Hybridization 97 



This preliminary discussion has been introduced because 

 we can understand crossing only as we make it a part of 

 the general philosophy of nature. There are the vaguest 

 notions concerning the possibilities of crossing, some of 

 which may be corrected by presenting the subject in its 

 relations to the general aspects of the vegetable world. 



Effects of crossing on the species. We are now pre- 

 pared to understand that crossing is good for the species, 

 because it constantly revitalizes offspring with the strong- 

 est traits of the parents, and ever presents new com- 

 binations that enable the individuals to stand a better 

 chance of securing a place in the polity of nature. The 

 further discussions of the subject are such as have to do 

 with the extent to which crossing is possible and advisable, 

 and the general results of the operation. 



The limits of crossing. If crossing is good for the 

 species, which philosophy and direct experiment abun- 

 dantly show, it is necessary at once to find out to what 

 extent it can be carried. Does the good increase in pro- 

 portion as the cross becomes more violent or as the parents 

 are more and more unlike ? Or do we soon find a limit 

 beyond which it is not profitable or even possible to go ? 

 If great variability is good for the species in the struggle 

 for existence, and if crossing induces variability because 

 of the union of unlike individuals, it would seem to follow 

 that the more unlike the parents, the greater will be 

 the variation in offspring and the more the type will 

 prosper; and, carrying this thought to its logical con- 

 clusion, we shall expect to find that the most closely 

 related plants would constantly tend to refuse to cross, 

 because the offspring of them would be little variable 



