I am convinced that a thorough analysis of our desert flora would uncover a number 

 of new sources of raw material. Already some are being exploited, and others are gain- 

 ing prominence in the thoughts of those who are concerned with such items. It must be 

 stressed, however, that all such efforts must be preceded by the work of an ecologist. 



Let me now give a few examples of potential sources of various raw materials : 



Oleagenous plants — Citrullus Coloquintus, Cucumis propbetarum, Cucurbita spp. 

 from the desert parts of the U.S. and Mexico, etc. 



Cellulose and Fibre plants — Agave, Retama roetam, Tbymelea birsuta, Juncus 

 arahicus and the Haifa grass of North Africa, Stipa tenacissima. 



Rubber plants — Astragalus species in south-west Asia, Guyaule from the semi- 

 deserts of northern Mexico, Acacias from north Africa, and many others. 



Significant progress in the search for raw material plants from arid regions has 

 been made in Australia, and probably also in Russia. In this field, also, international 

 co-operation will prove itself to be fruitful. I need only point out that exchange of spe- 

 cies and varieties between arid countries and particularly between the southern and 

 northern hemisphere alone promises to have tremendous influence on the regeneration of 

 these lands. 



So far I have deliberately not mentioned plants which grow only in oases. These 

 form a separate topic, and have already been discussed much more than actual desert 

 plants, both from the scientific and the economic point of view. Nevertheless, they 

 still present many ecological problems. Some of these are involved in the planning of 

 oasis economy; for example adjustment to the high salt concentration of the water, the 

 amount of available water, the fluctuation of the water table, the vertical zonation of 

 various plant associations with respect to the water table, and the economical possi- 

 bilities for agriculture. The details of the zonation of Ein Ghadian, an oasis in Wadi 

 Arabia are being measured and mapped by my department. 



It is interesting that, though Juncus arabicus appears only in a rather small area in 

 dense stands, my assistants Rawitz and Tadmor have found specimens growing at a 

 height of 2.60m. above the water table in June! I have initiated the careful collection 

 of seeds and rhizomes from these individuals, since they exhibit an ecological ampli- 

 tude far above the usual, implying a much extended area for the possible cultivation of 

 this plant. 



With the question of zonation above the water table, we enter another aspect of 

 plant ecology where the fields of ecology, hydrology and climatology meet. In conclud- 

 ing I would like to make a few remarks on these questions, since the possibilities for 

 their solution are as yet not widely enough known. In accordance with the introductory 

 nature of this lecture I cannot go into the details. Furthermore, these new methods have 

 been discussed at several international meetings during the last few years, and I had 

 the opportunity to refer to them only a few months ago at the UNESCO symposium in 

 Turkey. Here a group of new ecological methods, which enable us to measure quanti- 

 tatively certain geo- physical values by biological means is involved. Because of the 

 extraordinary importance of these methods, I should like to provide a summary of them. 



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