EUPHORBIA VIROSA AND ALOE DICIIOTOMA 
45 
In the wounding experiments the observations were made at intervals of 
2 minutes ; in other cases, of 30 minutes. The thermometers were read to 
0°'25 C. 
The direct heating effect of the sun’s rays was measured by a Negretti 
and Zambra’s Black-Bulb-in-vacuo thermometer, kindly lent for the purpose 
by Mr S. S. Hough, F.R.S. This thermometer was supported on two poles, 
4 feet from the ground, a few feet from the screen. A Stephenson’s screen of 
the regulation pattern and size was specially made, with the parts detachable 
Photograph 4. Stephenson’s screen, Radiation thermometers and Plants used in Experiments. 
(The plant Euphorbia B is out of sight, behind the screen a little to the left of Euphorbia A.) 
Euphorbia C 
Aloe A 
Aloe B 
Euphorbia 
for easy transport (Photograph 4). This was erected in such a mannei that 
the centre of the box was four feet from the ground. The shade temperatiues 
used in the following tables and curves were obtained from a thermometei 
hung in this screen ; its readings were checked by comparison with those of 
standardised maximum and minimum thermometers, for the loan of which I 
am indebted to the Director of the Union Department of Iirigation and 
Meteorology. These thermometers were erected about 15 feet fioin two of the 
Euphorbia bushes (A and B), whose internal temperatures were to be observed. 
