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.