CLOUDS HILL IMAGING LTD / SCIENCE PHOTO LIBRARY CLOUDS HILL IMAGING LTD / SCIENCE PHOTO LIBRARY
Wood structure. Coloured scanning electron micrograph (SEM) of a cross-section through a twig from a hardwood tree. This has revealed a set of concentric rings radiating out from the centre (top right). The rings form during successive periods of growth. The holes are where tube-like structures run along the length of the twig. These tend to be for structural support near the outer edge of the twig, and for sap and water transport (larger tubes) in the centre.
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