THE TEMPERATURE OF LEAVES OF PINUS IN WINTER 6 1 
Table XIII 
February 8, 1914 
Clear. Strong wind.'^ Relative humidity 71% 
I 
2 
3 
4 
5 
6 
7 
8 
9 
Time of 
Observa- 
tion 
No. of 
Obser- 
vations 
Aver. 
Bridge 
Reading 
in Cm. 
Calculated 
Temp. 
DifF. 
Shade 
Temp. 
Black Bulb 
in Vacuum 
Diff. 
Columns 
5 and 6 
Actual 
Leaf 
Temp. 
Wind 
Velocity- 
Miles 
per Hr. 
945 
10.15 
10.37 
10.47 
10.56 
11.04 
1 1 45 
12.17 
i.38« 
2 
I 
7 
7 
5 
6 
7 
12 
8 
16.7 
20.2 
24.0 
23.1 
30.1 
34-5 
32.8 
38.7 
28.7 
2.09° 
2.48 
3.00 
2.87 
3- 75 
4- v30 
4.09 
4-83 
3-58 
-15-5° 
-14-5 
-14-5 
-14-5 
-14-3 
-14.0 
-14.2 
-13-8 
-13.8 
10.0° 
II. I 
15.6 
17.2 
18.2 
19.8 
19.9 
22.2 
22.2 
25-5° 
25.6 
30.1 
31-7 
32.5 
33- 8 
34- 1 
36.0 
36.0 
-1341° 
— 12.02 
-11.50 
-11.63 
-10-55 
— 9-70 
— 10. II 
— 8.97 
— 10.22 
6.0 
6.0 
6.0 
6.0 
4.8 
6.0 
6.0 
6.0 
6.0 
Average 
344 
-14-34 
31-7 
— 10.90 
These fluctuations by no means represent all the changes in the leaf 
temperature. In fact, the changes were so rapid that it was not 
possible to adjust the sliding contact quickly enough to record them 
all. A somewhat nearer approach toward recording all the fluctu- 
ations was made in the following way: The galvanometer was cali- 
brated at the existing temperature in terms of displacement along the 
bridge wire. The sliding contact was held at a fixed point, and the 
galvanometer deflections read every five seconds for a period of two 
minutes, an assistant indicating the periods and recording the deflec- 
tions as read. To insure that the deflections should be. due solely to 
changes in the leaf temperature, the second junction was enclosed in a 
thermos-bottle and kept at a constant temperature. The results are 
graphically represented by figure 4. 
One series of observations and measurements was made on a 
detached branch with cut end immersed in water, and the preparation 
protected from the wind by a thin cloth screen except on the south 
side. The results, given in the following table, show that in quiet 
air the temperature of the leaf may rise to 10° above that of the sur- 
rounding air. 
In making up the averages the average readings for the periods 
are taken. 
Wind velocity, university observatory record, 18 miles per hour. 
^ Leaf in shadow for a part of the period. 
