Hybridization 121 



the chief use which nature makes of crossing, to strengthen 

 the type. 



How to overcome antipathy to crossing. We can over- 

 come the refusal to cross in many cases by bringing the 

 plant under cultivation; for the character of the species 

 becomes so changed by the wholly new conditions that its 

 former antipathies may be overpowered. Yet, it is doubt- 

 ful whether such a plant will ever acquire a complete willing- ' 

 ness to cross. In like manner we can overcome in a meas- 

 ure the comparative seedlessness of hybrids, but it is very 

 doubtful whether we can ever make such hybrids com- 

 pletely fruitful. 



It is evident that species which have been differentiated 

 or bred away from each other in a given locality will have 

 more opposed qualities or powers than similar species 

 which have arisen quite independently in places remote 

 from each other. In the one case the species have likely 

 struggled with each other until each one has attained to a 

 degree of divergence which allows it to persist ; while in 

 the other case, there has been no struggle between species, 

 but similar conditions have brought about similar results. 

 These similar species which appear independently of each 

 other in different places are called representative species. 

 Islands remote from each other but similarly situated with 

 reference to climate very often contain representative 

 species ; and the same may be said of other regions much 

 like each other, as eastern North America and Japan. 

 Now, it follows that, if representative species are less 

 opposed than others, they are more likely to hybridize with 

 good results ; and this fact is remarkably well illustrated in 

 the Kieffer and allied pears, which are hybrids between 



