THE TEMPERATURE OF LEAVES OF PINUS IN WINTER 59 
March 22, IQ14 
Cloudy. Light breeze 
2 
3 
4 
5 
6 
7 
8 
9 
8.40 
6 
2.8 
•34° 
-0.8° 
7.2° 
8.0° 
— 0.46° 
12.30 
7 
5-6 
.67 
1.4 
9.4 
8.0 
2.07 
1.30 
I 
0 
0 
1.0 
2.0 
1.0 
1. 00 
Average 
•34 
•53 
.87 
(4) The Leaf Temperature at Night. — Throughout February and a 
part of March readings were taken at six and ten p.m. The results 
obtained are represented by the values given in Table XI. A few 
readings show no difference in temperature between the leaf and the 
air, but, as a rule, the leaf is from 0.1° to 0.7° C. colder than the air. 
Table XI 
Date 
Bridge 
Read. 
Computed 
Temp. DifF. 
Air Temp. 
Rel. 
Humid- 
ity 
Atmospheric Conditions 
6 PM. 
10 PM. 
6 PM. 
10 PM. 
6 PM. 
ID PM. 
7 PM. 
Feb. 7 
8 
9 
" 10 
" IT 
" 12 
13 
16 
19 
25 
Mar. 5 
6 
7 
— 2.0^ 
0 
— 1.0 
-2.8 
-2.5 
— 2.0 
0 
-1-5 
-5.0 
-3^5 
— 1.0 
-0.5 
-0-3 
-2.55 
—2.0 
-2.5 
0 
-2.5 
-2.5 
-i^5 
— 1.2 
-3^6 
-6.0 
-i^5 
0 
0 
0.25° 
0 
0.13 
0-35 
0.31 
0.25 
0 
0.19 
0.62 
0.45 
0.12 
0.06 
0.04 
0.32° 
0.25 
0.31 
0 
0.32 
0.32 
0.19 
0.15 
©•45 
•73 
0.18 
0 
— 10.0° 
-18.5 
— lO.O 
— 12.0 
— 16.0 
-17.0 
-13.0 
— lO.O 
— 9.0 
— 7.0 
0 
^ 0.5 
— 1-5 
— 11.0° 
— 20.0 
— 9-5 
— 14.0 
-19-5 
— 19.0 
— 14.0 
— 12.0 
— 12.0 
— lO.O 
— 2.0 
0 
— 4.0 
80% 
67 
74 
55 
77 
73 
75 
81 
88 
44 
78 
73 
100 
Clear; wind light. 
Clear; wind strong. 
Clear; wind strong. 
Wind light 6 P.M.; 
Calm 10 P.M. 
Wind moderate. 
Wind moderate. 
Cloudy; wind 
moderate. 
Cloudy; wind 
moderate. 
Clear; calm. 
Clear; calm. 
Cloudy; wind light. 
Cloudy; wind light. 
Snowing; wind 
light. 
Average 
0.21 
0.25 
(5) Effect of the Wind in Reducing the Leaf Temperature, — The 
effect of the wind in reducing the leaf temperature is well illustrated 
in Tables XII and XIII. The average differential temperature 
between leaf and air for the two tables is 2.93° C. as compared with 
6.04° C. in Table IV. A part of this reduction in differential tempera- 
^ Negative sign under bridge reading indicates that the current was reversed 
and that the leaf was colder than the air. 
