472 



General Botany 



have only horizontal or inclined stems. They possess very simple 

 leaves, frequently only one cell layer in thickness, sometimes 

 thicker toward the midrib. Like the liverworts, mosses have 

 rhizoids. But the rhizoids of the liverworts are one-celled struc- 

 tures, while those of the mosses are branching, many-celled struc- 

 tures which penetrate the soil. These afford a firm anchorage for 

 the plant and absorb a part of the water used by it. The stems 

 of the largest mosses have elongated cells forming the central 

 axis. These cells probably form a primitive conducting tissue. 



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Fig. 288. Habitat sketch of three common mosses: Climacium 

 (at left), Polytrichum (above at right), and Mnium. 



