1048 



BIOLOGICAL EFFECTS OF RADIATION 



Table 6. — Warburg and Negelein's Results on the Energy Efficiency op 



Photosynthesis in Chlorella 



It appears, therefore, that the photosynthetic process is dependent 

 on the quantum action of the photons rather than on the total heat energy 

 which the hght imparts to the assimilating plant. 



Since Warburg and Negelein have shown that about four quanta are 

 necessary for the production of 1 mole of oxygen it is obvious that the 

 total energy requirements for the idealized photosynthetic equation are 

 satisfied. 



The relative energy efficiencies for different parts of the visible 

 spectrum have recently been determined by Schmucker (101) with 

 Cryptocoryne ciliata and Cabomba caroliniana. The relative values 

 obtained for different wave-lengths agreed with those of Warburg and 

 Negelein. Thus in two widely separated classes of plants the relative 

 energy efficiencies are the same in different parts of the spectrum. 



Briggs (8) has criticized the results of Warburg and Negelein because 

 "Warburg and Negelein measured the assimilation under conditions 

 where it was more than counterbalanced by respiration, and vmder such 

 conditions the high energy efficiencies which they observed may have 

 been due to the easy photolysis of some intermediate respiratory sub- 

 stance." This criticism seems unjustified when the primary objectives 

 of these investigations are considered; this was an attempt to establish 

 the theoretical basis on which the energy transfer depends. Under the 

 conditions employed the disturbing influences of diffusion, fatigue, and 

 photochemical inhibitions would be reduced to a minimum. 



On the other hand, it was necessary for Warburg and Negelein to 

 assume that the photosynthetic action alone is increased by the light 

 without any simultaneous influence on the respiration. Briggs presents 

 a further criticism that all the light absorbed by the algae was not 

 absorbed by the photosynthetic pigments and that on this account the 

 true energy efficiency of the assimilation process has not been determined 

 in these experiments. While this criticism is justified (and also realized 

 by the German investigators), it is difficult to see how any valid correction 

 can be made at the present time. No means of circumventing this 

 obstacle has as yet been found. 



Experiments on the energy efficiency of photosynthesis have been 

 carried out by Wurmser (148) using Ulva lactuca. The energy efficiency 



