THE METABOLISM OF PLANTS. 



321 



potential is the same on both surfaces of the leaf, and that 

 symmetrically placed points, one on the upper and the other 

 on the lower surface, are isoelectric. 



The accompanying diagram will make this description more in- 

 telligible. 



FlG. 39 (after Munk). Distribution of potential on the surface of the leaf of 

 Dioncea musciptila. The shaded vertical portion represents the mid-rib. The 

 curves with arrow-heads mark the directions of the currents passing through 

 the galvanometer from relatively positive to relatively negative points of the 

 ' surface of the leaf. 



Burdon-Sanderson however finds that any point on the 

 upper (ventral) surface of the leaf of Dionsea is usually nega- 

 tive to the corresponding point on the lower (dorsal) surface. 

 He has also made the interesting observation that when a 

 voltaic current is passed through the petiole near its junction 

 with the lamina, it affects any " normal " current in the mid- 

 rib in such a way that the normal current is strengthened 

 when the current led through the petiole travels in the same 

 direction as the normal current, and that the normal current 

 is weakened when the current led through the petiole travels 

 in the opposite direction. He draws attention to the simi- 

 larity between these phenomena and those exhibited by 

 nerves (electrotonus) under the same conditions. 



The question now arises whether or not these currents are 

 dependent upon the metabolism of the plant, that is, whether 

 they indicate a real dissipation of energy in the form of elec- 

 v. 21 



