304 THE BRITISH FERNS. 
growth during the season, but enduring two or three years under 
favourable cireumstances. 

FEE 
pem 
= 
The two British Hymenophyllums, may be known from other 
Ferns by the interlacing growth of their thread-like rhizomes, by 
the small size, and pellucid cellular texture of their fronds, whose 
segments have each only a central rib, and by the two-valved 
marginal fructifications. They may be best known from each other 
by the form of the involucres and of their valves; which in H. tun- 
bridgense are sessile and erect, with the valves roundish and flattish, 
the upper margin spinulosely-serrate, like the margin of the segments 
of the pinnæ, whilst in H. unilaterale they are stalked and deflexed, 
with the valves ovate and convex, and the margin quite even. 
No varieties of importance have been observed in the British 
species belonging to this genus. 
Fe 
ES 
PIE UN 
SEES 
er 3 
The Tunbridge Film Fern is found in mountainous and rocky 
situations, usually carpeting the damp surface of the rocks them- 
selves, but sometimes growing on the ground amongst moss in moist 
places, or moss-like on the trunks of trees. It is extensively dis- 
persed, being found in England in the south and south-west, 
extending northwards through Wales and the Midland Counties to 
York, and the Lake District; occurring also both in the Lowlands 
and Highlands of Scotland, as well as in the Isles of Mull and Bute. 
In Ireland it is abundant and remarkably fine in some localities. 
Mr. Newman mentions that H. tunbridgense exhibits a preference 
for shade, warmth, and shelter; whilst its ally; H. unilaterale, 
establishes itself on bleak and exposed rocks. According to Mr. 
Watson, our present species ranges from the coast level to an 
elevation of about 1200 feet. The following is a summary of 
habitats :— 
Peninsula.—Cornwall : Rough Tor near Camelford, C. C. Babing- 
ton; near Penryn, Miss Warren. Devonshire: Bickleigh Vale, 
Miss Griffiths; Vixen Tor, Staple Tor, Wistman's Wood, and 
Shaugh Bridge, Dartmoor, T. B. Flower ; Becky Fall, near Moreton, 
R. J. Gray; Dunsford Bridge; Cornwood, Fl. Plym. Somerset- 
shire: Shepton Mallet. 

