CHAPTER XXVII 



PHOTOSYNTHESIS UNDER SIMULTANEOUS VARIATION 

 OF DIFFERENT FACTORS 



Problem of effect of simultaneous variation — Mutual interaction or inde- 

 pendent reaction unaffected by other factors — Law of Product — Com- 

 bined effects of increasing complexity — I. Two variable factors : C0 2 - 

 concentration and light — II. Variable factors: C0 2 -concentration and 

 temperature — III. Variable factors : light and C0 2 -concentration ; light 

 carried through half a cycle and C0 2 -concentration in two stages — 

 IV. Variable factors: light and temperature; light of two intensities 

 and temperature carried through a cycle — V. Three variable factors : 

 light, C0 2 -concentration and temperature — VI. Four variable factors : 

 C0 2 -concentration, light, temperature and tonic condition. 



It has been shown that the effect of variation of the individual 

 factors in photosynthesis may be expressed by a correspond- 

 ing series of constants. We have now to consider the cases 

 in which two or more of the factors vary, and to attempt to 

 formulate a comprehensive law which will enable us to 

 express the combined effects produced by simultaneous 

 variation of the essential factors C0 2 -concentration, in- 

 tensity of light, temperature and tonic condition. Of 

 these the first three are under our control, while the tonic 

 condition cannot at present be modified in a quantitative 

 manner. There is no doubt that even this last factor comes 

 under the general law which it is our object to establish. 



In the following discussion we represent the strong 

 intensities by capitals (C, L, T), and the weak intensities by 

 italic letters (c, I, t) : the values on the physiological scale 

 are represented by thick capitals (C, L, T). 



Combined Effects of Different Factors 



The main problem is to ascertain whether the characteristic 

 effect produced by variation of one factor is modified by the 



