1912.] PUBLIC DOCUMENT — No. 31. 149 



being used as in the preceding experiments. The results shown 

 in these tables present similar features to those in the preceding 

 ones. 



The lowest average resistance during any single day for the 

 maple occurred May 14, when the temperature was highest, 

 while the highest average resistance was on May 28, when the 

 temperature was low, but not the lowest. The average resist- 

 ance for the different sides of the tree for the whole period was 

 the highest on the north side, followed by the west, east and 

 south sides. For the elm the lowest average resistance for a 

 single day was shown on May 14 and June 12, days when the 

 temperature was highest. The highest average resistance shown 

 corresponds to the lowest temperature, which was recorded on 

 April 7. The average resistance for the different sides of the 

 elm during the whole period was the highest on the south, fol- 

 lowed by the north, west and east sides. 



The experiments shown in Table V. were supervised by Mr. 

 Chapman during the spring of 1909. The resistances were 

 obtained from a large maple tree located near our laboratory 

 which was a different specimen from the one used in the pre- 

 ceding experiments. The tree was a typical rock maple of this 

 region, in fairly vigorous condition, slightly over 2 feet in 

 diameter at the base. The resistance readings were obtained 

 from a combination bridge, as in previous experiments, and a 

 battery of 8 Samson cells was used. The electrodes consisted of 

 galvanized iron nails about 3 inches long, which were driven 

 through the bark into the wood for about ll/o inches. The part 

 of the electrodes extending beyond the surface of the wood was 

 enclosed within porcelain insulators. Before the electrodes were 

 inserted into the tree at the various points a part of the bark 

 extending to the wood was removed with a chisel for a space of 

 2 inches. The electrodes were 8 feet apart in each case, the 

 lower ones being placed about 21/0 feet from the ground, and the 

 highest about IOI/2 feet, hence the resistances were taken from 

 that part of the tree between 214 and lOl/o feet of the trunk. 

 The wires, 8 in all, were connected with the electrodes by means 

 of solder and were run into the laboratory about 50 feet away, 

 all the readings being taken under cover. The resistances were 

 read three times each day, viz., at 8 a.m., 12 m. and 4 p.m. 

 from March 18 to March 30, inclusive. 



