The Study of Animal Life 



PART I 



3° 



insects which do no harm to the trees, but cleanse them 



from injurious fungi. 



In many ways plants are saved from the appetite ot 



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 ex- 

 cept those which are 

 repulsive, the snails are 

 at most only the second- 

 ary factors in the evolu- 

 tion of the repulsive 

 qualities. 



The strange inter-relations between plants and animals 

 are again illustrated by the carnivorous, generally insecti- 

 vorous, plants. It is not our business to discuss the 

 original or primary import of the pitchers of pitcher-plants, 



Fig. 4. — Acacia {A. sphterocephala), with hol- 

 low thorns in which ants find shelter. 

 (After Schimper.) 



