The offspring from a union between plants of the same
form are more or less sterile, like hybrids, and have their pollen in a
more or less aborted condition; and some of the seedlings are as barren
and as dwarfed as the most barren hybrid. They also resemble hybrids in
several other respects, which need not here be specified in
detail,--such as their sterility not corresponding in degree with that
of the parent plants,--the unequal sterility of the latter, when
reciprocally united,--and the varying sterility of the seedlings raised
from the same seed-capsule.
We thus have two grand classes of cases giving results which correspond
in the most striking manner with those which follow from the crossing of
so-called true and distinct species. With respect to the difference
between seedlings raised from cross and self-fertilised flowers, there
is good evidence that this depends altogether on whether the sexual
elements of the parents have been sufficiently differentiated, by
exposure to different conditions or by spontaneous variation. It is
probable that nearly the same conclusion may be extended to heterostyled
plants; but this is not the proper place for discussing the origin of
the long-styled, short-styled and mid-styled forms, which all belong to
the same species as certainly as do the two sexes of the same species.
We have therefore no right to maintain that the sterility of species
when first crossed and of their hybrid offspring, is determined by some
cause fundamentally different from that which determines the sterility
of the individuals both of ordinary and of heterostyled plants when
united in various ways.
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