74 THE NATURALIST IX NICARAGUA. [Ch. V. 



inquirer that, just as many insects are preserved by being 

 distasteful to insectivorous birds, so very many of the 

 forest trees are protected from the ravages of the ants 

 by their leaves either being distasteful to them, or un- 

 fitted for the purpose for which they are required, whilst 

 some have special means of defence against their attacks. 

 ]None of the indigenous trees appear so suitable for them 

 as the introduced ones. Through long ages the trees 

 and the ants of tropical America have been modified to- 

 gether. Varieties of plants that arose unsuitable for the 

 ants have had an immense advantage over others that 

 were more suitable ; and thus through time every indi- 

 genous tree that has survived in the great struggle has 

 done so because it has had originally, or has acquired, 

 some protection against the great destroyer. The leaf- 

 cutting ants are confined to tropical America ; and we 

 can easily understand that trees and vegetables introduced 

 from foreign lands where these ants are unknown could 

 not have acquired, excepting accidentally, and without 

 any reference to the ants, any protection against their 

 attacks, and now they are most eagerly sought by them. 

 Amongst introduced trees, some species of even the same 

 genus are more acceptable than others. Thus, in the 

 orange tribe, the lime (Citrus lemonum) is less liked 

 than the other species ; it is the only one that I ever 

 found growing really wild in Central America : and I 

 have sometimes thought that even in the short time since 

 the lime was first introduced, about three hundred years 

 ago, a wild variety may have arisen, less subject to the 

 attacks of the ants than the cultivated variety ; for in 

 many parts I saw them growing wild, and apparently 

 not touched. The orange (Citrus aurantium) and the 



