366 INTRODUCTION TO PLANT GEOGRAPHY 



Their leaves are commonly narrow, leathery and inrolled, less than 

 3 cm. long and often densely covered with hairs which give them a 

 greyish-white tint. Outside the rainy season, dependence is largely 

 on underground water. Except for those which are deciduous, the 

 dominants frequently show little contrast in appearance at different 

 times of the year — especially as few display at all large and bright 

 flowers. Matters are otherwise with the often plentiful associated 

 ephemerals which burst forth when rain allows, and form quite a 

 display with such succulents as Cacti, Mesembryanthemums, Aloes, 

 and Agaves, which contain considerable stores of water. 



With still more precarious precipitation or other water supply, 

 deserts usually result. But as these usually belong to tropical or 

 subtropical regions, or at least extend well into them, they are treated 

 chiefly in Chapter XIV. Exceptions are afforded by the Trans- 

 caspian desert which is an open plain and the Gobi Desert which 

 is a plateau, both lying in temperate parts of Asia. These are 

 mainly areas of prevailing drought and extreme temperature con- 

 ditions, and consequently are very little vegetated, such plant life 

 as exists being mainly the result of depauperation of the so-called 

 desert steppes described above. Thus dunes may be partly fixed 

 by low and open, shrubby growth, but siliceous and clayey soils, 

 often containing loess, are apt to be virtually barren, as are gravelly 

 and talus-strewn areas over considerable tracts of country. Nor do 

 the frequent saline or ' alkali ' and gypsiferous areas afford much 

 relief to the abiding monotony. Nevertheless one seldom finds at 

 all extensive tracts even in the Gobi that are entirely devoid of some 

 kind of vegetation, and very commonly the transition to steppe or 

 at least desert-steppe is marked by a scattering of poor Grasses 

 ranging from some 25 cm. high in exposed situations to a metre in 

 height in depressions where water collects in the rainy season. 

 Besides Grasses and some Sedges, xeromorphic members of the 

 Daisy (Compositae), Goosefoot (Chenopodiaceae), and Tamarisk 

 (Tamaricaceae) families tend to be prominent in these temperate 

 deserts, as do geophytic monocotyledons such as Tiilipa uniflora. Iris 

 sisyrinchium, and species of Gagea. Desert-like ' bad-lands ', often 

 characterized by lowly Cacti or brush-like shrubs, also occur more 

 locally in parts of temperate North America and southern South 

 America. 



For examples of desert areas in warm-temperate regions we may 

 go to central Iraq. Fig. 156, A, shows a quadrat in a typically 

 gravelly area in which one small perennial tuft is visible but there 



