114 HOW TO KNOW THE MOSSES 



Plants growing in wide, loose patches ; dull dark green, 

 often becoming blackish. 



Stems usually 1-2 inches long ; stout; pros- 

 trate to ascending, with ends of branches erect; 

 the lower part of the stem leafless; branched 

 by forking. 



Leaves short and broad; wide-spreading when 

 moist; closely folded when dry ; very dark ex- 

 cept at tips of branches. 

 Rhacomitrium Seta about ^ inch long ; dark brown ; some- 

 aticulare times appearing lateral by the new growth 



Leaf enlarged, of the plant. 



Capsule erect, elliptical; red-brown; mature in spring. 

 Operculum long-beaked. 



Range, Alaska, Canada, south to California and Ala- 

 bama; Europe; Africa. 



Rhacomitrium resembles Grimmia, the preceding 

 genus, in manner of growth and branching, but the 

 common species described above is found on rocks 

 along streams, sometimes overflowed, while the com- 

 mon Grimmias usually grow on rocks in woods. The 

 stems and branches are stouter and longer, except in 

 G. apocarpa var. rivulare, the leaves broader, and more 

 separated, and if the plants are fruited there is no diffl- 

 culty in distinguishing the two genera. The species 

 of Orthotrichum and Ulota (pp. 117, 119) that occur 

 on rocks are dark and somewhat branched; but like 

 Grhnmia they are also found in woods instead of 

 along streams; the stems are shorter, and the plants 

 grow in closer tufts. Associated with Rhacomitrium is 



