68 Rhodora [APRIL 
structure of the midrib in Metzgerta and in the remarkable South 
American genus Pferopsiella as described and figured by Spruce.’ 
The leaves are usually small and rudimentary at the base of a stem 
or branch, then increase rapidly in size toward the middle and become 
smaller again toward the apex. They vary from distant to loosely 
imbricated and spread widely from the axis, sometimes at nearly a 
right angle. In the median region, where they are most normally 
developed, they are ovate to broadly ovate in outline, 0.75-1.2 mm. 
long, 0.6-0.85 mm. wide, and plane or nearly so. The postical 
margin is usually a little more curved than the antical and either 
meets the axis at a wide angle or is short-decurrent. The leaves 
‚gradually narrow out toward the apex, which is uniformly bidentate 
with sharp parallel teeth separated by an obtuse to lunulate sinus. The 
teeth are usually three or four cells long and two cells wide at the 
base, but these numbers are subject to some variation (f. 2, 6). The 
leaf-cells are large, averaging about 60 X 40 u, but there is usually 
a sharp contrast between them and the lateral cortical cells, since 
the long axes of the latter extend in a different direction. The walls 
of the cells are either thin throughout or uniformly thickened and do 
not show distinct trigones. The free walls on both leaf-surfaces are 
characterized by being minutely verruculose, the walls in the other 
New England species being smooth throughout. 
‘The underleaves are distant and minute, measuring about 0.2 mm. 
in length and 0.25 mm. in width. They are sometimes appressed to 
the axis, sometimes more or less spreading and sometimes completely 
reflexed and give rise to a large number of long rhizoids. They are 
rectangular or trapezoidal in outline and deeply bifid with a lunulate 
sinus, the divisions being more or less divergent and acute. Each 
division is tipped with a hyaline papilla and bears a small and sharp 
tooth, also tipped with a papilla, on the outside. The underleaves 
are fairly definite in structure; each division is usually two or three 
cells wide at the base and three or four cells long, and the lateral 
tooth, which arises directly from the broad base, is usually composed 
of a single cell (J. 8). In the basal and apical regions of the stem the 
structure of the underleaves becomes somewhat simpler. ‘The inflores- 
cence in C. Sullivantii is dioicous but the sexual branches afford no 
differential characters of importance, and the perigynium and sporo 
phyte are still unknown. 
1 Hep. Amaz., et And. 390. pl. 16. 1885. 
