488 Prof. J. C. Bose. Influence of Electric 



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obtained on direct stimulation was, as stated before, 0*1 second. Eepetition 

 of the experiment always gave a time-interval of 1*5 seconds for indirect and 

 0"1 second for direct stimulation. Now, on completing the circuit of the 

 constant current, which for convenience I shall indicate as the polarising 

 circuit, the time-interval for indirect stimulation was at once reduced to 

 O'l second, which is the value of the latent period for direct stimulation. 

 This happened on the mere completion of the polarising circuit, with 

 current reduced even to zero. It is evident that this untoward result was 

 due to the escape of the alternating induction current, which went not 

 merely across the short path from E to E', but also round by the circuitous 

 path of the polarising circuit. It was the escaping current which caused the 

 direct excitation of the pulvinus. This particular difficulty I was finally 

 able to overcome by interposing the electromagnetic device of a choking coil, 

 which effectively prevented the passage of the alternating induction current 

 into the polarising circuit (fig. 2). 



Precaution has to be taken against another source of disturbance, namely, 

 the excitation caused by the sudden commencement or the cessation of the 

 constant current. I have shown elsewhere* that the sudden initiation or 

 cessation of the current induces an excitatory reaction in the plant-tissue 

 similar to that in the animal tissue. This difficulty is removed by the intro- 

 duction of a sliding potentiometer, which allows the applied electromotive 

 force to be gradually increased from zero to the maximum or decreased from 

 the maximum to zero. 



The experimental arrangement is diagrammatically shown in fig. 2. After 

 attaching the petiole to the recording lever, indirect stimulus is applied, 

 generally speaking, at a distance of 15 mm. from the responding pulvinus. 

 Stimulus of electric shock is applied in the usual manner, by means of a 

 sliding induction coil. The intensity of the induction shock is adjusted by 

 gradually changing the distance between the secondary and the primary, 

 till a minimally effective stimulus is found. In the study of the effect of 

 direction of constant current on conductivity, non-polarisable electrodes make 

 suitable electric connections, one with the stem and the other with the tip 

 of a sub-petiole, at a distance from each other of about 95 mm. The point 

 of stimulation and the responding pulvinus are thus situated at a consider- 

 able distance from the anode or the kathode, in the indifferent region in 

 which there is no polar variation of excitability. By means of a Pohl's 

 commutator or reverser, the constant current can be maintained either 

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



* Bose, ' Plant Eesponse ' (1906) ; ' Irritability of Plants ' (1913), Longmans, Green 

 and Co., London. 



