The degree of their sterility does not correspond with that of
the parent-plants when first self-fertilised. The offspring of
self-fertilised plants suffer in stature, weight, and constitutional
vigour more frequently and in a greater degree than do the hybrid
offspring of the greater number of crossed species. Decreased height is
transmitted to the next generation, but I did not ascertain whether this
applies to decreased fertility.
I have elsewhere shown that by uniting in various ways dimorphic or
trimorphic heterostyled plants, which belong to the same undoubted
species, we get another series of results exactly parallel with those
from crossing distinct species. (12/18. 'Journal of the Linnean Society
Botany' volume 10 1867 page 393.) Plants illegitimately fertilised with
pollen from a distinct plant belonging to the same form, yield fewer,
often much fewer seeds, than they do when legitimately fertilised with
pollen from a plant belonging to a distinct form. They sometimes yield
no seed, not even an empty capsule, like a species fertilised with
pollen from a distinct genus. The degree of sterility is much affected
by the conditions to which the plants have been subjected. (12/19.
'Journal of the Linnean Society Botany' volume 8 1864 page 180.) The
pollen from a distinct form is strongly prepotent over that from the
same form, although the former may have been placed on the stigma many
hours afterwards.
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