(g) Filago type. Ephemeral s finishing their life cycle long before the end of the 



rainy season. Very abundant. 



(h) Salsola type. Summer annuals starting to develop in spring and shedding their 

 large leaves in early summer, while retaining green, bract- like leaves up to 

 the end of summer. 



The above analysis demonstrates the great phenological diversity of the vege- 

 tation, and the accordance between phenological events associated with surface 

 reduction of the transpiring body and seasonal decrease in the moisture resources 

 of the desert. 



Morpho - Ecology 



By this term I refer to formal and dimensional changes in the plant body, direc- 

 tly or indirectly associated with its water economy. This subject also includes 

 the study of life forms but viewed from another angle than that exposed by Raun- 

 kiaer. It is not the position and protection of the renovation buds that affect the 

 water ecology of the plant, but the dimensions of the transpiring organs regularly 

 lost by the plant in the critical season, that is most essential for the maintenance 

 of desert summer vegetation. In an unpublished paper, Orshansky (1952) has shown 

 that in the evergreen Zygophyllum dumosum the summer reduction of the transpiring 

 surface amounts to V3 of the total transpiring body. In other plants even much high- 

 er values have been found. The following morphological types have been distin- 

 quished in the local vegetation. (Fig. 2). 



(a) Herbaceous whole- shoot shedders. This type comprises winter annuals, hemi- 

 cryptophytes and geophytes in which the whole plant or the epigaeous part 

 only dies away at the beginning of the dry season. This type comprises about 

 85% of the total flora. 



(b) Phanerophytic summer leaf shedders. These include shurbs shedding the 

 leaves in midsummer (e.g. Lycium arabicum). 



(c) Petiolate leaflet shedders. The leaf is composed of two leaflets borne on a 

 cylindrical leaf- like petiole, all succulent. In late spring the leaflets are 

 shed while the petioles remain physiologically active during summer (e.g. 

 Zygophyllum dumosum). 



(d) Aphyllous leaf and branch shedders. This type comprises broom- like shrubs, 

 like Retama spp., Calligonuni comosum, etc., which shed their leaves in 

 winter and remain green the year round, but in summer a part of the last year's 

 branches dry up and break down. In this way a considerable part of the trans- 

 piring surface is removed from the plant. 



(e) Aphyllous branch shedders {Ephedra type). They produce no leaves (except 

 scale- like ones); a considerable part of the green and brittle branches are 

 regularly shed in the dry season. 



(f) Basiphyllous leaf shedders. At the start of the dry period the large winter 

 leaves crowded at the base dry up and die away, while the flowering shoots 

 develop small leaves, active during the whole s\xvnmQt.{Artemisia type.). 



58 



