OF THE 



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CHAPTEE VI 



ELECTROMOTIVE ACTION IN VEGETABLE CELLS 



IT has long been known that electrical currents can be led off 

 from certain parts of plants, under given conditions. Becquerel, 

 Wartmann, and Buff all made important contributions to this 

 subject. The last author concluded from his experiments (carried 

 out with comparatively imperfect technical accessories) that " the 

 roots and all internal parts of the plant filled with air are in a 

 state of permanent negativity, while the moist or wetted outer 

 surfaces of fresh twigs, leaves, flowers, and fruits are positively 

 electrical" (1). He explained this to mean that the epidermis 

 of the plant forms a dividing line between the external water of 

 moisture and the salts, acids, and other constituents of the sap. 

 Electrical excitation occurs at this boundary, and current flows 

 in the direction observed in the leading-off circuit. Jlirgensen 

 (2), again, found the uninjured surface positive to the transverse 

 section, in the divided leaves of Vallisneria, spiralis, in conse- 

 quence, as he believed, of chemical differences between the 

 exposed fluid of the cell and the surface of the leaf. The same 

 negativity of injured points (artificial transverse or longitudinal 

 sections) obtains, according to Hermann (3), in living stalks of 

 different species of plants. The cross-section, or artificial long 

 section, is plainly negative to the uninjured surface. The intensity 

 of these currents, " generally speaking, varies in a marked degree 

 with the charge of moisture in the plant, and the resulting 

 conductivity. The deflections range from 20 degrees of the 

 scale to its disappearance from the field of vision. The 

 stalks of fungi yield the strongest currents." The E.M.F. varies 

 between O01 and 0'08 Dan., i.e. is of approximately the same 

 order as in the muscle current, although the deflections are often 

 VOL. n B 



