Experimental evidence for the failure of the Penman-Monteith equation in partially wet conditions

In a previous paper (Shuttleworth, 1975) the possibility of providing a theoretical description of evaporation from a partially wet canopy in terms of a simple planar model (of the Penman-Monteith type) was discussed. The object of the present note is to draw attention to recent experimental evidence which suggests the inapplicability of such a model in these conditions.