Leaf and Air Temperature — Noffsinger 
305 
TABLE 2 
Leaf and Air Temperature and Related Meteorological Data 
for 0800 April 11-0800 April 12, I960 
TIME 
0800 
1200 
1600 
2000 
2400 
0400 
SUNRISE 
Air temperature °C 
22.0 
25.7 
26.7 
22.3 
22.2 
21.9 
22.0 
Leaf temperature °C. 
Pineapple 
average 
23.5 
29.5 
27.1 
21.7 
21.5 
22.1 
. 21.7 
in sun 
25.0 
31.5 
29-0 
in shade 
21.9 
27.5 
25.1 
21.7 
21.5 
22.1 
21.7 
Papaya 
average 
21.3 
25.1 
24.8 
21.2 
20.5 
21.0 
21.7 
in sun 
21.6 
25.0 
26.0 
in shade 
21.0 
25.1 
23.5 
21.2 
20.5 
21.0 
21.7 
Insolation 
Langleys/min 
0.27 
1.43 
0.98 
Soil temperature 
Pineapple 
20.2 
26.5 
27.0 
23.7 
21.4 
21.4 
20.5 
Papaya 
20.5 
27.0 
30.5 
24.2 
21.2 
21.2 
20.5 
Cloud cover (1/8 S.) 
5 
6 
1 
1 
1 
5 
1 
Wind (knots) 
8 
8 
10 
5 
4 
0 
0 
temperature in the pineapple plant (29.6° C.) 
occurred at 1500 and in the papaya plant (26.8° 
C) at 1300. 
DISCUSSION 
Plants undergo irradiation from the sun, 
clouds, and sky during the daylight hours, and at 
night they radiate heat outward. Made (Geiger, 
1950: 278-280) kept a continuous record of 
leaf temperature over a period of two days and 
found that during the middle of the day the 
leaf surface of Bilbergia nutaus (a hothouse 
plant of the pineapple family) was as much as 
10° C. higher than the air temperature. The in- 
terior portion of the pineapple fruit exposed to 
the direct rays of the sun at latitude 2 1 ° N. may 
experience temperature from 5° to 8° C. above 
the free air temperature. In Formosa it has be- 
come a practice to shade the pineapple fruit in 
order to prevent heat damage from solar radia- 
tion (Ekern, personal communication). Wag- 
goner and Shaw ( 1952 ) have shown that energy 
losses from potato and tomato plants at night 
due to transpiration may be very small. Geiger 
(1950: 276) states that plant temperature is 
generally higher than that of air temperature 
when the ground surface is warmer than the air 
layer resting upon it, and that by night the 
plant is, for the most part, cooler than the air. 
An examination of air, soil, and leaf tempera- 
tures in Tables 1 and 2 shows that the gen- 
eralization made by Geiger holds for pineapple, 
but that the average leaf temperatures of the 
papaya were consistently lower than the air 
temperature even during periods of relatively 
high soil temperature. In one observation dur- 
ing the period (not shown in the table), the 
temperature of the papaya leaf exposed to the 
sun registered 2.6° C. higher than the air tem- 
perature. At that time the value for solar radia- 
tion was 1.42 calories per sq. cm. per min., the 
sky was five-eighths covered with cumulus and 
stratocumulus clouds and a light sprinkle of rain 
was falling from clouds immediately to the N.E. 
of the station. 
SUMMARY 
Air temperature in an instrument shelter at 
the level of the plants does not provide a good 
measure of plant temperature. Papaya, with a 
respiration and transpiration pattern character- 
istic of the mesophytes, shows a leaf temperature 
which remains relatively near the air tempera- 
ture but may be higher or lower than the air 
temperature, depending upon the condition of 
radiation, cloud cover, and wind. Pineapple, a 
xerophyte, has leaf temperature during the day- 
light hours which average 1.5° to 3.5° C. above 
