44 THE HUMAN SIDE OF PLANTS 



ing hairs, poison darts, and various other weapons 

 of defence; while acrid juices, poisons, and tough, 

 fibrous growths assure safety from both insect and 

 larger animal life. Some plants shoot their heads 

 above the surface of the water, to avoid the attack 

 of water insects ; and then, in order to prevent their 

 enemies from climbing up the stems to the heads, 

 they exude a thick, viscid varnish, which both op- 

 poses the passage of insects and protects the plant 

 against inclement weather conditions. 



Against the second general danger to plant life 

 voracious animals and voracious or hostile plants 

 there are four common means of defence : thorny 

 or dagger-like weapons; acrid or poisonous qual- 

 ities ; offensive odours ; and simulation and flight. 



The first defence is very common. Cattle have 

 learned in the past to avoid spinous or prickly 

 plants, the knowledge of the danger of interfer- 

 ence with such plants, which ancestor cattle have 

 learned by painful experience, having become an 

 inherited antipathy in their descendants. 



Against plants and grasses which secrete silica 

 this antipathy is apparent also ; and with good rea- 

 son. All animals intuitively have learned to avoid 

 the rough, "cutting" grasses and the bristly plants. 

 As the humans in ages past mixed iron with their 

 copper to make the weapons more durable, so have 



