Cover illustrations: View of the Zin valley in the Zin desert, near the Jacob Blaustein Institute for Desert Research at Sede Boker in the Negev Desert highlands of Israel (front cover) . Pteranthus dichotomus Forssk. (Caryophyllaceae), a winter annual on loess soil on the hillslopes of the Zin valley (front and backcover). Photographs taken byYitzchak Gutterman

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PrefaceThis book is based on the author's 30 years of research in the desert, as well as on the research of others, on the dispersal and germination of annual angiospermae, geophytes and other perennial desert plants of the Negev Desert Highlands and the other deserts of Israel and the Sinai Peninsula. The findings are compared with the results of research that has been carried out in other hot deserts of the world. The focus of the book is on the extreme and unpredictable environmental conditions which influence the germination and survival of plants in the desert. These include the wide variation in the amount and distribution of rain and the differences in the length of the growing season from one year to the next, wide fluctuations in temperature, high salinity and the pressures of seed predation. The book presents ·an overview of the environmental factors influencing seed germination during plant development ~nd seed maturation, the mechanisms of seed dispersal and storage of the seed bank as well as those that affect germination during seed imbibition and seedling survival.The survival of plants under desert conditions is connected mainly with the germination mechanisms which ensure germination and seedling development at the right time and in a suitable place. Thus, during the plant life cycle the seed has the highest resistance to extreme environmental factors, whereas the seedling has the lowest. Are there special mechanisms in some species which are able to predict the best time and place for germination? It seems that there are two main directions in which evolution has taken place: 1. Plants with survival mechanisms that will enable seeds to be dispersed and/or germinate when the chance of seedling establishment is very high and the risk relatively low. Seeds of these plants only germinate after relatively large amounts of rain and, in many cases, have relatively large seeds which are well protected against many granivores. 2. In the opposite direction of evolution are species which produce tiny seeds in very large numbers, and many of these seeds germinate after even less than 10 mm of rainfall. These are condi-VI Preface tions of high risk for seedling establishment if additional rain does .not follow fairly quickly.One of the main topics considers what is special about the dispersal and germination of the seeds of plants that are found in deserts.The dispersal and germination strategies and mechanisms discussed focus mainly on annual plants in which germination is the most critical process before each growing season.Limited seed separation -synaptospermyis common among plant species inhabiting extreme deserts. Many synaptospermic species disperse their seeds by rain. At least two advantages of species with synaptospermic seed dispersal are seen particularly in extreme deserts: the retention of seeds in the favourable microhabitat where the mother plant had successfully completed its life cycle; and the protection of these seeds against seed collectors during the period from seed maturation to germi...

This chapter discusses: seed position affecting seed germination; age effects; environmental effects; day-length during seed development; influences of light quality during maturation on seed germination; water stress during maturation affecting seed germination; temperatures during maturation affecting seed germination; mineral nutrition.

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