Pith

From Academic Kids

The centre dark spot (about 1 mm diameter) in this  wood is the pith
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The centre dark spot (about 1 mm diameter) in this yew wood is the pith

Pith is a light substance that is found in vascular plants. It consists of soft, spongy parenchyma cells, and is located in the center of the stem or root. It is encircled by a ring of xylem (woody tissue), and outside that, a ring of phloem (bark tissue). In most plants the pith is solid, but some plants, e.g. grasses and umbellifers, the pith has a hollow centre forming a hollow tube except at the points where leaves are produced, where there is a solid plate across the stem. A few plants, e.g. walnut, have distinctive chambered pith with numerous short cavities in the pith.

Missing image
Elder_pith.jpg
Elderberry shoot cut longitudinally to show the broad, solid pith (rough-textured, white) inside the wood (smooth, yellow-tinged). Scale in mm.
Missing image
Walnut_pith.jpg
Walnut shoot cut longitudinally to show the chambered pith found in this genus. Scale in mm.

The pith varies in diameter from about 0.5 mm to 6-8 mm in solid pith, and up to 150 mm or more in the stems of some plants with hollow pith, e.g. some bamboos. Freshly grown pith in young new shoots is typically white or pale brown, commonly darkening with age. In woody plants (trees, shrubs), the pith becomes surrounded by successive annual layers of wood; it may be very inconspicuous but is always present at the centre of a trunk or branch.

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