382 



LIGHT AND LIFE 





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AN ACY ST I S 



YIELD 



FRACTION 

 ABSORBED BY 

 PHYCOCYANIN 



a. 



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WAVE 



Fig. 4. I'pper curve, action spectrum of Kiiieison eliect in Aniicyslis. Lower curve, 

 fraction of absorbed light absorbed by pliycocyanin. (After Emerson and Rabino 

 witch. 14). 



tion, cf. Tanada, 19) , at 630 m^ (chlorophyll c) , and at 670 mix. 

 There is no chlorophyll b in these algae and therefore no peak at 

 650 m/x. 



These two curves seem to suggest that the form Chi a 680 does 

 not supplement effectively the photochemical action of Chi a 690. 



So far, so good; but now we are up for trouble. Fig. 4 was obtained 

 by Emerson with the blue-green alga Anacystis. It shows only one 

 peak, at 600 m^^, clearly attributable to phycocyanin; but when we 

 move to longer waves, not only is there no clear peak at 670 vcifi, 

 but there is a negative region. This means that combination of far- 

 red light (685-700 m^x) with monochromatic light in the region 670- 

 700 m/x produces, in Anacystis, less photosynthesis than the two light 

 beams separately! Emerson's measurements cf. 14 showed negative 



