RODENTS OF LIBYA 21 



Geophytes are plants which are able to survive periods of drought 

 by the development of enlarged subterranean organs such as bulbs 

 and rhizomes. These are represented chiefly by members of the 

 Umbelliferae. 



Permanent vegetation has adapted to the aridity of the desert by 

 the development of anatomical and morphological structures which 

 increase the amount of water absorption and decrease evaporating 

 surfaces. In general, a high level of absorption is insured by the 

 maintenance of greater hypertonicity in the roots than in the aerial 

 parts. The roots of these desert plants are frequently elongated and 

 specialized to absorb water more efficiently in any given type of soil. 



The problem of water retention in desert plants has been solved by 

 a reduction in the evaporating or transpirating surfaces, a reduction 

 in the speed of evaporation, and by the accumulation of water in the 

 tissues. Species belonging to the family Chenopodiaceae and to the 

 genera Ephedra L. and Calligonum L. have minute flowers and are 

 even apetalous. In the case of Anabasis articulata Moq., Tamarix 

 gallica L., and Calligonum, the leaves drop off during the dry season. 

 In other plants (sclerophy tes) , the epidermis is covered with a thick 

 cuticle formed of sclerified cells, which retard significantly the speed 

 of evaporation or transpiration. Succulent plants which store water in 

 the tissues are represented in the Sahara by relatively few species 

 belonging to the genera Mesembryanthemum L., Euphorbia, and 

 Caralluma R. Br. 



In the northern Sahara, including the steppe and deserts of Libya, 

 there are approximately 20 species of trees or arborescent plants. 

 These include such well-known genera as Ephedra, Cupressus L., 

 Phoenix L., Ficus L., Acacia Mill., Pistacia L., Tamarix, Calotropis 

 R. Br., Olea L., Calligonum, Rhus L., and certain arborescent genera of 

 the Chenopodiaceae. 



The Vegetative Cover of Libya 



Coastal Plain. Floral composition and density of plants of the 

 Libyan coastal plain varies considerably from region to region de- 

 pending upon the character of the soil and upon the season. Generally, 

 the vegetative cover of the coastal plain is denuded by overgrazing 

 but occasionally it is quite dense and uniform. The most typical 

 pattern consists of extensive areas of small hillocks supporting bush- 

 like plants. Emergent grasses and annuals are sometimes interspersed 

 among these hillocks. Zavattari (1934) states that the following 

 genera are the most typical of the coastal plain: Hyparrhenia Anderss., 

 Imperata Cyrill., Agropyron L., Cyperus L., Pancratium L., Silene L., 

 Euphorbia, and Ononis L. In sandy areas of the coastal plain, the 

 vegetative cover is sparser and consists of larger, bushlike species 



