THE POLYTRICHACE^E OF WESTERN NORTH AMERICA 



i . Cell walls in upper half of leaf approaching leaf margin diagonally. 

 2. Cells about midway between base and tip .020-. 030 mm. in their 



longer diameter. 

 3. Leaves entire or nearly so. 

 4. Vein smooth at back. 



5. Capsule distinctly plicate. 



3 a 



Fig. 8. 



Comparison of Oligotrichum incurvum (upper figure) with Oligotrichum 

 incurvum var. latifolium (lower figure). 



1 and la = Leaves, upper side, one narrower than the other. In 1 the margin is 

 usually serrate where it is rolled in, X 15. 2 and 2a = Leaf-tips, one usually with 

 serrate lamellae on the back, the other not, X 65. 3 and 3a = Portions of leaves show- 

 ing difference in size of leaf cells; also the cell walls meeting the margin perpendicu- 

 larly in 3 and diagonally in 3a, X 500. 



On Soil St. Lawrence Island, Bering Sea. 7 



7 Kindberg reports this from Rogers Pass, Selkirk Mountains, B. C-, but an examina" 

 tion of this material shows that in areolation, direction of marginal cell walls, and size 

 of leaves it is nearer to the type than to the variety. The leaf margin of O. incurvum 

 sometimes approaches entirety, and the back smoothness. 0. incurvum var. lati- 

 folium is therefore known only from St. Lawrence Island. 



Proc. Wash. Acad. Sci., August, 1910. 



