Seite - 325 - in The Origin of Species

FERTILITY OF VARIETIES 325 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 im- possible 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 spe- cies. 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 sev- eral 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 dis- tinct 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 different. 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 Sageret, who mainly founds his classifica- tion 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 num- ber of experiments made during many years on nine species of Verbascum, by so good an observer and so hostile a wit- ness 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 that when yellow and white varieties of one species are crossed