A. B. Plowman — Electrotrojpism of Roots. 233 



affected, even after several hours. This experiment was re- 

 peated by suspending two seedlings by hooks of platinum wire, 

 with the roots dipping several millimeters into a vessel of water. 

 'The platinum wires are connected through a resistance with the 

 battery, making a circuit downward through the first root, and 

 upward through the second. Under these conditions a *1 milli- 

 ampere current killed the second root in twelve hours, while 

 the first was not apparently affected. When a '5 milli-ampere 

 current was passed through the roots for half an hour and then 

 turned off, the second root was greatly checked in its growth, 

 and after a few hours it showed a pronounced bending toward 

 the other root. In every case the prolonged passage of even a 

 very weak current caused a loss of turgor in the parts of the 

 first seedling in the region of the platinum contact, even when 

 the root itself was unaffected. 



. In comparing the results of these studies with those given by 

 Elfving, it appears that there is substantial agreement in the 

 general fact of response curvatures. The plants examined in- 

 clude practically all those enumerated by Elfving, with the 

 addition of species of Zupinus, Zinurn, Fagopyrum, Milium, 

 Allium, and Hyacinthus. However, it has been shown that the 

 passage of an electric current* through water in which seedlings 

 are growing is not necessarily fatal to the plants, as asserted by 

 Elfving, but that the current may be so weak as not to kill the 

 roots and yet cause them to grow horizontally toward the 

 positive pole. 



Moreover, the so-called "negative galvanotropism " men- 

 tioned by Elfving does not seem to be a constant property of 

 any species thus far studied. That the usual curvature toward 

 the positive pole is less pronounced and less constant in some 

 species than in others, can not be denied. However, the re- 

 verse curvature has not been found to be constant in any case, 

 and even in the most doubtful species it has been possible, by 

 varying the density and time of action of the current, to pro- 

 duce the normal curvature in a majority of the roots. 



That Elfving was justified in concluding that galvanotropism 

 is not of the same order of phenomena as heliotropism, geo- 

 tropism, hydrotropism, etc., is made apparent by the facts just 

 pointed out. The great rapidity of the reaction under certain 

 conditions, and the fact that all but extremely weak currents 

 are very harmful to the plant, seem to indicate the same con- 

 clusion. But it must be admitted that so far as the real signifi- 

 cance and ultimate explanation of the phenomenon are concerned, 

 no satisfactory solution is offered either by mere external appear- 

 ances or by the purely biological features of the case. 



A comparative study of the internal structure of normal and 

 electrically curved roots has proved highly instructive in this 

 connection. Fig. 4 shows a longitudinal section of the tip of a 

 root of Hyacinthus orientalis, which had been acted upon for 



