Penhallow.] 
298 
[November 16, 
1.8° C. lower than that of the air; of maple No. 1, 3.8° C. lower, 
and of maple No. 2, 3.3° C. lower, as will be seen from the follow- 
ing table. 
No. of Obs. Temp, of Tree. Temp of Air. Diff. 
144 14.6 15.9 1.3 
184 12.2 15.5 3.3 
177 11.7 15.5 3.8 
Red Oak 
Sugar Maple No. 2 
Sugar Maple No. 1 
These figures relate wholly to hours of day, and show that 
during that time the tree is constantly cooler, while on the other 
hand, temperatures for hours of night would doubtless show the 
tree to be warmer than the surrounding air, and the mean tem- 
perature for the twenty-four hours would approach, if it would not 
equal, that of the air. In opposition to this, however, radiation 
would tend to make the temperature of the tree lower than that 
of the air, while transpiration, which is always accountable for 
the loss of much heat, would also tend to produce the same 
effect, though in case of a large tree trunk and at a point so far 
removed from the area of transpiration, the immediate effect, if 
any, must be slight. 
Influence of the soil. Changes of temperature in the soil occur- 
ing more slowly than in the air, according to the depth, we find a 
greater equality between temperature of soil and roots than 
between stem and air, and at certain depths it is easy to see that 
these temperatures must coincide. In small plants it is not diffi- 
cult to conceive that the entire structure would be greatly influ- 
enced by the soil temperature, but in large trees this influence 
probably extends but a short distance from the surface of the 
ground. Just how far it goes cannot at present be stated and 
would probably be difficult to determine exactly. 
Prof. W. H. Niles in behalf of the Council offered the following 
vote, which was passed unanimously : 
Voted : that in the opinion of the Members of the Boston Society of 
Natural History, the proposed arrangement between Harvard College 
and the city of Boston for the joint occupancy of the Arnold Arboretum, 
as recommended by the Park Commissioners, would give the community 
a popular means for the acquisition of botanical knowledge which would 
be of practical and educational value. 
