The seeds, however, were carefully counted, and the averages are shown in the right hand column. The ratio for the number of seeds produced by the two legitimate compared with the two illegitimate unions is here 100 to 53, which is probably more accurate than the foregoing one of 100 to 63.

TABLE 1.11. Primula Sinensis (from Hildebrand).

Column 1: Nature of the Union. Column 2: Number of Flowers fertilised. Column 3: Number of good Capsules produced. Column 4: Average Number of Seeds per Capsule.

Long-styled by pollen of short-styled. Legitimate union : 14 : 14 : 41.

Long-styled by own-form pollen, from a distinct plant. Illegitimate union : 26 : 26 : 18.

Long-styled by pollen from same flower. Illegitimate union : 27 : 21 : 17.

Short-styled by pollen of long-styled. Legitimate union: 14 : 14 : 44.

Short-styled by own-form pollen, from a distinct plant. Illegitimate union : 16 : 16 : 20.

Short-styled by pollen from the same flower. Illegitimate union : 21 : 11 : 8.

SUMMARY:

The two legitimate unions together : 28 : 28 : 43.

The two illegitimate unions together (own-form pollen): 42 : 42 : 18.

The two illegitimate unions together (pollen from the same flower ): 48 : 32 : 13.

Hildebrand in the paper above referred to gives the results of his experiments on the present species; and these are shown in a condensed form in Table 1.11. Besides using for the illegitimate unions pollen from a distinct plant of the same form, as was always done by me, he tried, in addition, the effects of the plant's own pollen. He counted the seeds.

It is remarkable that here all the flowers which were fertilised legitimately, as well as those fertilised illegitimately with pollen from a distinct plant belonging to the same form, yielded capsules; and from this fact it might be inferred that the two forms were reciprocally much more fertile in his case than in mine. But his illegitimately fertilised capsules from both forms contained fewer seeds relatively to the legitimately fertilised capsules than in my experiments; for the ratio in his case is as 42 to 100, instead of, as in mine, as 53 to 100. Fertility is a very variable element with most plants, being determined by the conditions to which they are subjected, of which fact I have observed striking instances with the present species; and this may account for the difference between my results and those of Hildebrand. His plants were kept in a room, and perhaps were grown in too small pots or under some other unfavourable conditions, for his capsules in almost every case contained a smaller number of seeds than mine, as may be seen by comparing the right hand columns in Tables 1.10 and 1.11.

The most interesting point in Hildebrand's experiments is the difference in the effects of illegitimate fertilisation with a flower's own pollen, and with that from a distinct plant of the same form. In the latter case all the flowers produced capsules, whilst only 67 out of 100 of those fertilised with their own pollen produced capsules. The self-fertilised capsules also contained seeds, as compared with capsules from flowers fertilised with pollen from a distinct plant of the same form, in the ratio of 72 to 100.

In order to ascertain how far the present species was spontaneously self- fertile, five long-styled plants were protected by me from insects; and they bore up to a given period 147 flowers which set 62 capsules; but many of these soon fell off, showing that they had not been properly fertilised. At the same time five short-styled plants were similarly treated, and they bore 116 flowers which ultimately produced only seven capsules. On another occasion 13 protected long-styled plants yielded by weight 25.9 grains of spontaneously self- fertilised seeds. At the same time seven protected short-styled plants yielded only half-a-grain weight of seeds. Therefore the long-styled plants yielded nearly 24 times as many spontaneously self-fertilised seeds as did the same number of short-styled plants. The chief cause of this great difference appears to be, that when the corolla of a long-styled plant falls off, the anthers, from being situated near the bottom of the tube are necessarily dragged over the stigma and leave pollen on it, as I saw when I hastened the fall of nearly withered flowers; whereas in the short-styled flowers, the stamens are seated at the mouth of the corolla, and in falling off do not brush over the lowly-seated stigmas.

The Different Forms of Flowers on Plants of the Same Species Page 19

19th Century English Literature

Charles Darwin

Free Books in the public domain from the Classic Literature Library ©

Charles Darwin

All Pages of This Book