44 J. SMITH ON THE GENERA OF FEHNS. 



attempt to point out the principal features which charac- 

 terize the natural groups of ferns, 1 have therefore refrained 

 from giving anything more than a few examples of the species 

 belonging to each genus ; as also a reference to one or more 

 published figures which best exemplify the genera. I have 

 also refrained from making any observations on the geogra- 

 phical distribution, as locality seldom marks any genus which 

 contains more than one species. 



DiV. 1. POLYPODIACE^. R. Br. 



Sporangia globose or oval, transparent, unilocular, pedicel- 

 late, rarely sessile, opening transversely, furnished with a 

 vertical, or rarely oblique, elastic, articulated, nearly complete 

 ring. 



Tribe I. PoLVPODiEiE. J. Sm. 



Sori round, oblong or elongated and linear, destitute of a 

 special indusiiim. (Sometimes the fertile fronds are con- 

 tracted, the margins of which are usually membraneous and 

 revolute, forming a universal indusium which includes the 

 whole of the sori of each segment of the frond.) 



Obs. This tribe contains upwards of 400 species, the typical 

 form being exemplified by the extensive genus Polypodium — 

 as characterized by Swartz, Willdenow, and others ; and, 

 according to their character of the genus, it would now con- 

 tain above 300 species, but which in the following arrange- 

 ment are divided into a number of genera, characterized by 

 the different modification of the veins, in conjunction with the 

 position of the sori on their branches. The remaining species 

 of the tribe have hitherto been distinguished from Polypodium, 

 by having elongated linear sori, but their venation is now also 

 made use of for characterizing the genera. 



