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 al ...

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 π ...

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 diets ...

. In

eudicotyledon The eudicots, Eudicotidae, or eudicotyledons are a clade of flowering plants mainly characterized by having two seed leaves upon germination. The term derives from Dicotyledons. Traditionally they were called tricolpates or non-magnoliid dicots ...

s, 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 of ...

s, it extends also into flowering stems and roots. The pith is encircled by a ring of

xylem Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word ''xylem'' is derived from ...

; the xylem, in turn, is encircled by a ring of

phloem Phloem (, ) is the living biological tissue, tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as ''photosynthates'', in particular the sugar sucrose, to the rest of the plant. This tran ...

. 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

walnut A walnut is the edible seed of a drupe of any tree of the genus ''Juglans'' (family Juglandaceae), particularly the Persian or English walnut, '' Juglans regia''. Although culinarily considered a "nut" and used as such, it is not a true ...

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 ''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 Fruit anatomy is the plant anatomy of the internal structure of fruit. Fruits are the mature ovary or ovaries of one or more flowers. They are found in three main anatomical categories: aggregate fruits, multiple fruits, and simple fruits. Aggre ...

or albedo, of

citrus ''Citrus'' is a genus of flowering plant, flowering trees and shrubs in the rue family, Rutaceae. Plants in the genus produce citrus fruits, including important crops such as Orange (fruit), oranges, Lemon, lemons, grapefruits, pomelos, and lim ...

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 settlement of Britain, Anglo ...

word ''piþa'', meaning substance, akin to

Middle Dutch Middle Dutch is a collective name for a number of closely related West Germanic dialects whose ancestor was Old Dutch. It was spoken and written between 1150 and 1500. Until the advent of Modern Dutch after 1500 or c. 1550, there was no overarch ...

''pitte'' (modern Dutch ''pit''), meaning the pit of a fruit.

Uses

Food

The pith of the

sago Sago () is a starch extracted from the pith, or spongy core tissue, of various tropical palm stems, especially those of ''Metroxylon sagu''. It is a major staple food for the lowland peoples of New Guinea and the Maluku Islands, where it is ...

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, Va ...

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, and ...

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 Region, Brazil, North and Northeast Region, Brazil, Northeast regions of Brazil, but wh ...

. Other foods sometimes mistakenly called piths include

heart of palm Heart of palm is a vegetable harvested from the inner core and growing bud of certain palm trees, most notably the coconut (''Cocos nucifera''), juçara (''Euterpe edulis''), açaí palm (''Euterpe oleracea''), palmetto (''Sabal'' spp.), and pe ...

(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 helmet The pith helmet, also known as the safari helmet, salacot, sola topee, sun helmet, topee, and topi) is a lightweight cloth-covered helmet made of sholapith. The pith helmet originates from the Spanish Empire, Spanish military adaptation of the na ...

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 coll ...

used in

watchmaking A watchmaker is an artisan who makes and repairs watches. Since a majority of watches are now factory-made, most modern watchmakers only repair watches. However, originally they were master craftsmen who built watches, including all their par ...

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 tr ...

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. The ...

, 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