CH. II 



CLIMATE 



21 



In the arid zone woody growth begins to establish 

 itself, but is usually confined, to shrubby or small trees, 

 mostly of a thorny character, leafless during the driest 

 part of the year, and when in leaf often provided with 

 a I light feathery foliage which reduces transpiration to 

 a minimum. In America especially, this zone is also 

 characterised by succulent Cactaceae, such as Opuntia 

 and Cereus, while on rocky ground and shallow soils, 

 both of the Old World and the New, woody succulent 

 Euphorbias also establish themselves. 



Fig. 4. Open forest of Acacia Verek, Sudan. 



This zone, therefore, does not lend itself much to 

 timber production, but is of importance to the forester 

 on account of the minor produce obtained from its trees. 

 Such are gums and frankincense, the former obtained 

 largely from Acacias and the latter from genera of the 

 Burseraceae, such as Balsamodendron and Boswellia. 

 The best gum-arabic of commerce is obtained from the 

 Acacia Verek (also called Acacia Senegal), which forms 

 open low forests near Gedaref, and on the sandy dunes 

 of Kordofan, in the Anglo-Egyptian Sudan, and also in 



