580 J. W. BEWS. 



gathered it where the light intensity was only '0025 of the 

 normal in the Stella Bush, Durban (see PL XXVI, fig. 2). 

 The light requirements of the commoner species is a subject 

 which must command attention as soon as possible. 



4. Movements of the Air. 



The following are the chief winds on the coast belt of 

 Natal : 



(a) During the summer months and exceptionally also in 

 winter, cyclones are frequent in the Indian Ocean, generally 

 moving from the north-east and recurving in towards the 

 coast of Natal. While the depression is in the north-east the 

 winds blow from the east over the coast belt and pressure 

 decreases. This east wind does not deposit moisture, though 

 near the coast line it sweeps up salt spray and sand, and its 

 effect on the vegetation is often very great, as is illustrated 

 in PL XXIV, fig. 2, where the umDoni (Eugenia cor data) 

 is shown greatly deformed, being blown over to the west. 

 The effect of this east wind is seen more markedly on the 

 coast south of Durban than on the north coast, since the 

 cyclonic depression usually recurves in towards the coast 

 about the latitude of Durbau. As the depression advances 

 over the coast belt the heat often becomes intense. 



(b) When pressure begins to increase the wind goes round 

 to the south-west and the change usually brings heavy rains. 

 This south or south-west wind is the chief rain-bearing Avind 

 over the coast belt, but the causes which bring rain further 

 inland are more obscure. The heaviest deposition takes 

 place at the stations near the coast and decreases slightly at 

 the stations further away from the sea. The rain-bearing 

 southerly winds do not affect the vegetation adversely. 



(c) Owing to the land heating up faster during the day 

 and the air consequently rising, a sea-breeze blows regularly 

 in the afternoons. It has the effect of tempering the heat 

 and consequently it influences the vegetation, especially near 

 the sea, where it is most felt. The corresponding land-breeze 



