Chap. IV. 
DIVERGENCE OF CHARACTER. 
115 
f)lants through man’s agency in foreign lands. It 
might have been expected that the plants which have 
succeeded 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 mighty 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 remarked 
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 belong to 162 genera. We thus 
see that these naturalised plants are of a higlily diversified 
nature. They differ, moreover, to a large extent from 
the indigenes, for out of the 162 genera, no less than 100 
genera are not there indigenous, and thus a large pro¬ 
portional addition is made to the genera of these States. 
By considering the nature of the plants or animals 
wliich have struggled successfully with the indigenes of 
any country, 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 the other natives ; and we may at least 
safely infer that diversification of structure, amount¬ 
ing to new generic differences, would be profitable to 
them. 
The advantage of diversification in the inhabitants of 
the same region is, in fact, the same as that of the phy¬ 
siological division of labour in the organs of the same 
individual body—a subject so well elucidated by Milne 
