DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Michaelmas daisy stem. Light micrograph of a section through the primary stem of a Michaelmas daisy (Aster novi-belgii), a typical dicotyledon. From the outer tissue to the pith (centre): epidermis with cuticle (red); cortex of parenchyma cells with large spaces (blue); a ring of separate vascular bundles made up of the outer phloem and xylem fibres (red); oval fibres (deep blue) and an oval-shaped phloem (violet); ring of cambium cells (blue); xylem vessels (violet and white). Between the vascular bundles are radial files of parenchyma cells, known as medullary rays. At the centre of the stem is the pith of parenchyma cells (blue). Magnification: x7 when printed 10 centimetres wide.
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