

112 HISTORY OP BRITISH FERNS. 



Genus XY. HYMENOPHYLLUM, Smith. 



THE British Hymenophyllwm*, or Filmy Ferns, are small 

 moss-like plants, with pellucid fronds, distinguished, along 

 with Trichomanes, by having the fructifications at the edge, 

 not on the back of the fronds ; and known from that 

 genus by having the involucres which surround the clusters 

 of spore-cases, two-valved instead of urn-shaped or entire. 

 So far as our native species go, these distinctions serve, but 

 they become puzzling in some exotic forms, which it is not 

 easy to refer to their proper genus. They are the smallest 

 of all our native Ferns, and, being somewhat rare, or at 

 least local in their distribution, they have always been re- 

 garded with much interest. Two native species are recog- 

 nized, much like each other in general aspect, and distin- 

 guished by one or two rather minute technicalities, which, 

 however, are sufficiently obvious to those who have learned 

 how to look for them. These peculiarities will be presently 

 explained. 



The name Hymenopliyllum is compounded from the two 

 Greek words hymen and phyllon, which mean a membrane, 

 and a leaf; and is applied to those plants with much pro- 

 priety, from the membranous texture of their fronds. 



