Chap. IV. DIVERGENCE OF CnARACTER. 113 



also, pcrliaps, liave been expected that naturalized plants would 

 have beloufred to a few groups more especially adapted to 

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

 ferent ; and Alpli. dc Candolle has well remarked, in his great 

 and admirable work, that floras gain by naturalization, propor- 

 tionally with the number of the native genera and species, far 

 more in new genera than in new species. To give a single 

 instance : in tiie 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. Wc 

 thus see that these naturalized plants are of a highly-diversified 

 nature. The}'" difler, moreover, to a large extent, from the in- 

 digenes, for, out of the 162 naturalized genera, no less than 100 

 genera arc not there indigenous, and thus a large proportional 

 addition is made to the genera now living in the United States. 



By considering tlie nature of the plants or animals which 

 have struggled successfully with the indigenes of any country, 

 and have there become naturalized, we may gain some crude 

 idea in what manner some of the natives would have to be 

 modilied, in order to gain an advantage over the other natives ; 

 and we may at least safely infer that diversification of struc- 

 ture, amounting to new generic differences, would be profit- 

 able to them. 



The advantage of diversification 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. Xo physiolo- 

 gist doubts that a stomach adapted to digest vegetable matter 

 alone, or llesh alone, draws most nutriment from these sub- 

 stances. So in the general economy of an}'' land, the more 

 widely and perfectly the animals and plants are diversified for 

 dilferent haljits of life, so will a greater number of inchviduals 

 be capable of there sujiporting themselves. A set of animals, 

 with their organization but little diversified, coulti hardly com- 

 pete with a set more perfectly diversified in structure. It may 

 be doubt(M], for instance, whether the Australian marsupials, 

 which are divided into groups differing but little from each 

 other, and feebly representing, as Mr, AVaterhouse antl others 

 have remarked, our carnivorous, ruminant, and rodent mam- 

 mals, could successfully compete with these well-pronounced 

 orders. In the Australian manmials, we see the process of 

 diversification in an early and incomplete stage of develop- 

 ment. 



