I04 HOW TO KNOW THE MOSSES 



The two species described above are not among our 

 common mosses. The long slender leaves, becoming 

 much curled and crisped when dry, and the long, slender^ 

 erect capsule are distinguishing characteristics. If the 

 plants are found in fruit, the student will be well repaid 

 to examine the peristome with a lens. The long teeth 

 are shaded from orange-red to yellow, and are spirally 

 twisted. The peristome of Barhula (p. 105) and Tortula 

 (p. 107) is similar to that of Tortella. 



14. DIDYMODON Hedw. (Di-dym-o-don) 



A genus of many species occurring in limestone re- 

 gions. Name derived from the Greek for '' twin " and 

 " tooth," referring to the divided teeth of the peristome. 

 Didymodon rubellus (Hoffm.) Bryol. Eur. is found 

 on wet ledges and rocks, usually limestone, 

 in mountainous or hilly regions; not com- 

 mon; fruit sometimes abundant. 



Plants growing close together; bright or dark 

 green above, rusty -red below. 

 Didymodon Stems usually less than i inch long; branched. 

 rubellus Leaves hair-like; wide-spreading when moist; 



Leaf and somewhat crisped when dry; bright or dark 

 lar^ed^^ ^"" g^^^n above, rusty-red on lower part of stem. 

 Seta about ^ inch long; reddish. 

 Capsule erect, cylindrical; reddish-brown ; mature in 

 summer. 



Operculum long-beaked. 



Range, Alaska, Canada, and the northern United States; 

 Europe; Asia; Africa. 



