CHAPTER XXI 



ON DETECTION OF EXCITATORY PULSE DURING TRANSIT 

 BY ELECTROTACTILE AND ELECTROMOTIVE METHODS 



Pfeffer's experiment on expulsion of water from excited cells — Author's experiment 

 on a delicate method of detecting excitatory expulsion of cell-sap —Chemical 

 method of determining velocity of transmission of excitation — Electrotactile 

 detector — Demonstration of passage of excitatory contractile wave by means 

 of electrotactile method — Determination of velocity of transmission of exci- 

 tation in ordinary plants by electromotive method — Excitatory versus hydro- 

 mechanical movement of water. 



The fact that the excitatory wave is propagated with a 

 constant and measurable velocity was demonstrated, with 

 regard to sensitive plants, in the last chapter, the arrival of 

 the wave from a distance at the motile organ being detected 

 by means of mechanical response. As ordinary plants, on 

 the other hand, do not possess such efficient motile indicators, 

 some other method, more universally applicable, is necessary 

 in order to show that in these also the state of excitation is 

 transmitted from point to point. 



Before describing the two methods which I have devised 

 for this purpose, I shall give an account of a very interesting 

 experiment, depending on chemical reaction, by which I have 

 been able not only to demonstrate in a striking manner the 

 expulsion of water from excited cells, but also to make a 

 rough determination of the velocity of transmission. It was 

 shown by Pfefferthat on exciting the lower side of a pulvinus, 

 water oozes out from the cut end. On taking a detached 

 pulvinus, and stimulating the lower surface with a blunt 

 needle, he found that the organ curved downwards, and a 

 drop of water was seen to escape from the cut end. 



