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.

Charles Darwin

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