Pith, or medulla, is a tissue in the

stem Stem or STEM may refer to: Plant structures * Plant stem, a plant's aboveground axis, made of vascular tissue, off which leaves and flowers hang * Stipe (botany), a stalk to support some other structure * Stipe (mycology), the stem of a mushro ...

s of

vascular plant Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They ...

s. Pith is composed of soft, spongy

parenchyma Parenchyma () is the bulk of functional substance in an animal organ or structure such as a tumour. In zoology it is the name for the tissue that fills the interior of flatworms. Etymology The term ''parenchyma'' is New Latin from the word � ...

cells, which in some cases can store

starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human die ...

. In eudicotyledons, pith is located in the center of the stem. In

monocotyledon Monocotyledons (), commonly referred to as monocots, ( Lilianae '' sensu'' Chase & Reveal) are grass and grass-like flowering plants (angiosperms), the seeds of which typically contain only one embryonic leaf, or cotyledon. They constitute one ...

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 In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...

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 walnuts, 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 ''Hedera'', commonly called ivy (plural ivies), is a genus of 12–15 species of evergreen climbing or ground-creeping woody plants in the family Araliaceae, native to western, central and southern Europe, Macaronesia, northwestern Africa and ...

. 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 ''Citrus'' is a genus of flowering trees and shrubs in the rue family, Rutaceae. Plants in the genus produce citrus fruits, including important crops such as oranges, lemons, grapefruits, pomelos, and limes. The genus ''Citrus'' is native to ...

fruits (such as oranges) and other hesperidia. The word comes from the

Old English Old English (, ), or Anglo-Saxon, is the earliest recorded form of the English language, spoken in England and southern and eastern Scotland in the early Middle Ages. It was brought to Great Britain by Anglo-Saxon settlers in the mid-5th ...

word ''piþa'', meaning substance, akin to Middle Dutch ''pitte'' (modern Dutch ''pit''), meaning the pit of a fruit.

Uses

Food

The pith of the sago palm, although highly toxic to animals in its raw form, is an important human food source in

Melanesia Melanesia (, ) is a subregion of Oceania in the southwestern Pacific Ocean. It extends from Indonesia's New Guinea in the west to Fiji in the east, and includes the Arafura Sea. The region includes the four independent countries of Fiji, V ...

and

Micronesia Micronesia (, ) is a subregion of Oceania, consisting of about 2,000 small islands in the western Pacific Ocean. It has a close shared cultural history with three other island regions: the Philippines to the west, Polynesia to the east, ...

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 Tapioca (; ) is a starch extracted from the storage roots of the cassava plant (''Manihot esculenta,'' also known as manioc), a species native to the North and Northeast regions of Brazil, but whose use is now spread throughout South America ...

. Other foods sometimes mistakenly called piths include heart of palm (actually the core of the bud) and

banana pith Banana pith or banana stem, is a vegetable harvested from the starchy inner core of banana pseudostems. It is used similarly to heart of palms in the cuisines of the Philippines, Malaysia, Indochina, Sri Lanka, and southern India. See also *Bana ...

s (actually the rolled up young leaves).

Pith helmets

The spongy wood of the pith wood plant or other similar species, often mistakenly called pith, was once used to make pith helmets.

Watch cleaning

Pith wood is a

cleaning tool Cleaning tools include the following: *Acoustic cleaning * Air blaster *Air knife *Besom *Broom *Brush * Building maintenance unit * Camel-hair brush *Carbon dioxide cleaning * Carpet beater * Carpet sweeper *Chamois leather * Cleret * Cyclone dust ...

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 (such as

elder An elder is someone with a degree of seniority or authority. Elder or elders may refer to: Positions Administrative * Elder (administrative title), a position of authority Cultural * North American Indigenous elder, a person who has and ...

or mullein).

Light

Dried pith (which is actually the center of the leaf) of certain rush plants soaked in fat or grease, held using a

rushlight A rushlight is a type of candle or miniature torch formed by soaking the dried pith of the rush plant in fat or grease. For several centuries, rushlights were a common source of artificial light for poor people throughout the British Isles. Th ...

, 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.

References

{{reflist Plant physiology Plant morphology Plant anatomy ln:Libúbú