necessary at the sacrifice of too much time to self-fertilise and
intercross plants during several successive generations, in order to
arrive at any result. I ought to have reflected that such elaborate
provisions favouring cross-fertilisation, as we see in innumerable
plants, would not have been acquired for the sake of gaining a distant
and slight advantage, or of avoiding a distant and slight evil.
Moreover, the fertilisation of a flower by its own pollen corresponds to
a closer form of interbreeding than is possible with ordinary bi-sexual
animals; so that an earlier result might have been expected.

I was at last led to make the experiments recorded in the present volume
from the following circumstance. For the sake of determining certain
points with respect to inheritance, and without any thought of the
effects of close interbreeding, I raised close together two large beds
of self-fertilised and crossed seedlings from the same plant of Linaria
vulgaris. To my surprise, the crossed plants when fully grown were
plainly taller and more vigorous than the self-fertilised ones. Bees
incessantly visit the flowers of this Linaria and carry pollen from one
to the other; and if insects are excluded, the flowers produce extremely
few seeds; so that the wild plants from which my seedlings were raised
must have been intercrossed during all previous generations. It seemed
therefore quite incredible that the difference between the two beds of
seedlings could have been due to a single act of self-fertilisation; and
I attributed the result to the self-fertilised seeds not having been
well ripened, improbable as it was that all should have been in this
state, or to some other accidental and inexplicable cause. During the
next year, I raised for the same purpose as before two large beds close
together of self-fertilised and crossed seedlings from the carnation,
Dianthus caryophyllus. This plant, like the Linaria, is almost sterile
if insects are excluded; and we may draw the same inference as before,