THE LAWS OF PHOTOSYNTHESIS 



249 



scale to obtain the intensity of light L on the physiological 

 scale. 



The physiological zero does not differ greatly from the 

 minimum intensity of light at which the evolution of gas 

 becomes arrested. There is incipient photosynthesis at a 

 minimum intensity of light though there is hardly any 

 collection of gas in the Bubbler : a few bubblets are, 

 however, formed at the cut end of the plant at as low an 

 intensity as 50 lux. As it is here shown that photosyn- 

 thetic activity is strictly proportional to the intensity of 

 light measured on the physiological scale, and as the 

 necessary correction is relatively small, the activity is 

 approximately proportional to the intensity measured on 

 the physical scale. 



Table XXXVI. — Determination of the Coefficient for 

 Variation of Intensity of Light 



