GLASSIFTCATION. 



29 



whilst in others they are covered with, or surrounded by, 

 a membrane of variable form. This enables us to con- 

 stitute two sections of our sub-group, in which — 



Sectiois' I. — The tufts of spore-cases are naked ; 



Sectiok" II. — The tufts of spore-cases are covered (in- 

 dusiate) . 



The Jirst section, with naked tufts, contains three 

 genera, which may be distinguished by the following cha- 

 racters : 



The clusters are circular, and the margin of the frond 

 is flat (not reflexed), in the PoLTPODrES {Foly podium). 



The clusters are at first circular, afterwards spreading 

 one to the other, and becoming confluent, the margin of 

 the frond bent back (reflexed), in the Parsley Peris' 

 (Allosorus) , 



The clusters are elongated, or linear, in the Jersey 

 Pern ( Gymnogramma) . 



By attention to the above characters, it will be easy to 

 refer any fern with naked sori which is a native of Grreat 

 Britain, to its proper genus. 



The second section, with covered or indusiate tufts, or 

 clusters of spore-cases, contain eleven genera, so that it 

 will be necessary to separate those with true or evident 

 coverings, from those in which the covering is imperfect. 

 If, with this limitation, we examine the seven genera in 

 which the clusters are truly and manifestly covered, we 

 shall find that in two of these the clusters are circular, 

 in four of them the clusters are elongated, and in the 

 seventh they form a continuous line' down the frond. 

 Thus we may state their characters : 



Fig. 12. 



Fig. 13. 



Fig. 14. 



