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TEXTBOOK OF BOTANY 



ones below. In most species the lower and older parts disintegrate about 

 as fast as new growths appear terminally. 



Fig. 297. Polijtrichum. Annual stem segments and terms applied to parts of 

 the capsule. A and B, gametophyte and sporophyte phases; C and D, male 

 gametophytes. 



The bog mosses grow in poorly aerated habitats, and as they die below 

 they accmiiulate as peat deposits, several to many feet in thickness. 

 Mosses that grow in springs heavily charged with calcium bicarbonate 

 become incrusted below with lime and build up layers of porous hard 

 tufa many feet thick. The tufa deposits later recrystallize and form solid 

 masses of limestone. The moss Gt/mnostomum, important in tufa forma- 

 tion, is known to elongate a little over an inch in four years. In a thou- 

 sand years these processes would form a layer of tufa and rock some 20 

 feet in thickness. Living cells occur onh' in the uppermost segments. 



