THE ARMED PLANT 319 



originated as a reaction against the attacks of 

 browsing animals and became hereditary, which 

 would be the inheritance of an acquired character, 

 or whether it originated in a chance variation 

 which, being useful, was fixed by natural selection. 

 There is, of course, nothing approaching unique- 

 ness in the fact that the holly has evolved for 

 itself a defensive arm against animal attack. In 

 a great variety of ways hundreds of plants and 

 whole families of plants have done as much, and 

 if the holly is at all distinguished, it is in its curious 

 economy of means. The thorns of hawthorn and 

 blackthorn and rose, the prickles of the whole 

 cactus family, the spines of the thistles, the sting 

 of the nettles, the harsh taste of many herbs and 

 the bad smell of many others, are all strictly 

 utilitarian adaptations aimed at defence. And it 

 is a pretty sound inference that when a plant arms 

 itself in any of those specialized ways for the 

 protection of its substance or its foliage, it con- 

 tains nutritious material which at one time was 

 used as food by animals. Probably it was preyed 

 upon to such an extent that the unprotected indi- 

 viduals of the species were exterminated, and only 

 those which varied in the defensive direction sur- 

 vived to perpetuate the race. When the defence 

 is purely mechanical, it often happens that some 

 one animal is capable of disregarding it, as, for 

 example, the donkey disregards the spines of the 

 thistle and the goat the thorns of the wild rose. 

 When it eats a thistle, the donkey may be said to 

 prove that the thistle is a food plant under its 

 forbidding exterior. A famous American experi- 







