If it became from any cause advantageous to a species to have its
capacity for self-fertilisation increased, there is little difficulty in
believing that this could readily be effected; for three cases of plants
varying in such a manner as to be more fertile with their own pollen
than they originally were, occurred in the course of my few experiments,
namely, with Mimulus, Ipomoea, and Nicotiana. Nor is there any reason to
doubt that many kinds of plants are capable under favourable
circumstances of propagating themselves for very many generations by
self-fertilisation. This is the case with the varieties of Pisum sativum
and of Lathyrus odoratus which are cultivated in England, and with
Ophrys apifera and some other plants in a state of nature. Nevertheless,
most or all of these plants retain structures in an efficient state
which cannot be of the least use excepting for cross-fertilisation. We
have also seen reason to suspect that self-fertilisation is in some
peculiar manner beneficial to certain plants; but if this be really the
case, the benefit thus derived is far more than counter-balanced by a
cross with a fresh stock or with a slightly different variety.
Notwithstanding the several considerations just advanced, it seems to me
highly improbable that plants bearing small and inconspicuous flowers
have been or should continue to be subjected to self-fertilisation for a
long series of generations.
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