42 THE HUMAN SIDE OF PLANTS 



coming out only when they know the pests will 

 not be around are in somewhat the same class as 

 the morally weak plants which buy off or pay 

 "blackmail" to their enemies. The bird-cherry is 

 one of this type; many of the vetches also bribe 

 their crawling ravagers by feeding them from a 

 special supply of nectar that is stored in epidermic 

 cells on the under side of the leaves. Insects, 

 mounting the stems in quest of alluring sweets, 

 make the most of the first supply that comes to 

 hand, revelling on this until their desire is satis- 

 fied, and then dropping off in a state of drunken 

 satiation, entirely fooled by the ingenious plant and 

 thwarted in their quest for the rarest wines which 

 have lain just beyond. It is the oldest of human 

 tricks ! 



Weapons are the most evident means of defence 

 man has; and to plants, thorns, spears, and dag- 

 gers form a very useful and common protection. 

 But the thorns and daggers on plant stems have 

 not, as many people think, like Topsy, "jes' 

 growed." Those plants which have adopted exter- 

 nal weapons as a means of self-defence have done 

 so with thought and consistency. One who notes 

 the position and arrangement of thorn armour will 

 see that all spikes and daggers point down to meet 

 the scaling forces. The guerilla worm or insect 



