A. B. Plowman — Electrotrojpism of Boots. 145 



Art. XIX. — Electrotrojpism of Boots ; by Amon B. 

 Plowman. (Preliminary Communication.) 



In a brief report some two years ago on the relations of 

 plant growth to ionization of soil* it was suggested that the 

 turning of root tips toward the anode is most easily accounted 

 for by attributing this reaction to the effect of the electrons, 

 or electric charges of the ions, rather than to any mere chem- 

 ical effects of the atoms. 



Since the publication of that report an extensive study of 

 electrotropic phenomena has been carried on at the Memorial 

 Research Laboratory of Harvard University. The results 

 seem to indicate that the explanation advanced in the above- 

 mentioned paper is entirely correct, and further, that the con- 

 clusion that "negative charges stimulate, and positive charges 

 paralyze, the embryonic protoplasm of plants," is well founded. 



Many kinds of seedlings have been grown both in ordinary 

 soil and by the water-culture method in the presence of an 

 electric currrent, under the most widely varied conditions of 

 temperature, current density and culture composition, with 

 results which are altogether uniform in kind. Even the least 

 perceptible current passing by the roots will in time overcome 

 their normal geotropic tendency, and will turn their tips toward 

 the anode. The passage of a comparatively strong current for 

 only a few minutes will produce a marked curvature after two 

 or three hours. Vigorous roots have been deflected 90° from 

 their downward course in half an hour by a moderately strong 

 current. In such a case as this, if the current is kept on, the 

 roots grow horizontally toward the anode, while if the current 

 is turned off they either continue curving until a complete coil 

 is formed, or they may gradually bend downward again, form- 

 ing a double curve. In any case the region of the initial 

 curvature is dwarfed in its growth and does not become nearly 

 as large in diameter as the parts either above or just below. 

 There is also always a flattening of the root on the concave 

 side of the curve. This flattened region always remains white 

 when the root tips are fixed in Flemming's fluid, while the 

 other parts, like normal roots, are blackened by a prolonged 

 action of osmic acid solutions. 



A study of the histology of such electrically curved roots 



shows that the protoplasm on the side nearest the anode has 



been coagulated and killed by the action of the current. The 



cells are completely plasmolyzed, and their walls are exceed- 



*This Journal, xiv, p. 131, Aug. 1902. 



Am. Jour. Sci. — Fourth Series, Vol. XV1I1, No. 104. — August, 1904. 

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