BAKNES — NORTH AMEEIOAN 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 P. urnigernm, 262. 



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



POLYTRICHUM, p. 263. 



Leaves entire, margins inflexed. 



Obtuse at apex P. sexangulare, S69. 



Arisfcate at apex. 

 Awn colored, short. 

 Leaves spreading when moist, subrecurved P. jnniperinam,' 265. 

 Leaves erect-open, strict .... P. gtrictnm, 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. graclle, 264. 



Capsule oblong, 4-6 angled, lid acutely conic P. formosnm,' 264. 



Marginal cells of lamellae enlarged, broader than 



high (2:1) P. Ohioense, 570. 



Marginal cells of lamellae semilunar, with two promi- , 



nent papillffi at corners .... P. commune,^ 266. 



P. polare C. MtUl., 373; P. hyperboreum R. Br.; P. boreale Kindb.; 

 P. IcBvipilum 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 5-9/1. 



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



Capsule much longer than broad (1 : 2-2.5) . . . B. Piperi, 576. 



Outer peristome quadruple or triple, spores lO-lG/i B. indnsiata, 375. 



1 See Appendix, no. 366. 



' See Appendix, no. 374. 



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



* See Appendix, nos. 371, 372. 



