R. P. PHARIS and D. M. REID The idea of a separate Encydopedia volume dealing with the "interrelations of plant hormones with factors in the environment of the plant, and its organs and tissues" originated with N. P. KEFFORD, and we are most appreciative of the help and advice provided by Prof. KEFFORD in the formative stages of this volume. We have thus interpreted "environment" very broadly to indude not only factors external to the plant, e. g. , gravity, light, temperature, wind, mechanieal wounding, water, organism s (induding pollen), and magnetic and electric stimuli, but internaI factors as well (e. g. , nutrients, both inorganic and photoassimilate, direction, and time). In our definition of "hormonaI effect", or "hormonaI involvement", we have asked our authors to take a broad ap­ proach, and to examine not only phenomena that are mediated by the known plant hormones, but to discuss as well a wide variety of processes and events where hormonal involvement is implied through more indirect analyses and observations. The volume begins with environmental factors internaI to the plant; R. J. WEAVER and J. O. JOHNSON thus examine "hormones and nutrients", their inter­ relationship in movement, accumulation, and diversion. As one studies a plant during its rapid growth phase, and later as maturation and aging proceed, it becomes apparent that time is an environmental cue of great significance, one which may exert a major influence via hormonal messages.