DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Pine stem. Polarised light micrograph of a section through a growth ring in the stem of a Scot's pine (Pinus sylvestris) tree, showing large thin-walled tracheid cells of younger spring wood and smaller thick-walled tracheid cells of older autumn wood. There are thin files of parenchyma and tracheid cells (black) of the subsidiary medullary rays, which pass food substances radially. The large circular lacuna (resin duct, centre) is lined with parenchyma cells (black). Magnification: x32 when printed 10 centimetres wide.
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