130 Plowman — Relations of Plant Growth to Ionization. 



When the seeds were germiDated in water this difference was 

 most pronounced when a relatively heavy current was passed 

 through the water for only a short time, in which case the 

 seeds near the anode were killed, while those near the cathode 

 were not apparently injured. If the current was allowed to 

 flow for twenty hours or longer the ill effects were produced 

 at all points between the electrodes, even when the current 

 amounted to only "003 ampere, at a voltage of 2 or more. 

 When the current was passed through ordinary sandy soil in 

 which the seeds were planted, the same results were obtained 

 at the anode, but a much longer time was required to extend 

 the injurious effects to the region of the cathode. Indeed, so 

 long as the current does not exceed about -08 amp. there is a 

 considerable increase in the rate of growth of the seedlings 

 near the cathode. 



In explanation of these phenomena the following provisional 

 theory is offered. 



Whenever two points in any electrolyte are electrically 

 charged to different potentials, the movement of the free ions 

 in the solution"^ is given definite direction, and, if the differ- 

 ence of potential is sufficient, further dissociation of the 

 electrolyte follows. The anions with their negative electrons 

 move toward the anode, and the cations with their positive 

 charges pass to the cathode. Since the movements of ions in 

 solutions are relatively slow,t it is reasonable to suppose that 

 in the region of the anodes there would be a slight excess of 

 positive ions, due to the rapid neutralization of the negative 

 ions by the positively charged electrode. In like manner the 

 cathode removes the positive ions in its immediate vicinity, and 

 is consequently surrounded by a slight excess of negative ions. 

 The more slowly the ions move through the electrolyte the 

 more marked will be the difference of conditions about the 

 two electrodes. 



How will seedlings respond to these differences of condi- 

 tions % It is clearly indicated by the results of our experiments 

 that vegetable protoplasm is paralyzed and quickly killed by 

 the conditions existing about the anode, while within certain 

 fairly broad limits it is stimulated by the conditions about the 

 cathode. While the dissociation of the atoms and electrical 

 separation of the ions nmst bring about slight differences of a 

 purely chemical nature in the region of the electrodes, yet 



* Ostwald and Nernst. Ztschr. phys. Chem. iii, 120, 1889. 



fKohlrausch (Wied. Ann. 1. 403, 1893) has shown that, in an electro- 

 lyte of unit potential gradient, the velocity in centimeters per second for 

 certain ions is as follows : — 



Cations I Anions. 



H -00320 NH3 -00066 \ OH -00182 I -00069 



Na -00045 Ag -00057 CI -00069 Ni '00064 



Li -00036 K -00066 i 



i 



