ELECTROMOTIVE DETECTION OF EXCITATORY PULSE 263 



have also seen that water is expelled from an excited and 

 therefore contracted cell. It is further clear that when an 

 excitatory wave is proceeding in any direction, this cell-to- 

 cell passage of excitation will give rise to a cell-to-cell 

 contraction, the result of which will be a forward movement 

 of water, which will have the velocity, not of hydrostatic 

 transmission, but of the excitatory wave. The hydrostatic 

 disturbance is quite distinct, being transmitted with great 

 rapidity, and its presence has been shown in the preliminary 

 abnormal response of erection in leaflets of BiopJiytum 

 (p. 24). But that propulsion of water which is con- 

 comitant to the passage of true excitation is very much 

 slower, having the same speed as that of excitation itself. 



Summary 



The direct effect of stimulus is not transmitted by means 

 of hydrostatic disturbance, but by a cell-to-cell propagation 

 of excitation. 



This transmission of excitation from cell to cell is attended 

 by a cell-to-celi contraction. 



The passage of such a contractile wave may be detected 

 by the electrotactile method, which thus enables us to 

 determine the velocity of transmission of excitation, even 

 in tissues which are not motile. 



In consequence of the concomitance of the excitatory 

 wave with cellular contraction, water is moved forward pro- 

 gressively, with a velocity and in a direction the same as that 

 of excitation. 



This movement of water is not brought about by any 

 hydro-mechanical action, but is the direct effect of the con- 

 tractile wave due to excitation. The hydrostatic disturbance, 

 when present, is transmitted with very great velocity, and its 

 effect is seen in the abnormal preliminary response of erection, 

 exhibited, for example, by the leaflets of Biophytum. 



The velocity of transmission of excitation in ordinary 

 plants may also be found by determining the velocity of the 

 concomitant electromotive wave. 



