POLAR EFFECTS UNDER STRONG CURRENTS 265 



excitations, moreover, cannot very well be explained on 

 the assumption of hypothetical secondary poles. The 

 view that these effects are physiological will become 

 strengthened when in the course of the next chapter 

 we shall observe the modification of polar effects under 

 physiological changes. 



Summary 



As moderate increase of intensity of current transforms 

 the polar reaction from Type I. to Type II., so also further 

 increase in the intensity of current gives rise to reactions 

 indicative of other types. 



Pfluger's Law is not a complete statement of the polar 

 action of currents. Under strong intensities of current, 

 two additional types of reaction — Type III. and Type IV. — 

 make their appearance. These are included in the 

 following supplementary Law of Polar Effect of Strong 

 Currents : — 



Under the action of strong current, excitation takes 

 place at the make of kathode and make and break of 

 anode. 



Under still stronger currents, excitation takes place at 

 the make and break of both kathode and anode. 



These four characteristic types of reactions are serially 

 observed in all sensitive plants under increasing intensities 

 of current. 



