A knowledge-based system, called INCA, for simulating the growth and development of a walnut tree is presented. This tool, that is curre ntly under development, aims at integrating architectural and physiological knowledge of the processes involved. Such a body of knowledge is still only incompletely available for walnut and, thus, INCA is built for helping physiology researchers in the exploration of hypotheses. Within INCA the tree organs and the surrounding environment are structured in a frame- based representation whereas the processes are coded in a rule-based language. The simulation mechanism is primarily based on the rule chaining capabilities of an inference engine.