93 



pine, nor on the hackberry (Ccltis Occident alls). The bark of 

 this tree is normally smooth like that of the beech, and though 

 it usually becomes very rough and scabby on the trunks and lower 

 branches of old trees, it is so hard and unretentive of moisture 

 that it does not attract the colonies of lichens and mosses which 

 establish themselves so freely on other species, and this fact 

 probably has a more direct influence upon the polypodium's choice 

 of a habitation than the character of the tree upon which it 

 lodges. The fern is not a parasite and its roots never penetrate 

 the living tissue of the host, but there seems to be a symbiotic 

 relation between it and a certain soft, plush-like moss with which 

 it is usually associated, the fern giving shade to the moss, while 

 the latter serves as a reservoir to retain the moisture without 

 which the rootstocks of its partner could not keep alive through 

 periods of protracted drought. 



Another peculiarity in regard to habitat is that our " little poly- 

 pody " does not seek the seclusion of deep sequestered woods 

 like most of the other ferns, but is most frequently found on the 

 trunks and boughs of shade trees around dwellings and on the 

 borders of roads and open woods. It is a familiar object on 

 shade trees in all our southern towns, and instead of avoiding 

 the presence of man seems to flourish best in his neighborhood. 

 This is readily explained as an adaptation to its aerial habit — or 

 possibly the habit may be an adaptation to the situation. If it had 

 always confined itself to low-lying positions on logs and stumps^ 

 or on tree trunks in the deep shade of crowded forests where its 

 spores could be carried only a short distance from the parent 

 plant, it is easy to see that it could hardly have become, as it now 

 is, one of the most widely distributed of American ferns. 



Its range frequently overlaps that of the common polypody, 

 especially among the Southern Appalachians and their foothills,, 

 where it occurs in patches on the face of rocky cliiTs and the 

 shelving sides of moss-covered bowlders, as well as on the roots 

 and trunks of trees. The common polypody is of frequent occur- 

 rence on top of Lookout Mountain, and I have found occasional 

 specimens of the " little Polly " in Walker Co., Ga., growing 



