Work Step by Step
The first dermal tissue that forms is called the epidermis; it is typically just one layer thick. A wax-like substance is secreted from the outside surface of the epidermal cell to help keep water from being lost. In leaves and young stems, the epidermis contains special cells that control openings to allow water vapor and gases to diffuse through. The periderm replaces the epidermis when the stem and roots get older.