HYMENOPHYLLUM. 
185 
dant membrane, and quite transparent. The pinnae are 
alternate, divided into from two to seven leaflets ; at the 
base of the higher pinnae on 
the upper side a vein passes 
beyond the membranous wing, 
and bears upon its summit a 
cluster of seed-masses, each 
encompassed by a ring, this 
fruitful vein is in its turn en- 
veloped in a membranous in- 
volucre, which is composed of 
two valves, open and sharply 
toothed at the upper end. 
This fern grows in extensive 
plots upon the surface of damp 
rocks, its caudex closely interlacing and soon hidden by 
a thick forest of tiny, transparent, moss-like fronds. It 
is found in Wales and Scotland, also in Cornwall, 
Devon, and at Tunbridge "Wells. Sir William Hooker 
states that it is found both in the New and Old World. 
The most suitable mode of cultivation for the Tun- 
bridge-fern is to place it in a Wardian case ; the next 
best plan is to treat it as Mr. Johnson recommends to 
be done to the Bristle-fern. 
44. Hymenophylliim Wiisom* Hook. Mr. W£lson 9 s 
Filmy-fern. 
Caudex creeping, thread-like. Stems slightly winged. Fronds 
rigid, transparent, pinnate. Pinnaj generally turned to one side. 
Involucre entire, upright. 
Mr. Wilson^s Filmy-fern closely resembles the Tun- 
bridge species, but the entire margin of the involucre at 
