vi ELECTROMOTIVE ACTION IN VEGETABLE CELLS 29 



begins to produce a downward movement of the petiole. There 

 is a rapid preliminary variation, which is soon exhausted, and is 

 followed immediately by a much more pronounced deflection in 

 the opposite direction. The mercury slowly returns from the 

 extreme point of this last, and either reaches its resting-point 

 or exhibits a variety of smaller and slower oscillations. 



Kunkel was quite aware of the difficulties of interpreting 

 these complicated excitatory variations from his own theory, 

 and was " not disinclined to refer them to single phases of the 

 active displacement of water." He derived the first rapid 

 negative swing from " alterations " of the protoplasm, which 

 disturb the diffusion-processes caused by the contact of the 

 moist electrodes, and fundamental to the current of rest. The 

 large positive deflection, 011 the contrary, " expresses the main 

 displacement of water which results in the movement of the 

 entire leaf; the (negative) return corresponds with the restitution 

 of the organ to its earlier state." Yet, as Kunkel himself 

 noticed, it must not be forgotten that in Mimosa, as in Dioncea, 

 electrical variations can still be observed when, after repeated 

 excitation, there is no longer any perceptible movement of the leaf, 

 so that there can hardly be any considerable displacement of water. 



If we endeavour, on the basis of these experiments on 

 Dioncea, to form any picture of the possible causes of the difference 

 in potential in the " resting " state and during artificial excitation, 

 it is in the first place clear that the same principles which we 

 have already accepted as determining the appearance of " cell 

 currents " must hold good for vegetable as for animal cells. The 

 only question is whether we are here justified, as in the uni- 

 aud multicellular animal glands, in regarding the single cells as 

 individually electromotive, or whether this property is not rather 

 attached to them solely in connection with other dissimilar 

 elements, whether, i.e., we are dealing with electromotive cells 

 or cell -complexes. Munk notably tried to develop a theory 

 from the first standpoint albeit in a very different sense from 

 electromotive activity of the isolated mucous cell. He held, as 

 was stated above, that the poles of each cell were positive to its 

 centre, and that after excitation the P.D. between the poles and 

 the negative equatorial zone either declined (as in the upper 

 layer of the parenchyma), or was augmented (cells of the lower 

 surface). Seeing, however, that the structure of these cells 



