DIVERGENCE OF CHARACTER 125 



(supposing its nature not to be in any way peculiar), and 

 may be said to be striving to the utmost to live there ; but, it 

 is seen, that where they come into the closest competition, the 

 advantages of diversification of structure, with the accom- 

 panying differences of habit and constitution, determine that 

 the inhabitants, which thus jostle each other most closely, 

 shall, as a general rule, belong to what we call different 

 genera and orders. 



The same principle is seen in the naturalisation of plants 

 through man's agency in foreign lands. It might have been 

 expected that the plants which would succeed in becoming 

 naturalised 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 naturalised 

 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 re- 

 marked, in his great and admirable work, that floras gain by 

 naturalisation, 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 be- 

 long 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 of the 162 natural- 

 ised 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 com- 

 patriots; 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 in- 

 habitants of the same region is, in fact, the same as that of 



