Fig. 10.5-4. Longitudinal section of corn stem (Zea mays). The epidermis of grasses often have two types of cells: long cells and short cells. The short cells themselves often occur in pairs, one being a silica cell (with a granule of silica in it), the other being a cork cell (with suberin in its walls). These three types of cells often have the pattern shown here: one long cell and a pair of short cells, but other patterns occur as well. The selective advantage or ecological implications of this type of epidermis are unknown.