594 Evans: REPORT ON THE HEPATICAE OF ALASKA 
one to three broad and short teeth in the outer part; postical 
margin strongly outwardly curved and dilated toward the base, 
sharply spinose-dentate; apex broad and rounded with teeth like 
those along the postical margin; total number of teeth mostly 
twelve to fifteen, unequal and variable, pointing in various direc- 
tions, mostly acuminate but sometimes merely acute, mostly two 
to six cells long and one to five cells wide at the base; leaf-cells 
plane, averaging 14 yu in the apical portion, 22 X14 u in the middle, 
and 40X14 u at the base, walls more or less thickened with well- 
developed but poorly defined trigones, the sides being straight or 
concave; coalescence between the trigones frequent especially in 
the median and basal portions, cuticle smooth: underleaves 
minute: remaining parts not seen. (PLATE 21, FIGS. 7-9.) 
It will be seen from the above description that P. Fryei and 
P. alaskana are very closely related species and that most of the 
vegetative characters emphasized under P. alaskana are exhibited 
equally well by P. Fryei. In spite of these facts it still seems jus- 
tifiable to consider the two plants distinct. The differences 
between them are found in the form of the leaves and in the pe- 
culiarities of the marginal teeth. The leaves of P. alaskana are 
relatively narrower than in P. Fryei, the ratio of width to length 
being only 0.7-0.75 instead of 0.85-1. As in the two species of 
tropical Asia, discussed under P. alaskana, the greater relative 
breadth in P. Fryei is due to the marked dilation of the postical 
base, a feature which appears to be constant.. The marginal 
teeth in P. alaskana are more numerous than in P. Fryei and tend 
to be narrower and more sharply pointed; they extend farther 
back toward the antical base and usually spread out widely from 
the margin, instead of being variously directed. The cell-structure 
is very much the same in the two species, the middle lamellae are 
usually discernible, and the cell-measurements are practically 
ideatical. In P. alaskana the trigones are somewhat more distinct 
and sometimes have bulging sides; in P. Fryei the trigones, although 
well-developed, more frequently coalesce, thus making the walls 
appear uniformly thickened, and their sides are concave or straight. 
- These differences, however, can not be regarded as very important 
in such a genus as Plagiochila, where the thickenings in the walls 
are subject to considerable variation. 
The Asian and South American species contrasted with P. 
alaskana may be considered in connection with P. Fryei also. 
