1897] NORTH AMERICAN SPECIES OF AMBLYSTEGIUM 261 
thin but distinct below, extending one half to two thirds the 
length of the leaf, one seventh to one fifth the entire width of 
leaf base at line of insertion, zwédely spreading in both moist and dry 
conditions, flat and straight or slightly concave at base, average 
leaves 300” wide by 1050u long, varying in width from 250 to 
370# and in length from 800 to 1200, leaves in smaller forms 
approaching those of A. serpens in form and size and in the larger 
forms reaching a length of 1400 to 1500 p; leaf cells short oblong, 
rectangular, or rarely quadrate across the base, prosenchymatous 
above, hexagonal in the middle, generally linear-hexagonal in the 
upper half of the acumen, longest cells usually found above the end of the 
costa, alar cells 13.4m wide by 24.4m long, varying in width 
from 10 to 17m and in length from 17 to 4o#, towards the mid- 
dle 11.34 wide by 52.4m long, ranging in width from 8.5 to 
13# and inlength from 40 to 70m, and at the apex usually a lit- 
tle longer and narrower, 10.2" wide by 63 long, varying in 
width from 8.5 to 12.5 and in length from 4o to 85, periche- 
tial leaves triangular lanceolate or ovate lanceolate, pale, strict, 
short acuminate by the excurrent costa. 
Sporophyte of medium size, 1.5 to 3™ long: seta 180 to 300 
in diameter, flexuous above, red at base, yellow or pale brown 
above; cortex of two to four layers of cells 6.4 to 17K in 
diameter ; central strand well developed, 35 to 454 in diameter, 
composed of fourteen to forty-five rows of cells; cells of 
ground tissue 13 to 35"; capsule 2.5 to 3.5™™ long, slender, 
cylindrical, asymmetric, either moderately or strongly incurved 
from an erect base, slightly constricted under the mouth 
when dry, pale at maturity, usually light brown on the con- 
vex side and yellow on the concave side, frequently becoming 
darker colored when empty, collum slender, about one-fourth 
the length of the sporangium; exothecium cells mixed prosen- 
chymatous and parenchymatous on the convex side, 34 wide by 
90m long, varying in width from 17 to 51.5# and in length from 
47 to 110M, parenchymatous on the concave side, 38.5 wide by 
O4u long, ranging from 21.5 to 56“ wide and from 30 to 9O# 
long, cell walls variable, 2 to 6 thick, two to four rows of cells 
