This study considers incorporation of applied ¹⁴CO₂ into ¹⁴C assimilate in tomato (Lycopersicum esculentum) and its translocation within plants. Such studies aim at defining sources for the various carbon sinks within plants by assessing the role of each leaf in the carbon balance in relation to fruit production, and defining the direction of assimilate movement as leaves pass through their life cycle. Conclusions reached will aid in designing more efficient plants or husbandry methods, and the setting up of models of the dynamic state of plants, as opposed to the classical static pictures. A better understanding of plant analyses, mineral nutrition, and changes in carbohydrate requirements during the life of plants will result. With the introduction of isotopes for tracer studies, a consistent pattern of carbon movement is beginning to emerge and clarify earlier deductions made from growth analyses.