False-colour transmission electron micrograph of a stomatal complex in a young leaf of the pea plant, Pisum sativum. The picture shows two developing guard cells separated by a cell wall which will split to form the stomatal opening. Both cells are dominated by a large nucleus containing clumps of chromatin (red). Stomata are pores in the epidermis of the leaf; they regulate the exchange of water & gases between the atmosphere & the leaf interior. When the guard cells are full of water the pore is open; when it loses water the pore closes. Closure is a natural response to darkness & drought. Magnification: x1500 at 35mm size, x2600 at 6x4.5cm size. Reference: MICROCOSMOS, figure 4.11, page 73.