352 U. KMKRSONT AND U. V. CIIALMKUS 



Figure 1 shows the results of such an experiment. Here 30-^1. 

 Chlorella pyrenoidosa cells were suspended in 8 ml. of carbonate buffer 

 No. 9. Light intensity was \'aried by means of calibrated wire screens. 

 The light source was a cadmium-mercury arc. On the left is shown the 

 full range of intensities used. On the right, on a scale expanded ap- 

 proximately tenfold, are shown the points up to just above com- 

 pensation of respiration. Since the rate of respiration varies with 

 time and in response to the light intensity being used, we have indi- 

 cated on the drawing the range of compensation in the course of the 

 experiment, rather than a compensation point. 



Other experiments have shown similar results. In all cases the rate 

 of photosynthesis has been linear through the region of compensa- 

 tion. No combination of cultural and experimental conditions which 

 we have yet tried has gi\'en any evidence of higher efficiency of photo- 

 synthesis below compensation. 



Acknowledgment. This work was supported by National Science Founda- 

 tion Grant G-1398. 



References 



1. Bassham, J. A., Shibata, K., and Calvin, M., "Quantum requirement in 



photosynthesis related to r ef^pimtion," Biochini. et Biopkys. Ada, 17, 332-340 

 (1955). 



2. Franck, J., "Participation of respiratory intermediates in photosynthesis as an 



explanation of abormally high quantum yields," Arch. Biochem. and Biophys., 

 45, 190-229(1953). 



3. Emerson, R., and Chalmers, R. V., "Transient changes in cellular gas exchange 



and the problem of maximum efficiency of photosynthesis," Plant Physiol., 

 SO, No. 6, 504-529 (1955). 



