Studying transport of sugar and water using ecophysiological experimentation in connection with modeling is a very useful tool for a deeper understanding of the role of the different branch organs and their geometrical and topological arrangement in the branch for sugar production and partitioning. In a schematic way, transport of sugars takes place from sugar synthesizing organs called sources to sugar consuming (or storing) organs called sinks. These generalities have been known in principle. However, many aspects of sugar assimilation and partitioning between source and sink organs are still poorly understood in several plant species including apple. This can partly be explained by the complex architecture and composition of the apple branch, and the diversity of branch organs involved in carbon transport. Additionally, rules governing the physiological mechanisms of transport depend on tree developmental stages, which make transport and the role of the different organs dynamic in time.