152 CHAP. XVIII. THE TONIC FACTOR IN PHOTOSYNTHESIS 



Photosynthesis increased with increasing intensity of light : 

 at o -50 S it was 145, and at 1 -25 S it increased to 243. In 



Table XX. — -Photosynthesis under Cyclic Variation 

 of Intensity of Light 



(Negative Hysteresis) 



the return-curve we observe a relative enhancement of activity 

 in consequence of the previous stimulation. For, during 

 descent, the activity at o • 75 S was found to be 208 in the 



Table XXI. — Cyclic Photosynthetic Curve exhibiting 

 Positive Hysteresis 



place of 194 ; at 0-50 S the increase was from 145 to 174 ; 

 and the enhancement of activity due to previous stimulation 

 was found to persist throughout the series (Table XXL). 

 The return-curve is thus to the left, indicative of enhanced 

 activity and of positive hysteresis (fig. 42, p. 151). 



