146 A. B. Plowman — Electrotropism of Roots. 



ingly thin and mnch crushed. Where the root has been acted 

 upon for but a very short time only a few of the cortical cells 

 are affected, while for longer action of the current, or more 

 intense current, the affected zone grows wider and wider, until 

 it may involve the entire structure of ,the root. In every case 

 the boundary line between the affected zone and the normal 

 part is practically a straight line exactly at right angles to the 

 path of the current. The effect is of course most pronounced 

 in the region of most rapid normal growth. Very weak cur- 

 rents tend to check growth in length, and the roots conse- 

 quently take on a more stocky appearance. They are often 

 actually thicker than the normal roots of the control. 



That the results of these experiments are to be attributed to 

 purely chemical causes is rendered highly improbable by the 

 fact that the results are practically uniform, no matter what 

 the ions of electrolysis may be. Distilled water, very dilute 

 acids, bases, and neutral salts all are apparently alike in this 

 relation, their effects differing only with their varying electri- 

 cal carrying power. Whatever may be the relation of mass 

 action and of chemical and physical affinity to growth under 

 normal conditions,* it would seem that in the present case the 

 all-important factor is the electron or electric charge of the 

 ion, and, more specifically for our purpose, the positive elec- 

 tron, since it is this one which produces the most striking 

 effects. And so far as is at present known, those effects are 

 always in the same direction, viz : paralysis or actual death of 

 the protoplasm exposed to the action of a positive charge. As 

 for the negative electrons, it seems safe to say that in the 

 majority of cases they are neutral in their relation to living 

 cells, and where any effect is perceptible it is in the way of 

 stimulation of the protoplasm. 



There is now in preparation for publication in this Journal 

 a fully illustrated report of this series of experiments, together 

 with a consideration of the practical and theoretical bearings 

 of the facts involved. 



Phanerogamic Laboratories, Harvard University, June 1904. 



* See the article by J. B. Dandeno, this Journal, xvii, pp. 437-458, June 

 1904. 



