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

figure "0" means that no capsule was produced, or if a capsule was produced that it contained no good seed. In some part of each row of figures in each compartment, a short horizontal line may be seen; the unions above this line were made in 1862, and below it in 1863. It is of importance to observe this, as it shows that the same general result was obtained during two successive years; but more especially because 1863 was a very hot and dry season, and the plants had occasionally to be watered. This did not prevent the full complement of seed being produced from the more fertile unions; but it rendered the less fertile ones even more sterile than they otherwise would have been. I have seen striking instances of this fact in making illegitimate and legitimate unions with Primula; and it is well known that the conditions of life must be highly favourable to give any chance of success in producing hybrids between species which are crossed with difficulty.
TABLE 4.23. Lythrum salicaria, long-styled form.
TABLE 4.23.1. Legitimate union.
13 flowers fertilised by the longest stamens of the mid-styled. These stamens equal in length the pistil of the long-styled.
Product of good seed in each capsule.
36 53 81 0 0 0 0 0 0 0 - 0 45 41
38 percent of these flowers yielded capsules. Each capsule contained, on an average, 51.2 seeds.
TABLE 4.23.2. Legitimate union.
13 flowers fertilised by the longest stamens of the short-styled. These stamens equal in length the pistil of the long-styled.
Product of good seed in each capsule.
159 104 43 119 96 poor seed. 96 103 99 0 131 0 116 - 114
84 percent of these flowers yielded capsules. Each capsule contained, on an average, 107.3 seeds.
TABLE 4.23.3. Illegitimate union.
14 flowers fertilised by the shortest stamens of the mid-styled.
3 0 0 0 0 0 0 0 0 0 - 0 0 0 0
Too sterile for any average.
TABLE 4.23.4. Illegitimate union.
12 flowers fertilised by the mid-length stamens of the short-styled.
20 0 0 0 0 0 0 0 - 0 0 0 0
Too sterile for any average.
TABLE 4.23.5. Illegitimate union.
15 flowers fertilised by own-form mid-length stamens.
2 - 10 0 23 0 0 0 0 0 0 0 0 0 0 0
Too sterile for any average.
TABLE 4.23.6. Illegitimate union.
15 flowers fertilised by own-form shortest stamens.
4 - 8 0 4 0 0 0 0 0 0 0 0 0 0 0
Too sterile for any average.
Besides the above experiments, I fertilised a considerable number of long-styled flowers with pollen, taken by a camel's-hair brush, from both the mid-length and shortest stamens of their own form: only 5 capsules were produced, and these yielded on an average 14.5 seeds. In 1863 I tried a much better experiment: a long-styled plant was grown by itself, miles away from any other plant, so that the flowers could have received only their own two kinds of pollen. The flowers were incessantly visited by bees, and their stigmas must have received successive applications of pollen on the most favourable days and at the most favourable hours: all who have crossed plants know that this highly favours fertilisation. This plant produced an abundant crop of capsules; I took by chance 20 capsules, and these contained seeds in number as follows:--
20 20 35 21 19 26 24 12 23 10 7 30 27 29 13 20 12 29 19 35
This gives an average of 21.5 seeds per capsule. As we know that the long-styled form, when standing near plants of the other two forms and fertilised by insects, produces on an average 93 seeds per capsule, we see that this form, fertilised by its own two pollens, yields only between one-fourth and one-fifth of the full number of seed. I have spoken as if the plant had received both its own kinds of pollen, and this is, of course, possible; but, from the enclosed position of the shortest stamens, it is much more probable that the stigma received exclusively pollen from the mid-length stamens; and this, as may be seen in Table 4.23.5, is the more fertile of the two self-unions.
TABLE 4.24. Lythrum salicaria, mid-styled form.
TABLE 4.24.1. Legitimate union.
12 flowers fertilised by the mid-length stamens of the long-styled. These stamens equal in length the pistil of the mid-styled.
Product of good seed in each capsule.
138 122 149 50 147 151 109 119 133 138 144 0 -
92 percent of these flowers (probably 100 per cent) yielded capsules. Each capsule contained, on an average, 127.3 seeds.
TABLE 4.24.2. Legitimate union.
12 flowers fertilised by the mid-length stamens of the short-styled. These stamens equal in length the pistil of the mid-styled.
Product of good seed in each capsule.
112 109 130 143 143 124 100 145 33 12 - 141 104
100 percent of these flowers yielded capsules. Each capsule contained, on an average, 108.0 seeds; or, excluding capsules with less than 20 seeds, the average is 116.7 seeds.
TABLE 4.24.3. Illegitimate union.
13 flowers fertilised by the shortest stamens of the long-styled.
83 12 0 19 0 85 seeds small and poor. - 0 44 0 44 0 45 0
54 percent of these flowers yielded capsules. Each capsule contained, on an average, 47.4 seeds; or, excluding capsules with less than 20 seeds, the average is 60.2 seeds.
TABLE 4.24.4. Illegitimate union.
15 flowers fertilised by the longest stamens of the short-styled.
130 86 115 113 14 29 6 17 2 113 9 79 - 128 132 0
93 percent of these flowers yielded capsules. Each capsule contained, on an average, 69.5 seeds; or, excluding capsules with less than 20 seeds, the average is 102.8 seeds.
TABLE 4.24.5. Illegitimate union.
12 flowers fertilised by own-form longest stamens.
92 0 9 0 63 0 - 0 136?* 0 0 0 0
(4/6. * I have hardly a doubt that this result of 136 seeds in Table 4.24.5 was due to a gross error. The flowers to be fertilised by their own longest stamens were first marked by "white thread," and those by the mid-length stamens of the long-styled form by "white silk;" a flower fertilised in the later manner would have yielded about 136 seeds, and it may be observed that one such pod is missing, namely at the bottom of Table 4.24.1. Therefore I have hardly any doubt that I fertilised a flower marked with "white thread" as if it had been marked with "white silk." With respect to the capsule which yielded 92 seeds, in the same column with that which yielded 136, I do not know what to think. I endeavoured to prevent pollen dropping from an upper to a lower flower, and I tried to remember to wipe the pincers carefully after each fertilisation; but in making eighteen different unions, sometimes on windy days, and pestered by bees and flies buzzing about, some few errors could hardly be avoided. One day I had to keep a third man by me all the time to prevent the bees visiting the uncovered plants, for in a few seconds' time they might have done irreparable mischief. It was also extremely difficult to exclude minute Diptera from the net. In 1862 I made the great mistake of placing a mid-styled and long-styled under the same huge net: in 1863 I avoided this error.)
Excluding the capsule with 136 seeds, 25 percent of the flowers yielded capsules, and each capsule contained, on an average, 54.6 seeds; or, excluding capsules with less than 20 seeds, the average is 77.5.
TABLE 4.24.6. Illegitimate union.
12 flowers fertilised by own-form shortest stamens.
0 0 0 0 0 0 - 0 0 0 0 0 0
Not one flower yielded a capsule.
Besides the experiments in Table 4.24, I fertilised a considerable number of mid-styled flowers with pollen, taken by a camel's-hair brush, from both the longest and shortest stamens of their own form: only 5 capsules were produced, and these yielded on an average 11.0 seeds.
TABLE 4.25. Lythrum salicaria, short-styled form.
TABLE 4.25.1. Legitimate union.
12 flowers fertilised by the shortest stamens of the long-styled. These stamens equal in length the pistil of the short-styled.
69 56 61 88 88 112 66 111 0 62 0 100 -
83 percent of the flowers yielded capsules. Each capsule contained, on an average, 81.3 seeds.
TABLE 4.25.2. Legitimate union.
13 flowers fertilised by the shortest stamens of the mid-styled. These stamens equal in length the pistil of the short-styled.
93 69