THE ENERGETICS OF PHOTOSYNTHESIS 97 



According to equation 42 



_ 16.8 - 9.06 _ ^ 

 " ~ 0.620 - 0.303 " ^ 



Chemical determination of chlorophyll: 22 /xl. Hence, two determinations 

 during stoichiometric Oo production enable the chlorophyll content of the 

 cells to be correctly calculated. 



The numerical examples of § 39 show that on the addition of measured 

 light the negative pressure changes are followed by positive pressure changes. 

 In Example a the negative pressure change of 22 mm in the small vessel during 

 illumination with blue-green light only is due to the stream of Oo passing from 

 the gas phase through the liquid into the cells. During 2.5 min illumination 

 with the measured light, this negative pressure change is followed by the 

 positive pressure change of 14.5 mm, due to the reversal of the O2 stream. 

 The reversal in pressure change takes some time and though vigorous shaking 

 (190 excursions per min) may decrease this time lag, it cannot be completely 

 avoided. The following experiment by Warburg (59) shows that positive 

 pressure change is still noted in the first dark minute after one minute illumina- 

 tion. 



Small Vessel Large Vessel 



Pressure Changes Pressure Changes 



mm mm 



10 min dark -5.0 -2.5 



1 min light +4.5 +2.5 



1 min dark +1.5 +0.5 



5 min dark —5.0 —3.0 



The values for 7 and ip are somewhat lower if the time lag is not taken into 

 consideration. To avoid these complications in experiments with short 

 illumination times, the manometric readings should be made one minute 

 after the change from light to dark and one minute before the change from 

 dark to light, so that it is not necessary to interrupt the shaking at the onset of 

 illumination (59). 



§ 41 Oxygen Capacity and Induced Respiration 



According to the reaction equation of photosynthesis discussed in § 35, the 

 O2 is produced by a chlorophyll-carrier-substance. When the end value of 

 stoichiometric O2 production is attained in light, a dark period is necessary 

 if further Oo is to be developed. Needless to say, Oo must be present in this 

 recovery period (e.g., 20 min) in order that the induced respiration, which, 

 according to Warburg (59, 62), makes possible O2 production in the light, 

 can proceed. After the dark recovery period, complete Oo capacity can be 



