es, having distinct stem and leaves, although their leaves
occasionally run together; while in others there is no distinction of
stem and leaf, but the whole plant is a leaf-like body, which produces
rootlets on the lower face and its fructification on the upper. Those of
the moss-like kind (sometimes called Scale-Mosses) have their tender
spore-cases splitting into four valves; and with their spores are
intermixed some slender spiral and very hygrometric threads (called
_Elaters_) which are thought to aid in the dispersion of the spores.
(Fig. 542-544.)

[Illustration: Fig. 542. Fructification of a Jungermannia, magnified;
its cellular spore-stalk, surrounded at base by some of the leaves, at
summit the 4-valved spore-case opening, discharging spores and elaters.
543. Two elaters and some spores from the same, highly magnified.]

[Illustration: Fig. 544. One of the frondose Liverworts, Steetzia,
otherwise like a Jungermannia; the spore-case not yet protruded from its
sheath.]

502. Marchantia, the commonest and largest of the true Liverworts, forms
large green plates or fronds on damp and shady ground, and sends up from
some part of the upper face a stout stalk, ending in a several-lobed
umbrella-shaped body, under the lobes of which hang several thin-walled
spore-cases, which burst open and discharge spores and elaters. Riccia
natans (Fig. 545) consists of wedge-shaped or heart-shaped fronds, which
float free in pools of still water. The under face bears copious
rootlets; in the substance of the upper face are the spore-cases, their
pointed tips merely projecting: there they burst open, and discharge
their spores. These are comparatively few and large, and are in fours;
so they are very like the macrospores of Pillworts or Quillworts.

503. =Thallophyta, or Thallophytes= in English form. This is the name
for the lower class of Cellular Cryptogams,--plants in which there is no
marked distinction into root, stem, and leaves. Roots in any proper
sense they never have, as organs for absorbing, although some of the
larger Seaweeds (such as the Sea Colander, Fig. 553) have them as
holdfasts. Instead of axis and foliage, there is a stratum of frond, in
such plants commonly called a THALLUS (by a strained use of a Greek and
Latin word which means a green shoot or bough), which may have any kind
of form, leaf-like, stem-like, branchy, extended to a flat plate, or
gathered into a sphere, or drawn out into threads, or reduced