ANIMALS AS FOOD, FOES, OR FRIENDS. 351 



476. 5. Crystals. — Plants protect themselves against soft- 

 bodied animals, such as snails and slugs, by means of the 

 sharp-pointed crystals which are present in the leaves of 

 many species. According to Slahl, all tissues containing 

 these crystals are avoided by such animals, but will be readily 

 eaten by them after the crystals are removed. 



