DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Dicotyledon plant stem. Light micrograph of a section through the one-year-old stem of a typical dicotyledon plant, showing secondary thickening. The outer cortex (red) has produced a phellogen and six files of phellem cells (red) of cork cambium tissue, preceding shedding of the epidermis. Below the inner cortex (blue) is the vascular ring; the first layer is a ring of fibres (red); the next ring is the phloem (blue) with sieve tubes; next is a ring of cambium cells (light blue). The wood under the cambium has a single ring of scattered large vessels (red circles, diffuse-porous wood), with the rest of the wood composed of smaller tracheid vessels and wood parenchyma. The radial lines running through the wood and phloem are medullary rays (red). The.
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