DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Himalayan balsam stem. Light micrograph of a section through the stem of a Himalayan balsam (Impatiens glandulifera) plant, showing one branch and two stipules stage. From the outer tissue to the pith (centre): epidermis with cuticle (red); collenchyma tissue (blue-violet, thick-walled) and cortex of large parenchyma cells (blue); ring of vascular bundles containing phloem cells (blue, small); single layer of thick files of cambium tissue (violet-blue); xylem vessels (red and white vessels). At the centre of the stem is the pith, which consists of very large parenchyma cells (red) that store water. Magnification: x4 when printed 10 centimetres wide.
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