238 COMPARATIVE ELECTRO-PHYSIOLOGY 



expression, the former is masked by it, and we obtain here 

 only the excitatory negative variation (fig. 155 (<:)). 



It only remains to consider the responses which Burdon 

 Sanderson obtained with symmetrical contacts (fig. 1 52) on the 

 under-surfaces of the two lobes. In the next figure (fig. 153) 

 is reproduced his record of electrical response, obtained on 

 mechanical stimulation of a sensitive filament situated on 

 the upper surface of the right lobe, vertically above the 

 right-hand led-off. This response is, as will be seen, di- 



FIG. 155. Photographic Records of Positive, Diphasic, and Negative 

 Responses of Petiole of Musa depending on the Effective Intensity 

 of Transmitted Stimulus 



(a) Here stimulus was applied at a distance and hydro-positive effect 

 alone transmitted ; (d) Stimulus was applied nearer, and the positive 

 effect was succeeded by the true excitatory negative ; (c) Stimulus was 

 applied very near, with the result of true excitatory negative response. 



phasic, its first phase being one of relative positivity of 

 the under-surface of the excited lobe, and the second 

 representing its subsequent relative negativity. This first 

 phase is clearly due to the earlier transmission of the 

 hydro-positive or indirect effect of excitation, from the 

 stimulated point on the upper surface. It was supposed 

 by Burdon Sanderson that the second phase of this re- 

 sponse represented the later arrival of the same positive 

 effect at the distal second contact, which would thus induce 

 reversal. But it appears much more probable that this 

 second phase of negativity is due to the arrival at the 



