346 FOUNDATIONS OF BOTANY 
there are plenty of instances of structures, habits, or accu- 
mulations of stored material in their tissue which plants 
seem 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) Mimicking the appearance of dangerous or uneatable plants, or 
imitating pebbles or earth, so that they may be overlooked. 
(3) Forming tough, corky, woody, limy or flinty and therefore 
nearly uneatable tissue. 
(4) Arming exposed parts with cutting edges, sharp or stinging 
hairs, prickles, or thorns. 
(5) Accumulating unpleasant or poisonous substances in exposed 
parts. 
414, 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 authority on this subject, that the 
ants of a single nest sometimes destroy as many as one 
hundred thousand insects ina 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. ) 
Certain tropical trees, in order to insure protection by 
ants, offer them especial inducements to establish colonies 
on their trunks and branches. The attractions which are 
offered to ants by various kinds of trees differ greatly. 
One of the most interesting adaptations is that of an 
acacia! (Fig. 242), which furnishes little growths at the 
ends of the leaflets which serve as ant food. These little - 
1 A, sphaerocephala. 
ee, 
