A key problem of functional-structural plant modelling is the partitioning of resources between plant components. One approach to addressing this problem is based on the simulation of transport between the sources and sinks of a resource. To this end, we exploit an analogy between the flow of resources in a plant and the flow of currents in an electric circuit, and we present a computationally effective method for solving this circuit. The method lends itself to a straightforward implementation using L-systems, and is thus well suited for simulating the partitioning of resources in spatially-explicit models of growing plants.