02 Rhodora (June 
In its variability B. denudata is a close rival of B. tricrenata. It 
is perhaps advisable, therefore, to base our conception of the species 
on vigorous specimens, since these may be assumed to approach the 
typical condition more closely than delicate and poorly developed 
specimens. Even in well-developed material the plants grow in 
depressed mats, the individual stems being prostrate or slightly 
ascending but apparently never approaching a suberect position. 
The younger portions and sometimes the entire plants are green or 
yellowish green and do not show the brownish pigmentation of the 
cell-walls, which constitutes so striking a feature of B. tricrenata. 
In the older portions a dull brownish hue occasionally becomes 
apparent, but this seems to be associated with age and death rather 
than with an active process of pigmentation. 
The stems, so far as the living portions are concerned, are mostly 
1-1.5 em. long and measure (with the leaves) 1-2 mm. in width. 
At irregular intervals branches of the Frullania type, diverging at a 
wide angle, are produced; while flagelliform branches, arising in the 
axils of the underleaves, are rare or abundant according to circum- 
stances. Occasionally a flagelliform branch gradually becomes 
transformed into a leafy branch as it increases in length, and a leafy 
branch may sometimes spring directly from the axil of an underleaf, 
showing that the distinction between leafy and flagelliform branches 
is by no means stable. Rhizoids are sparingly produced; in most 
cases they grow out from the basal cells of the reduced leaves on the 
flagelliform branches, but in very rare cases may take their origin 
from the basal cells of ordinary underleaves. 
The leaves are distant to somewhat imbricate. They spread 
widely, usually at a right angle, and lie in approximately the same 
plane. In most cases the leaves are flat but they are sometimes 
more or less convex when viewed from above. They vary in form 
from short-ovate to oblong-ovate, measuring in most cases 0.6-0.8 
mm. in length by 0.4-0.6 mm. in width, and are slightly or not at 
all faleate. The upper margin is more or less arched from a scarcely 
rounded base, while the lower margin tends to be more nearly straight, 
in rare cases showing a vague basal expansion. The apices are so 
variable that it is difficult to determine what represents the most 
typical condition. In some cases the leaf tapers gradually to an 
acute or obtuse point, but it is much more usual for the apex to Le 
broad and rounded or truncate. Under these circumstances there 
