GBO-BLECTRIC RESPONSE OP SHOOT 445 



Galvanometric negativity is thus seen to indicate the 

 effect of direct stimulus, and galvanometric positivity that 

 or indirect stimulus. We thus see the possibility of elec- 

 tric detection of the effects of geotropic stimulation. This 

 method would, moreover, enable' us to discriminate the side 

 of the organ which undergoes greater excitation. 



EXPERIMENTAL ARRANGEMENTS FOR OBTAINING GEO- 

 ELECTRIC RESPONSE. 



Returning to the investigation on electric response to 

 geotropic stimulus, the specimen of plant is at first held 

 erect ; two electrodes connected with a sensitive galvano- 

 meter are applied, one to an indifferent point, and the 

 other to one side of the shoot. The sensitiveness of the 

 galvanometer was such that a current of one milllionth of 

 an ampere produced a deflection of the reflected spot of 

 light through 1,000 divisions of the scale. An action 

 current is produced on displacement of the plant from 

 vertical to horizontal position. 



Non-pularisable electrodes. — The electrical connections 

 with the plant are usually made by means of non-polaris- 

 able electrodes (amalgamated zinc rod in zinc-sulphate solu- 

 tion and kaolin paste with normal saline), I at first 

 used this method and obtained all the results which will 

 be presently described. But the employment of the usual 

 non-polarisable electrodes with liquid electrolyte is, for our 

 present purpose, extremely inconvenient in practice ; for the 

 plant-holder with the electrodes has to be rotated from 

 vertical to horizontal through 90-'. The reliability of 

 the non-polarisable electrode, moreover, is not above 

 criticism. The zinc-sulphate solution percolates through 

 the kaolin paste and ultimately comes in contact with 

 the plant, and seriously affects its excitability. The 

 name non-polarisable electrode is in reality a misnomer ; 



