— 67 — 
but the other cells have thicker walls than usual and the trigones are distinctly 
larger. Even here, however, the trigones run out to acute points and have con- 
cave sides, so that the boundaries between the trigones and the thinner parts 
of the wall are not distinct. 
The conditions found in N. rubra may now be considered. In what may 
be regarded as the typical form of the species, such as the material collected at 
Renton, Washington, by Frye (No. 22 ), the leaves appear bordered (Plate II, 
fig. 7), but the marginal cells are distinguished less by their size than by the 
peculiarities of their walls. According to a series of measurements the marginal 
cells average 24/* in width and the submarginal 22/z; toward the base the usual 
increase in size is apparent but is more gradual and less marked than in typical 
N. crenulata, the median cells averaging about 30X25/*. The walls of the mar- 
ginal cells are thickened, much as in N. crenulata , and thin places can be dis- 
tinguished in the radial and inner walls, leaving large and sometimes confluent 
trigones; but the latter usually show straight or convex sides. The trigones are 
somewhat smaller along the inner walls of the submarginal cells, becoming still 
smaller farther inward, and yet they are distinct almost everywhere, and their 
sides often bulge strongly. They are thus distinctly bounded off from the thin 
places and differ in this respect from the trigones of the Alabama N. crenulata. 
The cuticle is striolate-verruculose and thus offers no points of distinction. 
In a specimen collected by Macoun at Hastings, British Columbia (No. 1245) 
the measurements of the marginal and submarginal cells are about the same 
as in the Washington specimen, but the thickenings of the wall are less pro- 
nounced. Even here, however, the trigones are distinct and sometimes show 
convex sides. In Underwood’s specimens from California (Hep. Amer. 200) 
another type of variation is to be observed. Both the marginal and submarginal 
cells are a little larger, averaging respectively 30 and 27/*, while the median cells 
measure about 32X24/*. In some of the leaves the trigones are just as distinct 
as in the Washington specimen, but in many of the older leaves they have be- 
come obscured by the deposition of additional layers of thickening. This con- 
dition is by no means confined to Californian specimens. It occurs also in a 
plant collected by Macoun at Ucluelet, British Columbia (No. 72), where it 
seems to be associated with a pigmentation of the wall. 
It will be seen from this account that the leaves of the more robust and 
typical forms of N. rubra are distinguished by very slightly enlarged marginal 
cells and by distinct trigones usually with bulging sides. In the typical form 
of N. crenulata , on the other hand, the leaves are distinguished by greatly en- 
larged marginal cells and by minute and often poorly defined trigones, usually 
with concave sides. If these distinct features are regarded as culminating con- 
ditions, they may well serve as the basis for a specific separation, even if poorly 
developed forms sometimes approach each other closely. 
Aside from the differences in the leaf-cells there are certain differences in 
habit and in the disposition of the leaves on the stem, which deserve a few words 
of comment. In N. crenulata the stems usually cling very closely to the sub- 
stratum, and rhizoids are found close to the growing tips; in N. rubra the older 
