Effects of Cross and Self Fertilisation in the Vegetable Kingdom eBook

This eBook from the Gutenberg Project consists of approximately 459 pages of information about Effects of Cross and Self Fertilisation in the Vegetable Kingdom.
by the agency of insects; and in the case of a closely allied species, Mimulus rosea, I have watched bees entering the flowers, thus getting their backs well dusted with pollen; and when they entered another flower the pollen was licked off their backs by the two-lipped stigma, the lips of which are irritable and close like a forceps on the pollen-grains.  If no pollen is enclosed between the lips, these open again after a time.  Mr. Kitchener has ingeniously explained the use of these movements, namely, to prevent the self-fertilisation of the flower. (3/2.  ‘A Year’s Botany’ 1874 page 118.) If a bee with no pollen on its back enters a flower it touches the stigma, which quickly closes, and when the bee retires dusted with pollen, it can leave none on the stigma of the same flower.  But as soon as it enters any other flower, plenty of pollen is left on the stigma, which will be thus cross-fertilised.  Nevertheless, if insects are excluded, the flowers fertilise themselves perfectly and produce plenty of seed; but I did not ascertain whether this is effected by the stamens increasing in length with advancing age, or by the bending down of the pistil.  The chief interest in my experiments on the present species, lies in the appearance in the fourth self-fertilised generation of a variety which bore large peculiarly-coloured flowers, and grew to a greater height than the other varieties; it likewise became more highly self-fertile, so that this variety resembles the plant named Hero, which appeared in the sixth self-fertilised generation of Ipomoea.

Some flowers on one of the plants raised from the purchased seeds were fertilised with their own pollen; and others on the same plant were crossed with pollen from a distinct plant.  The seeds from twelve capsules thus produced were placed in separate watch-glasses for comparison; and those from the six crossed capsules appeared to the eye hardly more numerous than those from the six self-fertilised capsules.  But when the seeds were weighed, those from the crossed capsules amounted to 1.02 grain, whilst those from the self-fertilised capsules were only .81 grain; so that the former were either heavier or more numerous than the latter, in the ratio of 100 to 79.

Crossed and self-fertilised plants of the first generation.

Having ascertained, by leaving crossed and self-fertilised seed on damp sand, that they germinated simultaneously, both kinds were thickly sown on opposite sides of a broad and rather shallow pan; so that the two sets of seedlings, which came up at the same time, were subjected to the same unfavourable conditions.  This was a bad method of treatment, but this species was one of the first on which I experimented.  When the crossed seedlings were on an average half an inch high, the self-fertilised ones were only a quarter of an inch high.  When grown to their full height under the above unfavourable conditions,

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Effects of Cross and Self Fertilisation in the Vegetable Kingdom from Project Gutenberg. Public domain.
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