THE DESERTS OF WESTERN EGYPT 



299 



but the plant was found on the summit of a high sandstone es- 

 carpment several hundred feet above the oasis of Dahkla in sit- 

 uations n which the ground water must have been very far 

 beneath its roots. Later its small cliunps dotting the landscape 

 at long intervals caused us to travel many miles to examine them 

 in the hope that another species had been found. This plant is 

 reported only from Egypt and the individuals seen were near the 

 western limits of its range. 



Imperata cylindrica is the "half a" grass of northern Africa and 

 according to Muschler it is widely distributed in warm dry coun- 

 tries with marked local variations, which however are of such quan- 

 titative character as to not serve to separate sub-species or varie- 

 ties. It is a tall grass and is usually seen along embankments and 

 in sandy places. 



Tamarix mannifera is a small tree with slender pUant branches 

 growing in sandy places and capable of enduring highly concen- 

 trated soil-solutions. The stems usually serve as accretion centers 

 for the formation of dunes which may rise so high as to cover the 

 tree, or to leave only the branches protruding. Probably more 

 than one species was seen but only one specimen was taken which 

 has been identified as above. The leaves are minute and while the 

 stems are small yet their slenderness gives them a switch-like 

 effect. The larger stems are used as camel-sticks. The genus 

 is made up of species found around the Alediterranean in warm 

 dry places. Xerophytism and halophytism are represented in the 

 habits of the group. (See Fig. 3.) 



Traganum nudatum (Chenopodiaceae) shares with Haloxylon 

 the characteristic of being found in the most arid situations in 

 sandy wastes and dry slopes. It is a small shrub branching from 

 the base, the axils are fleecy, and the slender grayish stems have 

 the general aspect of a highly speciaUzed xerophyte. 



Zygophyllum coccinea (Zygophyllaceae) is a small shrub 2 to 4 

 feet in height which is common in sandy places in the Libyan 

 desert and seems to be abundant over a wide area in Africa. 



In addition to these plants which were kindly identified by Dr. 

 A. B. Rendle of the British Museum of Natural History fsee 

 Rendle A. B.) Journal of Botany, 1913) the fruiting stems of a 



