C. S. FRENCH 



465 



100 



-C 



c 



o 



a 50 



0) 



> 





N = I7 



N = I0 



RE. of Ihe arithmehc mean 

 of N observations 



P.E. of single observation 



N = IO 



N = IO 



400 



500 600 



Wavelength, mp 



700 



Fig. 16. The action spectrum for photosynthesis by Chlorella at low and at sat- 

 urating light intensity. The low intensity curve is the reciprocal of the relative 

 cjuantum intensity needed to give a constant rate of photosynthesis at various 

 wavelengths. 



The high intensity curve is the measured rate at saturating intensity of each 

 wavelength. The rates for N experiments at each point were normalized at 650 

 nifi. According to the usual concepts of photosynthesis this should be a horizontal 

 line, with no structure. The photosynthesis rate at which the low intensity spec- 

 trum was measured was 0.006 X ^^^^^ ^^^ ^ typical measurement at light saturation 

 at 650 irifi. The scales for the two curves are not comparable. From McLeod (47). 



the "accessory pigment reaction" promoted by C,j650 and Ca695 to- 

 gether may well be involved in a way that is not yet understandable. 

 Certainly the relative photochemical activity of the less absorbing 

 pigments in proportion to the total activity woidd increase with in- 

 tensity at levels above the saturation range of the major absorber. 



