i 7 4 RESEARCHES ON IRRITABILITY OF PLANTS 



Record 3 was taken with the secondary pushed close to the 

 primary, the stimulus intensity being thus raised to 15 

 units. Even under this intense stimulation the conduction 

 was found to be arrested. Record 4 was obtained under 

 direct stimulation. The response shows that the sensi- 

 bility of the pulvinus had undergone no change. It is thus 

 clear that the abolition of response to indirect stimulation 

 was solely due to the abolition of conductivity induced by 

 the action of poison. 



The arrest of the transmitted impulse in Mimosa by 

 the physiological block induced by cold, by electrotonus, 

 and by local application of poison, completely disproves 

 the hydro-mechanical theory. The results of the various 

 investigations that have been described lead on the other 

 hand to the conclusion that the transmission of excitation 

 in the plant is a process fundamentally similar to that which 

 takes place in the animal, being in the one case as in the 

 other a propagation of protoplasmic change. 



Summary 



Excitatory reaction is initiated in the petiole of various 

 sensitive plants by the discriminative polar action of an 

 electric current. Excitation is induced at the kathodic 

 point at ' make ' and at the anodic point at ' break.' 



Transmission of such an excitatory impulse takes place 

 in the absence of all mechanical disturbances. 



The excitatory nature of the impulse in plants is further 

 demonstrated by the arrest of conduction brought about by 

 various physiological blocks. 



Local application of increasing cold retards and finally 

 abolishes the conducting-power. 



Conductivity is for a time paralysed as an after-effect of 

 application of cold. The lost conducting-power may, how- 

 ever, be quickly restored by tetanising electric shocks. 



The electrotonic block induces an arrest of conduction 



