Congo" tubers are typically cylindrical, the seedling " Flourball " was not especially described^ but the F^ series, see Plate XXIX, consisting of 29 individuals, all of which bore kidney-shaped tubers, is evidence that the " Flourball " seedling's parent must have been "round" and that "Congo" must be a pure dominant ; for if neither of these suppositions are true, then we should have expected pure "rounds," which are conspicuously absent, or if the " Flourball " seedlings were pebble or heterozygous in shape, then half of the K seedling family should be pure " longs," which they are not. F^ families were raised from K^ and if*, both elongated and more or less kidney-shaped. The following proportion of " rounds " and " longs " occurred Bounds Longs Family K« 65 210 Family K^ 13 69 78 279 * The B line planted in 1908 from the pollen of which this cross was made, was grown from long tubers arising both from the plant which gave the seed ball in 1908 and from its sister plants, sown indiscriminately. * The absence of a description of shape implies that it was "round" or "pebble" shaped and not markedly distinct from the parent " Flourball." 26 Colour and other Characters in the Potato i.e. 1 : 3'6. The families are illustrated in Plates XIII, XIV, XV, XVI, XVII, XVIII, XIX, XX. In the third experiment "Congo" was crossed by " Reading Russet." Only four F^ plants survived, and the tubers of these, Plate XII, are elongated, but here again the numbers are not large enough to draw conclusions from. The dominant character of length in the tubers has been isolated or identified in the potato G, and is represented by a very elongated kidney ; in B, where it is more pyriform ; and in " Congo," where the ends of the tubers are blunted and the tuber has a cylindrical appearance. It is not improbable, as was suggested earlier, that the allelomorphic pair to the character manifested in the " round " potato is length of axis, and that the kidney and cylindrical shapes, though inseparable with respect to length, are dependent on other factors governing shape besides that governing the length of the main axis. The dominance of the long potato tuber over the short is analogous to the dominance of the giant over the dwarf plant, as Mendel showed in the Pea Family. This dominance probably rests on the same ana- tomical basis, viz. the respective length and number of internodes involved. Tubers are borne on underground stems, called stolons, and the eyes may be regarded as buds or nodes, so that the number of eyes present may represent the number of internodes condensed into the length of a tuber. A study of the tubers from this point of view is not yet complete, but it is quite clear that as a general rule the " round," i.e. short axis potatoes, have less eyes than the long axis ones, i.e. they represent fewer internodal lengths. It has already been shown that the dominance of length is not equal in degree : sometimes the heterozygote is of the most attenuated form, but more often an intermediate shape is assumed varying from kidney to pebble and oval. The ordinary kidney of fair breadth is probably always an heterozygote. The Variations in the Shape of Tubers. The amount of variation has already been indicated in the case of the " round " potato ; in the "long" it is rather less. If "(7" and "Congo" be taken as pure "longs," then, accepting the typical well-grown tuber of each sort, it is apparent that they are as to their proportion between length and breadth much the same, and the form is fairly uniform. By far the greatest variation in shape, both amongst the indi- vidual members of the same family and the several tubers of the R. N. Salaman 27 same iDdividual, is met with in the case of the heterozygous variety. The examples of heterozygous potatoes which have been tested, viz. " Flourball " D\ H\ H'\ K*, K* and L\ varying as they do from kidney to pebble, testify to this. The degree of variation in the shape of tubers of some given sort is in itself very variable, but I think it would be acknowledged that the kidney types vary most. A striking example of this is shown on Plate XXVIII, reproduced by permission of Messrs Sutton, where a kidney potato, " Superlative," is photographed in the clamp, and whilst the majority of the tubers are kidneys, a large percentage are best described as pebbles. The variety H^, Plate X, so clearly demonstrated to be hetero- zygous, is a remarkably uniform kidney shape, but out of less than half-a-bushel it is possible to pick out potatoes varying from a very long to an obtuse ellipse. Fig. 2. Fig. 2. These drawings are tracings of sagittal sections of potatoes of the individoal H'. The long and transverse axes are shown. The depth is less than the transverse diameter. The Depth of the Eye. The potato tuber has scattered on its surface buds from which grow the shoots ; the buds are known as " eyes." The potato eye consists essentially of two parts, a central spot or shoot, and an overhanging ridge or brow which is curved, and whose concavity always points downwards or distally. The eye is recognized to occur in two forms and is known as either 28 Colour and other Characters in the Potato " shallow " or " deep," The " shallow " eye is a superficial eye, i.e. the central growing point is not depressed but is level with the general surface of the tuber and the brow is but very slightly marked. Typically " deep " eyes are those of " Congo " and most of the family K (" Congo " x " Flourball " seedling) and A^^, whilst typically " shallow " eyes are seen in A''' ; H' x A, Nos. 5, 37, 41. The " shallow" eye is a distinctive and an easily recognized feature. Briefly the "deep" eye is dominant to the "shallow," and the heterozygous "deep" eye is never quite so " deep " as the typically " deep " one. In " Flour- ball " the eye is " deep " but not remarkably so ; of its seedlings 14 out of 43 were definitely "shallow." In the family A, of 98 seedlings 21 were " shallow," and A the parent may be regarded as having the standard impure " deep " eye. The D^ X A families contain 16 "shallow"- and 33 "deep "-eyed individuals. The H^ X A families contain 22 "shallow"- and 71 "deep "-eyed. K^ is a further example of an impure dominant " deep "-eyed potato. Of the 73 seedlings of this family 23 are " shallow " and 51 " deep." Two F^ families were raised from the cross of " Red Fir Apple " x " Reading Russet." These two families differ a little in respect to the eyes. Both were raised respectively from sister tubers of the indi- vidual F^ plant (L^). Both parent plants grown from these tubers had "shallow" eyes, one family, Z^<^', consists of 54 individuals, all of which carry " shallow "-eyed tubers. In the other family, Z^'^', Plate XXIII, out of 55 individuals 5 (Nos. 4, 15, 51, 52, 59) must be described as medium, i.e. the eye is distinctly depressed and the brow is evident, though not heavily developed. The only other " shallow "-eyed potato that was selfed was " Bohemian Pearl," all the individual plants which have arisen from it that have come under my notice are " shallow "- eyed. Of the first generation there were some hundreds, of the second only five. If all the families arising out of matings of impure dominant eyes be put together, we obtain the following : ShaUow Deep "Flourbair seedling selfed 14 29 A 21 77 2)1 X 4 16 33 H^ X A 9 39 Hio X A ... ... ... 9 36 £9 ... ... ... ... 22 51 Total ... 91 to 265 This is almost exactly 1 : 3. R N. Salaman 29 K* is an example of a pure "deep "-eyed potato; all the 284 seedlings of which are " deep "-eyed. This family, K*, further illustrates a curious phenomenon. Certain individuals, such as iT"*', Nos. 28, 84 and 95, appear at first sight to be " shallow "-eyed. When, however, they are examined with their sister tubers from the same plant, it will be seen that the " shallowness " is only present at those points where an outgrowth or protuberation is taking place : elsewhere in the same tuber or on its sisters, the eyes are "deep" iT'*^. No. 28 is apparently "shallow," but here also outgrowths are just beginning. A true " shallow "-eyed potato is "shallow" in every tuber of the plant and a true " deep " is equally " deep " in every tuber. The heterozygote is more variable and, though " deepness " is dominant, the eye is often shallower than in the tubers of a pure dominant "deep" eye. The potato "eye" is therefore, like shape, a distinct character inherited on Mendel ian lines. The Coloub of Tubers. The colour is due to the presence of pigmented cell sap in the cells of the superficial layers. The white skinned or, more correctly, yellow skinned tuber, owes its colour on the one hand to the presence of the cork in the upper layer of the corky tissue, and on the other to the absence of any red or purple pigment. The red potato contains a vermilion pigment in solution and the black potato, which is in reality an intense purple, derives its colour from a deep blue purple sap pigment which, seen under the microscope in contrast with the red, is quite distinct. It was pointed out in the Introduction that potatoes of all colours, including the whitest — with white flowers — showed more or less purple pigment in the shoots, arising from the tubers in spring, if not in the haulm also. Vilmorin (lo), in his catalogue of all the known varieties, makes three classes in which the tubers possess white shoots; it is probable that small deposits of pigment were overlooked. Out of the 1200 separate and distinct varieties he describes some 45 as having white shoots. Often the pigment occurs in punctate deposits which need a lens to distinguish them clearly, but the pigment is unmis- takably present. From this fact it would seem clear that all tubers, coloured or not, possess the chromogen base, i.e. using the notation 30 Colour and other Characters in the Potato employed in the Mendelian analysis by Bateson, Miss Saunders and others, all potatoes possess the factor C. Miss Wheldale, who has very kindly examined many of ray tubers from this point of view of pigment analysis, confirms this view. If, then, colour can be present in the haulm and even in the shoot and still not be developed in the tuber, it would seem that there must be some factor which acts as a "developer" of pigment, and in its absence the tuber is white (yellow). The supposition that this factor might be an inhibitor of colour is negatived by the fact that white are recessive to coloured tubers. It is necessary now to observe how the potato plant behaves in actual breeding experiments. The white potato breeds true. Several hundred, about 600 in all, of seedlings of " Bohemian Pearl " and " Sole's Kidney," both white potatoes, were raised, and all the plants that bore tubers at all carried white ones only. A " Bohemian Pearl " seedling was selfed and gave a half-dozen white-tubered seedlings. A "Sole's Kidney" gave 300 white-tubered seedlings, and one of these selfed and produced fifty seedlings, all of which were white- tubered. A w^hite-tubered variety (D) extracted from " Flourball " has been bred now through three generations and gives rise to nothing but white-tubered plants. The variety "Early Regent" sown this season has produced 125 white-tubered plants and none carrying coloured tubers. The Colour Gomposition of the Red Potato. If seedlings of "Flourball" be grown and these, after harvesting, divided up in respect to colour, it will be found that red-tubered plants are to white as 9:7, The numbers in my experiments were : — 1907 271 Red plants 217 White June 1909 71 „ 60 „ Oct. 1909 24 „ 19 „ Aug. 13, 1910' 54 „ 44 „ Total 420 „ : 840 , Ratio 9 „ : 709, There are still about 100 plants to be harvested. R. N. Salaman 31 The ratio 9 : 7 is one very well-known in Mendelian analysis and is evidence of the interaction of complementary factors belonging to separate pairs of allelomorphs. Now if R be considered the factor which in presence of the developer D converts the chromogen into a red pigment, then the zygotic composition of " Flourball " should be written RrDd, which will on selfing give plants with the following composition : — 9 RD=' Reds S Rd = Whites S Dr = Whites I dr = White Further, it will be seen that there are five kinds of white and four of red plants, viz. — whites of the composition : — Rrdd, ddrr, RRdd, rrDD, rrdD, and reds of the composition, RRDD, RrDd, RrDD, RRDd. Of the red it is at present only possible to distinguish three kinds, viz., RRDD, RrDD, or RRDd and RrDd. Of these RrDd we know as the parent or type, the pigmentation of which is weak. RrDD or RRDd has been raised twice out of " Flourball " seedlings, and each case has given red and white tubered seedlings in the propor- tion 3:1. Thus, Family A 70 red 27 white „ G* 12 „ 5 „ The colour of the tuber RrDD is distinctly stronger than the colour of the ordinary " Flourball." There is good reason to hope that the type RRDD will be isolated this season : such a potato will breed true to red. "Reading Russet," a pale red, selfed in 1909 and planted out this year, already gives evidence of a 9:7 ratio. Amongst the whites no certain distinction has yet been made between the possible kinds, nor have two whites been yet successfully mated ; an experiment which when the two whites contain, one the R factor and the other the D respectively, will probably give rise to a coloured potato*. * This year, 1910, a laige number of crosses between Tarioos whites have been effected* 32 Colour and other Characters in the Potato " Flourball " has therefore yielded three types of potato which have been identified by reason of their gametic qualities, namely, two reds, one giving reds to whites in the ratio 9 : 7, another red to white in the ratio 3 : 1, and a white variety. In order to elucidate further the colour factors the white variety D was crossed by the 3 : 1 red variety A and the result was 27 Red to 22 White. This ratio is presumably to be taken as approaching equality, as 9 : 7 ratio would be here impossible. If the formula of A be RrDD then this particular white potato must be rrDD ; similarly if A be RRDd then the white variety must be RRdd. It is here assumed that A = RrDD, and the family D therefore will be represented by rrDD, it could of course be equally well rrDd. A cross of peculiar interest was made between " Flourball " and a potato called " Record " which, although of attractive appearance, was of such frail constitution that it has entirely died out everywhere. The result of the cross was a family H. Of the 30 individuals which lived through the following years 19 were white and 11 red. The numbers are small, but enough at least to show that the whites are in a very distinct majority. If the notes of the H family be examined from its first origin, one finds that there were 28 whites to 12 reds and two with no tubers, and that the mortality has taken place amongst the white and tuberless. The formula for " Flourball " was shown to be RrDd, and there are two possible formulas for a white potato which would, in union with " Flourball," give rise to a family having a majority of whites. They are rrdd and rrDd respectively ; — the first would give a family of three whites to one red ; the second would give a family of five whites to three reds. The numbers in the H family are not large enough to decide with certainty which formula for " Record " is the more correct. We have seen that the mortality affected those plants which were either white tuber bearers or tuberless, and that the approximation of the final result of two whites and one red is due to this mortality amongst the whites. Whether it is possible that plants pure to the absence of pigment factors are more weakly than others cannot, on the present evidence, be asserted, but the facts suggest such a possibility. Two white-tubered members of the H family were crossed by the red potato A, whose gametic composition we may assume to be RrDD, R. N. Salaman 33 seeing that on selBng it gives three red and one white. The results were different in each case — W xA gave 29 red 19 white lP»x A „ 18 „ 27 „ Total 47 „ 46 „ In either case it is possible that larger numbers would have shown a nearer approach to equality. It must however be noted that the family H^" x A, had far less pigment in its stem than H^ x A, and that the possible results of mating whites with reds of A's composition are equality, if the white is rrBD or rrdd, or three red to one white if Rrdd. One other cross was made between a pale red and a white-tubered plant. " Queen of the Valley " was crossed by a red seedling of " Flourball " and the F^ generation consisted of seven red to three white. One of these a pale red, M^, was crossed by a white seedling of the white " Bohemian Pearl " B. Forty-one seedlings grew and 38 survived to form tubers. Of these 19 had red and 19 had white tubers. This result of equality suggests that the composition of the two parents may have been — (M^) RrDd x {B) rrDD. if' is probably RrDd and not RRDD, RrDD, etc., because it is a particularly feeble red and might therefore be assumed to have the least possible factors that would give a red. Two reds, one very deep red, viz. " Red Fir Apple," and the other a weak one, " Reading Russet," were crossed. " Reading Russet " has now been selfed, and this year we shall learn its composition, but its colour is weak like that of " Flourball," and it has probably the same gametic composition, viz. RrDd^. " Red Fir Apple " is of a very deep colour and might be RRDd. The F^ raised were 117 seedlings, but only 11 of them came to maturity, viz. eight red, and three white, indicating, as would be expected from the union, a 3 : 1 ratio. RRDd X RrDd = 3 red : 1 white. Two plants arising both from tubers of the same individual of the F^ family, viz. L^ and L*, were selfed and produced in the F^ generation large families in which the ratio of red and white was 3 : 1. 1 The 1910 seedlings of "Reading Russet," so far as yet harvested, are divided into 14 red-tubered plants and 10 white-tnbered. Joam. of Qen. t 3 34 Colour and other Characters in the Potato The numbers in the latter are not conclusive in themselves, because only selections of these families were actually planted out ; but amongst the young seedlings, before planting out, there were 23 red to 8 white and the appearance of the harvested selections fully bear out the sug- gestion of a 3:1 ratio. Purple Coloured Tubers. — The "Congo" potato is a cylindrical potato of almost a black colour, the pigment extending within the tuber somewhat irregularly. The " Congo " flower, which is white with a purple tinge at the base of the petals, is completely sterile in the male organs, and it was therefore only used as a mother plant. Two crosses were made — 1. Congo X Reading Russet. There were eight seedlings and only four survived until the late autumn of 1906, of these Two were black like " Congo," Two bright red. But on July 25, 1907, there was a fifth plant with white tubers which died out subsequently. The numbers are too small to make any deduction as to ratios, but there is one factor of great importance which stands out, viz. — that out of a union of a deep purple and weak red, there have segregated out deep purple (black), bright red and white. The next cross was — Congo X Flourball Seedling. This cross was effected in 1906. The " Flourball " seedling was a stray plant growing in one of the experi- ment lines containing " Ringleader " and was used as pollen parent. " Ringleader " itself did not flower that year. Except that it was a red tubered variety nothing further can be told about it, as it was unfortunately not preserved. Its pollen was used in the cross with "Queen of the Valley" and, as has been mentioned before, it is probable, for the reasons already given, that it was a red of the formula RrDD or RRDd. The F^ generation contained 29 plants and these were 13 Black tubers. 12 Red tubers. 4 White tubers. Here again the important features are the complete segregation and the appearance of the white tubers. Before discussing the possible constitution of " Congo," it will be best to consider the F^ generation. R. N. Salaman 35 In 1908 two of the F^ plants, viz. K* and K^ both selfed and large families were planted ; those of K' did well, the K^ family fared badly in the wet summer of 1909. K* Family. K*, Plate XXIX, is a black (le. deep purple) potato. Several seedballs were collected from the plants, and one coming from a plant .ff^*"* was planted in its entirety. Originally 301, there were harvested but 160 seedlings. The tubers of the jP* family separate at once into blacks, reds and whites in the proportion of 77 black, 29 red, 54 white; the reds are either quite pale and similar to " Flourball " or " Reading Russet," or they have more purple colour and resemble " Red Fir Apple." Of the whites about one-sixth (9 in 54) are quite pure, i.e. no tinge of colour can be seen in the tubers or eye before sprouting, whilst the remainder may have a trace of colouring usually purple, in the eye or the skin and more especially in any scars following a wound by fungous disease or other lesion. Such pigment is minute in quantity and often needs a lens to demonstrate its presence. The reds are roughly of two kinds, a deep strong group, and a pale. The proportion between these is 23 deep red, and 6 pale red, and they can be classed fairly readily into these main groups. The blacks are all alike, viz. deep purple. In con- sidering the factors which underlie the phenomena of colour in the red- and white-tubered potatoes we assumed the presence of the two factors R and D. The purple potato is obviously bringing a fresh factor besides these into the field and this new or " purpling " factor can be called P. If ^* has the gametic formula Pp, Rr, Dd, then on selfing we should get plants or biotypes with the following gametic constitutions : 27 plants of the composition PRD = purple. " » >» 9 I, M 3 „ „ 3 „ „ 3 „ „ ■'• » » The numbers for the K^ family are :- PR = white (tinged). RD = red. PD = white. R = white. D = white. P = white. prd = white. Purple Bad White Calculated nambers 73 24 75 Actual Numbers 77 29 54 9—2 36 Colour and other Characters in the Potato The results^ are sufficiently close to give one some confidence that the phenomena are correctly represented by the assumption of the factors PR and D that have been supposed to be at work. The sister family K^ adds additional evidence of a strong nature. Several lots of seed of K^ plants were sown and in all some 300 seedlings raised. The majority were however planted in selections and therefore are of no use for quantitative purposes. All the groups, however, coincided in one feature — none produced a single red tuber; and the evidence from the selected groups strongly favour the view that purples to whites were as 9:7, whilst the groups that were planted in full give 26 : 14. The parent plant of such a family must be homozygous in the purpling factor and heterozygous in its two other colour factors. To K^, therefore, should be given the zygotic formula PP, Mr, Dd. Having considered K^ aod K^, we can now turn back to the original cross and the F^ family. The F^ family consisted of 13 purple, 12 red, 4 white. It is obvious that as regards P, " Congo " must be heter- ozygous, further we knew the " Flourball " seedling was red and therefore contained RD. If we represent the cross " Congo " PpRrDD x " Flourball " seedling RrDD we get 12 purple, 12 red, 8 white. The result of these experiments on colour inheritance would seem to be (1) that whilst colour may be present in the stem to any degree, a special developer D is necessary to bring it out in the tuber, (2) that redness is dependent on a separate factor R, (3) that purple is dependent on a further one P, and (4) that the purple colour cannot be developed except in the presence of all three factors PRD. In all the experiments there has been much to suggest that the degree of the " redness " is due to the homozygous condition or other- wise of the plant as regards both R and D, but the evidence has not been given in full because the classification into shades of " redness " would be too empirical and dependent on personal judgment. In one group the distinction was clearly made out, viz. in the family A where the formula was shown to be RrDD (or RRDd) the deep reds were to the remaining reds as 24 to 48, whilst in the K^ group the reds were 23 deep red to 6 pale red. Amongst the blacks (purple) no distinction could be made. 1 If the disproportionate mortality of the whites be remembered, the actual numbers will be seen to be not so far removed from the calculated ones. Thus the number of whites, had the mortality in all classes been equal, would be 66 instead of 54. R N. Salaman 37 SOLANUM ETUBBROSUM. The plant with which I have worked is identical with that used by Mr Sutton (8) and described and figured so fully by him. I obtained my tubers from Kew, whence it was sent to me with the name of "Maglia," though the misnomer was realized later. Mr Sutton has been good enough to see my plants growing, and has no hesitation in confirming that they are the same as his own obtained from Mr Lindsay of Edinburgh Botanical Gardens and which he has described under the name of " etuberosum." The Rev. Aikmau Paton's supply of etuberosum was derived from mine, and his results, as far as they are published, confirm mine in many particulars. It is not necessary to decide as to whether this plant is the one originally described by Lindley in 1834 as etvberosum ; the general feeling is that it is not the same, but that it is a plant of the greatest interest is none the less true though its name be a borrowed one. The contention of Sutton (s) that S. etuberosum is the parent plant of our domestic varieties has been considered by me in an earlier paper(9). Wittmack(i2) has also discussed this question, and though I do not share his opinion that etuberosum is an ordinary S. tuberosum, variety I, nevertheless, agree with hi m that there is no reason to regard it as the parent type of our domestic varieties. The etuberosum plant is a low growing one with very light green leaves which are of a different tone to any other I have had growing in my garden. It rather suggests the dusty appearance of the olive. The haulm spreads at its lower end, sending out lateral branches parallel to the ground. The average size of the leaf is 2 J inches by 1 inch ; the surface is soft and rather woolly ; the veins are marked, but the leaf not curled or rugose. Compared with most domestic varieties the nodes of the stem would be considered short, but they are, in proportion to the rather dwarf-like habits of the variety, about normal in length. Pigment in the stem is red, patchy, extending feebly into the petioles, and visible in the axils. The flowers occur in close clusters, and are of an extremely beautiful lilac, which, viewed from above, has a peculiarly soft appearance. This is due to the fact that the pigment is on the under surface of the petal, that is outside when the flower is closed. This lilac colour differs considerably from the heliotrope seen commonly in domestic varieties. The anthers are delicate and form 38 Colour and other Characters in the Potato a close cone similar to that seen in the various true wild species, and through the apex projects a short style ending in a simple knob. The anther contains abundant pollen. The corolla is very definitely wheel-shaped, the tips of the petals recurve ; they are rather sharp and hairy, and the calyx is hairy and its five processes are long. The tubers are borne on rather long stolons. They are white and round, but the shape (Plate XXVII) is not typical of " round " as we have met it before in this paper. The tubers are irregular, neither oval nor long, but are often depressed at various points, so that although the general shape is round, the actual circumference is not necessarily circular. The size is variable. When the tubers were first cultivated here they were not more than 1^ inches in diameter; in 1909 I had some up to 3 inches in diameter. The taste is bitter. In 1906 Mr Sutton informed me that he had for over 20 years tried to self and cross this variety and had failed. In that year, however, a plant bore one berry. I, also, after repeated trials, in 1906 succeeded in making a cross. In 1907 Mr Sutton again obtained selfed berries, and some tubers I had sent to the North of Scotland set seed naturally and crosses were made. Hence, after over 20 years of observed sterility, this variety suddenly flowers out into fertility in Reading, Scotland and North Herts, which, as we shall see, has cost it dear. The tubers in both 1906 and 1907 showed no variation, except a slightly enlarged size. In 1908 when the plant first set seed naturally in Barley, it was noticed that the tubers of one plant had a slight violet tinge in the skin in places ; this plant set seed in addition to one other, and 30 of the seedlings came from this plant. There is no evidence that the seedlings are, as a whole, different from those which did not show this vegetative variation. The fertilization of the plants took place naturally, but at a date when all the other potato plants in ray garden had ceased flowering and when some F^ " Congo " crosses, which were close by, had already formed good-sized berries. Immunity to Disease. (Phytophthora infestans.) During the culture of this variety in Reading it was noted for its immunity to disease. In my garden it was in 1906. Perfectly immune from disease in haulm and tubers. Three hybrid seeds only obtained. R N. Salaman 89 1907. Very slight touch of disease on haulm, none in tuber. No seed. 1908. Slight disease in haulm, none in tuber. Set seed freely. 1909. No disease in haulm on September 3, but some later, considerable disease in tubers. No Seed. 1910. Some disease in haulm in August. Selfed and crossed seed. The incidence of disease amongst the seedlings was remarkable, those attacked by disease were in some cases consumed away and all of them, excepting one which was but very slightly touched in the haulm and quite free in the tuber, were most seriously damaged. Out of 40 seedlings 34 were diseased and six were untouched, to these might be added the one only just touched by disease on a leaf or two, making seven. The ratio of 33 : 7 is of course suggestive of a 3 : 1 ratio. Resistance to disease being, as Biffen(2) found in the case of wheat, a recessive. Further careful observation will be needed before anything more definite can be asserted. Id is a most striking fact that although the parent etuberosum plant was for 20 years and upwards noted for its immunity to disease, yet directly its sexual life begins that immunity goes. The chain of events, the fact that the F^ family contains a number of immune plants, suggests that with the onset of sexual activity some disturbance in the mechanism by which the plant had hitherto security its immunity to Phytophthora had occurred — and that the dominantly susceptible state of the plant apparently heterozygous in this respect, has as it were been uncovered and its true nature laid bare. The immune seedlings in 1910 demonstrated afresh their resistance to Phytophthora. The etuberosum seedlings were so planted that on either side of an immune plant was a susceptible one, whilst immedi- ately behind was a row of ordinary domestic potatoes. The susceptible seedlings and the ordinary potatoes were devastated by disease. Before the end of July the haulms of both these latter were destroyed- Up till the beginning of September the immune plants were unscathed. Signs were not wanting that the immune plants had been attacked but had successfully withstood the enemy. Pale spots were seen on some of the green leaves during the height of the disease, whilst on these spots on a few fading leaves colonies of Cladosporium epiphyllum were found. The presence of the bright green healthy immune plants 40 Colour arid other Characters in the Potato standing out in the naidst of the blackened and diseased debris which marked the site of their destroyed neighbours formed a very striking picture. Successful crosses have been made this year between the immune seedlings and domestic varieties. The Flower. It has been already noted that the flower of this potato is of a very delicate lilac and that the pigment is on the under surface. The petal is entirely self-coloured ; there is neither an intensification or a weakening of the general tone in the central region of the petal, as one so commonly finds in potato flowers. The flowers of the seedlings offer considerable variations. Of the 40 plants 20 flowered, and of these — Nine plants were exactly like the parent, i.e. uniform colouring on under surface ; Two plants were similar to parent but double the intensity of colour ; Three plants had the same general colouring as the parent, but with a deep-coloured tongue in the middle of the petal, and in one it was noted (probably true for all) that the colour in the tongue was both in the upper and in the lower coats of the petal ; Three plants had white flowers with purple tongues in the centre of the petal, the colour in the tongue being on the upper surface ; Three plants were pure white. The sequence of the diverse flowers can be readily explained on the following hypothesis — that we have two pairs of characters at work — A. Colour. a. Colour absence. B. Uniform distribution of colour h. Distribution of colour in a on under surface. pattern on upper surface. We then get — 6 : Bh. Aa. = Parent type. 2 : Bb. AA. = „ „ with deeper-coloured tongue. 1 : AA. BB. = „ „ but deeper colour, S : A. b. = White with coloured tongue. 3 : a. B. = White. 1 : ab. = White. The numbers are too small to lay much stress on an explanation such as the one given, but the phenomena fall readily into line. R N. Salaman 41 Shape of Tuber. The tubers of etuberosum are, as already mentioned, " round " — the seedlings comprise both " rounds " and " longs," and amongst the latter are kidneys. The numbers are 18 round, 14 long. It is evident that the " roundness " of etuberosum is of a quite different order and with a different hereditary value to that of the domestic varieties, and moreover, it is obvious that the " round " here is dominant to the " long," whereas in the domestic types it was recessive. The Eyes. The eye of the parent tuber is " shallow " and very insigniHcaut. The seedlings can, as regards the tuber eye, be at once divided into " deep " and " shallow." These are 26 " shallow " to 8 " deep." " Shallow " eye is therefore clearly dominant : in the domestic variety it is as clearly recessive. The Colour of the Tuber. It will be remembered that, although the etuberosum tuber is white, yet in 1908 certain tubers were noted to have shown a slight purplish tinge. It is not therefore surprising to find that the seedlings are varied in colour and that the parental white is a dominant. The colours of the seedling tubers are white and deep purple. The latter are identical in colour to those purple tubers dealt with in the earlier part of this paper. The numbers of the different colourings are — White 13 White tinged 12 Deep purple (black) 13. 25. The numbers suggest that purple is a recessive character and that white is a simple dominant. In the domestic varieties the reverse is true. No reds were formed. Crosses with Domestic Varieties. In 1906 I succeeded in effecting a cross with " Queen of the Valley." Three seedlings only grew, and they all died out. Mr Paton(7) crossed etuberosum by the white kidney " Duchess of Cornwall," and he obtained 13 seedlings, the colour of 12 of which he describes, viz. 9 white, 2 purple, 1 red, showing the dominance of white. It is of further interest to note that he describes the shape of ten of them. Eight are " round " and two are "long" (kidney and oval), again showing the dominance of the etuberosum type of " roundness." 42 Colour and other Characters in the Potato Crosses with S. etuherosum and maglia. Sol. etuberosum x Sol. maglia (deep purple) One seedling white tuber. Sol. maglia x Sol. etuberosum. One seedling white tuber. Here again the " white " of etvherosum is dominant to the purple of the recognized species maglia. The relation of S. etuberosvm to other potatoes. Although the name " etuberosum " has been used in this paper, it has been done rather for convenience than with any idea of establishing its identity with the species described by Lindley. Whether S. etuberosum is to be classed with the domestic varieties or as a native species is a question that may have an increasing import- ance. It has been shown in this paper that in respect to such important characters as shape, eye and colour of tuber it behaves in a diametrically opposite way to the domestic varieties, and it is, therefore, likely that it is distinct from them. On the other hand, its white is dominant to the muglia purple, and its own purple is also recessive; so that in respect to this character it certainly more closely resembles maglia. The flower of etuberosum is much smaller and more compact than that of the domestic potato, and is much more like the wild S. etuberosum and S. maglia, and its scheme of colour as described here has no parallel amongst the domestic varieties. There would seem, therefore, to be no adequate reason at all for classing S. etuberosum amongst domestic varieties ; on the other hand, it has certain characters akin to those of recognized specific types, such as S. maglia. It has been suggested that the diversity of the S. etuberosum seedlings shows it clearly to be a hybrid. That may be, but we can feel at least equally sure that its parents are not domestic varieties. Conclusions. Very briefly the following conclusions have been reached in this paper. Domestic Varieties. 1. The twist of leaf, as seen in " Red Fir Apple," is a recessive character. R. N. Salaman 43 2. Length of tuber is dominant to " roundness." 3. Depth of " eye " is dominant to " shallowness." 4. Purple is dominant to red in the tubers. 5. Red is dominant to white, but is dependent on the presence of two factors in addition to a chroraogen. 6. S. etuberosum is not subject to the same laws of dominance as the domestic varieties of potatoes. 7. That amongst the seedlings of S. etuherosum occur some which are at present immune to the attacks of Phytophthora in/estans. 8. That immunity to the attacks of Phytophthora xnfestans is in S. etuherosum a recessive character. 9. S. etuherosum may be a hybrid and, if so, its parents are possibly native species. I take this opportunity of tendering my thanks to my head gardener, Mr E. Jones, for the assistance he has rendered, and the great care he has shown in the raising of the seedlings. DESCRIPTION OF PLATES. PLATE I. Tubers of seedlings of Sutton's "Floorball" selfed. "Bonnds" are — Nos. 40, 89, 92, 118, 132, 138, 155, 156, 162, 185. PUVTE 11. Family of seedlings of parent A selfed. The majority of the tubers are normal "rounds"; the least typical "round" has been chosen to represent each individual root. On Plates IV. and Y. can be seen the sister tubers of the more abnormally shaped "round" tubers. A family continued. PLATE iU. PLATE IV. All the available tubers of each root crop are shown of those individuals who vary from the typical " round." In all cases one or more typical " rounds " occur in eaeh root crop. PLATE V. Same as Plate lY. No. 100 is probably a stray plant and not a member of this family. 44 Colour and other Characters in the Potato PLATE VI. The G family, consisting of six individuals with their root crops are shown. G*, Q^ and G® are more or less typically "round." PLATE VII. The D family — Top row — Three tubers of parent plant. D^ and Ifi, 1908, are the seedlings raised in 1908 from D (1907) selfed, D^ and D^, 1909, are seedlings raised in 1909 from D (1907) selfed. PLATE VIII. Seedlings of the family raised from cross D y. A. The family consists of half "rounds" and half "non-rounds." The "rounds" are Nos. 3, 4, 5, 8, 13, 14, 15, 16, 18, 19, and 8, 6, 7, 10, 12, 14, 18, 19, 20, 21, 22, 28. PLATE IX. Seedlings of the family raised from the cross "Eecord" x "Flourball." "Eecord" is a kidney, "Flourball " a pebble-shaped potato (neither parents shown). One quarter of the seedUngs are "rounds," viz., Nos. 12, 13, 18, 21, 24, 25, 26, 30. PLATE X. Seedlings of the family raised from the cross E} {F^ of family B., Plate IX) x A. Half the seedhngs are "round," viz. : Nos. 4, 6, 7, 16, 17, 19, 22, 25, 26, 27, 29, 30, 34, 35, 36, 38, 39, 40, 42, 45, 49. PLATE XI. Seedlings of the family raised from the cross E>^ (i^i of family H, Plate IX) x A. Half the family are "rounds," viz. : Nos. 1, 2, 3, 4, 10, 11, 13, 13a, 15, 17, 18, 19, 26a, 29, 31, 32, 33, 34, 40, 46, 48, 49. PLATE XII. Family J raised from the cross "Congo" x "Beading Eusset." The fifth seedling, a long white-tubered one, died out and is not shown here. PLATES XIII— XVIII. The family raised from the individual K^ (i^' of "Congo" x "Flourball" seedling, see Plate XXIX). This family for convenience has been divided into sub-families K'c?, K^^, etc., according to the particular seedball from which the seedUngs were grown. " Rounds" are to "longs" as 1 : 3 in this series, and the eyes are all deep with the exceptions noted in the text. PLATES XiX, XX. The family raised from selfing K^ (F^ of "Congo" x "Flourball" seedling, see Plate XXIX) the "rounds" are rather deficient, viz. : 13 to 60; the eyes are deep to shallow, 3 : 1. R N. Salaman 46 PLATE XXI. The family L, raised from the cross of "Red Fir Apple" x "Reading Rasset." In the f, No. U, a kidney has been omitted. PLATES XXM, XXIII. F*, family raised from L\ selfed. The rounds are 1 in 4, viz.: Nos. 1, 2, 22, 35, 37, 46, 47, 49, 61, 63, 64 (Plate XXII). Five long- and three roand-tubered individuals have been omitted. In Plate XXIII the " rounds" are Nos. 6, 10, 17, 19, 22, 24, 29, 80, 33, 40, 47, 52, 54, 61. PLATE XXIV. The family raised by crossing SP (F^ of " Queen of the Valley " x " Flourball "' seedling) x" Bohemian Pearl" long-tubered seedling. Nos. 2 and 20 which in the plate look "round" are in reality much flattened and are clearly not rounds. Two other typical long members of this family have been omitted. PLATE XXV. Examples of tubers, not from individual roots, of B, " Bohemian Pearl " seedlings long and oval. "Congo." The long tubers are much more common than the stunted. "Red Fir Apple." The tubers in 1909 were all more or less stunted as shown in the Plate. PLATE XXVI. C, 1907, one of the seedlings of "Sole's Kidney." C, 1909, representatives of 4 seedlings of C, 1907. PLATE XXVII. Family raised from selfing Lindsay's etuberosum. The long-tubered seedlings are here in the minority. The ravages of the disease are clearly seen. PLATE XXVIII. (Reproduced by kind permission of Messrs Sutton of Reading.) The kidney potato "Super- lative" in clamp. The variability of shape amongst the kidney and pebble-shaped tubers is very marked. PLATE XXIX. The F^ family raised by crossing "Congo" x "Flourball." The segregation of the colours Purple, Red and White are well shown. The shapes are all "long" and the eyes all " deep," demonstrating the dominance of these characters. 46 Colour and other Characters in the Potato BIBLIOGRAPHY. 1. Bateson, Saunders and Punnett. Rep. Evol. Comm. Roy. Soc. 1904, Vol. II. p. 91. 2. BiFFEN. Journ. Agric. Sc. 1907, Vol. ii. p. 109. 3. Darwin. Animals and Plants, 1890, Vol. ii. p. 149. 4. East. Rep. Connecticut Agric. Exper. St. 1907—8, p. 429. 5. . " Transmission of Variations in Asexual Reproduction." Rep. Con- necticut Agric. Exper. St. 1909—10, p. 120. 6. Gaertner. Versiiche und Beohachtungen iiher Befruchtung-organe, Stuttgart, 1844, 849, S. 117. 7. Paton. J. R. Hort. Soc. Vol. xxxv. p. 33. 8. Sutton. Linn. Soc. J. Bot. Vol. xxxviii. 9. Salaman. Linn. Soc. J. Bot. 1910, Vol. xxxix. p. 301. 10. ViLMORiN. Catalogue M^thodique et Synonymique de Pommes de Terre, Paris, 1902. 11. WiTTMACK. Bericht. d. Deutscht. Bot. Ges. 1909, Bd. xxvii. S. 28. 12. . Zdt.f. wiss. Landunrt. 1909, Bd. xxxviii. erganz. Bd. v. JOURNAL OF GENETICS, VOL I. NO. 1 PLATE I JOURNAL OF GENETICS, VOL I. NO. 1 PUTE li JOURNAL OF GENETICS, VOL I. NO. 1 PLATE ^V -Deed t ir\9S . G,„f- 73 7S 7^ 77 7S Tf 80 81 8 2 83 54 Z5 S7 SS S«? 1o qi ^2^ **3 'n 'JS <|4 q7 q^ qq ■ ■/ -| •-• -J-J ^|00 «OI JOURNAL OF GENETICS, VOL I. NO. 1 PLATE IV • A ^1 Hw 8 Z& #3 36 4 /o // 21 # JB "•d'305 40| 6o J JOURNAL OF GENETICS, VOL I. NO. 1 PUTE V JOURNAL OF GENETICS, VOL I. NO. 1 PUTE VI G G ^ ^ f J G 3 G 4 G s G /^ 1^' . ;*^$ JOURNAL OF GENETICS, VOL I. NO. 1 PLATE VII D l^oj. I X)' •^'^S jy"^ l^aS 1^ ■* J^' •i*'1 V. I>" ..,^^. JOURNAL OF GENETICS, VOL I. NO. 1 PLATE VIII X JOURNAL OF GENETICS, VOL I. NO. 1 PUTE IX Ur^ ^^0^ JOURNAL OF GENETICS, VOL I. NO. 1 PLATE X JOURNAL OF GENETICS, VOL I. NO. 1 PUTE XI m^mm^ JOURNAL OF GENETICS, VOL I. NO. 1 PUTE XII CO C^ ¥ JOURNAL OF GENETICS, VOL I. NO. 1 PUTE XIII m m^ - • 1 ^9 : • « •^ '5 JOURNAL OF GENETICS, VOL I. NO. 1 PLATE XIY •4 m wB ' 9 # ■s. f^^ ? 2- % o ^ Jf^ "^ ' > Al ^ 1^ ^^v,^ 3 ^ ^.•^ ?J c^ JOURNAL OF GENETICS, VOL I. NO. 1 PLATE XV ««f ^^^ ^ o u W' ^ OS ^p ^ JOURNAL OF GENETICS, VOL I. NO. 1 PUTE XYI V^ JOURNAL OF GENETICS, VOL I. NO. 1 PUTE XVII JOURNAL OF GENETICS, VOL I. NO. 1 PUTE XYIII JOURNAL OF GENETICS, VOL \. NO. 1 PUTE XIX 1^8 ^ w rar« ^f 9 U /3 IS IS l<\ 23 31 33 35 48 J5 ^^'/ 71 • K^' ji^ 8q qo ^1 3 4 «1 iz i3 9 ^ y\^MJiji^ '^Cc % (o A/ C^ O ••i„§^ i I ^ }^ JOURNAL OF GENETICS, VOL I. NO. 1 PUTE XXVI c (i» 7 c I til ^ If» JOURNAL OF GENETICS, VOL I. NO. 1 PLATE XXVII JOURNAL OF GENETICS, VOL I. NO. 1 PLATE XXVIII [Reproduced by kind pertu.^.^.^,,, .,/ Messrs Sutton of Reading >< X X o > CO o UJ o z cr o THE MODE OF INHERITANCE OF STATURE AND OF TIME OF FLOWERING IN PEAS {PISUM SATIVUM). By FREDERICK KEEBLE, Professor of Botany, University College, Reading ; AND Miss C. PELLEW, Research Student, Botanical Laboratory, University College, Reading. The experiments recorded in the present paper, though incomplete, throw some light on the nature of the Mendelian factors which deter- mine stature in peas (Pisum sativum) and on the mode of inheritance of earliness and lateness of flowering in this species. The experiments were designed originally to investigate the latter problem — left un- decided by Mendel's classical experiments on the inheritance of " time of flowering," As our work proceeded, it became evident that this function of the plant is not unconnected with certain, definite, morpho- logical characters. Hence it becomes necessary to follow the course of inheritance of these characters, e.g. length of intemode and thickness of stem. In doing this, we have been led to conclusions concerning, not only the relation of these morphological characters with flowering period, but, also, the part which these characters play in determining the stature of peas. We deal first with the latter point. Stature. Certain garden races of Pisum sativum grow tall and give rise to tall-growing offspring ; other races are dwarf and breed true to this character. Adopting Bateson's classification (1909, a) we call "tall," those varieties which grow 5 — 6 or more feet high, "dwarf," those which range from 9 inches to 3 feet. Between dwarf and tall are various " half-dwarf" races which reach a height of about 4 feet The actual height attained by the various races is determined in any given 48 Inheritaiice in Pisum year, partly by gametic constitution and partly by the external condi- tions to which the plants are subjected during their growing period. Thus the two half-dwarf varieties Autocrat and Bountiful, used in our experiments, are so constant with respect to stature as to be described by Messrs Sutton and Sons, to whom we are indebted for seeds, as being, the former variety 8 — 4 feet, the latter '?>\ — 4 feet in height. Nevertheless, during the constantly wet summer of 1909 both Autocrat and Bountiful reached in the College Gardens at Reading an average height of 5 — 6 feet. We refer to these well-known seasonal fluctuations* in height in order to point out that particular care is required in the interpretation of the results obtained in any one year and in the comparison of the statures of plants grown during different years. The cross Autocrat and Bountiful and its reciprocal. This cross, made in 1907, and repeated in 1908, yielded an F^ generation, the plants comprising which were considerably taller than either parent grown under like conditions. The average height of F^ plants was 7 — 8 feet, that of the parent plants 5 — 6 feet. jPi selfed, yielded offspring {F^ which ranged in height from 8 feet down to 1^ feet. In all, 192 F^ plants were recorded. Of this number, 61 plants were the progeny of a single F^ plant of Autocrat x Bountiful grown in 1908. The remaining 131 plants of the F^ generation were descended from four F^ plants of the cross Bountiful x Autocrat. The seeds from these four plants were, owing to a mistake, harvested together. There is, however, no recognisable difference between the descendants of the single family from Autocrat x Bountiful and those derived from the four F^ plants of Bountiful x Autocrat. We will therefore consider the 192 F^ plants as a whole. The F2 plants, showing such marked differences among themselves with respect to height, fall into four groups which, for the moment, may be defined as follows: — F^ type, Autocrat type, Bountiful type, and Dwarf type. Moreover, when classified in this way, the numbers of plants in the four groups show a close approximation to those expected in the F^ generation derived from a dihybrid cross; that is one in which two pairs of characters are involved. Thus : ¥2= f, type Autocrat Bountiful Dwarf Observed 114 33 32 13 Calculated 108 36 36 12 9 : 3 : 3 : 1 Inspection of the parent plants. Autocrat and Bountiful, reveals the fact that, besides other, apparently minor, differentiating characters, F. Keeble and C. Pbllew 49 these two lialf-dwarf varieties are distinguished from one another by two well-marked characters, namely, length of internode and thickness of stem. Thus Autocrat, whose normal height is 3 — 4 feet, has thick stems (with large fleshy foliage of a bluish green colour) and short internodes of about 3 inches in length. Bountiful, whose normal height is 3^ — 4 feet, has thin stems (with foliage smaller than that of Autocrat and of a yellowish green colour) and long internodes (5 — 7 inches). It may be noted incidentally that the rates of growth of these two varieties are very different ; the growth in length of the axis of Autocrat being markedly slower than that of Bountiful. For example, when Autocrat and Bountiful are planted at the same time. Autocrat grows one foot whilst Bountiful grows two. The slowness of growth in length is asso- ciated with short internodes. The two varieties differ also with respect to mode of branching. Autocrat forms three to five branches at or near the ground-level. These branches develop at the same rate till they and the main axis are about 2 feet in height and then one axis takes the lead. Bountiful shows a less fixed mode of branching. Among the 1909 plants, some branched at the ground-level (2 — 4 branches), others formed their first branches a foot or so above the ground-level. Generally speaking, thick stem appears to be associated with branching, and thin stem with single stem, at the ground-level We are engaged in endeavouring to work out the anatomical bases for thick as opposed to thin stem, and for long as opposed to short inter- nodes, and the bearing of these factors on growth. We will now consider the factors, thickness of stem and length of internode, in relation with stature. That these factors maybe taken as valid representatives of those which determine height is evident from the following considerations : — Fi plants, 7 — 8 feet high, have all thick stems with long internodes (6 — 9 inches). If the factor for thick stems is represented by T, and its allelomorph (thin stem) by t, and if the factor for long internodes is represented by L, and its allelomorph (short internode) by I : then the gametic constitution of Autocrat is Tl, that of Bountiful is tL, and hence the gametic constitution of F^ = TtLl. We ascribe the great height of F^ plants to the presence of the factors T and L and to their dominance over t and I. The suggestion may be hazarded that the greater height and vigour which the F^ generation of hybrids commonly exhibit may be due to the meeting in the zygote of dominant growth- factors of more than one allelomorphic pair, one (or more) provided by the gametes of one parent, the other (or others) by the gametes of the Joam. of Gen. i 4 60 Inheritance in Pisum other parents. This provisional interpretation of increased vigour of ^1 plants, has at all events the merit of being less obscure than the hypotheses which are current in the literature of plant physiology (Jost, 1907). We return now to the F^ of the crosses between Autocrat and Bountiful. Since the constitution of F^ = TtLl, its gametes have con- stitutions :—TL :Tl:tL: tl, and hence, when F^ plants are self-fertilized, we expect the usual 9:3:3:1 ratio ; i.e. in 16 plants, 9 with both, dominants {T and Z); 3 with one dominant; 3 with the other and 1 with the two recessives {t and I). That the expectation is realised is seen from the following table in which the results already given are recorded in terms of Tt and LI. 2^8 = F, type Autocrat Bountiful Dwarf TL Tl tL tl Observed 114 33 32 13 Calculated 108 36 36 12 (9 : 3 : 3 : 1) Of the 13 dwarf (^Z) plants, all but one were below 3 feet in height, the three dwarfest being respectively 1^, 1|, and 2 feet. Table II gives the records of height, of thinness or thickness of stem, and of length of internode of the plants which we regard as true dwarfs. The classification is of course open to the objection that thick and thin are but qualitative terms, and that, in difficult cases, the criteria are purely subjective. An answer to this objection is that the records in Table II were made before we were aware that the characters "thin" or "thick" were of any considerable importance. We include in Table II the records of the characters oi F^ plants of a stature up to 4 feet. A com- parison of the descriptions of the stems of the shorter plants (above the horizontal line in Table II) with those of the stems of the less short plants (below the line) confirms, as we think, the view which we have expressed above, that the dwarf plants have thin stems and also short internodes. With regard to the range of variation in height, both among the dwarfs, and among the plants of the constitution Tl, it is probable that the character of number of nodes, and also that of the position of the first flowers, are also of importance. It is hoped that further investigation of these characters among the F^ families will determine this point. We conclude from the above experiments that tallness in peas (P. sativum) depends on the presence of two factors, long internode, and F. Keeblk and C. Pellew 61 thick stem: that these factors are Mendelian in their inheritance; being dominant respectively to short intemode and thin stem factors. Half-dwarf peas are of two kinds. One kind, represented by Autocrat, owes its semi-dwarfness to lack of the long intemode factor. In the absence of this factor, the thick-stem factor cannot effect more than a sturdy, medium growth. The other kind of semi-dwarf lacks the thick- stem factor, and, in the absence of this factor, the long intemode factor cannot build the stem-segments of a sufficient length to produce tallness in the plant. It may be urged that this, after all, is but a common-sense view of the way in which growth in length is effected : that only plants with long internodes among annuals are likely to be tall ; and that only when stems are sturdy may internodes reach their full length. This may well be and it is certainly not a reproach to Mendelism that it may lead to the discovery of the obvious which, without the method, remains obscure. The conclusions which we have reached as to the gametic constitu- tion of tall, semi-dwarf and dwarf peas may be summarised thus : — Tall = TL. Semi-dwarf = tL or Tl. Dwarf = tl. In a cross described by Lock (1905) we have what seems to us an interesting confirmation of this view of the chief factors involved in stature of Pisum. Lock's comment on the case is as follows {op. cU. p. 414): — "This cross seems to afford an example of remarkable inten- sification of both the allelomorphic characters of the same pair, viz. tallness and dwarfness — the former in F^ and both in F. and later generations." The cross in question was one between Satisfaction — a variety which at Peradeniya grew to an average height of 46 feet — described as of robust growth (which we may take to mean thick stem), and with internodes of an average length of 1'74 inches, and a Native Pea of less than 3 feet in height, but varying much in different years, with thin stem, and internodes of an average length of 1^ inches. In the four plants of the F^ generation, the internodes were of an average length of 2*4 inches — longer than in either parent — the height of the ^1 plants was about 6 feet, and the number of internodes was the same as in Satisfaction. It would seem that in the increased length of intemode of the Fi plants (an average of 24 inches as compared with the 174 inches of Satisfection) is seen the influence of thick stem on an intemode which, when combined with thin stem, is of an average 4—2 52 Inheritance in Pisum length of 1^ inches. In i^j. the preponderating type resembled the i^i plants, and the appearance of dwarfs, shorter than either parent, with internodes of 1"0 — 1'2 inches in length (the proportion of long to short being 19 : 6), confirms our belief that the characters thick and thin stem, long and short internodes were the chief stature-factors involved in this cross. Probably the difference in the number of^niodes intro- duces a complication, but the small numbers grown in F^ and the lack of further records, prevent a full analysis. We should mention that this cross was made primarily by Mr Lock with the object of inves- tigating the characters of the testa of the seeds of Pisum. In conclusion, with respect to the question of tallness and dwarfness, it is evident that a closer investigation will reveal facts of great import- ance to an understanding of the physiology of growth. Time of flowering : earliness and lateness. Certain varieties of peas are well known and prized for their stability with respect to time of flowering, and therefore it is to be supposed that the character is hereditary. Mendel many years ago commenced experiments with a view to determine the mode of inheritance, but few records of these experiments are left to us. In Mendel's memoir on the hybridizing of peas (1909b) we find the following: — "As regards the flowering time of the hybrids the experiments are not yet concluded. It can, however, already be stated that the time stands almost exactly between those of the seed and pollen parents, and that the constitution of the hybrids with respect to this character probably follows the rule ascertained in the case of the other characters." By the use of the varieties Autocrat and Bountiful for such an experiment, the advantage is gained of a long space of time between the flowering periods of the two varieties : the former variety flowers, in normal seasons, about 30 days after the latter. Thus, in 1909, from sowings made in April, 23 out of 28 plants of Bountiful were in flower on June 2nd, whereas Autocrat, sown at the same time, was only just coming into flower on June 30th (see Table I). In spite, how- ever, of the favourable nature of our material with respect to the character under consideration, we cannot claim to have arrived at a complete understanding of the mode of inheritance of earliness or lateness of flowering. Nevertheless, we publish our records, and our attempts to analyse them in Mendelian terms, since they appear to show definitely not only that the problem is capable of solution, but also the nature of the difficulties which have to be met before the solution is obtained. It will be seen from the records of the time of F. Keeble and C Pellew 53 flowering (Table I) that the Fi generation is intermediate with respect to time of flowering between the parents Autocrat and Bountiful. In 1909, whereas 23 out of 28 plants of Bountiful blossomed by June 2nd, and whereas Autocrat was beginning to flower by June 30th, 10 of the plants of ^1 (of a total of 12) were in flower by June 21st; and the remaining plants were in flower by June 30th. The ^i plants of Autocrat crossed Bountiful and those of the reciprocal cross, grown in 1908, confirm this result. From the appearance of such an intermediate form in i^i, it may be supposed, either that there is incomplete dominance of lateness over earliness, or that there are two (or more) factors con- nected with the time of flowering ; the meeting of the two, or more, dominant and antagonistic factors, from either parent in the Fi plant, giving an intermediate time of flowering. In the former case, the F^ plants, obtained by selfing F^, may be expected to give the 1:2:1 ratio ; but, though segregation of early and late occurs in F^, it is not of this simple type. If we tabulate the observations on time of flower- ing, not of the F^ generation as a whole, but of the several categories of that generation, viz. thick long {TL), thick short (Tl), thin long (tL), and thin short (tl), we obtain the results shown in the accompanying Table. TABLE I. The Accelerating Injluence of Long Intemodes on Time of Flowering of F^ Plants. (Times of Flowering of Boantiful, Autocrat and Fj are given for purposes of comparison.) Numbers of Plants iu Flower Thick Long Thick Short Thin Long Thin Short Date of Flowering Bountiful Autocrat F, 5 1 24 6 June 2 23 — 17 1 7 2 June 10 5 — 48 5 1 3 June 17 — — 8 36 16 — 1 June 21 — — 2 8 10 — — June 30 — — 2 "" 1 July 6 " (a few beginning to flower) These results show that plants with long intemodes, of both thick- and thin-stemmed types, flower, on the whole, earlier than the short internode types. Since long internode is dominant to short internode, ^1 plants may be subject to the same accelerating influence with respect to time of flowering as those of the groups, long thick and long thin. 54 Inheritance in Pisum We suggest therefore that lateness is dominaut to earliness, and that the reason why the plants of F^ flower before those of the late parent Autocrat, is that they possess the factor for long internodes, their gametic constitution being TtLl. The fact that the position of the flowers on the stem, in F^ plants, is about the same as in Autocrat, lends some support to the view that late is dominant to early. There was however a considerable range of variation in this character, both in Autocrat and in the F^ plants. Moreover, owing to the branched habit of Autocrat and of the ^i plants, and to the fact that this character was not considered until rather late in the season, it was impossible in some cases to recognise the main stem, i.e. the stem which flowered first, and this may have spoilt the records to some extent. This character of the position of the first flowers on the stem has been supposed to indicate time of flowering (1905b). Our records show that Autocrat bears its first flowers, on the average, at the thirteenth node. Bountiful at the seventh node, and the ^i plants at the twelfth. Many records of this character were made among the F^ plants. The average result of these records points to the conclusion that low-flowering indicates earliness, high-flowering lateness, but there were many exceptional cases among individuals. Further investiga- tions among F^ families, homozygous in respect of the many other charac- ters involved, should provide a solution to this question. Proceeding then on the basis that lateness is dominant to earliness, we observe, in the F^ generation, that the flowering period spreads over more than a month, from June 2nd — July 6th, that whereas many (36) plants of F2 flower as early as the early parent, few flower so late as Autocrat (Table I). That time of flowering is influenced by seasonal conditions is undoubted ; but the marked differences in flowering-time between the various plants of F^ show that the mode of influence of a given season is determined to a surprising degree by internal factors. A more detailed examination of the distribution of earliness and late- ness of flowering among the F^ plants, brings out several facts which lend support to the conclusions that time of flowering, though inherited, is modified in its expression in the zygote by morphological characters such as thickness of stem. As we have shown, the F^ plants group themselves into four classes: — thick long {TL\ thick short {Tl), thin long {tL), and thin short {tl). If we chose arbitrarily the date of flowering of Bountiful (June 2) as early and regard for our immediate purpose all plants flowering after this date as late, we find, on scruti- nizing the distribution of lateness and earliness among these classes, F. Keeblb and C. Pellew 65 that most of the thick-stemmed plants with short or long intemodes, are late (141 late, 6 early); that, of the thin, short-noded plants, 6 are early and 7 late, and that of the thin, long internoded plants, 24 are early and 8 are late. It is therefore apparent that there is a relation between morphological, vegetative characters and period of flowering. Thick-stemmed plants contain a very high proportion of late plants, thin-stemmed plants contain an almost equally large excess of earlies. As has been shown by Bateson, departures from normal, Mendelian expectation which manifest themselves by discriminate distribution of a character among the members of a generation, may be interpreted by the aid of the hypothesis of gametic coupling. Applying this hypothesis, and assuming that the coupling between thick stem and late factor is of the 7:1:1:7 order (Bateson, 1909, = Plants reckoned as Dwarf 5 X 3/5/10 June 2nd li feet Thin 3 inches Very small D 3 X 5/2/60 „ 9th If „ Thin 2| „ Bountiful type D 3 X 5/2/43 „ 2nd 2 „ Thin 3 ,, „ „ D 5 X 3/6/7 July 6th 2i „ Thin n „ Very small D 5 X 3/6/3 June 2nd 2i „ Thin 2 ,, Small ( = Bount.) D 6 X 3/4/34 „ 2nd 2i „ Thin 2 „ ? Intermed. D 5 X 3/2/4 „ 2nd 2i „ Thin 2 „ Bountiful D 5 X 3/4/19 „ 16th 2i „ Thin 3 „ Small D 5 X 3/5/34 „ 30th 2i „ Thick s „ ? Intermed. 5 X 3/6/6 „ 10th 2| „ ?Thin 2 „ ? D 3 X 5/2/20 ,, 2nd 2^—3 feet Thin 3 „ Bountiful D 3 X 5/2/34 „ 21st 24-3 „ ? Thin ^ ., ? Autocrat D 5 X 3/2/14 „ 16th 2^—3 ,, ? ? ? Bountiful D 6 X 3/5/12 „ 16th 3 ?Thiu 3 „ Intermed. D 5 X 3/5/41 „ 2lBt 3 ?Thin i „ Diseased 5 X 3/1/5 „ 21st 3— 3^ „ ? Thick 3 „ ? 5 X 3/3/5 „ 30th 3-3i „ ? Thick 3 — 3^ inche 3 Small 5 X 3/1/10 „ 16th 3i „ Thick H Small ( = Bount.) 3 X 5/2/8 „ 16th 3i— 4 „ Thick 3 ? Autocrat 3 X 5/2/52 „ 2nd 3i— 4 „ ? Thick 4 Autocrat 5 X 3/4/29 „ 21st 3i— 4 „ ? Thick 4 ? Autocrat REFERENCES CITED IN TEXT. 1905. Reports to the Evolution Committee, ii. p. 68. 1905. R. H. Lock. Studies in Plant Breeding in the Tropics, p. 403. 1907. JosT. Plant Physiology. Translation by R. J. Harvey Gibson, p. 375. 1909a. Bateson. Menders Principles of Heredity, p. 19. 1909b. Bateson. Mendel's Principles of Heredity. Translation of " Experiments in Plant Hybridization," Gregor Mendel, p. 337. STUDIES IN THE INHERITANCE OF DOUBLENESS IN FLOWERS. I. PETUNIA. By E. R. SAUNDERS, Lecturer and late Fellow, Neumham College, Cambridge. The tradition that the production of double flowers is largely a matter of external conditions has already been shown in the case of Matthiola to be at variance with the results of breeding experiments carried on for several years ^ The evidence, on the contrary, clearly shows that in this case doubleness, like the other characters investigated, is inherited according to definite laws, and in accordance with the Mendelian principle of segregation*. With a view to making a com- parative study of the inheritance of doubleness in plants a series of experiments has now been undertaken in various other genera. In the case of Petunia the results have already reached a point at which a definite statement can be made, and it is with these results that the following account is concerned. 1 Of the many beliefs still held regarding the occarrenoe of donbles in Stocks, the only one which I have so far been able to confirm is that seed which has been kept produces a higher proportion of doubles than that more recently harvested. This appears to be true to the extent that the seeds destined to give rise to donbles retain their vitality rather longer than those which give rise to singles. The higher proportion observed is not therefore due to any effect of age on the constitation of the seed, bat to an original difference in viability. * A general statement of these results has already appeared, and a more detailed account is now in preparation. (See Reports to the Evolution Committee, Royal Society, n. p. 29, 1905 ; m. p. 44, 1906 ; it. p. 36, 1908.) 68 Double Petunias The material used in these experiments included the following forms : — (1) P. violacea {phcenicia). Flowers deep magenta with very dark throat. Pollen blue. (2) P. nyctaginiflora. Flowers white with yellow flush in the throat. Pollen yellow. Of stouter habit than the preceding species and with larger flowers. (3) P. hyhrida grandiflora. Garden hybrids, (a) Flowers magenta or magenta and white, variously striped or blotched. Corolla plain edged. Pollen blue, (h) Var. fimhriata. Flowers nearly pure white. Corolla fringed. Sepals broad and slightly curled. (Lady of the Lake.) (4) Countess of Ellesmere. A garden variety. Flowers rose- coloured with throat nearly white. Pollen white. The plants were raised from seed. The two species P. violacea and P. nyctaginiflora and the garden form Countess of Ellesmere are all single-flowered. The seed from which the grandiflora plants were raised was stated to yield a proportion of doubles, and a mixture of singles and doubles was duly obtained. In growers' catalogues it is generally stated that the seed which is guaranteed to produce doubles has been obtained from flowers (i.e. singles) artificially fertilised with the pollen of doubles. This, as will appear presently, seems to be the only method of producing double-flowered plants from seed (see p. 60). The proportion of doubles obtainable is variously quoted as 20 — 40 per cent. The object of the present experiments was to discover under what circumstances doubles may be expected to occur, and also, if possible, to determine whether the proportion of doubles obtainable was constant. A. Description of the double flower. The plants which will bear double flowers may be recognised before the flower expands by the shape of the bud which is short, thick and blunt, whereas that of the single is long, slender and pointed. In the single flower we have a simple funnel-shaped corolla, five epipetalous stamens, and an ovary with a slender style terminating in the expanded disc of the stigma (see fig. 1). In many cases the connective is pro- longed above the anthers in the form of a petaloid structure varying in size from a short process so small as to be easily overlooked after the E. R Saunders 59 anthers have dehisced to flat expansions of considerable size (see fig. 7). But in these cases the stamens, always five in number, are otherwise normal. The gynoecium is also normal, and the corolla forms one petaloid funnel-shaped structure. The flower is obviously single. In the doubles the flower tube is filled with a number of additional petaloid structures and stamens (see figs. 2 and 3), or in rare cases mostly with additional stamens (see figs. 4 and 5). These extra petaloid structures are often variously folded, generally flat but oc- casionally funnel-shaped, more or less adherent below and free above. When folded the more deeply coloured, morphologically upper surfaces are generally opposed, the less deeply coloured, often hairy under surfaces being outside; but in the open flower the expanded upper portions of these structures come to lie for the most part with the upper surface exposed to view, thus giving a uniform colour eflfect. They vary considerably in size and number even in the different flowers on one individual. Many bear anther-like structures con- taining pollen, and some have occasionally been found with a structure resembling a stigma. The number of stamens proper is also variable, being usually more numerous in flowers with few petaloid structures and vice versa. The several members of the corolla and androecium may fuse to form an outer, single, conspicuous, and somewhat massive envelope, within which are concealed much smaller petal-like structures and stamens forming a central mass, which may arise at a distinctly higher level than the outer envelope owing to the development of an intemode. Or they may form three or four well-developed envelopes composed of petal-like structures and adherent stamens which can be successively peeled off. A further important characteristic of the double flower is the malformation of the gyneecium. The whole structure is often completely deformed, but when this is not the case and the style and stigma appear to be normal, the ovary is seen to be larger than in the single, and when opened is found to contain perianth parts, stamens with well-formed pollen, and in some cases also ovules below or among these other structures. All attempts to use the doubles as seed-parents however proved unsuccessful. Fertilisation produced no result. Hence the double character could only be introduced into the pedigree on the male side. The flowers on any individual are of one type, either all single or all double as the case may be. Among a large number of flowers from double-flowered plants only one was found in which both corolla and androecium appeared to be single, and in this case the flower was 60 Double Petunias malformed, the corolla being split and the segments curled ; the ovary was not opened. The remaining flowers on the plant showed the usual degree of doubleness. Among the flowers of single plants only two were observed in which there was any approach to doubling, and in each case the remaining flowers on the individual were normal singles. In one of these flowers a single large petaloid structure had developed in the corolla tube ; in the other a similar structure arose near each of the five stamens, the line of adhesion to the corolla coinciding with that of a stamen and forming a common decurrent ridge. It was noticed that in single plants kept through the winter under unfavourable conditions the first flowers produced in the following spring were often deformed, the corolla being split and infolded but without showing any tendency towards doubleness. B. Results of breeding experiments. The general results of the experiments carried on during the last five years may be briefly stated as follows: — 1. When a single is crossed with a double, doubles as well as singles occur in the first {F^ generation. 2. When such F^ singles are self- fertilised^ or fertilised inter se the resulting offspring are all single. Doubles in fact are only obtained when the pollen of doubles has been used to fertilise the seed-parent, so that this operation must be repeated in each generation. 3. The proportion of singles in a mixed family is probably always in excess of the doubles. Details of the experiments are given in the accompanying Tables. The results recorded in Tables I and II show that singles, whether belonging to one of the type forms or derived from a previous cross, when fertilised with pollen from a double yield a mixture of singles and doubles in the first generation. Out of a total of 41 families thus bred, 40 included some doubles. As regards the remaining case in which no doubles were recorded there is little doubt that their absence is due solely to the small size of the family (4), and that a larger sowing would have given the usual mixture. ^ If protected under muslin or glass and left undisturbed violaeea and hybrida rarely set seed ; even when artificially self-fertilised many pollinations give no result. On the other hand nyctaginijlora, under the same conditions will often set seed, and does so readily when artificially fertilised with its own poUen. Further experiments concerning the sterility of these forms are now in progress. E. R Saunders 61 It also seems clear that in such mixed families the singles pre- ponderate. This was the case in 33 out of 38 families, and although in the remaining five the doubles were equal in number to the singles or slightly in excess, it is very improbable that the deficiency of singles in these cases is real. In families 9, 10, 31, and 33 the numbers recorded are too small to be conclusive, and in family 35 the result (9 single, 11 double) is within the range of deviation which might be expected to occur, if, as appears to be the case in several families, the true ratio represents but a slight excess the other way. At present the data available are hardly suflScient to determine with certainty the real proportion of singles and doubles occurring in these families. Until the general occurrence of doubles in unions of this kind had been established the number rather than the size of the families was of first considei-ation. If for the moment, however, we consider only those families with more than 10 members we find that they fall naturally into two principal groups, in one of which the numbers suggest the possible ratio 3 s. : 1 d., while in the other they approximate closely to the ratio 9 s. : 7 d. Grouping these families in this way we get the result shown below : — Beferenoe number of Number of offspring Reference number of family Number of offspring Single Double Reference number of family Number of offspring famUy Single Doable Single Doable 3 19 4 1 82 67 25 22 11 7 14 4 2 54 35 11 18 6 4 28 21 37 34 17 14 12 2 5 13 12 19 15 2 6 10 9 20 11 1 17 24 22 24 18 2 22 26 9 17 6 13 39 17 7 27 28 29 18 13 13 13 11 8 41 12 3 32 35 36 38 40 24 9 53 16 14 21 11 35 14 9 Total 136 31 397 307 Where a ratio ofSs.: Id. cal- culated to the nearest whole number would Where a ratio of 9 s.: 7 d. cal- culated to the nearest whole number would give 125 42 give 3% 308 62 Double Petunias 9 families giving a total of 136 single, 31 double where a ratio of 3 s. : 1 d. would give 125 single, 42 double. 16 families giving a total of 397 single, 307 double where a ratio of 9 s. : 7 d, would give 396 single, 308 double. 2 families not included in either of the above groups giving a pro- portion of 2 single : 1 double. As yet it is not clear whether the occun-ence of these different ratios indicates that more than one factor is concerned in determining singleness and doubleness, or whether it results from the fact that the proportion of germ cells carrying singleness and doubleness varies in different individuals. In view of the results obtained with Stocks, the former explanation seems the more likely. The results given in Tables III and IV show that singles belonging to the various type forms, whether self- fertilised or crossed with another type yield only singles (see Table III); and further, that cross-bred singles having one parent single and one double are equally unable to produce doubles when self-fertilised or fertilised inter se (see Table IV), although the same individuals yield both singles and doubles when crossed with pollen from a double. It would therefore appear that the pollen of all the singles tested (23) was homogeneous as regards the presence of some factor x which is essential to the manifestation of singleness, and which is absent from some at least of the ovules. Whether the female germs are homogeneous in this respect, and are all thus deficient ; or whether they are heterogeneous, some lacking the necessary factor and some not is at present uncertain. Precisely the same may be stated in regard to the pollen of the doubles. In some of the grains some necessary factor is evidently wanting, but whether this is the case in all the male germs is not yet clear. It may however be safely asserted that whichever alternative represents the true condition as regards the ovules in the single, the converse will be found to hold good for the pollen of the doubles. For the results obtained would equally follow whether it were the ovules of the single which were homogeneous and the pollen of the doubles that was heterogeneous, or whether the reverse were the case. Analogy with Stocks^ would suggest that the first-mentioned ^ In the account of the results obtained with Stocks {Evolution Reports, loc. cit. ) it is stated that the homogeneous pollen of the heterozygous (ever-sporting) singles carries doubleness (i.e. absence of singleness), but that among the ovules some carry doubleness and some singleness. This mode of expressing the difference in constitution between the male and female germs is permissible if we suppose that the occurrence of singleness or E. R Saunders 63 alternative may be likely to prove correct (viz. ovules of singles hetero- geneous, pollen of doubles homogeneous as regards absence of the factor x) ; but the fact that if this were so we should expect a certain pro- portion of Petunia singles to be homozygous as to singleness, and therefore incapable of yielding doubles when crossed with the pollen of a double, whereas, as a matter of fact, no such singles were met with, lends considerable support to the opposite view (viz. ovules of singles homogeneous, pollen of doubles heterogeneous in regard to absence of a;). Thus we find in Petunia the same peculiar type of gametogenesis which has already been shown to occur in Matthiola. In both cases segregation proceeds in such a way that certain factors are distributed differently among the ovules and the pollen grains. It may also be noted that in both instances doubleness behaves as the recessive character, singleness as the dominant, but in other respects the two cases present an interesting contrast. In the double Stock, as is well known, the flower is completely sterile, whereas in Petunia the male organs are functional in the double though the female are not. Further it appears that although both in the single Stock which constantly throws doubles, and in the single Petunia which yield doubles when fertilised by a double, the pollen is homogeneous in respect of some factor needed to produce singleness, the homogeneity is brought about by the absence of this factor in the Stock, by its presence in Petunia. Consequently doubles are obtained in the Stock when heterozygous individuals are self-fertilised, or fertilised inter se, but not in Petunia. Lastly, in the Stock a heterozygous single fertilised with double-carrying pollen yields an excess of doubles ; in Petunia on the other hand singles crossed with pollen from a double yield a majority of singles. Summary. 1. Single Petunias belonging to the following forms : P. molacea, P. nyctaginiflora, P. hybrida grandifhra, and Countess of Ellesmere, whether self-fertilised or crossed with each other, yield only singles. doableness is determined by the presence or absence respectively of a single factor. Now however that the accumulated evidence points to the probability that more than one factor is involved this difference between the male and female germs is more correctly expressed in terms of some factor the. presence of which is essential to singleness (as above in Petunia) than in terms of the character singleness itself. 64 Double Petunias 2. Cross-bred singles derived from one single and one double parent also produce only singles when self-fertilised or fertilised inter se. 3. Singles crossed with pollen from a double yield doubles in the first generation. 4. In families containing a mixture of singles and doubles, the singles are in excess of the doubles. There is some evidence to show that in some cases the ratio approximates to 9 s. : 7 d. and in others to 3 s. : 1 d. The occurrence of the ratio 9 s. : 7 d. in many of the cross- bred families strongly suggests that more than one factor is concerned in determining the occurrence of singles and doubles, and this view is in harmony witii the conclusions formed in the case of Stocks. 5. The male organs are functional in doubles, but the gynoecium is more or less deformed, and when fertilised yields no seed, hence the double character can only be introduced on the male side. 6. Doubleness behaves as the recessive, singleness as the dominant character. 7. Gametogenesis is of the peculiar type which has already been shown to occur in Matthiola, the factors for singleness and doubleness being distributed differently among the ovules and the pollen grains. 8. The pollen of the singles is homogeneous as regards the presence of some factor essential to the manifestation of singleness. 9. With regard to the constitution of the ovules of the singles and the pollen of the doubles it may be said that the results obtained on crossing are such as would occur, if either the ovules were homogeneous and the pollen heterogeneous as regards the absence of some factor needed to produce singleness ; or if conversely the ovules were hetero- geneous and the pollen homogeneous in respect of this factor. The fact that all the singles appeared capable of yielding doubles when crossed with the pollen of a double points strongly to the first alternative, but the impossibility of making reciprocal crosses renders direct proof difficult. The expenses incurred in connection with these experiments have been in part defrayed by a grant from the British Association for the Advancement of Science. E. R. Saunders 65 TABLE I. Showing the mixture of singles and doubles obtained in /*,, in the ease of the type forms^ from the cross single 9 x double $ . Form of onion Reference number of family f rur»»^»» Single seed-parent Double pollen parent x^^mnbcr Oi v^ud|/iuik Single Doable V If 1 82 67 >> 2 54 35 f> S 19 4 N H 4 28 21 »» 5 13 12 ,, 6 10 9 >* 7 14 4 »» 8 4 2 „ 9 1 4 >i 10 1 3 H ff 11 18 6 »j 12 4 8 >> 13 6 3 »> 14 12 2 »» 15 6 4 „ 16 4 — >> 17 24 22 „ 18 8 2 CE H 19 15 2 >> 20 11 1 »» 21 3 1 >> 22 9 6 »» 2S 7 1 ♦» 24 18 2 »f 25 22 11 C£ H (var. ^mbn'ata) 26 17 13 »» »> ,, 27 18 13 »» »> >> 28 IS U V=xnolaeea. N = nyctaginiflora. C£=Goante88 of Ellesmere. H=kybrida gran- diflora. Jonrn. of Oen. i 66 Double Petunias TABLE 11. Showing a similar mixture of singles and doubles resulting from the union single $ x double S , where one or both of the individuals employed was descended from a previous cross. Form oi ' union Reference number of family ^fnmH*»r '^' C\fFoT\t^net Single seed-parent Double pollen-parent J.1 uiiiUcr Single Double r (single .HxN)x double H 29 13 8 » )> 30 6 4 >j ,, 31 4 4 agle HxN)x double H double H 82 24 21 >> ,, 38 4 4 »» »» 34 6 3 s> „ 35 9 11 (single HxN)x Self double H 36 53 35 (^x doubled) {Nxdonhle H) 37 34 17 jj ,, 38 16 14 (single HxN) double H 39 17 7 >> >> 40 14 9 5 9 41 12 3 The total number of individuals belonging to the type forms used as seed-parents in experiments 1 — 41 was as follows : 6 plants of Violacea 7 „ ,, Nyctaginiflora 5 ,, ,, Countess of Ellesmere 5 ,, „ Hyhrida grandiflora Total 23 E. R Saunders 67 TABLE III. Showing that doubles do not occur when singles belonging to the variotis type forms are self-fertilised or intercrossed. Ftvm (tf onion J Single pollen-parent Reference number of famUy Nomber of Offs; Single 'ring Single •eed-parent Doabl V self 42 13 — »» „ 43 6 — »t i« 44 6 — „ ,, 45 - 3 . — n self 46 47 — ,, ,, 47 2 — H self 48 . 18 — >< ,, 49 3 — CE self 50 . 9 — »♦ >t 51 4 — M i» 52 4 — V N 53 14 — „ »» 54 6 — N V 55 60 — J, »» 56 49 — ,j „ 57 36 — ff •• 58 35 — „ » 59 23 — H P 60 many (total not recorded) — H N 61 143 — „ »i 62 41 — »> n 63 36 — II »t 64 22 — »» 65 many (total not recorded) — u 11 66 i> II >i — {NxV} (NxV) 67 10 — {NxV) self 68 16 — „ M 69 10 — „ •t 70 4 — >i „ 71 3 — „ It 72 2 — " II 73 74 2 2 [single flxxV) self 76 33 — 11 •• 76 24 — 68 Double Petunias TABLE IV. Showing that doubles do not occur when the singles derived from a cross with a double are either self-fertilised, or crossed with other singles similarly derived. Form of union Single seed-parent (single H x double H) Single pollen-parent self (^■x double H) »> >» (single HxN)x double H >> (single H x double H) (single H xN) X double H (single H xN)x double H self self (single H x double H) (single HxN)x double H N X double (NxH=si, double) Reference numl>er Number of Otfspring of family Single Double 77 73 — 78 8* — 79 8 — 80 6 — 81 3 — 82 3 — 83 2 — 84 64 — 85 14 — 86 13 — 87 3 — 88 1 — 89 8 — 90 2 — 91 33 — 92 14 — 93 11 — 94 3 — 95 9 — 96 7 — * A double which occurred in this batch was evidently a rogue as the flower had some of the characters of nyctaginifiora. EXPLANATION OF FIGURES. I am indebted for the accompanying figures to Miss D. F. M. Pertz, to whom I here tender my best thanks. Fig. 1. Single flower seen split longitudinally. Fig. 2. Usual type of double flower showing extreme petalody, seen from above. The functional stamens are concealed by petaloid structures. (See next figure.) Fig. 3. Similar flower seen in longitudinal section. Pig. 4. Less common type of double flower. Stamens numerous, but supernumerary petaloid structures few and small. The corolla tube is curiously folded so as to form a kind of cup round the stamens. (See next figure.) Fig. 5. Same flower in longitudinal section. Between the lower region of the corolla tube which rises vertically, and the upper part which lies horizontally is seen the curious double bend which forms the cup-like structure surrounding the stamens. The ovary is aborted. Fig. 6. Group of stamens and a small supernumerary petaloid structure belonging to the same flower showing fusion for some distance above the point at which they become free from the corolla tube. Fig. 7. Two stamens showing prolongation of the connective. E. R. Saunders 69 Fig. 6. Fig. 3- Fig. 4- Fig. 5- THE EFFECTS OF ONE-SIDED OVAEIOTOMY ON THE SEX OF THE OFFSPEING. By L. DONCASTER, Fellow of King's College, Cambridge, AND F. H. A. MARSHALL, Fellow of Christ's College, Cambridge. {From the Physiology Laboratory, Cambridge.) It is now widely believed that sex is determined not by conditions acting upon the organism after fertilisation, but by determinants or " factors " existing in the gametes themselves. Since this view came into prominence several hypotheses have been put forward, suggesting that gametes bearing the factor for one or the other sex are produced in separate gonads. Some have believed that in vertebrates one testis yields male-producing spermatozoa, the other female-producing, but this has been disproved in rats by Copeman^ It is also known to stock breeders that bulls from which one testicle has been removed, give calves of both sexes. Meanwhile evidence has been accumulated that in several groups of animals it is the egg rather than the spermatozoon which plays the more important part in sex-determination, and in accordance with this, the opinion has been held that one ovary produces female eggs, the other male eggs. That this is not a general rule is proved by the case of birds, which have only one ovary, and in Amphibia by the experiments of H. D. King^, but in a recent book^ Dr Rumley Dawson has maintained that this hypothesis is valid at least for man, and probably for other mammals. Direct evidence of a con- 1 Experiments described at the Physiological Society, May 1908. 2 Biol. Bulletin, xvi. p. 27, 1909. ^ The Causation of Sex, London, 1909. L. DONCASTER AND F. H. A. MARSHALL 71 elusive kind is difficult to obtain in man, since even if children of both sexes are bom after single ovariotomy, it is rarely possible to prove that the ovary has been completely removed. It therefore seemed worth while to test the matter critically in some other mammal, and with that object the experiments described below were made on rats. Two female albino rats were taken, and in May 1910 the right ovary with the greater part of the fallopian tube was removed from one of them, and the same parts from the left side of the other. Both animals rapidly recovered from the operation and on being put with a buck, shortly became pregnant. The female from which the right ovary was removed gave birth to seven young on July 8. The young all died soon after birth, and one of them was almost entirely eaten by the mother. The rest were preserved for examination, and it was found on dissection that there were four females, one male, and one was too much decom- posed before being preserved for its sex to be determined with certainty; it appeared to be a female. The rat from which the left ovary had been removed gave birth to five young on July 28 ; one young died shortly after birth ; it was dis- sected when quite fresh and proved to be a male. The remainder lived until August 22 when they were killed and dissected ; there were three females and one male, giving three females and two males in all. On the same day the two rats which had been operated on were killed and dissected. In neither could any trace of ovary or ovarian tissue be found on the side from which the ovary had been removed. In that from which the left ovary was taken out there was about ^ inch of fallopian tube, ending apparently blindly; in the other the right fallopian tube had been cut ofif at its junction with the uterus. In each case the uteri were normal. They were congested on both sides in the rat lacking the right ovary, which was probably on heat at the time of killing. In the female (left ovary removed) which had suckled its young up to the time of killing all the mammae on both sides were normal and functional. In both rats the remaining ovary was ex- ceedingly large, and had doubtless undergone compensatory hypertrophy in consequence of the removal of the ovary of the other side^ The relatively large size of the litters (7 and 5) produced from one ovary may be thus accounted for. That the litters were produced from one ovary in each case is further shown by the fact that on microscopic examination it was found that in the rat from which the right ovary was ^ Cf. Carmichael and Marshall, Journal of Phytiology, voL xxxvi. p. 431. 72 Ovariotomy and Sex removed the remaining (left) ovary contained at least seven corpora lutea, and the remaining (right) ovary of the second rat contained at least eight. These corpora lutea were all of similar age in each animal, and clearly distinguishable from the older luteal tissue present in the ovaries. These facts seem to us to indicate without any doubt that in the rat it is not true that ova determining one sex are produced from one ovary, and those determining the opposite sex from the other, for each rat, with one ovary completely removed, produced young of both sexes. This does not of course prove that the " right and left ovary hypothesis" is not true for man, but its definite disproof for another mammal detracts from its probability. It should be pointed out however that the evidence for alternate male and female ovulations in man, collected by Dr Rum ley Dawson and others, is not in any way affected. In our opinion the weakest part of his evidence is that dealing with the pro- duction of ova determining different sexes by the two ovaries, and it is not impossible that this hypothesis may be false, and yet that in general alternate ovulations may be of different sex, so making sex- prediction possible. It is very desirable that those who have extensive opportunities of testing this hypothesis — which involves knowing not only the date of birth and whether the child is " full time " in each case, but also whether the menstrual periods are normal and regular — should have the matter in mind and keep records whenever possible. [Note. The operations described were performed by F. H. A. Marshall ; the dissections by L. Doncaster.] Volume I MARCH, 1911 No. 2 EXPERIMENTS WITH PRIMULA SINENSIS. By R. p. GREGORY, M.A., Fellow of St John's College, Cambridge ; University Lecturer in Botany. CONTENTS. Page istboduction 74 Hbtebostylism 78 Abnormal cases 84 Leaf-Shape 86 Palmate and Fern-leaf 87 Ivy-leaf 87 Habit 88 Double Flowers 89 Inheritance of ordinary double 91 Chaeactebs of the "Eye" of the Floweb .... 91 Large yellow eye x small eye 92 White eye x small yeUow eye 94 White eye x large yellow eye 94 GoLOUB 94 A. Stkh-Coloubs 95 Inheritance of Stem-colonrs 96 Partial Suppression of Colour 100 B. Floweb-Coloubs 101 Inheritance of Flower-colours 103 Partial Suppression of Colour 105 Inhibition 106 Experimental results : (1) Pale colours . . 108 (2) Full colours ... 109 (3) Inhibition . . .115 (4) Flakes . . . .121 Gametic Cocpldig and Repulsiox 124 Descbiption of Plates 130 Jonm. of Gen. i 74 J^xperiments with Primula sinensis Introduction. The experiments, of which the present paper is the outcome, were begun in 1903 by Mr Bateson and the present writer jointly, and in 1905 we published an account of our observations up to that time upon the inheritance of heterostylism^ Although I am alone responsible for the views put forward in the present paper, and for any errors which it may contain, the work with which it deals has been done in association with Mr Bateson, to whom much of such progress as has been made is due. Mr Bateson has given me the most generous help, not only in the elucidation of the results, but also in the practical business of carrying on the experiments. I am further indebted to him for giving house room to a large number of plants each year. The plates illustrating the various coloured forms which have been met with in the course of the experiments are reproduced from the beautiful and accurate water-colour drawings of Miss M. Wheldale, of Newnham College, Cambridge. I wish to take this opportunity of acknowledging again my in- debtedness to Messrs Sutton and Sons, who have most kindly given assistance in many ways during the course of this enquiry. My thanks are due also to the Botanic Garden Syndicate of Cam- bridge University, and to Mr R. I. Lynch, Curator of the Botanic Gardens, for the provision of housing, materials and labour. The principal objects of our investigations in Primula sinensis have been the inheritance of heterostylism and of colour. At the same time records have been kept of certain other characters, the inheritance of which has been found to be, for the most part, of a simple type and does not require any special comment here^ Heterostylism^. The dearth of short-styled plants occurring in the families raised from the self-fertilized heterozygote, which was noticed in our earlier experiments, is still maintained even in the larger numbers now obtained. On the other hand the same plants, crossed by the long-styled, give an excess of short-styled offspring. Our results do not as yet give a decisive answer as to whether these divergences, 1 Bateson and Gregory, Roy. Soc. Proc. B, Vol. 76, 1905, pp. 581—586. '■^ Some of these results have already been mentioned; see Bateson : "The progress of Genetics since the rediscovery of Mendel's papers," Prog. Rei. Bot., Vol. i. 1907, pp. 373, 383 ; Mendel's Principles of Heredity, Camb. Univ. Press, 1909. Gregory: "The inherit- ance of certain characters in Primula sinensis," Brit. Assoc. Rep., Leicester, 1907, pp. 691—693. 3 Bateson and Gregory, I.e. R. P. Gregory 76 in opposite directions in the two cases, are to be regarded as merely accidental, or whether they may have some significance, either in connexion with observed differences in the fertility of the various unions between plants of different form, or in other ways (p. 83). Colour. The colour of the stems and flowers in the coloured races is due to the presence of coloured sap. The colour may be absent from the flowers, which are then white, or from the stems, which are then green. Colour, both in flower and stem, is presumably produced, as in other cases, by the interaction of two or more complementary fectors. I have had no decisive case of the production of an ^i with coloured flowers from the mating of two albinos, but Keeble and Pellew^ record a coloured Fi from the mating of the red-stemmed "Snow King" with the green-stemmed "Snowdrift." Similarly as regards the stem-colours, I have no example of the production of a coloured ^i from the mating of two green-stemmed plants, but in two cases (p. 97) heterozygous plants with coloured stems have given unmistakably the ratio 9 coloured : 7 green stem. There exist several distinct types of coloration, both of the stem and of the flowers. Thus, the stem may be fully and evenly coloured (Plate XXX, figs. 1, 2), or it may possess only a faint colour, which is most easily recognized in the young leaves and leaf-stalks (Plate XXX, fig. 5). The faint colour is, in some cases, an elusive character, and the plants bearing it are only with difficulty to be distinguished from those devoid of colour in the stem. The inheritance of these two kinds of pigmentation of the stem may be explained most simply if we assume the existence of two separate and independent chromogen factors, each of which reacts with the common activator to produce, one the full colour, the other the faint colour (p. 96). The colours of the flowers and stems are inter-related in such a way that the more deeply coloured flowers never occur in conjunction with stems wholly green. Flower-colours may then be divided into two classes, namely, full colours, which are found only on plants having fiilly coloured stems ; and pale colours, which occur on plants having green or faintly coloured stems. White flowers may be associated with stems of any kind. When the albino " Snowdrift " (Plate XXX, fig. 7) was crossed with types having fully coloured flowers and stems, the ^2 contained only one real albino to every fifteen pigmented forms. These coloured forms were of three kinds, (1) full colours on red stems, (2) a type known in > Journ. of GeneticM, Vol. i. 1910, p. 4. 6—2 76 Experiments with Primula sinensis horticulture as " Sirdar" (Plate XXX, fig. 4 ; Plate XXXI, figs. 44, 45), (3) pale colours on faintly coloured or green stems. The " Sirdars " have a peculiar distribution of the colour. The pigment of the petals is one of the full colours, but it occurs in separate minute dots and the edges of the petals are white. Associated with flowers of this kind, the stems have pigment at the bases of the petioles and pedicels, the rest of the stem and leaves being green. The inheritance of the " Sirdar " character may be described conveniently if the " Sirdars " be looked upon as belonging to the fully coloured series, while they lack a factor, the presence of which is required to bring about the even distribution of the colour which is found in the full colours. The full colours and " Sirdars " together constitute three-fourths of the total F^ population. The remaining one-fourth consists of pale colours and whites in the ratio 3 : 1. The significance of the ratio 15 pigmented forms : 1 albino, and the relation of the pale colours to the full colours, is discussed in the text (pp. 103, 104). The full colours are divisible into three classes, namely, (1) shades of magenta, (2) shades of red or crimson, (3) shades of blue. The pale flower-colour is always a shade of pink, never magenta or red. This colour, in its deepest shade, is that of Sutton's " Reading Pink " (Plate XXX, fig. 13). Full colours are dominant to pale colour; magentas are dominant to reds, and blue is recessive to all magentas and reds. Whites may be dominant or recessive to colours. Suppression of colour, partial or complete, by dominant factors is a common phenomenon in Primula sinensis. Some of these factors affect the colour of the flowers only, and one, at least, affects the colour of both flowers and stems. When plants, which otherwise would have coloured flowers, are homozygous in the factors which suppress flower-colour, the flowers are quite white (dominant whites) ; when they are heterozygous in the inhibiting factors, the flowers are sometimes white, but are more often tinged with colour, the depth of the tinge varying with the races used and with the temperature of the house. As regards the suppression of flower-colour, the evidence reveals a curious complication in that the operation of two inhibiting factors, affecting distinct areas, can be separately traced. Of these factors, one suppresses colour in the peripheral parts of the corolla, the other affects the gynoecium and central part of the corolla. In consequence it follows that in F^ from fully coloured plants with coloured stigmas x dominant R P. Gregory 77 whites, there appears the peculiar type knowD as "Duchess" (Plate XXXI, figs. 27, 28), in which the flower is white peripherally and has a coloured centre. The mating of " Duchess " with plants having coloured flowers and green stigmas, gives a tinged white F^, exactly like that produced by the mating of coloured, red stigma x dominant white. Various light shades of flower-colour behave as dominants to the deep shades ; this dominance is due to the presence of factors which efifect the partial suppression of the colour. These factors are quite distinct, as regards their inheritance, from those described in the pre- ceding paragraph. Similarly, the light shades of stem-colour are dominant to the deep shades. The suppression of stem-colour is only partial, even in plants homozygous for the suppressing factors, and no dominant green stems are known. Flowers of a light shade may be borne by plants having deeply coloured stems, but the deep flower-colours never occur on stems not deeply coloured. It is clear, therefore, that the factor which effects the partial suppression of stem-colour exerts its action also upon the flower-colour. Besides the varieties constituted by combinations of the factors already enumerated, there occur various types having flakes or patches of colour (Plate XXXI, figs. 56 — 59) ^ As in other oases where such flaking has been encountered, the genetics of these varieties is not altogether clear, but in the case of Primula sinensis, as will be seen on reference to the text (p. 122), it is possible to frame a hypothesis which would give results consistent with those observed. Gametic Coupling and Repulsion (p. 124). Complete repulsion between the factor for the structural character of short-style and the magenta colour-factor was observed in a series of experiments in which short-styled salmon-pinks were mated with various long-styled plants carrying the magenta factor. The cases of partial gametic coupling which have been met with are interesting in that, in many of them, the two middle terms of the F^ series are much larger, relatively to the end terms, than they are in the majority of cases previously recorded. In the case of the coupling between magenta colour and green stigma, the results of several experiments approximate closely to the expectation based on the hypothesis that a coupling of the form 7:1:1:7 is present in the ^ Flaked forms mnst be carefully distingaished from " Sirdars." 78 Experime7its with Primula sinensis gametes of one sex only, those of the opposite sex consisting of equal numbers of the four kinds (p. 128). Other cases however are apparently not susceptible of complete explanation on these lines, and it seems possible that they may indicate the existence of lower forms of coupling than any given by the gametic series n-\ : 1 : 1 : w-l.» Further experiment however is needed before any definite opinion can be expressed upon this point. The history of P. sinensis, since its introduction into England in 1820, has been given by Mr A. W. Sutton^ and further notices by other writers have appeared from time to time^ It is interesting to notice that the earliest illustrations^ of the species represent short-styled plants of the ordinary habit (not stellata) with palmate leaves, light red stems, and light magenta flowers — all dominant characters. Heterostylism. In an earlier report Mr Bateson and the writer showed that the inheritance of the characters of long and short style is of a simple Mendelian type, the short style being dominant®. All the short-styled plants originally obtained for the purpose of these experiments proved to be heterozygous, but from their progeny pure short-styled plants have now been obtained. Nine such plants ^ Bateson, Saunders and Punnett, Rep. Evol. Comm. Roy. Soc. iv. 1908, p. 3. Lower series would be given by the general expression n-x : X : X : n-x where x is any odd number less than - . The expression may be made a general one, including all forms of partial repulsion as well as coupling, if x be taken as any number less than n. The F2 series would then be given by the expression 371^ - X (2n -x) : X (2n -x) : x (2n -x) : (n - x)^. ^ Journ. Roy. Hort. Soc. Mar. 1891, xiii. p. 99. 3 Gard. Chron. 1889, p. 115 ; Ibid. 1890, p. 564 ; Ibid. 1892, p. 12; Ibid. 1902, p. 269. * Bot. Reg. 539, May 1, 1821, under the name P. praenitens, and Lindley's Collectanea Botaniea, Tab. VII, 1821. The plants figured in the two works are clearly of very similar, if not identical, types. In Lindley's plate the drawings of the dissected flower apparently represent the short-styled form ; the flowers shown on the plant have rather the appearance of long-styled flowers. 5 Bateson and Gregory, Roy. Soc. Proc. B, Vol. 76, 1905, pp. 581—586. R. P. Gregory 79 have been used as parents : their offspring are shown in the following table: Number of short-styled ^lort- Long- Croas pUntsnsed styled styled Pare short-styled X Self 8 252 0 Pure short-styled ? x Long-styled ~1 ^ 1 Kl M ^H M •w ■e •o V «b t C3 00 «s CO -H i O 0-. (N (N c> k4 IH i* A CO CO f^l X - o* »o 1 s -* W5 OS ^ ^ i-H (M CO O! i-( tH 9 bD jj a CO o M l&g i-H «o t> 1 S3 o s i-H iH 1 ^ 1 "-I M f-i s 1 ^ >H ■^ f-K •o % 60 t^ % a o 05 o 05 ■H ^ t^ '^ l-H o SP I-l (M A( g 55 Q o» X - ot- ^ 1 o IM I-H CO 4 k. A 05 »o T»l to £» 1-H (M 9> ■g »«i o S? JS 3 03 5< », tc ■» a C5 O 05 -H m o «5 t- MS (N 1 ^ iZ°^ (M CO 1 o 1 : CD ^ 2 Ms ■^ 00 o GD a B ^ -*J> o CQ g) g*^ • a "S J3 60 a -5 -2 a '53 ■^■^ V. ■1^ a 1 § 1- >> 02 li GO 3 o "S 1 1 R. P. Gregory 81 TMe shotving individual families raised from the cross (DR xDR). Yeu Number in family =P Short Long Katio (*:l) JW d=(2^1-x cl< 9» Fi-$horU X self 1905 19 14 5 2-80 1 53-21 -11 •1210 2-299 21 10 11 0-91 : 1 19-11 2 00 4^0000 82-000 22 15 7 214 : 1 47-08 -77 •5929 13 044 26 20 6 3-33 1 86-66 -42 •1764 4-586 46 33 13 2-54 1 116-90 -37 •1369 6-298 31 20 11 1-82 1 56-43 1-09 1-1881 36-831 23 18 5 3-60 1 82-79 -69 -4761 10^950 51 40 11 3-64 1 185-70 •73 -5329 27-178 22 18 4 4-50 1 99-00 1-59 2-5281 55-618 25 19 6 3-17 1 79-25 -26 •0676 1-690 79 61 18 3-39 1 267-80 -48 -2304 18-202 27 20 7 2-86 1 77-23 •05 -0025 -068 . 106 76 30 2-53 1 268-18 -38 -1444 15-306 11 6 ^) 12 7 4 1-25 : 1 33-75 1-66 2-7556 74-401 4 2 2) 1906 84 60 24 2-50 1 210-00 -41 -1661 13-952 83 62 21 2-95 1 244-80 •04 -0016 -133 17 14 3 4-67 1 79-38 1-76 3-0976 52-659 22 15 7 2 14 1 47-08 -77 •5929 13 044 114 81 33 2-45 1 279-40 -46 -2116 24-122 1908 61 47 14 3-36 1 204-90 •45 •2025 12-353 24 18 6 3-00 1 7200 •09 •0081 •194 39 32 7 4-57 1 178-20 1-66 2-7556 107-468 40 31 9 3-44 1 137-60 •53 •2809 11-236 Other heterozygous shorts x self 1904 20 16 4 4 00 1 80-00 109 1^1881 23-762 10 10 6 9 4 1 300 1 ia5 00 •09 •0081 •162 1905 17 12 5 2-40 1 40-80 •51 •2601 4-422 1906 48 32 16 2-00 1 96-00 •91 •8-281 39-749 1907 68 51 17 3-00 1 20400 •09 -0081 -551 1910 44 32 12 2-67 1 117-50 •24 -0576 2-534 Totals 1226 897 329 84-83 29 3569-75 — — 654-816 Weighted Probable mean error o ratio = - f weieh ted I 3569-75 1226 nean ratio = 1 = 291 : •6745 A / 1. Zp

1-38 : 1 26-22 •15 •0225 •4275 9 5 4 3 2 1, 1905 20 9 11 •82 : 1 16-40 •41 •1681 3^3620 .. 24 12 12 1-00: 1 24-00 •23 •0529 1^2696 6 15 5 6 w 1^10: 1 23-10 -13 •0169 •3549 1907 50 33 17 1^94 : 1 97-00 •71 •5041 25-2050 1910 46 21 25 •84 : 1 38-64 •39 •1521 6-9966 Totals 724 382 ; 342 28-80 : : 25 891-88 — — 182-4512 Weighted mean ratio = ^ : 1 = Zp Probable error of weighted mean 891-88 " 724 ■ ~ ratio = -6745 123 : 1. 2pd2 :p{n-l) = -10. Ratio = 1-23 ±-10 : 1. R. P. Gregory 83 This would seem to imply the presence of some disturbing cause affecting the regular Meudelian distribution, but it is important to ascertain what reliance may be placed on the ratio determined from the sum of all the families taken together. If the total results be tested by the discordance of the results in the individual families which make up the total \ it is found that, in the case of the (DR x DR) crosses the approach to the normal 3 : 1 ratio is close, the observed result being 29 1 ± "09 : 1 (Table, p. 81). In the (DR x R) and (R X DR) crosses the observed result is 1-23 + lO : 1 (Table, p. 82) the theoretical ratio for 724 plants being 10 + 01 : 1. Examined in this way, the results obtained at present perhaps scarcely afford a clear indication as to whether the above noted diver- gences are to be regarded as merely accidental, or whether they may have some significance in regard to the observed differences in the relative fertilities of the various kinds of legitimate and illegitimate unions. Any significance, which the foregoing results may have in this connexion, lies in the possibility that the observed differences in the fertility of the legitimate and illegitimate onions^ may be, in part, due to differences in the fertility of the various kinds of gametic anions, or rather (since the results of the matings (DR x R) and (R x DR) are in sub- stantial agreement) to differences in the mortality of the three kinds of zygotes arising from these unions. All the experiments on relative fertility are in agreement in showing that the union (short-styled plant x short-styled plant) is distinctly the least fertile, while the legitimate unions are the most fertile. Assuming that all forms of gametic union are equaUy fertile, the cross (DR x DR) would give offspring in the proportion 1 DD : 2 DR : 1 RR while the cross (DR x jR) would give 1 DR : 1 RR. But if there are differences in the fertility of the various kinds of gametic union, the observed deficiency of short-styled offspring in the cross (DR x DR) might be due to the small number of pure short -styled plants which are produced, while the excess of short-styled offspring in the cross (DR x R) might be due to greater fertility of the union (D x R) as compared with that of the union (R X R). 1 I am greatly indebted to Mr F. J. M. Stratton, of Gonville and Cains College, Cambridge, for this method of examining the results. ^ See Darwin, Forms of Flowers, pp. 38 — 43, 246. Darwin found that the ratio of the fertility of the two legitimate unions taken together to that of the two illegitimate unions was 100 : 53. With this ratio that given by my experiments agrees very closely, but the fertility of the long-styled form, whether fertilized by its own or by the other form of pollen, is greater in the case of my plants than that observed by Darwin. The figures are Long X Short Short x Long Long x Long Short x Short Average number of seeds per capsule 33 25 21 11 It is to be presumed that the short-styled plants used by Darwin and Hildebrand included, like mine, heterozygoos as well aa pore individuals. 84 Experiments with Primula sinensis If we assume for the moment that the observed divergences from the simple Mendelian ratios are due to differences of this kind, then, if di, 02, 63 represent respectively the fertilities of the gametic unions Short x Long, Long x Long, and Short x Short, the results described above would give $1 :02 : 03=100: 89 : 44. These figures are quantitatively in general agreement with the relative fertilities, as determined by the average number of seeds per capsule, of the various kinds of union between plants of different form, the corresponding figures being 132 or 100 : 84 : 44 (see p. 83, footnote). The comparison must not be pressed too far, since the actual fertilities of the various unions, observed in any set of experiments, would depend in part upon racial characters. The agreement is however rather suggestive and, taken in con- junction with the results of our examination of the observed numbers by other methods, is suflScient to justify further investigation. The point can be tested experimentally by determining the constitution of all the short-styled plants in a number of large F2 families; we should then find whether there is any significant divergence from the theoretical proportion of 1 pure : 2 heterozygous short-styled offspring. Abnormal Cases. A case was described in the previous report^ in which the entire series of crosses made with a certain short-styled plant (No. 6/3) showed a definite and consistent departure from the normal expectation. The evidence already given showed that No. 6/3 behaved as an ordinary heterozygous short-styled plant when used as the female parent in crosses with long-styled plants, while its male gametes almost exclu- sively bore the dominant character^ The case promised to be of some interest, but unfortunately all the plants used as parents for succeeding generations proved to be normal pure short-styled plants, giving short- styled offspring only, when selfed and crossed either way with long- styled plants. No further elucidation of the case is therefore possible. The F^'s from crosses of this race with long-styled plants showed normal distribution of shorts and longs in the offspring, and are included in the F^ table given on p. 80. The results of all the crosses in which this particular race was used are recorded in the tables given on pp. 85, 86. 1 Bateson and Gregory, loc. cit. p. 584. 2 By an unfortunate error the statement made in the first paragraph on p. 585 of the previous report is inverted. The context makes it clear that the statement should have read: "the ovules of No. 6 gave a mixture of longs and shorts, and consequently were of two kinds, while all the plants raised from it as male were shorts." R. P. Gregory 85 Table showing the results of crosses made with No. 6/3 and its progeny in direct descent. Short- xSelf Short-Style d? xLon g-styled i Long-styled ? X Shor t styled (f styled ^ _j_ ^ parent Number Short- Long- Number Short- Long- Number Short- Long- of family styled styled of family styled styled of famUy styled styled r 37/4 4 0 39/4 4 2 24/4 3 0 40/4 6 1 35/4 4 0 6/3 J 43/4 3 0 72/4 7 0 I 45/4 4 2 74/4 1 0 17 5 15 0 / 126/5 22 0 127/5 3 3 80/5 14 0 128/5 11 21 87/5 104/5 143/5 10 17 9 0 0 1 37/4^ 149/5 8 0 177/5 14 0 183/5 14 1* 205/5 46 2 ■'■ 213/5 17 0 14 24 149 4(?3) [ 21/6 27 0 [126/5 was not used [126/5 was used as i 126/5 \ for crosses of parent m one cross. this type which [ ^ve no seeds] [ 24/7 25 0 27/7 27 0 2/7 12 0 211/6 ^ 28/7 33 0 60 0 25/7 41 0 [21V6 was not nsed 3/7 2 0 212/6 ■ for crosses of this type] 58/7 18 0 20 0 ' 26/7 54 0 29/7 23 0 4/7 54 0 31/7 43 0 57/7 68 0 21»/6 ^ I 32/7 33 0 99 0 122 0 • Beoorded as "doubtful." 86 Experiments with Primula sinensis Table showing the constitution of the F^s raised from crosses in which 6/3 and its progeny were used. f 1 Short-styled > {DR X DR) cSelf Fi Short-styled ? styled Cf. Masters, loc. cit. pp. 262, 297. - Bateeon, MendeV$ Principle* of Heredity, Camb. Univ. Press, 1910, p. 199. ' The discrepancy is almost entirely due to one F^ family which consisted of 66 singles and 45 doubles. Five other ^2*8 from the same parents however gave 188 singles, 61 doubles. 7—8 92 Experiments with Primula sinensis individual. The effect of the large yellow eye in giving rise, in the absence of the factor for short-style, to the " homostyled " form has been fully described on previous occasions'. Both the large yellow eye and the white eye have effects when combined with certain colour characters of the flower. Certain coloured forms possess a blotch of deep colour, which in flowers with the ordinary eye occupies a well- defined area at the base of the corolla lobes (Plate XXXI, figs. 50, 51). If this character be combined with the large yellow eye, the deep colour is, so to speak, pushed further outwards, and forms a rather ill-defined band round the periphery of the area occupied by the pigment of the eye^ But, so far as my observations go, when "Queen Alexandra" is crossed with the same coloured race, the blotch of deep colour is not developed in the F^ plants which have the white eye, though the corresponding forms with the ordinary eye are blotched. (1) Large yellow eye x small eye. The accompanying table (p. 93) shows the results, inclusive of those previously published', which have been obtained from crosses of the " homostyled " plants with both short- and long-styled plants having the ordinary eye. The crosses in which the F^ plant was selfed show a considerable deficiency of large-eyed offspring, and in those cases in which the small-eyed parent was short-styled, the deficiency is almost confined to the short-styled offspring. The crosses of the form {DR X R) have given results which, in the aggregate, do not differ appreciably from expectation, though again, in those cases where we are also concerned with short and long st)'le, the distribution of the offspring among the four types is not very smooth*, and is particularly irregular in one aberrant family (given separately in the table) where the excess of short-styled offspring with the small eye is very marked. It is only in the early years, however, that any great discrepancy manifests itself Very few crosses have been made with short-styled parents since 1906 ; but experiments with long-styled plants have been ^ Bateson and Gregory, loc. cit. pp. 582 — 584. * For illustration of flowers of this kind see Bateson, MendeV» Principles of Heredity, Camb. Univ. Press, 1910, Plate VI. figs. 19, 21. ^ Bateson and Gregory, he. cit. p. 584. •* In this connexion it must be borne in mind that in the crosses between short and long style there is throughout a deficiency of short-styled offspring when the f j is selfed, and an excess when the Fj is crossed with the long-styled. This would, of course, have a disturbing efifect in cases such as that under notice. R. P. Gregory 93 '^ g ^ tc £- 00 ^ 2 - 2 111 I i rH ;o 00 1-1 ^ ag" s ■^ 1-1 «o II S. S ^ 5i» Isl tCa -"K ^ Bo's .9ae '* Hi M A S S S3 9 I 6 iH I r 8? ^ 'So r>. « s S 3 (^ o a» as V t- K s >o C) a be s > t- 1 cS 3 1 Eh o H H ^ C4 00 n to 1 « ^ 1-1 v» 94 Experiments with Primula sinensis continued, and the totals for the last three years are 972 small-eyed, 326 large-eyed {expectation : 973-5 : 324-'6). It is therefore impossible to attach any great importance to the discrepancy in the early years, though at the same time it remains unexplained. (2) White eye x small yellow eye. The white-eyed race ("Queen Alexandra") is a recent addition to my collection and only a few F^ families have been raised from crosses in which it takes part. The heterozygote resulting from the cross with a small-eyed race can be distinguished, on close examination, from the pure "Queen Alexandra " by a faint appearance of yellow or yellowish-green, which is most pronounced on the rays corresponding with the median line of each petal (Plate XXXII, fig. 62, No. 35/9) i. Three F^ families have been raised from the gelf-fertilized hybrid, and have given 182 white eye and heterozygous, 67 small yellow eye {expectation : 186-75 : 62'25). (3) White eye x large yellow eye. The heterozygote resulting from this cross is not distinguishable to the eye from that of the preceding case (Plate XXXII, fig. 62, No. 36/9). The one F^ family raised from the hybrid by self- fertilization has given 52 white eye and heterozygous, 12 large yellow eye {expectation : 4^ : 16). An attempt to separate the pure from the heterozygous white-eyed offspring gave 19 with no trace of colour in the eye, 33 with faint yellow rays. Colour. The various forms of red stem, and the colours of the flowers, are due to the presence of coloured sap. Both in the stem and in the flower the simple colour may be modified by the action of numerous factors which affect its distribution, intensity and tint. There is a close relation between the colour of the flower and that of the stem, in that fully coloured flowers are only produced by plants having fully coloured stems. The deepest colour in the flowers of a green-stemmed plant is that exhibited by the pale pink strain known as "Reading Pink" (Plate XXX, fig. 13), while the white-edged type exemplified in "Sirdar " is characteristic of plants in which the stem-colour is restricted to the 1 The contrast between the yellow rays and the white ground is somewhat intensified in photographic reproduction. R P. Gregory 96 collar and bases of the petioles (Plate XXX, tig. 4 ; Plate XXXI, figs. 44, 45). The degree to which colour is developed in the stem may therefore be taken as an index of the limits within which the colour of the flowers will be confined. All the red-stemmed whites which I have examined were found to be white in virtue of factors which inhibit the development of colour in the flower, though their range of action does not extend to the stem'. A. Stem-Colours. Various types of coloured stems are illustrated in Plate XXX. The plants shown in figs. 1, 2, 4 and 5 all possess, in varying degrees, the common purplish-red sap. Sap of this colour is present in the stems of all the races which have the usual magenta or red flowers, and though there are, no doubt, minor dififerences in the tint in diflferent races, it is scarcely possible in practice to make any distinction between forms which differ in so slight a degree. There are, however, two kinds of flower-colour which are associated with distinctive stem-colours; in the races which have blue flowers the stem has a corresponding colour, as compared with that of the commoner purplish-red types; while the clean red stem, shown in fig. 3, is, so far as my observations go, limited, in the fully coloured form, to the strain known as " Orange King" (fig. 8). In coloured stems the red sap may be distributed over the whole of the stems and petioles (Plate XXX, figs. 1 and 2), or it may be developed only in certain regions, the other parts being green. Fig. 4 shows a form in which the colour occurs only in the collar and bases of the leaf and flower stalks ; in plants with coloured flowers this type of stem is always associated with a peculiar distribution of the flower-colour which is characteristic of the strain known as "Sirdar" (Plate XXXI, figs. 44, 45). In fig. 5 there is represented a lower type of stem-colour, in which the colour is most pronounced in the young petioles. It is often only faint, and is sometimes scarcely discernible in the older leaf stalks, so that the character is somewhat elusive. It is dominant to the complete absence of sap-colour exhibited by " Snowdrift " (fig. 7), but the discrimination between the various types in F^ is ditficult, the more so since " Snowdrift " brings in a factor which reduces the apparent colour to a minimum. ' Keeble and Pellew record the existence of a recessiTe white on red stem {Joum. Genetic*, Vol. i. 1910, p. 1). 96 Experiments with Primula sinensis In the foregoing types the colour extends into the root-stock and roots, and in the faintly coloured forms its presence is much more easily detected there than in the stem, where the colour of the sap is masked by the green colour of the chlorophyll. The plant represented in fig. 6 is the " Ivy-leaf." In this form the colour can be recognized most readily in the young petioles, and it also appears, though more faintly, in the pedicels. In older leaves the colour may bf noticed at the base and sometimes along the edges of the leaf-stalk. It does not appear to extend to the root-stock and roots. Outline of the inheritance of stem-colour. In its general outlines, the inheritance of stem-colour is simple. Thus, the red-stem crossed with a green-stem gives an F^ in which the red-stemmed offspring are either approximately 9 in 16, or 3 in 4, according to the constitution of the green-stemmed parent. The full colour crossed with the faint colour (fig. 5) gives, in F^, 3 of the former to 1 of the latter, and similarly the faint colour behaves as a simple dominant to the complete absence of colour. Although the character of the stem in " Sirdar " is, in its lighter shades, not very different in appearance from that of other faintly coloured types, the inheritance of stem-colour can be most simply explained if the " Sirdars," which appear in certain F^s, are regarded as forming a part of the fully coloured population, lacking, however, in the factor {F) which effects the even distribution of the colour in the stems and flowers. We have then a factor {R) for colour, and epistatic to R, and without effect in its absence, a distributing factor F^. In order to provide for the existence of the forms with some faint colour in the petioles we require to assume the existence of another factor {Q) determining this character, which is independent of R and F and is unaffected by them, except in so far as the faint colour is not discernible when R and F are present. In crosses between plants with the lower grade of stem-colour and those without colour, the last factor (Q) only comes into play, and the 3 : 1 ratio is obtained in F^ (Table, p. 98, II.). Since " Sirdars " have only occurred in my experiments in cases in which "Snowdrift" was 1 The use of a so-called distributing factor is intended merely as providing a simple means of formulating the observed results. The relation which subsists between the " Sirdar" types and the self -colours is probably different from that which obtains between flakes and self-colours (p. 122). R P. Gregory 97 used, we are justified in assuming that all the other races which have been used possess the factor F ; consequently, crosses between the full- coloured stem and the faint colour merely exhibit the segregation of the factor R, the effect of Q, which is present in all the offspring, being masked when R is also present (Table, p. 98, III.). The same applies to the crosses between the full colour and the green stem, but in this case one-third of the offspring have clean green stems (Table, p. 99. IV.). In the F^& from crosses between " Snowdrift " and races with fully coloured stems " Sirdars " occur ; and if the factors inhibiting flower- colour be absent, the F^ is found to contain approximately, in every 16 plants, 9 with fully coloured stems and flowers, and 3 " Sirdars " ; while of the remaining 4, 3 may have faint colour in the petioles, or they may all be devoid of colour in the stem, according to the presence or absence of the factor for faint colour in the coloured parent. The total numbers obtained in these crosses (Table, p. 99, V. C) show some divergence from the expectation set forth above, in giving an excess of " Sirdars." The divergence is however almost entirely due to the results obtained from the first two families raised, which gave 142 full, 75 "Sirdar" and 67 faint and green. In the later experiments a close approximation to the theoretical proportions has been maintained, the numbers obtained being 329 full, 110 " Sirdar," 134 faint and green. In crosses between " Snowdrift" and red-stemmed dominant whites, the "Sirdar" character cannot be determined with any accuracy in those offspring which have white flowers. In these F^s the observed numbers of full- coloured stems and light stems (including " Sirdars ") approximates very closely to the expected ratio of 9 : 7 (Table, p. 99, V. B). There remain however cases in which the 9 : 7 ratio is clearly indicated in F^s from which " Sirdars " are absent (Table, j). 98, I.). Only two such cases have been met with, but the result strongly suggests that, in Primula, as elsewhere, at least two complementary' factors are necessary for the production of colour. In one of the cases, the character of faint stem- colour was not recorded separately, and we only know that the family consisted of 51 fully coloured and 33 light or green stems. In the other case, the coloured parent was a dominant white, and the offspring consisted of 49 fully coloured, 13 with colour in the petioles, and 25 devoid of colour, or 49 fully coloured, 38 light stems (.9 : 7 = J^8•9^ : 38-06). In so far as reliance can be placed upon the distinction between plants with faint colour in the petioles and those devoid of colour, this result further suggests that one comple- 98 Experiments with Primula sinensis mentary factor (C) is common both to the factor for full colour {R) and to that for faint colour {Q), so that the combination CR gives full colour^, and the combination GQ gives faint colour in the collar. The constitution of the hybrid would then be Gc Rr Qq, and the F^ would consist of the three types in the proportion of 36 full : 9 faint : 19 green, or, in a total of 87 plants, 48-94 : 12-23 : 25-83. The only matings of the " Ivy-leaf" from which F^s have as yet been obtained, are its crosses with " Snowdrift " and with full-coloured forms. The ^2 from the cross with "Snowdrift" is chiefly interesting in con- nexion with the partial suppression of stem -colours, and is considered more fully under that head (p. 101). Unlike the majority of the experiments on stem-colour, in which the observed results agree witli the expectation very fairly closely, there is a great dearth of light- stemmed offspring in the F^'s from the crosses between "Ivy-leaf" and plants with fully coloured stems. The deficiency is most marked in the class in which the light colour is combined with the "Ivy-leaf" habit, but is also apparent, though in less degree, in the light-stemmed plants of the normal kind. There do not however appear to be sufficient grounds for supposing that any novel phenomenon occurs in these cases. Table shovnng the results of experiments in regard to stem-colour. I. Red stem (C EF Q) x Green stem {c rF q) Fi selfed 1 family Red 51 Light 33 Colour in petioles 13 Green 25 Red 49 38 Totals ... "lOO 71 Expectation (9 : 7) 96-2 74-8 11. Faint colour in petioles (C Q) x Green stem (C q) Fi selfed 9 families Faint colour 366 No colour seen 130 Expectation (3 : 1) 372-0 124-0 III. Red stem (G RF Q) x Faint colour (C rF Q) Fi selfed 11 families Red stem 384 Faint colour 120 Expectation (3:1) 378-0 126-0 » Strictly speaking this combination gives the parti-coloured type " Sirdar," but as no "Sirdars" appear in this F-y we are not here concerned with the distribution of the full colour. R P. Gregory 99 IV. Red ttrm (C RF) x Green item, no colour teen (C rF) \ selfed 11 families Red stem 39a No oolonr seen 128 Expectation (3.1) S92-25 13075 \ X green stem 6 families 99. 104 Expectation (1 : 1) 101-5 101-5 V. CroBiea giving " Sirdars." Red stem (C RF Q) x " Snowdrift " (C rf q) In 1905 many plants were discarded as seedlings ; as there is no record of the flower-characters of theae plants, the " Sirdars " cannot be distinguished from the other light-stemmed types. In the Fj's from (" Snow- drift "x dominant white) the flower-characters of a proportion of the family are masked by the presence of the dominant white character, and in such cases the " Sirdars " cannot be certainly distinguished from other light stems. A. 1905 crosses. F, selfed 4famiUe8 Red stem 76 Light stem (including >^ ' ' Sirdar ) ) Expectation (9 : 7) 69-2 53-8 B. Dominant white x " Snowdrift." Fi selfed 8 families Red stem 440 „ 337 Expectation (9 : 7) 4371 3399 C. Ck)lonred, red stem x " Snowdrift." 2?, selfed 11 families Red stem 471 "Sirdar" 185 Fa^^* colour) ^^^ and green ) Expectation (9:3:4) 482-1 160-69 214-25 VI. Red stem x " Ivy-leaf." Bed stem 1. Light stem F] selfed 7 families Expectation Palmate 626 587-25 Ivy 197 195-75 Palmate Ivy 177 44 195-75 65- 823 783-0 221 2610 The red stem of " Orange King " (Plate XXX, fig. 8). "Orange King" originated in horticulture a few years ago, and was obtained by Messrs Sutton as a sport from " Crimson King." The "Orange King" character of flower and stem is recessive to that of " Crimson King," and in the F^ the two forms reappear in numbers approximating to the 3 : 1 ratio. This result would indicate that a single factor suffices to restore those characters which diflferentiate " Orange King " from " Crimson King." The only other matings of " Orange King" of which I have experience are those with " Snowdrift." The hybrid resulting from this cross is indistinguishable to the eye from the hybrid between "Crimson King" and "Snowdrift." The 100 Experiments with Primula sinensis " Orange King " characters of stem and flower are however so intimately associated that the fuller consideration of this case may be deferred until the section dealing with flower-colour (p. 114), Partial Suppression of Colour. The light shades of the colour in the stem are dominant to the intense shades. This fact is well illustrated in the F^s from (" Ivy- leaf" X deep red stem), where the red-stemmed plants fall into two sharply separated categories. The numbers obtained are : Light Intense 3 families ... 157 49 Expectation ... 154'5 51'5 Similar sharply divided categories are found in families raised from the cross of a deep red stem with the jPj of (" Snowdrift " x deep red stem). The numbers obtained in these crosses are : Light Intense 9 families ... 198 202 + 3 doubtful (occurred in one family) Expectation ... equality. It is clear from these cases that the light class, taken as a whole, may be explained as being due to the presence of a single factor, epistatic to the factors for colour, which diminishes the intensity of the pigmentation (pallifying factor). In the F^'s produced by the self- fertilization of the Fi from the cross ("Snowdrift" x deep red stem) there are forms intermediate between the light and the very dark red stems, and the separation between the classes is by no means sharp. No doubt many of these intermediate forms are the result merely of heterozygosis in the factors for colour and for its partial suppression. In different pure races, however, and in the hybrids produced by their matings, colour is developed to very different degrees, and in order to account for the detailed phenomena it would probably be necessary further to elaborate the simple scheme put forward here, which is intended only to apply to the general outlines of the phenomena of the partial suppression of stem-colour. The partial suppression of flower-colour follows, in general, very similar lines to that of stem-colour, but is independent of the latter, at least to the extent that light flowers may occur on deeply coloured stems. In the lower grades of stem-colour the same relation subsists between the light and intense states as in the fully coloured types, but the separation of the categories is R. P. Gregory 101 of course a matter of much greater practical difficulty. The point has been studied with some care in the cross ("Snowdrift" x "Ivy-leaf" ^). The Fi has a faint trace of colour in the young petioles; the F^ consists of (1) plants with full colour in the young petioles, which grade through rather lighter forms to (2) those in which faint colour in the petioles can be recognized with certainty; and these again grade, through doubtful forms, to (3) those in which no colour can be detected. Precise numerical results cannot be given, but so far as can be judged the constitution of the families can be fully explained without the assumption of any other factors than those for colour and for its partial suppression. B. Flower-Colours. The various colours exhibited by Primula sinensis may be classified as (1) full colours, which jjaay exist either in the self or in flaked patterns (Plate XXXI, figs. 56 — 59), and are always associated with fully coloured stems; (2) "Sirdars" (Plate XXXI, figs. 44, 45), in which the characteristic distribution of the full colour is associated with a definite type of stem-colouring; and (3) pale colours (Plate XXXI, fig. 46) which occur only on green or faintly coloured stems. White flowers may occur in association with stems of any kind, and may be dominant or recessive to colours. The dominant whites owe their character to the possession of factors which inhibit the development of colour in the flower (see under "Inhibition," p. 105). The full colours and " Sirdars " may be sub-divided into blues, magentas and reds; in the pale class, however, no distinction of this kind can be drawn, for the pale forms which correspond with the magenta full colours (and give magenta offspring when crossed with a red) are quite indistinguishable to the eye from those which correspond with the red class (and give only red offspring when crossed with reds). Colours belonging to all these classes appear in the offspring of certain hybrids; the sharpness of the separation between the various classes of full colours varies, however, in different cases, and though in the majority the classes are fairly readily distinguished, in others intermediate forms occur. Whether these intermediate forms are always heterozygous cannot yet be said ; in the few experiments in which they have been tested they have proved to be so^ ' The "Ivy-leaf" used in the experiments on stem-colour was heterozygous for the pallifying factor. Hence the appearance of "Ivy-leaf" here as the parent lacking the pallifyiag factor, and previously as the parent bringing in that factor. ' A plant with red stigmas, which probably belonged to the red class but had flowers of a colour somewhat intermediate between the magenta and red classes, has since proved to be homozygous for its type of colour. 102 Experime7its with Primula sinensis I have not yet undertaken any systematic experiments with the blue-flowered strains of Primula sinensis. Bhies occurred among the offspring of a certain magenta plant obtained in 1903, in such propor- tions as to corroborate the more extended results obtained by Messrs Sutton, which show that the blue colour is an ultimate recessive \ For the purpose of these experiments it has been found convenient to work mainly with well-known horticultural strains, which provide a series of fixed standards of colour. The colours of the races of which principal use has been made are illustrated in Plate XXXI. For con- venience of reference descriptions of the various types are given below. Description of strains used in experiments on colour. Recessive White. " Snowdrift." (Plate XXX, figs. 7, 10.) Fern-leaf, green stem, white, green stigma. Pale colours. " Beading Pink." (Plate XXX, fig. 13. ) Palmate, green stem, pale-pink, green stigma. Full colours. Salmon Pink. Palmate, purplish-red stem (light), salmon-pink, green stigma, short style. Rosy Magenta. (Plate XXX, figs. 19, 20.) Palmate, purplish-red stem (light), magenta (rosier than Fj type, light), green stigma. "Crimson King." (Plate XXX, fig. 9.) Palmate, purplish-red stem (deep), deep crimson, red stigma. "Orange King." (Plate XXX, figs. 3, 8.) Palmate, red (not purplish-red) stem, pink flowers, red stigma. Dominant Whites. Double White. Palmate, green stem with colour in leaf bases (Plate XXX, fig. 6), double white flowers, green stigma. " Primrose Queen." (Plate XXX, fig. 12.) Palmate, purplish-red stem (light), white flowers, green stigma, large yellow eye. "Queen Alexandra." (Plate XXX, fig. 11.) Palmate, purplish-red stem, white, green stigma, white eye. Colour uncertain (see p. 122). "Ivy-Leaf." (Plate XXX, fig. 5, Plate XXXII, fig. 60.) Palmate, non-crenate, stellata, green stems with colour in leaf bases'^, flowers? very pale colour flaked, green stigma. The "Ivy-leaf" is a very monstrous type, the non-crenate character of the leaves being always accompanied by partial abortion of the floral organs. Stamens are often absent and the corolla may be reduced to a tube surrounding the style, without petal-lobes. Petal-lobes, when developed, may be only small strap-shaped structures. Owing to the poor development of the corolla the colour of the plant used in the experiments cannot be determined with certainty. Such plants as survive usually become fertile in the second year, producing however 1 Bateson's MendeVs Principles of Heredity, Camb. Univ. Press, 1909, p. 135. 2 The colour is insufiiciently shown against the dark background in the plate. R. P. Gregory 103 only small quantities of pollen. A very common character of the " Ivy-leaf" is that the axis of the inflorescence forms a more or less conical elongation above the whorl of pedicels, at the apex of which carpellary structures may be developed, or ovules may be borne on an exposed disc, which is sometimes surrounded by small lobed expansions (probably carpels) each terminating in a knob resembling a stigma ^ In extracted Fg-forms with green stigmas these expansions are green, in those with red stigmas they are coloured. Outline of the inheritance of flower-colour. When a plant with fully coloured stems and flowers is crossed with the albino " Snowdrift," the F^ consists of Full-colours, " Sirdars," Pale colours and Whites in the ratio of 9 full : 3 "Sirdar" : 4 pale colour and white. Although the number of whites recorded in these F^Q is somewhat less than 1 in 16, there can be no doubt, I think, that this represents the proportion in which they really occur*. In a family of this kind, the plants having fully coloured stems always have fully coloured flowers ; that is to say, the full colour, when present, is distributed throughout the whole plant. Consequently, it is not necessary in this case to draw a distinction between stem-colour and flower-colour, since the colour of both behaves as a single unit'. The inheritance of the full colour, then, follows the scheme outlined in the case of stem-colour (p. 96), in which the relation of the " Sirdars " to the full colours is also explained. The place of the pale colours in the scheme must be left undecided until further data are available. It may prove that they constitute an independent series of colours, comparable with the faint stem-colours in their relation to the full colours ; or they may perhaps result from the resolution of the combination of factors to which the full colour 1 The structures described by Mr L. Crawshay in a malformed Primula (Journ. Roy. Hort. Soc. XXXVI. 1910, p. xxix) are apparently of the same nature. ' The discrepancy is almost certainly due to the difficulties attending the separation of the pale colours from the whites. The fact that we have sometimes detected a trace of colour in pure " Snowdrift," when the plants have been kept cool, points in the same direction. ' Keeble and Pellew's experiments (Journ. Genetics, Vol. i. 1910, p. 1) indicate that in certain pigmented forms one, at least, of the factors which determine the production of colour may be absent from the flowers, which are then white, though it is present in the stem, which is therefore coloured. This evidence that, in certain cases, the factors for colour are not distributed throughout the whole plant, is indirectly supported by the results of my experiments with the red-stemmed dominant white "Primrose Queen" (pp. 116, 123). 104 Exjjeriments with Primula sinensis is due. If the former suggestion should prove to be correct, the fact that all our fully coloured races, when crossed with " Snowdrift," have given pale colours in t\ ; and the further fact that two heterozygous "Sirdars" have thrown only "Sirdars" and whites, would be merely fortuitous results depending on the particular races which have been used. It may be noted that, if the pale colours are an independent series, certain matings between F^ "Sirdars" and pale pinks should give full colours, while others should not do so; the alternative case would seem to imply that all these matings should give full colours. The primary colour of the fully coloured flower is red\ The numerous shades of red are due to the presence or absence of factors which reduce the intensity of the pigmentation, and other factors which produce slight changes of tint. In the simplest cases the magenta class may be regarded as due to the action of a factor epistatic to the factors which give rise to the red colour; in other cases, however, the proportions of the magenta and the more rosy class indicate the 9 : 7 ratio (see under " Rosy Magenta," p. 110) ; and in yet another case an intermediate, mated with a clean red, gave typical magentas among its offspring. There exist corresponding shades of magenta for many, if not all, the numerous shades of red. The flaked or splashed forms of coloured flowers show a considerable range of variation in the degree to which the flaking is developed, and in the size and form of the coloured areas. The distinction between the red and magenta colours in flakes is often attended with some difficulty. In self-coloured red flowers it will often be noticed that a bluer tint is developed at the edges of the petals, and in forms in which the colour is weakly developed just round the eye a similar bluish tint will be noticed in this region. In the same way, there seems to be a tendency for the red colour to pass into a bluer tint at the edges of the coloured stripes and splashes, and in flowers showing fine as well as coarse splashes, it is often to be noticed that the coarse splashes are red, while the minute dots of colour, viewed with the naked eye, would certainly be put down as magenta^ My experience of flaked flowers is limited to the F^a of crosses in which the "Ivy-leaf" took ' The relations of blue to the other colonrs have not been worked out. The fact that blues appeared in small numbers in a cross in which the rest of the coloured offspring were red suggests that blue is either hypostatic to red, or, if it forms an independent series, is masked by red. 2 A somewhat similar difficulty occurs in the "Sirdar" type, owing to the optical effect of the intermingled coloured and colourless dots. In this case, however, the distinction between magentas and reds can be made readily with the help of a microscope. R P. Gregory 105 part; the results are such as to indicate that the flaked condition behaves aa a recessive to the self-colour (see, however, p. 122). The pale-coloured flowers on green stems are scarcely affected in appearance by the presence or absence of the numerous factors which produce such marked changes in the fully coloured types of flower. It is often by no means easy to recognize the pale colour when it occurs in the flaked condition ; this is no doubt an optical difficulty, for the lower forms of this colour in any case need careful examination in order to distinguish them from white. Among the pale-pinks there occur forms in which the colour is more pronounced peripherally, others in which it is central, others again in which it forms peculiar bands. But the difficulty of observation is such that no attempt has yet been made to study the inheritance of these variations. Partial Suppression of Colour. As in the case of stem-colours, the intense colours of the flowers are produced only in the absence of a factor which diminishes the intensity of the pigmentation, and so gives rise to the dominant light shades. The partial suppression of flower-colour may be brought about by either of two factors, of which one affects the flower only, the other the whole plant. Hence light flowers may occur in association with dark stems, but deeply coloured flowers are limited to plants with deeply coloured stems. In many F^s there occur classes intermediate between the lightest and the very deep types, but, though the existence of such classes may be clear enough, it is difficult, if not impossible, to draw any sharp line between them, and, as in the case of stem-colours, it must remain undecided whether one pallifying factor, in its various pure and heterozygous combinations, is sufficient to account for all the shades, or whether a series of such factors is involved. The factors which effect the partial suppression of colour seem to diffier in degree rather than in kind from the factors which, in pure races, completely inhibit the development of colour in the flower. Inhibition. In the red-stemmed " Dominant WhitesS" the whiteness of the flower is due to the presence of a substance which inhibits the 1 Gregory, Rep. Brit. Auoc., Leicester, 1907, p. 692. Joam. of Gen. i 8 106 Experiments with Primula sinensis development of colour in the flower^ It has recently become clear that this inhibition is due to the action of two separate components, each of which has its own localized effect. The one component is present in the majority of the races which have coloured flowers, in the form of a factor which prevents the development of coloured sap in the ovary, style and stigma, and gives the green stigma. The second factor, on the other hand, affects only the peripheral parts of the corolla, and in the absence of its fellow, gives rise, in fully coloured forms, to the characteristic "Duchess" type of flower (Plate XXXI, figs. 27, 28), in which coloured sap occurs only in the gynoecium and in the flushed eye of the corolla^ In the pale colours the stigma is only faintly coloured, and the presence of coloured sap can be most easily detected in the placenta and ovules. The recessive green stigma (which corresponds with the recessive white flower, and is green through the absence of colour and not from its inhibition) has been recognized experimentally in F^ plants fi-om the crosses of "Snowdrift" with "Crimson King." The factors for inhibition may of course be present in plants which are devoid of the factors for colour ; thus the green stigma of " Snowdrift " is of the dominant kind, and other green-stemmed whites have been met with, which possess both the factors for inhibition. Plants which contain the factors for colour and are heterozygous for the inhibiting factors have tinged white flowers with green stigmas, the depth of the tinge varying with the intensity of the underlying colour (Plate XXXI, figs. 21, 24—26, 32). A heterozygous form of '•' Duchess " is represented in "Sir Red vers Buller" (Plate XXXI, fig. 29), and various other forms, depending on the presence or absence of the magenta and other factors epistatic to colour, exist (figs. 30, 31). In all of them the peripheral part of the corolla is tinged to a greater or less degree, and the full colour is only developed immediately around the eye. One other character of flower-colour should be mentioned here. In certain varieties there occur spots of deep colour on the petals just external to the eye (Plate XXXI, figs. 50, 51). The inheritance of this character is, in itself, simple ; but the full development of the spots is limited by the operation of other factors^. Thus, the deep spots are 1 In certain races belonging to this class an occasional splash or stripe of colour may often be observed, sometimes in only one or two, sometimes in many of the flowers. 2 The flush rouud the eye is often only faint, especially in flowers of the stellata variety. The flush is an independent character limited to plants with red stigmas (see p. 120). '^ Bateson, Mendel's Principles of Heredity, Camb. Univ. Press, 1909, p. 138. R P. Gregory 107 not fully developed unless the stigma is coloured ; nor, even if the stignia be coloured, are they developed in plants which have the white eye of the "Queen Alexandra" type (Plate XXX, fig. 11)'. Again, the spots are deeply coloured only in deeply coloured flowers, their appearance in flowers of a light shade somewhat resembling that which they assume in plants with green stigmas. The limitation imposed in these cases results from the dominance of an inhibiting character. There are also limitations due rather to the lack of a coloured base ; the spot is not visible in pale-coloured flowei-s, nor again in the flaked patterns of full colour, unless it should happen that the colour is distributed in any of the petals in a wide stripe covering the area occupied by the spot. Such petals exhibit the spot, which may not be visible in other petals of the same flower. Plants in which the development of the spot of deep colour is inhibited by the factor for green stigma have flowers of a definite type, characterized by the presence of a well-defined brownish spot. The character is a different one from the diffuse brownish band which appears in some plants as the flowers fade (Plate XXXI, figs. 54, 55), and is very clearly marked in the young flowers (Plate XXXI, fig. 50), becoming less conspicuous as they grow older (fig. 51). This "ghost" of the spot is well seen in the Fi from ('•Crimson King " x •' Rosy Magenta"), and in the F^ all the plants with red stignus have the spot of deep colour. The inheritance of the character is further illustrated in the subjoined experiments in which a series of F^ pale pinks were crossed with " Orange King." Green stignma Red stigma No spot Beference Number Ghost of spot No spot Spot 36/10 12 — 9 37/10 — — 8 38/10 — — 6 39/10 — 2 — 40/10 No plants 41/10 — — 4 42/10 6 7 — 43/10 44/10 No plants 45/10 3 — — 46/10 9 7 — 47/10 6 — — * These three had light stems, and a brownish marking in the region of the spot somewhat resembling the marking which represents the spot in plants with green stigmas. • In plants with the large yellow eye the spot is pushed outwards, so that it occupies the same position relative to the eye pigment as it does in the usual type (see Bateson, loc. eit. Plate VI, figs. 19, 21). a-2 108 Experiments with Primula sinensis Experimental results. (1) Pale colours. Pale-pink (Plate XXX, fig. 13 ; Plate XXXI, fig. 46). Pale-pinks have occurred in the F^s of all ray crosses between full colours and " Snowdrift," as well as among the progeny of certain heterozygous full colours obtained from various sources. It is also the characteristic coloured form thrown by heterozygous dominant whites having green or only slightly coloured stems. If the pale-pink be crossed with " Snowdrift " the resulting F^ shows some dilution of the colour. Heterozygous pale-pinks can throw nothing but pale-pinks and whites, and this they do in the proportion of 3 pinks : 1 white, the numbers obtained being 51 pink, 16 white. One of these plants crossed with "Snowdrift" gave 23 pink, 17 white. My experiments throw no definite light on the question of the dependence of the colour on two complementary factors, a chromogen and a ferment, but in this connexion the cross between "Ivy-leaf" and " Snowdrift " should be mentioned. Both parents appear white, while the hybrid has definite though faint colour in the flowers. In F.2 plants with definitely coloured flowers form approximately 9 in every 16 plants, the observed number being 144 coloured in a total of 273 plants. Subsequent experiments with the " Ivy-leaf," however, suggest the possibility that, instead of its being a white, as I had supposed, it may have the very pale pink colour in the flaked condition (see p. 122). The pale-pinks may or may not carry the magenta factor. Of 10 pale-pinks tested by crossing with reds, 6 were pure for the magenta factor and gave 65 offspring, all magenta ; 2 were heterozygous and gave 30 offspring, 14 magenta, 16 red ; and 2 were without the magenta factor and gave 16 offspring, all red. One other, mated with a magenta throwing magentas and reds, gave 5 magenta, 5 red, and was therefore without the magenta factor. The same set of experiments served to reveal other characters carried by the pale-pink. Nine F^ pale-pinks from the cross (" Crimson King" X "Snowdrift") gave offspring when crossed with "Orange King." In the resulting families there occurred intense and light colours, in one case rosy-magentas as well as the usual kind, in another case deep crimson-magentas together with reds very like "Crimson King," while in some cases the spot of deep colour was present in all the offspring having coloured stigmas, in others in only a proportion of them^ One pale-pink without colour in the stem was found to have 1 See Table, p. 107. R. P. Gregory 109 the recessive kind of green stigma, all the offspring resulting from its mating with "Orange King" having coloured stigmas^ As was to be expected from the origin of the pale- pinks, none of the offspring showed the colour characters of " Orange King," the stem-colour being always purplish-red, and the colours of the flowers those of types found in "Crimson King " F,'s (Plate XXXI, figs. 33, 36, 39, 41, 43). The pale- pink strain " Reading Pink," crossed with " Orange King," gives a red (Plate XXX, figs. 15, 16) rather towards the magenta side of the class and having purplish-red stems. (2) Full colours. Salmon-pink. The race of this colour which has been used for experiment was derived from a heterozygous crimson, or crimson- magenta, which threw forms like itself, together with salmon-pinks and blues. The crosses in which this race has been tested give very simple results, since the race was pure for the light colour, and was without factors producing, the minor variations of tint. Heterozygous salmon- pinks may throw pale-pinks only, or whites may appear in addition ; in either case the proportion of full colours in the offspring follows the stem character. Crosses between such heterozygous salmon-pinks and either " Snowdrift " or the pale-pink carrying magenta show the simple operation of the magenta factor; crosses of this kind have given 44 magenta, 52 pale colours. Salmon-pink x " Snowdrift." The F^ from this cross is a magenta with light red stems. In the F^ there were obtained, in 3 families : Foil coloan " Sirdsra " No ooloar in stems Ma^nta Salmon Magenta Salmon Pale-pink White 57 J6 16 6 19 10 52-3 17-4 17-4 5'8 23'3 7'8 The expectation, given in italics, is based on the scheme already set forth, namely, that the full colours represent the "Sirdars" -h a factor which effects the even distribution of the colour. The salmon-pink is one of the few short-styled races with which as yet detailed experiments upon the inheritance of colour have been made', and a most interesting relation between the structural character ' See Experiment 41/10 in the Table, p. 107. The pale-pinks used in Experiments 37/10 and 38/10 bad faintly coloured stigmas. ' The obvions advantages of working with pure horticultural strains entail the disadvantage of working exclasively with long-styled plants, since the short-styled form is eschewed by florists. 110 Experiments with Primula sinensis of short-style and the magenta colour has been revealed. In the F^s, bred from plants heterozygous for both characters, the salmon-pinks are invariably short-styled. The results clearly indicate complete repulsion in gametogenesis between the two dominant factors, short- style and magenta. The case is dealt with fully on p. 125. Rosy-Magenta. For the strain of this colour with which experi- ments have been made I am indebted to Messrs Sutton. Very similar types appear, as part of the magenta class, in the F^^a of certain crosses between reds and either "Snowdrift" or pale-pinks carrying magenta. The colour of the root-stock in this race bears the same relation to the colour which appears in the ordinary magentas as does the flower- colour in the two cases. The cross with " Snowdrift " gives an F^ of the ordinary magenta type. In the F^ the rosy-magentas take the place of the reds, but the distinction between the two classes is of course less obvious than that between magentas and reds. Like the salmon-pink, the rosy-magenta does not carry the factor for faint colour in the stem, and in the light class the stems and roots are devoid of coloured sap, so far as can be seen. The F^ obtained in one experiment of this kind suggests a ratio of 9 magentas : 7 rosy-magentas, the numbers obtained being : Full colours ' Sirdars ' No colour in stem Reference Number 9/9 Magenta 37 Rosy- magenta 22 Magenta 14 Rosy- magenta 10 Pale- pink 14 White 4 In the next two, however, the usual 3 : 1 ratio obtains : Full colours "Sirdars" No colour in stems Reference Number Magenta Rosy- magenta Magenta Rosy- magenta Pale- pink White 23/9 19 7 8 2 , 4 2 17/10 62 25 22 6 36 4 Totals 81 32 30 40 One can scarcely believe that the result shown in Experiment No, 9/9 is only a fortuitous departure from the 3 : 1 ratio, nor does it seem likely that it is due to experimental error in the separation of the classes, for both No. 9/9 and No. 23/9 were recorded within a day or two of one another, and in each case the separation of the classes was confirmed by another observer. The same rosy-magenta parent was used in Experiments 9/9 and 23/9, and one of its offspring in Experiment 17/10. The different results are not necessarily con- tradictory, for if the difference between magenta and rosy-magenta R. P. Gregory 111 does, in reality, depend upon the combination of two factors (of which "Snowdrift" must be assumed to have both) the rosy-magenta used in the 1909 experiments may have been heterozygous for one of them, without giving us any clue other than that which is suggested by these experiments. The mating between a sister plant of the rosy-magenta used in experiment No. 17/10 and a dominant white gave magentas and rosy-magentas in F^. The separation between the two classes was somewhat doubtful, but they apparently consisted of 20 and 19 plants respectively. So far as this observation carries weight, it tends to support the view that the difference between the two classes depends on the combination of two factors. " Crimson King." In all its crosses " Crimson King " gives a great variety of coloured forms in F.^, and it is clear, both from the number of these forms, and from the comparative rarity with which the " Crimson King " t}^e itself reappears, that its visible characters result from the interaction of several factors which are partially or wholly independent of one another in segregation. A series of F^ forms from the cross with the dominant white " Queen Alexandra " is shown in Plate XXXI, figs. 22 — 43. The types possessing some form of inhibition will be dealt with under that head (p. 115). Among the coloured forms (figs. 33 — 43) various types of light and dark magentas and reds occur, with or without the coloured stigma. This last character is recessive to the factor inhibiting the development of colour in stigma, and the observed numbers of green (colourless) stigmas and red stigmas approximate very closely to the ratio 3 : 1. But in the great majority of my experiments the two kinds of stigma are not evenly distributed among the magentas and reds, and there is clear indication of the existence of partial gametic coupling between the two factors magenta and green stigma (p. 127). "Crimson King" has the factor determining the spot of dark colour on the petals and accordingly this character appears in deeply-coloured flowers which have the coloured stigma and the ordinary or large yellow eye. " Crirtison King " x " Snowdrift." The F^ from this cross is an ordinary (light) magenta. The F^ contains fully coloured forms corre- sponding with those just described^ and in addition to these there occur magenta and red " Sirdars " (figs. 44, 45) in light and deep forms, pale-pinks (fig. 46) and whites, the last two classes having green 1 The white eye is a character derived from "Queen Alexandra" and does not appear in the experiments with " Snowdrift." 112 Experiments with Primula sinensis or only faintly coloured stems. The magenta and red classes form parallel series of light and intense shades ; the two classes as a whole are readily distinguished, though there usually occurs a small number of individuals whose proper position may be a matter of some doubt. In this connexion it may be remarked that the presence of the red stigma seems to have the effect of giving the flower in general a redder appearance than that of the corresponding type with green stigma. Two ^2 families raised from this cross in 1907 show some departure from the normal in the ratio of full colours and " Sirdars " ; the numbers obtained were : Full colours "Sirdars" Pale class Magenta Red Magenta Bed Pale-pink* White* Stigma Stigma green red Stigma Stigma green red Stigma Stigma green red Stigma Stigma green red 33 15 12 5 14 9 6 2 24 5 49 16 8 4 24 8 10 2 29 9 Totals 82 31 20 9 38 17 16 4 53 14 113 29 55 20 * The distinction between these two classes is not sharp. 67 The case does not perhaps merit any great consideration in view of the return to the normal ratio when the experiment was repeated in the succeeding years, and the lack of any other indications of a depar- ture from the normal distribution of self-colours and " Sirdars." Three families raised subsequentl}' gave : Full colours Magenta Red Stigma Stigma Stigma Stigma green red green red 16 7 7 5 14 3 6 1 13 4 3 5 " Sirdan i" Pale class Magenta Red Pale-pink* White Stigma Stigma green red Stigma Stigma green red 9 2 1 2 12 4 5 3 2 0 11 1 1 0 1 0 12 1 Totals 43 14 16 11 15 35t 57 27 20 41 * Distinction not sharply drawn. t Of 6 of these which had some colour in the stem, 4 had coloured stigmas, 2 green. The five families taken together give 245 magentas, 82 reds ; 234 green stigma, 93 red stigma; the calculated numbers in each case being 245*25 of the larger class, 81 '75 of the smaller. In the first two R. P. Gregory 113 experiments the distribution of the two kinds of stigma among the two classes of colours follows the normal 9:3:3:1 ratio, being : MagenU MagenU Red B«d green stigma red stigma green stigma red stigma Fall colours Sirdars 82 31 20 9 38 17 16 4 120 48 36 13 122-0 40-7 40-7 136 Totals Expectation In the later experiments there is considerable departure from this distribution, the first class being small and the last large. But it is to be noticed that in these two cases there is considerable departure from the normal ratio of 3 : 1 in each of two pairs of characters under con- sideration, the numbers observed being 77 magenta, 33 red ; and 78 green stigma, 32 red stigma. There seem to be no grounds for regard- ing this discrepancy as other than a chance departure from the normal, but it of course has a very material effect on the numbers observed in the four groups when the two pairs of characters are considered in conjunction with one another. If the theoretical ratio of 9 : 3 : 3 : 1 be weighted so as to allow for the two discrepancies a fairly close approximation to the observed numbers is obtained : Magenta green stigma Magenta red stigma Bed green stigma Bed red stigma Observed numbers 58 19 20 13 Expectation from weighted ratio 54-6 22-4 23-4 9-6 There is therefore no clear indication that partial gametic coupling between the factors for magenta and green stigma occurred during the gametogenesis in the ^j plants used in these experiments ; the point is of some interest because partial coupling of these two factors is clearly indicated in many of the experiments in which " Crimson King " was used. " Crimson King " x Rosy-Magenta. The F^ from this cross is a magenta of a rather deeper kind than that of the Fi from (" Crimson King " X " Snowdrift "). In the F^ there occurs, in addition to the ordinary magentas and reds, a curious parti- coloured type in which irregular masses of full colour are distributed over a lighter ground. These " Strawberries " (Plate XXXI, fig. 49) apparently belong to the red class and only occur in small numbers, probably as one in 64 of the total offspring. The magentas and reds may be subdivided into classes differing from one another in a minor degree. Thus, in the red class there 114 Experiments with Primula sinensis are dark reds, of which a few approximate to "Crimson King," terra- cottas of two shades, one bluer (Plate XXXI, fig. 47), the other a clean red (fig. 48) and light reds corresponding with both the shades of terra-cotta ; in the magenta class a similar series of forms occurs. The grading between the sub-classes is close and I am not able to give any precise numerical results as to the proportions of the various types. The distribution of the green and red stigma among the magentas and reds clearly indicates the existence of partial gametic coupling between the factors for magenta and green stigma (see p. 127). ^3 families have been raised from certain of the F^ forms in the hope of elucidating their relations to one another and to the " Straw- berries." The bluer terra-cotta appears to be differentiated from the red kind by the addition of a single factor, but for the most part the results are complex and further data are required for their detailed analysis. One result, however, is of interest in connexion with the relation between the magenta and red colour. An F^ plant with peculiar deep rosy flowers and red stigma, when selfed, gave forms like itself and strawberries ; a light red with green stigma, self- fertilized, gave light reds, terra-cottas of both shades, and strawberries, all with green stigma. The two plants were crossed together recipro- cally, and the two families thus obtained consisted of typical magentas, reds (including light reds and terra-cottas) and strawberries, all with green stigma. "Orange King." (Plate XXX, fig. 8.) "Orange King" originated with Messrs Sutton as a sport from a strain of " Crimson King " ; it bred true from its first appearance. The F^ from the cross with " Crimson King" bears an exceedingly close resemblance to the latter; the mature flowers of the hybrid are probably not to be distinguished from those of the pure race, but in the young flowers there is a slightly more magenta tint than in the pure strain of " Crimson King " with which I have worked. In the F^ from this cross there were obtained 55 plants like the F-^, and 14 "Orange King"; some very slight differences in the depth of the colour were noticeable among the latter. The ex- tracted "Orange King" had the true red stem-colour, as compared with the purplish-red colour of the forms resembling " Crimson King." " Orange King " x " Snowdrift." The F^ of this cross is indistin- guishable to the eye from that of the crosses of either the Rosy- magenta or "Crimson King" with "Snowdrift." The constitution of the F^ follows the general lines of the F^ from ("Crimson King"x "Snowdrift") but is of course rather more complex, since the ^i is i R. P. Grbgory 116 heterozygous for the factor determining the purplish-red stem and deep colour of " Crimson King," which is present both in that race and in *' Snowdrift." In addition therefore to the types found in the "Crimson King" F^ there appear extracted "Orange Kings," and a new class consisting of plants with pink or pale-pink flowers and stem-colours ranging from red collar to reddish stem. These plants are no doubt derivatives of "Orange King," whose appearance they rather recall; but further experiment is required upon this point, as well as upon the further point as to whether the " Sirdar " character is recognizable as such, if, and when, it occurs in the " Orange King " series of pigments. The numbers obtained in two F, families were : Pink, PiJepink, red collar to faint tin^e or .Mliite, Full colour " Sirdar " '' Orange King " reddish stem no colour m stem green stem 111 33 5 29 52 12 178 64 The numbers given in the last three classes can only be regarded as approximately representing their relative sizes, since one can hardly avoid some experimental error in a separation guided by external appearance only. It will be seen that, if the pink class prove to be derivatives of " Orange King," the numbers obtained agree with the ex- pectation based on the hypothesis suggested by the result of the cross (" Crimson King" x " Orange King"), namely, that the subtraction of a single factor will suffice to explain the behaviour of the "Orange King" type of pigment. The existence of some form of partial gametic coupling between the magenta and green stigma is clearly indicated (see p. 127). (3) Inhibition of Colour in the Flower. All the red-stemmed whites with which I have worked have been found to possess the factors which inhibit the development of colour in the flower; when crossed with the albino "Snowdrift," they have given colours in F^. Since fully coloured flowers only occur in con- junction with fully coloured stems, the stem-colour of the dominant white is a guide to the flower-colours which may appear in the F^; those with full red stems will give full colours, while those with no more than a tinge of colour in the stem can only give pale-pinks. The precise ratio in which the coloured forms appear in Fj is still in doubt. In the F^'s consisting of whites and pale-pinks only the former are in excess of the expected ratio of 13 : 3. Owing to the difficulty of distinguishing these faint colours, no great weight could be attached 116 Experiments with Primula sinensis to this discrepancy, were it not that in some F^%, which contain plants with fully coloured stems, there is again a considerable excess of whites in the red-stemmed class, where the distinction between white and coloured forms can be made with certainty. The numbers which have been obtained are' : stems not fully coloured (including Red stem those resembling " Sirdar " *) Dominant White ''■ ~ ' ^ Parent White Magenta "Sirdar" Pale pink White Giant White ' (18 5 0 2 4 (33 8 3 6 33 "Primrose Queen" 66 13 5 7 36 * Without the character of the flower-colour as a guide it is scarcely possible accurately to distinguish the " Sirdar" type of coloured stem from other low grades of stem-colora- tion. Before passing to a detailed consideration of these results, it is well to recall the fact that in the F.^ from crosses between plants having coloured flowers and stems x the albino " Snowdrift," oil the red- stemmed oflfspring have coloured flowers, whites being found only in the green-stemmed class. These results, together with the fact that all my red-stemmed whites proved to be dominant whites, suggested that the factors for full colour are common to the whole plant, and that, in general, red-stemmed whites are white in virtue of the suppression of the colour in the flower by inhibiting factors 2. Turning now to the results of the crosses between " Giant White" x " Snowdrift," it will be seen that the red-stemmed class consists of whites and colours, in proportions which do not diverge so greatly from the expected ratio (3 : 1) as to exclude the possibility of accounting for all the whites on red stems as resulting from the suppression of colour in the flower. In the red-stemmed class of the ^2 from "Primrose Queen" x " Snowdrift," however, the whites are much more than three times as numerous as the plants with coloured flowers. The observed ratio of colours to whites agrees closely with the expectation based on the hypothesis that the production of colour in the flower, even in the red-stemmed offspring of this cross, depends upon two complementary factors, for both of which the ^1 was heterozygous. An F-^ heterozygous for these factors and for inhibition, would give an F^ consisting of 9 coloured : 55 white ; the numbers obtained are 13 coloured, 66 white (easpectation : ll'll : 67'89). 1 The earlier experiments only give qualitative results, as many plants were discarded before the characters of the flower could be accurately determined. 2 Gregory, Rep. Brit. Assoc., Leicester, 1907, p. 692. R P. Gregory 117 Other experinietits made with " Primrose Queen " definitely support the view as to its constitution which is entailed by this hypothesis. The results of Keeble and Pellew's experiments with the red-stemmed "Snow King"* indicate that in certain cases the factors for colour may be absent from the flower, though present in the stem, and consequently that certain red-stemmed plants may have white flowers in the absence of inhibition. On the other hand, the mode of inheritance of the full colour in my crosses between coloured, red stem x " Snowdrift " suggests that in certain other cases the factors for colour are common to the whole plant, both stems and flowers. Dominant white x Coloured, green stigma. The simplest cases illus- trative of the operation of the factors which inhibit the development of colour in the flower are those in which a dominant white is crossed with a coloured form having green stigmas. The ^i in these cases is white or tinged-white, the depth of the tinge depending, under uniform conditions^ upon the intensity of the colour of the coloured parent, and to some extent upon the particular race of dominant white used. The ^2 from this cross consists of whites, tinged whites and colours, all with green stigmas. The numbers obtained are : fi X coloured, F^ X Self green stigma /^ ~\ /'ttemiliea White and Tinged white Coloored 17 782 271 Expectation 789-75 263;i5 Number of White and Ft familiee Tinged white Coloured 3 59 58 Equality The experiment has been repeated in a slightly different form by crossing coloured plants with the ^i of (Dominant white x Recessive white). The numbers obtained from these crosses are : Reference Xomber of 1*1 plant White Coloured 28/4 13 18 4/6 93 86 36/6 58 74 30/6 43 56 61/9 42 46 Totals 247 ~ 274 Expectation 260-5 260-5 > Joum. Genetic*, Vol. i, 1910, p. 1. * The depth of the tinge is dependent upon the conditions under which the Fi is grown, and its maximam development is only obtained by keeping the house as cold as is possible without injury to the plants. At higher temperatures very Uttle tinge is developed, and the F^ from the cross of such an intense colour as " Crimson King" with a dominant white is scarcely tinged. 118 Experwients with Primula sinensis The "dominant white" parent of Nos. 26/6 and 30/6 was one which gives a very fully tinged ^i when crossed with " Crimson King " — the coloured race with which 26/6 and 30/6 were mated ; the excess of coloured offspring shown in their crosses may therefore be in part due to experimental error, through the inclusion of some deeply tinged forms with the light colours, and in the absence of any other indica- tions of departure from normal segregation one does not feel inclined to attach any great weight to the discrepancy shown here. Dominant white x Coloured, red stigma. The ^i from this cross is again a tinged white with green stigma (Plate XXX, fig. 18; Plate XXXI, fig. 21). The F2 from one of these crosses — that between "Queen Alexandra" and "Crimson King" — is illustrated in Plate XXXI, figs. 22 — 43. As concerns the factors for inhibition, the F2 consists of four classes, namely, (1) whites and tinged-whites, with green stigma (Plate XXXI, figs. 22 — 26); (2) plants in which the peripheral part of the corolla is white or tinged, the central part flushed, with red stigma ("Duchess" and "Buller" types; figs. 27 — 31); (3) coloured, green stigma (figs. 33, 34, 38 — 41); (4) coloured, red stigma (figs. 35 — 37, 42, 43). The four classes are in the proportions of 9 : 3 : 3 : 1, the observed numbers being : White and tinged- svhite, green stfgma " Duchess " and " Buller " forms ; red stigma Coloured, green stigma Coloured, red stigma 193 61 65 21 Expectation 191-25 63-75 63'75 21-25 " Duchess." The " Duchess " types which appear in these -Fg's are shown by experiment to be homozygous for the peripheral inhibiting factor. Crossed with a coloured, red stigma, they give " Sir Redvers Buller," which in turn gives "Duchess," "Buller," and fully coloured, all with red stigma. The F^ types resembling "Buller" are therefore those which are heterozygous for the peripheral inhibiting factor. " Duchess " X green stigma. " Duchess," crossed with plants with green stigma, gives a white or tinged-white -Fj. The result is the same whether the parent having the dominant green stigma be a coloured form or a recessive white (" Snowdrift "), except that in the former case the Fi has a rather deeper tinge. In certain cases the flowers of the ^1 have a distinct tinge of colour in the corolla-tube, just below the region of the insertion of the anthers, although no tinge at all may be discernible in the petals^ The charac- 1 A similar character lias been observed in one other experiment where the Fi from (Dominant white x Crimson, green stigma) was crossed with a dominant white. In this case the character was coupled with that of short-style. Croas Namber of famUies ' Daebess ' ' x" Snowdrift" ... 2 'Duchess' ' X '* Sirdar " 1 ' Duchess "^ 'x "Ivy-leaf" 1 R. P. Grkcm)ry 119 ters of the F,'s from the various crosses which have been made are shown below : VntnhAr ni Deaeriptton 21 plants. White, petals tinged, no tinge in tube. 28 plants. White, no tinge seen. 42 plants. White, with faint tinge in petals ; no tinge in tube. " Dnchess " X Dominant White 1 8 plants. White, with distinct tinge in tube. " Dnchess "xfj (Dominant White X" Snowdrift") 2 White, no tinge seen, 15 plants; White, tinged in tube, 14 plants. " Duchess " X Rosy- Magenta 1 12 plants. White, rather fully tinged in petals. The Fi fix)m the cross between " Duchess " and " Snowdrift " con- tains a long series of types, for to the various inhibited and coloured forms corresponding with those obtained in the F.2 from (Dominant white X CJoloured, red stigma) there are added the " Sirdars," pale- pinks and whites on green stems which are characteristic of the F^'s from crosses between "Snowdrift" and plants possessing the factors for colour. And since the " Duchess " used in these experiments was of the red class, red as well as magenta forms of each coloured type are present. The numbers obtained in three families were : Green stems, red collar Bed stems (" Sirdar " tn>e8) Pale-pinks WMtes No colour No colour Bed seen in seen in Green stigma Bed stigma Green stigma Bed stigma oc^ar stem stem Tinged White and white and Tinged Tinged white Coloured Coloured White Sirdar White Sirdar 117 47 37 47 14 18 7 5 19 56 The tinged whites with green stigma are of two kinds, namely, (1) those which resemble the Fi in having a more or less evenly distributed tinge, which becomes more pronounced as the flowers fade, and (2) those with a definite central tinge surrounding the eye and most conspicuous in the young flower. All the tinged whites with red stigma have the colour disposed in the centre after the " Duchess " style. At the time when these families were recorded the distinctive character of the forms resembling "Buller" had not been recognized, and some of them were included with the class " Coloured, red stigma " ; in the table the two classes of red-stemmed plants with red stigma are therefore taken together ; it will be noticed that there is a deficiency 120 Experiments with Primula sinensis in these two classes as compared with the corresponding classes with green stigma ; on the other hand in the " Sirdar " classes the propor- tions of green stigma and red stigma are slightly less than 3 : 1, but further experiment is required before any suggestions can be made as to any possible significance of these departures from normal distri- bution. A further generation w^as raised by selfing one of the offspring of the cross [" Duchess " x ^i (Dominant white x " Snowdrift ")]. The most interesting point brought to light by this experiment is the fact that there occur whites (? with no tinge) having red stigmas, but without the central flush of deep colour which is characteristic of the " Duchess" strain \ The numbers obtained were : Ked stem Green stem, red collar No colour in stems White, White, green stigma red stigma 34* 13t Duchess, White, White, White, red stigma green stigma red stigma green stigma 4 16 5 19 • Two with definite central tinge. t Three with definite central tinge. Tinged-whites with red stigma and without the central flush occurred also among the offspring of a cross between " Duchess " and the i^i of ("Ivy-leaf" X " Crimson King"). From this cross 31 plants were obtained, 16 with green stigma, 15 red stigma. Those with green stigmas were white or slightly tinged (like the F^ of "Dominant white " X coloured, red stigma) ; those with the red stigma were deeply tinged, but whereas some were of typical "Duchess" or "Buller" types, others were without the deep central flush. The deep central flush of " Duchess" and "Buller" is therefore not a necessary consequence of the absence of the factor inhibiting colour in the stigma; it would appear rather that the character is an independent one, but, like the deep spot of colour just external to the eye (p. 106), is dependent for its full development on the presence of colour in the stigma. We may surmise that the definite central tinge found in some whites with green stigmas represents this character in combina- tion with the green stigma. Green stigma in coloured flowers. The results showing the behaviour of the green and red stigma in crosses between colours are : Number of families Green stigma Bed stigma 4 315 116 Expectation 323-25 107-75 1 In Stellata flowers the "Duchess" flush is often only poorly developed, but the phenomenon is of a different kind from that referred to here. R. P. Gregory 121 (4) Flakes. The Fj's from crosses between the "Ivy-leaf" and coloured races contain flakes (Plate XXXI, figs. 56—59) in addition to the self-colours. "Ivy-leaf" x "Crimson King" The Fi of this cross, and of that between "Ivy-leaf" and "Orange King," is indistinguishable to the eye from the Fi of the crosses between " Snowdrift " and the same coloured races. In the F,, the self-coloured flowers on red stems constitute a series of types similar to those of the F^ from ("Crimson King" x "Snowdrift"); the same series is probably repeated in the flaked patterns, though the distinction between the shades of red and magenta is much less easily made in the flakes. The flaking may be coarse, the coloured areas taking the form of wider or narrower radial stripes (Plate XXXI, fig. 56), or very fine flakes may be present in addition to the coarser ones (fig. 58). The flaking appears generally to be strongly marked in plants with red stigmas (figs. 57, 59). As in many other cases, the distribution of green and red stigmas among the magentas and reds clearly indicates the existence of partial gametic coupling (see pp. 127, 128). All the ofispring with light stems have some amount of colour in the bases of the leaves, as does the "Ivy-leaf" itself. The light- stemmed class consists of pale-pinks, and whites flaked with pale colour. The flaking in this class may be very sparse, and in that case is inconspicuous as the colour is so faint, but it was observed in all the plants except four. The F^ contains no " Sirdars." The numbers obtained were : Red stems Light stems Beference Self Pale WTiite, flaked White, no Number ooloor Flake pink pale pink flake seen 61/10 1 „ , , , I 97 33 30 6 2 Palmate leaves 62/lof '^*"^'^'^^^' 1173 42 35 25 2 Total, palmate 270 75 65 31 4 61/10 \ I 24 10 2 0 0 \ Ivy leaves s + 3 undetermined* 62/10) I 40 16 12 3 0 + 11 undetermined* +5 undetermined* Total, Ivy leaves 64 26 14 3 + 14 undetermined* + 5 undetermined* Grand total 334 101 79 34 * Owing to the poor development of the flowers. Joum. of Gen. i 122 Experiments with Primula sinensis Taking the red- and light-stemmed classes together, the self-colours are 413, the flakes 135, numbers which suggest that the flaked condition is a simple recessive, the expectation in such a case being 411 colours : 137 flakes. The distribution of the self-colours and flakes among the red and light stems is however irregular, especially in the palmate plants of 62/10. "Ivy-leaf" x Dominant white. Up to the present time F^b have been raised from only one cross of this kind, that of ("Ivy-leaf" x "Prim- rose Queen "). The F^ is noteworthy for two reasons : (1) no self-colours are obtained, all the coloured offspring being flaked ; and (2) no pale- pinks occur. The numbers are : Red stems Light steins White Magenta flakes White Flakes Palmate leaves 93 26 36 — Ivy leaves ... 43 4 8 — The flakes grade from fully-flaked to small and sparse flakes of colour. It may be noticed that the young flower-buds of the flaked forms are quite strongly tinged, even though the flaking may prove to be sparse. The great excess of whites, as compared with flakes, among the Ivy-leaved offspring is probably of no great significance, as it may well be due to the reduced corollas of the Ivy-leaves. The plants with light stems were carefully examined in view of the results obtained from the cross of ("Ivy-leaf " x "Crimson King"), and no trace of flaking was observed in any. It may be remarked however that both "Primrose Queen" and "Ivy-leaf" carry the factor which partially suppresses flower-colour, and even the full colours are very light. " Ivy-leaf" x " Snowdrift." The F^ from this cross has definite, though faint, colour in the flowers. In the F^, plants with definitely coloured flowers form approximately 9 in every 16 plants, the observed numbers being 144 definitely coloured in a total of 273 plants (t6 *^f ^'^^ — 1^3'5). The plants recorded as definitely coloured were, so far as could be judged, self-colours ; in one at least of the remainder the "ghost" of a coloured flake was recognized. In this cross, again, both parents bring in the factor which partially suppresses flower-colour. Discussion of the " Ivy -leaf " crosses. The appearance of the "Ivy- leaf" plants and the characters of the Fi obtained from their crosses with colours, led me to look upon " Ivy-leaf" as a recessive white ; but the result of the crosses with " Crimson King " suggests that this view will need revision, and that the plant may really possess the pale-pink K. P. Gregory 123 colour in the flaked condition. A re-examination of the parent " Ivy- leaf" in the light of this suggestion failed to reveal any definite coloration, but the pale colour is at best sometimes hard to discern and in the flaked condition might escape even close inspection, especially in such poorly developed flowers as are characteristic of the " Ivy-leaf." The suggestion is moreover supported by the fact that Keeble and Pellew^ obtained a flaked Fi from the cross of an "Ivy-leaf " of this strain with "Snow King." This view of the constitution of the " Ivy-leaf" would agree well enough with the results of the cross with " Snowdrift," for the latter possesses the factor for self, as against flaked, colour, and we should therefore expect a ratio of 9 self-coloured : 7 flaked and white. In the same way the absence of pale-pinks in the F^ of the cross with " Primrose Queen " may perhaps be put down to the difficulty of recognizing the colour in its most dilute and flaked condition-. The complete absence of self-colours from this ^3 is interesting in view of the results of the cross between " Primrose Queen " and " Snowdrift," and suggests some considerations as to the relation between flakes and self-colours. For if the self-colours result from the addition of a " distributing " factor epistatic to the factors for colour, it is clear that "Primrose Queen" must be without this factor; but in that case one-third of the coloured ofi^spring obtained in the F., from (" Primrose Queen " x " Snowdrift ") sh aromatic chromogen. Aromatic chromogen + oxygen = anthocyanin. The following possibilities may therefore arise. The amount of pigment is directly proportional to the amount of free chromogen. Increase of sugar would naturally lead to decrease of free chromogen, but if at the same time additional chromogen is formed from the sugar, the ultimate concentration of the glucoside, if it is not removed by trans- location, will be increased to such a degree that the final result is an increase of free chromogen accompanied by formation of pigment. A decrease of sugar, on the other hand, will increase the free chromogen, but at the same time it will lead to a decrease in the concentration of the glucoside, so that the final result is a decreased amount of free chromogen and less possibility of pigment formation. Or to state the case rather differently : so long as the concentration of glucoside remains low either as a result of translocation or of decreased formation, the amount of free chromogen is negligible, but if the concentration of glucoside is raised beyond a certain point as a result of diminished translocation or continual formation, the synthesis of free chromogen and sugar can no longer take place and the former becomes oxidised to anthocyanin. In the normal green leaf the absence of pigment from the mesophyll is in all probability due to the rapid translocation of aromatic gluco- sides away from the leaf. It is difficult to ascertain the precise reason for the presence of pigment when it appears in the epidermis of the lamina and in the epidermis and sub-epidermal layers of the veins and petiole. It may be caused either by low concentration of sugar or by increased concentration of glucosides due indirectly to excess of sugar. These tissues are without chlorophyll and the power to assimilate, but at the same time they are also apparently devoid of starch-forming capacity, since starch does not as a rule appear in them, so that the sugar concentration may or may not be greater than in the mesophyll of the leaf. In general the chlorophyll-containing tissues are most free from pigment, the non-chlorophyllous more frequently pigmented. Hence the appearance of pigment is undoubtedly connected with the concen- tration of sugar, but I am at present unable to give the exact sequence of events which affects the reversibility of the reaction. M. Wheldale 147 That a relationship exists between pigmentation and assimilation is further borne out by the appearance of anthocyanin in old leaves, variegated leaves (with parts free from chlorophyll), autumnal leaves, leaves exposed to drought or low temperature and in flowers and ripening fruits. In all these cases the same difficulty arises as to the real cause, since the starch-forming power may be diminished as well as the assimilative. Starch does not as a rule appear in petals ; and in fruits the colouring matter is often limited to the epidermis and sub- epidermal layers which are free from starch though the flesh of the fruit may be full of starch. In variegated leaves the chlorotic portions, in which pigment often appears, are unable to form starch. I have made a number of observations upon the starch contents of green leaves and of leaves, from the same plant, reddened as a result of cold, drought, etc., and I have found the red leaves almost invariably to contain less starch than the green. It must also be borne in mind that the translocation of both sugar and glucosides may be hindered by low temperature, drought, age, etc. I am inclined to believe, in the absence of more direct evidence, that the reddening under these conditions is due to diminished translocation of glucosides combined with increased formation of these substances due to the presence simultaneously of excess of siigar. Results lately published by Combes (3) corroborate this view to some extent. Combes has made comparative estimations of the glucosides and sugars in both red and green leaves of Ampelopsis hederacea in which reddening was due to light intensity, and in Rosa canina, Mahonia aquifolium and Sorbus latifolia showing autumnal colouration. His results may be expressed as follows : — Sugars Dextrins Ulucoeides Inaolnble CarbohTdntes Ampelopsis hederacea green •74 2-78 2-43 2-42 red •98 1^88 2^79 502 Bo$a canina green 2-42 1-30 8^22 972 red 264 1-23 8-24 533 Sorbm latifolia green •71 1^15 220 1199 red •80 1-07 2^52 120 Mahonia aquifolium green •57 •80 341 2-38 red 1-30 •60 430 8^78 From these numbers we see that the concentration of glucosides and sugars in red leaves is greater than in green, that of dextrins greater in green than red, whereas the amount of insoluble carbo- 148 071 the Formation of Anthocyanin hydrates varies, being sometimes greater in one, sometimes in the other. Since the concentration of both glucosides and sugars is greater in the red leaves, it is reasonable to interpret the pigment formation as being due to accumulation of glucosides, in which case the reaction Glucoside + vs^ater — *- sugar + chromogen would give rise to more free sugar (apart from other causes) in the red than in the green leaf from which the glucosides are continually removed, so that the concentration of glucoside is lowered Sugar + chromogen — *- glucoside + water. Kraus(6) has also shown that red autumnal leaves contain more aromatic substances than normal red leaves. Results, however, which are more convincing than these just stated, are those connected with the phenomenon of reddening produced by injury. Instances have already been quoted of pigment formation due to injury to the cortical tissues of the midrib and petiole or to the removal of a portion of the midrib or main veins of a leaf. According to Kraus(6) the path taken by aromatic substances in translocation is the vascular system of the leaf, but whether by the phloem or the surrounding parenchyma is not stated. In any case injury to the vascular system of the leaf or the living tissues of the petiole or stem would involve an accumulation of glucosides in the parts distal to the point of injury. It has been recently suggested by Mangham(8) that the sugars travel from the leaf by the phloem. If such is the case, the injury may also lead to accumulation of sugars and hence indirectly to more glucoside. Combes(3) has shown that decortication in spp. of Spiraea induces reddening of the leaves above the point of operation. A similar obser- vation has been made by Kraus for Cornus alba, and I have myself observed a similar result following upon decortication in Ribes Grossu- laria and a species of Salix. Combes (3) has shown by analysis that there is a large increase of both glucosides and sugars in the leaves of Spiraea which had reddened as a result of decortication. The following are the numbers given : — Insoluble Sugars Dextrins Glucosides Carbohydrates Spiraea paniculata green 2-21 1*01 1-64 10-75 red 4-26 '92 6-15 26-58 M. Wheldalb 149 Kraus(6) also found that some cut leaves redden when placed in water in bright sunshine, and on analysis gave greater quantities of aromatic substances than control leaves kept in the dark. Evidence for the Presence of Enzymes. If the formation of anthocyanin is dependent upon enzyme action, it should be possible to obtain evidence of the existence of both glucoside-splitting enzymes and oxidases in the tissues of anthocyanin plants. Glucoside-splitting enzymes. For the detection of glucoside-splitting enzymes I have employed the following method. The tissue to be examined is well ground and thoroughly washed with 75°/^ alcohol: it is then dried in air and extracted with distilled water. These processes are carried out as far as possible under sterilised conditions. The water extract is then added to a definite quantity of salicin solution and kept, together with a control flask, at a temperature of from 36° — 40° C. for 24 hours. The following reaction then takes place : — Salicin + water = saligenin + glucose. The saligenin is extracted from the liquid by shaking with ether and after evaporation of the ether its presence can be detected in the residue by means of ferric chloride with which it gives a violet colouration. By this method I have demonstrated the presence of a glucoside- splitting enzyme in the following : — leaves of Gorylus Avellana, Rumex crispus, Taraxacum officinale and Primula sinensis, flowers of Cytistis scoparius, Aquilegia vulgaris, Viola tricolor, Antirrhinum majus. Primula sinensis, Narcissus pseudonarcissvs, Cheiranthus cheiri, Fritil- laria imperialis, Polyanthus sp., Helleborus orientalis, Pyrus japonica, Prunus avium, Galanthus nivalis. Narcissus Tazetta, Pelargonium, zonule, and tubers of Solanum tuberosum. These results show that glucoside-splitting enzymes are widely distributed. In other species a negative result was obtained but this is to be expected, since all such enzymes may not be able to hydrolyse salicin. If glucose solution is added to the salicin solution plus the enzyme the hydrolysis of the salicin is greatly retarded. Also if the preliminary treatment with alcohol as described above is omitted and a water extract is made from the fresh plant tissues and added to salicin, very little or no hydrolysis of the latter takes place. 160 On the Formation of Anthocyanin This retardation is doubtless due to the fact that the water extract contains, in addition to the enzyme, the glucosides and sugars present in the plant. Thus the products of hydrolysis of the glucosides derived from the plant would retard or entirely prevent hydrolysis of the salicin added. By treatment with alcohol, all glucosides and some part of the sugars are removed previous to extraction with water. Oxidases. It has been previously mentioned that Palladin(14) considers anthocyanin to be a respiration pigment. That oxygen is necessary for its production has been shown experimentally both by Molliard(ll) and Katic(5). The dependence of pigment formation on the presence of oxygen can be readily demonstrated in a very simple way. If cut leaves of Taraxacum officinale are placed in sugar solution so that the lamina is partially immersed, reddening only takes place in the portion exposed to air and not in the submerged part. The oxygen may also be excluded by greasing part of the leaf with vaseline. The greased portion remains green while the ungreased portion develops a con- siderable quantity of pigment. Similar results have been obtained with leaves of Heracleum sphondylium, Sambucus nigra and Hiera- cium sp. Apparently no reverse process of deoxidation takes place when a coloured leaf is greased so as to prevent all gaseous exchange. If anthocyanin constitutes a medium for the transference of oxygen, we should expect the colour to disappear as a result of reduction when coloured leaves are deprived of oxygen, especially since respiration is one of the last " vital processes " to disappear. The strongest argument against Palladin's hypothesis is the existence of well-developed albino varieties of an almost innumerable number of species. The question of the oxidising enzyme presents some difficulty. In all plants forming post-mortem pigments, oxidases can be detected by means of guaiacum tincture, with which the extracts give a strong and rapid direct action. Yet blueing of guaiacum is not limited to these cases, for a less rapid direct action is also given by other plants (Lathyrus, Matthiola), which do not form pigments on autolysis. All the guaiacum-blueing species I have examined have been anthocyanic, and the possibility suggests itself that the oxidases may form antho- cyanin in the living plant but a post-mortem pigment after death. There is some evidence in favour of this supposition : first, when a plant forms anthocyanin and also a post-mortem pigment, the former is converted into the latter on autolysis and the organs which contain M. WUELDALE 161 most anthocyanin produce the greatest quantity of brown pigment. Secondly, when fully pigmented flowers of the type in any species (cultivated spp. of Chrysanthemum, Petunia and Pyrethrum) give a strong oxidase reaction, tinged or less intensely coloured varieties frequently give a less strong reaction, which may indicate that some part of the oxidising mechanism has been lost from the varieties, as I have previously suggested (19) for Lathynis and Matthiola. On the other hand, very many anthocyanic plants give no direct action with guaiacum, although nearly all living tissues give an indirect action (i.e. after addition of hydrogen peroxide). It is possible that the direct action is inhibited in these cases by some strong reducing sub- stance in the plant. It is also more than probable that anthocyanin oxidases are of a nature totally different from those connected with respiration pigments and may, many of them, not react with guaiacum. For the present no other explanation appears available. Some work on oxidising enzymes has been recently published by Moore and Whitley (12). These authors do not support the hypothesis of Bach and Chodat, i.e. th^t an oxidase consists of a mixture of two enzymes, an oxygenase which acts upon certain substances in the plant forming peroxides and a peroxidase which transfers the additional oxygen atom from the peroxide to other bodies. When both enzymes are present, the plant extracts have a direct blueing action on guaiacum, but when the peroxidase exists alone, hydrogen peroxide must be added before blueing results (indirect action). Moore and Whitley suggest that only one enzyme — peroxidase — is involved in the process and that the blueing, to a greater or less degree, of guaiacum by plant extracts, is due to the existence of more or less organic peroxide in the tissues and that no special enzyme involved in the formation of peroxide can be detected. This point of view greatly simplifies the conception of oxidation processes. I am nevertheless of the opinion that peroxide formation in the plant may be controlled by an enzyme, though it may not be pos- sible to extract this substance and to obtain an expression of its activities under artificial conditions. Since, moreover, the presence of organic peroxides in plants is directly connected with the appearance of post-mortem pigments, it must follow that the metabolism of this class of plants differs in some fundamental respect from that of others; and in my opinion such a constitutional difference may quite well involve the existence of at least one special enzyme. 152 On the Formation of Anthocyanin Sugar-Feeding. It is obvious that in the consideration of such an hypothesis as that which I have formulated, any evidence of a connection between in- creased pigmentation and increased concentration of sugars brought about by artificial feeding of plants or parts of plants with various sugars would be of considerable value. Such a method of research has been adopted by Overton(13). This author maintains that the conversion of sugar into starch is lessened by a lowering of the temperature. Hence the pigment of autumnal leaves and evergreen leaves in winter is due to excess of sugar induced by low temperature. In order to test his hypothesis, Overton made a number of sugar- feeding experiments with both water and land plants. The water plants were grown either submerged or floating in solutions of cane- sugar, glucose, fructose, etc. In the case of land plants, the cut ends of leafy stems or the petioles of leaves were placed in the solutions. Many of the species used {Hydrocharis morsus-ranae, Utricularia spp., Lilium Martagon, Ilex aquifolium, Hedera Helix, Ligustrum vulgare, Saxifraga spp., Crassula spp., Aquilegia vulgaris, Tm^axacum vulgare, Eupatorium cannahinum and Epilohium parviflorum), showed increased formation of pigment, but in other cases (Potamogeton spp., Lemna spp., Fritillaria imperialis, Mahonia aquifolium, Anthriscus sylvestris, Rubus spp., white flowers of Pelargonium zonale, and Anemone japonica) there was a negative result. Increased colour sometimes appeared in control plants kept in distilled water under good illumination. Corroborative results have also been obtained by Kati6(5) with plants of Hydrilla, Elodea canadensis, Hydrocharis morsus-ranae, leaves of Sagittaria natans, Canna indica, Veronica chamaedrys, Rosa sp., Saxifraga cordifolia, Pittosporum undulatum and Bellis perennis. Overton has proved his results to be due to the chemical nature of the dissolved substance and not to any osmotic action by the use of control solutions of neutral salts, i.e. sodium chloride, sodium sulphate, potassium sulphate of osmotic strengths equivalent to those of the sugar solutions employed. In no case where a neutral salt was used, was there any increase in pigmentation. In Lilium Martagon, an increase of pigment resulted from the use of ethyl and methyl alcohol solutions. In view of Overton's suggestion that increased sugar concentration may under some conditions be brought about by a decreased starch- forming capacity, I thought it possible that some connection might exist between the reddening of leaves and starch formation in sugar- M. Wheldale 153 cultures. I therefore made a number of sugar-feeding experiments with various species and at the same time I examined the starch contents of the leaves after this treatment. The leaves employed were first kept in the dark until starch-free, and a piece of each leaf was placed, after this treatment, in methylated spirit as a control. Portions of the same leaf were then floated, upper surface downwards, in two dishes, one containing 3°/^ cane-sugar solu- tion, the other distilled water. Both dishes were placed under a bell-jar together with a dish containing strong caustic potash solution, air being allowed to enter the bell-jar only by means of a tube containing soda- lime. Control dishes of sugar solution and distilled water containing further portions of the same leaf were placed under a bell-jar without potash solution. After an interval of from 7-10 days, any development of pigment was noted, and the leaf portions were then placed in methy- lated spirit until colourless and sections, after treatment with strong chloral hydrate solution and iodine, were examined for starch contents. The results are tabulated as follows : — Species 3 per cent cane sugar —carbon dioxide Distilled water — carbon dioxide 3 per cent. cane stigar +carbon dioxide DistiUed water +carbon dioxide Development of Pigment either with or without carbon dioxide Viola tricolor no starch no starch no Starch no starch + CapseUa bursa pastoris abandant starch no starch abandant starch abandant starch - Lactuca sativa no starch no starch no starch no starch + Reseda lutea abandant starch no starch abandant starch abandant starch + Matricaria sp. abandant starch no starch abandant starch abandant starch - Cheiranthws cheiri abundant starch no starch abandant starch considerable amount of starch — Nieotiana tabacum abandant starch no starch abandant starch abandant starch - Aquilegia vul- garis some starch in places no starch no starch no starch + Epilobium sp. abandant starch no starch abandant starch some starch - Ilex aqui/olium very little starch no starch very little starch no starch + Ligustrum vulgare no starch no starch very little starch no starch + Mahonia aquifolium very little starch no starch crammed starch crammed starch + Rumex crispus very little starch no starch very little starch no starch + Rubus fnUicostu crammed starch no starch crammed starch no starch - Joam. of Gen I U 154 On the Formation of Anthocyanin These results show that there is some connection between pro- duction of pigment and the capacity for forming starch from the sugar provided. As a rule, the leaves which turn red are those which form least starch from the sugar solution and several, in fact, form very little or no starch even under normal conditions. Hence experiments on sugar-feeding further strengthen the view that reddening is due to an increase in the concentration of sugar which ultimately leads to an increase in concentration of glucosides ; the latter, being formed from sugar, naturally accumulate in excess since there can be no translocation from the severed leaf Palladin(14) also maintains that the amount of aromatic chromogen is increased by sugar-feeding. In his experiments equal portions of leaves of Rumex patentia were placed in water and 20°/^ cane-sugar respectively. After four days the pieces in cane-sugar had developed anthocyanin, those in water none. The sugar-fed and the control portions were then heated with water and equal amounts of the extracts treated with horse-radish peroxidase and hydrogen peroxide. The extract from the sugar-fed portions produced considerably more pigment than that from the control portions. This view is quite in accordance with my suggestion that sugar-feeding leads to increase of free aromatic chro- mogen. With Vicia Faba leaves in sugar-cultures Palladin obtained a different result. In this case the extracts gave less not more pigment with peroxidase and hydrogen peroxide, whereas cultivation in water only increased the amount of free chromogen. As an explanation Palladin suggests that the free chromogen combines with sugar to form a glucoside — prochromogen — and as such cannot be oxidised by the oxidase. I should suppose the explanation to be as follows : — The chromogen in Vicia Faba is of a different nature from that in most plants in that it is oxidised by tyrosinase, and we may therefore suppose it to be a tyrosin-like compound and not capable of being synthesised from sugar alone. The increased concentration of sugar would only form a gluco- side from the existing chromogen and thereby decrease the amount of free chromogen and would not increase the total amount of glucoside. Cultivation in water would tend if anything to decrease the amount of sugar and hence the amount of free chromogen would increase. It may be also added that sugar-culture does not produce colour in Vida Faba leaves. The question as to whether sugar-feeding does or does not directly M. Wheldale 165 increase the concentration of aromatic glucosides is one which can only be solved by quantitative estimation. I am at present engaged in experiments in connection with this point. Application to Mendelian Factors. A question which now arises is how this hypothesis I have for- mulated fits in with our knowledge of the relationship between colour- varieties and the type from which they are derived. In the first place I shall deal with a variation which, though com- paratively rare, may be most closely connected with the reactions controlled by the glucoside-splitting enzymes. There are anthocyanic species which have given rise to varieties having some organ or part fully pigmented with anthocyanin, whereas, in the type, the same organ or part is unpigmented or only slightly so. The following are examples : — Flower. The type in Bellis pei'ennis, Cyclamen persicum, Primula acaulis, P. elatior, Cheiranthus cheiri, Crataegus oxyacantha, Achillea millefolium, is either without, or is only slightly tinged with, anthocyanin, but fully coloured varieties are known. Leaf. Fagus sylvatica, Coryllus Avellana, Beta vulgaris, Atriplex hortensis, Perilla nankinensis. Carina indica, Plantago major, Brassica sp., Lactuca saliva, produce red-leaved varieties. Fruit. The orange and banana have varieties in which the flesh and pericarp respectively are pigmented with anthocyanin. We may assume that the coloured varieties arise through the loss of some factor from the type, and in some cases it has been shown that the coloured variety is recessive to the type. If the petals and leaves of the coloured varieties are examined microscopically, it is found that the pigment is invariably limited to the epidermal cells, and it is reasonable to suppose that the loss of the factor is also limited to the epidermis. Previously (19) I have termed this unknown factor a reductase or inhibitor, but if the views I have expounded in the present paper are correct, the appearance of pigment in the epidermis might be explained on the supposition that the enzyme controlling hydrolysis and synthesis of the glucoside is absent from this tissue. Hence the chromogen is free from sugar and can be oxidised. In the type the 11—2 156 On the Formation of Anthocj/anin equilibrium position is such that very little or no free chromogen is present in the tissues subject to the variation : in the variety the equilibrium position is possibly one of complete hydrolysis and the tissue as a result becomes considerably pigmented. In the second place, there are anthocyanic species in which the type has coloured flowers, and has given rise to a large number of derivative varieties. Many of these have been fully described in Men- delian literature, and several classes of varieties can be recognized which are applicable to a number of different species. The main classes can be distinguished as : — I. The blue or purple anthocyanic class. II. The red anthocyanic class. III. The albino or non-anthocyanic class. Both I. and II. may in many cases exist in sub-classes common to both; i.e. (a) The tinged class. (6) The pale class. (c) The deep class. There is no further evidence in the present paper beyond that which I have previously given(20) as to the nature of the factors, the absence of which causes loss of blueing power and albinism respectively. They are in all probability oxidising enzymes, though I am by no means unwilling to admit that blueing may in some cases, considering the great number of possibilities in plant-metabolism, be due to alkalinity of the cell-sap brought about by some definite enzyme action. I am uncertain as to the nature of the factor, the absence of which causes the tingeing. I. (b) constitutes the type in many species and deeper varieties of both red and blue classes, i.e. I. (c) and II. (c) are known. They are recessive to the type and are due to the loss of some factor. It now seems probable that this factor is not a partial inhibitor or limiting factor of a reductase nature such as I have suggested, but a controlling enzyme, i.e. one which synthesises and hydrolyses the glucoside. Whereas loss of this enzyme may give rise to coloured varieties when the type is merely tinged and quite unpigmented, when the type is already coloured the loss deepens the colour by increasing the amount of pigment formed. Sometimes the loss is limited to the flower only — Lathyrus, Matthiola, Althaea, Cheiranthus; in other cases, the intense pigmentation of the M. Wheldale 157 flower is accompanied by increased pigmentation of the epidermis of the leaves which in the type are un pigmented : example — deep-flowered varieties of Antirrhinum majus, Dianthus barbatus. It is diflficult to devise a method for demonstrating the absence of an enzyme when the latter may be confined to the epidermis alone. It is possible that some micro-chemical method may be found. REFERENCES. lA. Bayliss, The Nature of Enzyme Acti(yn, 1908. 1. BuscALioyi, L., and Pollacci, G. Le antocianine ed U loro sigmficato bto- logico nelle piante, 1903. 2. BusGEX. Chem. Centralb., 1890 and 1894. 3. Combes, R. Du role de Poxyg^ne dans la formation et la destruction des pig- ments rouges anthocyaniques chez les vegetaui. C. K Acad. d. Sciences, mai, 1910. Sur le degagement simultan^ d'oxyg^ne et d'anhydride carbo- nique au cours de la disparition des pigments anthocyaniques chez les v^etaux. C. R. Acad. d. Sciences, juin, 1910. Les Changes gazeux des feuilles. Rev. gen. de Bot. torn, xxn., 1910. Production d'anthocyane sous I'influence de la decortication annulaire. Bv.U. Soc. bot. France, torn, n., 1909. Recherches biochimiques sur le d^veloppement de I'anthocyane chez les v^etaux. C. R. Acad. d. Sciences, 1909. Rapports entre les composes hydrocarbon^ et la formation de I'anthocyane. Ann. d. Sciences nat. ^ s^rie, 1909. 4. Grate, V. Studien iiber den mikrochemischen Nachweis verschiedener Zuckerarten in den Pflanzen-geweben mittels der Phenylhydraziiunethode. Sitzungsher. d. k. Akad. d. Wiss. Wien, Math. nat. Klasse, 1905. 5. Katic, D. L. J. Beitrag zur Kenntnis der Bildung des roten Farbstoffs in vegetativen Organen der Phanerogamen, 6. Kracs, G. Grundlinien zu einer Physiologic des Oerbstoffs. Leipzig, 1889. 7. Laborde, J. Sxu" le mecanisme physiologique de la coloration des raisins rouges et de la coloration automnale des feuilles. C. R. Acad. Sci., 1908. 8. !Mangham, S. The Translocation of Carbohydrates in Plants. Part I. Science Progress, October, 1910. 9. MiRANDE, M. Sur I'origine de I'anthocyanine d^uite de I'observation de quelques Insectes parasites des feuilles. C. R. Acad. ScL tom. cxlv., 1907. 10. MoLiscH. tTber ein neues, einen karmin-roten Farbstoff erzeugendes Chromogen bei Schenkia blumenaviana. Ber. d. d. bot. Gesell., 1901. 11. MoLLiARD, M. Action morphogenique de quelques substances organiques sur les vegdtaux sup^rieurs. Rev. g^. de Bot. torn, xix., 1907 ; also, Production experimentale de tuberculcs blancs et de tubercules noirs k partir de graines de Radis rose. C. R. Acad. Sci., 1909. 158 On the Formation of Anthocyanin 12. Moore, B., and Whitley, E, The Properties and Classification of the oxidising Enzymes and Analogies between Enzymic Activity and the EflFects of Immune Bodies and Complements. Biochemical Journal, Vol. IV., 1909. 1 3 Overton, E. Beobachtungen und Versucbe fiber das Auftreten von rothem Zellsaft bei Pflanzen. Prings. Jahr. f. wiss. Bat. Bd. xxxiii., 1899. 14. Palladin, W. tJber das "Wesen der Pflanzenatmung. Biochem. Zeitsckr., 1909. 15. t?ber Prochromogene der pflanzlichen Atmungschromogene. Ber. d. d. Bot. Gesdlsck, 1909. 16. Pick, H. Ueber die Bedeutung des rothen Farbstoffes bei den Phanerogamen und die Beziehungen desselben zur Starkewanderung. Bot. Centralh. Bd. XVI., 1883. 17. Senft, E. tJber den microchemischen Zuckernachweis durch essigsaures Phenylhydrazin. Sitzungsber, d. k. Akad. d. Wiss. Wien, Math. nat. Klasse, 1904. 18. Waage, T. Ber. d. Deutsch. botan. Ges. 8. 19. Wheldale, M. The Colours and Pigments of Flowers with special Reference to Genetics, P. R. Soc. B. Vol. lxxxi., 1909 ; also On the Nature of Anthocyanin. Proc. Cam. Phil. Soc. Vol. xv., 1909. 20. Note on the physiological Interpretation of the Mendelian factors for Colour. Rep. Evol. Com. Roy. Soc, Report v., 1909. 21. Wig AND, A. Die rothe und blaue Farbung von Laub und Frucht. Bot. Hefte. Forschungen a. d. hot. Garten zu Marburg, 1887. 22. ZiMMBRMANN. Botanical Microtechnique. I FURTHER EXPERIMENTS ON THE INHERITANCE OF COAT COLOUR IN MICE. By FLORENCE M. DURHAM. In Report IV of the Evolution Committee of the Royal Society, I published a preliminary account of the results of my breeding experi- ments to determine the inheritance of coat colour in mice. I now propose to complete that account by giving the results of my investiga- tions into the genetic behaviour of pink-eyed mice with coloured coats and also of yellow mice. I propose to begin with an account of the pink-eyed mice with coloured coats, but at the same time to leave the question of the behaviour of pink-eyed mice with yellow coats until I deal with dark- eyed yellow mice, and to confine myself at first to pink-eyed mice of any coat colour except yellow. The albinos have been dealt with in Report IV. The pink-eyed mice with coloured coats as stated in Report IV have only apparently unpigmented eyes. Examination of sections of the eyes microscopically reveals the presence of pigment both in the retina and iris. The amount of pigment present is however so little, that it is extremely difficult to say of what colour it is. There is a correlated absence of pigment in the hairs of these mice, so that they are much paler in colour than any of the corresponding varieties of dark-eyed mice. But this absence of pigment in the eyes and hair of the pink-eyed mice has a genetic significance different from that of the dilution of coat colour in the dark-eyed mice. For in the case of the dark-eyed mice, the absence of a factor which effects the den.se deposition of pigment in the hairs gives rise to what are known as the dilute forms, and for each coloured type there is a dilute variety. The pale colours of the pink-eyed mice are not due to the same cause, and cannot be explained in the same way. For pink- eyed mice behave genetically like the concentrated and diluted varieties 160 Inheritance of Coat Colour in Mice of dark-eyed mice and carry the conditions of concentration and dilu- tion just as they do, and in their colourings the effects of these are shown. The paleness of colour therefore which accompanies the pink eye must be due to some other cause. This statement however applies only to those mice in which yellow pigment is absent. For it is possible to produce pink-eyed yellow mice with hair as deeply pig- mented as that of dark-eyed yellow mice. These will be dealt with later on. Also in the case of the pink-eyed agouti mice, while the black and chocolate pigments are there in very much diminished quantities the yellow banding may be as deeply coloured as in the hair of the ordinary agouti. It is possible to arrange the pink-eyed mice in classes cor- responding to those which have been distinguished among the dark- eyed mice. Pink-eyed mice which behave genetically like black mice are of a pale greyish colour and were named lilacs by Mr Darbishire(6) who was the first to breed them and kindly gave me two living specimens. In order to distinguish them from other lilac mice, on account of their colour, I have called them " blue lilacs." They breed perfectly true mated inter se. Mated with chocolate mice, they never throw any other colour but black in Fj. In the F2 generation from this mating two new varieties appear which I have named "chocolate-lilac" and "champagne" i^'cafe au lait" of Cuenot) respectively. The chocolate-lilacs vary very much in appearance in depth of colouring, but the colour is always browner than that of the blue lilac more resembling that of the silver fawn. For this reason I called them chocolate-lilacs, and I thought at first they were a chocolate variety of the pink-eyed mouse. But when mated with chocolate mice they throw a mixture of blacks and chocolates. Chocolate-lilacs mated together throw blue lilacs, chocolate-lilacs and champagnes. The champagne mice, mated with chocolates, throw only chocolates and are I believe the pink-eyed variety of chocolate. Mated inUr se, they breed perfectly true, I therefore regard the blue lilacs as the homozygous pink-eyed variety of the dark-eyed black mouse, the chocolate -lilac mouse as the heterozygous variety of dark-eyed black (throwing chocolate) and the champagne as the homozygous chocolate pink-eyed form. When the various forms are mated with the dilute forms of dark- eyed mice, blues or silver fawns, then in the F^ generation pink-eyed F. M. Durham 161 mice without the factor for concentration are produced. These when mated with blues or silver fawns throw only the dilute varieties, whereas pink-eyed mice descended from unions between pink-eyed mice and dark-eyed mice of the concentrated form only throw concentrated forms when mated with the dilute varieties. There is a great deal of varia- tion in the depth of colour of the pink-eyed mice and I think that the presence or absence of the factor for concentration accounts for this. Unfortunately I did not recognize this fact early enough in my experi- ments to be able to give numbers in support of this view. In the case of the champagne mice, however, a different variety which I called " silver champagne," arose and always appeared in the F^ generation from a mating between champagne and silver fawn. These silver champagnes mated with dilute forms always gave dilute forms. When the chocolate lilac mouse is mated with the ordinary wild colour or golden agouti mouse, the ^i is always golden agouti. All possible forms should appear in F^. Black, chocolate, golden agouti, cinnamon agouti, blue lilac, chocolate lilac, champagne, pink-eyed golden agouti, pink-eyed cinnamon agouti. The pink-eyed agoutis, golden and cinnamon, are very much alike in appearance. In fact at first and for some time I took the pink-eyed cinnamon agouti to be a pale or dilute form of the pink-eyed golden agouti, and owing to the small amount of pigment present, I thought that the pink-eyed golden agouti must be the cinnamon variety. However, the genetic behaviour of the two forms when mated with chocolate showed their differences. The pink-eyed golden agouti gives only golden agouti when mated with chocolate and the pink-eyed cinnamon agouti gives only cinnamon agoutis as a result of mating with chocolate. The small amount of pigment present makes the microscopical determination very difficult. Pink-eyed coloured mice are recessive to dark-eyed mice and when mated inter se never throw the dark-eyed form. Taking all the results irrespective of colour and classifying only according to eye-colour, then as a result of mating pink-eyed mice with dark -eyed mice in F^ I obtained 875 dark eye, DE, 303 pink eye, PE, observed 883-5 „ 294-5 „ calculated. From matings between heterozygous DE with PE 105 DE, 113 PE, observed 109 109 calculated. 162 Inheritance of Coat Colour in Mice In the case of the first mating I made between blue mice and blue lilac the numbers yielded in the F^ generation are peculiar. Instead of a ratio of 9 : 3 : 4 as I expected, I got 27 blacks, 17 blues and 18 blue lilacs. The Fi mice were black and therefore the blue lilacs were carrying the determiner for concentration. The formula for the blue lilacs may be represented as eDB, where e is the absence of dark eye, D the factor for concentration, B the factor for blackness. The blue mouse can be represented as EdB, where E is the presence of dark eye, d is the absence of concentration. The figures given above may possibly be an indication of spurious allelomorphism between the factor for dark eye and the concentration factor. The F^ mating would then be EdeD x EdeD. The results would then be a ratio of 2 black to ] blue to 1 blue lilac, giving calculated results of 31 black to 15'5 blue to 15*5 blue lilac. I was unable to repeat the combination owing to either the blues used being heterozygous in chocolate or the blue lilacs heterozygous in concentration. If this interpretation be correct, then all the blacks should be hetero- zygous and all the blues homozygous. Unfortunately I only mated a few of the offspring. 6 blues only were mated and 3 of these died without young, the remaining 3 were homozygous ; 5 blacks were mated, 3 died without young, one had only 4 young and these were all black, and the fifth was heterozygous. The results of mating chocolate-lilac mice with dark-eyed varieties may give rise to various heterozygous forms. Thus the F^ generation of a mating between chocolate-lilac and blue (giving black Fi) was 19 black, 2 blue, 5 blue lilac, 6 chocolate-lilac. If the mating was EeDdBb x EeDdBB, the calculated numbers would be 18 black, 6 blue, 4 blue lilac and 4 chocolate-lilac. From a mating of chocolate-lilac and black heterozygous in blue giving black ^i, I got 10 black, 4 blue, 6 blue lilac and 2 chocolate-lilac. If the mating were as above between EeDdBb x EeDdBB, there should be 12"3 black, 4*3 blue, 27 blue lilac and 2*7 chocolate-lilac. F. M. Durham 163 Blue lilac x chocolate, eeDDBB x EEDDhb gives black F,. Fi. Observed Calculated Here no blue lilacs were obtained but an excess of champagnes. Bltie lilac x chocolate, eeDdBB x EEDdhh gives blues and blacks. BUck CbocoUte Blue lilac Chocolste- lilac Champagne 21 6 0 4 6 20-7 6-9 2-3 4-6 2-3 Black Blue Chocolate SUver fawn Blue Chocolate- lilac lilac Champagne Fj. Observed 4 3 0 0 11 0 Chocolate-lilac x chocolate, eBeb x EbEb gives blacks and choco Fr. Fi from blacks „, ^ ' Black Chocolate Blue mac Chocolate- lilac Champagne Observed ... 16 7 0 3 0 Calculated ... 14 4 4-8 1-6 3-2 1-6 From black and chocolate Observed ... 8 16 0 0 5 Calculated ... 10-8 10-8 0 3-6 3-6 From chocolate x chocolate Observed ... — 38 — — 16 Calculated ... — 40-5 — — 13-5 Bltie lilac x silver fawn, eeddBB x EEddbb giving blue F^. Bine SUver fawn Blue mac Chocolate- lilac Champagne Fi. Observed 43 19 3 10 3 Calculated ... 43*9 14-6 4-9 9-7 4-9 Chocolate-lilac x silver /aim, eeddBh x EEddbb giving blue Fi. Blue SUver fawn Blue Ulac Chocolate- lilac Champagne Fj. Observed ... 16 13 6 0 2 Calculated ... 20-7 6-9 2-3 4-6 2-3 The champagnes in these last two cases were silver champagnes. Silver fawn x champagne giving chocolate F^, EeDdbb x EeDdbb. Chocolate SUver fawn Champagne Observed 5 2 5 Calculated . 6-75 2-25 3 These champagnes should have been of two sorts, champagne and silver champagne. 164 Inheritance of Coat Colour in Mice Silver fawn x champagne giving silver fawn F^, Eeddhh x Eeddhh. Silver fawn Silver champagne F2> Observed 11 2 Calculated ... 9-75 3-25 Chocolate heterozygous in pink-eye x chocolate-lilac, Eebh X eeBh. Black 1 Chocolate unocoiate- Hlac Champagne Observed 2 3 2 3 Calculated ... 2-5 2-5 2-5 2-5 Blue X champagne giving black F^, EeDdBh x EeDdBh. Black Blue Chocolate Silver fawn Blue lilac Chocolate- lilac Champagne Observed 4 0 2 1 0 1 1 Calculated 3-5 1-17 1-17 •4 •5 1 •5 Blue X champagne giving blue and black F^, EeddBb x EeDdBh. Black Blue Chocolate Silver fawn Blue lilac Chocolate- lilac Champagne Fi- Observed 8 10 3 4 4 2 2 Calculated 9 9 3 3 2 4 2 Blue carrying chocolate x champagne giving blue and chocolate, EeddBh x EeDdhh. Black Blue Chocolate Silver fawn Chocolate- lilac Champagne Observed 2 8 4 1 1 0 Calculated 2-1 21 2-1 21 1-3 1-3 Blue heterozygous in pink-eye and chocolate x champagne, EeddBh x eeDdhh. Silver Chocolate- Black Blue Chocolate fawn lilac Champagne Observed ... 3 0 5 3 1 1 Calculated ... 1-6 1-6 1-6 1-6 3-2 3-2 Blues carrying pink-eye mated together, EeddBB x EeddBB. Blue Blue lilac Observed 19 6 Calculated 18-75 6-25 F. M. Durham 165 Golden agouti x chocolate-lilac gives golden agouti F,, GgBbEe x GgBhEe. Pink -eyed Golden Cinnamon Pink-eyed cinnamon Blue Chocolate- agouti agouti Black Chocolate agouti agouti lilac lilac Champagne Ft. Observed 83 8 31 2 26 7 0 11 Calculated 72-9 24 3 24 3 8 1 24 3 8 1 27 5 4 4 27 Golden agouti y. pink-eyed agouti gives golden agouti F^. Golden agouti Pink-eyed agouti Fa- Observed ... 32 17 Calculated ... 3675 12-25 F,. Cinnamon agouti mated with chocolate-lilac giving cinnamon agouti Cinnamon Pink-eyed agouti Chocolate Cinnamon agouti Champagne Fa. Observed ... 14 4 3 1 Calculated ... 12-3 4 1 4-1 1*4 Agouti heterozygous in pink-eyed agouti x pink-eyed agouti. Agouti Pink -eyed agouti Observed ... 11 8 Calculated ... 9*5 9-5 Agouti heterozygous in pink-eye and chocolate x pink-eyed agotUi heterozygous in chocolate. Pink-eyed CSnnamon Pink-eyed cinnamon Blue Chocolate- Agouti agouti Black Chocolate agouti agouti lilac lilac Champagne Observed 7 0 2 1 10 0 0 1 0 Calculated 5-85 1-95 1-95 -65 5-85 1-95 •65 1-3 •65 Agouti heterozygous in pink-eye and chocolate x black ditto. Pink -eyed Cinnamon Pink-eyed cinnamon Blue Chocolate- Agouti agouti Black Chocolate agouti agouti lilac lilac Champagne Observed 61 10 3 0 6024 Calculated 93 93 3 1121 Pink-eyed agouti x pink-eyed agouti. From this mating I obtained Pink-eyed Pink-eyed Chocolate- agouti cinnamon agouti lilac 37 4 8 There were no blue lilacs and no champagnes. The explanation of this may be that the pink-eyed agoutis were not all carrying the same characters. Another case I cannot explain is the following : An albino heterozygous in E was mated with a yellow carrying agouti. From the agoutis Fi of this union I obtained 17 agouti, 5 black, 1 chocolate-lilac, 1 champagne and 8 albinos. 166 Inheritance of Coat Colour in Mice There were no chocolates, no cinnamon agoutis, no pink-eyed agoutis of either sort, and no blue lilacs. I have tried other raatings of various sorts but the numbers yielded are too small to be worth quoting. Yellow Mice. The genetic behaviour of yellow mice differs in various particulars from that of other mice ; and there is at present no very satisfactory explanation possible to account for this. Hagedoorn(l) is the only one among many breeders of yellow mice whose experiences are not in accordance with my own. But from his account of his experiments, it is clear that he was using a different type of yellow mouse from that employed by the rest of us. The type, which I and other breeders have used, must be regarded as a heterozygous dominant. For it never breeds true, no homo- zygous form has yet been obtained; and when mated with mice of other colours than yellow, some of the offspring are always yellow. Hagedoorn's mouse was a recessive and did breed true. His experi- ments are of interest as showing that another type of yellow mouse exists, but his results need not be considered further here. I made 185- matings in all between yellows bred in every kind of way, but every one of these yellows proved to be heterozygous. As a result of 127 matings between yellows I obtained 448 yellows and 232 other colours. I purposely excluded from the list all matings from which sables and albinos were obtained, so as to count only the pure yellow forms. Albinos can carry the yellow determiner, and the sable mouse, which is perhaps only a variant of the yellow, presents so many peculiarities as I shall show later on that for the present purpose I preferred to exclude it. As a result of 104 matings between yellows and other colours I have obtained 297 yellows and 336 other colours. The problem created by the absence of pure yellows has been dis- cussed by Cu^not(2), Castle (5), Wilson, Morgan and others. There are two possibilities: (1) that in fertilization the zygotes, yellow x yellow, are never formed; (2) that these zygotes are formed but perish. If they are not formed we should expect the ratio of yellow to non-yellow to approximate in .Pg to 3 : 1, because the number of spermatozoa is indefinitely large; if on the other hand such zygotes are formed and perish, the F.^. ratio should be 2 : 1. F. M. Durham 167 The F^ numbers obtained are as follows : Yellow Non-yelloir Cu^not(2) 263 100 Castle (5) 800 435 My own 448 232 1511 767 Expectation at 2 : 1 1518-6 759 3 Expectation at 3 : 1 1708-5 5695 From these figures there can I think be no longer any serious doubt that the pure yellow zygotes are actually formed in fertilization, but that for some unknown cause they are unable to develop. The case becomes therefore exactly comparable with that observed by Baur(7) for the varietcUes aureae, which form albino embryos incapable of existence. It has been argued that if this representation is correct the average numbers per litter should be less for the mating yellow x yellow than for yellow mated with some other colour, and Cuenot and Castle record a difference of this kind, giving the following averages: YeUow X Yellow Yellow X Non-reOow Cuenot 3-38 3-74 Castle 4-71 6-57 From my experience I incline to doubt whether much importance can be attached to differences of this order. The following averages have been compiled from an ample series, 75 litters being the lowest included. yellow X yellow yellow X other colour black X black black X other colour (not yellow) chocolate x chocolate chocolate x other colour (not yellow) agouti X agouti agouti X other colour (not yellow) albinos x other colour (not yellow) I have not mated albinos together often enough to make it worth while to compare the results of mating albino x albino with the other figures. Only mice which lived long enough to have their colours determined are included in these averages, but Castle's figures evidently are based on the numbers actually born. It is clear nevertheless that large differences exist where no special disturbance, analogous to that we are 3-90 young 3-97 }> 4-60 » 3-99 »» 3-96 «i 3-93 >> 3-47 >i 3-32 >» 4-27 II / i/ 168 Inheritance of Coat Colour in Mice considering, is to be suspected, and I doubt whether the observations can be used either for or against the conclusion that the ratio of yellow to non-yellow in F»/\%1 -. 1. The non-viability of pure yellows raises an important physiological question, but we have no indication as to what may be its cause. It should be remembered that the mortality may, for aught we yet know, occur at any age between fertilization and maturity. In the report to the Evolution Committee (3), I have already stated, that the pigments of the eye of the yellow mouse may be black or chocolate but never yellow. If the yellow mouse throws chocolate young but never black the eye will be found to be pigmented with chocolate, often chocolate pigment will also be found in the hairs of this animal. A yellow mouse which throws black young will have black pigment in the eyes and some black pigment will always be found in the hair. I have never found black pigment in the hair of a mouse with chocolate only in the eyes. I have examined several hundred yellow mice and never found an exception to this statement. The hair and the eyes are a key to the genetic behaviour, or one may equally well say the genetic behaviour is the key to the pigments of the hair and eyes of the yellow mouse. Both black and chocolate pigments will be found in the eyes of the yellow mouse with agouti determiner. Yellow mice are subject to an abnormal development of fat in their tissues. All the fat depots become loaded to an extraordinary degree. This development of fat renders them unable to breed. It is a well- known fact to the breeders of Fancy mice. The question of dilution is also a difficulty in yellow mice. Yellow mice vary very much in their colouring. Some are very deep yellow, some much paler, some are deeply coloured dorsally and very light underneath, pale almost to whiteness. I do not mean piebald, but the colour fades off gradually to a very pale cream. The result is that it is very difficult and often impossible to decide whether a mouse belongs to the dilute variety or not. Of course many mice are so pale all over, one would not hesitate to class them as dilute yellows, that is creams. But there is a very large section whose classification can only be determined by their genetic behaviour. To illustrate the difficulty I will mention the case of two mice which I bred together and classed F. M. Durham 169 as creams and they threw chocolates. If they had been real creams they should have thrown silver fawns. Another cream mouse which I had grew a chocolate streak, late in life, down its back, a reversal of the ordinary procedure. When yellows are bred with pink-eyed mice, pink-eyed yellows will appear in Fo as deeply coloured as the original yellow mouse which was grand-parent. As stated before the yellow bar of the pink-eyed agouti mouse is so deeply coloured and so bright that the inexperienced observer would put them in the yellow class. I believe that the so-called pink- eyed yellow mice of Plate's (4) classification must be really pink-eyed agoutis, either golden or cinnamon. The pink-eyed yellow mice when produced behave exactly like the dark-eyed yellows. I have never succeeded in obtaining a homozygous pink-eyed yellow and when mated together they do not throw 3 yellows to 1 other colour; mated with any other colour they always throw some yellows. The dark eye is dominant to the pink eye, but the yellow colour behaves independently of the eye colour when pink-eyed yellow is mated with dark-eyed any other colour. Pink-eyed yellows mated together throw pink-eyed yellows, blue lilacs, chocolate-lilacs and champagnes according to their genetic con- stitution. From the matings of pink-eyed yellows I have obtained the follow- ing results, 17 matings PE7 x PEY gave 57 PEY, 45 PE other colour. 19 matings PEY x PE other colour gave 32 PEY, 33 PE other colour. Before proceeding to give the tables of the results of the various matings I have carried out, I must now refer to two cases in which I obtained yellow mice by breeding together other varieties than yellow. In each case the mice had pink- eyed ancestry. Case I. This mouse was not strictly speaking a yellow mouse. I could not class it as an agouti simply or as a sable. It was very yellow in colour, with the agouti barring on the dorsal surface and a yellow belly. It resembled a very yellow agouti with a yellow belly. Its ancestry is shown by the following scheme : Pink-cyed cfaooolate-lilac Yellow throwing agoutis 1188 X 1450 , i , 1667 . \ # ^ y o . o #' THE INHERITANCE OF THE PECULIAR PIGMENTATION OF THE SILKY FOWL. By W. BATESON, M.A., F.R.S. AND R. C. PUNNETT, M.A. CONTENTS. PAOB Introduction 186 General statement of resnlts 186 Detailed results of the various crosses 191 (1) The Fi generation 191 (2) The F2 generation 192 (3) Fi X Brown Leghorn 194 (4) Fi X fully pigmented birds 195 (5) The fully pigmented F^ birds 197 (6) The ppii strain : a test of the hypothesis . . 197 The constitution of the Brown Leghorn hen .... 199 Exceptions 200 The grades of pigmentation 200 Silky crosses other than with Brown Leghorns . . . 202 Introduction. During the past six years we have been engaged upon a series of experiments connected with the inheritance of the peculiar pigmenta- tion of the Silky Fowl. A brief account of the general features of this interesting case has already been published by one of us\ but as our experiments are now concluded we are able to give in greater detail the evidence upon which our views are based. As a description of the Silky Fowl may be found in any of the standard works on poultry it is unnecessary for us to dwell upon the characters of the breed except in so far as they enter into this particular series of experiments. One of its most remarkable features is the extraordinary abundance of black pigment which is generally distributed among most of the mesodermal » W. Bateson, Mendel's Principles 0/ Heredity, 1909, p. 181. 186 Peculiar Pigmentation of the Silky Fowl tissues of the body. Seen through the thin epidermis this pigment gives the bird the appearance of a fowl with a black skin, deep purple comb and wattles, and dark slaty shanks. The iris is heavily pigmented, and the usually white earlobe takes on a more or less intense turquoise tint which is especially noticeable in the hens. The somatic peritoiieum, the periosteum and pia mater are inky black from the pigment with which they are crowded. The splanchnopleure is much less pigmented, and the liver seen through this looks its normal colour. The muscles also have a blackish appearance, but we have not made any histological examination to determine the exact distribution of the pigment here. It is apparently confined to membranes of mesodermal origin, and is absent from the lungs, liver and other viscera, while at the same time the plumage is white. There is never any trace of it in the allantois, or other foetal membranes. Our experiments with this breed were begun with the idea of investigating the nature of the form of comb by which it is characterised, but we had not proceeded far before it became evident that the in- heritance of the peculiar pigmentation promised more interesting and novel results. As the case presents features unlike any hitherto met with elsewhere it will be convenient if we give a brief outline of the main results and of the interpretation before passing to a detailed examination of the experimental data. General statement of results. The breed with which the Silky was originally crossed was a strain of Brown Leghorns which had been in our possession since 1899. The first indication of something unusual was the definite difference found in the reciprocal crosses between these two breeds. While the mating of Silky % X Brown Leghorn j/* resulted in chicks of both sexes with little pigmentation, the mating of Brown Leghorn $ x Silky f^ gave a markedly different result. From this mating the (/• chicks had only a little pigment and were indistinguishable from those resulting from the previous cross, but the % chicks were all deeply pigmented, differing but little in this respect from a pure Silky ^ On breeding the F^ birds together there resulted in either case an F2 generation consisting of 1 The Fi chicks all had coloured plumage and subsequent breeding showed that the white of the Silky behaved as a simple recessive (cf. Rep. Evol. Comm. Roy. Soc. iv. 1908). Our experiments have led us to infer that the pigmentation is quite independent of the colour of the plumage. W. Bateson and R. C. Punnett 187 chicks of various grades of pigmentation ranging from the deepest pigment to none at all. The F^ generation however presented certain distinctions according as a pigmented, or a non-pigmented ^i hen was used (see p. 193). Brown Leghorn Silky Br.LO X ^ cTbp.l. 1 I r 1 1 Fig. I. Silky Brown Leghorn #" X ^ Br. L.C (5f CfBr.L I — I \ — I — f I — I — \ — I — I — I I — r Fig. 2. In these figures (J O represent un pigmented birds. deeply pigmented birds. birds with some grade of pigmentation other than the deeply pigmented type. The F^ birds were also crossed with the pure Brown Leghorn and the results were strikingly diflferent according as the sex of the ^i was male or female. When the F^ $ was crossed with the Brown Leghorn (^ none of the offspring were deeply pigmented, and this was true for the 188 Peculiar Pigmentation of the Silky Fowl pigmented F^ ? as well as for the unpigmented. But when the ^i j/" was crossed with a Brown Leghorn $ about one in eight of the offspring were deeply pigmented and these were alivays females. To assist the reader in following this somewhat complicated case we append a rough scheme. It will be understood of course that the scheme gives no indication of the proportions in which the various classes are produced, neither for the moment do we attempt to differentiate between the various grades of pigmentation other than the fully pigmented state. We may now state briefly the interpretation to which our various experiments have led us. We consider that three factors are involved of which two are directly concerned with the degree of pigmentation. These are (a) a pigmentation factor (P), and (/S) an inhibition factor (/) which can prevent the full development of the pigmentation ^ The various grades of pigmentation met with depend upon the various compositions of the zygotes in regard to these two factors ; e.g. a bird of the constitution PPii will be fully pigmented, a bird of the con- stitution Ppli will be slightly pigmented, while birds of the constitu- tion ppll, ppli, or ppii will be unpigmented (see also p. 200). The third element with which we are concerned in these experi- ments is sex. Here we have made certain assumptions. We regard the female as differing from the male in possessing a special element, F, of which the hereditary behaviour is like that of any other Mendelian factor. Moreover we consider that the female is always heterozygous for this factor so that the zygotic constitution of a female is Ff while that of a male is ff. Further we suppose that in such zygotes as are heterozygous for both F and / there occurs a repulsion between these two in gametogenesis so that F and / do not pass into the same gamete. We may allude to the cases of the inheritance of the lacticolor variety of Abraxas grossulariata^ and of the red eye of cinnamon canaries' in which similar phenomena can be shown to follow the same system of descent. It must be expressly stated that the suggestion that females are heterozygous for femaleness is offered without prejudice as to the possibility that males may also be heterozygous in maleness. The systems followed by the descent of colour-blindness* in Man and by ^ The condition of the gamete from which either or both of these factors are absent we shall denote in the conventional way by the use of the corresponding small letters p and i. ^ Doncaster, L., Reports to the Evolution Committee of the Royal Society, iv. 1908. 3 Durham, F. M., Reports to the Evolution Committee of the Royal Society, iv. 1908. * Mendel's Principles, 2nd imp., 1909, p. 195, note. W. Bateson and R. C. Punnktt 189 that of the white eye recorded by Morgan in Drosophila^ clearly point to the existence in those cases of a repulsion between a factor for maleness (M), and factors respectively for colour-blindness and for the red eye. The operation of the system of sex-limitation is similar in all these examples, the only difference being that in the one group the repulsion is from the factor F, in the other from the factor M. iiPPf gives gametes iPf] [9] lippFf gives gametes \ipF [9]Iippff gives gametes ^Pl\ ipF] j lpfi\ fpf^ fpf6 ipF Jpf9 Ipf iPfi ipF iPfi 1 ipF ^Pfi I I U^iiPpS iiPpFfii^ gives gametes [ IPf\ \ipf J gives gametes IP/ iPF^ IPf iPfi IPf IPf ip'F'% 1 ipf i iPF^ %, Ipf ipF^ ^pfS iPf iPF i \pfi iPf iPf ipFf ipfi f/z-f %i ipf \ ipf ipf 9 \ ipf 6 lippffU\ gives gametes Ipf iPF% Ipf ipf S Ipf ipF^ Ipf ipf 6 Fig. 3- Recognition of the existence of factors both for femaleness and for maleness of course involves the assumption that ova bearing F can only be effectively fertilised by sperms not bearing M, and vice versa. For that supposition no independent evidence yet exists, and we note that 1 Morgan, Science, 1910, N. S. xxxii. p. 120. 190 Peculiar Pigmentation of the Silky Fowl Morgan^ has made observations on Cumingia (Mollusca) distinctly unfavourable to it. At present however we think it is the most acceptable account of the facts ascertained both as to the heredity and the variability of sexual characters. Ilppff gives gametes [t] iiPPFf gives gametes iPF iPf Bp. Legh. [^]IippFf gives gametes lpf\ ipFj U]IiPpff liPfFfi^^ gives gametes i IPf] Ipf iPf ipf gives gametes Br. Legh. Ilppff 16} gives gametes ilpf Ipf --V \ ?//. ipF IPf ^ IPf Ipf $ IPf Ipf$ IPf iPF^ IPf ipF ^ %, '^fS IpF Ipf9 Ipf IPf$ %, Ipf iPF^ Ipf ipF^ %. Ipf iPf ^ ipF iPff iPf IPf S iPf Ipf $ iPf iPFf iPf ipF i %, ipf 6 ipF ipf 9 fpfi %f6 ipf iPFf ipf ipF ? Ipf ipF^ Fig. 4. The Silky Fowl normally breeds true to the fully pigmented con- dition and we consequently represent the cocks and hens of this breed as ffPPii and FfPPii respectively. The Brown Leghorn on the other hand never produces pigmented birds and we therefore regard it as being entirely without the factor P. But it possesses the inhibitor factor 7; and for reasons which will appear later the cock must be 1 Morgan, Payne, and Browne, Biol. Bull. 1910, xviii. p. 76. W. Bateson and R. C. Punnett 191 normally homozygous and the hen heterozygous for this factor. Con- stitutionally therefore we look upon the cocks and hens of this breed as being respectively ffllpp and Ffllpp. To illustrate what we imagine to happen in the several generations produced by mating a Silky ff with a Brown Leghorn % as well as in the reciprocal cross we have drawn up the appended schemes (Figs. 3 and 4) for comparison with Figs. 1 and 2. These schemes also indicate the composition on our hypothesis of the generations shown ar)d we may now proceed to test their validity by the facts witnessed in these and other forms of mating. Detailed results of the various crosses. 1. The F^ generation. (a) From the Silky %. [Nature of mating FfPPiixffppII.] We have bred from Silky $ x Brown Leghorn j/" on two occasions and ill neither case had any of the chicks more than a slight amount of pigment (cf. Fig. 1). Many of these were reared and in the adult state were almost indistinguishable in general appearance from pure unpigmented birds. Careful examination however revealed traces of pigment as patches either on the wattle, skin, or shanks. In most cases the presence of some pigment was most readily detected beneath the skin in the periosteum of the femoro-tibial or of the tarso-metatarsal joints. Dissection showed that some pigment was nearly always present in the ribs and in the occipital region of the skull. There was frequently a little peritoneal pigment more especially in the region of the ribs and some in the occipital pia mater. The amount of pigment varies somewhat and may be very slight. In some cases the chicks are recorded in our notes as being without pigment, but most of these TABLE I. Reference Males K»tare of mating Full Some None FuU Some None 1905 Pen 16, 349 SUky 9 X Br. L. ehaved similarly to the pure race. (^) ^1 ? (unpigmented) x Brovm Leghorn ^. [Nature of mating, FfPpIi xffppll.] Two -F, $ $ of this nature were crossed with a Brown Leghorn (^ and gave 26 j/'j/' and 18 $ $ of which none were deeply pigmented. This again fits in with our hypothesis (cf Fig. 4), for no deeply pigmented birds are to be looked for from this mating. 4. fj X Fully pigmented (PPii) birds, (a) F,^xPPii%. [Nature of mating, FfPPii x ffPpIi.] The expected result from this form of mating is equal numbers, in both sexes, of chicks with deep pigmentation and of chicks with some pigmentation. We have made this mating twice with the following results : TABLE VL * Hales Females Full pig- Some pig- Full pig- Some pig- Reference Nature of matiiig mentation mentation mentation mentation 1906 Pen 33, 349 Silky ?xFi 15 19 We have already alluded to the deeply pigmented hens which resulted from crossing the F^ ^ with the Brown Leghorn % . On our W. Bateson and R. C. Punnktt 197 hypothesis these birds are in constitution FfPpii and consequently should give the same result as the deeply pigmented ^i % when crossed with a pure Silky ff. We have made this cross on two occasions and in accordance with expectation all the chicks were deeply pigmented (cf. Table IX). TABLE IX. Males Females Keference Nature of mating Fun pigmentation Full pigmentation 1907 Pen 18, 344 ?Ppux Silky ,f 11 12 1907 „ 9, 376 l» u 10 12 5. Crosses with deeply pigmented F^ birds. In the course of our experiments we have made crosses with two deeply pigmented F^ birds, viz. f^ 40 (from Pen 15, 283 of 1907) and % 150 (from Pen 23, 114 of 1907). Each of these birds was as deeply pigmented in the adult stage as the pure Silky, and when bred together they gave only fully pigmented offspring (12 ^f^ and 1\ % %). <^ 40 was also mated with a pure Brown Leghorn $ and gave 2\ ^^^ with some pigment together with 33 deeply pigmented % $. But he is recorded as giving also one deeply pigmented ^ and 2 $ $ which were not deeply pigmented. To these exceptions we shall return and will merely state here that we regard them as due to a peculiarity in the behaviour of the Brown Leghorn hen. $ 150 behaved like a pure Silky when crossed with a Br. L. {/• (p. 192), and we look upon both these F^ birds as of the constitution PPii. 6. The ppii strain. In this account we have so far been concerned with the results of various crosses between the Silky and the Brown Leghorn breeds. By a happy accident we are able to adduce independent and cogent evidence in favour of the interpretation which we have put forward. In 1907 we bought a Silky ^^ which proved to be heterozygous for P (i.e. Ppii). Mated with an Eg}'ptian hen, a brown bird with light coloured shanks, he gave unpig merited as well as deeply pigmented hens. Two of these unpigmented birds were mated back to the heterozygous Silky f^ in 1908 and as was expected gave deeply pigmented and unpigmented birds of both sexes, viz. 18 j/'j^ deeply pigmented, 15 <^ff unpigmented, 21 %% deeply pigmented, 17 %% unpigmented. In this way we were able to establish a strain of birds containing neither 14-8 198 Peculiar Pigmentation of the Silky Fowl the pigmentation nor the inhibiting factor in either sex. These birds, on our system of notation, must be represented as ppii, and the possession of such a strain provided us with the means of testing the constitution of the ^i (Silky x Brown Leghorn) birds in the simplest and most direct way. The ^1 f^ on the hypothesis produces four kinds of gametes in equal numbers, viz. fPI, fPi, fpl and fpi. Crossed with Ffppii such a bird should give in both sexes equal numbers of birds with and without pigment. Again among the pigmented birds there should be equal numbers of deeply pigmented birds, and of birds with a small amount of pigment only. Table X shows that these expectations were closely realised in fact. TABLE X. Males Females Reference Nature of mating Full Some None Full Some None 1909 Pen 4, 408 ippiixF^^ 1 3 1 — 3 4 „ 17, 274 >, 8 8 16 6 6 20 „ 22, 261 „ 5 4 5 3 8 8 Total 14 15 22 9 12 32 Expectation 13 13 25 13 13 27 We have also made a similar set of experiments to test the gametic output of the slightly pigmented Fi $ (ex Silky $ x Br. L. (^). The constitution of such birds on the hypothesis is FfPpIi and owing to repulsion between F and / the gametes produced are of four kinds only, viz. FPi, Fpi, fPI, fpl (cf p. 188). Mated with c/c/ of the constitution ppii such birds should give equal numbers of pigmented and unpigmented chicks in both sexes. And since the female gametes which contain P all lack the inhibiting factor, all the $ $ pigmented TABLE XL Nature of mating Males Females Reference Full Some None Full Some I^one 1909 Pen 3, 467 Fj (slight pig.) ? X sppii — 1 2 — 1 4 ^^^^l 13 1910 i " ^^' 459 » >> — 11 9 16 2 12 1910 1 " ^^' 393 „ >, — 23 17 24 — 21 1910 „ 22, 4? ? ^ Ppii X ippii 1 67 67 61 1 56 Total 1 102 95 101 4 93 Expectation ^- 99 99 99 — 99 W. Bateson and R. C. Punnett 199 at all should be deeply pigmented. On the other hand all the male gametes of the F^ % which contain P contain also /, and consequently none of the pigmented ^/'j/' produced should be deeply pigmented. Table XI which gives the details of four such experiments shows how closely this expectation is realised, and offers strong corroborative evidence of the view here taken of the nature of the gametes produced by this type of jP, %. The five exceptions recorded we shall refer to again (p. 200). The Constitution of the Brown Leghorn Hen. While the Brown Leghorn tion ; and in Table VII even if such birds appeared they would not be noticed, since fully pigmented f^f^ are one of the classes normally produced from the mating of slightly pigmented F^ $ and the Silky 5» ,, lamina. ,, XXXV. 6 (4) ,, „ „ J» »l ,, veins. ,, XXXV. 7 (5) „ yellow colourless. f» XXXV. 8 (6) „ white «> II XXXV. 9 This behaviour is readily explained on the assumption that two pairs of allelomorphic characters are here being dealt with : (a) Presence of the red factor which has been shown to be dominant to absence of the same. (b) Presence of the yellow factor which has been shown (p. 213) to be dominant to absence of the same. 218 Studies in Indian Cotton The red type 3 possesses the two dominant, and the white type 9 the two recessive, factors. Denoting these two pairs by the letters Rr and Yy, the two parental types will bear the constitution i2F and ry, and the six groups which have been recognised the constitution given below with the numerical proportion between the individuals which is assigned to each group : (1) hryy 1) ^1 RRYy 2 (2) RrYY 2) RrYy 4^^ (3) RRyy 1 \^ (4) Rryy 2 J (5) rrYY 1 , , IM rrYy 2 (6) rryy 1 I The plants of the first group can be separated into two subsidiary groups, the members forming the one being pure with regard to both characters, while those forming the other will be pure with regard to the red, and impure with regard to the yellow, character. Groups (2) and (5) can be similarly divided and in all cases this division will be recognisable in the offspring. How far these assumptions are borne out in experiment will be seen from Table VII where the results of this cross are set out in detail. In all cases the expected groups have been formed and the actual numbers are in close accordance with those expected on the above scheme. The facts concerning the petal colour and the red anthocyanic colouring matter of the sap are, therefore, fully explained on the assumption that two pairs of allelomorphic characters enter into con- sideration, these two pairs being composed of the two factors producing the red colour and the yellow colour respectively, the presence of the colour producing factor being in both cases the dominant, and its absence, the recessive, condition. Starting with the red and the white flowered type, it has been found possible not only to produce, but to produce in a state of purity, two other types, one having a yellow (PI. XXXV), and the other a red on white (PI. XXXV), flower. Apart from complications introduced by the consideration that one of the parents is a monopodial, late flowering type, which may be put aside for the moment, the yellow flowered form is recognisable as type 8, and similarly the red on white flowered H. M. Leake 219 form is comparable to type 11, a type which is found cultivated in the Punjab. The conclusions drawn from the results obtained from the series derived from the direct crosses as described above, receive confirmation from a second series obtained from crosses between the Fi generation and the parental type. Owing to illness and consequent limitation of the working period, it became impossible to complete the records of this season and a part of this series had to be abandoned. The some- what meagre records which were obtained are tabulated in Table VIII. The number is too small to admit of any numerical comparison, the character of the offspring can alone be considered. In all cases involving one pair of characters only, the cross with the dominant parent has given only dominant and intermediate forms and that with the recessive parent only recessive and intermediate forms. In the single instance in which two pairs are concerned the cross between the intermediate form (RrYy) and the parent possessing both dominant characters (RRVY) has given offspring similar to the pure dominant (RRYY and RRYy) or to the F, intermediate (RrYY and RrYy), while that with the parent possessing both recessive characters has given, in addition to the form with both recessive characters, three of the four recognisable intermediate forms, that with a red (or red on yellow) flower and colour extemling to the veins {RrYy), that with red on white flower and colour extending to the veins (Rryy) and that with a yellow flower (rrYy). These forms are, in all cases, such as would be expected. In the one case where the recessive only has been obtained, the number of individuals (2) is too small to make the absence of the intermediate form a matter of any moment. Before concluding this section the cross between type 3 and type 10 may be briefly referred to. It has been already shown (p. 213) that the pale yellow of type 10 is recessive to the full yellow of types 2 and 4, and from the experiments last quoted it is apparent not only that a yellow underlies the red in the petal of type 3, but that this yellow is identical with the full yellow of type 4. It would, from this, appear probable that the cross between type 3 and type 10 would be comparable with the cross between the two types 3 and 9 just dis- cussed. This expectation is borne out in experiment. The plants of the ^1 generation of this cross are in all their petal characters similar to those of the cross between type 3 and type 9, that is of the form which has been denoted by the term red on yellow. In the F^ genera- tion four types of plants as distinguished by their petal colour appear : 220 Studies in Indian Cotton (a) Corolla red or red on yellow. (b) „ red on pale yellow. (c) „ yellow. (d) „ pale yellow. The number of individuals occurring in each group has been found as follows : (a) 263, (b) 88, (c) 83, (d) 17. Except for the paucity of the individuals in group (d) these numbers agree fairly with the Mendelian ratio of 9 : 3 : : 3 : 1. Further the two groups (a) and (b) are capable of subdivision in accordance with the degree to which the red colouring matter suffuses the leaf Owing, however, to the crosses from type 10 being discarded, no full records of this appearance are available and it can only be noted that, to the extent of these incomplete records, the two crosses between types 3 and 9 and between types 3 and 10 are strictly comparable. 3 (c). The leaf factor. The term leaf factor has been described by the author in his first introductory note to the cotton work undertaken by him (11). Fig. 1. It is the numerical value obtained by dividing the difference between the two measurements a and b in the accompanying diagram H. M. Leake 221 (Fig. 1) by the measurement e. It is not proposed to enter into a detailed discussion as to the significance of the constancy of this factor for the various types of Gossypia. It may be noted, however, that its identification was purely empirical and it is not to be taken as an absolute figure for each leaf of a plant ; there is a fair range of fluctua- tion as would be expected in the measurements of any series of multiple organs. In spite of these fluctuations it is a matter of little difficulty to recognise what may be termed a " typical " leaf and there is a very marked agreement between the leaf factor, as determined on such " typical " leaves, of individuals of the same type. The degree to which the leaf is incised forms a striking feature of the plant and has been adopted freely as a means of classification. Todaro (16) divides the Indian group (subsectio Indica) of Gossypia into two sections : A. Lobi breves, ratione longitudinis latiusculi. B. Folia palmato-partita, lobis angustis, oblongis, vel elongato- lanceolatis. Gammie (9), though he does not accord this character of the leaf a primary position in his scheme of classification, throughout refers to two gioups with the leaf lobes either broad or narrow. Watt (20) uses the leaf character to subdivide the section of " Fuzzy seeded cotton with united bracteoles." He distinguishes three groups : Leaves two-thirds palmately (sometimes almost pedately) 3 — 7 lobed. Leaves half-cut into 3 — 5 (mostly 3) lobes. Leaves less than half-cut into 5 (more rarely 3 or 7) lobes. It will be noticed that while these three schemes deal generally with the same character there is some difference in detail in the exact points involved. Watt simply deals with the degree of incision which is, perhaps, most closely given by the ratio r • Todaro's group B, as fully defined, is distinguished by not only the factor J- but by the breadth of the lobe, thus including the measure- ment e ; while for his group A he makes use of an expression which is, perhaps, the best form of definition that could be found for the author's " leaf factor." Gammie refers simply to the ratio , — %-r of the lobe, '^ •' breadth which is identical with the leaf factor. In a preliminary series, among other measurement determinations. 222 Studies in Indian Cotton Fig. 2. The top left figure is that of a broad lobed leaf, with leaf factor less than 2 ; the bottom figure is that of a narrow lobed leaf with leaf factor greater than 3 ; the top right figure shows an intermediate leaf with leaf factor 2-5. H. M. Leake 223 the ratio y was determined for a large series of plants but was found to be quite inconstant and useless as a means of identifying types which were readily distinguishable by eye. On the other hand in the leaf factor an expression was found not only for such differences as are of sufficient magnitude to be recognised by the eye but also for such as, though definite and constant, are elusive to the eye and incapable of adequate verbal definition. While there is thus found in the leaf factor a means of defining and expressing to a degree of minuteness hitherto impossible, what appears to be a unit character of the cotton leaf, it is necessary to beware of pressing it too far. It is physically impossible to measure every fully developed leaf and obtain fi:om such measure- ments an average. " Typical " leaves must be selected and in such selection the door is opened for the introduction of a considerable personal element. In the experiments recorded determinations have been made on at least two such " typical " leaves from each plant and the average between the two values so obtained is taken as the leaf factor of the individual. Before dealing with this character in detail therefore both the magnitude of the error met with in these determinations and the exact meaning to be ascribed to the term " typical " require brief consideration. It is clear that a larger experimental error is to be expected in the leaf factor of types with narrow lobed, than those with broad lobed, leaves. In the latter case the three measurements employed in the calculation are all large and errors of measurement proportionately small. In the former case, on the other hand, the divisor e is small and the errors proportionately large. The experimental error, con- sequently, increases as the value of the leaf factor rises. When this value falls below 2 the error, which is accepted, is normally less than 015 from the mean (giving a total range of 0'3) and, when this value lies above 3, this error may reach 0*3 (with a total i-ange of 06). These figures indicate the extreme variation met with. Where the error exceeds this amount duplicate determinations have been made. The recognition of this leaf factor was, as has been stated, in the first place purely empirical and resulted from an attempt to find some method of denoting by symbols the differences between the various characteristic shapes of the cotton leaf. In the selection of leaves used in the determinations certain precautions were found to be necessary and were consequently adopted. That such precautions were 224 Studies in Indian Cotton necessary receives recognition in the use of the word " typical," These precautions require examination since, in a purely arbitrary deter- mination of this nature, some control is required to ensure that the restrictions imposed by their use are not of a nature to render valueless the figures so obtained. Such a check has been found in the measure- ment of the leaves of one individual of each of the several pure types isolated, only the earliest leaves of the main stem and the diminutive leaves at the base of each branch being excluded. These measurements were made at intervals of about a week throughout the season, each leaf being thus measured as it became fully expanded. The results of one such determination in the case of a plant of type 5 are set out in Table IX. For the purpose of their understanding the leaves may be grouped into four sets : (1) Leaves borne on the main stem. (2) „ „ monopodial secondary branches. (3) „ „ tertiary branches. (4) „ „ sympodial secondary branches. It will be noticed that the monopodial secondary branches alone bear tertiary branches which are almost invariably sympodial. The values obtained for the average leaf factor of these four groups are respectively : (1) 1-82, (2) 1-84, (3) 1-73, (4) 1-72. It will be noticed that the leaf factor of the leaves borne on the monopodia is definitely larger than that of the leaves borne on the sympodia whether these be secondary or tertiary branches. The value of the leaf factor as determined for the leaves arising from the mono- podia, differs by between 0*06 and 0*04 from the value obtained by the empirical method of selection of " typical " leaves. This error lies well wdthin the limits of the experimental error as defined above. The " typical " leaf, therefore, may be defined as that leaf which possesses a factor having a value equal to the average of the factors of all leaves arising from the monopodial branches. It is not, as was anticipated when the author's earliest note (11) was published, the average of the factors of all the fully developed leaves. This result is in perfect accord with the main precaution which on empirical grounds it has been found advisable to take, namely, to select leaves from the monopodia. It is these leaves that the eye naturally selects as being typical of the plant. It is perhaps unnecessary to detail more than one further precaution which it has been found advisable to adopt. This is to avoid the H. M. Leake 225 determination of the value e where an accessory notch (vwie Fig. 1, p. 220) occurs in the re-entrant angle at the base of the main lobe. Such precautions are obviously necessary and cannot affect the value of the leaf factor as a definite character. The determination of the leaf factor for many thousands of plants has brought one remarkable feature into prominence. While every value has been obtained for the leaf factor from 1 ("broad" lobed) to 5 (" narrow " lobed) no case has been observed in which a plant with intermediate value (between 2 and 3) for the leaf factor breeds true to this character. All pure plants, and consequently all types, are divisible into two distinct groups : (1) With a leaf factor less than 2. (2) „ „ greater than 3. Within the limits 1 to 2 occur all the " broad " lobed types, while within the limits 3 to 5 occur all the " narrow " lobed types*. The accuracy of the expression — that is, the measure of agreement between different individuals of one type — is such that it is possible to recognise within, and isolate from, a type, otherwise pure, races separable only by the leaf factor. It seems probable that the existence of such "pure lines," t-o use Johannsen's term (10), is a phenomenon of general occurrence throughout this series of Gossypia and in some of the types such forms have been isolated. Thus within type 4 occur three "pure lines" with leaf factors of 1*37, 1*46 and 164 which have been isolated, and from type 9 "pure lines" with leaf factors of 3*34 and 359 which have similarly been isolated. Opportunity has not been forthcoming for treating this question in the detail it deserves and it seems probable that with a more detailed examination the number might be considerably increased. Indications of the existence of such " pure lines " are apparent in Table X. The behaviour of the leaf factor when crossing occurs. When a plant with leaf factor less than 2 is crossed with a plant with the leaf factor greater than 3 the leaf factor of the plants of the Fi generation is found to approximate to the mean of the two parental leaf factors. Table XI illustrates this point. At the time the crosses were made the character had not been identified and the figures given ^ In the fields plants are frequently found with a leaf factor less than 3 and greater than 2, and on this fact among others the author has based his views on the occurrence of cross-fertilisation under natural conditions (11). 226 Studies in Indian Cotton for the parental leaf factors are not those of the actual plant but the average of the type as given by the offspring (produced by self- fertilisation) in the two subsequent generations. In two cases only is the variation from the parental mean at all marked and in both these this difference is not shown by the reciprocal. In the F^ generation a continuous series of forms is produced in which every value of leaf factor between the parental limits is obtained. Diagram 1 illustrates one such case and is derived from the series given in Table XIII (6). It is here noticeable that, while the series appears continuous, in that every value of leaf factor (within the limits imposed by the experimental error) occur, the number of individuals is by no means regularly distributed throughout the series — in other words, the frequency of each class exhibits marked variation. The curve is, in fact, multimodal (Davenport (6)) and possesses three modes. The posi- tion and value of these modes are instructive. While the values of the outer modes differ but slightly from the values of the two parental leaf factors, the value of the intermediate mode shows a fair degree of approximation to the value of the mean between the leaf factors of the two parental types. The proportion between the number of individuals grouping themselves about these three points is 1 : 22 : 1. The curve retains its trimodal nature, if for the actual values obtained by direct measurement of the leaves of individual plants — the values here given — the mean value of the leaf factor of the ^3 offspring be substituted. A similar curve has with one exception been obtained in every case submitted to a critical examination. In this instance, the cross between type 2 and type 3, there is no trace of a multimodal curve and the ratio between the number of individuals in each group (Table XIII («)) diverges markedly from that obtained in the instance given above. Lack of opportunity and the difficulty of handling a cross between two monopodia! types have rendered it impossible to continue investigation into the behaviour of this cross and for the present it must remain undecided whether, on further examination, this too will fall into line with the example more fully investigated or whether a different series of phenomena is here instanced. So far the results have been described in outline only, and as a close examination of the tables will show, are only approximate. Complete agreement is, perhaps, hardly to be expected in dealing with a character which, as has been already shown, cannot be measured with absolute accuracy. It will be observed that the modal values of H. M. Leake 227 the leaf factor in all cases exceed the corresponding parental or mean parental value, the excess being practically identical (031, 035 and 0"38) in the three cases. This excess, though small, appears definite but has so fiir received no explanation. 1 i i... ^ i 1 T "T^ ! i t i jT:::i:::;::"::""it"-i ^ ■ ::: . ^ _ii * ...t±±i..i.^ I I t _i r :: :::: ::^^ i i 1 1 II _ _ ±1.... I ::i±_ Parents 11 16 21 26 31 36 41 Type 4 x Type 8 Diagram 1. In one case only has each plant of the F^ generation been self- fertilised and the ^3 generation raised from the seed so obtained. The results are set out in Table XIV. In this table the extreme and Joom. of Gen. i 16 228 Studies in Indian Cotton intermediate groups are given in a condensed form so that the offspring of all plants, the average leaf factor of whose offspring differs by O'lO or less, are grouped together. Full details of individual plants are only given at the two points where the change from the pure to the impure form takes place. It will be seen from this table that a marked difference exists in the behaviour of the individuals belonging to the three groups into which the F^ parents fell. The offspring of those Fn individuals of which the leaf factor was less than 2 have, with few individual exceptions, a leaf factor which is less than 2. In the same manner the offspring of plants with the leaf factor greater than 3'2 have a leaf factor which is greater than 3. As will be seen from the table the exceptions are relatively few and it may be said in general terms that the individuals of the two groups, having the leaf factor less than 2 and greater than 32 respectively, are pure with regard to this character. The dotted vertical lines in the Table drawn between the columns representing the values 2"1 and 2*2, and between those repre- senting the values 2*8 and 2*9, indicate the limits of experimental error recognised in the two groups. It will be noticed that in 5 only out of 1283 cases the limiting value of 2*1 is exceeded and in 7 out of 1274 cases the limiting value of 2*9 is not reached. These exceptions will form the subject of further investigation. It is, of course, possible that these plants have been introduced by accident. Nothing, however, in the further examination of these individuals lends support to this view. The third group, which is characterised by the intermediate value of the leaf factor, is not, like the previous groups, pure in this respect. Such plants have invariably given offspring which, as a group, exhibit the entire range of values obtained for the leaf factor. It will be noted that, though this variability exists, the average value of the leaf factor of the Fs generation from this intermediate group differs but slightly from the mean of the two parental values and further that the number of individuals comprising the three groups are in almost complete accordance with Mendelian expectation (1 : 2*04 : 1), while the mean values of leaf factors for the three groups taken severally show but slight variation from the values obtained for the corresponding groups of the jPa generation. It is impossible to avoid being impressed by the similarity which exists between these results and the more typical examples of Mendelian phenomena. It has frequently been pointed out {vide Bateson (3), p. 53) that H. M. Leake 229 dominance, which formed so striking a characteristic of the earlier experiments on these lines, holds no position of fundamental importance in Mendel's own statement of his law. In the present instance there is a complete absence of dominance and the direct offspring of a cross are as markedly distinct from one, as they are from the other, parent. It is possible, however, to discern more than this. The two factors appear capable of blending in any proportion, and there thus appear a continuous series of forms showing all stages from the typical broad lobed individual, with a leaf factor less than 2, to the typical narrow lobed individual with the leaf factor greater than 3. Owing, however, to some influence, of which, as yet, nothing is understood, these various degrees of blending do not occur with equal frequency. This is greatest at the point represented by a blending of equal proportions of the two factors and becomes less and less as this proportion becomes unequal, but increases again when the proportion of one or other of the factors is reduced to a negligible quantity or is entirely absent. This capacity of blending in unequal proportions is further shown by a comparison between the value of the leaf factor of the F^ parent with the mean value of that of the ^3 offspring. This comparison is given in the three last columns of Table XIV. The difference between these two values for the whole series is 0*07, a figure well within the limit of experimental error, which is, however, in a few individual cases exceeded. It may be generally stated, therefore, that the value of the parental leaf factor is the mean of the values for the offspring. Con- sequently, when unequal blending occurs in any plant, the number of offspring falling within the group whose leaf factor enters in greatest proportion into the blending will exceed the number of offspring which fall within the other group. In other words the ratio of the offspring having a leaf factor less than 2 to offspring having a leaf factor greater than 3 will increase as the parental leaf factor diminishes from the mean value of 26 and will conversely diminish as the parental leaf factor increases from this mean. That this is the case the detail columns of Table XIV clearly show. It is now necessary to glance for a moment at the lower limit of the " narrow " lobed group. It has been stated that this limit is 30, a figure which has, with one exception, been adopted in Table XL Reference to Table XIV, however, will show that the lower limit for the pure forms with narrow lobed leaves is 32 — a figure which exceeds the value of the corresponding parental leaf factor. In this connection it is noteworthy that a value of 3*5 is throughout obtained for the 16—2 230 Studies in Indian Cotton mean leaf factor of this group. It is possible that this figure, 3*52, more accurately represents the true value of the narrow lobed parent than that actually obtained by experiments (313). This latter figure is based on six determinations only and it is a matter for regret that more determinations were not possible. Not only, as has already been remarked, is type 3 difficult to handle, owing to its monopodial habit, but it has been found to be in a marked degree self-sterile. In the first generation only six plants were obtained by self- fertilisation, while in the second, numerous attempts were all unsuccessful. While, therefore, the value 3*13 has been adopted in these calculations it must be noted that this value is extremely low for the type 3 as determined on a set of pure, but unrelated, plants of this type. Acceptation of the figure 3'52 as more nearly representing the true parental value, while accounting in full for the difference of "38 found between the value of the narrow lobed parent and that of the corresponding F^ group, accounts only partially for the difference of 0*35 between that of the parental mean and of the intermediate group, and fails entirely in the case of the difference of 0'31 between the broad lobed parent and its corresponding F^ group. These differences must for the present remain without explanation. The few cases in which the F^ generation has been crossed with the parent types are given in Diagrams 1 and 2. In all cases the F^ intermediate, when crossed by the broad lobed parent, has given only intermediate and broad lobed offspring and, when crossed by the narrow lobed parent, only intermediate and narrow lobed offspring. The number of intermediates is far too small for any value to be attached to comparison of their relative numbers and of the mean value of leaf factor. It is impossible, therefore, to draw any further conclusion than that, within the limits imposed by their paucity, these figures are in complete accord with the expectation based on the conclusions derived from the direct series. 3 {d). The type of branching and the length of the vegetative period. The differences which exist in the form of the secondary branches and in the length of the vegetative period between the various types under consideration have been briefly noted above (p. 209). The intimate connection which has been found to exist between these two characters in the Indian cottons has already been pointed out by the author in Part 2 of his introductory note (12). In a still earlier H. M. Leake 231 publication Balls (1) foreshadows a similar interrelation between the type of secondary branching and the length of the vegetative period in the Egyptian and American upland*. Since the publication of the note referred to, a most interesting communication from J. V. Thompson to the Agri-Horticultural Society of India has been met with in the Journal of that Society for the year 1841, in which the intimate relation between the type of branching and date of flowering is clearly indicated. In this communication he states : " The cultivated varieties of cotton I find may be divided into two classes, viz. early and late kinds ; this precocity or tardiness being inherent in the particular variety, and derived from a peculiarity hitherto unnoticed, and which it will not be difficult to explain. It may be observed that all the varieties have a natural tendency to produce a central main stem furnished with a leaf at intervals of a few inches ; in the axillae of each leaf-stalk resides a pair of germs or buds, placed in the same plane or side by side ; one of these germs is destined to produce flowers only, the other only branches. In the early kinds the former or flowering branches alone are developed, while the late kinds expend their force exclusively in the production of multiplying branches. This peculiarity must for ever unfit these late kinds for a cold climate, such as Northern India." For the full communication, which is of some length, the reader is referred to the original source (18). Sufficient has been quoted, however, to show how fully the importance of the connection between the branching habit and the length of the vegetative period had thus early been recognised. The importance of two axillary buds, which is also indicated, has previously been dealt with by the author (12) in a preliminary note but has no concern with the experiments now under treatment It has already been noted, when defining the types which have been employed in these experiments, that the Indian cottons fall into two well-defined groups, those in which the secondary branches are always, or nearly always, monopodia, and those in which the secondary branches are always, or nearly always, sympodia. As long as observation * Since the above was written Balls. 147 and 155 Bureau of Plant Industry, U.S. Department of Agriculture have been received. In these the authors draw attention to this same point. According to them, however, this character is induced to vary in the types investigated by them as a consequence of change in environment. This and other differences in the method of branching between the observations of these investigators and those of the author are not concerned with the subject matter of this paper and most be left for consideration at a subsequent period. 232 Studies in Indian Cotton is limited to pure types these two groups are readily distinguished. When, however, the progeny of" crosses between types belonging to these two groups come to be considered, every gradation between the two extreme forms is found and it becomes a matter of extreme difficulty in individual cases to define the degree of approximation to one or the other extreme type. In such intermediate plants the passage from one type of secondary branching to the other is usually abrupt, the earlier branches being monopodia and the later sympodia. It is, therefore, possible to divide the main stem into two portions, a lower portion in which the branches are monopodia and an upper portion in which the branches are sympodia. The character can then be conveniently expressed as the percentage of the entire stem bearing monopodial branches. Expressed in these terms a pure monopodial type is indicated by the number 100 and a pure sympodial type by the number 0. It has already been stated that no pure type has been isolated which invariably produces sympodial secondary branches only. A few monopodial branches may in all cases occur at the base of the primary stem. It is convenient, therefore, to denote these also by the symbol 0 which indicates all such sympodial types as have been found to breed true. In like manner the symbol 100 may be used to denote cases in which a few of the most apical branches are sympodial. In the earlier experimental stages it was considered sufficient to recognise four divisions only : (1) The full monopodial type indicated by 100. (2) Approximately three-quarters of the secondary branches mono- podial, indicated by the symbol 75. (3) Approximately one-half of the secondary branches monopodial* indicated by the symbol 50. (4) The sympodial type indicated by the symbol 0. Recently the separate forms have been recorded in greater detail by which the fraction, recorded in tenths, of the main stem bearing monopodial secondary branches is used as a basis for division. By this method 10 groups are formed, the relation of which to the four groups given above is shown below. 100 75 50 0 100 90 80 70 60 60 40 30 20 10 0 In this notation the figures 100 and 0 apply respectively only to individuals in which sympodial and monopodial secondary branches are entirely absent. H. M. Leakb 233 It is clear that this system of record, though the best that has been devised, is subject to considerable disadvantage. It is, at the best, approximate and moreover the determination is only possible when the main stem has received no check to growth. In practice this continued growth of the main stem is rendered a fact of comparatively infrequent occurrence from the climatic conditions prevalent at the early stages of growth. These conditions favour insect life of all kinds and the larval stage of Earias sp. is commonly met with on the cotton plants. This pest penetrates the young stem at the leaf axil and from this point bores its way downwards. The stem so attacked withers and growth is continued by an enhanced development of the secondary branches. In such cases it becomes difficult and frequently impossible to determine this character even approximately. The length of the vegetative period is most readily expressed in the number of days from the date of sowing to the appearance of the first flower. Unlike the previous character this lends itself to accurate record. The fields are visited daily and the plants in flower for the first time noted. Yet numerous subsidiary influences are here found to aflfect the date of production of the first flower and render the figure, though accurate in itself, only approximately accurate as an indication of a definite individual character. The more important of these influences may be here referred to. In the first place, there has been found a considerable seasonal variation ; that is, a considerable difi"erence in the length of the vegetative period of a pure type from one year to another. Hence the figures obtained for one year only are strictly comparable and it is possible to compare the results of two or more years by introducing a seasonal factor by the addition (or subtraction) of which the results of any two years are rendered comparable. This is illustrated in the column of Table XV for the years 1907 and 1908. In the second place the length of the vegetative period is materially influenced by the method of cultivation. Two methods have been employed in the course of these experiments. In the first the seed is sown in pots and the young plants, when a month to six weeks old, planted out. In the second the seed is sown in the ground about a month after the sowings in pots have been eflfected. Here only indirect comparison is possible and the efifect of such variation in the method of cultivation is shown by a comparison between the third and the first two columns of Table XV. Unfortunately no records are available by which the direct influence 234 Studies in Indian Cotton of the method of cultivation may be calculated, for in no case has the same type been grown by both methods in a single season. In 1907 and 1908 all the pure types were grown in pots, while in 1909 they were sown in the field. To obtain a comparison between the two methods of cultivation it is necessary to resort to an indirect method based on the crosses. In 1908 the entire ^2 generation obtained from the crosses was raised in pots while of the seed of these plants only that of which a small amount was available was, in 1909, sown in pots, the remainder being sown in the field. In Table XVI is given the result of the comparison between the length of the vegetative period of the offspring of plants having a similar period when these offspring are grown under the two conditions. The difference due to the method of cultivation varies from a minimum of 21 days to a maximum of 31 days and, generally speaking, the greater the length of the vegetative period the greater will be this difference. A similar result is reached from a comparison of Tables XVIII — XXI. Tables XVIII and XX are based on the pot series and involve only the seasonal difference between the two years 1908 and 1909, which is foHind to be five and three days respectively. In Tables XIX and XXI, based on the field series, in addition to this seasonal differ- ence there also occurs the difference due to the method of cultivation, and the combined differences are in the two cases 31 and 28. By subtraction the average difference due to method of cultivation alone is found to be in the one case 26, and in the other 25 days. From the above it is noticeable that the difference in length of the vegetative period due to the method of cultivation is fairly constant for all types, increasing only slightly with the increase of what may be termed the standard vegetative period of the plant. The seasonal difference, on the other hand, depends in considerable measure on the type, being less for early flowering than for late flowering types. While, therefore, it is possible to reduce two series, differing only in the method of cultivation, to one standard, this is not possible when a seasonal difference enters into consideration. In addition to these two main causes, which, it will be noticed, affect the entire series, the length of the vegetative period of individual plants may be influenced through several minor causes and the actual figures, though accurate in themselves, are thus rendered only approxi- mate as a record of the standard length. Thus in a few cases the young flower buds have been observed to fall without opening {vide note to Table XVII) and an abnormally long vegetative period has been H. M. Leakb 235 the consequence. Again, dwarfing arises through numerous causes and leads to delay in the production of the first flowers. In one case plants of a monopodial type, with a normal vegetative period of over 200 days, commenced flowering within 100 days from the date of sowing and before they had been planted out. All cases where any such abnor- mality is apparent have been omitted from the following records. The interrelation between the type of branching and the len,gih of the vegetative period. The two characters just dealt with are mutually dependent. A plant of the sympodial type will commence flowering shortly after the secondary branches have developed, while a plant of the monopodial type will not flower until the tertiary branches develope. This lengthen- ing of the vegetative period is shown in Table XV, in which the length of the vegetative period of some of the more important types are recorded. The interdependence becomes still more marked when a continuous series, such as is obtained in the F^ and subsequent genera- tions of a cross, is considered. For this purpose the plants may be associated into groups in which the length of their vegetative periods is similar, each group being formed by the plants which flower during a ten-day interval. This method has been adopted for the series derived from the F^ generation of the crosses between types 3 and 4 and between types 3 and 9, and the results are recorded in Table XVII (cf. author's note). The figure given opposite each ten-day interval indicates the average type of branching occurring in plants falling within that interval and is obtained by adding the numbers indicative of the type of branching of each plant (100, 75, 50 or 0) and dividing by the total number of plants. Tables XXII — XXV show the same interrelation in the ^3 series only in a slightly diSerent and more detailed manner, the ten stages latterly recognised in the type of branching as above described, and two- and five-day intervals being respectively substituted for the four stages and the ten-day intervals. The closeness of the interrelation is given by the coefficient of correlation (Davenport (6)). This has been worked out for the series given in Table XXIV and found to be '6819. This interrelation, or correlation, is, therefore, a definite fact depen- dent on the limitation of the flower-producing habit to the sympodial branches. What appear to be two characters are merely two outward expressions of the same structural peculiarity. In other words a 236 St'udies in Indian Cotton definite reason exists for the correlation between these two measurable and apparently distinct characters, and it is permissible to select the one that appears to be more reliable for the purpose of recording the habit of the plants under consideration. While in neither case has an accurate method of record been obtainable, the date of appearance of the first flower is at once more readily determined and obtainable in a larger number of instances. The measure of the length of the vegetative period, therefore, probably affords a means of indicating the habit of the plant which is more accurate than the direct record of the percentage of monopodial second- ary branches, and has been adopted to record the behaviour of this character when plants of the two groups are intercrossed. The habit of the offspring from a cross between monopodial and sympodial types. In the ^1 generation derived from a cross between a plant belonging to a monopodial and one belonging to a sympodial type, the length of the vegetative period is intermediate between those of the two parental types. This is shown by Table XXVI in which the relative lengths of the vegetative periods of the F^ generation and of the two parental types are detailed. This table further shows that while the Fy^ genera- tion is intermediate in this respect, it does not hold a position corresponding to the mean of the two parental values but in all cases approaches the sympodial type. In this table the seasonal variation is eliminated by comparison of the F^ generation with the offspring of the parent plants. In the F^ generation the plants form a continuous series in which every stage from early flowering to late flowering forms occurs. It is noticeable, however, that while those individuals of the F^ series which have the shortest vegetative period are in flower as soon as, or even before, the plants of the parental type, in no case does the vegetative period equal in length that of the monopodial parental type. In other words, while the full sympodial type appears comparatively frequently the full monopodial type only rarely does so. The divergence from the mean length of the parental vegetative periods noticed in the F^ gene- ration is here even more marked. Diagram 2 illustrates these results for a single instance of a cross between a monopodial and a sympodial type. Owing to the seasonal variation above noted it is impossible to compare the periods for H. M. Leake 237 successive generations directly, and each must be compared with the values for the parental series grown in the corresponding season. It is impossible here to distinguish more than one mode ; there is no trace F2I909 Parents 1909 Fi 19u- Parents - n^Ll^,--fet;:^^ I1IIIIIIIIIIIIIIIIIIIIIIIIIIIIIII fe:"^' ::l:::-f— -j-zn: -^ !.::':j.J::' jEili — ^rtrr: ^ ! . . ! : . . — -— — ~H"' ;■■;;■; ; 'i ' ■ ^ "T*" '■■^' ■■ ■-- •---• : - ^- ::;:;■,, ""' : '* ] ' ' ' ' ■ . * " " ' ; : : -r^-t;-! --|--H-I.I| 1 i ' 1 1 ilijil U -- ^ ■- -- -^^^^--- ----- ~ - ----^^^ ::::.-T" ..... ... . . i i '■■'■■'' 1 ■■'■ ■ - — — ' ' i ' ~H — -■■■■■'■■■- — 1 j m ::,'|llli|li|ir :4'!i':' 1 ' \I\±M ■ : ; ■ t ■ ■ — • — — -m (X —^ ■ ;■:■■, -H- 1 1 ' ' ■ 1 ! ' ' 1 ' : ' • 1 ' ! 'itl'li 1' ■ ' ' ■ - • ■ ■ ■ ■ ■ ■■.■■■ ,.,. )., ■ ■ 'I'l — U-| 1908 70 ^° ^ ^00 1^° ^20 130 140 150 160 170 180 190 200 210 220 Type 3 x Type 10 Diagram 2. of a curve of frequency with three modes such as was found in the case of the leaf factor, nor has any instance of such a curve been obtained for the character under consideration. 238 Studies in Indian Cotton In the present instance there appears to exist an example of partial dominance combined with incomplete resolution of the component factors in the subsequent generations. It must, however, be admitted that the experimental error is undetermined and, from a consideration of Tables XVIII — XXI\ this would appear to be considerable in comparison with the magnitudes under measurement, and sufficiently large to render the character ill adapted to such analysis as has been attempted. The impossibility of determining this error was in itself sufficient to render the advisability of attacking this question as a purely theoretical problem exceedingly doubtful. The behaviour of this character is, however, a matter of vital practical importance. As has been stated, it is essential that a plant should be of the sympodial type if its cultiva- tion in the United Provinces is to be a commercial success. At the same time the majority of Indian cottons with a really valuable staple belong to the group of monopodial types. The chief hope of improve- ment of the cotton crop in the United Provinces, therefore, has been based on the isolation of pure sympodial forms with the staple of the monopodial type. 3 (e). The leaf glands. There frequently occur on the under surface of the leaf one to three (and rarely four) glands. When there is a single gland it is situated on the midrib a short distance from the point where this leaves the petiole. In addition to this gland, two more glands may occur similarly situated but on the two main lateral veins — giving three glands in all. The stage in which only one of these laterally situated glands developes is commonly met with. In one or two cases only have four glands been observed and in all such cases the addi- tional gland is situated on the midrib. It is not a condition which enters into the course of these experiments. The number of glands is definite and as a leaf character lends itself to ready determination. But the leaf is a multiple organ of the plant and it becomes possible for a plant to possess leaves differing in the number of their glands. Difficulty arises in this case similar to that met with in the leaf factor, and such as of necessity arises when the ^ Of these tables No. XVIII only is given in extenso. The subsequent Tables XIX — XXI are abbreviated and give the combined details for those plants the average dates of flowering of whose offspring fall into successive five-day periods. These three tables, in their expanded form, agree in all particulars with Table XVIII. H. M. Leakb 239 character of a multiple organ is employed as a plant character, owing to the character, definite for the organ, being indefinite for the plant. It is possible, however, to recognise two distinct forms in which the leaves are either all eglandular or all glandular. It is true that an intermediate condition has rarely been observed in which a few of the leaves may bear a minute and rudimentary gland. The condition is, however, extremely rare and though the plant would on direct observa- tion usually be entered as eglandular its true character will be identified through the occurrence of glandular offspring on selfing. If plants belonging to a single type and bearing glandular leaves be arranged in series according to the proportion of leaves bearing 1, 2 or 3 glands, the series will be practically continuous. Nevertheless it has been found possible to recognise three fairly distinct stages which have received the following notation : (1) Glands 1 ; in which all or nearly all the leaves bear a single gland. (2) Glands 1 — 3 ; in which the majority of the leaves bear one gland but those of the main stem and possibly one or two of those of the monopodial branches bear three glands. (3) Glands 3 — 1 ; in which the majority of the leaves, including all those of the main stem and monopodial branches, bear three glands. A few leaves of the sympodial branches may also bear three glands. It has been found possible to isolate and grow in a state of purity forms in which the leaves are eglandular and forms which fall within the third stage as given above. Plants with the leaf glands 1 — 3 on the other hand have invariably given mixed offspring^ There remains for consideration the second stage in which the leaves have a single gland only. This too may occur as an intermediate condition between the eglandular form and that with glands 3 — 1, and in such cases does not breed true. It appears probable, however, that it may also occur as a pure form. Within the author's experience plants of type 2 have invariably leaves with one gland, but, for reasons already given, this type has not been very fully investigated and, perhaps, to an extent hardly sufficient to justify the statement that one leaf gland is characteristic of the type though there can be little doubt that a pure form of type 2 so characterised does exist. This pure form with a single leaf gland does not enter further into the present ' The two cases noted in Table XVIII form apparent exceptions to this statement bat most, in the absence of farther evidence, be considered as extreme instances of divergence from the expected ratio. 240 Studies in Indian Cotton experiments in which the 1-gland stage will be grouped with the 1 — 3 stage to form one intermediate group. Excluding types 1 — 3 and 11, in all the remaining types two forms have been isolated which are characterised respectively by the absence of leaf glands and by the presence of these glands in the 3 — 1 stage, and both these forms have been pure bred. In type 1 the three forms have all been observed but their purity or the reverse has not been tested by experiment ; type 2 has already been dealt with ; in type 3 the 3 — 1 gland form has alone been met with, while of type 11, though the 3 — 1 form has similarly been the sole one observed, it is impos- sible to speak with much certainty since the plants on which the observations have been made are all derived from a single source. In the cross between type 3 and type 4 to which reference has already been made an eglandular form of type 4 was used as parent. This cross, therefore, illustrates the behaviour of this gland character under the influence of cross-fertilisation and the results are set out in Tables XXVII and XXVIII. In the ^i generation the plants are uniformly of the intermediate form (glands 1 — 3) while in the F^ generation the two parental forms reappear. It will be observed from Table XXVII that while the ratio between the eglandular and glandular forms agrees closely with the expectation there occurs among the glandular forms a large excess of that with the glands 3 — 1 and the same is found to hold among the F^ offspring of the impure F^ parents (Table XXVIII, last two columns). That this excess is due to the classification of certain intermediate forms as pure 3 — 1 forms is proved by the fact that 52 individuals which had been so characterised were found to be in reality impure. The F^ plants must in fact be considered as forming continuous series from the pure eglandular form to the pure glandular 3 — 1 form though, from the very nature of the case, the former is more readily identified than the latter. It has been seen that plants with a single leaf gland occur; and, if the 1 — 3 stage be considered as the full intermediate, this stage must be considered as an approach to the eglandular con- dition. In the same manner there appears to occur a stage which approaches the fully glandular condition sufficiently closely to be with diflSculty separated from it. By examining the plants at the end of the season it is possible to distinguish two conditions which may be termed the 3 — (1) stage, in which even the latest leaves of the monopodia bear three glands, and the 3 — 1 stage, in which these bear only one or at most two glands. It is not yet certain, however, that this distinction H. M. Leake 241 will afford a means of separating the impure forms, nor is it a method which becomes available till after the work of fertilisation is long over. At present no method of discriminating with certainty between the pure and impure forms during the major portion of the life of the plant has been discovered. Correlation. One instance of correlation has already been dealt with in section .3 (d) on the type of branching and the length of the vegetative period. In this instance the correlation was seen to depend on a recognisable feature — the flowers are only formed as a development of the apical buds of the sympodia the growth of which is carried on by the main lateral bud. In the present section reference will be made to two other instances of correlation, but in them the feature on which the interrelation between the two characters depends is thus not recog- nisable. Fig. 3. There appears to be complete correlation between the size of the petal and the colour of the flower. If the petals be white in colour they will be small and hardly project beyond the bracteoles ; on the other hand, if the colour be yellow, they will be large in length, about twice that of the bracteoles (vide Figs. 3 and 4)*. > The difference is well shown by a comparison between Plates 14 a and 16 Watt (20). 242 Studies in Lidian Cotton The petals may be of one of two sizes, either small, when they lie within the bracteoles whose length they do not exceed, or large, when they project beyond and are about double the length of the bracteoles {vide Figs. 3 and 4). The exact size of the larger petal varies somewhat with the particular type but in no case approaches that of the smaller, and the two stand in marked contrast without intermediate form. There appears to be complete correlation between the size of the petal and the colour. The smaller petal is invariably white and the larger petal invariably yellow. Among the plants under experiment, which now amount to over a hundred thousand, and among cottons under cultivation in the field no single exception has been observed. The correlation holds with the simple yellow and white types and also with those types in which a red colour is superimposed. It follows from this that all plants with a red on yellow flower, such as type 3, have large petals, while plants with a red on white flower, such as type 11, have small petals. The cross between types 3 and 9 illustrates this point well ; in all cases both plants with red on yellow, and those with yellow flowers, whether pure or impure, have large petals, while in the plants with red on white flowers, whether pure or impure, and in those with white flowers, the petals are small. A further instance of correlation, and one which is of considerable importance both practically and on account of its bearing on the argu- ment of section 3 {d), has been found to exist between the presence of the red colouring matter and an increase in the length of the vegetative period. There is a distinct retardation of the commencement of the flowering period when the red sap colour is present. This is shown in Table XXIX. In this table the unit is a plant of the F^ generation and the figure is, for the pure forms, taken as the average of the F^ offspring and, for the impure forms, as the average calculated from only those ^3 offspring which are, judging by the depth (to lamina), or absence, of the red colour, pure in this character. In the light of this correlation it is necessary to reconsider the results detailed in section 3 {d). In that section attention was drawn to the monomodal curve as indicating incomplete resolution. No distinction was, however, made between plants with, and plants without, the red colouring matter. It would appear possible that a separation of the plants into two groups dependent on the presence or absence of the red colouring matter might disclose two trimodal curves, whose presence is rendered obscure through superposition. Table XXIX, however, in which such a separation is effected, shows no such trimodal H. M. Leake 243 curves and it has not been possible to obtain from the records available any clear indication of their existence. For the present, therefore, it is impossible to do more than recognise that in this correlation between the flower colour and the length of the vegetative period may lie the explanation for the failure of the early and late flowering characters to fall into line with other Mendelian phenomena. LITERATURE. 1. Balls, W. L. Joum. of Agricultural Science, Vol. ii. No. 2. 2. Tear Book of Khedivial Agricultural Society, 1909. 3. Bateson, W. MendeTs Principles of Heredity. 4. BuRKiLL, I. H. Joum. and Proc. Asiatic Society of Bengal (New Series), Vol. m. No. 7, p. 517. 5. Darwin, C. Effects of Gross and Self-fertilization in the Vegetable Kingdom. 6. Davenport, C. B. Statistical Methods. 7. Ftson, p. F. Memoirs of the Department of Agriculture in India (Botanical Series), VoL ii. No. 6. 8. Gam](IE, G. a. The Indian Cottons. 9. Memoirs of the Department of Agriculture in India (Botanical Series), Vol. II. No. 2. 10. JoHANNSEN, W. UebcT ErUichkeit in Populationen und in reinen Linien. Jena, 1903. 11. Leake, H. M. Joum. and Proc. Asiatic Society of Bengal (New Series), VoL rv. No. 1, p. 13. 12. Joum. and Proc. Asiatic Society of Bengal (New Series), VoL v. Na 1, p. 23. 13. Middleton, T. H. The Agricultural Ledger, 1895, No. 8. 14. Parlatore, F, Le Specie dei Cotoni-Firenze, 1866. 15. ToDARO, A. Osserv. Sui Specie dei Cotoni coltivati in Palermo, 1863>. 16. Relazione Sulla Cultura dei Cotoni, 1877-78. 17. Prodromus Monographic Generis Gossypii. 18. Thompson, J. V. Proc. Agricultural and Horticultural Society of India, 1841, Dec., p. 15. 19. Watt, Sir G. Dictionary of the Economic Products of India. Article on Gossypium. 20. The Wild and Cultivated Cotton Plants of the World. 21. Burkill, I. H. Metnoirs of the Department of Agriculture in India (RotamcsX Series), VoL L No. 4. 22. Fletcher, F. Joum. of Agrictdtural Science, VoL ii. p. 281. 23. Hartley, C. P. U.S. Department of Agriculture, Bureau of Plant Industry, BulL No. 22. . Joam. of Gen. i 17 244 Studies in Indian Cotton TABLE l\ Flower Colour. Type 4 {yellow coloured) x Type 6 {white flowered). Fi 68 plants all yellow flowered F, \ \ ratio 109 plants yellow flowered 21 52 plants white flowered 1 F2 plants used as parents 5 21 13 102 6 13 J yellow 65 35 34 0 ^ I white 0 0 11 100 ^ No difference has been observed between the direct cross and its reciprocal. The two have, therefore, been grouped together in this and subsequent tables. ^ Number of offspring too small to be a reliable guide to purity of parent. TABLE II. The occurrence of the red colouring matter in vegetative organs. Types Coloured RR and Rr Colourless rr Total 3x 2 106 29 135 3x 4 224 69 293 8x 5 299 102 401 3x 8 180 64 244 3x 9 374 120 494 3x101 351 100 461 Total 1534 484 2018 Batio 3-17 1 417 1 Determined on flower colour only. H. M. Leake 245 TABLE III. The intensity of the. red colouring nuUter in the leaf as an indication of purity. Leaf of Fi parent recordea as Constitution, as by Ft offspring, determined of the form ToU (o) Type 3 x Type 4 RR Rr Lamina 61 5 66 Veins 2 ao 22 Ribs 0 116 116 Total 63 141 204 Ratio 1 2-2 (6) Type 3 x Type 9 Lamina 59 4 63 Veins 13 2 15 Ribs 9 188 197 Total 81 194 275 Ratio 1 2-4 TABLE IV. The intensity of the red colouring matter in the petal as an indication of purity. Flower of /".parent recordea as Constitution, as determined by Fi offspring, of the form Total RR Rr (a) Type 3 X Type 4 Red Red on yellow 28 35 2 136 30 171 Total Ratio 63 1 138 2-2 201 (6) Type 3 x Type 9 Red Red on yellow 11 46 3 136 14 182 Total Ratio 67 1 139 8*4 196 17—2 246 Studies in Indian Cotton TABLE V. 7'Ae F^ generation of crosses between type 3, in which the red colouring matter is present, and types in which it is absent. Coloured Colourless ^ RR Rr Lamina Veina Eibs Total rr Total (1) 3x2 Ratio 10 1 23 73 96 9-6 29 2-9 135 (2) 3x4 69 24 90 114 55 228 4x3 18 — 33 33 14 65 Total 771 242 123 147 69 293 Ratio 11 21 1 (3) 3x5 44 5 62 67 35 146 5x3 71 3 114 117 67 255 Total 115 8 176 174 102 401 Ratio 11 1-7 1 (4) 3x8 33 5 58 63 38 134 8x3 26 6 52 ■08 26 110 Total 59 11 110 121 64 244 Ratio 1 2-0 1-1 (5) 3x9 46 5 132 137 69 252 9x3 51 15 124 139 52 242 Total 973 20 256 276* 121 494 Ratio 1 2-8 1-2 Grand total 358 86 739 825 384 1567 Ratio 1 2-3 1-1 ^ 5 of these shown by experiment to be impure. 22 „ „ „ pure. 34 „ ,, ,, impure. * 22 „ „ „ pure. Flower colour. TABLE VI. Type 3 {red flowered) x Type 4 {yellow flowered). Fi 38 plants with flowers red on yellow and the red colouring matter extending to veins. RR Fj Foliage (lamina) 77 Ratio 1-1 Used as J 61 lamina parents 1 2 veins Rr RR+Rr rr (Ribs or Veins) (Total coloured) (Colourless) 147 224 69 2 1 1 5 lamina 204 68 136 veins RR Rr RR+Rr rr (Lamina) (Ribs or veins) (Total coloured) (Colourless) Fs 1328 832 1692 2524 773 12451 Ratio 107 2-18 1-90 1 And 4 red plants. A consideration of other characters indicates that 2 of these are without doubt either volunteer plants or have arisen through an accidental mixing of seed. H. M. Leake 247 CQ 1 s g o '^i. ^ s -8. ^& S 00 OS O -^ i-H X X eo OS ^^ ^^ 1 ^.^ ^^ M ! 2 =^6 S4 f 1 <^ ' 1 *^ ,,^ ^1^ 1 ^ fl i iH rH ^-. ee to "-^ „-« t s s «Doeo fcfc 1 1 ©» s 00 0* 00 fc ^ tH "U ? 1 2«5 ^^_^ _,_^ ^ 1 s OS ,^ iH i 00 I-l c— 1 §1 » 00 '^e* 04 II o« »o JO e« ^ >. § ■^0. «o •* c« 1 ^^ ^ '* a-~ 1 - s 1 on 11 § r-l §5 11 " r1 l-l If §5 11 .-( 1-1 S<1 ^^ ^_^ g a 5 1 g r-i I-l "^ 1 s W5 eo l:fc & 9 >> so ! --^ B^^ II OS II CO 04 iM s 9> ^ s o >> § 1 oooe Si § 1 li U3 OS o i-< It C<1 OS 50 1 0» OS CO ? -HO I-H f-l 5 >> •«*' so rH S2 !^ 3 11 1= « 04 t I S" IQO i-l fH a; g 2 I^ » a §5 X f^ rt osooee ^ 1 11 1-1 ®« ^11 I i eo 1 a o 1 eS M C 1 3 '«ao ^ 1 I i-H M a 1 flg- o o .2 O.C8 *e ?;» u, ^ 1 o o o -9 (^ 1 S2 P r 248 Sttidies in Indian Cotton TABLE VIII. Flower colour. F^ plants x parents. (Type 2 x Type 3) x Type 3 {red (lamina) x yellow} x red (lamina) (Type 2 x Type 8) x Type 2 {red (lamina) x yellow} x yellow (Type 3 x Type 4) x Type 3 {red (lamina) x yellow} x red (lamina) (Type 3 x Type 4) x Type 4 {red (lamina) x yellow} x yellow (Type 3 x Type 9) x Type 3 {red (lamina) x white} x red (lamina) (Type 3 x Type 9) x Type 9 {red (lamina) x white} x white (Type 4 x Type 6) x Type 4 {yellow X white} x yellow (Type 4 x Type 6) x Type 6 {yellow x white} x white Red on Red on Red Red white white (lamina) (veins) (lamina) (veins) yellow white 13 18 31 — 2 21 1 — 15 — _ — 2 — — — 8 — TABLE IX. Detail of individual of type having leaf factor 1'88. Number of leaves Leaf factor Main stem 31 1-82 Secondary branched (a) Monopodial arising from leaf 7 9 1-81 Number Tertiary of Leaf branches leaves factor arising from leaf 8 21 1-86 arising from leaf 9 17 1 '90 Sympodial arising from leaf 8 2 1-64 „ 10 3 1-66 arising from leaf 10 2 1-72 » >> 12 3 1-74 >> >> 13 2 1-70 »> >> 15 1 1-79 Monopodial arising from leaf 5 3 1-74 j> >> 6 3 1-86 H. M. Leake 249 TABLE IX (continued). arising from leaf 10 arisiiig &om leaf 11 arising from leaf 12 arising from leaf 13 arising from leaf 14 Number of leavea Leaf factor Tertiary branches Sympodial Nnmber of leaves factor arising from leaf 8 4 1-78 >> 10 3 1-72 » 11 3 1-81 t» 12 3 1-66 >* 13 3 1-74 »» 14 1 1-83 >f 15 3 1-76 ft 17 3 1-64 >> 18 4 1-64 12 1-86 arising from leaf 8 2 1-75 >» ,, 10 1 1-68 >> » 11 1 1-74 » »> 13 2 1-87 >> ti 14 3 1-75 23 1-91 arising from leaf 5 2 180 „ 7 2 1-84 >> 8 3 1-74 ft 10 2 1-73 ft 11 3 1-69 f> 13 3 1-76 » 14 3 1-68 » 15 1 1-71 »> 16 1 1-78 „ 18 2 1-72 » 19 1 1-71 19 1-84 arising from leaf 5 1 1-61 >> f » 6 2 1-65 » >f 8 2 1-78 „ i> 11 2 1-73 21 1-88 arising from leaf 5 1 1-71 »» 9 3 1-73 »» 10 3 1-76 >t 12 1 1-72 »» 13 4 1-78 >> 15 1 1-76 >> 16 2 1-69 >t 17 1 1-74 >> 18 2 1-77 19 1-77 arising from leaf 6 1 1-52 »» >• 8 1 1-57 »> 10 11 2 3 1-75 1-79 250 Stiidies in Indian Cotton TABLE IX {continiied). Number of Leaf leaves factor Tertiary branches Number of leaves Leaf factor 15 1-76 arising from leaf 5 3 1-73 6 2 1-85 8 1 1-76 „ 10 1 1-68 arising from leaf 16 8 1-83 arising from leaf 17 16 1"71 18 13 1-97 arising from leaf 19 16 1-81 arising from leaf 24 14 1*78 Average of leaves on Monopodia — 1-84 (6) Sympodial arising from leaf 20 4 1-76 >> 21 6 1-75 J J 22 3 1-66 >> 23 1 2-07 ,, 25 6 1-81 » » 26 2 1-73 jj 27 6 1-78 ?> 28 5 1-80 j> 29 4 1-79 >) 30 4 1-63 )> 31 3 1-69 >» ji 32 5 1-66 )> 33 1 1-65 >> ,, 34 3 1-67 jj ,, 35 3 1-71 >» ,, 36 3 1-70 jj 37 2 1-70 ,, 38 2 1-68 „ J J 39 3 1-60 99 „ 40 3 1-69 , J 41 1 1-85 Average of leaves on Sympodia — 1-72 arising from leaf 5 2 1*73 arising from leaf 1 1 1*72 „ 5 2 1-55 „ 7 2 1-79 11 2 1-73 arising from leaf 1 6 1*87 „ 10 1 1-73 arising from leaf 1 5 171 „ 2 1 1-79 „ 6 2 1-57 „ 7 1 1-59 Average of leaves on tertiary branches — 1'73 H. M. Leake 251 TABLE X. Variation of the leaf factor toithin the type. Extremes of leaf factor Leaf factor (average of offspring) Nnmber of offspring used in determination Max. Mtn. 1907 1908 1907 1908 Type 4 1-57 117 1-37 — 32 — 1-71 1-27 1-46 1-49 20 2 1-92 1-42 1-65 1-73 17 5 Type 5 1-80 1-56 1-68 1-73 20 9 1-94 1-73 1-78 1-80 20 14 1-98 1G9 1-88 1-84 20 16 Type 6 1-98 1-69 1-81 1-88 20 20 Type 8 3-83 2-96 3-35 3-26 18 20 3-64 3-55 3-59 3-71 2 10 Type 9 418 318 3-64 407 20 20 4-34 3-80 416 — 20 TABLE XI. The relation between the leaf factor of the F-^ generation of a cross and those of the parents. s ParenU rUen Leaf factor of parents Mean of parental leaf factor Leaf factor of offspring Difference Number of fi eed Pc Seed PoUen indiTidoals Type 3 Type 2 313 1-45 2-29 2-26 -003 25 , 3 , 4 313 1-45 224 2-21 -003 12 , 3 , 4 313 1-64 2-38 2-49 + 011 13 , 4 , 3 1-46 313 2-29 2-42 + 013 3 , 4 , 3 1-64 313 2-38 2-45 + 0-07 9 , 3 , 5 313 1-78 2-45 2-70 + 0-25 31 , 5 , 3 1-78 313 2-45 2-45 — 6 , 2 . 8 1-46 3-59 2-52 2-18 -0 34 12 , 2 , 8 1-46 3-34 2-40 2-37 -003 3 . 8 , 2 3-59 1-46 2-52 2-49 -003 3 , 8 , 4 3-59 1-64 2-61 2-53 -0 08 6 . 8 , 4 3-34 1-64 2-49 2-54 + 0-05 9 , 4 . 8 1-46 3-59 2-52 2-36 -016 13 . 4 . 8 1-64 3-34 2-49 2-42 -007 18 252 Studies in Indian Cotton TABLE XII. The leaf factor. Type 3 (1. f. > 3) x Type 4 (1. f. < 2). Leaf factor 313 1-401. Mean 2-27. F\ 15 plants mean leaf factor 2'21. Leaf factor <2 >2 and 3 F2 Number of individuals Eatio Mean leaf factor 64 1 1-71 143 2-3 2-57 83 1-3 3-54 Leaf factor <2 > 2 and <3-2 >3-2 Individuals used as parents Ratio Mean leaf factor ^ 65 1 1-72 143 2-3 2-62 64 1 3-51 Leaf factor <2 >2 <2 > 2 and < 3 >3 <3 >3 Fz Number of individuals Ratio 1222 5 784 . 1 1602 204 791 1 6 1273 Mean leaf factor 1-71 1-62 2-62 3-42 3-51 1 The mean value between 1'35 and 1*46, the values of the pure lines used in this experiment. At the time when the original cross was made these two forms had not been isolated. ^ The value of each individual is here taken as the mean of the values obtained from its offspring. H. M. Leake 253 TABLE XIII. The leaf factor. Re-appearance of parental values in the F^ offspring. (a) Type 2 x Type 3. Leaf factor 1-40 3 13. Mean 2-26. Fi 21 plants mean leaf factor 2-33 Leaf factor <2 =>2and<3 >3 F, Number of individnals 40 82 11 Ratio 3-6 7-4 1 Mean of leaf factor ... 1-63 2-43 3-41 (6) Type 4 X Type 8. Leaf factor 1-52 3-47. Mean 2-49. Fi 28 plants mean leaf factor 2-39 Leaf factor <2 >2 and <3 >3 Fi Number of individnals 47 102 46 Ratio 1 2-2 1 Mean of leaf factor ... 1-66 2-59 3-42 254 Stvdies in Indian Cotton TABLE XIV. The leaf factor. F^ generation '2 ^ S S So £ S ^ c('C 0-22 #2-2=»' «a< " « Til lo «) r- 00 OS o .-I c« eo rH « to «>aD^2ea5o8S^ ^.g £ eb eb as « « « « rh tp -♦ -* ti< Tf >* •*-*c^*>^^o >o -- a S5 •< Z < a — — — — — — — — — — — — — — — — 2 1-68 84 1-48 +0^ — — — — — — — — — — — — — — — — 8 1-66 149 1-54 +012 — — — — — — — — — — — — — — — — 17 1-77 284 1-64 +0-13 — — — — — — — — — — — — — — — — 24 1-75 522 1*74 +001 — — — — — — — — — — — — — — — — 12 1-81 237 1-84 -003 — — — — — — — — — — — — — — — — 1 1-91 11 1-93 -002 — — — — — — — — — — — — — — — — 1 1-79 46 1-98 -019 — — — — — — — — — — — — — — — — 1 2-26 21 2-05 +0-21 — — —— — — — — — — — — — — — — 1 2-67 9 206 +0-61 5 3 — — 111— 1— — — — — — — 5 2-31 141 218 +013 2 3— 1— 3 1 — ________ 10 2-47 187 225 +0-22 85113— 1 — — 1 — — — — — — 8 2-38 179 235 +0K)3 15 117 4322 11 l______20 2-56 450 246 +010 16 19 13 10 6 8 2 5 2 !______ 24 268 634 2-54 +0-14 7 118 126 44 12 l_ — ____15 2-74 314 264 +010 20 11 17 8 10 10 6 76 8 51 — 1__ 20 2-73 468 2-74 -0K)1 10 14 12775932 23 — — 11— 16 296 315 2 84 +012 6766 10 6484 3 12— — — 1 11 292 219 295 -003 252531443 2—112—— 4 322 126 3-06 +0-16 14 64 10 55243 1_____1 7 302 131 312 -0-10 2 12 11__— __ — — __ — — 1 3-51 19 317 +034 1 1 1 2 — — — — — — — — — — ~— 1 291 8 318 -0-27 _2_-____ — — — — — — — — 1 3-22 4 319 +0-08 954 5 2 3 — — — — — — — — — — 3 3 47 61 323 +0-24 30 23 23 12 9 3 2 — — — — — — — — — 7344 145 3-33 +011 36 47 27 29 18 17 12 6 2 3 1 _ _ _ _ _ 14 3-54 274 3-44 +011 7 23 33 25 21 18 10 8 9 2 12 1 — _ — 10 362 192 3-55 +007 23 24 44 40 33 25 18 18 8 10 5 — 1 — 1 — 13 372 274 365 +007 5 10 12 12 14 11 15 7 9 9 4 2 — — — — 6 387 119 375 +0-12 149469366 86112— — 4 3-95 70 3-85 +0-02 166656 17 89 11 74-2 — 2 3 399 91 3-93 +006 — — — —1122112123 — 1 1 3 92 17 4-24 -0-32 256 Studies in Indian Cotton TABLE XV. The length of the vegetative period as affected by the season. Sown in Pots Field Season 1907 1908 Difference = seasonal variation 1909 Type 3 146 210 + 64 146 » 4 83 111 + 28 83 » 5 80 110 + 30 73 „ 6 90 114 + 24 84 » 7 — 96 — 62 8 78 106 + 28 72 ,. 9 93 117 + 24 92 ,, 10 96 115 + 19 94 Seasonal variation for monopodial types 64. „ ,, ,, sympodial types 25. TABLE XVI. The length of the vegetative period as affected hy the method of cultivation. Type3xType4 Type3xType9 Pots Field Number of plants Days Ditfer- ence Pots Field Number of plants Days Period in Days Number of plants Days Number of plants Days DifTer- ence Below 101 3 105 — — — 2 127 — — — 101—110 11 108 30 85 23 13 109 8 88 21 111—120 29 115 52 89 26 47 118 30 93 25 121—130 22 122 36 96 26 92 122 41 98 24 131—140 15 126 31 95 31 40 130 20 102 28 141—150 11 127 19 98 29 21 132 9 105 27 151—160 8 132 3 104 28 16 132 _ — 161 and over 2 123 __ — — 3 135 _ _ — H. M. Leake 257 TABLE XVII. The length of the vegetative period. The F^ generation from the cross. Type 3 x Type 4 and Type 3 x Type 9. Type3xType4 Type 3xTypc9 Interrals Number of days from sowing to flowering Number of plants Number indicative of type of branching Number of plants Number indiottlTe of type of branching Above 170 2 75 — — 166—170 3 91 2 87 161—165 4 87 3 75 156—160 13 79 51 40 151 — 155 16 62 8 69 146—150 13 57 9 50 141—145 14 54 ^ 44 136—140 19 64 22 30 131—135 25 42 33 21 126—130 89 29 21 15 121—125 37 26 31 2 116—120 43 11 36 1 111—115 46 5 26 — 106—110 14 4 10 — 101—105 3 — 3 — below 101 1 — — In this table, which is based on the F-i generation, only the four degrees, indicated by the numbers 100, 75, 50, 0, of secondary branching have been recognised. ' Of these five plants two are of the sympodial type. One of these was dwarfed, and the date of appearance of first flower consequently very late. The second produced flowers at the extremities of the sympodial branches only. On account of these two plants, which appear somewhat normal, the figure for this interval is abnormally low. 258 Studies in Indian Cotton TABLE XVIII. The length of the vegetative period. The F.^ generation _, 01 'S > .2 2 <=iS. ^ QbQ0a6ciC>oiO5Ci — — 2 — — 1 — — 1 — 1 — 106 128 115 281 282 110 300 329 104 118 280 150 241 320 151 131 327 142 284 114 65 219 170 119 139 163 127 138 87 166 162 324 156 314 112 242 195 153 158 274 181 140 — — — — — — 210 — — — — — — 225 — — — — — — 134 — — ___ — 264 _ — _ — __ 264 — — — ___ 214 ______ 221 ______ 1 — — 3 — 3 2 1 2 3 4 1 _ 1 _____ ____1 i__ 3_2 l___ — __3_1 3 l_ __2 l__l_ 2122121_ 14 5 1 — 11111 1 — 2 — — 212 11— — — — 1 — 1 _ _ — 1 — 1 _ 1 _ — 1 — 1 2 — 3 1 — 1 1 — 2 1 2 1 — 1 111111 — 1 1 2 — 6 — _ 1 _ 2 1 1 _ _ 1 — 1 — _ _ 2 _ 1 1 _ 1 — _ 1 — 1 2 1 _ 1 — — 1 4 _ 1 1 1 _ _ 1 1 — — 1 — 1 1 — — — — 1 1 — _ 1 1 _ 2 1 _ _ _ 1 _ _ 2 — 1 1 1 — 1 1 1 — — — — 1 2 1 — — 12 — — 1 2 — 1 — 1 — 113 11- — — 1 1 — — — — 1 - — 1 - — 1 4 — 1 - — — 2 1 - — 11 — 1 1 — - 3 - 3 — 1 1 — 4 2 2 — 2 — 111 1 — — — 42 — — 1 2 1 — 1 2 2 — — 1 2 — 1 — 1 1 1 — 1 — 2 — 1 1 1 — 3 4 — 1 — — 2 1 — 1 1 — 1 — 3 3 3 1 — 2 5 H. M. Lkake 259 from ihA cross. Type 3 x Tt/pe 4. Pot Series. o V ^ o flo o^g-25 2 1"^ 5 g _________________ _ _ _ 10 107 -10 97 __________ — — — — — — — — — _ 7 112 -14 98 _1 _______ — -___ — — — — — — 10 101 +2 103 _________ _ __________ 18 100 +3 103 __________ — _ — — _ — _ — — — 22 99 +5 104 _1 _______ — __ — — ___ — — — 10 110 -5 105 __________ — — — — — — _ — _— 13 107 -2 105 __________ — __ — — — — — — — 24 113 -7 106 ___ 1 ________________ 10 109 -2 107 ________________ — — — — 21 102 +5 107 __2— — — — — — — — — — — — — — — — — 22 98+9 107 1 ___________ — — _ — _ — — — 5 113 -5 108 _ ___________________ 6 132 -22 110 ________________ _ __ 19 118 -8 110 __ 1 _ 1 ______________ 22 115 -5 110 1_ — __1 ____ — — — _ — ___— 22 115 -5 110 ___________________ 12 114 -4 110 ____________________ 8 111-1 110 __ — — _ — — _________ — __ 14 109+1 110 ___________________ 21 109+1 110 _ _ _________________ 16 108 +2 110 __1— ___ — — — ____ — — — __ 11 1-24 -13 111 1 _________ 1 ________ 21 114 -3 111 _1 1 ___________ _____ 12 119 -7 112 1 1 2 1 l____l_ — _______ 25 117 -5 112 ___________________ 8 113-1 112 ___________________ 22 112 — 112 1 — 1 ________________ 5 117 -4 113 _1_____ — _ — — — — __ — — — — 17 131 -16 115 — 1 _ — ___ — ___________ 9 115 — 115 2 1 1___1 _!__________ 31 113 +2 115 _1 !________________ 13 119 -3 116 1 1— — — __ — _l_ — _ — _ — ___ 19 119 -3 116 __ — ___—_____ — — _____ 7 116 — 116 1 ___ — _ — —— 1 !_____ — — _ 11 108 +8 116 2— —- — _ — __ — _— — ______ 11 132 -15 117 1 2 _ I ____ 1 __________ 19 121 -7 117 2 1___— !____________ 16 118-1 117 2 — 1_1— — — — — _____ — _ — _ 14 115 +2 117 2_1 1 1— _ — _ — — __ — — ___— 16 155 -37 118 1 — 1 1 1 — 1- l__________ '20 127 -9 118 4 3 2 l_l _____________ 43 120 -2 118 2 _ _ — 1 1 ___ — 1 _____ — — — 16 130 -11 119 — 2 1__ — — — —— — — _______ 24 128 -9 119 1— _1 1 — !____________ 11 119 _ 119 2 — 1 — 1 1 _____________ 13 148 -28 120 1_2__1____— 1 _ — ___ — — 18 141 -21 120 4 6 2 _— 1— — _1 ____ — __ — _ 36 130 -10 120 1— — — 1— — __ — _ — _______ 9 126 -6 190 Joam. of G^en. i 18 260 Studies in Indian Cotton TABLE XVIII 2^ c^ "^££.S'^°°00<30<»<'*^05(3505OOOOOf-lr-l^.-(i-l5l-Hl-l>-)>-I^Og^-g C 4 2 1 — 1 i__2— — — — — — — — — — — 22 117 +3 120 1_— 1 — 1- — — — — — — — — — — — — — 11 117 +3 120 2 4__ — — — — — — — — — — — — — — — — 12 156 -35 121 — __ 2 — — — — — — — — — — — — — ——— 6 124 -3 121 3 1 ______ — — — — — — — — — — — — 7 123 -2 121 3 — 1 2 — 3 1— — — 1— — — — — — — — — 25 122-1 121 2 1 1— _l 1— — __ — — — — — _ — — _ 12 121 — 121 _2 2 l___ — — — — — — — — — — — — — 15 120+1 121 2 3 1 1 1— — — — — — — — — — — — — — — 16 119 +2 121 __2 1 1— — 1— — — — — — — — — — — — 12 141 -19 122 _1 2— — 1— — 1— — — — — — — — — — — 11 129 -7 1-22 7 4_2 1— — 1— — — _ — — _ — _ — — — 31 112 +10 122 1 i__— 1— — — — — — — — — — — — _— 7 166 -43 123 — 3 2 1 2 1— — — — — 1— __ — — — — _ 17 141 -18 123 — 2 1 — — 1 — — — — — — — — — — — — — — 7 128 -5 123 3 1 1 1 — 4— — — 1— — — — — — — — — — 22 128 -5 123 1 1 _________! ___ — __ — _ 6 118 +5 123 1 3 — 1 — _ — — 1 — - 1 — — — — — — — — 15 118 +5 123 1 l___i____i _ — _ — — — — — — 11 163 -39 124 1 2 2 — 2 — 1 1 — — 1 _ _ 1 _ — — — — — 20 143 -19 124 — 5 5 __ 2 — — — — — I — — — — — — — — 22 133 - 8 125 _3 3 — 1— — — 1— — — — — — — — — — — 13 133 -8 125 1 — 2 — — — — — — — — 2 — — — — — — — — 11 130 - 5 125 2 1 — — — 1 — — — — — 2 — — — — — — — — 12 129 - 4 125 — 1 — — 3 — 1 — — 1 — — — — — — — — — — 14 141 -15 126 1 5 2— — 1— — — — 1 — 1— — — — — — — 13 132 -6 126 2 4 6 3 — — — — — — 1 2— — — — — — — — 25 126 — 126 1 5_ — — _ — _2 — 1— — — — — — — — — 16 153 -26 127 1 1 1 1 i_ — — _ — — — — — __ — — — — 7 133 -6 127 _1 — 1— __ — _ — — 1— — — — — — — — 6 131 -4 127 1 — 4 1 2 2 1 1— — — — — — — — — — — — 17 134 -6 128 2— — 11— — 11— —— — — — — — — — — 7 133 -5 128 1 11— — 1 — I— — — — — — — — — — — — 6 129-1 128 4 — 1 — — 1 ——— — — — — — — — — — — — 6 126 +2 128 4 2 4 5 4 4 1 1 1 — 1— — — 1 _— _ — — 36 124 +4 128 — — 1 1 1 1 — 1— — _______ — — — 6 129 — 129 1 —__ — ______ 1 _ _ ______ 3 155 -25 130 1 1 — 1— — 1 — 1 — i_ — _______ 8 148 -18 130 — 2— — — — — — — — 2— — — — — — — — — 6 135 -5 130 4 5 4 1 1 1 — 4— — — 1— — 1— — — — — 24 134 -3 131 1 1 2 3 2 — 1— — —— — — 3 1 3— — — — 23 150 -17 133 2 2 — 4 1 2 1 1 — 1— — 1— — — — — — 1 16 143 -9 134 •2 2 1 — 1 1— — — 1 i_i_i___ — — 12 140 -6 134 1 — _— 1 _ 1 ____ 1 _____ — — — 4 155 -20 135 — 1 2 1 2 1 1 1 — 1 4_____ — — — — 15 153 -18 135 — 2 1 3 — 2— — — 1 1 2— — — 1 1— — — 16 1-29 +6 135 — 2 — 2 1 1— — 1— — — 1 — 2— — — — — 10 138 — 138 — 2 1 1 1 1 — 1 1 2— — 1 — 1 — 1— — — 13 139 — 139 _____1 1 1 ______ 1____— 4 133 +7 140 18—2 262 Studies in Indian Cotton TABLE XIX. The hngth of the vegetative period. The F, generation n «0 CO CO O 05 0> 05 Below 80 — — — — — — — 2 3 4 3 4 1 l_— 1 l___ — 80— 84 — — — 1 2 2 13 8 32 43 74 72 66 50 45 18 19 14 13 12 10 6 85— 89 — — — 1 — 1 6 8 15 44 68 83 78 59 57 40 31 33 45 30 33 28 90— 94 1 _ _ _ _ 1 _ 2 12 19 30 61 63 65 62 52 66 58 63 80 76 70 95— 99 2 1 — _ — _ _ 3 i 5 13 18 26 31 39 44 32 35 68 75 9t 97 100—104 — — — — — — — — 1— 1 2 3 3 1 6 5 7 16 20 30 27 105—109 — — — — — — — — — — — 1___ 1 1 1 2 3 10 12 110—114 — — — — ___________ !_____ 1 TABLE XX. The length of the vegetative period. The F^ generation O rH 1— I r-4 Below 104— ___3 21 1— 1— 1 1— 1 1___ — — — 105—109 — 1235 775 57 13 76 17 12 16 13 651— 2 110—114 — — 1 6 3 10 7 8 16 17 21 20 21 31 31 34 46 35 23 26 30 9 115—119 — — _ 2 7 8 5 9 8 21 20 22 18 34 46 58 79 76 57 64 60 36 120—124 ———14 125 7 7 9 10 11 11 16 40 36 53 44 63 70 46 125—129 — — — — 1 12 2 4 2 3 3 4 5 10 26 32 42 41 63 86 66 130—134 — _________ 2 1 2 1 2 9 14 16 17 30 44 42 135—139 — — — ___________ — — — 1 3 3 9 11 140—144 — _____________ 1— 2— 1 4 8 5 145—149 — — — — — — — — — — — — — — — — — — — — — — 150—154 — —__________ — — — — — — — — — — TABLE XXI. The length of the vegetative period. The F^ generation Below 80 — — — 1 — 1 1 2 3 l_ — — — — ____ — — — 80— 84 — — 1317 852434517113—1 — — 85— 89—1 1 1 2 6 11 17 24 18 19 16 18 15 13 22 13 14 8 8 3 2 90— 94 1 — — 1 3 8 14 20 27 18 24 24 16 29 40 42 35 48 27 22 21 11 95_ 99 _ _ _ _ 1 _ 7 6 13 4 6 14 9 17 19 35 24 33 26 26 18 14 100—104 — — 1 — 1 1 3 2 5 4 9 5 6 3 11 14 25 30 17 22 19 21 105—109 1— — — — — — — — 2 1 4 1 6 5 4 14 11 15 17 13 11 110—114 — — — — — — — — — — — — — — 2— 1 2 2 3 4 6 115—119 — — — — — — — — — — — — — — — — — — — 1 4 3 H. M. Leakk 263 from the cross. Type 3 x Type 9. Pot Series. O-4-^^-H-HlM?JCq5^ ^*- ^'^ ^ i- o *» ""J" as » o ■?» -* 5s X o CO •* to X o~>-22dCi-^^ 35 33 35 33 35 -^ ■* ~>< •* ■>*" lo >o lo o «o «rio3*S;«*>5 Z -sj Z^ C v. ^2 z^ ^^ S — — — — — — — — — — — — — — — — — — 1 117 12 101 -16 — 2 — — — — — — — — — — — — — — — — 10 119 142 108 -11 10 5 2 1 2 — — — — 3 — — — — — — — — 2S 120 418 113 - 7 25 24 13 10 5 3 4 2 — 4 4 — — — — — — — 47 122 724 117 - 5 42 39 24 15 9 15 5 6 8 6 2 i __ _ i _ _ l 41 126 610 122 - 4 78 47 37 31 20 25 19 16 19 18 20 2 1 2 1 — — — 47 130 729 127 - 3 40 48 24 28 21 18 19 32 25 9 11 12 8 4 2 — — 2 37 132 483 133 + 1 10 11 8 5 5 9 7 9 8 7 7 3 — 5 2 1 12 9 139 127 136 - 3 5 9 12 14 6 7 9 10 10 12 11 10 6 11 4 2 5 7 12 142 171 141 - 1 _ 211 — — 2741232 2 — — 2— 4 137 31 147 +10 — — — — — — — — — 12 — — 1— 11— 1154 6 154 — from the cross. Type 3 x Type 9. Field Series. - z"" ^-^ z= ^ = X O 0» 'I* «0 X O CO -* so X O 9« ■* O X o*?-2£e32-5a«39< — — — — — — — — __________ 1 — — — — — — — — __________ 3 1 1 — — — — — — — — ________ 13 8 7 1 3— — 1— — — — — — — — ___ 33 4 10 1 6 3 2 3 2 1— _l !_____ 20 12 13 9731831 151— — — — — 1 20 11 786745625323- — — — 4 14 2 3 2 7 4 4 2 4 — 2 2 3 1 1 _ _ _ _ 5 138 57 112 -26 1 11 — 3 1 3 — 2 1 — 3 — 1— — — — 2 140 25 115 -26 111 9 77 -34 116 57 83 -33 115 234 87 -28 124 451 92 -32 124 306 97 -27 129 264 102 -27 130 178 107 -23 264 Studies in Indian Cotton TABLE XXII. The interrelation between the length of the vegetative period and the type of branching. Type 3 x Type 4. Pot Series. Branching ofTays'^ 10 20 30 40 50 60 70 80 90 ^'^^ Below 90 3 6 2 — — — — — — 19 19 92 2 4 4 1— l___27 ~ 94— 8 4 !_____ 24 26 95 2 1 10 2 — — — — — 32 96 — — 8 1______ 98— 3 4 3 — — — — — 30 31 100 2 4 4 4 3 i___33 102 — 4 2 1 2 1 _ _ _ 34 104 2 3 4 5 2 — — — — 31 34 105 1 3 5 2 4 2 — — — 36 106— 3 4 2 1 2 — — — — 108 2 5 12 5 4 — — — — 31 33 110 — 3 4 3 1 1 _ _ — 34 112 1 4 7 11 3 — 1 _ _ 86 114 1 1 5 3 4 3 1 _ — 42 35 115 — 4 5 1 1 1 _ _ _ 35 116 — _ 5 — — 1 1___ 118 — 1 8 11 5 3 4 1 — 45 44 120 — — 6 12 3 2 2 — — 43 122 — 4 4 7 7 4 4 1 — 46 124 — 2 4 4 3 5 1 i — 46 47 125 — — 4 2 7 6 1 _ — 50 126— 15 64272 — — 128 — — 2 2 3 6 7 4 — 61 56 130 1 — 2 4 4 4 6 2 1 58 132 — — — 2 9 4 5 1 1 59 134 — — _ _ 2 2 7 2 — 67 62 135 — — — 1 2 1 2 — 1 64 136 — — _ — — 2 2 1 — — 138 — — 1 1 — 1 1 1 — 56 64 140 — — — — — 2 1 — 1 70 142 — — — — 1 1 1 3 1 73 144 — — — — 1 3 — — 1 64 65 145 — 1 _ _ _ 1 1 4 — 65 146 — — — — — 4 1 — — — 148 — — — — — 1 1 3 — 74 68 150 — — — — — 2 1 1 — 67 152 — — — — — 1 2 — — 67 154 — — — — 1 — 2 1 — 67 66 155 — — ~ — — 1 _ _ _ 75 156 — — — — — — — — 1 — 80 158 — — — — — — 1 _ — 70 ^rioF 1 ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ '^^'^ H. M. Leake 265 TABLE XXIII. The interrelation between the length of the vegetative period and the type of branching. Type 3 x Type 4. Field Series. Brandling Namber iQ 20 30 40 50 60 70 80 90 ^^ ^ aidt^B Below 65— i___ — — — — 15 20 66 1_ — — — — — — — — 68— 1 1_ — — — — — 25 18 70 3 2 i__ — — — — 16 72 4 6 3__ — — — — 19 74 7 11 2 — 1 __ — — 19 19 75 7 15 1 . 2 — — — — — 20 76 10 17 8 2 — — — — — — 78 27 40 29 7 1 — — — — 21 21 80 46 65 32 12 1 1 i _ _ 21 82 30 76 58 16 7 6 — — — 25 84 24 59 44 16 9 6 2 — — 27 26 85 6 25 25 13 2 i _ _ — 32 86 3 19 18 15 4 6 5 2 — — 88 17 33 35 26 13 11 4 2 1 33 36 90 7 17 19 22 12 11 5 2 1 39 92 1 5 20 15 16 13 7 13 i _ 40 94 5 16 20 15 10 10 6 1 — 38 39 95 3 6 11 8 4 7 4 — — 41 96 3 7 16 12 13 8 3 2 1 — 98 6 12 24 31 18 18 10 5 — 43 44 100 4 14 21 30 23 31 16 4 2 47 102 8 8 18 28 32 20 20 3 2 47 104 5 9 10 34 25 25 9 1 3 46 49 105 — 2 5 5 8 10 4 1 2 50 106 42379 11 51 — — 108 — 4 9 12 10 19 12 3 — 52 52 110 — — 2 12 9 18 9 3 1 56 112 — — 1 8 13 10 8 1 1 55 114 1 1 — 4 5 12 7 2 — 56 55 115 — — — 4 1 3 1 _ _ 52 116 — — — — 2— 1___ 118 — — 1 1 2 6 5 1 — 6058 120 — — — 2 4 2 3 — — 55 122 — — 1 — 2 — 4 1 — 61 124 — — — 1 1 4 2 1 — 61 61 125 — — — 1 _ _ 2 — — 55 126 — — — — — — — 1__ 128 — — 1__ i___45 59 ISO — — —■_ — — _ — — 182 — — — — 1 1__ 16666 134 — — — — l__ i_65 ^^^Jl® I 83 84 88 94 98 100 101 104 104 266 Studies in Indian Cotton TABLE XXIV. The interrelation between the length of the vegetative period and the iyj>e of branching. Type 3 x Type 9. Pot iSeries. Branching Number of days 10 20 30 40 50 60 70 80 90 2 day period 5 day period Below 85 86 1 30 88 — — — — — — — — — — 26 90 — 5 4 1 — — — — — 26 - 92 — 5 5 1 1 1 — — — 31 94 — 8 10 3 — 1 — — — 29 29 95 — 2 4 — — — — — — 25 - 96 1 6 4 1 — — — — — — 98 — 7 9 8 — 1 — — — 32 31 100 — 12 6 8 3 2 — — — 33 - 102 — 5 16 6 — 2 — — — 33 104 — 9 15 8 5 1 — — — 33 83 105 — 3 6 3 1 — — — — 31 - 106 — 7 8 3 2 — — — — — 108 1 8 16 3 5 — — — ^ 31 32 110 — 12 24 21 2 2 — — — 33 - 112 — 21 24 15 6 2 — — — 32 114 — 15 28 15 18 4 — — — 36 35 115 6 22 21 13 1 — — — 37 - 116 7 17 26 4 5 — — — — 118 18 38 41 22 15 2 — — 39 39 120 10 27 29 23 6 3 1 — 40 - 122 — 13 17 36 27 13 4 2 — 45 124 10 27 34 36 20 1 1 — 42 45 125 1 7 18 27 18 7 1 — 50 - 126 — 1 5 7 14 16 5 — — — 128 — 5 10 11 24 22 10 3 — 51 52 130 — 2 7 10 18 34 12 5 — 55 - 132 — 1 5 15 11 19 13 2 — 53 134 — — 3 4 13 21 7 3 — 57 55 135 — — 3 2 4 5 6 — — 57 - 136 — — 1 2 3 6 7 1 — — 138 — — 2 6 2 11 8 3 — 59 60 140 — — 1 3 4 11 10 3 — 61 - 142 — — 1 4 5 10 9 1 — 58 144 — 1 1 3 11 11 20 5 — 61 60 145 — — 2 — — 3 6 1 — 64 - 146 — — — 1 3 6 5 5 — — 148 — — 2 4 2 8 9 8 — 63 64 150 — — 1 — 4 7 7 7 — 65 - 152 — — — — 1 4 8 7 — 70 154 — — — 1 4 4 4 — 68 70 155 — — — — — 1 1 1 — 64 - 156 — — — — 1 3 1 — — — 158 — — — — — — 2 2 — 75 67 160 _ — — — 1 — 1 — 70 - 1G2 — — — — — — 2 — 80 164 — — — — — — — — — — 75 165 — — — — — — 4 3 — 74 - Average [ period j 116 110 113 118 123 129 137 144 — H. M. Leake 267 TABLE XXV. The interrelation b'-tioeen tlie leiu/lh of the vegetative period and the type of branching. Type 3 x Type 9. Field Series. ^rsDching Noinber of — — 44 44 105 — 1 2 5 3 3 1 — — 44 - 106 — 1 2 3 3 7 — — — — 108 — — 1 11 9 10 3 — — 51 48 110 — 1 — 8 5 10 1 — — 50 - 112 — — — 4 5 4 2 1 — 54 114 — — — 5 C . 5 3 1 — 54 54 115 — — — 1 1 1 1 — — 58 - 116 — — — 1 1 1 3 — — — 118 — — 1 2 3 3 2 — — 53 53 120 — 1 1 3 — 1 1 1 — 47 - 122 — — — 3 1 3 4 — — 57 124 — — — 2 — 2 — — — 50 53 135 126 128 — — — — — 1 1 1 2 — — 65 - 1 1 _ 66 67 130 — — — — — 2 3 — — 66 - 132 — — 1 — — 1 4 1 — 64 67 134 — — — — — — 1 — — 70 Over 135 — — — — 1 2 — — — — 136 — — — — — — — — — — 138 — — — — — — — — — 140 — — — — — — — — — — Average ) period j 85 86 89 95 98 104 113 121 — 268 Studies in Indian Cotton TABLE XXVI. The relatioii between the length of the vegetative period of the F-^ generation of a cross and those of the parents. Monopodial Parent Sympodial Parent i^i generation 1 Mean of Parents ^A^ Type Days Type Days Maximum Minimum Mean Diffen Type 3 146 Type 4 83 114 108 80 94 20 „ 3 146 ,, 5 80 113 111 77 98 15 „ 3 146 » 8 78 112 118 82 96 16 „ 3 146 „ 9 94 120 123 88 105 15 „ 3 146 „ 7 62 104 78 93 86 18 TABLE XXVII. The leaf glands. F^ and F^ generations of the cross. Type 3 (leaf glands 3 — 1) X Type 4 (leaf glands 0). Leaf glands 3 — 1 Leaf gland 0 Fi 15 plants Leaf gland 1 — 3 F, Jew Hybrid Gentile Jew 9 „ „ 13 12 4 Hybrid Jew 2 5 Total 13 — — 16 17 number of families where a hybrid has married a Gentile. In 4 the father is hybrid, the mother Gentile, with 8 offspring all Gentile in appearance. In one the mother is hybrid and father Gentile with 3 Gentile offspring (cf. Table III). I have indirect knowledge of several other families comprising a large number of children all of whom are 19—5 284 Heredity and the Jew said to be Gentile in appearance, but I have not included them as the observations were not sufficiently reliable. TABLE III. Second Generation. Children Number of Families Father Gentile Hybrid Mother Hybrid Gentile Gentile 3 Jew Total 5 11 In figs. 2, S, 4, and 5 are given further pedigrees showing the results of the matings of hybrid individuals with Jews and Gentiles respectively. Family A. pxCf cT-x-^ f cf- 4^ I I 1 I ^ O O © Fig. 2. Family B. pxCT ^x«r CT ^ px^© 0 ® © ©®^^f oo Fig. 3. ©© R. N. Salaman Family C. 285 — # 0x ® "1 © e Fig. 4. Family E. 9 ^ ^ © X cT PI XXXVII fig4* IP! XXXVII fig 3 CT figl PI XXXIX X X fig 2 PI XXXIX fig2 PI XXXVIII Cf figl PI XXXVIII fig 3 rig4 PI XXXIX ? 9 9 . fig 4 fig 5 fig 6 fig3 V ^ ' PI XXXVIII Fig. 5. 0 = Jewish appearance. 0 = Gentile appearance. ^ = Gentile appearance and birth. The conclusion to which these results inevitably lead is that the Jewish facial type, whether it be considered to rest on a gross anatomical basis, or whether it be regarded as the reflection in the facial musculature of a peculiar psychical state, is a character which is subject to the Mendel ian law of Heredity. With the knowledge gained from these observations one can now understand the somewhat conflicting reports that travellers and others have given of those outlying Jewish communities which are found on the Malabar coast where they are known as the Beni-Israel ; in China where they are known to the Chinese as the " people who remove 286 Heredity and the Jew the sinew of the leg " ; in Abyssinia where they are known as the Falashas, and in Jamaica and the West Indies. The Beni-Israel of India have been settled in India at any rate since 1400 of the present era, but traditionally from pre-exilic times. They are essentially a black people quite unlike the European Jew. They have always been looked down on by their white brethren in India and they have lived as the natives amongst whom they dwell, and with whom there is little doubt they have freely mixed. In the description of them given by Fischberg, he agrees that they are non-Jewish looking and dark skinned ; he remarks, however, that every now and again a practically ordinary white skinned individual with Jewish features occurs amongst them. If, as is probable, the Jewish facial features are recessive to the native, then it is only what one should expect to find that the great majority of this isolated community are native-looking and that an occasional recessive should crop out from the mating of two hybrids. The Chinese Jews are an even more isolated group who probably reached China through India, possibly a thousand years ago, but traditionally at a far earlier date. I have only seen photographs of these so-called Jews, in which they are typically Chinese in appearance, even as regards the eye shaped The Chinese Jews have lost practically all knowledge of the tenets of Judaism and there is but little doubt that the Jewish facial type has been swamped by the Chinese. The Falashas of Abyssinia are simply negroid. Some doubt whether they had at any time any Jewish blood or whether they were not merely converts by Jewish missionaries. Faitlovitch, who has spent many years amongst the Falashas, whilst admitting that they are not Jewish in appearance but on the other hand closely resemble the neighbouring black peoples, assures me that it is his belief that originally and at a very early period a considerable body of Palestinian Jews did settle in Abyssinia. The Jewish settlers freely intermarried with the natives at first, but during the last two hundred years they have become isolated. If the origin of the Falashas is such, then the swamping of the Jewish type of facial expression is only what would be expected when a recessive character is introduced into a community of dominants. In Jamaica and the West Indies Jews, from the 17th century and onward, have played a very important part as traders and settlers. 1 Dr C. G. Seligmann informs me that in a number of crosses occurring in Australasia and the east, whether between Chinese and White, Malay and Melanesian, or Malay and White, the peculiar Mongolian eye with its epicanthus is always dominant. This fact is amply borne out in the photographs of the hybrids which he has shown me. R. N. Salaman 287 These Jewish settlers employed negro slaves, with a result that a number of their illegitimate children have founded families bearing Biblical names but negroid features. It hiis already been noted that amongst the Ashkenazic Jews in England and elsewhere, one does meet with individuals who have not cjxcj (^ 9 § 99Gf ? P P P~~] ^' (3S & & (^(^^9 n '^ O0O0 Fig. 6. (IS(^P oooo n" O000 0 = Exaggerated Jewish type with long nose. 0 = Jewish type — readily recognisable but not exaggerated. 9 = Gentile appearance and birth. 0 = Gentile appearance, mixed Jewish-Gentile birth. 0 = Gentile appearance, pure Jewish origin. The original Parents were first cousins. The Daughter (No. 6) whose features were of an extreme Jewish type married a Gentile and their child is totally un-Jewish in appearance. The Son (No. 7) married a woman of pure Jewish descent but with features entirely nn-Jewish. AU their children are of the exaggeratedly Jewish type. a peculiarly Jewish facial type and in some eases the keenest eyed Jew would not recognise these men as his brethren. At other times it is only the superficial observer who fails to recognise the type. I have attempted to follow out the results of the mating of such non-Jewish- looking Jews who may be said to have a " pseudo-Gentile " appearance with Jews who have a pronouncedly Jewish cast of feature. The case whose pedigree is shown in fig. 6 is an interesting example, the Jewish features being of the most pronounced, whilst the pseudo-Gentile- looking mate is equally pronouncedly un-Jewish. All the children are as typically Jewish as the Jewish father. A sister of this same father, whose features are indeed almost a caricature, married an English 288 Heredity and the Jew Gentile husband, and she has a child who is without a trace of Jewish- ness. I have met with an abundance of cases which illustrate the same phenomenon, but I have not classified them statistically nor do I show the pedigrees, because it is rarely that one can describe individuals without the smallest possible hesitation, as " characteristically Jewish," " Jewish," or " non-Jewish " in expression, as one is able to do in this family. Nevertheless, I have not met an exception to the rule that the pseudo-Gentile appearance is recessive to the fully Jewish, where the Jewishness of the features are strongly pronounced. In those cases where the Jewishness of the features is weak and more or less con- jectural, then in raatings of such with the pseudo-Gentile type, both Jewish and non-Jewish types may be found amongst the children. The results, therefore, seem to show with very little doubt, that this pseudo-Gentile face is an essentially different thing from its Teutonic counterpart. Whereas the latter is dominant to the Jewish, the former is as decidedly recessive. Such an apparent paradox as the dominance of one type and the recessiveness of an apparently exactly similar one is not unknown to the student of heredity. It has been met with by Bateson and Punnett(l) in their research on the plumage of fowls, and by Bateson in the colour of flowers (3). I have myself, working on heredity in potatoes (13), come across one case where the white potato is recessive to the purple and another where an apparently similar white is dominant to the purple. The facts that have been described above may, I think, throw some light on the question of the purity or otherwise of the Jews. The Jewish features have been shown to be recessive to the Northern European (and I have cases indicating that they are recessive to the native Italian), to the native Indian, to the Chinaman, and to the negro. If then the Jew had freely intermixed with the European races as some authors think is the case, it is obvious that, the characteristic facial type being recessive, it would have been rapidly swamped. But the very reverse is the case : it is the one thing which practically all observers are agreed is common to the Jewish people. It has been suggested by the Pan-Germanic school of Chamberlain and others, that whatever good qualities the Jews possess are due to the admixture in them of a fair-haired race, probably Amorites who were, according to these writers, of Germanic origin. It is indeed more than probable that the fair features found amongst Jews are derived from Amorites or other people of non-Semitic blood in their early home, but it has R. N. Salaman 289 already been shown that this non-Jewish type found amongst Jews is recessive to the typically Jewish, whereas the German or Teutonic type is undoubtedly dominant ; hence, if the non-Jewish type is Amoritic, then it is quite certain that the Araorites were not Germanic. Conversely if it is not derived from the Amorites, it is at least quite certain that it cannot be Teutonic in origin. In marriages between Sephardic Jews of a markedly southern European or Spanish type and Ashkenazic Jews, the former's facial characteristics seem always to be dominant. This fact, when one remembers the infusion of Iberian blood in the Sephardim already referred to, is not indeed surprising. In a previous paragraph, it was stated that many people regarded the Jewish expression as the result of age-long homelessness and persecution. Whether it is meant that this expression is acquired in the life of the individual or whether it is an example of the heredity of an acquired character, is not decisively stated. My results would seem to throw some light on this point. In the first instance, I have frequently seen new-born babies with an unmistakably Jewish cast of feature, and secondly, in those families arising from the mating of hybrid and Jew where the children are brought up in a Jewish home with Jewish surroundings, half the children are Jewish-looking, and half are non-Jewish, a fact which the inheritance of an acquired character fails to explain. Again, if the expression is the result of landlessness and the tausend-jdhrigen Schmerz, is it not peculiar that of two children born of the same parents and reared in the same home, one should have it and the other not ? I think it is clear, therefore, that this Jewish facial expression is a fundamental character, and it is necessary to trace, if we can, its origin. All observers are agreed that it cannot be described as Semitic. It is seen in, but is not the peculiar property of the Armenians who certainly resemble the Jews and who probably have in some degree a common ancestry. Is it perhaps possible that this peculiar facial type has arisen from the fusion of characters derived from two or more of the original races from which the Jews sprang ? The experiments of Bateson and others(2) with the sweet pea, paralleled as they have been in the animal world, are not unsuggestive in this respect. On mating together two apparently similar but really distinct white sweet peas, they obtained the common purple pea. When this latter was bred inter se, it gave rise to a series of purples, reds and whites. Of each of these classes, some, when self-fertilised, bred 290 Heredity and the Jew perfectly true, so that from the union of two apparently similar whites, arose such distinct and dissimilar individuals as the red and the purple pea. Could not this Jewish facial expression be due to the union of characters in a manner similar to that which gave rise to the purple in the pea ? In this way one would be able to explain on the one hand the practically constant presence of the Jewish facial character, and on the other, the wide divergence of head characters and the rest, which is found throughout the Jewish communities of Europe. It is necessary before leaving our subject, to enquire whether there are no other characters common to the Jew which are as frequently present as the facial expression, or which are in any way peculiar to Jews. There would seem to be two instances of such peculiarity which fulfil these conditions. The disease known as Amaurotic Family Idiocy, the victims of which die in early childhood, is probably unknown outside the Jewish people. Fischberg states that cases are met with outside, but all the authorities I have been able to consult agree that it is peculiarly Jewish. Another character which would seem to be peculiar to the Jewish people as a whole, is the absence of alcoholism in their midst. This is acknowledged by every authority. Indeed the Jewish Board of Guardians finds it unnecessary to make any special provision for alcoholic cases as distress arising from this cause does not occur more often than once in a thousand cases, and my own experience of over nine years at the Loudon Hospital fully bears out the statement that drunkards are practically unknown. This absence of the desire for drink cannot be ascribed to the result of religious training. There seems to be a real lack of that desire for drink which is so common amongst the North European races. The deductions which might be drawn from these two sets of facts can naturally have no very great weight, but they do, in conjunction with what has gone before, strengthen the view that complex as the origin of the Jew may be, close inbreeding for at least two thousand years, has resulted in certain stable or homozygous combinations of factors which react in accordance with the laws of Mendel and which may explain the occurrence of the peculiar facial expression recognised as Jewish. R N. Salaman 291 DESCRIPTION OF PLATES. PLATE XXXVI. Jewish Prisoners bearing tribute from King Jehu to Shalmaneser II. 9th century, B.C., Brit. Mus. PLATE XXXVII. Fig. 1. Jewish Prisoners at lacbish. 9th century, B.C., Brit. Mus. Fig. 2. Pen and ink sketch in margin of Essex Forest Roll, 1277 a.d. Fig. 3. Jewish parent of Family E. Fig. 4. Gentile parent of Family E. (see text, p. 285). PLATE XXXVIH. Fig. 1. Man of pure Jewish birth, brother to the man represented in Plate XXXIX. Fig. 1, and husband to the woman shown in Plate XXXVIII. Fig. 2. Fig. 2. Daughter of Jewish and Gentile parents represented in Plate XXXVIl. Figs. 3 and 4, and sister to woman shown in Plate XXXIX. Fig. 2, is non-Jewish in appear- ance. Figs. 3 and 4 are the non-Jewish looking children of parents shown in Plate XXXVIU. Figs. 1 and 2. Figs. 5 and 6 are the Jewish looking children of the same parents. PLATE XXXIX. Fig. 1. Man of pure Jewish birth brother to the man represented in Plate XXXVIIL Fig. 1, and husband to woman shown in Plate XXXIX. Fig. 2. Fig. 2. Daughter of Jewish and Gentile parents represented in Plate XXXVIl. Figs. 3 and 4. Herself non-Jewish in appearance. Figs. 3 and 4. Non-Jewish and Jewish sons respectively of parents shown in Plate XXXIX. Figs. 1 and 2. Figs. 5 and 6. Two brothers thoroughly non-Jewish in appearance, the children of a father of Jewish birth and appearance, and of a Welsh Grentile mother. Note. I am greatly indebted to the ladies and gentlemen who have so kindly allowed me to use their photographs to illustrate this paper. Far more striking examples could have been shown, but permission to publish was in no case obtainable. The description "Jewish" and "Non- Jewish" ascribed to the portraits is arrived at by personal knowledge and by the emphatic assurances of nearest relatives. It may be noted that photographs are not a really satisfactory means of demonstrating so peculiar a character as that of Jewishness. 292 Heredity atid the Jew LITERATURE. 1. Bateson and Punnett. Rep. Evol. Comm. Roy. Soc. Vol. iii. p. 18, 1906. 2. Bateson, Saunders, and Punnett. Ibid. Vol. ii. p. 84, 1905. 3. Bateson. MendeVs Prin. Hered. 1909, p. 105. 4. C. B. Davenport. A mer. Nat. Vol. xliv. No. 527, p. 641, 1910. 5. Farabbe. Papers of Peabody Mus. of Amer. Arch, and Ethn. 1905. 6. Fischberg. "The Jews. A Study of Race and Environment." Contemporary Science Series, 191 1. 7. Hurst. Proc. Roy. Soc. Vol. lxxx. B, 1908, p. 85. 8. Huxley. Zeitschrift f. Demographic u. Statistik d. Jxid. Rasse, Heft ix. 1906. 9. Joseph Jacobs. "Appendix on Racial Characters of Modern Jews." Anthro- pological Institute, Feb. 1885. 10. JuDT. Zeitschrift f. Demog. u. Stat. d. Juden, 1905, Ht. 5. Die Juden als Rasse, 1901. 11. Petrie. "Palace of Apries Memphis," Vol. ii. Plate XXVIII. Brit. Sch. Arch. Egypt, 1909. 12. Ripley. Races of Europe, 1900. 13. Salaman. Journ. Genetics, Vol. i. p. 41, 1910. 14. Weissenberg. "Die Siid. Russischen Juden." Arch. f. Anthrop. Vol. xxiii. 15. Globus, Vol. xcvii. 9. 6. 10, 1910. 16. ZoLLSCHAN. Das Rassenproblem. Wien, 1911. JOURNAL OF GENETICS, VOL I. NO. 3 PUTE XXXVI JOURNAL OF GENETICS, VOL I. NO. 3 PUTE XXXVII -.-r^@^^ JOURNAL OF GENETICS, VOL I. NO. 3 PLATE XXXVIII JOURNAL OF GENETICS, VOL I. NO. 3 PUTE XXXIX Volume I NOVEMBER, 1911 Na 4 ON GAMETIC SERIES INVOLVING REDUPLICATION OF CERTAIN TERMS\ By W. BATESON, M.A., F.R.S. AKD R. C. PUNNETT, M.A. In a paper recently published' we gave a brief account of some peculiar phenomena relating to the coupling and repulsion of factors in the garaetogenesis of the sweet pea and of several other plants. The view there stated was that if A and B represent two factors between which coupling or repulsion can exist then the nature of the F^ generation depends upon whether A and B were carried into the F^ heterozygote by the same gamete or by different gametes. If the heterozygote AaBb is formed by the gametes AB and ab partial coupling between A and B occurs in ^2 according to a definite system, and it must be supposed that the gametes formed by the heterozygote belong to one or other of the series SAB :Ab:aB: Sab, 7AB :Ab:aB: lab, loAB : Ab : aB : 15ab, &c. If on the other hand the heterozygote, AaBb, is formed by the gametes Ab and aB repulsion occurs between A and B, so that only the two classes of gametes Ab and aB are formed. In the account to which we have alluded we supposed that such repulsion was complete, and that the two classes of gamete AB and ab were not formed. Our work on sweet peas during the present summer has led us to modify oar conception of the nature of the gametes produced in cases where repulsion occurs, and this modification will perhaps be made clearer if we begin by giving an account of the experiments upon which it is based. 1 This paper is also appearing in the 49th volnme of the Brnnn VerhantUungen which is to be published as a Mendel FesUchrift. » Proe. Roy. Soe. B, VoL 84, 1911, p. 1. )9Vn. of Gen. I 20 294 Reduplication in Gametic Series During the years 1906 and 1907 we were engaged upon an investi- gation of the inheritance of the hooded character in the sweet pea, of which an account appeared in Report IV to the Evolution Committee of the Royal Society, 1908, pp. 7 — 15. Among several thousand plants bred and recorded in this set of experiments there occurred a single individual (in Exp. 35, R.E.C. IV, p. 15) exhibiting striking peculiarities in the form of its flowers. These were small and much deformed (cf. PI. XL, fig. 1). The standard failed to become elevated, the keel was cleft distally so that the anthers were partially protruded, while the stigma projected far beyond the petals, and was carried on in the line of the carpels instead of being abruptly bent at right angles to them as in the normal flower. At the time of its discovery, in reference to the open " mouth," and the protruding " tongue " represented by the pro- jecting style, the plant was dubbed " the cretin," by which term we shall subsequently refer to this peculiar malformation. The fact that the style protrudes is due to the malformation of the keel which is unable to curve the growing style and cause it to assume its natural position. Fuller experience of these cretins has shewn us that the petals may sometimes be nearly as large as in normal flowers (cf. PI. XL, fig. 2), and that the standard may sometimes become elevated in the normal way (cf PI. XL, fig. 3). The size of the flowers may vary considerably on the same plant, and hitherto where the larger form of flower has occurred the plant has also borne others more nearly resembling the original type. The degree to which the keel is cleft also shews some variation, but in all cases these cretins have the peculiar and character- istic straight stigma. Our original cretin was found in 1907 and was used as the pollen parent to fertilise various sterile^ sweet peas. The F^ plants, which flowered in 1908, were all indistinguishable from normal sweet peas. The normal form of flower (N) was completely dominant to the cretin {n), and fertility {F) of the anthers was of course dominant to sterility (/), We may draw attention to the fact that the crosses were in all cases of the nature Nfx nF, one of the two factors entering with each gamete. In the following year a single F^ family was raised and consisted of 51 normal fertile, 30 normal sterile, 33 cretin fertile, and 1 cretin sterile ^ The cretin character behaved as recessive to the normal flower, but the * In this family and in one of those grown later both light and dark axilled plants occurred. In each case the dark axil went in from the fertile cretin parent, and in Fg there is some coupling between the dark axil and fertility. The numerical results however are complex and must be left over for discussion until more material is available. W. Bateson and R. O. Punnett 295 relative distribution of the different characters evidently pointed to some form of repulsion between the normal flower and fertility. Had it not been for the appearance of the single sterile cretin we could have regarded this case as one of complete repulsion between the factors N and F. The problem was to account for the sterile cretin, and at the time we were inclined to regard it as due to an unaccountable failure of repulsion between N and F. Lack of opportunity prevented us from following up this case in 1910, but in the present year we sowed the seed 'of the rest of the F^ plants harvested in 1908 and obtained details of eight more families which are set out in the accompanying table (Table I). TABLE L fieferenoe Number Normal fertile Normal sterile Cretin fertile Cretin sterile Number 5, 1909 51 30 33 1 72, 1911 26 14 10 1 73, „ 21 12 12 1 74, „ 24 9 8 — 75, „ 22 4 4 2 , 76, „ 30 12 5 1 , 77, „ 78 43 32 3 , 78, „ 59 15 24 — 79, „ 25 12 15 2 Total 336 150 143 11 Expectation 330 150 150 10 These records shew that the appearance of a small proportion of sterile cretins is a constant feature in these families and we suggest that their presence may be accounted for as follows. The repulsion between N and ^ is to be regarded as partial, and of such a nature that the series of gametes produced by the ^j plant is NF, SNf, ZnF, nf. Such a series of ovules fertilised by a similar series of pollen grains would give rise to a generation consisting of 33 normal fertiles, 15 normal steriles, 15 cretin fertiles, and 1 cretin sterile. As the figures given in Table I shew, this expectation is closely realised by the facts of experiment, and we have little hesitation in regarding this explana- tion as the correct one. Moreover we ar6 inclined to go further and to extend the principle to all cases of repulsion in plants. We consider then that where A and B are two factors between which repulsion occurs in the gametogenesis of the heterozygote formed by union of 20—2 296 Reduplication in Gametic Series the gametes Ah and aB, the gametes produced by the heterozygote so derived form one or other term of the series AB: ^Ab AB'. 7Ab AB : 15Ab SaB : ab, 7aB : ab, 15aB : ab, &c. And if we take 2n as the number of gametes in the series we may generalise it under the expression AB : (n—l) Ab : {n — l)aB : ab. As the repulsion increases in intensity it is obvious that the zygotes of the form A ABB and aabb will become relatively scarcer, for there will be only one of each of these two homozygous forms in the complete series of zygotes. At the same time the ratio of the three zygotic forms AB : Ab : aB approaches more and more nearly to the ratio 2:1:1 such as would occur if the repulsion were complete. This is brought out in the upper part of Table II where we have set out some of the gametic series in which partial repulsion is involved together with the series of resulting zygotes. The latter, as the Table shews, are covered by the general formula (2n^+l)AB : {ri'-l)Ab : {n^--i)aB : ab*. Partial repulsion ' from zygote of form AbxaB Partial coupling from zygote . of form ABxab TABLE II. Gametic series Number of gametes in series Number of zygotes formed Nature of zygotic series AB Ab aB ab AB^ Ab aB ab 1 (n-1) (n-1) 1 2re 4na 2n2 + l n«-l n2-l 1 31 31 1 64 4096 2049 1023 1023 1 15 15 1 32 1024 513 255 255 1 7 7 1 16 256 129 63 63 1 3 3 1 8 64 33 15 15 1 1 1 1 4 16 9 3 3 3 1 1 3 8 64 41 7 7 9 7 1 1 7 16 258 177 15 15 49 15 1 1 15 32 1024 737 31 31 225 31 1 1 31 64 4096 3009 63 63 961 63 1 1 63 128 16384 12161 127 127 3969 (n-1) 1 1 ( n-1 ) 2n 4n2 3n2 -(2re- 1) 2n-l 2n-l n 2-(2re Hitherto the only repulsion series which we have been able to identify with certainty is the one with which we have just dealt, i.e. 1:3:3:1 series for the factors N and F. * The general formulae made use of here and in Table II are purely empirical, and offer a convenient way of calculating the nature of the zygotic series from any series of gametes. W. Bateson and R. C. Punnett 297 It is probable, however, that the case of blue and long pollen' is one in which the repulsion is of the 1 : 7 order. Up to the present time we have had four families of the mating Bl x bL and the 419 plants recorded in F^ were distributed in the four possible zygotic classes as follows : Beference Number Blue long Blue ronnd Red long Red round Number 61, 1910 85 33 41 1 J^28, „ 60 20 23 — „ Fil, ,. 9 7 5 — „ F32, „ 72 35 28 — Total 226 95 97 1 Though the evidence for partial repulsion rests here upon the single red round plant which occurred in family 61, it is in reality very much stronger than it appears at first sight, for the following reason. All the plants in the above four families were hooded, i.e. lacking in the factor for erect standard (E). As we have already pointed out^ the three factors E, B, and L constitute a series such that if any two are brought into a zygote by different gametes repulsion occurs between them. Until the present round hooded red plant appeared we had never encountered this combination in any of our experiments. It cannot therefore be regarded as due to a stray seed from another family. And it is evident that if the repulsion between any pair of these three factors were complete such a plant could never arise. For in the normal course the ehl gamete could never be formed. Only two possibilities therefore are open. Either we must look upon it as an unaccountable mutation, or we must consider that the repulsion between B and L is partial. In the light of the evidence afforded by the cretin sweet pea we prefer the latter hypothesis, and we are inclined to regard the partial repulsion between B and Z as of the 1:7:7:1 type. On this hypothesis we should expect one red round in every 256 plants (cf. Table II) whereas experiment gave 1 in 419. At the same time we recognise that the data are not yet sufficient to preclude the 1 : 15 : 15 : 1 system. It is worthy of note that the coupling between B and L is usually on the 7:1:1:7 system, and it would be interest- ing if in such cases as these the repulsion and coupling systems for a given pair of factors were shewn to be of the same intensity. In most cases this could not be tested in practice owing to the verj' large 1 Blue in the flower colour (B) is dominant to red (b), and long pollen (L) is dominant to ronnd pollen ({)• « Proe. Roy. Soe. 1911, p. 7. 298 Reduplication in Gametic Series number of plants required. Thus the coupling between erect standard and blue is on the 127 : 1 : 1 : 127 system, and if the repulsion were of similar intensity we should expect only one hooded red in every 65,536 plants. We may, however, state that in this particular case we have grown over 4000 plants without meeting with a hooded red, so that the facts, so far as they go, point to a high intensity of repulsion for factors exhibiting a high intensity of coupling. It is obvious that the relation can only be worked out where the intensity of repulsion is low, and it is_hoped that the case of the cretin may eventually throw light upon this point when the system in which iV^ and F are coupled shall have been determined. The question now arises how these gametic systems are formed. In each the characteristic phenomenon is that the heterozygote produces a comparatively large number of gametes representing the parental combinations of factors and comparatively few representing the other combinations. In describing the original case of coupling, namely that between the blue colour and long pollen in the sweet pea, we pointed put that no simple system of dichotomies could bring about these numbers, and also that it was scarcely possible that such a series could be constituted in the process of gametogenesis of a plant, in whatever manner the divisions took place. In saying this, regard was of course had especially to the female side, and this deduction has become even more clear in view of the fact that we now know a series consisting of 256 terms. It is practically certain that the ovules derived from one flower of the sweet pea, even if all collateral cells be included, cannot possibly be arranged in groups of this magnitude. A pod rarely contains more than nine or ten good seeds at the most, so that if we even reckon twelve potential seeds to the pod and eight potential gametic cells to the ovule, the total is still only 96, which is much too few\ Nevertheless our series of numbers is plainly a consequence of some geometrically ordered series of divisions. There is evidence also from other sources that segregation may occur earlier than gametogenesis. Miss Saunders' observations on Matthiola^ and on Petunia^ proved that in those plants the factors for singleness are not similarly distributed to the male and female cells. 1 From the fact that in maize the endosperm characters are the same as those of the seed itself we know moreover that segi-egation must have been completed before the divisions at which the male and female cells which constitute the endosperm are set apart. 2 Kep. Evol. Committee R. S. IV, 1908, p. 36. . .J 3 Jour. Gen. i. 1911. W. Bateson and R. C. Punnett 26k The recent work of de Vries' on Oenothera biennis and muricata has provided other instances of dissimilarity between the factors borne by the male and female organs of the same flower. In all these examples it is almost certain that segregation cannot take place later than the formation of the rudiments of the carpels and of the stamens respec- tively. The only visible alternative Is that in each sex the missing allelo- morphs are represented by somatic parts of the sexual apparatus, which for various reasons seems improbable. There is therefore much reason for thinking that segregation can occur before gametogenesis begins, but there is no indication as to which are the critical divisions. Now that we may regard the formation of four cells of composition AB, Ab, aB, ab, as the foundation both of the coupling- and of the repulsion-series the problem is manifestly somewhat simplified. The time, excluding gametogenesis, at which we can most readily imagine four such definite quadrants to be formed is during the delimitation of the embryonic tissues. It is then that the plant is most clearly a single geometrical system. Moreover the excess of gametes of parental composition characterising the coupling- and repulsion-series must certainly mean that the position of the planes of division by which the four quadrants are constituted is determined with regard to the gametes taking part in fertilisation. Though the relative positions of the constituents of the cells may perhaps be maintained throughout the history of the tissues, it is easier to suppose that the original planes of embryonic division are determined according to those positions than that their influence can operate after complex somatic diflferentiation has been brought about. At some early stage in the embryonic development or perhaps in later apical divisions we can suppose that the n — 1 cells of the parental constitution are formed by successive periclinal and anticlinal divisions of the original quadrants which occupy corresponding positions. The accompanying diagram gives a schematic representation of the process as we imagine it. Obviously it does not pretend to give more than a logical or symbolic presentation of the phenomena. If such a sy.stem of segregation is actually formed at the apex, it must be supposed that the axes of the system revolve with th& generating spiral. Whatever hypothesis be assumed the following points remain for consideration, 1. We are as yet unable to imagine any simple system by which the four original quadrants can be formed by two similar divisions. Evidently there must be two cell-divisions, and if in one of them we » Biol. Centralbl. xxxi. 1911, p. 97. 800 Reduplication in Gametic Series suppose AB to separate from ah, we caunot then represent the formation of Ah and aB. Therefore we are almost compelled to suppose that the original zygotic cell forms two similar halves, each AaBh, and that the next division passes differently through each of these two halves, in the one half separating AB from ah, and in the other half separating Ah from aB. The formation of these four quadrants must take place ABxab Ab X aB ( Ab.aB I n- 1 n -1 SAB lAb Iba 3ab 3Ab IBa lAB Fig. 4. 3aB in every case in which there is segregation in respect of two pairs of factors, (For three pairs there must similarly be eight segments, and so on.) The axes of this system may well be determined by the position of the constituent parental gametes. Reduplication or pro- liferation resulting in w - 1 gametes may then take place in either of the opposite pairs of quadrants according to the parental composition. W. Bateson and R C. Punnbtt 301 2. If in the gametes of any plant some factors are distributed according to one of the reduplicated series and other factors according to the normal Mendelian system — as we know they may be — the segrega- tions by which such a system is brought about cannot have happened simultaneously. Moreover if various reduplications can take place very early iu some individuals and not in others, we cannot imagine how the normal form of the plant remains unchanged, unless these reduplications affect tissues originally set apart as germinal. As possibly significant we note here the fact that in the embryonic development of plants the order of the various divisions is known to be subject to great variation and it is not inconceivable that such disturbances of the order in which the planes of division occur may indicate variations in the process of segregation \ 3. We do not yet know whether independent reduplicated systems can be formed in the same individual. In the sweet pea for instance we have not yet seen the consequences of combining blue, erect standard, and long pollen with the fertile-sterile, dark-light axil series, and much may be discovered when such families come to be examined. Animals. The phenomena seen in animals may well be produced by the segmentations in which the parts of the ovary or testis are determined. Hitherto no case of coupling has been found in animals. Among the phenomena of repulsion, however, of which many examples exist, certain suspicious cases have been observed which may mean that in animals reduplicated systems exist like those of the plants. Nevertheless at present it seems not impossible that the two forms of life are really distinguished from each other in these respects. Terminology. Lastly, in view of what we now know, it is obvious that the terms " coupling " and " repulsion " are misnomers. " Coupling " was first introduced to denote the association of special factors, while "repulsion" was used to describe dissociation of special factors. Now that both phenomena are seen to be caused not by any association or dissociation, but by the development of certain cells in excess, those expressions * See Coolter and Chamberlain, Morphology of Angiotperms, 1903, p. 187. 802 Reduplication in Gametic Series must lapse. It is likely that terms indicative of differential multiplica- tion or proliferation will be most appropriate. At the present stage of the inquiry we hesitate to suggest such terms, but the various systems may conveniently be referred to as examples of reduplication, by whatever means the numerical composition of the gametic series may be produced. EXPLANATION OF PLATE XL. Fig. 1. Photograph of the flowering stalks of two cretins. The flowers are here as fully opened as they usually become in this variety, and they are represented slightly smaller than natural size. Fig. 2. Flower of cretin which has larger petals than usual. The standard however is not elevated and the straight stigma protrudes beyond the rest of the flower. Fig. 3. In the centre two flowers from a cretin in which, the standards are fully elevated. On the right are two other mature flowers from the same plant shewing petals of the usual cretin form. On the left are two old buds. *"^ JOURNAL OF GENETICS, VOL I. NO. 4 PLATE XL Fig. I. Fig. 2. Fig. 3- FURTHER EXPERIMENTS ON THE INHERITANCE OF "DOUBLENESS" AND OTHER CHARACTERS IN STOCKS. By EDITH R. SAUNDERS, Lecturer and late Fellow of Newnham College, Ccembridge. TABLE OF CONTENTS. PAOK Statement of conclusions arriTed at in the earlier experiments .... 303 Later experiments on the inheritance of " doableness " and plastid colour . . 306 I. Baces which were obtained only in the double-throwing form • . . . 306 II. Baces which occur both in the form of double-throwing and non-double- throwing strains 311 III. Proportion of doubles obtained from the eversporting strains when self- fertilised or inter-crossed 317 lY. Constitution of the zygote and segregation in the eversporting forms . 321 V. Segregation in Fi orossbreds derived from two eversporting forms and statement of the results obtained in F2 324 YI. Constitution of the zygote and segregation in the pore-breeding (non- double-throwing) strains 334 VJi. Segregation in Fj crossbreds derived from unions between eversporting and non-double-throwing forms and statement of the results obtained inFa 336 Yin. Summary 356 Appendix. Note 1. On the relative viability of seeds giving rise to singles and doubles 361 Note 2. On the inheritance of the branched and the nnbranched habit 368 Note 3. On certain sap-colours not dealt with in the earlier accounts, and on the constitution of the sulphur-white race . 369 Statement of conclusions arriyed at in the earlier experiments. The experiments recorded in the present paper form a continuation of those of which I have already given some account elsewhere*, and it may be well, before considering these later records, to recall the main conclusions given in the earlier accounts. * Beports I — lY to the Evolution Committee of the Boyal Society. In regard to "donbling" see II, 1905, p. 29; m, 1906, p. 44; lY, 1908, pp. 4, 36. 304 Doubleness in Stocks Double stocks are completely sterile, forming neither pollen nor ovules, and consequently they are always obtained from seed set by singles. Among the singles certain strains breed true to singleness, producing only singles in successive generations, whether self-fertilised or inter- bred ; these are referred to as no-d-strains. Other strains of singles, indistinguishable to the eye from those of the previous class, yield a mixed offspring of singles and doubles when self-fertilised or inter- bred, the doubles being mostly (? invariably) in excess of the singles — referred to as d-strains^. The behaviour of these two types of singles may be graphically contrasted thus : no-d-single d-single singles singles singles and so on indefinitely. doubles (sterile) singles doubles (sterile) singles doubles (sterile) and so on indefinitely. A strain composed entirely of c?-singles would thus be " ever- sporting." Further progress in the elucidation of this peculiar type of inheritance was made when it was shown that the eversporting character results from a difference in distribution of the factors concerned, among the ovules and the pollen grains respectively. In a single belonging to an eversporting strain the pollen grains all appear to behave alike and all carry doubleness, whereas the ovules are evidently heterogeneous, rather more than half carrying the double, and the remainder the single character. These conclusions were arrived at through the different results obtained in reciprocal unions between pure-breeding and ever- sporting individuals. For while no-d-single $ x c^-single (^ gives Fi plants all throwing doubles on self-fertilisation, the reciprocal cross rf-single $ X no-d-single j/* gives Fi individuals of two kinds, viz. those which, when self-fertilised, throw doubles, and those which breed true to singleness. The composition of the resulting generations in the two cases is compared below. '■ Crosabreds are not here in question. E. R. Saunders 305 fuhd-wag]e d-single no-d-mngle pollen X ovules pollen x ovoles Fi singlefl singles singles • I II I . » . u, Ff singles singles singles doubles singles singles doubles F3 singles singles singles singles doubles singles singles singles doubles As there is no reason to suppose that the ovules and pollen of the no-d-singles are unlike in constitution, this difference in behaviour of the ^1 crossbreds resulting from reciprocal unions must be due to a difference in the composition of the ovules and pollen produced by the dsingles; and the experimental data are in accordance with the explanation already given, viz. that the d-singles produce two kinds of ovules, but only one kind of pollen grain\ Moreover this interpretation is confirmed by the fact that doubles are always produced in Fi from a cross between two rf-singles, whereas doubles are never obtained in ^i when the mating is between a d- and a wo-d-single. Doubleness in this respect behaves as a recessive. So far the case is clear, and the explanation just given has been amply borne out by subsequent experiments. But certain points in the relations existing between singles and doubles still remained obscure. Though it was now clearly established that the appearance of doubles in Stocks is exhibited in an orderly and definite manner, and is entirely independent of external conditions, it still remained to determine the proportion of doubles thrown by the eversporting singles, and to ascertain, if possible, whether this proportion is constant. Doubleness behaves as a recessive to singleness; how then are we to account for the production of doubles in excess ? Nor is doubleness the only character which behaves in this remarkable way. In a certain race of double-throwing singles, viz. sulphur-white, the plants are also ever- sporting in regard to plastid colour ; every individual yields both whites 1 The conception of a difference in constitution between the ovules and pollen grains of a plant was first put forward in 1908 in connection with the Stocks. It is interesting to find that a difference in reciprocal crosses among certain forms of Oenothera has led de Yries to the conclusion that differences between the ovule and pollen series of the same plant may altso occur in this genus. (Cf. de Tries, BioU Centr. 1911.) 80^ Douhleness in Stocks and creams. From independent experiments^ we know that white plastid colour is dominant to cream, nevertheless among the offspring of the sulphur-whites the dominant whites are not more numerous than the recessive creams. Moreover the inheritance of plastid colour is curiously bound up with the inheritance of singleness and douhleness ; for whereas in the sulphur-white race the singles, so far as experiment has yet gone, are all white, the doubles are for the most part cream, though a few are white like the singles. It was with the aim of elucidating these phenomena that the present experiments were under- takfen, and in the following account I have attempted to show that by a conception of coupling and repulsion^ among the factors, and a peculiar but definite distribution of the factors among the reproductive cells de- pending upon their sex, these hitherto unexplained facts can be related to our previous knowledge, and brought together into a general scheme. Later experiments on the inheritance of "doubleness" and plastid colour. ' I. Races which were obtained only in the double-throwing forrn. Two of the Ten-week wallflower-leaved varieties, viz. red (crimson) and sulphur-white, appear to be obtainable only in the double-throwing form. Direct proof of the eversporting character is obtained if doubles are always found to occur when individuals of the race in question are self- fertilised, while corroborative evidence is afforded by the indirect method of crossing. For if the conclusion in regard to the character of the pollen grains in eversporting races given above (p. 304) be correct, it follows (1) that when an eversporting race is used as the pollen parent in a cross with a true-breeding (no-d) race, doubles, though absent in Fi, may be expected to occur in every family in ^2; (2) that 1 Eep. Evol. Committee, IV, 1908, p. 35. 2 The terms coupling and repulsion have been employed by Bateson and Punnett in explanation of certain results obtained by them in the Sweet Pea, which seemed to suggest that the inter-relation between certain factors was of the nature of attraction or repulsion according as these factors were received separately from the parents or associated together (see Proc. Roy. Soc. B, Vol. 84, 1911). In a later communication which appeared after the present paper had been sent to press (see Verhandlungen des naturforschenden Vereines in Brilnn, Bd. xlix. and also the present number of this Jownal of Genetics), these authors suggest the substitution of the general expression "reduplica- tion of terms " to cover both cases. Pending the acceptance of other terms which will serve to distinguish results which would have been classed under the head of coupling from those coming under the head of repulsion the original terms are here retained, as convenieritly descriptive of the two types of results, not as connoting necessarily the real cause of the phenomena. . E. R Saunders 307 when two eversporting races are bred together, doubles will, on the other hand, occur in each F^^ family as well as in each family in all later generations, just as when either race is repeatedly self-fertilised. The evidence at present available in each case may be summed up as follows : Red Race. 87 individuals were tested directly by self-fertilisation. The pedigree of these plants is shown below. 1 Parent plant (A) 11 Fi Plants derived by self-fertilisation from the parent plant A 64 F2 „ M M >> 11 of thfi ^1 individuals 3 F3 „ „ ,. „ 3 „ F2 7 Fi „ „ „ „ 1 „ Fs „ 1 Fs „ „ „ „ 1 „ Ft Total 87 Doubles occurred in each of the 87 families (see Table III). Thus every attempt to breed out the doubles proved unsuccessful, and the evidence shows that this form, at least so far as the material used in these experiments is concerned, is eversporting. Efforts to obtain from other seed on the market a true-breeding (no-d) strain of this race proved equally unsuccessful. Two or three large firms to whom application was made were unable to supply such a strain ^ ^ In the catalogues of the large Stock Growers the varions stock races are catalogued in different colours, but not as a rule according as they do, or do not, produce doubles. It has however been found that commercial seed, stated to give only singles, does in fact breed true; and that from seed stated to yield doubles, doubles are obtained in such abundance that for testing purposes small sample savings are suflBcient. It might perhaps be supposed that, since the aim of the grower is to produce seed which will yield as high a percentage of doubles as possible, a true-breeding strain, should it by chance appear, would be at once discarded; and hence the fact that it had not been found possible to obtain such a strain in the red race, might not necessarily indicate that no true-breeding individuals occurred when the race was cultivated without selection. But this assumption does not explain the fact, that in the case of the other sap-coloured forms employed, true-breeding seed is on the market and easily obtainable. There is no reason to suppose that modem taste demands a pure-breeding single in various other shades but rejects it if coloured red. Nevertheless there is no doubt that a pure-breeding red strain could at once be made by crossing an eversporting red with a no-d type. If the resulting crossbreds are self-fertilised, F^ will contain a proportion of glabrous red singles some of which will be found to breed true. We may therefore safely class the red race with the other sap-coloured types as one which can exist both as a pure-breeding and a double-throwing form. Whether a non-double-throwing sulphur-white race, i.e. to say a white race composed entirely of individuals throwing a proportion of creams but breeding true to singleness, can exist, or not, we cannot tell. At present no such race is known, and we are unable to make it. 308 Doubleness in Stocks Sulphur-white Race. 62 individuals were self-fertilised, but in this case they were not all descended in one line. Their relationship is shown below. 1 Parent plant (-4)1 7 Fi Plants derived by self-fertilisation from the parent plant A 19 Fj ,, ,, „ ,, 3 of the Fi individuals 3 i^s >» 5> » >> 1 »» F2 „ 1 Parent plant (J5)i 20 Fi Plants derived by self- fertilisation from the parent plant B 5 Fz „ „ ,, ,, 2 of the Fj individuals 5 Fz >> » >i >i 3 y, Fi „ 1 Parent plant (C) Total 62 Families were obtained from each of these 62 individuals and here again doubles occurred in every case (see Table III). It is therefore evident that this race also is wholly composed of eversporting individuals. So much seems clear from the results of self-fertilisation, but it is only on crossing that the real explanation of these results becomes apparent. Reciprocal crosses between cZ-strains and ?20-c?- strains afford a con- venient means of separately testing the ovules and the pollen of the ci-strain, and it is through the different behaviour of such reciprocals that we are enabled to understand the true cause of the eversporting habit. At this point it will be convenient to consider transmission of the double character by the pollen in these two strains ^ When the red or sulphur-white was used as the pollen parent in a cross with a pure-breeding (no-d) strain all self-fertilised i^. plants, with three exceptions, produced a mixture of singles and doubles in ^2 (see Table IV). In view of all the evidence it is unlikely that any of these three cases really indicates a genuine exception ; each will be fully discussed later (see pp. 309, 310). The experiments with the red race were as follows : — Pollen from 6 individuals of this race was used to fertilise 10 plants belonging to 4 different pure-breeding strains. The number of seed- parents in each case was as follows: 2^o-d-glabrou8 cream 4 „ „ white 4 „ ,, flesh 1 „ hoary white (Brompton) 1 Total ... 10 ^ A and B were obtained from different growers. 3 Transmission by the ovules will be dealt with in a later section (see p. 323). E. R. Saunders 309 91 of the resulting Fi crossbreds were self-fertilised to produce F,. The number of these ^i plants derived from the 6 rf-parents used as f^, representing in each case an equivalent number of pollen grains, were respectively 57 19 7 8 8 8 Total "91 Doubles occurred in every F, family. Each of the 91 pollen grains tested 7nust therefore have been carrying the double character. In the sulphur- white race 7 individuals were employed as the rf-pollen-parent in matings with 9 individuals belonging to 3 different pure-breeding strains. The number of seed-parents used in each case was as follows : ^o-d-glabrou8 cream 5 flesh 3 „ hoary white (Bromptou) 1 Total ... 9 93 of the crossbreds were tested as in the red race. The number of these ^j plants derived from the 7 c?-parents were respectively 22 22 16 15 8 7 3 Total "93 Doubles were obtained in 90 out of the 93 families. It remains to consider whether in the 3 families in which no doubles were recorded their absence is probably real or not. It would seem that in two of the three cases, at least, we may fairly regard the totals, viz. 8 and 17, as too small to be conclusive, for we find among the mixed families a case where the proportion of singles to doubles was as high as 20 : 1 (the actual numbers were 40 s. 2 d.). This being so, it is clear that the two cases in question fall within the range of what may be expecte«l from Joum. of Gen. 1 21 310 Doubleness in Stocks an F^ crossbred, bred as above, but from which nevertheless doubles would be obtained if a further sowing was made. The remaining exception was a family of 33 singles, but even this total constitutes no very strong case for the genuineness of the exception, seeing that in another case a result of 40 s. 2 d. (see above) was actually observed. It represents, it is true, a greater excess of singles than was recorded in any other family of the same parentage, but much stress cannot be laid upon this point, since among the mixed F. families obtained when one of the sap-coloured forms was used as the double-throwing parent in similar matings, we find a case where the proportion of singles was as high as 30 : 1 (the actual numbers were 60 s. 2 d.). An equally high proportion might presumably be obtained with the sulphur-white ; so that even in this last case it is quite possible that doubles would have occurred in a larger sowing. Another possibility is worth noting in this connection. The plant from which the F^, family of 33 singles was derived was one of 46 obtained from pure-breeding creams which had been fertilised with the pollen of sulphur-whites. The other 45 all yielded a mixed offspring of singles and doubles. Now the strain of sulphur-white used in this experiment evidently did not contain the colour factor G found in the ordinary pure white glabrous race^ for the mating with the cream produced offspring which were all cream, and, as we should expect under these circumstances, all glabrous. Thus the Fi plants obtained from crossing the cream with the sulphur-white are indistinguishable in appearance from Fy^ plants derived from the same cream parent by 5eZ/*-fertilisation. Where F^ shows reversion in colour and surface character we know that we are dealing with a genuine crossbred, but in this case we have no such proof It is in fact within the bounds of possibility that the F^ plant which produced the 33 singles, although supposed to be a crossbred, may in reality have been a pure-bred resulting from accidental self-fertilisation. To sum up the evidence in regard to these two double-throwing forms, red and sulphur-white : Experiments carried through 6 generations showed that the 149 individuals tested were all throwing doubles. It therefore seems beyond doubt that both forms are genuinely eversporting — that in 1 As stated in the Evolution Reports one of the two factors C and R which are essential to the production of sap-colour is found in the pure white race, the other in the cream. As white is there represented as containing C and cream as containing R, it will be convenient to retain the same formulae here (see Report IV, p. 36). For a fuller account of the constitution of the sulphur-white, see p. 370 of the present account. E. R. Saunders 311 both cases every pollen grain is carrjang the double character. This view receives strong confirmation from the results of cross-breeding. 184 pollen grains were tested by crossing with a pure-breeding form. From the mixed character of the F^ families it was definitely ascertained that 181 of these grains must have been carrying doubleness. The absence of doubles in the 3 remaining families can scarcely be regarded as other than accidental, since if genuine it would presumably imply the production by the double-thro\ving forms of a certain number of single-carrying pollen grains, a condition which is not borne out by the results of self-fertilisation. II. Races which occur both in the form of double-throwing and non-double-throwing strains. The question now arises as to the behaviour of those races which can be obtained both in a pure-breeding and in a sporting form. Are these d-strains also strictly eversporting ? In these cases is it also impossible to breed out the doubles ? From the results which have now been obtained it would seem that to these questions we may safely return an affirmative answer. It will however be convenient to consider the evidence from the sap-coloured and the non-sap-coloured forms separately. Commercial seed of both double-throwing and non-double-tbrowing strains was obtained in the case of the two glabrous non-sap-coloured forms white and cream, and of several sap-coloured forms, viz. very light purple or azure (both hoary and glabrous), light purple, dark purple, marine blue, flesh and copper (all glabrous)^ The seed supplied as giving only singles was found, as previously stated, to answer to description ; in no case were doubles obtained from such seed either when the strains were self- fertilised, or bred together. The strains stated to give doubles were tested both (1) by self-fertilisation which affords the readiest means of detecting the sporting individual, though it leaves undetermined the share in the results to be attributed to pollen and ovules respectively ; (2) by crossing with pure-breeding strains, a method which enables us to sample ovules and pollen inde- pendently of each other. In the latter case the experiment has to be carried to F, before a result is obtained. ^ Unless otherwise stated all races employed in these experiments were of the Ten- week class. 21—2 312 Douhleness in Stocks (a) Sap-coloured races. i. Evidence from self-fertilisation. The number of individuals tested in each case is shown below Number of Individuals Tested. Azure hoary Azure glabrous Light purple glabrous Dark purple glabrous Marine blue glabrous ( Flesh ?labrou8 Parent plants 1 2 2 1 3 2 Fi individuals 5 3 21 4 19 0 derived from self-fertilisation (all of one (all of one (all of one (all of one (belonging to three of parent plants family) family) family) family) families) Fi individuals derived from self-fertilisation 0 2 (belong- ing to two 9 (belong- ing to six 2 (both from one 0 0 of Fi plants families) families) family) Fs individuals 0 9 22 0 0 0 derived from self-fertilisation (all of one" (belong- ing to five of F2 plants family) families) Copper glabrous Totals 12 0 52 0 13 0 31 Totals 16 54 22 108 Twelve individuals belonging to different sap-coloured forms were taken at random, and they and 96 of their descendants were self- fertilised. Doubles were obtained from each of these 108 plants. (For details see Table III.) Thus the evidence, so far as experiment has yet gone, indicates that the double-throwing strains of these forms now on the market are similar to the red and sulphur-white races in that they are genuinel}' eversporting, and that it is in fact impossible to breed out the doubles. ii. Evidence from cross-breeding. To obtain the further proof that the double character is being carried by all the pollen in each of these sap-coloured strains necessi- tates the raising of a large number of F^ plants which have been bred by self- fertilisation from the mating no-d $ x c? -d-glabrons cream) X Plant I x Plant Jx +llx +7# 240x T ! r ~i I I 1 1 1 1 1 — — I 1 1 1 1 1 1 I i I I I I I I I I 1 I 1 I i 1 \ i xxxxxxxx XX xxxx XX 62 X 107 < I I i I I I I I I I I I i I I I X 5x oxlOx 6x 5x Ix 5x 8x 6x 2x 6x 5x Ix 4x 6x !• 3« 10« 18« 59 im 4« 12« 12« 10« 4« 6« 6« 1« 4« 2« h?j self-fertilisation, or hy crossing, and the results obtained. (no-d-glabrous flesh ? ) X Plant Xx + 8 x + 17( 1 1 X 1 1 1 X 1 x 1 1 x x ■ 1 1 2x 1 1 11 1 22x 13 • 40x 26« 1 10 X 23« 1 20x 169 1 14 X 21* glabrous white ? ) X Plant F x X ^^-g^abroas red -l OS "^ CC « «0 «£ seiqnoa QO «£ '-' L BaiSnjg « S '"' sppsBtd , , , saiqnoo; SpnSBld _H (M W5 ajiqiimiM S O i-H r-l w ^ gpi^sBid aresJo qiiA B8l3Utg »o «S "^^ gpnseid e^iqM q^m » ^ S8x3uis eo "5 =2 t S S ^ "^ S ^ gaiqnopmox O q| — H OS OS aonpojd o^ pasn sx^npiA ^ qo (M us 2 JO jaqintiK! 5*j = ^ •-t! m eS _d _e8 ^ "ao 6C SO 60 tg -rj "« 'tt X XX X s •a •3 B. R Saunders 327 that in case 2 the result will be the same as in case 3 which is already known ; while in raatings 5 and 6 the result will presumably be the same as if the seed parent had in each case been self- bred instead of cross-bred. We have then to consider the results in matings 1, 3 and 4 in the light of the assumptions made above. Mating 1. rf-sulphur-white ? x d-non-cream ^. Five diflferent matings of this kind were made (see p. 326). This type of mating gives only white plastids in JP,, a result fully in accord with expectation. For the sulphur-white ovules which carry creamness, by assumption, also carry doubleness ; hence when this race is crossed with any non-cream form w^hose pollen carries doubleness, cream will not presumably reappear in any succeeding generation. It will have been bred out completely, though in the recessive condition, in the F^^ non-cream doubles. Thus only those sulphur-white ovules which carry the white plastid factor give rise to singles in F^. These F^ singles are therefore all homozygous as regards the factor TF, since the mating will have been between XYW ovules and xyW pollen; segregation in their case may therefore be expected to proceed on the same lines as in a pure-bred d-race with uncoloured plastids, and to yield a similar proportion of singles and doubles. As regards the question whether a ratio of 7*5 s. : 8"5 d. or 7 s. : 9 d. more nearly repre- sents the facts, it happens that the numbers obtained in this case agree better with the latter alternative (7 s. : 9 d.). It is just worth noting however that the mating in which the largest record was obtained, both absolutely and in proportion to the quantity of seed sown, and in which therefore the result might be supposed to be the most reliable, viz. the mating with d-glabrous red, leaves either alternative equally probable. In three out of the five matings the experiment was carried to ^3, where the complete breeding out of the cream was further confirmed, but where again the evidence is not quite decisive as between the two ratios. For, though the sum of the three totals gives 7 s. : 9 d., one of the two larger sowings gives almost exactly 7'5 s. : 8'5 d. The results are summarised below (see p. 328). We may then conclude that in the unions of the form rf-glabrous sulphur-white % x d-glabrous non-cream <^ segregation in single Fi plants and in later self-bred generations is like that in any pure-bred eversporting glabrous form with white plastids. 28—8 328 Douhleness in Stocks .2 S^5_j wop. 8^.2 "P."- Wog, «^ saiqnoa sax8nig co g 8 l-H spiisw[d saxqnoo: spuseid sgxqnod g3X3u|S spusBid ga^auig (M IN \ saxSnis \v\03. \n 05 aonpojd «n pasn si^npiA '^ ^ -ipni ''J JO laqranil « 3 45 ^ -« 13 1 I E. R. Saundehs 329 wiqnoa g »I^8 sJ « H O H S3i8ins saiqnoQ ** spii8«id *»tiii qiim I I saiqnoa spi^ffBtd 8pt)8«id «>niii q»ui 5 g 88iqnopi«;ox S S aonpoido} pasn ErprapiA cfl ih -rpui i^ ' "H JO laqinn j{ I I oq S' Ph Cm £ !S ►*; ^ >. a X 2 0 a 1— 1 .5 "3. a a X 0 •3 .5 t-i i X 05 rs C3 5 '? ci C .2P .s i ■3 "x 2 cS J is 0 «^ 0 c 0 e3 'w <9 0 s "i "a h a 0 ^ a 'x 2 ^ a "S eS 0) It CS « hi 0 0 X X 0 X S) 3 X S IS X -*a -4-1 ■♦* C 0 [5: s c > "3) '3 X 0 0 0 0 3) 0 h 0 cS ^ Cu 0 Pi a A s 0) CO X '2 TS _c 0 "3 ^ 0 ea 19 a 9 'a c •-• 0 s CO X X d "^ a e s> &, » O eS a *? •s 330 Doiibleness in Stocks Mating 3. c^-glabrous non-cream $ x c?-glabrous cream ^. Only one mating of this kind was made, two cream plants being employed as the pollen parents (see p. 329). The totals from this mating were 270 singles and 281 doubles, a result which agrees with the view provisionally adopted that 7 + a? : 9 — a; rather than 7 : 9 probably represents the true ratio of s. : d. All but 8 plants were flowered and the 543 individuals recorded included singles with white plastids and doubles with cream plastids, but the reciprocal combinations of whiteness with doubleness and singleness with creamness did not appear. Now in matings of this type all single ^1 plants will presumably be derived from the meeting of XFTT ovules with xyw pollen, i.e. from unions in which all three dominant factors are carried by the ovules and none by the pollen. In other words the union is a union between the combination white plastid colour with singleness brought in by the female parent and creamness with double- ness brought in by the male. Since out of a total of 548 plants in F.^ all were either singles with white plastids or doubles with cream plastids, it follows that redistribution of the factors in such a way as to lead to the combination of singleness with creamness or of doubleness with whiteness either does not occur when segregation takes place, or it must occur very rarely. The above result seems to necessitate not only that the F^ pollen should, as already inferred on other grounds (see p. 321), all carry doubleness, but also that it should all carry cream- ness. There is in fact a strong presumption that we have in these F^ plants a condition similar to that obtaining in the sulphur-white race. In both cases the singles result from the union of the same combinations of factors {XYW % x xyw (^). If none of the pollen of the sulphur- white can carry the factors XYW although all three are present in the sulphur-white zygote, it need not surprise us if the same should hold good for an F^ cross-bred of the same composition. The absence in F^ of singles with cream plastids would thus be explained. The absence of doubles with white plastids would seem to show that the factor W must stand in some different relation to X and Y in the pure white race to what it does in the sulphur-white. In the present case W, which is introduced into the cross in combination with XY, appears only to occur in combination with XY in the gametes of F^. If any gametic combination is formed in which W is dissociated from X or F, such as is presumed to occur in the sulphur-white, it must evidently be rare, since no indication of such a gametic combination was apparent in an F^ population numbering 543. E. R. Saunders 331 If the above account is correct, then so far as can be seen a similar result will ensue in the succeeding self-bred generations F,^ F^, &c., since in each case the singles produced by self-pollination would appear to result from the meeting of XYW ovules and xyw pollen. The record obtained in ^j, so far as it goes, is entirely confirmatory. 54 families were raised and all included some doubles, a result which may be taken to establish the double-carrying character of all the Fi pollen grains from which the F^ parents were descended. The totals obtained in the whole number of ^3 families were 354 singles and 372 doubles. Only a few plants in each family were flowered ; they proved to be again all singles with white plastids and doubles with cream plastids, thus confirming the results obtained in F^. We are thus led to conclude in regard to unions of the form d-non-cream ? x d-cream j/": (1) That segregation in the male cells of the cross-breds exhibits the same peculiarity as in a sulphur-white, and that the pollen grains do not carry XYW, although all these three factors are present in the F^ zygote. Thus the pollen of F^ is similar to the pollen of the ^^ parent which was used to produce it. (2) That the factor for whiteness (W) which is brought into the pedigree by the ? parent in combination with X and Y remains in association with X and Fin the ? gametes of ^i- If exceptions occur in either case they must be extremely rare. Mating 4. d-glabrous cream ? x ti-glabrous and d-hoary non- cream f^. The matings were the converse of those just described, d-cream being here used as the $ parent, d-red as the i Z g •« ""•§ ^ no-d-glabrous flesh ? x d-glabrons dark parple i \ 0 \ ' no-d-glabroas white ? x d-glabrons copper i 10 1 * ,, I, ? X d-glabrou8 red i=16 Coupling complete Coupling partial n=32 Conpling complete Singles, plastids white 513 512 2049 2048 Singles, plastids cream 255 256 1023 1024 Doubles, plastids white 255 256 1023 1024 Doubles, plastids cream 1 0 1 0 Totals ... 1024 1024 4096 4096 As between complete repulsion on the one hand, or partial repulsion on either a 15 : 1 or a 31 : 1 basis on the other, the evidence therefore is not absolutely clear. If the former assumption (coupling complete) should prove correct, then, as stated above, all F^ singles with white plastids should prove heterozygous in singleness and doubleness and also in plastid character; while all the singles with cream plastids should be homozygous in both characters : further, the observed absence of doubles with cream plastids will be absolute. If on the other hand the repulsion is partial, then certain of the F2 singles with white plastids will breed true both to singleness and to whiteness, others to singleness though not to whiteness, others to whiteness though not to singleness, while others again will be heterozygous as regards both characters: similarly some of the singles with cream plastids will prove to be breeding pure to singleness, others not. In this case it most be supposed that with a larger count in F, an occasional double with cream plastids would appear. The available evidence from the F, 352 Douhleness in Stocks generation leaves the question still undecided. 38 F.^ singles with cream plastids were tested, 33 from the mating with d-\\g\\t purple and 5 from that with c^-red ; none yielded doubles in ^3. So far as it goes this fact is against the view that the repulsion is only partial, but again it is doubtful whether the experiment is on a sufficient scale for the result to be regarded as conclusive. iii. One parent is homozygous and the other heterozygous in regard to plastid colour. Mating 5. c?-sulphur- white % x no-d-cxeaxa ^ . Not yet carried toF,. Mating 1 1. Reciprocal cross, wo-c^-cream $ x c?-sulphur- white » 3 all 3 plants „ „ ,, 3. . 19 „ II 3 2 were double, 1 died before flowering „ 4. 228 „ 11 33 17 were double, 8 died before flowering, and 8 were single The seeds from the 5 other Fi plants gave no result. In 1909, 30 seeds from one of the F^ singles were sown, only 1 germinated and this proved to be a double. In 1910, > 130 seeds from another F^ single were sown ; 21 germi- nated, all of which lived to flower ; 7 were single and 14 double. ii In 1907 a glabrous white plant yielded an F^ of 83 singles and 100 doubles. 364 Dotibleness in Stocks In 1908, 30 more seeds of this plant were sown ; only 2 germinated ; both were double. In 1909, 47 more seeds were sown ; only 7 germinated and again all were double. Of 5 seeds, harvested also in 1906, from a sister plant, but not sown till 1909, only 2 germinated and both produced doubles. In 1908 nearly 200 seeds harvested from 5 of the ^i singles were sown ; 40 germinated of which 27 lived to flower, 5 being single and 22 double. The families were composed as follows: Family 1. > 30 seeds so\m. 1 germinated and produced a double ,, 2. 34 ,, ,, 12 ,, 8 were double, 4 died before flowering „ 3. 33 ,, ,, 15 „ 8 were double, 4 died before flowering and 3 were siogle „ 4. 30 „ ,, 12 ,, 5 were double, 5 died before flowering and 2 were single All the seeds from the fifth ^i plant failed to germinate. In 1910, 85 more seeds from 3 of these same ^i plants were sown, but none germinated. About 500 seeds from 20 others among the ^i singles gave a total of 79 singles and 114 doubles. Here the proportion of seeds still capable of germination, though less than 50 per cent., was considerably greater than in the lot sown in 1908, and the result is not very different from what we should expect had the seeds been sown in the season following that in which they were harvested. From this and other facts it is evident that the length of time during which the seeds retain their power of germinating is not fixed but depends probably on the quality of the seed in the first instance, and on the conditions under which it is kept. iii. In 1908, 69 seeds of a sulphur-white which had been harvested in 1906 gave 23 singles and 32 doubles. In 1910, 128 more seeds were sown; only 5 germinated of which 4 lived to flower : all were double. A similar increase in the proportion of doubles was observed in many cases where the seed was originally of bad quality, and where only a small percentage germinated even when sown the following season. This is well shown in the case of the two type forms from which the largest sowings were made in 1910. Owing to a bad season in 1909 a great deal of the seed harvested was of miserable quality and a large proportion failed to germinate. Though no real line of E. R Saunders 365 division exists, since all grades occur, some arbitrary classification must be made for the purpose of comparison, and the line is therefore drawn between those pods where at least half the number of seeds sown germinated, and those in which less than half proved to be good. The results may be summarised thus : Nnmber of Namber of seeds sown seeds sown where less Namber of Number Namber where st Number of Namber Namber th&D half seeds which of of least half seeds wbkh of of Type germinated germinated singles doables germinated germinated singles doaUes Marine blae 744 161 42 108 238 162 67 71 Light purple 790 237 85 125 1439 1040 447 494 In both cases the fruits containing the less good seed have given a higher percentage of doubles. As to the proportion of doubles actually obtainable from the various types the numbers quoted in seed catalogues range from about 50 per cent, to as much as 90 per cent. In the case of the Erfurt Ten Week strains from 60 to 75 per cent, is given. This is a rather higher proportion than was found to occur in the breedings here described, where the average ranged between 53 and 57 per cent., though a considerably higher proportion might now and again be obtained in individual sowings. Chate^ believed his experiments to show that a larger percentage of doubles could be obtained from the pods on the main stem and from the lower ones on the primary laterals than from those on the laterals of a higher order; and similarly from the seeds from the lower region of a pod as compared with the upper : the difference is given as 20 per cent, only of doubles from branches of a higher order as compared with 65 per cent, from those of a lower order, and 30 to 35 per cent, from the upper region of the pods as compared with 75 to 80 per cent, from the lower region. These two latter numbers would give an average of 55 per cent, for the fruit as a whole, which agrees very closely with the observations contained in the present paper, and with the avei*age which the theoretical considerations here advanced would lead us to expect. No indication of the aggregation of seeds giving rise to doubles in definite regions of the fruit was obtained, although a number of observations were made with a view to testing this point. 68 pods belonging to three different strains (red, marine blue, and Princess May) were halved transversely, the seeds from the upper and lower halves being sown separately. The same result was ' loc. eit. p. 79. 366 Douhleness in Stocks obtained as in the case where the seeds were sorted according to shape (see below). Sometimes a higher proportion of doubles would be obtained from the lower half, sometimes from the upper, making it evident that no constant difference exists in the two regions with regard to the distribution of the two kinds of seed. It seems in fact probable that the distribution observed by Chat^ was accidental, and not the result of any general arrangement throughout the individual. {h) On the possibility of distinguishing the seeds giving rise to singles and doubles respectively. In several papers by earlier writers, treating of Stocks, we find the statement repeated that more doubles are obtained from the lumpy irregular-shaped seeds than from the typical regular disc-shaped seeds. No figures are quoted in support of this view, which is probably the outcome of an association of ideas rather than of critical experiments, which would need to be carried out on a considerable scale in order to allow for any disturbing effect due to the frequent marked irregularity of distribution which has already been noted. So far no indication has been observed of any connection between the shape of the seed and the character of the flower. The glabrous-red race being one in which many lumpy or irregular seeds constantly occur, the seeds from a certain number of pods belonging to this race were sorted according to shape, the flat seeds being sown separately in one lot, the irregular- shaped seeds in another. It was found that cases where more doubles were obtained from the flat seeds were about as numerous as those where the reverse was true, and that so evenly did the variations in the one direction balance those in the opposite direction that the ratio obtained from the totals in the two cases was almost identical. Thus in 1 906 the seeds of 10 pods of the red race were sorted before sowing. The results were : From the flat seeds a total of 65 singles and 93 doubles or 1 : 1'43 lumpy „ 19 „ 28 „ 1 : 1-47 Similar sowings in other years gave similar results. It seems much more probable that the irregular shape of the seeds is connected with the way in which they are packed in the pod. In the case of the cream race Princess May, and of a certain strain of sulphur- whites, the pods are often some inches in length. The seeds are borne at some distance from one another, and although a pod may contain from 60 to 70 or even more, they do not overlap. They are so regular E. R. Saunders 367 in shape that a lumpy seed can only be found now and again. In the glabrous red, on the other hand, the pods are so short that though very much fewer in number the ripe seeds are crowded together. Yet the same proportion of doubles is obtained from each of the three strains. We may therefore conclude that no system of selection based on the shape of the seed will enable us to obtain a proportion of doubles which is constantly above the average. In the case of certain sulphur- whites however it is quite possible by sorting the seeds according to colour to separate almost completely those giving rise to singles from those producing doubles. The present experiments have shown that there are at least two types of sulphur-white on the market, one in which the seeds are small, brown, often irregular in shape, and indistinguishable in appearance from those of a true-breeding white ; the other in which the seeds are very regular, larger, of a lighter yellowish colour, and similar to those of the cream race Princess May. These two types have no doubt a different origin, and are different in constitution (see later, p. 370). In the case of the type with the yellow seeds it was found possible in well ripened pods to sort the very yellow seeds which give rise to the creams which are all double from the less yellow seeds which give rise to whites of which nearly all are single. The following result will show the degree of accuracy which can be reached by this method. Of 81 seeds taken from one pod 48 were expected to give rise to creams 33 to whites 38 germinated 27 germinated 34 flowered 26 flowered 30 were cream doubles 24 were white and all single 4 were white and all single 2 were cream doubles Of 72 seeds taken from another pod 44 were expected to give rise to creams 28 to whites 28 germinated 25 germinated 28 flowered 16 flowered 27 were cream doables 16 were white (15 single, 1 doable) 1 was white and single 0 were cream Thus of the 60 doubles which were obtained 57 were recognised by the seed-colour ; of the whites 5 were wrongly classed as probable creams, but the remaining 40 were correctly identiBed, and 39 proved to be single. A very slight error must however always remain in sorting the singles from doubles, since the rare double white is not distinguishable in seed-colour from a single white. 368 Douhleness in Stocks Note 2. On the inheritance of the branched and the unbranched habit. Most races of Stocks branch freely, and in the case of biennial types form large bushy plants. Of the various sorts used in the present experiments the Ten Week strains all have the branched habit, as have also among the biennials, incana and the Brompton strains raised by Continental growers. The typical English Brompton is on the other hand wwbranched, the single stout stem being prolonged above the region of the leaves as a simple raceme. Both leaves and fruits in this type are thick and somewhat fleshy. The unbranched habit is recessive to the branched. "When a cross is made between an English type of Brompton and a branched form the Fi cross-breds are bushy plants like incana. In F^ the pure Brompton habit reappears in a proportion of the plants. The sorting of the F^ plants is rendered difficult owing to the fact that the formation of branches can no doubt be induced by a variety of causes producing a check in growth. An injury to the terminal bud or to the roots may cause a check in the growth of the main axis and lead to the development of one or more axillary buds which otherwise would have remained dormant. Injuries of this kind, resulting in a check to growth, are very likely to occur when the young plants are planted out, and hence in a strict count a certain number of individuals are likely to be classed as normally producing branches which in fact only do so owing to unfavourable conditions, or to accident ; thus the proportion of individuals inheriting the unbranched habit is likely to appear less than it actually is. In the one mating in which an English Brompton stock was crossed with a branched form 394 plants were raised in F^. Of these 66 were recorded as typical Brompton plants and 31 others as being unbranched except for a single lateral. These numbers suggest that the true proportion of plants inheriting the unbranched habit in F^ is probably 1 in 4 as in the ordinary case of a simple recessive. The characteristic appearance of the unbranched as compared with a branched type is shown in the accompanying figures showing two of the Ffi plants derived from a cross between an English Brompton and a branched Ten Week strain. (Fig. 1 shows the branched, fig. 2 the unbranched habit.) The photographs were taken at the end of the season when the plants were in fruit and the leaves had fallen. In the Fi generation the Brompton plants presented a very curious appearance, the single stem in many cases reaching a height of from 3 to 3| feet. E. R. Saunders 369 Fig. 1. Pig. 2. Note 3. On certain sap-colours not dealt with in the earlier accounts, and on the constitution of the sulphur-white RACE. Sap-colours. Rose is obtained from unions where the colour factors C and R are present together with a factor for paleness, provided the blue factor B is absent from at least one of the parents. Hence it is obtained when flesh or a certain type of sulphur-white (type 1 of p. 367) is crossed with any form which gives a coloured jPj. If both parents lack B then it appears in Fi , but if one or other contain B it does not occur till F,. Thus when sulphur-white type 1 was crossed with red, flesh, cream, or Brompton white, F^ was rose ; whereas when bred with azure or light purple the rose colour only appeared in certain plants in F,. Owing 370 Doubleuess in Stocks to the presence of the B factor, azure and light purple can never give rose in the first generation, but in any mating with a 6-forni they will presumably give it in F2. Rose is epistatic both to the deeper colours carmine and crimson, and to the purer red shades flesh and terra-cotta. Lilac is a somewhat bluish pink form, the blue tinge becoming more marked on fading. It occurs in ^2 from certain unions where flesh is used, as, e.g. flesh x light purple or white incana. Its position in the colour series has not yet been determined owing to the failure of the crop in 1910. Terra-cotta (? Rothbraun of German catalogues) is a full pure colour. So far it has only been obtained in F^ from matings between flesh and sulphur-white or cream. It is recessive to flesh, and possibly stands at the hypostatic end of the scale of the pure reds as copper probably does of the impure series. Carmine and Crimson. These full red colours have hitherto been spoken of collectively as " red." But carmine certainly includes three distinct shades, and crimson probably more than one. The two colour groups together form a very closely graduated series, and a full analysis of these shades has not been attempted. When, as here, a considerable deepening of the colour occurs between the unfolding and the fading of the flower, the range of shades exhibited by individuals of a pale grade may overlap those of an intermediate class, and so on up the scale, thus increasing the difficulty of sorting. The same difficulty is met with among some grades in. the blue series, but the three main classes, dark purple, light purple and azure or very light purple, are easily distinguished. Marine blue is a larger- flowered form, in range of tint between unfolding and fading covering almost those of azure and light purple together. The two paler forms azure and marine blue, differ from the more deeply coloured purple types in having brown and not green seeds. Constitution of the sulphur -white race. All sulphur-whites were found to behave alike when self-fertilised, in giving a mixture of white singles and cream doubles ; all probably also give a small percentage of white doubles. When bred with other glabrous forms the results varied according to the type of sulphur- white employed. Seed supplied by Messrs Haage and Schmidt proved to belong to the second type described above (p. 367, seeds yellow, large, regular). The plants crossed with glabrous cream gave F^ all glabrous, and either all cream or mixed white and cream, according as the E. R Saundkes 371 sulphur-white was used as <^ or $. When crossed with glabrous white or glabrous sap-coloured strains F^ was hoary and sap-coloured. If a full sap-colour as e.g. red was used, a full colour was obtained in F^. This type of sulphur-white contains the hoary factor K\ and one of the two factors G and R necessary for the production of sap-colour; the one present must be the one which occurs in Princess May (= R). The other colour factor (G) and the factor which turns red blue (B) are both absent. We can therefore express the composition of this type of sulphur-white thus — bcRK. The seed obtained frqp Herr Benary showed the characteristics described under type 1 (p. 367, seeds small, brown, irregular). This form evidently has the composition bCrK, and has also a factor causing paleness, so that in a cross a full sap-colour carried by the other parent becomes pale in Fi. This type when bred with glabrous cream or a glabrous sap-coloured form gives F^ all hoary sap-coloured; with glabrous white on the other hand it gives Fi all glabrous white. Bred together these two sulphur-whites should give a sap-coloured hoary Fi of a pale red colour (=rose). It was hoped that plants from this mating would have been raised this year, but unfortunately owing to the bad season in 1910 no good seed was obtained. Indirect proof however is already forthcoming, for a mating in the form [sulphur-white (type 2) x glabrous red] x sulphur-white (type 1) gave all rose hoary (217); whereas the mating [sulphur-white (type 2) x glabrous red] x sulphur-white (type 2) gave the expected result — half the offspring being red hoary and half white smooth. The expense incurred in the course of the present work has been in part defrayed by a grant from the British Association for the Advance- ment of Learning, and also during the present year by a grant from the Gordon Wigan Fund. The experiments were carried out in one of the allotment gardens of the Cambridge Botanic Garden, which for some years, by the kindness of the Botanic Garden Syndicate, has been permitted rent free. I wish here to express my thanks to Miss Killby, who in the course of the work has given me much valuable assistance in the garden, and who kindly took the photographs here reproduced ; also to those friends who were kind enough to raise and record a number of the plants. » See Evolution Report IV. p. 36. 372 Douhleness in Stocks •2 t-i-HC5O5iNU5W5C<5-^fHa0'* gi-(COi-l OrH(Nt-i-iaO t- •g « t- l.O IM o ■> Q a O CO 0» rH iH t- US 04 U5 S" T-t (N «5 iH •S «3 S TttlNi-HOOOJ-^eOCfSOKN^OOOlCOi-l O i-H COeO>-l-^rHiH 3 » * « S Cqi-lTt(«50»0-»fTj<05C 00 O OS 00 CO OS O '5 3i-iaOOOi-IQ0»OTj((MC<10S a -"H 1-1 -* -* 1-1 CO o "^ I 3 «005Oi-lOS<)i-IC^>niM«0 OrH CO rHf-llO ^O »0 •<*l Q •2 OOOSCOTt<»Co co-^eoooseOrH o -2 eot-coooostocooocoooioooosos SPr-li-lrHi-l'H rH (MCMi-leO "Soc^i-tOJcoust-THosoootoeo a (M»o i-(C^iMi-(c-usi-< E. R Saunders 373 "5© 3 f^ 33 " 2 >. ra i «2 — I. — "3 o _2 ^ "B. C I >0 ^ 3J »3 35 U5 C e O £ I ^ •§ ^ ^ as* £ ^ S 0» S •* = "i 1 w 1 I |CJe-e ' £ I £ <-< -2 X X X 33 X g •I a O O ® C3 "* IB s a lo rj e« >o CO C4 ■« us cq >o 'sdr-ica soo-^om S >a >o 3 "t* 2 30 5" Sou,-* J ooo>t- g S •* ^ 2 'H 5 ff>Hc« 5'"' B>oxt-l J^*^' 5*" — 00 33 35 X CO S. Joam. of Gen. i 85 374 Douhleness in Stocks TABLE IV. Showing the number of singles and doubles obtained in F^ families derived from matings of the form no-d '^ x-d $ . wo-d-Klabrous white ? 1 10-d-glabrous flesh ? d-siilphur white S no-d-glabrous cream ? d-glabrous red $ d-glabrous azure S A Single Double Single Double Single Double Single Double Single Double Single Double 16 8 21 7 2 1 9 2 41 22 23 8 3 1 46 18 9 1 17 — 148 62 14 12 18 8 43 14 8 3 3 6 14 5 12 4 20 7 20 6 23 7 7 1 7 9 51 19 3 3 14 1 no-d-glabrous cream ? 16 13 9 6 15 47 6 16 1 8 1 1 1 7 1 3 d-sulphur white (f A 1 N 17 2 53 21 8 2 7 2 Single Double Single Double 20 3 37 9 37 4 4 3 64 15 24 11 25 4 15 6 6 1 10 3 55 11 25 3 28 8 41 13 19 3 40 2 12 1 22 6 37 9 35 9 11 2 6 1 16 6 14 3 42 13 24 6 21 4 9 1 21 7 17 3 44 10 41 16 3 2 6 6 20 5 20 4 13 5 44 12 7 2 7 1 6 1 8 6 40 12 50 13 18 1 6 1 29 7 8 4 27 10 27 13 8 10 2 32 8 7 1 18 8 32 8 26 6 4 3 50 5 11 3 37 8 59 26 17 1 19 7 ?[33 -] 12 2 66 22 47 21 28 6 38 6 7 1 10 3 5 2 28 2 19 8 10 2 12 1 65 20 24 6 18 5 23 4 111 39 69 18 no-d-elabrous cream ? 43 5 8 1 d-hoary wLite (intermediate) i i A 11 20 2 6 9 3 7 2 no-d- -hoary white (Brompton) ? ^ d-glabrous red-< Single Double Single Double 31 6 11 2 ^ 21 8 8 2 21 8 4 2 5 2 29 6 Single Double Single Double 17 6 9 4 42 21 44 13 9 2 10 3 3 no-d-glabrous cream 2 21 9 19 no-d-glabrous flesh ? d-glabrous white ■ 19 4 21 3 Single Double -;U / Single Double Single Double no-d-glabrous cream ? d-glabrous red S A 54 15 5 1 6 6 8 1 4 /■ — ^ mod-glabrous flesh 2 9 3 8 2 Single Double Single Double 9 d-glabrous light purple < ? 7 2 73 26 28 11 17 A 9 1 44 12 42 6 Single Double Single Double 56 9 38 22 208 12 64 6 no-d-glabrous cream 2 47 17 43 15 116 7 92 5 d-glabfous light purple -d-glabroaa white S 36 48 13 42 7 7 6 7 Mngle 36 79 Doable Single 42 10 Doable 7 3 55 — 8 4 20 6 4 15 — 5 2 30 — 29 3 83 — 1 1 58 7 1 17 — 1 1 20 — 6 2 7 — 66 27 8 — 93 23 9 99 138 13 32 39 6 376 Doiibleness in Stocks TABLE Vl. Showing the number of singles and doubles obtained in 50 Fi families derived from matings between two ever- sporting forms. (Seep. 319.) Single Double TABLE Vn. 2 3 11 2 1 56 3 25 63 10 14 18 14 9 8 14 11 5 8 71 3 3 8 5 8 9 22 6 18 18 4 9 7 18 3 14 1 1 9 2 28 14 8 5 1 2 14 7 14 8 52 2 31 78 13 17 16 13 8 18 23 7 1 1 12 13 16 6 12 86 4 2 13 9 18 10 29 11 25 17 7 12 8 21 4 19 12 11 8 S 24 7 7 Shovnng the number of singles and doubles obtained m 81 F^ families when i the Fi cross -breds f rom matings between two eversporting forms are self-fertilised. (See p. 324.) Single Double Single Double 24 24 5 6 29 18 39 60 5 12 6 9 36 44 16 15 9 17 35 45 40 26 3 2 19 25 6 8 13 19 3 4 22 13 7 13 10 23 1 1 20 16 — 2 14 21 6 9 29 23 — 4 74 81 1 1 7 4 8 15 3 8 20 23 81 63 5 4 56 65 2 4 4 41 86 22 22 16 22 28 37 12 16 65 61 6 16 2 7 22 24 28 40 24 18 30 38 1 1 7 13 3 14 57 70 — 4 5 20 2 7 5 11 5 4 5 12 24 28 4 13 6 7 3 7 3 7 10 21 1 1 29 33 a3 "1 5 15 1*2 5 6 7 20 6 8 ( 12 17) 141 4 8 1*94 4 6 17 16 7 12 *85 146 37 53 *12 29 13 12 TABLE VIII. Shounng the number of singles and doubles obtained in 35 F2 families when Fi cross- bretds from matings between two eversporting forms were crossed back with one of the eversporting parents. (See p. 319.) Single Double 4 2 44 48 14 8 9 12 8 6 3 3 33 37 16 28 30 36 3 3 20 30 10 12 18 19 11 18 23 37 18 9 16 14 10 3 1 11 9 13 17 29 7 9 9 6 11 8 11 14 5 2 3 3 9 17 8 11 8 7 12 19 9 11 9 13 4 6 * Eecords marked with an asterisk were obtained from delayed sowings (see Appendix, Note 1). Below are shown the matings from which the above families were derived. Fam. 1-2 cream 3-4 5-7 red 8-11 ,, 28-55 56-57 58-62 X white xred X cream X sulphur- white 12-19 sulphur- white X white(hoary) 63-75 ,, 20-40 „ „ xred 76-79 cream 41 jj „ X white 80-81 ,, 42-44 „ ,, X azure 45 ,, ,, X light purple 46 azure(hoary) x sulphur- white 47 flesh X azure 48 azure x red 49 light purple x „ 50 red x light purple Fam. 1-13 red x cream 14-27 sulphur-white x red X azure x light purple X white X white(hoary) xred X white Fam. 1-2 red x (red x sulph.-wh.) 3-5 ,, X (sulph.-wh. X red) 6 (sulph.-wh. X red) x red 7-31 ,, ,, X sulph.-wh. 32-33 (red x sulph.-wh.) x sulph.- wh. 34-35 (cream x sulph.-wh.) x red NOTE ON THE INHERITANCE OF CHARACTERS IN WHICH DOMINANCE APPEARS TO BE INFLUENCED BY SEX. By L. DONG ASTER, M.A. Fellow of King's College, Cambridge. A NUMBER of cases have been described, in which it appears that a character is dominant in one sex, recessive in the other. Such cases fall into two categories, according to whether the character concerned is inherited in the normal Mendelian manner, or is sex-limited in its inheritance. Examples of the former type are the homed character in sheep (horns dominant in the male^), and probably the white colour in the butterfly Colias (white dominant in the female') ; of the sex-limited type examples are colour-blindness, hereditary nystagmus and haemo- philia in man, and probably the orange colour in cats'. In the latter class it has frequently been stated that the character concerned is dominant in the male, recessive in the female. Taking colour-blind- ness as an example, we find the following facts. A colour-blind man married to a normal woman has usually only normal offspring ; his sons do not transmit the affection, but his daughters transmit it to some of their male children, as in the following scheme: ^ X 9 i colovu*-blind man (J 9 X (J (J normal man i 6 9 9 9 normal woman. A colour-blind man married to the normal daughter of a colour-blind man may have colour-blind daughters as well as sons, thus : I I 1 i 6 f 9 * Wood, Journ. Agric. Science, in. 1909, p. 145. * Geroald, Amer. Naturalist, 45. 1911, p. 257. In this case there is the complication that homozygous white females have not been observed. 3 Doncaster, Proc, Camb. Phil. Soc. xni. 1905, p. 35. Since the pablication of that paper I have obtained evidence, not yet conclusive, that the inheritance of the orange colour is sex-limited. Experiments to test this more fully are being made. 378 Inheritance of Characters The explanation commonly given of these facts has been that colour-blindness is dominant in the male, recessive in the female, so that the male heterozygote is colour-blind, the female heterozygote normal ; a colour-blind woman can thus arise only when the affection is inherited from both parents. It is also evident that the affected male transmits the factor for the disease only to his daughters ; the heterozygous female, however, transmits to some of the offspring of both sexes. This sex-limitation of the transmission makes a different explanation possible, which is also more in accord with other cases of sex-limited inheritance. Since the male transmits the factor for colour-blindness only to his daughters, it must be assumed that the male in this case is heterozygous for the sex-determiner. In former papers I have sug- gested that if maleness is determined by a factor ^, femaleness by a factor % epistatic to ^ when both are present, then a male individual may be represented <^0, a. female jf $; i.e. that both sexes are hetero- zygous for sex-determiners, with selective fertilisation between (/-bearing eggs and 0-bearing spermatozoa, and between $ -bearing eggs and