62 COMPARATIVE ELECTRO-PHYSIOLOGY 



indication was found to be one of considerable electro- 

 positivity. On finally killing the plant, however, the positive 

 change due to water-movement was. found to represent so 

 insignificant a proportion of the whole as to be negligible, 



In order to exhibit the electrical expression of the 

 excitatory and hydro-positive effects of stimulation, in 

 ordinary plants, I took a petiole of cauliflower and made 



one connection, the proximal, 

 with a point on it, and the other 

 with an indifferent point on the 

 surface of the lamina. In order 

 to obtain the unmistakable hydro- 

 static effect, the petiole was sud- 

 denly squeezed, at a distance of 

 6 cm. from the proximal contact, 

 and this gave rise, as will be seen 

 (fig. 47, a), to a positive response, 

 represented downwards. This 

 was repeated once more, and the 

 same effect observed. I next 

 applied thermal stimulus at a dis- 

 tance of 4 cm. from the respond- 

 ing point. In this case hydro- 

 static and excitatory disturbances 

 reached the contact, the hydro- 

 "ok static shortly followed by the 

 of Cauliflower excitatory, as in the case of the 



a, hydro-positive ; b, di-phasic ; experiment on Mimosa. This 



c, excitatory negative responses. r 



is seen in the record, as a di- 

 phasic response, the hydrostatic positive being followed by 

 the excitatory negative (fig. 47, &). 



Reference has already been made to the observation of 

 Burdon Sanderson, that in the lamina of the Dioncea leaf the 

 immediate response was one of galvanometric positivity. Mis- 

 taking this for the true excitatory effect, he concluded that 

 the response of the plant was of opposite sign to that of the 



