384 



Max H, Hommersand 



tNTENSITY (Rclorive units) 



Fig. 3 (left). Uptake of C O2 at different 

 intensities of far-red light compared to the rate of 

 uptake in the dark. A Wratten sharp-cut filter #45 

 (17o transmission at 705mM) backed with a Corning filter 

 #2418 was employed. Relative intensities were measured 

 with a Kipp thermopile and the data are all plotted on 

 the same intensity scale. 



Fig, 4 (right). Comparison between the net rate 

 (light rate minus dark rate) of CO2 uptake and O2 

 evolution in far-red light as a function of the light 

 intensity, showing an intensity threshold for CO2 

 fixation, CO2 uptake was measured as described in 

 figure 3 and O2 evolution was followed polarographic- 

 ally. The relation between the slopes of the curves 

 is arbitrary. The curves are; •, oxygen evolution; 

 o, /i , CO2 fixation (two experiments). 



when the shift is to a region where the pigments of System I 

 predominate, and is slow--slow enough to be reflected in the 

 transient- -when a shift in the opposite direction occurs. The 

 conditions imposed at one wavelength which affect the magnitude 

 and shape of a transient at another wavelength appear to be 

 dissipated slowly over a period of several hours in the dark. 



