A BED OF NETTLES. 117 



creature receives at once a life-long warning 

 against attacking nettles in future. 



The way in which so curious a device has 

 grown up is not, it seems to me, very diffi- 

 cult to guess. Many plants are armed with 

 small sharp hairs, which act as a protection to 

 them against the incursions of ants and other 

 destructive insects. These hairs are often 

 enough more or less glandular in structure, 

 and therefore liable to contain various waste 

 products of the plant. Suppose one of these 

 waste products in the ancestors of the nettle 

 to be at first slightly pungent, by accident, as 

 it were, then it would exercise a slightly 

 deterrent effect upon nettle-eating animals. 

 The more stinging it grew, the more 

 effectual would the protection be ; and as in 

 each generation the least protected plants 

 would get eaten down, while the more pro- 

 tected were spared, the tendency would be 

 for the juice to grow more and more stinging 

 till at last it reached the present high point 

 of development. It is noticeable, too, that in 



