Table 2.

The basic equivalent electrical circuit models (derivations and modifications of) which are commonly used in the modeling of plant EIS measurements.

Equivalent electrical circuit	Description
	The simple Voigt or Debye circuit without inductor. The single dispersion Cole model proposed by Cole (1940) can be seen as the fractional elaboration of Voigt circuits, where a CPE replaces the capacitor. This is one of the oldest fractional circuit models and is often used to model biosystem impedance spectra. In that case, R ∞ is the high-frequency resistance, and R 1 + R ∞ is the low-frequency resistance. A drawback is the limited biological interpretability.
	The single shell model (Toyoda and Tsenkova, 1998), also called the simplified Hayden model (Hayden et al., 1969). R E is the extracellular resistance of the apoplastic fluid, R I is the intracellular resistance, and C M is the capacitance of the cell membrane. The name of the model was coined by Zhang et al., contrasting it with their proposed double shell model (Zhang and Willison, 1992).
	The double shell model proposed by Zhang and Wilson (1991). C M is capacitance of the cell membrane, C T is the capacitance of the tonoplast, R CYT is the cytoplasmic resistance, R V is the vacuolar resistance, and R E is the extracellular resistance. In some works, R V is referred to as the resistance of the cell wall (Harker and Maindonald, 1994).