HYBRIDISM 221 



when first crossed, and the sterility of the hybrids pro- 

 duced from them. 



Pure species have of course their organs of reproduc- 

 tion in a perfect condition, yet when intercrossed they 

 produce either few or no offspring*. Hybrids, on the 

 other hand, have their reproductive organs functionally 

 impotent, as may be clearly seen in the state of the 

 male element in both plants and animals ; though the 

 organs themselves are perfect in structure, as far as the 

 microscope reveals. In the first case the two sexual 

 elements which go to form the embryo are perfect ; in 

 the second case they are either not at all developed, or 

 are imperfectly developed. This distinction is important, 

 when the cause of the sterility, which is common to the 

 two cases, has to be considered. The distinction has 

 probably been slurred over, owing to the sterility in 

 both cases being looked on as a special endowment, 

 beyond the province of our reasoning powers. 



The fertility of varieties, that is of the forms known 

 or believed to have descended from common parents, 

 when intercrossed, and likewise the fertility of their 

 mongrel offspring, is, on my theory, of equal import- 

 ance with the sterility of species ; for it seems to make 

 a broad and clear distinction between varieties and 

 species. 



First, for the sterility of species when crossed and of 

 their hybrid offspring. It is impossible to study the 

 several memoirs and works of those two conscientious 

 and admirable observers, Kolreuter and Gartner, who 

 almost devoted their lives to this subject, without being 

 deeply impressed with the high generality of some degree 

 of sterility. Kolreuter makes the rule universal ; but 

 then he cuts the knot, for in ten cases in which he 

 found two forms, considered by most authors as distinct 

 species, quite fertile together, he unhesitatingly ranks 

 them as varieties. Gartner, also, makes the rule 

 equally universal ; and he disputes the entire fertility 

 of Kolreuter' s ten cases. But in these and in many 

 other cases, Gartner is obliged carefully to count the 

 aeeds, in order to show that there is any degree of 



