Perennial deciduous fruit trees are very complex organisms that are governed and influenced by a multitude of factors. Empirical research approaches are generally limited to dealing with a couple factors at a time and integration of the effects of multiple factors affecting tree growth and productivity are generally limited to verbal descriptions and displaying data with two or three dimensional diagrams. The goal of functional-structural plant models (FSPM) is to simulate plant growth in silico on a computer with as much functional realism as is possible. The L-PEACH model is an example of an FSPM that simultaneously incorporates physiological (photosynthesis, transpiration, respiration, phloem transport, xylem water potential) architectural (bud fates and leaf, stem, branch and trunk structure) growth (stem extension and diameter, leaf area and thickness, fruit size) and productivity (fruit sizes and numbers) responses to environmental stimuli (light, temperature, water availability) and management (irrigation, pruning and fruit thinning) practices. The model can also be adapted relatively easily to simulate effects of specific genetic traits of scions and rootstocks on long term tree performance. In the L-PEACH model the plant is expressed in terms of modules that represent plant organs (including stems). An organ is represented as an elementary source/sink for carbohydrates and the whole plant is modeled as a branching network of organs that conduct carbohydrates and water. An analogy to an electrical network is used to calculate the flow and partitioning of carbohydrates between the individual organs in the current model but now that water uptake and transport are incorporated in the model we are attempting to simulate phloem transport directly using principles of hydrostatics. Other major contributors to this work: David Da Silva, Romeo Favreau, Inigo Auzmendi, Gerardo Lopez, Evelyne Costes and P. Prusinkiewicz