It is also a remarkable fact, that
hybrids raised from reciprocal crosses, though of course compounded of
the very same two species, the one species having first been used as
the father and then as the mother, generally differ in fertility in a
small, and occasionally in a high degree.
Several other singular rules could be given from Gartner: for
instance, some species have a remarkable power of crossing with other
species; other species of the same genus have a remarkable power of
impressing their likeness on their hybrid offspring; but these two
powers do not at all necessarily go together. There are certain
hybrids which instead of having, as is usual, an intermediate
character between their two parents, always closely resemble one of
them; and such hybrids, though externally so like one of their pure
parent-species, are with rare exceptions extremely sterile. So again
amongst hybrids which are usually intermediate in structure between
their parents, exceptional and abnormal individuals sometimes are
born, which closely resemble one of their pure parents; and these
hybrids are almost always utterly sterile, even when the other hybrids
raised from seed from the same capsule have a considerable degree of
fertility. These facts show how completely fertility in the hybrid is
independent of its external resemblance to either pure parent.
Considering the several rules now given, which govern the fertility of
first crosses and of hybrids, we see that when forms, which must be
considered as good and distinct species, are united, their fertility
graduates from zero to perfect fertility, or even to fertility under
certain conditions in excess.
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