CHAPTER XIV 



POLAR EFFECTS OF ELECTRICAL CURRENT IN EXCITATION 

 OF PLANTS 



Polar excitation in animal tissues — Anomalous reactions in Protozoa — 

 Mono-polar method — Current Reverser — Excitatory polar action in 

 plant — Method of record — Effects of ascending and descending 

 currents in animal and plant — Records giving time-relations — 

 Potential slide — Measurement of e.m.f. and current — Potential key- 

 board. 



Towards the end of a previous chapter I made brief refer- 

 ence to certain remarkable excitatory effects which I have 

 observed in the plant tissue at the initiation or cessation of 

 a constant current. Electrical currents are well known 

 to have certain characteristic effects in the case of animal 

 tissues. On applying a current of feeble intensity to a 

 muscle-preparation by means of two suitable electrodes, 

 it is found that, at the moment of its sudden starting, an 

 excitatory contraction is initiated at the point of kathode — 

 that is to say, where the current leaves the tissue ; no such 

 effect takes place at the anode, the point at which it enters. 

 With current of feeble intensity there is, again, no excitatory 

 effect either at the anode or the kathode on the cessation or 

 break of current. It should be remembered that these 

 marked exhibitions of excitation are caused by sudden 

 variation of the current. They do not take place if the 

 current variation is made very gradual. 



These excitatory effects occur not only when the appli- 

 cation of the current is direct but also when it is indirect. 

 That is to say, when the two electrodes are applied on 

 the conducting nerve in a nerve-and-muscle preparation, 



