Adaptation to Environment. 317 



the coils tight to obtain a firm hold. In this way this 

 plant is enabled to reach the tops of trees and spread 

 itself out over their crowns ; or it may cover the tops of 

 thickets of undershrubs, greatly to its own advantage in 

 obtaining light. The tendrils are so quick to take ad- 

 vantage of any suitable object of support that within a few 

 minutes after they have perceived its presence by contact 

 with it they may have made at least one turn about it. 

 Figure 165 shows undershrubs in the foreground, and wil- 

 lows in the background, almost completely hidden by the 

 foliage and white flowers of this plant, demonstrating how 

 efficiently it has employed its method of using other plants 

 as supports. 



202. Protective Adaptations. — Factors in the environ- 

 ment which are a source of danger to plants have resulted 

 in adaptive modifications of various sorts. Not infre- 

 quently branches and leaves become modified to form 

 spines which may serve as a means of protection against 

 marauding animals. In desert plants, such as the cacti, 

 whose succulent tissues are greedily sought by animals, 

 these modes of protection are of vital importance. Still 

 other plants find protection in bitter and poisonous se- 

 cretions. 



One of the most wonderful devices to secure protection 

 against the destruction of leaves by leaf-cutting ants is 

 found in the BraziUan tree, Cecropia adenopiis. When one 

 shakes the tree, an army of ants pours forth from small 

 openings in the branches and makes a vicious attack on 

 the intruder. These are the most warlike of known ants, 

 and their bite is very painful. Their chief service to the- 

 tree is the prevention of the depredations of leaf-cutting 

 ants, which abound in these regions and are wont to strip 

 the leaves of unprotected trees clean to the midrib, carry- 



