156 
TUNBRIDGE FILM FFRN. 
also, but not found in the Lake Country) they project 
more, so that the fronds become bristly when very 
full of spores. Hence the name of Bristle Fern. 
They are known also by the farther difference that 
the involucres of Trichomanes are entire, and those of 
Hymenophyllum split lengthwise into two valves. 
The Tunbridge Film Fern (named from its being, 
first found near Tunbridge, in Kent) grows in matted 
tufts upon rocks in moist warm places, usually carpet¬ 
ing the damp surfaces of the rocks themselves, but, 
sometimes choosing the mossy ground, or living moss¬ 
like on the trunks of trees — the black wiry rhizomes 
or creeping caudices interlacing themselves among 
their neighbour plants. The fronds are very short, 
from an inch to three or at most six inches long, 
membranous and half-transparent, almost erect, and 
of a dull dead-looking brownish-green even when at 
their freshest; lanceolate or slightly ovate, pinnate, 
with pinnae pinnatifid or bipinnatifid, and having their 
branches mostly on the upper side, though sometimes 
alternately on each side of the pinna. The fronds are 
virtually a branched series of rigid veins, winged 
throughout, except on the lower part of the short 
stipes, by a narrow membranous leafy margin. The 
sori are produced around the axis of a vein, which, as 
before said, is continued beyond the frond-margins 
and enclosed in an urn-shaped indusium, involucre 
or cover, consisting of two almost perfectly round 
(orbicular) compressed valves, spinosely serrate on 
the upper margin. It will grow well in pots in equal 
parts of peat and silver sand, scarcely caring for any 
