264 CHAP. XXVII. SIMULTANEOUS VARIATION OF FACTORS 



Theoretically, (1) x (2) X (3) X original activity 



= 1-65 x 1-96 x 1-49 X 50-4 = 242 -9 c.mm. 

 Observed value (d) = 245-4 >> 

 Thus it is evident that when there are three variable 

 factors the results conform to the Law of Product. 



A 



LCT 



is a constant. 



VI. Four Variables : C0 2 -Concentration, Light, 

 Temperature, and Tonic Condition 



Having determined the effect of simultaneous variation 

 of C0 2 -concentration, light and temperature, there remains 

 only the factor of tonic condition. As previously explained 

 it is not easy to produce a definite change of tonicity at will. 

 The effect of season was, however, found to be fairly definite, 

 the photosynthetic activity in spring being about 1-8 times 

 that in winter (p. 40). 



One of the means of raising the tonic level of the plant 

 is by supplying it with infinitesimal quantities of certain 

 chemical substances. It was found that an addition of 0-5 

 part of HNO3 in a billion greatly increased the photo- 

 synthetic activity. In specimens already active the increase 

 was about 50 per cent., while in less active specimens it was 

 as high as 200 per cent. 



In the experiments carried out to observe the effect of 

 change in four variables, the sequence was as follows : — 



(a) Activity for C0 2 -concentration 3 mg., 



light 750 lux, temperature 20° C. 



without any trace of HNO3 . . 110-5 c. mm. O 



(b) Activity for C0 2 -concentration 5 mg., 



light 750 lux, temperature 20 C. 



without trace of HN0 3 . . 183-0 c.mm. O 



(c) Activity for C0 2 -concentration 5 mg., 



light 1500 lux, temperature 24 C. 

 with addition of -5 part of HN0 3 

 in a billion . . . .748 -2 c.mm. 



