Coiled wax ribbons have been found intermingled among the long, thin tubes characteristic of some barley and wheat cuticles. An analysis of the structure of these wax ribbons and their relationship to the tubes has led to the following hypothesis to explain the origin of the broad spectrum of observed epicuticular wax structures. Upon contact with air the wax extruded through pores onto the cuticle surface polymerizes. Fusion of wax from adjacent pores occurs before polymerization is complete. Continuous exudation of new wax pushes the initial wax away from the surface, thus leaving the most recent wax at the base of the structures. The particular morphologies produced depend on chemical composition of the exudate, as well as the number, closeness and arrangement of the pores, and the rate of exudation. These parameters are controlled by genes in interaction with the environment.