410 



EFFECT OF ELECTRICITY 



[Ch. XVI 



Brtjnchoest ('84, p. 209) found- that the radicles of seedlings 

 of Brassica grow, under otherwise similar conditions, at a cur- 

 rent intensity* of 0.03 B to 0.05 B, towards the kathode, and at 

 a current intensity of 3.0 8 towards the anode (Fig. 116). 



BRASSICA 



Fig, 116. — Effect of different strengths of electric current on the radicle of Brassiea. 

 At the right : strength of current, 1.1 S ; all strongly negative and growing well. 

 At the middle: strength of current, 1.8 S; after a few hours negative at the apex 

 but positive higher up. At the left : strength of current, 3.1 S ; all positive, weak, 

 and dead. (From Brunchoest, '84.) 



If decapitation has occurred the kathode turning does not 

 follow, whereas the anode turning does occur as in the intact 

 root. A similar result having been obtained with seedlings of 

 various species, the conclusion was drawn that "the positive 

 galvanotropic curving is a simple chemico-pathological phenom- 

 enon which has only a superficial analogy with the directive 

 movements of roots, and therefore does not deserve the name 

 galvanotropism " [electrotropism] . 



The cause of the positive turning effect, it has been sug- 

 gested, lies in the fact that certain substances, perhaps 

 hydrogen peroxide and ozone, produced in electrolysis act 

 more injuriously upon the positive than upon the negative 

 side. According to another explanation, offered by RiscHAWi 

 ('85), the positive curvature is due to the kathophoric action 



*The current density (see Chapter VI, § 1) is calculated from the following- 

 data : The amount of copper deposited in a voltameter was 0.14 mg. to 35 mg. 

 per hour during the course of experimentation. A current of one ampere 

 intensity deposits 0.000326 gramme of copper per second or 1.17 mg. per 

 hour per milliampere. Thus the strength of current varied from 0.12 to 30' 

 milliamperes. The determination of the density requires a knowledge of the 

 cross-section over which the current spread itself. For this we may take the 

 given area of the electrodes, 6499 sq. mm., which is not far from the cross- 

 section of the trough. 



