— 50 — 



DD. Cells of the leaf-middle 2 or more times as long as wide. 

 E. Cells of the leaf-base 5-8 times as long as wide; marginal cells of 

 leaf-apex mostly 1-2 times as long as wide. 3. Trichodon 



EE. Cells of the leaf-base 1-5 times as long as wide; marginal cells of 

 apex longer than in E. 

 F. Leaves 3-7 mm. long. 5. Ditrichum schimperi 



FF. Leaves 1-3 mm. long. 



G. Leaves abruptly narrowed. 5. Ditrichum heteromallum 

 GG. Leaves gradually narrowed. 



H. Stems 2-5 mm. long; cross section of leaf-vein with 2 rows 

 of guide cells. i. Pleuridium 



HH. Stems 10-20 mm. long; cross section of leaf- vein with i 

 row of guide cells. 5. Ditrichum 



I. Pleuridium 



Plants in low dense cushions. Leaves not crispate when dry, entire or minutely 

 serrulate; vein filling most of the awn, usually rough. Calyptra cucullate. Seta 

 very short. Capsule immersed, ovoid; lid none; peristome none; spores brown, 

 rough. — (Gk. pleuridion = on one side; because the capsule occasionally appears 

 to arise laterally on the stem.) 



la. Vein rough at tip only; paroicous; perichaetial leaves gradually subulate; 

 spore surface finely granular. 



Pleuridium holande'i'^ C. Miill. — -Wash, to Calif. 



Plate IV. — Pleuridium bolanderi 

 (i) Plants, XI. (2) Plants, X3 (3) Leaf, X32. (4) Leaf-tip, X400. (5) Cells 

 from leaf-base, X^03. (6) Cells from leaf-middle, X403. (7) Capsule; c, calyptra; 

 (after Cardot aid Th'^riot) X about 13. (8) Spore, X550. 



lb. Vein rough some distance down from the tip; autoicous; perichaetial 

 leaves abruptly subulate; spore surface densely papillose. 



Pleuriiium alterni folium Brid. — Calif. ; Kan. and eastward in the U. S. 



^ P. stramineum Lesq.; P. aliernifolium howei R. & C; P. bakeri C. & Th. 



