Johnsongrass leaves were covered with epicuticular wax that varied from 16 to 25 μg/cm2 on leaf blades and 56 to 206 μg/cm2 on leaf sheaths. At emergence, leaves were covered with a layer of smooth amorphous wax, but crystalline wax (wax plates) began to form on the amorphous wax within 1 or 2 days. This continued until all leaf surfaces were covered with wax plates. At 3 to 4 weeks of age, a smooth layer of coalescence wax was deposited over the wax plates. Formation of coalescence wax continued until nearly all leaf surfaces were covered with a smooth wax layer. Production of wax filaments began when plants were 3 to 4 weeks old and these tubular structures extended 100 to 200 μm above all other wax formations. Deposition of amorphous wax continued after stomata closed in the darkness, sealing over stomata, but the wax layer was broken when stomata opened again in the light. A capillary method was devised that was used to evaporate chloroform containing leaf waxes through 0.1- to 1.2-μm pores in inert filters to recrystallize amorphous wax and wax plates similar to that produced on johnsongrass leaves. Recrystallization of wax from wax filaments dissolved in chloroform produced the same structures of amorphous wax and wax plates as when only wax from leaves with amorphous wax and wax plates was used. Wax washed from leaves also produced wax plates and a variety of crystalline structures on the walls of glass vials after chloroform solutions were evaporated. This result indicated that the morphology of epicuticular waxes is influenced more by their inherent chemical and physical properties than by underlying cells or the cuticular membrane.

Studies were conducted to investigate the uniformity of epicuticular wax deposition on leaf blades of johnsongrass. Johnsongrass leaves grown under drought stress had greatly increased epicuticular wax weights compared to leaves from plants with adequate moisture, but relative humidity (95% vs. 40 ± 5%) had little effect on wax deposition. Wax weights decreased as leaves matured. Sections of lower leaf surfaces of young johnsongrass leaves tended to have more wax than sections of upper leaf surfaces, but weights were nearly equal on upper vs. lower leaf surfaces of older leaves. The narrow side of asymmetrical johnsongrass leaf blades often had more wax per unit area than the wide side. The area over the midvein contained more wax per unit area than either the narrow or wide side of the leaf blade. Greatest wax concentrations on individual leaves were over the midvein area near the leaf apex. Leaf blades of johnsongrass had more wax per unit area than leaves of corn or grain sorghum.

Wax filaments > 100 μm long on the epidermis of johnsongrass leaves and culms occurred only around the edge of costal cork-silica cell pairs and intercostal silica cells. Silica cells alternating with cork cells occurred in rows over veins. Solitary or occasionally paired cork-silica cells occurred between veins. The high silicon content of silica cells was verified with X-ray mapping of silicon. X-ray analysis also indicated that wax filaments contained silicon. Scanning electron micrographs (SEM) of dislodged intercostal silica cells showed that wax filaments emerged from an integument that surrounded the silica cell. It is theorized that at high ambient temperatures the silica gel in silica cells provides the localized cooling necessary to solidify liquid wax constituents as they are extruded onto the surface of the plant.