Chap. IX.] HYBRIDS AND MONGRELS COMPARED. 259 



of this one variety must Lave 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 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 con- 

 clude 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 acquire- 

 ment or endowment, but as incidental on changes of an unknown 

 nature in then 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 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 unimportant differences between the so-called hybrid 

 offspring of species, and the so-called mongrel offspring of varieties. 

 And, on the other hand, they agree most closely in many important 

 respects. 



I shall here discuss this subject with extreme brevity. The most 

 important distinction is, that in the first generation mongrels are 

 more variable than hybrids ; but Gartner admits that hybrids from 

 species which have long been cultivated are often variable in the 

 first generation ; and I have myself seen striking instances of this 

 fact. Gartner further admits that hybrids between very closely 

 allied species are more variable than those from very distinct 

 species ; and this shows that the difference in the degree of varia- 

 bility graduates away. When mongrels and the more fertile hybrids 

 are propagated for several generations, an extreme amount of varia- 

 bility in the offspring in both cases is notorious ; but some few 

 instances of both hybrids and mongrels long retaining a uniform 

 character could be given. The variability, however, in the succes- 

 sive generations of mongrels is, perhaps, greater than in hybrids. 



This greater variability in mongrels than in hybrids does not 

 seem at all surprising. For the parents of mongrels are varieties, 

 and mostly domestic varisties (very few experiments having been 



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