Genus XV. HYMENOPHYLLUM, Smith.
The British HymenophjUums, or Eilmy Eerns, are small
moss-lihe plants, with pellucid fronds, distinguished, along
with Trichomanes, by having the fructifications at the edge,
not on the back of the fronds; and known from that
genus by having the involucres which surround the_clusters
of spore-cases, two-valved instead of urn-shaped or entire.
So far as our native species go, these distinctions serve, but
they become puzzling in some exotic forms, which it is not
easy to refer to their proper genus. They are the smallest
of all our native Eerns, and, being somewhat rare, or at
least local in their distribution, they have always been regarded
with much interest. Two native species are recognized,
much like each other in general aspect, and distinguished
by one or two rather minute technicalities, which,
however, are sufficiently obvious to those who have learned
how to look for them. These peculiarities will be presently
explained.
The name TLymenophyllum is compounded from the two
Greek words hymen an i phyllon, which mean a membrane,
and a leaf; and is applied to those plants with much propriety,
from the membranous texture of their fronds.
h ym e n o ph y l l um . 113
H ym en o ph y l l um t u n b r id g e n s e . Smith. — The Tunbridge
Eilmy Eern. (Plate XV. fig. 2.)
This is so named in consequence of its having been
found in the neighbourhood of Tunbridge, though occurring
also in many other parts of the United Kingdom. It grows
in the form of matted tufts, on the surface of damp rocks,
in the sheltered, humid localities which are congenial to
it; the-black, wire-like, creeping stems being entangled
together, and interlaced with the mosses and allied plants
which are often found in its company. The fronds are very
short, from one to three or four inches long, membranous
and semitransparent, ahnost erect, and of a dull brownish-
green even when fresh, which gives them in some measure
the appearance of being dead. These fronds are lanceolate,
or somewhat ovate ; they are pinnate, with the pinnæ pinnatifid
or bipinnatifid, and having their branches mostly
produced on the upper side, though sometimes alternately
on each side the pinna.
The fronds are virtually, as is the case with the Trichomanes,
a branched series of rigid veins, winged throughout,
except on the lower part of the short stipes, by a narrow,
membranous, leafy margin. The clusters of spore-cases are
here produced around the axis of a vein, which is continued
I