1889.] 



BOTANICAL GAZETTE. 



217 



An experiment was made upon a good-sized shag-bark 

 hickory (Carya alba) to see to what extent the temperature 

 of the interior of the tree followed that of the exterior. The 

 tree was about 30 cm. in diameter, and the borings, which 

 were on the south side, were made at the following depths, 

 viz.: 3, 6, 10, and 12 cm. Readings were taken from the 

 thermometers at these varying depths, and also from one 

 placed on the north side of the tree, not in contact with the 

 bark or exposed to the direct rays of the sun. These read- 

 ings were noted at intervals of 1 to 2 hours during the day, 

 and in a number of instances were continued through the 

 night. The period of time embraced by the experiment 

 was about fifteen days, and covered several days of warm 

 weather as well as our coldest days. 



The detailed readings are not given here, but the results 

 arrived at are essentially as follows. The temperature of 

 the tree as a general rule ranged higher than the outside, 

 with two or three exceptions, when the air temperature was 

 higher during the warmer portions of the day. The maxi- 

 mum temperature of the air was generally between 1 and ^2 

 p. m., while the minimum ranged from 6 A. m. to 7. The 

 following table indicates the average time of the maximum 

 and minimum temperatures for the different depths : 



Outside. 



Maximum. 



1 .00 p. M. 



Minimum. 



6.45 a. m. 



3 cm. deep. 



6 cm. deep. 

 10 cm. deep. 

 12 cm. deep. 



2.00 p. M. 



4.15 p. m 



7.00 A. M. 



6.15 p. m 



8.00 a. M. 



9.30 a. m. 



6.45 p. m 





10.00 A. M. 



It will be seen by reference to this table that the rate of 

 conduction varies somewhat for different depths ; that the 

 heat is both absorbed and radiated more rapidly in the outer 



layers than in the center. 



Representing the temperatures graphically, it was seen 

 that that of the interior of the tree presented the most uni- 

 form curve, i. c, one whose amplitude was the least. Ihe 

 mean daily variation for the outside and the shallowest boring 

 was about 12.5 C, while that of the interior was only 7 U 

 Thus the average temperature of the tree, in its most central 

 part, is not much above the temperature of the air during 



