288 SYLVICULTURE IN THE TROPICS pt. 



IV 



completed, seeds are dibbled in all over the area, which 

 is also irregularly covered by loose branches which can 

 be stuck into the ground as indicated above. 



If it be possible, the afforestation of the area from 

 which the sand is derived should also be taken in hand 

 so as to stop the source of supply. 



In order to effect a successful afforestation of the 

 sand-swept areas, and thus to arrest the movement of 

 these sands, a study of the plants which thrive in these 

 conditions should also be made. In Kordofan, for 

 example, besides the species mentioned above, I have 

 noticed on these sand-hills, among the trees, Acacia spiro- 

 carpa, A. albida, and Albizzia amara; among the shrubs, 

 Leptadenia Spartium and three species of Boscia; 

 among herbaceous plants, fatty plants belonging to 

 Zygophyllaceae and Ficoideae, and numerous grasses, a 

 large portion of them belonging to the genus Aristida. 



In districts with an unappreciable rainfall the 

 question of how to fix sands is one of extreme difficulty. 

 Where the sand does not shift, a number of plants 

 manage to keep themselves alive for at least part of the 

 year ; they evidently germinate very easily, for the 

 amount of moisture available for this purpose is 

 extremely small ; but on the dunes themselves there 

 is often no trace of vegetation of any sort. In the 

 Dongola province of the Sudan I have searched for 

 plants which might help in fixing the sands which invade 

 much of the cultivation. The most hardy plants found 

 by me have been two grasses, Panicum turgidwn and 

 Aristida plumosa var. berbe'rica, and a woolly, semi- 

 woody plant, Aerva tomentosa var. Bovei. In such places 

 the problem of how to fix the sands has not yet been 

 solved ; it can, no doubt, be arrested temporarily by means 

 of fences and scattered branches, and it is possible that 

 when in this arrested condition some of the desert 

 plants might be induced to spring up. Among these 

 may be mentioned those quoted above, as well as the 

 desert-acacia [A. tortilis) ; Leptadenia Spartium, which 

 may grow into a small tree ; semi-woody herbs, such as 



