30 



THE STUDY OF ANIMAL LIFE CHAP. 



innocent themselves, ward off the attacks of the deadly 

 leaf-cutters. In some cases the bodyguard and the 

 plants are always found together, and the plants exhibit 

 structures which look almost as if they had been made 



as shelters for the ants. 

 On some of our European 

 trees similar little homes 

 or domatia constantly 

 occur, and shelter small 

 insects, or, it may be, 

 mites, which do no harm 

 to the trees, but cleanse 

 them from injurious 

 fungi. 



In many ways plants 

 are saved from the ap- 

 petite of animals. The 

 nettle has poisonous 

 hairs ; thistles, furze, and 

 holly are covered with 

 spines ; the hawthorn has 

 its thorns and the rose 

 its prickles ; some have 

 repulsive odours ; others 

 contain oils, acids, fer- 

 ments, and poisons which 

 many animals dislike ; 

 the cuckoo-pint (Arum) 

 is full of little crystals 

 which make our lips 

 smart if we nibble a leaf. 

 In our studies of plants 

 we endeavour to find 

 out what these qualities 

 primarily mean to their 

 possessors ; here we think rather of their secondary 

 significance as protections against animals. For though 

 snails ravage all the plants in a district except those which 

 are repulsive, the snails are at most only the secondary 

 factors in the evolution of the repulsive qualities. 



FIG. 5. ACACIA (A. sphtcrocephala), 

 WITH HOLLOW THORNS IN WHICH 

 ANTS FIND SHELTER. 



(After Schimper.) 



