Chap. IX.] WHEN CROSSED. 37 



in their conditions of life, and which can now generally 

 resist with undiminished fertility repeated changes of 

 conditions, might he 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 fertihty 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 sepa- 

 rated sexes. No one, I beHeve, has suspected that these 

 varieties of maize are distinct species; and it is impor- 

 tant 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 



