720 



Edgar Inselberg and J. L. Rosenberg 



possibly due to excessive flash intensity, 



•Die possibility of instnimental artifacts was investigated by 

 coEiparing the waveforms, with and without measuring li^t, of 

 several non-photochemical systems, such as a CaCO^ suspension and 

 nutrient medium. The data obtained indicated the absence of such 

 artifacts , 



An extended spectrxira of the changes in Porphyridium (Fig. h) 

 was obtained by exciting the sample, in nutrient medi\am, with 

 li^t absorbed primarily by chlorophyll a (Coming Pllter 5-58, 

 transmitting between 350 and U80 m\i)» (i*eater reproducibility was 

 attained by taking h pictures with the flash pliis measuring li^t 

 on, and 2 flash-only pictures, at each wavelength. The effect of 

 reducing the range of the exciting li^t was a nearly threefold 

 reduction in the magnitude of the change at 700 my., partially at- 

 tributable to a considerable reduction in integrated flash inten- 

 sity. Several maxima are apparent in Fig. U, including one at 700 

 mp,« 



Since the magnitude of the change at 700 m\i was approxJ.mately 

 5 times that reported by Kok and Hoch (^/, we investigated the 

 possibility that the negative change observed was partially at- 

 tributable to increased emission (rather than transmission) dur- 

 ing and following the flash. To this end, we successively placed 

 various interference filters in front of the phototube, setting 



■0.005 



-o.oio 



-OOI5 



500 550 



600 650 700 



WAVELENGTH - m^ 



750 



BOO 



Fig. U. Extended spectrum of the changes in PorphjTi- 

 dium, with chloropihyll excitation. The vertical line 

 at 700 mp. represents the range of several means at 

 that wavelength. M: apparent change in absorbance, 

 Az-o^: absorbance at 680 m^i. 



