262 THE ORIGIN OF SPECIES 



species, owing to their struggle for existence with numerous 

 competitors, will have been exposed during long periods of time 

 to more uniform conditions, than have domestic varieties; and 

 this may well make a wide difference in the result. For we know 

 how commonly wild animals and plants, when taken from their 

 natural conditions and subjected to captivity, are rendered 

 sterile; and the reproductive functions of organic beings whicli 

 have always lived under natural conditions would probably in 

 like manner be eminently sensitive to the influence of an un- 

 natural cross. 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 

 fertihty repeated changes of conditions, might be expected to 

 produce varieties, which would be little hable 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 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 sepa- 

 rated 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 pro- 

 duced 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 dis- 

 tinct. 



Girou de Buzareingues crossed three varieties of gourd, which 

 like the maize has separate sexes, and he asserts that their mu- 

 tual 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 



