THE POLYTRICHACE^ OF WESTERN NORTH AMERICA 



321 



7. Polytrichum yukonense C. & Ther. in Proc. Wash. Acad. Sci. 



4: 329 (1902). 



Named after its locality, the Yukon river in Alaska. 



Plants 5-8 cm. high. Stems simple or nearly so, rather naked 

 below, base covered with white tomentum. 



Leaves rigid, when dry suberect, when damp erecto-patent, 4-6 

 mm. long, i mm. broad, shortly linear-acuminate from an appressed 

 yellowish sheath. Margin erect, entire. Lamellae about 30, mar- 

 gins crenulate, 8-12 cells high. Vein excurrent as an opaque red 

 entire arista; marginal cells higher than the others, deeply grooved. 

 Otherwise unknown. — Yukon River, Alaska. 



Fig. 26. Polytrichum sexangulare. 



1 = Moist plant, X i. 2 = Dry plant, X i. 3 = Capsule with calyptra, immature, 

 X 5. 4= Capsule, X 5. 5 = Peristome, X 150. 6 = Leaf showing lamellae on upper 

 surface, X 15. 7 = Leaf tip, showing teeth at back, and involute margins making it 

 cucullate, X 65. 8 = Cross section of leaf showing lamellae, X 65. 9 = Cross section 

 of a few lamellae, X 250. (Nos. 6 and 7 after Dixon and Jameson.) 



8. Polytrichum sexangulare Floerke, in Hoppe Bot. Taschenb. 



1799. p. 126. 



Name derived from sex = six, and angularis = angled; referring 

 to the 6-angled capsule. 



Plants 2.5-10 cm. high, in tufts or loose patches. Stems erect or 

 decumbent, simple or slightly divided, rigid, not tomentose at base. 



