650 Lewis. — The Life History of Griffithsia Borne.tiana . 
nor is its formation visibly associated in any way with nuclear division. 
The membrane is, however, never formed until there is an accumulation of 
nuclei and cytoplasm in the tip of the cell. The young cell, at first a solid 
cap over the tip of the apical cell, grows rapidly, soon acquiring a central 
vacuole (Fig. 36), and forming a typical vegetative cell. During the growth 
of the young cell, the cross-partition loses its convex appearance and 
becomes flattened. It becomes overlaid on each side by a cellulose wall, 
which does not cover the membrane completely (Fig. 37). There is left in 
the centre a circular area or pit, which is noticeable because of the early 
development of the cytoplasmic plugs described on page 642. 
This is a very unusual method of cell-division in coenocytes (Davis, 25 , 
pp. 452-3). So far as I know, it has been described in detail in no other 
form, though a somewhat similar process appears to take place in the large 
vesicles of Valonia (Schmitz, 67 ). 
The details of the division which gives rise to a lateral branch are very 
similar to those of the division of the apical cell. The daughter-segments 
of the subterminal cells are formed on the side of the upper border of 
the cell, usually four or five cells from the apex. There is first a solid 
accumulation of protoplasm, then the adjoining cell-wall bulges outward, 
and a dome-shaped membrane cuts the outer part of the protoplasmic mass 
from the inner, precisely as in the division of the apical cell. The young 
segment pushes out and becomes cylindrical, a vacuole early appearing in 
its middle, and forms the apical cell of a new branch (Fig. 38). The branch 
thus initiated grows for a time more rapidly than the main filament, until it 
about equals it in size. Thus an apparent, or false, dichotomy results. 
True dichotomy appears never to occur, as in no case has a branch been 
found to divide longitudinally. Frequently more than one branch is laid 
down at a node, so that trichotomy results, and in the larger cells near the 
base of the plant, four branches have been observed to proceed from the 
summit of the same cell. 
A second method of cell-division occurs commonly in the apical cells 
of the smaller branches, and sometimes in the division of the larger cells 
below the apex. A ring of cellulose projects inward from the cell-wall 
a short distance from the apex, very much as was described for Cladophora 
by Strasburger ( 77 ) (Figs. 39, 40, 41). The ring grows inward, but not so 
as to cut off the new cell completely. An open circular pore is left in the 
centre, across which the protoplasmic plugs are soon formed in the usual 
way. No pit-closing membrane is formed between cells separated in this 
manner. 
The second method of division, which is the usual one in coenocytes, 
differs from the first in that the daughter-cell is from the beginning much 
more nearly equal in size to the cell from which it is cut than is the case in 
the first method of division. 
