486 



Prof. J. C. Bose. Influence of Electric 



results of experiments carried out by this method on the effect of feeble 

 current on conductivity, the conclusion was arrived at that excitation is better 

 conducted against the direction of the current than with it. In other words the 

 influence of an electric current is to confer a preferential or selective direction 

 of conductivity for excitation, the tissue becoming a better conductor in an 

 electric uphill direction compared with a downhill. 



The result was so unexpected that I have been long desirous of testing the 

 validity of this conclusion by independent methods of enquiry. In the paper 

 already referred to, I have described an automatic method for recording the 

 velocity of transmission of excitation in Mimosa where the excitatory fall of 

 the motile leaf gave a signal for the arrival of the excitation initiated at a 

 distant point. In this method the responding leaf is attached to a light 

 lever, the writer being placed at right angles to it. The record is taken on a 

 smoked glass plate which during its descent makes an instantaneous electric 

 contact, in consequence of which a stimulating electric shock is applied at a 

 given point E of the petiole (fig. 2). A mark in the recording plate indicates 

 the moment of application of stimulus. After a definite interval, the excitation 

 is conducted to the responding pulvinus P, when the excitatory fall of the 

 leaf pulls the writer suddenly to the left. From the curve traced in this 

 manner the time-interval between the application of stimulus and the 

 initiation of response can be found and the normal rate of transmission of 

 excitation through a given length of the conducting tissue deduced. The 

 experiment is then repeated with an electrical current flowing along the 

 petiole with or against the direction of transmission of excitation. The 

 records thus obtained enable us to determine the influence of the direction of 

 the current on the rate of transmission. I shall presently describe the 

 various difficulties which have to be overcome before the method just 

 indicated can be rendered practical. 



The scope of the investigation will be best described according to the 

 following plan. 



Part I. — Influence of direction of electric current on conduction of 

 excitation in plants. 



1. The genera] method of experiment. 



2. The effect of feeble heterodromous and homodromous currents on rate 

 of conduction. 



3. Determination of variation of conductivity by the method of minimal 

 stimulus and response. . 



4. The after-effects of heterodromous and homodromous currents. 



5. Phenomenon of reversal under moderate current. 



