248 BOTANICAL GAZETTE [APRIL 
I cannot say, but as to the common origin of both plasma starch 
and pyrenoid starch around some pyrenoid I can entirely confirm 
TIMBERLAKE’S results on Hydrodictyon. In C. moniliferum the 
stroma starch is also present and is located in the same position, 
at the surface of the chromatophore. 
The pyrenoids 
The pyrenoids of Closterium, like those of all the Conjugatae 
and unlike those of Hydrodictyon, as described by TIMBERLAKE, 
have a single layer of starch grains around them. In size the pyrenoids 
vary all the way from bodies almost impossible to see even with the 
highest magnification to spheres whose diameter is a fifteenth that 
of the Closterium body itself. Even the small pyrenoids have usually 
a little starch around them; frequently this is only on one side, but 
at other times it may extend all the way around (jigs. 18, 21). These 
forms in which the starch occurs largely on one side are rather diffi- 
cult of explanation; the one-sidedness may be due to a difference in 
the amount of carbohydrate food supply furnished to the two sides, 
or it may be due to the method of origin of the pyrenoid, as will be 
discussed later. A more typical form and one more frequently 
figured is that in which the starch lies as a mass of about uniform 
thickness in the form of a hollow sphere about the pyrenoid body 
(figs. 10-13). ‘This sphere is only one layer of grains in thickness, 
although there were a few cases where more than one layer was SUg- 
gested by the appearance of other grains just outside the regular 
layer. The clefts between the grains usually extend out radially, but 
may at times be almost tangential. The grains around any one 
pyrenoid vary greatly in thickness, and there are usually one or two 
grains of relatively larger size. The number of grains in the series 
around a pyrenoid is correlated with their thickness; the thicker the 
grains the more numerous they are and the more irregular their 
shape. No two pyrenoids are alike as to the shape of the grains 
around them. No stratification is visible either in grains or pyrenoids. 
It must not be inferred that there is a correlation between the size ~ 
of the pyrenoid and the thickness of the grains around it. In 4 
general way large pyrenoids have thick grains around them (fg. 12), 
but many very small pyrenoids have thick layers of starch around 
