1910] - LUTMAN—CELL STRUCTURE OF CLOSTERIUM 245 
the glass carefully picked away from the paraffin, and the bottom 
_layer sectioned. I am indebted for this method to Dr. Overton 
of this laboratory, who has used it very successfully in sectioning 
Paramoecium. 
Material was fixed in Flemming’s medium, Flemming’s weaker, 
_and Flemming’s weaker half strength, and Merkel’s solutions. Flem- 
ming’s weaker half solution strength gave the best results both 
on the nuclei and on the pyrenoids, causing very little shrinkage 
and preserving the internal structures well. With the exception of 
the pyrenoids, Merkel’s solution preserved the cytoplasm structures 
better, but in the former caused shrinkage, as did the Flemming’s 
medium solution. The sections were stained with the triple stain, 
the pyrenoid itself taking on a brilliant red color, while the starch 
around it always took the gentian stain as has already been described. | 
The chromatophore 
As noted above, the only figures of the cross section of a chro- 
matophore of Closterium, so far published, are those of NAGELI, in 
which it is shown as composed of a central cylinder from which 
radiate ridges like the spokes of a wheel. In his figures NAGELI does 
not show these ridges as extending to the cell wall, but in his descrip- 
tion he says they do. The form of the chromatophore is quite differ- 
ent in C. Ehrenbergii from that described by NAGELI for C. parvulum 
and C. monilijerum. In this form the central cylinder is quite large, 
Occupying practically the entire cell space, while the ridges are com- 
paratively narrow and extend practically to the cell wall, only an 
extremely thin layer of cytoplasm separating the latter from it. The 
chromatophore of C. Ehrenbergii in cross section (fig. 2), instead of 
tesembling a hub with radiating spokes, as in NAGELI’s two ‘forms, 
is more like a coarsely cogged wheel. The cytoplasm of the grooves 
between the ridges is sometimes very densely stained, being much 
darker than the chromatophore itself, but containing a great number 
of vacuoles of varying sizes (figs. r, 2). Atother times, however, these 
Spaces between the ridges are almost free from stainable materials, 
showing only a few large vacuoles or having a very reticulate structure 
§. 2). When the green plants in the living condition are examined. 
under the microscope, it can be noticed at once that there is great 
