Zanclian 1. An age in the Early Pliocene, preceded by the Messinian (Miocene), followed by the Piacenzian (Late Pliocene), and dated at 5.2 to 3.4 million years ago. 2. The name of the corresponding European stage, which has a greater correlation potential than the contemporary Tabianian Stage. It is roughly contemporaneous with part of the Delmontian (N. America), upper Kapitean and Opoitian (New Zealand), and the upper Mitchellian, Cheltenhamian, and lower Kalimnan (Australia).

zeatin n. A naturally occurring cytokinin that was first identified in 1963 in the grains of the maize plant (Zea mais).

Zechstein n. The final epoch of the Permian Period, dated at 256.1 to 245 million years ago.

zonate (Gr. z˘nŕ: belt) adj. Marked or colored in circular rings or zones. Also zonated.

zonated See zonate.

zone (Gr. z˘nŕ: belt) n. (As biostratigraphic zone) A unit of rock characterized by a clearly defined fossil content. To avoid confusion with other types of zone the term 'biozone' (short for 'biostratigraphic zone') is preferred by many authorities, although the term 'biozone' is also used in a different sense. The term is usually qualified to denote the type of zone. See acme zone; Assemblage Zone; Concurrent Range Zone; Lineage Zone; Oppel Zone; Range Zone; Subzone; Taxon Range Zone; Teilzone; Zonule; and Index Fossil.

zoochore (Gr. z˘on: animal; kh˘re˘: to move) n. A plant whose structure adapts it for dispersion by animals; a plant the spores or seeds of which are dispersed by animals. Also zo÷chore.

zo÷chore See zoochore.

zoochory (Gr. z˘on: animal; kh˘re˘: to move) n. The dispersal of fruits with the aid of animals. See zoochore.

zoophilous (Gr. z˘on: animal; philos: loved, friend) adj. Animal-pollinated

zooplankton n. Microscopic animals which move passively in aquatic ecosystems.

zoosperm (Gr. z˘on: animal; sperma: seed) n. See zoospore.

zo÷sperm (Gr. z˘on: animal; sperma: seed) n. See zoospore.

zoospermatic (Gr. z˘on: animal; sperma, spermatos: seed) adj. See zoosperm

zo÷spermatic (Gr. z˘on: animal; sperma, spermatos: seed) adj. See zoosperm

zoosporangia See zoosporangium.

zo÷sporangia See zo÷sporangium.

zoosporangial adj. See zoosporangium.

zo÷sporangial adj. See zo÷sporangium.

zoosporangium (Gr. z˘on: animal; spora: seed; aggeion: vase, bowl, container) n. (pl. zoosporangia) A sporangium or spore case in which zoospores are produced. Also zo÷sporangium.

zo÷sporangium n. (pl. zo÷sporangia) See zoosporangium.

zoospore (Gr. z˘on: animal; spora: seed) n. An asexual spore produced by certain algae and some fungi, capable of moving about by means of a flagella. Also zoosperm, zo÷sperm, zo÷spore.

zo÷spore See zoospore.

zoosporic adj. See zoospore.

zo÷sporic adj. See zoospore.

zoosporous adj. See zoospore.

zo÷sporous adj. See zoospore.

zygogeneses See zygogenesis

zygogenesis n. (pl. zygogeneses) Reproduction involving the formation of a zygote.

zygomorphic (Gr. zygos: yoke; morphŕ: shape) adj. Bilaterally symmetrical, so that a line drawn through the middle of the structure along only one plane will produce a mirror image on either side. Said of the corolla or calyx when divisible into equal halves in one plane only bilaterally symmetrical, with only one plane of symmetry, usually the plane that bisects the flower vertically. Of a flower divisible into similar halves by only one plane of symmetry. Cf. actinomorphic, and see irregular. Also zygomorphous.

zygomorphism n. See zygomorphic.

zygomorphous adj. See zygomorphic.

zygomorphy n. See zygomorphic.

Zygomycota n. A phylum of saprotrophic or parasitic fungi that includes the bread mould (Mucor). Their hyphae lack cross walls and they can reproduce asexually by sporangiospores formed within a sporangium or sexually by means of zygospores.

zygophore (Gr. zygos: yoke; phora: carrying) n. In certain fungi, any of several specialized branches of hyphae, bearing the isogametes that unite to produce a zygospore.

zygophoric adj. See zygophore.

zygophyte (Gr. zygos: yoke; phyton: plant) n. A plant which reproduces by means of zygospores.

zygospore (Gr. zygos: yoke; spora: seed) n. A zygote with a thick resistant wall, formed by some algae and fungi (see Zygomycota). It results from the fusion of two gametes, neither of which is retained by the parent in any specialized sex organ (such as an oogonium). It enters a resting phase before germination. Cf. oospore.

zygote (Gr. zygo˘, to yoke) n. A cell formed by the union of two gametes; broadly: the developing individual produced from such a cell.

zygotene n. A stage in the meiotic process when the threadlike chromosomes pair.