SIDNEY MOULDS / SCIENCE PHOTO LIBRARY SIDNEY MOULDS / SCIENCE PHOTO LIBRARY
Light micrograph of a transverse section through a Scots pine tree (Pinus sylvestris) twig, showing the pith (green & brown, centre), xylem (pink) and phloem (green) and the corky outer layers (brown & green, top). The pith forms the central core of the young stem. The xylem is composed of vertical, pillar-like cells (seen here in cross-section) which conduct the sap upwards from the tree roots. It contains horizontal vascular rays (green lines), which supply it with nutrients, and vertical resin ducts (green circles). The phloem is responsible for the distribution of the carbohydrates produced by photosynthesis in the leaves. Magnification: x36 at 35mm size.
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