POLYTRICHACEAE 171 



The following Key may help to separate Polytri- 

 chum, Catharinaea, and Dicranum, the three common- 

 est genera of the acrocarpous mosses having long nar- 

 row leaves. 



Leaves more or less turned to one side (sccund), both 



when moist and when dry .... Dicrafium (p. 87). 

 Leaves equally spreading when moist; folded or crisped 

 when dry. 



Leaves folded straight against the stem when dry; 

 stems not conspicuously covered with radicles ex- 

 cept in P. strictum .... FolytricJiufn (p. 162). 



Leaves strongly crisped when dry; stems not covered 

 with radicles .... Catharinaea (p. 156). 



Leaves more or less crisped or not much changed when 

 dry; stems covered with radicles, especially in the 

 lower part .... Dicranum (p. 87). 



