Cell and Nuclear Division in Closterium

I. Closterium divides from 10 P.M. to 5 A.M., and the new half has become practically symmetrical with the old one by 9 A.M. 2. Division is dependent upon the storage of a considerable quantity of starch in the chromatophore and around the pyrenoids. 3. The chromatophore divides by a constriction located about a third of the distance out from the middle. This constriction is due to the enlargement of a ring-shaped vacuole under the plasma membrane. 4. The resting nucleus of C. Ehrenbergii is made up of a very fine reticulum carrying little if any chromatin in the form of granules. At the center of this reticulum is a large compound nucleolus made up of a number of partially fused nucleoli. The resting nucleus of C. moniliferum has essentially the same structure, but the nucleoli at the center are more completely fused. 5. The spireme is formed outside the nucleolus and apparently separate from it. During its formation that body breaks down, but it is impossible to decide whether its material goes to the spireme or is used up for some other purpose. No chromosomes come bodily out of the nucleolus as has been described for Spirogyra. 6. The spindle is cylindrical, with broad poles, much resembling that of Spirogyra. 7. In the telophase a dispireme is formed, and in this the nucleoli reappear as small spheres which later partially fuse to form larger masses. 8. The two daughter nuclei move around the chromatophore? between its ridges, apparently in an amoeboid manner, to their new positions. 9. The new end wall is put across in essentially the same manner as in Spirogyra, that is, by a growth inward from the periphery. 10. Division in these species of Closterium is at least a twonight process' the chromatophore divides the first night; the nucleus the second night. 11. The position of the young transverse wall would seem to indicate that the .pointed ends are secondarily formed, and that Closterium was originally a filamentous alga, which has developed the habit of breaking up into single cells.