Fig. 4.

Relationships between the lumped model parameters, i.e. interfacial capacitances (A) and superposition resistance and interfacial root resistance (B), with the contact area of stem and root with the solution of willows in three experimental set-ups: ‘Stem and root’ (filled squares, circles, and triangles), ‘Root’ (open triangle), and ‘Stem’ (open squares and circles) (see Fig. 1, 2). Squares, circles, and triangles refer to the longitudinal (C_ss and R_sup) and cross-sectional interface (C_sc and R_sup) of stem and to the interface of roots (C_r, R_r, and R_sup) with the solution, respectively. The detailed regression results can be seen in Table 2.