92 



B. L. STREHLER AND V. H. LYNCH 



tensity during the induction maximnm (n) and at steady state (h) 

 The process saturates at different incident intensities during the suc- 

 cessive phases of the induction period. In this respect it is strikingly 

 similar to the luminescence. 



500 



550 600 



Wavelength (millimicrons) 



650 



Fig. 3. Difference spectrum of Chlorella obtained with a flow system. Illumina- 

 tion with white light of 600 foot-candles intensity. Calibrated at each wavelength 

 against a known transmission change of ca. 0.5%. 



3. In order to extend the observations into the red region of the 

 spectrum we found it necessary to utilize the flowing systems. Figure 

 8 illustrates the effect of illumination on the difference spectrum from 

 about 470 mix to 670 mju. Note that the bands at 480 and 520 m/x 

 are inverted with respect to the results obtained during illumination. 

 It therefore appears (as is also evident from the time course illus- 

 trated in Fig. 1) that immediately following illumination there is a 

 decrease in absorption at 520 m^u and an increase at 480 m/x. 



4. Of particular note in Fig. 3 are the pair of strong bands appear- 

 ing at 648 m/i and disappearing at 660 m^u. 



5. Our measurements extended as far as 720 m/x and no changes 

 were observed in the region 670 to 720 m/x greater than 10% of the 

 change at 520 m/x, if there were indeed changes at all in this far red 

 region. 



6. When the cells were illuminated for a fraction of a second and 

 then assayed simultaneously for luminescence and absorption, changes 

 in absorption were found to be similar to the changes occurring under 

 direct illumination. Apparently the inversion effect requires at least 



