250 CHAP. XXVI. THE PHYSIOLOGICAL SCALE 



The detailed results of measurement on the physiological 

 scale are given in the table on p. 249, for the spring-speci- 

 mens I. and II. and for the winter-specimen V. (cf. Tables V., 

 VI., pp. 36, 37). 



The coefficient determined on the physiological scale is 

 thus found to be a constant for every point in the median 

 range, its value being the same as that determined by the 

 differential method. 



The law of photosynthesis under variation of light is that the 

 ratio of activity to light is constant. 



y is a constant. 



Photosynthesis under Variation of Tonic 



Condition 



The experimental investigation of the effect of variation 

 in tonic condition is rendered difficult, since the conditions 

 for inducing a definite and quantitative variation in the 

 tonic level are, generally speaking, beyond our control. A 

 certain variation was produced by the addition of minute 

 traces of certain chemical substances such as HN0 3 , the 

 enhancement of activity thus produced varying in different 

 specimens from 50 to 200 per cent., the smaller increase 

 taking place in cases where the plant was already very active 

 (p. 68). 



The change in the tonic condition due to the influence 

 of season is, however, more definite than the foregoing. It 

 is possible to obtain a measure of the tonicity from the co- 

 efficient for light ; activity of an ascertained value of 13 -2 in 

 winter, increased to 24.' 9 in spring (p. 40). Hence the ratio 

 of tonicity in spring P s to that in winter P w is : 



Ps 24 • 9 _ 1 • 8 



The tonicity for spring is thus 1 • 8 times that of winter. 



The coefficient of activity for C0 2 -concentration in spring- 



