lU FEENS OF GREAT BRITAIN. 



broader lanceolate, somewhat egg-shaped form, has been 

 termed Andrewsii, after its discoverer. The Bristle Fern 

 is by various v?riters called Trichdmanes brevisetum, 

 specidsum, or aldtum ; and also IIymenoj)hyllum aldtum. 



16. Hymenophyllum (Filmy Fern). 



1. H. Tunbridgense (Tunbridge Filmy Fern). — Fronds 

 pinnate ; pinna pinnatifid, forming a wing on each side 

 of the rachis ; the segments serrated and spinous. This 

 delicate, flaccid, membrane-like fern, grows in matted 

 tufts, looking rather like a withered than a living plant, 

 on account of its olive-brown tint, though when really 

 dried in the herbarium it retains much elasticity. The 

 slender, delicate Filmy Ferns are the smallest of our 

 native species, and are somewhat like delicate mosses. 

 The veins are so strongly marked, that, as in Trichomanes, 

 they seem to form the fronds ; the filmy cellular portion 

 surrounding them like a wing. Their length is from 

 one to three inches, they grow almost erect, and their 

 outline is lanceolate, or somewhat egg-shaped. They 

 are flat, and their pinnae once or twice pinnatifid, their 

 branches mostly on the upper side, though sometimes 

 alternately on each side of the pinna. The clusters of 

 capsules are formed round the axis of a vein, which runs 

 beyond the margin of the frond ; this vein, or receptacle, 

 being enclosed in a kind of cup forming the involucre. 

 This consists of two compressed valves, which are nearly 

 round, and are swollen shghtly at the base, and have 

 a notched and spinous upper margin ; and it is by this 

 two-valved involucre that this genus is distinguished 

 from the nearly allied Bristle-Ferns. 



