98 



The Maximum Efficiency of Photosynthesis : A Rediscovery 



Red light, 630 — 660 m //. I ~ 0.25 microeinsteins/min 20° C. 



1 hv 

 Quantum requirement — = for the added red light. 



1 



In carbonate buffer, respiration compensated by white light, — = = 10.5 



In culture medium, respiration compensated by white light, — = 3.9 (y = - 1.04) 



In carbonate buffer, respiration not compensad — = 9.8 



In culture medium, respiration not compensated 







3.6 (y = 1.18) 



In carbonate buffer, respiration not compensated — =11.3 



5. Results by 2-vessel method for a series of experiments that were carried out from May 26 to 

 June 16 of this year, at 20° C, in culture medium at pH 5, with an intensity of red light not exceeding 

 0.25 microeinsteins/min. No experiment is omitted. 



1 







hv 



O, 



3.2 



4.6 

 4.5 

 3.9 

 3.6 

 4.2 

 2.8 

 2.8 

 2.5 

 4.5 

 4.7 

 3.5 

 4.2 

 3.0 



CO-2 



o 2 



- 1.08 



- 0.80 

 -0.90* 



- 1.04 



- 1.18 

 -0.97 



— 1.16 

 -1.23 



- 1.25 

 1.00** 



-0.93** 



- 1.27 



- 1.00 



- 1.33 



Average 3.7 



1.08 



It may gathered from Example 5 that the quantum requirement for carbon 

 dioxide consumed can be equal to or somewhat greater or smaller than the require- 

 ment for oxygen produced. For we have 



1 1 hv 2 j™_ 



" co 2 ' 







O, CO., 



a magnitude which here for the first time, to our knowledge, has been determined 

 in nutrient medium at low pH (about 5), and has been found to approximate 



hv_ 

 ~<X 



3to 5. 



Yet the quantum requirement for oxygen is the more fundamental energy 

 measure, because there is only one reaction in photosynthesis that produces oxy- 



* Respiration overcompensated by white light from above. 

 ** Respiration compensated by white light from above. 



