DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Plant breathing pore. Light micrograph of a transverse section through a young woody stem from a lime tree (Tilia europaeus), showing a young breathing pore (lenticel) at centre. The outside tissue of the stem is made of cork (dark green and brown), composed of dead cells. The cork prevents water loss, pathogens entering the stem, and insulates the stem against fire damage. To allow gas into the stem for respiration, a lenticel is formed in the cork layer, eventually forming a powdery cork tissue that allows gases into the stem. Magnification: x230 when printed 10 centimetres wide.
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