320 LECTURE XIV. 



Jiirgensen and by Heidenhain. Ranke not only succeeded in 

 detecting the above-mentioned currents which, as he points 

 out, resemble the so-called "normal currents" of du Bois- 

 Reymond in muscle and nerve, but he detected .others as 

 well. He found, namely, that if the epidermis of a piece of a 

 stem or of a petiole be removed and one electrode be placed 

 upon this artificial longitudinal section and the other on the 

 transverse section, a current passes through the galvanometer 

 from the transverse to the longitudinal section. This current 

 he distinguishes, as the " true current," from the current men- 

 tioned above as passing from the uninjured surface to the 

 transverse section which he calls the " false current." 



A series of minute observations of this kind has been 

 made by Munk on the leaf of Dioncea mtiscipula (Venus' fly- 

 trap). He finds, first, that the mid-rib is positive to all points 

 of the lamina on either surface : secondly, that a point on 

 the mid-rib, at the junction of its proximal third with its 

 distal two-thirds, is positive as regards all other points on 

 the mid-rib ; this is, therefore, the point of greatest positivity 

 of the whole surface : thirdly, that in any transverse strip 

 taken right across the leaf, the most positive point lies in the 

 portion of the midrrib included in the strip, and there are 

 two points on the portion of lamina included in the strip 

 which are negative with regard to all other points on the 

 strip ; these points, the points of greatest negativity of the 

 strip, are situated in the lamina, one on each side of the, 

 mid-rib, about half-way between it and the margin : by im- 

 agining the leaf to be divided into a number of such strips, 

 and by joining the negative points of the successive strips 

 the two negative lines are obtained ; all points in the two 

 negative lines are isoelectric : fourthly, that all points situated 

 symmetrically with regard to the mid-rib are isoelectric : 

 fifthly, that a point on the mid-rib which is relatively near the 

 point of greatest positivity is positive as regards all points 

 which are relatively distant from that point ; in the lamina, 

 a point which is relatively near to one of the lines of nega- 

 tivity is negative as regards all points which are relatively 

 distant from it : sixthly and lastly, that the distribution of 



