INBREEDING AND CROSSBREEDING 233 



exterminate them; and inbreeding only tends to bring them 

 to the surface, not to create them. We may not, therefore, 

 lightly ascribe to inbreeding or intermarriage the creation of 

 bad racial traits, but only their manifestation. Further, any 

 racial stock which maintains a high standard of excellence 

 under inbreeding is certainly one of great vigor, and free from 

 inherent defects. 



The animal breeder is therefore amply justified in doing 

 what human society at present is probably not warranted in 

 doing, — viz., in practicing close inbreeding in building up 

 families of superior excellence and then keeping these pure, 

 while using them in crosses with other stocks. For an animal 

 of such a superior race should have only vigorous, strong off- 

 spring if mated with a healthy individual of any family what- 

 ever, within the same species. For this reason the production 

 of "thoroughbred" animals and their use in crosses is both 

 scientifically correct and commercially remunerative. 



The early plant hybridizers found that frequently (but not 

 always) hybrids produced by the crossing of distinct species 

 or genera are characterized by remarkably vigorous growth 

 and large size, superior to that of either parent. But these 

 same large vigorous hybrids produced little or no seed. 

 Vegetative and reproductive activity are to some extent 

 complementary and opposed activities of the plant. A vig- 

 orously growing young fruit tree may be brought into 

 bearing early if it is cut partly in two, or a ring of bark is 

 removed from it in the growing season, thus checking its 

 growth. Under such circumstances fruit buds are formed. 

 In many hybrid plants, in which the vegetative vigor is great, 

 partial or complete sterility exists. This, however, is not 

 invariably the case. The offspring of a cross between geo- 

 graphic varieties of the same species are usually both vigor- 

 ous and fertile, but the offspring of widely separated species 

 or genera may be lacking in vigor as well as fertility. With 

 increasing diversity of the parents the following series of 

 conditions obtains: 



1 . The mating of parents belonging to the same pure race 



