152 STEMS 



on account of this struggle for light, that climbing stems 

 show their greatest display. 



In the dense forests of the tropics great woody vines 

 abound. They hang from the trees and grow up from the 

 ground, for they come from seeds which sprout on the 

 branches of the trees as well as in the soil. Those which 

 are growing down in the air as well as up in the air have 

 free strands which swing like ropes from lofty branches, 

 but when they have taken root, these strands become 

 stretched taut. The whole forest top seems sometimes 

 interlaced with these woody vines. They make easy high- 

 ways for the troops of monkeys. They mount to the tops 

 of the tallest trees where sprays of their flowers may be 

 seen in the midst of the dense crown of the tree which 

 supports them. Sometimes their growth is so vigorous 

 and the burden of carrying them so great that the sup- 

 porting tree perishes under its load. 



Such woody, rope-like vines are called lianas (pro- 

 nounced le-a'na). (See Figure 57.) Our own wild grape 

 often grows as a liana. In river bottoms it is common to 

 find trees which have been broken down by the weight of 

 grapevines upon them. 



In the intense struggle for light in tropical forests some 

 plants are found climbing which under other conditions 

 stand erect. This is evidence of a rather unusual capacity 

 to respond to environment. 



There are three quite distinct ways in which climbing 

 plants attach themselves to their supports: (i) by twining 

 their stems about the support, (2) by tendrils which twine 

 about the support, and (3) by tendrils which end in sucking 

 disks or holdfasts. The poison ivy is a common climbing 

 plant whose climbing organs seem more like roots than 



