PHOTOSYNTHESIS 



suspension, then through an oxygen analyzer and a carbon 

 dioxide analyzer. The circulation of gas through this closed 

 system was accomplished by means of a pump. The indications 

 from the analyzers were continuously recorded on a multipoint 

 recorder. A uniform light field of 6300 A light was obtained 

 from a spiral neon tube with suitable filters and incident and 

 transmitted light intensities measured with a bolometer, which 

 was frequently calibrated against three standard lamps. Small 

 variations in the light field were mapped by a small photo- 

 electric cell and suitable corrections made. 



The measurements of photosynthetic rate were dependent 

 only on the measured change in the percentage oxygen in the 

 system and the known volume of the system. Both of these are 

 directly measured quantities which can be, and were, checked 

 frequently with standard gas mixtures. Virtually no variation 

 was found from time to time. The energy measurements were 

 also simple and straightforward, since they involved essentially 

 the measurement of energy absorption in a thin layer of large 

 area. 



The algae, Chlorella pyrenoidosa, were grown according to 

 previously described conditions (6) in 4% COo. The quantum 

 requirements of these algae were tested after a variety of pre- 

 conditions. The best condition found was selected and determi- 

 nations were made as a function of light intensity. The values 

 of the quantum requirement were determined both for the un- 

 corrected rate of photosynthesis and for the rate, which we will 

 call photosynthesis, obtained by subtracting the dark respiration 

 rate from the uncorrected rate. 



This correction seems justified in view of Brown's (10) study 

 in which isotopic oxygen was used to demonstrate that no sig- 

 nificant change in rate of respiration of Chlorella pyrenoidosa took 

 place during alternate 1 5 or 20 minutes of light and dark. The 

 same paper, as well as the earlier ones by Emerson and Lewis 

 (25), Weigl et al. (62), and Brackett et al. (8), showed an increase 

 in the dark respiration rate (and the light rate as well in Brown's 

 paper) which is produced by conditioning the plants with photo- 



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