196 HISTORY OF BRITISH FERNS. 



except on the lower part of the short stipes, by a narrow, 

 membranous, leafy margin. The clusters of spore-cases 

 are produced around the axis of a vein, which is continued 

 beyond the margin of the fronds, this vein or receptacle 

 being enclosed within an urn-shaped involucre, consisting 

 of two nearly orbicular compressed valves, which are 

 spinosely serrate on the upper margin. 



This species is widely distributed throughout the United 

 Kingdom, and is found in many other parts of the world. 

 It requires the same conditions for its successful cultiva- 

 tion as does the Trichomanes, to which genus the reader 

 is referred. 



It is the Trichomanes tunhridgensis of Linnasus. 



Hymenophyllum unilaterale, Willdenow. 



Wilsons Film Fern. (Plate XV. fig. 3.) 



This plant is by English botanists most commonly 

 called Hymenoj)hi/llum Tnisoni, but it is identical with 

 H. unilaterale, a name published long antecedently by 

 Willdenow. The species is a small moss-like plant, with 

 numerous creeping filiform stems, generally growing in 

 dense tufts, and producing a crowded mass of semi-droop- 



