III. PHYSICAL AND VEGETATIONAL ASPECTS OF THE SAHARA
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Fig. 13. Principal comb-shaped distributor dispensing the water surging out of
the "foggara" (oasis of Timimoun).
ficial water streams running sporadically on its surface and which participate in replenishing the water-bearing strata linked to the inferoflux of
the wadis (an example of this are the Saoura valley and the wadi's aquiferous stratum); these waters contain tritium of thermonuclear origin. Most
of the ancient water-bearing strata are the suppliers of ancient waters
which have been accumulated in aquiferous reservoirs thousands or even
tens of thousands of years ago, such as, for example, the inferior continental Cretaceous one (Conrad and Fontes, 1970). The existence of such
superficial and deep underground water-bearing strata, as well as the vast
aquiferous system of the Sahara, are the determining factors of life in this
boundless desert.
III. Vegetation in the Sahara Desert
A. GENERAL CONSIDERATIONS
1. Paucity
The phanerogamic flora of the Sahara is very poor if one compares the
number of species of vascular plants (about 1200) in the desert to the