Pine stem. Polarised light micrograph of a section through a single annual growth ring in the stem of a pine (Pinus sp.) tree, showing xylem tissue. The large thin-walled tracheid cells (blue) are of younger spring wood, whilst smaller thick-walled tracheid cells (yellow-orange) are of older autumn wood. There are horizontal thin files of parenchyma and tracheid cells (yellow-brown) of the subsidiary medullary rays, which pass food substances radially. Many of the tracheid cell walls have bordered pits (oval, yellow-brown) that pass water and minerals side-ways. Magnification: x37 when printed 10 centimetres wide.
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