This book contains the results of a Symposium on the physiological ecology of plants of the lowland wet tropics held in Mexico in June 1983 organized by the Instituto de Biologla of the National University of M"exico (U. N . A. M. ), and sponsored by UNAM, CONACYT, NSF and UNESCO (CIET). A workshop portion of the Symposium was held at the tropical research station at Los Tuxtlas, Veracruz. This Symposium originated in response to the increasing interest in the physiological ecology of tropical plants, because of the potential. of this field to provide a basic understanding of functioning of tropical plant communities. The study of physiological ecology of tropical plants has been delayed in some cases by the lack of conceptual framework, but also by the absence of appropriate instrumentation and techniques with which to conduct precise measurements under high temperature, high humidity field conditions. Hypotheses and concepts of the physiological ecology of tropical plants have been based mainly on observational data and the analysis of growth forms and leaf anatomf. The early work of A. F. W. Schimper and o. Sker in Asia, and the extensive surveys made by H. Walter on the osmotic potentials of plants in the tropics and subtropics, constituted, until relatively recently, the only available information on the water and carbon relations of tropical plants.