GA3 See gibberellic acid.

galactomannan n. A hemicellulose containing galactose and mannose.

galactose n. A hexose sugar, isomer of glucose, gives rise to galacturonic acid, COOH - (CHOH)4 - HC=O.

galactostasis n. An excessive accumulation of milk in the gland that causes an inflammatory response.

galbulus (L. galbulus: cypress cone) n. The cone of the cypress trees.

galea (L. galea: helmet) n. (pl. galeae) A hooded or helmet-shaped portion of a perianth, as the upper sepal of Aconitum, and the upper lip of some bilabiate corollas; a structure like a helmet in shape, form, or function.

galeae See galea.

galeate (L. galea: helmet) adj. Hollow and vaulted; like a helmet; e.g., the lobule in certain species of Frullania.

galeated See galeate.

galeiform (L. galea: helmet; forma: shape) adj. Helmet-shaped; galea-like.

galericulate (L. galericulum: a kind of skullcap) adj. Having hat-like covering.

gall (L. galla: tumor) n. A swelling or excrescence on plants caused by abnormal proliferation of cells due to mechanical injury or attack by insects, mites, fungi, bacteria, or viruses. Some galls are self-limiting, including the oak apples caused by the gall wasp, while others are tumorous, such as the crown gall induced by the bacterium Agrobacterium tumefaciens. See also cecidium.

gall wasp A small wasp (6-8 mm long), also called gallfly, of the family Cynipidae. Gall wasps lay eggs in plant tissues, particularly oak trees and rose plants, which respond by producing galls. Thus, Biorhiza pallida produces the oak apple gall and Diplolepis rosae, the robin's pincushion gall.

gallic acid 3,4,5-trihydroxybenzoic acid, when esterified with a carbohydrate; gallic acid contributes to the formation of gallotannins, a type of hydrolyzable tannin.

gallicole adj. Living or dwelling in galls.

gametangia See gametangium.

gametangiogamy n. The fusion of sexually differentiated hypha.

gametangiophore n. A specialized gametangia-bearing branch, producing either archegonia (archegoniophore) or antheridia (antheridiophore).

gametangium (Gr. gametęs: spouse; aggeion: bowl) n. (pl. gametangia) An organ that produces gametes. The term is usually restricted to the sex organs of algae, fungi, mosses, and ferns. Cf. antheridium, archegonium, oogonium, androecium, gametoecium, gynoecium.

gamete (Gr. gametęs: spouse) n. A reproductive cell that fuses with another gamete to form a zygote. Examples of gametes are ova (eggs) and spermatozoa (sperms); eggs and sperm are gametes and are structurally differentiated. Gametes are haploid, i.e. they contain half the normal (diploid) number of chromosomes; thus when two fuse, the diploid number is restored (see fertilization). Gametes are formed by meiosis. See also sexual reproduction.

gametic See gamete.

gametically See gamete.

gametocyte (Gr. gametęs: spouse; kytos: what covers) n. A cell that produces gametes.

gametogenesis n. The process of gamete development.

gametophore (Gr. gametęs: spouse; phora: carrying) n. A gametangium-bearing stalk; loosely used for the mature gametophyte plant developed from a protonema. Cf. gametangiophore, gametophyte.

gametophyte (Gr. gametęs: spouse; phyton: plant) n. The haploid (1n), gamete-producing generation of the plant reproductive cycle, the reduced and inconspicuous portion of the life cycle in the vascular plants; it is the dominant phase in the life cycle of mosses and liverworts, the sporophyte generation depending on it either partially or completely and it consist normally of green, leafy or thalloid plants, bearing antheridia r archegonia; in clubmosses, horsetails, and ferns it is the prothallus; in seed plants it is very much reduced; for example, in angiosperms the pollen grain is the male gametophyte and the embryo sac is the female gametophyte. See also alternation of generations.

gamic (Gr. gamikos: bridal, of marriage) adj. Sexual.

gamo- (Gr. gamos: marriage) prefix. Meaning union of like parts.

gamopetalous (Gr. gamos: marriage; petalon: leaf) adj. Having the petals of the corolla more or less united. Having the petals united so as to form a tubelike corolla. Same as sympetalous. See also polypetalous.

gamophyllous (Gr. gamos: marriage; phyllon: a leaf) adj. Having the leaves or perianth segments united by their margins, at least at the base.

gamosepalous (Gr. gamos: marriage; skepas: covering, shelter; [pe]talon: leaf) adj. Having the sepals united by their margins, at least at the base.

garden escape Garden species known to have escaped either directly by seed or other propagules moving out of the garden or indirectly by establishing from dumped garden waste. Other garden escapes originate from abandoned gardens, graveyards and commercial tips to name just a few.

gasteropodous adj. Bulging on one side. Cf. gibbous and ventricose.

tritisastroenteric n. Inflammation of the lining of the stomach.

gastroenteric adj. Pertaining to the stomach and intestines.

gastroid adj. Saif of basidia which do not actively discharge their basidiospores.

Gedinnian n. 1. The earliest age in the Devonian Period, preceded by the Silurian, followed by the Siegenian, and dated at 408 to 401 million years ago. 2. The name of the corresponding European stage, which is roughly contemporaneous with the Crudinian (Australia) and the lower/middle Helderbergian (N. America). The boundary (also the Silurian-Devonian boundary) stratotype section is at Klonk, near Prague.

geitonogamous adj. See geitonogamy.

geitonogamy (Gr. geitonia: neighborhood; gamos: marriage) n. Pollination between flowers of the same plant, i.e. pollination of a flower from another flower on the same plant. Cf. xenogamy.

gelatinous (L. gelatus: frozen) adj. Jelly-like in texture.

geminate (L. geminatus: doubled) adj. In equal pairs like twins; doubled; e.g., the peristome teeth of Fabronia, the marginal hairs of Metzgeria.

gemma (L. gemma: bud) n. (pl. gemmae) A bud or outgrowth of a plant which develops into a new organism. An asexual reproductive body that becomes detached from a parent plant and propagates offspring plants genetically identical to the parent plant.

gemmaceous (L. gemma: bud) adj. Of, pertaining to, or ressembling gemmae.

gemma cup Cup-shaped, gemmae-containing structure of thalline (Marchantia) or foliar (Tetraphis) origin, presumably structured to aid in distribution of gemmae by water splash.

gemmae See gemma.

gemmate (L. gemmare: to put forth buds; gemmatus: covered with buds) adj. v. Budlike; with gemmae; reproducing by gemmae; having buds or outgrowths which develop into a new individual.

gemmation (L. gemmare: to put forth buds) n. The process of reproduction by gemmae; a type of vegetative propagation in which small clumps of undifferentiated cells (gemmae) develop on the surface of a plant. These are shed and dispersed to other areas, where they grow to produce new individuals. Gemmation is found only in certain lower plants, such as mosses and liverworts.

gemmiferous (L. gemma, a bud; ferre: to carry) adj. Producing, bearing gemmae or buds.

gemmiform (L. gemma, a bud; forma: shape) adj. Shaped like a bud.

gemminate adj. Applied to plants with short bud-like branches.

gemmiparous (L. gemma: a bud; parere: to bear) adj. Producing or reproducing by buds or gemmae. Cf. gemmiferous.

gemmule (L. gemmula: little bud) See gemma.

gene (Gr. genea: what is generated, kind) n. A chromosomal unit carrying information which can be inherited. The fundamental physical unit of heredity. It occupies a fixed chromosomal locus, and when transcribed has a specific effect upon the phenotype. It may mutate, and so yield various allelic forms. A gene comprises a segment of DNA (in some viruses it is RNA) coding for one function or several related functions. The DNA is usually situated in thread-like chromosomes, together with protein, within the nucleus; in bacteria and viruses, though, the chromosomes comprise simply a long thread of DNA.

gene clone An exact replica of a gene. Cf. gene cloning.

gene cloning The production of exact copies (clones) of a particular gene or genes using genetic engineering techniques. The DNA containing the target gene(s) is split into fragments using restriction enzymes. These fragments are then inserted into cloning vectors, such as bacterial plasmids or bacteriophages, which transfer the recombinant DNA to suitable host cells, such as the bacterium E. coli. Alternatively, complementary DNA is inserted into the vectors, or 'naked' DNA fragments can be taken up directly by a host bacterium from its medium (this is less efficient than vector transfer). Inside the host cell the recombinant DNA undergoes replication; thus, a bacterial host will give rise to a colony of cells containing the cloned target gene. Various screening methods may be used to identify such colonies, enabling them to be selected and cultured. Gene cloning facilitates gene sequencing; it also enables large quantities of a desired protein product to be produced: human insulin, for example, is now produced by bacteria containing the cloned insulin gene.

gene flow The Spread of genes by crossing.

gene frequency The proportion in which alternative alleles of a gene occur in a population.

gene interaction Modification of gene action by a non-allelic gene or genes.

gene pool system The three informal categories by Harlan and de Wet (cited in Harlan, 1975) to provide a genetic perspective and focus for cultivated plants.

genera See genus.

generative cell A cell of the male gametophyte of angiosperms that divides to produce two male gametes or sperm.

generic (L. genus, generis: race, kind) adj. Relating to or having the rank of a biological genus.

generitype n. The type specimen of a genus. It is designated by using the type for the name of a particular species within that genus. For example, the generitype for Aster is the type for Aster amellus L.

genet n. The connected plants of the colony of a clonal species; individual plants within the genet are called ramets.

genetic adj. Of the normal or usual pattern of change in a morphological character that occurs after development of an organism is initiated.

genetic drif Changes in the genetic composition of a population which are the result of chance. Genetic drift is more important in smaller populations.

genetic equilibrium The condition in which successive generations of a population contain the same genotypes in the same proportions with respect to particular genes or combinations of genes.

genetic spiral A spiral drawn around the stem that joins the positions of successively initiated primordia at the stem apex.

genetically adv. See genetic.

genic sterility A type of male sterility conditioned by nuclear genes; it may be transmitted by either parent.

genicula See geniculum.

geniculate (L. geniculatus: knotty, gnarled) adj. Bent like a knee, often with a subtending spur; bent abruptly at the nodes.

geniculum n. (pl. genicula) A small knee-shaped anatomical structure or abrupt bend.

genome (Gr. genos: origin. race) n. All the genetic material of an organism; one haploid set of chromosomes and the genes they contain; a complete chromosome set. Each parent, through its reproductive cells, contributes its genome to its offspring. A single chromosome in bacteria, or in the DNA or RNA of viruses. An organism's genetic material.

genomic adj. Related to the genome.

genotype (Gr. genos: race. orogin; typos: mark, image) n. The genetic constitution of an individual, i.e. the combination of alleles it possesses, i.e. the total complement of hereditary factors (genes) acquired by an organism from its parents and available for transmission to its offspring. Cf. phenotype.

genotypic adj. See genotype.

genotypical adj. See genotype.

genotypically adv. See genotype.

gensenoside See gensenosides.

gensenosides n. pl. A class of steroid-like compounds, triterpene saponins, found exclusively in the plant genus Panax (ginseng).

genus (L. genus, race) n. (pl. genera) A group of closely related species; the taxonomic category ranking above a species and below a family; a class, kind, or group marked by common characteristics or by one common characteristic; specifically a category of biological classification ranking between the family and the species, comprising structurally or phylogenetically related species or an isolated species exhibiting unusual differentiation, and being designated by a Latin or latinized capitalized singular noun. Distinctions between genera are sometimes empirical or arbitrary and liable to modification as knowledge advances. A category antedating binomial nomenclature, composed of plants with two or three characters of reproductive structures in common, although characters used for separation vary widely among different families.

geocarpic (Gr. ge: earth; karpos: fruit) adj. Of fruits carried on long peduncles into the soil, e.g. Trifolium subterraneum.

geocarpous adj. Said when the fruit matures underground, whether or not the flower is above ground (Arachis) or not (Rhizanthella).

geocarpy (Gr. ge: earth; karpos: fruit) n. The underground maturation of fruits developed from flowers borne above ground, as in peanuts, Arachis hypogaea.

geochronologic unit See geologic-time unit

geologic-time unit A subdivision of geologic time, based on the rock record of the corresponding chronostratigraphic unit. Each time unit coincides with a particular chronostratigraphic unit and, like them, time units are ranked in order of decreasing duration, each unit comprising a number of units of shorter time interval (e.g. two or more chrons comprise an age, two or more ages comprise an epoch, etc.).

-----------------------------------------------------
| Chronostratigraphic Unit  | Geologic-time Unit    |
-----------------------------------------------------
|       eonothem            |       eon (longest)   |
|       erathem             |       era             |
|       system              |       period          |
|       series              |       epoch           |
|       stage               |       age             |
|       chronozone          |       chron           |
-----------------------------------------------------

geophyte (Gr. ge: earth; phyton, plant) n. Perennial (or biennial) herbaceous plant in which the stems die back to a remnant shoot system with storage organs that are imbedded in the soil and that help the plant survive adverse conditions. These are the plants gardeners call bulbs (including corms, rhizomes, and tubers as well as true bulbs).

geotropic (Gr. ge: earth; tropos: direction) adj. Growing towards gravity; roots often grow geotropically to reach the water table.

geotropism (Gr. ge: earth; tropos: direction) n. An organism's growth determined by the force of gravity, as roots growing downward and stems upward.

germ (L. germen: germ) n. A small mass of protoplasm capable of developing into an organism or one' of its parts. A microorganism pathogen. The embryo with the scutellum of a cereal grain that is usually separated from the starchy endosperm during milling.

germ cell A reproductive cell, or gamete, or a cell that will develop into a reproductive cell, such as a spermatocyte or an oocyte.

germinate (L. germinare: to sprout) v. To develop a young plant from seed.

germination (L. germinatio: germination) n. The process by which an embryo plant within a seed is transformed into a recognizable plant with roots, stem, and leaves. Water, warmth, and oxygen stimulate germination, which begins with the emergence of the root (radicle) and is followed by the shoot (plumule). Energy for the process is provided by the cotyledons (seed leaves), which either remain below ground (hypogeal germination, as in the broad bean) or form the first leaves of the seedling (epigeal germination, as in the marrow).

germination rate The proportion of seeds in a given seed lot that are likely to germinate under favorable conditions.

germplasm n. See germ plasm.

germ plasm The cytoplasm of the germ cell, particularly that containing the genetic material. The genetic material with its specific molecular and chemical makeup that comprises the physical foundation of the hereditary qualities of an organism. Also germplasm.

gibberellic acid A plant growth substance that is extracted from fungal cultures and is one of the most important commercially available gibberellins. It was discovered in 1954. Syn. gibberellin.

gibberellin n. Any of a group of plant growth substances chemically related to terpenes and occurring naturally in plants and fungi. They promote elongation of stems, e.g. bolting in cabbage plants, and the mobilization of food reserves in germinating seeds, and are influential in inducing flowering and fruit development. Commercially available gibberellins, such as gibberellic acid, are used to manipulate the onset of sexual maturity in various species, e.g. to induce cone-bearing in young conifer trees. First discovered in the fungus Gibberella fujikuroi, and later in other plants.

gibbose See gibbous.

gibbosely See gibbous.

gibbosity (L. gibbus: hump) n. A swelling or protuberance; the state of being gibbous.

gibbous (L. gibbus: hump) adj. With a distended, rounded swelling on one side, as on a calyx or corolla tube or segment. Very convex or tumid. Syn. gibbose.

gibbously n. See gibbous

gibbouness n. Something that bulges out or is protuberant or projects form a form. Also gibbosity.

gibrous adj. Swollen at one side,

gill n. One of the radiating plates forming the undersurface of the cap of a mushroom fungus.

ginkgo See ginko.

ginko n. A deciduous gymnosperm tree, Ginkgo biloba, also called maidenhair tree, that is the sole living representative of a group of trees that flourished in the Carboniferous period (370-280 million years ago). Growing to a height of 30 m, it has lobed fan-shaped leaves, 12 × 10 cm, which are pale green and turn yellow in autumn, and fleshy plumlike yellow fruits containing edible kernels. The ginkgo is native to China and widely planted for ornament. Family: Ginkgoaceae; phylum: Ginkgophyta.

ginsenoside See ginsenosides.

ginsenosides A class of steroid-like compounds, triterpene saponins, found exclusively in the plant genus Panax (ginseng). Ginsenosides have been the target of research, as they are viewed as the active compounds behind the claims of ginseng's efficacy. Because ginsenosides appear to affect multiple pathways, their effects are complex and difficult to isolate.

Givetian n. 1. An age in the Middle Devonian Epoch preceded by the Eifelian, followed by the Frasnian, and dated at 380.8 to 377.4 million years. 2. The name of the corresponding European stage that is zoned on goniatites and spiriferid brachiopods. It is roughly contemporaneous with the lower Condobolinian (Australia) and Erian (N. America).

glabrate (L. glaber, glabra: without hair) adj. Becoming glabrous with age.

glabrescent (L. glaber, glabra: without hair) adj. Becoming glabrous with age.

glabrous (L. glaber, glabra: without hair) a. With a smooth, even surface; without hairs.

glade n. Open space surrounded bywoods or a forest; a marshy and usually low-lying area; a periodically inundated grassy marsh often running between adjacent slopes; a marshy area bounding or forming the headwaters of a stream.

gladiate adj. Sword-shaped; ensiform

gland (L. glans, glandis: acorn) n. A secreting part or appendage, a structure, within or on the surface of a plant, with a secretory function; any protuberance or appendage having the appearence of such an organ.

gland-dot n. A tiny gland or pore, usually secreting fluid.

glandspine n. A short spine found in the upper part of a cactus areole, bearing nectar in its first year.

glandular (L. glandula: gland) adj. Of or pertaining to a gland. Having or bearing secreting organs, glands, or trichomes.

glandular-toothed adj. Bearing teeth that bear glands.

glanduliferous (L. glandula: gland; ferre: to carry) adj. Bearing glands.

glandulose adj. See glandular.

glandulous adj. See glandular.

glans (L. glans, glandis: acorn) n. A dry, indehiscent fruit borne in a cupule, as the acorn.

glaucescent (L. glaucus: greenish, pale green) adj. Somewhat glaucous; becoming glaucous

glauconite n. A greenish mineral consisting of a silicate of iron, magnesium, aluminum or potassium found in greensand and often used as a fertilizer or soil supplement.

glaucous (L. glaucus: greenish, pale green) adj. Bluish green; covered with a pale green bloom; having a bluish grey bloom; with a whitish bloom, that rubs off readily (as in the juvenile leaves of many eucalypts, the bloom on many sorts of grape).

Gleicheniaceae n. A family of the phylum Filicinophyta.

globose (L. globosus: spherical, rounded) adj. Rounded; almost spherical; globular; globe-shaped.

globular (L. globulus: little ball) adj. Globe-shaped, sherical; composed of or having globules.

globule (L. globulus: little ball) n. A small spherical body.

glochid See glochidium.

glochidia See glochidium.

glochidiate (Gr. glôkhis: any pointed end) adj. Barbed at the tip, as a bristle or hair; bearing glochidia.

glochidium (Gr. glôkhis: any pointed end) n. (pl. glochidia) A barbed hair or bristle, as the fine hairs in Opuntia. Also glochid.

gloeoplerous adj. Said of hypha with hyaline or yellowish and highly refractile fluid.

glomerate (L. glomeratus: rolled in a ball [of yarn]) adj., vt. To gather or wind into a ball; growing, collected or arranged in a rounded mass, as glands, flowers, etc.; densely, compactly clustered.

glomerulate adj. Having a compact, cymose cluster of flowers. See glomerule.

glomerule (L. glomerare: to roll in a ball [of yarn]) n. A condensed cyme of almost sessile flowers; a compact cluster as of spores.

glucose (Gr. glukus: sweet) n. A simple sugar, and the primary product of photosynthesis. It is polymerized to make cellulose and chitin.

glucoside n. A glycoside in which the sugar constituent is glucose (originally the term glucoside was used whatever the sugar involved).

glucosinolate n. a.k.a. mustard oil glycoside, mostly colorless, with a sharp, odor, which via hydrolysis with myrosine yield isothiocyanates or mustard oils.

glucurono-arabinoxylan n. a.k.a. arabinoxylan or pentosan, the main component of hemicellulose in the cell wall.

glumaceous (L. gluma: husk) adj. Glume-like, tending to be chaffy or membranous in texture; consisting of or having glumes.

glume (L. gluma: husk) n. Either member of a pair of empty chaffy bracts that are found at the base of a spikelet (see spike) of the grasses, sedges or similar plants. Cf. lemma.

glutinose See glutinous.

glutinous (L. glutinum: glue) adj. Having a sticky, moist surface; a gluey or sticky exudation. Also glutinose.

glycoflavone See glycoflavones.

glycoflavones n. A class of flavonoids which have a sugar attached, often C-glycosyl.

glycoprotein (Gr. glykus: sweet; prôteyô: to be first) n. A membrane-bound protein which has attached branching carbohydrates. These may function in cell-cell recognition, such as in human blood groups and immune system response, as well as in resisting compression of cells.

glycoside (Gr. glykus: sweet) n. Any one of a group of compounds consisting of a pyranose sugar residue, such as glucose, linked to a noncarbohydrate residue (R) by a glycosidic bond: the hydroxyl group (-OH) on carbon-1 of the sugar is replaced by -OR. Glycosides are widely distributed in plants; examples are the anthocyanin pigments and the cardiac glycosides, such as digoxin (see digitalis) and ouabain, which are used medicinally for their stimulant effects on the heart.

glycosidic bond The type of chemical linkage between the monosaccharide units of disaccharides, oligosaccharides, and polysaccharides, which is formed by the removal of a molecule of water (i.e. a condensation reaction). The bond is normally formed between the carbon-1 on one sugar and the carbon-4 on the other. An -glycosidic bond is formed when the -OH group on carbon-1 is below the plane of the glucose ring and a -glycosidic bond is formed when it is above the plane. Cellulose is formed of glucose molecules linked by 1-4 -glycosidic bonds, whereas starch is composed of 1-4 -glycosidic bonds.

glycosidic adj. See glycoside.

glycosidic link See glycosidic bond

glycosidically adv. See glycoside.

gneiss n. A banded or foliated metamorphic rock, usually of the same composition as granite.

Golgi apparatus See Golgi body.

Golgi body An organelle of eukaryotic cells consisting of a series of stacked pouches (cisternae) complexed with networks of tubules. It appears that components of membranes are synthesized and transported in the Golgi body. Varying numbers are found in cells, from one or two to over a hundred. The Golgi body is also the centre for glycoprotein metabolism, and is involved in mitosis and meiosis. In plant cells Golgi bodies play a major role in the synthesis of cellulose derivatives used in the structure of cell walls. Named after Camillo Golgi (1843 - 1926). Also Golgi complex, Golgi apparatus.

Golgi Complex See Golgi body.

Gondwana The ancient continent that is supposed to have fragmented and drifted apart during the Triassic to form eventually the present continents. Also known as Gondwanaland.

Gondwanaland See Gondwana.

gonioautoicous adj. With the androecium bud-like and axillary on the same stem or branch as the gynoecium.

goniocyst n. In lichens, discrete, more or less globular structures from 12 to 40 ĩm diameter, ecorticate granules consisting of photobiont cells intertwined and surrounded by short-celled hyphae never protected by an amorphous covering layer (in Micarea).

gonorrhea n. A sexually transmitted disease caused by gonococcal bacteria that affects the mucous membrane chiefly of the genital and urinary tracts and is characterized by an acute purulent discharge and painful or difficult urination, though women often have no symptoms. Also gonorrhoea.

gonorrhoea See gonorrhea.

gorge n. The throat of a flower.

gossypetin n. A 8-hydroxyflavonoid, a yellow flavonoid.

gossypine (L. gossipinus: a tree, its fruit contains a cotton like stuff) adj. Flocculent; cottony.

gourd n. A climbing, often perennial, plant belonging to the pumpkin family, Cucurbitaceae. This includes cucumbers, melons, and marrows. Several different species are given the name of gourd, although the name is used when referring mainly to Cucurbita species. Other species include the bottle gourd, Lagenaria siceraria, the bitter gourd, Momordica charantia, and the snake gourd, Trichosanthes cucumerina. Although some Cucurbita species have fruits that can be used as a vegetable, most are grown for their hard-skinned fruits which, although inedible, have a multitude of uses. See pepo.

gout n. A disturbance of uric-acid metabolism occurring chiefly in males, characterized by painful inflammation of the joints, especially of the feet and hands, and arthritic attacks resulting from elevated levels of uric acid in the blood and the deposition of urate crystals around the joints. The condition can become chronic and result in deformity.

gracile adj. Slender and graceful.

grade n. A group of organisms with a similar level of organisation, paraphyletic or polyphyletic.

gradualism (L. gradus: step) n. A model of evolution that assumes slow, steady rates of change. Charles Darwin's original concept of evolution by natural selection assumed gradualism. Contrast with punctuated equilibrium.

graduate (L. gradus: step) adj. Divided or marked at regular intervals; with parts of progressively different lengths, as in some Compositae (Asteraceae) in which the outer involucral bracts are shorter than the inner

graft n. Formed from two plants, the stock and the scion, which may be the same or different species, one, the scion; a graft hybrid is a stable association of cells from both stock and scion that makes up a distinctive free-living.

graft chimaera See graft-chimaera.

graft-chimaera n. Plants composed of tissues in intimate association from two different individuals; they originate by grafting name with a plus (+) sign used instead of a X, as for a graft hybrid.

graft hybrid See graft-hybrid.

graft-hybrid n. A sexual hybrid between two or more species or genera, which can be denoted by the botanical names of the parents connected by a multiplication sign (X) formula, or a botanical name for an interspecific hybrid consisting of the generic name followed by a Latin collective epithet, the latter immediately preceded by X; or for an intergeneric hybrid, a `generic name' preceded by X and normally followed by a Latin collective epithet; a `generic' name of a multigeneric hybrid usually consists of a personal name with the suffix -ara.

grain (L. granum: grain, seed) n. A dry single-seeded indehiscent fruit that differs from an achene in that the fruit wall is fused to the testa of the seed. It is the fruit of cereals and grasses. See also caryopsis. The texture of wood, produced by the kinds of xylem cells present.

graminaceous adj. grass-like; pertaining to grass family of plants; related to grain-bearing plants. Also gramineal, gramineous.

gramineal See graminaceous.

gramineous See graminaceous.

graminoids n. Grass-like herbs, with very narrow leaves.

Grammitidaceae n. A family of the phylum Filicinophyta.

Gram negative See Gram stain.

Gram-negative See Gram stain.

Gram positive See Gram stain.

Gram-positive See Gram stain.

Gram's stain See Gram stain.

Gram stain A staining technique for the preliminary identification of bacteria, in which a violet dye is applied, followed by a decolorizing agent and then a red dye. The cell walls of certain bacteria (denoted Gram-positive) retain the first dye and appear violet, while those that lose it (denoted Gram-negative) appear red. [Hans Christian Joachim Gram, Danish physician (1853-1938)]

grana See granum.

granite n. A common, coarse-grained, light-colored, hard igneous rock consisting chiefly of quartz, orthoclase or microcline, and mica, used in monuments and for building.

granular (L. granulum: little grain) adj. With small granules or grains; of the nature of granules; showing a granulated structure. Also granuliferous.

granulate (L. granulum: little grain) adj., b. Of a surface, granular. To form into granules or grains; to become granular.

granulation n. Any soft, pink, fleshy projections that form during the healing process in a wound not healing by first intent. Granulation tissue consists of many capillaries surrounded by fibrous collagen. p>granule (L. granulum: little grain) n. A small grain.

granuliferous (L. granulum: little grain; ferre: to carry) adj. See granular.

granulose (L. granulum: little grain) adj. Roughened with minute, blunt projections; composed of or appearing as if covered by minute grains. Also granular.

granum (L. granum: grain, seed) n. (plural grana) A stack of platelike bodies (thylakoids), many of which are found in plant chloroplasts (each chloroplast contains about 50 grana). Grana bear the light-receptive pigment chlorophyll and contain the enzymes responsible for the light reaction of photosynthesis.

graptolite See Graptolithina.

Graptolithina n. An extinct class of stick-like, colonial, marine organisms that existed from the Middle Cambrian to the Lower Carboniferous. Their fossils are used to establish a stratigraphical time-scale for the Lower Palaeozoic. There were 2 principal orders, Dendroidea and Graptoloidea, and a number of minor, short-lived orders.

grass n. Any of the monocotyledonous, mostly herbaceous plants of the family Gramineae, having jointed stems, slender sheathing leaves, and flowers borne in spikelets of bracts.

gravel n. In Pathology: the sandlike granular material of urinary calculi.

green algae See Chlorophyta.

gregarious (L. gregarius: pertaining to a flock) adj. Growing together in loose tufts or mixed mats; growing in open clusters, not matted together.

grenadine adj. Bright red.

Griesbachian n. The first stage of the Scythian Epoch, overlain by the Nammalian.

griselinoside n. An iridoid glucoside.

groove n. A long narrow channel or depression.

grooved adj. Forming a groove. Marked with long narrow furrows or channels. A general term for sulcate or striate.

ground cover See basal area.

ground meristem The meristem in plant shoots and roots, derived from the apical meristem, that gives rise to the cortex and pith (the ground tissues) in stems and the cortex and endodermis in roots.

ground tissue See ground tissues.

ground tissues All the plant tissues formed by the apical meristems except the epidermis and vascular tissue. A tissue consisting mostly of parenchyma cells that makes up the bulk of a young plant. The principal ground tissues are the cortex, pith, and primary medullary rays, and they consist chiefly of parenchyma. See also collenchyma; sclerenchyma.

groundwater n. All water found under the surface of the ground which is not chemically combined with any minerals present, but not including underground streams.

growth form General description of the type of growth exhibited by a plant, such as herbaceous, shrubby (bush-like) and arborescent (tree-like).

growth substance Any of a number of organic chemicals that are synthesized by plants and regulate growth and development. They are usually made in a particular region, such as the shoot tip, and transported to other regions, where they take effect. See abscisic acid; auxin; cytokinin; ethylene; gibberellin.

grumous (L. grumus: little hillock) adj. In the form of clustered grains, as somme roots.

Guadalupian n. A series in the Upper Permian of N. America, underlain by the Leonardian, overlain by the Ochoan, and roughly contemporaneous with the Ufimian and lower Kazanian Stages.

guard cells A pair of cells which surround a stomate and regulate its size by altering their shape. Cf. stoma.

guide cells Large, highly vacuolated, thin-walled and longitudinally arranged cells found in a median layer across the costa of many mosses, part of conducting parenchyma; e.g., taxa of Pottiaceae characteristically have guide cells sandwiched between two layers of stereid cells in the costal cross-section (sometimes referred to as interstereid cells, deuters, central cells, and socii).

guild n. A group of plants, as parasites, having a similar habit of growth and nutrition.

gum (L. gumen: gum) n. A viscid sap exuding from stems, often air hardened. Any of a variety of substances obtained from plants. Typically they are insoluble in organic solvents but form gelatinous or sticky solutions with water. Most gums are complex polysaccharides. Commercially important examples are gum arabic and gum tragacanth. Gum arabic (or gum acacia) is obtained from various acacia trees; it is used in the manufacture of confectionery, cosmetics, linctuses and other medicinal products, and gummed labels. Gum tragacanth, extracted from trees of the genus Astragalus, forms a thick mucilage in water; it is used in the manufacture of pills and confectionery and as a sauce thickener. Gum resins are mixtures of gums and natural resins. Gums are produced by the young xylem vessels of some plants (mainly trees) in response to wounding or pruning. The exudate hardens when it reaches the plant surface and thus provides a temporary protective seal while the cells below divide to form a permanent repair. Excessive gum formation is a symptom of some plant diseases.

gummosis (L. gumen: gum) n. A pathological condition in certains plants, characterized by the excessive formation of gum.

guttation (L. gutta: drop) n. Formation of drops of water on plants from moisture in air; the process of water being exuded from hydathodes at the enlarged terminations of veins around the margins of the leaves.

guttulate adj. With cell lumen rounded because of strong wall thickening; resembling drops of oil or resin.

gymnocarpous (Gr. gymnos: uncovered, naked; karpos: fruit) adj. Of a fungus or lichen having the apothecium open and attached to the surface of the thallus.

gymnogynous (Gr. gymnos: uncovered, naked; gynę: female) adj. having a naked ovary.

gymnosperm (Gr. gymnos: uncovered, naked; sperma: seed) n. Generally any seed plant which does not produce flowers. The term may or may not exclude the pteridosperms. Any plant whose ovules and the seeds into which they develop are borne unprotected, rather than enclosed in ovaries, as are those of the flowering plants (the term gymnosperm means naked seed). In traditional systems of classification such plants were classified as the Gymnospermae, a class of the Spermatophyta, but they are now divided into separate phyla: Coniferophyta (conifers), Cycadophyta (cycads), Ginkgophyta (ginkgo), and Gnetophyta (e.g. Welwitschia). A group of plants, most of which are trees, whose sole consistent characteristic is that their seeds are not enclosed within a fruit but are borne naked, in many species on cone scales. Gymnosperms originated in the late Devonian period (about 380 million years ago). They were formerly classified as a class, Gymnospermae, but are now generally split into separate phyla (or divisions): Coniferophyta (see conifer); Ginkgophyta (see ginkgo); Cycadophyta (see cycad); Gnetophyta (e.g. welwitschia); and several extinct orders, including the Cycadofilicales (see seed fern) and the Cordaitales. Cf. angiosperm.

Gymnospermae (Gr. gymnos: uncovered, naked; sperma: seed) n. An important division of the plant kingdom, being woody plants with alternation of generations, having the gametophyte retained on the sporophyte and seeds produced on the surface of the sporophylls and not enclosed in an ovary. See Pinopsida.

gymnospermous (Gr. gymnos: uncovered, naked; sperma: seed) adj. Of or pertaining to a gymnosperm; having naked seeds.

gymnospore (Gr. gymnos: uncovered, naked; spora: seed) n. A naked spore, espacially one not produced in a sporangium or not having a protective envelope.

gymnostomous adj. Lacking a peristome.

gynaeceum See gynoecium

gynaecia See gynaecium.

gynaecium n. (pl. gynaecia) See gynoecium.

gynandria See gynandrium.

gynandrial See gynandrous.

gynandrium (Gr. gynę: female; anęr, andros: male) n. (pl. gynandria) A column bearing stamens and pistils.

gynandrous (Gr. gynę: female; anęr, andros: male; gynandros: hermaphodite) adj. With the stamens adnate to the pistil, i.e. with stamens and pistils fused into a column, as in orchids. Syn. gynandrial.

gynantherous (Gr. gynę: female; anthęros: flowered) adj. Having the stamens coverted into pistils by the action of frost, disease, or insects.

gynecandrous (Gr. gynę: female; anęr, andros: male) adj. Having staminate and pistillate flowers in the same spike or spikelet, the latter above the former, as in the inflorescence of some Carex species. cf androgynous.

gynecia See gynecium.

gynecium n. (pl. gynecia) See gynoecium.

gynobase (Gr. gynę: female; L. basis: base) n. An enlargement or prolongation of the receptacle bearing the ovary, as in the flowers of the Boraginaceae..

gynobasic (Gr. gynę: female; L. basis: base) adj. Of a style, arising near the base of the gynoecium, e.g. between the lobes of the ovary. i.e. a style which is attached to the gynobase as well as to the carpels.

gynocardin n. A cyclopentenoid cyanogenic glycoside.

gynodioecious (Gr. gynę: female; dyo: two; oikos: house) adj. Having bisexual flowers and female flowers, on separate plants, i.e. having pistillate and perfect flowers on separate plants.

gynodioecy n. The fact of being gynodioecious.

gynoecia See gynoecium.

gynoecious A plant having all pistillate flowers (sometimes called all-female). Cf. androecious, andromonoecious, dioecious, gynomonoecious, hermaphroditic, monoecious, trimonoecious.

gynoecium (Gr. gynę: woman; oikos: house) n. (pl. gynoecia) All of the female sex organs, i.e. the carpels or pistils, with their stigmas and styles, of a flower, collectively; the female gametoecium, consisting of archegonia and the surrounding bracts (perichaetial leaf or involucre). Syn. gynecium, gynaeceum, gynaecium.

gynogametophyte n. Infrequently used term for the female gametophyte. Cf. androgametophyte, androgynogametophyte.

gynomonoecious (Gr. gynę: female; monos: alone, single; oikos: house) adj. With perfect and pistillate flowers on the same plant. Cf. androecious, andromonoecious, dioecious, gynoecious, hermaphroditic, monoecious, trimonoecious.

gynophore (Gr. gynę: woman; phora, carrying) n. A stalk supporting the ovary; a stalk bearing the gynoecium above the level of insertion of the other floral parts.

gynosporangia See gynosporangium.

gynosporangium (Gr. gynę: female; spora: seed, aggeion: vase) n. (pl. gynosporangia) The receptacle in which gynospores are developed.

gynospore (Gr. gynę: female; spora: seed) n. See megaspore.

gynostegia See gynostegium.

gynostegial corona In Asclepiadaceae, a collective term for the staminal and interstaminal coronas, both of which are associated with the gynostegium. Cf. staminal corona.

gynostegium (Gr. gynę: female; stegos: shelter, roof) n. (pl. gynostegia) A structure formed from the fusion of the anthers with the stigmatic region of the gynoecium, as in the Asclepiadaceae. A protective covering for a gynaecium, especially as formed by the union of stamens and style. See column.

gynostemia See gynostemium.

gynostemial adj. Related to the gynostemium. See gynostemium.

gynostemium (Gr. gynę: female; stęmôn: thread) n. (pl. gynostemia) The central reproductive stalk of an orchid, which consists of a stamen and pistil fused together.

gyrate (L. gyratus: wheeled around, turned) adj. Curved into a spiral, circinate; in rings; coiled or convoluted.

gyrose adj. Said of an apothecial disc, concentrically folded or ridged, especially in Pannaria, Psoroma, Umbilicaria.

gyrothecal adj. With a sheath of tissue; found at the base of endogenous and certain exogenously developed, collared branches in some liverworts.