458 



LIGHT AND LIFE 



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600 



700 



650 

 Wavelength, mp 



Fig. 9. An automatically recorded action spectrum for photosynthesis in Botryd- 

 iopsis alpiua, Starr No. 295. The wavelength was \aried at about 10 mju/min; 

 after each segment of about 20 m/x the wavelength was returned to 680 m/x and 

 the zero point readjusted if necessary. The points were plotted by changing rapidly 

 from 680 m^ to the indicated wavelength and then waiting about 1 min for the 

 steady rate to be reached. I'he lower point at 680 ni^ shows the drift in twice 

 the time used to plot a point. (With G. C. McLeod). 



The device is well adapted for studies of the Emerson enhancement 

 effect of photosynthesis by added background light of controlled 

 wavelength and intensity. 



Action Spectra for Enhancement and for Chromatic Transients 



Emerson and Lewis (18) found the efficiency of photosynthesis to 

 decline much more steeply than does the absorption itself on the 

 long-wave side of the red chlorophyll absorption band. Many years 

 later, Emerson, Chalmers, and Cederstrand (16) found that the low 

 efficiency of light in this 680-710 m^ region could be greatly increased 

 by adding light of shorter wavelengths during the measurements. 

 This Emerson enhancement effect is illustrated in Fig. 10, where it 

 is seen that a65() and a70(), when given together, give more photo- 



