Cytological Studies in the Protococcales. 
I. Zoospore Formation in Characium Sieboldii, A. Br. 
BY 
GILBERT MORGAN SMITH. 
With Plate XI and two Figures in the Text. 
Introduction. 
T HE first account of reproduction in Characium is that of Braun ( 1 ) in 
which the process is described for several species. Characium acitmi- 
natum (A. Br.), De Toni, he says, has a cell structure of a pale green cytoplasm 
and a single pyrenoid which is located in the middle of the cell. Reproduc- 
tion takes place by the gradual disappearance of the pyrenoid and a cyto- 
plasmic division into irregular polygons. These pieces then separate, become 
rounded up, and elongate to form 80-150 zoospores, which are liberated by 
a lateral rupture of the mother-cell wall and remain in motion 2-3 hours, 
then affix themselves to the substratum, elongate, and become pointed. In 
C. Sieboldii , A. Br., division may take place before the cell is fully grown, 
the cell contents dividing transversely. There may also be a median longi- 
tudinal division of the cytoplasmic contents. Each division of the cytoplasm 
is preceded by a division of the pyrenoid so that every cytoplasmic fragment 
contains 1-4 pyrenoids. The cytoplasmic parts which have been formed by 
these repeated divisions are the zoospores ; they vary somewhat in size and 
shape. The smallest number formed is 8, most frequently 16, but there may 
be 30-60. Microzoospores are also formed. 
West (11) states that there is a repeated division of the cell contents, 
transverse divisions occurring before the longitudinal ones. In a short time 
each portion loses its angular character, becomes rounded up, and forms 
a biciliate zoospore. In some species the pyrenoid disappears during the 
formation of the zoospores and reappears upon their germination. 
Lambert ( 5 ) has described the reproduction of two forms that are 
parasitic on Crustaceans. The chromatophore of Characium gracilipes , 
Lamb., is single, parietal, and situated in the convex side of the cell, while 
the pyrenoid is always a small hyaline body separated from the chlorophyll- 
bearing portion of the cell. The elongation of the pyrenoid is the first 
evidence of reproduction. It assumes a dumb-bell shape and finally separates 
[Annals of Botany, Vol. XXX. No. CXIX. July, 1916.J 
