Ultrastructural and cytochemical studies have shown that the orbicule core is surrounded by a sheet about 90 Å in thickness. It is stained by KMnO4 and composed of proteins, unsaturated lipids and esterified pectins. These data indicate that there is a biological membrane between the orbicule core and the wall. It is thought that this membrane is coated by a glycocalyx and supports the orbicule sporopollenic wall biosynthesis.