— 55 — 



2a. Marginal 2 or more rows of cells at leaf-middle irregular; (3) leaf-margin 

 incurved, serrulate; (4) seta pale red, 3-3.5 cm. long; (5) stems up to 

 150 mm. long. 



Ditrichum giganteum^ Wms. — 'Yukon to Mont.; Mich., Minn. 



Plate XII. — Ditrichum giganteum 

 (i) Plant, X about i. (2) Leaf-tip, X about 350. (3) Perichaetial leaf, X 

 about 18. (4) Leaf, X about 22. (5) Cells of leaf-middle, X about 350. — (After 

 R. S. Williams.) 



2b. Marginal 2 or more rows of cells at leaf-middle rectangular, 2-8 times 



as long as wide; (3) leaf-margin incurved, entire to faintly serrulate; 



(4) seta pale yellow, 1-2 cm. long; (5) stems up to 5 mm. long; spores 



21-27 in all our other species 14 or less. 



Ditrichum schimperi^ (Lesq.) Paris — B.C. to Calif, 

 lb. Leaves 1-3 mm. long, only the longer reaching 3 mm. 



2a. Marginal 2 or more rows of cells at leaf-middle isodiametric or nearly 



so, irregular; (3) leaf-margin incurved, entire or with a few teeth 



^ D. flexicaule longifolium Hag. 

 ® Leptotrichum schimperi Lesq. 



