DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Mare's tail stem. Polarised light micrograph of a transverse section through a stem of the aquatic mare's tail (Hippuris vulgaris) plant. All aquatic plants (hydrophytes) have a similar stem structure. The epidermis (outer layer) has a thin cuticle that is permeable to water. The cortex is very wide and the parenchyma has large air spaces (lacunae, blue spaces). The vascular tissue is at centre and there is an outer endodermis (blue ring) above a ring of phloem (yellow-green) and an inner ring of xylem. The pith (centre) consists of large-celled parenchyma (deep green). Magnification: x103 when printed 10 centimetres wide.
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