388 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
that the temperature of grapes in the morning, before they were exposed 
to the sun, was only about one degree above that of the air, whereas in 
the early afternoon red grapes exposed to direct sunlight had, on the day 
of his observations, a temperature of 37° C. and white grapes a temperature 
of 34° C. while the temperature of the air in the shade was only 24° C. 
He found, moreover, that grapes with a dull surface reached a slightly 
higher temperature when exposed to the sun than those with a bright 
surface. The importance of these high temperatures in the growth of the 
numerous fungi found on grapes and strawberries is obvious. 
Dufrenoy*^ (p. 16) found that the temperature of leaves of Prunus 
affected by Polystigma ruhrum when exposed to sunlight showed a tempera- 
ture from 8°C.toii°C. above that of the air. The temperature of the 
air at the time of the observation was 20° C. while that of the leaves varied 
with their color from 28.5° C. to 31° C. 
The temperature of plant parts underground must fluctuate less rapidly 
than that of the parts exposed to direct sunlight in the air. Table 3 shows, 
however, that a fungus like orange leaf rust on Rubus, which is so fre- 
quently found on railroad embankments and other sandy, exposed places, 
may often be subjected, even when underground, to a temperature well 
above that of the air. The difference in the temperature of the various 
plants referred to in table 3 was clearly due to the difference in exposure 
and slope. 
Table 3. Temperature in Degrees Centigrade of Soil immediately about the Bases 
of Dewberry Plants {Rubus villosus Ait.), Affected with Orange Rust, in 
Typical Location on Side of Gravelly Bank with Eastern Exposure, 
North Carver, Mass., May 20, igzi 
Time A.M. 
Air in Shade 
PlaAt I 
Plant 2 
Plant 3 
Plant 4 
8:00 
14 
17 
18 
17-5 
18 
8:30 
15 
18.5 
30 
19 
20 
9:00 
17 
20 
21 
20 
21 
P.M. 
I :oo 
23 
22 
24 
25 
28 
3:00 
23 
22 
22 
24 
26 
Similarly, the weather and soil conditions recorded by Shantz and 
PiemeiseF in connection with their studies of the growth and fructification 
of Agaricus tahularis Peck and Calvatia cyathiformis Bosc. at Akron, Colo- 
rado, show that the mean temperature of the soil, in which themycelia 
of these fairy-ring fungi were growing, was usually different from the 
Dufrenoy, M. J. Les conditions ecologique du developpement des champignons 
parasites. Bull. Soc. Mycol. France 34: 8-26. 1918. 
^ Shantz, H. L., and Piemeisel, R. L. Fungus fairy rings in eastern Colorado and 
their effect on vegetation. Jour. Agr. Res. 11: 191-245. 1917. 
