Pith

 ( Plant Anatomy ) 

Pith, or medulla, is a tissue in the Plant stem of . Pith is composed of soft, spongy parenchyma cells, which in some cases can store starch. In , pith is located in the center of the stem. In , it extends only into 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 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 juglans, have distinctive chambered pith with numerous short cavities. 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. 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.

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Uses

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Food 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 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.

Takashi Mishima (2026). 9789811052682, Springer. ISBN 9789811052682

The form of the starch after processing is similar to tapioca.

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

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Pith helmets The spongy wood of the pith wood plant or other similar species, often mistakenly called pith, was once used to make . target="_blank" rel="nofollow"> AskOxford.com - Pith helmet

(2026). 9789251050644, Food and Agriculture Organization Interdepartmental Working Group on Biological Diversity for Food and Agriculture. . ISBN 9789251050644

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Watch cleaning 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 (such as Sambucus or mullein).

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Light

Dried pith (which is actually the center of the leaf) of certain Juncaceae 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.

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See also

• Papyrus

Categories: Plant Anatomy, Plant Morphology, Plant Physiology

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