NATURAL SELECTION- 163 



plants through man's agency in foreign lands. It might 

 have been expected that the plants which would succeed 

 in becoming naturalized in any land would generally 

 have been closely allied to the indigenes; for these are 

 commonly looked at as specially created and adapted for 

 their own country. It might also, perhaps, have been 

 expected that naturalized plants would have belonged to 

 a few groups more especially adapted to certain stations 

 in their new homes. But the case is very different; and 

 Alph. de Candolle has well remarked, in his great and 

 admirable work, that floras gain by naturalization, pro- 

 portionally with the number of the native genera and 

 species, far more in new genera than in new species. To 

 give a single instance: in the last edition of Dr. Asa 

 Gray's "Manual of the Flora of the Northern United 

 States," 260 naturalized plants are enumerated, and these 

 belong to 162 genera. We thus see that these naturalized 

 plants are of a highly diversified nature. They differ, 

 moreover, to a large extent, from the indigenes, for out 

 of the 162 naturalized genera no less than 100 genera 

 are not there indigenous, and thus a large proportional 

 addition is made to the genera now living in the United 

 States. 



By considering the nature of the plants or animals 

 jwjiich have in any country struggled successfully with 

 [the indigenes, and have there become naturalized, we 

 ay gain some crude idea in what manner some of the 

 atives would have to be modified, in order to gain an 

 [advantage over their compatriots; and we may at least 

 J infer that diversification of structure, amounting to new 

 [generic differences, would be profitable to them. 



The advantage of diversification of structure in the 



