414 



HOW PLANTS PROTECT THEMSELVES 



to have acquired mainly or entirely as means of defense. Some 

 of the most important are : 



1. The habit of keeping a bodyguard of ants. 



2. Forming tough, corky, woody, limy, or flinty, and therefore 



nearly uneatable, tissue. 



3. Arming exposed parts with cutting edges, sharp or stinging hairs, 



prickles, or thorns. 



4. Accumulating unpleasant or poisonous substances in exposed 



parts. 



386. Ant plants. Some ants live on vegetable food, but most 

 of them eat only animal food, and these latter are extremely 

 voracious. It has been estimated by a careful scientist, an 



FIG. 315. An ant plant (Acacia sphcerocephala) 



t, thorns; h, hole in thorn; n, nectary; 6, Belt's body on tip of leaflet. After 



Schimper 



authority on this subject, that the ants of a single nest some- 

 times destroy as many as one hundred thousand insects in a 

 day. The Chinese orange growers in the province of Canton 

 have found how useful ants may be as destroyers of other 

 insects, and so they place ant nests in the orange trees and 

 extend bamboos across from one tree to another, to serve as 

 bridges for the ants to travel on. 



