DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Pine stem. Light micrograph of a section through the stem of a pine (Pinus sp.) tree, showing tracheid cells (white-brown) in the xylem tissue. There are thin files of parenchyma and tracheid cells (yellow-white) of the subsidiary medullary rays, which pass food substances radially. Many of the tracheid cell walls have bordered pits (circles) that pass water and minerals side-ways. Magnification: x37 when printed 10 centimetres wide.
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