 CHAPTER ONE OF EXPERIMENTS IN PLANT HYBRIDIZATION CHAPTER ONE OF EXPERIMENTS IN PLANT HYBRIDIZATION CHAPTER ONE EXPERIMENTS IN PLANT HYBRIDIZATION by Gregor Mendel, read at the meetings of the 8th February and 8th March, 1865. Introductory remarks. Experience of artificial fertilization, such as is affected with ornamental plants in order to obtain new variations in color, has led to the experiments which will here be discussed. The striking regularity with which the same hybrid forms always reappeared whenever fertilization took place between the same species induced further experiments to be undertaken, the object of which was to follow up the developments of the hybrids in their progeny. To this object numerous careful observers such as Kölreuter, Gertner, Herbert, Lecoq, Wichura and others have devoted a part of their lives with inexhaustible perseverance. Gertner especially in his work, Die Basta der Zeugung im Pflanzenreiche, the production of hybrids in the vegetable kingdom, has recorded very valuable observations and quite recently Wichura published the results of some profound investigations into the hybrids of the willow. That so far, no generally applicable law governing the formation and development of hybrids has been successfully formulated, can hardly be wondered at by anyone who is acquainted with the extent of the task and can appreciate the difficulties with which experiments of this class have to contend. A final decision can only be arrived at when we shall have before us the results of detailed experiments made on plants belonging to the most diverse orders. Those who survey the work done in this department will arrive at the conviction that among all the numerous experiments made not one has been carried out to such an extent and in such a way as to make it possible to determine the number of different forms under which the offspring of hybrids appear or to arrange these forms with certainty according to their separate generations or definitely to ascertain their statistical relations. It requires indeed some courage to undertake a labor of such far-reaching extent. This appears, however, to be the only right way by which we can finally reach the solution of a question the importance of which cannot be overestimated in connection with the history of the evolution of organic forms. The paper now presented records the results of such a detailed experiment. This experiment was practically confined to a small plant group and is now, after eight years' pursuit, concluded in all essentials. Whether the plan upon which the separate experiments were conducted and carried out was the best suit to attain the desired end is left to the friendly decision of the reader. This LibriVox recording is in the public domain, recording by Avae in February 2010. Experiments in Plant Hybridization by Gregor Mendel, translated by William Bateson, Chapter 2, Selection of the Experimental Plants The value and utility of any experiment are determined by the fitness of the material and the purpose for which it is used and thus in the case before us it cannot be immaterial what plants are subjected to experiment and in what manner such experiments are conducted. The selection of the plant group which shall serve for experiments of this kind must be made with all possible care if it be desired to avoid from the outset every risk of questionable results. The experimental plants must necessarily, one, possess constant differentiating characters. Two, the hybrids of such plants must, during the flowering period, be protected from the influence of all foreign pollen or be easily capable of such protection. The hybrids and their offspring should suffer no marked disturbance in their fertility in the successive generations. Accidental impregnation by foreign pollen, if it occurred during the experiments and were not recognized, would lead to entirely erroneous conclusions. Reduced fertility or entire sterility of certain forms, such as occurs in the offspring of many hybrids, would render the experiments very difficult or entirely frustrate them. In order to discover the relations in which the hybrid forms stand towards each other and also towards their progenitors, it appears to be necessary that all members of the series developed in each successive generation should be, without exception, subjected to observation. At the very outset special attention was devoted to the leguminose on account of their peculiar floral structure. Experiments which were made with several members of this family led to the results that the genus Pesum was found to possess the necessary qualifications. Some terribly distinct forms of these genus possess characters which are constant and easily and certainly recognizable, and when their hybrids are mutually crossed they yield perfectly fertile progeny. Furthermore, a disturbance through foreign pollen cannot easily occur as the fertilizing organs are closely packed inside the keel and the enter bursts within the bud so that the stigma becomes covered with pollen even before the flower opens. This circumstance is of a special importance. As additional advantages worth mentioning, there may be cited the easy culture of these plants in the open ground and in pots and also their relatively short period of growth. Artificial fertilization is certainly a somewhat elaborate process, but nearly always succeeds. For this purpose the bud is opened before it is perfectly developed, the keel is removed and each stamen carefully extracted by means of forceps after which the stigma can at once be dusted over with the foreign pollen. In all, 34 more or less distinct varieties of peas were obtained from several seedsmen and subjected to a two-year's trial. In the case of one variety, there were noticed among a larger number of plants all alike a few forms which were markedly different. These, however, did not vary in the following year and agreed entirely with another variety obtained from the same seedsmen. The seeds were therefore doubtless merely accidentally mixed. All the other varieties yielded perfectly constant and similar offspring at any rate no essential difference was observed during two trial years. For fertilization, 22 of these were selected and cultivated during the whole period of the experiments. They remained constant without any exception. Their systematic classification is difficult and uncertain. If we adopt the strictest definition of a species according to which only those individuals belong to a species which under precisely the same circumstances display precisely similar characters no two of these varieties could be referred to one species. According to the opinion of experts, however, the majority belong to the species Pism Sativum while the rest are regarded and classed, some as subspecies of Pism Sativum and some as independent species such as Pism Quadratum, Pism Zakaratum and Pism Umbelatum. The positions, however, which may be assigned to them in a classificatory system are quite immaterial for the purposes of the experiments in question. It has so far been found to be just as impossible to draw a sharp line between the hybrids of species and varieties as between species and varieties themselves. Experiments in Plant Hybridization This LibriVox recording is in the public domain. Recording by Avayee in February 2010. Experiments in Plant Hybridization by Gregor Mendel translated by William Bateson. Chapter 3 Division and Arrangement of the Experiments If two plants which differ constantly in one or several characters be crossed numerous experiments have demonstrated that the common characters are transmitted unchanged to the hybrids and their progeny. But each pair of differentiating characters, on the other hand, unite in the hybrid to form a new character which in the progeny of the hybrid is usually variable. The object of the experiment was to observe these variations in the case of each pair of differentiating characters to deduce the law according to which they appear in the successive generations. The experiment results itself, therefore, into just as many separate experiments as there are constantly differentiating characters presented in the experimental plants. The various forms of peas selected for crossing showed differences in the length and color of the stem in the size and form of the leaves, in the position, color and size of the flowers, in the length of the flower stalk, in the color, form and size of the pods, in the form and size of the seeds, and in the color of the seed coats and of the albumen, cutelidons. Some of the characters noted do not permit of a sharp and certain separation since the difference is of a more or less nature which is often difficult to define. These characters could not be utilized for the separate experiments. These could only be applied to characters which stand out clearly and definitely in the plants. Lastly, the results must show whether they, in their entirety, observe regular behavior in the hybrid unions and whether from these facts any conclusion can become to regarding those characters which possesses subordinate significance in the type. The characters which were selected for experiment relate. One, to the difference in the form of the ripe seeds. These are either round or roundish, the depressions, if any, occur on the surface, being always only shallow, or they are irregularly angular and deeply wrinkled, pism quadratum. Two, to the difference in the color of the seed albumen and those sperm. The albumen of the ripe seeds is either pale yellow, bright yellow, and orange colored, or it possesses a more or less intense green tint. This difference of color is easily seen in the seeds as equals if their coats are transparent. Three, to the difference in the color of the seed coat. This is either white, with which character white flowers are constantly correlated, or it is gray, gray brown, leather brown, with or without violet spotting, in which case the color of the standards is violet, that of the wings purple, and the stem in the axels of the leaves is of a reddish tint. The gray seed coats become dark brown in boiling water. Four, to the difference in the form of the ripe pods. These are either simply inflated, not contracted in places, or they are deeply constricted between the seeds and more or less wrinkled, pism sagaratum. Five, to the difference in the color of the unripe pods. They are either light to dark green, or vividly yellow, in which coloring the stalks, leaf veins, and calyx participate. Footnote. One species possesses a beautifully brownish red colored pod, which when ripening turns to violet and blue. Trials with this character were only begun last year. End footnote. Six, to the difference in the position of the flowers. They are either axial, that is distributed along the main stem, or they are terminal, that is bunched at the top of the stem, and arranged almost in a false umbil. In this case, the upper part of the stem is more or less widened in section. Pism umbilatum. Seven, to the difference in the length of the stem. The length of the stem is very various in some forms. It is, however, a constant character for each, insofar that healthy plants grown in the same soil, are only subject to unimportant variations in this character. In experiments with this character, in order to be able to discriminate with certainty, the long axis of six to seven feet was always crossed with a short one of three quarter feet to one and a half feet. Each two of the differentiating characters enumerated above were united by cross fertilization. They were made for the first trial, 60 fertilizations on 15 plants. Second trial, 58 fertilizations on 10 plants. Third trial, 35 fertilizations on 10 plants. Fourth trial, 40 fertilizations on 10 plants. Fifth trial, 23 fertilizations on 5 plants. Sixth trial, 34 fertilizations on 10 plants. Seventh trial, 37 fertilizations on 10 plants. From a larger number of plants of the same variety only the most vigorous were chosen for fertilization. Weekly plants always afford uncertain results because even in the first generation of hybrids and still more so in the subsequent ones, many of the offspring either entirely fail to flower or only form a few and inferior seeds. Furthermore, in all the experiments reciprocal crossings were affected in such a way that each of the two varieties, which in one set of fertilizations served as seed bearer, in the other set was used as the pollen plant. The plants were grown in garden beds, a few also in pots and were maintained in their naturally upright position by means of sticks, branches of trees and strings stretched between. For each experiment, a number of pot plants were placed during the blooming period in a greenhouse to serve as control plants for the main experiment in the open as regards possible disturbance by insects. Among the insects which visit peas, the beetle Brohu's peasy might be detrimental to the experiment should it appear in numbers. The female of this species is known to lay the eggs in the flower and in so doing opens the keel. Upon the taracy of one specimen which was caught in a flower, some pollen grains could clearly be seen under a lens. Mention must also be made of a circumstance which possibly might lead to the introduction of foreign pollen. It occurs, for instance, in some rare cases that certain parts of an otherwise quite normally developed flower wither, resulting in a partial exposure of the fertilizing organs. A defective development of the keel has also been observed, a wing to which the stigma and anthors remained partially uncovered. It also sometimes happens that the pollen does not reach full perfection. In this event, there occurs a gradual lengthening of the pistil during the blooming period until the stigmatic tip protrudes at the point of the keel. This remarkable appearance has also been observed in hybrids of faziolus and latyrus. The risk of false impregnation by foreign pollen is, however, a very slight one with piezum and is quite incapable of disturbing the general result. Among more than 10,000 plants which were carefully examined, there were only a very few cases where an indubitable false impregnation had occurred. Since the greenhouse such a case was never remarked, it may well be supposed that Pohu's Pisi and possibly also the described abnormalities in the floral structure were to blame. Like Gregor Mendel translated by William Bateson. Experiments which in previous years were made with ornamental plants have already afforded evidence that the hybrids, as a rule, are not exactly intermediate between the parental species. With some of the more striking characters, those, for instance, which relate to the form and size of the leaves, the pubescence of the several parts, etc., the intermediate, indeed, is nearly always to be seen. In other cases, however, one of the two parental characters is so preponderant that it is difficult or quite impossible to detect the other in the hybrid. This is precisely the case with the P-hybrids. In the case of each of the seven crosses, the hybrid character resembles that of one of the parental forms so closely that the other either escapes observation completely or cannot be detected with certainty. This circumstance is of great importance in the determination and classification of the forms under which the offspring of the hybrids appear. Henceforth in this paper, those characters which are transmitted entire are almost unchanged in the hybridization and therefore in themselves constitute the characters of the hybrid, are termed the dominant, and those which become latent in the process recessive. The expression recessive has been chosen because the characters thereby designated withdraw or entirely disappear in the hybrids, but nevertheless reappear unchanged in their progeny as will be demonstrated later on. It was furthermore shown by the whole of the experiments that it is perfectly immaterial whether the dominant character belonged to the seed bearer or to the pollen parent. The form of the hybrid remains identical in both cases. This interesting fact was also emphasized by Gertner with the remark that even the most practiced expert is not in a position to determine in a hybrid which of the two parental species was the seed or the pollen plant. Of the differentiating characters which were used in the experiments, the following are dominant. 1. The round or roundish form of the seed with or without shallow depressions. 2. The yellow coloring of the seed albumen, Cotyledons. 3. The gray, gray-brown or leather-brown color of the seed coat in association with violet red blossoms and reddish spots in the leaf axils. 4. The simply inflated form of the pod. 5. The green coloring of the unripe pod in association with the same color in the stems, the leaf veins and the calyx. 6. The distribution of the flowers along the stem. 7. The greater length of the stem. With regard to this last character, it must be stated that the longer of the two parental stems is usually exceeded by the hybrid, a fact which is possibly only attributable to the greater luxuriance which appears in all parts of plants when stems of very different length are crossed. Thus, for instance, in repeated experiments stems of one foot and six feet in length yielded without exception hybrids which varied in length between six feet and seven and a half feet. The hybrid seeds in the experiments with seed coat are often more spotted and the spots sometimes coalesce into small bluish violet patches. The spotting also frequently appears even when it is absent as a parental character. The hybrid forms of the seed shape and of the albumen, color, are developed immediately after the artificial fertilization by the mere influence of the foreign pollen. They can, therefore, be observed even in the first year of experiment, whilst all the other characters naturally only appear in the following year, in such plants as have been raised from the crossed seed. End of Chapter 4 Chapter 5 of Experiments in Plant Hybridization This LibriVox recording is in the public domain. Recording by Avae in February 2010. Experiments in Plant Hybridization by Gregor Mendel translated by William Bateson. Chapter 5 Chapter 2 The first generation bred from the hybrids. In this generation they reappear, together with the dominant characters, also the recessive ones, with their peculiarities fully developed. And this occurs in the definitely expressed average proportion of three to one, so that among each four plants of this generation, three display the dominant character and one the recessive. This relates without exception to all the characters which were investigated in the experiments. The angular wrinkled form of the seed, the green color of the albumen, the white color of the seed codes and the flowers, the constrictions of the pods, the yellow color of the unripe pod of the stalk of the calyx and of the leaf venation, the umbil-like form of the inflorescence and the dwarfed stem all reappear in the numerical proportion given without any essential alteration. Transitional forms were not observed in any experiment. Since the hybrids resulting from reciprocal crosses are formed alike and present no appreciable difference in their subsequent development, consequently the results of the reciprocal crosses can be reckoned together in each experiment. The relative numbers which were obtained for each pair of differentiating characters are as follows. Experiment one, form of seed. From 253 hybrids, 7,324 seeds were obtained in the second trial year. Among them were 5,474 round or roundish ones and 1,850 angular wrinkled ones. They are from the ratio 2.96 to 1 is deduced. Experiment two, color of albumen. 258 plants yielded 8,023 seeds, 6,022 yellow and 2,001 green. Their ratio, therefore, is as 3.01 to 1. In these two experiments each pod yielded usually both kinds of seed. In well-developed pods which contained on the average 6 to 9 seeds, it often happened that all the seeds were round, experiment one, or all yellow, experiment two. On the other hand, they were never observed more than 5 wrinkled or 5 green ones in one pod. It appears to make no difference whether the pods are developed early or later in the hybrid or whether they spring from the main axis or from a lateral one. In some few plants only a few seeds developed in the first formed pods and these possessed exclusively one of the two characters, but in the subsequently developed pods the normal proportions were maintained nevertheless. As in separate pods so did the distribution of the characters vary in separate plants. By way of illustration the first 10 individuals from both series of experiments may serve. Experiment one, form of seed. Plant one, 45 round, 12 angular. Plant two, 27 round, 8 angular. Plant three, 24 round, 7 angular. Plant four, 19 round, 10 angular. Plant five, 32 round, 11 angular. Plant six, 26 round, 6 angular. Plant seven, 88 round, 24 angular. Plant eight, 22 round, 10 angular. Plant nine, 28 round, 6 angular. Plant 10, 25 round, 7 angular. Experiment two, color of albumen. Plant one, 25 yellow, 11 green. Plant two, 32 yellow, 7 green. Plant three, 14 yellow, 5 green. Plant four, 70 yellow, 27 green. Plant five, 24 yellow, 13 green. Plant six, 20 yellow, 6 green. Plant seven, 32 yellow, 13 green. Plant eight, 44 yellow, 9 green. Plant nine, 50 yellow, 14 green. Plant 10, 44 yellow, 18 green. As extremes in the distribution of the two seed characters in one plant there were observed in experiment one an instance of 43 round and only two angular and another of 14 round and 15 angular seeds. In experiment two there was a case of 32 yellow and only one green seed but also one of 20 yellow and 19 green. These two experiments are important for the determination of the average ratios because with a smaller number of experimental plants they show that very considerable fluctuations may occur. In counting the seeds also, especially in experiment two, some care is requisite since in some of the seeds of many plants the green color of the albumen is less developed and at first may be easily overlooked. The cause of this partial disappearance of the green coloring has no connection with the hybrid character of the plants as it likewise occurs in the parental variety. This peculiarity, bleaching, is also confined to the individual and is not inherited by the offspring. In luxuriant plants disappearance was frequently noted. Seeds which are damaged by insects during their development often vary in color and form but with a little practice in sorting errors are easily avoided. It is almost superfluous to mention that the pods must remain on the plants until they are thoroughly ripened and have become dried since it is only then that the shape and color of the seed are fully developed. Experiment three, color of the seed coats. Among 929 plants, 705 bore violet red flowers and gray brown seed coats. 224 had white flowers and white seed coats giving the proportion 3.15 to 1. Experiment four, form of pods. Of 1181 plants, 882 had them simply inflated and in 299 they were constricted. Resulting ratio 2.95 to 1. Experiment five, color of the unripe pods. The number of trial plants was 580 of which 428 had green pods and 152 yellow ones. Consequently they stand in the ratio 2.82 to 1. Experiment six, position of flowers. Among 858 cases, 651 had inflorescences axial and 207 terminal. Ratio 3.14 to 1. Experiment seven, length of stem. Out of 1064 plants, in 787 cases the stem was long and in 277 short. Hence a mutual ratio of 2.84 to 1. In this experiment the dwarfed plants were carefully lifted and transferred to a special bed. This precaution was necessary as otherwise they would have perished through being overgrown by their tall relatives. Even in the quite young state they can be easily picked out by their compact growth and thick dark green foliage. If now the results of the whole of the experiments be brought together there is found as between the number of forms with the dominant and recessive characters an average ratio of 2.98 to 1 or 3 to 1. The dominant character can have here a double signification that is that of a parental character or a hybrid character. In which of the two significations it appears in each separate case can only be determined by the following generation. As a parental character it must pass over unchanged to the whole of the offspring. As a hybrid character on the other hand it must maintain the same behavior as in the first generation, F2. The second generation bred from the hybrids. Those forms which in the first generation F2 exhibit the recessive character do not further vary in the second generation F3 as regards this character they remain constant in their offspring. It is otherwise with those which possess the dominant character in the first generation bred from the hybrids. Of these two thirds yield offspring which display the dominant and recessive characters in the proportion of 3 to 1 and thereby show exactly the same ratio as the hybrid forms while only one third remains with the dominant character constant. The separate experiments yield the following results. Experiment 1 Among 565 plants which were raised from round seeds of the first generation 193 yielded round seeds only and remained therefore constant in this character. 372 however gave both round and wrinkled seeds in the proportion of 3 to 1. The number of the hybrids therefore as compared with the constants is 1.93 to 1. Experiment 2 Of 519 plants which were raised from seeds whose albumen was of yellow color in the first generation 166 yielded exclusively yellow while 353 yielded yellow and green seeds in the proportion of 3 to 1. They resulted therefore a division into hybrid and constant forms in the proportion of 2.13 to 1. For each separate trial in the following experiments 100 plants were selected and this played the dominant character in the first generation and in order to ascertain the significance of this 10 seeds of each were cultivated. Experiment 3 The offspring of 36 plants yielded exclusively gray brown seed coats while of the offspring of 64 plants some had gray brown and some had white. Experiment 4 The offspring of 29 plants had only simply inflated pots of the offspring of 71 on the other hand some had inflated and some constricted. Experiment 5 The offspring of 40 plants had only green pots of the offspring of 60 plants some had green, some yellow ones. Experiment 6 The offspring of 33 plants had only axial flowers of the offspring of 67 on the other hand some had axial and some terminal flowers. Experiment 7 The offspring of 28 plants inherited the long axis and those of 72 plants summed along and summed the short axis. In each of these experiments a certain number of the plants came constant with the dominant character for the determination of the proportion in which the separation of the forms with the constantly persistent character results. The two first experiments are of special importance since in these a larger number of plants can be compared. The ratios 1.93 to 1 and 2.13 to 1 gave together almost exactly the average ratio of 2 to 1. The sixth experiment gave a quite concordant result. In the others the ratio varies more or less as was only to be expected in view of the smaller number of 100 trial plants. Experiment 5 which shows the greatest departure was repeated and then in lieu of the ratio of 60 and 40 that of 65 and 35 resulted. The average ratio of 2 to 1 appears therefore as fixed with certainty. It is therefore demonstrated that of those forms with the dominant character in the first generation two thirds have the hybrid character while one third remains constant with the dominant character. The ratio of 3 to 1 in accordance with which the distribution of the dominant and recessive characters results in the first generation resolves itself therefore in all experiments into the ratio of 2 to 1 to 1 if the dominant character begins as a hybrid character or as a parental one. Since the members of the first generation F2 spring directly from the seed of the hybrids F1 it is now clear that the hybrids form seeds having one or other of the two differentiating characters and of these one half develop again the hybrid form while the other half yield plants which remain constant and receive the dominant equal numbers. The proportions in which the descendants of the hybrids develop and split up in the first and second generations presumably hold good for all subsequent progeny. Experiments 1 and 2 have already been carried through 6 generations 3 and 7 through 5 and 4, 5 and 6 through 4. These experiments being continued from the third generation with a small number of plants from the rule has been perceptible. The offspring of the hybrids separated in each generation in the ratio of 2 to 1 to 1 into hybrids and constant forms. If capital A be taken as denoting one of the two constant characters for instance the dominant A the recessive and capital A A the hybrid form in which both are conjoined the expression capital A capital A A and A shows the terms in the series for the progeny of the hybrids of two differentiating characters. The observation made by Gertzner, Kölrheuter and others that hybrids are inclined to revert to the parental forms is also confirmed by the experiments described. It is seen that the number of the hybrids which arise from one fertilization as compared with the number of forms which become constant and their progeny from generation to generation is continually diminishing but that nevertheless they could not entirely disappear. If an average quality of fertility in all plants in all generations be assumed and if furthermore each hybrid forms seed of which one half yields hybrids again while the other half is constant to both characters with equal proportions the ratio of numbers for the offspring in each generation is seen by the following summary in which capital A and A denote again the two parental characters and capital A A the hybrid forms. For brevity's sake it may be assumed that each plant in each generation furnishes only four seeds. Generation one one capital A two capital A A one A ratios one capital A to two capital A A to one A Generation two six capital A four capital A A six A ratios three capital A to two capital A A to three A Generation three 28 capital A eight capital A A 28 A ratios seven capital A to two capital A A to seven A Generation four 120 capital A 16 capital A A 120 A ratios 15 capital A to two capital A A to 15 A Generation five 496 capital A 32 capital A A 496 A ratios 31 capital A to two capital A A to 31 A Generation N ratios two to the power of N minus one capital A to two capital A A to two to the power of N minus one A In the tenth generation, for instance two to the power of N minus one equals 1023 The result, therefore in each 2048 plants which rise in this generation 1023 with the constant dominant character 1023 with the recessive character and only two hybrids End of chapter 7 Chapter 8 of Experiments in Plant Hybridization This Librevox recording is in the public domain Recording by Availlie in February 2010 Experiments in Plant Hybridization by Gregor Mendel translated by William Bateson Chapter 8 The offspring of hybrids in which several differentiating characters are associated In the experiments above described plants were used which differed only in one essential character The next task consisted in ascertaining whether the law of development discovered in these applied to each pair of differentiating characters when several diverse characters are united in the hybrid by crossing As regards the form of the hybrids in these cases the experiments showed throughout that this invariably more nearly approaches to that one of the two parental plants which possesses the greater number of dominant characters If, for instance, the seed plant has a short stem terminal white flowers and simply inflated pods The pollen plant on the other hand a long stem and red flowers distributed along the stem and constricted pods the hybrid resembled the seed parent only in the form of the pod in the other characters it agrees with the pollen parent Should one of the two parental types possess only dominant characters then the hybrid is scarcely or not at all distinguishable from it Two experiments were made with a considerable number of plants In the first experiment the parental plants differed in the form of the seed and in the color of the albumen In the second in the form of the seed in the color of the albumen and in the color of the seed codes Experiments with seed characters give the result in the simplest and most certain way In order to facilitate study of the data in these experiments the different characters of the seed plant will be indicated by capital A, capital B, capital C those of the pollen plant by A, B, C and the hybrid forms of the characters by capital A, A capital B, B and capital C, C Experiment one capital A, capital B seed parents capital A form round capital B albumen yellow A, B pollen parents A form wrinkled B albumen green The fertilized seeds appeared round and yellow like those of the seed parents The plants raised therefrom yielded seeds of four sorts which frequently presented themselves in one pot In all, 556 seeds were yielded by 15 plants and of these 315 round and yellow 101 wrinkled and yellow 108 round and green 32 wrinkled and green All were sown the following year 11 of the round yellow seeds did not yield plants and 3 plants did not form seeds Among the rest 38 had round yellow seeds capital A, capital B 65 round yellow and green seeds capital A, capital B, B 60 round yellow and wrinkled yellow seeds capital A, A capital B 138 round yellow and green wrinkled yellow and green seeds capital A, A capital B, B From the wrinkled yellow seeds 96 resulting plants bore seeds of which 28 had only wrinkled yellow seeds A, capital B 60A wrinkled yellow and green seeds A, capital B, B From 108 round green seeds 102 resulting plants fruited of which 35 had only round green seeds capital A, B 67 round and wrinkled green seeds capital A, A, B The wrinkled green seeds yielded 30 plants which bore seeds all of like character they remained constant A, B The offspring of the hybrids appeared therefore under 9 different forms some of them in very unequal numbers When these are collected and coordinated we find 38 plants with the sign capital A, B 35 plants with the sign capital A, B 28 plants with the sign A, B 30 plants with the sign A, B 65 plants with the sign capital A, B, B 68 plants with the sign A, B, B 60 plants with the sign capital A, A, B B. 67 plants with the sign AAB. 138 plants with the sign AAB. The whole of the forms may be classed into three essentially different groups. The first includes those with the signs capital A, capital B, capital AB, A capital B, and AB. They possess only constant characters and do not vary again in the next generation. Each of these forms is represented on the average 33 times. The second group includes the signs capital A, capital B, B, A, B, A, B, A, B, A, B. These are constant in one character and hybrid in another and vary in the next generation only as regards the hybrid character. Each of these appears on an average 65 times. The form capital A, A, B, B occurs 138 times. It is hybrid in both characters and behaves exactly as do the hybrids from which it is derived. If the numbers in which the forms belonging to these classes appear be compared, the ratios of 1, 2, 4 are unmistakably evident. The numbers 32, 65, 138 present very fair approximations to the ratio numbers of 33, 66, 132. The developmental series consists therefore of nine classes of which four appear therein always once and are constant in both characters. The forms capital A, capital B, A, B resemble the parental forms. The two others present combinations between the conjoined characters capital A, A, capital B, B, which combinations are likewise possibly constant. Four classes appear always twice and are constant in one character and hybrid in the other. One class appears four times and is hybrid in both characters. Consequently the offspring of the hybrids, if two kinds of differentiating characters are combined therein, are represented by the expression capital A, capital B and capital A, B and A, B and AB and two capital A, B and two A, B and two capital A, B and two capital A, A, B and four capital A, A, capital B, B. This expression is indisputably a combination series in which the two expressions for the characters capital A and A, capital B and B are combined. We arrive at the full number of the classes of the series by the combination of the expressions capital A and two capital A, A and A, capital B and two capital B, B and B. Experiment two, capital A, capital B, capital C, seed parents, capital A, form round, capital B, albumen yellow, capital C, seed coat gray brown, ABC, pollen parents, A, form wrinkled, B, albumen green, C, seed coat white. This experiment was made in precisely the same way as the previous one. Among all the experiments it demanded the most time and trouble. From 24 hybrids, 687 seeds were obtained in all. These were all either spotted gray brown or gray green, round or wrinkled. From these in the following year, 639 plants fruited and as further investigation showed, there were among them eight plants, capital A, capital B, capital C, 14 plants, capital A, capital B, C, nine plants, capital A, B, capital C, 11 plants, capital A, B, C, eight plants, A, capital B, capital C, 10 plants, A, capital B, C, 10 plants, A, B, capital C, 7 plants, A, B, C, 22 plants, capital A, capital B, capital C, C, 17 plants, A, B, C, C 25 plants, A, B, C 20 plants, A, B, C, C 15 plants, A, B, C 18 plants, A, B, C 19 plants, A, B, C 24 plants, A, B, C 14 plants, A, B, C 18 plants, A, B, C 20 plants, A, B, C 16 plants, A, B, C 45 plants, A, B, C, C 36 plants, A, B, C 38 plants, A, B, C, C 40 plants, A, B, C, C 49 plants, A, B, C 48 plants, A, B, C 78 plants, A, B, C, C The whole expression contains 27 terms. Of these, 8 are constant in all characters, and each appears on the average 10 times. 12 are constant in 2 characters, and hybrid in the 3rd. Each appears on the average 19 times. 6 are constant in 1 character, and hybrid in the other 2. Each appears on the average 43 times. One form appears 78 times, and is hybrid in all of the characters. The ratios 10, 19, 43, 78 agree so closely with the ratios 10, 20, 40, 80, or 1, 2, 4, 8, that this last undoubtedly represents the true value. The development of the hybrids, when the original parents differ in 3 characters, results therefore according to the following expression. Capital A, capital B, capital C, and capital A, capital B, C, and capital A, B, capital C, and capital A, B, C, and A, capital B, capital C, and A, capital B, C, and A, B, capital C, and A, B, C, and 2, capital A, capital B, capital C, C, and 2, capital A, B, capital C, C and 2a B C C and 2ab C C and 2a B C and 2a B C and 2a B C and 2a B two capital A, A, capital B, capital C, and two capital A, A, capital B, C, and two capital A, A, B, capital C, and two capital A, A, B, C, and four capital A, capital B, B, capital C C and for A B B C C and for A A B C C and for A A A B B B C and for A A A B C and for A A B B C and A A A B B C C. Here also is involved the combination series in which the expressions for the characters A and A, B and B, C and C are united. The expressions capital A and 2 capital A A and A, capital B and 2 capital B B and B, capital C and 2 capital C C and C give all the classes of the series. The constant combinations which occur therein agree with all combinations which are possible between the characters capital A, capital B, capital C, A, B, C, 2 thereof capital A, capital B, capital C and A, B, C resemble the two original parental stocks. In addition further experiments were made with a smaller number of experimental plants in which the remaining characters by 2s and 3s were united as hybrids. All yielded approximately the same results. There is therefore no doubt that for the whole of the characters involved in the experiments the principle applies that the offspring of the hybrids in which several essentially different characters are combined exhibit the terms of a series of combinations in which the developmental series for each pair of differentiating characters are united. It is demonstrated at the same time that the relation of each pair of different characters in hybrid union is independent of the other differences in the two original parental stocks. If n represent the number of the differentiating characters in the two original stocks, 3 to the power of n gives the number of terms of the combination series, 4 to the power of n the number of individuals which belong to the series and 2 to the power of n the number of unions which remain constant. The series therefore contains if the original stocks differ in four characters, 3 to the power of 4 equals 81 classes, 4 to the power of 4 equals 256 individuals and 2 to the power of 4 equals 16 constant forms or which is the same among each 256 offspring of the hybrids there are 81 different combinations 16 of which are constant. All constant combinations which in p's are possible by the combination of the set seven differentiating characters were actually obtained by repeated crossing. Their number is given by 2 to the power of 7 equals 128. Thereby is simultaneously given the practical proof that the constant characters which appear in the several varieties of a group of plants may be obtained in all the associations which are possible according to the mathematical laws of combination by means of repeated artificial fertilization. As regards the flowering time of the hybrids the experiments are not yet concluded it can however already be stated that the time stands almost exactly between those of the seed and pollen parents and that the constitution of the hybrids with respect to this character probably follows the rule ascertained in the case of the other characters. The forms which are selected for experiments of this class must have a difference of at least 20 days from the middle flowering period of one to that of the other. Furthermore the seeds when sown must all be placed at the same depth in the earth so that they may germinate simultaneously. Also during the whole flowering period the more important variations in temperature must be taken into account and the partial hastening or delaying of the flowering which may result therefrom. It is clear that this experiment presents many difficulties to be overcome and necessitates great attention. If we endeavor to collate in a brief form the results arrived at we find that those differentiating characters which admit of easy and certain recognition in the experimental plants all behave exactly alike in the hybrid associations. The offspring of the hybrids of each pair of differentiating characters are one half hybrid again while the other half are constant in equal proportions having the characters of the seed and pollen parents respectively. If several differentiating characters are combined by cross fertilization in a hybrid the resulting offspring form the terms of a combination series in which the combination series for each pair of differentiating characters are united. The uniformity of behavior shown by the whole of the characters submitted to experiment permits and fully justifies the acceptance of the principle that a similar relation exists in the other characters which appear less sharply defined in plants and therefore could not be included in the separate experiments. An experiment with peduncles of different lengths gave on the whole a fairly satisfactory result although the differentiation and serial arrangement of the forms could not be affected with that certainty which is indispensable for correct experiment. End of chapter 8 Chapter 9 of Experiments in Plant Hybridization This liprivox recording is in the public domain. Recording by Avae in February 2010. Experiments in Plant Hybridization by Gregor Mendel translated by William Bateson. Chapter 9 The Reproductive Cells of the Hybrids The results of the previously described experiments led to further experiments, the results of which appear fitted to afford some conclusions as regards to composition of the egg and pollen cells of hybrids. An important clue is afforded in pism by the circumstance that among the progeny of the hybrids constant forms appear and that this occurs too in respect of all combinations of the associated characters. So far as experience goes we find it in every case confirmed that constant progeny can only be formed when the egg cells and the fertilizing pollen are of like character so that both are provided with the material for creating quite similar individuals as is the case with the normal fertilization of pure species. We must therefore regard it as certain that exactly similar factors must be at work also in the production of the constant forms in the hybrid plants. Since the various constant forms are produced in one plant or even in one flower of a plant the conclusion appears logical that in the ovaries of the hybrids there are formed as many sorts of egg cells and in the anthers as many sorts of pollen cells as there are possible constant combination forms and that these egg and pollen cells agree in their internal composition with those of the separate forms. In point of fact it is possible to demonstrate theoretically that this hypothesis would fully suffice to account for the development of the hybrids in the separate generations if we might at the same time assume that the various kinds of egg and pollen cells were formed in the hybrids on the average in equal numbers. In order to bring these assumptions to an experimental proof the following experiments were designed. Two forms which were constantly different in the form of the seed and the color of the albumen were united by fertilization. If the differentiating characters are again indicated as capital A capital B A B we have capital A capital B seed parent capital A form round capital B albumen yellow A B pollen parent A form wrinkled B albumen green. The artificially fertilized seeds were sown together with several seeds of both original stocks and the most vigorous examples were chosen for a reciprocal crossing. There were fertilized one the hybrids with the pollen of capital A capital B two the hybrids with the pollen of A B three capital A capital B with the pollen of the hybrids four A B with the pollen of the hybrids for each of these four experiments the whole of the flowers and three plants were fertilized. If the above theory be correct there must be developed on the hybrids egg and pollen cells of the forms capital A capital B capital A B A capital B A B and there would be combined one the axels capital A capital B capital A B A capital B AB with the pollen cells capital A capital B Two The axels capital A B A B with the pollen cells AB 3. The axels A, B with the pollen cells A, B, A, B. 4. The axels A, B with the pollen cells A, B, A, B, A. From each of these experiments, they could then result only the following forms. 1. A B, A B, B, A, B, A, B, A, B, A, B, A, B, A, B, A, B, A, B, A, B, A, B. 3. Capital A, B. A, B, B, A, B, A, B, A, B, B. 4. Capital A, B, A, B, A, B, A, B. If, furthermore, the several forms of the egg and pollen cells of the hybrids were produced on an average in equal numbers, then in each experiment the set for combinations should stand in the same ratio to each other. A perfect agreement in the numerical relations was, however, not to be expected, since in each fertilization, even in normal cases, some egg cells remain undeveloped or subsequently die, and many even of the well-formed seeds fail to germinate when sown. The above assumption is also limited insofar that, while it demands the formation of an equal number of the various sorts of egg and pollen cells, it does not require that this should apply to each separate hybrid with mathematical exactness. The first and second experiments had primarily the object of proving the composition of the hybrid egg cells, while the third and fourth experiments were to decide that of the pollen cells. As is shown by the above demonstration, the first and third experiments and the second and fourth experiments should produce precisely the same combinations, and even in the second year the result should be partially visible in the form and color of the artificially fertilized seed. In the first and third experiments, the dominant characters of form and color, capital A and capital B, appear in each union and are also partly constant and partly in hybrid union with the recessive characters A and B, for which reason they must impress their peculiarity upon the whole of the seeds. All seeds should therefore appear round and yellow if the theory be justified. In the second and fourth experiments, on the other hand, one union is hybrid in form and in color, and consequently the seeds are round and yellow. Another is hybrid in form, but constant in the recessive character of color, when the seeds are round and green. The third is constant in the recessive character of form, but hybrid in color. Consequently the seeds are wrinkled and yellow. The fourth is constant in both recessive characters, so that the seeds are wrinkled and green. In both these experiments there were consequently four sorts of seeds to be expected, that is round and yellow, round and green, wrinkled and yellow, wrinkled and green. The crop fulfilled these expectations perfectly. There were obtained in the first experiment 98 exclusively round yellow seeds, third experiment 94 exclusively round yellow seeds, in the second experiment 31 round and yellow, 26 round and green, 27 wrinkled and yellow, 26 wrinkled and green seeds. In the fourth experiment 24 round and yellow, 25 round and green, 22 wrinkled and yellow, 27 wrinkled and green seeds. There could scarcely be now any doubt of the success of the experiment, the next generation must afford the final proof. From the seeds sown, they resulted for the first experiment 90 plants and for the third 87 plants which fruited. These yielded for the first experiment 20, third experiment 25 round yellow seeds, capital A capital B, first experiment 23, third experiment 19 round yellow and green seeds, capital A capital B B, first experiment 25, third experiment 22 round and wrinkled yellow seeds, capital A A capital B, first experiment 22, third experiment 21 round and wrinkled green and yellow seeds, capital A A capital B B. In the second and fourth experiments the round and yellow seeds yielded plants with round and wrinkled yellow and green seeds, capital A A capital B B. From the round green seeds plants resulted with round and wrinkled green seeds, capital A A B. The wrinkled yellow seeds gave plants with wrinkled yellow and green seeds, A capital B B. From the wrinkled green seeds plants were raised which yielded again only wrinkled and green seeds, A B. Although in these two experiments likewise some seeds did not germinate, the figures arrived at already in the previous year were not affected thereby, since each kind of seed gave plants which, as regards their seed, were like each other and different from the others. They resulted therefore from the second experiment 31, fourth experiment 24 plants of the form capital A A capital B B, second experiment 26, fourth experiment 25 plants of the form capital A A B, second experiment 27, fourth experiment 22 plants of the form A capital B B, second experiment 26, fourth experiment 27 plants of the form A B. In all the experiments therefore there appeared all the forms which the proposed theory demands and they came in nearly equal numbers. In a further experiment the characters of flower color and length of stem were experimented upon and selection was so made that in the third year of the experiment each character ought to appear in half of all the plants if the above theory were correct. Capital A capital B A B serve again as indicating the various characters. Capital A violet red flowers, capital B X is long, A white flowers, B X is short. The form capital A B was fertilized with A B which produced the hybrid capital A A B. Furthermore A capital B was also fertilized with A B when the hybrid A capital B B. In the second year for further fertilization the hybrid capital A A B was used as seed parent and hybrid A capital B B as pollen parent. Seed parent capital A A B, possible egg cells capital A B A B, pollen parent A B B, pollen cells A B A B. From the fertilization between the possible egg and pollen cells four combinations should result that is capital A A capital B B and A capital B B and capital A A B and A B. From this it is perceived that according to the above theory in the third year of the experiment out of all the plants half should have violet red flowers, capital A A, classes one three, half should have white flowers, A, classes two four, half should have a long axis, capital B B, classes one two, half should have a short axis, B, classes three four. From 45 fertilizations of the second year 187 seeds resulted of which only 166 reached the flowering stage in the third year. Among these the separate classes appeared in the numbers following. Class one violet red color of flower long stem 47 times. Class two white color of flower long stem 40 times. Class three violet red color of flower short stem 38 times. Class four white color of flower short stem 41 times. There subsequently appeared the violet red flower color capital A A in 85 plants. The white flower color A in 81 plants. The long stem capital B B in 87 plants. The short stem B in 79 plants. The theory adduced is therefore satisfactorily confirmed in this experiment also. For the characters of form of pot, color of pot and position of flowers, experiments were also made on a small scale and results obtained in perfect agreement. All combinations which were possible through the union of the differentiating characters duly appeared and in nearly equal numbers. Experimentally, therefore, the theory is confirmed that the P hybrids form egg and pollen cells which in their constitution representing equal numbers all constant forms which result from the combination of the characters united in fertilization. The difference of the forms among the progeny of the hybrids as well as the respective ratios of the numbers in which they are observed find a sufficient explanation in the principle above deduced. The simplest case is afforded by the developmental series of each pair of differentiating characters. This series is represented by the expression capital A and 2 capital AA and A in which capital A and A signify the forms with constant differentiating characters and capital AA the hybrid form of both. It includes in three different classes four individuals. In the formation of these pollen and exels of the form capital A and A take part on the average equally in the fertilization. Hence, each form occurs twice since four individuals are formed. They participate consequently in the fertilization. The pollen cells capital A and capital A and A and A the exels capital A and capital A and A and A. It remains therefore purely a matter of chance which of the two sorts of pollen will become united with each separate exel. According however to the law of probability it will always happen on the average of many cases that each pollen form capital A and A will unite equally often with each exel form capital A and A. Consequently one of the two pollen cells capital A in the fertilization will meet with the exel capital A and the other with an exel A. And so likewise one pollen cell A will unite with an exel capital A and the other with exel A. The result of the fertilization may be made clear by putting the signs for the conjoined egg and pollen cells in the form of fractions those for the pollen cells above and those for the exels below the line. We then have capital A over capital A and capital A over A and A over capital A and A over A. In the first and fourth term the egg and pollen cells are of like kind. Consequently the product of the union must be constant that is capital A and A. In the second and third on the other hand there again results a union of the two differentiating characters of the stocks. Consequently the forms resulting from these fertilizations are identical with those of the hybrid from which they spring. There occurs accordingly a repeated hybridization. This explains the striking fact that the hybrids are able to produce besides the two parental forms of spring which are like themselves. Capital A over A and A over capital A both give the same union capital A A since as already remarked above it makes no difference in the result of fertilization to which of the two characters the pollen or exels belong. We may write then capital A over capital A and capital A over A and A over capital A and A over A equals capital A and two capital A A and A. This represents the average result of the self fertilization of the hybrids when two differentiating characters are united in them. In individual flowers and in individual plants however the ratios in which the forms of the series are produced may suffer not inconsiderable fluctuations. Apart from the fact that the numbers in which both sorts of exels occurring the seed vessels can only be regarded as equal on the average it remains purely a matter of chance which of the two sorts of pollen may fertilize each separate exel. For this reason the separate values must necessarily be subject to fluctuations and there are even extreme cases possible as were described earlier in connection with the experiments on the form of the seed and the color of the albumen. The true ratios of the numbers can only be ascertained by an average deduced from the sum of as many single values as possible. The greater the number the more are merely chance effects eliminated. The developmental series for hybrids in which two kinds of differentiating characters are united contains among 16 individuals nine different forms that is capital A capital B and capital AB and A capital B and AB and two capital A capital B B and two A capital B B and two capital A A capital B and two capital A A B and four capital A A B between the differentiating characters of the original stocks capital A A and capital B B four constant combinations are possible and consequently the hybrids produce the corresponding four forms of egg and pollen cells capital A capital B capital A B A capital B A B and each of these will on the average figure four times in the fertilization since 16 individuals are included in the series. Therefore the participators in the fertilization are pollen cells capital A capital B and capital A capital B and capital A capital B and capital A capital B and capital AB and capital AB and capital AB and capital AB and A capital B and A capital B and A capital B and A capital B and A capital B and AB and AB and AB and A capital B and A capital A B. Excels capital A capital B and capital A capital B and capital A capital B and capital A capital B and capital A B and capital A B and capital A B and capital A B and A capital B and A capital B and A capital B and A capital B, and AB, and AB, and AB. In the process of fertilization, each pollen form unites on an average equally often with each Excel form, so that each of the four pollen cells, capital A, capital B, unites once with one of the forms of Excel, capital A, capital B, capital AB, A, capital B, AB. In precisely the same way, the rest of the pollen cells of the forms capital AB, A, capital B, AB, unite with all the other Excel's. We obtain therefore capital A, capital B, over capital A, capital B, and capital A, capital B, over capital AB, and capital A, capital B, over A, capital B, and capital A, capital B, over AB, and capital AB, over capital A, capital B, and capital AB, over capital AB, and capital AB, over A, capital B, and capital AB, over AB, and A capital B over A capital B and A capital B over A B and A capital B over A capital B and A capital B over A B and A B over A capital B and A B over A capital A B and A B over A capital B and A B over A B or capital A capital B and capital A capital B B and capital A A capital B B and capital A A B and A capital B B and A B is equal to capital A capital B and capital A B and A A capital B and A B and 2 capital A capital B B and 2 A capital B B and 2 A A capital B and 2 A A B and 4 A A capital B B In precisely similar fashion is the developmental series of hybrids exhibited when three kinds of differentiating characters are conjoined in them. The hybrids form eight various kinds of egg and pollen cells. A A B B C A B C A B C A B C A B C A B C and each pollen form unites itself again on the average once with each form of excel. The law of combination of different characters which governs the development of the hybrids finds therefore its foundation and explanation in the principle enunciated that the hybrids produce egg cells and pollen cells which in equal numbers represent all constant forms which result from the combinations of the characters brought together in fertilization. End of Chapter 9 Chapter 10 of Experiments in Plant Hybridization This LibriVox recording is in the public domain. Recording by Avae in February 2010. Experiments in Plant Hybridization by Gregor Mendel translated by William Bateson. Chapter 10 Experiments with hybrids of other species of plants. It must be the object of further experiments to ascertain whether the law of development discovered for Pison applies also to the hybrids of other plants. To this end several experiments were recently commenced. Two minor experiments with species of Phaseolus have been completed and maybe here mentioned. An experiment with Phaseolus vulgaris and Phaseolus nanus gave results in perfect agreement. Phaseolus nanus had together with the dwarf axis simply inflated green pods. Phaseolus vulgaris had on the other hand an axis 10 feet to 12 feet high and yellow colored pods constricted when ripe. The ratios of the numbers in which the different forms appeared in the separate generations were the same as with Pison. Also the development of the constant combinations resulted according to the law of simple combination of characters exactly as in the case of Pison. They were obtained. First constant combination. Long axis, green color of the unripe pods, inflated form of the ripe pods. Second constant combination. Long axis, green color of the unripe pods, constricted form of the ripe pods. Third constant combination. Long axis, yellow color of the unripe pods, inflated form of the ripe pods. Fourth constant combination. Long axis, yellow color of the unripe pods, constricted form of the ripe pods. Fifth constant combination. Short axis, green color of the unripe pods, inflated form of the ripe pods. Sixth constant combination. Short axis, green color of the unripe pods, constricted form of the ripe pods. Seventh constant combination. Short axis, yellow color of the unripe pods, inflated form of the ripe pods. 8th constant combination, short axis, yellow color of the unripe pods, constricted form of the ripe pods. The green color of the pod, the inflated forms and the long axis were, as in Pism, dominant characters. Another experiment with two very different species of Phaseolus had only a partial result. Phaseolus nanus L served as seed parent, a perfectly constant species, with white flowers in short racemes and small white seeds in straight, inflated, smooth pods. As pollen parent was used Phaseolus multiflorus W, with tall winding stem, purple red flowers in very long racemes, rough, sickle-shaped, crooked pods and large seeds which bore black flecks and splashes on a peach blood red ground. The hybrids had the greatest similarity to the pollen parent, but the flowers appeared less intensely colored. Their fertility was very limited, from 17 plants which together developed many hundreds of flowers, only 49 seeds in all were obtained. These were of medium size and were flecked and splashed similarly to those of Phaseolus multiflorus, while the ground color was not materially different. The next year, 44 plants were raised from these seeds, of which only 31 reached a flowering stage. The characters of Phaseolus nanus, which had been altogether latent in the hybrids, reappeared in various combinations. Their ratio, however, with relation to the dominant plants, was necessarily very fluctuating, owing to the small number of trial plants. With certain characters, as in those of the axis and a form of pod, it was, however, as in the case of Pesum, almost exactly 1 to 3. Insignificant as the results of this experiment may be, as regards the determination of the relative numbers in which the various forms appeared, it presents on the other hand the phenomenon of a remarkable change of color in the flowers and seed of the hybrids. In Pesum it is known that the characters of the flower and seed color present themselves unchanged in the first and further generations, and that the offspring of the hybrids display exclusively the one or the other of the characters of the original stalks. It is otherwise in the experiment we are considering. The white flowers in the seed color of Fasiolus nanus appeared, it is true, at once in the first generation from the hybrids in one fairly fertile example, but the remaining 30 plants developed flower colors which were of various grades of purple-red to pale-violet. The coloring of the seed coat was no less varied than that of the flowers. No plant could rank as fully fertile. Many produced no fruit at all. Others only yielded fruits from the flowers last produced, which did not ripen. From 15 plants only were well-developed seeds obtained. The greatest disposition to infertility was seen in the forms with preponderantly red flowers since out of 16 of these only four yielded ripe seed. Three of these had a similar seed pattern to Fasiolus multiflorus, but with a more or less pale ground color. The fourth plant yielded only one seed of plain brown tint. The forms with preponderantly violet colored flowers had dark brown, black brown and quite black seeds. The experiment was continued through two more generations under similar unfavorable circumstances. Since even among the offspring of fairly fertile plants there came again some which were less fertile or even quite sterile. Other flower and seed colors than those cited did not subsequently present themselves. The forms which in the first generation bred from the hybrids contained one or more of the recessive characters remained, as regards these, constant without exception. Also of those plants which possessed violet flowers and brown or black seeds, some did not vary again in these respects in the next generation. The majority however yielded together with offspring exactly like themselves, some which displayed white flowers and white seed coats. The red flowering plants remained so slightly fertile that nothing can be said with certainty as regards the further development. Despite the many disturbing factors with which the observations had to contend, it is nevertheless seen by this experiment that the development of the hybrids with regard to those characters which concern the form of the plants follows the same laws as in piezoom. With regard to the color characters it certainly appears difficult to perceive a substantial agreement. Apart from the fact that from the union of a white and a purple red coloring a whole series of colors results in F2, from purple to pale violet and white. The circumstances is striking one that among thirty-one flowering plants only one received the recessive character of the white color, while in piezoom this occurs on the average in every fourth plant. Even these enigmatic results, however, might probably be explained by the law governing piezoom if we might assume that the color of the flowers and seeds of aziolus multiflorus is a combination of two or more entirely independent colors which individually act like any other constant character in the plant. If the flower color capital A were a combination of the individual characters capital A1 and capital A2 and so forth which produce the total impression of a purple coloration then by fertilization with the differentiating character white color A there would be produced the hybrid unions capital A1, A and capital A2, A and so forth and so would it be with the corresponding coloring of the seed codes. According to the above assumption each of these hybrid color unions would be independent and would consequently develop quite independently from the others. It is then easily seen that from the combination of the separate developmental series a complete color series must result. If for instance capital A equals capital A1 and capital A2 then the hybrids capital A1, A and capital A2, A from the developmental series capital A1 and two capital A1, A and A, capital A2 and two capital A2, A and A. The members of this series can enter into nine different combinations and each of these denotes another color. One capital A1, capital A2, two capital A1, capital A2, A, one capital A1, A, two capital A1, A, two capital A1, A, capital A2, four capital A1, A, capital A2, A, two capital A1, A, A, one capital A2, A, two capital A2, A, A, one A, A. The figures prescribed for the separate combinations also indicate how many plants with the corresponding coloring belong to the series. Since the total is 16, the whole of the colors are on the average distributed over each 16 plants, but as the series itself indicates in unequal proportions. Should the color development really happen in this way, we could offer an explanation of the case above described, that is, that the white flowers in seed coat color only appeared once among 31 plants of the first generation. This coloring appears only once in the series, and could therefore also only be developed once in the average in each 16, and with 3 color characters only once even in 64 plants. It must nevertheless not be forgotten that the explanation here attempted is based on a mere hypothesis, only supported by the very imperfect result of the experiment just described. It would, however, be well worthwhile to follow up the development of coloring hybrids by similar experiments, since it is probable that in this way we might learn the significance of the extraordinary variety in the coloring of our ornamental flowers. So far, little at present is known with certainty beyond the fact that the color of the flowers in most ornamental plants is an extremely variable character. The opinion has often been expressed that the stability of the species is greatly disturbed or entirely upset by cultivation, and consequently there is an inclination to regard to the development of cultivated forms as a matter of chance devoid of rules. The coloring of ornamental plants is indeed usually cited as an example of great instability. It is, however, not clear why the simple transference into garden soil should result in such a thorough and persistent revolution in the plant organism. No one will seriously maintain that in the open country the development of plants is ruled by other laws than in the garden bed. Here as there, changes of type must take place if the conditions of life be altered, and a species possesses the capacity of fitting itself to its new environment. It is willingly granted that by cultivation the origination of new varieties is favored, and that by man's labor many varieties are acquired which, under natural conditions, would be lost. But nothing justifies the assumption that the tendency to the formation of varieties is so extraordinarily increased that the species speedily lose all stability and their offspring diverge into an endless series of extremely variable forms. While the change in the conditions, the sole cause of variability, we might expect that those cultivated plants which are grown for centuries under almost identical conditions would again attain constancy. That, as is well known, is not the case, since it is precisely under such circumstances that not only the most varied but also the most variable forms are found. It is only the leguminose, like pism, fazeolus, lens, whose organs of fertilization are protected by the keel, which constitute a noteworthy exception. Even here, there have arisen numerous varieties during a cultural period of more than one thousand years under most various conditions. These maintain, however, under unchanging environments, as stability as great as that of species growing wild. It is more than probable that as regards the variability of cultivated plants, there exists a factor which so far has received little attention. Various experiments force us to the conclusion that our cultivated plants, with few exceptions, are members of various hybrid series whose further development in conformity with law is varied and interrupted by frequent crossings interse. The circumstance must not be overlooked that cultivated plants are mostly grown in great numbers and close together, affording the most favorable conditions for reciprocal fertilization between the varieties present and the species itself. The probability of this is supported by the fact that among the great array of variable forms, solitary examples are always found, which in one character or another remain constant if only foreign influence be carefully excluded. These forms behave precisely as do those which are known to be members of the compound hybrid series. Also with the most susceptible of all characters, that of color, it cannot escape the careful observer that in the separate forms the inclination to vary is displayed in very different degrees. Among plants which arise from one spontaneous fertilization, there are often some whose offspring vary widely in the constitution and arrangement of the colors, while that of others shows little deviation, and among a greater number solitary examples occur which transmit the color of the flowers unchanged to their offspring. The cultivated species of diantus afford an instructive example of this. A white-flowered example of diantus cariophilus, which itself was derived from a white-flowered variety, was shot up during its blooming period in a greenhouse. The numerous seeds obtained therefrom yielded plants entirely white-flowered like itself. A similar result was obtained from a subspecies, with red flowers somewhat flushed with violet and one with flowers white, striped with red. Many others on the other hand, which were similarly protected, yielded progeny which were more or less variously colored and marked. Whoever studies the coloration which results in ornamental plants from similar fertilization can hardly escape the conviction that here also the development follows a definite law which possibly finds its expression in the combination of several independent color characters.