324 



ZONES AND REGIONS 



[Pt. Ill, Sect. I 



In other cases, either all the leaves or some of them go to form pockets, 

 as they assume such a position against the stem as to make with it a 

 receptacle in which humus can accumulate. Either each leaf by itself 

 forms a pocket, or several leaves take part in the formation of a general 

 pocket. In many species, there has arisen a differentiation between 

 pocket-leaves, which fulfil the function of assimilation only to a subor- 



Fig. 164. Platycerium grande. Nest-epiphyte with pocket-leaves. Pasoeroean, East Java. 

 From a photograph by J. Kobus. 



dinate extent and for a short time, and assimilating leaves endowed with 

 quite other characters. 



The most remarkable examples of pocket-leaves appear in the fern-genus 

 Platycerium (Fig. 164), in which they are sessile and broad, are closely 

 applied below to the bark of the tree, and form a pocket above, whereas 

 the stalked, narrow, dichotomons foliage-leaves hang loosely down. 



