Editing Pith

[[Image:Elder pith.jpg|250px|right|thumb|[[Elderberry]] shoot cut longitudinally to show the broad, solid pith (rough-textured, white) inside the wood (smooth, yellow-tinged). Scale in mm.]]
[[Image:Walnut pith.jpg|250px|right|thumb|[[Walnut]] shoot cut longitudinally to show the chambered pith found in this genus. Scale in mm.]]
[[Image:Taxus wood.jpg|250px|right|thumb|The tiny centre dark spot (about 1 mm diameter) in this [[Taxaceae|yew]] [[wood]] is the pith]]
'''Pith''', or '''medulla''', is a [[Tissue (biology)|tissue]] in the [[Plant stem|stem]]s of [[vascular plant]]s. Pith is composed of soft, spongy [[ground tissue#Parenchyma|parenchyma]] cells, which store and transport nutrients throughout the plant. In [[eudicot]]s, pith is located in the center of the stem. In [[monocot]]s, it extends also into flowering stems and roots. The pith is encircled by a ring of [[xylem]]; the xylem, in turn, is encircled by a ring of [[phloem]].

While new pith growth is usually white or pale in color, as the tissue ages it commonly darkens to a deeper brown color. In [[tree]]s pith is generally present in young growth, but in the trunk and older branches the pith often gets replaced - in great part - by xylem. In some plants, the pith in the middle of the stem may dry out and disintegrate, resulting in a hollow stem. A few plants, such as [[walnut]]s, have distinctive chambered pith with numerous short cavities (See image at middle right). The cells in the peripheral parts of the pith may, in some plants, develop to be different from cells in the rest of the pith. This layer of cells is then called ''the perimedullary region of the pithamus''. An example of this can be observed in ''Hedera helix'', a species of [[ivy]].

The term pith is also used to refer to the pale, spongy inner layer of the rind - more properly called [[mesocarp]] or albedo - of [[citrus]] fruits (such as oranges) and other [[hesperidium|hesperidia]]. The word comes from the [[Old English]] word ''piþa'', meaning substance, akin to [[Middle Dutch]] ''pitt'', meaning the pit of a fruit.

The pith of the [[Aeschynomene aspera|sola]] or other similar plants is used to make the [[pith helmet]].

The pith of the [[sago]] palm, although highly toxic to animals in its raw form, is an important human food source in [[Melanesia]] and [[Micronesia]] by virtue of its starch content and its availability. There is an easy, primitive process of starch extraction from sago pith that leaches away a sufficient amount of the toxins and thus only the starch component is consumed. The form of the starch after processing is similar to [[tapioca]].

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[[Category:Plant physiology]]
[[Category:Plant morphology]]
[[Category:Plant anatomy]]