DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Radish hypocotyl. Light micrograph of a section through the hypocotyl of a young radish (Raphanus sativus) plant. A hypocotyl is the stem of a germinating seedling, found below the cotyledons (seed leaves) and above the radicle (root). From outside in: stem epidermis (small cells, blue-red), cortex parenchyma - lacking air spaces; ring of vascular bundles made up of phloem, cambium and then xylem (characteristic of the stem), and radiating vascular bundles (just outside centre). At the centre there is no pith but radiating xylem tissue with five arms (red) and phloem, which is characteristic of the root. Magnification: x5 when printed 10 centimetres wide.
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