species six unions are legitimate, or fully fertile, and
twelve are illegitimate, or more or less infertile.
The infertility which may be observed in various dimorphic and
trimorphic plants, when they are illegitimately fertilised, that is by
pollen taken from stamens not corresponding in height with the pistil,
differs much in degree, up to absolute and utter sterility; just in the
same manner as occurs in crossing distinct species. As the degree
of sterility in the latter case depends in an eminent degree on the
conditions of life being more or less favourable, so I have found it
with illegitimate unions. It is well known that if pollen of a distinct
species be placed on the stigma of a flower, and its own pollen be
afterwards, even after a considerable interval of time, placed on the
same stigma, its action is so strongly prepotent that it generally
annihilates the effect of the foreign pollen; so it is with the pollen
of the several forms of the same species, for legitimate pollen is
strongly prepotent over illegitimate pollen, when both are placed on the
same stigma. I ascertained this by fertilising several flowers, first
illegitimately, and twenty-four hours afterwards legitimately, with
pollen taken from a peculiarly coloured variety, and all the seedlings
were similarly coloured; this shows that the legitimate pollen,
though applied twenty-four hours subsequently, had wholly destroyed
or prevented the action of the previously applied illegitimate pollen.
Again, as in making reciprocal crosses between the same two species,
there is occasionally a great difference in the result, so the same
thing occurs with trimorphic plants; for instance, the mid-styled form
of Lythrum salicaria was illegitimately fertilised with the greatest
ease by pollen from the longer stamens of the short-styled form, and
yielded many seeds; but the latter form did not yield a single seed when
fertilised by the longer stamens of the mid-styled form.
In all these respects, and in others which might be added, the forms
of the same undoubted species, when illegitimately united, behave in
exactly the same manner as do two distinct species when crossed. This
led me carefully to observe during four years many seedlings, raised
from several illegitimate unions. The chief result is that these
illegitimate plants, as they may be called, are not fully fertile. It
is possible to raise from dimorphic species, both long-styled and
short-styled ille
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