THE WATER SUPPLY OF DESERT PLANTS 205 



morphological one rather than a physiological one. The chief adaptation 

 is the reduction of the transpiring surface, the better development of the 

 main root system, and the ability to reduce water loss during prolonged 

 drought periods to nearly nil. 



A special group are the succulents in the arid parts of North and South 

 America and of South Africa. In the Sahara and in the arid parts of Asia 

 they do not play a role and in the arid parts of Austraha they are absent.* 

 Most of the succulents prefer an arid climate with two rainy seasons in 

 order to replenish their water storage tissues. 



During the dry seasons the succulents can remain without water uptake. 

 Therefore their root system is weakly developed and shallow. The water 

 economy of succulent plants is quite different from that of other xerophytes 

 and is not considered here. 



The annual or ephemeral plants and also the geophytes in arid countries 

 grow during the short periods when water is in abundance. Their water 

 supply is guaranteed and therefore does not present any problenas for them. 



REFERENCES 



Kausch, W. (1955) Saugkraft und Wassemachleitung ini Boden als physiologische 



Faktoren. Planta, 45, 217-263. 

 Kausch, W. (i960) Unesco Document NS-914-58. 

 SiMONis, W.(i936) Untersuchungen iiber die Abhangigkeit des osmotischeu Wertes 



vom Bodenwassergehalt bei Pflanzen verschiedener okologischer Gruppeu. jb. 



wiss. Bot. 83, 191-239. 

 Waltek, H. (1924) Plasmaquellung und Wachstum. Z. Bot. 16, 353-417- 

 Walter, H. (1954) Gmiuilagen dcr Weidewirtschaft in Siidwestafrika. E. Ulmer, Stuttgart. 

 Walter, H. (i960) Standortslchre {Einf. in die Phytologie, Bd. Ill, i) 2. Aufl., p. 265 ff. 



E. Ulmer, Stuttgart. 

 Walter, H.(i962) Die Vegetation derErde, Bd. L 

 Walter, H. (1962) Grtmdlagen des Pflanzenlebens{Einfiihmng in die Phytologie, Bd. I) 4. 



Aufl., p. 344 flf. E. Ulmer, Stuttgart. 



* One exception is the rather rare species Sarcostemma australis. 



