CHARACTER OF TRANSMITTED IMPULSE 171 



tatory action induced by this reagent ; its toxic power in 

 abolishing conductivity is however very great. A strong 

 solution is applied on a portion of the petiole in the usual 

 manner, the leaflets remaining open and fully sensitive all 

 the time. After an interval of an hour it is found that 

 the effect of a strong thermal stimulus applied in the stem 

 fails to be transmitted across the poisoned zone. The 

 sensibility of the leaflets is however found unaffected. 

 The leaflets in those petioles which have not been poisoned 

 exhibit vigorous response to transmitted excitation. 



(2) Experiment with Mimosa 



I was next desirous of testing the effect of poison on a 

 different species of plant and verifying the result by means of 

 automatic records. The effect of copper sulphate solution in 

 abolishing conductivity was not, as we saw, immediate ; 

 it required time to have its toxic effect fully developed. 

 Hence it appeared of much interest to test, by means of 

 successive records, the progressive diminution of conducting 

 power culminating in actual arrest. The specimen employed 

 for these series of investigations was the petiole of Mimosa. 

 Successive records of transmission-time were taken at 

 intervals of 20 minutes, before and after subjecting an inter- 

 mediate portion of the petiole to the action of poison. Effec- 

 tive stimulus of the induction-shock was applied on the 

 petiole, generally at a distance of 30 mm. from the responding 

 pulvinus. The intensity of stimulus employed was maximal, 

 being 2 units. The first record of the series gives the velocity 

 of normal conduction ; the second and the subsequent 

 records exhibit progressive action of the toxic agent. This 

 latter was applied on a strip of cloth 10 mm. wide, wrapped 

 round the petiole midway between the point of stimulation 

 and the responding pulvinus. 



Copper sulphate solution. — ^The normal record (i) in 

 fig. 94 shows response to have taken place 27 spaces after 

 the application of the stimulus, the interval between the 



