DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Australian she oak stem. Light micrograph of a transverse section through the stem of an Australian she-oak (Casuarina equisetifolia). The she-oak is a drought-tolerant plant (xerophyte). Xerophytes have evolved an anatomy that cuts down water loss through transpiration. There stems have deep narrow furrows (outer cuttings), and whorls of scale leaves (outer edge) to reduce the area for water loss. The epidermis (outer layer) has thick-walled cells covered in a thick cuticle, and a v-shaped hypodermis of sclerenchyma cells and fibres. Photosynthesis is confined to the three layers of palisade cells (long, pink). The vascular bundles (yellow-brown) can be seen at centre. Magnification: x37 when printed 10 centimetres wide.
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