Penkallow.] 
296 
[November 16 , 
It is obvious that the temperature of the tree not arising from 
chemical changes incident to the processes of growth, must 
depend upon the temperature of the surrounding medium, i. e., 
in this case, the soil and air, and as Krutzsch has shown : “ These 
two influences are exerted equally for a little distance above and 
below the surface of the earth. While the upper portions of the 
tree are subject only to the temperature of the air, the lower roots 
are influenced solely by the temperature of the soil, and it is not 
possible to trace an exact limit at which the influence of the first 
upon the trunk and of the second upon the roots ceases ” 
In accordance with the well known law that the temperature 
of all bodies approaches that of the surrounding medium, we find 
as we should naturally expect, that the temperature of trees is 
constantly varying, and further, that these changes follow those of 
the soil (?) and air upon which they are dependent. 
Influence of the air. The temperature of the tree at any one 
time is subject to certain modifications dependent: 
1st. Upon the size of the tree itself. 
This is so obvious as hardly to need further consideration, 
though it may be well to note that, in the case of the maples, the 
difference in their temperatures would range from 1°— 4° C. accord- 
ing to the rapidity and degree of change in the surrounding air. 
The small, tree was much the more sensitive to change than the 
large one. This relation will be readily seen in the accompanying 
chart, in which it will be observed that the curves are longer and 
lower in maple No. 2 than in No. 1. A similar difference was 
found to occur between the maples and the oak, the latter being 
much less susceptible to changes and giving temperatures varying 
from those of the maples, from 0.5°-6.5° C. While difference in 
size would doubtless account satisfactorily for the difference in 
temperature of the maples, the greater difference found between 
maples and oak is partly due to difference of diameter and partly 
to differences of conductive power. 
2nd. Upon the conductive power of the wood and bark. 
Trees are but poor conductors of heat at best, and whatever 
their capacity may be in this direction, it must vary with the 
structure as well as the degree of saturation with water. Thus 
the wood and bark will have very different degrees of conductive 
