THE ARCHEGONIAT^E 



239 



podium," which gives the capsule the appearance of having a seta 

 (Fig. 201). 



The species of Sphagnum are especially abundant in moist northern 

 countries, where they form the most important element in the peat- 

 bogs. The plants are perennial, forming new shoots at the top and 

 slowly dying away below, the compact masses of dead tissue becoming 

 gradually transformed into 



Peat " Ifa^ A. 



n // /,-, /A\\ 



Order II. Andreaeales 



This order has but a 

 single genus, Andresea, 

 small, dark-colored Mosses 

 growing upon rocks, and to 

 some degree intermediate 

 between the Sphagnales 

 and Bryales, but on the 

 whole approaching more 

 nearly the latter order 

 (Fig. 204). The protonema 

 is more or less flattened, 

 and the archesporium,, 

 although derived from the 

 endothecium, extends over 

 the top of the columella. 

 The capsule opens by four 

 longitudinal slits. 



Order III. Bryales 



V 



Ps. 



FIG. 204. Andresea petrophila. A, plant with 

 mature sporophyte (X 10). , longitudinal 

 section of sporophyte ( X 80) ; ps, pseudo- 

 podium ; col, columella. 



All of the commoner 

 Mosses except Sphagnum 

 belong to the Bryales. 

 They show great range of size and have adapted themselves to a 

 great variety of environment. A few, like Fontinalis and Ambly- 

 stegium, are true aquatics. Most of them prefer moist, shaded situ- 

 ations upon the earth or upon trunks of trees ; some, however, thrive 

 in exposed, dry places, where they receive water only at long intervals. 



Classification. The Bryales are sometimes divided into two orders, 

 Cleistocarpae and Stegocarpae, based upon the method of dehiscence 

 of the capsule. The former, e.g. Phascum, Ephemerum, do not de- 

 velop an operculum, but the capsule breaks irregularly. There is 

 no question, however, that the two groups are closely related. 



Another division, based upon the position of the sporophyte, is 



