THE POLYTRICHACEZ OF WESTERN NORTH AMERICA 321 
7. Polytrichum yukonense C. & Thér. 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, 1 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 1. 2 = Dryplant, x1. 3 = Capsule with calyptra, immature, 
X 5. 4=Capsule,X5. 5 = Peristome, X 150. 6 = Leafshowinglamelle 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 lamella, 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. 
E7990.  p. 120: 
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. 
