1903] ODONTOSCHISMA MACOUNIT AND ITS ALLIES 331 
these leafy forms, it divides by a periclinal wall into an inner 
and an outer cell, of which the latter gives rise to the papillae. 
In some cases this outer cell forms a single papilla before 
dividing. This is true, for example, of Cephalozia bicuspidata, 
Nardia hyalina, and WN. scalaris. In other cases the outer cell 
divides by anticlinal walls into two, three, or four cells, each of 
which gives rise to a papilla. In Plagiochila asplenioides, for 
example, two papillae are formed; in Acromastigum integrifolium,*s 
three; and in Bazzania trilobata, four. Ina few species without 
underleaves, such as Radula complanata and Cololejeunea calcarea, 
no primordial papillae are formed by the ventral segments; but, 
on the other hand, the mere presence of papillae by no means 
insures the development of underleaves. When the latter are 
to be formed the papillae elongate, cells are cut off from their 
bases, and these cells by irregular divisions, both longitudinal 
and transverse, give rise to the permanent cells of the under- 
leaves. In some cases there are as many lobes or divisions to 
the underleaf as there are primordial papillae, but usually the 
portions developing from the different papillae coalesce through- 
out more or less of their extent, and in some cases this coales- 
cence extends to the very apex of the underleaf, which becomes 
thereby truncate or rounded. 
In all our species of Odontoschisma two primordial papillae 
are formed and are succeeded by well developed underleaves. 
In O. Sphagni these are unfortunately short-lived, and the species 
has been described as being without underleaves or as having 
them rare and minute. As a matter of fact, they are always 
easy to demonstrate both in this species and in O. Grddsiae near 
the apex of a vegetative branch, and in our other species they 
can usually be detected in the older parts of a plant as well. 
With regard to their structure and development two types of 
underleaf may be recognized. The first is found in O. prostratum 
and O. Sphagni, the other in our remaining three species. In 
the first type, through a succession of transverse walls in the 
cells cut off at the base of the papillae, two rows of cells are 
formed, growth and division continuing for some time at the 
*S Evans, Bull. Torr. Bot. Club 27: 100. f/. 7. 1900. 
