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Sir J. C. Bose and Mr. S. C. Guha. 



but this will undergo a rapid diminution in radial directions outwards. If 

 the stimulus be moderate or feeble the irradiation will be slight. 



Fig. 5. — The Electric Probe for localisation of nervous tissue in plants. P, the probe 

 in circuit with the galvanometer, G ; S, the screw head, by the rotation of which 

 the probe enters the petiole in successive steps ; I, index by which the depth of 

 intrusion may be determined. 



The experimental procedure is as follows : — The probe is intruded perpen- 

 dicularly along the diameter of the petiole. The intrusion of the probe is by 

 steps, say of 0'05 or 01 mm. at a time. The slight wound produced by the 

 insertion of the tip of the probe causes an excitation, which subsides completely 

 in the course of about fifteen minutes. The sub-petioles are now stimulated 

 by suitable stimuli, which may be chemical, thermal, mechanical or electric. 

 The excitatory impulse is propagated preferentially along certain conducting 

 channels in the petiole. The results to be described were obtained with all 

 the different modes of stimulation. The electric mode of stimulation has the 

 advantage that it can be maintained constant or varied in a graduated manner. 

 Special precautions are taken that there should be no disturbance caused by 

 leakage of the stimulating current ; this is verified by the fact that reversal 

 of primary current which actuates the secondary coil causes no change in the 

 electric response ; the excitatory electric change in different layers of tissue 

 is, moreover, definitely related to the character of the tissue. 



I shall anticipate results by describing the characteristic effects. The 

 excitatory electric change detectable in different layers as the probe passes 



