e other above specified respects as if they had been two
distinct species. But to make the case sure, he would raise plants from
his supposed hybridised seed, and he would find that the seedlings were
miserably dwarfed and utterly sterile, and that they behaved in all
other respects like ordinary hybrids. He might then maintain that he
had actually proved, in accordance with the common view, that his two
varieties were as good and as distinct species as any in the world; but
he would be completely mistaken.

The facts now given on dimorphic and trimorphic plants are important,
because they show us, first, that the physiological test of lessened
fertility, both in first crosses and in hybrids, is no safe criterion
of specific distinction; secondly, because we may conclude that there is
some unknown bond which connects the infertility of illegitimate unions
with that of their illegitimate offspring, and we are led to extend the
same view to first crosses and hybrids; thirdly, because we find, and
this seems to me of especial importance, that two or three forms of the
same species may exist and may differ in no respect whatever, either in
structure or in constitution, relatively to external conditions, and yet
be sterile when united in certain ways. For we must remember that it is
the union of the sexual elements of individuals of the same form, for
instance, of two long-styled forms, which results in sterility; while it
is the union of the sexual elements proper to two distinct forms which
is fertile. Hence the case appears at first sight exactly the reverse
of what occurs, in the ordinary unions of the individuals of the same
species and with crosses between distinct species. It is, however,
doubtful whether this is really so; but I will not enlarge on this
obscure subject.

We may, however, infer as probable from the consideration of dimorphic
and trimorphic plants, that the sterility of distinct species when
crossed and of their hybrid progeny, depends exclusively on the nature
of their sexual elements, and not on any difference in their structure
or general constitution. We are also led to this same conclusion by
considering reciprocal crosses, in which the male of one species cannot
be united, or can be united with great difficulty, with the female of
a second species, while the converse cross can be effected with perfect
facility. That excellent observer, Gartner, likewise concluded that
species when crossed are st