746 



Constantine Sorokin 



2. A careful, repeated centrifugation and rejection of the 

 largest portion of the intermediate cells; 



3. A prevention of large cells from dividing during the 

 process of centrifugation; 



4. Prolonged observations on the activity of small and large 

 cell fractions. 



In our investigations under various temperature and illumi- 

 nance conditions and in such diverse suspending fluids as 

 phosphate buffer at pH 4.5, bicarbonate buffer at neutral pH, and 

 carbonate -bicarbonate buffer at pH above 9, the fraction of 

 larger cells consistently displayed an inferior photosynthetic 

 activity provided the separation of cells into fractions by 

 centrifugation was reasonably good (Fig. 3). 



In studies on nonsynchronized algal populations a gradual , 

 slow change in age composition of the batch of cells and an accu- 

 mulation of small cells occur. Actual progress in cell division 

 in a batch of cells under observation depends on the hereditary 

 constitution of the organism, the external conditions, and the 

 physiological state of the cells, the last one largely dependent 

 on their prehistory. An interaction of these factors affects 

 individual cells against their developmental background. Thus, 

 the chance of a particular cell to enter the division stage, the 

 degree of completion of cell division, and the time course of the 

 division process depend on how far the cell progressed in its 

 development by the time it was taken for observation. The com- 

 plexity of the situation makes it unreasonable to expect a ready 

 standardization of age composition of cells used in a series of 

 experiments. 



Eventually all cells capable of division divide and the age 

 composition of the batch of cells stabilizes. These cells have 

 been described as "active dark" cells (2), However, for a number 

 of reasons, cells maintained on the electrode surface hardly can 

 be called "active dark" cells. For one reason, under unfavorable 

 conditions, not all the cells divide and some cells do not attain 

 the status of a small (dark) cell. For another reason, the 

 "active dark" cells, in the sense used by Tamiya group (°) , are 

 recognized to be actually starved cells (3^. 35), Thirdly, 

 physical conditions on the electrode surface are even less favor- 

 able for cell division and maintenance of cells than those 

 stipulated by Tamiya's synchronization technique. 



