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TEXTBOOK OF BOTANY 



Fig. 299. Three species of Sphagnum (A-C), reproductive structures (D-G), 

 and thalloid protonema with young leafy shoot ( H ) . G represents the sporophyte 

 stage, which consists of a sporangium and a very short stalk. The small urn-shaped 

 bodies on A, B, and C are sporophytes. 



the absence of oxygen, and become peat ( Fig. 300 ) . These mosses may 

 also become estabhshed on the shore of a lake and gradually encroach on 

 the water, forming a quaking bog. Creeping bogs may develop in very 

 moist climates. The sphagnum mat grows out of the depression, invades 

 forested land, and kills the trees by raising the water table and excluding 

 oxygen from the tree roots. The characteristic genus of peat mosses is 

 Sphagnum, more than 300 species of which have been described. 



Mature peat mosses have no rhizoids, and absorption of water is 

 direct. The upward movement of water is largely effected bv capillarity 

 through the closely adhering lateral branches and the compactness of 

 the plant mass. 



The rock mosses, Andreaeales, grow principally in arctic and alpine 

 regions upon granite or slate. They are dark or almost black in appear- 

 ance, have very brittle leaves densely aggregated, and are rarely more 

 than an inch or two long. The gametophytes resemble the true mosses, 

 while the sporophyte is supported by a pseudopodium as in the peat 

 mosses. The capsule is unique among mosses in its longitudinal de- 

 hiscence by four valves when mature. There are approximately 120 

 species of rock mosses. 



