POWER AND SYRED / SCIENCE PHOTO LIBRARY POWER AND SYRED / SCIENCE PHOTO LIBRARY
English oak leaf pores. Coloured scanning electron micrograph (SEM) of stomata (round) on the underside of a leaf from an English oak (Quercus robur) tree. Stomata are pores that open and close in order to regulate gas exchange in a plant. A pair of specialized cells known as guard cells (sausage-shaped), control the size of the opening. When the guard cells are turgid the stomata are open and when they are flaccid the stomata are closed. Stomata are found mainly on the underside of leaves. Magnification: x347 when printed 10 centimetres wide. False colour SEM of oak leaf stomata (Quercus robur).
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