392 THE PRODUCTION OF HEAT, LIGHT, AND ELECTRICITY 



cells are better known, we shall still be unable to accurately determine the 

 magnitude and current-density of the internal streams of electricity. The 

 tissues of plants have in general, like the tissues of animals, a very low 

 electrical conductivity, their resistance being often one or two million times 

 greater than that of mercury 1 . The resistance will naturally depend upon 

 the substances present in the cell, upon the arrangement of the cells, 

 upon the nature of the imbibed solutions, upon secretory activity, and upon 

 the presence of air or of sap in the intercellular spaces. Hence it is hardly 

 surprising to find that the transitory passage of a strong electrical current 

 through a tissue may cause a diminution of its electrical resistance 2 . A fall 

 of resistance between two points will tend to lower the difference of 

 potential between them, for if the resistance between them was nil no 

 perceptible difference of potential could be maintained. 



Ewart 3 has shown that in plant-cells the protoplasm offers a greater 

 resistance to the passage of an electrical current than the cell-sap, or even 

 than the cell-wall when the latter is saturated with sap. The resistance 

 decreases considerably as the temperature rises, and in egg-albumin, which 

 appears to conduct in much the same way that protoplasm does, the 

 resistance of 501 ohms per centimetre cube at 16 C. sinks to one of 188 ohms 

 at 85 C., the coagulation of the albumin exercising no effect upon its con- 

 ductivity. Young highly protoplasmic organs have a very low conductivity, 

 which is presumably due to their deficiency in electrolytes 3 . 



Apart from the electrical fishes which use their special powers for 

 attack and defence, we know of no definite cases in which the production 

 of electricity is of use to the organism. Very possibly the production of 

 electricity is largely an accidental accompaniment of metabolism, although 

 the weak currents circulating in plants may exert stimulating or orienting 

 actions 4 on the protoplast, or may aid by the transport of ions in the 

 conveyance of food and other materials from one part to another. No 

 conclusions can, however, be drawn from the galvanotactic responses of 

 certain organisms, and the facts known as to the influence of external 



1 Cf. Biedermann, Electrophysiologie, 1895, p. 704; Kunkel, Arb. d. bot. Inst. in Wiirzburg, 

 1879, Bd. II, p. 333; Wjasemsky, Ueber den Einfluss d. elektrischen Strome auf d. Leitungswider- 

 stand der Pflanzengewebe, 1901; Galeotti, Zeitschr. f. Biologic, 1902, Bd. XLIII, p. 289. On the 

 conductivity of wet and dry wood cf. Villari, Ann. d. Physik u. Chemie, 1868, Bd. cxxxill, 

 p. 418; Mazotto, Bot. Jahresb., 1897, p. 92. 



a Wjasemsky (1. c., p. 20) concludes that the fall of resistance is due to the passage of water 

 inwards from the moist electrodes, through the cuticle. Waller has shown, however (Journ. Linn. 

 Soc., Vol. xxxvii, 1904, p. 46), that the same fall of resistance is shown in peas after the skin has 

 been removed, and suggests that the action of the original current is to cause an increase in the number 

 of conducting electrolytes, which appear to be deficient in young highly protoplasmic organs. Ewart 

 (On Protoplasmic Streaming in Plants, 1903, pp. 96, 123) observed a fall of resistance in the proto- 

 plasm on death, and ascribes this to the same cause, since coagulation exercises no effect on 

 conductivity (1. c., p. 124). 



3 Ewart, 1. c. * Cf. Ewart, 1. c., p. 116. 



