THE VEGETATION OF NATAL. 285 



The observations so far referred to were those taken near 

 mid-day. At that time the full amount of sunlight is so great 

 that though the relative amount of light which penetrates is 

 very small the absolute amount is not so. Earlier in the day 

 the absolute amount is less, but the relative amount is greater. 

 This kind of bush always grows on the south-eastern slopes, 

 and the slanting rays of the rising sun are better able to 

 penetrate underneath the canopy. This is most marked near 

 the edge of the bush, and is also more the case in the less 

 dense rocky stream bush than in the closer types. 



In the Thorn Veld the trees usually grow isolated^ and 

 only occasionally form clamps. The intensely xerophytic 

 species of Acacia give but little shade. The typical form is 

 the flat-crowned umbrella-shape, and the light penetrating 

 through the branches gives a variegated shadow-pattern on 

 the ground. It is difficult, therefore, to measure the total 

 amount penetrating. As the result of several observations 

 taken under a large specimen of Acacia arabica var. 

 kraussiana, I came to the conclusion that at mid-day about 

 Jjp of the full sunlight passed through. But the amount is 

 exceedingly variable, and for a large part of the day the 

 plants growing around the base of the trees in the Tliorn 

 Veld are exposed to full sunlight. 



Among the tall grasses of the veld tlie varying intensity of 

 light is of great importance, especially with reference to the 

 associated plants. 



It is the custom to burn the grass regularly once a year, and 

 I have classified the associated plants into : 



(1) those that flower immediately after the burning of the 

 grass ; 



(2) those that flower after the first rains and before the 

 grass grows tall enough to shade them; 



(3) those that grow with the grass, and flower late. 



The first two classes flowei* while they are obtaining the 

 full amount of sunlight, and perform their vegetative work 

 afterwards. The third class consists of taller species that 

 grow as high or higher than the grasses. It will be seen, 



VOL. 2, PART 3. 20 



