78 L. Beesley. 
filaments. The cells themselves are of equal diameter all ways, of a 
roughly oval or spherical shape, and show a distinct tendency to 
round themselves off from one another. 
This rounding off of the cells always begins almost exactly in 
the centre and proceeds outwards along radial lines, gradually 
breaking up the filaments into the rounded cells of darker colour. 
This breaking up, however, does not as yet reach to the end of the 
filaments. 
By this time the cells in the centre which first became rounded 
off have divided by transverse walls at right angles into four cells. 
These at first grow into about the same size as the cell from which 
they were formed and then divide again into four. This division 
goes on continuously in all the cells which have become rounded off, 
so that at this period the thallus, at first one cell thick, now pre¬ 
sents the appearance of a piled-up mass of dark-green cells in the 
centre several layers thick, surrounded everywhere by filaments 
still undifferentiated and only one cell thick. The colour contrast 
between the thickened central mass, which under a low power 
appears almost black, and the encircling lighter green filaments 
is very striking (Fig. 8). 
About this time— i.e., seven to eight weeks from the germina¬ 
tion of the zoospore—zoospores may be seen to issue from some of 
the central cells of the thallus. Apparently these zoospores are 
never produced from the encircling filaments. 
The breaking up of the filaments now begins to spread nearer 
and nearer to the edge of the thallus, until finally at one point two 
or three of the encircling filaments are broken up right to the tip 
into the rounded cells and a “break” is formed in the hitherto 
continuous margin of lighter green undifferentiated filaments. 
It seems probable that there must exist considerable tension in 
the central mass of cells, for at the point where the break is formed 
the central rounded cells “ flow out” laterally quite a considerable 
distance from the margin of the thallus (Fig. 9). 
These rounded cells are now seen to present a marked palmel- 
loid appearance, being quite separated and distinct from one 
another, and of a spherical or ovo-spherical shape. The chloroplasts 
are typically four—and may be five or six—parietal, convex, with 
the convex edge turned inwards (Figs. 9, 10). 
These palmelloid cells may at once divide into four zoospores 
or into four daughter cells which may grow and again divide 
(Fig. 10). 
