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Transactions of the Society. 
papers on the peristome in the ‘ Revue Bryologique/ commencing in 
1884, p. 49. He divides the Arthrodontes into Aplolepideae and 
Diplolepideae ; in the former each tooth consists of a single row of 
external plates and a double row of internal as in Dicranum, Grimmia , 
and Tortula; in the latter of a double series of outer plates and a 
single series of inner as in Bryum, Mnium, and Hypnum. On the 
inner surface of the teeth are transverse plates or lamellae formed by 
the thickened transverse walls of two adjacent cells, and on the outer 
surface the projecting crossbars or articulations are termed trabeculae. 
At base the teeth are united to the inner layer of cells of the capsule 
wall, and sometimes their points are attached to a little central plate, 
as we see in Funaria hygrometrica. 
The colour of the teeth is sometimes very rich, so that they make 
interesting objects for the Microscope, and we may instance the 
common Ceratodon purpureus and Funaria hygrometrica , Bryum 
erythrocarpon, various species of Orthotrichum , Mnium, and Hypnum 
as well worthy of observation. 
Occasionally, when the lid is removed, no trace of a peristome is 
to he seen, and the moss is said to be gymnostomous ; this absence of 
peristome was formerly regarded as of generic importance, but most 
modern writers now look upon it as evidence of a want of develop- 
ment, and place them in peristomate genera if they agree in leaf- 
structure and other essential characters. 
The endostome or internal peristome is found in the more highly 
developed species of Bryum, Mnium , Hypnum, &c., and arises from 
the outer wall of the spore-sac ; it is a thin transparent membrane 
composed at base, according to Mitten, of 80 quadrangular cells, and 
its upper margin projected into sixteen processes which alternate with 
the outer teeth, and are generally cleft or perforated along the middle 
line, and in its most highly developed condition, having also 1 to 4 
slender articulated cilia between each pair of processes. In Buxbaumia 
and Weber a the endostome is a plicate tube, in Cinclidium the processes 
are united at the upper part into a dome-shaped membrane, and in 
Fontinalis they are of a brilliant red colour and united by cross-bars. 
The air-cavity is a ring-like intercellular space between the wall of 
capsule and the spore-sac, and it is usually traversed by branched 
chlorophyllose cellular filaments. The columella is the central axis 
of the capsule enclosed by the spore-sac. 
The Sphagna or Peat-mosses differ considerably from the true 
Mosses, though they present great uniformity of structure among 
themselves. The stem is more highly organized, a pith of elongated 
colourless cells occupies the centre, which is surrounded by a cylinder 
of firm thick- walled cells, the outer layers of which are often richly 
coloured, and enveloping all is a cuticle of 1-4 strata of large empty 
thin-walled cells. The branches are in fascicles or bundles, some of 
which are slender, pendent, and closely applied to the stem, the rest 
being divergent and arching outward horizontally, and at the summit 
