HYBRIDISM 45 



fectly 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 ster- 

 ile 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 of varie- 

 ties in a state of nature, for a supposed variety, if proved 

 \so be infertile in any degree, would almost universally be 

 ranked as a species; — from man attending only to exter- 

 nal 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 con- 

 siderations we may conclude that fertility does not con- 

 stitute a fundamental distinction between varieties and 

 species when crossed. The general sterility of crossed 

 species may safely be looked at, not as a special ac- 

 quirement or endowment, but as incidental on changes 

 of an unknown nature in their sexual elements. 



Hybrids and Mongrels compared, independently of their 



fertility 



Independently of the question of fertility, the offspring 

 of species and of varieties when crossed may be com- 

 pared 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 unimportant differences between the so-called hy- 



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