Stomata on tulip leaf. Light micrograph of the surface of the leaf of a tulip Tulipa sp. , showing open stomata. Elongated epidermal cells cover the leaf surface. Each stomata appears as a pore bordered by two kidney-shaped guard cells. Guard cells serve to open and close the stomata: opening the pore to allow gases to be exchanged by leaf tissues during photosynthesis; and closing the pore at night or during dry periods to prevent water loss. Tulips are extremely popular garden plants and many varieties have been cultivated. Plane light illumination. Magnification: x100 at 35mm size.