THPJ PLANT ECOLOGY OF DRAKENSBERG RANGE. 523 



The range for Weenen is seen to be much greater, both for 

 maxima and minima. The average of the absolute maxima 

 for the period 1897-1908 for Weenen was 41-7° C; for the 

 period 1901-1905 (the only period for wliich records are 

 available) for Qudeni it was 31*7° C. only : the corresponding 

 averages for mean maxima being 29'1° and 20'0°C. The 

 average of the absolute minima for the same period for 

 Weenen was — 5° and for Qudeni — 1-7 °C., the average of 

 mean minima for Weenen being 11*6° and for Qudeni 

 8-0° C. 



It is clear, therefore, that so far as temperature in general 

 is concerned, two antagonistic phenomena have to be taken 

 into consideration in dealing with mountain vegetation. The 

 temperature of the soil, owing to the great increase in 

 insolation, is relatively high during the daytime, and at 

 night the soil cools rapidly owing to the increased radiation, 

 so that the range of soil temperature is greater at high 

 altitudes. The temperature of the air, on the other hand, 

 decreases with rise in altitude (0-57° C. for every 100 m.), 

 so that it is less during the daytime at high altitudes than in 

 the valleys and lowlands, but again, owing to radiation and 

 cold air drainage, we get an inversion of temperature at 

 night, the valleys being colder. As regards the temperature 

 of the air, therefore, it is the valleys that show a greater 

 range than the mountains. 



