(n6) 



3 mm. long). Leaf-cells above rhomboidal to hexagonal, 

 about .016 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 1 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). 



Scouleria aquatica Hook. Fine fruiting specimens col- 

 lected near Canon City, Dyea Creek. As usual in clear moun- 

 tain streams, the plants are blackish and robust. Also col- 

 lected sterile in Miles's Canon 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 conferla 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 apocarfa (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 \ 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). 



