Domesticated productions, on the other hand, which, as shown by the mere fact of their domestication, were not originally highly sensitive to changes 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.