The Maximum Efficiency of Photosynthesis 121 



The duration of the experiment was about 8 hr. No notable decrease of the efficiency was ob- 

 served. 



In culture medium at pH 5 the quantum requirement was the same below and above the 

 compensation point and was on the average 3.75. 



In carbonate buffer at pH 9.2 the quantum requirement was the same below and at the compen- 

 sation point, and 10.6 as average. 



Thus, the quantum requirement for aliquots of the same cell Suspension was nearly 3 times 

 greater in carbonate buffer than in culture medium. 



Experiment 3 



June 6, 1949 



Culture medium, pH 5. Gas phase 5% CO-2 in air. 290 cu. mm. cells in each vessel. 



AJ = 6.05 



yo 2 + 43.4 cu. mm. 1 __ g? 



yco 2 — 42.2 cu. mm. J ' 



1 JJ x 30 



— = — =42 



43.4 



An aliquot of the same cell Suspension was placed in a rectangular vessel with 2 side-arms, 

 to which were added 0.2 ml. of 1 normal NaOH and filter paper. 



Culture medium pH 5, gas space, air. 



v = 18.477; v F = 7.40; k G . 2 = 1.062. 



290 cu. mm. of cells. 



60'dark— 183 60' JJ— 163 



60' H + 20 mm. 



yo 2 = 20 x 1.06 = 21 cu. mm. 



1 JJ x 60 6.05 x 60 



21 21 



= 17.3 



This was one of our first experiments to indicate that light does not act on respiration at in- 

 tensities otherwise yielding high efficiencies with adequate CO-j pressure. Later experiments 

 showed that with better CO-2 removal by alkali still less light action was obtained when the filter 

 paper was replaced with glass beads. 



