104 A. B. Plowman — Electromotive Force in Plants. 



tion of heat to any part of the plant, — other conditions being 

 normal, — will invariably increase the physiological activity of 

 that part, so long as the temperature does not exceed a certain 

 optimum degree. Moreover, the increase of temperature is 

 attended by, or rather is due to, an increased kinetic energy of 

 the atoms. But any acceleration of the motions of the atoms 

 in a solution is normally attended by a corresponding increase 

 in dissociation and electrical conductivity. In like manner, 

 slight pressure on the walls of any plant-structure is attended 

 by violent molecular displacements through the cell walls and 

 protoplasmic films. This, also, destroys the kinetic equilib- 

 rium of atomic relations, and a local E.M.F. is the natural 

 consequence. Temperatures above a certain maximum kill 

 the protoplasm, and the "normal plant-current," which is an 

 index of physiological activity, necessarily disappears. We 

 have now to deal with dead protoplasm, and the only differ- 

 ence in reaction worthy of note is a slight decrease in specific 

 resistance of the tissues, due to a more ready diffusion of the 

 conducting liquids. 



These few experiments, while they are of a preliminary and 

 very general character, seem to point with a fair degree of cer- 

 tainty to the following conclusions : 



1. The functional activities of a plant give rise to differences 

 of electrical potential in its parts. 



2. The intensity and relative sign of these differences de- 

 pend upon the physiological condition of the plant, as well as 

 upon its electrical conductivity. 



3. The normal E.M.F. in a plant may be modified in inten- 

 sity or direction by brief application of forced currents. This 

 appears to be due in part to a change in resistance, and in part 

 to a modification in the vital activity of the protoplasm. 



4. Slight mechanical injuries do not perceptibly modify the 

 normal current. 



5. Extensive mechanical injuries or high temperatures destroy 

 the normal current, but do not modify the reaction current, ex- 

 cept by a slight increase in the conductivity of the tissues. 



6. Extensive injuries to a plant excite an E.M.F. spread- 

 ing from the point of injury through the tissues. 



7. " Reaction currents," in the sense in which this term is 

 used in this paper, depend but little, if at all, upon the vital- 

 ity of the plant, and can be duplicated in non-living substances. 



Harvard University, 

 Cambridge, Mass. 



