Guard cells regulate the opening of the stoma.
Link to face view of Zea (Corn) epidermis with guard cells and basal cells of the epidermis. Link to view of basal epidermal cells in a paradermal section of Syringa (lilac) These are on the left side of the section. Link to image of a face view of Setcreasea leaf epidermis with guard cells lining a stoma, and with basal epidermal cells. Link to image of a cross section of the epidermis of a Medicago Stem, with a view of a stoma with guard cells and with basal cells of the epidermis. Link to a view of a stoma with guard cells from a hornwort, a non-vascular plant. Link to the view of a pore of Marchantia without guard cells.