i62 HOW TO KNOW THE MOSSES 



spheres. The protonema is not persistent, and the 

 stems are longer and the leaves more numerous than in 

 the preceding species. P. urnigerum is from 

 1-3 inches high, sometimes branched, and 

 usually the leaves thickly cover most of the 

 stem, while P. capillar e is much smaller, 

 I inch high or less, unbranched, with the 

 leaves often clustered at the tip of the stem. 

 The color of the leaves in both species is 

 capiiiare o^i^e or dark green. 



Leaf en- The Cylindrical capsule separates Pogon- 



^^^^ ' atum from Polytrichum, the following genus, 

 except Polytrichum alpinum var. arcticum; for com- 

 parison see under that species (p. 167). The leaves 

 and calyptra resemble those of Polytrichum in general 

 character, but a little experience will enable one to 

 note that the leaves of Polytrichum are less rigid and 

 the calyptra is longer in most cases. The common 

 Pogonatum hrevicaule is readily distinguished by the 

 presence of protonema, which is not found in Poly- 

 trichum, and by the smaller size. Pogonatum is dis- 

 tinguished from Catharinaea (p. 156) by the opaque 

 leaves J folding when dry and not crisped, 



41. POLYTRICHUM Dill. (Po-ly-tri-chum) 



A genus containing over one hundred species, some 

 of which are our commonest mosses, found chiefly on soil 

 in the cooler regions. Commonly called " hair-cap 



