DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Young pine tree stem. Light micrograph of a transverse section through a one-year-old primary stem of a pine tree (Pinus sp.). The cells of the outer epidermis (bright red) are thick-walled and covered with a thick layer of cuticle to stop water loss. Beginning to form underneath the epidermis is the cork cambium (phellogen) which has produced 2-3 layers of cork (orange-brown), to resist forest fires. The vascular cylinder (centre) consists of a thin layer of phloem (pale blue). The first year xylem (red) consists of tracheids and embedded in the xylem are scattered resin canals. Magnification: x14 when printed 10 centimetres wide.
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