-58- 



Ditrichum heteromallum^^ (Hedw.) E. G. B. — Alaska to Oreg.; N. H. 

 3b. Leaves somewhat revolute, gradually narrowed; (4) seta red, 1-2 

 cm. long; (5) stems up to 10-20 mm. long. 



Plate XVI. — Ditrichum heteromallum 

 (i) Lecf, X22. (2) Leaf-tip, X400. (3) Leaf-tip, X32. (4) Cells of leaf- 

 middle, X400. 



4a. Peristome-teeth bifid to base, not connate nor perforate; leaf-tip 

 wide; basal marginal leaf-cells short. 

 Ditrichum ambiguum Best — Wash, and Oreg. 

 4b. Peristome-teeth not bifid to base, more or less connate or perforate; 

 leaf-tip narrow; basal marginal leaf-cells long. 

 Ditrichum pusillum^"^ (Hedw.) Timm. — Wash., Calif.; eastern N. 

 Amer. 



Plate XVI L — Ditrichum ambiguum 

 (i) Leaf-tip, X32. (2) Leaf, X22. (3) Plant, Xi. (4) Cells of leaf-middle, 

 X400. (5) Cells of leaf-base, X400. (6) Leaf-tip, X400. (7) A split tooth of 

 the peristome, X125. (8) Capsule, X18. 



Ditrichum homomallum Hampe; Trichostomum heteromallum Lindb. 

 Leptotrichum pusillum Hampe; Ditrichum tortile Mul\.;Leptobarbula berica Mac. 



