322 MODIFICATIOX OF SOt'TH AFKECAX RAIXFAI.L. 



first instance on plant-life — directly or indirectly — for food, so 

 this ]jlant-life is a^ain dependent on the |)ro(lucino; power of 

 the earth, and this in large ])art is the outcome of the presence 

 of ahsence of moisttire. W'hat, then, is it which "governs the 

 ahsorption of moisture, apart from the actual texture of the 

 ground, which is unchangeable for any particular i)lace? The 

 governing factors are twofold: firstly, there is the manner ol 

 precipitation of the moisture; and secondly, the condition of tin 

 ground surface. 



Maimer of Precipitation. — No detailed exi)lanation is neces- 

 sary to make it clear that infinitely more st)akage takes place 

 and more good is done to the vegetation of the country by the 

 precipitation of, say, one inch of rainfall in the form (^f soft 

 showers and mists than by the ]ireci]iitation of the same amount 

 in one torrential downpour. 



Condition of Ground Surface. — The more obstruction there 

 is to the fiow^ off of preci])itated moisture the more soakage takes 

 place. 



Now the one point of jjrimar)- importance in ccjnnection 

 with these two facts which must be grasped i^ the interactiou 

 of them on one another. It is this interaction wJiich has been 

 responsible for the desiccation of South Africa, for tlie disas- 

 terous droughts and floods we have had such a striking examj^le 

 of this }'ear. and f(^r the decrease in the power of production of 

 the whole country. We may say that in the iiUeraction of tlu- 

 manner of ])recipitati(Mi ori the ground surface anil tin- groiuid 

 surface on the manner of jjrecipitation is wrai)ped up the whok- 

 problem of the future destin\ of .South Africa, ^o 1 would now 

 pro])ose to deal with theiu. 



If a current of air laden with moisture — a sea-breeze, for 

 instance — meets a land surface, the question of whether or inn 

 the moisture shall be ])recipitated depends on the temperature 

 of the land surface met. If this land surface is cooler than the 

 vapour-laden air. it causes the density of the air \o increase, the 

 air becomes satin"ited. and preci])itation takes |)lace. If, on 

 the other hand, the temperature of the ground surface is higher 

 than .that of the air. it causes the aid to expand, rise and carry 

 with it the moisture it brought. This explains the enormous 

 influence forests exert on the rainfall of a countrv. Nc)W, since 

 the indigenous forests of South Africa s!o\vl\- spread westward 

 — and it must liave taken thousands of vears for this extension 

 to have taken place in — we must presume that the rt'lation be- 

 tween the ground-coN'ering and rainfall remained in a state of 

 C(|uilibrium. P)Ut as soon as man interfei"ed with tile t^round- 

 covering, the rainfall began to change. 



'i'he original inhabitants of South .\frica. the Ibittentot 

 tribes, were a noiuadic race, their whole interest beiug in their 

 herds and in hunting. Tlnr^ they were not intentional de- 

 stroyers of either forest or grass, although their carelessness 

 in lighting fires at their cami)s undoubtedly was the cau.se of 



