228 A. B. Plowman — Electrotropism of Roots. 



Art. XXVII. — Electrotropism of Roots; by Amon B. 

 Plowman. (With Plates IX and X.) 



In a brief report published in this Journal last month, the 

 writer gave the more important results of a series of experi- 

 ments in the field indicated by the above title. These obser- 

 vations extend over a period of more than two years, and have 

 been carried on as a part of a general study of the electrical 

 relations of plants, at the Memorial Research Laboratory of 

 Harvard University. As indicated in the preliminary paper, 

 this particular phase of the work has had for its object the ex- 

 planation of the behavior of roots growing in the presence of 

 an electrical current. 



The general fact of galvanotropic response in roots was 

 established in 1882 by the careful studies of Elfving,* who 

 found that the roots of young seedlings growing in spring-water 

 through which a current of electricity was flowing, almost in- 

 variably turned, after a little time, toward the positive electrode. 

 Elfving modified his experiment by using from one to six 

 Leclanche cells in his battery ; by varying the distance between 

 electrodes from 2'5 cm to 15 cm ; by the use of zinc, copper, plati- 

 num, and carbon electrodes ; and by a study of various plants, 

 including species of Vicia, Zea, Seoale, Ilordeum, Cannabis, 

 Ricinus, Cueurbita, Tropaeolum, Convolvulus, Cynara, 

 Helianthus, and several others. He found that throughout all 

 these variations in conditions the results remained practically 

 constant in kind, the roots always turning, sooner or later, 

 toward the positive pole. He observed, also, that the roots 

 were invariably killed by the prolonged action of the current 

 from even a single Leclanche cell. 



By way of explanation of his results, Elfving showed that the 

 elongation of a, root in the presence of an electric current is 

 approximately only half as great in a period of 12 hours as is 

 that of a similar root growing under normal conditions for the 

 same length of time. Hence it was evident that growth was 

 retarded by the electric current, and the greater retardation on 

 one side than the other of the root was attributed to some un- 

 known property of the root itself. This view of the matter was 

 apparently fully justified by certain results obtained by Elfving 

 in his trials with seedlings of JBrassica and Raphanus. In the 

 former the majority of the roots turned toward the negative 

 pole, while in the latter there was no well defined response in 

 either direction. This would indicate a specific difference 

 which could be attributed only to the protoplasm itself, and it 

 was upon this difference that Elfving proposed to separate 

 plants into two groups, the one positively galvanotropic, the 



*Bot. Zeit., 1882. 



