SIDNEY MOULDS / SCIENCE PHOTO LIBRARY SIDNEY MOULDS / SCIENCE PHOTO LIBRARY
Light micrograph of a transverse section through a yew tree (Taxus sp.) twig, showing the pith (green & brown, bottom right), xylem (pink, centre) and phloem (green, upper left). The pith forms the central core of the young stem and is composed of parenchyma tissue. The xylem is composed of vertical, pillar-like cells (seen here in cross- section) which conduct the sap upwards from the tree roots. It is crossed by horizontal vascular rays (green) which supply it with nutrients. The phloem is a spongy layer, lying just underneath the bark, which is responsible for distributing the carbohydrates produced by photosynthesis in the leaves. Magnification: x50 at 35mm size.
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