The objectives of the present monograph are multiple: to review the recent contributions to the knowledge of the structure and function of roots, to outline the frontiers of root sciences, to point out the areas where gaps in knowledge exist, and to indicate the direction toward which basic and applied root research should proceed in the future. Plant Roots: The Hidden Half consists of 40 chapters that are grouped into the following seven sections deals with the structure and development of roots and with their assemblage into roots systems. This section also tackles some of the genetic and physiological bases that control the development of individual roots and that eventually determine the structure, position, and function of root systems. It also discusses in detail the individual root anatomy, with emphasis on root meristems, root caps, root hairs, and the cambium. The second section covers several aspects of the growth and metabolism of roots. It starts with the delicate hormonal relationships of roots and their effects on root growth and gravireaction, touches on various specific metabolic processes, and concludes with a discussion of root turnover and senescence. Studying roots, one can neither ignore the shoots nor disregard the constraints of the environement. The relationships between roots and shoots are, therefore, discussed here. The third section deals with one of the very critical aspects of growth of plant root-their encounter with stressing environments. This section covers the behavior of roots under temperature, low oxygen, heavy metal, and salinity stresses, as well as under the mechanical constraints of the soil. The fourth group of chapters discusses the uptake of minerals and water by roots and their subsequent transport into all other plant organs. Some chapters deal with nutrient availability, movement of ions across the soil-roots interface, and the mechanisms of ion uptake. Three chapters discuss several aspects of the water relations of roots, and one chapter investigates an exceptional function of some roots: uptake of CO2. The various aspects of interactions that occur at the rhizosphere level are compiled in the fifth and sixth sections. Those include discussion of the interrelationship of roots with the biotic and abiotic components of their environment. In some cases the biotic interactions in the rhizosphere are obligatory and neither the roots nor the microorganisms can survive independently in nature. The application of these phenomena in agricultural practice is discussed in several of the chapters. In other cases the rootmicroorganism relationships are facultative. Still they may exert positive effects on the roots even if the soil organisms feed exclusively on root excretions and on their sloughed cells, without contacting live root cells. Other organisms exploit the roots as pathogens or as parasites..
