Grex or GREX may refer to:
- Grex (biology), a multicellular aggregate of amoeba of the phyla Acrasiomycota or Dictyosteliomycota
- Grex (horticulture), (pl. greges) a kind of group used in horticultural nomenclature applied to the progeny of an artificial cross from specified parents
- Formerly used to mean species aggregate
- Georgetown Rail Equipment Company, a provider of railway maintenance equipment and related services based in Georgetown, Texas
A grex, (also called a pseudoplasmodium, or slug) starts as a crowd of single-celled amoebae of the groups Acrasiomycota or Dictyosteliida; grex is the Latin word for flock. The cells flock together, forming a mass that behaves as an organised, slug-like unit. Before they get stimulated to crowd together to form a grex, the amoebae simply wander as independent cells grazing on bacteria and other suitable food items. They continue in that way of life as long as conditions are favourable. When the amoebae are stressed, typically by a shortage of food, they form a grex.
According to species and circumstances, details of the shape of the grex and how it may form will vary but typically the stressed amoebae first produce pheromones that stimulate the flock to assemble in a vertical column. When the column of aggregated cells becomes too high and narrow to stay upright, it topples and becomes a slug-shaped mass: the grex. The grex is mobile; in its form as a slug-like unit it can glide over a moist surface. Once it has moved far enough to complete its development, the cells of the amoebae differentiate according to their positions in the grex; some become the spore cells and the covering shell of the fruiting body near the tip, and others form structures such as the stalk. Cells forming the structural items, such as the stalk and shell, desiccate and die; only the spores in the fruiting body survive to propagate. When circumstances are right and the fruiting body is mature, its shell ruptures and releases the spores. The spores then may be transported by media such as wind or water; they then may cover distances far greater than any that they could have achieved in their amoeboid form, and over regions where amoebae could not travel at all, such as dry surfaces.
The term grex (pl. greges or grexes, abbreviation gx), derived from the Latin noun grex, gregis meaning 'flock', has been coined to expand botanical nomenclature to describe hybrids of orchids, based solely on their parentage. Grex names are one of the three categories of plant names governed by the International Code of Nomenclature for Cultivated Plants; within a grex the Groups category can be used to refer to plants by their shared characteristics (rather than by their parentage), and individual orchid plants can be selected (and propagated) and named as cultivars.
When the name of a grex is first established, a description is required that specifies two particular parents, where each parent is specified either as a species (or nothospecies) or as a grex. The grex name then applies to all hybrids between those two parents. There is a permitted exception if the full name of one of the parents is known but the other is known only to genus level or nothogenus level.
New grex names are now established by the Royal Horticultural Society, which receives applications from orchid hybridizers.
n. 1 A multicellular aggregate of amoeba. 2 A kind of group used in horticultural nomenclature, applied to the progeny of an artificial cross from specified parents.
Usage examples of "grex".
Unlike most other top-level officers, Grex had come to his position out of an unusual combination of circumstances and experience: academics—he had been chancellor of a great university— and the military, in which he had begun his career, rising to be one of the youngest ressaldar-generais in history.
Though he had not come up through the ranks from a young embassy officer as had most of his peers, Grex had the wit and the confidence to surround himself with polished professionals, and he was afraid of neither title nor talent.
Beside him, Deonora stood still as a statue, but, Grex well knew, with every sense alert to the scene.
Saluting Grex, they took up positions of attention, facing inward, on either side of the door.
Valadon and Deonora took their own places a little way down the table, with the other two Kelts— Morgan Cairbre and Emrys Penmarc'h, as Grex had by now learned.
The two Kelts spoke no word aloud, but even Grex could sense the wordless negatives sent back to the Earl.
She ran it over briefly in her mind while Elathan spoke, addressing those few hundreds here in the Hall and all the watching billions: In only one day, she, Elathan and Haco Grex together had hammered out a preliminary treaty that, if all went according to plan in the coming battles, would put their three allied nations into such a position of galactic pre-eminence that not for the foreseeable future would Imperium or Phalanx or any other nascent and acquisitive superentity be able to challenge them.
Elathan, who had fought alongside Niall O Kerevan, Tanaxio of the Yamazai and Haco Grex for one epic hour against a cohort of Jaun Akhera's personal guards.
Even Elathan and Grex have urged you to do so—shall you be any less as Empress than you are as Ard-rian, or prove worse than Strephon or Jaun Akhera?
Roads in Sogo—and elsewhere on Grex, Kirk had always assumed—were evolutionary end products of the organic, looping footpaths Kozhu and Vragax had made over the generations.
Thinking back on it now, he realized that this was the moment when he became truly afraid, the point at which he understood that things on Grex had gotten so bad that they would never be fixed and the people crowded into this shuttle alongside him were actually fleeing for their lives.
It may not be possible to send crewmen to Grex, then wait to make certain they safely deliver the boy to his father before we are driven away from the machine.
George Kirk was not left behind on Grex to fend for himself and possibly die.
Kirk back to Grex from Tlaoli must have spirited his younger self away at the same time.
And if anything happened to George before the younger Kirk was returned, there would be no one on Grex to protect the boy, no one to guarantee he escaped off-planet.