Leaf anatomy. Light micrograph of an epidermal peel of the underside of a leaf, showing a pattern of leaf veins, cells and stomata. Cell outlines are white and their contents black. Also seen are the veins, which channel fluids around the leaf, and the stomata (red circles with a central dark line), little holes in the surface of the leaf that are opened and closed using guard cells. The guard cells can expand and contract and this regulates the passage of air into and out of the leaf. The epidermal peel was obtained using nail varnish, and was painted with dilute Indian ink and imaged using transmitted light and colour filters.