SINCLAIR STAMMERS / SCIENCE PHOTO LIBRARY SINCLAIR STAMMERS / SCIENCE PHOTO LIBRARY
Wood. Light micrograph of a transverse section through wood showing annual growth rings (near horizontal bands). A years growth consists of a porous band, which is the slow winter growth, and a more dense band, which is the faster summer growth. The Xylem vessels (large holes) are also seen in the wood. The xylem transports water and mineral nutrients from the roots throughout the plant. Its thick lignin walls also provide structural support for the stem.
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