POWER AND SYRED / SCIENCE PHOTO LIBRARY POWER AND SYRED / SCIENCE PHOTO LIBRARY
Light micrograph of a transverse section through the wood (secondary xylem) of an oak tree, Quercus robur, showing annual growth rings (horizontal bands) & prominent rays (pale, vertical stripes). Xylem tissue is composed of tracheary vessels which carry water & nutrients from the roots to the leaves. This image shows about six years' growth; the porous horizontal bands are layers of large-vesseled spring wood, whereas the bands of dense, compact wood were laid down in the summer, at the end of the growing season. The change from spring to summer wood occurs suddenly in oaks, whereas the transition is often much more gradual in other trees. Magnification: x5 at 35mm size.
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