(129) 
PLAGIOBRYUM ARGENTEOIDES R. S. Williams sp. nov. 
With the appearance of Bryum argenteum. In dense 
tufts up tor cm. high. Stems simple or branching, vineous 
red, radiculose below, in cross section showing an outer wall 
of one layer of irregular, somewhat thick-walled cells, with 
ground tissue of very large, thin-walled cells, becoming 
smaller toward center and enclosing a distinct central strand. 
Leaves concave, appressed, broadly ovate, with short abrupt 
point, entire, mostly } mm. long or less or occasionally the 
terminal leaves lanceolate pointed and up to 1 mm. long. 
Costa vanishing from } to? up. Upper 4 of leaf usually 
hyaline. Alar cells and most basal cells square (sides 12 to 
16 mm.) to short rectangular (z to 2). Median cells irregu- 
larly rhomboidal to oblong-linear, up to .040 or .o50 mm. by 
.or2 mm. Cell walls somewhat thickened, especially above. 
(Plate 21.) 
This species is distinguished from the preceding by its 
small size and nerve vanishing far below the apex as well as 
by the short, square alar cells. Found on bare rock in dry 
places on the Yukon River, just below Dawson, March 19, 
1899 (659). 
Karl Mueller described in Flora, 70: 221, 1887, a Bryum 
bullatum, which he compares with small Plagzvobryum Zier. 
As this comparison well fits my plant I was in some doubt as 
to the two being distinct, but having lately received a speci- 
men of duld/atum from the Mueller collection, through the 
kindness of the Berlin authorities, the two plants prove to be 
perfectly distinct, du/latum being an Anomobryum (Sclero- 
dictyon) as described. 
Mnium medium B.& S. Left bank of the Klondike River 
just below Bonanza Creek, not common, also collected at 
Skagway, growing abundantly under the heavy evergreen 
forests. Cell walls thickened and pitted, cells somewhat 
elongated, not in oblique rows, stomata immersed (661). 
Mnium rugicum Laur. Head of Lake Bennett. In 
these specimens the leaf-cells are somewhat obliquely elon- 
gated but not inrows. The leaves are narrow at base, not 
decurrent and without distinct rectangular basal cells, the 
margin with very small irregular teeth or entire (662). 
