162 



EXPERIAIENT STATION. 



[Jan. 



ment III. there was little variation in temperature, although 

 variation in resistance occurred. In averaging up the tempera- 

 ture and resistance for those periods where all the data are pres- 

 ent it is found that there is a relationship between the tempera- 

 ture and the resistance. For example, it was found that the 

 lowest temperature occurred on the last three periods, that is, 

 from -t p.:\r. to 5 p.m., and that the highest average resistance 

 occurred during these periods also. On the other hand, the low- 

 est average resistance coincides in a general way with those 

 periods which gave the highest temperature readings. 



Relation of Electrical Resistance to Flow of Sap. 



Some observations were made on a rock maple in regard to 

 the relation of electrical resistance to the flow of sap, but these 

 were not extensive and lasted onlj a few days. The following- 

 results were obtained by collecting sap on the north, south, east 

 and west sides of the tree. The amount of sap represents the 

 amount of flow between 9 a.m. and 12 m., and 12 m, and 4 p.:m., 

 but the table gives the total amount obtained as well as the aver- 

 age resistances for the whole period. 



The highest average resistance and greatest sap flow occurred 

 on the south side of the tree. The sequence of the average resist- 

 ance was as follows : north, south, east and west, and that for 

 the sap flow, south, north, east and west. Our records, more- 

 over, showed that sap flowed more freely in the morning than in 

 the afternoon, also that the average resistance was higher in 

 the morning than in the afternoon. Since these observations 

 were not prolonged the results are not conclusive, but we do not 

 believe that electrical resistance is affected materially by sap 

 flow. Since our resistance readings were obtained from the 

 trees ofi"ering the least resistance, which is no doubt in all cases 

 the cambium layer, it is questionable whether sap flow, which 

 is characteristic of the woody tissue, would aifect our results. 



