SEASONAL DIMORPHISM OF CHAMAEPHYTES 207 



quantitatively under natural conditions (Zohary and Orshan, 1954; 

 Orshansky, 1952; Orshan and Zand, 1961). Ten species have been selected 

 for the present discussion for which information both about the transpira- 

 tion rates and about the extent of the seasonal reduction in the plant body is 

 available and in addition the Hfe cycles of which are known. Six of them 

 are dominants of desert plant associations while four are leading species of 

 Mediterranean plant communities. 



The measurements were carried out in several stands in two different 

 locaHties, a desert one nearRevivim in the Northern Negev, where annual 

 rainfall averages 80 mm, and a Mediterranean one in the vicinity of 

 Jerusalem where annual rainfall averages 550 mm. The climate in both 

 locaHties is typical Mediterranean. The rainy season lasts from September 

 to May while the summer is hot and rainless. 



The desert plants which were selected for presentation are: Artemisia 

 herba alba Asso., and Noea mncronata (Forsk.) Asch. et Schw. which are 

 leading species of the Artemisietum herbae albae, one of the most wide- 

 spread Irano-Turanian plant associations in the Middle East (Zohary and 

 Feinbrunn, 195 1); Haloxylon articnlatum (Cav.) Bge. the leading species of 

 the Haloxylonetum articulatae plant association dominating the pluviatile 

 loess plains in the Northern Negev (Zohary and Feinbrunn, 195 1) ; Anabasis 

 articnlata (Forsk.) Moq., the leading species of the Anabasidetum articulatae 

 plant association dominating the small, shallow, and dry water courses 

 cutting the plantless Hamada plains of the Southern Negev (Zohary, 1953) ; 

 and Zygophylhim dumosum Boiss., the leading species of the Zygophylletum 

 dumosi which is the plant community occupying the most extreme habitat 

 within the Saharo-Sindian territory in Israel (Zohary and Orshan, 1954). 



The following are the Mediterranean plants presented : Poterium spinosum 

 L., the leading species of the widespread Poterietum spinosi dwarf shrub 

 plant community which is one of the first stages in the succession from 

 abandoned fields; Cistus salvifolius L., one of the leading species of the 

 Grigue succeeding in many places the Poterietum in the succession; Thymus 

 capitattis (L.) Lk. et HofFm. which dominates the Thymetum capitati 

 occupying stands with shallow soil layers both on limestone and on a 

 sandstone locally called 'Kurkar', and Teucrium polium L. which is an 

 important component of several dwarf shrub communities (Zohary, 1955). 



In addition, data are presented o£ Artemisia monosperma Del. which is a 

 dominant of the Artemisietum monospermae, the most important plant 

 community of the sand dunes of the Northern Negev (Zohary and 

 Feinbrunn, 195 1). 



