AskDefine | Define rachis

Dictionary Definition

rachis

Noun

1 axis of a compound leaf or compound inflorescence
2 the series of vertebrae forming the axis of the skeleton and protecting the spinal cord; "the fall broke his back" [syn: spinal column, vertebral column, spine, backbone, back] [also: rhachises (pl)]

User Contributed Dictionary

English

Alternative forms

Etymology

From , from ῥάχις.

Pronunciation

  • (UK) /ˈɹeɪkɪs/

Noun

  1. The main shaft of a grain or fern.
  2. In the context of "zoology|anatomy": The spine or the vertebrae of the spine.
  3. The central shaft of a feather.

Usage notes

  • The plural form rachides is technically erroneous, being based on a mistaken impression of the Ancient Greek stem.

Extensive Definition

Rachis is also the alternate spelling of Ratchis, king of the Lombards, 744-749.
The rachis () is the main axis of the inflorescence, or spike, of wheat and other cereals, to which the spikelets are attached. It is also the part of the axis that the pinnae are attached to in ferns, the main stem of a compound leaf (such as in Acacia), or the main axis in compound inflorescences in other angiosperms.
Spikelets are small inflorescences bearing one or more florets, or small flowers, along with a set of miniature bractlike leaves. When the fruits of the wild-type wheat are fully ripened, a series of abscission layers forms that divides the rachis into dispersal units consisting of a single spikelet attached to a short segment of the rachis. A ripe head of wheat is thus easily shattered into dispersal units when touched or blown by the wind. This is referred to by archaeologists as a "brittle rachis".
In animal anatomy, rachis is the series of articulated vertebrae, which encase the spinal cord and forms the supporting axis of the body; the spine. This is also called vertebral column. In feathers, rachis refers to the central shaft.
rachis in Catalan: Raquis
rachis in Spanish: Raquis
rachis in French: Rachis (botanique)
rachis in Italian: Rachide (botanica)
rachis in Dutch: Bloemspil
rachis in Portuguese: Ráquis
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