24 THE SPHAGNACEZ OR PEAT-MOSSES OF 
spherical, but when the lid is cast off it becomes urn-shaped or 
cylindric, and the mouth never exhibits any trace of peristome ; the 
walls are brittle and bear numerous stomata on the surface, and 
when ripe are of a deep chestnut brown colour. 
The operculum or lid is flattened or in form of an inverted 
saucer, and is cast off by contraction of the capsule with a crackling 
noise or slight explosion, and at the same time the spores are 
driven forth by compression of the capsule walls. Not unfrequently 
the lid remains attached by one margin, which acts as a hinge, and 
the capsule is closed again when moistened. If the capsule remains 
submerged or always wet, the lid does not open, but the capsule 
falls away from the vaginula and a hole is left at the base, the 
columella decays and the spores can escape in this way, or it 
happens that they germinate while still enclosed in the capsule 
and burst it by expansion, or the lid may be forced off and the 
capsular wall only left with a hole at each pole, and such barrel- 
shaped shells we frequently meet with in our examination of 
Sphagnum tufts. 
The spore sac differs in shape from that of the true mosses, 
for it is in form of a hollow hemisphere, occupying the upper part 
of the capsule and resting on the top of the columella to which its 
inner wall is united, while the outer wall coheres to the inner cell- 
layer of the capsule wall. When mature, the columella breaks 
away from the vaulted under side of the spore sac and shrivels 
back to the base of the capsule, leaving an empty space, which is 
probably concerned in the bursting of the capsule. 
The two kinds of spores are found in the same capsule or 
in different ones. The large spores vary between 23 and 4} 
hundredths of a millimetre in diameter, and in colour present various 
shades of yellow, ochraceous, or ferruginous brown ; the exospore 
or external coat is covered with scattered papille. 
