50 SYLVICULTURE IN THE TROPICS R . i 



at Erkoweit, which enables moisture in the soil to be 

 retained, causes arborescent growth to appear, among 

 which, in order to avoid heavy transpiration, the 

 evergreens are very apparent. The principal repre- 

 sentatives are Diosjyyros mespiliformis, Olea europaea 

 var. nubica, Euclea Kellau, Carissa edulis, Nuxia 

 dentata, Dodonea viscosa, Ximenia americana, Rhus 

 abyssinica, R. viscosa, Gymnosporia luteola, G. rnon- 

 tana, and Ficus glumosa, while among the undergrowth 

 will be found Labiatae, Umbelliferae (Pimpi?iella), 

 various Compositae, Plumbago zeylanica, ground 

 orchids (Bonatea), lilies, and, in cool nooks, various 

 delicate ferns (Adiantum, Asplenium, and Cheilanthes). 

 Climbers are few, the most important being the 

 "Traveller's joy" (Clematis TJiunbergii) and a vine 

 ( Vitis concinna). 



The number of species of trees which are able to 

 have their roots covered by fresh water, even when it 

 is well-aired, flowing water, is comparatively limited, 

 and areas subjected to periodic floods are often covered 

 by a type of forest very different from that found on 

 the adjoining higher ground. For example, both on 

 the Nile (as far south as about 12 N. lat.) and on 

 the Indus pure forests of Acacia arabica cover the 

 low banks, which are perhaps one to two metres under 

 water during flood time. At other places Tamarisk 

 (Tamariscus articulatus and T. gallica) takes the 

 place of the Acacia. Farther south on the Nile Acacia 

 Suma and Acacia verugera replace the A. arabica. 

 In the periodically inundated littoral forests on the 

 western shores of Lake Victoria a variety of the same 

 Podocarpus which forms forests on the slopes of 

 Ruwenzori (P. milanjianus var. arborescens) lias 

 established itself, and, as has been mentioned already, 

 another species of the same follows the same example 

 in the Andamans. In the wet zone of Ceylon one of 

 the Dipterocarps ( Vatica Roxburghiana) will be found 

 growing in places, with not too swift a current, which 

 are inundated each year. The fruit gets ripe just about 



