DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY
False-colour scanning electron micrograph of oak heartwood, the wood (secondary xylem) of Quercus robur, showing both vertical (bottom) & horizontal (top) cut surfaces. The large, vertical tube-like structures are tracheary vessels which have become blocked by bladder-like ingrowths known as tyloses. In young sapwood the vessels carry water & nutrients from the roots to the leaves, but after a few years they become blocked & no longer carry sap. The large vessels occur in early (spring) wood; the small, dark circles at top are the cut ends of the smaller late-wood vessels. A broad ray, split due to drying, is seen at top. Oak is graded as a hardwood. Mag: x8 at 35mm size.
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