Plowman — Relations of Plant Growth to Ionization, 131 



these mere chemical differences can hardly account for the 

 effects upon the plants, even near the electrodes, and certainly 

 not for certain effects at points mid-way between the elec- 

 trodes. This conclusion is borne out by the following facts : — 



1. When seeds are germinated in distilled water through 

 which a weak current is forced, the O ions are in excess in 

 that part of the solution where stimulation occurs, and the H 

 ions are in excess where the plants are killed. But it may be" 

 shown that small quantities of hydrogen are not markedly 

 harmful to plants. And the quantity of oxygen set free in 

 distilled water by a weak electric current is certainly no greater 

 than that normally present in ordinary tap-water, such as was 

 used for the controls ; yet germination is often more rapid 

 near the cathode than in the case of the control. 



Apparently, the eft'ects are produced by the electrical 

 charges of the ions, rather than by any mere chemical activity 

 of the atoms. 



2. When seeds are placed in solutions of various acids, 

 bases, or salts, of a degree of concentration far below the 

 ^' killing point," they will germinate quite as well as in ordi- 

 nary distilled water. But when a current of electricity of 

 sufficient strength to propel the ions is passed through the 

 solution, that part about the anode becomes destructive to 

 plant life. 



From these and other facts we conclude that negative 

 charges stimulate^ dindi positive charges paralyze^ the embryonic 

 protoplasm of these plants. This is strikingly in accord with 

 the conclusions reached by Matthews^ in his experiments on 

 the nature of nerve stimulation, in which he shows that the 

 sciatic nerve of the frog is stimulated by negative ions, and 

 rendered less irritable by positive ions. 



In support of the theory here advanced the following facts 

 may be mentioned : — - 



1. When a flower-pot containing several lupines of about 

 four weeks growth is charged to relatively high potential 

 (500v.) with positive electricity, the plants cease to grow, 

 gradually lose their turgidity and finally die. On the other 

 hand, when a negative charge is used these effects are not pro- 

 duced, but the plants are actually stimulated. 



It is evident that, in the first case, the negative ions in the 

 soil are drawn to the positive terminal, while the positive ions 

 are driven to the plant. In the second case, the positive ions 

 are drawn to the negative electrode, and negative ions are 

 driven to the plants. 



2. When seedlings are grown in an aqueous culture-medium 

 through which a weak current of electricity is flowing, the 



* Science, vol. xv, No. 378, 1902. 



