論文-植物雜交試驗(yàn)（1865）

1、<p>　　論文——植物雜交試驗(yàn)（1865）</p><p>　　Experiments in Plant Hybridization (1865)by Gregor Mendel</p><p>　　Introductory Remarks</p><p>　　Experience of artificial fertilization, such a

2、s is effected 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 wheneve

3、r 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. </p><p>　　To this obje

4、ct numerous careful observers, such as Kölreuter, Gärtner, Herbert, Lecoq, Wichura and others, have devoted a part of their lives with inexhaustible perseverance. Gärtner especially in his work Die Bastard

5、erzeugung 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

6、 of the Willow. That, so far, no generally applicable law gover</p><p>　　Those who survey the work done in this department will arrive at the conviction that among all the numerous experiments made, not one

7、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 the hybrids appear, or to arrange these forms with certainty accordi

8、ng to their separate generations, or definitely to ascertain their statistical relations. </p><p>　　It requires indeed some courage to undertake a labor of such far-reaching extent; this appears, however, to

9、 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. </p><p>　　The

10、 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 th

11、e plan upon which the separate experiments were conducted and carried out was the best suited to attain the desired end is left to the friendly decision of the reader.</p><p>　　Selection of the Experimental

12、Plants</p><p>　　The value and utility of any experiment are determined by the fitness of the material to the purpose for which it is used, and thus in the case before us it cannot be immaterial what plants a

13、re subjected to experiment and in what manner such experiment is conducted. </p><p>　　The selection of the plant group which shall serve for experiments of this kind must be made with all possible care if it

14、 be desired to avoid from the outset every risk of questionable results. </p><p>　　The experimental plants must necessarily: </p><p>　　Possess constant differentiating characteristics. </p>

15、;<p>　　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.</p><p>　　The hybrids and their offs

16、pring should suffer no marked disturbance in their fertility in the successive generations. </p><p>　　Accidental impregnation by foreign pollen, if it occurred during the experiments and were not recognized,

17、 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 th

18、em. 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 member of the </p><p>　　At the very outset spe

19、cial attention was devoted to the Leguminosae on account of their peculiar floral structure. Experiments which were made with several members of this family led to the result that the genus Pisum was found to possess the

20、 necessary qualifications. </p><p>　　Some thoroughly distinct forms of this genus possess characters which are constant, and easily and certainly recognizable, and when their hybrids are mutually crossed the

21、y yield perfectly fertile progeny. Furthermore, a disturbance through foreign pollen cannot easily occur, since the fertilizing organs are closely packed inside the keel and the anthers burst within the bud, so that the

22、stigma becomes covered with pollen even before the flower opens. This circumstance is especially important. As</p><p>　　In all, 34 more or less distinct varieties of Peas were obtained from several seedsmen

23、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

24、year, and agreed entirely with another variety obtained from the same seedsman; the seeds were therefore doubtless merely accidentally mixed. All the other varieties yielded perfectly constant and </p><p>　　

25、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 di

26、splay 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 Pisum sativum; while the rest are regarded

27、and classed, some as sub-species of P. sativum, and some as </p><p>　　Division and Arrangement of the Experiments</p><p>　　If two plants which differ constantly in one or several characters be c

28、rossed, 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

29、 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, and to deduce</p>

30、<p>　　The various forms of Peas selected for crossing showed differences in length and color of the stem; in the size and form of the leaves; in the position, color, size of the flowers; in the length of the flower

31、 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 [cotyledons]. Some of the characters noted do not permit of a sharp and certain s

32、eparation, since the difference is of a "more or less" nature, which is </p><p>　　The characters which were selected for experiment relate: </p><p>　　To the difference in the form of t

33、he 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 (P. quadratum). </p><p>　　To t

34、he difference in the color of the seed albumen (endosperm). 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 col

35、or is easily seen in the seeds as their coats are transparent. </p><p>　　To the difference in the color of the seed-coat. This is either white, with which character white flowers are constantly correlated; o

36、r 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 axils of the leaves is of a reddish tint. The gr

37、ay seed-coats become dark brown in boiling water. </p><p>　　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

38、the seeds and more or less wrinkled (P. saccharatum). </p><p>　　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-v

39、eins, and calyx participate.* </p><p>　　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

40、 the stem and arranged almost in a false umbel; in this case the upper part of the stem is more or less widened in section (P. umbellatum). </p><p>　　To the difference in the length of the stem. The length o

41、f the stem is very various in some forms; it is, however, a constant character for each, in so far that healthy plants, grown in the same soil, are only subject to unimportant variations in this character. In experiments

42、 with this character, in order to be able to discriminate with certainty, the long axis of 6 to 7 ft. was always crossed with the short one of 3/4 ft. to 1 and 1/2 ft. </p><p>　　Each two of the differentiati

43、ng characters enumerated above were united by cross-fertilization. There were made for the </p><p>　　1st trial 60 fertilizations on 15 plants.</p><p>　　2nd trial 58 fertilizations on 10 plan

44、ts.</p><p>　　3rd trial 35 fertilizations on 10 plants.</p><p>　　4th trial 40 fertilizations on 10 plants.</p><p>　　5th trial 23 fertilizations on 5 plants.</p><p&g

45、t;　　6th trial 34 fertilizations on 10 plants.</p><p>　　7th trial 37 fertilizations on 10 plants.</p><p>　　*One species possesses a beautifully brownish-red colored pod, which when ripening t

46、urns to violet and blue. Trials with this character were only begun last year.</p><p>　　From a larger number of plants of the same variety only the most vigorous were chosen for fertilization. Weakly plants

47、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. <

48、/p><p>　　Furthermore, in all the experiments reciprocal crossings were effected 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

49、 the pollen plant. </p><p>　　The plants were grown in garden beds, a few also in pots, and were maintained in their natural upright position by means of sticks, branches of trees, and strings stretched betwe

50、en. 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

51、insects which visit Peas the beetle Buchus pisi might be detrimental to the experiments should it appe</p><p>　　The risk of false impregnation by foreign pollen is, however, a very slight one with Pisum, and

52、 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 in the greenh

53、ouse such a case was never remarked, it may well be supposed that Brucus pisi, and possibly also the described abnormalities in the floral structure, were to blame.</p><p>　　The Forms of the Hybrids</p>

54、;<p>　　Experiments which in previous years were made with ornamental plants have already affording evidence that the hybrids, as a rule, are not exactly intermediate between the parental species. With some of the

55、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, o

56、ne of the two parental characters is so preponderant that it is difficult,</p><p>　　This is precisely the case with the Pea hybrids. In the case of each of the 7 crosses the hybrid-character resembles that o

57、f 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 fo

58、rms under which the offspring of the hybrids appear. Henceforth in this paper those characters which are transmitted entire, or almost unchanged in the hybri</p><p>　　It was furthermore shown by the whole of

59、 the experiments that it is perfectly immaterial whether the dominant character belongs to the seed plant or to the pollen plant; the form of the hybrid remains identical in both cases. This interesting fact was also emp

60、hasized by Gärtner, 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. </p><p>　　Of the

61、 differentiating characters which were used in the experiments the following are dominant: </p><p>　　The round or roundish form of the seed with or without shallow depressions. </p><p>　　The yel

62、low coloring of the seed albumen [cotyledons]. </p><p>　　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. </p>

63、<p>　　The simply inflated form of the pod. </p><p>　　The green coloring of the unripe pod in association with the same color of the stems, the leaf-veins and the calyx. </p><p>　　The dist

64、ribution of the flowers along the stem. </p><p>　　The greater length of stem. </p><p>　　With regard to this last character it must be stated that the longer of the two parental stems is usually

65、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 lengths are crossed. Thus, for instance, in repeated experime

66、nts, stems of 1 ft. and 6 ft. in length yielded without exception hybrids which varied in length between 6 ft. and 7 [and] 1/2 ft. </p><p>　　The hybrid seeds in the experiments with seed-coat are often more

67、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. </p><p>　　The hybrid forms of the seed-shape a

68、nd of the [color of the] albumen 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

69、 the other characters naturally only appear in the following year in such plants as have been raised from the crossed seed.</p><p>　　The First Generation From the Hybrids</p><p>　　In this genera

70、tion there 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 3:1, so that among each 4 pl

71、ants of this generation 3 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

72、green color of the albumen, the while color of</p><p>　　Since the hybrids resulting from reciprocal crosses are formed alike and present no appreciable difference in their subsequent development, consequentl

73、y these results can be reckoned together in each experiment. The relative numbers which were obtained for each pair of differentiating characters are as follows: </p><p>　　Expt. 1. Form of seed. -- From 253

74、hybrids 7324 seeds were obtained in the second trial year. Among them were 5474 round or roundish ones and 1850 angular wrinkled ones. Therefrom the ratio 2.96:1 is deduced. </p><p>　　Expt. 2. Color of album

75、en. -- 258 plants yielded 8023 seeds, 6022 yellow, and 2001 green; their ratio, therefore, is as 3.01:1. </p><p>　　In these two experiments each pod yielded usually both kinds of seed. In well-developed pods

76、 which contained on the average 6 to 9 seeds, it often happened that all the seeds were round (Expt. 1) or all yellow (Expt. 2); on the other hand there were never observed more than 5 wrinkled or 5 green ones on one pod

77、. 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 fe</p><p>　　As in sep

78、arate 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. </p><p>　　Experiment 1 Exp

79、eriment 2</p><p>　　Form of Seed Color of Albumen</p><p>　　Plants Round Angular Yellow Green</p><p>　　1 45 12 25 11</p><p>　　2

80、 27 8 32 7</p><p>　　3 24 7 14 5</p><p>　　4 19 10 70 27</p><p>　　5 32 11 24 13

81、</p><p>　　6 26 6 20 6</p><p>　　7 88 24 32 13</p><p>　　8 22 10 44 9</p><p>　　9 28

82、 6 50 14</p><p>　　10 25 7 44 18</p><p>　　As extremes in the distribution of the two seed characters in one plant, there were observed in Expt. 1 an insta

83、nce of 43 round and only 2 angular, and another of 14 round and 15 angular seeds. In Expt. 2 there was a case of 32 yellow and only 1 green seed, but also one of 20 yellow and 19 green. </p><p>　　These two e

84、xperiments 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

85、in Expt. 2, 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

86、coloring has no connection with the hybrid-charac</p><p>　　Expt. 3. 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-c

87、oats, giving the proportion 3.15:1. </p><p>　　Expt. 4. Form of pods. -- Of 1181 plants, 882 had them simply inflated, and in 299 they were constricted. Resulting ratio, 2.95:1. </p><p>　　Expt. 5

88、. Color of the unripe pods. -- The number of trial plants was 580, of which 428 had green pods and 152 yellow ones. Consequently these stand in the ratio of 2.82:1. </p><p>　　Expt. 6. Position of flowers. --

89、 Among 858 cases 651 had inflorescences axial and 207 terminal. Ratio, 3.14:1. </p><p>　　Expt. 7. Length of stem. -- Out of 1064 plants, in 787 cases the stem was long, and in 277 short. Hence a mutual ratio

90、 of 2.84:1. 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 relativ

91、es. Even in their quite young state they can be easily picked out by their compact growth and thick dark-green foliage. </p><p>　　If now the results of the whole of the experiments be brought together, there

92、 is found, as between the number of forms with the dominant and recessive characters, an average ratio of 2.98:1, or 3:1. </p><p>　　The dominant character can have here a double signification; namely, that o

93、f 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 t

94、o the whole of the offspring; as a hybrid-character, on the other hand, it must maintain the same behavior as in the first generation.</p><p>　　The Second Generation From the Hybrids</p><p>　　Th

95、ose forms which in the first generation exhibit the recessive character do not further vary in the second generation as regards this character; they remain constant in their offspring. </p><p>　　It is otherw

96、ise with those which possess the dominant character in the first generation. Of these two-thirds yield offspring which display the dominant and recessive characters in the proportion of 3:1, and thereby show exactly the

97、same ratio as the hybrid forms, while only one-third remains with the dominant character constant. </p><p>　　The separate experiments yielded the following results: </p><p>　　Expt. 1. Among 565

98、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