40 



PLANT RESPONSE 



that fundamental molecular change which underlies excita- 

 tion, and which disappears on the restoration of molecular 

 equilibrium. 



Universality of responsiveness in matter. — If we take 

 a plant-tissue and subject it to a sufficient degree of cold, its 

 responsive power will be found to disappear. It reappears, 

 however, on the return of the tissue to the normal tempera- 

 ture. The power of response is thus seen to depend on the 

 molecular condition of the substance. 



Now this irritability, or power of responding to stimulus, 

 may be vaguely regarded as a characteristic property of 



living substances ; and we 

 may evade the difficulty of 

 any attempt at a real ex- 

 planation by describing it 

 as a ' vital ' phenomenon. 

 But if we regard all such 

 phenomena as due ulti- 

 mately to physico-chemical 

 actions, we cannot rest 

 satisfied with what is, after 

 all, a mere descriptive 

 phrase. Progress can only 

 be made in scientific in- 

 quiry by attempting gradu- 

 ally to discard all such 

 assumptions of the working 

 of mystical forces in favour 

 of simpler and more rational 

 explanations. 

 By following the electrical method of inquiry which has 

 just been described, I have been able to prove that the power 

 of responding to stimulus, and, under certain conditions, the 

 arrest of this power, is the characteristic not of organic matter 

 only, but of all matter, both organic and inorganic ; ' and that 

 in general the various agencies which bring on the modifica- 



' Bose, Ri'spoiisf in the Lh'ing and N'on-Li7<iug. 



Fig. 29. Response of Metal abolished 

 by the action of ' Poison ' (Oxalic 

 Acid) 



The record to the left is the normal 

 response, and the line to the right 

 shows abolition of response on 

 application. 



