520 



J. W. BEWS. 



Chemical Intensity of Sunlight (in percentages 

 of the maximum),^ 



According to this table, when the sun is low, the chemical 

 intensity of sunlight on the Drakensberg is three or four 

 times greater than on the coast-belt, but the difference 

 decreases as the sun rises to the zenith, when it is only 11 or 

 12 per cent, greater. 



The remai-kable colour changes in the flowers of species 

 which extend from the coast to the higher altitudes is one of 

 the many physiological effects of this factor. Helichrysum 

 adenocarpnm has flower-heads white or pale pinkish on 

 the coast, but brilliant crimson in upper districts. Dierama 

 pendula has pure white flowers on the coast, pink in the 

 midlands, and deep purple on the mountains. Moraea 

 spathacea shows similar variations. 



A relatively high surface temperature of the soil is a direct 

 result of the increased insolation. The temperature of the 

 soil to a depth of several centimetres is often much higher 

 during the daytime than that of the atmosphere. On the 

 other hand, owing to the rarity of the air and the decrease 

 in the amount of water-vapoui% radiation of heat at night is 

 increased, the temperature of the surface falls, and there is 

 thus a much larger range of surface temperatures' on the 

 Drakensberg than on the lower terraces. The exposure is of 



1 Hann, J., ' Handbook of Climatology," Trans, by D. C. Warfl. 

 New York, 1903. 



