236 A. B. Plowman — Electrotropism of Boots. 



tive electrons through its root, chiefly from the side toward the 

 other seedling, hence it is curved and ultimately killed. 



So far as can be made out from these studies up to the 

 present time, the negative electrons are in no case harmful to 

 plant protoplasm ; and in several instances a marked acceler- 

 ation in growth may reasonably be attributed to their influ- 

 ence. However, in the present state of knowledge, it would 

 be imprudent to assert without qualification that negative 

 electrons stimulate vegetable protoplasm. 



A study is now being made of the effects of electric light 

 and power-currents upon trees growing near to or in contact 

 with the conductors. The facts thus far collected are in per- 

 fect accord w T ith those outlined in this paper. 



For the present, the point of principal interest lies in the 

 fact that the phenomenon termed " galvanotropism " by Elf ving 

 has its ultimate cause in the effects of the electrons, or elec- 

 tricity per se, and apart from any streaming of ions or any 

 ordinary chemical reaction. It is for this reason that the term 

 "electrotropism" is deemed more appropriate than the term 

 " galvanotropism " as used by Elfving. 



Aside from their purely biological relations, the results of 

 this investigation are of interest, in their bearing upon the 

 theory of ionization and upon the electron theory. For every 

 new problem that is satisfactorily solved by a theory renders 

 that theory more credible ; and the problem of electrotropism 

 is certainly of this nature, in its* relation to the theories mentioned. 



The results of these studies seem to indicate that whatever 

 advantages may be derived from the use of electricity in prac- 

 tical horticulture are to be attributed rather to secondary 

 chemical and thermal effects than to electrical energy as such, 

 except perhaps in cases where the plants are negatively charged. 



Harvard University, July, 1904. 



EXPLANATION OF THE FIGUEES, PLATES IX AND X. 



Fig. 1. Cubette jar, with electrical connections, for subjecting roots of 

 seedlings to the action of an electric current, (x -g-.) 



Fig. 2. Young seedlings of Zea mais, after exposure for one hour to the 

 action of a weak current, (x %.) 



Fig. 3. Young seedlings of Zea mais which were exposed to the action of 

 an electric current for one hour, then left in the water for an hour without 

 current flowing, (x £.) 



Fig. 4. Longitudinal section of a root-tip of Hyacinthus orientalis, which 

 had been subjected to the action of an electric current for thirty minutes, 

 (x 75.) 



Fig. 5. Longitudinal section of a root of H. orientalis, showing the effect 

 of three hours action of the electric current, (x 75.) 



Fig. 6. Transverse section of a normal root of H. orientalis, 8 mm from the 

 tip. (x 75.) 



Fig. 7. Transverse section of a root of H. orientalis, 8 mm from the tip, 

 after exposure for five minutes to a very strong current, (x 75.) 



Fig. 8. Transverse section of a root of H, orientalis, 10 mm from the tip, 

 showing effect of a moderate current acting for one hour, (x 75.) 



Fig. 9. Transverse section of a root of H. orientalis, 12 mm from the tip, 

 after exposure for two hours to a moderate current, (x 75.) 



Fig. 10. A part of fig. 9 more highly magnified, (x 350.) 



