12 



milliamperes, (1-227 am P-)> /^ i n - in diameter, 25 milliamperes, 

 (1-40 amp.), and on another of the same size, 50 milliamperes, (1-20 

 amp.). In the latter case, and some others not included here, the 

 currents went down from the 50 milliamperes to nothing almost 

 instantly. From these experiments it would appear that the current 

 burned out the cambium, or vital layer of the stem, thus leaving the 

 dry and highly resistant wood which was unable to transmit a cur- 

 rent that was perceptible. 



Some young sunflowers and tomato plants grown in 3 in. pots, 

 with copper plates at the bottom, were treated from a direct current 

 dynamo which generated an electro motive force of about 60 volts. 

 The plants were from 6 in. to 2^ ft. high, and ^ to ^ in. in 

 diameter. The current passing through the soil and roots in 16 in. 

 of stem of the Helianthus plant, 3-16 in. in diameter, gave a reading 

 that was scarcely perceptible. When, however, it passed through 

 only one inch of the stem and root to the copper plate at the bottom, 

 the maximum current was 2.6 milliamperes, (1-384 amp.). This 

 caused blackening and death of the tissues which were perceptible 

 a few hours afterwards about the points of insertion of the electrodes 

 on the stem, and the plant was girdled for about 2-3 of its circum- 

 ference. Practically similar results were obtained with other sun- 

 flower plants treated in the same way. A sunflower, 30 in. high and 

 1-4 in. in diameter, subject to a current of 10 milliamperes for some 

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

 passed through about i in. of stem and ^ in. of soil. A young 

 succulent tomato plant, ^ of an inch in diameter and 5 in. high, 

 was instantly killed when treated in the same manner, with a current 

 of 20 milliamperes. A current equal to 2 and 3 milliamperes of 30 

 to 60 seconds duration, accomplished the same result. In all the 

 tomato plants considerable heat was developed. The tissues changed 

 color, and the plants collapsed, although in one case where an 

 alternating current was employed the collapsed plant lived for a 

 number of days, as the vascular bundles, or water conducting tissues, 

 were not injured. 



There are certain instances, however, where large trees have been 

 killed by direct currents employed by electric railroads. In some 

 cases which have come under our observation, the escaping current 

 had girdled trees at the base, a distance of 5 to 10 ft. in height, 

 whereas, the point of contact of the feed wire to the limb, 16 or 18 



