146 Dr. J. Bur don-Sander son [June 9, 



WEEKLY EVENING MEETING, 



Friday, June 9, 1882. 



Sir Frederick Bramwell, F.K.S. in the Cliair. 



J. Burdon-Sanderson, M.D. LL.D. F.R.S. Joclrcll Professor of 

 Physiology in University Collega 



The Excitability of Plants.* 



Part I. Animal Excitability. 



The subject which I have to bring before you this evening may be 

 best defined as relating to one of the essential endowments of proto- 

 plasm, i. e. of the living material out of which the forms of animal 

 and plant life are moulded. It is one which we associate rather with 

 the nature of animals than with that of plants, though it is common 

 to both. In every kind of living matter we are able to observe an 

 alternation between quiescence and activity ; and that the transi- 

 tion from the former to the latter is determined by external influences, 

 in other words, excited by stimuli. But in general we confine the 

 term excitability to those cases in which the transition is sudden and 

 obvious, and particularly to those in which it is attended or followed 

 by visible changes of form of the excited jiarts. 



"When, in 1874, 1 had the honour of giving an address on a subject 

 included in the present, I had to announce what was then a new 

 discovery, namely, that a phenomenon which had been long known to 

 be characteristic of the transition from rest to action in animal proto- 

 plasm also manifested itself in the plant. In all animal structures 

 which are excitable or irritable, i.e. which possess the property of 

 being suddenly called into action when excited, it is found that the 

 waking up — the transition from rest to action — is attended by an 

 electrical disturbance which is of short duration, precedes action, and 

 follows excitation. 



It is well known that there are parts of plants which show the 

 same kind of " wakeableness " — which pass suddenly from quiescence 

 into motion when stimulated ; but until 1873 the question had not 

 been asked whether, here also, the going into action is attended with 

 electrical change ? 



In consequence of a suggestion made by Mr. Darwin one summer 



* Preceded by an abstract of a discourse on "Animal Excitability," delivered 

 on February 25, 1881. 



