POLYPODIUM INCANUM. 



HOARY POLYPODY. 



NATURAL ORDER, FILICES {Polypodiaceai). 



PoLYPODlUM INCANUM, Swartz. — Fronds leathery, evergreen, veins obscure, sometimes 

 reticulating near the margin, smooth and green above, pinnately parted; the divisions 

 oblong, obtuse, entire. The frond beneath, as well as the stipe, thickly beset with 

 peltate, chaffy scales ; fruit dots near the margin. (See Chapman's Flora of the Southern 

 United Stales.) 



ERNS which grow on trees are confined to a very few 

 species in the United States, and of all of them the 

 pretty little species, called Polypodium incanum, is perhaps the 

 most frequently found here. In Europe, at least in England, 

 the most common fern found growing on trees is an allied 

 species, P. vulgarc, a native also of the United States, where, 

 however, it is more often found in the clefts and on the 

 ledges of shaded rocks than on trees. It is interesting to note 

 that the species now illustrated, which, as we have just remarked, 

 is allied to P. vulgarc, seems to have advanced from the south 

 towards the north, while P. vulgare has travelled towards the 

 south, so that the advancing colonies have met and intermingled 

 in the northern parts of the Southern States. And here we find 

 that, while in the centre of its range, and where we may suppose 

 was its original home, the Polypodium- incanum is mostly found 

 on trees, when it meets its northern friend it takes to the same 

 habit of often growing on rocks. As so few ferns in our district 

 grow on trees, as compared with those which we might suppose 

 to be able to adapt themselves to such situations, it is more than 

 probable that, in the order of evolution, ferns growing on trees — 

 epiphytal ferns — are a comparatively late class in the sequence 



