470 Smith . — - Cytological Studies in the Protococcules . //. 
division takes place (Fig. 2). After the cell becomes binucleate there 
is still further growth before the next divisions occur (Fig. 4). Askenasy ( 1 ) 
states that the mature cells of Pediastrum contain large numbers of nuclei, 
but my observations show that the number is rarely greater than four, 
although 8- and 16-nucleate cells have been found. The nuclei in 
the mature cell lie equidistant from one another in the central portion 
of the cell. Since all the cells of a colony are of the same age, it might 
be expected that karyokinesis would take place in them simultaneously ; 
I have never found this to be the case, however, since it often happens that 
some of the cells in a mature colony are binucleate and others tetranucleate. 
Pyrenoids are present in the youngest cells. Usually but a single 
one appears, although cells with two, and even three pyrenoids, have been 
observed. There is no relationship between the size of the cell and the 
Text-fig. 2. Portions of cells showing irregularly shaped pyrenoids. G shows that 
very young cells may contain two pyrenoids. 
number of pyrenoids, since the occurrence of more than one pyrenoid is as 
frequent in young as in old cells (Text-fig. 2). The shape of the pyrenoid 
varies considerably. Spherical ones are most abundant, angular ones are by 
no means rare, and in isolated instances they have small bud-like extrusions 
or projections. Timberlake ( 16 ) has regarded angular pyrenoids as evi- 
dence of rapid starch formation in Hydrodictyon , but in the case of Pediastrum 
the angular and the spherical pyrenoids are found in cells of the same colony. 
Pyrenoids with bud-like projections (Text-fig. 2) are of interest as being 
possible stages in the division of the pyrenoid ; but I am of the opinion that 
such is not the case, and that this peculiarity is merely an irregularity in the 
shape similar to that which I have found in Characium ( 15 ). When stained 
with Flemming’s triple stain the pyrenoid is normally a homogeneous, 
red-staining body surrounded by angular starch plates which stain blue 
(Fig. 10). I have never found the pyrenoid staining blue, as McAllister ( 9 ) 
finds to be the case in Tetraspora . Cases have been found in which one 
