DIVERGENCE OF CHARACTER. 99 



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, 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 naturalized plants are enumerated, and 

 these belong to 162 genera. We thus see that these natur- 

 alized 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 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 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 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 different 

 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 

 compete with a set more perfectly diversified in structure. 

 It may be doubted, for instance, whether the Australian 

 marsupials, which are divided into groups differing but 

 little from each other, and feebly representing, as Mr. 

 Waterhouse and others have remarked, our carnivorous, 

 ruminant, and rodent mammals, could successfully com- 

 pete with these well-developed orders. In the Australian 

 mammals, we see the process of diversification in an early 

 and incomplete stage of improvement. 



