What are plant growth regulators? In the title, and throughout the text, we have adopted this expression to describe a population of endogenous molecules and synthetic compounds of similar structure that are be lieved to play important roles in the regulation of plant differentiation and development. For many years, plant scientists have endeavoured to understand the nature and action of plant growth regulators and, as a result, an awesome quantity of written material now exists describing these chemicals and their effects. In this book we have aimed to distil this wealth of information into a more digestible form, and in particular we have focused our attention on a critical appraisal of the literature. The past few years have witnessed a change of emphasis in plant growth regulator research, which has been fuelled by powerful new techniques in molecular and cell biology. Today we can do more than just apply a plant growth regulator and quantify its effects; we have reached an exciting crossroads where plant scientists, molecular bio logists and chemists can pool their expertise and apply it to the out standing problems in this area. The combination of these three disciplines within the book is clear evidence of this. In keeping with a volume of this size, we have assumed that the reader has a sound knowledge of plant physiology and biochemistry. However, wherever possible, we have highlighted useful reviews which provide background information, along with recent publications that have contributed significantly to the literature.

The current growing interest of molecular biologists in plant hormone research is undoubtedly the most promising development of recent times. Many papers were presented during the 14th International Conference on Plant Growth Substances illustrating the impact of this new approach on our understanding of hormone-controlled processes. The specific character is the integrated study of plant growth regulation at all levels ranging from single molecules to the entire plant and its functioning in the environment. Hormones play an essential role in the regulation, but not an exclusive one. Other compounds and factors, such as Ca2+, for instance are often of equal relevance, because they may take part in the signal transduction pathway. Moreover, regulation of the regulator by non-hormonal factors is an essential part of any control mechanism. The present volume reflects the change in interest from plant growth substances to plant growth regulation.

The 9th International Conference on Plant Growth Substances was held at the University of Lausanne, August 30-September 4, 1976. This meet ing was sponsored by the National Swiss Foundation for Scientific Re search (FNRS), the Fonds Herbette of the Faculty of Sciences of Lau sanne, by several other official sources, and by a few Swiss indus tries. The conference was attended by over 420 scientists, represent ing 42 countries, with a total of 550 participants. Our 9th conference was rather different from the previous ones. The usual short submitted papers followed by a too brief discussion were replaced by three kinds of scientific communications. First in the reports, authors gave a critical analysis of a selection of broad to pics, directing their comments to new perspectives of research and me thodology. Second, the paper demonstrations, presented by over 200 scientists, induced large and fruitful discussions and ensured that personal contacts were made. Finally, during four workshops, several interesting points - introduced in the reports and paper demonstra tions - were developed and discussed.