■w-MI ■• . J ';L .-i- *^' .W«.'SrA.?Kl: 1 -s-i.,>'" ■i4,j,.,^ :A'k^V:^^-;. ■r^m .*. '; ., ■ ' >> . .Vt<-^^^ ^ >■-■■> -tx^^V^^i ^-i>i- ' S ^^r:.o<^ 1« ^<.'.'W^ JOURNAL OF GENETICS CAMBRIDGE UNIVERSITY PRESS konBon: FETTER LANE, E.G. C. F. CLAY, Manager also H. K. Lewis, Gower Street aud William Wesley and vSon', 28, Essex Street, W.C. ^ ■i.i i i h m t i i 1 * f iH ^ «Hl)tnburBl) : luu, PRINCES STREET Btrlin: A. ASHER AND CO. IcipjiB: F. A. BROCKHAUS BtXo iork: G. P. PUTNAM'S SONS JSombao anO Cakiitta: MACMILLAN AND CO., Ltd. All rii/lils reserved 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 BIOLOGV IN THE UNIVERSITY OF CAMBRIDGE Volume I. 1910— iQii Cambridge : at the University Press 191 I ffambnttgr : PRINTED BY JOHN CLAY, M.A. AT THE UNIVERSITY PRESS CONTENTS. No. 1 (November, 1910) PAGE Frederick Keeble and Miss C. Pellew. White Flowered Varieties of Primula sinensis ......... 1 Redcliffe N. Salaman. The Inheritance of Colour and other Characters in the Potato. (Plates I — XXIX, one coloured, and 2 Text-Figures) 7 Fuederick 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. Petunia. (Seven Figures) ..... 57 L. DoNCASTER and F. H. A. Marshall. The Effects of one-sided Ovariotomy on the Sex of the Offspring ..... 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 Authocyanin . . .133 Florence M. Durham. Further Experiments on the Inheritance of Coat Colour in Mice 159 vi Contents No. 3 (August, 1911) PAGE L. DoNCASTER. Some Stages in the Spermatogenesis of Abraxas G rossulariata 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 Texf> Figures) 303 L. DoNCASTEH. Note on the Inheritance of Characters in which Dominance appears to be Intluenced by Sex . . . .377 Correction. On Plate XXXIV, to face p. 208, /or " Monopodial" yead " Sympodial,' and for " S.ympodial " read "Monopodia!." Vol, 1, No. 1 November, 1910 JOURNAL OF GENETICS EDITED BY W. BATESON, MA., F.R.S. (director of the JOHN INNES HORTICULTURAL INSTITUTION) AND R. C. PUNNETT, M.A. (professor of BIOLOGY IN THE UNIVERSITY OF CAMBRIDGE) Cambridge : at the University Press London : Fetter Lane, E.C. C. F. Clay, Manager and H. K. Lewis, Gower Street lEBmbutgf): 100, PRINCES STREET ©trim: A. ASHER AND CO ILripjia: F. A. BROCKHAUS' mia inrit: G. P. PUTNAM'S SONS ISombag anB Calratta: MACMILLAN AND CO., Ltd Price Ten Shillings net [Issued November IS, 1910] CAMBRIDGE UNIVERSITY PRESS Mendel's Principles of Heredity By W. Bateson, M.A., F.R.S., V.M.H. With 3 portraits, 6 coloured plates and 33 figures. " The present work is the most complete treatise on the Mendelian aspect of Heredity which has yet appeared in English It is a privilege to have read Mr Bateson's work, and to have assimilated the exposition of the principles which he so ably advocates, illustrated with concise tables, as well as figures and coloured plates, which enhance its value as a solid contribution to English Science." — Journal of Botany "Mr Bateson's long-expected volume on Mendelism undoubtedly marks a P I _ new stage, probably a new era, in the investigation of the origin of species 12s net ^' '^' of course, impossible in so short a notice to do more than draw attention to a volume that works out in close detail applications to natural phenomena of Mendel's wonderful discovery. We can, therefore, merely commend in general terms a work of the first order in the thought of our generation." — Contemporary Review " Professor Bateson's admhable book puts out in the clearest possible manner the whole story of Mendelism up to the present hour We have read this book with the greatest possible interest and recommend it to all our readers." — Lancet The Methods and Scope of Genetics By W. Bateson, M.A., F.R.S., V.M.H. "Professor Bateson is undoubtedly one of the most distinguished of living Biologists, so that in any case the inaugural lecture delivered by him would have been read with interest by all those students of biology who had not the opportunity of being present on that occasion Professor Bateson tells how Crown 8vo Mendel's law works out with the colours of certain flowers, moths, and canaries, Is 6d net and with colour-blindness in men and women. More than this, he describes the outlook over this field of research in a manner that will greatly interest and attract all intelligent people, for, as he rightly says, ' Mendel's clue has shown the way into a realm of nature which for surprising novelty and adventure is hardly to be excelled'." — Morning Post Darwin and Modern Science Essays in Commemoration of the centenary of the birth of Charles Darwin and of the fiftieth anniversary of the publication of The Origin of Species. Edited by A. C. Seward, Professor of Botany in the University of Cambridge. With 2 portraits and 3 plates. " This volume is a worthy tribute to the laboms of a great man. It is no ordinary panegyric, but an examination of the principles of Darwinism in the light of our present knowledge. In a (series of twenty-nine essays, written for the most part by leaders of scientific thought of our day, it shows how the Royal 8vo seed that Darwin sowed has stood the test of fifty years of criticism, and has 18s net fructified, prospered, and extended into all departments of biology and beyond. The Syndics of the University Press, and particularly the editor. Prof. Seward, deserve every congratulation on the production of a book which marks an era in the progress of science. In printing and binding the volume is in all respects worthy of the occasion." — Athenteum LONDON: CAMBRIDGE UNIVEBSITY PRESS: FETTER LANE 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 Laboratory, University College, Reading. LIBRARY NEW Y. BOTANt CIAKUA- [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 Floiuered 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 F^ with white or tinged white flowers. Green stemmed whites, when similarly crossed, yield an F^ with coloured flowers. Since the white or tinged white F^ plants give rise, on selling, 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 ^i, it is inferred that they lack the dominant white factor as well as one or more of the colour-factors. Journ. of Gen. i I 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 1908, 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 offspring. The F^ generations, obtained from the crosses between Snow King and the several plants enumerated above, were as follows : — Expt. No. Cross Descri|.tion of /•, plants 20-2 Snow King x Crimson King' 10 tinged white : 9 magenta 52 EeaJing Piukx Snow King' 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^ f:imily 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 pro])ortions. ' The same plant of Snow King was used in crosses 20-2 and 52. F. Keeble and C. Pbllew 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 F^ 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. Fo_. Observed 20 coloured : 8 white and flaked white. Calculated 21 ,, 7 ,, „ „ ij O ,. X ,, ,, ,, Experiment No. 52, two magenta plants selfed. F„. Observed .54 coloured : 19 white and flaked white. Calculated 55 ,, 18 ,, „ „ „ O „ 1 .> .. )) Experiment No. 2 Al, two magenta plants selfed. F^. Observed 77 coloured : 22 white and flaked white. Calculated 74 „ 25 „ „ „ ,> o „ 1 „ ,, „ 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 „ „ J-O ,, ,, „ o ,, Experiment No. 52, two tinged whites selfed. F.,. Observed 63 white and tinged white : 15 coloured. Calculated 63 ,, ,, „ 15 „ 13 „ „ „ 3 Experiment No. 200'1, a white plant selfed. F„. Observed 13 white : 9 coloured. Calculated 18 „ 4 13 „ 3 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- 1-3 4 White Primula sinensis mately 13 white (and tinged) : 3 coloured. A departure from the 13 : 3 ratio should be noted in Experiment 2001. 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 F^ from white and coloured F^, showed a considerable increase of flaking as compared with that observed in certain plants of Snow King. Among those flaked, white plants from coloured F^ 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 F^, is homozygous (TTTf) for the domi- nant white factor. That used in Experiment No. 2 A, which gives a magenta J^i, is homozygous {xvw) 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 ciu and plant 2a, Cw, Fi = Ccw = coloured. The plant of Snow King used in Experiments Nos. 202 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 = CcW'W, white or tinged white and Ccww, coloured. I I F,= 9CW,ScW,S Cw, 1 cw. F, = lCw,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. Kebble and C. Pellew 5 From Ivy leaf x Snow King an F^ 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 F-^ is obtained as the result of a cross between two white flowered varieties. The -fo generation from these crosses has not yet been obtained. Table of Floiver and Stem colour in ¥„. stem Flower colour -■^. . White No. of Expt. Dark and Pale plants not No. Reddish red Green Magenta Pink tinged pink flowered F2 family from (20-2-1 magenta F^ plants ] — Fi family from ting- j 20-2-2 ed white F^ plant ( — / f52-3 Fo families from magenta ^ Fi plants F2 families from magenta f 1 plants F^ families from 2 magenta Fi plants 52-5 52-4 52-6 2 .a 2a5 Fo family from (200-2 white Fi plant ( — 23 — — 5 28 — — 1.5 23 — — 9 — 14 — 3 — 3 — B — 10 27 — — 7 32 — — — 14 15 — — 21 39 ■ 17 — — — 5 — 21 17 1 6 — _ — _ 5 — 30 2 28 8 12 14 2 4 4 1 9 3 6 10 3 Cross •2 Z Z ) s°°" ^'°s 17 — 2 f Crimson King 12 — — ) 6 — 1 — 2 8 — 1 \ — 1 Heading Pink X Snow King 1 / 16 — / 2A X Snow King — [Pink Stellatax — f Snow King THE INHERITANCE OF COLOUR AND OTHER CHARACTERS IN THE POTATO. By REDOLIFFE 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 wh(_)se 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 numbers 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 iemale 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 7o 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 offer 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 difficult to define that except in one instance, which will be considered later in detail, I have not made out anything sufliciently 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 " Congo," 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 etuherosum 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 {Phytopthora 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 (8), and known as Lindsay's etuherosum, 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 Coloiir 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 ray 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. I/i 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. etuberosum. For observations on pollen. B. Varieties in list A. Ringleader. Supreme. Dutch Cornwall. Peckover. The Dean. Purple Eyes. Up-to-Date. Duke of York. - species. S. commersonii 8. tuberosum S. verrucosum S. maglia Several other varieties were used in class A without success. Sterility of Anthers. Contabescence. 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. Gaertuer 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 (1). 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 '2() of the F^ 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 F^ 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 F'^, from the pollen bearing i^', 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 with 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 G, 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 oi Solanum are discussed elsewhere (9). Heredity 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 " Readinsf 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 thaa " 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 ii^- 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 different shapes are suflScient 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 ' In 1910 out of 71 F- seedlings on Aug. 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 1^ 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 Batio (1) (2) (3) 2, 3 2, 12/16 4/16 1, 1, 1, 0/16 7/16 7/16 1, 1, 1, 3/16 3/16 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, 1, 1, 4/16 4/16 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, 1, 1, 6/16 9/16 8/16 = 49 : 30 ; = 48 : 32 : = 49 : 31 : 22 :25 ;24 "Sir John Llewellyn' (1) (2) (3) 3 2, 2, 1.3/16 11/16 1, 1, 1, 10/16 10/16 13/16 1, 1, 1, 2/16 4/16 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 Busset," see Plate XXI. Length Breadth Depth Ratio (1) 2, 6/16 1, 15/16 1, 7/16 = 38 : 31 ; : 23 (2) 1, 15/lG 1, 12/16 1, 3/16 = 31 :28 : 19 (3) 1, 15/16 1, 13/16 1, 8/16 = 31 :29 :24 "FlourbaU,'^ ' 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 iu " 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 (.4). 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 resembling "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 tirmer basis. Journ. of Gen. i • 2 18 Colour and other Characters in the Potato On Plate V, Nos. 67, S7, 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 vvere grown on this ground. Efforts are being made this year (1910) to obtain selfed seed from this plant. On Plate VI a further illustration {G 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 G^ 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 ^ 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." E. N. Salaman 19 bred it, this type of " round " potato assuming large proportions ; fevv 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 (?", 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 Batio 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 Ratio 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 A 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 3—2 20 Colour and 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 190G, 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 i)^ 1908, a long pyriform tuber. D'^, 1909, cylindrical tubers tending to kidney shape. D^, 1908, oval or blunt kidney with a sister tuber nearer circular. ^M909 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 190S this same D was crossed by A, and on Plate VIII the family is shown, or rather two families, because two D plants (Z)' and -D") both grown from tubers of the original D of 1907 were fertilized by pollen of ^. 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 heterozj'gous in that character — a fact which was already strongly indicated befoi-e. 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 A), and 1, 4, 11 and 26 of (B^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 i/', 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, 2.5, 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 //' 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 jjebble-tubered plant H^" was crossed by the same " round " A as lias 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 inade between a kidney potato, " Record " on the one hand, and the pebble-shaped " Flourball " on the other. The offspring 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 the pebble-shaped parent are heterozygous as regards shape, i.e. " length," and amougst the dominants some are excellent kidneys, others pebbles. No. 3 is interesting because it shows on one and the same root a cylindrical fiotato 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 " Flomball " 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 argument 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 Z>'^', both derived from the selfing of a kidney-shaped F'- plant. The first family, Z''^', 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, afifords 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 heterozj'gous 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 XXIIl, 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 criticall}' 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. Eftbrts are being made to self the oval tubered plants this season. ' I was presented with several hundred of tlie seed of both these stocks hy the Manager of the Cambridge University Farm. R. N. Salaman 25 In 1908 a cross was effected between a pebble-shaped tuber (71/°, 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 i^' 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 K^, both elongated and more or less kidney-shaped. The following proportion of "rounds" and " longs " occurred : Eounds Longs Family 7C6 65 210 FamHy A'3 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 ia 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 "0" 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 individual, 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 D, 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 iu 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 b}' 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 tlie individual 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 ^"'", 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 (i'). 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, X'"', 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 : "Flourball" seedling selfed A D^ X A W X A H'O X A K» Total ... 91 to 265 This is almost exactly 1 : 3. laUow Deep 14 29 21 77 16 33 9 39 9 36 22 51 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 K^^-\ 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" K^'-^K 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 Mendelian lines. The Colour 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 do), 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 Wlieldale, who has very kindly examined many of my 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 800 white-tubered seedlings, and one of these selfed and produced fifty seedlings, all of which were white- tubered. A white-tubered variety (Z)) 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 Composition 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 „ GO „ Oct. 1909 24 „ 19 „ Aug. 13, 1910' 54 „ 44 „ Total 420 „ : 340 „ Ratio 9 „ : 709,, 1 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 iJZ> = Reds ^ Rd = Whites 3 Dr = Whites 1 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'. 1 This year, 1910, a large number of crosses between various 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 rvDd. 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 " Floui-ball " 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 r7-dd 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 selfing it gives three red and one white. The results were different in each case — H^ X A gave 29 red 19 white Jfi»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 .4's composition are equality, if the white is rrDD 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, 3I\ 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 — (AP) RrDd x (B) rrDD. M^ 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-tubered. Journ. of Gen. i 3 34 Colour and oilier 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 i^' 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 Z« did well, the K^ family fared badly in the wet summer of 1909. K^ Family. K\ Plate XXIX, is a black (i.e. deep purple) potato. Several seedballs were collected from the plants, and one coming from a plant K^'-^^ was planted in its eutii-ety. Originally 301, there wei'e harvested but 160 seedlings. The tubers of the F- 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 K^ 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. y » » " )> >> " I) )) " )) » 3 ,1 „ 3 „ ,1 The numbers for the K"^ family are : — PR = white (tinged). RD = red. PD = white. R = white. D = white. P = white. prd = white. Purple Red White Calculated numbers 73 24 75 Actual Numbers 77 29 54 3-3 36 Colour and other Characters m the Potato The results' are sufficiently close to give one some confidence that the phenomena are correctly represented by the assumptiou of the factors PR and I) 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, Rr, Dd. Having considered K*^ and 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 necesisary to bring it out in the tuber, (2) that redne.ss is dependent on a separate factor R, (•'?) 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 depemlent 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. ' 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 ETVBEROSUM. 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. Aikman Paton's supply of etuherosum 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 etuherosum ; 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 Suttoncs) that S. etuberosum is the parent plant of our domestic varieties has been considered by me in an earlier paperte). Wittmackda) has also discussed this question, and though I do not share his opinion that etuberostim is an ordinary S. tuberosum variety I, nevertheless, agree with him 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\ 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 circulai-. The size is variable. When the tubers were first cultivated here they were not more than \\ 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 my garden had ceased flowering and when some F^ " Congo " crosses, which were close by, had already formed good-sized berries. Immunity to Disease. (Phi/tophthora 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 39 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. It is a most striking fact that although the parent etuberosuni 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 etuberosuni 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 enemj'. 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 and other Characters in the Potato standing out in the midst 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 b. Distribution of colour in a on under surface. pattern on upper surface. We then get — 6 : Bh. Aa. = Parent type. Bb. AA. = „ „ with deeper-coloured tongue. AA. BB. = „ „ but deeper colour. A. b. = White with coloured tongue. a. B. = White. 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. Sal A MAN 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. TIte Eyes. The eye of the parent tuber is " shallow " and very insignificant. 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. 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. etuberosum and niaglia. 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 etuherosimi is dominant to the purple of the recognized species maglia. The relation of S. ettiherosum to otJier jmtatoes. 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 maglia 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 8. 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 chromogen. 6. S. etuherosum 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 Phytojihthora infestans. 8. That immunity to the attacks of Phytophthora infestans 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 "Flourball" selfed. "Rounds" are — Nos. 40, 89, 92, 118, 132, 138, 155, 156, 162, 185. PLATE II. 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 V. can be seen the sister tubers of the more abnormally shaped "round" tubers. PLATE III. A family continued. 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 each root crop. PLATE V. Same as Plate IV. No. 100 is probably a stray plant and not a member of this family. 44 Colour and other Characters in the Potato PLATE VI. rhe G family, consisting of six individuals with their root crops are shown. G', G^ and G^ are more or less typically "round." PLATE VII. The D family— Top row— Three tubers of parent plant. D' and D-, 1908, are the seedlings raised in 1908 from D (l',)07) selfed. D' and D-, 1909, are seedlings raised in 1909 from D (1907) selfed. PLATE VIII. Seedlings of the family raised from cross D x A. The family consists of half "rounds" and half "non-rounds." The "rounds" are Nos. 3, 4, 5, 8, 13, 11, 1-5, 16, 18, 19, and 3, 6, 7, 10, 12, 14, 18, 19, 20, 21, 22, 28. PLATE IX. Seedlings of the family raised from the cross "Record" x "FlourbaU." "Record" is a kidney, "FlourbaU " a pebble-shaped potato (neither parents shown). One quarter of the seedlings are "rounds," viz., Nos. 12, 13, 18, 21, 24, 2.5, 26, 30. PLATE X. Seedlings of the family raised from the cross i/' (f of family H, Plate IX) x A. Half the seedUngs 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 H'° (F' 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 "Reading Russet." 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^ {F' of "Congo" x "FlourbaU" seedling, s?e Plate XXIX). This family for convenience has been divided into sub-families 7i6^, A'6^, etc., according to the particular seedball from which the seedlings 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" y. "FlourbaU" seedling, see Plate XXI.X) the "rounds" are rather deficient, viz. : 13 to 60; the eyes are deep to shallow, 3 : 1. K. N. Salaman 4'5 PLATE XXI. The family L, raised from the cross of "Red Fir Apple" x "Reading Russet." In the F^, No. L', a Iddney has been omitted. PLATES XXII, XXIIl. 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 round-tubered individuals have been omitted. In Plate XXIII the " rounds" are Nos. 6, 10, 17, 19, 22, 24, 29, 30, 33, 40, 47, 52, 54, 61. PLATE XXIV. The family raised by crossing IP (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, Bed 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 Ponnett. Rep. Evol. Comm. Roy. Soc. 1904, Vol. II. p. 91. 2. BiPFEN. Joxirn. Agric. Sc. 1907, Vol. il. p. 109. 3. Darwin. Animals and Plants, 1890, Vol. ii. p. 149. 4. East. Rep. Connecticut Agric. E.rper. St. 1907—8, p. 429. 5. . " Transmission of Variations in Asexual Reproduction." Rep. Con- 7>ecticut Agric. Exper. St. 1909—10, p. 120. 6. Gaertner. Verswche und Beohachtungen uher Befnichtung-organe, Stuttgart, 1844, 849, S. 117. 7. Paton. J. R. Hort. Soc. Vol. xxxv. p. 33. 8. Sdtton. Linn. Soc. J. Bot. Vol. xsxviii. 9. Salaman. Linn. Soc. J. Bot. 1910, Vol. xxxix. p. 301. 10. ViLMORiN. Catalogue M^thodiqwe et Synonymique de Pommes de Terre, Paris, 1902. 11. Wittmack. Bericht. d. Deutscht. Bot. Ges. 1909, Bd. xxvii. S. 28. 12. . 2ei<./. Wss. iawrfjOTrt. 1909, Bd. XXXVIII. erganz. Bd. V. JOURNAL OF GENETICS, VOL. \. NO. 1 PLATE JOURNAL OF GENETICS, VOL I. NO. 1 PLATE II • I'l'^s r*' i'^^' D"- i^,o. JOURNAL OF GENETICS, VOL. \. NO. 1 PLATE VIM JOURNAL OF GENETICS, VOL. L NO. 1 PLATE IX JOURNAL OF GENETICS, VOL. \. NO. 1 PLATE X '^^ © JOURNAL OF GENETICS, VOL. L NO. 1 PLATE XI JOURNAL OF GENETICS, VOL, 1. NO. 1 PLATE XII CO CM JOURNAL OF GENETICS, VOL. \. NO. 1 PLATE XIII • ^!^ 0 ^^ ■4- t^ 1^*^ i^L ■liwS ~-3 I'i "^^ i o ■^ # i 00 ■"^ •3 1^ -^ ^ ■^^ ^.i^ ^ i»^ ^n JOURNAL OF GENETICS, VOL. \. NO. 1 PLATE XIV ^^^ '(S ^'^'iWf ■? ^Cn N <4 JOURNAL OF GENETICS, VOL. L NO. 1 PLATE XV nf C o u « ' f '^# ^^^ ^^% H In "%■ ¥ 9 JOURNAL OF GENETICS, VOL. \. NO. 1 PLATE XVI .^*|f<». 4- V £^ <4 JOURNAL OF GENETICS, VOL. L NO. 1 PLATE XVII ^fr ■i p ip ^^ ^ ^p 4 00 ■^-l ■^■^^1^ *"":>**" \/|-:--^ JOURNAL OF GENETICS, VOL. I. NO. 1 PLATE XVIII m m fc # ? 9 « -§P^ 1^ " ^ ■^W| '^W f^ m JOURNAL OF GENETICS, VOL. I. NO. 1 PLATE XIX K^' ^ J -MsS X -J 3 i J i^ 15 )S 1 74 «9 MO s' ^ '^ ^ '^ '^ #> 9 « /3 l(^ 23 31 33 35 4S J5 ,^^^v' 7i IJ /S 2.° 22- JOURNAL OF GENETICS, VOL. L NO. 1 PLATE XX pwr,: O" ^^ ^ t -^^sn?!T^-^:'^rr!ifmny:>!!^W^fKm?rW!^^^^:^^^^s^^^^^l o n3 •*4 m ^ ) >o N O JOURNAL OF GENETICS, VOL. L NO. 1 PLATE XXI <=^i-^^-yr\_j' Z_ ^ -^''''--C'-^T.^L-Le. . r?. ex, *T-«/TT_^-3 '\-«- CO o O _l plants of Heights between 1| and 4 feet. Date Length B=Plants of of reckoned Label Flowering Height Stem Internode Foliage as Dwarf 5 X S/.-./lO June 2i]d U feet Thin 3 inches Very small D 3 X 5/2/60 „ 9th li „ Thin 2j „ Bountiful type D 3 X 5/2/43 „ 2nd 0 Thin 3 „ 0 ,, Small ( = Bount.) D 5 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 n „ Thick 5 „ ? Intermed. 5 X 3/6/6 „ 10th n ., ? Tliin 2 ,, ? D 3 X 5/2/20 „ 2nd 2J~3 ft et Thin 3 ,, Bountiful D 3 X 5/2/34 „ 21st 24—3 , ? Thin 4 ») ? Autocrat D 5 X 3/2/14 „ 16th 24-3 , •> 9 ? Bountiful D 5x3/5/12 „ 16th 3 ? Thin 3 I» Intermed. D 5 x 3/5/41 „ 21st 3 ?Thin 4 »» Diseased 5 X 3/1/5 „ 21st 3—34 , ? Thick 3 ,, ? 5 X 3/3/5 „ 30th 3—34 , ? Thick 3- -34 inches Small 5 X 3/1/10 „ 16th 34 Thick 34 t) Small ( = Bount. ) 3 X 5/2/8 „ 16th 34—4 , Tliick 3 J) ? Autocrat 3 X 5/2/52 „ 2nd 34—4 , ? Thick 4 „ Autocrat 5 X 3/4/29 „ 21st 34-4 , ? Thick 4 >. ? Autocrat REFERENCES CITED IN TEKT. 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. Mendel's 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 mid late Fellow, Newnham 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. ' Of the many beliefs still held regarding the occurrence of doubles 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 doubles 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 constitution of the seed, but 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, II. p. 29, 1905 ; III. p. 44, 1906 ; iv. p. 36, 1908.) 58 Dotible Petunias The material used in these experiments included the following forms : — (1) P. violacea (phoenicia). 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. hybrida grandiflora. Garden hybrids, (a) Flowers magenta or magenta and white, variously striped or blotched. Corolla plain edged. Pollen blue. (6) Var. fimbriata. 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 au 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 gyncecium 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 effect. 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 internode. 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 imjjortant 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 he 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 andrcecium 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 {Fi) 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 violacea and hybrida rarely set seed ; even wlien artificially self-fertilised many pollinations give no result. On the other hand nyctaginiftora, under the same conditions will often set seed, and does so readily when artificially fertilised with its own pollen. 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 sufficient 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 consideration. 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 3s. : Id., 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 : — Reference number of family Number of offspring Single Double Reference number of family Number of offspring Single Double Reference number of family Number of offspring Single Double 3 19 i 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 fi 10 1) 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 of3s.: Id. cal- culated to the nearest whole number would give 12.5 42 Where a ratio of 9 s.:7d. cal- culated to the nearest whole number would give 396 308 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 pi'o- portion of 2 single : 1 double. As yet it is not clear whether the occurrence 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 manife.station 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 x). 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 j'ields 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. violacea, P. nyctaginiflora, P. hybrida grandiflora, and Countess of Ellesmere, whether self-fertilised or crossed with each other, yield only singles. doubleness 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 lohich 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 iu 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 with the conclusions formed in the case of Stocks. .5. The male organs are functional in doubles, but the gyncecium is more or less deformed, and when fertilised yields no seed, hence the d(Aible 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 cro.ssed 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. mixlure of singles and doubles obtained in F^, in the case of the type forms, from the cross single 9 x double $ . Form of union Single Beed-jiarent Double pollen-parent Reference number of family Number of Offsprmg Single Double r n 1 82 67 ,, „ 2 54 35 )> „ 3 19 4 N H 4 28 21 ,, ,, 5 13 12 5) 1) 6 7 8 10 14 4 9 4 2 9 1 4 )» - 10 1 2 H H 11 18 6 „ ,, 12 4 3 „ ,, 13 5 3 „ „ 14 12 2 " - 15 16 6 4 4 »> )» 17 24 22 „ „ 18 8 2 CE H 19 15 2 >» >j 20 11 1 21 22 23 3 9 7 1 6 1 ,, „ 24 18 2 25 23 11 C£ H (var. fimbriata) 26 27 17 18 13 13 ^^ t* 28 13 11 V=violacea. N=nyctaginiflora. C£ = Countess of Ellesmere. H = hiibrida gran- diflora. Journ. of Gen. i 66 Do^ible Petunias TABLE II. Showing a similar mixture of singles and doubles resulting from the imion si^igle^ X double $, tvhere one or both of the individuals employed was descended from a previous cross. Form of union Single seed-parent Double pollen-parent (single H X N) X double H (single H \ N)x double H (single H x N) x Self (N X double H] (single H X N) double // double 7/ (N^x double H) double H Reference number of family Number of Offspring Single Double 29 13 8 30 6 4 31 4 4 32 24 21 33 4 4 34 6 3 85 9 11 36 53 35 37 34 17 38 16 14 39 17 7 40 14 9 41 12 3 The total number of individuals belonging to the type forms used as seed-parents in axperiments 1 — 41 was as follows : 6 plants of Violacea 7 ,, „ Nyctaginifiora 5 ,, ,, Countess of Ellesmere 5 ,, „ Hybrida grandifiora Total 23 E. R. Saunders 67 TABLE III. Shoiving that doubles do not occur when singles belonging to the various type forms are self-fertilised or intercrossed. Fonn of union Reference number of family Number of Offspring Single seed-parent Single pollen -parent Single Doul V self 42 13 — 11 n 43 6 — 11 i» 44 6 — 1» „ 45 3 — N self 46 47 — )» ,^ 47 2 — H self 48 18 — 1» »' 49 3 — CE self 50 9 - ») >l 51 4 — »» n 52 4 - V w 53 14 — »1 ») 54 6 - N F 55 60 - jj }) 56 49 - )» ») 57 36 - 1* ») 58 35 — »» J, 39 23 — H P 60 many (total not recorded) — H N- 61 143 — If )l 62 41 - »» ») 63 36 l» )» 64 22 „ 65 many (total not recorded) — tt ,, 66 H ») '» (W X F) (iV X F) 67 10 - (N X K) self 68 16 — If )1 69 10 - »» M 70 4 - fl I* 71 3 — »f It 72 2 — II »» 73 2 — l» )) 71 2 — single HxN) self 75 33 — »» jj 76 24 — 68 Double Petunias TABLE IV. Showing that doubles do not occur wlieii the singles derived from a cross luith a double are either self-fertilised, or crossed with other singles similarly derived. Form of union Single single pollen -parent Reference Dumber of family Number of offspring seed-parent Single Double (single H x double //) self 77 73 — „ ji 78 6* — ,, >» 79 8 — ,, >f 80 5 — ,, >i 81 3 — ») it 82 3 — ») tf 83 2 — (N X double H) self 84 64 „ J* 85 14 — )» J1 86 87 13 3 — ,, It 88 1 (single HxN)x double H self 89 90 8 2 — (single H X double H) (single 1 H X doul ble //) 91 92 93 33 14 11 single II X N) X double H (single H " X JV) X tlo uble // 94 3 single H xN) X double H N X double (Nxi/ = adouble) 95 9 „ ») 9C 7 * A double which occurred in this batch was evidently a rogue as the flower had some of the characters of nyctaginiflora. 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. Fig. 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. 7 Fig. 4- Fig. 5- THE EFFECTS OF ONE-SIDED OVAKIOTOMY ON THE SEX OF THE OFFSPRING. By L. DONCASTER, Fellow of Xiiig'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- ' Experiments described at tlie Physiological Society, May 1908. = Biol. Btdletin, xvi. p. 27, 1909. ^ The Causation of Sex, Loudon, 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 born 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 froin 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 I'est 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 off 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 Physiology, vol. xxxvi. p. 431. 72 Ooariotomy and Sex removed tbe 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 Rumley 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. Marshal] ; the disisections by L. Doncaster.] K THE SPECTATOR A WEEKLY REVIEW OF POLITICS, LITERATURE, THEOLOGY, AND ART. ESTABLISHED 1828. EVERY SATURDAY, Price 6d. ; by Post, 6id. Circulates throughout the educated classes in the United Kinqdom, the Empire, and America. Scale of Charges for Advertisements. Outside Page (when Available), Fourteen Guineas. £. s. d Page 12 12 0 Half -page (Column) 6 6 0 Quarter-page (HaLf-Column) ... 3 3 0 £. s. d. Narrow Column (Third of Page) .. . 4 4 0 Half Narrow Column 2 2 0 Quarter Narrow Column 1 1 0 Column, two-thirds width of page, £8. 8s. 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" We have to thank Mr Darwin for preserving for us with filial care a frag- Demy 8vo ment of real value To the student of Darwinian hterature no occupation could 7s 6d net be more pleasurable than to make a detailed comparison between these first fruits of a master mind and his later work." — Atheiueum LONDON : CAIIBELDGE UNIVEESITY PRESS : FETTER LANE CONTENTS All Rights reserved PAGE Frederick Keeble and Miss C. Pellew. White Flowered Varieties of Primula sinensis 1 Redcliffe N. Salaman. The Inheritance of Colour and other Characters in the Potato. (Plates I — XXIX, one coloured, and 2 Text-Figures) 7 Frederick 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. Petunia. (Seven Figures) ..... 57 L. DoNCASTER and F. H. A. Marshall. The Effects of one-sided Ovariotomy on the Sex of the Offspring 70 The Journal of Genetics is a periodical for the publication of records of original research in Heredity, Variation and allied subjects. The Journal will also, from time to time, contain articles summarising the existing state of knowledge in the various branches of Genetics, but reviews and abstracts of work published elsewhere will not, as a rule, be inckided. Adequate illustration will be provided, and, where the subject matter demands it, free use will be made of coloured plates. The Journal will be issued in parts as material accumulates, and a volume, appearing, so far as possible, annually, will consist of four such parts. Papers for publication may be sent either to Dr Bateson, Manor House, Merton Park, Surrey, or to Professor PunNett, Gonville and Caius College, Cambridge. Other communications should be addressed to the University Press, Cambridge. 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"In August 1883, Krakatau and two neighbouring islands in the Strait PI g between Sumatra and Java were absolutely desolated by a volcanic eruption. 9 mans 'The islands,' writes Dr Ernst, 'which were fomierly green, assumed the , g" appearance of a desert of the most desolate type.' Now they are green again, illustrations '^o^®'^^'^ with a vegetation so luxuriant that in places it is necessary to cut 4s net ^ ^'^y through it. Here we have the story of how this result was brought about. Ocean currents, winds, and birds were the main factors ; and it is highly interesting to see what they and other agencies produced." — Spectator A Naturalist's Calendar, kept at Swaffham Bulbeck, Cambridgeshire By Leonard Blomefield (formerly Jenyus). Edited by Francis Darwin, Fellow of Christ's College. " The relatively early date (previous to 1846) at which the record was kept renders it extremely valuable for comparison with observations of a similar nature made at the present day The well-known scrupulous accuracy of its Crown 8vo "ompi'^'' renders his calendar of nature a record of exceptional value and 2s 6d net 'iterest, belonging to a period when such compilations were rare. There is, therefore, every justification for its re-publicatiou in the present convenient form, and its appearance at a morphological centre like Cambridge may certainly be regarded as a good augury for the future of natural history studies." — Nature LONDON: CAMBRIDGE UNIVERSITY PRESS: FETTER LANE 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. ivoiNvxon NaOA M3M Aavaan CONTENTS. Page Intkoduciion 74 Heteeosiylism "^^ Abnormal cases 84 Leaf-Shape 86 Palmate and Fern-leaf . 87 Ivy-leaf 87 Habit 88 Double Flowees 89 Inheritance of ordinary double 91 Chaeactees of the "Eye" of the Flowee .... 91 Large yellow eye x small eye ...... 92 White eye x small yellow eye 94 White eye x large yellow eye 94 CoLOTJK 94 A. Stem-Coloues 9-5 Inheritance of Stem-colours 96 Partial Suppression of Colour 100 B. Flowee-Coloues 101 Inheritance of Flower-colours 103 Partial Suppression of Colour 10.5 Inhibition 10.5 Experimental results : (1) Pale colours . . . 108 (2) Full colours . . .109 (3) Inhibition . . .115 (4) Flakes .... 121 Gametic Codpling and Repulsion 124 Description of Plates 130 Journ. of Gen. i 74 Experiments ivith Primula sinensis Introduction. The experiments, of which the present jsaper is the outcome, were begun in 1903 by Mr Bateson and the present writer jointl}', 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. Wheklale, of Newnliam 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 eailier 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 o£ Genetics since the rediscovery of Mendel's papers,'' Prog. Itei. Bot., Vol. i. 1907, pp. 373, 383 ; MendeVs Principles of Heredity, Camb. Univ. Press, 1909. Gregory: " The inherit- ance of certain characters in Primula sinensis," Brit. Assoc. Bep., Leicester, 1907, pp. 691—693. •* Bateson and Gregory, I.e. R. P. Gregory 75 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 factors. I have had no decisive case of the production of an F^ with coloured flowers from the mating of two albinos, but Keeble and Pellew^ record a coloured F-^ from the mating of the red-stemmed "Snow King" with the gi'een-stemmed "Snowdrift."' Similarly as regards the stem-colours, I have no example of the production of a coloured F^ 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. 9(5). 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 fully 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 cros.sed with types having fully coloured flowers and stems, the F^ 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 ' Jouin. of Genetics, Vol. i. 1910, p. 4. 6-2 7(j Ex:periments ivith Primula sinensis horticulture as "Sirdar" (Plate XXX, fig. 4; Plate XXXI, figs. 44, 45), (3) pale colours on faintly coloured or green stem.s. 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, aff'ecting 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 ceutral 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 knowu as " Duchess" (Plate XXXI, figs. 27, 28), ill 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 F2 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 must be carefully distinguished from " Sirdars." 78 Experiments loith 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 w-1 : 1 : 1 : // - 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 apj3eared from time to timel It is interesting to notice that the earliest illustrations'* of the species represent short-styled plants of the ordinary habit (not stellatu) with palmate leaves, light red stems, and light magenta flowers — all dominant characters. Hetercstylism. 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 typo, the short style being dominanf^. 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. Erol. Comiii. Roy. Soc. iv. 1908, p. 3. Lower series would be given by the general expression where .r 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 .v be taken as any number less than n. The F^ series would then be given by the expression 3/1= - X (2n - .t) : x {2n -x) -.x (2n - :r) : (n - .t)^. - 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. 2C9. * Bot. Reg. 539, May 1, 1821, under the name P. praenitens, and Lindley's Collectanea Botanica, 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. ^ Bateson and Gregory, Roy. Soc. Proc. B, Vol. 70, 1905, pp. 581—586. Number of short-styled plants used Short- styled Long- styled 8 252 0 5 290 0 4 247 0 R. P. Gregory 79 have been used as parents : their offspring are shown in the following table : Cross Pure short-styled X Self Pure short-styled ? x Long- sty led s Long-styled? x Pure short-styled b ^ g> a. U5 eo -H o av GO c^ 9 X. i-H o •-1 M ^ tfL ^-1 X - Ot >o 1 o f lO CI "^ ^ ^ C>1 cc M X '-' I-H 9> tic '-H n c^ o ^-^ 5 « oj ^ CO o . ? V S <-H I-H 1 Zlt; ~ K ° ( t -^ ■^ >— I =. 1 ^ '^ "^ •^ *T3 'O =>! ^ bc ^s. "?. g o o Oi •tt 3 "^ '^ "9 te -ri ^-^ n CO 3 !^; X - o+ 1 *3 *^ O -M -H cc -H 5 j= CI »c -* 1c :/: (N o *j f^ O "5 J=. ^i cn S X 2 oc CI o 1 5* S I— 1 c^ . ^-5 r g '-I >*-( *^ 1 ;S ^ c^ ^ »> O 60 1^ "i? c c: o C5 X o .o !>. CT •ti X I-:] CM CO ■o ■c 'b o X =>5 t-r 0^ o O CO c: b- X. "^ CO O -« iX ^ t* 00 *^ •- * Ol »o (N 1 C*J CO 1 0 ^ 2 ■ 3 ■ cs p s ^ *« Cf. Masters, Vegetable Teratology, 1809, p. 449. - Cf. Masters, loc. cit. p. 315. ■' lu both kinds of doubles the morphology of the reversed segments i.s obscure, and it is not clear that these structures are of the same nature in the two case.s. R. P. Gregory 91 a group of foliar carpels', surrounding an axis on which are borne naked ovules. Proliferation of the axis is frequent. Hitherto I have not been able to raise any seed from these plants, but some cuttings, taken late in the season and only coming into flower in May last, have developed what appear to be normal ovaries, and it is hoped that experiments will be possible in the future. Inheritance of ordinary double. The ordinary form of doubleness is a recessive character^ When crossed with singles, it gives a single F^, which on self-fertilization gives singles and doubles in the proportion of 3 : 1. The actual numbers obtained in 15 families are 762 singles, 284 doubles {expectation: 78J^5 : 261-5)\ The double race used in all the foregoing experiments had its origin in a white single obtained from a nurseryman in 1903. The plant proved to be heterozygous, throwing singles and doubles. Every degree of doubleness was exhibited among the various individuals of this race, and the phenomenon was repeated in some of our F^s. On the other hand, certain plants, derived from the same strain, produced nothing but full doubles, and in the Fjs from their crosses with singles, the distinction between the singles and the doubles was quite sharp, all the latter being fuUy double. Characters of the "Eye" of the Flower. In the majority of horticultural strains the yellow or yellowish-green " eye " of the flower occupies a small and well-defined area round the mouth of the corolla tube. Besides this type of eye there exist two other kinds; in the first, the eye occupies a much larger area, the yellow colour extending well over the bases of the corolla lobes ("Primrose Queen," Plate XXX, fig. 12 and Plate XXXII, figs. 62 and 63, No. 37/9) ; the second type is represented by the white-flowered race " Queen Alexandra," in which the eye is not distinguished from the rest of the corolla, the whole flower being uniformly white (Plate XXX, fig. 11 and Plate XXXII, fig. 62, No. 34/9). Eye-characters are inherited quite independently of any of the other characters which I have studied, but they affect certain other characters with which they may occur in combination in the same 1 Cf. Masters, loc. cit. pp. 262, 297. '•^ Bateson, Mendel's Principles of Heredity, Camb. Univ. Press, 1910, p. 199. 3 The discrepancy is almost entirely due to one F^ family which consisted of 66 singles and 45 doubles. Five other F2S from the same parents however gave 188 singles, 61 doubles. 7—2 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 style, 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, MeiideVs Principles of Heredity, Camb. Univ. Press, 1910, Plate VI. figs. 19, 21. ' Bateson and Gregory, loc. 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, is selfed, and an excess when the Fj is crossed with the long-styled. This would, of course, have a disturbing effect in oases such as that under notice. R. P. Gregory 93 <3 8 '^ ■« -^ ^ >. ^' S 00 0) 5a& X CO Sill I I I I I IS. 2 s^^ so a gffg. ess. oas? 2 §>■ 1 3^ i I I I I I I I I I I I I I I I C5 C5 a: 03 * S "^ S I ^iS S f-H r>. 0) > 'So o be a; > vz; 94 Experiments with Primula sinensis continued, and the totals for the last three years are 972 small-eyed, 326 large-eyed {expectation : 973-5 : SH^-'S). 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 con-esponding with the median line of each petal (Plate XXXII, fig. 62, No. 3.5/9)'. Three F„ families have been raised from the self-fertilized hybrid, and have given 1S2 white eye and heterozygous, 67 small yellow eye {expectation : 186-75 : 63-25). (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 Fr, 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 re.stricted to the • The contrast between the yellow rays and the white i,'rouud is somewhat intensified in photographic reproduction. R. P. GrbcxORy 95 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-Coloues. 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 differences in the tint in different 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.2, is difficult, 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 recessive white on red stem (Journ. Genetics, 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 be 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 i^^'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 tlie 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 ' 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^s 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, p. 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 = ^8'9Ji, : 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 tcith 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 CQ gives faint colour in tlie collar. The constitution of the hybrid would then be 6'c 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 FJs have as yet been obtained, are its crosses with " Snowdrift " and with full-coloui-ed forms. The F2 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 with the expectation very fairly closely, there is a great dearth of light- stemmed offspring in the F.,'s from the crosses between "Ivy-leal" 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 sfwiving the results of experiments in regard to stem-colour. I. Red stem (C RF Q) x Green stem (c rF q) i<', selfed 1 family Ked 51 Light 33 Colour in petioles 13 Green 25 Red 49 38 Totals ... 100 71 Expectation (9 : 7) 96-2 74-S ' II. 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 (C RF Q) x Faint colour (C rF Q) Fi selfed 11 families Red stem 384 Faint colour 120 Expectation (3 : 1) 378-0 12(;-0 I Strictly speaking this combination gives the parti-coloured type " Sirdar," but as no " Sirdars " appear in this F2 we are not here concerned with the distribution of the full colour. R. P. Gregory "99 IV. Red stem (C RF) x Green stem, no colour seen {C rF) Fi selfed 11 families Red stem 395 No colour seen 128 Expectation (3:1) 39S-25 130-7S F, X green stem 6 families 99 104 Expectation {1 : 1) 101-5 101-5 V. Crosses 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 these plants, the *' Sirdars " cannot be distinguished from the other light-stemmed types. In the FoS 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 items. A. 1905 crosses. F. selfed 4 families Red stem 70 Light stem (including )^ " Sndar ) ) Expectation [9 : 7} 69-2 53-8 B. Dominant white x "Snowdrift." fi selfed 8 families Red stem 440 „ 337 Expectation (9 : 7) 437-1 339-9 C. Colom'ed, red stem x " Snowdrift." Ji-i selfed 11 families Red stem 471 "Sirdar" 185 ^amt colour) ,^^^ and green ( Expectation {9 : 3 : 4) 483-1 160-69 214-25 VI. Red stem x " h'y-leaf." Red stem Light stem Palmate Ivy Palmate Ix-y F, selfed 7 families 626 197 177 44 Expectation ... 587-25 195-75 195-75 65-25 823 221 783-0 261-0 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 sufiices to restore those characters which differentiate " 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 sharpl}' divided categories are found in families raised from the cross of a deep red stem with the F^ of (" Snowdrift " x deep red stem). The numbers obtained in these crosses are : Light Intense 9 families ... 198 202 + 3 doubtful (occurred in cue 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 steni-eolour 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 Fj has a faint trace of colour in the young petioles; the ^2 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 may 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 pallifying 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 Experiments ivith Primula sinensis I have not yet undertaken any systematic experiments with the blue-flowered strains of Primula sinensis. Blues 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 expe7-iments on colour. Recessive White. " Snowdbift." (Tlate XXX, figs. 7, 10.) Fern-leaf, green stem, white, green stigma. Pale colours. " Reading Pink." (Plate XXX, fig. 13.) Palmate, green stem, pale-pink, green stigma. Full colours. Saluon Pink. Palmate, purplish-red stem (light), salmon-pink, gieen stigma, short style. Rosy Magent.\. (Plate XXX, figs. 19, 20.) Palmate, purplish-red stem (light), magenta (rosier than Fi type, light), green stigma. "Crimson King." (Plate XXX, fig. 9.) Palmate, purplieh-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). "Ivt-Leaf." (Plate XXX, fig. 5, Plate XXXII, fig. 60.) Palmate, uon-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 nou-crenate character o£ 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 Mendel's PriM'iples of Heredity, Camb. Univ. Press, 1909, p. 135. ^ 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 i-'^-forms with green stigmas these expansions are green, in those with red stigmas they are coloured. Outline of the inhentance of flower -colour. When a plant with fully coloured stems and flowers is crossed with the albino " Snowdrift," the F„ consists of Full-colours, " Sii'dars," 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^b is somewhat less than 1 in 16, there can be no doubt, I think, that this represents the proportion in which they really occurl 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 ' The structures described by Mr L. Crawsbay 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 (lowers, 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 Expeinments ivith 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 F., ; 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 ^2 " 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 rosj' 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 coloureil 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^s of crosses in which the "Ivy-leaf" took • The relations of blue to the other colours 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. - 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 I'esults are such as to indicate that the flaked condition behaves as 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 diflScuIty 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 factor.?, 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 F2S 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 differ 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 Whites'," the whiteness of the flower is due to the presence of a substance which inhibits the ' Gregory, Rep. Brit. Assoc, Leicester, 1907, p. 692. Journ. 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 from 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 Redvers Buller" (Plate XXXI, fig. 29), and various other forms, depending on the presence or absence of the magenta and other factors epistatic to colour, e.\ist (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 ' 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. - The flush round the eye is often only faint, especially in Howers of the slellata variety. The flush is an independent character limited to plants with red stigmas (see p. 120). ^ Bateson, Mendel's Principles of Hereditij, Camb. Univ. Press, 1909, p. 13H. R. P. Gregory 107 not fully developed unless the stigma is coloured ; nor, even if the stigma 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 tlie lack of a coloured base ; the spot is not visible in pale-coloured flowers, 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 F^ from ("Crimson King " x " Rosy Magenta"), and in the Fa all the plants with red stigmas have the spot of deep colour. The inheritance of the character is further illustrated in the subjoined experiments in which a series of F2 pale pinks were crossed with " Orange King." Green stigma Red stigma Reference Ghost of Number spot 36/10 12 37/10 — 38/10 — 39/10 — 40/10 41/10 — 42/10 6 43/101 44/lOf 45/10 3 46/10 9 47/10 6 No spot Spot No spot — 9 — _ 8 3 — 6 3* No plants — 4 1 7 — — No plants * 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. 1 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. cit. Plate VI, figs. 19, 21). 8—2 108 Ex])erhnents 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 my crosse.s 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.^ 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 ' 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" FJs (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 : Full colours " Sirdars " No colour in stems . I- . Magenta Salmon 57 16 52-3 17^4 Magenta 16 17 -i Salmon 6 5-8 Pale-pink White 19 10 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 "-|- 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 1 See Experiment 41/10 in the Table, p. 107. The pale-pinks used in Experiments 37/10 and 38/10 had faintly coloured stigmas. ^ The obvious advantages of working with pure Irorticultural strains entail the disadvantage of working exclusively with long-styled plants, since the short-styled form is eschewed by florists. 110 Experiments loith 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 imlicate complete I'epulsion 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.!fi 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 ro.sy-magentas, the numbers obtained being : Full colours " Sirdars " No colour in stem Reference Rosy- Rosy- Pale- Number Magenta magenta Magenta magenta pink White 9/9 37 22 14 10 14 4 In the next two, however, the usual 3 : 1 ratio obtains: Full colours "Sirdars" No colour in stems Reference Rosy- Rosy- Pale- Number .Magenta magenta Magenta magenta pink White 23/9 19 7 8 2 4 2 17/10 62 25 22 6 36 4 Totals 81 32 30 8 40 6 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 lesults 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 " type 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. 11.5). 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. " Crimson King " x " Snowdrift." The Fj 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 ' The white eye is a character derived from "Queen Alexandra" and does not appear in the experiments with " Snowdrift." 112 Ex2)eriments 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. Ill 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 F„ 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 Red Pale-pink* White - Sti^ia Stigma green reel 33 15 Stigma Stigma green red 12 5 Stigma Stigma green red 14 9 Stigma Stigma green red 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 subsequently gave : Full colours ■"Siritars" Pale class Magenta Red Stigma Stigma green red Magenta Stigma Stigma green red Red Pale-pink ' Whiti Stigma stigma green red Stigma green Stigma red 16 7 7 5 (1 2 1 2 12 4 14 3 6 1 5 3 2 0 11 1 13 4 3 5 1 0 1 0 12 1 15 35t 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 : Magenta green stiguia Magenta red Btigma Red green stigma Red red stigma Full colours 82 31 20 9 Sirdars 38 17 16 4 Totals 120 48 36 13 Expectation 122-0 40-7 40-7 13-6 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 foin- 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 Magenta Red Red green stigma red stigma green stigma 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 F^ 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 F^ 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 Kiug," 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). F^ 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 Fo, 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 Kiug " 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 tbe eye from that of the crosses of either the Rosy- magenta or "Crimson King" with "Snowdrift." The constitution of the Fz follows the general lines of the F., from (" Crimson King " x "Snowdrift") but is of course rather more complex, since the F, is R P. Gregory 115 heterozygous for the factor determining the purjdisli-red stem and deep colour of " Crimson Kiug, " which is present both in that race and in " Snowdrift." In addition therefore to the types found in the "Crimson King" i^o, 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 " Oraoge 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, Pale pink, red collar to faint tinge or White, Full colour "Sirdar" "Orange King" reddish stem no colour in stem green stem 111 i-i 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 Fo ; 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 F„ 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 coukl be attached 116 Experiments with Primula sinensis to this discrepancy, wei-e it not that in some i^/s, 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 those resembling " Sirdar'") Dominant White Parent "Giant White' Parent White Magenta " Sirdar " Pale pink 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," all the red- stemmed offspring 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^. 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 F„ 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 oflFspring of this cross, depends upon two complementary factors, for both of which the F^ 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 {expectation: IVll : 67-89). ' The earlier experiments only give qualitative results, as many plants were discarded before the characters of the flower could be accurately determined. ' Gregory, Eep. Brit. Assoc, Leicester, 1907, p. 692. R. P. Gregory 117 Other experiments 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. Doviinant 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 Fi 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 F„ from this cross consists of whites, tinged whites and colours, all with green stigmas. The numbers obtained are : Fi X coloured, Fi X Self green stigma Number of ^2 families White and Tinged wliite Coloured 17 782 271 rpectation 789-75 263-^5 Number of White and F2 families Tinged white Coloured 3 59 58 Equality The experiment has been repeated iu a slightly different form by crossing coloured plants with the F^ of (Dominant white x Recessive white). The numbers obtained from these crosses are : Reference Number of Fi plant White Coloured 28/4 12 13 4/6 92 86 26/6 58 74 30/6 43 55 51/9 42 46 Totals 247 274 Expectation 260-5 260-5 1 Journ. Genetics, Vol. i. 1910, p. 1. 2 The depth of the tinge is dependent upon the conditions under which the F^ is grown, and its maximum development is only obtained by keeping the house as cold as is possible without injury to the plants. At higher temperatures very little tinge is developed, and the Fj from the cross of such an intense colour as " Crimson King " with a dominant white is scarcely tinged. 118 Expermients with Primula sinensis The " dominant white " parent of Nos. 26/6 and 30/6 was cue which gives a very fully tinged F^ 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, througii the inclusion of some deeply tinged firms 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 F^ from this cross is again a tinged white with green stigma (Plate XXX, fig. 18; Plate XXXI, fig. 21). The F„ 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 i^, 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 tinned- •■ Duchess" and "' Buller" Coloured. Coloured, white, green stigma forms ; red stigma green stigma red stigma 193 61 6-5 21 E.rpniatioii 191-25 63-75 63-75 21-25 " Ducltess." The "Duchess" types whicli appear in these i'Vs 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-ivhite F^. 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 tiowers of the F^ 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- ' A similar ebaracter lias been observed in one otber experiment where the f i 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. R. P. Gregory 119 ters of the i'Vs from the various crosses which have been made are s^howu below : Cross Duchess ' 'x' ' Snowdrift" Duchess ' ' X ' ' Sirdar" Duchess ' ' X ' 'Ivy-leaf" Number of families " Duchess " X Dominant White 1 "Duchess" xFi (Dominant White x "Snowdrift") 2 "Duchess" X Rosy-Magenta ... 1 Description 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. 8 plants. White, with distinct tinge in tube. White, no tinge seen, 15 plants ; White, tingedin tube, 14 plants. 12 plants. White, rather fully tinged in petals. The Fo from 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., from (Dominant white X Coloured, 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 : Red stems Green stems, red collar (" Sirdar " types) Pale-pinks Whites Green stigma Red stigma Green stigma Tinged White and white and Tinged white Coloured Coloured White Sirdar 117 47 37 47 14 Red stigma Tinged White Sirdar Red collar No colour No colour seen in seen in stem stem 18 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 "BuUer" had not been recognized, and some of them were included with the class " Coloured, red stigma " ; in the table the two clas.ses of red-stemmed plants with red stigma are therefore taken together ; it will be noticed that there is a deficiency 120 Exjierinients tvitli 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 was raised by selling one of the offspring of the cross [" Duchess " x F^ (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 Hush 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, Duchess, White. White, White, green stigma red stigma red stigma green stigma red stigma green stigma 3i* 13t 4 16 5 19 * Two with definite ceutral tinge. + Three with definite central tinge. Tinged-whites with red stigma and without the ceutral 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 "Duller" 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 liefinite 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 4 Expectation ' In Stellata flowers the "Duchess" flush is often only poorly developed, but the phenomenon is of a different kind from that referred to here. Green stigma Red stigma 315 116 323-25 107-75 R. P. Gregory 121 (4) Flakes. The FJs from crosses between the "Ivj'-leaf" and coloured races contain flakes (Plate XXXI, figs. 56 — 59) in addition to the self-colours. "Ivy-leaf" x "Crimson King." The F^ of this cross, and of that between "Ivy-leaf" and "Orange King," is indistinguishable to the eye from the F^ 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 coar.se, 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 offspring 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 Eeterence Self Number colour g^jij,^ Palmate leaves -,^^3 Flake 33 42 Pale pink 30 35 White, flaked White, no pale pink flake seen 6 2 25 2 Total, palmate 270 61/10 j ( 24 \ Ivy leaves \ +^ 62/10 ( 1 40 + 11 75 10 undetermined* 16 undetermined* 65 2 12 31 4 0 0 3 0 + 5 undetermined* Total, Ivy leaves 64 + 14 26 undetermined* 14 a 0 + 5 undetermined* Grand total 334 * Owing to the Journ. of Geu. i 101 79 34 4 poor development of the flowers. 9 122 Ex^terhnents 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^'s 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 oifspring being flaked ; and (2) no pale- pinks occur. The numbers are : Bed stems Light stems WTiite 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. " Iv\j-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 (_9^ of 273 = 153-5). 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 F^ 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 snggestion 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 F^ 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 ¥„ of the cross with " Primrose Queen " may perhaps be put down to the difliculty of recognizing the colour in its most dilute and flaked condition ^ The complete absence of self-colours from this ^2 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 offspring obtained in the F. from (" Primrose Queen " x " Snowdrift ") should be flaked, and no flakes have been obtained in this cross. If, then, the conception of distributing factors is to be retained, it would be necessary to construct an elaborate scheme of factors, for the existence of which there is at present no evidence. In the absence of such evidence, it is more simple to suppose that one, at least, of colour factors may exist either in the flaked or in the distributed condition. The F^ from (self-colour x flake) then appears self-coloured because the flaked character is masked when the flower as a whole is coloured*; and the segregation which takes place in the hybrid consists in the • Journ. Genetics, Vol. i. 1910, p. 4. 2 Flaked pale-pinks have now (Feb. 1911) been definitely recognized in I\ from this cross. A red-stemmed magenta flake, self-fertilized, gave two kinds of offspring, namely (1) plants with red stems and flowers flaked magenta, (2) plants almost devoid of colour in the stem, in the flowers of which the flakes of pale pink were recognized with certainty. Temperature of the house, 5.5° F. " Whether any jja/e self-colours, crossed with flakes, would give an Fj of a visibly flaked character depends upon the relation between full and pale colours, which is not yet fully understood. 9—2 124 Experiments ivith Primula sinensis separation of the flaked and distributed forms of the same factor, and not in a segregation of the factors for flaked and for self-colour from their respective " absences." On this hypothesis the results of the crosses with "Primrose Queen" may be explained as in the subjoined scheme, where X, Y, the colour factors in the distributed condition ; X', Y', the colour factors in the flaked condition ; R, inhibition. Assuming the constitution of the parents to be " Snowdrift" = xYr ; " Primrose Queen " = XyR ; " Ivy-leaf" = XY'r ; then "Snowdrift" x "Primrose Queen," Fi = XxYi/Rr, F.2 should give 9 se//-coloured : ho white Observed 13 „ : 66' „ Calculated ll'l „ : 67'9 „ "Ivy-leaf" x " Primrose Queen," F, = XXY'yRr, F„ should give 3 flakes : 13 whites Observed 26 „ : 93' Calculated 22-3 „ : 96-7 „ "Ivy-leaf" x "Snowdrift," F, = XxYY'rr, F^ should give 9 self-coloured : 7 flaked and white Observed 144 „ : 129 Calculated 153-5 „ : 110-4. The conception of the relation between the flaked and self-colour characters set forth above does not pretend to do more than provide a means by which the results of the experiments may be described. It brings us no nearer the solution of the problem as to how the flaked distribution is brought about, nor is it intended as implying that the colour-factors themselves may not be the same in the flakes as in the self-colours, the mode of distribution of the colour being determined independently. Gametic Coupling and Repulsion. Evidence has been obtained of the existence of (1) a repulsion between the factor for the structural character of short-style and certain factors affecting the colour of the flower, and (2) of a partial coupling between two colour factors. ' The numbers given are those obtained in the red-stemmed class only, since the distinction between coloured and white green-stemmed plants is not critical. R. P. Gregory 125 (1) Repulsion between short-style and colour characters. Shurt-style and Magenta-colour. The results of my crosses in which a shorf-styied coloured race (Salmon-pink, p. 109) was mated with various long-styled plants carrying the magenta factor, show that in the gametogenesis of the hybrids so produced, a complete repulsion between the factor for short-style and the magenta factor takes place. The numbers obtained in these experiments are given below, together with the expectation based on the assumption of complete repulsion between the two factors under consideration. Magenta short-siylpd l'\, giving magentas and salmon-pinks. Short-style Long-style Observed Numbers Magenta 54 Salmon 18 Magenta 24 Salmon 0 Expected 48 2i 24, 0 Tinged-white short-styled Fj, giving tinged-white, magenta, and salmon-pink. short-style Long-style Tinged-white Magenta Salmon Tinged-white Magenta Salmon Observed numbers 157 46 19 66 20 0 Expected ,, 173-25 SSS 19-2.5 57-75 19-25 0 Tinged-white short-styled F^, giving tinged-ivhite, magenta, salmon-pink, and blue. Short-style Long-style Tinged- Tinged- white Magenta Sahnon Blue white Magenta Salmon Blue Observed numbers 15 4 3 2 10 6 0 0 Expectation (omitting\ ^^^^ ^.^ ^.^ _ ^._j ^.^ ^ _ blues) I The deficiency in the tinged-white short-styles is referred to below. Short-style and inhibition. Certain families raised from one heterozygous short-styled tinged-white (No. 51/9) have shown an interesting departure from the normal distribution of the four kinds of offspring. The results of the experiments made with this plant are : Offspring Cross Short-style Long -style Reference Number Tinned- white Coloured Tinged- white Coloured 66/10 0l/9xSelf 25 7 9 3 67/10 51/9 ? X Long-style, coloured s 4 9 11 4 68/10 51/9 $ X Long-style, coloured s 5 6 5 5 79/10 Long-style, coloured ? x 51/9 d 7 14 17 8 120 Ex2)erhnents ivith Primula sinensis In Experiments G6/10 and 68/10 the distribution is normal, but in Nos. 67/10 and 79/10, where we expect equality of all four classes, the two middle classes are much larger than the end terms, and though the total numbers are small, the divergence is such that it can scarcely be dismissed as fortuitous. The relative sizes of the four classes in the families Nos. 67/10 and 79/10, indicate that any repulsion which may take place must be of a low order. The family of 67/10 was raised from seeds obtained from two capsules; but in Experiment 79/10, pollen was taken from only one flower, so that the low type of repulsion indicated by the constitution of that family cannot be regarded as due to a mixture of families of more than one kind. For the solution of the problems presented by the results of these experiments further data are required. The constitution of the F^s obtained from our other plants heterozygous for short style and for inhibition, throws little light on the case. In these families the distribution of the four kinds of offspring does not depart very greatly from the normal. The numbers obtained are : Short-style Long-style White and Tinged-white Coloured %Vhite and Tinged-white Coloured 327 126 128 39 3i8-75 116-25 116-25 38-75 Observed Expected There are small departures from tlie 3 : 1 ratio in the cases both of the short- and long-style and of inhibition and colour ; the deficiency of dominants of both kinds has of course a marked effect upon the size of the first category. The excess in the two middle classes and the deficiency in the first class appear to be more or less constant throughout the families, which, combined together, furnish the totals given above. Short-style and tinge in corolla-tube. In one experiment clear indications were obtained of a coupling between the short-style and a tinge in the corolla-tube just below the level of the anthers. So far as the character of the petals was concerned, the family consisted of tinged-whites and whites ; of the whites, however, some were tinged in the tube, others were colourless. Of the short-styled whites, 20 were tinged in the tube, 1 was colourless ; of the long-styled whites 5 had the tinge and 11 were colourless. The ratio of short- to long-style in this family was very much less than the expected 3 : 1, the numbers being 33 short, 21 long. The asymmetry of the four classes is no doubt R. P. Gregory 127 partly a result of this, and the numbers obtained suggest that a coupling of a fairly high order was present. (2) Coupling between colour characters. With the exception of the mating between " Crimson King " and "Snowdrift," all the experiments in crossing either "Crimson King" or " Orange King " (red, red stigma) with plants carrying the factors for magenta colour and green stigma, have given results which point clearly to the existence of a partial coupling between these factors in gameto- genesis. The results in general show some deficiency of the two dominant characters, magenta and green stigma, as compared with the expected ratio, in each case, of 3 D : 1 R ; the classes consisting of plants having one or both recessive characters are therefore unduly large, and it is necessary to make allowance for this in attempting to compare the observed numbers with the expectation calculated upon various systems of partial coupling. The distribution of the four characters in the offspring possessing fully-coloured flowers and red stems is set out below : Constitution of -Fo ' Orange King ' Cross X "Snowdrift" " Crimson King " x Rosy Magenta "Crimson King"x "Queen Alexandra' "Crimson King "x " Ivy-leaf ' Magenta Red Reference Green Red Green Red Number stigma stigma stigma stigma 10/9 19 4 6 6 11/9 28 9 6 8 33/9 54 13 12 14 Total 101 26 24 28 17/9 85 24 24 21 18/9 73 12 15 22 24/9 81 18 19 17 32/10 19 5 5 4 33/10 20 2 7 3 Total 39 7 12 7 61/10 69 23 14 15 62/10 137 80 28 18 Total 206 53 42 33 In these results, that obtained in No. 18/9 stands alone in that the fourth term of the series is distinctly larger than either of the middle 128 Experiments with Primula sinensis terms. On the basis of the 3:1:1:3 system of partial coupling, the 122 plants of which the family consists should be distributed in tlie proportions of 78'1 magenta, green stigma : 133 magenta, red stigma : 13'3 red, green stigma : 17 '2 red, red stigma. The distribution thus calculated would, however, give magenta : red = green stigma : red stigma = 3:1, while the observed numbers are magenta 85, red 37 ; green stigma 88, red stigma 34. That is to say, tliere is a deficiency of plants bearing the dominant characters, and, consequently, the first term will be smaller and the fourth term will be larger than the calculated numbers. Apart from this divergence, there is a close approximation between the observed and calculated numbers, and there can be little doubt that the partial coupling was of the type 3:1:1:3. The crosses between " Orange King " and " Snowdrift " have given results which may perhaps allow of the same explanation, but in the remaining experiments the fourth term is definitely smaller than the middle ones. Each family was raised from seed obtained from several capsules borne on one plant ; and, until the completion of experiments which are now in progress, it is not possible fully to analyse the results. For the time being it may be pointed out that a very close approximation to the observed numbers is given by the assumption that a coupling of the form 7:1:1:7 is present in gametes of one sex only, gametes of the opposite sex being pi-oduced in equal numbers of all four kinds. The numbers are Magenta, green stigma Magenta, red stigma Red, green stigma Red. red stigma 411 98 97 78 !• 416-S 96-2 96 -2 74-S Observed Calculated for 7:1:1:7 coupling in gametes of one se.v only As was stated above^ the distribution of the four kinds of offspring in the i^„'s from the cross ("Crimson King" x "Snowdrift") gives no clear indication of the existence of any form of partial coupling during gametogenesis of the F,. In two Fo families raised in 1907, the results differ very little from the simple 9:3:3:1 ratio. In the later experi- ments there is some departure from this ratio, principally due to the dearth of plants carrying the positive characters, magenta and green stigma. ' p. 113. R. P. Gregory 129 lu conclusion, it may be pointed out that here, as elsewhere, families raised from sister plants do not necessarily follow the same system of distribution. Thus the parent of the family 18/10, which apparently conforms to the 3:1:1:3 system, was the sister plant to the parent of the family 17/10, in which the fourth term is smaller than the nudclie ones. Note added February 17, 1911. Since the foregoing was written some interesting results have been obtained in connexion with the phenomena of coupling and repulsion. These results are briefly described below. The constitution of a certain type of coloured flower, which was previously uncertain, has also been ascertained. Coupling and repulsion. (1) Magenta and short-style. On p. 12-5 a series of experiments is described in which a complete repulsion between the factors for short-style and magenta colour is shown. It will be noticed that in this series of experiments one of the dominant characters was possessed by the one parent race, the other by the other parent. In a new series of experiments a race possessing both dominant characters (i.e. magenta, short- style) was mated with races which bad the recessive characters only. The results show that when the cross is made in this way, partial coupling takes place between the factors for the two dominant characters. In the experiments in which the recessive parent was a long-styled red with double flowers, the coupling shown is almost certainly of the form 7:1:1:7; in these experi- ments there is no indication that coupling occurs between either the factor for short-style or that for magenta and any third factor. In a second set of experiments, in which the recessive parent was the long-styled "Crimson King," the form of the coupling between magenta and short-style is as yet uncertain, the numbers obtained being almost exactly intermediate between the expectation based on the series 7:1:1:7 and that based on the series 15 : 1 : 1 : 15. In these experiments there is clear evidence that the factor for magenta is coupled, not only with the factor for short-style, but also with the factor for green stigma. The coupling between magenta and green stigma is of a much lower order than that between magenta and short- style. (2) Light red stem and green stigma. A new instance of complete repulsion between two factors has been obtained. The factors are (1) the pallifying factor for stem colour (p. 100), and (2) the factor for gi'een stigma. This repulsion was observed in the progeny of a cross between "Crimson King " and "Ivy Leaf." Certain individuals of the F^ from this cross were tested by self-fertilization. Three of these plants, all having light red stems and gi-een stigma, were found to be heterozygous in these characters, giving offspring having either light or dark red stems, and either green or red stigmas, but none of the dark-stemmed offspring had red stigmas. Floicer colour. The deeply tinged type of flower shown in Plate XXXI, fig. 32, the consti- tution of which was formerly in doubt, has proved itself to be heterozygous for the factors which inhibit flower-colour. Self-fertilized, it has thrown tinged whites with gi'een stigma, " Duchess " and " BuUer " types with red stigma, coloured with green stigma and coloured with red stigma. The flush shown in the "Duchess "and "Duller" types is of a very deep kind, and the coloured types have flowers of a very deep crimson, at least as deep as that of " Crimson King. " 130 Experiments lolth Primula sinensis DESCRIPTION OF PLATES. The figures illustrating the colours of the flowers are from water-colour drawings by Miss M. Wheldale. PLATE XXX. Figs. 1 — 7 illustrate various types of coloration of the stem. Fig. 1. Dominant white with deep purplish-red stem. Fig. 2. Dominant white with light purplish-red stem. Fig. 3. "Orange King," red stem (cf. the more usual purplish-red colour of the stem). Fig. 4. " Sirdar." The characteristic distribution of the fjower-colour, which is associated with this type of stem, is shown in Plate XXXI, figs. 44, 45. Fig. 5. Green stem, with slight purplish-red colour in young petioles. Fig. 6. "Ivy-leaf." Non-crenate leaves, and monstrous flowers. Stems green, with some purplish-red colour in young petioles. Fig. 7. " Snowdrift," stem devoid of sap-colour. Figs. 8 — 20 illustrate the colour of the flower of various pure races and F{s. Fig. 8. "Orange King" (cf. fig. 3). Fig. 9. " Crimson King." Fig. 10. "Snowdrift" (cf. fig. 7). Fig. 11. "Queen Alexandra" (dominant white, white eye). Fig. 12. "Primrose Queen" (dominant white, large yellow eye). Fig. 13. "Reading Pink." The deepest colour found in association with green stems devoid of sap-colour. Fig. 14. F, ("Reading Pink" x" Snowdrift"). Figs. 15 and 16. Young and mature flowers of the Fj from ("Reading Pink " x " Orange King"). Fig. 17. Fi ("Crimson King " x " Snowdrift "). Fig. 18. F, ("Crimson King" x Dominant white, ordinary eye). Figs. 19 and 20. Rosy-magenta, young and old flowers. PLATE XXXI. Figs. 21—43 illustrate the cross between "Crimson King" and "Queen Alexandra." Fig. 21 is the Fj; figs. 22—43 illustrate the series of F^ forms. Figs. 22 — 20. Inhibited whites, green stigma. Fig. 22. White, white eye. Fig. 23. White, ordinary eye. Fig. 24. Tinged-white, white eye (F, type). Fig. 25. Tinged-white, ordinary eye. Fig. 20. Fuller tinged-white, tinge central Fig. 28. Fig. 29. Fig. 30. Fig. 31. Fig. 32. Figs . 33 figs. Fig. 33. Fig. 34. Fig. 35. Fig. 36. Fig. 37. Figs ;. 38- R. P. Gregory 131 Figs. 27 — 31. Plants with the factor for inhibition of colour in periphery of petals, but with red stigma. Fig. 27. Red " Duchess," Fi type of eye. Magenta "Duchess," Fi type of eye. "Sir Redvers BuUer" (red), ordinary eye. Red " Buller " of rather bluer type, white eye. Magenta " Buller," ordinary eye. Light red, ? inhibited form, green stigma '. —37 represent types belonging to the Red class. Figs. 33, 34, green stigma; 35 — 37, red stigma. Red, ordinary eye. Red (bluer type), white eye. Red, white eye. Red, ordinary eye, band of deep colour rouud the eye. Deep red, white eye. —43 represent types belonging to the Magenta class. Figs. 38 — 41, green stigma ; figs. 42, 43, red stigma. Figs. 41 and 43 are corresponding forms with green and red stigma respectively. Fig. 38. Magenta, Fi type of eye. Fig. 39. Magenta, ordinary eye. Fig. 40. Fuller magenta, white eye. Fig. 41. Rosy-magenta, ordinary eye. Fig. 42. Magenta, Fi type of eye. Fig. 43. Rosy-magenta, ordinary eye, spots of deep colour round the eye. Figs. 44 — 45 represent additional coloured types which occur in the Fj from (" Snow- drift" X " Crimson King "). Fig. 44. Red "Sirdar." Fig. 45. Magenta "Sirdar." Fig. 46. Pale-pink on green stem (cf. figs. 13, 14). Figs. 47 — 49. Other types belonging to the red class from the F^ from (" Crimson Ring " X Rosy-magenta). Fig. 47. Terra-cotta (bluer type), green stigma. Fig. 48. Terra-cotta, green stigma. Fig. 49. Strawberry. Figs. 50 — 55 represent various types of special coloration just external to the eye. Figs. 50, 51. Magenta, red stigma, with the spots of deep colour which are only fully developed in flowers possessing the red stigma. Young and mature flowers. Figs. 52, 53. Magenta, green stigma, corresponding with the foregoing types. Young and mature flowers. Figs. 54, 55. Young and mature flowers of a magenta with green stigma, showing the rather diffuse band of brownish colour, which only becomes conspicuous in the older flower (fig. 55). Figs. 56 — 59 represent Flalsed types. Fig. 56. Flakes medium to coarse ; no fine flakes, green stigma. Stellata. Fig. 57. Some coarse flakes ; finer flakes rather peripheral in distribution ; red stigma. Stellata. Fig. .58. Fully flaked, coarse and fine flakes, green stigma. Fig. 59. Fully flaked, coarse and fine flakes, red stigma. 1 See note added February 17, 1911, p. 129. 132 Experime^its wif/i Primula sinensis PLATE XXXII. Fig. 60. Seedling plant of "Ivy-leaf," sliowin;,' the non-orenate leaves. Fig. 61. Illustrating the cioss between " Ivy-leaf" and "Snowdrift " (Fern-leaf, crenate). Top row: "Ivy-leaf" (left), "Snowdrift" (right). Middle: Fi (palmate, crenate). Bottom row: the four F-t types (1) palmate, crenate, (2) palmate, non-ci'enate, (3) fern-leaf, crenate, (4) fern-leaf, non-crenate. The four types occur in the proportions 9:3:3:1. Fig. 62. Showing the Fi's from crosses of the white-eyed race "Queen Alexandra" with the large-eyed " Primrose Queen," and with ' ' Snowdrift " (ordinary eye). Top row: "Primrose Queen," No. 37/9; "Queen Alexandra," No. 34/9; "Snowdrift," No. 1/9. Second row: 36/9 Fi from ("Primrose Queen " x " Queen Alexandra"). 35/9 Fi from ("Queen Alexandra " x " Snowdrift "). Fig. 63. Showing the J'Vs from crosses of the large yellow eye, stellata, with the ordinary eye in the stellata and typical siitetisis forms. Top row: Stellata, white, ordinary eye. No. 55/9; "Primrose Queen," No. 37/9 ; "Snowdrift" 1/9. Second row: 48/9 Fi from {Stellata, ordinary eye x " Primrose Queen"). 38/9 Fi from ("Primrose Queen " x sJjk'Hsis, ordinary eye). Fig. 64. Showing the variation in the form of the corolla in a plant No. 54/9 and its offspring. Top row : flowers from the same plant, No. 54/9. Second and third rows : Flowers from four plants illustrating the various types produced by the self-fertilization of 54/9. The flowers from each plant are arranged in pairs, one above the other. The first three represent the nearest approach to sinensis, the intermediate and the stellata types in the Giant form. The last pair of flowers are those of a stellata plant which did not possess the Giant character of its parent. JOURNAL OF GENETICS, VOL. L NO. 2 l^ « f 13 14 IS 16 PLATE XXX 17 18 19 20 JOURNAL OF GENETICS, VOL. \ NO. 2 ^^^^ml^J^' ^^^uA^'ii^^ 29 & .>*^»~ 1' :-(»>(!^!l%,''^"' 23 33 38 39 O 44 45 * 46 47 5- 53 54 55 PLATE XXXI JOURNAL OF GENETICS, VOL. 1. NO. 2. m •*^_ :5' ^1 ^^H l^gl^i ~ 9 ^ J iH HMl Fig. 6o Fig. 6i PLATE XXXII Fig. 62 Fig. 63 Fig. 64 ON THE FORMATION OF ANTHOCYANIN. By M. WHELDALE, Fellow of Neivnham College, Cambridge. Nature of Problem and Preliminary Statement of Conclusions. The problem to which I have attempted to give a solution in the following pages may be briefly stated as follows : — what are the chemical processes which underlie the formation of anthocyanin ? In my attempt to arrive at some solution I have used as data the results of observations upon the general distribution of pigment, its formation in relation to other metabolic processes and to the chemical constituents of the tissue : also the conditions, both natural and artificial, which lead to its appearance, and lastly, the detection of enzymes which may be involved in its production. As an outcome of this general investigation, I venture to bring forward an hypothesis which may afford in many respects an explana- tion, in terms of chemical reactions, of the mechanism underlying the phenomenon of soluble pigment formation. At the same time I may say that I look upon my suggestions as tentative and as having value possibly only in so far as they combine together into a general scheme a number of more or less isolated facts. I fully realise that the under- lying causes of such a phenomenon are of a complex nature and may in reality demand a very different explanation from that which I am able to offer. The ultimate object of the enquiry is the identification of the Mendelian factors for colour. There is little doubt that the formation of anthocyanin does involve a series of progressive reactions each of which is contioUed by a certain enzyme. In variation, whatever that may be, the loss of these enzymes gives rise to different colour varie- ties. Hence the greater the complexity of the pigment-forming process 134 On the Fortnaflou of Anthocyanin in any species, the greater the number of derivative varieties we may expect to appear under cultivation. Only an exact knowledge of the chemical reactions involved in the formation of pigment will enable us to explain the mechanism of colour inheritance and the cause of differ- ences between varieties. The main conclusions arrived at in the present paper may be summarised as follows : — (1) The soluble pigments of flowering plants, collectively termed anthocyanin, are oxidation products of colourless chromogens of an aromatic nature which are present in the living tissues in combination with sugar as glucosides. (2) The process of formation of the glucoside from chromogen and sugar is of the nature of a reversible enzyme action : Chromogen + sugar '*~7' glucoside + water. (3) The chromogen can only be oxidised to anthocyanin after liberation from the glucoside and the process of oxidation is carried out by one or more oxidising enzymes : Chromogen + oxygen = anthocyanin. (4) From (2) and (3) we may deduce that the amount of free chromogen, and hence the quantity of pigment formed at any time in a tissue, is inversely proportional to the concentration of sugar and directly proportional to the concentration of glucoside in that tissue. (5) The local formation of anthocyanin which is characteristic of the normal plant is due to local variation in concentration of either the free sugars or the glucosides in the tissues in which the pigment appears. The abnormal formation of pigment under altered conditions is due to differences in the concentration of these same substances due to changes in metabolism brought about by these conditions. (6) On the above hypothesis the formation of anthocyanin is brought into line with that of other pigments produced after the death of the plant, as, for example, indigo, the respiration pigments of Palladin, etc. Results obtained by Previous Investigatohs. Although the soluble pigments of plants have afforded material for a considerable amount of investigation, the sum total of results gives us very little knowledge either of the composition of these substances or of the processes which underlie their formation. M. Whbldalb 135 With regard to their chemical nature, I have previously(l9) given reasons for the statement that the red, purple and blue pigments, collectively termed anthocyanin, are oxidation products of chromogens of an aromatic nature^ That, moreover, these chromogens, in the form of glucosides, are present in solution in the cell-sap throughout the living tissues and in the unoxidised state cause no colouration, but under certain conditions through the agency of an oxidase the chromo- gens may be oxidised to pigments, i.e. anthocyanin. This point of view is in agreement with that held by other investigators: VVigand(21), Pick(16), Mirande(9), Laborde(7), Overton(13) and Palladin(14), who have considered the soluble pigments either to be themselves aromatic compounds or to be intimately connected with tannins and allied substances. That oxygen is necessary for pigment formation and that the oxidation is probably brought about through the agency of au oxidase has been suggested by Mirande(9), Palladin(14), and by Buscalioni and Pollacci(l). Katic(5) and Molliard(ll) have also shown experimentally that oxygen plays an important part in the appearance of pigment in certain organs. So far, however, no hypothesis has been formulated as to the more exact mechanism of pigment formation, the reasons for its appearance only under certain conditions and for its localisation in definite organs and parts of the plant. Wi<^and(21), it is true, has pointed out that the occurrence of antho- cyanin in autumnal leaves, evergreen leaves in winter, injured or dying leaves, flowers and ripening fruits, indicates a connection between lessened assimilative activity and the production of pigment, though the nature of the connection remains unexplained. Overton (13), on the other hand, basing his conclusions on results obtained from feeding leaves and plants with sugar solution, maintains that increase of sugar in the cell gives rise to formation of anthocyanin. He considers the pigment itself to be a glucoside of which the non- sugar part is a tannin-like compound. Ao^ain no indication is given as to the exact nature of the con- nection between the excess of sugar and the appearance of pigment. Kati6(5), Molliard(ll), Mirande(9) and Palladin(14) also support the statement that an accumulation of sugar increases the formation of • In many cases, probably, members of the flavone and xanthone classes of com- powids. 136 O)} the Formation of Anthocyanin pigment. In addition Kati6 has shown experimentally that the pro- duction of pigment, though dependent upon the presence of oxygen, is independent of the presence of carbon dioxide. Some important additions to our knowledge concerning the forma- tion of anthocyanin have recently been published by Combes(3). This author has shown that the reddening of leaves is accompanied by an accumidation of oxygen in the tissues and that the disappearance of pigment on the other hand is accompanied by a loss of oxygen. In addition he has shown that red leaves contain proportionally greater amounts of glucosides and sugars than green leaves of the same plant. Combes considers the cause of oxidation to be this accumulation of glucosides and sugars which may arise from various external causes. These substances accelerate the processes of oxidation and hence the gaseous exchange may be fundamentally modified. Statement of Hypothesis. From evidence which will be given in detail later I have been led to conclude that the formation of anthocyanin from a chromogen depends upon two processes, in which two different enzymes at least are involved. The first reaction is reversible and may be expressed as follows : — Glucoside + water t"** chromogen + sugar. The same enzyme may be supposed to accelerate both the synthetic and hydrolytic reactions. The second reaction is one of oxidation and is carried out by an oxidising enzyme or oxidase : — Chromogen + oxygen = anthocyanin. It must be further assumed that the chromogen can only be oxidised after liberation from the glucoside. On the basis of this hypothesis, it follows that the amount of antho- cyanin in any tissue depends upon the amount of free chromogen, and the latter, in accordance with the reversibility of the first reaction, is directly proportional to the concentration of glucoside and inversely proportional to the concentration of sugar in the tissue. The frequent appearance of pigment, under abnormal conditions, in tissues which are normally unpigmented, justifies the supposition that every part of an anthocyanic plant is provided with this mechanism for the formation of pigment. M. Wheldalb 137 The local appearance of pigment in various plant tissues thus resolves itself into a matter of local variations in the concentration of sugars and glucosides in the tissues. In order to test the validity of the hypothesis as stated above, it must be ascertained whether the conditions which give rise to forma- tion of pigment are such as would influence the amount of glucosides and sugars present, and in this way it should be possible to demonstrate a connection, if it exists, between the two phenomena. I have classified my evidence from various sources under the following headings :— (1) Analogous reactions. (2) Distribution of anthocyanin. (8) Concentration of sugars and glucosides in various tissues. (4) Existence of enzymes. (5) Sugar-feeding. Evidence from Analogous Reactions^ Many of the reactions involved in plant metabolism are known to be of a reversible or balanced nature. Excess of sugar, for instance, may be converted into starch and thereby stored up in an insoluble form which is again hydrolysed into sugar when required. Similarly oils may be hydrolysed into fatty acids and glycerine, and these products again synthesised into oils. Synthesis and hydrolysis are also con- tinually taking place between the disaccharides and the monosaccha- rides. Cane-sugar is synthesised from glucose and fructose and hydrolysed into the same products: dextrose is synthesised into maltose which is hydrolysed into dextrose and so forth. As a typical rever-sible reaction we may quote the hydrolysis of ethyl acetate. When ethyl acetate is treated with water, hydrolysis into acetic acid and ethyl alcohol commences at once, but as soon as any products of hydrolysis are formed, the reverse action is also set up, namely the synthesis of ethyl acetate from acetic acid and ethyl alcohol. Hence in any mixture of the four substances, ethyl acetate, acetic acid, ethyl alcohol and water, two opposite reactions will proceed at different rates : — Ethyl acetate + water ■j-*' ethyl alcohol + acetic acid. 1 In connection with enzyme action I liave freely quoted from Bayliss, Tlie Nature of Enzyme Action, 1908. Journ. of Gen. i 10 138 On the Formation of Anthocyanin After a time a certain relative concentration of the four constituents results and at this stage the velocities of the two reactions are equal and equilibrium is established. If to a system of this kind, a catalyst, such as hydrochloric acid, is added, the equilibrium position has been shown to remain unaltered. From this it may be inferred that both the hydrolytic and synthetic reactions are equally accelerated by the catalyst. In plants the greater number of reversible reactions are of a hydro- lytic nature and are controlled by special catalysts, known as enzymes, produced by the living organism. It is now known that a considerable number of these enzymes, as, for example, invertase, maltase, lipase, diastase and emulsin, can be extracted from the living tissues and their activities can be demon- strated under artificial conditions outside the plant. It is then found that in many cases the velocity of the hydrolytic reaction is so much greater than that of the synthetic that the equilibrium position is very near complete hydrolysis. When such is the case, we may infer that there is some, though very little, reversibility of the reaction. Hence if enzymes behave in the same way as inorganic catalysts, it should be possible to show that they are able to again synthesise the products they produce in hydrolysis if the right conditions can be found. Croft Hill was the first observer to give experimental proof that enzymes accelerate synthetic processes, though in the special case investigated by him the synthesised product was an isomeric form of the compound hydrolysed. From a concentrated solution of glucose he obtained, through the action of maltase, small quantities of isomaltose which was again hydrolysed in dilute solution. Since then many other cases have been discovered, such as the S3mthesis of the ester, ethyl butyrate, by lipase from a mixture of eth}^ alcohol and butyric acid, of the glucoside, salicin, from saligenin and glucose, and of cane-sugar by invertase from glucose and fructose. The value to the plant of even a slight reversible action has been pointed out by Bayliss(lA), for if the synthesised product is removed from the sphere of action as rapidly as it is formed, either owing to its insolubility or by translocation, a considerable amount of synthesis may eventually take place. There is also in many enzyme actions a special retarding influence exerted by the respective products of action in addition to that due to reversibility of the reaction. Usually the retarding effect exerted by one of the products of action is greater than that exerted by the other ; M. Wheldalb 139 or again one may have a retarding influence and the other none, as for instance in the case of invertase, which is retarded by fructose, whereas glucose has no effect. There is little doubt that the retarding influence is due to the fact that the enzyme enters into some form of compound with the sugar and is thereby removed from the sphere of activity, with the resultant slowing down of the hydrolytic process. There is a similar retardation in many cases in the synthetic process due to the combination of enzyme with the substrate. A full account of these retardation processes is given by Bayliss in The Nature of Enzyme Action. The enzymes with which we are chiefly concerned in the present paper comprise the glucoside-splitting class. The term glucoside is applied to a large number of substances occurring in plants, all of which have the property of being hydrolysed by enzymes or by acids into glucose and one or more other products such as alcohols, aldehydes, phenols, etc' In some cases a glucoside, as, for example, xanthorhamnin, is only hydrolysed, as far as we know, by one particular enzyme, rhamnase, though sometimes one enzyme, such as emulsin, will hydrolyse a con- siderable number of different glucosides, i.e. arbutin, salicin, coniferin, syringin, helicin, amygdalin, aesculin, daphnin, and others. An interesting point in connection with the glucoside-splitting class of enzymes is the rapidity with which the hydrolytic reactions take place when the plant is submitted to the action of chloroform vapour or other anaesthetics. Injury to the tissues will also bring about the same result. This reaction is readily detected if the products of hydrolysis have a characteristic odour, as for instance in the case of cyanogenetic glucosides, of which amygdalin is the best known example. Amygdalin occurs in bitter almonds and in the kernels of peaches, apricots, plums and other fruits of the Rosaceae. By emulsin it is hydrolysed according to the equation : — a„H2;0uN + 2H.,0 = CVHeO + HON + 2C,B.,,0, amygdalin benzal- hydrogen glucose dehyde cyanide and the progress of the reaction can be detected by means of the characteristic odour of the products. 1 An account of these substances is given by E. F. Armstrong in The Simple Carbo- hydrates and Glucosides. 10—2 140 On, the Formation of Anthocyanin The mustard oil glucosides, sinigrin and sinalbin, occurring in mustard and other Cruciferae, also give products with a characteristic odour of mustard oil on hydrolysis : — C,„H,eOsNS,K + H,0 = C3H5CNS + CeHiA + KHSO, sinigrin allyl sulpho-cyanide The hydrolysis of glucosides on autolysis in chloroform or through injury, can also be detected when the non-sugar component of the glucoside molecule is an aromatic substance, which when free from glucose is subsequently oxidised to a coloured compound through the agency of an oxidising enzyme (oxidase); in this case the development of colour indicates the progress of the reaction. In some genera the pigments produced in this way after death or injury to the plant are red, purple or blue, and hence attention has been di'awn to the phenomenon, and the products so formed have been used commercially for dyeing purposes. The best known examples are the " indigo plants," Indigofera spp., Isatis tinctoria, Polygonum, tinctorium, etc. The processes taking place in the formation of indigo have been very fully investigated and can be expressed as follows: — Ci,Hi70eN + H,0 = QHiA + CsH.ON indicau glucose indoxyl 2C8H,ON + 0, = 2H,0 + CaaH,„0,N, indigotin The first reaction is brought about by a glucoside-splitting enzyme, indimulsin, which hydrolyses the glucoside, indican ; the second by an oxidase which oxidises the colourless indoxyl to the pigment indigotin or indigo. Another striking example is the rapid formation of a bright red pigment in the flowers and leaves of Schenkia blumenaviana on autolysis in chloroform as described by Molisch(lO). Though the formation of a brightly coloured pigment after death is a comparatively rare phenomenon, yet many plants rapidly turn brown or reddish-brown when placed in chloroform vapour. The same effect is produced by mechanical injury and sometimes by immersion in absolute alcohol (Mirnbilis Jalapa). Extracts from such plants give a blue colour with guaiacum tincture and there is little doubt that the production of pigment is due to the oxidation of an aromatic substance through the activity of the oxidase. M. Wheldale ■ 141 This appearance of pigment on autolysis is especially frequent among genera of the Labiatae, Boraginaceae, Scrophulariaceae and Umbelliferae, though it is also generally characteristic of some of the genera in most Natural Orders. Often, as in the Ranunculaceae, this phenomenon is peculiar to all species of certain genera {Anemone, Hellehorus, Clematis, TroUius, Caltha and Aconituvi), which rapidly yield brown pigment on autolysis in chloroform, whereas all species of other genera {Ranunculus, Paeonia, Aquilegia and Thalictrum) give no colour in the same time of exposure. It is probable that the processes involved in the formation of post- mortem pigments are in all cases analogous to those known to take place in the production of indigo. The aromatic chromogen, from which the pigment is produced, is combined with sugar in the form of a glucoside in the living cell. In such a form the chromogen cannot be attacked by the oxidase. When the cell is subjected to chloroform vapour, the velocity of the hydrolytic reaction is accelerated and the whole of the glucoside is split into chromogen and sugar. The free chromogen is then fully oxidised by the oxidase. Accoi'ding to the view held by Palladin(14), these aromatic glucosides, together with the glucoside-splitting and oxidising enzymes, form an important system in the plant for the purpose of oxidising respirable materials, and the post-mortem pigments have been termed by him " respiration pigments." In the living unpigmented cell, the processes of oxidation, reduction and the glucoside splitting reaction are so balanced that no free pigment appears. To quote Palladin(l.T): — " Einer sparsamen Hausfrau vergleichbar, halt die Zelle die Chro- mogene verschlossen und verausgiebt sie in geringen Mengen fiir Oxydationsprozesse. Die Ausgabe wird durch ein die Prochromogene spaltendes Enzyme besorgt." To the chromogen in combination with sugar as a glucoside, Palladin has applied the term " prochromogen." He also includes anthocyanin among the respiration pigments, but does not offer any very definite explanation of the appearance of anthocyanin in various plant organs. I am inclined to believe that anthocyanin itself has no direct respiratory function in that it is absent from albino varieties, which do not appear to suffer from the loss of j)igment, since they grow and reproduce quite as vigorously as the pigmented types. From the description of enzyme actions given above it will be .seen that a series of reactions such as I have supposed to take place in the 142 On the Formation of Anthocyanin formation of authocyaniu is kuowu to occur in connection with the oxidation of aromatic compounds in the plant. The essential difference between such reactions as lead to the formation of indigo, and those which have been suggested for anthocyanin, lies in the nature of the oxidase. In the former case the oxidase continues its function after the death of tlie cell, but so far there is no evidence of anthocyanin being formed in extracts from the plant', and it seems highly probable that it is a process which is difficult or perhaps impossible to induce under artificial conditions. The nature of the oxidases concerned will be discussed later. Distribution of Pigment. The various organs of the plant in which anthocyanin may appear can be enumerated as follows : Under normal conditions. (1) Veins, midribs and petioles of many leaves. Herbaceous stems and the young stems of shrubs and trees. (2) Leaves of red-leaved species {Amaranthus, Goleus, etc.). (3) Leaves of red-leaved varieties of green-leaved types {Fagus, Corylus, Beta, Atriplex, etc.). (4) Young developing leaves {Quercus, Rosa, Crataegus, etc.). (5) The older leaves of many plants {Fragaria, Aquilegia, etc.), and sometimes the whole plant (many Umbelliferae, Galium aparine, etc.) towards the end of tiie vegetative season. (6) Variegated leaves in which the chlorophyll is absent from certain areas. (7) Flowers and ripe fruits. Under abnormal conditions. (1) Leaves which have been injured either mechanically or through the attacks of insects and fungi. (2) Autumnal leaves. (3) Leaves exposed to low temperatures, such as evergreen leaves in winter {Hedera Helix, Ligustrum vulgare, Mahonia sp., etc.). (4) Leaves exposed to drought. 1 Except in so far as I have been able to induce a formation of colour in an extract from Primula flowers by means of Horseradish peroxidase in presence of h3'drogen peroxide. Proc. Camh. Phil Soc. Vol. xv. 1909. M. Wheldale 143 Leaves. The majority of leaves during the active vegetative period are entirely without soluble pigment so far as the eye can detect. Nevertheless it is possible that the leaves of anthoeyanic plants may contain a small amount of pigment though it is not apparent as such. The leaves of albinos, for instance, are frequently of a brighter and lighter shade of green than leaves of the pigmented type even when the latter are without obvious pigment, and this difference can often be detected before the plant flowers. The deeper colour may, however, be due to some other cause. When pigment is present in the veins and midrib, as is normally the case in many leaves, it is usually confined to the epidermal (gene- rally upper) and sub-epidermal layers. In leaves which are more or less permanently red {Amaranthus spp.), the pigment is commonly present in the epidermis only, both upper and lower, all over the leaf, but in the midrib and veins it may appear in the sub-epidermal layers also. In red-leaved varieties {Atriplex hortensis v. rubra, Beta vulgaris V. rubra, etc.) arising from a green-leaved type, the pigment is again usually only present in the epidermis, both upper and under, of which the cells are intensely coloured. It is an interesting fact that the guard-cells of the stomata in the epidermis of permanently red-leaved plants and red-leaved varieties are colourless when all the surrounding epidermal cells are intensely coloured. The cases of abnormal formation of pigment in leaves may now be considered. If a leaf is subjected to any kind of injury, this is accompanied in many plants by a more or less intense colouration of the tissues. The injury ma}' be a mechanical one, such as tearing of the lamina, partial breaking of the midrib, petiole or stem, or the removal of a portion of the midrib. In each case the leaf becomes pigmented in the part distal to the point of injury. Sometimes the whole leaf when severed from the plant and lying in a fairly moist situation will turn red or purple. Injury may also be brought about by attacks of insects, leaf-boring larvae, aphides and fungi. In all such cases pig- mentation results. Sections of leaves which have been injured show a different distri- bution of pigment from those which are normally coloured. Antho- cyanin is most frequently present in the palisade parenchyma, often in the spongy parenchyma, and more rarely in the epidermis and veins, unless these were originally coloured in the normal leaf. 144 On the Formation of Anthocyanin Hence we may state that iu injured leaves the formatiou of pigment commences in tissues which in the liealthy plant are usually unpig- mented. The same internal distribution of pigment is found in leaves red- dened by low temperature, i.e. autumnal leaves and evergreen leaves in winter, and also in the older dying leaves of plants at the end of their vegetative season or after exposure to drought. It is an interesting coincidence that the phenomenon of increased pigmentation accompanying age is also characteristic of young develop- ing leaves. In these again the pigment is formed in the assimilating tissue, chiefly palisade parenchyma, though it may also appear in the epidermis. Anthocyanin is very frequent in variegated leaves and it is then often limited to the stripes or patches free from chlorophyll (variegated Zea Mais). In other cases {Codiaeum sp., Acalypha sp., Tradescantia sp.), the whole leaf may be pigmented. Stems and Petioles. The distribution of pigment in petioles, herba- ceous stems and the young stems of trees and shrubs is very much the same as in the midribs of leaves. Anthocyanin is usually confined either to the epidermis alone or to one or more sub-epidermal layers in addition, of which the cells are frequently coUenchymatous in structure. Floivers and Fruit. In the corolla, anthocyanin is located in the epidermis, usually both upper and under, sometimes only upper. The upper pigmented epidermal cells are almost always more or less pro- longed into papillae but this prolongation is less characteristic of the under epidermal cells. In fruits the colouring matter may be limited to the epidermis and sub-epidermal layers or may extend into the inner tissues. Concentration of Sugars and Glucosides in various Tissues. To ascertain the relative concentrations of sugars and glucosides in the different tissues of a leaf is a difficult problem. The presence or absence of glucose can be detected micro-chemically by means of Fehling's solution (22), and to some extent glucose, fructose, malto.se and cane-sugar can be dififereutiated micro-chemically by a modification, employed by Grafe(4), of Senft's(l7) phenyl hydrazine method. For detection of differences in amount I have not found these methods reliable. M. Wheldale 145 Since no absolute reliance can be placed on the above tests, it is only possible to draw deductions indirectly from such evidence as we possess from other sources. Broadly speaking the concentration of sugars in a leaf depends upon : (1) The assimilative activity. (2) The starch-forming activity. (3) The rate of translocation of sugars. Since these three factors are more or less intei'dependent and form in co-operation a self-regulating mechanism, the concentration of sugar as the outcome of their combined activities may under normal con- ditions remain fairly constant. But if a tissue has assimilative without starch-forming power or vice versa, we have perhaps some basis for conjecture as to the concentration of its sugar-contents compared to that of other tissues possessing both activities. There is a like possi- bility if the different activities are affected in varying degrees by changed conditions, and this question will be considered again in connection with abnormal reddening in leaves. The question of the concentration of aromatic glucosides in a leaf is even more problematic. Kraus(6) has given experimental evidence for regarding the assimilating leaf as the seat of metabolism of aromatic substances. This author found, as a result of analysis, that aromatic compounds' accumulate in a cut leaf exposed to illumination but decrease in a leaf kept in darkness. He moreover states the amount of aromatic substances formed to be proportional to the assimilative activity of the leaf Palladin(14) also holds the view that the aromatic materials of a plant are manufactured from the carbohydrate series. In corroboration of his view, he quotes the results of Waage(18), who obtained an increased amount of phloroglucin in leaves fed on glucose solution ; also those of Biisgen(2), who found that the tannin contents of plants increase in glucose cultures. On such evidence as we have, we may say that the concentration of aromatic substances in a leaf depends upon : — (1) The amount of sugars present in the leaf. (2) The rate of translocation of aromatic substances. ' In this case, tanning, but the precise nature of the products is immaterial provided they belong to the aromatic series. 146 0)1 the Formation of AntJiocyanin In the formation of authocyauin the following reactions must be taken into consideration : — Aromatic glucoside + water '*^ aromatic cliromogen + sugar. Sugar — »- aromatic chromogen. Aroma.tic chromogen + oxygen = aothoc3'anin. 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. The.se 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 tlie 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 sugar. 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 : — Ampelopsis hederacea Rosa canina Sorbns latifolia Mahonia aquifolium 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- Sugars Dextrins Glucosides Insoluble Carbohydrates greeu •74 2^78 2^43 2^42 red •98 1-88 2-79 502 green '2-42 1-30 8^22 9-72 red 204 1-23 8^24 5^33 green •71 1^15 2-20 11-99 red •80 r07 2-52 120 green •57 •80 3-41 2-38 : red 1^30 •60 4^30 8^78 148 On the Formation of Anthoci/anin hydrates varies, being sometimes greater in one, sometimes in the other. Since the concentration of both gliicosides and sugars is greater in the red leaves, it is reasonable to interpret the pigment formation as being due to accumulation of gliicosides, in which case the reaction Glucoside + water — *- sugar + chromogen would give rise to more free sugar (apart from other causes) in the red than in the green leaf from whicii 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 thei-e 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-Ul 1'64 10'75 red 4-2G -92 6-15 26-58 M. Wheldale 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 Corylus Avellana, Rumex crispus, Taraxacum officinale and Primula sinensis, flowers of Gytisus scoparius, Aquilegia vulgaris, Viola tricolor, Antirrhinum majus, Primula sinensis, Narcissus pseudonarcissus, Cheiranthiis cheiri, Fritil- laria imperialis, Polyanthus sp., Hellehorus 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. 150 On the Formation of Anthoci/anin This retardation is doubtless due to the fact tliat 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 nigi-a and Hiera- ciuin 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. Wheldalb 151 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 Lathyrus and Matthiola. On the other hand, very many anthocyanic plants give no direct action withguaiacum, 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. that 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 Wliitley 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 enz^'me 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 diff'erence 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 aqui/olium, Hedera Helix, Ligustrum vulgare, Saxifraga spp., Grassula spp., Aquilegia vidgaris. Taraxacum vulgare, Eupatorium cannabinum and Epilohium parviflorum), showed increased formation of pigment, but in other cases (Potamogeton spp., Lemna spp., Fritillaria imperialis, Alahonia aqidfoliutn, Anthnscus 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 Katie (.5) with plants of Hydnlla, Elodea canadensis, Hydrocharis morsus-ranae, leaves of Sagittaria natans, Canna indica, Veronica chamaedrys, Rusa sp., Saxifraga cordifolia, Pitfosporum undulatuni 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 connectidu might exist between the reddening of leaves and starch formation in sugar- M. Whbldalb 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 7o 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 sugar +carbon dioxide Distilled water +carbon dioxide Development of Pigment eitlier with or witbout carbon dioxide Viola tricolor no starch no starch no Starch no starch + Capsella bursa pastoris abundant starch no starch abundant starch abundant starch - Lactuca sativa no starch no starch no Starch no starch + Reseda lutea abundant starch no starch abundant starch abundant starch + Matricaria sp. abundant starch no starch abundant starch abundant starch - Cheiranthus cheiri abundant starch no starch abundant starch considerable amount of starch — Nicotiana tabacum abundant starch no starch abundant starch abundant starch - Aquilegia vul- garis some starch in places no starch no starch no starch + Epilobium sp. abundant starch no starch abundant starch some starch - Ilex aquifolium 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 starcli + Rumex crispus very little starch no starch very little starch no starch + Rubus fruticosus crammed starch no starch crammed starch no starch - Journ. of Gen, . I 11 154 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 imierttia 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 witii 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 siich 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 syuthesised 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 Vicia Faba leaves. The question as to whether sugar-feeding does or does not directly M. Wheldale 155 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 Mendklian 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 ■perennis, 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 syivatica, Coryllus Avellana, Beta vulgaris, Atrijjlex hortensis, Perilla nankinensis, Canna indica, Plantago major, Brassica sp., Lactuca sativa, 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 AutJioci/anin equilibrium poisition is such that very little or no free chroniogen 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 iiigraented. 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 arc 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. (b) 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) constitute.s 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 — Latlnjrus, 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 an pigmented : example — deep-flowered varieties oi Antirrhinum inajus, Dianthus harhatus. It is difficult 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. 1a. Bayliss, The Nature of Enzyme Action, 1908. 1. BuscALiONl, L., and Pollacci, G. Le antocianine ed il loro significato hio- logico nelle piante, 1903. 2. BtiSGEN. Chem. Centralh., 1890 and 1894. 3. Combes, R. Du role de I'oxygfene dans la formation et la de.struction des pig- ments rouges anthocyaniques chez les vegetaux. C. R. Acad. d. Sciences, mai, 1910. Sur le degagement simultane d'oxygfene et d'anhydride carbo- nique au cours de la disparitiou des pigments anthocyaniques chez les v(^getaux. C. R. Acad. d. Sciences, ]mn, 1910. Les echanges gazeux des feuilles. Rev. gen. de Bot. torn, xxii., 1910. Production d'anthocyane sous I'influence de la decortication annulaire. Bull. Soc. bot. France, torn, ix., 1909. Recherches biochimiques sur le developpement de I'anthocyane chez les v^gi^taux. C. R. Acad. d. Sciences, 1909. Rapports entre les composes hydrooarbon^s et la formation de I'anthocyane. Ann. d. Sciences nat. 9= s^rie, 1909. 4. Grafe, V. Studien liber den mikrochemischen Naohweis verschiedener Zuckerarten in den Pflanzen-geweben mittels der Phenylhydrazinmethode. Sitzungsher. d. k. Akad. d. Wiss. Wien, Math. nat. Klasse, 1905. 5. Katic, D. L. J. Beitrag zur Kenntnis der Bildung des roten Farhstoffs in vegetativen Organen der Phanerogamen. 6. Kraus, G. Grundlinien zu einer Physiologic des Gerbstoffs. Leipzig, 1889. 7. Laborde, J. Sur le mecanisme physiologique de la coloration des ratsins rouges et de la coloration automnale des feuiUes. C. R. Acad. Sci., 1908. 8. Mangham, S. The Translocation (jf Carbohydrates in Plants. Part I. Science Progress, October, 1910. 9. MiRANDE, M. Sur I'origine de I'anthocyanine deduite de I'observation de quelques Insectes parasites des feuilles. C. R. Acad. Sci. tom. cxLV., 1907. 10. MoLiscH. fiber ein neues, eiuen karmin-roten Farbstoff e.rzeugendes Chromogen bei Schenkia blumenaviana. Ber. d. d. bot. Oesell., 1901. 11. MoLLlARD, M. Action morphogenique de quelques substances organiques sur le,s vegetaux superieurs. Rev. gen. de Bot. tom. xix., 1907 ; also, Production experimental de tubercules blancs et de tubercules noirs k partir de graines de Radis rose. C. R. Acad. Sci., 1909. 158 071 the Formation of AntJwcyaniu 12. Moore, B., and Whitley, E. The Properties and (Uassitication of the oxidising Enzymes and Analogies between Enzymic Activity and tlie Effects of Immune Bodies and Complements. Biochemical Journal, Vol. IV., 1909. 13 Overton, E. Beobachtungen und Versuche iiber das Auftreten von rothem Zellsaft bei Pflanzen. Prings. Jahr. f. mss. Bot. Bd. xxxill., 1899. 14. Palladin, AV. Tiber das Wesen der Pflanzenatmung. Biochem. Zcitschr., 1909. 15. tFber Prochromogene der pflanzlichen Atmung.schromogene. Ber. d. cl. Bot. OesellscL, 1909. 16. Pick, H. Ueber die Bedeutung des rothen Farbstoffes bei den Phanerogamen und die Beziehungen desselben zur Stiirkewanderung. Bot. Centralb. Bd. XVI., 1883. 17. Senft, E. Tiber den microchemischen Zuckernachweis durch essigsaures Phenylhydrazin. Sit:ungsber.d.k: Akad. d. ^Yiss. Wien, Math. nat. Klasse, 1904. 18. Waage, T. Ber. d. Deatsch. botan. Ges. 8. 19. VVheldalb, 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. Wigand, A. Die rothe und blaue Fiirbung von Laub und Frucht. Bot. Hefte. Forschungen a. d. bot. Garten zu Marburg, 1887. 22. ZiMMERMANN. Botanical Microtechnique. 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-ej^ed 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 dense 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. Tiiis 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 F^. In the F.2 generation from this mating two new varieties appear which I have named "chocolate-lilac" and "champagne" {"cafe au lait" of Cu^not) 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 inter 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 homoz^'gous 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 proilucetl. 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-eyeiJ 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 ditferent 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 Fi 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 inte)- se never throw the dark-eyed form. Taking all the results in-espective of colour and classifying only according to eye-colour, then as a result of mating pink-eyed mice with dark-eyed mice in Fo I obtained 875 dark eye, BE, 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 Colovr in Mice 111 the case of the first mating I made between bhie mice and bhie lilac the numbers yielded in the Fo 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 1 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 F^) 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 F^, I got 10 black, 4 blue, G blue lilac and 2 chocolate-lilac. If the mating were as above between EeBdBb x EeDdBB, there should be 12'3 black, 4'3 blue, 2"7 blue lilac and 2*7 chocolate-lilac. F,. F. M. Durham 163 Blue lilac x chocolate, eeDDBB x EEDDhh gives black F^. Blue Chocolate- Black Chocolate lilac lilac Champagne Fi. Observed ... 21 G 0 4 C Calculated ... 20-7 0'9 2-3 4-G 2-3 Here no blue lilacs were obtained but an excess of champagnes. Blue lilac x chocolate, eeDdBB x EEDdhh gives blues and blacks. .Silver Blue Chocolate- Black Blue Chocolate fawn lilac lilac Champagne F^. Observed 4 3 0 0 11 0 Chocolate-lilac x chocolate, eBeb x EbEb gives blacks and chocolates F-j from blacks Blue Cliocolate- Black Chocolate lilac lilac Champagne Observed ... Iti 7 0 3 0 Calculated ... 14-4 4-8 I'O 3-2 1-6 From black and chocolate Observed ... 8 16 0 0 5 Calculated ... 10 8 10-8 0 3-G 3-6 From chocolate x chocolate Observed ... — 38 — — 16 Calculated ... — 40-5 — — 13-5 Blue lilac x silver fawn, eeddBB x EEddbb giving blue F^. Silver Blue Chocolate- Blue fawn lilac lilac Champagne Fi. Observed .. 43 19 3 10 3 Calculated ... 43-9 14-6 4-9 9-7 4-9 Chocolate-lilac x silver fatun, eeddBb x EEddbb giving blue F^. Silver Blue Chocolate- Blue fawn lilac lilac Champagne F,. 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. Silver Chocolate fawn Champagne f,. 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 Eeddbb. Silver fawn Silver cliampagne Fi- Observed 11 2 Calculated ... 9-75 3-25 Chocolate heterozygous in pink-eye x chocolate-lilac, Eehb X eeBh. Black Chocolate Chocolate- Ulac Champagne Observed 2 3 2 3 Calculated ... 25 2-5 2-5 2-5 Blue X champagne giving black F^, EeDdBh x EeDdBb. Black Blue Chocolate Silver fawn Blue Ulac Chocolate- lilac Champagne \ . Observed 4 0 2 1 0 1 1 Calculated 3-5 117 1-17 •4 •5 1 •5 Blue X champagne giving blue and black Fi, EeddBb x EeDdBb. Black Blue chocolate Silver fawn Blue lilac Chocolate- lilac Champagne \ . 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, EeddBb x EeDdbb. Black Blue Chocolate Silver fawn Chocolate- lilac Champagne Observed 2 3 4 1 1 0 Calculated 2-1 21 21 21 1-3 1-3 Blue heterozygous in pink-eye and chocolate x champagne, EeddBb x eeDdbb. Observed Calculated Black 3 1-6 Blue 0 1-6 Cliocolate 5 1-G Silver Chocolate- fawn lilac 3 1-6 1 3-2 Champagne 1 3-2 Blues carrying pink-eye mated together, EeddBB x EeddBB. Blue Blue lilac Observed 19 6 Calculated 18-75 ti-25 F,. F. M. Durham 165 Golden agouti x chocolate-lilac gives golden agouti F^, GgBhEe x GgBhEe. Pink-eyed Golden Cinnamon Pinli-eyed cinnamon Blue Chocolate- agouti agouti Black Chocolate agouti agouti lilac lilac Champagne Observed 83 8 31 2 26 7 0 11 4 Calculated 72-9 24-3 24-3 8-1 24-3 S'l 27 5 '4 2-7 Golden agouti x pink-eyed agouti gives golden agouti F^. Golden agouti Pink-eyed agouti F^. Observed ... 32 17 Calculated ... 36 ^o 12-25 Cinnamon agouti mated ivith chocolate-lilac giving cinnamon agouti Cinnamon Pink-eyed agouti Chocolate Cinnamon agouti Champagne F,. Observed ... 14 4 3 1 Calculated ... 12-3 4-1 4-1 1-4 Agouti heterozygous in pink-eyed agouti y. pink-eyed agouti. Agouti Pink-eyed agouti Observed ... 11 8 Calculated ... 9-5 9-5 Agouti heterozygous in pink-eye and chocolate y. pink-eyed agouti heterozygous in chocolate. Pink-eyed Cinnamon Pink-eyed cinnamon Blue Chocolate- Agouti agouti Black Chocolate agouti agouti lilac lilac Champagne Observed 70 2 1 10 001 0 Calculated 5-8-5 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 6 1 10 3 0 6 0 2 4 Calculated 9 3 9 3 3 1 1 2 1 Pink-eyed agouti y. 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 F^ 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 matings 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 i.s 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 C\ieuot(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 F^ 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 bo 2 : 1. Yellow Non-yellow 263 100 800 435 448 232 1511 767 1518-6 759-3 1708-5 569-5 [ow X Yellow Yellow X Non-yellow 3-38 3-74 4-71 5-57 F. M. Durham 167 The F„ numbers obtained are as follows : Cuenot(2) Castle(5) My own Expectation at 2 : 1 Expectation at 3 : 1 From these figures there can I think be no longer any serious doubt that the pure yellow zygotes aie 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 varietates 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: Cuenot Castle 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 3'90 young yellow X other colour 3'97 „ black X black 460 black X other colour (not yellow) 3'99 „ chocolate x chocolate 3'96 „ chocolate x other colour (not yellow) 3'93 „ agouti X agouti 3"47 „ agouti X other colour (not yellow) 3'32 „ albinos x other colour (not yellow) 4'27 „ 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 168 Inheritance of Coat Colour in Mice considering, is to be suspected, and 1 doubt whctlier the observations can be used either for or against the conclusion that the ratio of yellow to non-yellow in F„ is 2 : 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 chocohite 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. DuEHAM 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 yellowy will appear in Fn 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 prodnced 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 3'ellows I have obtained the follow- ing results, 17 matings PEY 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 aud a yellow belly. It resembled a very yellow agouti with a yellow belly. Its ancestry is shown by the followiog scheme : Pink-eyed chocolate-lilac Yellow throwing agoutis 1188 X 1450 1667 ^ X 1555 ? I 1 ' — I 1 1 3 black 3 agoutis 1 blue 1 pink-ejed 1 yellow champagne agouti 1825 Joum. of Gen. i 12 170 Inheritance of Coat Coloxir in Mice Both 1667 j/ aud 1555 $ were agoutis and not to be distinguished in any way externally from any ordinary agouti. I mated the yellow agouti mouse (1825 (/) with 6 does, but unfor- tunately the niatings were not all successful. With a chocolate $ there were 20 young (not one of which was agouti), 1 yellow, 4 blacks, 7 sables, 1 ch(jcolate yellow belly, 3 chocolates, 8 albinos, 1 chocolate- lilac. Mated with a yellow mouse carrying chocolate he gave 2 yellows, 2 sables, 3 blacks and 1 chocolate. I tried him four times with agouti mice but in each case there was no result. I had hoped by such niatings to obtain agoutis which would throw yellows or sables. None of the offspring mated together produced any agoutis. Case II. A champagne $ was mated with an agouti ,/. In the first generation there were 1 agouti, 4 cinnamon agouti, 1 chocolate. The agouti which was a ^ was mated with the only % a cinnamon agouti, and there resulted 1 sooty yellow, 2 silver cinnamon agouti and 1 black. Unfortunately death carried off the yellow before she could be mated. Subsequent litters of the parents did not contain any yellows. In the subjoined tables the calculations are made on a 2 to 1 basis instead of the ordinary 3 to 1, adapting the conclusion indicated above. TABLE OF RESULTS. Dark-eyed Yellows. Yellows carrying chocolate mated together : Yellow Chocolate 136 68 observed 136 68 calculated Yellows carrying chocolate x chocolate : Yellow Cliocolate 66 46 observed 56 56 calculated Yellows carrying black and chocolate mated together : Yellow Black Chocolate 65 35 9 observed 72 27 9 calculated F. M. Durham 171 Yellows carrying black and chocolate x chocolate : Yellow Black Chocolate 23 11 9 observed ■21-4 10-7 10-7 calculated Yellows carrying black x chocolate : Yellow Black 6 18 observed 12 12 calculated Yellows carrying black and chocolate x black heterozygous in chocolate : Yellow Black Chocolate 25 17 18 observed 30 15 15 calculated Yellows carrying black x black : Yellow Black 29 24 observed 26-5 26-5 calculated Yellows heterozygous in black, chocolate and albino mated together : Yellow Black Chocolate Albino 59 27 5 30 observed 45-3 34 11-3 30-4 calculated Albinos heterozygous in yellow and chocolate :< chocolate heterozygous in albino : YeUow Chocolate Albino 12 5 7 observed 8 4 12 calculated In the following tables the yellows are not separated into yellows and creams on account of the difficulty stated above of distinguishing between them. Yellows heterozygous in chocolate and silver fawn mated together : Yellow and Cream Cliocolate Silver fawn 5 7 5 observed 11-2 4 2 1-4 calculated Yellows heterozygous in chocolate and silver fawn x silver fawn : Yellow and Cream Chocolate Silver fawn 83 11 13 observed 29-0 14 '5 14-5 calculated Yellows heterozygous in chocolate and silver fawn x chocolate heterozygous in silver fawn: YeUow 13 16 Yellow heterozygous in black and albino x albino heterozygous in yellow and black : Yellow Black Albino 5 2 7 observed 4-6 g'S 6-9 jalculated Chocolate Silver fawn 10 9 observed 12 4 calculated 172 Inheritance of Coat Colour in Mice Yellow X Agouti gives Yellow and Agouti. Fi yellow x Fi yellow : YeUow Agouti 60 32 observed 61 '2 30-6 calculated Fi yellow x Fi agouti : YeUow Agouti 38 32 observed 35 35 calculated Yellow heterozygous in agouti X chocolate : YeUow Agouti 19 19 observed 19 19 calculated Yellow heterozygous in agouti x black : Yellow Agouti 11 18 observed 14-5 14-5 calculated Yellow X Chocolate-Lilac gives Yellow and Black. Fi yellow x Fi yellow : Dark -eyed yellow Black Cliocolate Pink-eyed yellow lUue lilac Chocolate- lilac Cliampagne 46 12 3 24 0 1 9 observed 48 18 6 16 2 4 2 calculated Here there was an excess of champagnes, no bhie lilacs and only one chocolate-lilac. -Fj yellow x F^ black : ark-eyed yellow Black Chocolate Pink-eyed yellow Blue lilac Chocolate- lilac Champagne 26 20 2 11 0 15 3 observed 28-8 21-6 7-2 9-6 2-4 4-8 2-4 calculated Here there was an excess of chocolate-lilacs, no blue lilacs. Dark-eyed yellow heterozygous in pink-eye x pink-eyed yellow ; Dark-eyed yellow Black Chocolate Pink eyed yellow Blue lilac Chocolate- lilac Champagne 34 5 5 27 0 2 7 observed 26-4 9-9 3-3 26-4 3-3 6-6 3-3 calculated FixFi: Yelloiv X Pink-eyed Agouti gives Yellows. Dark-eyed Pink-eyed Pink-eyed yellow Agouti yellow agouti 25 17 11 5 observed 28-8 14-4 9-6 4-8 calculated F. M. Durham 173 Dark-eyeil yellow heterozygous in chocolate and pink-eye : Dark-eyed yellow 11 9-C Chocolate 9 4-8 Pink-eyed yellow 1 4-8 Champagne 1 observed 2-4 calculated Dark-eyed yellow heterozygous in chocolate and pink-eye x chocolate heterozygous in pink-eye : Dark-eyed yellow 8-4 Chocolate 7 8-4 Pink-eyed yellow 1 2-8 Yellow heterozygous in pink-eye x blue lilac : Dark-eyed yellow Black 0 Chocolate 2 Pink-eyed yellow Blue lilac Yellow heterozygous in pink-eye x chocolate-lilac : Dark-eyed yellow Black 2 Chocolate 4 Pink-eyed yellow Blue lilac 0 Champagne 6 2-8 Chocolate- lilac Chocolate- lilac 0 observed calculated champagne 0 observed Champagne 2 observed Yellow heterozygous in pink-eye and chocolate x champagne : Dark-eyed yellow Chocolate 4 Pink-eyed yellow Cliampagne 9 observed 14 3 Here there is an excess of pink-eye. Pink-eyed yellow x pink-eyed yellow heterozygous in black and chocolate : 'ink-eyed yellow Blue lilac Chocolate- lilac Champagne 25 3 15 1 observed 28 8 3-6 7'2 3-6 calculated Here there is an excess of chocolate-lilac possibly due to the fact that some of the yellows were heterozygous in blue lilac only and others in chocolate only, and those mated together would give chocolate lilacs only, no blues and no champagnes. Pink-eyed yellow x pink-eyed yellow heterozygous in chocolate only: Pink-eyed yellow Champagne 18 12 observed 20 10 calculated Pink-eyed yellow x pink-eyed agouti : Pink-eyed yellow 15 11 Pink-eyed agouti 7 observed 11 calculated Pink-eyed yellow heterozygous in pink-eyed agouti : Pink-eyed yellow Pink-eyed agouti 12 8 observed 13-2 6-6 calculated 12- 3 174 Inheritance of Coat Colour in Mice Pink-eyed yellow x chocolate-lilac : Pink-eyed yellow Blue lilac Cliocolate- lilac Champagne 8 2 8 3 observed 10-4 2 -6 0-2 2 '6 calculated 'ink-eyed yellow x champagne Pink-eyeil yellow Chocolate- lilac Champagne 7 4 7 observed 9-0 4-.5 4-5 calculated Sable Mice. Among the yellow mice I used for my experiments were some individuals, which produced sables when mated with blacks or choco- lates. As these appeared very early in my experiments, I at first concluded that sables would always result from such raatings. Subse- quent investigation however showed that the power to produce sables was limited only to certain mice and that it was a hereditary quality. At present I am unable to offer a scheme which correctly represents the relation of sables to the other colours. Sable mice are well known to the Fancy. They differ from yellow mice in having a dark black or brown streak down the middle dorsal region while the rest of the mouse is yellow. The streak maj' be very narrow, when the mouse is said to be a light sable, or very broad when the mouse is a dark sable. As a general rule, the hairs in this dark streak show an agouti pattern, being black or chocolate barred with yellow. But this does not mean that the mouse is carrying agouti determiner. But it is possible to pi'oduce sables in which the barring of the dorsal hairs is absent, and at various times I have had black, blue, chocolate and silver fawn mice which differ only from the ordinary forms by having yellow bellies, and which from their genetic behaviour must be classed with the sables. They always moulted subsequent!}^ into ordinary sables. The appearance of the sable mouse varies very much according to age. During the first few months the marking is very definite, but as age comes on the sable appearance is lost, so that a mouse, which was a very good specimen at three months may be hardly distinguishable from an ordinary yellow mouse at 18 months old. The amount of yellow in its colouring increases with the successive moults. Sables are not to be confused with sooty yellow mice, which result from mating ordinary yellows with blacks or chocolates. The sooty yellow is a dirty colour all over and never shows a definite pattern. F. M. Durham 175 I have never bred a homozygous sable mouse. Bred together, sables may throw sables, yellows, blacks, chocolates, and also agouti, if they are carrying the agouti determiner. Yellows carr3dng the sable determiner mated together will throw sables, and sables mated together may throw yellows. By mating together yellows carrying sable I have obtained 111 yellows, 38 sables, and 69 other coloured mice. By mating yellows carrying sable with other coloured mice, not yellows, I have obtained 78 yellows, 5.5 sables, and 80 other coloured mice. Mating together sables, I have obtained 161 sables, 43 yellows, and 142 other coloured mice. Mating sables with other colours, not yellow, I have obtained 93 sables, 90 yellows, and 174 other coloured mice. Examination of the records suggests, that there is more than one sort of sable mouse, and that it is possible to produce sables which never throw yellows at all. Thus I had as a result of 5 matings between blue sables, 29 blue sables, and 23 blue mice, and no yellows at all. 4 matings between blue sables and dark sables gave 16 sables and 8 other colours (no yellows). 7 matings between blue sables and blue gave 20 blue sables and 19 blues. On examination of the results produced by mating sables together, I find that the matings in which yellows were produced, the offspring consist of 62 sables, 43 yellows and 64 other colours, while the offspring of the matings in which no yellows were produced, consist of 99 sables and 78 other colours, suggesting a 9 to 7 ratio. The matiuors of sable x other colour show that the families iu which yellow appeared consisted of 48 sables, 90 yellows, and 107 other colours, in the remaining families there were 45 sables and 67 other colours. Matings between sables and yellow^s .without the sable determiner give 23 yellows and 18 other coloured mice, no sables. Matings between yellows canying sables with sables give 14 yellows, 28 sables and 17 other coloured mice. 176 Inheritance of Coat Colour In Mice These results suggest th, 11, 459 ,, 6 8 1 5 11 1 „ 20, 461 ji 2 14 8 10 7 4 1908 „ 19, 459 ,, — 2 3 2 3 — „ 19, 393 II 3 14 8 5 7 6 „ 22, 467 .- — 1 - 4 — — Total 12 42 21 28 28 13 Expectation lS-75 37-5 lS-75 26 26 17 194 Peculiar Pigmentation, of the Silki/ Fowl the constitution ffPPII or ffPPIi and suppose that in the presence of a double dose of the pigmentation factor the effects of the inhibitor are in considerable measure overcome in the younger stages. In cor- i-oboration of this view we may state that we reared several of these deeply pigmented ^^ and that they all became far less heavily pig- mented in appearance as they approached maturity. In external appearance indeed they showed little more pigmentation than the i^, cocks. This explanation is the natural one if we regard the constitu- tion of the slightly pigmented Fi % as FfPpIi, and further evidence (p. 198) in favour of this view will be adduced from an entirely different set of experiments. 3. fj X Brown Leghorn. (o) Broiuii Leghorn % x F^ ^. [Nature of mating, FfppIi x fPpIi.'] On our hypothesis this form of mating should give a specific result, for while the (^ ^ should all be either without, or with comparatively little, pigment, one quarter of the % % should be fully pigmented (cf. Figs. 3 and 4). We have bred a considerable number of birds (nearly 700) in this way, and the figures given in Table V show that this expectation is closely realised. None of the 336 c/',/ produced 1006 1907 1908 1909 TABLE V. ce Nature of mating Full Males Some None Females Referen Full Some None Pen 9, 207 Brown ? x Fi (^ — 28 8 29 „ 3.3, 248 If — 8 1 1 ,, 33,. 159 II — 13 5 13 ,, 11, 203 11 — 34 8 24 „ 12, 264 }i — 13 3 8 ,, 12, 159 ,, — 19 3 18 „ 15, 347 Br. L. ? xFxS — 34 11 37 „ 16 ? $Br.L. Brown ? x Fj — 17 3 20 „ 16, 345 Br. L. s X F, J — 20 7 16 „ 22, 129 Brown ? x Fj ,J — 40 8 31 „ 20, 347 Br. L. 9 X Fi g — 4 1 4 Total — 336 82 280 Expectation — 336 90-5 271-5 W. Bateson and R. C. Punnett 195 were deeply pigmented, while of the 362 $ $ 82 were deeply pig- mented, a proportion approximating fairly closely to the expected quarter. We should add that owing to a deficiency of pure Brown Leghorns some of the hens used were light-shanked brown birds of Brown Leghorn extraction. With regard to the transmission of pig- mentation these behaved similarly to the pure race. i/S) F^ ^ {unpigmented) x Broivn Leghorn ^. [Nature of mating, FfPpIixffppIL] Two i^i $ 5 of this nature were crossed with a Brown Leghorn ^ and gave 2(5 (/"(/' 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. f 1 X Fully pigmented (PPii) birds. («) F,^xPPii%. [Nature of mating, FfPPiixffPpIi.] 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 Males Females Full pig- Some pig- Full pig- Some pig- Reference Nature of mating mentation mentation mentation mentation 1906 Pen 33, 349 Silky ? x Fj » »» 10 15 1907 1908 „ 9, 283 it »* 15 19 We have already alluded to the deeply pigmented hens which resulted from crossing the F^ t )) ,, ,, ,, veins. „ XXXV. 7 (5) yellow colourless. „ XXXV. 8 (6) white ,, „ 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 Sttulies in IiuViun 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 KFand ry, and the six groups which have been recognised the constitution given below with the numerical proportion between the individuals which is assigned to eacli group: (1) ««"■ Mo^ RRYy -2 P I (2) KrYY 2j [ * RrYy 4^ J (3) HRyy 1 \g W liniV -i J '■'•ly 2S ) (6) rnj,j 1 1 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, tlierefore, fully explained on the assumption that two pairs of allelomorphic characters enter into con- sideration, these two pairs being composed of the two fiictors 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 yellotu (PI. XXXV), and the other a red on white (PL 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 S, 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 froTu 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 (RRYY) 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 extending to the veins {RrYy), that with red on white flower and colour extending to the veins (Rryy) and that with a yellow flower {7-rYy). 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 -f, 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 Shfdies in Indian Cotton (a) Corolla red or red on yellow. (h) „ red on pale yellow. (c) „ yellow. (d) ,, pale yellow. The miiuber 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 gi-oup (rf) these numbers agree fairly with the Mendelian ratio of 0 : 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 intr(]ductory 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 constancj' of this factor for the various tj'pes of Gossj'pia. 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 groups 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 ^ . Todaro 's group B, as fully defined, is distinguished by not only the factor - 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 , ° . of the lobe, 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 hroad lobed leaf, with leaf factor less than a ; 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 a 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 evei-y full}- developed leaf and obtain from 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 O'lo from the mean (giving a total range of 03) and, when this value lies above 3, this error may reach 0'3 (with a total range of 0'6). 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 ludian Cotton necessary receives recognition in the use of the word " typical." Tiiese precautions require examination since, in a purely arbitrary deter- mination of this nature, some control is required to ensui-e 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 undersUmding 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 arc almost invariably sympodial. The values obtained for the average leaf factor of these four groups are respectively : (1) 1-82, (2) rs-i, (3) 1-73, (4) 172. 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 006 and 004 from the value obtained by the empirical method of selection of " typical " leaves. This error lies well within 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 ecpial 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 pulilished, the average of th factors of all the fully developed leaves. 'J'liis 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 c H. M. Leake 225 determination of the value e where an accessory notch {vide 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) „ „ gi-eater 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," to use Johannsou'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 1-64 which have been isolated, and from type 9 " pure linos " with leaf factors of 3'34 and 3-59 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 8 the leaf factor of the plants of the F^ 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 1 In the fields plants are frequently founil 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 (b). 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 p;ireutal 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 F3 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 monopodial 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 examinatioQ 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 (0'31, OSo and 0"38) in the three cases. This excess, thmigh small, appears definite but has so far received no explanation. Fi t: : " it--+-4^t:""' II T r^ . . Tit"" ""I c+ii"ii _i::..:. ..:in: ::::::::::ii :::::: :::::::::: _ 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 F.^ generation raised from the seed so obtained. The results are set out in Table XIV. In this table the extreme and Journ. of Gen. i 16 228 Sfufh'es 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 F« 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 21 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 F3 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 F„ 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 F^ 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 2'6 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 3'0, 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 3"2 — a figure which exceeds the vahie of the corresponding parental leaf factor. In this connection it is noteworthy that a value of 35 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 313 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 0'3-5 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 i^i 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 br'anches 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 1 Since the above was written Bulls. 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 must 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 monopodiah 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 90 80 70 60 50 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. Leake 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 affect 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 difference 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 effected. Here only indirect comparison is possible and the effect 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 iu 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 F„ 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 daj's 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 fo^md 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 iu 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 earl)' 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 appro.xi- 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. Leake 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 length 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 F, series only in a slightly different 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 Studies 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 offspnng from a cross between monopodial and sympodial types. In the Fi 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 J''i generation and of the two parental types are detailed. This table further shows that while the F^ 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 Fi 1909 Parents 1909 Fi 1908 Parents 1908 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 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 — XXP, 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 1 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. Leake 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 1 The two cases noted in Table XVIII form apparent exceptions to this statement but must, in the absence of further evidence, be considered as extreme instances of divergence from the expected ratio. 240 Studies in Tndian 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 F^ 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 thecase, 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 difficulty 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. Fig. 4. 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 bi-acteoles (vide Figs. 3 and 4)'. ^ The difference is well shown by a comparison between Plates 14 a and 16 Watt (20). 242 Studies in Indian 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 invai'iably 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 7-ed 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 F^ 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 betw^een 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. Bails, W. L. Joiirn. of Agricultural Science, Vol. ii. No. 2. 2. Year Book of Khedivial Agricultural Society, \Q09. 3. Bateson, W. MendeVs Principles i Plants of the World. 21. BuRKiLL, I. H. Memoirs of the Department of Agriculture in India (Botanical Series), Vol. i. No. 4. 22. Fletcher, F. Journ. of Agricultural Science, Vol. II. p. 281. 23. Hartley, C. P. U.S. Department of Agriculture, Bureau of Plant Industry, Bull. No. 22. Journ. of Gen. i 17 244 Studies in Indian Cotton TABLE P. Flotoer Colour. Type 4 [yellow coloured) x Type 6 [lohite flowered). Fi 68 plants all yellow flowered \ 109 plants yellow flowered 52 plants wbite flowered - 1 ratio 2-1 1 F2 plants used as parents 21 13 10^ 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 3x 5 299 102 401 3x 8 180 64 244 3x 9 374 120 494 3x101 351 100 451 Total 1534 484 2018 Eatio 317 1 417 ' Determined on flower colour only. H. M. Leake 245 TABLE III. The intensity of the red colouring matter in the leaf as an indication of -purity. Leaf of F-i parent recorded as Type 3 X Type 4 Constitution, as by Fz offspring, determined of the form Tola («) HR Rr Lamina 61 5 66 Veins 2 20 22 Ribs 0 116 116 Total 63 141 204 Eatio 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 TV. The intensity of the red colouring matter in the petal as an indication of purity. Flower of F., parent reeorde'd as Type 3 x Type 4 Constitution, as by F3 offspring, determined of the form Total (a) RR Rt Bed 28 2 30 Red on yellow 35 136 171 Total 63 138 201 Ratio 1 2-2 (b) Type 3 x Type 9 Red 11 3 14 Red on yellow 46 136 182 Total 57 139 196 Ratio 1 2-4 17—2 246 Studies in Indian Cotton TABLE V. The F2 geimralioii of crosses between type 3, in ivhirh t/ie red colourittg matter is present, and types in which it is absent. Coloured Colourless RR Lamina Rr ^ rr Veins Kibs Total Total (1) 3x2 Ratio 10 1 23 73 96 9-6 29 2-9 135 (2) 3x4 59 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 1-1 1-7 1 W 3x8 33 5 58 63 38 134 8x3 26 6 52 58 26 110 Total 59 11 110 121 04 244 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 J 121 494 Ratio 1 2-8 1-2 Grand total 358 86 739 - 825 384 1567 Ratio 1 23 1-1 ' 5 of these shown by experiment to be impure. - 2 „ ,, ,, pure. 24 „ „ ,, impure. * 22 „ „ „ pure. TABLE VL Flower colour. Type 3 {red flowered) x Type 4 (yelloiv flowered). to veins. RR Rr RR+Rr rr F^ Foliage (lamina) (Ribs or Veins) (Total coloured) (Colourless) 77 147 224 69 Ratio 1-1 2 1 1 Used as J 61 lamina 5 lamina 204 68 parents \ 2 veins 136 veins RR Rr RR+Rr rr (Lamina) (Ri ibs or veins) (Total colon red) (Colourless) F3 1328 832 1692 2524 773 12451 Ratio 1-07 2-18 1-90 ' 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 CD 'e 'K, "« •«. :;> v^^ fl c3 05 m a ^ s e^ en X X CO CTi _ _ ^_^ __ Si s IC CO rH CQ d -2 CO ^ a s ^6 1 CD O CO S s C<1 00 CO CO CO >, Ti i" I> ZO fc „. .^ a 5 3 ^ CO ^ iH E & __ a - 1 ^ CO T}< Cl CI 1 fl o_2 lO CO cci Z' '3 o ■^A >o 1^ '3 II CI I §2 I-H I-H a; a II O O r-l t> lO 5- "5" s c — o » lO 0^ CO ^ 15 0^ a II I-H ^ '~li^ ,^ Sa a 0) Si o I-H 1 J3 1 00 o ip CO it I CO CO _ C'^ ^ J o^ (?3 cp CI E* CO CI . 00 oj c-~ a o » ? ^ s II o o o -3 a o CO o o 1^^ .5 'S 11 CJ CO CO ii- «d __ |i •s CO CI CO >H fl" o ^S ^ ^ j*i -* CO fc 3 - 1—1 ^ "^-T « >■ _ Oi CO t*. c °o 9-^ CI CI CO <-t 0^ I 0>. S-" -O »0 CO tH I-H a; £ CI fH 63 ta-r- S a o^ X .— t ,_, a "C'S -p ir- ^ i* ■■^ OT 00 CO CM ^ ^i, ^^ rt ;::■ -t< CO CO t-, ^S 'g 1 CO CO CI §1 N a S°s ^ ^ £ o 5^ -^•^^ t-. 5 CI "5" ,£3 a _ o g ce ^ a •n i i = •^ ft p. >H _rt I 1 r-( o o 1a ^ 1-3 m eg as 65 1 o .9 ft o o S '^ O o '12 *-■ ft s p &^ fc X tu kT f? Ph H 248 Studies in Indian Cotton TABLE VIII. Flower colour. F^ plants x jinrents. (Type 2 x Type 3) x Type 3 {red (lamina) x yellow j x red (lamina) (Type 2 x Type 3) 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 i) 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 wliite (lamina) (veins) (lamina) (veins) yellow white 13 31 — — 2 — 21 6 — — — 18 15 TABLE IX. Detail of individual of type having leaf factor 1"88. Number of leaves Leaf factor Tertiary branches Number of leaves Leaf factor Main stem 31 1-82 Secondary branches (a) Monopodial arising from leaf 7 9 1-81 arising from leaf 8 21 1-8G 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 3 1-70 15 1 1-79 Monopodial arising from leaf 5 3 1-74 6 3 1-8G H. M. Leake 249 arising from leaf 10 arising from leaf 11 arising from leaf 12 arising from leaf 13 21 arising from leaf 14 19 TABLE IX {continued). Number of Leaf leaves factor Tertiary branches Number o£ leaves Leaf factor a Sympodial arising from leaf ■ 8 4 1-78 )> 10 3 1-72 a 11 3 1-81 »» 12 3 1-66 )i 13 3 1-74 f » 14 1 1-83 >f 15 3 1-76 »> 17 3 1-64 »» 18 4 1-64 12 1-86 arising from leaf ' 8 2 1-75 j» ,, 10 1 1-68 >f J) 11 1 1-74 )» 11 13 2 1-87 ,, )] 14 3 1-75 23 1-91 arising from leaf : 5 2 180 i> 7 2 1-84 ») 8 3 1-74 >) 10 2 1-73 J> 11 3 1-69 »» 13 3 1-76 J» 14 3 1-68 i» 15 1 1-71 »J 16 1 1-78 )> 18 2 1-72 19 1 1-71 19 1-84 arising from leaf 5 1 1-61 9J »> 6 2 1-65 9> ,j 8 2 1-78 1» ?) 11 2 1-73 21 1-88 arising from leaf 5 1 1-71 n 9 3 1-73 »l 10 3 1-76 7) 12 1 1-72 >> 13 4 1-78 ») 15 1 1-76 M 16 2 1-69 J» 17 18 1 2 1-74 1-77 19 1-77 arising from leaf 6 1 1d2 >i J, 8 1 1-57 )) 10 11 2 3 1-75 1-79 250 Studies in Indian Cotton arising from leaf 15 15 TABLE IX {continued). Number of Leaf leaves factor Tertiary branches Number of leaves Leaf factor 15 1-70 arisint; from leaf 5 3 1-73 6 2 1-85 8 1 1-70 10 1 1-68 arising from leaf 1(5 8 1-83 arising from leaf 5 arising from leaf 17 IG 1-71 18 13 l-;)7 Average of leaves on Syrapodia 1-73 arising from leaf 1 1 1-72 5 2 1-55 7 2 1-79 „ 11 2 1-73 arising from leaf 19 ii; 1-81 arising from leaf 1 6 1-87 10 1 1-73 arising from leaf 2i 14 1-78 arising from leaf 1 5 1 71 2 1 1-79 G 2 1-57 7 1 1-59 Average of leaves on Monopodia — 1-84 Average of leaves on tertiary branches — 1-73 [b) Sj-rapodial arising from leaf 20 4 1-76 21 6 1-75 22 3 1-66 23 1 2-07 25 6 1-81 26 2 1-73 27 6 1-78 28 5 1-80 29 4 1-79 30 4 1-63 31 3 1-69 32 5 1-66 33 1 1-65 34 3 1-67 35 3 1-71 36 3 1-70 37 2 1-70 38 2 1-68 39 3 1-60 40 3 1-69 41 1 1-85 1-72 H. M. Leake 251 Type 4 Type 5 Type G Type 8 Type 9 TABLE X. Variation of the leaf factor within the type. Extremes of leaf factor Leaf factor (average of offspring) Number of offspring used in determination Max. Mill 1907 1908 1907 1908 1-57 1-17 1-37 — 32 — 1-71 1-27 1-4G 1-49 20 2 1-92 1-42 1-6.5 1-73 17 5 1-80 l-oO 1-68 1-73 20 9 1-94 1-73 1-78 1-80 20 14 1-98 1-69 1-88 1-84 20 16 1-98 1-69 1-81 1-88 20 20 3-83 2-96 3-35 8-26 18 20 3-64 3-5o 3-59 3-71 2 10 4-18 3-18 3-G4 407 20 20 4-34 3-80 4-lo — 20 — TABLE XL The relation between the leaf factor of the F^ generation of a cross and those of the parents. s Parents rUen Leaf factor of parents Mean of parental leaf factor Leaf factor of offspring Difference Number of >, individuals eed Pc Seed Pollen Type 3 Ty pe 2 3-13 1-45 2-29 2-26 -0-03 23 , 3 , 4 313 1-45 2-24 2-21 -003 12 , 3 , 4 3 13 1-64 2-38 2-49 + 0-11 13 , 4 , 3 1-4G 3-13 2-29 2-42 + 0-13 3 , 4 , 3 1-64 3- 13 2-38 2-45 + 0-07 9 , 3 , 5 3-13 1-78 2-45 2-70 + 0-25 31 1 5 ' , 3 1-78 3-13 2-4.5 2-45 — 6 , 2 . 8 1-46 3-.J9 2-52 2-18 -0-34 12 > 2 , 8 1-46 3-34 2-40 2-37 -003 3 , 8 , 2 3-59 1-4G 2-52 2-49 -0-03 3 , 8 , 4 3-59 1-64 2'61 2-53 -008 6 , 8 , 4 3-34 1-G4 2-49 2-54 + 0-0.5 9 > 4 , 8 1-46 3-59 2-52 2-3G -OIG 13 , 4 , 8 1-64 3-34 2'49 2-42 -0-07 18 252 Studies in Indian Cotton TABLE XII. The leaf factor. Type 3 (1. f. > 3) x Type 4 (1. f. < 2). Fi Leaf 1 15 plants mean leaf fact factor 3-13 Mean 2-27. or 2-21. ...1-40 1, Leaf factor <:2 >2 and 3 ^2 Number of individuals Ratio 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 Batio 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 J-'a Number of individuals Ratio 1222 5 784 1 1602 204 791 1 6 1273 Mean leaf factor 1-71 102 262 3-42 3-51 ' 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-ajypearance 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 >2 and <3 >3 F«. Number of individuals 40 82 Ratio 3-6 74 Mean of leaf factor ... 1-63 2-43 (b) Type 4 x Type 8. Leaf factor 1'52 3-47. Mean 2-49. 11 1 3-41 Pi 28 plants mean leaf factor 2-39 Leaf factor -c 2 > 2 and <3 >3 F2 Number of individuals 47 102 Batio 1 22 Mean of leaf factor ... 1-66 2-59 46 1 3-42 254 Studies in Indian Cotton TABLE XIV. The leaf factor. F^ generation ?'3 r-i '"* •-H fH f-i F-H i-H c^ ci C-l c^ •M •M C-l C-l Cl •M m pe 3 V Type 9 Pots Fiel 1 DiHer- ence Pots Field Number of plants Days Period in Days Number of plants Days Number of plants Days Number of plants Days Differ 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 20 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. Type 3 X Type 4 Number Intervals Number indicative Number of days from sowing of of type of to flowering plants branching Above 170 2 75 166—170 3 91 161—165 4 87 156—160 13 79 151—155 16 62 146—150 13 57 141—145 14 54 136—140 19 64 131—135 25 42 126—130 89 29 121—125 37 26 116—120 43 11 111—115 46 •* 5 106—110 14 4 101—105 3 — below 101 1 — Type 3 X Type 9 Number of plants 2 3 51 8 9 9 22 33 21 31 36 26 10 3 Number indicative of type of branching 87 75 40 69 50 44 30 21 15 2 1 In this table, which is based on the F-, 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 fiulian Cotton TABLE XVIII. The lewjlh of the vegetative period. The Fj tjeneraliou 3-^ 2 3 nH ^ ^ — . Cl 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 87 166 162 324 156 314 112 242 195 153 158 274 181 140 210 225 134 264 254 214 221 1 1 1 — 2 — — 1 1111 1 1 6 — 1 — 1 — 2 — 4 — 14 — — 1 1 2 — 1 — 1 — 1 1 1 — 1 2 — — 1 — 1 1111 -112 1 — — 1 1 — — 1 1 — 2 1 2 1 — 1 — 1 2 1 — 2 1 — 1 1 — 1 1 2-1 1 1 1 — — 1 ^ — 1 2 1 — 1 1 1 1 4 — 1 — 1 — 1 — — 2 1 3 — 1 — 2 1 2 2 — 1 1 1 6 2 1 — 1 — 1 1 1 1 1 — 1 1 1 — 3 1 2 1 4 2 2 1 1 1 — — 4 1 2 1 2 2 — 2 1 1 — 1 — 1 3 1 2 — 1 1 2 — 3 1 — 1 — 1 — 1 — — 2 2 1 1 3 1 1 1 — - 2 — 2 1 3 2 — 2 — H. M. Leake 259 from th". cross. Type 3 x Ti/pe i. Pot Series. * T3 O tn c K — — — — — — — — — — — — — — — — — — — 10 107 — — — — — — — — — — — — — ______ 7 112 1 — — — — — — — — _—________ 10 101 — — — — — — — — — — — — — — — — — — — 18 100 — — — — — — — — — — — — — — — — — — — 22 99 1— — — — — — — — — — — — — — — — — — 10 110 — — — — — — — — — — — — — — — — — — — 13 107 — — — — — — — — — — — — — — — — — — — 24 113 — — 1— — — — — —— — — — — — — — — — 10 109 — — — — — — — — — — — — — — — — — — — 21 102 — 2 — — — — — — — — — — — — 22 98 — — — — — — — — — — — — — — — — — — — 5 113 — — — — — — — — — — — — — — — — — — — 6 132 — — — — — — — — — — — — — — — — — — — 19 118 — — 1 — 1— — — — — — — — — — — — — — 22 11.5 1— — — — 1— — — — — — — — — — — — — 22 115 — — — — — — — — — — — — — — — — — — — 12 lU — — — — — — — — — — — — ____ — ___ 8 111 — — — — — — — — — — — — — — — — — — — 14 109 — — — — — — — — — — — — — — — — — — — 21 109 — — — — — — — — — — — — — — — — — — — 16 108 — — 1— — — — — — — — — — — — ____ 11 124 1— — — — — — — — — 1— — — — — — — — 21 114 — 1 1— — — — — — — — ________ 12 119 1 1 2 1 1 _ _ _ - 1 _ _ _ _ _ _ _ _ _ 25 117 — — — — — — — — — — — — — — — — — — — 8 113 — — — — — — — — — — — — — — — — — — — 22 112 1 — 1— — — — — — — __ — ______ 5 117 — 1 — — — — — — — — — _ — ______ 17 131 — 1— — — — — — — — — — — ______ 9 115 2 1 l---l-l-_________ 81 113 — 1 1— _ — — — _ — _________ 13 119 1 1— — — — — — _!_________ 19 119 — — — — — — —— — — — — — — — — — — — 7 116 1— — — — — — — — 1 1— _______ 11 108 2— — — — — — — — — — — — — — — — — — 11 132 1 2 — I— ___!__________ 19 124 2 1— __— 1__ — _________ 16 118 2-1-1---- ________ 14 115 2-1 1 1 - __________ IB 155 1 — 1 1 1 — I — 1 _ — _ — _____ _ 20 127 4 3 2 1_1_____________ ^3 120 2— — -1 l___-l ________ 16 130 — 2 1 __ — — — __________ _ 24 128 1--1 1 _!___-________ 11 119 2-1-1 1 ---__-_______ 13 148 1-2— _l_____i _______ 18 141 4 6 2__l___l _________ 36 130 1— — — 1— — — — — — — — — — ___— 9 126 Joum. of Gen. i 18 itl 5 o -10 97 -14 98 + 2 103 + 3 103 + 5 104 - 5 105 - 2 105 - 7 106 - 2 107 + 5 107 + 9 107 — 5 108 -22 110 - 8 110 - 5 110 — 5 110 - 4 no - 1 110 + 1 110 + 1 no + 2 no -13 111 - 3 111 - 7 112 - 5 112 - 1 112 — 112 - 4 113 -16 115 — 115 + 2 115 - 3 116 - 3 116 — 116 + 8 116 -15 117 - 7 117 - 1 117 + 2 117 -37 118 - 9 118 _ 2 118 -11 119 - 9 119 — 119 -28 120 -21 120 -10 120 - 6 120 2(30 Studies in Indian Cotton TABLE XVIII — — 1 — 4 1 1 1 1 1 1 1 3 1 — 1 1 1 188 _______1 2 — 1— — — 1 1 — 100 ____________ — — — — — 273 ________ — __ — — — _ — — 33.5 ________ — _ — — — _ 1 __ 71 _________________ 1 _ 1 _ 1 — 187 __________^1 2 3— — 1 — 1 — 1 3 2 182 ______________ 1 — 2 1___1 1 132 ______________1__2 2— — 3 2 147 _____________ 1 2_ — — 1 2 — 1 1 179 ___________ 1— ______ 4— — 1 310 _____________ 2 2— — 1— — 1 6 4 97 _ — — — __________ — _1_____ 3 263 _____________2_ — — 2 2 1— — — 221 — — — __________ 1 __ — _ — — _2 — 223 — — ______• ___l___l 3___1 1 3 328 _ — _ — — — ____ — — — — 1 — — 1 ___ 1 _ 155 _______________2 — 2— — 2 1 1 275 _____________ 1 ____.__2 2 2 259 __________1_1___— 1 1 1 1 — 3 246 _ — — _ — — _ — — — — — _l— — — — 2 — 2 3 1 75 — — — — _________ — ___1 1 1 — 1 1 194 _ — — — — — — — _ — _ — __ — — 1 — 1— — 2 2 266 _ — — — ____ — — — — _—__ — — 1 — 2 3 2 249 _ — _ — — — — — _—__ — — — 1— — 1— — - — 185 — — _ — — — — — ____ — _l 2 1 1— — 1 — 1 271 — — _ — — — — __ — ______ — — _— 1 2 4 235 _ — — — — — — — _ — — ____- — — — _ — — 1 1 227 — — — — _ — — __ — _ — — — — 1 — — _ 1 — 1 — 77 —_ — __ — __ — — ______ 1___ 2 1 1 245 ____________ 1 ____ — — — — — — 176 ________________ 1 ______ 215 _______________________ 212 __________l____l — 1_1 2 1 1 175 _ — — — — — __________— 1 _____ 272 ____________________ 1__ 256 __________________ 1__— 1 345 __ — — — — ___- — — — _. — — _ — — — 1 _ 1 239 — — — — — — — — _____________ 1 1 251 —— — — — — ____ — — — _ — _1__— 1 1 3 89 —____________ — _ — — ____ — _ 255 _ _ ____________________ 1 269 __________ — _______ — — — — — 93 _-___-__-_-_-_________ 1 220 ____ — __ — ______ — _ — — 1— — — 1 245 __ — __ — — _ — — — — — — — — _ — — — — — — 244 — — — — — — — — — — — — — — — — — — — — —— — 240 _________________ — — — — — — H. M. Leake 261 {continued). o a a, ^^ '^ 3 ° = a. O 4 2 1 — 1 1 __ 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 — — 1 1 — — _____ — — _ — _ _ 12 121 — 121 — 2 2 1 — — — — — —— — — — — — — — — — 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 - 7 122 7 4 — 2 1 — — 1 — — — — — — — — — — — _ 31 112 +10 122 1 1— — — 1— — — — — — — — — — — — — _ 7 166 -43 123 — 3 2 1 2 1 — — — — — 1 — — — — — — — _ 17 141 -18 123 — 2 1— — 1— — — — — — — — —— — — — — 7 128 -5 123 1 11 — 4— — — 1— — — — — — — — — — 22 128 -5 123 1— — — — — — ——— 1— — — — — — — — 6 118 +5 123 3 — 1 — — — — 1 — - 1 _________ 15 118 + 5 123 1 — — _ 1 — — — _ 1 _________ 11 163 -39 124 2 2 — 2 — 1 1 — — 1 __!______ 20 143 -19 124 _ 5 5 — — 2 — — — — — 1 — — — — — — — — 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 1 — — — _ — — — — — ___-— — 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 — 1— — — — — — — — — — — — 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 l_l_— 1 — !_!_________ 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 1 _ 1 _ 1 _ — — — — 12 140 - 6 134 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— _— 16 129 +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 i______l_ — — — — 4 133 +7 140 18--2 262 Studies in Indian Cotton TABLE XIX. The letiylh bf the vegetative period. The F, rjeneralioii 3 4 3 4 1 1 — — 1 1 — — — — 32 4) 74 72 W 50 45 18 1!) 14 13 12 10 6 15 44 63 83 78 59 57 40 31 33 45 30 33 28 12 19 30 61 6S ()5 62 52 66 58 63 80 76 70 t 5 13 18 26 31 39 41 32 35 68 75 91 97 1 — 1 2 3 3 1 6 0 7 16 20 30 27 — — — 1 — — — 1 1 1 2 3 10 12 110—114 — — — — — — — — — — — — — — — 1 — — — — — 1 TABLE XX. The length of the vegetative period. The F^ generation -r? iO GD c^ iM -+( -n m *^ r>i -*t -^5 -n i-^ -M Below 80 — — — — — — — 2 80— 84 — — — 1 2 2 13 8 85— 89 — — — 1 — 1 6 8 90— 94 1 — — — — 1 — 2 95— 99 2 1 — — — — — 3 100—104 — — — — — — — — 105—109 — — — — — — — Below 104— — — — 3 2 1 1— 1— 1 1— 1 l — — — — — _ 105—109 — 12 3 5 7 7 5 5 7 13 7 6 17 12 16 13 6 5 1 — 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 — — — 1 4 12 5 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 852434 5 17113—1 — — 8.5— 89—1 1 1 2 6 11 17 21 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 9g_ 99 _ _ _ _ 1 _ 7 i; 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 (; 5 4 14 11 15 17 13 11 110—114 — — — — — — — — — — — — — — 2— 1 2 2 3 4 6 115—119 — — — — — — — — — — — — — — — — — — — 1 4 3 H. M. Leake 263 from the cross. Type 3 x Type 9. Pot Series. •tH o a) a O ^ ^ ^ ^ f^ c-l 3 CI, ___________________ 1 6 2 2_______ — _____ _ _ 33 12 13 3 3______ — _______ 37 56 26 30 16 12 5 5 2 3 1 ________ 40 68 37 46 33 16 12 5 3 4 4 2 1 _ _ 2 _ _ _ 43 13 9 20 12 11 8 6 3 1 3 _ 2 1 1 _ _ _ _ 14 4 17 21 7 14 53 1_2_2_1_1__ 6 _ 1 1__ 11_2 1 l____l__ 2 II •4 o to If to ^ o a s 106 20 79 -27 112 512 83 -29 116 691 87 -29 123 942 92 -31 125 815 97 -28 136 212 102 -34 137 109 106 -31 127 11 111 -16 /ro7n the cross. Type 3 x Type 9. Pot Series. 3a3 ^5^ So^ ^^ ^1^ '^ o CM -* o X o ci '^ cr: X o c^ -# o X o_,>'^2;^i-^^rfi=^ a3 CO CO CO CO CO -* -* -^ "tH --h ir> in m m tm to^^nfarfiH3a"-fiijyi .* 3S go; 2 S sg ;* ^ o >o " Z << Z-- -r!^ fi — — — — — — ___ — — — — — — — __ 1 111 9 77-34 — — — —'— — — __________— 3 116 57 83-33 1 1 __ — _____ — — — — ___ _ 13 115 234 87-28 8 7 1 3 __ 1 __________ — 33 124 451 92-32 4 10 1 6 3 2 3 2 1 _ _ 1 !____— 20 124 306 97-27 12 13 9 7 3 1 8 3 1 1 5 1 _ _ — _ — 1 20 129 264 102 -27 11 7 8 6 7 4 5 6 2 5 3 2 3 ^ _ _ — 4 14 130 178 107 - 23 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 -26 264 Studies in Indian Cotton TABLE XXII. The itderrelation between the length of the i^egetative period and the type of hmnching. Type 3 x Type 4. Pot Series. ii ranching Number jq 20 30 40 50 CO 70 80 90 j^Sl_^riS^ Below 90 3 6 2 — — — — — — 19 ^9 92 2 4 4 1— 1___27 94 — 8 4 1 _____ 24 20 95 2 1 10 2 _____ 32 9fi_— 3 !______ 98 _ 3 4 3__ — — — 30 31 100 2 4 4 4 3 1 _ _ — 33 ■ 102 — 4 2 1 2 1 _ — _ 34 104 2 3 4 5 2 — — — — 31 34 105 1 3 5 2 4 2 — — — 30 ■ 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 _ — 36 114 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 1 — 46 47 125 — — 4 2 7 0 1 _ — 50 126 — 1 5 G 4 2 7 2 — — 128 — — 2 2 3 6 7 4 _ 61 56 130 1 — 2 4 4 4 e 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 04 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 Average [ j^g j^^ j^^ jj^ j.^j j^e 130 135 147 penoa J H. M. Leake 265 TABLE XXIII. The interrelation between the length of the vegetative period and the type of branching. Ti/pe 3 x 7'gpe 4. Field Series. Branching ^"dayY 10 20 30 40 50 00 70 80 90 p^^f/^ peS Below 65— !______ — 15 20 66 !____ — _ — — — 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 l _ _ _ _ 21 21 80 46 65 32 12 1 1 l _ _ 21 82 30 76 58 16 7 |j _ _ _ 23 84 24 59 44 16 9 6 2 — — 27 26 85 6 25 25 13 2 1 _ — — 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 5 20 15 16 13 7 13 1 _ 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 4 2 3 7 9 11 5 1 — — 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 _ 60 58 120 _ — — 2 4 2 3 _ _ 55 122 — _ 1 _ 2 _ 4 1 _ 61 124 __ — 1 1 4 2 1 _ 61 61 125 — — — 1 _ _ 2 _ _ 55 128 _ _ 1 _ _ 1 _ _ _ 45 59 130 _________ . 132 _ _ _ _ 1 1 _ _ 1 66 66 134 _ _ _ _ 1 _ _ 1 _ 65 Average j gg g^ gg y^ yg j^^, ,^^ ^^^ ,^^ period ) 266 Studies in Indian Cotton TABLE XXIV. The interrelation between the length of the vegetative period and the tyfe of hranching. Type 3 x Type 9. Pot Series. Branching Number jq gg 30 ^^ 50 60 70 80 90 „V^fJ, ^ Below 85 — — — ^ — — — — — 80 — — 1_ — — — — — 30 88 — — — — — — — — — — 26 90— 5 4 !_____ 20 92 — 5 5 1 1 1 _ — — 31 94 — 8 10 3 — 1 — — — 29 29 95 — 2 4 — — — — — — 25 96 1 0 4 l__ — — — — 98 — 7 9 8 — 1 _ — — 32 31 100-12 6 8 3 2 — — — 33 102 — 5 10 6 — 2 — — — 33 104 — 9 15 8 5 1 _ — — 33 33 105 — 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 0 2 — — — 32 11-4 — 15 28 15 18 4 — — — 30 35 115 1 0 22 21 13 1 _ — _ 37 116 1 7 17 26 4 5 — — — — lis 2 18 38 41 22 15 2 — — 39 39 120 1 10 27 29 23 6 3 1 — 40 122 — 13 17 36 27 13 4 2 — 45 124 1 10 27 34 36 20 1 1 — 42 45 125 1 1 7 IS 27 18 7 1 — 50 120 — 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 0 — — 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 — 01 00 145 — — 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 — 70 102 — — — — — — — 2 — 80 164 — — — — — — — - — — 75 165 — — — — — — 4 3 — 74 Average [ ^^g ^^^ ^^^ j^g ^33 ^gg 137 144 — period I H. M. Leake 267 TABLE XXV. Dip. interrelation bi-ticeen tlie Ifrnjlh uj the veijeiative 2}friod and tlie type of hranchiny. Ti/pe 3 < Type 9. Field Series. Branching ^JZt 10 20 30 40 50 60 70 80 90 l^'^ Beluw G5 — — — — — 1 — — — — OG ___ — — — — ___ 68 1 1 — — ___ — __ 15 24 70 — H 1 — 1 _ _ _ _ 29 72 1 2 3 — — — — — _ 20 74 1 6 3 2 — — — — — 25 26 75 2 7 2 7 — — — — — 27 ■ 76— 9 G 9 — — — — — — 78 6 11 14 16 1 — — _ _ 29 27 80 9 17 21 7 2 1 _ — _ 27 82 7 18 15 7 2 3 — — — 28 84 1 16 14 5 3 1 _ — _ 29 29 85 — 7 12 7 3 — — — — 32 SO 1 9 12 7 3 1 — — __ 88 1 6 12 16 5 1 1 - _ 3G 33 90 2 1.3 15 9 3 3 — — — 31 . 92 1 10 19 14 13 3 — — — 36 94 1 12 22 20 11 9 — — — 37 38 95 — 3 12 17 10 5 2 — — 39 96 4 4 >< 8 4 3 — — — ^ 98 2 12 12 30 2G 12 1 — — 41 41 100 1 6 10 17 15 7 5 — — 43 ■ 102 1 5 9 20 15 13 2 — — 44 104 1 5 12 11 13 12 3 — — 44 44 105 — 1 2 5 3 3 1 — — 44 lOG — 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 6 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 53 125 — — — — — — — — — 65 126 — — — — — 1 1 — — _ 128 — — — — 1 1 2 1 — 66 G7 ISO — — — — — 2 3 — — 66 132 — — 1 — — 1 4 1 _ 64 67 134 — — — — — — 1 — „ 70 Over 135 — — — — 1 2 — — — — 136 — — — — — — — — — — 138 —_ — — — — ___ 140 — — — — — — — — — — Average | gg gg gg yg gg JQ^ j^g j.,j _ period J 268 Studies in Indian Cotton TABLE XXVI. I'he relation between the lerujtli of the veyetalive period of the F^ ge7ieratlon of a crons and those of the parents. Monopodia! Parent Sympodial Parent Fi generation ^ '- ^ ■'- . Mean of ^'- ■^— .^ Type Days Type Days Parents Maxiinuni Minimum Aleau Difference Type 3 14(5 Type 4 83 114 108 80 94 20 „ 3 140 „ -, 80 113 111 77 98 1.-) „ 3 14li „ 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. Tlie leaf ylands. F^ and F.^ r/etierations 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-i Leaf glands 0 1—3 3—1 Total glandular Number of individual ... 68 113 100 213 Eatio 1 1-7 1-5 31 Used as parents 64 107 90 197 Pure Impure Pure Impure Pure Impure 60 4 2 105 38 52 Corrected distribution ... 62 Expectation ... ... 65 161 130 38 65 201 195 H. M. Leake 269 TABLE XXVIII. The leaf glands. The F.j yenerafion of the cross. Type 3 x Type i. Leaf glands Total Total Fj Character of Fo No. of glan- indivi- Expecta- Character of F^ parent plants 0 1 — 3 3—1 dular duals tion offspring 60 1381 — — — 1381 — Leaf glands 0 Leaf glands 0 18 4 0 — — — 1 4 2 1 — — — 1 32 0 1 — 818 872 Leaf glands 0 1 18 1 0 62 Leaf glands 1—3 1 — 23 — — — — 1 — 6 — — 1080 1744 Leaf glands 1—3 2 — 29 — — — — Expectation . . . 105 557 567 822 1134 899 567 1712 1701 — — Leaf glands 3 — 1 Expectation ... 52 199 278 222 550 690 278 912 834 1591 872 Leaf glands 3 — 1 38 _ — 679 — 679 — Leaf glands 3—1 270 Studies in Indian Cotton TABLE XXEX. Correlation between the presence oj the red Flower colour Leaf ■m^:dxo'm-*:ooooct'*:c>xo colour ^CV3^050000 0.-Hr-tr-(t-I^C^ lamina — — — — — — — — — 1 — 3 4 G 4 green ______4 4 12 20 6 5 5— 1 Type 3 x Type 4 Pure forms Red on Yellow Yellow Impure forms (Eed on yellow lamina — — — — — — 1 — — 3 1 2 3 10 12 (Yellow green 1 1 1 — 4 3 _ 5 11 11 15 11 18 11 4 Type 3 x Type 9 Pure forms Red on yellow lamina — — — — — — — — — — — — — 2 1 Red on white lamina — — — — — — — — — — — 1 1 1 — Yellow green — — — — — — — — — 1 2 1 3 3 1 White green __ _ — — 1 — 1- 2 2— 4 3 1 (u) In one character only. Impure forms (Red on yellow lamina — — — — — — — — — — — — 1 5 — |l!ed on white lamina — — — — — — — — 1 — — 1 — 2 — IRed on yellow lamina — — — — — — — — — — — — 2 — — (Yellow green — — — — — 1 — — 1 2 — 1 3 1 — (Red on white lamina — — — — — — — — 1 — 1 1 2 — o (White green — __ — _1 — 1 1—3 2 2 — — (h) lu both characters. Red on yellow lamina — — — — — — — — — — 1 3 2 2 2 Red on white lamina — — — — — — — — — 2 2 1 1 3 3 Yellow green __ — _— 22 1 826 5 251 White green _ — _— 3 2 — 2 5 1 3 4 1— 1 H. M. Leake 271 colouring matter of the sup and a lengthened vegetative period. 'Moic^cocc«ccco^-*'*-t<-i n — ^-]5 — F—pT~T r 1^ i" I" (■" 0 0 0 0 &a&(»0'«.^ JOURNAL OF GENETICS, VOL. \. NO. 3 PLATE XXXVIII ,»sv JOURNAL OF GENETICS, VOL. I. NO. 3 PLATE XXXIX 'f.v u= '">,- l: ^pw , The GARDENERS' CHRONICLE The leading Horticultural Journal in the World INVALUABLE TO STUDENTS OF GENETICS Subscription: Great Britain 15/-. Abroad 17/6 per ann. Specimen Copy on application to the Publisher H. G. Cove, 41, Wellington Street, Strand, London, W.C. CAMBRIDGE UNIVERSITY PRESS Trees A Handbook of Forest-Botany for the Woodlands and the Laboratory. By H. Marshall Ward, Sc.D., F.R.S. Vol. I. Buds and Twigs, pp. xiv + 271. Vol. II. Leaves, pp. x + 348. Vol. III. Flowers and Inflorescences, pp. xii + 402. Vol. IV. 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Its object is to enable agricultural and other students to recognize the common grasses of our fields Crown 8vo at any time of the year, whether in flower or not. To this end the appear- 81 figures ances presented by roots, stems, foliage, and flowers are carefully noted and 6s usefully tabulated..,. Botanists and agriculturists alike have reason to thank Prof. Ward for this very serviceable addition to the literature of grasses." — Athenceum Agriculture in the Tropics An elementary treatise. By J. 0. Willis, M.A., Sc.D. pp. xviii-f222. "Mr Willis exhibits in his instructive volume an intimate knowledge of the agricultural features of most of the tropical areas, and the information he gives concerning the soils and climates, and the principal cultivations at the Demv 8vo present time, will be read with interest by those experienced in tropical 25 Diates farming, and will be of inestimable benefit to intending emigrants and the 7s 6d net inexperienced. A study of this handsomely illustrated volume may help to influence those who contemplate emigration to tropical countries to decide the colony or country that offers the best opportimities for their particular proclivities, and to this ever-increasing class the book can be confidently recommended. " — Field LONDON: CAMBBIDGB UNIVEESITY PRESS: FETTER LANE CONTENTS All Rights reserved PAOE L. DoNCASTER. 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 The Journal of Genetics is a periodical for the publication of records of original research in Heredity, Variation and allied subjects. The Journal will also, from time to time, contain articles summarising the existing state of knowledge in the various branches of Genetics, but reviews and abstracts of work published elsewhere will not, as a rule, be included. Adequate illustration will be provided, and, where the subject matter demands it, free use will be made of coloured plates. The Journal will be issued in parts as material accumulates, and a volume, appearing, so far as possible, annually, will consist of four such parts. Papers for publication may be sent either to Mr Bateson, Manor House, Merton Park, Surrey, or to Professor Punnett, Gonville and Caius College, Cambridge. Other communications should be addressed to the University Press, Cambridge. Papers forwarded to the Editors for publication are understood to be offered to the Journal of Genetics alone, unless the contrary is stated. Contributors will receive 50 separate copies of their papers free. 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Types of British Vegetation By members of the Central Committee for the Survey and Study of British Vegetation. Edited by A. G. Tansley, M.A., F.L.S., University Lecturer ou Botany in the University of Cambridge. Crown 8vo liiis is tbe first general systematic description of the different types of g . wild vegetation in this country that has ever appeared. It is illustrated by more than sixty carefully selected photographs. LONDON : CAMBRIDGE UNIVERSITY PRESS : FETTER LANE Volume I NOVEMBER, 1911 No. 4 Nr;\V Yoj^ ON GAMETIC SERIES INVOLVING REDUPLICATION *"" ' ^ "^'^ac OF CERTAIN TERMS\ "''"'"'' By W. BATESON, M.A., F.R.S. AND 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 gainetogeiiesis 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 Fj 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 F.^ 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 •3AB : Ab : aB : 'Sab, 7AB -.Ab-.aB: Tab, loAB -.Ab-.aB: \5ab, &c. If on the other hand the heterozygote, AaBb, is formed by the gametes Ah 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 our 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. ' This papeV is also appearing in the 49th volume of the Briinn Verhandlungen which is to be published as a Mendel Festschrift. 2 Proc. Ray. Soc. B, Vol. 84, 1911, p. 1. Journ. of Gen, i 20 2M Rediqdication 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 Evohitiou Committee of the Rojal 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. Tiie 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 N/x 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 behaveil 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 F, there is some coupling between the dark axil and fertility. The numerical result-s however are complex and must be left over for discussion until more material is available. W. Bateson and R. C. Punnbtt 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 I. Reference Number Normal Normal fertile sterile Cretin fertUe 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 8 78, 59 15 24 — 79, 25 12 15 2 Total 336 150 143 11 Expei-tation 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 F is to be regarded as partial, and of such a nature that the series of gametes produced by the F^ plant is NF, 'SNf, SnF, 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 norrhal 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 are 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 Red^iplimtion in Gametic Series the gametes Ab and aB, the gametes produced by the heterozygote so derived form one or other term of the series AB : SAb : SaB : ab, AB : 7Ab : 7aB : ab, AB : l5Ab : l5aB : ab, &c. And if we take 2n as the number of gametes in the series we may generalise it under the expression AB : (n — 1) Ab : (n — 1) aB : ab. As the repulsion increases in intensity it is obvious that the zygotes of the form AABB 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 (2?i= +1)AB: {n- -l)Ab: {71' - 1 ) aS : ab*. TABLE II. Gametic series Number of gametes in series Number of zygotes formed Natxire of zygotic series AB Ab aB ab AB Ab aB nb 1 1 («- 1) n-1) 2« 4tt--= 2)1^+1 K^-l n^-1 1 Partial repulsion from zygote of form AbxaB 1 3] 31 64 4096 2049 1023 1023 1 1 1.- 1.5 32 1024 513 255 255 1 1 i, 1 7 3 16 8 256 64 129 33 63 15 63 15 1 1 1 L 1 4 16 9 3 3 1 3 1 8 64 41 7 7 9 Partial coupling from zygote . of form 7 15 31 1 1 1 1.5 31 16 32 64 258 1024 4096 177 737 3009 15 31 63 15 81 63 49 225 961 ABxab 63 1 63 128 16384 12161 127 127 3969 (M-1) 1 («-l ) 2n in- 3k -(2k- 1) 2rt-l 2« -1 n- - (2n - 1) 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 hL and the 419 plants recorded in F.^ were distributed in the four possible zygotic classes as follows : Reference Number Blue long Blue round Red long Red round Number 61, 1910 85 33 41 1 ■F28, „ 60 20 23 — „ ^31, „ 9 7 5 — „ •F'32, „ 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 aiforded by the cretin sweet pea we prefer the latter hypothesis, and we are inclined to regard the partial repulsion between B and L as of the 1:7:7:1 type. On this hypothesis we should expect one red round in every 256 plants (of. 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 intcusit}'. In most cases this could not be tested in practice owing to the very large 1 Blue in the flower colour (jB) is dominant to red (b), and long poUen (L) is dominant to round pollen (/). 2 Proc. Roy. Soc. 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 N 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 out 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 vievr 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 onl}' 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 Mattkiola- and on Petunia'^ proved that in those plants the factors for singleness are not similarly distributed to the male and female cells. ' From the fact that in maize the endosperm characters are the same as those of the seed itself we know moreover that segregation must have been completed before the divisions at which the male and female cells which constitute the endosperm are set apart. - Hep. Evol. Committee E. S. IV, 1908, p. 36. 2 Jour. Gen. i. 1911. W. Batbson and R. C. Punnett 299 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 differentiation has been brought about. At some early stage in the embryonic development or perhaps in later apical divisions we can suppose that the ?i — 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 system of segregation is actually formed at the apex, it must be supposed that the axes of the system revolve with the 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 1 Biol. Centralbl. xxxi. 1911, p. 97. 300 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 AuBh, 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 AB X ab I AB ab j Ab . aB I Ab.aB I 3AB lAb Iba Sab 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 aa-es of this system may well be determined by the position of the constituent parental gametes. Reduplication or pro- liferation resulting in n - 1 gametes may then take place in either of the opposite pairs of quadrants according to the parental composition. W. Bateson and R. C. Punnett 301 2. If in the gametes of auy 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 liave happened simultaneously. Moreover if various reduplications can take place very early in some individuals and not in others, we cannot imagine how the normal form of the plant remains unchanged, unless these reduplications afifect 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 coiipling 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 1 See Coulter and Chamberlain, Morphology of Angiosperms, 1903, p. 187. 302 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. L 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, Cambridge. TABLE OF CONTENTS. PAGE Statement of conclusions arrived at in the earlier experiments .... 303 Later experiments on the inheritance of " doubleness " and plastid colour . . 306 I. Races which were obtained only in the double-throwing form . . . 300 II. Races 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 IV. Constitution of the zygote and segregation in the eversporting forms . 321 V. Segregation in F^ crossbreds derived from two eversporting forms and statement of the results obtained in ^2 324 VI. Constitution of the zygote and segregation in the pure-breeding (non- double-throwing) strains 334 VII. Segregation in Fy crossbreds derived from unions between eversporting and non-double-throwing forms and statement of the results obtained in F2 336 VIII. 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 unbranohed 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 arrived 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. ' Reports I — IV to the Evolution Committee of the Royal Society. In regard to "doubling" see II, 1905, p. 29; III, 1906, p. 44; IV, 1908, pp. 4, 36. 804 Douhleness 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-Bingle singles singles (J-single singles doubles (sterile) singles doubles (sterile) and so on indefinitely. singles doubles (sterile) and so on indefinitely. A strain composed entirely of d-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 ;io-cZ-single $ x rf-single (/* gives Fi plants all throwing doubles on self- fertilisation, the recipi'ocal cross d-single $ x /!o-d-single , 3 of the Fi indiWduals 3 Fi „ „ „ „ 1 „ Pi 1 Parent plant (B)' 20 Fi Plants derived by self-fertilisation from the parent plant B 5 Fo „ ,, ,, ,, 2 of the Fi individuals 5 F3 „ „ „ „ 3 „ F-i 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 rf-strains and ?!0-rf- strains afford a con- venient means of separately testing the ovules and the pollen of the (Z-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 Fo (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: iSTo-rf-glabrous cream 4 ,, „ white 4 „ ,, flesh 1 „ hoary white (Brompton) 1 Total ... 10 ' A and B were obtained from different growers. - Transmission by the ovules will be dealt with in a later section (see p. 323). E. R. Saunders 309 91 of the resulting ^i crossbreds were self-fertilised to produce F^. The number of these ^i plants derived from the 6 rf-parents used as ^, representing in each case an equivalent number of pollen grains, were respectively 57 19 7 3 3 2 Total 91 Doubles occurred in every F„ family. Each of the 91 pollen grains tested must therefore have been carrying the double character. In the sulphur-white race 7 individuals were employed as the c?-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 : W^o-d-glabi'ous 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 F^ plants derived from the 7 d-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 expecteil from Joura. of Gen. i 21 310 DouhJeness in Stocks an Fi 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 83 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. Tlie other 4.5 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 C found in the ordinary pure white glabrous race', for the mating witli the cream pruduced offspring which were all cream, and, as we should expect under these circumstances, all glabrous. Thus the F^ plants obtained from crossmg the cream with the sulphur-white are indistinguishable in appearance from .^i plants derived from the same cream parent by .se^/"-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 Tegard 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 ' As stated in the Evolution Reports one of the two factors C and It 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 carrying 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-throwing 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 (i-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-throwing 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. 1 Unless otherwise stated all races employed in these experiments were ol the Ten- week class. 21—2 312 Doubleness in Stocks s (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 glabrous Copper glabrous Totals Parent plants 1 2 2 1 3 2 1 12 Fi individuals derived from self-fertilisation of parent plants 5 (all of one family) 3 (all of one family) 21 (all of one family) 4 (all of one family) 19 (belonging to three families) 0 0 52 Fo individuals derived from self-fertilisation of F] plants 0 2 (belong- ing to two families) 9 (belong- ing to six families) 2 (both from one family) 0 0 0 13 F^ individuals derived from self-fertilisation of F-i plants 0 9 (all of one family) 22 (belong- ing to five families) 0 0 0 0 31 Totals 16 54 22 1 108 Twelve individuals belonging to different sap-coloured forms were taken at random, and they and 90 of tlieir 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 genuinely eversporting, and that it is iu 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 iiave been bred by self-fertilisation from the mating no-d $ x d (/' where the (/* parent belongs to the sap-coloured form which is to be tested. Up to the present 36 F^ plants representing as many pollen grains contributed by 6 c?-parents have been tested in this wa}'. The parentage of these F^ plants and the number of pollen grains tested in the case of each parent are shown below ; the composition of the F^ families will be discu.ssed later (see p. 336 and Table IV) ; those marked thus * have already been recorded (see Report II, p. 37). E. R. Saunders 313 Number of pollen Number of f , Matings from which the Fi grains tested in the case plants tested plants were derived of each <^ parent 6 Ho-d-cream J x d-light purple ,? (plant /I) 6 14 ,, „ X „ „ (plant £) 14 7 mo-rf-flesh ? x „ „ (plant B) 7 1 *7io-d-dark purple $ x d ,, (plant C) 1 6 Mo-d-cream ? x rf-azure s 6 1 *no-d-flesli ? x d-dark purple i 1 1 *no-d-white ? x d-copper which were all single. Further, when nsed as ? with two ((-strains the 28 individuals obtained in f 1 were all single. Seeds from Source 1 TcMe I showin ^1/ self -fertilisation, or by crossing I single individual. •=» double individual. I +2x +4» S. — r— I I XXX I I I 124 X 160 X 8 > 57* 47* 64 1 Seeds from Source 2 Sample sowing of Plant C x abrous cream) X Plant / x Plant <7x+llx+7« commercial seed | 200 X I 240 X I , , 1 ' 1 1 1 T 1 1 1 1 1 1 1 T T^ I i I I I I I I I I X X X X xxxxxxxx62x 1079 I I I I I I I I I I I I j5j( X 5 X 1 X ^'^ fi'^ 2>^ 6x 5x Ix 4x 6x S« !• 6« 3« 12* 10« 4* 6* 6« 1« 4« 2« ieeds from Source 1 Sample sowing of commercial seed Table II i^'^9' <^''^f^ ^he results obtained.- (jio-d-glabrous flesh ? ) X Plant Xx + 8 x +17# Plant A > I I I Plant N X Plant 0 x 33 X 62* 52 X 70* Jeeds from Source 2 Samp J ^^^ rf-glabrons red i X Plant G I I X Hi X 21 X I 44 X 16 • te d 13 X r 3x urn XXX Table I showing in the case of the white glabrous race the mimber and pedigree of the individvals tested by self-fertilisation^ or with a no-d-strain, and the results obtained. x =a single mdividuai. ©^n double Seeds from Source 1 HeedB from Souroe 2 Sample sowing of commercial teed Sample sowing of commercial seed (no- d.glabroas cream) X Plant B x by crossiyig individual. +2x +i4 "1 1 \ 1 Plant c > I 200x Plant D X 245 X (Plant AT Plant B > 1 37 X I 66 X 2S* 98 X 2S« 121 X 32 • 116 X 37* 49 X 25 a 107 X 39 • I 124 X 57 • 160 X 47 • Plant F X I many x total not recorded Plant G X I many x total not recorded (no-d-glabrou» cream) X Plant /x I Plant ./x +11 X +7« 240 X 1 r^T^i I I 16x 5t 5'x -' I I I i 7x 6x 9x 6x 7> 3* 2a la la 4i i I 8x 56 X 3a 2ia r~T" X X _l _l la 1* "T~"r~T I I I I 3x «a 1: 4a I I I 5x 5x 10 X 3a loa isa 6'x sa I I I I I I I 5x 8x 6x 2x 12a 12a 10a 4a I I 6x 6a 6: r>a I I I Ix 4x Ox la 4a 2a 62 X 107 a Tah/c II shoioimj the numher and pedigree of the cream p?a?i«s tested by self-fertilisation, or by erossing, and the results obtained.- Sfedg from Source 1 Sample HowioR o[ commercial Beed {d-glabrouB red $ ) X Plant B x Plant N X Plant O x I I 33 X 52 X 62 a 70 a 1 I I I I I I I I I I I I I 24 X 29 X 5x 36 X 9x 19 x 13 x 22 x 40 x 10 x 20 x 14 x 24a 18a 12a 44a na 25a i9a i3a 26a 23a loa 21a 1 1 1 2x ua {liod-glabroUB flesh J ) X Plant X X +8x +17a 44 X 16 a Swdg from Source 2 Sample sowing of Plant C x Plant D x Plant E > commercial seed I | | I 1 1 14 X 19 X Plant P X 41 X 19 X (uo-d-g , , i.-i „ ^ V 111 * f V d-glabrouB red ^ and rf-glabrou8 redj X Plant Ox .glabrouB white ! ) X Plant f x X ,,.';,|^|,roua white i 11 r" 3x 14 < XXX I I J 10 X 21 X 2x 10 X 5x 4x Ix 8x Seeds from Source 2 (continued) Plant iilx X 7iO-(i-glabrous white s I I I I I I 44 X 36 X 37 X 40 x 30 x 6* 10* 11* 10* 13* Plant K X I T I I I 1 66 X 93 X 1 X 27* 23* 1* I I I XXX I I J 22 X 2 X 6 X 6* 1* 5« + llx +8» X X 27x 81( I I 1 I I i I ll25x 17 x 8x 68 X 40 x 9x 44 x 2( I I I I X X X X I I I I 9x 3x 3x 18 X 4* !• 1« 0* 13 X 13» I I I I I I I 25 X 21 X 27 X 19 X 14 x 29 x 7x Seeds liom Source 2 {coniijtutd) T I (no-d-glabrouB white ? ) X Plant H * I I I I I I I I I I I I I I 44 X 36 X 37 X 40 X SO x 55 X 41 X 50 x 51 X 33 x 65 x 56 x Six 39 x 54 x C* 10* 11« ID* 13* 8* 6a 17* 9* 15* 7* 14* 12* 14* 15a TcMe II (continued) 4a Plant / X I Plant Qx 16 X 34 a I 58 X 99 a Plant J X I (/-sulphnr white ,f X Plant .S x Plant R x 6x 70 X 13 a 108 a -t-1 PlantMx X +llx +8a «o-d-glabrou8 white j I I 4Sx 18a i~r I I I I I I 66 X 9b X Ix Ix lOx 8x il9 27a 23a la la ■*• 4a 32a la sa sga I — X 4a "T~r I I Plant (/ X 7io-(i-i;labrou8 white s rf-eulphur white rf X Plant Tx x > I III —I 1—^ 1 \ 1 1 1 1 4x 2x 9x 38 I I I I I.I I I 4a 4a 8a 7' X X X X X X x6x I I I I I I I li-glabrous flesh s X x X rf-glabroun flesh j 7x 16x 138X 20x 36x 79x 56x j | 10 ^ 12 X 4a 10a I I I I I I -X 26 X 2x Ix 4x —X la 9a 5a 5a 3a ■'• 'T X I 7x 6a I I I 3x 6x — X 7a 3a la r~T~T" T~^i r I I I I I I I I I I I I I I I 22 X 2x 6x Ix 12x 2x 3x 4x 3x 3x Ix 4x 6x 6x 5x 6a la 5a 2a 5a 3a 5a 5a 7a 2a ea la la 2a 2a (i-hoary azure s X x (f-hoary aznie ? X > I i J 3x 8x 7x 6a 3a 29 X 7a -T-T-r~T~T-T-T-T-T-T-T~r-T^T-T-;T-r" X X X X X X X X X X X X X X x27x81a 11111111111111,1 3x —X 7x Ix 7x -X 7x —X 26x 17x 8x 6ex 40x 9x 44x 2a 2a la 4a la la 2a 5a 18 X 7a I'x 1 3x 25 X 1 2x la la 8a 3a 25 X 16 X 5a 71 X (j-glabrous 1 red J Six 16 X 5a I I 3x 2i la 2( d-8ulphur X X white s 1 92 X I I — X 9x 2a la X X (f-eulphur white f I 147 X 64 a 14 I I 34 X 21 X T~T" "1 — r~T"T" I I 27 X 19 X E. R. Saunders 315 proportion of single to double, but both plants were presumably producing an excess of doubles as was also apparently K, probably J, and certainly /; L on the other hand yielded a proportion of about 3 s. : 1 d., i.e., the proportion we should expect from a cross-bred rather than a pure-bred. In the next generation a single descendant from each of the two plants / and / was selfed, and both like their parents gave doubles in excess ; both in short behaved like eversporting indi- viduals as we should naturally expect. In the case of K and L however the results obtained in F„ are not so easily comprehended, for in neither case did all the Fi singles yield doubles in F^. In fact the same diversity of behaviour exhibited by the haphazard collection of singles (plants C — M) is here found among the sister plants of a self-bred family derived from one of these singles {K). 48 F^ descendants of K were tested, 1 (plant U) by cross-fertilisation only, 47 by self-fertilisation either alone or in addition to cross-fertilisation. [Where self-fertilisation shows that an individual was throwing doubles it is unnecessary for the present purpose to comjjlicate the pedigree further by introducing into it the results of cross-fertilisation, and these results have therefore been omitted where the evidence from self-fertilisation was sufficient.] The former plant {U) and 40 of the latter again produced doubles in the next generation, but the remaining 7 yielded only singles, the numbers in these 7 families ranging from 8 to 68. How many among the 40 mixed families can be regarded as showing the true proportion of singles and doubles is uncertain, since in many the totals are very small ; moreover the seed was not sown until two years after it was harvested, and in some cases germinated badly. (See later, p. 361, where the probability that seeds giving rise to singles and doubles respectively differ in viability is discussed.) To sum up the foregoing results : Plant K as 2k matter of fact gave a very slight excess of doubles, but among the F^ singles derived from K some were evidently giving doubles in the proportion of only 1 d. : 3 s. while others were apparently breeding true to singleness. Some of the F„ singles similarly yielded the pro- portion 1 d. : 3 s. in F^. (See Table II.) In the case of plant L, 31 F^ descendants were tested by self- fertilisation ; 18 of the resulting F^ families included some doubles, 13 were composed entirely of singles, the numbers in the latter class of families ranging from 7 to 34. If we review these 18 families we find that in 13 the numbers agree well with the ratio 3 s. : 1 d., and that in the remaining 5, none of which included more than 6 individuals, there 316 Donbleness in Stocks is either equality or a slight excess of doubles. In the next generation this diversity of behaviour was again apparent ; 3 F2 plants belonging to 2 Fi families, both of which included some doubles, were tested by cross-breeding. One was used as (/" in a mating with the rf-red strain and gave a total of 36 all single. Another was employed as the J J» * X d-glabrous azure (J 3 35 44 « X d-gabrous light purple cT ... 2 2 23 d-hoary azure $ X d-glabrous sulphur-white i 1 9 8 rf-glabrous flesh ? X d-glabrous azure (f 1 2 3 rf-glabrous light purple ? X d-glabrous red ? X d-gkbrouB sulphur white i 3 22 35 rf-glabrous sulphur-white ? X d-glabrous cream • saiSaig CO « «D tiO r-l ^ ^5 .-< i-H O Si , R^, the presence of any one of which will suffice to render the grain red. Hence only those F2 plants in which aJl tliree factors are absent will have white grains, and these wiU only occur in the proportion of 1 in 64. (See Nilsson-Ehle, Kreuzungsuntersuchungen an Hafer und Weizen, Lund, 1909.) The Stocks appear to offer a parallel but more complex case, as in this instance pairs of factors instead of single factors are concerned. 23—2 344 Doubleness in Stocks Mating 3. cZ-cream $ x no-d-iion-cvea,m ^. Summary of results. For details see Table V. Only one kind of mating of this type was made, viz. rf-glabrous cream % x ??,o-d-glabrous white J". The d-cream plant M as % was crossed with the no-cZ-white plant J as 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 Doubleness in StocJcs 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 F^ 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 sown. 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 single ,, 4. 30 „ ,, 12 „ 5 were double, 5 died before floweriug and 2 were single All the seeds from the fifth F^ plant failed to germinate. In 1910, 85 more seeds from 3 of these same F^ plants were sown, but none germinated. About 500 seeds from 20 others among the F^ 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 fi.xed 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. E. 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 : Number of Number of seeds sown seeds sown where less Number of Number Number where at Number of Number Number than half seeds which of of least half seeds which of of Type germinated germinated singles doubles germinated germinated singles doubles Marine blue 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 average 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. c.it. p. 79. 366 Doubleness 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 Chate was accidental, and not the result of any general arrangement throughout the individual. (b) On the jMSsibilitt/ 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 woidd 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 1906 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 ajjpeai-ance from those of a true-breeding white ; the other in which the seeds are very regular, larger, of a lighter j'ellowish 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 doubles 16 were white (15 single, 1 double) 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 identified, 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 Doubhmess 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 wnbranched, 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 F^ cross-breds are bushy plants like incana. In F.. the pure Brompton habit reappears in a proportion of the plants. The sorting of the F2 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 injur}' 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 accomjDanying figures showing two of the F2 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 F.^ generation the Brompton plants presented a very curious appearance, the single stem in many cases reaching a height of from 3 to 3i feet. E, R. Saunders 369 V Fig. 1. Note 3. On certain sap-colours not dealt with in the earlier accounts, and on the constitution of the sulphur-white RACE. Swp-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 F-^. If both parents lack B then it appears in F^, 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 Doubleness 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-form 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 F^ 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 rece.ssive 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 diSiculty 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. Alarine 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-iuhite 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 pi'oved 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 mi.Ked white and cream, according as the E. R Saunders 371 sulphur-white was used as jj" 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 C 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 (C) and the factor which turns red blue (B) are both absent. We can therefore express the composition of this type of sulphur-white thus — hcRK. The seed obtained from Herr Benary showed the characteristics described under type 1 (p. 867, seeds small, brown, irregular). This form evidently has the coi^position 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 F^ 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. 1 See Evolution Report IV. p. 36. 372 Doubleness in Stocks 2iHC0i-l OiHlMt-rHCO t- ^^ W IC^ fe -3 Tt^fMiHCOCl-^COfOOiOqtDOXCOi-H O i-l CCCOrHTtiiHi-H O C^ .-( CO i-H i-H ft 8 CO fH t-l CO CO w? 00 O (H ?0 to iH !> "« 3 ■^J)iCeO«*0050C>lWOCi-*W5«.-l o (M Oa 04 CO (N "M C^ W CO ■* Tj< a a 3 t^-^OC0-^03eC"t)-^-*C0'H o ft 52, -^j^COlCiCC^iHiMCOiOrH I "^ ffl H ^ 3 3 c*00COCiQ0CCC^tOC^O5-*COU5CD-i# Q 04 Ml CO»J5fNOai»00>-lXiC'^C I »n I CO O CD IN Tt< '&cit>fH'MCOxratr-<-iasQOO<:DCO a 01>C i-l(MfMi— lt-tC»-t E. R. Saunders 373 I S, Oi CO CO Oi CO CD CO 00 g o o*"* I fl p I J I .2 iiCi-HOriocomw ^2 ^Ot-ncD oi -^ co Oi -^ O'i'oc S'^j'^ I'M'-H .5'-'»0"-"C'-' .5 ef^c coco QJa^ ^ ^ '3: o o 1^ ^ o g § ^ -s % 3TjlFH 3CO-**-' ■^-^"'^COCO 3M gt* o a g fi fi p? 5 Journ, of Gen, i 25 374 Doubleuess in Stocks TABLE IV. Showitig the number of singles and doubles obtained in F„ families derived from matings of the form no-d ^ x d S ■ 1 jo-rf-glabrous white ? 7io-rf-glabrous flesh ? no-(?-glabro«8 creanr 9 r/ -glabrous ra\i d-sulphur w llite,? (/-glabrous azure d" 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 /it?-(i-glabrous cream $ 16 13 17 9 6 2 15 47 53 6 16 21 1 8 8 1 1 2 1 7 7 1 3 2 (/•sulphur w hite 11 29 9 2 6 ■ 4 Single Double Single Double 6 42 21 44 13 9 2 10 3 no-rf-glabrous cream 9 21 9 19 3 7trt-rf-glabrous flesh ? (/-glabrous wliite c? 19 4 21 3 fMio ary white (intermediate) (J i Single Double f — HO-(/-glabrous ; cream 9 Single Double Single Double 54 15 5 1 6 6 8 1 d-glabrous red 3 4 f — >t<'-(?-glabrous flesh $ 9 3 8 2 Single Double Single Double d -glabrous light purple M)-d-glabrous white -(i-glabrous white 3 4 22 3 61 7 60 13 87 7 13 2 33 7 d-glabrous cream ? ok a ,,. -J -.i™k-^„c. ™k;+^ t ^o o 36 7 48 7 IH 6 42 7 Single Double Single Double 36 42 7 79 — 10 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 32 138 39 13 6 376 Doiibleness in Stocks TABLE VI. Showing the number of singles add doubles obtained in 50 Fi families derived from matings between two ever- sportiiig forms. (Seep. 319.) Single Double 2 5 , 1 2 2 3 14 11 7 2 14 1 8 56 52 3 2 25 31 63 78 10 13 14 17 18 16 U 13 9 8 8 18 14 23 8 7 1 1 7 12 8 13 11 16 5 6 8 12 71 86 3 4 3 2 8 13 5 9 8 18 9 10 22 29 6 11 18 25 18 17 4 7 9 12 7 8 18 21 3 4 14 19 1 12 1 11 9 8 2 3 23 24 14 7 8 7 TABLE VII. Showing the number of singles and doubles obtained in 81 F-i families when the Fx cross-breds from 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 53 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 as 13) 5 15 1*2 4i 5 6 7 20 6 8 1 12 •94 171 4 8 141 f 4 6 17 16 7 12 *85 146 37 53 ♦12 29 13 12 TABLE VIIL Sho7oing the number of singles and doubles obtained in 35 /", families when F^ cross- breds 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 Becords 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 3-4 5-7 8-11 cream red X white xred X cream X sulphur- white 12-19 sulphur-white x white(hoary) 20-40 „ „ xred 41 „ 1, X white 42-44 ,, X azure Fam. 1-13 red x cream 14-27 sulphur-white x red ; (redx sulph.-wh.) ; (sulph.-wh. X red) 28-55 ,, ,, X azure 56-57 „ ,, X light purple 58-62 „ ,, X white 63-75 ,, ,, X white(hoary) 76-79 cream X red 80-81 „ X white Fam. 1-2 red 3-5 „ , . 6 (sulph.-wii. 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 45 46 47 48 49 50 : light purple azure(hoary) x sulphur-white flesh X azure azure x red light purple x „ led X light purple NOTE ON THE INHERITANCE OF CHARACTERS IN WHICH DOMINANCE APPEARS TO BE INFLUENCED BY SEX. By L. DONCASTER, 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 horned character in sheep (horns dominant in the male'), and probably the white colour in the butterfly Golias (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 colour-blind man $ 'i y. S cJ normal man I I 1 ^ (J $ ? $ 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 i X ? I I 1 i c? ? $ 1 Wood, Journ. Agric. Science, ni. 1909, p. 145. " Gerould, Amer. Naturalist, 45. 1911, p. 257. In this ease there is the complication that homozygous white females have not been observed. 3 Doncaster, Proc. Camb. Phil. Soc. xiii. 1905, p. 35. Since the publication 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 diffei'ent 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-determinei\ In former papers I have sug- gested that if maleness is determined by a factor J*, femaleness by a factor % epistatic to ^ when both are present, then a male individual may be represented cfO, a female ,c<*' ,i#--