This is the first of the set of three volumes in the Encyclopedia of
Plant Physiology, New Series, that will cover the area of the hormonal
regulation of plant growth and development. The overall plan for the set
assumes that this area of plant physiology is sufficiently mature for a
review of current knowledge to be organized in terms of unifying
principles and processes. Reviews in the past have generally treated
each class of hormone individually, but this set of volumes is
subdivided according to the properties common to all classes. Such an
organization permits the examination of the hypothesis that differing
classes of hormones, acting according to common principles, are
determinants of processes and phases in plant development. Also in
keeping with this theme, a plant hormone is defined as a compound with
the properties held in common by the native members of the recognized
classes of hormone. Current knowledge of the hormonal regulation of
plant development is grouped so that the three volumes consider
advancing levels of organizational complexity, viz: molecular and
subcellular; cells, tissues, organs, and the plant as an organized
whole; and the plant in relation to its environment. The present volume
treats the molecular and subcellular aspects of hormones and the
processes they regulate. Although it deals with chemically distinct
classes of hormone, this volume stresses properties and modes of
studying them, that are common to all classes.