HYBRIDISM 263 



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 Ver- 

 bascum, by so good an observer and so hostile a witness as Gart- 

 ner: namely, that the yellow and white varieties when crossed 

 produce less seed than the similarly colored varieties of the same 

 species. Moreover, he asserts that, when yellow and white vari- 

 eties 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 con- 

 firm 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 sub- 

 sequent observer, has proved the remarkable fact that one 

 particular variety of the common tobacco was more fertile 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 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 it can no longer be maintained that varieties 

 when crossed are invariably quite fertile. From the great difficulty 

 of ascertaining the infertility ot 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 characters in his domestic varieties, and from 

 such varieties not having been exposed for very long periods to 

 uniform conditions of life; from these several considerations we 

 may conclude that fertility does not constitute a fundamental 

 distinction between varieties and species when crossed. The 



