by pollen from the same plant, but can be fertilised by pollen from any
other individual of the same species. There are also very many species
which are partially sterile with their own pollen. Lastly, there is a
large class in which the flowers present no apparent obstacle of any
kind to self-fertilisation, nevertheless these plants are frequently
intercrossed, owing to the prepotency of pollen from another individual
or variety over the plant's own pollen.

As plants are adapted by such diversified and effective means for
cross-fertilisation, it might have been inferred from this fact alone
that they derived some great advantage from the process; and it is the
object of the present work to show the nature and importance of the
benefits thus derived. There are, however, some exceptions to the rule
of plants being constructed so as to allow of or to favour
cross-fertilisation, for some few plants seem to be invariably
self-fertilised; yet even these retain traces of having been formerly
adapted for cross-fertilisation. These exceptions need not make us doubt
the truth of the above rule, any more than the existence of some few
plants which produce flowers, and yet never set seed, should make us
doubt that flowers are adapted for the production of seed and the
propagation of the species.

We should always keep in mind the obvious fact that the production of
seed is the chief end of the act of fertilisation; and that this end can
be gained by hermaphrodite plants with incomparably greater certainty by
self-fertilisation, than by the union of the sexual elements belonging
to two distinct flowers or plants. Yet it is as unmistakably plain that
innumerable flowers are adapted for cross-fertilisation, as that the
teeth and talons of a carnivorous animal are adapted for catching prey;
or that the plumes, wings, and hooks of a seed are adapted for its