42 
INTERNAL TEMPERATURES OF 
Therefore the maxima of internal temperature may be higher later in the 
summer than during December. On the other hand, the few very small 
leaves of Euphorbia virosa appear in January, and the soil is normally moister 
at the end than at the beginning of the summer. Conditions' are therefore 
most favourable for transpiration and surface-evaporation during the hottest 
months. In view of what has now been stated, it will be seen that the results 
here recorded are not to be regarded as extreme. It is probable that the 
great bulk of the vegetation of Great Namaqualand and of some parts of 
Little Namaqualand must protect itself against higher air-temperatures and 
more powerful solar radiation than obtain here, or must endure higher internal 
Photograph 1. Euphorbia virosa (Euphorbia A), Wasserfall, Great Karasberg, 4200 ft. 
December, 1912. 
temperatures than those now recorded. And, indeed, higher internal tem- 
peratures than those obtained in these experiments have been recorded by 
other observers 1 , even in plants growing normally in a cooler climate. 
Euphorbia virosa (Photograph 1) is a comparatively shallow rooted plant 
with numerous 5-7 angled suberect or ascending branches arising from a short 
main stem to a height of 5-8 feet. The first aerial shoot of the seedling, which 
in due course becomes the main stem, has all the external characters of the 
later-formed primary branches. Secondary branches in this locality are rare ; 
if present they are seldom more than a few inches in length. The projecting 
1 Jost, L., ’07, p. 44. 
