CHAP. MI.] EPIPHYTES AS XEROPHYTES 57 



weather, they have to store up water and food. 

 This they do in their leaves or stems, called 

 "pseudo-bulbs," or sometimes in their roots. 

 They are mostly fixed at one spot, but some 

 can creep along the branches (as Zygopetalum 

 rostratum) in the Guiana forests. They are, 

 therefore, xerophytical in their nature, as the 

 amount of water at their disposal is a more 

 or less limited quantity, situated as they often 

 are at the tops of trees, though the ground 

 below in the moist tropical forest may be 

 saturated. 



In some cases epiphytes may have no roots, 

 when the leaves act as adherent absorptive organs ; 

 as in Tillandsia usneoides (a plant allied to the 

 pine -apple of the order Bromeliacece}. This 

 clothes the branches of tropical trees like a 

 grey moss. 



Some epiphytic ferns have two kinds of leaves. 

 One sort is applied to the stem, the other grow- 

 ing out freely. The former absorbs the water 

 necessary for growth, etc., the latter assimilates 

 the carbonic acid of the air and bears the 

 fructification. Platycerium grande, the elk's-horn 

 fern, is an example often grown in greenhouses, 

 bearing a large shield -like frond below and 

 divided fronds above. 



Summarising the distribution of epiphytes in 

 tropical countries, it is found that this aerial 

 flora can exist in very different conditions. It 



H 



