356 PROTOPLASM 



of a magnitude that cannot possibly be duplicated in the labora- 

 tory without metals, and we have no knowledge of the means by 

 which nature accomplishes this. 



The thought that potential differences exist between parts of 

 organisms, e.g., between leaf and stem, stem and root, has long 

 prevailed. Some early experiments on plants were done by Buff 

 (1854), Elfving (1882), and others, and more recently by Votchal 

 and particularly Lund. The zoologists followed with determina- 

 tions of potential differences in hydroids. The most extensive 

 of this work is that of Lund. He finds that a continuous output 

 of electrical energy is produced in living tissues. He beheves that 

 there is a definite relation among polarity, oxidation, and poten- 

 tial, and that the total electromotive force between two points is 

 the algebraic sum of all the individual electromotive forces of the 

 cells between which the potential is measured. The work of 

 Lund has had to do primarily with fir trees, where he finds a 

 potential difference varying from 30 to 200 mv. The growing 

 point at the apex of the tree is positive to more basal parts. 

 The external polarity, Lund says, is merely evidence of a com- 

 plex but definite pattern of internal electric polarities, which serve 

 to correlate the activities of one cell with another. There is 

 also the possibihty that "one of the functions of the continuous 

 electric current which is directed upward in the wood is to supply 

 electrical energy for electroendosmotic flow of sap" (see also 

 page 379). 



