246 HYBRIDISM. Chap. VIII. 



species when first crossed, and the sterility of the hybrids 

 produced 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 import- 

 ant, 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 im- 

 portance 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 conscien- 

 tious 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 



