FRANK FOX / SCIENCE PHOTO LIBRARY FRANK FOX / SCIENCE PHOTO LIBRARY
Pine stem (Pinus silvestris). Fluorescence and polarised light micrograph of a section through a single annual growth ring in the stem of a pine (Pinus sp.) tree, showing large thin-walled tracheid cells of younger spring wood and smaller thick-walled tracheid cells of older autumn wood. Magnification: x40 when printed 10 centimetres wide.
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