INFLUENCE OF DIRECTION OF ELECTRICAL CURRENT 99 



Cells laid upon the positive electrode may, if dead, evolve electrolytic 

 oxygen for a short time after the current has ceased, but this is a purely 

 electro-chemical phenomenon, and in living cells this oxygen is absorbed 

 by the protoplasm, and hastens its death. 



SECTION 44. The Influence of the Direction of the Electrical 

 Current. 



Elfving l found that when a fairly strong electric current passes 

 longitudinally through a root, growth is retarded, and that most markedly 

 when the direction of the current is opposed to that of growth. Weaker 

 currents, however, yield negative results 2 , and we may safely regard the 

 positive results as being due to the electrolytic action of the stronger 

 current, the electrolytic ions liberated at the anode acting more injuriously 

 upon the growing apex than those liberated at the kathode. It must, 

 moreover, be remembered that the electrolytic effect is not confined to 

 the electrodes, but may take place at every point in the path of the current 

 at which it passes from a conducting medium to an electrolytic solution, 

 or even from one electrolytic solution to another, if these are dissimilar 

 and of restricted distribution. The ions of water, and of all salts uniformly 

 permeating the plant, will appear mainly at the electrodes, but any electro- 

 lytic substance present in a particular cell only will be electrolyzed in that 

 cell, and its ions will appear on the opposite sides of the cell. The action 

 is the same as when a current is led in series through solutions of gold, 

 silver, and copper, all of which it decomposes simultaneously. 



Recent investigations 3 have shown that when a weak current passes 

 transversely through roots growing in soil, it apparently accelerates their 

 growth, but this is probably owing to the influence of the current in 

 accelerating the solution and absorption of the insoluble food-constituents 

 present in the soil. In any case, it seemed of interest to determine 

 whether any relation exists between the direction of streaming and the 

 action of the current. Velten 4 has shown that electrical currents affect 

 streaming equally, whether in the same or in the opposed direction, 

 although in dead cells filled with floating particles, a fictitious streaming 

 may be induced which is reversed on reversing the current. 



Hermann (I.e.) has already shown that the increased excitability 

 at the kathode on making, and at the anode on breaking, the current 

 constitutes an excitation when sufficiently strong currents are used, so that 



1 Bot. ztg., 1 882, p. 257. 



8 Muller-Hettlingen, Pfliiger's Archiv f. Physiol., 1883, Ed. xxxi, p. 212. 



3 For literature see Pfeffer, Pflanzenphysiologie, 2nd ed., Vol. xi, p. 132. 



4 Flora, 1873, p. 122. 



H 2 



