shoot cut longitudinally to show the broad, solid pith (rough-textured, white) inside the wood (smooth, yellow-tinged). Scale in mm.]]
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 eudicotyledon
s, pith is located in the center of the stem. In monocotyledon
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 colour, 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 ''Lund lele'', 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 hesperidia
. The word comes from the Old English
word ''piþa'', meaning substance, akin to Middle Dutch
''pitte'' (modern Dutch ''pit''), meaning the pit of a fruit.
The pith of the sago
palm, although highly toxic to animals in its raw form, is an important human food source in Melanesia
by virtue of its starch content and its availability. There is a simple process of starch extraction from sago pith that leaches away a sufficient amount of the toxins and thus only the starch component is consumed. Current processes for starch extraction are generally only about 50% efficient, however, with the other half remaining in residual pith waste.
The form of the starch after processing is similar to tapioca
Other edible piths traditionally used as food include heart of palm
and banana pith
The pith of the sola
or other similar plants is used to make the pith helmet
Pith wood is a cleaning tool
used in watchmaking
to clean watch parts
and tools. It is used to remove oil from the tips of tools to prevent the contamination of watch movements. A pith wood consists of a piece of pith wood (such as elder
[ or mullein] ).
Dried pith of the rush plant soaked in fat or grease, held using a Rushlight was used as home lighting. Beginning in the 17th century, it would continue to be used in this method until the mid-20th century. It saw a brief revival during World War 2.