The Maximum Efficiency of Photosynthesis 117 



manometer vessel, the too few cells in the manometer vessels, the too great time differences bet- 

 ween manometric readings of the two vessels where J = 0, the damage done to the cells when 

 shaken too long in the dark, the too high intensity of the measured red-light beam, etc. In addition, 

 all our early experiments were carried out at 10°C. (as in 1923) where manometric uncertainties are 

 greater than at 20° C. the temperature finally adopted here. 



We therefore decided to report here in detail only experiments performed since May 30th. 

 In these experiments all necessary requirements that we know of were complied with and therefore 

 we feit justified in averaging the results as reported in the Summary and Conclusions. Earlier reports 

 of various aspects of the work, with various collaborators, have appeared elsewhere" 20 ' 21 > --. The 

 present work is based upon a background of a total of more than one hundred experiments of the 

 type illustrated in the ten examples shortly to follow. Many minor aspects of the work, and miscel- 

 laneous control experiments, have not been detailed, but brief mention may be made of some as 

 follows: (1) The measured red light beam (. \J) when first filtered through the actinometric Solution 

 produced no photosynthetic action. (2) The high photosynthetic efficiency was not decreased in 

 vessels containing Pd catalyst in the side-arm to remove IT possibly formed. Mass spectrographic 

 analysis of the vessel gas phase at the end of a prolonged experiment (without Pd in side-arm) 

 indicated no significant occurence of Hj or other unusual gases (oxides of nitrogen, etc.) (3) The 

 photosynthetic yield in bicarbonate medium with 5% CO: in air, at pH ca. 7—7.5, was less {ca. 

 8 quanta/O-i) than in culture medium at pH 5. (4) In an experiment carried out with the cells washed 

 and taken up in distilled water instead of culture medium, but with 5% CO2 in air as usual (pH 5), 

 the photosynthetic efficiency remained high, indicating that low pH rather than sah composition 

 is the more important prerequisite for high efficiency. (5) For any period that an illuminated 

 manometer was not shaken, a considerable fraction of the photosynthetic activity might be lost; 

 this was tested for stationary periods of 30 sec. and more. Thus, a vessel alternately shaken and 

 halted every 30 sec. (or every 1, 2, or 5 min.) might give during a total elapsed time of 10 min. only 

 about 60 — 70% of the pressure change shown upon 10 min. continuous shaking; it was not practic- 

 able to use periods much shorter than 30 sec, but in this connection rotating sector intermittency 

 experiments are projected. 



The letter Symbols used in the following description of the experiments signify : 



J Intensity of the compensating light absorbed per minute in the cell 



Suspension. J had to be kept constant during an experiment, but was 

 not measured. 



AJ Intensity of the added measured red light, incident and absorbed per 



minute in the cell Suspension, measured actinometrically and expressed 

 as cu. mm. Oo/min. 



hj Millimeters of observed pressure change in t minutes in vessel I, 



when J < * is absorbed by the cell Suspension. 



h J+A j Millimeters of observed pressure change in t minutes in vessel I, 



when (J — . 1 J) X t is absorbed by the cell Suspension. 



H h J+A j + hj. 



h'j, A'j+jj, and H' refer, correspondingly, to vessel IL 



02 n simple vessel constants (mm. 2 ) for vessel I 

 «co-2 



0-2 simple vessel constants (mm. 2 ) for vessel II 



k CO2 



ao, =-- 0.03 



flco-2 = 0.87. 



y Ö2 Cubic mm. of O2 produced by the action of AJ X t in the cell Sus- 



pension. 



