labellum (L. labellum: small lip) n. (pl. labella) The peculiar upper (but by a twist of the pedicel apparently lower) petal of the Orchidaceae, usually large and unlike the others. In Zingiberaceae (ginger family) and Costaceae, a usually showy petaloid structure, staminodal in origin.

labia See labium.

labiate (L. labia: lip) adj., n. With parts which are arranged like lips or shaped like lips; pertaining to a member of the Labiatae (Lamiaceae). A plant of the large family Labiatae.

labium (L. labium: lip) n. (pl. labia). The lower lip of a bilabiate corolla.

labriform adj. Lip-shaped, said especially of soralia.

lacerate (L. laceratus: torn, ripped) adj. Said of a margin cut or cleft irregularly as if torn; e.g. the leaves of Sphagnum riparium. Syn. lacerated.

lacerated adj. See lacerate.

lachrymiform (L. lachrima: tear; forma: shape) adj. See lacrymiform.

lacinia (L. lacinia: flap of a garment) n. (pl. laciniae) An irregular narrow strip; an appendage coarser than a cilium and more than one cell wide; a narrow, linear-elongate lobe of a foliose lichen, often arising from the primary lobes.

laciniae See lacinia.

laciniate (L. lacinia: flap of a garment) adj. Cut into narrow, jagged, irregular pointed lobes or segments; fringed with lacinia. Also laciniated.

laciniated See laciniate.

lacrymiform (L. lacrima: tear; forma: shape) adj. Tear-shaped, i.e. more or less ovoid or obovoid. Syn. lachrymiform

lactescency n. See lactescent.

lactescense n. See lactescent.

lactescent (L. lactescere: to become milky) adj. Secreting or producing a milky juice.

lacticifer See lactifer.

lacticiferous See lactiferous.

lactifer (L. lac, lactis: milk; ferre: to carry) n. A latex duct, which may or may not produce the milky sap. Syn. lacticifer.

lactiferous (L. lac, lactis: milk; ferre: to carry) adj. Describing a plant with a milky sap; producing latex. Syn. lacticiferous.

lactone n. A cyclic compound with a 5-6-membered ring in which the chain is closed by ester formation between a carboxyl and a hydroxyl group in the same molecule.

lacuna (L. lacuna: cavity, hole, ditch, pit) n. (pl. lacunae) A gap, depression or cavity in the tissues of an organism; for example, the hollow centre of certain plant stems or any of the small cavities in bone in which the bone-forming cells are found. An empty air space or gap within a tissue.

lacunae See lacuna.

lacunate (L. lacuna: cavity, hole, ditch, pit) adj. With air spaces or chambers in the midst of tissue.

lacunose (L. lacuna: cavity, hole, ditch, pit) adj. Perforated with holes; e.g., the surface of various thalloid liverworts.

lacustrine (L. lacus: lake, tank) adj. Growing around lakes.

laesura n. (pl. laesurae) The arm of a proximal fissura or scar of a spore. A monolete spore has one laesura, a trilete spore three (although some palynologists consider a trilete spore to have a single triradiate laesura). A laesura comprises a commissure which may be bordered by a margo (lab rum).

laesurae See laesura.

laevigate (L. levigatus: made smooth, polished) adj. Lustrous; shining; having a smooth surface, as if polished. Syn. levigate.

lageniform (L. lag­na: bottle, flask; forma: shape) adj. Shaped like a bottle or flask; having an enlarged base, tapering to a narrow neck.

lamella (L. lamella: little strip) n. (pl. lamellae) A thin, plate-like scale, membrane, or layer as a gill of a mushroom; middle lamella, the layer between the walls of two adjacent cells; an erect scale or blade inserted at the junction of the claw and limb in some corollas and forming part of their corona or crown; in mosses: parallel photosynthetic ridges or plates along a leaf blade, costa or thallus; e.g. Polytrichum, Pterygoneurum, Petalophyllum; the plates of secondary wall deposition occurring between trabeculae on the dorsal and ventral surfaces of an arthrodontous peristome. A thin layer, membrane, or plate of tissue.

lamellae See lamella.

lamellar (L. lamella: little strip) adj. Referring to a lamella or lamellae; lamellate.

lamellate (L. lamella: little strip) adj. Made up of thin plates or lamina; flat, plate-like; with parallel green ridges. Syn. lamellose,

lamellose See lamellate.

lamina (L. lamina: thin piece [of metal, wood...]) n. (pl. laminae or laminas) The surface of a leaf excluding the petiole; the thin and usually flattened blade of a leaf, in which photosynthesis and transpiration occurs; the bulk of the lamina is made up of mesophyll cells interspersed by a network of veins (vascular bundles); the mesophyll is enclosed by a protective epidermis that produces a waxy cuticle. The leaflike part of the thallus of certain algae, notably kelps. In bryophytes, the flattened, generally unistratose and green part of the leaf blade excluding the costa and border; the expanded part of a thallus. A narrow, linear-elongate lobe of a foliose lichen, often arising from the primary lobes. See also stipe.

laminae See lamina.

laminal (L. lamina: thin piece [of metal, wood...]) adj. Superficial on the surface of thalli or lobes of lichens. On or pertaining to upper surface.

laminar (L. lamina: thin piece [of metal, wood...]) adj. Thin, flat, and expanded, as the blade of a leaf; composed of or arranged in laminae. Syn. laminal.

laminarin n. A beta-glucan polysaccharide produced by many chromists through photosynthesis.

laminary adv. See laminar.

laminate (L. lamina: thin piece [of metal, wood...]) adj. With plates or layers; separating into plates or layers; composed of or having a lamina or laminae. Syn. laminous, laminose.

laminose (L. lamina: thin piece [of metal, wood...]) adj. See laminate.

laminous (L. lamina: thin piece [of metal, wood...]) adj. See laminate.

lampshells See Brachiopoda.

lanate (L. lanatus: covered with wool, woolly) adj. Wooly, with long intertwined, curled hairs. Syn. lanose.

lance-linear adj. Long, thin and pointed.

lanceolate (L. lancea: spear, pike, lance) adj. Shaped like a lance; broadest toward the base and narrowed to the apex, several times longer than wide; specifically tapering to a point at the apex and sometimes at the base. Of a leaf, about four times as long as it is broad, broadest in the lower half and tapering towards the tip.

lanceolately adv. See lanceolate.

land capability See capability.

land race Mixture of genotypes of an inbred crop locally adapted as a population; now largely superseded in most areas of crop culture but used and useful in less developed countries.

lanolin (L. lana: wool) n. A purified wax extracted from wool. It is a mixture of cholesterol and other sterols, aliphatic alcohols, and esters. Because it is easily absorbed by the skin, lanolin is used as a base for creams, soaps, and other skin preparations.

lanose See lanate.

lanuginose See lanuginous.

lanuginous (L. lanugineus: downy) adj. Downy or woolly; with soft downy hairs.

lanugo (L. lanago: wool, cotton of plants) n. A covering of soft downy hairs.

lanulose (L. lanula: small flock of wool) adj. Diminutive of lanate; minutely woolly.

lateral (L. lateralis: of the sid) adj. At or near edge, especially side or secondary branches. Cf. basal and terminal.

lateral bud A bud borne in the axil of a previous season's leaf.

lateral meristem See cambium.

latex (L. latex: liquid) n. A liquid, often milky, emulsion found in certain flowering plants. It has a complex composition and its function in the plant is not fully understood. The latex of the rubber tree is used in rubber manufacture, while opium and morphine are obtained from the latex of the opium poppy. A viscous fluid exuded from the cut surfaces of the leaves and stems of certain plants.

latexy adv. See latex.

laticifer (L. latex, laticis: liquid; ferre: to carry) n. A tube or channel or cell or group of celle containing latex.

laticiferous (L. latex, laticis: liquid; ferre: to carry) adj. Bearing or containing latex.

latifoliate (L. latus: broad, wide; folia: leaf) adj. With broad leaves.

latifolious adj. See latifoliate.

latiseptate (L. latus: broad, wide; septum: fence, partition) adj. With broad partitions, with a broad septum. Cf. angustiseptate.

latrorse adj. Dehiscing longitudinally and laterally. Of anthers, opening laterally towards adjacent anthers. Turned sideways, i.e. not or away from axis.

lauric acid A saturated fatty acid.

lax adj. Loosely arranged.

laxative adj., n. Having a tendency to loosen or relax; having the effect of loosening or opening the intestines, and relieving from constipation opposed to astringent). A laxative medicine.

leader n. The terminal shoot of a tree or branch

leaf n. A flattened structure that develops from a superficial group of tissues, the leaf buttress, on the side of the stem apex. Each leaf has a lateral bud in its axil. Leaves are arranged in a definite pattern (see phyllotaxis) and usually show limited growth. Each consists of a broad flat lamina (leaf blade) and a leaf base, which attaches the leaf to the stem; a leaf stalk (petiole) may also be present. The leaves of bryophytes are simple appendages, which are not homologous with the leaves of vascular plants as they develop on the gametophyte generation. Leaves show considerable variation in size, shape, arrangement of veins, type of attachment to the stem, and texture. They may be simple or divided into leaflets, i.e. compound. Types of leaf include: cotyledons (seed leaves); scale leaves, which lack chlorophyll and develop on rhizomes or protect the inner leaves of a bud; foliage leaves, which are the main organs for photosynthesis and transpiration; and bracts and floral leaves, such as sepals, petals, stamens, and carpels, which are specialized for reproduction. Leaves may be modified for special purposes. For example the leaf bases of bulbs are swollen with food to survive the winter. In some plants leaves are reduced to spines for protection and their photosynthetic function is carried out by another organ, such as a cladode. Usually flattened, usually green plant structure being most often the primary organ of photosynthesis.

leaf axil The angle between a petiole and the stem.

leaf blight Any of various diseases which lead to the browning and dropping of a plants leaves.

leaf bud A bud which contains undeveloped leaves.

leaf curl A disease that causes leaves to roll up.

leaf gap A break in a stem's vascular tissue above the leaf trace.

leaf trace In nodal anatomy, a vascular bundle supplying a leaf. The strand of vascular tissue which connects the leaf veins to the central vascular system of the stem.

leaflet n. A single division of a compound leaf. One of the ultimate segments of a compound leaf.

leaf primordium A lateral outgrowth from the apical meristem that develops into a leaf.

leafscar See leafscar.

leaf scar The mark remaining after the leaf falls off a twig.

leafstalk n. Petiole.

lecanorine adj. Said of an apothecium, with a thalline exciple, photobiont in margin.

lecideine adj. Said of an apothecium, with a proper exciple, without photobiont in margin.

lectin See lectins.

lectins n. A group of hemagglutinating proteins (hemagglutinins) found primarily in plant seeds, which bind specifically to the branching sugar molecules of glycoproteins and glycolipids on the surface of cells.

lectotype (Gr. lektos: chosen; typos: mark, image) n. A specimen selected from among those cited with the original description to serve in place of a holotype where the holotype is missing or destroyed, or where no holotype was designated.

legitimate adj. The name of a taxon is legitimate when published validly in accordance with the roles of nomenclature set out in either the Code of Nomenclature of cultivated Plants or the Code of botanical Nomenclature.

legume (L. legumen: vegetable [especially those wiht pod, hull]) n. A 1-locular fruit, usually dehiscent along two sutures, bearing seeds along the ventral suture; a leguminous plant. A fruit characteristic of the families Mimosaceae, Caesalpiniaceae and Fabaceae, formed from one carpel and either dehiscent along both sides, or indehiscent; in particular, such a fruit that is grown as an edible crop; a crop species in the family Fabaceae.

leguminous (L. legumen, leguminis: vegetable [especially those wiht pod, hull]) adj. Of or pertaining to a legume or a member of the Leguminosae (Fabaceae); legume-like

leiodont n. A ype of nematodontous peristome found in the Polytrichales that lacks a longitudinal wing-like crest on the inner (ventral) surface. Cf. pterygodont.

lemma (Gr. lemma: husk, peel) n. One of two bracts that protects the floret of grasses. The lemma is situated beneath the second (smaller) bract, known as the palea, which it surrounds. See spike.

lentic (L. lentus: slow) adj. Of, relating to, or living in still water. Cf. lotic.

lenticel (L. lenticula: lentil) n. A loosely-packed mass of cells in the bark of a woody plant, visible on the surface of a young stem as a raised powdery spot, somewhat corky, often lens-shaped, through which gaseous exchange occurs, between the inner tissues and the atmosphere. Also lenticle.

lenticellate (L. lenticulatus: lentil-shaped) adj. With lenticels

lenticle n. See lenticel.

lenticular (L. lenticula: lentil) adj. Shaped like a double-convex (biconvex) lens; e.g. the gemma of Oedipodiella, the apical cell with two segmenting surfaces as in Metzgeria, Fissidens.

lenticulate (L. lenticula: lentil) adj. See lenticular.

lentiform (L. lens, lentis: lentil; forma: shape) See lenticular.

lentiginose (L. lentigo, lentiginis: freckles) adj. Covered with minute dots; freckled, speckled. Syn. lentiginous. See scurfy.

lentiginous See lentiginose.

Leonardian A series in the Lower Permian of N. America, underlain by the Wolfcampian, overlain by the Guadalupian, and roughly contemporaneous with the Artinskian and Kungurian Stages. In some areas it is zoned by the use of fusilinid foraminiferids. It is the N. American equivalent of the Rotliegende. Red-bed localities of Wolfcampian-Leonardian age in Texas and Colorado have yielded many vertebrate fossils.

lepidoid (Gr. lepis, lepidos: scale; eid˘: to look like) adj. Scale-like.

Lepidopter (Gr. lepis, idos: scale; pteron: feather, wing.) n. One of the Lepidoptera.

Lepidoptera (Gr. lepis, idos: scale; pteron: feather, wing.) n. pl. An order of insects, which includes the butterflies and moths. They have broad wings, covered with minute overlapping scales, usually brightly colored. They have a tubular proboscis, or haustellum, formed by the two slender maxillŠ. The labial palpi are usually large, and the proboscis, when not in use, can be coiled up spirally between them. The mandibles are rudimentary. The larvŠ, called caterpillars, are often brightly colored, and they commonly feed on leaves. The adults feed chiefly on the honey of flowers.

lepidote (Gr. lepid˘tos: covered with scales) adj., n. (Covered with) small, membranous, scurfy scale(s) or scaly spot(s).

leprose adj. Having the surface dissolved into soredia, loose, powdery, without any cortex.

leprous (Gr. lŕpros: scaly, rough) adj. Scurfy, covered with tiny scales. Also lepidote.

leptocaul (Gr. leptos: thin; kaulos: stem) Twiggy, with abundant, relatively slender branches; with a thin primary stem. Also leptocladous.

leptocladous (Gr. leptos: thin; klados: branchlet) See leptocaul.

leptodermous (Gr. leptos: thin; derma: skin) adj. Thin-walled; thin-coated; applied to capsules when soft and pliable.

leptokurtic n. A flat-topped, bell-shaped curve of frequency distribution.

leptoid n. The photosynthate conducting cells of bryophytes; cf. hydroid.

leptom See leptome.

leptome n. A phloem-like tissue consisting of leptoids and parenchymatous cells. Also leptom.

leptosphyllous (Gr. leptos: thin; phyllon: leaf) adj. Having long, slender leaves.

leptosporangia See leptosporangium.

leptosporangiate (Gr. leptos: thin; spora: seed; aggeion: vase, bowl, container) adj. Of ferns, having sporangia with walls only one cell thick. Cf. eusporangiate.

leptosporangium (Gr. leptos: thin; spora: seed; aggeion: vase, bowl, container) n. (pl. leptosporangia) A thin-walled sporangium originating from a single epidermal cell. This is a derived character state in the fern clade; cf. eusporangium.

lethal gene A gene that renders inviable an organism or cell possessing it.

leucoanthocyanin Same as proanthocyanidin.

leucobryoid adj. Having leaves in cross section with inner layer(s) of chlorocyst sandwiched between outer layers of hyalocyst; e.g. Leucobryum, Theriotia .

leucodelphinidin n. A proanthocyanidin.

leucoplast (Gr. leukos: white; plastos: formed, modelled) n. Any of various organelles in plant cells that contain no pigment and are therefore colourless. Leucoplasts are usually found in tissues not normally exposed to light and frequently contain reserves of starch (in amyloplasts), protein, or oil. See plastid. Cf. chromoplast.

leukorrhea (Gr. lenkas: white; re˘: to flow) n. A discharge of a white, yellowish, or greenish, viscid mucus, resulting from inflammation or irritation of the membrane lining the genital organs of the female. Also leucorrhea.

leucorrhea See leukorrhea.

levigate See laevigate.

liana n. A plant that germinates on the ground and maintains soil contact while using another plant for support. Grape vines are typical lianas. See liane.

liane n. A climbing or twining plant (usually applied to woody climbers); it climbs via tendrils, hooks, pads, aerial roots, or other mechanisms. See liana.

lianoid adj. Vine-like. See liana, liane.

lianous adj. See liana, liane.

liber (L. liber: liber [living part of bark]) n. Phloem.

libriform (L. liber, libris: liber; forma: shape) adj. Having the form of or ressembling liber or phloem.

libriform fibre A fiber that has bordered pits found in wood tissue.

lichen An organism formed by the symbiotic association of an alga and a fungus. They form a large group of organisms (about 15 000 species) consisting of two components, an alga or a bacterium (usually a green alga or blue-green bacterium) and a fungus (usually an ascomycete), in a mutually beneficial association. Millions of algal or bacterial cells (the phycobiont) are interwoven with fungal filaments (the mycobiont) to form the lichen body (a thallus), which may be crusty, scaly, leafy, or stalked and shrublike in appearance. Lichens were formerly regarded as plants; they are now classified as fungi. They occur in almost all areas of the world, mainly on tree trunks, rocks, and soil, and can survive in extremely harsh conditions. They normally reproduce asexually by fragmentation, budding, or by producing special structures (soredia), consisting of a few algal or bacterial cells enmeshed with fungal threads. Lichens are an important source of food for browsing animals of tundra regions (reindeer moss) and they are used by humans for food, dyes, medicine, in perfume, and as pollution indicators. Cf. crottle; oak moss; orchil; rock tripe.

lichenicolous adj. Growing on lichens.

life cycle The complete sequence of events undergone by organisms of a particular species from the fusion of gametes in one generation to the same stage in the following generation. In most animals gametes are formed by meiosis of germ cells in the reproductive organs of the parents. The zygote, formed by the fusion of two gametes, eventually develops into an organism essentially similar to the parents. In plants, however, the products of meiosis are spores, which develop into plants (the gametophyte generation) often very different in form from the spore-forming (sporophyte) generation. The sporophyte generation is restored when gametes, formed by the gametophyte generation, fuse. See alternation of generations.

life forms A classification of the growth forms of plants based on the position of the resting buds and the duration of the life of the shoot.

lignan n. A colorless, crystalline, solid, dimeric compound derived from precursors related to those involved in the formation of lignin, i.e. the union of two units of phenylpropane, cinnamic acid, or their derivatives, through their aliphatic side-chains, they occur in chiral forms (as opposed to lignins).

ligneous (L. ligneus: woody) adj. Woody; of the nature of or ressembling wood. Syn. lignose.

lignicolous (L. lignum, ligni: wood; colere: to inhabit) adj. Growing on or in wood, as certains mosses, lichens, or fungi.

lignification n. See lignify.

lignified (L. lignum, ligni: wood) adj. Converted into wood. Cf. lignify.

lignify (L. lignum, ligni: wood) vt. To convert into wood or woody tissue; to become wood or woody by chemical and physical changes in the cell walls that convert some or all of the constituents into lignin or lignocellulose.

lignin (L. lignum, ligni: wood) n. The chief noncarbohydrate constituent of wood; organic substances which act as binders for the cellulose fibers in wood and certain plants, and adds strength and stiffness to the cell walls; lignin is composed of a polymer of high carbon content but distinct from the carbonates.

lignocellulose (L. lignum: wood; cellula: cell [of a monk]) n. Alternative name for lignin.

lignose See ligneous.

lignotuber (L. lignum: wood; tuber: bump, outgrowth) n. A woody swelling below or just above the ground, containing adventitious buds from which new shoots develop if the top of the plant is cut or burnt (common in the shrubby eucalypts and in many other fire-tolerant Australian shrubs).

ligula (L. ligula: little tongue) n. (pl. ligulae) A tonguelike or strap-shaped part of an organ; a ligule.

ligulae See ligula.

ligulate (L. ligula: little tongue) adj. Having or pertaining to ligules; strap-shaped; narrow, moderately long, with the sides parallel.

ligule (L. ligula: little tongue) n. A strap-shaped structure; a hyaline, membranous or hairy appendage on the adaxial surface of a leaf, especially in grasses, at the junction between sheath and blade; a small adaxial appendage near the leaf base in some pteridophytes, e.g. a tongue-like projection borne at the base of the leaves above the sporangia in Isoetes; the corolla limb in ray flowers of Asteraceae.

liguliform (L. ligula: little tongue; forma: shape) adj. Strap-shaped. See ligule.

limb (L. limbus: border, edge) n. A branch of a tree. The expanded portion of any petal, or of a leaf, such as the expanded portion of a gamopetalous corolla above the throat. The upper part of a leaf as distinct from the leaf base. The spreading part of a synsepalous calyx or sympetalous corolla, usually referring only to the calyx or corolla lobes, sometimes to their lips. The upper, free, spreading portion of a corolla or perianth that is connate at the base.

limbate (L. limbus: border, edge) adj. Bordered, as in a leaf or flower in which one color forms an edging or margin around another; bordered by distinct, elongate and incrassate marginal cells; e.g. Fissidens, Syrrhopodon.

limbidia See limbidium.

limbidium n. (pl. limbidia) A Border, a differentiated leaf margin; e.g. in Fissidens bryoides.

lime n. Any of various mineral and industrial forms of calcium oxide differing chiefly in water content and percentage of constituents such as silica, alumina, and iron.

limen (L. limen: threshold, start) n. A cup-like structure at the base of the androgynophore in Passiflora.

limestone n. A common sedimentary rock consisting mostly of calcium carbonate, used as a building stone and in the manufacture of lime, carbon dioxide, and cement.

limicolous adj. Growing in mud, margin of pools or lakes.

limnodophilous adj. Thriving in marshes.

limnology (Gr. limnŕ: marsh, lake, pond; logos: word, reason) n. The scientific study of physical, chemical, meteorological, and biological conditions in fresh waters, lakes, rivers, etc.

limonoid n. A type of triterpenoid (tetranortripterpenes), bitter compound, pentacyclic, with a furan ring attached as a side chain.

linea fissura An inconspicuous line on the surface of the seed coat that delimits a more or less circular area, an areole, as in Fabaceae and Mimosoideae.

linea lucida of the testa or tegmen, A bright line running periclinally through heavily thickened palisade cells of the testa or tegmen, often separating more or less thickened parts of the cells.

lineage (L. linea: line) n. Any continuous line of descent; any series of organisms connected by reproduction by parent of offspring.

lineage pattern The direct line of descent from an initial to the mature tissue or organ.

linear (L. linea: line) adj. Long and slender with parallel or nearly parallel sides, as in blades of grass. Narrow with untapering margins and a length to breadth ratio between 6 to 1 and 3 to 1.

lineate adj. Marked with parallel lines.

line breeding A system of breeding in which a number of genotypes which have been progeny tested in respect to some character or group of characters are composited to form a variety.

line varieties One or more lines of self-fertilizing or cross-fertilizing plants and single-line facultative apomicts with largely the same genetic background (a theoretical coefficient of parentage of 0.87 or higher and 95% apomixis for the single-line facultative apomicts, except in cases in which it is not possible to achieve 95% apomixis; a level as low as 80% may be classed as line varieties even though the variant plants present may differ in morphological characteristics) which are similar in essential and distinctive characteristics and are maintained or reproduced by controlled self-fertilization or sib-fertilization or line crossing of the plants (for self-fertilizing or cross-fertilizing plants) and by close generation control (for single-line facultative apomicts). Examples of line varieties from normally self-fertilized crops: `Gaines' wheat, `tendercrop' snap bean, `Wayne' soybean; examples of line (inbred) varieties for normally cross-fertilized crops: `MSU-713-5' gynoecious cucumber, `WF9' corn, `Nittany Lion Red' geranium, `B2108A x B2108B' (line cross of onion, `B2215C' onion; examples of single-line facultative apomicts meeting 95% apomixis requirement): `Penstar' Kentucky bluegrass, `Merion' Kentucky bluegrass; examples below 95% apomixis; `Adelphi Kentucky' bluegrass and `Bristol Kentucky' bluegrass.

linguiform (L. lingua: tongue; forma: shape( adj. Tongue-shaped.

lingulate (L. lingula: little tongue) adj. Strap-shaped; longer than linear but shorter than fasciarate, with a length to breadth ratio of between 6 to 1 and 12 to 1; tongue-shaped; oblong with a slightly broadened apex. Cf. ligulate.

liniment n. A medicinal fluid rubbed into the skin to soothe pain or relieve stiffness.

linkage n. The association of characters in inheritance due to location of genes in proximity on the same chromosome.

linkage group See Linkage.

linkage map Map of position of genes in chromosomes determined by recombination relationships.

linkage value Recombination fraction expressing the proportion of crossovers versus parental types in a progeny. The recombination fraction can vary from zero to one half.

linoleic acid An unsaturated fatty acid essential to nutrition. Linoleic acid occurs in many plant glycerides. it is predominant in most edible vegetable oils.

lip n. The upper or lower part of a bilabiate calyx or corolla; the peculiar upper (but by a twist of the pedicel apparently lower) petal in orchids. One of the two projections or segments of an irregular, two-lipped corolla or calyx; a labium.

lipid (Gr. lipos: fat, oil) n. Any of the group of lipids. See lipids.

lipids (Gr. lipos: fat, oil) n. A group of compounds, generally insoluble in water but soluble in organic solvents, that includes fats and oils, waxes, phospholipids, sphingolipids, and steroids. Fats and oils function as energy reserves in plants and animals and form a major source of dietary energy in animals. Phospholipids are important structural components of cell membranes, and sphingolipids are found predominantly in nerve tissues. Steroids have many important derivatives, including cholesterol, bile salts, and certain hormones. Prostaglandins, carotenoids, and terpenes are also classified as lipids. Lipids often occur in association with proteins as lipoproteins.

lirella (diminutive of L. lira: ridge, furrow) n. (pl. lirellae) The elongated, narrow apothecium of certain lichens. An ascoma with a long, narrow disc often branching or more or less stellate. E.g. Graphis, Phaeographis, etc.

lirellae See lirella.

lirellate (diminutive of L. lira: ridge, furrow) adj. Of, pertaining to, or ressembling a lirella.

lithocyst n. An enlarged epidermal cell, usually of a leaf, containing a cystolith.

lithology (Gr. lithos: stone; logos: word, reason) n. The description of the macroscopic features of a rock, e.g. its texture or petrology.

lithontripic adj. Having the quality of, or used for, dissolving or destroying stone in the bladder or kidneys.

lithontriptic adj. ; n. Having the quality of, or used for, dissolving or destroying stone in the bladder or kidneys; a lithontriptic remedy or agent, as distilled water.

lithophyte (Gr. lithos: stone; phyton: plant) n. A plant that grows on rock and derives its nourishment chiefly from the atmosphere.

lithophytic adj. See lithophyte. Also epilithic.

littoral adj. Growing along the shore.

liver spots Flat brown-black spots that usually occur in sun-exposed areas of the body. They are also called age spots. They are unrelated to the liver or liver function. Also written liverspots.

liverspots See liver spots.

liverwort n. A bryophyte plant of the phylum Hepatophyta (c. 6000 species), found growing on moist soil, rocks, trees, etc. There are two groups: leafy liverworts, in which the plant body is differentiated into stems and leaves; and thallose liverworts, which have a flat lobed liverlike body (thallus). The liverwort plant is the gamete-producing phase (gametophyte) and gives rise to a capsule, the spore-producing phase (sporophyte), which is sometimes borne on a slender erect column. See also hornwort.

livid (L. lividus: bluish, blackish) adj. Pale grayish-blue

living fossil An organism that has persisted, essentially unchanged, since its first appearance. For example, Lingula (a brachiopod) has remained much the same since Ordovician times and Sphenodon (tuatara) since the early Mesozoic.

loam n. A rich soil consisting of a mixture of sand and clay and decaying organic materials.

loamy adv. See loam.

lobate (Gr. lobos: lobe) adj. In the form of a lobe; lobed.

lobe (Gr. lobos: lobe) n. Any segment of an organ, as of a leaf, especially if rounded.

lobed (Gr. lobos: lobe) adj. Bearing lobes which are cut less than half way to the base or midvein. Divided into usually rounded segments.

lobed leaf A leaf whose margin is shallowly divided, i.e. cut to about the middle, i.e. midway between margin and midrib.

lobulate (diminitive of Gr. lobos: lobe) adj. Divided into small lobes; having small or indistinct lobes; with lobules.

lobule (diminitive of Gr. lobos: lobe) n. A small lobe; a lobe-like subdivision of a lobe.

locellate adj. Divided into locelli. See locellus.

locelli See locellus.

locellus (L. locellus: box) n. (pl. locelli ) A compartment of a cell.

lochmocolous adj. Dwelling in thickets.

loci See locus.

locular (L. loculus: small spot, small box) adj. Having a cavity or chamber inside the ovary, anther or fruit. Having the nature of, or consisting of cells. Of or pertaining to locules; with locules. Syn. loculate.

loculate See locular.

locule (L. loculus: little spot, little box) n. A compartment of an anther, ovary, or fruit. The chamber or cavity (cell) of an organ, as in the cell of an ovary containing the seed or the pollen bearing compartment of an anther. An enclosed compartment within an organ e.g. an ovary, an anther.

loculi See loculus.

loculicidal (L. loculus: little box, little spot; cŠdes: cutting) adj. Dehiscent dorsally down the middle of carpels. Of the dehiscence of a fruit, along lines coinciding with the centres of loculi. Dehiscing through the locules of a fruit rather than through the septa. Cf. septicidal and poricidal. Pertaining to small separate cavities.

loculus n. (pl. loculi) See locule.

locus (L. locus: spot, place) n. (plural loci) The position of a gene on a chromosome or within a nucleic acid molecule. The two alleles of a gene occupy the same locus on homologous chromosomes.

locusta n. (pl. locustae) The spikelet of grasses.

locustae See locustae.

lodicule (L. lodicula: little blanket) n. One of a pair of tiny scales in a grass floret, between the lemma and the fertile parts of the flower, which may be reduced perianth segments, and be involved in the opening of the floret at the time of pollination.

loess n. A light-coloured fine-grained accumulation of clay and silt particles that have been deposited by the wind.

loganin n. A route-I iridoid.

loment (L. lomentum: bean flour) n. A type of dry dehiscent fruit formed from a single carpel but divided into one-seeded compartments by constrictions between the seeds. Legumes (e.g. those of Acacia) and siliquas (e.g. those of wild radish) can be divided in this way. Syn. lomentum.

lomenta See lomentum.

lomentaceous adj. Loment-like; with loments

lomentiform adj. Loment-like.

lomentum n. (pl. lomenta) See loment.

long-day plant A plant that requires more than 12 hours of daylight before flowering will occur.

longitudinal adj. Lengthwise, parallel to the long axis.

Longtanian n. A stage of the Zechstein Epoch, preceded by the Capitanian.

loofa n. Any of several Old World tropical vines of the genus Luffa, having cylindrical fruit with a fibrous, spongelike interior. The dried, fibrous part of the loofa fruit, used as a washing sponge or as a filter. Also loofah, luffa.

loofah See loofah.

lorate (L. lorum: strap, thong) adj. Of leaves, strap-shaped (moderately long with the two margins parallel); longer than linear but shorter than fasciarate, with a length to breadth ratio of between 6 to 1 and 12 to 1.

lotic (L. lautus: bathed, watered) adj. Of, relating to, or living in actively moving water. Cf. lentic.

luciferase (L. lux,lucis: light; ferre: to carry) n. An enzyme which activates luciferin to produce bioluminescence.

luciferin (L. lux,lucis: light; ferre: to carry) n. A compound whose activated form emits light.

luffa See loofa.

lumbago n. A painful condition of the lower back, as one resulting from muscle strain or a slipped disk.

lumen n. A cavity within a plant cell enclosed by the cell walls.

lunar (L. luna: moon) adj. Crescent-shaped, of the shape of a half-moon.

lunate (L. luna: moon) adj. Crescent-shaped. Syn. lunated, lunar.

lunated See lunate.

lunula (diminutive of L. luna: moon) n. (pl. lunula) Something shaped like a narrow crescent, as the white area at the base of the human fingernail.

lunulae See lunula.

lunular (diminutive of L. luna: moon) adj. Crescent-shaped. See lunula.

lunulate (diminutive of L. luna: moon) adj. Diminutive of lunate; crescent-shaped; having lunular markings.

lupinine n. A quinolizidine alkaloid.

lurid (L. luridus: pale yellow, pallid) adj. Pale brown to yellowish-brown in color.

lustrous adj. Shiny or glossy.

lutein (L. luteus: yellow, reddish) A yellow-red, water insoluble, crystalline, carotenoid alcohol, C40H56O2, also called xanthophyll, and found in the petals of marigold and certain other flowers, algae, etc.

luteolin n. A hydroxylated flavone derivative, common in leaves and flowers.

luteone n. An isoflavone.

luteous (L. luteus: yellow, reddish) adj. Having a light to medium yellowish or greenish tinge. Syn. lutescent.

lutescent (L. luteus: yellow, reddish) adj. Yellowish. Syn. luteous.

luticolous adj. Growing in mires, inhabiting mud.

Lycophyta n. A phylum of tracheophyte plants containing the clubmosses (genus Lycopodium) and related genera (including Selaginella) as well as numerous extinct forms, which reached their peak in the Carboniferous period with giant coal-forming tree species. Lycophytes have roots and their stems are covered with numerous small leaves. Reproduction is by means of spores; the sporangia are usually grouped into cones. Syn. Lycopodophyta, Lycopodiopsida.

Lycopodiaceae n. A family of the phylum Filicinophyta. See Lycophyta.

Lycopodium n. A genus of the phylum Lycophyta (Lycopodiopsida, Lycopodophyta).

Lycopodophyta See Lycophyta.

Lygodiaceae n. A family of the phylum Filicinophyta.

lyrate adj. Deeply lobed, with a large terminal lobe and smaller lateral ones; pinnatifid, with the terminal lobe large and rounded and the lower lobes much smaller. Like pandurate, but pinched several times to produce several sets of smaller lobes.

lyse v. To undergo or cause to undergo lysis.

lysigenous (Gr. lysis: dissolution; genea: what is generated) adj. Formed by the dissolution of tissue.

lysis n. The dissolution or destruction of cells, such as blood cells or bacteria, as by the action of a specific lysin that disrupts the cell membrane. The gradual subsiding of the symptoms of an acute disease.

lysosome (Gr. lysis: dissolution; s˘ma: body) n. One of a variety of membrane-bound organelles in eukaryotic cells containing various hydrolytic enzymes. They function by bringing about the degradation of substances taken into the cell for digestion (in the cells lining parts of the gut, for example) and are also used to remove substances in the cell that have become inappropriate for its current physiological or developmental state. They are formed by budding of the membrane system of the Golgi body.

lysotroph adj. That obtains food by extracellular enzymes (absorbtive nutrition).