THE POLYTRICHACE.E OF WESTERN NORTH AMERICA 315 



grooved. Vein scarcely or shortly excurrent, the point smooth. 

 Cells in limb between lamellae and margin mostly .012 by .016 mm. 

 to .016 by .020 mm.; cell walls on back of leaf not thickened. 

 Otherwise unknown. Lake Lindeman, Yukon region of British 

 America; Norway; Iceland. 



5. Polytrichum commune L., in Sp. PL II, p. 1109, (1753). 



Commune = common. It is quite common in Europe where 

 Linnaeus found it. 



Plants very tall, 5-45 cm. high, in large loose cushions, deep green 

 tomentose at base; male plants shorter, with longer leaves, repeat- 

 edly proliferous from the center of the antheridial disk or cup. 

 Stems simple, rarely forked, flexuose, wiry. 



Upper leaves very long, squarrose or recurved when moist, erect 

 and appressed when dry, with the apex flexuose, rather laxly ar- 

 ranged, very long, suddenly narrowed from an oblong sheathing 

 base; limb lanceolate, gradually narrowing from its base upward 

 to a sharp dentate acumen. Margin densely and sharply serrate 

 to the base of the limb, very narrow, of about i row of small cells. 

 Lamellae about 60, low, thickened at the upper border and chan- 

 nelled, 4-6 cells high; marginal cells broader than the others, de- 

 pressed in the center and bicuspidate in section. Cells of leaf- 

 base and of margin similar to those of P. attenuatum. Perichaetial 

 leaves more distinct than in P. attenuatum, long-sheathing membran- 

 eous, without lamellae, ending in an arista formed by the excur- 

 rent vein. 



Calyptra large, golden-brown, descending below the capsule. 



Capsule at first erect, when ripe reddish-brown and horizontal, 

 4-angled, with the two lateral angles usually larger and more prom- 

 inent than the upper and lower, slightly flattened, shortly rectangu- 

 lar or almost cubic ; hypophysis discoid, very distinct, narrowly con- 

 stricted above; surface cells each with a high conical papilla bear- 

 ing a small narrowly-elliptical or slit-shaped pore at the apex. Lid 

 with short rostellate beak. Pedicel 6 - 10 cm. long, stout. On soil. 

 Between Cook Inlet and Tanana River, Kodiak Island, and Sitka, 

 Alaska; Dawson and Lake Lindeman in Yukon region of British 

 America; Washington; Oregon; Eastern United States and British 

 America; Europe; Asia; Australia; South America. 



