re-case is like a pyxis (376),
that is, the top at maturity comes off as a lid (_Operculum_); and that
the interior is filled with a green powder, the spores, which are
discharged through the open mouth. In most Mosses there is a fringe of
one or two rows of teeth or membrane around this mouth or orifice, the
_Peristome_. When moist the peristome closes hygrometrically over the
orifice more or less; when drier the teeth or processes commonly bend
outward or recurve; and then the spores more readily escape. In Hair-cap
Moss a membrane is stretched quite across the mouth, like a drum-head,
retaining the spores until this wears away. See Figures 527-541 for
details.

500. Fertilization in Mosses is by the analogues of stamens and pistils,
which are hidden in the axils of leaves, or in the cluster of leaves at
the end of the stem. The analogue of the anther (_Antheridium_) is a
cellular sac, which in bursting discharges innumerable delicate cells
floating in a mucilaginous liquid; each of these bursts and sets free a
vibratile self-moving thread. These threads, one or more, reach the
orifice of the pistil-shaped body, the _Pistillidium_, and act upon a
particular cell at its base within. This cell in its growth develops
into the spore-case and its stalk (when there is any), carrying on its
summit the wall of the pistillidium, which becomes the calyptra.

[Illustration: Fig. 529. Mnium cuspidatum, smaller than nature. 530. Its
calyptra, detached, enlarged. 531. Its spore-case, with top of stalk,
magnified, the lid (532) being detached, the outer peristome appears.
533. Part of a cellular ring (_annulus_) which was under the lid,
outside of the peristome, more magnified. 534. Some of the outer and of
the inner peristome (consisting of jointed teeth) much magnified. 535.
Antheridia and a pistillidium (the so-called flower) at end of a stem of
same plant, the leaves torn away ([Symbol for Male], antheridia, [Symbol
for Female], pistillidium), magnified. 536. A bursting antheridium, and
some of the accompanying jointed threads, highly magnified. 537. Summit
of an open spore-case of a Moss, which has a peristome of 16 pairs of
teeth. 538. The double peristome of a Hypnum. 539-541. Spore-case,
detached calyptra, and top of more enlarged spore-case and detached lid,
of Physcomitrium pyriforme (Fig. 527): orifice shows that there is no
peristome.]

501. =Liverworts or Hepatic Mosses= (_Hepaticae_) in some kinds resemble
true Moss