1881.] Electromotive Properties of the Leaf of Dwncea. 141) 



have been published in Germany since the date of the author's first 

 communication to the Royal Society in 1873,* namely, that of Pro- 

 fessor Munk on Dionsea, and of Dr. Kunkel on electromotive action in 

 the living organs of plants. According to Dr. Munk, the electric pro- 

 perties of the leaf may be explained on the theory that each cylindrical 

 cell of its parenchyma is an electromotor, of which the middle is, in 

 the unexcited state, negative to the ends, and that on excitation the 

 electromotive forces of the cells of the upper layer undergo diminution, 

 those of the lower layer an increase. He accounts for the diphasic 

 character of the electrical disturbance which follows mechanical exci- 

 tation by attributing it to the opposite electromotive reactions of the 

 two layers of cells. According to this theory, the cells resemble in 

 their properties the " electromotive muscle-molecules " (" Unter- 

 suchungen," vol. i, p. 682, 1848, of du Bois Reymond) differing from 

 fchem in so far that their poles are positive instead of being negative 

 to their equatorial zones. Professor Munk has constructed a schematic 

 leaf in which the cells are represented by zinc cylinders with copper 

 zones. A schema so made is said by him to have the electromotive 

 properties of the unexcited leaf. 



Dr. Kunkel's experiments have for their purpose to show that all 

 the electromotive phenomena of plants may be explained as conse- 

 quences of the movement of water in the organs at the surfaces of 

 which they manifest themselves. 



Part II contains a description of the apparatus and methods used in 

 the present investigation. 



In Part III are given the experimental results relating to the electro- 

 motive properties in the unexcited state, a subject of which the discussion 

 was deferred in the paper communicated by the author (with Mr. Page) 

 in 1876.f The fundamental fact relating to the distribution of electrical 

 tension on the surface of the leaf when in the unexcited state is found 

 to be that (whatever may be the previous electrical relation between 

 the two surfaces) the upper surface becomes after one or two excita- 

 tions negative to the under, and remains so for some time. This 

 difference of potential between the two surfaces the author calls the 

 " cross difference." It is shown that, under the conditions stated, its 

 occurrence is constant, and that the differences of potential which 

 present themselves when other points of the surface of the leaf are 

 compared, may be explained as derived from, or dependent on, this 

 fundamental difference. 



Part IY relates to the immediate electrical results of excitation, i.e., 

 to the electrical phenomena of the excitatory process. In investigating 

 these the author takes as the point of departure, an experiment which 

 includes and serves to explain those obtained by other methods, and 



* " Proceedings," vol. 21, p. 495. 

 f " Proceedings," vol. 25, p. 411. 



