1897 ] NORTH AMERICAN SPECIES OF AMBLYSTEGIUM 259 
times abruptly acuminate, acumen short, broadly costate to apex ; 
outer triangular lanceolate, erect or slightly spreading; inner 
much larger, oblong, all costate, costa distinct, excurrent, form- 
ing a slender short acumen. 
Sporophyte small to medium, 1™ (rarely less) to 3.5°™ long: 
seta slender, 180 to 240m in diameter, flexuous above, reddish 
brown at base, stramineous above; central strand well differen- 
tiated, 25 to 33m in diameter, composed of thirty to forty rows 
of cells; cortex of three to five (usually four) layers of cells 6.5 
to 13min diameter; cells of ground tissue 13 to 21.5@: capsule 
1.5 to 3™" long, cylindrical or occasionally thickest at the 
mouth, tapering regularly from there to the seta, asymmetric, 
suberect to strongly incurved, collum one sixth the length of the 
sporangium, reddish or yellowish brown, frequently of two shades, 
becoming dull dirty brown with age, when empty frequently 
strongly incurved and constricted below the mouth; cells of the 
exothecium more or less prosenchymatous on the convex side, 
23.5@ wide by §1.5u long, varying from 13 to 37m wide and 
from 30 to 82 long, parenchymatous on the concave side, 
25.5@ wide by 38.5ulong, ranging in width from 17 to 39m and 
in length from 21 to 65m, cell walls 3 to 4m thick, three to five 
rows of cells under peristome isodiametric hexagonal, sometimes 
transversely elongated, 10.5 to 25min diameter ; stomata eighteen 
to twenty-five, scattered, 424 wide by 48m long, ranging from 
37 to 47m wide and from 42 to 56m long; peristome teeth 
lanceolate, dull brown below, pale above, marginal serrulate 
above, transversely striate on the back to beyond the middle, 
above this point faintly papillose ; endostome equaling or slightly 
exceeding the teeth; membrane two thirds the length of the seg- 
ments, the latter lanceolate, carinate, split along the keel between 
the articulations though scarcely gaping, papillose, as are also the 
one to three nodulose cilia which scarcely equal the segments ; 
operculum apiculate from a highly convex or conic base; annu- 
lus ‘broad of two or three rows of cells: spores finely papillose, 
light brown, 12 to 15 in diameter: calyptra equaling capsule or 
shorter, split one half its length. 
