(116) 
3 mm. long). Leaf-cells above rhomboidal to hexagonal, 
about .o16 mm. in diameter, becoming gradually elongated 
below and hyaline, the cells near margin a little above base 
.004—.006 mm. wide and up to .160 mm. long, toward costa 
-020-.025 mm. wide and up to .100 mm. or more long. 
Cross-sections of costa show in the ventral half about 4 guide- 
cells with a few accessory cells or even I or 2 rows of 
accessory cells nearly as large, in addition to the row of 
mamillose cells on ventral surface. The dorsal half of costa 
consists of a stereid band, the outer row of cells a little larger 
than the others with a distinct central strand of small, irreg- 
ular, thin-walled cells. (Plate 16.) 
Yukon River bluff, just below Dawson. Collected April 
6, 1899, on rock (587). 
Scoulerta aquatica Hook. Fine fruiting specimens col- 
lected near Cajion City, Dyea Creek. As usual in clear moun- 
tain streams, the plants are blackish and robust. Also col- 
lected sterile in Miles’s Cafion and in fruit on the Yukon at 
Dawson. These latter specimens are more slender and of a 
dull green color, such as are usually found in larger streams 
that become swift and muddy in high water. ‘There seems to 
be no microscopical differences between the different speci- 
mens (588) and (806). 
Grimmia conferta Funck. Marsh Lake. This plant has 
cell walls thin, not or scarcely sinuous, the upper cells 
roundish, the lower short rectangular, about 1 to 3 (589). 
Grimmia apocarpa (L..) Hedw. Lake Lindeman. Grow- 
ing in blackish tufts on perpendicular walls. This species 
has cells of leaf above, mostly oblong to square, with thick, 
sinuate, angular walls, especially near middle, toward base 
becoming hyaline and long-rectangular with thin walls. 
The leaf towards apex consists of a double layer of cells 
throughout; about 4 down the cells are double only in margin 
and here and there within (591). 
Grimmia apocarpa gracilis Web. & Mohr. Lake Linde- 
man. ‘The cell structure of the leaves is similar to the pre- 
ceding, I believe. The plant differs in being rather more 
slender, with leaves more papillose and lateral appearing 
fruit (592). 
