B A small chromosome whose presence or absence varies according to the tissue, individual or population. It is therefore associated with an abnormal meiotic and/or mitotic process; Cf. accessary chromosom.

bacca (L. bacca, baca: berry) n. (pl. baccae) Berry.

baccae See bacca.

baccate (L. bacca, baca: berry) adj. Berry-like and soft; of seeds, having a succulent or pulpy testa; of fruits, having the seeds embedded in pulp. Bearing berries.

bacciferous (L. bacca, baca: berry; ferre: to carry) adj. Bearing or producing berries.

bacciform (L. bacca, baca: berry; forma: shape) adj. Berry-shaped.

bacillar adj. Shaped like a short rod.

Bacillariophyceae n. Class of unicellular algae, usually occurring singly, but may be colonial or filamentous. Cell size ranges from 5 to 2000 microns. The cell wall (frustule) is impregnated with silica and consists of two valves, one of which overlaps the other like the lid on a box. The frustule is commonly delicately ornamented and pierced by tiny holes (punctae) which may be covered by porous sieve membranes. There are two orders. The Centrales (centric diatoms) are circular, with radial symmetry, and are predominantly marine. The Pennales (pennate diatoms) are elliptical, with bilateral symmetry, and dominate freshwater environments. The frustules have formed an important constituent of deep-sea deposits since the Cretaceous. The oldest known diatom is usually taken to be Pyxidicula bollensis from the Jurassic. See also diatom.

bacilliform adj. Rod-shaped, usually more than 3 times as long as wide. Also baculiform.

backbulb n. A dormant water-storing thickened stem that looks like a bulb, found in Orchidaceae. It grows actively as a pseudobulb the first year, then becomes dormant when the next year's pseudobulb takes over.

backcross n. To cross a first-generation hybrid with one of the parental types. The offspring of a cross between a hybrid and one of its parents. A cross of a hybrid to either of its parent heterozygote to a homozygous recessive. Cf. test cross. Also back cross, back-cross.

back cross See backcross.

back-cross See backcross.

backcross breeding A system of breeding whereby recurrent backcrosses are made to one of the parents of a hybrid accompanied by selection for a specific character or characters.

backfire n. A fire purposely set ahead of an advancing fire to destroy flammable materials, enabling workers to control the main fire.

backshore n. That part of the beach from the first crest toward the land.

Bacteria (Gr. baktęria: stick) n. The domain comprising the kingdom Eubacteria.

bactericidal See bactericide.

bactericide adj. Something, such as an herbal preparation, capable of destroying bacteria. Also bactericidal.

bacteriorhizae n. Nodules on the roots of most legumes and a few other plants, which contain bacteria that uses atmospheric nitrogen to synthesize organic compounds.

bacula See baculum.

baculate adj. Of the baculum.

baculiform See bacilliform.

baculum n. (pl. bacula) In pollen, a cylindrical, free standing exine or sexine element more than 1 µm in length and less than this in diameter. Cf. columella.

badlands n. Regions of eroded land on which most of the surface is covered with ridges, gullies, and deep channels, having sparse vegetation.

balance n. The condition in which genetic components are adjusted in proportions that give satisfactory development. Balance applies to individuals and populations.

balance of nature A term for an ideal condition in which the interrelationships of organisms to one another and their environment appear harmonious, like a climax forest. In reality, the balance is continually upset by natural events. Syn. biological equilibrium.

balausta (Gr. balauston: flower of the pomegranate) n. A pomegranate fruit.

balaustine (Gr. balauston: flower of the pomegranate) n. Of or pertaining to the pomegranate.

bald adj. A treeless region in forest vegetation; perhaps an area of grasses or shrubs in southern Appalachia, or a mountaintop.

balling n. A condition where outer petals stick together and fail to open, often occurring in damp weather.

ballistoconidia See ballistoconidium.

ballistoconidium n. (pl. ballistoconidia) Forcibly discharged vegetative spore.

ballistic adj. Refers to fruits that discharge their seeds forcefully; catapult fruits.

ballistospore n. A spore that when mature is actively projected.

balsam (Gr. balsamon: balm) n. An aromatic, fragrant, resinous, sticky exudate from any of various tree species, especially those of the genus Commiphora, used in medicine for its soothing and healing properties and in perfumery. Balsam of Peru is derived from the Central American leguminous tree Myroxylon peneirae, grown in El Salvador. The name is also given to many plants of the family Balsaminaceae. The garden balsam (Impatiens balsamina), native to India, is widely cultivated for its showy red flowers, which have a tubular spur and five unequal petals. The balsam apple (Momardica balsamina) is an ornamental vine. Canada balsam is a transparent resin obtained from fir trees. It is used as an adhesive in optical instruments because its refractive index is similar to that of glass.

balsamic adj. Of, relating to, or resembling balsam. Containing or yielding balsam. Restorative; curative.

balsamiferous (Gr. balsamon, L. balsamum: balm; L. ferre: to carry) adj. Producing balsam; balsam-like.

Baltica n. The continental mass of north-western Europe (including most of what are now the UK, Scandinavia, European Russia, and Central Europe) that formed the south-eastern margin of the Iapetus Ocean. During the Caledonian orogenic event, this continental mass was brought into juxtaposition against N. America and Greenland by subduction of the Iapetus Ocean during the Silurian and Early Devonian.

Baltoscandia See Baltica

bamboo n. Any of various usually woody, eventually arborescent grasses of the tropical or temperate regions belonging to the genera Bambusa, Arundinaria, Phyllostachys, Sasa, Dendrocalamus, etc., most having hard, hollow stems.

Bancroft's Law A generalization that organisms and communities tend toward a state of dynamic equilibrium with the environment.

banded adj. Striped.

bank storage Water absorbed by the bed and banks of a stream, returned in whole or part after ground water level falls.

banner n. The upper and usually largest petal of a papilionaceous flower, i.e. the standard or vexillum of a papilionaceous corolla, as in peas and sweet peas.

bar n. A continually moving deposit of sand forming a ridge along the seashore or the coasts of large lakes. A unit of atmospheric pressure equivalent to 29.53 inches (750.1 mm) of mercury at 32 degrees at latitude 45 degrees.

barachore n. A species in which the fruit or seed is desseminated by its own weight, e.g., walnuts, Juglans, falling to the ground. Cf. autochore, diaspore.

barachory n. The dispersion of a species in which the fruit or seed is desseminated by its own weight, e.g., walnuts, Juglans, falling to the ground. Cf. autochory, allochory, anemochory, etc.

barb (L. barba: beard) n. A beardlike growth or part. A hooked or sharp bristle.

barbate (L. barbatus: bearded) adj. Bearded or tufted with long, stiff hairs. Cf. versatile, dorsifixed.

barbed (L. barba: beard) adj. With short, rigid, reflexed points, like the barb of a fishhook.

barbed trichome A trichome with terminal or lateral retrorse projections, each projection being a barb.

barbella (L. barbula: little beard, hairs of plants) n. (pl. barbellae) Short, straight, stiff hairs or barbs.

barbellae See barbella.

barbellate (L. barbula: little beard, hairs of plants) adj. Provided, usually laterally, with fine, short points or barbs.

barbellulate (L. barbula: little beard, hairs of plants) adj. With very tiny short, stiff hairs or barbs.

barbulae (L. barbula: little beard) n. In Scaevola, outgrowths on the margin of the wings or in the throat of the corolla; they may be simple or have apical hairs or papillae.

barbulate (L. barbula: little beard) adj. Finely bearded.

bark n. The outermost covering of trunks or branches of trees, shrubs and some plants. This is composed of the cuticle or epidermis, the outer bark or cortex, and the inner bark or fiber.

bark-cambium n. The layer of cells that produces new bark.

barotaxis n. The response of an organism in response to barometric stimulus.

barotropism n. The change of position of a plant or sedentary animal in response to a barometric stimulus.

barrel structure The superficial cells of a thallus, arranged in concentric rings around an air pore, that are elevated above the surface and project down into the air chambers; e.g., Marchantia.

barren n. A tract of unproductive land, often with a scrubby growth of trees. A region where vegetation is absent or poorly developed. Often used in the plural.

barrens See barren.

barrier n. Any feature or condition that restricts movement of organisms or prevents establishment of organisms which have migrated there. A condition that prevents or significantly reduces crossbreeding of organisms.

barrier beach A strip of land built up by the action of waves, currents and winds, and which protects inner areas.

basal (Gr. basis: base) adj. At the base; growing from the base of a stem; used in reference to leaves at the base of the stem; of a placenta, at the base of the ovary. One of the main canes of a rose bush, originating from the bud union. Describing cells at the base or insertion of the leaf, often of different shape and color from those of the main part of the leaf. Syn. basilar. Cf. terminal, distal.

basal area The area of the cross section of a tree at height of 4.5 feet above the ground, generally written as the total of the basal area of the trees in a forest in square feet per acre. The surface of the soil actually covered by a plant, as compared to the full spread of the herbage, in grassland ecology often measured at one inch above the ground. (alt. basal cover, alt. ground cover, alt. cover)

basal cell A cell at the base; in leaves, frequently differentiated cells of the lower half or third of a leaf; cell at point of attachment of an axillary hair. Cf. laminal cells.

basal cover See basal area.

basal group The earliest diverging group within a clade; for instance, to hypothesize that sponges are basal animals is to suggest that the lineage(s) leading to sponges diverged from the lineage that gave rise to all other animals. Also basal taxon.

basal leaves The leaves at the base of the stem. Cf. rosette leaves, cauline.

basal membrane A short tube or cylinder often supporting segments and cilia of the endostome, e.g. Bryum, or teeth of the haplolepidous peristome, e.g. Tortula.

basal placentation Ovules positioned at the base of a single-loculed ovary.

basal scale A vestigal or reduced scale-like leaf borne near the base of the stem or branches.

basal taxon See basal group.

base (Gr. basis: base) n. The proximal portion of a structure, that part nearest the point of attachment.

base exchange capacity A measure of the absorptive capacity of a soil for materials with exchangeable cations, a nonacid reaction. A soil with a high base exchange capacity will retain more plant nutrients and is less apt to leach than one with a low exchange capacity.

base flow Springs; stream flow coming from subterranean sources in contrast to surface runoff.

base level The lowest level to which a land surface can drop by action of water; permanent base level is sea level.

base number The haploid chromosome number of the common ancestor of a group, represented as x followed by the actual number.

base saturation The proportion of the base exchange capacity that is saturated with metallic cations.

Bashkirian n. 1. The earliest epoch in the Pennsylvanian, comprising the Kinderscoutian, Marsdenian, and Yeadonian Ages (these are also stage names in British stratigraphy), and the Cheremshanskian and Melekesskian Ages (stage names in Russian stratigraphy). The Bashkirian Age is preceded by the Serpukhovian, followed by the Moscovian, and has its initial boundary (the Mississippian-Pennsylvanian boundary) dated at 322.8 million years ago. 2. The name of the corresponding eastern European series, which is roughly contemporaneous with the Namurian B and C plus the Westphalian A (western Europe), and the Morrowan Series (N. America).

basicarpy (Gr. basis: base; karpos: fruit) n. Fruits produced at the base of the plant.

basic number The number of chromosomes in ancestral diploid ancestors of polyploids, represented by `x'.

basic seed Means the seed planted to produce certified or commercial seed.

basidia See basidium.

basidiocarp (Gr. basis: base; karpos: fruit) n. A basidium-bearing structure found in such basidiomycetous fungi as mushrooms and puffballs. A sporocarp produced by a member of the Basidiomycotina and which bears basidiospores.

basidiole n. A structure in the hymenium of a member of the Basidiomycotina that is morphologically similar to a basidium without sterigmata. It may be an immature basidium or a permanently sterile structure in the hymenium.

basidiolichen n. Symbiosis between an alga and a basidiomycete.

basidioma n. (pl. basidiomata) The basidium bearing organ of Basidiomycotina.

basidiomata See basidioma.

basidiomycete See Basidiomycetes.

Basidiomycetes See Basidiomycota.

basidiomycetous (Gr. basis: base; mykęs: fungus) adj. Of the Basidiomycetes.

Basidiomycota (Gr. basis: base; mykęs: fungus) n. A large phylum of fungi, 22 000 to 25 000 species, that includes many mushrooms, the bracket fungi, puffballs, etc., as well as important microscopic forms, such as the parasitic rust fungi and smuts of crops. They reproduce by basidia, which are typically club-shaped and produce spores at the tips of stalklike projections.

basidiospore (Gr. basis: base; spora: seed) n. A spore that is borne by a basidium. The characteristic spore of fungi belonging to the phylum Basidiomycota. See basidium.

basidium (Gr. basis: base) n. (pl. basidia) A microscopic spore-bearing structure produced by certain fungi; a specialized cell in fungi of the phylum Basidiomycota, in which nuclear fission and meiosis occur. This results in the formation of four basidiospores, which are attached to the basidium by means of sterigmata (short stalks).

basifixed (L. basis: base; fixus: fixed, fastened) adj. Attached at or by the base, e.g. of anthers, by the base of the connective.

basiflorous (Gr. basis: base; L. flos, floris: flower) adj. With flowers to the base of the trunk or stem, touching the ground.

basiflory (Gr. basis: base; L. flos, floris: flower) n. Said of a plant with flower to the base of the trunk or stem, touching the ground.

basifugal adj. Same as acropetal.

basilar (L. basis: base) adj. Of, relating to, or situated at the base. See basal.

basinerved (L. basis: base; nervus; tendon, ligament, nerve) adj. With veins arising from the base. Also palmate.

basionym n. A specific or infraspecific name which has priority over other names later given to the same plant by different authors. Cf. synonym, homonym, tautonym, autonym.

basipetal (Gr. basis: base; petere: to seek) adj. Near the base rather than the tip; produced sequentially from the apex toward the base, as the flowers in a determinate inflorescence. Developing, in sequence, from the apex towards the base. Cf. acropetal.

basiphile adj. Of plants of basic habitats, such as limestone, dolomite, sandstone, or chalk. Cf. acidophile. Also basiphilous.

basiphilous See basiphile.

basiscopic (Gr. basis: base; skopeô: to aim) adj. Pointing towards the base (applied to the first lateral vein of a leaflet on the side nearer the leaf base); the triangular surface of a merophyte that is not in contact with the apical cell. Cf. acroscopic.

basitonic (Gr. basis: base; tonos: intensity, strength) adj. Describes flowering seasonal shoots which produce no leaves (except for bracts in some cases) below the inflorescence. Cf. acrotonic.

basophilous adj. Refers to organisms which have adapted for life in alkaline soil or other medium.

basotonic (Gr. basis: base; tonos: intensity, strength) Of growth that is intensified in the lower part of a plant, resulting in a trianglular shaped plant. Cf. acrotonic, mesotonic.

bast n. Strong woody fibers obtained especially from the phloem of from various plants. Tissue that conducts synthesized food substances (e.g., from leaves) to parts where needed; consists primarily of sieve tubes. Syn: phloem.

bathyal zone The deep part of the ocean where light does not penetrate sufficiently for normal plant growth.

bathypelagic adj. Refers to deep parts of the ocean, but not including the ocean bottom.

bathyphyll (Gr. bathys: deep; phyllon, leaf) n. A leaf at the base of a stem with the function of attachment to a substrate.

batture n. That part of the shore (of a river) that the ebb uncovers.

beach n. Where water meets land at the edge of lakes, oceans, etc. A barrier beach is a ridge of sandy deposits separated from the mainland by a section of water.

beak n. A prominent terminal projection, especially of a carpel or fruit. A prolonged narrow tip, elongated apex of an operculum, calyptra or perianth.

beaked adj. Ending in a prolonged tip; bearing a beak.

beard n. A tuft or growth of awns or the like, as in wheat, barley, etc.

bearded adj. Bearing a long awn, or furnished with long or stiff hairs, as seen on the lower petals of some irises.

bedrock n. The layer of solid rock underlying a soil profile or other surface materials.

bee fly Bee flies belong to the Bombyliidae family, a large family of flies with hundreds of genera. Adults generally feed on nectar and pollen, thus are pollinators of flowers. They superficially resemble bees, thus are commonly called bee flies, and this may offer the adults some protection from predators.

beeswax n. A substance produced by bees to build honeycombs. It is collected by heating the honeycomb in water (after removing the honey) so that the floating wax can be separated after solidification on cooling. Beeswax (melting point 61-69°C) is used in high-quality polishes, etc.

beetle n. Any of numerous insects of the order Coleoptera, having biting mouthparts and forewings modified to form horny coverings that protect the underlying pair of membranous hind wings when at rest.

begonioid adj. Of a leaf tooth in which there is a translucent apical pad of densely packed cells, one lateral vein strengthened at the expense of the apical and the other lateral vein, perhaps a close to a cucurbitoid tooth.

below adv. Refers to the position of one portion of an organ or plant in relation to another portion; the part 'below' is the nearest to the attachment. Cf. above.

belt n. A long narrow area or strip of vegetation with characteristics which define it from adjoining areas.

belt transect A type of vegetational analysis in which a portion of land a few inches or a few feet wide, and often a meter wide and 10 to 100 meters long, has constituent plants recorded.

benthic adj. Refers to the bottom of any body of water, regardless of depth. Oceanic benthic division is composed of littoral, sublittoral, archibenthic, and abyssal-benthic zones.

benthos n. Organisms which live on or at the bottom of oceans or fresh water, from the water's edge down to the deepest water depths. Cf. nekton.

benzene n. An aromatic 6-carbon ring.

benzofuran n. A type of terpene formed from dimethylallyl pyrophosphate and an acetate-derived polyketide precursor.

benzoisoquinoline See benzoisoquinolines.

benzoisoquinolines n. Organic compounds where the benzene ring is added to an isoquinoline nucleus.

benzopyran n. A type of terpene, pigments, a class of chromone.

benzoquinone See benzoquinones.

benzoquinones n. Simple quinones in which an aromatic ring is fused to two oxygen atoms, there being two carbonyl groups, usually in the para (1,4) position; often yellow in color.

benzylisoquinoline alkaloids A group of isoquinoline alkaloids, usually poisonous; modified dimers of tyrosine derived from 3.4-dihydroxytyramine (dopamine) condensed with a carbonyl compound (4-hydroxyphenylacetaldehyde), a benzene ring added to an isoquinoline nucleus.

berberine n. A benzylisoquinoline alkaloid.

berry n. A fleshy fruit formed from either one carpel or from several fused together and containing many seeds. The fruit wall may have two or three layers but the inner layer is never hard and stony (as in some drupes). Examples of berries are grapes and tomatoes. A berry, such as a cucumber, that develops a hard outer rind is called a pepo. One that is segmented and has a leathery rind, such as a citrus fruit, is called a hesperidium. The rind contains oil glands and is lined by the white mesocarp, commonly called pith. Cf. drupe, pyrene.

beta-carbaline alkaloids A class of indole alkaloids which are derived from the amino acid L-tryptophan.

betacyanin n. Any of a group of red pigments found mainly in plants of the order Chenopodiales, which includes the goosefoot, cactus, and portulaca families. They are nitrogen-containing glycosylated compounds responsible for the red colour of beetroot, for example, and are chemically distinct from the anthocyanins, which include many red and pink plant pigments. A group of yellow pigments, called betaxanthins, are chemically similar to betacyanins and are restricted to the same families. Both betacyanins and betaxanthins are classed as betalains.

betaine See betaines.

betaines n. Alkaloid-like compound, a quaternary ammonium basic derivative, may play a role in osmotic regulation in halophytes.

betalain n. Water-soluble, nitrogen-containing pigments.

betaxanthin n. Betalain pigment varying from yellow to red.

B horizon The soil layer between A and C horizons, in which materials from overlying horizons accumulate from precipitation or suspension.

bi- (L. bis: twice) prefix. Meaning two or twice.

biannual adj. Occurring twice a year. See also: biennial.

bias n. A consistent and false departure of a statistic from its proper value.

biauriculate adj. Having two auricles.

bibracteolate (L. bis: twice; bracteola: thin and small gold plate) adj. Having two bracteoles.

bicalcarate adj. Having two spurs.

bicallose adj. Having two callosities.

bicarinate adj. Having two keels.

bicarpellary (L. bis: twice; karpos: fruit) See bicarpellate.

bicarpellate (L. bis: twice; karpos: fruit) adj. With two carpels. Syn. dicarpellate.

bicentric adj. Refers to a taxon which has two centers of dissemination or evolution.

bicollateral adj. Of vascular bundles with phloem on both abaxial and adaxial sides, Cf. amphicribral, amphivasal, collateral.

bicolored (L. bis: twice; color: color) adj. Of two distinct colors.

biconcave (L. bis: twice; cum: with: cavus: bored, hollow) adj. Concave on both sides.

biconic adj. In the shape of two cones joined by their base.

biconvex (L. bis: twice; convexus: rounded, curved) adj. Convex on both sides.

bicornute adj. Having two horns.

bicostate adj. In mosses, having a double costa, which is usually much shorter than in leaves having a single costa.

bicrenate (L. bis: twice; crena: notch) adj. Doubly crenates as when the teeth of a crenate leaf are also crenate.

bicuspidate (L. bis: twice; cuspis: point) adj. With two sharp points.

bidentate (L. bis: twice; dens, dentis: tooth) adj. With two teeth.

biduous (L. bis: twice; dies: day) adj. Lasting two days.

biennial (L. bis: twice; annus: year) adj. A plant whose life span extends for more than one but less than two years after germination, i.e. which lives two years, i.e. requiring two years in which to complete its life cycle, the first year growing only vegetatively, usually forming a basal rosette of leaves, the second flowering, fruiting, then dying.

bifacial (L. bis: twice; facies: aspect, face) adj. Having two faces. Of leaves, flat or channelled with distinct in color or texture adaxial and abaxial surfaces. A vascular cambium that produces cells on both sides; in seed plants phloem is produced to the outside and xylem to the inside; compare to unifacial (vascular cambium); see cambium.

bifarious (L. bifarius: double) adj. In two vertical rows; distichous.

bifid (L. bis: twice; findere: to split) adj. Forked; divided by a cleft, i.e. divided, for about half the length, into two parts; deeply two-cleft or two-lobed, usually from the tip. Cf. bipartite.

biflavonoid See biflavonoids.

biflavonoids n. A class of flavonoids, most of which are flavone and flavanone dimers with a simple 5, 7-4'- or 5,7,3',4'-oxygenation pattern, derived from the oxidative coupling of two chalcone units and subsequent modification of the central C3 units.

biflavonyl See biflavonyls.

biflavonyls n. A class of flavonoids formed by the dimerization of the flavone apigenin.

biflorous (L. bis: twice; florus: flowered) adj. Flowering in the spring and again in the autumn. Also biflorus.

biflorus See biflorous.

bifoliate (L. bis: twice; folium: leaf) adj. Of plants, having two leaves; of leaves, having two leaflets. Cf. bifoliolate.

bifoliolate (L. bis: twice; foliolum: little leaf) adj. Having just two leaflets per leaf. Cf. bifoliate.

bifurcate (L. bis: twice; furca: fork) adj. Two-forked; divided into two branches; split into two; Y-shaped. Also bifurcated.

bifurcated See bifurcate.

bifusiform adj. Fusiform but constricted in the middle.

bigeminate (L. bis: twice; geminatus: doubled) adj. Twice divided into equal pairs.

bigeneric adj. A hybrid produced by crossing parents from two genera.

bijugate (L. bis: twice; jugum: yoke) adj. Of leaves, having two pairs of leaflets or pinnae. Synonym: bijugous.

bijugous See bijugate.

bilabiate (L. bis: twice; labia: lip) adj. Having two lips, as a bilabiate corolla of a flower, i.e. of a corolla in which fusion of an anterior group and a posterior group of petals extends beyond the top of the corolla tube, as in many irregular flowers.

bilamellate adj. Made up of two plates.

bilateral (L. bis: twice; latus, lateris: side) adj. Pertaining to the right side and left side of a structure, plane, etc. Arranged two sides, as leaves on a stem.

bilaterally symmetrical Said of corolla or calyx (or flower) when divisible into equal halves in one plane only; zygomorphic.

bilateral symmetry A type of arrangement of the parts and organs of an animal in which the body can be divided into two halves that are mirror images of each other along one plane only (usually passing through the midline at right angles to the dorsal and ventral surfaces). Bilaterally symmetrical animals are characterized by a type of movement in which one end of the body always leads. In botany this type of symmetry is usually called zygomorphy when applicable to flowers (e.g. foxglove and antirrhinum flowers are zygomorphic). Cf. radial symmetry.

bilobate See bilobed.

bilobed (L. bis: twice; Gr. lobos: lobe) adj. Divided into two lobes or segments.

bilocellate (L. bis: twice; locellus: box) adj. Divided into two locelli or secondary locules, as when a main locule of an ovary is partitioned into two cavities.

bilocular (L. bis: twice; loculus: little spot) adj. With two locules, as in some ovaries; divided into two cells or compartments; having two small, independent chambers.

biloculate See bilocular.

bimestrial (L. bimenstruus: lasting two month) adj, Lasting two months; occurring every two months.

binary combination See binomial.

binary fission The division of a single-celled organism into two daughter cells.

binary name See binomial.

binate adj. Borne, growing in pairs; composed of two equal parts.

bine A climbing plant which climbs by its shoots growing in a helix around a support. It is distinct from a vine, which climbs using tendrils or suckers.

binomial (L. bis: twice; nomen: name) n. A name consisting of two parts, the first being the genus and capitalized, the second the species and usually lower case initial with both names being italicized, e.g., Gypsophila elegans. Syn. binary name, binary combination.

binomial nomenclature The use of the genus and species names together to identify a given organism in the taxonomic system.

binucleate ad. Of pollen grains in which the male gametophyte has two nuclei when shed from the anther. Cf. trinucleate.

bioaerosol n. Biological airborne particle(s), for instance fungal spores, pollen etc.

biocenose n. All of the interacting organisms living together in specific habitat, usually containing producer, consumer, reducer, and transformer types. Life assemblage; an assemblage of fossils that reflects associations characteristic of the community when it was living. Cf. ecosystem, community, association. Also biocoenose, biocoenosis.

biochemical oxygen demand A test to detect and measure pollution in water by determining the quantity of oxygen already used up by oxidizable materials (abbreviated B.O.D. or BOD).

biochemistry n. The study of those molecules used and manufactured by living things.

biochore n. A subdivision of the biocycle which contains a group of biotopes which resemble one another; habitat. Examples are grassland, forest and desert.

biochron (Gr. bios: life; khronos: time) n. The length of time represented by a biostratigraphic zone.

bioclimate adj. Microclimate.

bioclimatic law The generalization that in temperate North America, weather-related events, such as bloom time, can be determined to be similar as you move up or down a mountain 400 feet, or one degree of latitude, or 5 degrees of longitude. In the spring, each of these measurements are eastward or upward and are four days later; in autumn, they are westward or downward and are four days earlier. Syn. Hopkins' law.

bioclimatology n. The study of interrelationships between living things and the climate.

biocoenology n. The study of communities including qualitative and quantitative analyses. Also biocoenotics.

biocoenose See biocenose.

biocoenosis See biocenose.

biocoenotics See biocoenology.

biocycle n. A subdivision of the biosphere, including saltwater, freshwater and land. Each consists of biochores. Cf. biotope.

biodemography n. Numerical and mathematical treatment of population problems.

biodiversity n. The totality of genes, species, and ecosystems in a specified area, or the entire world.

bioecology n. A branch of biology treating interrelationships of both plants and animals among themselves and with their environment. Cf. ecology.

biogenesis n. The principle that plants or animals can originate only from other plants or animals. Cf. spontaneous generation.

biogenetic law A theory postulated by Ernst Haeckel in 1866 stating that the development of an animal in its lifetime tends to recapitulate the evolutionary development of its ancestors. Also known as recapitulation theory. See phylogeny.

biogenic adj. See biogenesis.

biogeocenose n. A specific ecosystem unique to a designated geographic area.

biogeochemical cycle The circulation of chemical elements (e.g., oxygen, carbon, etc.) from the environment into plants and animals and back again into the environment.

biogeographic region A biome.

biogeography n. The branch of biology that treats the latitude and longitude of the location of plants and animals; range. See also: chorology.

biological efficiency The ratio of the productivity of an organism or community of organisms to that of its supply of energy. A black bear would have a much higher efficiency hunting in the summer than in winter, so it is more efficient to hibernate during the winter months.

biological equilibrium The state of natural control, self-regulation of the numbers of plants and animals in a community, brought about by interactions within and between plants and animals and the effects of environment such as weather. For example, as the numbers of white-footed mice, Paramyscus, rise, grass seeds, Graminae, decrease and the numbers of foxes, Vulpes, increase. Cf. life cycle, pyramid of numbers. Syn. biotic balance, balance of nature.

biological factor An influence that results from biological agents, including biotic factors such as lack of sunshine and physiologic factors like hormones. For example, death rates of white-tailed deer, Odocoilus, increase along highways during rutting season at night. Also factor.

biological race A group of organisms which differ only in their physiological or ecological behavior from other groups in the same species, e.g., woodland white footed mice, Paramyscus, run in straight lines where meadow white footed mice run zigzag lines. Syn. biological strain.

biological resources The factors of biodiversity which are of direct, indirect, or potential use to humanity. Syn. biotic resources.

biological spectrum A percentile tabulation of the plants of a community into the life form classes according to Raunkiaer's classification.

biological strain See biological race.

biologics n. Biological products such as vaccines.

biology n. The study of living organisms.

bioluminescence (Gr. bios: life; L. lumen, luminis: light) n. The production of light by a chemical reaction within an organism. The process occurs in many bacteria and protists, as well as certain animals and fungi.

biomass (Gr. bios: life; L. massa: heap, pile) n. Weight of all living material in a unit area at an instantaneous time. May be expressed as g/m2, mt/ha, or other similar expressions.

biome (Gr. bios: life) n. The ecology of a particular habitat, characterized by its unique plant and animal symbiotic relationships, and maintained by local climatic conditions; major ecological community type, geographical region that is characterized by a predominant type of vegetation and associated fauna, as tropical rain forest, grassland, desert, etc. A large-scale plant or ecosystem formation (such as a coniferous forest, savannah, steppe, etc.) defined by broadly similar characteristics and contained within the same physical and climatic environment. Syn. biotic formation.

biometrical adj. Related to biometry.

biometry n. The statistical study of organisms. The branch of science which deals with statistical procedures in biology.

biome-type A group of similar biomes, such as the temperate deciduous biome-type which includes all the deciduous forests of eastern North America, China and Manchuria, and Europe. (syn. biorealm)

bionomics n. The study of the relationship of organisms to each other and their environment. Cf. ecology.

biorealm See biome-type.

bioregion n. An area defined by social, biological, and geographic criteria, rather than geopolitical jurisdictions.

bioregional management Directional supervision over an area of similar habitat rather than by standard state or county lines, e.g., cooperative public, private, and business environmental planning for a major watershed such as Chesapeake bay. Syn. bioregional planning.

bioregional planning See bioregional management.

bios n. Plant and animal life.

bioseston n. All living components of the seston.

biosphere n. That part of the earth and its atmosphere that can support life. The layer at the earth's surface that contains all living organisms and their environments (biotopes).

biosynthesis n. See biosynthetic.

biosynthetic adj. Describes a chemical compound produced by a living organism.

biosystem n. Ecosystem.

biosystematics n. The classification of living organisms that recognizes and differentiates biotic units into taxa on the basis of genetic relationships.

biota n. All of the living things, including animals, plants, fungi, and microorganisms, located in a given area. Syn. flora and fauna.

biotic (Gr. bios: life) adj. Of or relating to life or to living things; caused or produced by living beings; of biological origin.

biotic area A general term delineating any large area from adjacent areas on the basis of the composition of its biota. Syn. biotic region.

biotic balance See biological equilibrium.

biotic climax The type of community capable of lasting for long periods of time under the present soil and climate conditions, in combination with the animals living there, including humans. Cf. edaphic climax, physiographic climax, sere.

biotic environment All living things found in the environment of an organism or community.

biotic factor Environmental influences caused by plants or animals like shading or trampling. Sometimes used so nonliving effects are included, like landslides. Cf. coaction. Syn. biological factor, biotic influence.

biotic influence See biotic factor.

biotic pressure The tendency of a species or community to extend its range.

biotic province A major ecological section of a continent containing one or more regional communities of plants and animals. Cf. biome, formation.

biotic region See biotic area.

biotic resources See biological resources.

biotope n. A region environmentally uniform in conditions and in the flora and fauna which live there.

biotroph n. See biotrophic.

biotrophic adj. Describes an organism which cannot survive or reproduce unless it is on another organism. An organism that derives nutrients from the living tissues of another organism (its host).

biotype (Gr. bios: life; typos: mark, image) n. A group of organisms having the same hereditary characteristics, i.e. with the same genotype. Biotypes may be homozygous or heterozygous. Distinct physiological races or strains within morphological species; a population of individuals with identical genetic constitution; may be made up of homozygotes or heterozygotes, of which the former would be expected to breed true.

biovulvate adj. Having two ovules.

bipalmate (L. bis: twice; palma: palm) adj. Twice palmate; with the divisions again palmately divided.

bipartite (L. bipartitus: divided into two parts) adj. Divided, nearly to the base, into two parts. Cf. bifid.

bipectinate (L. bis: twice; pecten: comb) adj. Having both margins toothed, like a comb, as certain antennae

bipetalous (L. bis: twice; Gr. petalon: leaf) adj. Having two petals. Syn. dipetalous.

bipinnate (L. bis: twice; pinna: feather) adj. Of leaves, twice pinnately divided, the primary leaflets being again divided into secondary leaflets, i.e. having leaflets that are further subdivided in a pinnate arrangement; twice-pinnately branched. Cf. pinnate, tripinnate.

bipinnately adv. See bipinnate.

bipinnatifid (L. bis: twice; pinna: feather; findere: to split) adj. Pinnatifid with the segments also pinnatifid; twice pinnately cleft.

bipinnatisect (L. bis: twice; pinna: feather; sectus: cut) adj. Referring to a pinnately compound leaf, in which each leaflet is again divided into pinnae. (alt. 2-pinnatisect)

bipolar adj. At both ends or poles.

bipolar distribution Refers to a taxon present in both the northern and southern hemispheres with no apparent connection between populations.

biradial adj. (Of symmetry) same as bisymmetric.

bisaccate adj. Of a pollen grain with two sacci.

bisbifid adj. Twice bifid, i.e. bifid with the subsequent parts more shallowly bifid.

bisect n. A line transect which shows the vertical and lateral distribution of roots at the walls of a trench with the above-ground parts of plants along the verge.

bisected (L. bis: twice; sectus: cut) adj. Split into two parts. See bifid and bipartite.

biseptate adj. Having two septa (partitions).

biseriate (L. bis: twice; series: line) adj. Arranged in two rows, series or whorls.

biserrate (L. bis: twice; serratus: shaped like a saw, toothed) adj. Serrate with the teeth also serrate.

bisexual (L. bis: twice; sexus: sex) adj. Having both female and male reproductive organs present and functional in the same flower; hermaphrodite; amphisporangiate; said of a plant having all bisexual flowers. Syn. perfect. Cf. monoicous.

bisporangiate (L. bis: twice; spora: seed; aggeion: vase, bowl, container) adj. Said of a flower or cone that produces both megaspores and microspores. Most flowers are bisporangiate.

bisporic (L. bis: twice; spora: seed) adj. With two spores.

bistomal adj. Where the micropyle of an ovule is formed from both integuments. Cf. amphistomal, endostomal, exostomal.

bistratose adj. Having two layers of cells, e.g. leaf blades that are two cells thick.

bisymmetric adj. Said especially of a flower, with two main planes of symmetry, as in Dicentra.

bitegmic adj. Of an ovule possessing two integuments. Plants with monocotyledonous features tend to be unitegmic, whereas those groups with dicotyledonous features tend to have two integuments (or, to be bitegmic). Integuments are protective layers of cells surrounding the ovule. At the point where sperm enter the egg, the protective layers may be seen as one or two distincts layers (the layers are obscure elsewhere). They are best seen in a longitudinal section of the ovule.

biternate (L. bis: twice; terni: by three, three each) adj. Doubly ternate with the ternate divisions again ternately divided.

bithecal (L. bis: twice; (Gr. thękę: box, case) adj. With two compartments.

bitten adj. Praemorose, with ragged edges as though chewed.

bitunicate adj. Having two walls.

biturbinate (L. bis: twice; turbinatus: of a conical shape) adj. Top-shaped, but with the widest part some distance from one end.

bivalent n. A pair of chromosomes, usually one from each parent. A pair of homologous chromosomes united in the first meiotic division.

bivalve (L. bis: twice; valvć: door) adj. Having two valves, as a seedcase.

bivalvular See bivalve.

bivoltine adj. Refers to organisms which produce two generations each year, like raspberries, Rubus, which produces fruit in late spring and fall.

black alkaline adj. Of a soil with a pH well over 7.5, covered with a dark crust of sodium or potassium carbonates.

black earth See chernozem.

bladder n. A structure which is thin-walled and inflated; a hollow chamber designed for trapping or flotation.

bladder-like See bladdery.

bladdery adj. Inflated, with thin walls like the bladder of an animal. (alt. bladder-like)

blade n. The leaf of a plant, especially grass; the flat or expanded portion of a leaf; lamina; the portion of leaf, held away from stem when moist; generally the green portion of the leaf above the base, including costa, border and lamina.

blast n. Injury caused by disease or conditions such as hot winds that shrivel buds, branches, etc.

blastidia n. Small subsidiary locules in a thick-walled spore - especially in Physciaceae.

blasting n. A symptom of plant disease characterized by shedding of unopened buds; classically, the failure to produce fruit or seed.

blastospore n. A conidium formed by budding.

Blechnaceae n. A family of the phylum Filicinophyta.

blet v. To decay internally when overripe; said of fruits.

bletted See blet.

blight n. The rapid and extensive discoloration, wilting, and death of plant tissues. A general term applied to any of a wide range of unrelated plant diseases. (e.g., chestnut blight, fireblight, late blight, halo blight).

blistered adj. Where the surface of an organ is puckered, the veins being tighter allowing the tissue to round up.

bloom n. A blossom; the flower of a plant; an expanded bud; the opening of flowers in general, leaves, flowers, or fruits. A waxy or powdery whitish to bluish coating on the surface of certain plant parts, as on cabbage leaves or on a plum or grape.

blossom n. A flower or bloom, esp. of a fruit bearing plant. A state or time of flowering, literally, and figuratively.

blotch n. A large, irregular spot or blot. A disease characterized by large, and irregular in shape, spots or blots on leaves, shoots, and stems.

blotched adj. Marked with irregular spots or blots.

blowout n. A wind-blown excavation in loose soil.

bluff n. A steep headland, promontory, riverbank, or cliff, (usually formed by river erosion).

blunt adj. Not pointed.

boat-shaped adj. Carinate, cymbiform, navicular.

bog n. A quagmire covered with grass or other plants; wet, spongy ground; a small marsh; plant community on wet, very acid peat.

boggy adj. See bog.

bog soil A mucky or peaty surface horizon with a peat underlayment.

boil n. A painful, circumscribed pus-filled inflammation of the skin and subcutaneous tissue usually caused by a local staphylococcal infection. Also called furuncle.

bole n. The trunk of a tree, below the lowest branch. Cf. canopy.

bolete n. A mushroom-like fungus, with tubes and pores below the cap; usually soft and fleshy, unlike pored polypores which are usually rubbery, corky or woody.

boletoid adj. Resembling a bolete, but not belonging to the bolete group, i.e. mushroom-like, with tubes and pores below the cap.

bolt v. To produce flowers and seeds prematurely.

bonitation n. The state of well being in a population, reflected by increasing numbers of individuals.

bordered adj. Having a margin different from the rest of the main body of the organ or structure, e.g. with the edge of a different color as the rest of the leaf.

boreal (L. borealis: northern) adj. Northern; a climatic zone bordering the Arctic or Antarctic; especially of the coniferous forests that occur in the Northern Hemisphere between the treeless tundra and deciduous forest of temperate latitudes. Cf. austral.

boreal forest A forest made up mostly of conifers, such as that reaching across North America from Newfoundland to Alaska.

boreal period The climatic period from about 7500 to 5500 B.C., typified by warm dry conditions.

borealis (L. borealis: northern) adj. Pertaining to the north.

borer n. An insect larva that tunnels into stems and trunks of shrubs, trees, etc.

boss n. A protuberance or projection from a surface or organ.

bossed adj. With a conical protuberance rising from the center of a surface, like the bump on a scale of a pine cone.

bostryces See bostryx.

bostryx n. (pl. bostryces) A one-sided helicoid cyme.

botanical adj. Of or relating to plants or botany.

botany (Gr. botanę: herbe) n. The science of plants; the branch of biology that deals with plants; the plant life of a region; the biology of a plant or plant group.

botryoid adj. With the appearance of a bunch of grapes.

botrytis n. A group of fungi that causes plant diseases. The disease caused by such fungi.

bottom deposits Those materials composing and overlaying the original basin or channel floor of a waterway.

bottomland n. Lowlands along streams and rivers, usually on alluvial floodplains that are periodically flooded.

botuliform (L. botulus: sausage; forma: shape) adj. Sausage shaped; long and cylindrical with each end curved inwards.

bough n. A branch of a tree, especially one of the larger or main branches.

boulder clay Unstratified intermix of clay and stones deposited by glaciers. Cf. till, drift.

brachy- prefix. Meaning short.

brachiate (L. brachiatus: branchy) adj. With paired branches diverging from the stem at nearly right angles.

brachiopod (Gr. brakhion: arm; pous, podos: foot) n. A membre of the phylum Brachiopoda.

Brachiopoda (Gr. brakhion: arm; pous, podos: foot) n. A phylum of solitary, benthic, marine, bivalved, coelomate, invertebrate animals that have existed from the Lower Cambrian to the present day. Brachiopods are commonly attached posteriorly to the sea bed by a stalk (pedicle), but may be secondarily cemented, or free-living (e.g. the fossil form Productus which, like many productids, was spinose, thick-shelled, and lived partly buried in the mud of the sea bed). Usually they consist of two unequal valves: a larger pedicle (ventral) valve and a brachial (dorsal) valve, lined by reduplications (mantle lobes) of the body wall which enclose the large mantle cavity. They are bilaterally symmetrical about the posterior-anterior mid-line of the valves (i.e. through the valves, Cf. Bivalvia). The characteristic feeding and respiratory organ, the lophophore, surrounds the mouth and is covered by ciliated tentacles. It may be a simple horseshoe but more often forms two ciliated arms or brachia that project through the gape (thus giving the phylum its name). The alimentary canal is divided into oesophagus, stomach, and intestine, with or without an anus. The nervous system consists of a circum-oesophogeal ring with a small aggregation of nerve cells on the ventral side. The excretory organs are one or two pairs of nephridia (excretory tubules) also acting as gonoducts (for the release of eggs and sperm). The circulatory system is open, with the contractile vesicle (heart) near the stomach. Considerably more than 3000 fossil species are known and about 100 are alive today; these are widely distributed and occur at all depths. Brachiopods are divided into three classes: Lingulata, Inarticulata, and Articulata.

brachyblast (Gr. brakhys: short; blasti: bud, sprout) n. A short branch; a spur shoot.

brachyparacytic adj. Said of paracytic stomata, with two subsidiary cells parallel to the guard cells but not entirely enveloping them.

brachysclereid adj. Said of a sclereid cell about as long as broad, lacking processes, a stone cell. Cf. astrosclereid, macrosclereid, trichosclereid.

brachypterous adj. Refers to organisms with short wings.

brackish adj. Mixed with salt; briny; somewhat saline.

bract (L. bractea: thin metal plate) n. A modified leaf, growing at the base or on the stalk of a flower. It usually differs from other leaves in shape or color. A leaf-like structure, different in form from the foliage leaves and without an axillary bud, associated with an inflorescence or flower. A more or less modified leaf subtending a flower or belonging to an inflorescence, or sometimes cauline. The similar structure in cryptogams surrounding reproductive organs. A leaf from the axil of which a flower or floral axis arises. A leaf borne on a floral axis; especially one subtending a flower or flower cluster; a more or less modified leaf subtending a flower or belonging to an inflorescence, or sometimes cauline. The similar structure in cryptogams surrounding reproductive organs. A modified leaf providing an axil for a flower or inflorescence to grow from, or found on a flowering stem. In conifers, one of the main structures arising from the cone axis.

bracteal adj. Of or pertaining to the bracts.

bracteate adj. Having bracts.

bracteiform (L. bractea: thin and small gold plate; forma: shape) adj. Bractlike. See bract.

bracteody n. With bracts mimicking floral whorls.

bracteolate adj. Furnished with bracteoles, bractlets.

bracteole (L. bracteola: thin and small gold plate) n. A small bract, a reduced leaf, a small bract-like structure, borne singly or in pairs on the pedicel or calyx of a flower; a modified underleaf associated with a gametangium in liverworts. Cf. perichaetial leaf, perigonial leaf.

bracteose adj. With many bracts or with conspicuous bracts.

bractlet n. A secondary bract, as one upon the pedicel of a flower.

bradytelic (Gr. bradys: slow; telikos: tending to a definite end) adj. Of or pertaining to evolution at a rate slower than the standard for a given group of plants or animals. Cf. horotelic, tachytelic.

bradytely n. See bradytelic.

brambles n. Plants of the genus Rubus, Rosaceae family, usually prickly and bearing fruit, e.g., raspberries and blackberries.

branch n. A natural division of a plant stem; a secondary woody stem growing off of the trunk, or main stem of a woody plant.

branchlet n. A small usually terminal branch; except for the twig, the youngest and smallest division of a branch.

breathing pore A specialized compound air pore that contains 3 to 5 enlarged, hygroscopically active cells at the base of the barrel structure, allowing for closure; e.g. Pressia.

breeder seed A class of certified seed directly controlled by the originating or sponsoring plant breeding institution, or person, or designee thereof, and that is the source for the production of seed of the other classes of certified seed.

breeding n. The propagation of plants for the purpose of improvement by deliberate selfings or hybridizations and subsequent testing and selection for desired criteria and objectives. The art and science of changing plants or animals genetically.

breeding cycle The shortest period between successive generations from germination of a seed to reproduction of the progeny; i.e., the seed-to-seed cycle. Also breeding rotation.

breeding rotation See breeding cycle.

breeding system A particular mating system that involves a certain type or types of plant material, together with the necessary selection procedures; different strategies are used to improve self-pollinated crops to extract inbred pure lines and to improve cross-pollinated crops for population performance per se for the selection of superior heterozygous individuals to be vegetatively reproduced as clones or for the extraction of improved inbreds for use in hybrid production.

brevitoxin n. Neurotoxin produced by the dinoflagellate Ptychodiscus brevis.

bridge n. A band of tissue connecting the corolla scales, as in Cuscuta.

bristle n. A hairlike prickle; a stiff, strong but slender hair or trichome.

bristly adj. Covered with bristles. Same as setose.

broad-elliptic adj. Wider than elliptic.

broadleaf See broad leafed.

broad leafed Referring to a plant which does not have coniferous needles or grasslike leaves. Also broad leaved, broadleaf, broad-leaved, broad-leafed.

broad-leafed See broad leafed.

broadleaf evergreen An evergreen plant that is not a conifer. Also broad-leaved evergreen.

broad leaved See broad leafed.

broad-leaved See broad leafed.

broad-leaved evergreen See broadleaf evergreen

broad-ovate adj. Wider than ovate.

brochidodromous adj. Describes leaves with pinnate venation in which the secondary veins do not terminate at the margins but rather are joined in a series of prominent arches; e.g. the veins of the leaves of Vaccinium angustifolium. Cf. acrodromous, eucamptodromous, semicraspedodromous.

bromeliad n. Any of the mostly epiphytic herbaceous plants of the family Bromeliaceae found primarily in the tropical and subtropical regions of the Americas, including the pineapple and Spanish moss.

bronchitis n. Chronic or acute inflammation of the mucous membrane of the bronchial tubes. A disease marked by this inflammation.

brood body A generalized term used to denote various types of specialized vegetative reproductive structures; e.g. reduced buds, leaves, branches or plant fragments (propagules). Cf. diaspore.

brood branch See cladium.

broom n. In plant pathology: A symptom in which lateral branches proliferate in a dense cluster on the main branch (witches'-broom).

broom-like adj. With many branches parallel or almost so and usually erect, as in Spartium (Spanish broom).

brown algae See Phaeophyta.

brown earth Any of a group of intrazonal soils developed under deciduous forests. Soils needing replanting or restoration, especially damaged wetlands.

brown forest soils Those soils with dark brown surface horizons, but becoming lighter-colored beneath. They are rich in humus and are neutral to slightly acidic in composition, commonly appearing under deciduous forests that are quite rich in calcium or other bases. Cf. brown soils.

brown podzolic soils Those soils with thin layers of partly decayed leaves over a gray-brown layer of mineral matter and humus that covers yellow or yellow-brown acid B horizons. These appear under deciduous or mixed forests in cool, humid, temperate regions.

brown soils Those soils with brown surface horizon, becoming lighter in color with depth. Calcium carbonate appears at one to three feet. These develop under grasslands and shrubs in temperate to cool semiarid climates. Cf. brown forest soils.

browse n., v. Food for livestock or wild members of the extended deer family, Cervidae, consisting of woody twigs and shoots, with or without leaves. To feed on those plants.

browse line A condition found in forests or brushland with an over population of browse animals like deer or goats, all branches and twigs eaten as high as the animals can reach.

brunescent adj. Brownish.

brunisol n. Type of soil associated with forest vegetation; it is usually poorly developed and immature; the most identifying trait of this soil is the presence of a brown B horizon.

brunisolic adj. See brunisol

rush n. A thicket of shrubs, small trees, etc. Branches lopped off trees.

brush presentation A type of secondary pollen presentation in which the pollen in presented to the pollinator entangled in a mass of hairs.

brushland n. An area with shrubs and little other vegetation.

bryophilous adj. Living on or with bryophytes.

Bryophyta (Gr. bryon: moss; phyton: plant) n. A phylum of simple plants possessing no vascular tissue and rudimentary rootlike organs (rhizoids). They grow in a variety of damp habitats, from fresh water to rock surfaces. Some use other plants for support. Mosses show a marked alternation of generations between gamete-bearing forms (gametophytes) and spore-bearing forms (sporophytes): they possess erect or prostrate leafy stems (the gametophyte generation, which is haploid); these give rise to leafless stalks bearing capsules (the sporophyte generation, which is diploid), the latter being dependent on the former for water and nutrients. Spores formed in the capsules are released and grow to produce new plants. Formerly, this phylum also included the liverworts and hornworts, now regarded as separate phyla (see Hepatophyta; Anthocerophyta) and the mosses were classified as a class (Musci) of the Bryophyta. The term 'bryophytes' is still used informally to refer to members of all three phyla. Syn. Bryopsida.

bryophyte (Gr. bryon: moss; phyton: plant) n. A member of the phylum Bryopsida (Bryophyta) within the plant kingdom, comprising plants that lack a vascular system and reproduce by spores. There are two main classes: the mosses (class Musci) and the liverworts (class Hepaticae), which differ mainly in the details of how the spore-bearing structure develops. Most bryophytes prefer damp shady conditions, but they are also often the dominant plants on damp moorlands, and some species are highly drought-tolerant. In a bryophyte the gametophyte generation is the larger, persistent phase; bryophytes generally lack conducting tissues. Bryophytes usually include the Hepaticophyta (liverworts), Anthocerotophyta (hornworts), and Bryophyta (mosses).

Bryopsida n. A class of the phylum Bryophyta.

bubo An inflamed, tender swelling of a lymph node, especially in the area of the armpit or groin, that is characteristic of certain infections, such as bubonic plague and syphilis.

bud n. A small swelling, cell-mass, or projection on a plant, in the process of dividing from a stem to form a flower, leaf or another stem. A condensed immature shoot with a short stem bearing small folded or rolled leaves. The outer leaves of a bud are often scalelike and protect the delicate inner leaves. A terminal (or apical) bud exists at the tip of a stem or branch while axillary (or lateral) buds develop in the axils of leaves. However, in certain circumstances buds can be produced anywhere on the surface of a plant. Some buds remain dormant, but may become active if the terminal bud is removed. It is common gardening practice to remove the terminal buds of some shoots to induce the development of lateral shoots from axillary buds. See also apical dominance.

budding n. In biology, a method of asexual reproduction in which a new individual is derived from an outgrowth (bud) that becomes detached from the body of the parent. In animals the process is also called gemmation; it is common in cnidarians (e.g. Hydra) and also occurs in some sponges and other invertebrates. Among fungi, budding is characteristic of the yeasts.

bud scale See bud-scale

bud-scale n. A modified leaf, without lamina, protecting a bud. A modified leaf or stipule (there may be one, a few, or many) protective of the embryonic tissue of the bud.

bud scale scar The mark left by the sloughing off of the bud scale.

bud sport Branch, flower, or fruit that differs genetically from the remainder of the plant. Cf. Chimera.

bufadienolide See bufadienolides.

bufadienolides n. A subclass of triterpenoids (nortriterpenoid) composed of 24 carbon atoms ; heart poisons and toxins.

buffering n. Modification of environmental conditions by planting vegetation or changing topographic features. Cf. reaction.

buffer species A plant or animal which may serve as an alternate food supply for a consumer animal, lessening the demand for a more desirable food species.

buffer strip A transect of grassland or other erosion resistant vegetation located between or below cultivated lengths or fields.

buffer zone A strip that partially or fully encloses a study area or other designated area to protect the inner section from ecological disturbance by outside pressures; a transition zone between districts managed for different objectives, such as a wildlife preserve and a state hunting area.

bulb (L. bulbus: bulb) n. An underground plant organ that enables a plant to survive from one growing season to the next. It is a modified shoot with a short flattened stem. A terminal bud develops at the centre of its upper surface, surrounded by swollen leaf bases that contain food stored from the previous growing season. Papery brown scale leaves cover the outside of the bulb. The stored food is used in the growing season when the terminal bud produces foliage leaves and flowers. The new leaves photosynthesize and some of the manufactured food passes into the leaf bases forming a new bulb. If more than one bud develops, then additional bulbs form, resulting in vegetative propagation. Examples of bulb-forming plants are daffodil, onion, and tulip. Cf. corm.

bulbate adj. Inflated.

bulbel (L. bulbulus: diminutive of bulbus: bulb) n. A bulb arising from another bulb.

bulbiferous (L. bulbus: bulb; ferre: to carry) adj. Producing bulbs.

bulbil (L. bulbulus: diminutive of bulbus: bulb) n. A small deciduous bulb replacing flowers in an inflorescence, and functioning to propagate the plant vegetatively. A starch-rich underground cell in Charophytes. A small, deciduous, bulb-like axillary propagulum or rhizoidal gemmae,

bulblet See bulbel.

bulbocapnine n. (CI9HI9NO4) An aporphine alkaloid extracted from roots of Corydalis.

bulbose (L. bulbus: bulb) adj. Bulblike; with bulbs; of or pertaining to bulbs.

bulbous adj. See bulbose.

bulbule (L. bulbulus: diminutive of bulbus: bulb) n. A little bulb.

bulk breeding The growing of genetically diverse populations of self-pollinated crops in a bulk plot with or without mass selection, followed by single-plant selection.

bullate (L. bullatus: embellished with nails) adj. With rounded, blistery projections covering the surface, as in a leaf with the surface raised above the veins.

bullation n. A bullate structure.

bulliform cells Large, thin-walled epidermal cells of the intercostal zone of the leaf blade in some members of the grass family.

bunch grass A style of grass that grows in tufts.

bundle n. Short for vascular bundle, often visible as a bundle scar marking the course of a vascular bundle in the outer cortex and evident when the leaf falls from the stem; the number of bundle scars allows one to infer (sometimes incorrectly!) the number of leaf traces and hence aspects of nodal anatomy.

bundle cap Sclerenchyma or collenchyma that forms a cap on either or both the adaxial and abaxial sides of a vascular bundle.

bundle cluster A cluster such as that of pine needles.

bundle scar Scar left on a twig by the vascular bundles when a leaf falls. Tiny, somewhat circular dots within the leaf scar, caused by the breaking of the fibrovascular bundles which run through the petioles into the blades of the leaves.

bundle sheath A clasping collar surrounding a collection of similar parts such as the collar on pine needles. Distinctive cells that entirely surround the vascular bundle.

bur See burr.

burl n. A deformed outgrowth on the trunk of a tree, often half a hemisphere in form, valued for the unusual wood grain; also the veneer made of such growths.

burn scar A scar on a tree trunk left when tissues were damaged by fire. It may later be covered by new tissue.

burr n. A rough or prickly propagule consisting of a seed or fruit, such as the husk on a chestnut, and associated floral parts or bracts. Also bur.

bursicle n. A pouch-like, purse-like receptacle.

bursicula n. The part of the rostellum which includes the viscid matter.

bursiculate adj. Pouch-like or purse-like in form. See bursicle.

bush n. A shrub, especially one that is low and thick with many stems rather than a single trunk.

buttress n. A flange of tissue protruding from the main outline of the base of a tree.

buttressed adj. With props or supports, as in the flared trunks of some trees.

buzz pollination A variant of mellitophily where the bee vibrates a pendulous flower (its own wing muscles vibrate) causing the pollen to fall out of the anthers, the bee then collecting it; the flowers are polysymmetrical, the anthers often form a cone, and the petals are also reflexed, i.e. a very different floral morphology from that of many bee-pollinated flowers.

byssaceous (Gr. byssos: cotton, fine line thread) adj. Divided into threads.

byssoid (Gr. byssos: cotton, fine line thread) adj. Cottony, composed of delicate threads, floccose.