Unfortunately the relative weight of the two lots of seeds
was ascertained in only a few instances in which their germination was
observed; but with Ipomoea and I believe with some of the other species,
the relative lightness of the self-fertilised seeds apparently
determined their early germination, probably owing to the smaller mass
being favourable to the more rapid completion of the chemical and
morphological changes necessary for germination. On the other hand, Mr.
Galton gave me seeds (no doubt all self-fertilised) of Lathyrus
odoratus, which were divided into two lots of heavier and lighter seeds;
and several of the former germinated first. It is evident that many more
observations are necessary before anything can be decided with respect
to the relative period of germination of crossed and self-fertilised
seeds.
CHAPTER X.
MEANS OF FERTILISATION.
Sterility and fertility of plants when insects are excluded.
The means by which flowers are cross-fertilised.
Structures favourable to self-fertilisation.
Relation between the structure and conspicuousness of flowers, the
visits of insects, and the advantages of cross-fertilisation.
The means by which flowers are fertilised with pollen from a distinct
plant.
Greater fertilising power of such pollen.
Anemophilous species.
Conversion of anemophilous species into entomophilous.
Origin of nectar.
Anemophilous plants generally have their sexes separated.
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