SUMMARY 97 



Summary 



Intermittent illumination of increasing duration lowers 

 photosynthetic efficiency till a turning-point is reached, after 

 which there is a partial recovery of efficiency. 



This is a crucial test, the results of which support the 

 theory of photic stress and resulting molecular strain. 



With a short intermission-period the efficiency is mo- 

 mentarily above the normal. A probable explanation of 

 this is found in the fact that under continuous illumination 

 the resultant effect is A— D ; on the cessation of light A 

 persists "longer than D, as demonstrated in the experiment 

 described in Chapter X. 



H 



