14 Rhodora [JANUARY 
(Huds.) M. A. Howe, and it is interesting to note that the same 
species occurs in connection with the material from New Hampshire. 
The color of O. elongatum is sometimes a bright green, but a yellowish 
or brownish pigmentation is usually present and a deep blackish 
purple hue is not uncommon. The shoots at first produce branches 
very sparingly, and the long unbranched ascending axes are a striking 
feature of the species. As the stems become prostrate with their 
increase in length, branches of the usual intercalary kind are pro- 
duced, some lateral in position and some ventral. Among the latter, 
as in other members of the genus, a few show a flagelliform char- 
acter and grow downward, holding the plant firmly in place. Except 
on these specialized branches rhizoids are sparingly developed. 
The orbicular leaves, which usually measure 0.5-0.7 mm. in diame- 
ter, are sometimes distant but more frequently contiguous or imbri- 
cated. In most cases they are distinctly concave. "The leaf-cells 
average about 20 u along the margin and about 23 u in the median 
and basal portions of the leaf. The marginal cells sometimes form an 
indistinct border, but the texture of the leaves is usually uniform 
throughout. When the trigones are well developed they are orbicular 
and project into the cell-cavities; when poorly developed they may 
be triangular with concave sides. 
Lindberg considered his variety elongatum poorly supplied with 
underleaves, but they are really better developed than in most spe- 
cles of Odontoschisma and often acquire a size of 0.2 X 0.15 mm. 
They are not very definite in outline but tend to be ovate from a 
broad base. In some cases they may be shortly bidentate at the 
apex but this condition is far from constant; occasionally an indis- 
tinct lateral tooth is present. Slime papillae are unusually abundant; 
they occur not only along the margin but also on the surfaces, being 
especially numerous on the upper or inner surface. "The writer! 
has already called attention to the constant presence of underleaves 
in Odontoschisma and has emphasized the fact that they yield specific 
characters of importance. Unfortunately, on account of their 
fragility, they are often overlooked. A clear idea of them can be 
readily obtained by dissecting off the tip of a vigorous shoot, mount- 
ing it in the usual way, and then crushing it by a gentle rubbing 
pressure on the cover-glass. In this way the underleaves can be 
separated from the other parts and examined by themselves. Since 
1 Bot. Gaz. 36: 330. 1903. 
