OF DENISON UNIVERSITY. 
167 
a series of rows, or on account of the disturbing influences of the 
structure next to be described. Between the cell rows at variable dis- 
tances over the frond are distributed a number of raised lines which 
are more or less connected with each other and have the appearance 
of a branching structure trailing over the surface of the frond. These 
may become quite conspicuous and form a marked feature of the frond, 
but they do not seem to have any very intimate connection with the 
rest of the frond. This they very frequently show by entirely weather- 
ing away from the surface of the frond. The place they occupied is 
then marked by a groove which becomes quite conspicuous in the 
specimens which were characterized by large raised lines. These 
raised lines extend along the grooves between the cell rows usually in- 
cluding and resting upon the inner half of the cells between which 
they extend. Usually they leave the arrangement of the cells unaf- 
fected, but the arrangement of the rows may be more or less disturbed 
in crossing these lines. At the junction of the raised lines, especially 
where several lines meet, the cells are apt to be more separated at this 
point than elsewhere on the frond ; the cells then frequently become of 
somewhat larger size, are more prominent, and form slightly elevated 
clusters of moderate size, over the surface of the frond, which some- 
times occur at quite regular intervals and form conspicuous features of 
the frond. When the raised lines in such specimens were quite nar- 
row and then weathered away, these low elevations are still more con- 
spicuous. The center of the elevations is frequently marked by an ir- 
regular, non-celluliferous portion where the lines meet ; these spaces 
then may suggest maculae. The prominent surrounding cells of the 
elevated parts, are frequently crowded back upon each other for a short 
distance by the dividing ridges and then also are more inclined to form 
conspicuous elevations. The apertures of the cells are produced in 
the form of round papillae above the surface of the frond. The mouth 
is situated at the very summit of the papillae, but may appear more or 
l«ss lateral by the unequal wearing away of the cells. Near the base 
on one side of the cell may be found a small depression, the precise 
nature of which is unknown. It may have had some connection 
with the interior of the frond, but such connection has not been estab- 
lished. No interstitial tissue has been satisfactorily determined. The 
cells vary from 50 to 60 in the distance of 25 mm. In R. iiibulosa, 
Hall^ they are said to be more crowded, numbering from 80 to 85 in 
the same distance. 
