Other facts could be
given, but these will suffice for us. Naturalists formerly attributed
all these results to the difference between species being fundamentally
distinct from that between the varieties of the same species; and this
is still the verdict of some naturalists.
The results of my experiments in self-fertilising and cross-fertilising
the individuals or the varieties of the same species, are strikingly
analogous with those just given, though in a reversed manner. With the
majority of species flowers fertilised with their own pollen yield
fewer, sometimes much fewer seeds, than those fertilised with pollen
from another individual or variety. Some self-fertilised flowers are
absolutely sterile; but the degree of their sterility is largely
determined by the conditions to which the parent plants have been
exposed, as was well exemplified in the case of Eschscholtzia and
Abutilon. The effects of pollen from the same plant are obliterated by
the prepotent influence of pollen from another individual or variety,
although the latter may have been placed on the stigma some hours
afterwards. The offspring from self-fertilised flowers are themselves
more or less sterile, sometimes highly sterile, and their pollen is
sometimes in an imperfect condition; but I have not met with any case of
complete sterility in self-fertilised seedlings, as is so common with
hybrids.
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