nges in their conditions of life, and which can
now generally resist with undiminished fertility repeated changes of
conditions, might be expected to produce varieties, which would be
little liable to have their reproductive powers injuriously affected by
the act of crossing with other varieties which had originated in a like
manner.

I have as yet spoken as if the varieties of the same species were
invariably fertile when intercrossed. But it is impossible to resist the
evidence of the existence of a certain amount of sterility in the few
following cases, which I will briefly abstract. The evidence is at least
as good as that from which we believe in the sterility of a multitude of
species. The evidence is also derived from hostile witnesses, who in
all other cases consider fertility and sterility as safe criterions of
specific distinction. Gartner kept, during several years, a dwarf kind
of maize with yellow seeds, and a tall variety with red seeds growing
near each other in his garden; and although these plants have separated
sexes, they never naturally crossed. He then fertilised thirteen
flowers of the one kind with pollen of the other; but only a single
head produced any seed, and this one head produced only five grains.
Manipulation in this case could not have been injurious, as the plants
have separated sexes. No one, I believe, has suspected that these
varieties of maize are distinct species; and it is important to notice
that the hybrid plants thus raised were themselves PERFECTLY fertile;
so that even Gartner did not venture to consider the two varieties as
specifically distinct.

Girou de Buzareingues crossed three varieties of gourd, which like
the maize has separated sexes, and he asserts that their mutual
fertilisation is by so much the less easy as their differences are
greater. How far these experiments may be trusted, I know not; but
the forms experimented on are ranked by Sagaret, who mainly founds his
classification by the test of infertility, as varieties, and Naudin has
come to the same conclusion.

The following case is far more remarkable, and seems at first
incredible; but it is the result of an astonishing number of experiments
made during many years on nine species of Verbascum, by so good an
observer and so hostile a witness as Gartner: namely, that the yellow
and white varieties when crossed produce less seed than the similarly
coloured varieties of the same species. Moreover, he asserts