The appearance of such varieties is interesting, as it bears
on the existence under nature of plants which regularly fertilise
themselves, such as Ophrys apifera and a few other orchids, or as
Leersia oryzoides, which produces an abundance of cleistogene flowers,
but most rarely flowers capable of cross-fertilisation.
Some observations made on other plants lead me to suspect that
self-fertilisation is in some respects beneficial; although the benefit
thus derived is as a rule very small compared with that from a cross
with a distinct plant. Thus we have seen in the last chapter that
seedlings of Ipomoea and Mimulus raised from flowers fertilised with
their own pollen, which is the strictest possible form of
self-fertilisation, were superior in height, weight, and in early
flowering to the seedlings raised from flowers crossed with pollen from
other flowers on the same plant; and this superiority apparently was too
strongly marked to be accidental. Again, the cultivated varieties of the
common pea are highly self-fertile, although they have been
self-fertilised for many generations; and they exceeded in height
seedlings from a cross between two plants belonging to the same variety
in the ratio of 115 to 100; but then only four pairs of plants were
measured and compared. The self-fertility of Primula veris increased
after several generations of illegitimate fertilisation, which is a
process closely analogous to self-fertilisation, but only as long as the
plants were cultivated under the same favourable conditions.
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