Chap. IV] TROPICAL DISTRICTS CONSTANTLY MOIST 317 



deposited on the curved ones (Fig. 157). The original wavy part of the 

 axis then represents a narrow ladder between two massive ladder- 

 standards. 



The oecological significance of the undulations is apparent so soon as an 

 attempt is made to pull down the liane. The branches of the supporting 

 tree are so firmly caught into the concavities, which are aided by the 

 downwardly directed hook-like stumps of the lateral branches, that such 

 attempts, if they succeed at all, do so only by the breakage of many twigs. 

 On the other hand, when 

 once the stem has become 

 straight, no further hindrance 

 occurs, and its weight causes 

 it to slip gradually to the 

 ground. That even wavy 

 axes may slip down owing 

 to the death of supporting 

 branches and to their own 

 considerable weight is shown 

 by their frequently hanging 

 down from the leaf-canopy. 



Of other lofty tendril- 

 climbers in the tropical rain- 

 forest we have of branch- 

 climbers many Sapindaceae 

 {watch-spring climbers) with 

 remarkable cable-like stems 

 composed of strands, species 

 of Securidaca (Polygalaceae) 

 (Fig. 103), species of Hippo- 

 cratea in both the Old and 

 New Worlds, species of Dal- 

 bergia (Fig. 104) and Ma- 

 chaerium in Brazil, many Anonaceae [hook-climbers) in tropical Asia, and 

 species of Cissus {stem-tendril climbers) ; of leaf-tendril climbers the 

 Bignoniaceae have a wood that is cruciform in transverse section. 



iST— 



Fig. 157. Bauhinia sp. , Pernambuco. The wavy young 

 axis is placed between two straight layers of growth. 



iv. EPIPHYTES OF THE RAIN-FOREST 1 . 



To a still greater degree than lianes, epiphytes contribute to the charac- 

 teristic physiognomy of the tropical virgin forest. Resting on the trunks 

 of the trees and on the twigs right up to their extreme tips is a wealth of 

 phanerogams and ferns, not only herbs, but also shrubs and even trees 



1 Schimper, I and II. 



