central nerve, more or le.s.s defined, which is the axis
of the frond (fig. i). These
fronds lie flat upon the matrix,
or in a few cases are
floating, and are attached by
delicate radicles proceeding
from the under surface, which
'may be quite smooth, or
scaly, or more or less hairy.
Sometimes the fronds are
deeply and intricately lobed,
I- and at others nearly
simple, or notched at the apex. Occasionally
solitary, but more usually radiating, overlapping,
and forming imbricated tufts. In rare instances
the upper surface of the frond is punctate with
minute pores, which are the analogues of stomata
in the higher plants.
The foliaceous Hepatics have a thin thread-like
stem, which is so weak that the plants are only
erect when growing in dense tufts, or mixed with
Sphagnum or other mosses, the lower portion being
mostly naked or only furnished with radicles.
Upwards the stem is forked or branched, and the
branches themselves sometimes pinnate ; occasionally
it is normally simple. The stems being so
often prostrate the arrangement of the leaves is in
two rows, on opposite sides of the stem, but inserted
more or less obliquely, so as to lie nearly
flat, in prostrate forms (fig. 2). The leaves are e x ceedingly
variable in outline, seldom so simple as in
mosses, and without any mid-rib or nerve. In
many cases they consist of two unequal lobes,
folded together face to face, with the margin
either entire or toothed. The arrangement of
leaves on the stem may be succubous, or disposed
in a spiral which turns from left to right, so
that the anterior border of each inferior leaf
is covered by the posterior border of that immediately
above Or the arrangement may be
incubous, in which case the spiral turns from
right to left, and the anterior border of each
inferior leaf covers the posterior border of the leaf
placed immediately above it. If one of these stems
is e x am in e d
I c a r e fu l ly on
both sides with
a lens, it will be
observed that
J ■
6.
2^ theydiffermuch
in appearance, and especially that the under, or ventral,
surface exhibits a series of smaller leaves, somey