36 CHAP. V. PHOTOSYNTHESIS AND INTENSITY OF LIGHT 



rate was very slow. At 300 lux the rate was 77-1 cubic 

 mm. per hour. This increased continuously with increased 

 intensity of light till at 1000 lux the rate was 265-6. The 

 curve is straight from 300 to 1200 lux, after which it tends 

 to become horizontal, the turning-point being slightly above 

 1200 lux (fig. 7). In summer, when the temperature is 

 relatively high, the curve exhibits a reversal above an 

 intensity of 1500 lux or so. Very strong light thus induces 

 an actual depression in photosynthesis. The general formula 

 for the upper curve in fig. 7 is : 



y = 3-13% — o-o8^ 2 — o-ooo2% 3 . 

 I give below detailed results of three typical experiments 

 carried out in spring. 



Table V. — -Variation of Activity under Increasing Intensity 

 of Light from Pointolite. (Spring-specimens) 



