Part of the epidermis is the cuticle, which is composed of a waxy substance called cutin that protects the leaf from dehydration and prevents penetration of some diseases. The amount of cutin is a direct response to sunlight, increasing with increasing light intensity. For this reason, plants grown in the shade should be moved into full sunlight gradually, over a period of a few weeks, to allow the cutin layer to increase and to protect the leaves from the shock of rapid water loss or sun scald. The waxy cutin also repels water and can shed pesticides if spreader-sticker agents or soaps are not used. This is the reason many pesticide manufacturers include some sort of spray additive to adhere to or penetrate the cuticle.
Some epidermal cells are capable of opening and closing.
These cells guard the interior of the leaf and regulate the passage of water, oxygen, and carbon dioxide through the leaf. These regulatory cells are called guard cells. They protect openings in the leaf surface called stoma. The opening and closing of the cells are determined by the weather. Mild weather conditions leave guard cells in an open condition.