178 



HYBRIDISM. 



Chap. XIX. 



the most widely distinct domestic varieties are invariably quit 



fertile when crossed, we do not positively know ; much time and 



trouble would be requisite for the necessary experiments and 



many difficulties 



such as the descent of the 



various 



races from aboriginally distinct species, and the doubts whethe 



theless 



forms ought to be ranked as species 



wide 



Nev 



er- 



expenence of practical breeders proves that 



the great majority of 



if some should hereafter 



prove not to be indefinitely fertile inter se, are far more fertile 

 when crossed, than the vast majority of closely allied natural 

 species. A few remarkable cases have, however, been given on 







the authority of excellent observers, showing that with plants 

 certain forms, which undoubtedly must be ranked as varieties 

 yield fewer seeds when crossed than is natural to the parent- 

 species. Other varieties have had their reproductive powers so 

 far modified that they are 



either more 



less fertile 



their parents, when crossed with a distinct species. 



Nevertheless, the fact remains indisputable that domesticated 

 varieties of animals and of plants, which differ greatly from each 

 other in structure, but which are certainly descended from the 



aboriginal species, such as the 



of the fowl, pi 



many vegetables, and a host of other productions, are extremely 

 fertile when crossed ; and this seems to make a broad and im- 

 passable barrier between domestic varieties and natural species. 

 But, as I will now attempt to show, the distinction is not so 

 great and overwhelmingly important as it at first appears. 



On the Difference in Fertility between Varieties and Species when 



crossed. 



This work is not the proper place for fully treating tl 

 subject of hybridism, and I have already given in my ' Orig 



of Sp 



a moderately full abstract. I will her 



merate the general conclusions which may be relied on, and 



law 



which bear on our present point 



Firstly, tl 

 identical, or 

 kingdoms. 



g the production of hybrids 



are 



ly identical, in the animal and 



vegetable 



& 



the sterility of distinct species when first 



ted 



