of Pilularia globulifera , L. 
253 
found to be decidedly convex above, in consequence of more 
active growth on the upper side, and the young ground-tissue 
is much more strongly developed than on the ventral side, 
where there was but a single layer of cells separating the 
young epidermis from the young vascular bundle. The inner 
procambium-cells at this stage have increased considerably 
in length, and begin to show the pointed ends character- 
istic of the elements of the mature bundle, but no tracheids 
are yet distinguishable, these appearing first about the ninth 
day. 
The Root-quadrant. 
The first wall in the root-quadrant (PL XIV, Fig. 5) forms 
an angle of about 6o° with the basal wall, and thus divides the 
quadrant into two unequal tetrahedral cells. The larger of 
the two is the future apical cell of the root, and from the first 
it forms regular series of segments, but at the beginning only 
the lateral faces give rise to segments, that is, three series only 
are developed, the first segment of the root-cap being cut off 
only after about two complete sets of lateral segments have 
been formed (PL XIV, Figs. 12-16#). The apical cell of the 
root is from the first very conspicuous, and immediately re- 
cognizable as such. By the fourth day there have been two 
segments cut off from each lateral face of the apical cell, and 
the first segment of the root-cap has also appeared. The cell- 
division in the segments is very regular, and corresponds with 
what has been observed in other Pteridophytes. The first 
wall in the lateral segment (PL XIV, Fig. 20, I, 11) is perpen- 
dicular to the broad faces of the tabular segment, and divides 
it into two nearly, but not quite, equal cells, as the wall does 
not extend quite to the centre, but meets one of the lateral 
walls a short distance above it. Each of the cells thus formed 
next divides by a tangential wall into an inner and an outer 
cell, the former giving rise to the cells of the plerome-cylinder, 
the latter to the epidermis and periblem. 
An excellent idea of the succession of the divisions can be 
had by making a series of cross-sections through the tip of the 
