Pith
From Wikipedia, the free encyclopedia
The centre dark spot (about 1 mm diameter) in this
yew wood is the pith
Elderberry shoot cut longitudinally to show the broad, solid pith (rough-textured, white) inside the wood (smooth, yellow-tinged). Scale in mm.
Walnut shoot cut longitudinally to show the chambered pith found in this genus. Scale in mm.
Pith is a substance that is found in
vascular plants. It consists of soft, spongy
parenchyma cells, and is located in the center of the
stem in eudicots (both herbaceous and woody) and in the center of the roots in monocots. It is encircled by a ring of
xylem (
woody tissue), and outside that, a ring of
phloem (
bark tissue). In some plants the pith is solid, but for most it is soft. A few plants, such as
walnuts, have distinctive chambered pith with numerous short cavities.
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. 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 center of a trunk or branch. 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. One example is
Hedera helix.
The pith of the
sola or other similar plants is used to make the
pith helmethttp://en.wikipedia.org/wiki/Pith#cite_note-0.
The pith of some plants, such as
sago, is edible to humans.
The inner rind or
albedo of
hesperidium is also called pith.