THE ORIGIN OF WALNUTS. 165 



seeds, richly stored with oils and starches for 

 aiding the growth of the young plant, are 

 exposed to the attacks of squirrels, monkeys, 

 parrots, and other arboreal animals. The 

 greater part of them are eaten and completely 

 destroyed by these their enemies, and so 

 never hand down their peculiarities to any 

 descendants. But all fruits vary a little in 

 sweetness and bitterness, pulpy or stringy 

 tendencies. Thus a few among them happen 

 to be protected from destruction by their 

 originally accidental possession of a bitter 

 husk, a hard shell, or a few awkward spines 

 and bristles. These the monkeys and squir- 

 rels reject ; and they alone survive as the 

 parents of future generations. The more per- 

 sistent and the hungrier their foes become, 

 the less will a small degree of bitterness or 

 hardness serve to protect them. Hence, from 

 generation to generation, the bitterness and 

 the hardness will go on increasing, because 

 only those nuts which are the nastiest and 

 the most difficult to crack will escape destruc- 



