Aged preparations are electrophysiologically more representative of intact tissue than are freshly excised preparations.

Studies using excised tissues usually suffer from a discrepancy in the results between freshly excised preparations and "aged" ones (i.e. preparations which are allowed to rest and-or regenerate for about a day between excision and experimentation). This is especially true for measurements of the membrane potential (Vm) and its changes upon exposure to light in slices of extensor tissue of the laminar pulvini of Phaseolus coccineus L. Measurements of the V m of extensor cells in situ reveal virtually identifical results to those obtained from aged excised preparations (more negative resting V m; dramatic, light-induced transients of V m), whereas freshly excised preparations display a small and light-insensitive V m. It is concluded, therefore, that for the given example aged preparations are more suitable than fresh ones for investigating the properties of intact tissues.