1903] ODONTOSCHISMA MACOUNIT AND ITS ALLIES 329 
for the thin partitions separating the cells of which they are com- 
posed. These tubes are bounded without and within by the 
thickened cuticle, and are separated from one another by the 
coalescent trigones. In the upper part of the perianth the cells 
are uniformly and only slightly thickened (fig. 2¢), and there is 
a gradual transition from these to the thick-walled cells just 
described. The thickenings of the cell walls, although found in 
all the specimens of O. Macounii examined, are especially pro- 
nounced in those from the far north. 
If we confine our attention to the median leaf-cells, our five 
species of Odontoschisma will be found to exhibit a regular 
descending series with respect to their trigones. O. Macounii 
stands at the beginning of this series. In O. Gibdsiae, which 
comes next, the trigones are still large, and the cavities are 
stellate, but the pits are broader and the trigones are less fre- 
quently confluent (fig. 37). Inthis species the trigones rarely 
show a line of demarcation, except when the portion lining the 
cavity becomes pigmented, and they also fail to respond directly 
to the cellulose test. In O. denudatum the trigones are still pro- 
nounced, but the cavities are less distinctly stellate, the trigones 
not projecting far enough out into the cavities to leave narrow 
pits (fig. 35). In O. Sphagni the trigones are smaller and project 
only slightly into the cavities, which in consequence become 
rounded in outline (fg.39). In O. prostratum the trigones are 
still less conspicuous and commonly turn a concave face toward 
the cavity, which acquires in this way a polygonal outline with 
rounded angles (jigs. 55, 56). 
Throughout the genus Odontoschisma the median leaf-cells, 
if we consider them bounded by their middle lamellae, are 
polygonal in outline and isodiametric. The marginal leaf-cells, 
however, are quadrate or rectangular in outline, and in the latter 
case the long axis of the cell is commonly at right angfes to the 
margin. In most species the marginal cells are not very different 
from the median cells, except for this slight difference in shape. 
This is true of O. Macounii, O. Gibbsiae, and O. denudatum (figs. 
7,32, 306). In other species there are several successive rows of 
four-sided cells, forming a distinct border around a considerable 
