DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Young yew tree stem. Light micrograph of a transverse section through a one-year-old stem of a yew tree (Taxus baccata). The epidermis (outer layer) has thick-walled cells with a thick waterproof cuticle (green). The stem is furrowed to increase surface area for photosynthesis by the chlorenchyma cells of the outer cortex (pink). The vascular ring (centre) consists of phloem sieve cells (blue) on the outside and inner xylem tracheids (green-orange-blue). Magnification: x14 when printed 10 centimetres wide.
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