1897 | NORTH AMERICAN SPECIES OF AMBLYSTEGIUM 269 
ExsiccaTl: Amblystegiuin serpens var. irriguum Austin, Musc. App. 
375. 
TYPE in Herb. Wilson. 
Gametophyte bisexual, of medium size or larger, closely ces- 
pitose, usually dark green, sometimes light green or yellowish 
or brown: stems rigid, prostrate or ascending, irregularly sub- 
pinnately branched, 2° to 6™ long, 200 to 350m in diameter, 
cylindrical ; central strand well differentiated, 25 to 40m in diam- 
eter of sixteen to twenty-five rows of cells; cortex of three or 
four layers of cells, 6.5 to 13m in diameter, walls strongly 
thickened, cells of ground tissue abruptly enlarged just within 
the cortex and increasing uniformly toward the center of the 
stem, reaching the greatest size near the central strand, 18 to 38.5 
in diameter; branches in the looser forms creeping or ascending, 
erect or ascending in the compactly growing patches, 0.5 to 3™ 
long: leaves deltoid ovate, or ovate lanceolate, 400m wide by 
1000 long, in large forms reaching 1500 long, more or less 
cordate and decurrent, reaching greatest width in basal fifth, 
occasionally just above the line of insertion, acuminate, subser- 
rulate, open-erect or spreading, frequently subfalcate and subsecunad, 
costate to near the apex of the wsually long and slender acumen, 
costa strong, thick, one-fifth to one-third the entire leaf base at line 
of insertion, 60 to 8 5 wide, tapering uniformly to the tip of the 
leaf, biconvex, in the dry condition leaf points slightly incurved, 
otherwise as in the moist condition; leaf cells parenchymatous at 
base, prosenchymatous above, usually one row of cells across the 
base of the leaf much enlarged, 13 to 21.5 wide by 30 to 55 long, 
cells immediately above these short-oblong, 13 wide by 21.5m 
long, narrowing rapidly and becoming prosenchymatous at the 
Steatest width of leaf, the cells in the alar regions (excluding 
the row of large cells at base) slightly transversely elongated, 
quadrate or short oblong, soon becoming oblong or rhomboidal 
above, 12 to 16 wide by 9 to 20m long, cells in the middle and 
upper parts of the leaf rhomboidal or hexagonal, the former 8.6% 
wide by 31.5 long, occasionally somewhat narrower, 64 wide 
by 40m long, the latter 9.5m wide by 43» long; perichetial 
