Pith


Pith

Pith is a light substance that is found in vascular plants. It consists of soft, spongy parenchyma cells, and is located in the center of the stem. It is encircled by a ring of xylem (woody tissue), and outside that, a ring of phloem (bark tissue). In most plants the pith is solid, but some plants, e.g. grasses and umbellifers, the pith has a hollow centre forming a hollow tube except at the points where leaves are produced, where there is a solid plate across the stem. A few plants, e.g. walnut, have distinctive chambered pith with numerous short cavities in the pith.

The word comes from the Old English word "piþa", meaning substance, akin to Middle Dutch "pit", meaning the pit of a fruit.

The pith varies in diameter from about 0.5 mm to 6-8 mm in solid pith, and up to 150 mm or more in the stems of some plants with hollow pith, e.g. some bamboos. Freshly grown pith in young new shoots is typically white or pale brown, commonly darkening with age. In woody plants (trees, shrubs), the pith becomes surrounded by successive annual layers of wood; it may be very inconspicuous but is always present at the centre of a trunk or branch.

The cells in the peripheral parts of the pith may in some plants (e.g. "Hedera helix") 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".

The pith of the sola or other similar plants is used to make the pith helmet [ [http://www.askoxford.com/concise_oed/pithhelmet AskOxford.com - Pith helmet] ] .

The pith of some plants, as sago, is edible to humans.

The inner rind or albedo of hesperidium is also called Pith.

References


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  • Pith — Pith, n. [AS. pi?a; akin to D. pit pith, kernel, LG. peddik. Cf. {Pit} a kernel.] 1. (Bot.) The soft spongy substance in the center of the stems of many plants and trees, especially those of the dicotyledonous or exogenous classes. It consists of …   The Collaborative International Dictionary of English

  • pith — /pith/, n. 1. Bot. the soft, spongy central cylinder of parenchymatous tissue in the stems of dicotyledonous plants. 2. Zool. the soft inner part of a feather, a hair, etc. 3. the important or essential part; essence; core; heart: the pith of the …   Universalium

  • pith — O.E. piþa pith of plants, also essential part, from W.Gmc. *pithan (Cf. M.Du. pitte, E.Fris. pit), a Low Ger. root of uncertain origin. Figurative sense was in O.E. The verb meaning to kill by piercing the spinal cord is from 1805. Pith helmet… …   Etymology dictionary

  • pith — [pith] n. [ME pithe < OE pitha, akin to MDu pitte, pit of a fruit, kernel, pith of a tree] 1. the soft, spongy tissue in the center of certain plant stems 2. the soft core of various other things, as of a bone or feather 3. the spongy, fibrous …   English World dictionary

  • pith|y — «PIHTH ee», adjective, pith|i|er, pith|i|est. 1. full of substance, meaning, force, or vigor; crisply concise and to the point: »pithy phrases, a pithy speaker. SYNONYM(S): pointed …   Useful english dictionary

  • pith — [pıθ] n [U] ↑segment, ↑pith, ↑peel [: Old English; Origin: pitha] 1.) a white substance just under the outside skin of oranges and similar fruit ▪ Peel the oranges with a sharp knife to remove all pith. 2.) a soft white substance that fills the… …   Dictionary of contemporary English

  • Pith — Pith, v. t. (Physiol.) To destroy the central nervous system of (an animal, as a frog), as by passing a stout wire or needle up and down the vertebral canal. [1913 Webster] …   The Collaborative International Dictionary of English

  • pith — index center (essence), contents, corpus, essence, gist (substance), import, main point …   Law dictionary

  • pith — [ pıθ ] noun uncount 1. ) the white substance under the skin of oranges and similar fruits a ) the white substance inside the stems of some plants 2. ) the main and most important part of a problem, argument, etc …   Usage of the words and phrases in modern English

  • pith — *substance, purport, gist, burden, core Analogous words: *center, nucleus, heart, focus: spirit, *soul …   New Dictionary of Synonyms


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