THE BRYOLOGIS 



Vol. XX July, 1917 No. 4 



ILLUSTRATED KEY TO THE WESTERN DITRIGHAGEAEi 



T. C. Frye 



Key and Comparison of the Genera 



la. Seta .4-1 mm. long, not projecting above the upper leaves; lid none; peristome 

 none; (2) leaves not 2-ranked; (3) teeth none; (4) leaves ovate or lanceolate 

 at base, subulate or mucronate at tip; capsule ovoid-apiculate, not stru- 

 mose, not grooved; (5) leaves not glaucous, not circinate nor secund. 



I. Pleuridium 



lb. Seta 5-40 mm. long, usually projecting above the upper leaves; lid present; 

 peristome of 16 often split or perforate teeth. 

 2a. Leaves 2-ranked; (3) teeth perforate to regularly bifid or trifid, the joints 

 not thickened; (4) leaves subulate from a broader base; capsule cylindric 

 or ovoid, not strumose, not grooved; (5) leaves not glaucous, not cir- 

 cinate nor secund. 2. Swartzia 

 2b. Leaves not 2-ranked. 



3a. Teeth regularly bifid, the joints thickened. 



4a. Leaves subulate; capsule narrowly cylindric, not strumose, not 

 grooved; (5) leaves not glaucous, circinate. 3. Trichodon 



4b. Leaves lanceolate or mucronate; capsule ovoid, strumose, grooved; 

 (5) leaves not glaucous, not circinate nor secund. 4. Ceratodon 

 3b. Teeth irregularly split, slender, papillose, the joints not thickened; 

 (4) leaves lanceolate to subulate; capsule ovoid to cylindric, not 

 strumose, smooth or slightly grooved. 

 5a. Leaves glossy, often secund and subulate. 5. Ditrichum 



5b. Leaves glaucous with a waxy bloom, not secund. 6. Saelania 



Key to the Genera, Based on Vegetative Plants 



A. Leaves glaucous with a white-filamentous or granular dorsal surface; cells 

 of leaf-apex quite long and narrow in the lower leaves. 6. Saelania 



AA. Leaves not glaucous; cells of leaf-apex shorter for the width than in A. 

 B. Leaves lanceolate, not subulate, green but not glossy; cells of the leaf- 

 middle isodiametric. 4. Ceratodon 

 BB. Leaves lanceolate-subulate or narrower; most species but not all with 

 cells of leaf-middle 2 or more times as long as wide. 

 C. Leaves 2-ranked; cells of the leaf-middle irregular. 2. Swartzia 

 CC. Leaves not 2-ranked. 



D. Cells of the leaf-middle irregular or roundish or square. 5. Ditrichum 



^ Geographically this paper covers the region from the Rocky Mountains to the Pacific Ocean 

 from Mexico to the Arctic Ocean. The aim has been to make useful what is already known, rather 

 than add to our knowledge of the group. The work of E. G. Britton in "North American Flora" 

 has been specially helpful. 



The May number of The Bryologist was published May 29, 19 17. 



