This book contains the majority of the presentations of the Second International Symposium on the Biology of Root Formation and Development that was hcld in Jerusa lem, Israel, June 23---28, 1996. Following the First Symposium on the Biology of Adventi tious Root Formation, held in Dallas. USA, 1993, we perceived the need to include all kinds of roots, not only the shoot-borne ones. The endogenous signals that control root formation. and the subsequent growth and development processes, are very much alike, re gardless of the sites and sources of origin of the roots. Therefore, we included in the Sec ond Symposium contributions on both shoot-borne (i.e., adventitious) roots and root-borne (i.e., lateral) roots. Plant roots have remained an exciting and an intriguing field of sciencc. During thc years that followed the first symposium, an exceptional proliferation of interest in root biology has developed, associated with the intensive research activity in this field and the contemporary developments in the understanding of root function and development. New methods have been applied, and old ideas and interprctations werc rccxamined. Alto gether, it became necessary to update our viewpoints and to expand them.

Charles E. Hess Department of Environmental Horticulture University of California Davis, CA 95616 Research in the biology of adventitious root formation has a special place in science. It provides an excellent forum in which to pursue fundamental research on the regulation of plant growth and development. At the same time the results of the research have been quickly applied by commercial plant propagators, agronomists, foresters and horticulturists (see the chapter by Kovar and Kuchenbuch, by Ritchie, and by Davies and coworkers in this volume). In an era when there is great interest in speeding technology transfer, the experiences gained in research in adventitious root formation may provide useful examples for other areas of science. Interaction between the fundamental and the applied have been and continue to be facilitated by the establishment, in 1951, of the Plant Propagators' Society, which has evolved into the International Plant Propagators' Society, with active programs in six regions around the world. It is a unique organization which brings together researchers in universities, botanical gardens and arboreta, and commercial plant propagators. In this synergistic environment new knowledge is rapidly transferred and new ideas for fundamental research evolve from the presentations and discussions by experienced plant propagators. In the past 50 years, based on research related to the biology of adventitious root formation, advances in plant propagation have been made on two major fronts.