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abiotic: Pertaining to nonbiological factors.

abrasion: Mechanical process of gradually breaking down a hard layer, as in a seed coat.

abscisic acid: Plant hormone associated with dormancy, abscission of organs, and water stress.

abscission layer: Detachment of leaves, flowers, or fruits from a plant, usually at a mechanically weak location, termed the abscission zone.

absorption: Process of taking in, as uptake by roots.

accessory buds: Buds adjacent to a primary bud and usually smaller in size.

achene: Small, dry, one-seeded indehiscent fruit; the pericarp is easily separated from the seed coat.

acid: [H.sup.+] (proton) donor; a substance that associates to release [H.sup.+] and thus cause the pH of the solution to be less than 7.0.

acidic: Possessing a relatively large number of hydrogen ions; having a pH of less than 7.0.

aconitine: A highly poisonous alkaloid derived from various aconite species. It is a neurotoxin that opens TTX-sensitive Na+ channels in the heart.

acridine dyes: Organic pigment molecules that are capable of causing permanent genetic changes (mutations).

active transport: Movement of ions or molecules against a concentration gradient using metabolic energy.

adaptation: Conforming to a given set of environmental conditions.

adenine: Nitrogen base found in both DNA and RNA.

adenosine diphosphate (ADP): Building block for ATP; by adding a terminal phosphate group and a large amount of energy, ATP can be formed.

adenosine triphosphate (ATP): Major source of chemical energy for biochemical reactions; metabolic energy is stored primarily in the terminal phosphate ester linkage.

adhesion: Attraction of unlike particles; water particles adhere to the surface of clays.

adventitious roots: Structure arising at some location not usually expected, such as on a stem.

aerate: To supply with oxygen.

aerial: Pertaining to being in the air, such as a root projecting from an aboveground stem.

aerobic organisms: Organisms that have to have atmospheric oxygen to live. aerobic respiration: The process in which glucose is converted into C[O.sub.2] and [H.sub.2]O in the presence of oxygen, releasing large amounts of ATP. This process includes the krebs cycle, electron transport chain, and oxidative phosphorylation.

after-ripening dormancy: Changes that must take place in a seed to overcome dormancy or the dormancy period following seed formation, necessary for embryo changes that insure germination.

agar (ah-ger): Complex polysaccharide made from red algae and used for preparing a semisolid substrate for growing microorganisms.

agent orange: Herbicide used as a defoliant in the Vietnam War; composed of 2,4-D and 2,4,5-T.

aggregate fruit: Fruit developing from numerous simple carpels from a single flower.

aleurone layer (al-u-roan): Group of cells rich in protein granules and located as the outer layer of the endosperm of many grain seeds.

algal bloom: Proliferation of algae due to a nutrient rich medium, usually resulting in a green scum of the water surface.

algin: Polysaccharide derived from brown algae and used for many industrial processes.

alkaline: Denoting substances that release hydroxyl (O[H.sup.-]) ions into solution; see Basic.

alkaloid: Group of nitrogen-containing compounds having diverse structures; many alkaloids have medicinal, hallucinogenic, or toxic properties.

allele: One of the two genes for a given trait at a specific locus on homologous chromosomes.

[alpha] (alpha) amylase: Enzyme that converts starch to sugars.

alternate host: Alternate plant required to complete the life cycle of some microorganisms (for example, for Puccinia graminis tritici, wheat is the primary host and Berberis vulgaris is the alternate host).

alternate leaf arrangement: Leaf arrangement in which there is only one leaf per node.

alternation of generations: Sequence of a diploid sporophyte plant producing haploid spores that develop into gameophyte plants (or stages); gametophytes produce gametes, which fuse to form a sporophyte again.

amber: Fossilized resin of ancient trees. amino acid (ah-mean-o): Organic molecule including one or more amino (-N[H.sub.2]) and acid (-COOH) groups; proteins are made up of these molecules.

amino group (-N[H.sub.2]): Chemical part of molecule that imparts basic properties to an amino acid.

ammonia: Colorless, pungent gas, N[H.sub.3], extensively used in a wide variety of nitrogen-containing organic and inorganic chemicals.

anaerobic: Without atmospheric oxygen.

anaerobic respiration: Partial oxidation of pyruvate to lactic acid without atmospheric oxygen.

analgesic: Chemical that reduces the body's sensitivity to pain.

anaphase: Stage of nuclear division in which the chromosomes are pulled to opposite poles while attached to spindle fibers at the centromere.

anchorage: A function of the plant roots.

androsterone: Animal hormone not synthesized by plant.

angiosperm: Group of plants characterized by having flowers as their sexual reproductive structures.

anion: Negatively charged ion in an electrolyte solution, attracted to the anode under the influence of a difference in electrical potential.

annual: Plant that completes its life cycle during one growing season.

annual tree ring: Secondary xylem produced during a single growing season.

anther: Male reproductive organ enclosing and containing the pollen grains.

antheridium: A sperm-producing organ occurring in seedless plants, fungi, and algae.

anthocyanins: Group of water-soluble red to blue flavonoid pigments found in certain plants; especially important pigmentation in flower petals.

anthraquinone glycosides: Derivative of anthracene, a dyestuff. Its derivatives found in aloes, cascara sagrada, senna, and rhubarb act as cathartics.

antibiosis: Inhibition of growth of a microorganism by a substance produced by another microorganism.

antibiotic: Organic molecule naturally produced by one microorganism that retards or prevents the growth of another organism.

anticodon loop: Portion of a tRNA molecule responsible for the anticodon triplet, which pairs with the codon of mRNA.

antiparallel: Opposite in direction, as in the structure of the two strands of DNA.

antipoidal cell: Three haploid cells, at the end of the embryo sac away from the micropyle.

apex: Tip of a structure; a leaf apex, for example, is the tip of the leaf.

apical dominance: Phenomenon leading to controlled growth of lateral shoots; growth occurs primarily at the top of plant.

apoplastic movement: Pertaining to the movement of water in the free space of tissue; free space includes cell walls and intercellular spaces.

archegonium: A multicellular, often flask-shaped, egg-producing organ occurring in mosses, ferns, and most gymnosperms.

asexual: Lacking sexual reproduction; vegetative reproduction.

aspartate: An excitatory amino acid. atmospheric pressure: Ambient pressure created near the earth's surface by large air cells that circulate around the globe.

atom: The basic unit of matter; the smallest complete unit of the elements, consisting of protons, neutrons, and electrons.

atomic number: Number of protons within the nucleus of an atom, which determines the elemental properties of that atom.

atomic weight: Weight of an atom determined by adding the number of protons and neutrons (the mass of electrons is usually considered to be negligible).

atropine: Drug obtained from belladonna that is administered via injection, eye drops, or in oral form to relax muscles.

autonomic nervous system: Portion of the nervous system that regulates involuntary body functions, including those of the heart and intestine; controls blood flow, digestion, and temperature regulation.

autotrophic (au-to-tro-fik): Organism that produces its own food by photosynthesis; green plant.

auxin: Hormone that has the capacity to induce lengthening of cells.

auxin thresholds: Protein involved in the auxin signaling pathway (e.g., transport and signal).

axil: Lateral; the point of attachment of a bud or shoot other than at the apex of the stem.

axillary bud: Any bud on a stem other than the terminal bud at the shoot apex.

backcross: Crossing a hybrid offspring back to either parent.

bacteria (singular: bacterium): Unicellular microorganisms; typically a few micrometres in length, individual bacteria have a wide-range of shapes.

balsa: Density of dry balsa wood ranges from 100-200 kg/[m.sup.3]; used to make very light, stiff structures in model building.

baobab tree: African tree having an exceedingly thick trunk and fruit that resembles a gourd and has an edible pulp called monkey bread.

bare root: Not potted; no soil around root.

bark: Portions of a woody plant stem or truck exterior to the vascular cambium.

barley (Hordeum jubatum): Plant grown for forage and grain, used for livestock feed, malt production, and cereal; cultivated since prehistoric times.

basal rosette: Leaves clustered at ground level; can be alternate or whorled, but with extremely short internodes.

basalt: Semiviscous layer of igneous rock underlying the granite continental plates.

basic: Possessing a large number of hydroxyl (O[H.sup.-]) ions; a pH of more than 7.0.

bedrock: Solid rock that underlies all soil, sand, clay, gravel, and loose material on the earth's surface.

benign: Not dangerous to health; not recurrent or progressive.

benthic (ben-thik): Pertaining to the bottom region of an ocean, lake, or pond.

berry: Fleshy, two or multiple-carpeled ovary, each carpel having many seeds.

[beta] (beta) carotene: Most abundant of the carotenoids; strong provitamin A activity; unlike vitamin A, it is a strong antioxidant.

biennial: Plant requiring two growing seasons to complete its life cycle.

big bang: Theory is that the entire universe was created at one time.

binomial: Two names, genus and species, comprising the scientific name.

bioassay: Quantitative assay of a particular substance using a portion of or an entire living organism.

bioinformatics: Refers to the use of computer science, mathematics, and information theory to model and analyze biological systems, specifically in systems with genetic material.

biological clock: Internal biological timing system that relates cyclic phenomena within the organism to the diurnal or annual clock.

biological control: Control of pests by disrupting their ecological status, as through the use of organisms that are natural predators, parasites, or pathogens. Also called biocontrol.

bioluminescence: Biological production of light using ATP as an energy source.

biomass: Total amount of organic material produced; usually expressed on a dry weight basis.

biomes: Worldwide groupings of similar ecosystems.

biopharmaceuticals: Medicines produced by biotechnology and genetic engineering.

biosphere: Earth and all of its ecological interactions considered as a single system.

biotechnology: Application of biological and engineering techniques to microorganisms, plants, and animals; sometimes used in the narrower sense of genetic engineering. It is the application of scientific and engineering principles to the processing of materials by biological agents to provide goods and services. The three major techniques are genetic engineering, monoclonal antibody technology, and bioprocessing.

biotic: Pertaining to the living part of the environment.

bisexual: Flower having both stamens and pistil (both sexes); a perfect flower.

bivalent: Two homologous chromosomes associated in a parallel fashion; formed during prophase I of meiosis.

blade: Flattened portion of the leaf.

board feet: Volume of measurement for lumber equal to 144 square inches (1" x 12" x 12").

bog: Wet, marshy region, such as a peat bog.

bomb calorimeter: Instrument used for measuring the caloric content of any organic materials to C[O.sub.2] and [H.sub.2]O.

boot: One of the growth stages of small grains; during the boot stage, the head can be felt inside the upper leaf sheath and the flag (last) leaf has developed.

bract: Modified leaf or leaflike structure, usually much reduced in size.

brambles: Plants like the raspberry, loganberry, boysenberry, dewberry, and tayberry.

branch roots: Lateral roots arising from the pericycle of a larger root.

broadcast planting: Seeds scattered over a wide area.

bromeliads: Flowering plants native to the tropical and warm temperature regions including both epiphytes and terrestrial.

bronchodilator: Medicine that relaxes the smooth muscles of the airways, allowing the airway to open up (to dilate) since the muscles are not squeezing it shut.

bryophytes: Are all embryophytes ('land plants') that are non-vascular: they have tissues and enclosed reproductive systems, but they lack vascular tissue.

bud: Meristematic shoot located at a terminal or lateral position of a shoot. bud scales: Modified leaves surrounding and protecting a bud.

budding: Method of asexual propagation characterized by placing a bud of one plant onto the stem of another plant.

buffer: Any substance that absorbs or releases protons (H+) so that the pH of the solution remains stable, even when acid or base is added.

bulb: Underground storage organ characterized by fleshy leaves attached to a stem base.

bulliform cell: Large epidermal cell found on the upper surface of many grass leaves; turgor pressure in these cells controls the lateral rolling of the leaves during water stress.

bunch grass: Grass growing in clumps rather than spreading out.

bundle sheath cells: Cells surrounding the vascular bundle in C4 plants.

buttressing: Stem modification in which the diameter is larger near the ground giving additional mechanical support.

C3 pathway: Calvin cycle of carbon fixation in which C[O.sub.2] is incorporated into ribulose 1,5-bisphosphate.

C4 pathway: Also called the Hatch-Slack pathway of photosynthesis; C[O.sub.2] is initially fixed in mesophyll cells into malate and aspartate.

callose: Complex carbohydrate found in the sieve areas of sieve tube elements; particularly abundant at the time of injury.

callus: Undifferentiated group of cells formed as a response to wounding (as at the base of a stem) or in tissue culture.

calorie: Unit of heat; one calorie is the amount of heat required to raise the temperature of 1 gm of water 1[degrees]C.

Calvin cycle: Series of biochemical, enzyme-mediated reactions during which atmospheric carbon dioxide is reduced and incorporated into organic molecules, eventually some of this forms sugars; in eukaryotes it occurs in the stroma of the chloroplast.

calyx: Referring to all the sepals of a flower collectively.

CAM: see Crassulacean acid metabolism.

candelilla wax: Is derived from a shrub native to that country and the southwestern US. Ever wonder why lipstick can stay hard in all but the most sultry of conditions? Thank candelilla wax. It has also been used in both the chewing gum and varnish industries.

cane: Part of the vine left that will produce fruit the next growing season.

canopy: Upper portion of a population of plants; the term is usually associated with forests and agricultural crops.

capillary pores: Small spaces in the soil that become filled with a fluid (such as water) because of the adhesion of particles to the matrix (solid substrate) and the cohesion of the water molecules to themselves.

capsule: Simple fruit that develops from a compound ovary with two or more carpels; capsules dehisce in many ways.

carbohydrate: Organic molecule consisting of a chain of carbon atoms, each having hydrogen ([H.sup.+]) and ([H.sup.-]) groups attached in the basic pattern C[H.sub.2]O; simple sugars and polysaccharides such as starch and cellulose.

carbon dioxide (C[O.sub.2]): Colorless, odorless incombustible gas; formed during respiration and organic decomposition. carbon fixation: Process by which C[O.sub.2] is incorporated into organic molecules.

carboniferous period: The Carboniferous period was marked by vast, coalforming swamps (see also bog) and a succession of changes in the earth's surface that, continuing into the Permian Period, ended the Paleozoic era.

carboxyl group: Acid group attached to a molecule--COOH.

cardiac glycosides: Steroid glycosides that have stimulative effects on the heart, for example digitoxin, digoxin, and gitoxin from the foxglove (Digitalis spp.); help to support the rate and strength of the heart's contraction when it is failing, and are strongly diuretic (increase urine output).

carnauba wax (car-now-bah): Highquality, hard industrial wax extracted from the carnauba palm tree.

carnivore: An animal that feeds on other animals.

carotenoids pigments: Plant cell pigments: red, orange, and yellow lipid soluble pigments found embedded in the membrane of chloroplast and chromoplast.

carpel: Reproduction unit composed of a placental surface and ovules.

carpellate: Unisexual flower having carpels but no stamens.

carrageenan: Polysaccharide extracted from red algae and used for many industrial products.

carrying capacity: Maximum number of organisms that can live in balance within the natural food supply of a given area.

caryopsis: Dry, indehiscent one-seeded fruit in which the pericarp is united to the seed coat.

casparian strip: Suberized layer covering the radial and transverse walls of endodermal cells.

cassava: Edible, starchy root used in making bread or cakes.

cassia: Any of various plants of the genus used medicinally as a cathartic.

catalyst: Any substance that causes a chemical reaction to proceed much faster than it would without the catalyst. In biochemical reactions, enzymes are proteins that act as catalysts.

cations: An ion or group of ions having a positive charge and characteristically moving toward the negative electrode in electrolysis.

cell expansion: Proper development of plant shape is at least partly dependent on regulated cell expansion.

cell membrane: Semipermeable membrane that encloses the cytoplasm of a cell.

cellulase: An enzyme that breaks down cellulose.

cellulose: Primary structural carbohydrate plant cells; composed of many glucose molecules.

cellulose microfibrils: Cellulose molecules oriented parallel to the long axis of the microfibril in a paracrystalline array, which provides great tensile strength; held in place by the wall matrix and their orientation is closely controlled by the protoplast.

central bud: Main bud in a cluster located at one position.

central cell: Also known as the polar cell, the binucleated cell in the center of an embryo sac containing the two haploid polar nuclei.

central nervous system: Portion of the vertebrate nervous system consisting of the brain and spinal cord.

centromere: Most condensed and constricted region of a chromosome, to which the spindle fiber is attached during mitosis.

century plant: Tropical American plants with basal rosettes of fibrous sword-shaped leaves.

chaparral (shap-a-ral): Vegetative association typical of the Mediterranean region dominated by smaller, often thorny or roughly branched evergreen trees and shrubs and deciduous trees; included in the temperate deciduous forest biome.

charcoal: Carbonaceous material obtained by heating wood or other organic matter in the absence of air.

chemical energy: Potential energy stored in chemical bonds of molecules.

chemotaxonomy: Using the identification of groups of chemical compounds as genetic indicators in the establishment of taxonomic relationships.

chiasma (pl., chiasmata): Point of physical exchange of equal segments of adjacent nonsister chromatids during the bivalent stage of meiosis.

chinampas: Areas of fertile reclaimed land, constructed by the Aztecs, and made of mud dredged from canals.

chlorophyll: Pigment molecule responsible for trapping light energy in the primary events of photosynthesis.

chloroplasts: Organelles found in cells of the aboveground portions of green plants; specialized for photosynthesis.

cholesterol: Animal steroid found in some plants in low concentrations.

chromatid: One replicate of a chromosome visible in prophase following DNA replication during interphase.

chromatin: Dark-staining nuclear material present during interphase; includes the SNA and nuclear proteins.

chromatophore: Discrete spherical bodies located in the membranes of prokaryotes that carry the enzymes and pigments important in photosynthesis.

chromoplast: Found in colored organs of plants such as fruit and floral petals, to which they give their distinctive colors and or nonphotosynthetic carotenoidbearing; membrane-bound organelles specialized for carotenoid storage.

chromosome: Microscopic strands within the nucleus of eukaryotic cells that carry DNA, which is responsible for inheritance.

cicutoxin: Active principle of the water hemlock extracted as a poisonous gummy substance.

circulation cells: Air movement in a circular pattern from the earth's surface up into the outer atmosphere and then back down again; produce high and low pressure systems and dictate precipitation patterns at different latitudes.

cis-polyisoprene-: Properties are also close to that of natural rubber.

cladophyll: Stem or branch that resembles a leaf.

climacteric rise: Point during the ripening process of certain fruits in which the respiration rates rise to very high levels.

climatology: Study of climates and the factors influencing them.

climax community: Ultimate vegetative community that any given habitat can support; the final stage in ecological succession.

clone: Genetically identical organisms. coastal shelf: Shallow region of the ocean surrounding a large land mass.

cocaine: Highly addictive stimulant drug derived from the coca plant that produces profound feelings of pleasure.

coconut palm: Tall palm tree bearing coconuts as fruits; widely planted throughout the tropics.

codeine: Sedative and pain-relieving agent found in opium. Structurally related to morphine but less potent, and constituting approximately 0.5% of the opium extract.

codon: Three-nucleotide sequence of mRNA responsible for coding of a specific amino acid.

coenzymes: Various substances, including certain vitamins and heavy metals, required, in conjunction with a specific enzyme, to bring about a biochemical reaction.

co-evolution: Evolution of two species in concert, such that their survival and reproduction are mutually beneficial.

cofactor: Nonprotein substance required by enzymes for proper function; they may be metallic ions or organic molecules called coenzymes.

cohesive: Attraction of like particles; water molecules cohere to each other.

cold damage: Temperature range through which flower bud, leaf, or structure can be expected to occur.

cold frame: Frame house built for growing plants that has no inside heating provided.

coleoptiles: Protective sheath enclosing the shoot tip and embryonic leaves of grasses.

collenchymas: Tissue-type characteristic by primary cell walls with thickened corners.

colonial: Multicellular organism that produces a colony of cells, usually referring to colonial algae.

colonization: Pioneer establishment of vegetation on a previously unvegetated area.

colonizer: Organism that initiates the biological "conquest" of soil or rock.

colony: Group of microorganisms growing in a confined area so that the population as a whole has color and texture.

combine: Type of machine that harvests seed crops.

commensalism: Interaction between two species in which one population is benefited but the other is not affected.

common name: Regional name for well-known plants; in the language of the region, rather than in Latin, and not necessarily paralleling any scientific name.

community: All living organisms sharing a given area.

companion cell: Small cell adjacent to a sieve tube element within phloem tissue.

companion crop: Crop grown specifically with another crop because it recovers the land or protects another crop until it can get established; also called a nurse crop.

compartmentalization of enzymes: Division of labor in living cells such that enzymes related to a particular function are packaged and separated from the other cell contents, usually by a membrane.

compensation point: Condition in a living system in which the uptake of

C[O.sub.2] equals the release of C[O.sub.2]; that is, photosynthesis equals respiration.

competition: Demand by two or more organisms for the same resources.

complementary strand: Two polynucleotide chains in which the pairing of adenine is always with thymine (in DNA) or uracil (in RNA), and guanine is always paired with cytosine.

complete flower: Having all four floral parts; sepals, petals, stamens, and pistil.

compost: Partially decayed organic matter used in gardening and farming to enrich the soil and increase water-holding capacity.

compound fruit: Fruit that develops from several ovaries in either a single flower or multiple flowers.

compound leaf: Leaf composed of two or more completely independent blade units called leaflets.

compound pistil: Ovary composed of two or more carpels.

compression: Fossil formed when carbonized plant material is still present in the original shape but is greatly compressed and reduced in size by pressure.

compression wood: Reaction wood produced along the lower side of leaning trees, straightening the trunk by expanding and pushing the tree upright.

concentration gradient: Difference in concentration in two parts of a system.

condensation: To change from a gas to a liquid or solid.

conduction: The flow of thermal energy through a substance from a higher- to a lower-temperature region.

cone: Strobilus; the reproductive structure of a gymnosperm.

conifer: Any of a group of plants that produce a strobilus or cone as a reproductive structure.

container-grown: Plants grown in pots, planters or other containers.

controlled atmosphere: Specified gas or mixture of gases at a predetermined temperature.

controlled burning: Intentionally ignited fire contained within a designated area.

convergent evolution: Groups of unrelated organisms becoming similar in appearance because of evolutionary change in response to similar environments.

coral reef: Hard, rocklike structure in shallow tropical waters; structure is composed of plants and animals encrusted with calcium carbonate.

corepressor: Substance that inhibits production of a particular enzyme.

cork: Secondary tissue produced by cord cambium; the outer part of the periderm.

cork cambium: Secondary cambium giving rise to cork tissue.

corm: Enlarged underground vertical stem.

corolla: Pertaining to all petals of a flower.

cortex: Ground tissue located between the vascular bundles and epidermis of stems and roots.

cortisone: Animal hormone not synthesized by plants.

cosmopolitan: Worldwide in distribution.

cotton: Soft silky fibers from cotton plants in their raw state.

cotyledon: Seed leaf; the first leaf formed in a seed.

covalent bond: Chemical bond between two atoms created as the result of sharing of electrons.

crassulacean acid metabolism (CAM): Type of carbon metabolism in which stomata open only at night, thus conserving water and allowing the leaves to take in C[O.sub.2]; photosynthesis is completed during the day, allowing a partitioning of reactions in time.

cristae: Folded-membrane inner structure of mitochondria.

cross-pollinated: Pertaining to a flower having pollen deposited on it from a different flower.

cross-protection: Infection of plant tissues by one virus suppresses the disease caused by another closely related strain of the virus; protecting strain must have negligible impact on the host.

crossing over: Physical exchange of equal segments of adjacent nonsister chromatids during the bivalent stage of meiosis; formation of a chiasma.

crown: Topmost portion of a plant.

curare: A variety of poisonous plant extracts from the bark, roots, stems, and tendrils of several woody lianas, including Chondodendron tomentosum.

cuticle (kute-i-kuhl) thickness: Waxy coating of the epidermis on all aboveground parts of a plant.

cuticular transpiration: Water loss through the cuticles of the epidermis cells, these account for around 5% of water loss.

cutin (kute-in): Lipid layer found in the outer walls of epidermal cells.

cuttings: Portions of stems, usually consisting of two or three nodes, used for propagation by the production of adventitious roots.

cyanobacteria: Are mainly responsible for generating the oxygen that is found in the earth's atmosphere today.

cycads: Any of various palmlike gymnospermous cone-bearing evergreen plants, native to warm regions and having large pinnately compound leaves.

cyclic photophosphorylation: Formation of ATP by activation of PS I, but failure to activate PS II. Consequently ATP is formed, but NADP is not reduced.

cyclosis: Spontaneous movement of cytoplasm and some organelles within the cell.

cytochrome: Group of proteins involved in electron transfer in biological systems.

cytokinesis: Cell division; the process accompanying nuclear division in which the cytoplasmic contents are divided between the daughter cells.

cytokinin: Group of hormones that promote growth by stimulating cell division.

cytoplasm: Viscous contents of a cell within the plasma membrane, but generally excluding the nucleus.

cytoplasmic streaming: Flowing of cytoplasm in eukaryotic cells.

cytosine: Nitrogen base found in both DNA and RNA.

day neutral plant: Plant whose flowering is not controlled by the length of day.

daylength: Number of hours that sunlight illuminates a given area on earth; dependent on the angle of the earth relative to the rays of the sun.

deadheading: Removal of old blooms.

decarboxylation: The removal of a single carbon atom as C[O.sub.2] from an organic molecule.

deciduous (de-sid-u-us): Referring to plants that lose all their leaves during the cool season; as opposed to evergreen plants.

decomposer: Organism that acquires its nutrition by feeding on dead organisms.

deficit irrigation: Concept of low levels of irrigation to achieve a moderate level of productivity; even though yields are not maximized, limited water supplies are conserved.

dehiscent: Mature fruit that splits open to release the seed.

deletion mutant: Mutation in which a base pair is deleted and shifts the sequence out of phase by one pair; also called a frame shift.

denature: To change the configuration of a protein molecule such that it loses specificity and no longer functions as an enzyme.

dendrochronology: Science of studying growth rings of trees to determine past conditions.

dentate: Toothed leaf margin.

deoxyribonucleic acid (DNA): Double-stranded nucleic acid composed of adenine, guanine, cytosine, and thymine, in addition to phosphate and deoxyribose.

deplasmolysis: Dehydration injury.

depressants: Drugs that relieve anxiety and produce sleep; depressants include barbiturates, benzodiazepines, and alcohol.

deoxyribose: Five-carbon sugar contained in DNA.

desert: Arid region that receives annual rainfall of 10 inches (25 cm) or less.

desertification (de-surt-i-fi-ka-shun): Process by which fragile, semiarid ecosystems lose productivity because of loss of plant cover, soil erosion, salinization, or waterlogging; usually associated with human misuse.

desiccation (des-i-kay-shun): Process of drying.

destructive distillation: Decomposition of wood by heating out of contact with air, producing primarily charcoal.

determinate growth: Pertaining to a leaf or stem that stops growing after differentiating into a terminal flower.

developmental biology: A large field of investigation that includes the study of all changes associated with an organism as it progresses through life.

Devonian period: A geologic division of the Paleozoic Era following the Silurian Period and preceding the Permian.

diatomaceous earth: Powdery, soil-like material formed by the glass cell walls of dead diatoms deposited on the marine floor.

dichotomous (di-kot-o-mus): Pertaining to the division or forking of a single axis into two branches.

dicotyledon (dicot): Group of angiosperms that produce two cotyledons.

differentiation: Chemical and physical changes associated with the developmental process of an organism or cell.

diffuse-porous wood: Secondary xylem characterized by the same-sized vessels and tracheids through the growing season so that growth rings are difficult or impossible to detect.

diffusion: Random movement of particles from a region of high concentration to a region of low concentration.

digestion: Process by which macromolecules are broken down into smaller molecules.

dihybrid cross: Cross in which the inheritance of two characteristics is studied.

dioecious: Process by which macromolecules are broken down into smaller molecules.

diploid: Nucleus with two sets of identical chromosomes; the sporophyte is diploid, having the 2n number of chromosomes.

dispersal: How seeds distribute themselves before germination is done-by, wind, water, animals, and people.

disulfide bond: Linkage between the sulfur atoms of two different amino acids in a protein.

diurnal (dye-urn-al): Pertaining to daily cycles or events.

diurnally: Daily cycle that occurs or is active during the daytime rather than at night.

DNA replication: Use of existing DNA as a template for the synthesis of new DNA strands; in humans and other eukaryotes, replication occurs in the cell nucleus.

doctrine of signatures: Concept that any organic substance carries within itself the likeness of some organ or part of the human economy, as a sign that this particular substance was applicable to disturbances of that organ.

dominant: (1) most prevalent species in a plant community; (2) allele that has its trait expressed; (3) gene that has its phenotypic expression appear in the offspring, regardless of the nature of its allelic partner.

dormant: Having reduced metabolic and respiratory activity.

double fertilization: Reproduction strategy in angiosperms in which two sperm are involved in the fusion with other nuclei.

double helix: Term used to describe the configuration of a DNA molecule. The helix consists of two spiraling strands of nucleotides held together with chemical bonds.

drifts: Color grouping of plants.

drill: Machinery for evenly spacing seeds (grain) in the soil at a uniform depth and giving good soil-seed contact.

drought (drout): Environmental condition in which precipitation is not sufficient to maximize biological productivity.

drupe: Fleshy fruit with a one-carpeled ovary and only one seed; endocarp is hard and stony, tightly enclosing the seed; the mesocarp is fleshy, and the exocarp is soft and thin.

dry fruit: Fruit that has dry ovary tissue unlike fleshy fruits that have a fleshy ovary.

duration: Refers to the number of hours of light a plant receives in a 24-hour period.

dusting: Sprinkling flowers or plants with pesticides to protect them from insects and rodents.

dwarf: Tree that grows to about 4 to 10 feet in height.

early wood: Large, thin-walled xylem cells produced early in the growing season, which appear less dense than latewood.

ecological succession: Sequential replacement of one vegetative community by another through a series of stages; succession ends when the climax community is established.

ecology: Total interrelationships among all the living organisms with each other and with the nonliving components of their environment.

ecosystem: Natural interrelationships among all the living organisms in a given area and with the environmental factors of that area. Ecosystems are self-sustaining, balanced, and self-perpetuating.

edema: The extended swelling in plant organs caused primarily by an excessive accumulation of water. This occurs since the cell walls are composed of flexible cellulose.

effluent: Water from industrial facilities, municipalities, and other such sources.

egg or egg cell: Middle of three haploid cells at the micropylar end of the embryo sac; when fertilized, it will form the zygote.

electrical energy: Carbon and energy enter living organisms through the process of photosynthesis.

electromagnetic spectrum: Entire radiation spectrum from the high-energy levels of cosmic rays to the low-energy level of radio waves; a small portion in the center provides wavelengths visible to humans.

electron: Negatively charged particle that orbits around the atomic nucleus; number of electrons is always equivalent to the number of protons.

electron transfer: Process of energy transfer in biological systems, usually in small steps with only slight changes in energy levels.

electron transport: Successive passage of electrons from one cytochrome or flavoprotein to another by a series of oxidation-reduction reactions.

element: Substance compound of a single kind of number of protons in the nucleus.

embryo: In plants, that portion of a seed that will form the growing seedling following germination; it has a radicle, apical meristem, and embryonic leaf or leaves.

embryo sac: Mature megagametophyte; contains eight haploid nuclei.

embryonic axis: Main root/shoot body of a seedling.

endangered species: Living species that is in danger of becoming extinct because of small population sizes, poor reproduction, reduced available habitat, or a combination of these factors.

endergonic: Pertaining to a reaction that requires energy input before it will occur; endergonic reactions never occur spontaneously.

endocarp: Interior layer of the fruit wall.

endodermis: Layer of cells directly outside the pericycle and inside the cortex of roots; a portion of the cell layer is suberized by the Casparian strip.

endogenous: Originating or produced within an organism, tissue, or cell.

endophyte: Internal plant fungus.

endoplasmic reticulum (ER): Flattened membrane from a network running throughout the cytoplasm of cells; if ribosomes are attached, it is termed rough endoplasmic reticulum; if ribosomes are not present, the membrane is termed smooth endoplasmic reticulum.

endosperm: Triploid nutritive tissue resulting form the fusion of a haploid sperm nucleus with the two. haploid polar nuclei in the ovule of angiosperms.

endosymbiosis: Theory that some cellular organelles arose by the incorporation of a prokaryote into the cytoplasm of a eukaryote.

entine: Inner layer of a pollen grain shell. entire: Smooth leaf margin without teeth, lobes, or undulations.

entropy: Physical concept describing the degree of orderliness in a system.

environment insults: Factor in the physical environment that inhibits the growth and/or development of an organism.

enzyme: Protein that functions as a catalyst in biochemical reactions.

ephedrine: Common ingredient in herbal dietary supplements used for weight loss; ephedrine can slightly suppress your appetite, but no studies have shown it to be effective in weight loss; ephedrine is the main active ingredient of ephedra. Ephedra is also known as Ma Huang, not ephedrine; high doses of ephedra can cause very fast heartbeat, high blood pressure, irregular heart beats, stroke, vomiting, psychoses and even death.

ephemeral (e-fem-er-uhl): Temporary, such as vegetation that completes its life cycle in a short time.

epicotyl: That portion of a seedling above the cotyledonary node.

epidermal cells: Outermost layer of cells covering the entire plant body.

epinasty: Unequal growth of petioles causing the leaf blade to curve downward.

epiphyte (ep-i-fight): Plant that grows on another plant as a support but derives no nutrition from the host.

epistasis: When one gene has a masking effect of the expression of another nonallelic gene, the former is said to be epistatic.

equatorial plate: Figure formed by the chromosomes in the center (equatorial plane) of the spindle in mitosis.

ergot: Spore-producing reproductive body of a fungus that infects grain crops; ergot contains lysergic acid and ergonovine.

essential oils: Highly volatile and aromatic oils formed in glands or special cells by some plants; probably involved in pollinator attraction or repulsion of herbivores; used in perfumes, soaps, medicine, and food.

estrone: Animal steroid (hormone) found in some plants in low concentration.

estuary: Marshy region where fresh water from a stream or river merges with salt water from the ocean.

ethylene: Plant hormone that promotes fruit ripening in addition to other physiological responses.

etiolation: Abnormal elongation of stems caused by insufficient light or unbalanced hormonal relationships. Etiolated stems often lack chlorophyll.

eukaryotic: Possessing a nucleus.

eutrophication (you-tro-fi-ka-shun): Natural process of dead organisms gradually filling a standing body of water (pond, lake) as eutrophic (nutrient-rich) cycles cause rapid population increases followed by crashes due to shortages of nutrients.

evaporation: Process by which any substance is converted from a liquid state into, and carried off in, vapor.

evapotranspiration: Combined water loss from both leaf surfaces and from the soil surface; the sum of transpiration and evaporation.

evolution: Process by which a lower, simpler form of life is changed through genetic mutations to a higher, more complicated form of life.

exergonic: Pertaining to a reaction that gives off energy and occurs spontaneously.

exine: Hard outer coat of a pollen grain.

exobilogy: Study of evidence relative to the possibility of life on other planets.

exocarp: Outer layer of the mature ovary (fruit wall).

exogenous: Developing outside an organism, tissue, or cell.

exon: "Sense" segments of mRNA that contain the actual genetic message for producing a given protein.

extinction: Permanent removal of all individuals of a species from earth.

F1 Generation (first filial): Hybrid offspring produced in the cross-pollination of parent generation plants.

F2 Generation: Progeny of self-pollinated F1 generation plants.

fact: Concept whose truth can be proved; scientific hypotheses are not facts.

facultative anaerobes: Microorganisms capable of switching pathways of respiration, depending on the presence or absence of oxygen.

family: Taxonomic category composed of one or more related genera.

far red light (Pfr): Light at the extreme red end of the visible spectrum, between red and infrared light; usually regarded as the region between 700 and 800 nanometers.

fascicular cambium: Layer of cambium that develops between the xylem and phloem within a vascular bundle.

fats: Organic molecules containing high levels of carbon and hydrogen, but little oxygen. Oils are merely fats in a liquid state.

fatty acid: Long-chain hydrocarbon with little or no oxygen and terminating in an acid (-COOH) group.

fermentation: Process of ethanol formation by partially oxidizing pyruvic acid; no oxygen is involved in this process.

fertile crescent: Crescent-shaped region stretching from Armenia to Arabia, formerly fertile but now mainly desert, considered to be the cradle of civilization.

fertilization: Fusion of two haploid gametes, egg and sperm, producing a diploid zygote.

fiber: Elongated cell type found in many plants and associated as a support tissue of xylem or phloem; highly sclerified and usually dead at maturity.

fiberboard: Building material composed of wood chips or plant fibers bonded together and compressed into rigid sheets.

fibrous root: Root system with many equally sized roots forming a mat, as in grasses; there is no primary taproot.

fiddlehead: Curled fern frond prior to unrolling and elongation; also known as a crozier.

field capacity: Soil water storage capacity; the saturated soil profile after gravitational percolation ceases to flow.

filament: Elongated stalk of a stamen. filial: Offspring generation, for example F1, the first filial generation.

finite resources: Resources that have a limit to their availability; not boundless. fire ecology: Study of the environmental effects of fire.

first agriculture revolution: Relative suddenness of the beginnings of agriculture.

flaccid: Pertaining to a cell or tissue with less than full turgor pressure.

flavin mononucleotide: Electron acceptor in the electron transport scheme of aerobic respiration.

flavonoids: Group of secondary compounds produced by plants and important in chemical identification of those plants; believed to be contained in petals that reflect ultraviolet patterns and thus as element in pollinator attraction.

fleshy fruit: After fertilization, the ovary develops into fleshy tissue, for example, the apple.

flora: All the plants of a given area.

florigen: Flowering hormone are the terms used for the hypothesized hormone-like molecules that control and/or trigger flowering in plants.

fluorescence: Release of energy at a longer wavelength than the absorption wavelength, but still in the visible spectrum.

fly agaric: (A. muscaria), mushroom having hallucinogenic properties is also a poisonous mushroom.

follicle: Fruit that develops from a single-carpeled ovary and splits down one side when mature.

food chain: Sequence of organisms in which plants are the primary food source for herbivores, which are in turn the food source for carnivores, etc., until the top carnivore level is reached.

food web: Community food chain depicting what species feed on each other and how many interrelationships are involved.

forage: Foodstuffs from the leaves and stocks of plants. These could be grasses, legumes, or other cultivated crops.

forcing: Making bulbs artificially break dormancy so that they will flower when brought into a warm room.

fossil fuels: Organic molecules derived from partially decayed plant and animal matter produced primarily during the Carboniferous period; includes oil, gas, and coal.

fraction I protein: Equivalent to RuBP carboxylase; the primary leaf protein in many green plants.

fragmentation: Method of asexual reproduction by simply breaking into parts.

frame shift: see Deletion mutant; Insertion mutant.

fresh water: Water of relatively low salt concentration, as opposed to sea matter or salt water.

frond: Photosynthetic leaf blade of a fern.

fruit: Mature ovary.

funiculus: Stalklike structure connecting an ovule to its placental surface within an ovary.

fused: Flower parts that grow together.

galactose: Six-carbon sugar.

galactosidase: Enzyme responsible for the splitting of lactose into glucose and galactose.

gametangia: Cell or organ in which gametes are formed.

gamete: Sex cell; the mature haploid reproductive cell of either sex.

gametophyte: Haploid, gameteproducing plants in the alternation of generations; undergoes mitosis to produce the haploid gametes, which fuse to form the diploid zygote of the sporophyte.

gamma rays: That portion of the sun's total range of radiation in which rays are shorter than X-rays; below 0.1 nm in length.

gas exchange: Movement of oxygen and carbon dioxide between the cells.

gene: Unit of inheritance; a group of nucleotides on the DNA molecule responsible for the inheritance of a particular character.

gene activators: System that would allow gene expression to be activated by crossing reporter and activator plants.

gene regulation: Process by which genes are turned on and off to regulate growth and development of an organism.

generative nucleus: Produced by the haploid microspore nucleus of a pollen grain, the generative nucleus divides mitotically to form two sperm nuclei.

genetic code: Set of 64 different possible condons (codes) or nucleic acid triplets and their corresponding amino acids; determines which amino acids will be added during protein synthesis.

genetic engineering: Modifying the genetic structure of one organism by splicing in selected genetic information from another organism.

genome: Complete set of genetic information of an organism including DNA and RNA.

genomics: Study of genomes.

genotype: Genetic composition of an organism.

genus: Grouping of closely related species; the first word of a scientific binomial.

geotropism: Bending responses of a plant to the forces of gravity.

germinate: To resume growth and increase metabolic activity, as in a seed.

gibberellin: Group of related compounds that cause single-gene dwarf mutants of corn and peas to elongate normally.

ginkgos: A deciduous, dioecious tree (Ginkgo biloba) native to China and having fan-shaped leaves and fleshy yellowish seeds with a disagreeable odor. The male plants are often grown as ornamental street trees. Also called maidenhair tree.

girth: Circumference, as of a tree trunk.

glucose: Six-carbon monosaccharide (simple sugar); the primary substrate for respiration.

glycerol: Organic molecule to which fatty acids are attached to form a fat.

glycogen: Primary storage carbohydrate of animal cells.

glycolysis: Series of reactions preceding anaerobic or aerobic respiration in which glucose is oxidized to pyruvic acid.

glycoprotein: Macromolecule composed of a carbohydrate-protein complex.

glycosides: Cyanogenic glycosides, which are based in cyanide, are sedative and relaxant to muscles, but must be used in very small doses, under the care of a qualified herbalist or holistic physician; vary in solubility, most are soluble in water and alcohol.

glyoxysomes: Subcellular microbody present in the cytoplasm of many oil seeds; enzymes packaged in the glyoxysome convert lipids to carbohydrates during the germination process.

golgi apparatus: Organelles consisting of stacks of flattened membranes that function in packaging and synthesis of membranes and cell walls.

gradient: Rate of change with respect to distance of a variable quantity, as temperature or pressure, in the direction of maximum change.

grafting: Method of asexual propagation characterized by placing a shoot (the scion) onto the rootstock (the stock) of another plant.

granite: Igneous rock overlying most of the land masses of the earth.

granum: Stacks of thylakoids that are the site of light reactions in the chloroplast.

grassland: Land where vegetation is primarily grasses.

greenhouse effect: Climatic effect attributed to high levels of C[O.sub.2] in the atmosphere that traps incoming infrared radiation and raises the temperature of the earth.

Gregor Mendel: Monk known as the father of genetics.

growth retardants: Chemical applied as a spray or a drench on plants to reduce their size; commonly used by growers to dwarf potted plants such as chrysanthemums.

growth rings: Layers of wood produced around a tree's stem and branches during each growing season; also called annual rings. The number of annual rings indicates a tree's age, while the thickness of rings provides an estimate of a tree's growth rate. Rings are frequently visible when a tree is cut.

ground meristem: Basic or fundamental tissue of the apical meristem; dermal tissues surround the ground meristem, and the provascular strands are embedded in it.

ground parenchyma: Basic ground tissue consisting of living parenchymal cells.

guanine: Nitrogen base found in both DNA and RNA.

guard cell: One of two epidermal cells associated with the stomatal apparatus.

guttation: Exudation of liquid water from hydathodes fed by vascular xylem traces.

gymnosperms: Plant group that bears naked seeds in cones.

habitat: Biotic and abiotic components making up the home of all the organisms in a given region.

half-life: Time required for half the radiation of a radioisotope to be emitted.

hallucinogen: Compound that produces a mind-altering effect.

halophilic: Pertaining to microorganisms that tolerate high concentrations of saline media.

haploid: Single set of chromosomes (half the full set of genetic material), present in the egg and sperm cells of animals and in the egg and pollen cells of plants.

hardpan: Impervious layer in the soil that restricts root penetration as well as movement of air and water.

hardwood: A term used in reference to all woody dicot, more accurately, wood having a high specific gravity.

hashish: Purified resin prepared from the flowering tops of the female cannabis plant.

haustorial roots: Parasitic plants may form specialized haustorial roots that form an attachment disc to the host during the first stage of colonization.

head: Many individual flowers tightly compressed into the shape of a single large flower; edible or harvestable part of the grain.

heading: One of the growth stages of small grains; when wheat or oat emerges; when the florets are fertilized and the kernels develop.

heartwood: Wood found in the center of a tree trunk; often a darker color due to the accumulation of resins, oils, gums, and other metabolic by-products, which prevent water movement through this tissue.

heavy metals: Metallic chemicals like cadmium, arsenic, copper, and zinc that can be harmful pollutants when they enter soil and water.

heeling in: Temporary planting in a trench.

helix: Spiral; DNA is a long double-stranded molecule wound in a spiral.

hemicellulose: Polysaccharide component of primary cell walls; similar to cellulose, but more easily degraded.

hemoglobin: Blood protein responsible for the transport of oxygen throughout the body.

hemp: Cannabis sativa; source for fibers used in making hemp rope.

hemp plant: The tough, coarse fiber of the cannabis plant, used to make cordage. Any of various plants similar to cannabis, especially one yielding a similar fiber.

herbaceous perennials: Without woody tissues; typical of most annuals and biennials; herbaceous perennials die back to the soil level each year.

herbarium: Collection of pressed, dried plant specimens mounted on sturdy (rag) paper and stored for reference and research.

herbicide: Plant growth regulator that inhibits growth or kills a plant when applied at relatively low concentrations.

herbivore: Animals that feed only on plants.

heredity: Transmission of genetically controlled characters from parents to offspring through sexual reproduction.

hereditary factors: If F2 has two, all have to have two; inbred parents only produce one kind of gamete, so they have only one kind of hereditary factor.

heritable: Capable of being inherited, such as physical trait.

heroin: An opiate processed directly from the extracts of the opium.

hesperidium: Berry with a thick leathery peel (exocarp and mesocarp) and a fleshy endocarp arranged in sections.

heterosporous: Producing two distinct types of spores.

heterotrophic: Organism that obtains its food from other organisms.

heterotrophic theory: Theory of the origin of life that proposes that the first organisms obtained nutrition from the spontaneous formation of organic molecules derived from primordial gases.

heterozygous: Genotype for a given phenotypic expression containing a dominant and a recessive allele for that trait.

hexose: Six-carbon sugar.

hill reaction: Splitting of a molecule of water during the light reactions of photosynthesis; the photolysis of water.

hill system: Method of planting strawberries; the hill system is used for everbearers; plants are set 12 to 15 inches apart; because all runners are removed, three rows can grow together to form one large row; three rows are spaced 1 foot apart.

histones: Basic proteins constituting a portion of the nuclear material and functionally associated with DNA.

holdfast: Organ at the base of macroalgae that attaches the stalk to a rocky surface.

homogeneous: Consistent and similar in composition.

homologous pairs: Two chromosomes that are morphologically and structurally identical and that pair during prophase of meiosis.

homologue: One chromosome morphologically and structurally identical and that pair during prophase of meiosis.

homosporous: Producing only one kind of spore.

homozygous: Genotype for a given phenotypic expression containing either two dominant or two recessive alleles for that trait.

hormone: Organic molecule synthesized by a plant that exerts, even in low concentrations, profound regulation of growth and/or development.

humid: Containing or characterized by a great deal of water vapor; "humid air"; "humid weather."

humus: Organic portion of soil derived from partially decayed plant and animal matter.

hybrid: Organism resulting from the fusion of gametes from different parental species.

hydrocooling: Removing heat from freshly harvested fruits and vegetables by immersion in ice water.

hydrolysis: Splitting of a large molecule into smaller molecules by the addition of water.

hydrophilic: Property of a substance that has a tendency to repel water.

hydroponics: System of growing plants in a liquid nutrient solution without soil.

hyoscyamine: Poisonous crystalline alkaloid (isometric with atropine but more potent); used to treat excess motility of the gastrointestinal tract.

hypocotyl: Shoot portion of a seedling below the cotyledonary node.

hypocotyl hook: Hooked portion of a hypocotyl formed at germination that assists a dicot shoot in pulling itself through the soil crust.

hypothesis: Proposed solution of a problem; a theory to explain unproven events or observations.

identical genetic makeup: Cell or collection of cells containing identical genetic material.

igneous: Rock of molten or volcanic origin.

imbibition: Process of taking up water physically.

immunological: Pertaining to the immune response, in which a protein antibody is synthesized by an organism to counteract some pathogenic factor.

imperfect: Has only one set of reproductive parts.

impermeable: Having the property of restricting the passage of substances.

incomplete dominance: Referring to the phenotypic expression for a given trait demonstrating a blending of the genetic messages from the allele partners controlling that trait; no dominant allelic partner.

incomplete flower: Lacking one or more of the four floral parts (sepals, petals, stamens, pistil).

indehiscent: Denoting mature fruit that do not split open to release their seed.

independent assortment: Random alignment of homologous chromosomes in meiosis.

indeterminate: Pertaining to a stem that produces unrestricted vegetative growth; the stem does not terminate in flowering.

indigenous: Native to or originating in a particular area.

indoleacetic acid (IAA): Naturally occurring auxin.

inducer: Compound that causes the induction of a particular enzyme.

inducible enzyme: Enzyme present only when induced by some particular substrate.

indusium: Thin membrane that covers the sori of many ferns; the membrane often breaks at the time of spore maturation.

inferior ovary: Ovary attachment to a modified receptacle in which other floral parts are fused to the ovary.

inflorescence: Flower cluster with a definite arrangement of individual flowers.

infrared: That portion of the sun's total range of radiation having wavelengths immediately longer than the longest of the visible spectrum (red); between approximately 750 nm and 1 m in length.

inhibitors: Agents that block or suppress the activity of cell growth.

inorganic nitrogen: Chemical compound without carbon as its skeleton atom.

insectivorous plant: Plant capable of deriving nutrition by digesting insects.

insertion mutant: Type of mutation in which an extra base pair is inserted and shifts the sequence out of phase by one pair; also called a frame shift.

installation: Refers to putting sod in a permanent location after having been grown elsewhere.

integrated pest management (IPM): Eco-sensitive way to manage pests of all kinds in the garden and landscape; an approach that focuses on the use of various biological controls.

integuments: Two outer layers of an ovule that enclose the nucleus tissue within.

intensity: State or quality of being intense; intenseness; extreme degree; as, intensity of heat, cold, or light.

intercalary meristem: Type of meristem present at the base of the blade and/or sheath of many monocots.

interfascicular cambium: Layer of cambium that develops between vascular bundles and connects with the fascicular cambium to form the vascular cambium of woody tissues.

interkinesis: Activities occurring between meiosis I and meiosis II; similar to interphase but without chromosome replication.

internode: Stem distance between nodes.

interphase: Nuclear condition between one mitosis and the next; chromosomes are not visible, but intense metabolic activity is occurring.

intertidal zone: Region between high and low tide.

intine: Inner wall of a pollen grain that does not contain sporopollenin.

intron: Intragene segments of genetic gibberish that do not code for the production of a given protein; these segments are left out of the mRNA that leaves the nucleus to direct protein synthesis.

involutions: Infolding of membranes to increase surface area.

ion: Atom or molecule that has gained or lost an electron, causing the particle to become electrically charged.

ionize: To split a molecule into two or more parts, each part becoming an electrically charged particle.

irish potato: Edible tuber native to South America; a staple food of Ireland.

irregular: Bilateral symmetry; having only one plane through which the structure (flower) could be cut to result in mirror image halves; zygomomorphy.

irritants: Things that bother the nose, throat, or airways when they are inhaled (not an allergen).

island of fertility: Region in a desert ecosystem directly beneath a tree or shrub; leaf fall and accumulation of litter result in nutrient cycling directly around the plant, even though the bare soil between plants may be depleted of nutrients.

isogamy: Union of gametes or gametangia of equal size.

isoprenes: Five-carbon compounds that are the basic unit of terpenes.

isozyme: Different chemical forms of the same enzyme; thought to be important in adaptation to environmental extremes.

Jarmo: Ancient city located in the foothills of the Zagros Mountains in the Middle East; studied by archaeologists, who have documented the existence of agriculture activities there between 10,000 and 12,000 years ago.

jointing: One of the growth stages of small grains; at jointing stage, the nodes begin to separate and can be felt in the lower part of the stem.

kinetic energy: Energy resulting from the random movement of molecules.

kinetin: Plant-based, nonirritating growth factor extract that has shown to significantly reduce free-radical damage and slows down aging of plant cells.

knots: Defects that weaken the timber and interfere with its ease of working and other properties.

Kranz anatomy: Specialized leaf anatomy found in C4 plants in which the vascular bundle is surrounded by bundle sheath cells.

Krebs cycle: Mitochondrial oxidation of pyruvic acid by considering acetyl coenzyme A with oxaloacetic acid to form a series of 6-, 5-, and 4-carbon organic acids.

lactose: Milk sugar; a disaccharide composed of glucose and galactose.

lateral buds: Produced in the apex of lateral branches.

lateral meristem: Meristem giving rise to secondary plant tissues, such as the vascular and cork cambia; term is sometimes used to refer to an axillary meristem.

laterite: Type of tropical soil in which iron and aluminum oxides cause the soil structure to harden like concrete.

latewood: Small, thick-walled xylem cells produced at the end of the growing season that appear as a dense ring of wood adjacent to the thin-walled early wood.

latitude: Geographical unit used to measure the distance from the equator toward either pole.

lattice: A crystalline-like structure caused by the precise orientation of molecules in a solid or liquid.

laudanum: Narcotic consisting of an alcohol solution of opium or any preparation in which opium is the main ingredient.

layering: Method of asexual propagation in which portions of the stem are wounded and covered with a medium, usually soil, to stimulate the production of adventitious roots.

leaching: Process of removal of ions or molecules by flushing with water.

leaf area index: Numerical index of the ratio of leaf area to ground area in a plant community.

leaf venation: Leaf skeleton as those axes constituting the primary and secondary vines.

leaflet: Individual blade unit of a compound leaf.

leeward: Side away from the direction of a prevailing wind.

legume: Fruit that develops from a single-carpeled ovary and splits along two sides when mature; plants with the characteristic of forming nitrogen-fixing nodules on its roots, in this way making use of atmospheric nitrogen.

lethal: Gene or genotype that is fatal for the individual gene.

leucine: Essential amino acid, [C.sub.4][H.sub.9] CH(N[H.sub.2])COOH, obtained by the hydrolysis of protein by pancreatic enzymes during digestion.

leucoplasts: Membrane-bound organelles specialized for starch storage.

levee: Earthen dike used to enclose water.

liana: Large, woody vine common to the tropical forest; it climbs the tall trees and often trails from the canopy.

lichen: Organism composed of a symbiotic association of an ascomycete fungus with algal or cyanobacterial cells.

light: Electromagnetic radiation produced by the sun that heats and illuminates the earth.

light intensity: Strength of light rays; the degree of brightness dependent on the number of photons striking a given area at a point in time; measure of the brightness of light reaching a surface; decreases as the distance from the source of the light increases.

lignified: Impregnated with lignin, such as the secondary cell walls of woody plants.

lignin: Complicated organic molecule found as an important constituent of many secondary cell walls; imparts strength and rigidity to the cellulose microfibrils.

limiting factor : Climatic factor that would first curtail plant growth if unavailable.

limnetic zone: Open-water zone of a lake or pond; extends to the depth of effective light penetration.

limnologist: Scientist who studies freshwater biology.

linkage: Occurrence of alleles for a different trait.

lipid: Fat or oil; composed of fatty acids and glycerol.

litter: Dead organic material such as branches, tree trunks, and dry grass that accumulates on the floor of a forest; litter acts as additional fuel in a forest fire, producing increased destruction.

littoral zone: Shallow-water zone of a lake or pond; light penetrates to the bottom, and the area is occupied by rooted plants such as water lilies, rushes, and sedges.

lobed: Leaf having deeply indented margins.

locoweed: Any of several leguminous plants of western North America causing locoism in livestock.

locus (pl., loci): Position that a given gene occupies on a chromosome.

long day plant: Plant that flowers when the length of day exceeds some critical value.

LSD: Lysergic acid diethylamide; a synthetic hallucinogenic derivative of lysergic acid.

lumen: Central cavity of a cell.

lysosome: Enzymes that break down proteins and other macro molecules.

macromolecule: Very large complex molecule; found only in plants and animals.

macronutrient or macroelements: Actual chemical form or compound, which enters the root system of a plant.

macropores: Large pore spaces caused by invertebrates and larger animals, including reptiles and mammals that permeate the soil; drain water not held by capillarity.

maize: Worldwide name for corn; a tall annual cereal grass bearing kernels on large ears; widely cultivated in America in many varieties; the principal cereal in Mexico and Central and South America since pre-Columbian times.

margin: Edge of a flattened structure; in leaves, the lateral edge of the blade. marine biome: Of or pertaining to the ocean.

market gardening: Refers to growing a wide variety of vegetables for local or roadside markets.

marsh: Wetland along the shallow margins of the lakes and ponds and in low, poorly drained lands where water stands for several months of the year.

mass: Fundamental unit of measurement equivalent to the weight of a substance when compared with the weight of hydrogen.

matrix potential: Water potential component caused by the attraction of water molecules to a hydrophilic matrix.

meadow: Open clearing in a landscape in which low-growing, herbaceous plants dominate.

mean: Arithmetic average of a set of data points or values; the sum of each data point or value divided by the number of data points.

media: Growing materials in which plants can be started that are loose, well drained, fine textured, low in nutrients, and free of disease.

megagametogenesis: Production of megagametes (large gametes) from megaspore in the ovules of angiosperms.

megagametophyte: Gametophyte stage containing eight haploid nuclei within the embryo sac.

megaspore: Haploid cell produced by meiosis in the ovules of angiosperms; a single megasporocyte produces four megaspores, only one of which remains functional.

megasporocyte: Megaspore mother cell; this diploid cell undergoes meiosis to produce four haploid megaspores in the ovules of angiosperms.

megasporogenesis: Process of megaspores (large spores) being produced via meiosis in the ovules of angiosperms.

meiosis: Process of two sequential nuclear and cellular divisions resulting in four haploid cells from a single diploid cell; occurs in reproductive organs.

membrane: Phospholipid bilayer impregnated with protein and certain other compounds in living organisms; functions in partitioning of cellulose activities.

membrane-bound: Eukaryotic with many membrane-bound organelle ... but plants have only the large vacuole, the chloroplast, the cell wall, and the plastids.

meristematic cells: Meristem is a tissue in plants consisting of undifferentiated cells. Combine to make meristematic tissues.

meristematic regions: Region of cells capable of division and growth; classified by location as apical, or primary (at root and shoot tips).

mescaline: A norepinephrine-related hallucinogenic drug. Its source is the peyote cactus.

mesic: Referring to a region that receives adequate precipitation to maintain biological productivity.

mesocarp: Middle layer of the fruit wall, located between the exocarp and endocarp.

mesophyll: Parenchymal tissue in the center of a leaf.

messenger RNA (mRNa): Ribonucleic acid transcribed from the DNA template.

metabolic energy: Energy obtained from ATP produced in metabolism.

metabolism: Summation of all the biochemical events within a cell or organism; it includes both synthesis and breakdown of molecules.

metabolities: Chemical substances required in metabolism.

metacentric: Denoting a chromosome with a centromere located at the center.

metamorphic rock: Type of rock, either granite or sedimentary in origin, and structurally changed by high temperature and pressure.

metaphase: Stage of nuclear division in which the chromosomes migrate to the center of the cell.

methane: C[H.sub.4], natural gas. methanogen: Bacterium that obtains energy from C[O.sub.2] and [H.sub.2] and forms methane.

microelements or micronutrients: Nutrients required in smaller concentrations, but vital to plants.

microfibril: Elongated strand of cellulose molecules.

microgametogenesis: Production of microgametes (small gametes) from microspores in the anthers of flowering plants.

microorganisms: Single-celled living organisms that can be seen only with the aid of a microscope.

micropores: Spaces between soil particles that hold water by means of capillary forces.

micropropagation: Tissue culture.

micropyle: Small opening at one end of an ovale where the integuments come together.

microsporangia: Receptacle in which microspores (male spores) are developed.

microspore: Haploid cells produced by meiosis in the anthers of angiosperms; four microspores are produced from a single microsporocyte.

microspore mother cell: Diploid mother cell that will go through meiosis to produce the (4) haploid microspores.

microsporocyte: Microspore mother cell, this diploid cell undergoes meiosis to produce four haploid microspores in the anthers of angiosperms.

microsporogenesis: Process of microspores (small spores) being produced via meiosis in the anthers of the angiosperms.

microsporophyll: Leaflike structure giving rise to one or more microsporangia.

microtubules: Tiny rodlike structures made of the protein tublin and important in the synthesis of certain membranes.

middle lamella: Cementing layer of pectic substances between primary cell walls.

midrib: Central large vein of a leaf.

millet: Annual grass (Panicum milaiceum) cultivated in Eurasia for its grains and in North America for hay.

mimicry: Pertaining to the resemblance of one organism to a totally unrelated organism; the similarity in color, form, or behavior may result in protection or some other advantage to the mimic.

mitochondrion (pl., mitochondria): Membrane-bound organelle associated with the Krebs cycle and electron transport aspects of respiration.

mitosis: Nuclear divisions of somatic cells resulting in two genetically identical daughter nuclei.

modification: Change, as in morphology, usually associated with a functional advantage.

mole: One gram molecular weight of any substance; that is, the molecular weight of any substance in grams.

molecular weight: Sum of all the atomic weights of a molecule.

molecules: Groups of atoms that share electrons and therefore bond together.

monocarpic: Denoting a plant that flowers only once.

monocotyledon (monocot): One of the two primary groups of angiosperms characterized by a single cotyledon, parallel venation of leaves, and floral parts in threes.

monoculture: Agricultural system in which only one crop species is cultivated.

monoecious: Condition of being unisexual with both pistillate and staminate flowers on the same plant.

monohybrid cross: Cross in which the inheritance of only one character at a time is studied.

monosaccharide: Sugar broken down to its simplest functional unit--a single saccharide.

monsoon: Exceptionally heavy precipitation that occurs seasonally in certain parts of the world.

Mormon's tea: Common name of Ephedra.

morphine: Pain-relieving and addictive compound derived from the opium poppy (Papaver somniferum).

morphology: Study of form and structure of living organisms.

mountain tundra: Portion of tundra vegetation confined to alpine meadows; low-growing grasses, sedges, and forbs with very short growing seasons; permafrost is typical.

mucilaginous: Containing a mucilage, usually composed of mucopolysaccharides.

muck soil: Soil found in old bogs, river deltas, and lake beds; contains high organic matter and has good waterholding capacity; nitrogen is also readily available through mineralization of organic matter.

mulberry tree: Species of deciduous trees native to warm, temperate, and subtropical regions; produces a small multiple fruit, 2-3 centimeters (0.8-1.2 in) long, that is dark purple to black, edible, and sweet.

mulch: Materials such as straw, sawdust, leaves, plastic film, and the like, spread upon the surface of the soil to protect the soil and plant roots from the effects of raindrops, soil crusting, freezing, evaporation, and so on; to apply protective materials to the soil surface.

multigenic (polygenic): Inheritance in which the genetic control for a trait results in the phenotypic expression varying continuously.

multiple fruit: Ovaries of many separate flowers clustered together.

multipurpose plant: Plant used for more than one purpose. For example, the baobab tree has many uses: oil from the seeds, the vitamin C and tartaric acid from the pulp, the leaves for their medicinal value, and the trunk for its fibers to make rope.

muscarine: Toxic quaternary ammonium compound found in species of Clitocybe and Inocybe; causes perspiration-salivation-lacrymation syndrome.

mushroom: Common name for a group of fungi (basidiomyctes) that produce an aboveground reproductive structure.

mutagen: Substance capable of causing a mutation.

mutation: Permanent heritable change in the genetic code of the DNA.

mutualistic: Having an interrelationship in which both (or all) organisms benefit from their association.

mycelium: Tangled mass of fungal hyphae.

mycorrhiza: Study of form and structure of living organisms.

N-formylmethionine: Effective in the initiation of protein synthesis.

NAD (nicotinamide adenine dinucleotide): Coenzyme that acts as an electron acceptor; particularly important in respiration.

NADP (nicotinamide adenine disnucleotide phosphate): Coenzyme that acts as an electron acceptor; particularly important in photosynthesis.

nastic movements: Movement of plant parts in response either to certain external stimuli or to internal growth stimuli; generally slow.

natural law: Proven event of nature with consistent results, such as the laws of gravity and thermodynamics.

nectar: Sweet syrupy exudate produced by some flowers as an attractant for pollinators.

negative matrix potential: Inside plant cells, the matrix potential is always negative and is caused by attraction of water, although water movement in passive plants can regulate transpirational flow.

negative solute potential: Inside plant cells, water potential is always negative; solutes reduce the free energy of water.

netted venation: Veins reticulated and resembling a fish net.

neutron: Uncharged atomic particle; in most common stable atoms the number of neutrons is equivalent to the number of protons.

niche: Specific and unique set of environmental conditions for a given species.

nicotine: Addictive drug in tobacco; nicotine activates a specific type of acetylcholine receptor.

nitrates: Only form in which nitrogen can be used directly by plants.

nitrites: Intermediate product in the conversion breakdown of ammonium to nitrate; nitrite is very unstable, and is almost immediately converted into nitrate.

nitrogen base: Basic component of nucleic acids; composed of a nitrogen-containing molecule of purine and pyrimidine.

nitrogen fixation: Process by which nitrogen gas ([N.sub.2]) in the atmosphere is reduced to ammonia by certain microorganisms.

nitrogen gas: Nonmetallic, colorless, odorless, and tasteless inert diatomic gas that makes up 78% of the atmosphere by volume; nitrogen is found in all living tissues.

nitogenase: Enzyme involved in the conversion of atmospheric nitrogen gas into ammonia.

nastic movements: Movement of plant parts in response either to certain external stimuli or to internal growth stimuli; generally slow.

natural law: Proven event of nature with consistent results, such as the laws of gravity and thermodynamics.

nectar: Sweet syrupy exudate produced by some flowers as an attractant for pollinators.

negative matrix potential: Inside plant cells, the matrix potential is always negative and is caused by attraction of water, although water movement in passive plants can regulate transpirational flow.

negative solute potential: Inside plant cells, water potential is always negative; solutes reduce the free energy of water.

netted venation: Veins reticulated and resembling a fish net.

neutron: Uncharged atomic particle; in most common stable atoms the number of neutrons is equivalent to the number of protons.

niche: Specific and unique set of environmental conditions for a given species.

nicotine: Addictive drug in tobacco; nicotine activates a specific type of acetylcholine receptor.

nitrates: Only form in which nitrogen can be used directly by plants.

nitrites: Intermediate product in the conversion breakdown of ammonium to nitrate; nitrite is very unstable, and is almost immediately converted into nitrate.

nitrogen base: Basic component of nucleic acids; composed of a nitrogen-containing molecule of purine and pyrimidine.

nitrogen fixation: Process by which nitrogen gas ([N.sub.2]) in the atmosphere is reduced to ammonia by certain microorganisms.

nitrogen gas: Nonmetallic, colorless, odorless, and tasteless inert diatomic gas that makes up 78% of the atmosphere by volume; nitrogen is found in all living tissues.

nitogenase: Enzyme involved in the conversion of atmospheric nitrogen gas into ammonia.

oat (Avena sativa): Species of cereal grain, and the seeds of this plant; used for food for people, and also as fodder for animals, especially poultry and horses; oat straw is used as animal bedding and also sometimes used as animal feed.

obligate anaerobe: Microorganism that can survive only under anaerobic conditions.

ocean desert: Concept of a region in a lack of plants and animals; a region of low biological productivity.

olericulture: Vegetable production.

omnivore: Organism that feeds on other plants and animals.

operator gene: Gene responsible for the activation and deactivation of the structural genes.

operon: Gene regulation of the system consisting of an operator gene and one or more structural genes controlled by the operator.

opposite leaf arrangement: Leaves are attached at a node directly across from one another on the stem.

orbital: Discrete pathways or bands surrounding an atom through which electrons move.

organelle: Subcellular particles that perform some particular function within the cell; compound of carbon and another element or a radical.

organic matter: Living or once living material; compounds containing carbon formed by living organisms.

osmoregulator: Substance, either organic or inorganic, that functions to change the solute potential of a solution and thereby controls the water relations of the solution by osmosis.

osmosis: Diffusion of water molecules across a selectively permeable membrane.

osmotic agents: Induce transcription in eukaryotic organisms.

outcrossing: Flower that must be cross-pollinated to successfully complete the reproductive process.

ovary: Lower, enlarged portion of the female reproductive structure in a flower that gives rise to the fruit.

ovule: Female reproductive structure of a flower enclosed by an ovary; a developing embryo that gives rise to a seed.

oxalates: Group of molecules called organic acids, and are routinely made by plants, animals, and humans.

oxidation: Loss of electrons by an atom.

oxidation phosphorylation: Electron transport system associated with aerobic respiration and mitochondria.

oxidation reduction: Chemical reaction in which an atom or ion loses electrons to another atom or ion.

oxygen ([O.sub.2]): Essential element in the respiration process to sustain life; colorless, odorless gas makes up about 21% of the air.

oxytocic agent: Having similar actions as those of the natural hormone oxytocin, primarily contraction of smooth muscle such as the uterus.

ozone ([O.sub.3]): Molecular form of oxygen in equilibrium with [O.sub.2]; layer of ozone in the stratosphere, which protects the earth form harmful ultraviolet radiation. palatability: Taste potential for an animal.

paleobotanist: Studies the fossilize record of plants.

Paleozoic era: Lasted from about 540 to 250 million years ago, and is divided into six periods; time of many important events, including the development of most invertebrate groups, the evolution of fish, reptiles, insects, and vascular plants.

palisade: Vertical photosynthetic cells below the upper epidermis in leaf tissue; these cells are a specialized parenchyma.

palmate: Arrangement of leaflets (or lobes on a simple leaf), each originating from a common point, usually the axial end of a petiole.

palmately compound: Arrangement of leaflets in whorled fashion around the top of the petiole, which then attaches to the stem of the plant; resembles the arrangement of fingers attached to the palm of a hand.

paper chromatography: Process of separating small quantities of a substance in a mixture (often a solution) through ultrathin pieces of paper to show the selective absorption.

parallel: Veins that run parallel to each other; a characteristic of the monocot.

parasitic: Denoting an association where one living organism benefits at the expense of another.

parchment: Superior paper resembling sheepskin.

parenchyma: Tissue type characterized by simple, living cells with only primary cell walls.

parthenocarpy: Fruit development without fertilization.

parthenocarpic fruits: Fruits devoid of embryo and endosperm; such as seedless grapes; bred to provide the taste of the fruit without the seed.

pathogen: Any organism that causes a disease of another organism.

peat moss: Relatively sterile, inert medium composed of partially decomposed plants of the genus Sphagnum; exceptionally high water-holding capacity.

pectin: Cementing substance of which the middle lamella is composed; primarily calcium pectate and pectic acid.

peduncle: Stalk of a single flower or an inflorescence.

pelagic: Refers to fish and animals that live in the open sea, away from the sea bottom.

pellicle: A protein layer located just inside the plasma membrane in euglenoids.

peltate: Shield-shaped; having a flat circular structure attached to a stalk near the center, rather than at or near the margin.

PEP carboxylase: Enzyme responsible for C[O.sub.2] fixation in the primary fixation of [C.sub.4] metabolism.

pepo: Berry with the outer wall formed from receptacle tissue fused to the exocarp; the fleshy interior is mesocarp and endocarp.

peptide bond: Chemical bond formed between the amino group of one amino acid and the carboxyl (acidic) group of an adjacent amino acid.

percent purity: 100% minus (percentage inert matter + percentage other crop seed + percentage weed seed).

percolate: Gravity-induced movement of water down through the soil.

perennial: Plant that overwinters and continues to grow for many years; may reproduce every year, or only on rare occasions.

perfect flower: Having both stamens and carpels and therefore bisexual.

perianth: Referring to all the sepals and petals collectively.

pericarp: Fruit wall that develops from the ovary wall.

pericycle: Layer of cells surrounding the xylem and phloem of roots and considered to be a part of the vascular cylinder.

periderm: Protective tissue that replaces epidermis when it is sloughed off during secondary growth; includes cork, cork cambium (phellogen), and phelloderm.

permafrost: Permanently frozen soil in polar regions.

permanent wilting point: Soil moisture content at the point when a given plant's root system can no longer absorb water.

permeability: Property of membranes allowing all substances to pass freely.

peroxisome: Cellular micro-body containing enzymes involved with photorespiration and photosynthesis.

pesticides: Pesticides classified according to the organisms that they are used to control; for example: fungicides, herbicides, insecticides, molluscicides, nematicides, and rodenticides.

petal: Showy flower component attached just inside the sepals; usually colorful to attract pollinators.

petaloid: Modified, flattened filament of a stamen that may resemble a petal.

petiole: Stalklike portion of a leaf connecting the blade to the stem or branch.

petrifaction: Fossil formed when plant parts are infiltrated or replaced by mineral substances such that the structure is preserved but the fossil is actually rock.

peyote: Hallucinogenic drug containing mescaline that is derived from peyote buttons.

pH: (1) Negative logarithm of the hydrogen ion concentration; (2) numerical scale used to measure the acidity or basicity of any substance.

pharmaceuticals: Medicinal drugs.

phelloderm: Tissue laid down to the inside of the phellogen; the inner part of the periderm.

phellogen: Cork cambium.

phenotype: Physical features of an organism; the manifestation of the genotype as influenced by the environment.

phospholipid: Molecule in which glycerol is attached to two fatty acids plus a phosphate group; important part of biological membranes.

photolysis: Splitting of a molecule of water during the light reactions of photosynthesis; the Hill reaction.

photon: Elementary particle of light; a discrete unit of light energy.

photoperiodism: System within organisms that causes certain events, including the onset of reproduction, to be related to the length of day.

photophosphorylation: Formation of ATP utilizing light energy in photosynthesis.

photorespiration: Production of glycolic acid in chloroplasts in the light; glycolic acid may be oxidized by enzymes of peroxisomes.

photosynthesis: Production of carbohydrates by combining carbon dioxide and water in the presence of light energy; occurs in chlorophyll pigments of plants and releases oxygen as a by-product.

photosynthesis bacteria: Bacteria able to carry out photosynthesis; light is absorbed by bacteriochlorophyll and carotenoids.

photosynthetic unit: Group of associated chlorophyll molecules, including antenna molecules and a central chlorophyll a collector molecule.

photosystem I: Second part of the Z-scheme in which a chlorophyll a molecule absorbs most effectively at 700 nm.

photosystem II: First part of the Z-scheme in which the chlorophyll a absorbs most effectively at 680 nm.

phototropism: Bending of a plant toward a unidirectional light source.

phycobilins: Red and blue accessory pigments found in certain photosynthetic organisms.

phytochrome: Protein pigment responsible for the phenomenon of photoperiodism.

phytoplankton: Single-celled plants of aquatic biomes; the food source for zooplankton.

phytotoxins: Substance produced by plants that is similar in its properties to extracellular bacterial toxin.

phytrochrome red (Pr) far red (Pfr): Is a photoreceptor, a pigment that plants use to detect light. It is sensitive to light in the red and far-red region of the visible spectrum. Many flowering plants use it to regulate the time of flowering based on the length of day and night (photoperiodism) and to set circadian rhythms. It also regulates other responses including the germination of seeds, elongation of seedlings, the size, shape and number of leaves, the synthesis of chlorophyll, and the straightening of the epicotyl or hypocotyl hook of dicot seedlings.

pigment: Molecules that reflect and absorb light at particular wavelengths.

pinnate: Denoting an arrangement of leaflets (or lobes on a simple leaf) along a main central unit.

pinnately compound: Leaflets arranged along a single axis much like a feather.

pistil: Reproductive part of a flower, consisting of female stigma, style, and ovary.

pistillate: Denoting a unisexual flower having a pistil but no stamens (carpellate).

pith: Parenchymal tissue in the center of a stem located interior to the vascular bundles.

placental: Of the tissue to which an ovary is attached.

planed: Leveled or smoothed.

plant growth regulator: Any molecule that exhibits hormone-like effects in a plant, whether synthesized or naturally occurring.

plasma membrane: Cell membrane that holds the cytoplasm and lies against the cell wall (in plant and fungal cells).

plasmids: Circular, double-stranded unit of DNA that replicates within a cell independently of the chromosomal DNA; most often found in bacteria; and used in recombinant DNA research to transfer genes between cells.

plasmodesma (pl., plasmodesmata): Cellular microbody containing enzymes involved with photorespiration and photosynthesis.

plasmodium: Naked body of cytoplasm with many nuclei.

plasmolysis: Osmotic removal of water from the cytoplasm and vacuole, causing the cytoplasm to pull away from the cell wall and clump in the center.

plastids: Any of several pigmented cytoplasmic organelles including chloroplasts, chromoplasts, and leucoplasts.

pleiotropic: Action of single genes that affect the expression of several traits.

plumule: Shoot apex of a seedling, including embryonic leaves.

plywood: Panel products manufactured by gluing together layers of veneer with the grain of alternate layers oriented at right angles to provide strength.

point mutation: Change in the genetic composition of a cell to a change in a single triplet of the DNA template.

polar ice cap: Portions of the globe close to the poles that are permanently covered with ice.

polarity: Establishment of poles or areas of specialization at opposite ends of a cell, tissue, organ, or organism; polarity leads to the differentiation of roots from shoots.

polar nuclei: Two of the eight haploid nuclei of a megagametophyte that migrate, one from each end, to the middle of the embryo sac; two nucleifuse with a sperm nucleus during double fertilization.

pollen: Collective term of pollen grains, the male gametophytes.

pollen grain: Structure into which a haploid microspore develops; contains a haploid tube nucleus and two haploid sperm nuclei at maturity.

pollination: When the pollen grain is dispersed on the stigma.

pollinator: Organism that effects pollination.

polycarpic: Denoting a plant that flowers more than once during its lifetime.

polyembryony: Development of more than one embryo.

polymer: Large molecule formed by the linkage of many smaller, identical molecules.

polymerases chain reaction (PCR): Technique for amplifying DNA sequences in vitro by separating the DNA into two strands and incubating it.

polynucleotide chain: Attachment of one nucleotide to another in a linear fashion.

polypeptide: Any number of amino acids linked by peptide bonds.

polyploid: Term describing a cell with more than two sets (2n) of chromosomes.

polysaccharide: Large molecule formed by joining sugar molecules end to end.

polysome: Group of ribosomes functionally related and held together by a strand, presumable mRNA.

pome: Fleshy fruit derived from a compound inferior ovary; the fleshy edible part is the ripened tissue surrounding the ovary (derived from receptacle and perianth tissue); the ovary matures into the core and contains the seed.

pomologist: Fruit scientist. population: All individuals of a given species in a given area.

porosity: Degree to which soil, gravel, sediment, or rock is permeated with pores or cavities through which water or air can move.

postharvest physiology: Study of the functioning of crop tissues and cells following harvest; seeks to maintain quality and prevent spoilage of crop.

potential energy: Energy available to do work, but not yet expressed.

prairie: Area of land dominated by grasses with occasional shrubby plants and small trees occurring where the grass cover is broken and with herbaceous perennials during certain seasons.

precipitation: Moisture falling from the atmosphere in the form of rain, sleet, snow, or hail.

precooling: Process of rapidly removing heat from vegetables before shipping.

preplant fumigation: Fumigation of weeds before planting.

pressure potential: Component of water potential caused by the force created by real pressure (turgor pressure) against a membrane.

prickle: Small, spine-like growth that is attached only to the epidermis; can be removed easily; for example roses have prickles.

primary cell wall: Cellulose wall of all plant cells laid down at time of mitosis and cytokinesis.

primary consumer: An organism that consumes a producer organism as a food source; a herbivore.

primary pit fields: Regions within the primary cell wall in which plasmodesmata traverse the cell wall.

primary succession: Plant successional events occurring in a pristine or newly forming habitat.

primary tissue: Any tissue derived from the apical meristem, either shoot or root.

primary xylem: Derived from procambium and divided into the earlier protoxylem and the later metaxylem.

primordia: Organ or tissue in its earliest recognizable stage of development.

principle of independent assortment: Mendel's law states that allele pairs separate independently during the formation of gametes.

principle of segregation: Mendel's law states that allele pairs separate or segregate during gamete formation, and randomly unite.

pristine: Denoting a natural and undisturbed state.

producers: Autotrophic organisms that synthesize organic molecules directly from C[O.sub.2] and [H.sub.2]O.

profundal zone: Deepest portion of a lake.

progymnosperms: Generally looked like gymnosperms, did not produce seeds, reproduced by releasing spores into the environment, but lacked other characteristics of ferns.

prokaryotes: Organisms whose cells have no nucleus, including bacteria and cyanobacteria.

promoter: Segment of DNA that controls a group of structural genes.

prop roots: Adventitious roots arising on a stem above the ground and imparting some mechanical support to plants; angled roots may provide for adsorption.

propagation: Process of increasing in number.

prophase: First stage of nuclear division, characterized by the disappearance of the shorten chromosome.

proplastid: Membrane-bound particles that develop some internal structure; may subsequently develop into chloroplast. chromoplasts, or leucoplasts.

protected ovules: Adaptation such as cones.

protein: Macromolecule composed of a given linear sequence of amino acids.

protein sequencer: Determination of the identity and order of the amino acids present in a protein of interest.

proteomics: Branch of genetics that studies the full set of proteins encoded by a genome.

prothallium cells: Fern that produces both male and female sex cells.

protoderm: Dermal or outer tissue of an apical meristem that gives rise to the epidermis.

proton: Positively charged atomic particles that determine the elemental characteristics of an atom.

protoplast: Living portion of the cell.

protoplast fusion: Technique of enzymatically digesting the cell wall of two distinctly different cells, then treating the plasma membrane so that protoplasts of the two cells fuse. The resulting hybrid may be difficult or impossible to achieve with traditional plant breeding.

protoxylem: First xylem cells formed in the primary xylem.

proviral state: Condition of a host cell after having been transformed.

pruning: Selective removal of parts of a plant, usually woody shrubs or trees.

pseudocopulation: Sexual deception; generally applied to a pollinator attempting to copulate with a flower.

pseudohallucinogens: Produce psychotic and delirious effects without the classic visual disturbances of true hallucinogens.

psilocin: Hallucinogenic drug that is obtained from Psilocybe mexicana mushrooms.

psilophyta: First fossil of land plants had both horizontal and vertical shoots.

psychoactive: Having effects on the mind.

pterophyta: Group of non-seed plants with a fossil record dating back to the lower Devonian; consists of about 11,000 living species.

pubescenct: Having hairs or trichomes on the surface.

pulping: Process of partially digesting and breaking up wood fibers to make paper.

pumice: Lightweight white, yellow, or gray stone formed from volcanic glass; used in polishing and cleaning.

punnett square: Visual aid in determining the possible recombination frequencies for the existing gamete types of a cross.

pure opium: A pure form; morphine is derived (refined) from pure opium; heroine is a "synthetic" form of morphine.

pure parents: Deliberate mating of selected parents based on particular genetic traits; inbred line; group of identical purebreeding diploid or polyploidy.

purgative: Tending to cleanse or purge, especially causing evacuation of the bowels.

purine: Double-ring nitrogen base found in the nucleic acids, including adenine and guanine.

pyrimidine: Single-ring nitrogen base found in the nucleic acids including cytosine, thymine, and uracil.

quality of light: Where the particular wavelength of light falls on the light spectrum.

quarter-sawed: To saw into quarters and then into boards, as by cutting alternately from each face of a quarter.

quinine: Bitter-tasting drug obtained from the bark of the cinchona tree; related to coffee and gardenia; used in the treatment of malaria.

radial micellation: Reinforcement of the cell wall of guard cells in specific regions such that the cells curve outward when fully turgid.

radially cut: One of the three standard cuts of wood are transverse (cross sectional), radial, and tangential.

radiation: Energy in the form of waves or particles.

radicle: Primary root of a germinated seed.

radiocarbon dating: Dating method based on the radioactive decay of Carbon-14 ([C.sup.14]) contained in organic materials.

rain-shadow desert: Desert on the leeward side of a mountain range.

ratoon: Shoot growing from the root of a plant, providing a second harvest.

rayon: Manufactured fiber composed of regenerated cellulose, derived from wood pulp, cotton linters, or other vegetable matter.

rays: Parenchymal cells found in secondary xylem and phloem in both woody angiosperms and gymnosperms, which provide for lateral (radial) transport.

reaction wood: Wood produced in response to a tree that has lost it's vertical position, causing the tree to straighten.

receptacle: Modified apex of a stem to which the floral parts are attached.

recessive: Gene masked by its dominant allelic partner, having the recessive phenotype expressed only when both alleles for a given trait are recessive.

recognition surface: Three-dimensional structure of a biological membrane surface that gives specificity due to macromolecules of various sizes and shapes that extend above the lipid layer.

recolonization: Revegetate; reestablishment of a natural community following a natural or unnatural event that removed the existing vegetation.

recombinant DNA (rDNA): Genes produced by genetic engineering manipulations that contain genetic segments from other organisms.

red light (Pr): Since plants use red light for photosynthesis, and reflect and transmit far-red light, the shade of other plants also can make Pfr into Pr.

reduction division: First nuclear division of meiosis during which the paired homologues migrate to opposite poles, resulting in cells with a reduction from a diploid to a haploid number of chromosomes.

regular symmetry: Radial symmetry; having two or more planes through which the structure (flower) could be cut to result in mirror-image halves; actinomorphy.

regulator gene: Gene that inhibits the structural genes of an operon.

relative density: Heterogeneous matrix such as wood; density differences between layers of cell; breakdown in the regular structure of cell walls.

relative humidity (RH): Measure of the amount of water in the atmosphere.

remote sensing: Means of acquiring information using airborne equipment and techniques to determine the characteristics of an area; aerial photographs from aircraft and satellite are the most common form of remote sensing.

renewable natural resources: Natural resources that can be replaced or renewed within a short time span.

repressible enzymes: Enzymes whose production can be a corepressor.

repressor: Compound that binds to and controls the regulator in gene regulation.

reserpine: Active ingredient isolated from the root of the snakeroot plant (Rauwolfia serpentina), a small evergreen climbing shrub of the Dogbane family.

resin canal: Long intercellular spaces present in the longitudinal system of vascular cells of pine, spruce, larch, and Douglas fir; adjacent parenchymal cells secrete the resin into the canals.

resins: Carbohydrates synthesized by certain plants in glands, canals, or ducts; insoluble in water; used in various industrial products, including paints and varnishes; aid in resistance of wood to decay.

resistant: Treated so as not to get certain diseases.

respiration: Process of converting food energy in the form of glucose to ATP energy; occurs in the cells of all living organisms and releases carbon dioxide as a by-product; aerobic respiration requires the presence of oxygen, but some organisms can respire anaerobically.

revegetate: Natural or induced replacement of plants into a cleared area; the recurrence of the same plant community that existed prior to clearing.

rhizobium: Soil bacteria that fix nitrogen after becoming established inside root nodules of legumes.

rhizoid: Rootlike absorptive structures on the underside of certain gametophytes. rhizome: Fleshy, horizontal underground stem.

rhyniophyta: Earliest known division of vascular plants.

ribonucleic acid (RNA): Single-stranded nucleic acid composed of adenine, guanine, cytosine, uracil, phosphate, and ribose.

ribose: Five-carbon sugar important in RNA and many other compounds.

ribosomal RNA (rRNA): Ribonucleic acid involved in the formation of the ribosome.

ribosome: Cellular organelle responsible for the translation part of protein synthesis.

ring-porous wood: Secondary xylem characterized by large vessels and tracheids being produced early in the season (following favorable growing conditions); each term of growth activity is seen as a ring.

RNA polymerase: Enzyme responsible for forming mRNA during transcription. roll: System of cleaning and preparing ground to receive sod.

rootbound: Condition of a restricted root system.

root cap: Group of cells covering the root meristem that aid the root's penetration through the soil.

root hairs: Root epidermal cells that elongate, increasing the total absorptive surface area.

root pressure: Positive pressure in the xylem due to a negative solute potential and closed stomata.

rootstock: Root onto which a scion or bud is grafted or budded.

rosettes: Consists of a single, compact stem, with long, spiraled leaves distributed in a short portion of the stem.

rough endoplasmic reticulum: Function is to synthesize and export proteins and glycoproteins.

rubber: Elastic material obtained from the latex sap of trees (especially trees of the genera Hevea and Ficus) that can be vulcanized and finished into a variety of products.

RuBP carboxylase: Enzyme that fixes C[O.sub.2] in the Calvin cycle of photosynthesis.

runners: New plants are formed at nodes by runners, which are stems from old plants; the stems grow along the ground.

salicylic acid (sal-ah-sill-ik): Compound with pain-relieving characteristic, found in willow bar and other plants; basic ingredient of aspirin.

samara: One- or two-seeded dry indehiscent fruit in which the ovary wall forms as outgrowth to form a wing.

sandstone: Sedimentary rock formed by the consolidation and compaction of sand, held together by a natural cement such as silica.

sapwood: Functional secondary xylem found between the vascular cambium and the nonfunctional heartwood in the center of the trunk or branch.

savannas: Lands with herbaceous understory, typically graminoids, and with shrub cover between 10% to 30%; tree/shrub cover height exceeds 2 meters.

scarification: Mechanical or chemical degradation of a hard surface, such as seed coats, so that oxygen and water can penetrate the hard layers.

scavengers: Any animal that eats refuse and decaying organic matter.

schizocarp: Dry, indehiscent two- or multiple-carpeled ovary that splits at maturity into separate one-seeded section that falls away.

scientific method: Objective process of approaching a problem. Involves hypothesis establishment, testing, observing the results, revaluation of the hypothesis in light of new knowledge, and retesting to seek repeatability and thus validity of the hypothesis.

scientific name: Latinized binomial (genus an species) unique to each identified organism.

scion: Short length of stem, taken from one plant which is then grafted onto the rootstock of another plant.

sclereids: Stone cells found in tissues varying from pear fruit to the hard shell of nuts.

sclerenchyma: Tissue type characterized by thick, sclerified cell walls; includes both fibers and sclereids (stone cells).

scopolamine: Alkaloid with anticholinergic effects that is used as a sedative and to treat nausea and to dilate the pupils in ophthalmic procedures; transdermal scopolamine is used to treat motion sickness.

seasonal cycles: Periodic, repetitive sequence of events in climate that play out over time; based on the earth's tilt on its axis and rotation around the sun.

secondary cell wall: Cellulose wall, often impregnated with lignin, laid down inside the primary cell wall of many woody species.

secondary compounds: Organic molecules synthesized by certain species of plants and not thought to be directly involved in essential metabolism.

secondary consumer: Organism that consumes a primary consumer; a carnivore.

secondary phloem: Phloem tissue formed by the vascular cambium in woody stems.

secondary succession: Revegetation of cleared land; return to previous community structure.

secondary tissue: Pliable sheet of tissue that covers, lines, or connects the organs or cells of plants.

secondary xylem: Xylem tissue formed by the vascular cambium in woody plants.

sedative: Substance that reduces nervous tension; usually stronger than a calmative.

sedentary: Inactive.

sedimentary rock: Rock formed by cementation and solidification of sedimentary deposits weathered from granite.

seed: Mature ovule within a fruit.

seed coat: Protective layer that develops from the integuments around a maturing ovule.

seedbed: Area of soil cultivated and prepared for planting seeds.

seed ferns: Any plant of the extinct order Pteridospermales; modern ferns reproduce by spores.

seedling: Embryonic product of the germination of a seed; the young shoot and root axis.

seed-scales complex: Spirally arranged scales on a female strobilus in gymnosperms.

sieve cell: Organic solute-conducting cell of the phloem in gymnosperms.

sieve tube members: Sieve areas more specialized than the sieve; sievetube members are joined end to end to form a tube that conducts food.

seismonasty: Plant's reaction to being touched, or the movement of a plant in response to a shock, such as shaking, intense heat, wind, or rain.

self-incompatibility-: Conditions of a flower that cannot successfully complete the reproductive process with pollen produced by its own stamens.

self-pollinating: Plant that has its own pollen fall on its own stigma.

semi-dwarf: Tree that grows to about 10 to 15 feet.

senescence: Aging process, usually characterized by the loss of some functional capacity, including reproduction.

sepal: Flower part attached outside the others, enclosing the flower when in bud.

seral: One stage of the communities in an ecological succession.

sessile: Referring to leaf blades without petioles in which the blade is attached directly to the stem.

sex cells: Specialized cells from a female fuse with a specialized cell from a male. Each of these sex cells contains the genetic from their parents.

sexual propagation: Pertaining to the fusion of gametes; sexual reproduction.

sexual reproduction: Gives plant offspring the genetic variability that enables them to adapt to changes in the environment.

shale: Sedimentary rock composed of mud.

shard: Piece of broken clay or ceramic pot placed over a drainage hole of a pot to prevent the loss of soil during watering.

sheath: Base of a leaf in monocots, usually wrapping around the stem.

shoots: Aboveground portions of a plant.

short day plant: Plant that flowers when the length of day is shorter than some critical value.

shrub: Plant that is shrublike in growth habit; usually a short, perennial plant without strong apical dominance.

silent mutation: Permanent genetic change, but one that is never expressed by the phenotype.

silique: Simple fruit that develops from a two-carpeled ovary; at maturity the two halves fall away, leaving the seeds attached to the persistent central wall.

simple leaf: Leaf having a single blade portion; may be highly lobed or dissected.

simple fruit: Fruits in which part or all of the pericarp (fruit wall) is fleshy at maturity; types of fleshy, simple fruits are apples, peaches, and pears.

simple pistil: Composed of one carpel.

sink: Site of collection of metabolites, such as sugar; metabolic sinks may exist anywhere in the plant where organic solutes are being transported by the phloem and stored.

slash and burn: Method of cultivation whereby areas of the forest are burnt and cleared for planting.

smooth endoplasmic reticulum: Cellular organelle; consists of tubules and vesicles that branch forming a network; allows increased surface area for the action or storage of key enzymes and the products of these enzymes.

sphenophyta: Division of primitive spore-bearing vascular plants; most members of the group are extinct and known only from their fossilized remains.

sociobiologist: Study of the biological basis of human social behavior.

sociopolitical conservation: Policies must be tailored to local contexts, both ecological and sociopolitical.

sod: Grass that has soil and roots attached.

sod-forming: Grasses that grow to produce a densely matted sod from the spread of stolons and rhizomes; covers more uniformly than bunch-type grasses.

softwoods: Functional secondary xylem found between the vascular cambium and the nonfunctional heartwood in the center of the trunk or branch.

soil probe: Tool used to withdraw small cylindrical samples of soil for analysis or for determining moist soil depth.

soil profile: Vertical section of a soil, showing horizons and parent material.

solarization: Vegetation is removed, soil is broken up and then wetted to activate the nematode population. Next, the soil is covered with a sturdy clear plastic film during the warmest six weeks of summer. High temperatures (above 130[degrees]F) must be maintained during this time for best results.

solubility: Relative ability of a solute to be dissolved.

solute: Any substance dissolved in a solvent.

solute potential: Water potential component caused by the presence of solutes in water.

solvent: Liquid matrix in which a solute is dissolved.

somatic cells: All body cells other than sex cells, containing at least the two sets of chromosomes inherited by both parents.

somatic nervous system: Part of the autonomic nervous system.

sorghum: Old World grass (Sorghum bicolor), several varieties of which are widely cultivated as grain and forage or as a source of syrup.

SPAC (soil-plant-air continuum): Concepts and theories that describe the dynamics of water, carbon, and nitrogen in the soil-plant-air continuum.

speciation (spe-see-s-shun): Evolutionary processes leading to the development of new species.

species: Group of similar organisms that are capable of interbreeding with each other and can interbreed with members of a different species with only minimal success or not at all; the second word of a scientific binomial, always in Latin.

specific gravity: Ratio of the density of a material to the density of water.

specific heat: Amount of heat required to raise the temperature of 1 gm of any substance 1[degrees]C.

sperm nuclei: Each pollen grain produces two sperm nuclei, which effects double fertilization in angiosperms.

spindle fibers: Protein fibers formed during prophase of nuclear division; chromosomes attached to these fibers at the centromere.

spine: Leaf or leaf part modified as a hard, sharp-pointed structure.

spongy parenchyma: Leaf tissue composed of columnar cells containing numerous chloroplasts in which the long axis of each cell is perpendicular.

sporangiospore: Any spore produced from a sporangium.

sporangium: Spore case; a hollow structure in which spores are produced.

spore: Haploid structures produced by the sporophyte plant via meiosis that develop into the gametophyte.

sporophyte: Diploid, spore-producing plant in the alternation of generations; undergoes meiosis to produce the haploid spores.

staking: Keeping plants in the correct growing position by using wires, wooden posts, or similar supports.

stamen: Male reproductive structure in a flower, consisting of an anther supported on a filament.

staminate: Unisexual flower having stamens but no pistil.

staminodium: Sterile stamen, nonfunctional anthers and often with petaloid filaments.

starch: Polysaccharide composed of glucose linkages; the primary storage carbohydrate of plants.

stele: Central vascular cylinder of roots and stems of vascular plants.

stem cuttings: Piece of stem is part buried in the soil, including at least one leaf node; produces new roots, usually at the node.

sterols: Complex alcohols (steroid alcohols) that are important in animals as hormones, coenzymes, and precursors for vitamin D.

stigma: Apical portion of the pistil, the surface on which pollen lands and germinates.

stimulants: Drug that increases the activity of the sympathetic nervous system and produces a sense of euphoria or wakefulness.

stimulates: Mode of action of plant hormones.

stolon: Horizontal aboveground stem.

stoma (pl., stomata): Epidermal complex consisting of two guard cells and the pore between them.

stomatal regulation: Complex process depending on microclimate and measured soil water potential.

strata: Layers of sedimentary rock, the oldest rocks occurring at the bottom of the ocean.

stroma: Matrix between the grana in chloroplasts and site of the dark reactions of photosynthesis.

structural genes: Genes that are transcribed into proteins.

style: Central, elongated portions of the pistil between the stigma and ovary.

sulfite process: Process for the digestion of wood chips in a solution of magnesium.

suberin: Lipid material found in the Casparian strip of the endodermis and in the cell walls of cork tissue.

submetacentric: Pertaining to a chromosome with a centromere located between the center and one end of the chromosome.

substrate: Beginning substance from which other molecules are synthesized.

succession: Processes of vegetation change over time, or plant succession, are also the processes involved in plant community restoration.

succulent: Plant characterized by thick, fleshy leaves or stems; an adaptation usually associated with a water or salt stress.

sulfite process: Chemical process for the manufacture of paper pulp; uses an acid bisulfite solution to soften the wood material by removing the lignin from the cellulose.

sunken stomata: Specially adapted structures reduce transpiration.

superior ovary: Attachment of the ovary to the receptacle above and free from the attachment of the other floral parts.

symbiotic: Plant characterized by thick, fleshy leaves or stems; an adaptation usually associated with a water or salt stress.

symplastic movement: Pertaining to the movement of water and solutes through tissues by passing through biological membranes.

synapsis: Coming together of homologous chromosomes to form bivalents during prophase I of meiosis.

synergid: Two haploid cells on either side of the egg cell at the micropylar end of the embryo sac.

synthetic pyrethrums: Type of chrysanthemum, as there are not enough flowers available to meet the demand; synthetic pyrethrums are on the market that are very safe. They are used in IPM rotations.

system toxins: Poisons (toxins) that work on the nervous system.

taiga (tie-ga): Northernmost coniferous forest, characterized by cold winters and heavy snowpack.

tannin: Hemi-cellulose and lignins produce a host of volatile phenols.

tapetum: Nutritive somatic tissue surrounding the microsporocyte.

taproot: Primary root from which secondary roots originate.

taq polymerase: Enzyme frequently used in polymerase chain reaction (PCR), methods for greatly amplifying short segments of DNA.

taro: Early root crop from Asia with swollen underground stems with stem buds that can each produce a new plant--like a potato.

taxine: Drug that inhibits cell growth by stopping cell division; used as treatment for cancer; also called antimitotic or antimicrotubule agents or mitotic inhibitors.

telocentric: Pertaining to a chromosome with a centromere located at one end.

telophase: Stage of nuclear division in which sets of chromosomes finally arrive at the poles of the dividing cell; new nuclear envelope forms at this stage.

temperate deciduous forest: Characterized by a mild or moderate temperature with deciduous trees.

temperature shock treatments: Sudden change in temperature.

template: Genetic message on the sense strand of DNA as determined by the sequence of nucleotides.

tendril: Modified leaf or stem in which only a slender strand of tissue constitutes the entire structure.

tension wood: Reaction wood produced along the upper side of leaning woody trees, straightening the trunk by contracting and "pulling" the tree upright.

terminal bud: Meristematic tissue located at the tip of a stem.

terpenes: Group of secondary compounds composed of two to many isoprene units in a chain or ring; sometimes categorized as hydrocarbons only, sometimes to include terpenoids.

terpenoids: Term referring to all compounds composed of isoprene units.

terrarium: Closed biological system in which plants and animals coexist without external inputs or discharges; [H.sub.2]O, C[O.sub.2], [O.sub.2], and nutrients cycle in the closed system.

terrestrial biomes: Pertaining to the land.

testcross: Crossing an organism having a dominant expression for a trait with an organism having a dominant homozygous recessive genotype for that trait to determine the genotype of the organism expressing the dominant phenotype.

thermal stratification: Layering of different temperatures of water or air caused by different densities, less dense floating on more dense layers.

thermonasty: Plant movement caused by temperature: The movement of plant parts in response to a change in temperature, for example, the opening of flowers.

thigmotropism: Turning or bending response of a plant upon direct contact with a solid surface or object.

thorn: Modified stem termination in a sharp point that is attached to the vascular system of the plant.

thorn forest: Type of vegetation in the warm, semiarid zones in which the predominant vegetation is scrubby, has thick leathery leaves, and is characterized by sharp or thorny stems.

thylakoid: Lamellar structure of the grana of chloroplasts.

thymine: Nitrogen base found in DNA. tiga: Snow forest.

tillers: First side shoots in small grains.

tillering: Production of lateral buds and shoots near the ground to result in a plant with several shoots instead of one; particularly important in grasses and grain crops.

tonoplast: Membrane surrounding the vacuole.

top carnivore: Consumer at the end of a food chain or web; a carnivore that ordinarily has no predator under those ecological conditions.

topography: Surface condition of an area of land; relief features.

topsoil: Uppermost layer of soil, highly weathered and often rich in organic matter nutrients.

total body mass: Measurement of the relative percentages of fat that correlates strongly with the total body fat content.

tracheids: Elongated, spindle-shaped cells that conduct water in the xylem; particularly important in gymnosperms.

tracheophytes: Plants with a well-defined vascular system.

training: Directing plants to grow certain directions by using different methods.

transcription: First stage of protein synthesis in which the template of DNA is transcribed into mRNA.

transfer RNA (tRNA): Small ribonucleic acid molecule involved in the transfer of specific amino acids to a protein being synthesized.

transformation: Incorporation of viral nucleic acid into the nucleic acid of the host cell.

transforming factor: Substance that can be passed from one cell to another and cause a permanent change in heredity.

transgenic: Plants and animals result from genetic engineering experiments in which genetic material is moved from one organism to another, so that the latter will exhibit a desired characteristic.

transitional mutants: Type of mutation in which a single purine-pyrimidine base pair is replaced by another.

translation: Second stage of protein synthesis in which the codon of mRNA pairs with the anticodon of tRNA at the surface of the ribosome.

transpiration: Evaporation of water from the surface of plant leaves and stems.

transpirational pull: Main phenomenon driving the flow of sap in the xylem tissues of large plants.

transplantability: Success of plants being transplanted after starting indoors.

transversional mutant: Type of mutation in which a purine-pyrimidine base pair is replaced by a pyrimidinepurine base pair.

transverse cut: Longitudinal cut of wood.

trellis: Support system of wires or wood for growing certain plants.

trichome: Epidermal protrusion such as a hair or scale.

trihybrid cross: Cross between individuals of the same type that are heterozygous for three pairs of alleles at three different loci.

triplet: Group of three nucleotides on a nucleic acid that codes for a particular amino acid.

trophic: Feeding level; a step in the energy flow through a food chain.

tropical rain forest: Forest that gains more water from precipitation than it loses through evaporation; located in the tropical zone and having an average temperature between 70[degrees] and 85[degrees]F (21[degrees] and 29[degrees]C) and average yearly rainfall of more than 80 inches (200 cm).

tropism: Turning or bending movement of an organism or a part toward or away from an external stimulus, such as light, heat, or gravity.

truck cropping: Refers to commercial, large-scale production of selected vegetable crops for wholesale markets and shipping.

tryptophan: Essential amino acid involved in human nutrition; one of the 20 amino acids encoded by the genetic code.

tube cell: Nucleus of a pollen grain believed to influence the growth and development of the pollen tube.

tube nucleus: One division of the microspore nucleus in a pollen grain that is responsible for the formation of pollen tube from the stigma through the style to the ovule.

tuber: Horizontal, underground stem with a very enlarged tip.

tubocurarine: Alkaloid isolated from the bark and stems of Chondodendron tomentosum (Menispermaceae); active principle of curare.

tubulin: Protein of which microtubules are composed.

tumor: Spherical mass of cells in which cell division occurs at random and often in an uncontrolled fashion.

tundra: Treeless plain characteristic of the arctic and subarctic regions.

turf: Intertwined fibrous roots of grasses forming a mass with the soil just below ground level.

turgidity: Full, even distended with water taken in by osmosis.

turgor pressure: Real pressure developed in living cells by pressing against a membrane.

turpentine: Solvent that includes two terpenes: camphor and pinene.

ultraviolet: Portion of the sun's total range of radiation having wavelengths immediately shorter than the shortest of the visible spectrum (purple); between approximately 380 and 100 nm.

understory: Vegetation that characterizes the lower level of plants in a forest; the vegetation below the canopy.

unisexual: Condition of having either stamens or pistil, not both; an imperfect flower.

unit membrane: Transmission electron microscopic interpretation of a biological membrane, consisting of two electron-dense lines separated by translucent space.

uracil: Nitrogen base found in RNA.

uredospore (u-reed-o-spore): Binucleate spore produced by rust during the summer.

vacuolar sap: Aqueous substances inside the vacuole.

vacuole: Aqueous cavity within the cytoplasm and surrounded by the tonoplast that stores low molecular weight ions and molecules.

vapor concentration: Gradient equals the water vapor concentration inside the product minus that of the surrounding air.

variability: How plants differ from each other.

vascular bundle: Veins in herbaceous plants and in leaves of all plants, including the specialized cells of both xylem and phloem.

vascular cambium: Lateral meristem characteristic of secondary growth; gives rise to secondary xylem and secondary phloem.

vascular plants: Plants that have lignified tissues for conducting water, minerals, and photosynthetic products through the plant, includes the ferns, club mosses, flowering plants, conifers, and other gymnosperms.

vascular systems: Lignified tissues for conducting water, minerals, and photosynthetic products through the plant.

vector: Agent of transfer, such as insects and other animals in pollinations.

vegetative: Period when the plant grows vigorously and rapidly.

vegetative reproduction: Reproductive process that is asexual and so does not involve a recombination of genetic material. It involves unspecialized plant parts that may become reproductive structures (such as roots, stems, or leaves).

venation: Pattern of vein development in leaves.

veneer: Rotary-cut from a bolt of wood, called a flitch, centered in chucks.

vermiculite: Expanded mica used as a sterile medium for the rooting of cuttings; high water-holding capacity and relatively inert.

vesicles: Membrane-found particles pinched off by constriction of a membrane, as in the Golgi apparatus.

vessel: Primary water-conducting cell-system in the xylem of most angiosperms.

vessel element: Individual cells of xylem that combine end-to-end to form a vessel.

viability: Period of time an organism remains alive; often used to describe the length of time before a seed will fail to germinate.

virus: Crystal-like particle composed of a protein coat and a central core of DNA or RNA, but never both.

viscous: Thick and highly dense.

visible spectrum: That portion of all the sun's radiation that can be perceived as light by humans; between approximately 380 and 100 nm wavelength.

viviparous: Characterized by beginning embryo growth while still attached to the mother plant.

volatile oils: Terpenes composed of two to four isoprene units; also known as essentials oils, such as lemon and peppermint.

volatilization: Process of evaporation; to pass into the atmosphere as gas.

volunteer plants: Plants that may grow following harvest or the next season without being planted.

vulcanization: Process of treating rubber or rubberlike materials with sulphur at great heat to improve elasticity and strength or to harden them.

wadi: Dry riverbed that only contains water during times of heavy rain.

water potential: Relative ability of water molecules to do work by interacting with each other.

water quality: Describes the chemical, physical, and biological characteristics of water, usually in respect to its suitability for a particular purpose.

water stress: Occurs when the demand for water exceeds the available amount during growth.

wax: Lipid material with considerable oxygen inserted in the molecule; high melting point and relatively impermeable to water.

weed: Any plant growing in an area where it is not desired.

wheat: Cereal grass (Triticum vulgare) and its grain, which furnishes white flour for bread, and, next to rice, is the grain most largely used by the human race.

white light: Sunlight integrated over the visible portion of the spectrum (4,000-7,000 angstroms) so that all colors are blended to appear white to the eye.

whorled: Three or more leaves attached at a node.

windward: Side toward which the wind is blowing.

winter hardy: Seeds that can be seeded even where temperatures frequently fall to 40[degrees]F, below zero, or where mean winter temperatures are about 0[degrees]F.

wolfbane: Aconitum known as aconite or monkshood.

world supply: To meet essential food import needs in all countries, considering world price and supply fluctuations and taking especially into account food consumption, each nation can define for itself what is required for survival.

xeric (zee-rick): Characterized by very dry environment.

xerophyte: Plant adapted for growth under arid conditions.

X-ray: Portion of the sun's total range of radiations, which is immediately shorter than ultraviolet; between 0.1 and 100 nm.

X-ray crystallography: Technique for studying molecular and atomic structure of a substance.

Yellow river : River of north China; flows from the west starting at the high plateau of Tibet eastward into the Yellow Sea; complex society of East Asia originated from the valley of this river.

zone of elongation: Area in plant roots where recently produced cells grow and elongate prior to differentiation.

zooplankton (zo-o-plank-tun): Single-celled and small multicellular animals that feed on phytoplankton in aquatic ecosystems.

zoospore: Motile asexual spore.

zosterophyllophyta: Division of fossil plants; among the first vascular plants.

Z-scheme: Diagrammatic representation of electron flow through PS II and PS I.

zygospore: Thick-walled, resistant spore resulting from a zygote.

zygote: Diploid cell formed by the fusion of two haploid gametes; the result of fertilization.
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Publication:Fundamentals of Plant Science
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Date:Jan 1, 2009
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