156 EXPERIMENT STATION. [Jan. 



The data obtained from hourly readings on the north, south, 

 east and west sides of the tree are given in Table IX. These 

 were taken from the same tree (rock maple) as the records 

 shown in Table L, and while they were continued only for one 

 day, they undoubtedly show typical variations which occur. 

 The resistances given are for 10 feet of the tree trunk, and the 

 day selected for the readings was free from clouds, the sun being 

 quite bright throughout the day for this period of the year 

 (April 27). 



At times, however, a slight haze was present which affected 

 to some extent the intensity of the light. The highest resistance 

 was shown in the early morning, when the temperature was the 

 lowest, and as it had become warmer the resistance decreased. 

 The lowest resistance occurred at 2.15 p.m., after which time 

 there was a slight increase in the resistance. It will be noticed, 

 however, that the least increase in the resistance after 2 p.m. 

 occurred on the west side of the tree, which received at that time 

 the benefits of the heat from the sun's rays during the afternoon. 

 On the other hand, the north, east and south sides showed a 

 greater increase for this period, as they were more or less shaded 

 from the sun's rays. The north side of the tree gave the highest 

 average resistance, followed by the east, south and west sides. 

 The lowest average resistance occurred on the west side of the 

 tree. 



Sap commenced flowing freely at 9.15, and at 2.15, the time 

 of the lowest resistance, it had commenced to cease flowing. As 

 is well kno^vu, there is a relationship between the flow of sap and 

 temperature, but there is no indication from these observations 

 or from any of our experiments that there is any relationship 

 between resistance and flow of sap. 



Experiments with Cut Bkancties of Trees. 

 A number of resistances were obtained from cut branches of 

 maple trees by Mr. Chapman. These were taken when the trees 

 were in a dormant condition, and in some cases when the buds 

 were developing. 



Experiment A. 

 A maple branch 11^ inches in diameter and several feet long 

 was used for this purpose. The branches showed slight bleed- 



