26 



H. TAMIYA et al. 



VOL. 12 (1953) 



RESULTS 



Characteristics of dark cells and light cells 



Stationary cultures grown under a moderate intensity of light usually show the 

 dark cell ratio of 0.4 to o.S, the value being, as a rule, higher in weakly illuminated 

 cultures than in strongly illuminated ones. By fractional centrifugation of these cultures 

 we can obtain cell suspensions which consist practically entirely of dark cells or light 

 cells. In Fig. 2 are shown the microphotographs of the two kinds of cells in such 

 suspensions. 



Microscopic observation shows that the light cells may further be divided, according 

 to the grade of ripening, into two categories, sporulated and non-sporulated, but they 

 can hardly be separated by such a technique as fractional centrifugation. On the other 



Fig. 2. Microphotographs of two types of cells at the same magnification. 



hand, the dark cells, in so far as they are defined by their cell diameters less than 4.5 

 microns, appear under the microscope to be quite uniform in appearance. During the 

 course of the present study, however, it was found that among dark cells there are also 

 two distinct categories whicli can be obtained separately by a certain procedure. 



The one category, which we call "nascent dark cells" in tlK> following, consists of 

 cells which represent the nascent state of dark cells derived from light cells. These cells 

 can be obtained from light cells by incubating the latter in the dark while being well 

 aerated. The other category, which we call "active dark cells", consists of dark cells 

 derived from nascent dark cells by illuminating the latter for a few hours. Since the 

 transformation in the light of the nascent dark cells into active dark cells takes place 

 relatively rapidly, the dark cells contained in continuously illuminated cultures are 

 mostly in the active form. 

 References p. 40. 



