DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Pine stem. 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 (yellow) of younger spring wood and smaller thick-walled tracheid cells (bright yellow) of older autumn wood. The large circular lacuna (resin duct, upper left) is lined with parenchyma cells. Magnification: x32 when printed 10 centimetres wide.
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