Rachis is also the alternate spelling of Ratchis, king of the Lombards, 744-749.

Rachis (pronounced /ˈreɪkɪs/^{[verification needed]}) is a biological term for a main axis or "shaft".

[edit] In zoology

In animal anatomy, a rachis is the series of articulated vertebrae, which encase the spinal cord. The rachis may form the supporting axis of the body, and is then called the spine or vertebral column.

In ornithology, rachis refers to the central shaft of pennaceous feathers.

[edit] In botany

In plants, a 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 significant in the history of agriculture, and referred to by archaeologists as a "brittle rachis".