RELATIONS OF ANIMALS AND PLANTS 139 



is even more defenceless, for it is neither bitter nor 

 purgative, and yet it frequently escapes from 

 cultivation and thrives without protection from man 

 in India, Palestine, and doubtless other places. 



The conclusion to which these facts lead me is 

 that thorns were not developed as a defence against 

 grazing animals or rodents, and that they do not 

 usually act in that way : I freely admit that they 

 occasionally may exercise such a defensive function. 

 They were probably developed in the first place as a 

 response to the dry atmosphere. 



