1919] Evans,— Notes on New England Hepaticae,—XV 161 
Although N. obscura descends into the lowlands it is more at home 
in the hills and lower mountains, not ascending above the tree line. 
It prefers steep rocks in dark shaded ravines, especially where trickling 
water is present during a part of the year; and the creeping stems and 
stolons cling so closely to the substratum that it is difficult to separate 
them. In some cases a sandy sediment collects about the plants, 
only the tips protruding. In its choice of a habitat it therefore differs 
from N. hyalina,* which prefers the lowlands and is almost never 
directly attached to rocks, growing by preference on sandy banks or 
in similar situations. There are also certain differences in color to 
be observed: in N. obscura the color is originally a bright green, but 
the pigmentation, which is purple rather than red, is usually present 
to a greater or less extent and not infrequently involves the entire 
plant; in N. hyalina the original color is pale or yellowish green, and 
the pigmentation, which is reddish rather than purple, is often absent 
altogether and very rarely involves the entire plant. Stolons can 
nearly always be demonstrated in N. obscura, if the plants are care- 
fully dissected apart, while in N. hyalina they are often not developed 
at all. 
In the leaves (Figs. 1—5) there are certain differences to be detected 
when the plants are directly compared, but it is difficult to describe 
them in words. Although the leaves are attached in both species by 
long oblique lines, the basal part of the leaf in N. hyalina is usually 
plane or convex, somewhat as it is in Plagiochila; in N. obscura, on 
the other hand, it shows a tendency to be appressed to the stem for a 
short distance and then sharply revolute, giving the effect of a more 
transverse attachment.  Retuse apices are perhaps a little commoner 
in N. obscura than in N. hyalina, and sometimes, when taken in con- 
nection with the purple pigmentation and the apparent subtransverse 
insertion of the leaves, produce a vague resemblance to certain species 
of Marsupella. According to the average measurements the leaf- 
cells of N. obscura are a trifle smaller than those of N. hyalina, and the 
cells are further distinguished by slightly smaller trigones (Figs. 6, 7). 
The inflorescences, both male and female, yield excellent differential 
characters. In N. obscura the perigynium equals or exceeds the 
perianth in length (Figs. 1, 2, 8), and the latter organ is composed 
throughout of more or less elongated cells and does not project beyond 
the bracts; in N. hyalina the perigynium is considerably shorter 
than the perianth, and the latter organ (at least when fertilized) is 
