EvANS: HEPATICAE OF PUERTO RICO 255 
minute size and also because they frequently occur in admixture 
with other bryophytes. 
The various species of Cololejeunea have slender and fragile 
stems which branch irregularly according to the typical Lejeunea 
type. They cling closely to the substratum by means of rhizoids, 
which are borne in clusters, one at the base of each leaf. In some 
cases the leaves are loosely imbricated but it is much more usual 
for them to be separated. The lobes are attached to the axis 
along an exceedingly short line which is almost transverse. The 
same condition is found in Leptocolea, Aphanolejeunea, and Di- 
plasiolejeunea and is in marked contrast to the method of attach- 
ment found in most of the other genera of the Lejeuneae, where the 
line is long and oblique. The lobes exhibit considerable diversity, 
not only in form but in the finer details of structure. They are 
more or less convex and spread widely from the axis, which is some- 
times partly covered by the arching bases. In outline the lobes 
vary from broadly ovate to lanceolate, the apex showing all 
gradations from rounded to acuminate. The margin is usually 
crenulate or denticulate from projecting cells but is occasionally 
entire. 
The cells of the lobe are sometimes plane and sometimes convex 
or conical, and the antical surface of the lobe is smooth or rough 
in consequence. The roughness, however, rarely affects the por- 
tion of the lobe which helps enclose the basal water sac but is 
almost always restricted toa narrow or broad band involving the 
apical region and perhaps the antical portion as well. The walls 
of the cells are usually thin and delicate throughout, but in some 
cases minute trigones are developed and the wall at the tip of a 
conical cell may also be slightly thickened. Hyaline marginal 
cells and ocelli, which are characteristic of certain species of 
Leptocolea, are apparently not found in Cololejeunea. 
The peculiarities of the lobule have already been noted, but 
another foliar structure, the stylus, should be briefly alluded to. 
This is situated at the base of the lobule and usually consists of a 
hyaline papilla only, similar to what is found in the other genera 
of the Lejeuneae. In many cases, however, the hyaline papilla 
cuts off a single cell at the base, thus making the stylus two-celled, 
while in a few species a whole series of cells is cut off and the stylus 
