CH. IV 



ALLIES AND ENEMIES 61 



a very slow period of regeneration, and the dense under- 

 growth, from this point of view, may be considered as 

 an enemy. An allied genus, Stenosiphonium, performs 

 a similar office in the dry low country, while, in places, 

 where shifting cultivation has taken place, the whole 

 area may be invaded by a dense mass of grass such as 

 Imperata arundinacea, which is very slow in giving 

 way to forest. In other places, both in dry and wet 

 zones, a secondary forest springs up, composed, in the 

 drier zones, mostly of thorny and small trees and shrubs, 

 and, in the wet zones, of evergreens, frequently thorny 

 too, which protect the soil and improve it for the 

 gradual reintroduction of tree forest. It is an interest- 

 ing fact that Nature, in its last desperate attempt to 

 protect the soil, arms a large number of the plants she 

 uses for that protection with defensive weapons which 

 ward off the attacks of most animals excepting, perhaps, 

 man. 



Climbing plants may generally be considered as 

 enemies of the forest, for they use the stems and branches 

 of trees in order to reach the light, and, when they have 

 done that, they establish themselves among the crowns 

 and keep light and air from them. The most deadly 

 are the twiners which constrict the plants which help 

 them up and prevent their regular growth. It has 

 already been mentioned that lianas, in passing from one 

 crown to another, bind trees together, and that if one of 

 these falls or is felled it is liable in its fall to pull 

 others down. Of course, among these climbers there 

 are some which, although they are unfriendly to their 

 hosts, have an intrinsic economic value of their own and 

 deserve encouragement for that purpose. Among them 

 the most noteworthy are those yielding rubber, such 

 as certain species of Landolphia, Carpodinus, and 

 Clitandra, or certain Cane-Palms [Calamus). 



Climbing plants obtain their greatest development 

 in the wet zone or in damp localities such as banks of 

 rivers (Fig. 12), and the damage done to trees is not 

 only due to woody climbers, but also to herbaceous or 



