Squires: TREE temperatures. 459 



Remarks. — During the entire period it may be noticed that 

 the temperature of the tree is lower than the air in the morn- 

 ing, and at noon, and is higher in the evening. On four days 

 in January the temperature of the air and the tree fell below 

 -25 °C. and beyond the range of the instruments. The lowest 

 temperature of the tree recorded in February was -21.1. 



The lowest temperature records of this character accessible 

 to the writer are those made by Bourgeau in 1858 at Fort 

 Carleton, Canada, in latitude 50° N.* Bourgeau noted temper- 

 atures of -25°(F.?) in the trunk of a species of Populus. The 

 mean temperature of the tree observed by Mr. Squires, for 

 January, was 1.31°C. higher than the air. In February the 

 mean temperatures of the tree and air were practically identical. 

 In March the mean temperature of the tree was nearly 1°C. 

 lower than the air; in April .85°C. higher; and in May 1.13°C. 

 lower than the air. The difference between the mean temper- 

 ature of the tree for January and May was 22.33°C. The mean 

 temperature for January of the tree was -8.57''C., of the air 

 -9.88°C. For February the mean temperature of the tree was 

 -8.34.°C., for the air -8.34°C. For March the mean tempera- 

 ture of the tree was 1.69°C., of the air 2.68°C. For April the 

 mean temperature of the tree was 9.16°C., of the air 8.3L°C* 

 For May the mean temperature of the tree was 13.78°C., of the 

 air 14.91'C. 



The relatively high temperature of the tree during April was 

 doubtless due in part to the heightened metabolic activity pre- 

 vailing at this time, in the formation and development of the 

 reproductive organs. To determine the actual influence of this 

 factor in the absolute temperature of the body of the tree, more 

 extended experiments and a careful analysis of the results al- 

 ready in hand would be necessary. 



* Proc. Linn. Soc. 4 : 1. 1860. 



