THE VEGETATION OP NATAL. 



283 



(4) LIGHT. 



1. Duration. — The relative lengtlis of day and iiiglit are 

 as foUoAvs for Pietermaintzburo- and Dui'ban. 



Darkness falls quickly after sunset, and there is no long- 

 twilight as at higlier latitudes. Since there is only one 

 minute difference in duration of light between Durban and 

 Maritzburg, it is obvious that the whole of the province of 

 Natal is practically uniform in this respect, and that no 

 differential effect on the vegetation of the various parts is 

 produced. 



Owingj however, to the physical configui*ation of the 

 country — the rapid rise from sea-level to an altitude of over 

 10,000 feet — plants on the Drakensberg are under conditions 

 as regards light which, in other respects than mere duration, 

 differ Avidely from those on the coast. 



2. Intensity.- — No figures were available of the relative 

 intensities of light in different places. I can only giverougli 

 figures obtained by using a Watkin's actinoineter, such as is 

 used in photographic work. 



In the brilliant sunshine the sensitive paper darkens so 

 quickly that it was found that at Pietermaritzburg in the 

 month of April (when I began taking observations) at 

 midday the normal tint usually employed could often be 

 obtained in a little over two seconds. To insure as great 

 accuracy as possible it was found necessary to have a series 

 of graded tints, five in number, and in open sunlight to allow 

 the paper to darken to the darkest tint, the time required for 

 this being sixteen times that recpiired for the lightest tint. 



