14 American Midland Naturalist Monograph No. 6 



present; leaf-cells rectangular below, rhomboid-hexagonal above 



Bryum, p. 127 



5 1 . Sporogonia often several in a cluster; stems erect from rhizome-like stolons; 

 annulus present; median leaf-cells rhomboid-hexagonal with pitted walls 



Rhodobryum, p. 134 



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. 120 



53. Leaves on the sterile stem not thus arranged 54 



54. Leaves distichous, closely imbricate, carinate-plicate; stems radiculose and 



bulbiform at base Bryoxiphium, p. 68 



54. Leaves not as above; stem not bulbiferous at base 55 



55. Leaves ecostate; seta less than 1 mm long; operculum apiculate 



Hedwigia, p. 171 



55. Leaves costate; operculum rostrate 56 



56. Capsule smooth, terminating the main axis; plants often on calcareous 



rocks 57 



56. Capsule ribbed, borne on a short lateral branch;' plants not often on cal- 

 careous rocks Amphidium, p. 101 



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. 81 



57. Leaf-margins always plane: upper leaf-cells densely papillose and obscure; 



columella remaining in the capsule after the ojjerculum falls away 



Gymnostomum, p. 80 



57. Leaves canaliculate-subulate from a concave, lanceolate base; basal leaf-cells 



thin-walled rectangular, upper cells isodiametric incrassate Seligeria, p. 53 



58. Calyptra cucullate; cells isodiametric above the middle of the leaf (see 



also Astomum) Pottia, p. 89 



58. Calypra mitrate; cells elongated above the middle of the leaf 59 



59. Capsule immersed and sessile, splitting equatorially and without very specially 



modified cells at the line of dehiscence Aphanorhegma, p. 115 



59. Capsule exserted on a lon^ seta, or, if immersed, ojxrculate with 1-3 rows of 



denser cells below the line of dehiscence Physcomitrium, p. 117 



60. Capsule symmetric; peristome single 61 



60. Capsule unsymmetric; peristome double, the inner in the formi of a short 



conical tube 64 



61. Peristome teeth 4 Tetraphis, p. 158 



61. Peristome teeth 32 or 64 62 



61. Peristome teeth 16 Trichostomum, p. 82 



62. Capsule usually square or hexagonal; calyptra densely hairy; teeth gener- 

 ally 64 PolytTtchum, p. 166 



62. Capsule cylindrical; teeth 32 63 



63. Calyptra densely hairy; leaves not crisped when dry; protonema persistent 



Pogonatum, p. 165 



63. Calyptra cucullate, almost smooth; leaves crisped when dry Atrichum, p. 159 



64. Leaves green, costate, conspicuous; capsule sessile and immersed 



• Diphyscium, p. 155 



64. Leaves almost microscopic, colorless; capsule exserted on a thick, red stalk 



Buxbaumia, p. 156 



B. Pleurocarpi 



65. Leaves distichous, dorsally wmged and clasping at the base Fissidens, p. 69 



65. Leaves plun-seriate, or, if distichous not clasping at the base 66 



66. Cilia none; segments none, irregular, or rudimentary, or filiform and not 



