OF WESTERN PENNSYLVANIA. IS 



51. Annulus present; leaf-cells narrowly 

 rhombic to linear; leaves green to yel- 

 low-green, often glossy Webera, p. 140 



52. Rock- or crevice-inhabiting 



mosses 53 



52. Earth-inhabiting plants 58 



53. Leaves on the sterile stems in two rows, 



forming a continuous marginal wing... Schistostega, p. 137 

 S3. Leaves on the sterile stem not thus ar- 

 ranged 54 



54. Leaves distichous, closely imbri- 

 cate, carinate-plicate; stems radicu- 



lose and bulbiform at base Bryoxiphium, p. 78 



54. Leaves not as above; stem not 



bulbiferous at base 55 



SS. Leaves ecostate; stalk less than 1 mm. 



long; operculum apiculate Hedwigia, p. zoi 



55. Leaves costate; stalk 2 to 12 mm. long; 



operculum rostrate 56 



56. Capsule smooth, terminating the 

 main axis; plants often on calcare- 

 ous rocks 57 



56. Capsule ribbed, borne on a short 

 lateral branch; plants not often on 



calcareous rocks Amphidium, p. 114 



57. Leaf-margins revolute on one or both 

 sides; upper leaf-cells clear and pellucid; 

 columella remaining attached to the 



operculum and falling away with it Hymenostylium, p. 9^ 



57. Leaf -margins always plane; upper leaf- 

 cells densely papillose and obscure; 

 columella remaining in the capsule after 



the operculum falls away Gymnostomum, p. 92 



58. Calyptra cucullate; cells iso-dia- 



metric above the middle of the leaf Pottia, p. loi 

 58. Calyptra mitrate; cells elongated 



above the middle of the leaf .• • . ^^ 



59. Capsule immersed and sessile, splitting 

 equatorially and without specially modi- 

 fied cells at the line of dehiscence Aphanorhegma, p. 131 



59. Capsule exserted on a long seta, or, if 

 immersed, operculate with 1 — 3 rows of 



denser cells below the line of dehiscence. Physcomitriwn, p. 13s 

 60. Capsule symmetric; peristome 



single ; ■ • 61 



60. Capsule unsymmetric; peristome 

 double, the inner in the form of a 



short conical tube 64 



61. Peristome teeth 4 Tetraphis, p. 184 



61. Peristome teeth 32 or 64 62 



62. Capsule usually square or hexa- 

 gonal; calyptra densely hairy; teeth 



generally 64 Polytrichum, p. 194 



62. Capsule cylindrical; teeth 32... 63 

 63. Calyptra densely hairy; leaves not 



crisped when dry ■ Pogonatum, p. 192 



63 Calyptra cucullate, almost smooth; leaves 



crisped when dry Cothannaea, p. 186 



64. Leaves green, costate, conspicuous: 



capsule sessile and immersed Diphyscium, p. 181 



