Smith . — Cy to logical Studies in the Protococcales. /. 465 
knowledge of other algae it would seem probable that they always come to 
rest with the cilia downward, and yet from the examination of the relation- 
ship between the nucleus and pyrenoid in uninucleate stages there is no 
definite relationship between the pyrenoid, nucleus, and base of the cell. 
Text-fig. 2 shows that the pyrenoid may be between the base of the cell 
and the nucleus, or the position of the two may be reversed, while at other 
times both pyrenoid and nucleus are side by side in the middle of the cell. 
After the zoospore becomes attached the young cell grows considerably 
before becoming binucleate (Figs. 8 and 9), but after the cells have reached 
a certain size each is found to contain two or more nuclei, the position of 
which, in the binucleate cells, is quite variable, that shown in Fig. 9 being 
the most common. With the further growth of the cell there is a simul- 
taneous mitotic division of the nuclei into four (Fig. 10), eight (Fig. 1 1) 
Text-fig. 2. Uninucleate cells showing that the relative position of nucleus and pyrenoid 
is not constant. ( x 2,000.) 
sixteen, and so on until the maximum number of nuclei is reached. Division 
stages in the two- and four-nucleate cells were not found in great abundance, 
but in all cases found the nuclei were dividing simultaneously in each cell. 
In the youngest cells the pyrenoids are generally spherical, but in older cells 
various irregularities, that have been described above, are found. Irregularly 
shaped pyrenoids may be found as early as the binucleate stage, but they 
are not found in the majority of cells until the eight-nucleate stage has been 
reached. The fact that these pyrenoids are regular in the earliest stages 
may be considered a proof that irregularities found in the older cells are not 
artifacts due to the treatment during fixation and embedding. 
Summary. 
Mature cells of Characium Sieboldii contain 32-64 nuclei and one or 
more irregularly shaped pyrenoids. 
The process of zoospore formation is one of progressive cleavage, the 
first cleavage planes being transverse and the later ones longitudinal. The 
cleavage continues until angular uninucleate protoplasts are formed. The 
pyrenoid does not divide, but disappears during the process. 
The angular protoplasts become zoospores by rounding up, forming 
pyrenoids and cilia. 
