COMBINED EFFECTS OF DIFFERENT FACTORS 253 



interaction of another which is also varying independently, 

 or whether each factor produces its own characteristic effect 

 unaffected by the action of any other factor. 



An illustrative example borrowed from Physics will 

 make the meaning clear. The volume of a given quantity 

 of a gas is determined by the action of two different factors 

 —temperature and pressure. Thus if T represents the 

 absolute temperature, and if the pressure remains unchanged, 



V 



V oc T or - is a constant. 



When the temperature remains constant 



V oc — or VP is a constant. 



If the pressure be doubled the volume will be halved. 

 But this increased pressure will not in any way affect the 



ratio ^ being a constant ; that is to say each factor acts 



VP 



independently, so that we arrive at the general formula -^- 



which is constant under all variations of the constituent 

 factors. It is to be understood that the above law holds 

 good in regard to the median range of variation, i.e. as long 

 as the physical condition of the gas does not undergo any 

 transformation. The law is no longer applicable at the 

 limit where the gas, under excessive pressure, becomes 

 converted into a liquid. Both physical and physiological 

 laws are understood to be applicable within certain normal 



limits. 



I will now proceed to adduce experimental evidence 

 proving that in photosynthesis the characteristic effect of each 

 factor is unaffected by that produced by others ; and further, 

 that if the increase of photosynthetic activity 



by change from c to C be x times 

 ItoLbey „ 

 t toTbe z ,, 



then the resulting variation in activity by simultaneous 



