THE POLYTRICHACE^ OF WESTERN NORTH AMERICA 309 



4. Arista hyaline, rough, i^ mm. or shorter. 



5. Marginal cells of lamellae ovate or flask-shaped, thickened, 

 width to height about as i :i 0-2. 

 6. Capsule about as i:i-i:J, sharply 4-angled. 

 7. Plants 3-12 cm. high, 

 c. Stems mostly branched //. P. hyperboreum. 



4. Arista hyaline, rough, 3 mm. or shorter. 



5. Marginal cells of lamelhe ovate or flask-shaped, thickened, 

 width to height about as 1:12-2. 

 6. Capsule about as i:ii-i^, sharply 4-angled. 

 7. Plants 2 . 5-4 cm. high, 

 c. Stems simple 12. P. piliferum. 



1. Polytrichum gracile Dicks., in MSS. 



Name derived from gracilis = slender; probably referring to the 

 rather tall stem, naked below. 



Plants tufted, dark green 2.5-10 cm. high. Stems matted to- 

 gether below with whitish tomentum, simple or slightly divided, 

 leafless below. 



Leaves erecto-patent, somewhat flexuous or patent when dry, 8-10 

 mm. long, the limb lanceolate, gradually narrowed to a short acumen, 

 limb usually about 4-6 cells wide in the middle of the leaf. Margin 

 erect, sharply serrate, variable in width. Lamellae about 40, 4-6 

 cells high; marginal cells about equalling the others, not papillose, 

 rounded or a little higher than wide; vein toothed above at back, 

 excurrent; point short, red, dentate. Cells of limb .015-.018 mm., 

 round-quadrate to transversely elliptical; cells of sheathing base 

 thin, rectangular, in middle of wing length to width about as i : 3-4. 

 Perichaitial leaves long-sheathing. 



Calyptra hardly covering the capsule. 



Capsule short, broadly ovate, inflated, erect, horizontal when 

 dry, with 5-6 obtuse and often obscure angles, smooth, narrowed 

 at mouth; h}^ophysis rather indistinct, hardly constricted above. 

 Teeth often confluent and unequal. Lid large with a rather long 

 beak. Snores .018-.022 mm. Pedicel 4-5 cm. long, thin, flexuous. 

 — On soil. — Kotzebue Sound north of Bering Strait, and Kodiak 

 Island, Alaska; below White Horse Rapids, Yukon region, western 

 British America; Rocky ]\fountain region of British Columbia; 

 Eastern United States and British America. 



