BABNES NORTH AMERICAN MOSSES. 223 



III. Plants usually robust (4-15 cm.), rarely small, often much 

 branched above, leaves straight when dry. 



Capsule papillose, marginal cells of lamellae round in 



section i? . .^ . * ; . . . P. urnigemm, 262. 

 Capsule smooth, marginal cells of lamellae ovate in section P. alpinnm, 1 263. 



POLYTRICHUM, p. 263. 



Leaves entire, margins inflexed. 



Obtuse at apex P. sexangulare, 369. 



Aristate at apex. 

 Awn colored, short. 



Leaves spreading when moist, subrecurved P. juniperinuin, 8 265. 

 Leaves erect-open, strict , . . . P. strictum, 265. 



Awn hyaline, long , P. piliferum, 264. 



Leaves serrate. 

 Marginal cells of lamellae like rest, oval, higher 



than broad in section. 



Capsule ovate, obscurely angled, lid rostrate . P. gracile, 264. 

 Capsule oblong, 4-6 angled, lid acutely conic P. formosum, 3 264. 



Marginal cells of lamellae enlarged, broader than 



high (2:1) P. Ohioense, 370. 



Marginal cells of lamellae semilunar, with two promi- 

 nent papillae at corners .... P. commune, 4 266. 



P. polar e C. Mull., 373; P. hyperboreum R. Br.; P. boreale Kindb.; 

 P. Icevipilum Hpe., are not included in the key since no authentic ma- 

 terial is at hand, and the descriptions are not sufficient to determine their 

 position. The first three are arctic species and their omission is compara- 

 tively unimportant. 



BUXBAUMIA, p. 267. 



Outer peristome simple, spores 5-9//. 



Capsule little longer than broad . . . . B. aphylla, 268. 



Capsule much longer than broad (1 : 2-2.5) . . . B. Piperi, 376. 



Outer peristome quadruple or triple, spores 10-16/* B. indusiata, 375. 



1 See Appendix, no. 366. 



2 See Appendix, no. 374. 



8 P. conorhynchum Kindb., evidently falls here. See Appendix, no. 368. 

 4 See Appendix, nos. 371, 372. 



