FRANCIS LEROY, BIOCOSMOS / SCIENCE PHOTO LIBRARY FRANCIS LEROY, BIOCOSMOS / SCIENCE PHOTO LIBRARY
Illustration of the vascular system in a plant root. Cross-sections through different layers of this root show elements of its internal anatomy. At lower frame, surface root hairs are involved in water absorption from the soil; the single outer layer of cells (exodermis) and thicker cortex are seen. At centre, the root's internal vascular system contains different types of cells: four groups of phloem cells (two groups are visible here, dark brown); a central area of angular xylem cells with thick lignified walls. Xylem vessels transport water and mineral salts from the root upwards; phloem conducts food down to the root.
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