LIVERWORTS AND MOSSES. 



55 



worts, by numerous usually much branched rhizoids (A, fig. 

 67; w, fig. 68). Similar filaments may be produced, often 

 in great numbers, along the stem and especially in the axils 

 of the leaves, or they may even arise from the leaves them- 

 selves, when the plants grow in dense patches or in a very 

 moist place. 



Fig. 67. — A, gametophyte of Polytrichunt commune, with rhizoids below. B, 

 gametophyte of Hylocomiutu splendens, bearing three sporophytes near top. 

 Natural size. — After Kerner. 



63. The stem is usually cylindrical and covered by the 

 crowded leaves. In structure it generally shows an advance 

 upon that of the liverworts in having the whole of the outer 

 region occupied by a distinct mass of mechanical tissue com- 

 posed of thick-walled cells, and, near the center, a strand of 

 elongated small cells, known as "conducting tissue" (fig. 

 68), though it is doubtful whether it conducts anything. 



