[The wettability of leaf surfaces and the submicroscopic structure of their wax]

Abstract

The wettability of a leaf surface is defined by the contact angle between a water-droplet and the surface of the leaf.Contact angles of 60-80° were measured on easily wettable leaves. These leaves have no wax on the outer cuticular layer.Contact angles of 130-160° were measured on leaves with a low wettability. These leaves have wax on the outer cuticular layer, which shows submicroscopic structures characteristic of the particular plants.A comparison of the wettability and the different structures of the wax showed no true distinctions.The wax does not adhere strongly to the outer cuticular layer and is cast off in the case of old leaves. Therefore the wetability alters with the age of the leaves. If the wax on young leaves is destroyed or removed by outer influences it can be produced again within a few hours.The rebuilt structure of the wax is not always similar to the original one. When the wax was dissolved by organic solvents no new wax formation was observed.Cigarette smoke greatly increases the wettability of leaves of Tropaeolum majus, parochetus communis and Chelidonium majus without causing a visible alteration of the submicroscopic structure. In this case the leaves recover their water-repellency within a few hours, but not if they were treated with Diesel smoke.When the wax structure was destroyed by fungus or Aleurodina no new wax formation was observed.