THE DESERTS OF WESTERN EGYPT 



301 



All of the species with but one exception are characterized by a 

 wide distribution, spreading over northern Africa, into Asia Minor 

 and some go still farther east into the drier regions of India. If 

 this region has ever been subjected to the conditions now preva- 

 lent in the interior deserts of America, in which a diversified topog- 

 raphy and periodic rainfall make for a high degree of differentia- 

 tion of the floral constituents and a narrow localization of the 

 species, progressive desiccation and base levehng have long since 

 reduced the country to a great expanse of low stony and sandy 

 stretches with wind worn hills and low plateaus in which the 

 environmental conditions are monotonous and arid. Such a 

 change would of course be followed by the extermination of all 

 but a few forms, and these would naturally be of the kinds included 

 in the list given above. 



Haloxylon Schweinfurthii is limited to an extent of territory no 

 larger than Arizona, but many dozens of species are known from 

 places in American deserts no larger than an ordinary farm, in 

 single canons, or on one slope of unique environic combinations. 



Travelers' tales of great stretches absolutely devoid of vegeta- 

 tion and of boundless seas of desert sands are common in books 

 descriptive of journeys in northern Africa. Schimper however, 

 says in regard to such statements "Notwithstanding the extreme 

 dryness of the climate,the occasional abundance of common salt and 

 the fact that the soil except in loamy localities permits the rapid 

 percolation of the scanty rainwater, there are nevertheless few 

 places where a glance around fails to reveal a single plant (Plant 

 Geography, p. 608, 1904). 



In view of these conflicting opinions interest ran high as to the 

 outcome of our own experience. Two conditions affect the ob- 

 server which might have an important bearing on his conclusions. 

 First of all travel is usually by caravan and a track is not a single 

 path, or road, but is a web of trails which may cover a strip of 

 ground a mile or more in width in the open. The camels weave 

 about, crossing from side to side as they go along, and ravage any- 

 thing but rock and sand, eating the most unpromising things. 

 Thus the camel boys found it necessary to guard the small fagots 

 collected for fuel during the day's march to prevent them being 



