HYBRIDISM 17 



as an indelible characteristic, but as one capable of being 

 removed by domestication. 



Finally, considering all the ascertained facts on the 

 intercrossing of plants and animals, it may be concluded 

 that some degree of sterility, both in first crosses and in 

 hybrids, is an extremely general result; but that it can- 

 not, under our present state of knowledge, be considered 

 as absolutely universal. 



Laws governing the /Sterility of first Grosses and of Hybrids 



We will now consider a little more in detail the laws 

 governing the sterility of first crosses and of hybrids. 

 Our chief object will be to see whether or not these laws 

 indicate that species have been specially endowed with 

 this quality, in order to prevent their crossing and blend- 

 ing together in utter confusion. The following conclu- 

 sions are drawn up chiefly from Gartner's admirable work 

 on the hybridization of plants. I have taken much 

 pains to ascertain how far they apply to animals, and, 

 considering how scanty our knowledge is in regard to 

 hybrid animals, I have been surprised to find how gener- 

 ally the same rules apply to both kingdoms. 



It has been already remarked, that the degree of fer- 

 tility, both of first crosses and of hybrids, graduates from 

 zero to perfect fertility. It is surprising in how many 

 curious ways this gradation can be shown; but only the 

 barest outline of the facts can here be given. When 

 pollen from a plant of one family is placed on the 

 stigma of a plant of a distinct family, it exerts no 

 more influence than so much inorganic dust. From this 

 absolute zero of fertility, the pollen of different species, 

 applied to the stigma of some one species of the same 



