244 



CHAP. XXVI. THE PHYSIOLOGICAL SCALE 



the physiological constants with a high degree of accuracy. 

 The photosynthetic curve in the median range is straight ; 



Fig. 57. Photosynthetic Curve under Variation of Temperature 



Curve produced backwards cuts abscissa at 9°-2, which is the 



physiological zero. The temperatures T 1( T 2 , T 3 , T 4 on the 



physiological scale are given in the upper and on the 



centigrade scale in the lower line. 



when produced it cuts the abscissa at a point which is taken 

 as the physiological zero. In the photosynthetic curve 

 under variation of temperature given in fig. 57, the zero is 

 at 9 -2. This physiological zero-temperature is not very 



