208 S. MIYACIII. T. HIROKAWA, H. TAMIYA 



development of C**-fixing capacity was measured, by transferring at 

 intervals aliquots of cell suspension into C^^O-z solution kept in the dark, 

 and by measuring the C^^ fixed within 30 seconds (R), on the one hand, 

 and that fixed within 5 minutes (R+n), on the other. After 60 minutes 

 of illumination, when the 7^ level was at the stationary state, the light 

 was turned off, and by the same method as above, the course of 

 decay of C^^-fixing power was traced. As reported elsewhere (3), 

 the R level showed an induction period with two depressions at the 

 beginning of illumination. When the light was turned off at the sta- 

 tionary state in the light, the decay of R occurred immediately, as it 

 has already been observed by Calvin and Benson (1). A quite dif- 

 ferent phenomenon was observed in the decay-curve which was 

 measured by 5-minute C^^02 fixation; immediately after cessation of 

 illumination, there occurred an abrupt temporary increase of the 

 C'*-fixing capacity, after which the capacity decayed steeply to 

 attain eventually a steady level. 



On the upper part of the figure, the difference between the (R+r^) 

 curve and the R curve is plotted. This difference curve, representing 

 the time course of rg, shows us: (1) that on illuminating the dark- 

 adapted algae, the background fixing capacity decreased temporarily, 

 then increased, and eventually attained a steady level, which was 

 considerably higher than the steady level observed in the darkness; 

 and (2) that when the light was turned off, the background ca- 

 pacity increased abruptly, and after attaining a certain maximum 

 value, it gradually decreased to a final level which was lower than the 

 steady level observed during the illumination. 



PHOTOCHEMICAL CO2 OUTBURST FROM THE PRODUCT 

 OF BACKGROUND CO2 FIXATION 



An interesting phenomenon was observed when, during the course 

 of dark C^^02 fixation, the cells were subjected to brief illumination. 

 The experimental results are presented in Fig. 3. To the algal sus- 

 pension which has previously been kept dark for 25 minutes in N2 

 atmosphere, C'^02 was added and the course of dark C'^ fixation was 

 followed. As shown by the curve on the lowest part of the figure, 

 the C* fixation proceeded almost linearly wdth time when the dark- 

 ness was continued uninterrupted. When, however, during the 

 course of this process, the algae were exposed to a 1 -second light 



