96 



The Maximum Efficiency of Photosynthesis : A Rediscovery 



pidly, and in the dark or in the light. By changing the rate of shaking the steady- 

 state pressures of CO2 in liquid and gas phases were changed, but in the dark this 

 had no effect on the observed rate of respiration. In the light, the rate of oxygen 

 consumption decreased in the slowly shaken vessel ; but in the rapidly shaken vessel, 

 where the steady-state pressure of CO2 was lower, no action of light on the rate of 

 oxygen consumption was observed when the intensity of the light entering the vessel 

 was about 0.25 microeinsteins/min., an intensity that with adequately high CO2 

 pressures gave high photosynthetic efficiencies (3 to 5 quanta per molecule of O2 

 developed). The shaking effect was reversible, the action of the light alternately 

 appearing or disappearing with decreasing or increasing shaking rate. 



The experiments may be extended to higher light intensities, but the higher the 

 light intensity the more effective must be the removal of the carbon dioxide, for 

 which the light and the alkali compete. The CO2 pressure required to yield maxi- 

 mum respiration is clearly below that needed for effective photosynthesis where 

 CO2, functions as subtrate and not merely catalytically. 



Such experiments prove that the light did not interfere with the process of 

 respiration, either anticatalytically or stoichiometrically by reduction of inter- 

 mediates.* Light, when it compensated respiration, did so by producing oxygen, 

 and because the gas exchange of photosynthesis happens to be the reverse of the 

 gas exchange of respiration. Thus a question, old as the science of photosynthesis, 

 has been answered by the most simple of experiments. 



Examples 



1. Manometric pressure changes effected by red light when respiration was not compensated 

 by white light. Two-vessel method, culture medium pH 5, gas phase 5% CO> in air. 20° C 



Vessel I Vessel II 



v == 13.913, v F = 7.00 v' = 17.993, v' F = 7.00 



Actinometer 5.4 mm. 3 CWmin 



Vessel I 



10 min dark — 26 mm 

 10 min dark — 23 mm 

 10 min dark — 23 mm 

 10 min dark -23 mm 



Vessel II 

 10 min dark — 12 mm 

 10 min dark — 10 mm 

 10 min dark — 11 mm 

 10 min dark —11 mm 



xo 2 in 40 min — 51.6 mm. 3 

 *co 2 m 40 min — 53.7 mm. 3 



1 hv 40 ■ 5.4 



~0 ~ 



O., 



51.6 



CQ 2 



4.2 



1.04 



* Zusatz 1961. Aber vergleiche Arbeit 11 dieses Buchs. 



