from The American Heritage® Dictionary of the English Language, 4th Edition
- n. Biology A main axis or shaft, such as the main stem of an inflorescence, the stalk of a pinnately compound leaf, or the spinal column.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The main shaft of either a compound leaf, head of grain, or fern frond.
- n. The spine or the vertebrae of the spine.
- n. The central shaft of a feather.
from the GNU version of the Collaborative International Dictionary of English
- n. The spine; the vertebral column.
- n. Same as Rhachis.
from The Century Dictionary and Cyclopedia
- n. In botany:
- n. The axis of an inflorescence when somewhat elongated; the continuation of the peduncle along which the flowers are ranged, as in a spike or a raceme.
- n. In a pinnately compound leaf or frond, the prolongation of the petiole along which the leaflets or pinnæ are disposed, corresponding to the midrib of a pinnately veined simple leaf. See cut under compound.
- n. In zoöl. and anatomy:
- n. The vertebral column.
- n. The stem, shaft, or scape of a feather, as distinguished from the web, vane, or vexillum; especially, that part of the stem which bears the vexillum. as distinguished from the calamus or quill. See quill, 4.
- n. The median part of the radula of a mollusk, usually bearing teeth which differ from those on each side of it.
- n. The axial skeleton of various polyp-colonies, as of Gorgonia; some axial part, or formation like a midrib, as in crinoids.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. axis of a compound leaf or compound inflorescence
- n. the series of vertebrae forming the axis of the skeleton and protecting the spinal cord
Pinnately compound leaves have the leaflets arranged along the main or mid-vein (called a rachis in this case). odd pinnate: with a terminal leaflet, e.g. Fraxinus (ash). even pinnate: lacking a terminal leaflet, e.g. Swietenia (mahogany).
Zoom out, and we see that feathers have a central shaft called the rachis with two vanes on either side.
The spikelets are unilaterally biseriate on the rachis which is not jointed at the base.
At last, quhen he wes cumin throw the vail that lyis to the gret eist fra the said castell, quhare now lyis the Canongait, the staik past throw the wod with sic noyis and din of rachis and bugillis, that all the bestis were rasit fra thair dennis.
Dodonaea microzyga, F.M. Somewhat viscid, almost glabrous; leaves with 1 to 2 pairs of small obovate-cuneate leaflets; in front rounded, or truncate, or retuse, or sometimes 3-toothed, flat at the margin; rachis dilated; fruit-bearing pedicels solitary; capsules 3 to 4-celled; valves cymbeo-semiorbicular, all around broadly winged; the wing rounded-blunt on both extremities; dissepiments persistent with the columella.
Theoretically, humans should have influenced the changes from wild to domesticated rice mainly by continuous cultivation and selection of wild rice with mutated biological characteristics of more seeds, tough rachis, higher germination rates, etc.
The baby Anzu bird that Lugalbanda feeds and decorates is spotted with a multitude of tiny flowers and you can make out every barb, calamus, and rachis on the bird's feathered body.
But Archaeopteryx was very likely capable of powered fligh sic judging from its relatively massive furcula and the asymmetric rachis of its primary flight feathers Feduccia and Tordoff 1979; Olson and Feduccia 1979.
The “same mechanisms” that produce the main vane ALSO bring about: (1) the division of the posterior new barb locus, (2) the creation of a second rachis ridge, and (3) an entire second vane growing simultaneously from a single follicle.
As a consequence of duplication and direction, the same mechanisms that produce the main vane of the feather result in the division of the posterior new barb locus into two laterally displaced new barb loci, the creation of a second rachis ridge the hyporachis, and ultimately an entire second vane growing simultaneously from a single follicle.