The Different Forms of Flowers on Plants of the Same Species - Charles Robert Darwin (ebook reader screen TXT) 📗

the normal standard.]


CLASS 7. ILLEGITIMATE PLANTS RAISED FROM MID-STYLED PARENTS FERTILISED WITH POLLEN FROM THE LONGEST STAMENS OF THE SHORT-STYLED FORM.
It was shown in the last chapter that the union from which these illegitimate plants were raised is far more fertile than any other illegitimate union; for the mid-styled parent, when thus fertilised, yielded an average (all very poor capsules being excluded) of 102.8 seeds, with a maximum of 130; and the seedlings in the present class likewise have their fertility not at all lessened. Forty plants were raised; and these attained their full height and were covered with seed-capsules. Nor did I observe any contabescent anthers. It deserves, also, particular notice that these plants, differently from what occurred in any of the previous classes, consisted of all three forms, namely, eighteen short-styled, fourteen long-styled, and eight mid-styled plants. As these plants were so fertile, I counted the seeds only in the two following cases.
[PLANT 32.
This mid-styled plant was freely and legitimately fertilised during the unfavourable year of 1864, by numerous surrounding legitimate and illegitimate plants. Eight capsules yielded an average of 127.2 seeds, with a maximum of 144 and a minimum of 96; so that this plant attained 98 per cent of the normal standard.
PLANT 33.
This short-styled plant was fertilised in the same manner and at the same time with the last; and ten capsules yielded an average of 113.9, with a maximum of 137 and a minimum of 90. Hence this plant produced no less than 137 per cent of seeds in comparison with the normal standard.]


CONCLUDING REMARKS ON THE ILLEGITIMATE OFFSPRING OF THE THREE FORMS OF Lythrum salicaria.
From the three forms occurring in approximately equal numbers in a state of nature, and from the results of sowing seed naturally produced, there is reason to believe that each form, when legitimately fertilised, reproduces all three forms in about equal numbers. Now, we have seen (and the fact is a very singular one) that the fifty-six plants produced from the long-styled form, illegitimately fertilised with pollen from the same form (Class 1 and 2), were all long-styled. The short-styled form, when self-fertilised (Class 3), produced eight short-styled and one long-styled plant; and the mid-styled form, similarly treated (Class 4), produced three mid-styled and one long-styled offspring; so that these two forms, when illegitimately fertilised with pollen from the same form, evince a strong, but not exclusive, tendency to reproduce the parent-form. When the short-styled form was illegitimately fertilised by the long-styled form (Class 5), and again when the mid-styled was illegitimately fertilised by the long-styled (Class 6), in each case the two parent-forms alone were reproduced. As thirty-seven plants were raised from these two unions, we may, with much confidence, believe that it is the rule that plants thus derived usually consist of both parent-forms, but not of the third form. When, however, the mid-styled form was illegitimately fertilised by the longest stamens of the short-styled (Class 7), the same rule did not hold good; for the seedlings consisted of all three forms. The illegitimate union from which these latter seedlings were raised is, as previously stated, singularly fertile, and the seedlings themselves exhibited no signs of sterility and grew to their full height. From the consideration of these several facts, and from analogous ones to be given under Oxalis, it seems probable that in a state of nature the pistil of each form usually receives, through the agency of insects, pollen from the stamens of corresponding height from both the other forms. But the case last given shows that the application of two kinds of pollen is not indispensable for the production of all three forms. Hildebrand has suggested that the cause of all three forms being regularly and naturally reproduced, may be that some of the flowers are fertilised with one kind of pollen, and others on the same plant with the other kind of pollen. Finally, of the three forms, the long-styled evinces somewhat the strongest tendency to reappear amongst the offspring, whether both, or one, or neither of the parents are long-styled.
[TABLE 5.30. Tabulated results of the fertility of the foregoing illegitimate plants, when legitimately fertilised, generally by illegitimate plants, as described under each experiment. Plants 11, 12 and 13 are excluded, as they were illegitimately fertilised.


NORMAL STANDARD OF FERTILITY OF THE THREE FORMS, WHEN LEGITIMATELY AND NATURALLY FERTILISED.
Column 1: Form. Column 2: Average number of seeds per capsule. Column 3: Maximum number in any one capsule. Column 4: Minimum number in any one capsule.
Long-styled : 93 : 159 : No record was kept as all very poor capsules were rejected. Mid-styled : 130 : 151 : No record was kept as all very poor capsules were rejected. Short-styled : 83.5 : 112 : No record was kept as all very poor capsules were rejected.
TABLE 5.30. Continued.
CLASS 1 AND CLASS 2.--ILLEGITIMATE PLANTS RAISED FROM LONG-STYLED PARENTS FERTILISED WITH POLLEN FROM OWN-FORM MID-LENGTH OR SHORTEST STAMENS.
Column 1: Number (name) of plant. Column 2: Form. Column 3: Average number of seeds per capsule. Column 4: Maximum number of seeds in any one capsule. Column 5: Minimum number of seeds in any one capsule. Column 6: Average number of seeds, expressed as the percentage of the normal standard.
1 : Long-styled : 0 : 0 : 0 : 0. 2 : Long-styled : 4.5 : ? : 0 : 5. 3 : Long-styled : 4.5 : ? : 0 : 5. 4 : Long-styled : 4.5 : ? : 0 : 5. 5 : Long-styled : 0 or 1 : 2 : 0 : 0 or 1. 6 : Long-styled : 0 : 0 : 0 : 0. 7 : Long-styled : 36.1 : 47 : 22 : 39. 8 : Long-styled : 41.1 : 73 : 11 : 44. 9 : Long-styled : 57.1 : 86 : 23 : 61. 10 : Long-styled : 44.2 : 69 : 25 : 47.
CLASS 3. ILLEGITIMATE PLANTS RAISED FROM SHORT-STYLED PARENTS FERTILISED WITH POLLEN FROM OWN-FORM SHORTEST STAMENS.
14 : Short-styled : 28.3 : 51 : 11 : 33. 15 : Short-styled : 32.6 : 49 : 20 : 38. 16 : Short-styled : 77.8 : 97 : 60 : 94. 17 : Long-styled : 76.3 : 88 : 57 : 82.
CLASS 4. ILLEGITIMATE PLANTS RAISED FROM MID-STYLED PARENTS FERTILISED WITH POLLEN FROM OWN-FORM LONGEST STAMENS.
18 : Mid-styled : 102.6 : 131 : 63 : 80. 19 : Mid-styled : 73.4 : 87 : 64 : 56. 20 : Long-styled : 69.6 : 83 : 52 : 75.
CLASS 5. ILLEGITIMATE PLANTS RAISED FROM SHORT-STYLED PARENTS FERTILISED WITH POLLEN FROM THE MID-LENGTH STAMENS OF THE LONG-STYLED FORM.
21 : Short-styled : 43.0 : 63 : 26 : 52. 22 : Short-styled : 100.5 : 123 : 86 : 121. 23 : Short-styled : 113.5 : 123 : 93 : 136. 24 : Long-styled : 82.0 : 120 : 67 : 88. 25 : Long-styled : 122.5 : 149 : 84 : 131.
CLASS 6. ILLEGITIMATE PLANTS RAISED FROM MID-STYLED PARENTS FERTILISED WITH POLLEN FROM THE SHORTEST STAMENS OF THE LONG-STYLED FORM.
26 : Mid-styled : 86.0 : 109 : 61 : 66. 27 : Mid-styled : 99.4 : 122 : 53 : 76. 28 : Mid-styled : 89.0 : 119 : 69 : 68. 29 : Long-styled : 100.0 : 121 : 77 : 107. 30 : Long-styled : 94.0 : 106 : 66 : 101. 31 : Long-styled : 90.6 : 97 : 79 : 98.
CLASS 7. ILLEGITIMATE PLANTS RAISED FROM MID-STYLED PARENTS FERTILISED WITH POLLEN FROM THE LONGEST STAMENS OF THE SHORT-STYLED FORM.
32 : Mid-styled : 127.2 : 144 : 96 : 98. 33 : Short-styled : 113.9 : 137 : 90 : 137.
The lessened fertility of most of these illegitimate plants is in many respects a highly remarkable phenomenon. Thirty-three plants in the seven classes were subjected to various trials, and the seeds carefully counted. Some of them were artificially fertilised, but the far greater number were freely fertilised (and this is the better and natural plan) through the agency of insects, by other illegitimate plants. In the right hand, or percentage column, in Table 5.30, a wide difference in fertility between the plants in the first four and the last three classes may be perceived. In the first four classes the plants are descended from the three forms illegitimately fertilised with pollen taken from the same form, but only rarely from the same plant. It is necessary to observe this latter circumstance; for, as I have elsewhere shown, most plants, when fertilised with their own pollen, or that from the same plant, are in some degree sterile, and the seedlings raised from such unions are likewise in some degree sterile, dwarfed, and feeble. (5/3. 'The Effects of Cross and Self- fertilisation in the Vegetable Kingdom' 1876.) None of the nineteen illegitimate plants in the first four classes were completely fertile; one, however, was nearly so, yielding 96 per cent of the proper number of seeds. From this high degree of fertility we have many descending gradations, till we reach an absolute zero, when the plants, though bearing many flowers, did not produce, during successive years, a single seed or even seed-capsule. Some of the most sterile plants did not even yield a single seed when legitimately fertilised with pollen from legitimate plants. There is good reason to believe that the first seven plants in Class 1 and 2 were the offspring of a long-styled plant fertilised with pollen from its own-form shortest stamens, and these plants were the most sterile of all. The remaining plants in Class 1 and 2 were almost certainly the product of pollen from the mid-length stamens, and although very sterile, they were less so than the first set. None of the plants in the first four classes attained their full and proper stature; the first seven, which were the most sterile of all (as already stated), were by far the most dwarfed, several of them never reaching to half their proper height. These same plants did not flower at so early an age, or at so early a period in the season, as they ought to have done. The anthers in many of their flowers, and in the flowers of some other plants in the first six classes, were either contabescent or included numerous small and shrivelled pollen-grains. As the suspicion at one time occurred to me that the lessened fertility of the illegitimate plants might be due to the pollen alone having been affected, I may remark that this certainly was not the case; for several of them, when fertilised by sound pollen from legitimate plants, did not yield the full complement of seeds; hence it is certain that both the female and male reproductive organs were affected. In each of the seven classes, the plants, though descended from the same parents, sown at the same time and in the same soil, differed much in their average degree of fertility.
Turning now to the fifth, sixth, and seventh classes, and looking to the right hand column of Table 5.30, we find nearly as many plants with a percentage of seeds above the normal standard as beneath it. As with most plants the number of seeds produced varies much, it