414 EFFECT OF ELECTRICITY UPON GROWTH [Ch. XVI 



It is possible that the stimulus is due to a chemical agent pro- 

 duced by the current, or directly to the current itself. The 

 first alternative is opposed by the fact that the reflected 

 Hertz waves, which have little or no gross chemical effect, 

 still incite a response. There is every reason for concluding 

 that the electric current, like gravity, and, as we shall see, 

 light, acts in determining the direction of growth immediately. 



The electric current appears to affect the rate of growth of 

 some plants, so that they grow more rapidly when lying in the 

 magnetic field or in a highly electrified atmosphere than other- 

 wise ; but this effect is often slight and uncertain. The direc- 

 tive effect on the growth of elongated organs is more marked. 

 Apart from a false electrotropic effect produced by the injury 

 of the positive side of the root, so that growth ceases on that 

 side, there is a true electrotropic effect, which shows itself in a 

 turning of the root from the anode. This is a true response to 

 stimulus, depending for its consummation upon the presence of 

 the root tip. The Hertz waves produce this effect in Phyco- 

 myces. Magnetism has an uncertain effect. The whole phe- 

 nomenon is closely like that of response to gravity and light. 



LITERATURE 



Aloi, a. '91. Deir influenza dell' elettricita atmosferica. Malpighia. V, 



116-125. 

 '95. Dell' influenza dell' elettricita atmosferica suUa vegetazione delle 



piante. Bull. Soc. Bot. Italiana. Oct. 1895. pp. 188-195. 

 Berthelon db St. Lazare 1783. De I'eleetricite des vegetaux, ouvrage 



dans lequel ou traite de I'eleetricite de I'atmosphere sur les plantes, etc. 



Paris et Lyon : Bidot. 468 pp. 3 Tab. 

 Brunchorst, J. '84. Die Funktion der Spitze bei den Richtungsbewegungen 



der Wurzeln. II. Galvanotropismus. Ber. D. Bot. Ges. II, 204-219. 

 '89. Notizen iiber den Galvanotropismus. Bergens Mus. Aarsberetning 



for 1888. Ko. 5. 35 pp. 

 Celi '78. Appareil pour experimenter Taction de I'eleetricite sur les plantes 



vivantes. Comp. Reird. LXXXVII, 611-612. 22 Oct. 1878. 

 Chodat, R. '92. Quelques effets de I'eleetricite statique sur la vegetation. 



Arch. Physiq. et Nat. (3), XXVIII, 478-481. 

 DuBois-Reymond, fi. '60. Ueber den secundaren Widerstand, ein durch 



den Strom bewirktes Widerstandsphiinomen an feuchten porosen 



Korpern. Monatsber. Berlin Ak. 1860. pp. 846-906. 



