VALLEY OF THE SOANE. 83 
covered with Rhamnee, Olax, and a tall Sida (?), which I had not seen 
elsewhere. A Menispermum was very abundant. 
At 2 P.M., the surface sand was heated to 110° where sheltered 
from the ad: and 104° in the broad bed of the river. Finding the 
fresh juice of Calotropis to be only at 72°, I was curious to ascertain at 
what depth this temperature was to be obtained in the sand of the 
river-bed, where the plant grew. 
Surface . 104? 5' 
1 inch 102 
2 94 
21. 90 
8$ 5 85 compact 
8: : à 13 wet. 
bibi . . 72 ditto. 
The alluvium of the banks communicated heat much better than the 
sand, but was so very hard that I had difficulty in taking the fol- 
lowing :— 
Surface : 104° (colour light grey). 
25 inch . | 98 
5 : 88 In sand 78°. 
The power this plant exercises of maintaining a low temperature of 
72°, though the main portion that is subterraneous is surrounded by a 
soil heated between 90 and 100°, is very remarkable, and no doubt 
proximately due to the rapidity of evaporation from the foliage, and 
consequent activity in the circulation. Its exposed leaves maintained 
a temperature of 80°, nearly 25° lower than the similarly exposed sand 
and alluvium. On the same night the leaves were cooled down to 54°, 
when the sand had cooled to 51°. Before daylight the following 'morn- 
ing the sand had cooled to 43, and the leaves of the Calotropis to 45° 5’. 
I omitted to observed the temperature of the sap at daylight the 
following morning; but the sand at the same depth (fifteen inches) as 
that on which its temperature and that of the plant agreed at mid-day, 
was 68°, » And assuming this to be the heat of the plant, we find that 
the leaves are heated by solar radiation during the day 8°, and cooled 
by nocturnal radiation, 22° 5’. 
Mr. Theobald (my companion in this and many other rambles) 
pulled a lizard from a hole in the bank. Its throat was mottled with 
M 2 
