ELECTRICAL INJURIES TO TREES. 7 



direct current dynamo which generated an electro-motive force of about 

 60 volte. The plants were from 6 inches to 2^/^ feet high, and Vg to 

 14 inch in diameter. When the current passed through 16 inches of 

 the stem and copper plate to the bottom of the pot, a sunflower plant 

 ?i6 inch in diameter gave scarcely perceptible readings; but when the 

 current passed through only 1 inch of the stem and root to the copper 

 plate at the bottom, the maximum current was % milliampere (%84 

 ampere). This caused blackening and death of the tissues, percepti- 

 ble a few hours afterwards about the points of insertion of the positive 

 electrodes into the stem, and the plant was girdled for about two-thirds 

 of its circumference. Very similar results were obtained with other 

 sunflower plants treated in the same way. A plant 30 inches high and 

 14 inch in diameter, subjected to a current of 10 milliamperes for 

 some minutes, was not injured to any extent. In this case the current 

 passed through about 1 inch of stem and Yo inch of soil. A young, 

 succulent tomato plant, % inch in diameter and 5 inches high, was 

 instantly killed when treated in the same manner with a current of 

 20 milliamperes, and a current of 2 and 3 milliamperes of 30 to 60 

 seconds duration accomplished the same result. In all the tomato 

 plants considerable heat was developed. In one case in which an alter- 

 nating current was used the plant lived for a number of days after the 

 tissues had changed color and the plant had collapsed, as the vascular 

 bundles or water-conducting tissues were not injured. 



In the experiments cited all the injuries occurring were due to the 

 efuects of heat generated by the current. The experiments also showed 

 that the strength of current which will kill one plant will produce not 

 the slightest effect on another ; in other words, the maximum current 

 for each individual varies materially. Small, tender plants possess a 

 maximum much below that of woody plants. The experiments were 

 all carried on under normal moisture conditions; but when trees with 

 a more or less thick bark are drenched with rain the conditions are 

 quite different. A large maple tree which was in circuit with a feed 

 wire (500 volts) and rail of an electric road gave a current equal to 

 70 milliamperes (H4 ampere) with the electrodes placed vertically 

 1 foot apart. These connections were left on the tree for several 

 months. The observations were made on dry days, and no heat devel- 

 oped with this current. During periods of wet weather considerable 

 heat always developed, especially at the positive electrode, but not 

 enough to melt the soft solder which connected the wires with the 

 electrodes. 



Examination of the tree ten months later showed that a portion of 

 the tissues near the electrodes had been killed. After removing the 

 dead bark an oval space 6 by 11 inches was found to be dead about 

 the positive electrode and a space about 1^/2 by 3 inches near the nega- 

 tive electrode. The burned area about the positive electrode was about 



