TRICIIOMAI^ES.
from which in the native species it is easily distinguishable,
although in some exotic kinds the differences almost vanish.
The sure technical mark by which to distinguish Trichomanes
and Hymenophyllum among the British Terns, lies m the
fact of their spore-cases being contained within deep urnshaped
pits or recesses at the margin: in these two families
the fructification is at the margin instead of being situated
at the bach of the fronds. Trichomanes is known from Hymenophyllum
by its urns, or involucres as they are called,
being entire, while those of Hymenophyllum are split lengthwise
into two valves. In both cases the spore-cases are
' clustered around hair-like receptacles, which are, in fact,
the ends of the veins of the fronds projecting into the urns.
In Hymenophyllum these hairs are always shorter than the
urn, but in Trichomanes it is usual for them to project more
or less, so that the fronds become somewhat bristly when
very full of fructification; and hence has arisen the common
name of Bristle Tern, which is applied to the group.
The name Trichomanes itself has the same signification ;
it comes from two Greek words, meaning hair, and excess,
in reference to these projecting hair-like receptacles.
T richomanes radicans, Swartz.—Tue. Bristle Tern.
(Plate X Y III. fig. 1.)