DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Cedar tree stem. Light micrograph of a transverse section through a stem of a cedar tree (Thujopsis dolobrata). The four ridges on the outer surface are microphyllous leaves, which surround the stem with their inner surfaces fused to the stem cortex. On the outside of the vascular cylinder (centre, round) is the secondary phloem consisting of sieve cells (pink bands) and phloem fibres (black bands). The inner xylem (orange) is made up of thick walled tracheid cells. Radial lines (dark orange) are the single celled rays composed of tracheid cells. In-between the phloem and xylem is the cambium (red band). Magnification: x14 when printed 10 centimetres wide.
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