DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Scots pine (Pinus sylvestris) root. Light micrograph of a section through a root from a Scots pine tree, showing (from outside in): outer bark with early periderm; cork cells (black-red); cortex of parenchyma cells; primary phloem and secondary phloem (brown). Next, the vascular cambium, secondary xylem (red) and resin canals (green). Then the primary xylem consisting of protoxylem (small cells, dark red). At centre is the metaxylem (larger cells, dark-red). The subsidiary medullary rays and the principal medullary rays, composed of parenchyma cells (light green), are also seen. Magnification: x5 when printed 10 centimetres wide.
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