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.
