90 B. L. STREHLER AND V. H. LYNCH 



magnitude and even the «ign of the spectral changes as a result of 

 illumination are dependent on the manner, intensity, and duration of 

 exposure to light and on the time elapsing between illumination and 

 measurement. 



MATERIALS AND METHODS 



The details of the experimental methods and modifications of the 

 derivative spectrophotometer used in these studies are described else- 

 where (7). Chlorella pyrenoidosa was cultured under incandescent 

 light at ca. 20°C. in ca. 5% COa-air. 



Three methods of illumination were used in these experiments: 

 /. Direct cross illumination during measurement. Filters were used 

 to protect the phototube from the photosynthesis-inducing light and 

 to pass the measuring beam. 



2. A circulating system in which the algae were illuminated for 

 periods of 5 to 60 seconds outside of the spectrophotometer and then 

 pumped rapidly through a cuvette placed in the measuring beam. 



3. Same as the second method, except that the cells were illumi- 

 nated for a fraction of a second in the flow system prior to measure- 

 ment. 



In order to compare the Iviminescence of Chlorella under various 

 conditions with the simultaneous absorption spectrum changes, the 

 flow of algae from the illumination chamber (in the second and third 

 methods above) was divided into two parallel streams, one passing 

 into the difference spectrophotometer, the other in front of a photo- 

 multiplier sensitive to the red luminescence emitted by the plants. 

 The respective signals were recorded simultaneously on Brown 

 Electronik recorders. 



RESULTS 



/. In conformity with Duysen's findings, we obser^'ed spectral 

 changes in the wav^elength regions 480 m^ and 520 niju. We did not, 

 however, observe the band around 420 mn which Duysens noted, 

 either because our apparatus may ha\'e been less sensitive than his or 

 because our algae were grown under different conditions. 



2. We observed striking induction changes not mentioned by 

 Duysens. These effects are illustrated in Fig. 1. In Fig. 2 are illus- 

 trated the changes in absorption as a function of incident light in- 



