Friends and Foes 257 



From the point of view of the destroyed — the victims — 

 these creatures were undoubtedly foes; but from that of 

 the survivors they were as certainly friends, for the latter 

 would grow up all the more vigorous for having plenty of 

 space. 



But if slugs and insects were allowed to multiply with- 

 out check, they would become foes and nothing else, and 

 would end by eating up every green thing. There are 

 checks upon their increase, however; and besides this, 

 many plants are to some extent protected against them, 

 as otherwise certain species might be exterminated 

 altogether. 



Plants like the grasses, which bear vast quantities of 

 seed, are protected by their very numbers, and can well 

 afford to be eaten, if but a small proportion be allowed to 

 perfect and disperse their seed; but others, less prolific, 

 are guarded in various ways, being made either disagree- 

 able or difficult of approach. 



The whole of the Gentian order, for example, are so 

 extremely bitter, that they are seldom touched even by 

 caterpillars; and the Eschscholtzia, which is of another 

 order, is also so intensely bitter as to be more avoided by 

 slugs and the like than any other plant, it is said. Even 

 Eschscholtzias are, however, a good deal bitten at times, 

 probably by earwigs, but this may be owing to drought 

 and consequent scarcity of vegetable matter, as it is not a 

 common occurrence. It is at least something to be proof 

 against certain classes of enemies; and no plants are 

 defended against all, since they are intended to be eaten, 

 though not exterminated. 



The bark of oaks, elms, and willows is made sufficiently 

 unpleasant to most animals by the presence of tannin; and 



