DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Nettle leaf stalk structures. Polarised light micrograph (LM) of a nettle leaf (Urtica dioica), which has been boiled up with dilute sodium hydroxide to separate the cells, washed in water and stained with blue ink. The long tubes that carry water and minerals up the stem can be seen in blue and the lignin thickenings that strengthen the tubes show up mainly in black, in different annular (rings), spiral and scalariform ladder-like) formations. Lignin is a complex chemical compound and is hydrophobic (repelled from a mass of water). As well as providing structural support, the hydrophobicity of lignin also means that the plant's vascular tissue is able to conduct water efficiently.
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