WHEN UBOaSED. 305 



their flowers; and one variety can sometimes be raised 

 from tlie 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 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 recipro- 

 cal 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 Nico- 

 tiana 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. Prom 

 the great diSiculty of ascertaining the infertility of varie- 

 ties 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 considera- 

 tions we may conclude that fertility does not constitute a 

 fundamental distinction between varieties and species when 

 crossed. The general sterility of crossed species may 

 safely be looked at, not as a special acquirement or endow- 

 ment, but as incidental on changes of an unknown nature 

 in their sexual elements. 



HTBKIDS AND MOITGEELS COMPARED, INDEPENDENTLY 

 OF THEIR FERTILITY. 



Independently of the question of fertility, the offspring 

 of species and of varieties when crossed may be compared 

 in several other respects. Gartner, whose strong wish it 

 was to draw a distinct line between species and varieties, 

 could find very few, and, as it seems to me, quite unim- 

 portant differences between the so-called hybrid offspring 



