DIVERGENCE OF OEARAOTER. 105 



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

 have been expected that the plants which would suc- 

 ceed 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 county. It might also, perhaps, have been ex- 

 pected 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 difEerent; and 

 Alpli. 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 163 

 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 tlian 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 indi- 

 genes, and have there become naturalized, 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 dif- 

 ferences, 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 labor 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 

 general economy of any land, the more widely and per- 

 fectly the animals and plants are diversified for difEerent 

 habits of life, so will a greater number of individuals be 

 capable of there supporting themselves. A set of animals, 

 with their organization but little diversified, could hardly 



