24 U.S. NATIONAL MUSEUM BULLETIN 275 



plants develop and sometimes extend over large areas of the hamadas. 

 These annuals are represented by Erodium L'Herit, Lifago Schweinf. 

 and Muschl., Convolvulus L., and Urginea Steinheil. 



In the serirs, where the surface layer is sandy, grasses belonging to 

 the genus Aristida constitute the major vegetative cover. The floral 

 cover of these sandy plains is generally denser and more varied than 

 that of the hamadas. The following genera are most common : Andro- 

 cymbium Willd. and Asphodelus, representing forms with underground 

 bulbs or tubers; Daucus L. and Ammodaucus Coss. and Dur., which are 

 annuals; Cornulaca Del., a thorny chenopod; and Randonia Coss., a 

 bushlike perennial. Wild gourds, Colocynthis vulgaris (L.) Schrad., 

 occur in both hamadas and serirs. 



Depressions or sebchets. The large saline depressions or sebchets in 

 various parts of Libya have a distinctive flora consisting of salt-tolerant 

 representatives of the Chenopodiaceae, such as Salsola, Traganum 

 Del., Atriplex L., Cornulaca, and Suaeda. Other families are repre- 

 sented by Zygophytlum L. and Frankenia L. 



Sixty-five species of herbaceous and woody plants are recorded from 

 the vicinity of Giarabub Oasis, many of which belong to well-known 

 salt-tolerant genera and are capable of existing under conditions of 

 marked alkalinity. The most salt- tolerant of these include Chenopodium 

 L., Arthrocnemum, and Salsola. In some of the larger sebchets, several 

 successional stages are apparent in the flora extending from areas of 

 high-salt concentrations to those of lower concentrations. Along the 

 margins of the depressions where the soil is less saline, tamarix and 

 date palms are sometimes abundant. Near the saline lake of Bahr el 

 Tubat in eastern Cyrenaica, dense growths of Phragmites occur on 

 the moist, sandy-clay soils near the margins of the zone of true 

 halophytic plants. 



Oases. Owing to their high water tables, the oases in the interior of 

 Libya support a lush flora entirely unlike that of other areas. Large 

 groves of date palms (Phoenix dactylifera) are the dominant vegeta- 

 tive feature of the oases, but numerous other plants of agricultural 

 significance, such as figs, wheat, and alfalfa, are also present. On the 

 periphery of the oases, and to a lesser extent in the interior, tamarix 

 is relatively common. This outer zone of tamarix is typical of almost 

 all larger oases in Libya. In these outlying areas tamarix forms 

 clones of considerable size on sandy soils and occurs sparingly on top 

 of large sandy-clay hummocks. Frequently, Calligonum occupies these 

 same hummocks. The hummocks supporting Tamarix and Calligonum 

 frequently occur for 20 kilometers or more beyond the palm groves 

 of the oases. 



In many large oases, such as Cufra, Tazerbo, and Bzema, small 

 lakes (mostly saline) occupy the central portions and are bordered 



