# Rachis

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{{other}}
{{Short description|Biological term for axis or shaft}}
[[Image:Turkey feather close sdetwiler.JPG|thumb|upright=1.1|The dark rachis of a [wild turkey](/source/wild_turkey) feather]]

In [biology](/source/biology), a '''rachis''' {{IPAc-en|ˈ|r|eɪ|k|ᵻ|s}} (from the {{langx|grc|ῥάχις}} [{{lang|grc-Latn|rhákhis}}], "backbone, spine")<ref>[https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aalphabetic+letter%3D*r%3Aentry+group%3D5%3Aentry%3Dr%28a%2Fxis Henry George Liddell, Robert Scott, A Greek–English Lexicon, ράχις]</ref> is a main axis or "shaft".

==In zoology and microbiology==
In [vertebrate](/source/vertebrate)s, ''rachis'' can refer to the series of articulated [vertebrae](/source/vertebrae), which encase the [spinal cord](/source/spinal_cord). In this case the ''rachis'' usually forms the supporting axis of the body and is then called the [spine](/source/Vertebral_column) or [vertebral column](/source/vertebral_column).  ''Rachis'' can also mean the central shaft of [pennaceous feather](/source/pennaceous_feather)s.

In the [gonad](/source/gonad) of the invertebrate nematode ''[Caenorhabditis elegans](/source/Caenorhabditis_elegans)'', a rachis is the central cell-free core or axis of the gonadal arm of both adult males and [hermaphrodite](/source/hermaphrodite)s where the [germ cell](/source/germ_cell)s have achieved [pachytene](/source/pachytene) and are attached to the walls of the gonadal tube.  The rachis is filled with [cytoplasm](/source/cytoplasm).<ref name="Schedl2012">{{cite book|author=Tim Schedl|title=Germ Cell Development in C. elegans|url=https://books.google.com/books?id=2poB6z05ZlsC&pg=PA11|access-date=6 August 2013|date=9 August 2012|publisher=Springer|isbn=978-1-4614-4015-4|page=11}}</ref>

==In botany<span class="anchor" id="Botany"></span><span class="anchor" id="botany"></span><span class="anchor" id="In botany"></span>==
In [plant](/source/plant)s, a rachis is the main axis of a compound structure. It can be the main stem of a compound [leaf](/source/leaf), such as in ''[Acacia](/source/Acacia)'' or [fern](/source/fern)s, or the main, flower-bearing portion of an [inflorescence](/source/inflorescence) above a supporting [peduncle](/source/Peduncle_(botany)). Where it subdivides into further branches, these are known as '''rachillae''' (singular rachilla). The central spine that remains when an ''[Abies](/source/Abies)'' seed cone disintegrates is also called the rachis.

A ripe head of wild-type wheat is easily [shattered](/source/shattering_(agriculture)) into dispersal units when touched or blown by the [wind](/source/wind). A series of abscission layers forms that divides the rachis into dispersal units consisting of a small group of flowers (a single spikelet) attached to a short segment of the rachis. This is significant in the [history of agriculture](/source/history_of_agriculture), and referred to by [archaeologists](/source/archaeologists) as a "brittle rachis", one type of [shattering](/source/shattering_(agriculture)) in crop plants.{{Cn|date=June 2021}}

{{gallery
|Fern detail.jpg|[Fern](/source/Fern) rachis with alternating 'pinnae', rachillae with attached leaflets
|Buddleja paniculata inflorescence.jpg|Inflorescence of ''[Buddleja paniculata](/source/Buddleja_paniculata)''
}}

==See also==
* [Stipe (botany)](/source/Stipe_(botany))

==References==
{{Reflist}}

Category:Vertebrate anatomy
Category:Plant morphology

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Adapted from the Wikipedia article [Rachis](https://en.wikipedia.org/wiki/Rachis) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Rachis?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.