Chap. IV.] DIVERGENCE OF CHARACTER. 139 



commonly looked at as specially created and adapted 

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

 been expected that naturalised plants would have be- 

 longed to a few groups more especially adapted to certain 

 stations in their new homes. But the case is very dif- 

 ferent ; and Alph. de Candolle has well remarked, in his 

 great and admirable work, that floras gain by naturalisa- 

 tion, proportionally 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 naturalised plants are enumerated, and these 

 belong to 162 genera. We thus see that these naturalised 

 plants are of a highly diversified nature. They differ, 

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

 the 162 naturalised 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 

 which have in any country struggled successfully with 

 the indigenes, and have there become naturalised, we 

 may gain some crude idea in what manner some of the 

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

 advantage over their compatriots • and we may at least 

 infer that diversification of structure, amounting to new 

 generic differences, would be profitable to them. 



The advantage of diversification of structure in the 

 inhabitants of the same region is, in fact, the same as 

 that of the physiological division of labour in the organs of 

 the same individual body— a subject so well elucidated by 

 Milne Edwards. No physiologist doubts that a stomach 

 adapted to digest vegetable matter alone, or flesh alone, 

 draws most nutriment from these substances. So in the 



