DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Elm stem. Light micrograph of a transverse section through the one-year-old woody stem of an elm (Ulmus procera) tree. The outer layer (epidermis, dark ring) is being sloughed (pushed/broken) off by developing underlying cork (red-brown), underneath which is the cortex made of collenchyma (orange-red). The lower cortex has bands of phloem fibres (red) and a layer of phloem sieve tubes (solid red with cavities). Under the phloem is a ring of cambium (light-red circle) and under this is a thick layer of wood (xylem, purple-red) with six vascular bundles. The solid pith (pink, centre) is composed of parenchyma cells. Magnification: x46 when printed 10 centimetres wide.
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