24 THE SPHAGNA CEsE 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 %\ 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 papillae. 



