286 FERTILITY OF VARIETIES WHEN CROSSED. 



colored 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 

 colored flowers, than between those which are differently 

 colored. Mr. Scott also has experimented on the species 

 and varieties of Verbascum ; and although unable to confirm 

 Gartner's results on the crossing of the distinct species, 

 he finds that the dissimilarly colored varieties of the same 

 species yield fewer seeds, in the proportion of eighty-six 

 to one hundred, than the similarly colored varieties. Yet 

 these varieties differ in no respect, except in the color of 

 their flowers ; and one variety can sometimes be raised 

 from the seed of another. 



Kolreuter, whose accuracy has been confirmed by every 

 subsequent observer, has proved the remarkable fact that 

 one particular variety of the common tobacco was more fer- 

 tile than the other varieties, when crossed with a widely 

 distinct species. He experimented on five forms which are 

 commonly reputed to be varieties, and which he tested by 

 the severest trial, namely, by reciprocal crosses, and he 

 found their mongrel offspring perfectly fertile. But one of 

 these five varieties, when used either as the father or mother, 

 and crossed with the Nicotian a 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 it can no longer be maintained that vari- 

 eties when crossed are invariably quite fertile. From the 

 great difficulty of ascertaining the infertility of varieties in 

 a state of nature, for a supposed variety, if proved to be 

 infertile in any degree, would almost universally be ranked 

 as a species ; from man attending only to external charac- 

 ters in his domestic varieties, and from such varieties not 

 having been exposed for very long periods to uniform condi- 

 tions of life ; from these several considerations we may con- 

 clude that fertility does not constitute a fundamental dis- 

 tinction between varieties and species when crossed. The 

 general sterility of crossed species may safely be looked at, 

 not as a special acquirement or endowment, but as inciden- 

 tal on changes of an unknown nature in their sexual elements. 



