224 COMPARATIVE ELECTRO-PHYSIOLOGY 



These observations relate firstly to the existing current of 

 rest in the petiole and midrib, and the variations of this 

 resting-current, whether under excitation of the lamina, or by 

 section of the petiole, or again, by the action of electro- 

 tonus; and secondly, to the induction of variations of a 

 transverse current between the upper and lower surfaces, of 

 the lamina. As regards the current in the petiole and its 

 prolongation the midrib, which I shall distinguish as ( the 

 longitudinal petiolar current/ Burdon Sanderson found this 



X ^ X 



FIG. 147. Natural and Responsive Currents in Leaves 



(a) Leaf-Jand stalk-currents in Diotiira. Natural current, N, flows out- 

 wards <-A->, s being stalk-current, and L leaf-current. Stimulation 

 of lamina at x gives rise to responsive current, R, from right to left, 

 inducing negative variation of leaf-current and positive variation of 

 stalk-current. When stimulus, however, is applied on left at x , 

 responsive current, R, is from left to right, inducing effects exactly 

 opposite of former, viz. negative -variation of stalk-current and positive 

 variation of leaf-current ; (b) Leaf- and stalk-currents in Fit us rtli- 

 giosa similar to those of Dioticea. Natural current flows out \\ards 

 <-A->. Stimulation of lamina at x gives rise to responsive current, 

 R, inducing negative variation of leaf- and positive variation of stalk- 

 currents ; (c) Leaf- and stalk-currents of Citrus decutnana, opposite 

 to those of Ficus and Dionma, -- A <-. Stimulation at x induces 

 positive variation of leaf and negative variation of stalk-currents. 



to flow in the midrib, from the end proximal to the stalk to 

 the distal end. This he designated as the ' normal leaf- 

 current.' He further found that if electrical connections were 

 made, so that one contact was near the lamina, and the other 

 away from it, the stalk-current was opposite in direction to 

 the leaf-current (fig. 147 (#)). 



On stimulation of the lamina, these resting leaf-and-stalk 

 currents were found to undergo responsive variations. But 

 these changes were exactly opposite to each other. That is 

 to say, the leaf-current underwent a negative, and the stalk- 



