MODE ОЕ GROWTH ОЕ BALLIA CALLITRICHA.  - 228 
. portion is now itself about twice as long downwards as broad. This point attained, now 
another septum is formed, of peculiar curvature, and stretching into the cavity of the 
large ovate new extension thereto, and thus, whilst it cuts off the larger portion, still 
leaves the ramification-cell of the third degree larger than it was originally—in fact, 
nearly twice the size. Having progressed so far in the examination, the structure 
becomes more and more difficult to follow. However, the septum last mentioned seems 
to take a curve from a point opposite to the sudden outer doubling back of the wall, and 
with a considerable sweep (something like the curved hook of a “ note of interrogation ”’) 
then passes quickly round to a point pretty nearly opposite the lower angle of the rami- 
fication-cell of the first degree. Thus the ramification-cell of the third degree, viewed in 
connexion with the portion added to it, has acquired a somewhat sigmoid curvature, the 
extremities broadly rounded ; or it presents the figure of a subcylindrical cell with bluntly 
rounded apices, somewhat suddenly twice bent near the middle. Now, in the lower portion 
сиё off (after forming this curved cell, and not belonging thereto) we have the first cell 
of a dependent appressed filament, thereafter elongating and repeatedly subdividing by 
oblique septa, and contributing to form the cortical stratum described. The cells go on so 
growing until they reach the node below, and there seem to divaricate. But the bent cell 
above seems to have more to do: it sends a protuberance out from each side (that is, towards 
each “ front ” of the flat frond of the Ballia plant), each of these forming a basal joint of 
further dependent cortical filaments, which, by passing downwards somewhat obliquely, 
cover more of the front of such main stems and principal rachises as proceed to this 
development (cort. cell 2, figs. 17, 18). At what point the very first septum is formed 
I could not make out exactly. Arguing from the analogy afforded by the mode of 
branching lower down, Г suppose a septum is very early interposed upon the formation 
_ of a convex expansion, at both “ fronts ” (of the frond) of the lower portion of the bent 
cell—such septum eutting off that portion as the first joint of the cortical filament, which 
is dependent at each side of that previously described, these two having the latter between 
them, one running down on one front of the frond, the other on the other aspect. 
It seems, however, sometimes to happen that no septum is formed in the ramification- 
cell of the second degree, and thus no portion thereof is cut off behind as useless; but the 
process described can go on, this omission notwithstanding. There is then no ramifica- 
tion-cell of the “ third ” degree formed. That of the second degree having had cut off 
from it the first cell of the lower accessory branch, proceeds to develop from its basal 
portion, by the outgrowing thereof and formation of the curved septum as described. The 
extreme lateral cortical filament, and at both front surfaces (of the frond), gives off the 
protuberances (keeping the former between them as described), which grow into further 
cortical filaments, directed more across the front aspects of the rachis as described. 
The mode of branching of the dependent cortical cells is by repeated dichotomy. Close 
to the rounded apex of the terminal cell two septa are formed (making a У); these оз 
course cut off two chords or cells of at first plano-convex figure, which, expanding and 
` elongating downwards, grow side by side as the first joints of two collateral branches. 
As the filaments grow downwards, occasionally thus branching, they cover first the 
margins, then more and more of the frontal surfaces of the stem; and they keep closely 
212 
