658 ECOLOGY 



Probably the absence of epiphytic seed plants and ferns in most dry 

 and cold climates is due to the long period of excessive transpiration 

 with little or no aerial absorption, characteristic of such climates. The 

 most northern of such epiphytes in the eastern United States, Tillandsia 

 usneoides (fig. 903) and Polypodium polypodioides, in their structural 



FIG. 969. Epiphytes on a live oak (Quercus virginiana\ the dominating form being a 

 species of Tillandsia; Miami, Fla. Photograph by MEYERS. 



features and life habits are most pronounced xerophytes. Even 

 mosses and lichens as epiphytes are much more abundant in humid 

 climates than elsewhere. 



Structures characterizing epiphytes. Epiphytes commonly are char- 

 acterized by highly specialized organs of absorption, or by structures 

 which effectively reduce transpiration or accumulate large quantities 



