THE GREAT GROUPS OF BRYOPHYTES ^27 



center of the capsule to the lid-like operculum (Figs. 108, 

 109). When the operculum falls oft' the capsule is left 

 like an urn full of spores, and at the mouth of the urn 

 there is usually displayed a set of slender, often very beau- 

 tiful teeth (Fig. 110), radiating from the circumference to 

 the center, and called the peristome, meaning '"about the 

 mouth." These teeth are hygroscopic, and by bending 

 inward and outward help to discharge the spores. 



