162 
William J. Hodgetts. 
and filaments which had obviously become loosened in some way 
were not uncommonly seen in samples from the pond, although 
normally they always remain attached. 
No mucous sheath is present round the filaments, the cell- 
wall being firm, rather thin, the longitudinal and transverse walls 
generally being uniform in thickness, and with a sharp relief; 
with iodine and sulphuric acid, or with chlor-zinc-iodine its 
substance is easily coloured a fine blue, and is therefore cellulose. 
Each cell has a single parietal bright green chloroplast which is 
rather small and characterised by occupying only the median part 
of the cell (see Figs. 1, 2, 10), generally extending (-^) of the 
total length of the cell, the two ends of the latter being free of 
chloroplast, while it passes round of the cell’s circumference. 
Its edges are usually very irregular and frequently more or less 
incised. In the young cell the chloroplast has only one pyrenoid 
(Fig. 6), but in the older cells the chloroplast almost always has 
two (rarely three) pyrenoids, each showing a conspicuous starch- 
sheath, while, in addition, numerous small grains of “ stroma- 
starch ” are generally scattered throughout the chloroplast. A 
small nucleus is suspended in the cytoplasm in the middle of the 
cell within the fold of the chloroplast; in favourable cases it can 
be seen without the aid of stains, but in material fixed in weak 
Flemming’s solution its presence can easily be demonstrated by 
staining with Heidenhain’s Haematoxylin. 
Cell division takes place as in Ulothrix; the nucleus divides, 
and the chloroplast becomes constricted and divides into two equal 
parts, each with one pyrenoid (Fig. 6), a new cross-wall being 
formed between the two. Dividing cells are not uncommonly 
slightly swollen as shown in Fig. 6. The filaments do not readily 
break up, and vegetative propagation by fragmentation of the 
filaments does not seem to take place normally. 
The only method of reproduction observed was by 4-ciliate 
macrozoogonidia, which are formed singly in the cells. Any cell 
—including the apical and basal cells—may function as a 
zoogonidangium, and in every sample taken from the pond 
numerous empty cells, showing the lateral pore through which 
the zoogonidium had escaped (Fig. 7), were seen in many of the 
filaments, showing that this method of reproduction is the chief, 
if not the sole, one employed by the alga, during the Spring at any 
rate. On keeping filaments under close observation in the laboratory 
for several days the production of zoogonidia was abserved; 
apparently it takes place exactly as in Uronema confervicolum. 
