THE METHOD OF CYCLIC CURVE 



151 



descending curves did not coincide, but the return-curve was 

 to the right of the ascending curve, indicative of depression of 

 activity, the physiological hysteresis being negative (fig. 41). 

 Positive hysteresis. — In this experiment the specimen was 

 in sub-tonic condition, and sunlight had to be employed for 



Fig. 41 Fig. 42 



Fig. 41. Negative Hysteresis 



The return-curve is to the right, photosynthetic activity being 

 depressed after the cycle. 



Fig. 42. Positive Hysteresis 



The return-curve is to the left, photosynthetic activity being 

 enhanced after the cycle. 



initiating photosynthesis. The Cyclic Curve was obtained 

 under an intensity of light increasing by steps from o • 10 S 

 to 1-25 S and back once more to o-io S. At the com- 

 mencement of the experiment the intensity of o-io S was 

 below the minimum ; hence it did not cause any photo- 

 synthesis : at o -20 S the activity was 104 c.mm. per hour. 



