l62 CHAP. XIX. THE DAILY VARIATION IN ACTIVITY 



the curve of light between 10 a.m. and I p.m., during which 

 time the light remained approximately constant at about 

 68. It should, however, be remembered that there was 

 always a slight fluctuation brought about by changes in 

 the direction of the wind, charged as it was with relatively 



Table XXIII. — Giving Variation of Light, Temperature, 



and the Resulting Photosynthetic Activity, in the 



Course of the Day 



(On the day of the experiment, January 24, 1923, the sun rose 

 at 6.46 a.m. and set at 5.38 p m.) 



dry and moist air. The temperature rose to a maximum 

 of 3o°'9 at 2 p.m. ; it had already attained 30°- 5 at 1 p.m., 

 this temperature being above the general optimum for the 

 light from the sky. 



Such were the simultaneous variations of the two factors, 

 light and temperature, producing resultant variations in 

 photosynthetic activity which at first sight would appear 

 to be almost inexplicable. For, while the light was practi- 

 cally at its constant maximum between 10 a.m. and 1 p.m., 

 photosynthetic activity was being enhanced because of the 



