THE MOSS WORLD. 
371 
sule and the lid an elastic ring, the annulus, and in none is it 
more evident than in Funaria hygrometrica, where its rich 
purple colour contrasts remarkably with the parts adjoining. 
The cells of which it consists are vesicular, and form several 
series ; these contract in drying and are suddenly dilated when 
moistened, and thus the separation of the operculum is greatly 
facilitated. The lid having fallen, there is now brought into 
view in most mosses a beautiful fringe of teeth called the 
peristome, which originates from the inner wall of the capsule* 
and is most remarkable for the definite number of its consti- 
tuent parts, 4, 8, 16, 32 or 64 ; frequently also an inner peri- 
stome is present, continued from the outer membrane of the 
spore sac. 
If we take the most perfect form of teeth, as seen inMnium* 
Hypnum, or Funaria, we find that each consists of two rows of 
firm coloured cells, separated in the middle by a divisural line, 
and also articulated with each other transversely ; on the inner 
face there is only one row of cells, and these frequently project 
at the margin beyond the outer layer, and also form transverse 
lamellae at their junction ; their texture is also quite different 
from those of the outside layer, for they are pale and vesicular* 
and on them the hygroscopic property of the peristome depends. 
When moistened these internal cells expand, and thus shorten 
the teeth and draw them inward into a cone, their usual posi- 
tion in the dry state being radiating round the mouth of the 
capsule or reflexed against its outer wall. 
Numerous modifications of the teeth occur, which render the 
peristome of interest as a microscopic object, the inner layer of 
cells being frequently abortive, the teeth become rigid, and 
sometimes quite rudimentary, and not unfrequently they dis- 
appear altogether, the capsule being then termed gymno- 
stomous. In Funaria the teeth are curiously gyrate, and also 
attached to an unusual appendage in the form of a little perfo- 
rated central disc, to which the points curve down, so that the 
part not inaptly resembles the inverted bottom of a wine- 
bottle ; in Tortula they are twisted together spirally, and 
sometimes united at base into a tubiform membrane ; in Dicra- 
num and Fissidens they are cleft along the divisional line, and 
in Gfrimmia apocarpa perforated or cribrose. Two other forms 
of peristome, however, are met with, in which the structure of 
the teeth is essentially different. In Georgia and Tetrodon- 
tium the four teeth consist of numerous confluent cells, and 
in Polytrichaceas the numerous teeth are composed of slender 
filaments agglutinated together into tongue-shaped processes* 
which adhere to the tympanum or expanded apex of the colu- 
mella; in the Australian genus Dawsonia the filaments are 
free, and project from the capsule like a brush. These three 
