DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Acorus calamus rhizome. Light micrograph of a section through a rhizome from a sweet flag (Acorus calamus) plant. The rhizome has an outer layer with scattered collateral vascular bundles and a central cylindrical core of larger vascular bundles. The inner core has an outer ring (endodermis) and an inner layer (pericycle). The ground tissue is spongy aerenchyma with thin-walled cells and larger inter-cellular spaces to store oxygen. The vascular bundles have a ring of outer xylem (red), which carries water and minerals to the stems, and a surrounding inner phloem (blue), which carries sugar to the rhizome to be stored as starch. Magnification: x4 when printed 10 centimetres wide.
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