DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Canadian pondweed leaf. Light micrograph of a section through a leaf from a Canadian pondweed (Elodea canadiensis) plant. The centre of the stem has a vascular system (blue) made up of a primitive axial strand that consists of the fusion of several vascular bundles but lacks xylem vessels. It doesn’t need a strong vascular tissue because the water-pressure supports the stem and the epidermis is permeable to water and mineral salts. The cortex (outer layer) is made up aerenchyma tissue (red) with wide inter-cellar spaces for buoyancy and storing gases e.g. oxygen. The cells within the cortex are full of chloroplasts (red). Magnification: x70 when printed 10 centimetres wide.
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