92 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 steins 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 cm. long and measure (with the leaves) 1-2 mm. in width. 

 At irregular intervals branches of the Frullauia 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 falcate. 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 be 

 broad and rounded or truncate. Under these circumstances there 



