DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Willow stem. Light micrograph of a cross-section through the stem of a willow (Salix sp.) tree. At centre is the pith (white), surrounded by woody xylem tissue (pink), then the cortex and outer cork layers (brown). Magnification: x14 when printed 10 centimetres wide.
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