I70 HOW TO KNOW THE MOSSES 



P, commune is used in Lapland for beds and pillows 

 and occasionally in certain parts of England for stuffing 

 mattresses and for brooms. 



Polytrichum gracile Dicks. (Plate VII, Fig. 8) is a 

 rare species found especially in higher altitudes. The 

 capsule is obscurely 5-6 angled, the operculum has a 

 long beak, and the calyptra does not wholly cover the 

 capsule. This species most closely resembles P. ohio- 

 ense, but it is not so common, the growth is somewhat 

 more slender, and the capsule does not gradually 

 taper to the seta as in P. ohioense. The leaves are dark 

 green or olive-green. 



Range, northern part of North America, eastern United 

 States; Europe. 



The Polytrichums are among our commonest mosses 

 and are easily recognized as a genus, although the 

 species cannot always be determined unless fruited. 

 The opaque character of the leaves is due to thin, longi- 

 tudinal strips of tissue called lamellae, standing on edge 

 and running parallel to one another along the leaf, 

 forming what appears to be a wide midrib. This inter- 

 esting characteristic is best seen in cross-section of the 

 leaves under a compound microscope (Plate VII, Fig. 

 3). The lamellae also occur on the leaves of Pogona- 

 tum and Catharinaea, though much reduced in number 

 in Catharinaea. They are easily seen with the aid of a 

 hand-lens on the leaves of C. anguslata, p. 158. 



