WHEN CROSSED. 285 



tRe 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 pro- 

 duce varieties, which would be little liable to have their 

 reproductive powers injuriously affected by the act of cross- 

 ing with other varieties which had originated in a like 

 manner. 



I have as yet spoken as if the varieties of the same 

 "tpecies 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 wit- 

 nesses, 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 separ- 

 ated sexes, they never naturally crossed. He then fertilized 

 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 separate sexes, and he asserts that 

 their mutual fertilization 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 classifi- 

 cation by the test of infertility, as varieties, and Naadin 

 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 varie- 

 ties when crossed produce less seed than the similarly 



