38 CHAP. V. PHOTOSYNTHESIS AND INTENSITY OF LIGHT 



of light. — The photosynthetic activity increases, up to the 

 turning-point, with the intensity of light. The formula 

 given below gives the approximate value of activity A L at 



a higher intensity of light L, from the activity Aj at the 



lower intensity /. A more exact formula will be given later. 



A = A/ x ^ (!) 



Examples : 



Specimen I. 



Activity at 500 lux = 131 -4 c.mm. per hour. 



Calculated value for 1000 ,, = 131-4 X ' =262-8 



500 



Observed activity = 265 • 6 



Specimen III. 



Activity at 750 lux = 184 • o 



Calculated value for 1000 ,, = 184-0 x = 245-3 



Observed activity . = 240 • 



Specimen IV. 



Activity at 750 lux = 64-5 



112^ 



Calculated value for 1 1 25 ,, = 64-5 X - == 96-5 



Observed activity .... =102-0 



For the determination of the coefficient for light I 

 employ two independent methods — the Direct, in which 

 the measurements are made on the physiological scale 

 (Chap. XXVI.), and, secondly, the Differential Method. It 

 may be stated here that the coefficients obtained by these 

 two independent methods show a very close agreement with 

 each other. 



Determination of the Coefficient by the 

 Differential Method 



We found that the photosynthetic curve is practically 

 straight in the middle range. The coefficient for light is 



