446 LIFE MOVEMENTS IN PLANTS 



for the action current (whose polarising effect is to 

 be guarded against) is excessively feeble, being of the 

 order of a millionth of an ampere or even less ; the 

 counter polarisation induced by such a feeble current is 

 practically negligible. 



The idea that non-polarisable electrodes are meant to 

 ged rid of polarisation is not thus justified by the facts 

 of the case. The real reason for its use is very 

 different ; the electrical connections with the plant has 

 to be made ultimately by means of two metal contacts. 

 If we take two pieces of metal even from the same 

 sheet, and put them in connection with the plant, a 

 voltaic couple is produced owing to slight physical 

 differences between the two electrodes. Amalgamation of 

 the two zinc rods with mercury reduces the electric 

 difference but cannot altogether eliminate it. 



I have been able to wipe off the difference of poten- 

 tial between two pieces of the same metal, say of plati- 

 num, and by immersing them in dilute salt solution 

 from a voltaic couple. The circuit is kept complete 

 for 24 hours, and the potential of the two electrodes 

 by this process is nearly equalised. A perfect equality 

 is secured by repeated warming and cooling of the 

 solution and by sending through the circuit, alternat- 

 ing current which is gradually reduced to zero. I have 

 by this means been able to obtain two electrodes which 

 are iso-electric. The specially prepared electrodes (made 

 of gold or platinum wire) are put in connection with 

 the plant through kaolin paste moistened with normal, 

 saline solution. Care should be taken to use opaque cover 

 over the plant-holder, so as to guard against any possible 

 photo-electric action ; moistened blotting paper maintains, 

 the closed chamber in a uniform humid condition. 



