DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Water lily leaf stalk. Light micrograph of a transverse section through the leaf stalk (petiole) of a water lily (Nymphaea sp.). All aquatic plants (hydrophytes) have a similar structure. The epidermis of the petiole has a thin cuticle (outer layer) and is permeable to water. The whole petiole consists of parenchyma cells with large air spaces (lacunae, white circles). The vascular bundles consist of a lysigenous xylem canal (green ring of cells around a cavity) and phloem (dark-green ovals either side of small green cells). The parenchyma tissue contains thick-walled sclereids (deep red) with pointed arms for support. There is no central pith. Magnification: x14 when printed 10 centimetres wide.
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