A. B. Plowman — Electromotive Force in Plants. 99 



ends of the roll. So long as the paper was dry there was, of 

 course, no current. Calling one end of the roll " A " and the 

 other " B " we shall represent any current from " A " to " B " 

 through the paper by displacement of the curve upward from 

 the zero line. N/50 NaCl was now added slowly to the paper 

 at " A." When the moisture reached " B " there was a rapid 

 deflection of the mirror, which increased for about 20 sec, then 

 fell to zero at 1 inin. 20 sec, then slowly turned in the opposite 

 direction, but not so far as it had gone in the first direction. 

 For an explanation of this we must, no doubt, look to the differ- 

 ent diffusion velocities of the free ions in the solution. 



The next live figures represent the "reaction currents" of 

 solutions of various salts. In each case a roll of filter paper was 

 arranged as for determining the " saturation current," with the 

 difference that it was uniformly saturated at once. After pass- 

 ing a 3v. current through the roll for one second the galva- 

 nometer circuit was closed and the reaction current was noted. 

 Of course the reaction current was always in the direction op- 

 posite to that of the battery current, through the paper. The 

 peculiarities of the curves may be readily and satisfactorily ex- 

 plained on the principles of physical chemistry, but our present 

 attention should be directed rather to the striking similarity be- 

 tween these curves and those in figs. 9, 10, 11 and 12, which rep- 

 resent the reaction currents in various plants after forcing a 3v. 

 current through them. The direction of the reaction is always 

 opposed to that of the battery current. A comparison of figs. 5 

 and 11, 7 and 10, 8 and 9, 6 and 12, makes this similarity 

 fnlly apparent. The longer action of the forced current in the 

 plants is necessitated by their higher resistance, which means 

 that the compounds in them yield less readily to electrolytic dis- 

 sociation. The only difference worthy of note is the presence 

 in the plants of a " normal current" of greater or less intensity. 

 All the figures show the temporary reduction of this current 

 by the action of the forced current. 



Fig. 12 deserves special notice, since it furnished the first 

 hint of the diurnal variation in the normal pi ant- current. The 

 plant used in this experiment showed a normal upward current of 

 •8 between two points 20 cm apart on the stem. The usual battery 

 current was passed upward through the stem for 10 min., with 

 the reaction shown at I in the figure. At II the forced current 

 was repeated. Its reaction is slightly more abrupt in neutraliza- 

 tion. At III the forced current was again repeated. The reac- 

 tion was still more abrupt, and also more intense, owing to the 

 increased conductivity of the stem. The recovery of the normal 

 current was slow, and incomplete yet at IY. This was at about 

 5 P. M. Two hours later the plant was found to have a normal 

 current downward. A forced current in this direction gave 



