172 EXPERIMENT STATION. [Jan. 



In the curve shown in Fig. 3 it will be observed that there is 

 a close relationship between temperature and resistance. 



Light, so far as we have observed, influences resistance only so 

 far as it modifies temperature. The southeast side of the tree 

 receives the most light, since the morning light is more intense 

 than the afternoon light. Photosynthesis is more active on that 

 side of the tree, and growth greater. Since there is a relation- 

 ship between photosynthesis and light intensity, and also be- 

 tween growth, there occurs more activity, as a rule, on the 

 southeast side of the tree than on any other, but whether the 

 greater flow of plastic substances in any given tissue would 

 affect resistance, our data do not show. So far, however, as the 

 greater light intensity is associated with increased temperature, 

 we should expect to find corresponding modifications in resist- 

 ance. 



Influence of temperature is shown in the difference existing 

 between the resistance occurring on the north and south sides of 

 trees. Some of our temperature records taken on the north, 

 south, east and west sides of a rock maple were not satisfactory 

 on account of the constant breakage of thermometers. These 

 temperatures were taken three times daily, at 8 a.m.^ 12 m. and 

 4 P.M., for a period of five days. The records, however, gave 

 the lowest average temperature on the north side of the tree, 

 followed by the west, east and south sides respectively. 



Other observations carried on for a brief period on a rock 

 maple tree gave the following results. In both cases the ther- 

 mometers were inserted into holes bored in the tree. The rec- 

 ords obtained in the second series of observations, which are 

 averages for a period of seven days, are as follows : — 



The average of three observations daily, at 8 a.m., 12 m. and 

 4 P.M. on the north, south, east and west sides of a rock maple 

 tree, gave the lowest temperature on the north, this being fol- 

 lowed by the west, east and south sides respectively. These 

 temperatures were taken in December, when the tree was in a 

 dormant condition, and the temperature given by the north side 

 of the tree was invariably the lowest. 



Jones, Edson and Morse obtained careful temperature rec- 

 ords from a rock maple tree. The observations were made on 

 the north and south exposures, and extended from February 8 



