DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Young pine tree stem. Light micrograph of a transverse section through a two and a half-year-old stem of a pine tree (Pinus sp.). The cells of the outer epidermis (bright red) are thick-walled with a thick covering of cuticle beginning to break up. Beneath the epidermis is a cork cambium (phellogen) which has produced 2-3 layers of cork (orange-brown), to resist forest fires. The vascular cylinder has a thick layer of phloem (pale blue and deep blue) with a layer of cambium (light grey-blue) formed between the phloem and xylem (red). Spring wood consists of large thin-walled cells whilst the autumn wood (last formed) has small thick-walled cells. Since there are three layers of spring wood and two layers of autumn wood the stem is two and a half years old. Magnification: x14 when printed 10 centimetres wide.
Model release not available. Property release not required.