** Minimum epidermal conductance – g_{min}** (mmol � m

^{-2}� s

^{-1})

The *g _{min}* is the conductance to vapor diffusion across the epidermis once stomata are closed, i.e., through the cuticle and any leaky stomata. The

*g*varies many-fold across species, and can be a potentially strong determinant of drought tolerance, since a lower

_{min}*g*better enables maintenance of hydration based on stored water.

_{min}The g_{min} is calculated as the difference in leaf mass for a given drying interval divided by the vapor pressure driving force for diffusion of vapor pressure out of the leaf, normalized by leaf area. Alternatively, g_{min} is calculated as the slope of leaf mass vs time during drying divided by the average mole fraction driving force over the interval, normalized by leaf area.

**Note** that by convention for g_{min}, the area of both leaf surfaces is used.