DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Protea plant stem. Light micrograph of a transverse section through a stem from the protea plant (Roupala polhii). The outer layer is the epidermis and cuticle (red), with single-celled hairs or trichomes. Below this is the lamella collenchyma (red) and a ring of vascular bundles. These bundles contain phloem, cambium, and xylem tissue. Between the vascular bundles are medullary rays of parenchyma. At the centre of the stem is the large pith of parenchyma cells (white and crimson). Magnification: x14 when printed at 10 centimetres wide.
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