1 1 8 Bristol. — Life-history and Cytology of Chlorochy triuni grande 
numerous minute starch-grains. Pyrenoids are usually present and are 
frequently much larger than those in the vegetative cell. 
When the zoogonidangium has attained its full size it enters upon 
a period of rest which may last for some months. Borzi states that 
zoogonidangia formed in the spring remained in a resting condition until 
the following autumn, while in the present work most of the zoogonid- 
angia which were found in the material in the middle of October were 
still inactive at the middle of the following April. Finally, however, the 
lobes of the chloroplast disappear, and the whole protoplast rounds itself off 
from the cell-wall and assumes a uniformly granular appearance. Multipli- 
cation takes place by the successive bipartition of the whole protoplast 
(Figs. 17-20) into a very large number of small green zoogonidia, the 
number varying according to the size of the cell ; from some of the larger 
zoogonidangia as many as a thousand may be produced. The rate at which 
the successive partitions take place varies apparently with the external con- 
ditions ; in one case, during the changes which accompanied one partition 
more than an hour elapsed, while in another the complete change from an 
8- to a 32-celled stage was accomplished in forty minutes. No cell-walls are 
formed during these rapid changes ; the cytoplasm divides by simple con- 
striction, and the products of division are intensely granular and are 
completely saturated with chlorophyll. They round themselves off from 
one another, and usually dispose themselves towards the periphery of 
the cell-cavity, but as the divisions become more numerous the whole cavity 
becomes filled, and the daughter-cells lose their spherical shape, becoming 
angular by compression. The final products of division are the zoogonidia, 
and when their formation has nearly been completed a large vesicle is 
formed on some part of the cell-wall (Fig. 19). This vesicle appears to be 
produced as a result of changes in the composition of the cellulose layer of 
the wall, so that it swells up and inflates the outer pectic layer, which, how- 
ever, never loses its identity. The inner layer of the wall at this point 
gradually decomposes to form a mucilaginous mass, which fills the vesicle 
and eventually causes a splitting of the pectic layer, so that the cavity 
of the zoogonidangium is put into communication with the outside water. 
At this stage the zoogonidia near the opening round themselves off from the 
mass within the mother-cell and by means of rotatory movements make 
their way through the vesicle into the water. This gives an opportunity for 
those farther within the cell to become free, and in a very short time, often 
as little as ten minutes, the whole mass of zoogonidia escape one by one 
from the mother-cell ; a few individuals become entangled in the muci- 
lage of the vesicle and are unable to escape (Fig. 20). 
The zoogonidia are little oval or pear-shaped masses of naked proto- 
plasm, varying in length from 3-5 to 5 ju, and not more than 2-4 /x in breadth. 
Their chlorophyll appears to be distributed evenly except at the centre, 
