Glossary of Terms

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z #

Select the first letter of the word from the list above to jump to appropriate section of the glossary. If the term you are looking for starts with a digit or symbol, choose the '#' link.

- A -

achene: A type of dry, indehiscent (closed) fruit that contains a single seed and develops from a simple ovary. The pericarp often adheres to the seed at only one point. Example: strawberry.

Alfisols: Soil taxonomic order consisting usually of deciduous or mixed forest soils having distinct horizons, neutral to slightly acidic pH, a subsoil layer high in clay and nutrients, and relatively high fertility for crop cultivation. Suffix: -alf.

allele: A form or variant of a particular gene.

allelopathy: Situation in which one plant detrimentally affects the growth of a nearby plant, presumably through exudation of toxic or growth-inhibiting substances through the roots.

Andisols: Soil taxonomic order consisting of soils that form primarily from volcanic parent material. They are often laden with minerals and have a high water-holding capacity due to their porosity. In the U.S., they are found primarily in Alaska, Hawaii, Washington and Oregon. Suffix: -and.

androecium: Another name for the stamen, or male floral whorl. ('andro'=male, 'oecium'=house).

angiosperm: Flowering plant producing a covered seed.

anion: An atom or molecule carrying one or more surplus electrons, and therefore having a negative charge.

anther: Main male reproductive structure, in which pollen are formed and stored.

Anthophyta: Order of flowering, covered-seeded plants, including monocots and dicots.

apical dominance: The tendency for a plant's apical meristem to be more active than its lateral or axial meristems. It is particularly evident in young trees, and is due to production of auxins in the apical meristem.

apomixis: Seed production without fertilization. The embryo forms from maternal ovule tissue or from an egg that spontaneously doubles.

Aridisols: Soil taxonomic order consisting of dry, high-pH, sometimes calcic, sodic or saline desert soils. Suffix: -id.

auxins: Plant growth regulators involved in apical dominance, phototropism, root induction, and numerous other plant physiological functions. Indoleacetic acid (IAA) is the natural form; others include NAA, IBA, and the herbicide 2,4-D.

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- B -

berry: A type of simple fruit having a fleshy exocarp, mesocarp, and endocarp. Example: tomato.

biological pest control: The use of organisms that do not compete with the crop to control populations of crop competitors.

bolting: Untimely formation of a seed stalk, typically in leafy biennials in response to prolonged cold or low-light conditions.

bonsai: The Japanese horticultural art of pruning plants to maintain an extreme dwarf growth habit.

boron (B): Plant essential micronutrient, usually found in the soil in a borate anionic form.

Bt: Insect-toxic bacterial protein (from Bacillus thuringiensis), produced by a gene that has been cloned and introduced into various crops to provide transgenic insect protection.

bud sport: Mutations in perennial buds that give rise to entire branches having a unique phenotypic characteristic. Example: the red delicious apple.

budding: A type of graft in which the scion is a bud. See asexual propagation page.

bulb: A type of modified subterranean storage stem/bud consisting of overlapping fleshy leaf bases or scales. Example: garlic and onions.

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- C -

C3 plant: Plants whose photosynthetic process first fixes CO2 into a three-carbon organic acid. Example: cool-season grasses such as wheat, rye, oats.

C4 plant: Includes many tropical or subtropical plants whose photosynthetic process first fixes CO2 into a four-carbon organic acid (Hatch-Slack pathway) and which have special bundle-sheath cells in the leaves wherein the Calvin-Benson cycle occurs. Example: warm-season grasses such as corn, sorghum, bluestem.

callus: Parenchymatous cell mass that forms over plant wounds and is commonly seen growing as white, undifferentiated cells from cultured plant cells or tissues.

calyx: Outermost floral whorl, consisting usually of modified leaves known as sepals.

CAM plant: Includes desert succulents. Carbon from CO2 is fixed at night (Hatch-Slack pathway) while stomata are open, then stomata close and the Calvin-Benson cycle occurs during the daytime.

capillary or available water: Soil water present in micropores between field capacity and the wilting point; ie, water available for plant growth.

caryopsis: Dry fruit of the grains, having an adhering pericarp and usually abundant endosperm in the mature seed.

cation: An atom or molecule lacking one or more electrons, and thus carrying a net positive charge.

cation exchange capacity (CEC): The ability of a soil's colloids to attract and hold onto its cations. Soils high in humus and expanding clays tend to have the highest CECs.

center-pivot: A sprinkler irrigation system consisting of a mobile line attached to a fixed central well, resulting in a cultivated field arranged within a circle. Center-pivots are commonly used on the semiarid High Plains from Texas to Nebraska, where the Ogallala Aquifer provides an enormous subterranean water source.

chemical pest control: The use of chemicals to kill or deter pathogens and weeds.

chlorophyll: Metalloproteins containing a magnesium atom and which harvest light energy for photosynthesis.

chloroplast: Cellular organelle containing membranes (thylakoids) in which photosynthesis takes place. Chloroplasts also have a DNA chromosome, which is generally maternally inherited through the egg cytoplasm.

clean cultivation: The complete cultivation or removal of all plant residues from the soil surface.

climacteric: Point in time when fruit can be harvested and still ripen to maximum quality.

Coleoptera: Insect order that includes beetles and weevils, which damage plants mainly by chewing plant parts. Examples of economically-important species: Colorado potato beetle, alfalfa weevil, boll weevil, bean weevil, cucumber beetle. The lady bird beetle (lady bug) is an important biological control organism for aphid infestations, particularly in greenhouses.

collenchyma: Usually juvenile supportive tissue, consisting of living cells with thickened walls.

colloid: Insoluble soil microparticles including clays and humus. These soil colloids have a net negative charge.

complete flower: A flower having all four floral whorls: stamens, pistils, petals, and sepals.

composting: Controlled decomposition of leaves and other wastes to humus.

corm: An enlarged, compressed, underground modified stem, often with scaly leaves.

corolla: Second of the four floral whorls moving inward, containing the modified leaves known as petals.

crown division: Propagation of a plant through separation of rooted offshoots from specialized, thickened root-stem junctures, or crowns.

crucifers: Plants of the mustard family (Brassicaceae). The term "crucifer" comes from the cross-shaped configuration of the four flower petals. Ex., broccoli, cabbage, canola, turnips.

cucurbits: Plants of the cucumber/melon family (Cucurbitaceae). Ex., cantaloupe, cucumber, squash, watermelon, etc.

cultivation: The turning of surface soil to prepare a seedbed, aerate, and/or eliminate weeds.

cultural pest control: The use of various cultivation techniques or practices to limit pathogen infestations. It includes hoeing, crop rotation, manual insect or weed removal, roguing of diseased or infested plants, cleaning of pruning shears and field implements, etc.

cuttage: Removal of plant parts in order to propagate new plants. See asexual propagation page.

cytokinins: A group of plant hormones involved in cell division, apical dominance, rooting inhibition, senescence inhibition, germination, etc. Zeatin is a natural form. Synthetic forms include BA and kinetin.

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- D -

day neutral plant: One that does not respond to any particular light/dark regime.

determinate: Plants having a bushlike growth habit whose floral buds all appear in unison.

dicots: Plants having netted veins, taproot systems, embryos with two cotyledons, a vascular core in the stem, and usually four or five floral whorls. Ex., legumes, cucurbits, roses, maples, sunflowers, etc.

differentiation: Cell specialization.

dioecious: Plant species having male (staminate) and female (pistillate) flowers on separate plants. Examples: asparagus , kiwi, and hemp.

Diptera: Insect order consisting of true flies. Important plant pests include the cabbage root maggot, Hessian fly (wheat), Mediterranean fruit fly (Medfly), and Caribbean fruit fly.

disbudding: The elimination through pruning of reproductive buds or small fruit, so as to encourage increased fruit size from the remaining buds.

dormancy: The period of plant growth inactivity. May be in the seed (in some annuals such as wild oats) or in the whole plant.

double fertilization: Union of one sperm + egg to form a diploid (2n) zygote, while the second sperm + fused polar nuclei unite to form triploid (3n) endosperm. Common fertilization method of angiosperms.

drupe: The fruit of certain plants of the laurel and rose families, having a thin exocarp, fleshy or leathery mesocarp, and a hard, stony endocarp. Examples: avocadoes, almonds and peaches.

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- E -

endosperm: Nutritive, usually triploid, seed storage tissue arising from the fusion of sperm and polar nuclei in angiosperm double fertilization.

Entisol: Soil taxonomic order consisting of the youngest soils, having little or no differentiation into distinct horizons, such as on sand dunes or flood plains. Suffix: -ent.

epinasty: The downward curling of leaf edges, typically a symptom of certain viral diseases.

ethylene: A plant growth-regulating gas, naturally produced in ripening fruit as well as other parts of the plant, responsible for promoting ripening and involved in abscission and other plant processes.

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- F -

F1 hybrid: A plant derived from a sexual cross between two homozygous but different parents.

fallowing: Practice of leaving a field unplanted during a growing season, usually to conserve moisture and nutrients.

family: Plant taxonomic category consisting of a group of related subfamilies, tribes (as in grasses), or genera. Examples: Fabaceae (legume family), Poaceae (grass family), Solanaceae (nightshade family). See Top 25 Most Economically Important Angiosperm Families.

field capacity: The point at which all excess gravitational water has drained from a soil.

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- G -

gamete: Haploid reproductive body arising from meiosis, either the sperm (male) or egg (female).

Gelisols: Tundra soils having a dark surface layer high in organic matter, underlain by permafrost. Suffix -els.

genotype: The genetic composition of an individual.

gibberellins: A group of 50-odd plant hormones involved in stimulating plant growth, breaking dormancy, and affecting fruit set and morphology.

girdling: A phloem-disruption method of inducing reproductive bud development. All of the cambium except for small patches are severed in a ring around the stem, thus causing a localized increase in the carbohydrate/nitrogen ratio in the upper portion of the plant. This method is often used in seedless grape production.

grafting or graftage: The union of two different plant parts to create a single new plant. See asexual propagation page.

gravitational water: Water that drains freely from a soil's macropores through the action of gravity.

greenhouse effect: The warming of the earth's atmosphere via the trapping effect of solar infrared radiation from atmospheric greenhouse gases.

greenhouse gas: An atmospheric gas that tends to prevent heat from radiating back into space, thus having a warming effect on the atmosphere. Examples: water vapor, carbon dioxide, methane.

gymnosperms: Plants having uncovered ("naked") seed. Ex., pines, spruces, firs, and other conifers.

gynoecium: Female floral whorl, also known as the pistil ('gyno'=female, 'oecium'=house).

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- H -

haploid: A sexual gamete, or a plant having a chromosomal set from only one parent, ie, with half the normal diploid chromosome number.

hardening: Gradual exposure of greenhouse plants to colder temperatures, drier conditions, reduced light, or reduced fertility in preparation for transplanting outdoors.

heading back: Pruning of a portion of a limb.

heaving: Throwing up, or the repeated freezing and thawing of moist soil during winter conditions.

herbicide: Chemical that destroys plant life. Categories include narrow vs. broad spectrum; systemic or translocated vs. contact; persistent vs. non-persistent; and preplant, preemergence, and postemergence types.

hesperidium: Type of berry having an exocarp/mesocarp rind and a pulpy endocarp. Example: grapefruit and other citrus.

heterozygous (heterozygote): Having different, or contrasting, alleles on the two parental chromosomes at a given locus.

Histosols: Soil taxonomic order consisting of soils having organic matter as the primary parent material, often forming under marshy wetlands and in other poorly-drained areas. Suffix: -ist.

homologous chromosomes (homologues): The same chromosome in the two parental chromosome sets. Homologues pair and their genes recombine in meiosis.

Homoptera: Insect order consisting of phloem-sucking insects, including whiteflies and aphids. Economically important species include green peach aphid, Russian wheat aphid, greenbug, whiteflies.

homozygous (homozygote): Having the same allele on both parental chromosomes at a particular locus.

horizon: A given soil layer in a soil profile. Horizons are designated as A, B, C, or D, with the A horizon being the surface layer, usually.

host range: The series of plants that a particular pathogen can infect or parasitize.

humus: Dark brown, decomposed, colloidal organic matter found in soils. Humus usually has a beneficial effect on aeration and soil structure due to its ability to flocculate, or aggregate, multivalent cations.

hybrid vigor or heterosis: The superior phenotypic characteristics of an F1 hybrid when compared with its two distinct, homozygous parents.

hygroscopic or unavailable water: Water remaining in soil past the wilting point; ie, water that the plant cannot extract for growth purposes.

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- I -

inbreeding depression: The successive loss of population vigor with each generation of selfing of an F1 hybrid. It is often seen in outcrossing, vegetatively-propagated, and/or heterozygous autotetraploid plants.

Inceptisols: Soil taxonomic order consisting of young soils with weak horizonal differentiation. They are found in diverse environments. Suffix: -ept.

indeterminate: Plants having a viney growth habit and which continue producing floral buds after flowering initiation.

intercropping: The planting of two different crops together in the same field.

inversion or temperature inversion: When cold air sinks to the bottom of a valley and becomes trapped beneath a layer of warmer air, usually in the absence of a strong breeze.

IPM: Integrated pest management, a strategy for controlling crop pests using a combination of tactics, including crop management practices, pesticides, biological competitors, etc.

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- J -

juvenility: Plant growth phase characterized by vegetative growth, little or no food storage, and lack of reproductive structures. Juvenile tissue is typically more able to be propagated vegetatively than adult or mature tissue.

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- K -

karyopsis: Same as caryopsis.

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- L -

landraces or landrace cultivars: Relatively primitive, often heterogeneous crop plants grown for centuries in a given area, and which have been improved through selection pressure of local pests, pathogens, and by selection of superior types by indigenous farmers.

layering: Root induction on stem tissue in order to eventually sever the tissue for propagating a new individual plant. See asexual propagation page.

leaching: Gravitational movement of water, dissolved, and colloidal substances from the surface or upper horizons to lower horizons in a soil.

legumes: Plants of the pea family (Fabaceae) that form characteristic elongated seed pods and fix atmospheric nitrogen through symbiotic interaction with soil bacteria of the genera Rhizobium and Bradyrhizobium. Ex., alfalfa, beans, clovers, peas, peanuts, soybeans, tamarind, etc.

Lepidoptera: Order of chewing insects that have a caterpillar or worm stage and a flying adult stage. Examples: tomato hornworm, fall armyworm, southwestern and European corn borers, codling moth, corn earworm, cutworms.

locus: Specific place on a chromosome or genetic map where a gene and its alleles are found.

lodging: When plants fall over and lie flat on the soil surface, especially cereal grain crops, often due to wind, hail, and/or excessive stem growth.

long-day plant: A plant that flowers, bulbs, tillers, etc., in response to daylengths increasing above some critical minimum number of hours.

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- M -

magnesium (Mg): Secondary macronutrient critical for plant growth, as it is the central metal in chlorophyll. Magnesium forms a divalent soil cation.

manganese (Mn): Micronutrient critical for plant growth, usually found as the manganous oxide anion in soil.

meiosis: Chromosome number-reductional cell divisions in the formation of sexual gametes.

mesophyte: A plant adapted to growing in mild conditions.

mesophyll: Parenchymatous, photosynthetic cell layers within the leaf, consisting usually of palisade and spongy mesophyll tissues.

mitochondria: Power-producing organelles of the cell, site of catabolic aerobic respiration. Mitochondria contain their own chromosome of DNA, which are generally maternally inherited through the egg.

mitosis: Chromosome number-equational cell divisions in the production of daughter cells.

Mollisols: Soil taxonomic order consisting of semiarid grassland prairie soils of high fertility, near-neutral pH, a thick A horizon high in dark organic matter, and excellent structure for cultivation. Suffix: - oll.

monocots: Plants having parallel veins and straplike or fanlike leaves, fibrous root systems, embryos with a single cotyledon, scattered vascular bundles in the stem, and three or six floral whorls. Ex., grasses, sedges, palms, lilies.

monoecious: Plants having separate male and female flowers on the same plant. Examples: cucumbers and corn.

mosaic: Leaf mottling and yellowing symptoms, typical of certain viral diseases.

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- N -

nitrogen (N): Primary plant macronutrient and a major component of proteins and nucleic acids. Inert atmospheric dinitrogen gas must be converted to soluble forms in the soil. A major way it is converted is through the action of nitrogen-fixing bacteria symbiotically associated with the roots of leguminous plants. Common soluble soil forms are the ammonium monovalent cation and the nitrate monovalent anion.

node: Place on the stem where one or more leaves arise; often, buds arise at nodes.

no-till, minimum-till, or reduced tillage cultivation: Direct seeding of a crop through some or all of the previous growing season's crop residues, usually done to conserve moisture, prevent erosion, and reduce tillage compaction.

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- O -

organic matter (O.M.): Soil fraction consisting of live, dead, and decomposed organisms or parts thereof.

Orthoptera: Insect order that includes grasshoppers, crickets, and locusts.

ovary: Female floral structure located at the base of the style, containing the ovule(s).

Oxisols: Soil taxonomic order consisting of highly-weathered, acidic, infertile tropical rainforest soils with low organic matter content and high iron and aluminum oxide content. They often lack distinct horizons. Suffix: - ox.

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- P -

parenchyma: Plant tissue type composed of relatively undifferentiated (non-specialized) cells. Found primarily in leaf (mesophyll), cortex, and also in conductive tissues.

parent material: Substance(s) from which a soil forms.

parthenocarpic fruit: Fruit production due to enlargement of the ovary without fertilization, ie, seedless fruit. Examples: bananas, cucumbers, and oranges.
pepo: Type of berry-fruit consisting of an exocarp rind, fleshy mesocarp, and watery endocarp. Example: cantaloupe and other cucurbits.
petals: Modified leaves of the second floral whorl moving inward, or corolla.

phenotype: What the plant looks like, ie, its morphology.

phloem: Plant vascular tissue composed of specialized cells that conduct photosynthate throughout the plant body.

phosphorus (P): A primary plant macronutrient, usually found in slow-leaching soil forms, that is a main component of nucleic acids, including energy-transmitting ATP, as well as phosphoproteins and phospholipids.

photoperiodism: Response of plants to increasing (long-day plants) or decreasing (short-day plants) daylengths, in terms of flowering, bulbing, tillering, etc.

phototropism: Photo-mediated degradation of epidermal cell auxin, resulting in decreased cell elongation on the light-exposed side of the plant and, hence, bending of the plant toward the light source.

physical dormancy: Aka hard seed, physical dormancy is the inability of a seed to germinate due to an impenetrable, or water-impervious, seed coat.

physiological dormancy: Aka chemical dormancy, physiological dormancy in seed is caused by the presence of chemical germination inhibitors or by embryonic immaturity.

physiological drought: Dessication of plant parts during the wintertime, due to inability of the plant to absorb frozen soil water.

pistil: Female flower parts: stigma, style, ovary. Also, the innermost floral whorl, or gynoecium.

pistillate flowers: Flowers with female, but not male, parts, as the tassel in monoecious corn or flowers on a male plant in a dioecious species.

plasmalemma: The outer membrane of the plant cell.

plasmodesmata: Cytoplasmic connections between adjacent plant cells.

pome: A fruit type consisting of a thin exocarp, fleshy mesocarp, and a papery endocarp, found in certain members of the rose family. Examples: apples and pears.

potassium (K): Primary plant macronutrient, commonly found in soil solution as a monovalent cation. Potassium is essentially involved in cellular water balance.

propagule: Plant part that is being propagated.

pterophytes: Spore-producing plants, ie, the ferns (Pterophyta).

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- Q -

qualitative trait: A hereditary characteristic of a plant controlled by one or a very small number of genes.

quantitative trait: A hereditary characteristic of a plant controlled by a large number of genes. Expression of the trait is variable from year to year, and from environment to environment.

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- R -

rhizome: Modified subterranean stem that runs horizontally, usually capable of producing new shoots from bud-nodes. Example: ginger.

rotation cropping: Alternating crops in successive years in order to restrict pest and disease buildup and to limit nutrient depletion.

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- S -

sclerenchyma: Plant tissue type composed of dead cells with thickened walls, usually for support or protection. Two types are fibers and sclereids.

segregation: Mendelian hereditary principle explaining the distribution of alleles among the offspring of a selfed heterozygous individual.

senescence: Terminal life phase of plants, characterized by the irreversible deterioration of tissue.

sepals: Modified leaves in the outermost floral whorl, or calyx.

short-day plant: A plant that flowers, bulbs, tillers, etc., in response to daylengths decreasing below some critical maximum number of hours. Examples: soybeans, chrysanthemums.

small grains: Term usually applied to the cool-season cereals (wheat, oats, barley, rye) and, sometimes, rice.

soil profile: A vertical cross-section of a given soil, showing the different layers or horizons, if present.

soil structure: The size, shape, and properties of aggregated soil particles in a given soil. Examples: crumb, blocky, prismatic, spherical, platy, etc.

soil texture: The relative amounts of sand, silt, and clay particles in a given soil.

somaclone: A diploid plant obtained by cell or tissue culture (micropropagation).

somaclonal variation: Phenotypic evidence of mutation arising from cell or tissue culture.

spermatophytes: Seed-producing plants.

Spodosols: Soil taxonomic order consisting usually of acidic coniferous forest soils having a distinct, light gray leached horizon underlain by a layer of accumulated silicates and oxides and dark organic matter. Suffix: -od.
stamen: Male flower parts: pollen, anthers, filaments. Also, the third floral whorl moving inward, or androecium.

stolon: Horizontal aboveground stem, aka 'runner', capable of producing new plants from bud-nodes. Example: strawberry.

succession cropping: Planting of different crops in immediate succession in order to maximize production on a given piece of ground.

suffocants: Chemicals, usually containing oils, which kill by coating the bodies of arthropods, preventing gas exchange and respiration.

sulfur (S): Secondary macronutrient for plants, usually found as the sulfate divalent anion in soil solution. Sulfur is a main component of a group of amino acids.

supercooling: Subfreezing of water without ice crystal formation.

sustainable agriculture: Crop production practices designed to minimize undesirable environmental consequences of modern mechanized agriculture such as chemical pollution, soil erosion, soil compaction, etc.

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- T -

T-bud: A type of budding graft in which a T-shaped incision is made in the bark of the stock, then a scion consisting of a bud and attached bark segment is placed into the incision with the bud facing outward.

thinning out: Pruning of entire limbs.

Thysanoptera: Order of flying, sucking insects that includes the thrips.

topiary: The ornamental horticultural art of pruning and training trees or shrubs to resemble animals or other objects.

tracheophytes: Plants having a vascular system.

training: Alteration of a plant's morphology through pruning of limbs or limb portions.

tuber: A type of modified stem or root, consisting of enlarged subterranean storage tissue. Potato tubers are stem tissue which have nodes, or "eyes", from which whole plants are propagated. Sweet potato tubers have similar nodal structures but are actually root, not stem, tissue.

turgidity: Condition in which plant tissues/organs are fully distended due to the presence of abundant water.

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- U -

Ultisols: Soil taxonomic order consisting of acidic soils with high clay content near the surface. They are often found in humid subtropical forests, have high iron oxide content, and are of moderate fertility. Suffix: -ult.

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- V -

vacuole: Plant "organelle" consisting of a membrane (tonoplast)-bound storage cavity. Vacuoles tend to grow larger as the cell matures.

vector: Transmitter of a viral disease, often a specific insect.

vegetative phase: Juvenile plant growth phase characterized by foliar growth, lack of carbohydrate storage, and lack of floral bud initiation.

vernalization: Flowering induction in response to prolonged exposure to cold temperatures, as occurs in winter cereals.

Vertisols: Soil taxonomic order consisting of soils with a high percentage of shrinking-swelling bentonite or montmorillonite clay particles, resulting in upheaval of horizons. Suffix: -ert.

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- W -

whorl: A circle of floral organs or branches or leaves at a node.

wilting point or permanent wilting point (PWP): The point at which all plant-available water has been depleted from a soil, after which plants begin to wilt.

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- X -

xerophyte: A plant adapted to growth in arid conditions.

xylem: Plant vascular organ composed of tissues that conduct water and dissolved nutrients from the roots upward throughout the plant body.