Chap. VIII. FERTILITY OF MONGRELS. 271 



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 same 

 coloured flowers, than between those which are differ- 

 ently coloured. Yet these varieties of Verbascum pre- 

 sent no other difference besides the mere colour of the 

 flower ; and one variety can sometimes be raised from 

 the seed of the other. 



From observations which I have made on certain 

 varieties of hollyhock, I am inclined to suspect that 

 tUey present analogous facts. 



Kolreuter, whose accuracy has been confirmed by 

 every subsequent observer, has proved the remarkable 

 fact, that one variety of the common tobacco is more 

 fertile, when crossed with a widely distinct species, 

 than are the other varieties. He experimentised on five 

 forms, which are commonly reputed to be varieties, and 

 which he tested by the severest trial, namely, by reci- 

 procal crosses, and he found their mongrel offspring 

 perfectly fertile. But one of these five varieties, when 

 used either as father or mother, and crossed with the 

 Nicotiana glutinosa, always yielded hybrids not so 

 sterile as those which were produced from the four 

 other varieties when crossed with N. glutinosa. Hence 

 the reproductive system of this one variety must have 

 been in some manner and in some degree modified. 



From these facts ; from the great difficulty of ascer- 

 taining the infertility of varieties in a state of nature, 

 for a supposed variety if infertile in any degree would 

 generally be ranked as species ; from man selecting only 

 external characters in the production of the most dis- 

 tinct domestic varieties, and from not wishing or being 

 able to produce recondite and functional differences in 

 the reproductive system; from these several consider- 

 ations and facts, I do not think that the very general 



