132 Plowman — Relations of Plant Growth to Ionization. 



root-tips turn toward the anode. An attempt lias been made 

 to show an analogy between this movement and a similar 

 turning of root-tips "up stream" against a water current. 

 However, the analogy is of little value, owing to the fact that 

 in the electrolyte there is a streaming of ions in hoth direc- 

 tions. Hence, the question is not so much a matter of the 

 direction of the electric current as it is of the difference in 

 effects of the two streams of ions. 



Upon examination of the conditions which prevail about 

 roots growiug in an active electrolyte, we Und that the side of 

 the root toward the anode is being bombarded by a stream of 

 'positive ions moving toward the negative electrode, while the 

 side toward the cathode is exposed to the stream of negative 

 ions on tbeir way to the anode. Consequently the side of the 

 root toward the cathode is stimulated, and that toward the 

 anode is retarded, in its growth, and of necessity the root-tip 

 curves toward the anode. 



Seedlings grown in ordinary soil show this curvature even 

 more strikingly. The main axis of the plant is frequently 

 curved almost 90° just below the surface of the soil. The 

 curvature is toward the anode and away from the cathode, 

 whether these be in circuit or isolated. 



3. formally, the plant body is electro-positive to the soil 

 in which it grows. The potential difference appears to be a 

 function of the physiological activity of the plant. The 

 positive charge of the plant attracts the negative ions of the 

 soil to its roots. Thus it seems that negative electrons are 

 being constantly discharged to the plant as a natural condition 

 of its life-activity. Any circumstance which would facilitate 

 this electrical interchange we should naturally expect to be 

 beneficial to the plant, while the reverse condition would be 

 detrimental. 



It must be borne in mind that the phenomena with which 

 we have been dealing are conditioned not only by temperature, 

 light, aeration and moisture, but also by the nature of the 

 electric current used, the solution-tension of the electrodes, the 

 osmotic pressure of the electrolyte, the degree of dissociation 

 of the electrolyte, the valence of the ions, the physical state of 

 the ions, the chemical relations of the ions to metabolic 

 processes in the plant, besides certain peculiarities of the living 

 protoplasm with which we are working, and which should 

 doubtless be taken into account in connection with each of the 

 conditions named above. 



Evidently, any theory which may be advanced in explanation 

 of the various phenomena of plant-growth in the electrical 

 field, musi stand the most exacting tests of physical chemistry, 

 in order to be worthy of serious consideration. 



Harvard Universitv, 



I 



