PEPPER TREE AS A CAUSE OF HAY FEVER. 149 



Hours of Sunshine : 



The mean number of horn's of bright sunshine experienced 

 daily at Kimberley is 9-4, and at Johannesburg 8-7, as compared 

 with 3-8 for London and 6-9 for New York (Cox, 1922). There 

 are no records available for Bloemfontein, but the figures for it 

 would probably lie between those for Johannesburg and 

 Kimberley. 



Wind : 



The prevailing wind at Bloemfontein is westerlj^ ; it is dry 

 and frequently strong and gusty. The north-easterly and easter- 

 ly winds caiTy moisture to this part of the country, but unfor- 

 tunately they have dropped much of their water-content in rising 

 to the High Veld; they are rarely stx'onger than a gentle breeze 

 and always pleasantly moist. The south wind is also only 

 rarely strong ; it always causes a considerable fall in temperature 

 and, in winter, is bitterly cold. 



The official daily weather observations for Bloemfontein, 

 which it should be remembered are taken at 8.30 a.m., are really 

 very misleading as regards the wind. Many of them are given 

 in connection with the exposure of pollen plates at Bloem- 

 fontein. They leave the impression that Bloemfontein is fanned 

 by gentle breezes even in the spring and early summer. In 

 reality, at this season a dry westerly wind frequently springs 

 up towards the middle of the forenoon and blows in gusts imtil 

 late in the afternoon. It is almost invariably dusty, and, though 

 not of daily occurrence, is a distinguishing and unpleasant fea- 

 ture of the Bloemfontein climate, especially from July until the 

 summer rains begin, which may be as late as February. During 

 the hot weather this wind is correspondingly hot, dry and parch- 

 ing. Its influence on the climate and vegetation is very marked, 

 and it also plays a role in connection with hay fever. 



Rainfall and Evaporation : 



The average annual rainfall at Bloemfontein since 1880 is 

 21-73 inches (Cox, 1922). Its effect on the climate and vege- 

 tation is, however, reduced by the unequal distribution through- 

 out the year, the manner in which it falls, the bare and 

 frequently baked surface of the ground, and the intense 

 evaporation. 



From an inspection of Table II it will be evident that the 

 bulk of it falls at one season — in the late summer, especially 

 m February and i\Iarch. The heavy rains usually fall in the 

 fonn of violent thunderstorms, and so rapidly that much of the 

 water cannot be absorbed by the ground. A large proportion 

 therefore inins off as surface water and, incidentally, causes 

 sluiting. Another large proportion is lost by falling in showers 



