POWER AND SYRED / SCIENCE PHOTO LIBRARY POWER AND SYRED / SCIENCE PHOTO LIBRARY
Rhubarb stem. Coloured scanning electron micrograph (SEM) of a longitudinal section through a rhubarb stem, Rheum rhaponticum. Cut xylem vessels are coloured brown, and parenchyma cells are coloured green. Xylem vessels are responsible for the upward transport of water and solutes in the plant, from the roots into the stem and leaves. Here, these vessels are reinforced and strengthened with spiral bands of lignin. Spiral bands allow xylem vessels to elongate and grow lengthwise. Parenchyma cells form a ground tissue in which other tissues, such as xylem, are embedded. Magnification: x290 at 5x7cm size.
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