DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Maple stem. Light micrograph of a cross-section of a stem from the field maple (Acer campestre). This shows the thick layer of cork (phellem) on the outside of the stem which insulates the stem, prevents water loss and the ingress of pathogens, and reduces fire damage. The stem proper is the central round area, containing annual rings of woody xylem tissue.
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