Electrical analog used for the hydraulic architecture of maize. The root is represented by a single resistance *R*_{root} and the stem is divided into 10 segments, the divisions being at the middle of the nodes, each with a resistance *R*_{s,1} to *R*_{s,10}. A leaf insertion resistance is assumed, *R*_{I,1} to *R*_{I,10}, is assigned to the resistance of the complex vascular structure of the node. Each of the 10 leaves are divided into 10-mm segments (up to 130 segments for the longest leaves). Each leaf segment (for both leaf sheath and leaf blade) has an axial resistance, *R*_{x,i}, for the resistance of all the vessels in parallel and *R*_{m,i}, the resistance of water movement from the vessels to the internal mesophyll air spaces where water evaporates. The rate of evaporation from each leaf segment is represented by a constant current source (circle with arrow). This is justified because the normal range of leaf water potential has little impact on the magnitude of the driving force for water vapor diffusion (Δ*X*). The rate of evaporation is given by *A*_{i} *g*_{L} Δ*X*, where *A*_{i} is the surface area of the *i*th leaf segment and *g*_{L} is the vapor diffusion conductance (stomates, cuticle plus boundary layer). The guttation pathway is represented by a diode. The diode permits liquid water flow (advance of the meniscus) through leaf air spaces when the fluid pressure is >0. The diode prohibits the movement of the meniscus (liquid flow) into the cell wall (because of surface tension) when the fluid pressure in the wall is <0 but still in a physiological range. These two electrical components are best interpreted as a visualization of the boundary conditions at the evaporative surface. Finally, a variable battery represents the water potential of the soil plus the gas pressure applied in the root pressure bomb (Ψ_{soil} + *P*_{g}).

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