300 



THE BRYOPHYTES 



teeth (Fig. 269, B, ), which meet at the center of the opening 

 when folded inwards. The number of teeth is fixed for differ- 

 ent mosses. Under the circle of teeth various mosses have 

 another circle of much more delicate segments (Fig. 269, B, s) 



FIG. 269. The spore case of a common moss (Bryum) 



A, the closed spore case : c, the cover (operculum) ; r, the ring. S, the rim of 

 an open spore case, showing the outer circle of teeth t, inside of which is indi- 

 cated the inner circle of delicate segments s: sp, spores. C, the cover after 

 remaining for a minute in water : the cells of the ring r have absorbed the 

 water and have swollen so that the ring has broken and curled backwards on 

 two sides 



of the same number and general form. The teeth are sensitive 

 to moisture, curling inwards and outwards with changes in the 

 amount of vapor in the air, and by these movements they prob- 

 ably help in some types to empty the case of its spores, retain- 

 ing them in wet weather and letting them fall out in dry. 



