The simplest and best known
case of prepotent action in pollen, though it does not bear directly on
our present subject, is that of a plant's own pollen over that from a
distinct species. If pollen from a distinct species be placed on the
stigma of a castrated flower, and then after the interval of several
hours, pollen from the same species be placed on the stigma, the effects
of the former are wholly obliterated, excepting in some rare cases. If
two varieties are treated in the same manner, the result is analogous,
though of directly opposite nature; for pollen from any other variety is
often or generally prepotent over that from the same flower. I will give
some instances: the pollen of Mimulus luteus regularly falls on the
stigma of its own flower, for the plant is highly fertile when insects
are excluded. Now several flowers on a remarkably constant whitish
variety were fertilised without being castrated with pollen from a
yellowish variety; and of the twenty-eight seedlings thus raised, every
one bore yellowish flowers, so that the pollen of the yellow variety
completely overwhelmed that of the mother-plant. Again, Iberis umbellata
is spontaneously self-fertile, and I saw an abundance of pollen from
their own flowers on the stigmas; nevertheless, of thirty seedlings
raised from non-castrated fflowers of a crimson variety crossed with
pollen from a pink variety, twenty-four bore pink flowers, like those of
the male or pollen-bearing parent.
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