In biology, a rachis (from the grc, ῥάχις [], "backbone, spine")Henry George Liddell, Robert Scott, A Greek–English Lexicon, ράχις
/ref> is a main axis or "shaft".

In zoology and microbiology

In vertebrates, ''rachis'' can refer to the series of articulated vertebrae, which encase the spinal cord. In this case the ''rachis'' usually forms the supporting axis of the body and is then called the

spine Spine or spinal may refer to: Science Biology * Vertebral column, also known as the backbone * Dendritic spine, a small membranous protrusion from a neuron's dendrite * Thorns, spines, and prickles, needle-like structures in plants * Spine (zoolog ...

or vertebral column. ''Rachis'' can also mean the central shaft of pennaceous feathers. In the

gonad A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sper ...

of the invertebrate nematode ''

Caenorhabditis elegans ''Caenorhabditis elegans'' () is a free-living transparent nematode about 1 mm in length that lives in temperate soil environments. It is the type species of its genus. The name is a blend of the Greek ''caeno-'' (recent), ''rhabditis'' (ro ...

'', a rachis is the central cell-free core or axis of the gonadal arm of both adult males and

hermaphrodite In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many Taxonomy (biology), taxonomic groups of animals (mostly invertebrate ...

s where the germ cells have achieved pachytene and are attached to the walls of the gonadal tube. The rachis is filled with cytoplasm.

In botany

In plants, a rachis is the main axis of a compound structure. It can be the main stem of a compound leaf, such as in ''

Acacia ''Acacia'', commonly known as the wattles or acacias, is a large genus of shrubs and trees in the subfamily Mimosoideae of the pea family Fabaceae. Initially, it comprised a group of plant species native to Africa and Australasia. The genus na ...

'' or ferns, or the main, flower-bearing portion of an inflorescence above a supporting

peduncle Peduncle may refer to: *Peduncle (botany), a stalk supporting an inflorescence, which is the part of the shoot of seed plants where flowers are formed *Peduncle (anatomy), a stem, through which a mass of tissue is attached to a body **Peduncle (art ...

. Where it subdivides into further branches, these are known as rachillae (singular rachilla). A ripe head of wild-type wheat is easily

shattered Shattered may refer to: Books * ''Shattered'' (Casey book), a 2010 non-fiction book: true-crime account of pregnant mother's murder * ''Shattered'' (Francis novel), a 2000 novel by Dick Francis: glassblower seeks videotape following death of j ...

into dispersal units when touched or blown by the 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, and referred to by

archaeologists Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landscap ...

as a "brittle rachis", one type of shattering in crop plants.

References

{{Reflist Vertebrate anatomy Plant morphology

In zoology and microbiology

In botany

See also

References