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



the same direction, and followed by a slow return to the normal 

 state. 



III. This reversal of sign occurs when the leaf is excited 

 either mechanically or electrically, in the same or the opposite 

 lobe. 



IV. Repeated excitation of the leaf reduces the normal 

 difference of potential, and may even reverse its sign for a 

 considerable length of time. 



V. Very slight electric shock tends to increase the normal 

 potential difference without reversal of sign and regardless of 

 the direction of the applied current. 



YI. In addition to these conclusions, we may readily infer 

 that Sanderson considers the transfer of impulses in the plant 

 as of an electrical nature. 



From a repetition of some parts of Sanderson's work it 

 appears that the above conclusions are, in the main, correctly 

 drawn. It is the purpose of this paper to offer some hints as 

 to the explanation, from a purely physical point of view, of 

 the phenomena on which those conclusions are based. 



1. As has already been pointed out, it is to be expected that 

 different parts of a living, functionally active plant will show 

 differences of electrical potential. Hence the first conclusion 

 may be accepted without further question. 



2. The mechanical closure of the lobes of a Dioneea leaf con- 

 sists in a sudden loss of turgor by the cells on the upper or inner 

 side of the " hinge," and a slow increase of turgor on the lower 

 side. The disturbance on the upper side is of a truly molar 

 order, while that on the lower side is comparable to molecular 

 movements. The protoplasm of the upper parts may merely 

 cease to be active upon receiving the impulse, or it may undergo 

 a sudden modification before becoming passive. That these 

 changes in condition of the protoplasm, as well as the shifting 

 relations of the cell-sap, excite differences of electrical poten- 

 tial, is highly probable, to say the least. 



3. Since the electrical phenomena shown by the excited lobe 

 are the result of its response to the stimulus, it is not to be 

 supposed that they will be modified by the varying source of 

 the stimulus. 



4. Repeated excitation of E.M.F. in the leaf, followed in 

 each case by diffusion of the charge through the tissues, must 

 increase the number of free ions in the solution,* and thus the 

 conductivity is increased. As a result, the slight normal dif- 

 ference of potential is more quickly neutralized and becomes 

 imperceptible. Reversal of sign must apparently be attributed 

 to "fatigue" of the protoplasm in one part of the leaf. 



* See paper by A. Crum Brown on "The Ions of Electrolysis," Science, 



