Uptake, transport, and accumulation of organic chemicals by plants are influenced by characteristics of the plant and properties of the chemical, soil, and environmental conditions. A mathematical model was formulated which, when adequately tested, can be used to provide information about potential contamination. The model consists of one root compartment, one stem compartment, and three leaf compartments - each compartment subdivided into xylem, phloem, and storage. Chemical uptake is modeled from the soil solution to the root surface, through the apparent free space, endodermis into the xylem and throughout the plant. This article shows formulations of the mass balance equations, which lead to the complete system of equations that describe uptake. The solution gives chemical mass in each compartment as a function of time. The mathematical development yielded a well-defined concept of uptake, in-plant transport, and local accumulation of organic chemicals by plants.