46 
INTERNAL TEMPERATURES OF 
The results of the first few days’ observations made it desirable to perform 
similar experiments with other succulents. The only suitable plants in the 
neighbourhood were two trees of Aloe dichotoma (A and B), growing at a 
slightly higher elevation some 300 yards to the east of the screen, on the steep 
slope of a hill facing north-west. The direct investigation of the relations 
between the shade temperature and the internal temperatures of these plants 
would have necessitated the erection of a second screen in their immediate 
vicinity. This, however, was impossible. The omission was as far as possible 
made good by concurrent readings of the internal temperatures of a Euphorbia 
(Euphorbia C) growing about 6 yards from one of the aloes and 10 yards from 
the other. The temperatures of this Euphorbia when compared with those 
obtained from plants close to the screen (Euphorbia A and B ) give some idea 
of the extent to which the local conditions affecting the aloes differed from 
those prevailing near the screen. 
The thermometers used for the readings of internal temperature were 
pushed into the stem far enough to place the bulbs approximately in the 
centre. The internal temperature actually measured in the Euphorbia is 
therefore that of the gas contained in the pith cavities. In the case of the 
Euphorbia, a small hole was first made with an awl. A flow of latex followed, 
and, as it congealed, it securely sealed the thermometer in place. In the Aloe 
a hole was easily made in the soft wood with a narrow scalpel. The stem of 
the thermometer was tightly plugged in position with cotton wool ; care was 
taken not to place any cotton wool between the bulb and the internal tissues. 
In both cases the stem of the thermometer was inclined above the horizontal 
just sufficiently to ensure that when the mercury contracted the thread did 
not break. 
The thermometers used are distinguished by the following symbols ; in 
the charts, the curves of their readings are denoted by various types of lines 
as indicated below : 
Thermometer 
Black-Bulb-in-vacuo 
Shade (in screen) . . 
Thermometers used for 
readings of internal 
temperature 
3. Observations on Normal Internal Temperatures. 
The observations made on December 13 and 18 may be taken as typical of 
the rest in regard to the relation between the sun, shade, and internal tem- 
peratures. 
Symbol 
BB 
Sh 
w 
T 
\ P 
\lv 
Line 
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