DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Waterweed stem. Polarised light micrograph of a transverse section through a stem of the aquatic western waterweed (Elodea nuttallii) 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, white spaces). This plant has an outer endodermis (ring of small blue cells) under which is a ring of phloem (blue and purple cells) and an inner single layered ring of xylem, around a central canal. Magnification: x103 when printed 10 centimetres wide.
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