254 



D. T. MacDOUGAL 



one passes from a flora, rich in succulents, to a region in which the 

 prevaiHng types are spinose xerophj^tes, or forms with switch-Uke 

 branches. Succulents do not find place, in any number, in a cli- 

 mate in which the rainfall is uncertain in occurrence. 



The tree milkweed (Calotropis) fringed the channels of the khors; 

 and we had our car set out on a side track along the Khorel Ushari, 

 at the station of Talgwarab. Awa}'" from the khor the country 

 presented the aspect of endless, flattened ridges of coarsely broken 



Fig. 8. Fertile eastern bank of the Nile with palms 



stone, the exposed surfaces of which were deeply browned by the 

 desert sun. (Fig. 7). The depressions contained some finer mate- 

 rial, and in these lower places were the few plants constituting the 

 entire vegetation; among which were included the switch-like 

 Leptadenia, camel-grass and a composite or two. One might read- 

 ily believe that these plants would need a sap so concentrated as 

 to show over a hundred atmospheres of osmotic pressure in order 

 to draw solution from such a substratum. 



