CHAP. IX.] WHEN CROSSED. 241 



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. 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 im- 

 portant to notice that the hybrid plants thus raised were them- 

 selves jwfectly 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 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 classification 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 number of 

 experiments made during many years on nine species of Verbas- 

 cum, by so good an observer and so hostile a witness 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 with yellow and white varieties of a distinct 

 species, more seed is produced by the crosses between the similarly 

 coloured flowers, than between those which are differently coloured. 

 Mr. Scott also has experimented on the species and varieties of 



