Stomata are the structural elements of the epidermis and participate in the regulation of gas exchange and water regime in plants. Each stoma is composed of two guard cells separated by the stomatal pore. The pore width is known to depend on the turgor pressure amount in the guard cells and structure of their walls. In this work, the role of peristomatal rims - protrusions of the cell wall which encircles stomata on several plants in the stomatal complex functioning is inferred by means of the finite element method in the ANSYS software. They are shown to exert influence onto the degree and pattern of the guard cells deformation. In combination with uneven thickening of their walls and presence of the outer cuticular ledge, the rims provide immersion of the opening stomatal pore downwards into the leaf. The biological significance of the present phenomenon is discussed.