Thus pollen will be
regularly carried from the one form to the other, and they will reciprocally
fertilise one another. Nevertheless an insect in withdrawing its proboscis from
the corolla of the long-styled form cannot fail occasionally to leave pollen
from the same flower on the stigma; and in this case there might be self-
fertilisation. But this will be much more likely to occur with the short-styled
form; for when I inserted a bristle or other such object into the corolla of
this form, and had, therefore, to pass it down between the anthers seated round
the mouth of the corolla, some pollen was almost invariably carried down and
left on the stigma. Minute insects, such as Thrips, which sometimes haunt the
flowers, would likewise be apt to cause the self-fertilisation of both forms.
The several foregoing facts led me to try the effects of the two kinds of pollen
on the stigmas of the two forms. Four essentially different unions are possible;
namely, the fertilisation of the stigma of the long-styled form by its own-form
pollen, and by that of the short-styled; and the stigma of the short-styled form
by its own-form pollen, and by that of the long-styled. The fertilisation of
either form with pollen from the other form may be conveniently called a
LEGITIMATE UNION, from reasons hereafter to be made clear; and that of either
form with its own-form pollen an ILLEGITIMATE UNION.
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