Abscisic acid - a growth-inhibiting hormone of plants; it is involved with other hormones in dormancy.

Abscission - the separation of leaves, flowers, and fruits from plants after the formation of an abscission zone at the base of their petioles, peduncles, and pedicels.

Achene - a single-seeded fruit in which the seed is attached to the pericarp only at its base.

Acid - a substance that dissociates in water, releasing hydrogen ions.

Active transport - the expenditure of energy by a cell in moving a substance across a plasma membrane against a diffusion gradient.

Adventitious - said of buds developing in internodes or on roots, or of roots developing along stems or on leaves.

Aerobic respiration - respiration that requires free oxygen.

Agar - a gelatinous substance produced by certain red algae and also a few brown algae; it is often used as a culture medium, particularly for bacteria.

Aggregate fruit - a fruit derived from a single flower having several to many pistils.

Air layering - an asexual plant propagation technique whereby aerial stems are induced to form roots. The rooted portion of the stem is then cut and planted.

Algin - a gelatinous substance produced by certain brown algae; it is used in a wide variety of food substances and in pharmaceutical, industrial, and household products.

Allele - one of at least two alternative forms of a gene.

Alternation of Generations - alternation between a haploid gametophyte phase and a diploid sporophyte phase in the life cycle of sexually reproducing organisms.

Amino acid - one of the organic, nitrogen-containing units from which proteins are synthesized; there are about 20 in all proteins.

Anaerobic respiration - respiration in which the hydrogen removed from the glucose during glycolysis is combined with an organic ion (instead of oxygen).

Aneuploid - an aberration in normal chromosome number in which one or more extra chromosomes are present or one or more chromosomes are missing.

Angiosperm - a plant whose seeds develop within ovaries that mature into fruits.

Annual - a plant that completes its entire life cycle in a single growing season.

Annual ring - a single season's production of xylem by the vascular cambium.

Annulus - a specialized layer of cells around a fern sporangium: it aids in spore dispersal through a spring like action; also a membranous ring around the stripe of a mushroom.

Anther - the pollen-bearing part of a stamen.

Antheridiophore - a stalk that bears an antheridium.

Antheridium - the male gametangium of certain algae, fungi, bryophytes, and vascular plants other than gymnosperms and angiosperms.

Anthocyanin - a water-soluble pigment found in cell sap; anthocyamins vary in colour from red to blue.

Antibiotic a substance produced by a living organism that interferes with the normal metabolism of another living organism

Anticodon the three nucleotide sequences in a RNA molecule that base pairs with the complementary RNA codon for the amino acid carried by that specific RNA.

Apical dominance - suppression of growth of lateral buds by hormones.

Apical meristem - a meristem at the tip of a shoot or root.

Apomixes - reproduction without fusion of gametes or meiosis in otherwise normal sexual structures.

Archegoniophore - a stalk bearing an archegonium.

Archegonium - the muilticelluar female gametangium of bryophytes and most vascular plants other than angiosperms.

Aril - an often brightly coloured appendage surrounding the seed of certain plants like yew.

Ascus - one of often numerous, frequently finger like hollow structures in which the fusion of two haploid nuclei is followed by meiosis; a row of ascosporic (usually eight) is ultimately produced in each ascus on or within the sexually initiated reproductive bodies of cup (sac) fungi.

Asexual reproduction - any form of reproduction not involving the union of gametes.

Assimilation - cellular conversion of raw materials into protoplasm and cell walls.

Atom - the smallest individual unit of an element that retains the properties of the element.

ATP (ay-tee-pee) adenosine troposphere. A molecule with three phosphate groups found in all living cells; it is the principal vehicle for energy storage and exchange in cell metabolism.

Autotrophic - descriptive of an organism capable of sustaining itself through conversion of inorganic substances to organic material.

Axuin – a growth-regulating substance produced either naturally by plants or synthetically.

Axial - the angle formed between a twig and the petiole of a leaf; normally the site of an axillary bud.

Backcross - a cross involving a hybrid and one of its parents.

Bacteriophage - a virus whose host is a bacterium.

Bark - tissues of a woody stem between the vascular cambium and the exterior.

Base - a substance that dissociates in water, relea.5ing hydroxyl (OH-) ions.

Basidiospore - a spore produced on a basilicum.

Basilicum - one of usually numerous, frequently club-shaped hollow structures in which the fusion of two haploid nuclei is followed by meio5is, the four resulting nuclei becoming a borne basidiospore.

Berry - a thin-skinned fruit that usually develops from a compound ovary and commonly contains more than one seed.

Biennial - a plant that normally requires two seasons to complete its life cycle, the first season's growth being strictly vegetative.

Biological controls - the use of natural enemies and inhibitors in combating insect pests and other destructive organisms.

Biomass (by-oh-ma.5s) the total mass of living organisms present.

Biome - similar biotic communities considered on a world wide scale.

Biotechnology - the manipulation of organisms, tissues, cells or molecules for specific applications primarily intended for human benefit.

Biotic community - an association of plants, animals, and other organisms.

Blade - the conspicuous, flattened part of a leaf or seaweed.

Bond (bond) a force that holds atoms together.

Bonsai - container-grown plants that have been dwarfed artificially through skilful pruning and manipulation of the growing medium.

Botany - science involving the study of plants.

Botulism - poisoning from consumption of food infected by botulism bacteria.

Bract - a structure that is usually leaf like and modified in size, shape, or colour.

Bryophyte - a photosynthetic, terrestrial, aquatic or epiphytic, embryo-producing plant without xylem and phloem.

Budding - a form of asexual reproduction in which a new cell develops to full size from a protuberance arising from a mature cell, as in yeasts.

bulb - an underground food-storage organ that is essentially a modified bud consisting of fleshy leaves that surround and are attached to a small stem

Bundle scar - a small scar left by a vascular bundle within a leaf scar when the leaf separates from its stem through abscission.

Bundle sheath - the parenchyma and sclerenchyma cells surrounding a vascular bundle.

Callose - a complex carbohydrate that develops in sieve tubes following an injury; it is commonly as.5ociated

with the sieve areas of sieve tube members.

callus - undifferentiated tissue that develops around injured areas of stems and roots; also the undifferentiated tissue that develops during tissue culture.

Calyptras -tissue from the enlarged archegonia wall of many mosses that forms a partial or complete cap over the capsule.

Calyx - collective term for the sepals of a flower.

Cambium - a meristem producing secondary tissues.

Capillary water - water held in the soil against the force of gravity; capillary water is available to plants.

Capsule - a dry fruit that splits in various ways at maturity, often along or between carpel margins; also the main part of a sporophyte in which different types of tissues develop.

Carbohydrate - an organic compound containing carbon, hydrogen, and oxygen. With twice as many hydrogen as oxygen atoms per molecule.

Carpel - an ovule-bearing unit that is a part of a pistil.

Caryopsis - a dry fruit in which the pericarp is tightly fused to the seed; it does not split at maturity.

Casparian strip - a band of suberin around the radial and transverse walls of an endodermal cell.

Cell - the basic structural and functional unit of living organisms; in plants, it consists of protoplasm surrounded by a cell wall.

Cell biology - the biological discipline involving the study of cells and their functions.

Cell cycle - a sequence of events involved in the division of a cell.

Cell plate - the precursor of the middle lamella; it forms at the equator during telophase.

Cell sap - the liquid contents of a vacuole.

Cell wall - the relatively rigid boundary of cells of plants and certain other organisms.

Central cell nuclei - nuclei, frequently two in number, that unite with a sperm in an embryo sac, forming a primary endosperm nucleus.

Centromere - the dense, constricted portion of a chromosome to which a spindle fibre is attached.

Chemiosmosis - a theory that energy is provided for phosphorylation by protons being "pumped" across inner mitochondrial and thylakoid membranes.

Chiasma - the X-shaped configuration formed by two chromatids of homologous chromosomes as they remain attached to each other during prophase I of meiosis.

Chlorenchyma - tissue composed of parenchyma cells that contain chloroplasts.

Chlorophyll - green pigments essential to photosynthesis.

Chloroplast - an organelle containing chlorophyll, found in cells of most photosynthetic organisms.

Chromatid - one of the two strands of a chromosome; they are united by a centromere.

Chromatin - a readily staining complex of DNA and proteins found in chromosomes.

Chromoplast - a plastid containing pigments other than chlorophyll; the pigments are usually yellow to orange.

Chromosome - a body consisting of a linear sequence of genes and composed of DNA and proteins; chromosomes are found in cell nuclei and appear in contracted form during mitosis and meiosis.

Cilium - a short hair like structure usually found on the cells of unicellular aquatic organisms, normally in large numbers and arranged in rows; the most corrmlon tunction of cilia is propulsion of the cell.

Circadian rhythm - a mostly daily rhythm of growth and activity found in living organisms.

citric acid cycle - a complex series of reactions following glycolysis in aerobic respiration that involves ATP, mitochondria, and enzymes and that results in the combining of free oxygen with protons and electrons from pyruvic acid to make water.

Class - a category of classification between a division and an order.

Climax vegetation - vegetation association that perpetuates itself indefinitely at the culmination of ecological succession.

Cloning vector - a DNA molecule that can replicate and transfer DNA between cells.

Codon - the sequence of three nucleotides in an mRNA molecule that constitutes the code for a specific amino acid or a stop signal in protein synthesis; it is complementary to an anticodon.

Coenocytic - multinucleate, the nuclei not individually separated from one another by cross walls, as in the hyphae of water moulds.

Cohesion-tension theory - theory that explains the rise of water in plants through a combination of cohesion of water molecules in vessels and tracheids and tension on the water columns brought about by transpiration.

Coleoptile - a protective sheath surrounding the emerging shoot of seedlings of the Grass Family.

Coleorhiza - a protective sheath surrounding the emerging radicle of members of the Grass Family.

Collenchyma - tissue composed of cells with unevenly thickened walls.

Colloid - a substance consisting of a medium in which fine particles are permanently dispersed.

Community - a collective tern for all the living organisms sharing a common environment and interacting with one another.

Companion cell - a specialized cell derived from the same parent cell as the closely associated sieve tube member immediately adjacent to it.

Compost - a mixture of decomposed organic matter, particularly decomposed plant materials.

Compound - a substance hose molecules are composed of two or more elements.

Compound leaf - a leaf whose blade is divided into distinct leaflets.

Conidium - an asexually produced fungal spore formed outside of a sporangium.

Conjugation - a process leading to the fusion of isogametes in algae, fungi, and protozoa; also the means by which certain bacteria exchange DNA.

Conjugation tube - a tube permitting transfer of a game1e or gametes between adjacent cells, as in Spirogyra or desmids.

Consumer organisms that feed on producers.

Cork tissue composed of cells whose walls are impregnated with suberin at maturity; the outer layer of tissue of an older woody stem: produced by the cork cambium.

Cork cambium - a narrow cylindrical sheath of cells between the exterior of a woody root or stem and the central vascular tissue: it produces cork to its exterior and phelloderm to its interior: it is also called phellogen.

Corm - a vertically oriented, thickened food-storage stem that is usually enveloped by a few papery non-functional leaves.

Corolla - collective term for the petals of a flower.

Cortex - a primary tissue composed mainly of parenchyma: the tissue usually extends between the epidermis and the vascular tissue.

Cotyledon - an embryo leaf “seed leaf” that usually either stores or absorbs food.

Covalent bond - a force provided by pairs of electrons that travel between two or more atomic nuclei: holding atoms together and keeping them at a stable distance from each other.

Crossing-over - the exchange of corresponding segments of chromatids between homologous chromosomes during prophase me of meiosis.

Crown division - the asexual production of multiple plants by division of the base of a stem.

Cuticle - a waxy or fatty layer of varying thickness on the outer walls of epidermal cells.

Cutin - the waxy or fatty substance of which a cuticle is composed.

Cutting - any vegetative plant part used for asexual propagation.

Cyclosis - the flowing or streaming of cytoplasm within a cell.

Crythochrome - iron containing protein involved in molecule transfer in an electron transport system.

Cytogenetic - the study of the genetic effects of chromosome structure and behaviour.

Cytokinesis - division of a cell, usually following mitosis.

Cytokinins - a growth hormone involved in cell division and several other metabolic activities of cells.

Cytology - the protoplasm of a cell exclusive of the nucleus.

Cytoskeleton - a network of microtubules and microfilaments involved in movement within a cell.

Dark reactions - see light-independent reactions

Day-neutral plant - a plant that is not dependent on specific day lengths for the initiation of flowering.

Deciduous - shedding leaves annually.

Decomposer - organism that breaks down organic material to forms capable of being recycled.

Dedifferentiate - to become less specialized.

Development - changes in the form of a plant resulting from growth and differentiation of its cells into tissues and organs.

Dicotyledon - a class of angiosperms whose seeds commonly have two cotyledons; frequently abbreviated to dicot.

Dictyosome - an organelle consisting of disc-shaped, often branching hollow tubules that function in accumulating and packaging substances used In the synthesis of materials by the cell.

Differentially permeable membrane - a membrane through which different substances diffuse at different rates.

Differentiation - the change of a relatively unspecialized cell to a more specialized one.

Diffusion - the random movement of molecules or particles from a region of higher concentration to a region of lower concentration, ultimately resulting in uniform distribution.

Dihybrid cross - a cross involving two different pairs of genes and heterozygous parents.

Dikaryotic - having a pair of nuclei in each cell or a type of the mycelium in club fungi.

Dioecious - having unisexual flowers or cones. With the male flowers or cones confined to certain plants and the female flowers or cones of the same species confined to other different plants.

Diploid - having two sets of chromosomes in each cell; the 2n chromosome number characteristic of the sporophyte generation.

Disinfest - the removing of surface contaminants from a plant surface.

Division - the largest undivided category of classification of organisms within a kingdom; considered synonymous with phylum.

DNA - standard abbreviation of deoxyribonucleic acid, the carrier of genetic information in cells and viruses.

Dominance - a condition in which one allele of a gene (dominant allele) masks the phenotypic expression of another allele (recessive allele).

Dormancy - a period of growth inactivity in seeds, buds, bulbs, and other plant organs even when environmental conditions normally required for growth are met.

Double fusion - more or less simultaneous union of one sperm and egg and union of another sperm and central cell nuclei (forming a primary endosperm nucleus) that occur in the mega gametophyte of flowering plants.

Drupe - a simple fleshy fruit whose single seed is enclosed within a hard endocarp.

Ecology - the biological discipline involving the study of the relationships of organisms to each other and to their environment.

Ecosystem - a system involving interactions of living organisms with one another and with their nonliving environment.

Egg - a nonmotile female gamete

Elater - a strap like appendage attached to a horsetail spore, a somewhat spindle-shaped sterile cell occurring in large numbers in liverwort sporangia; both types of elaters facilitate spore dispersal.

Electron - a negatively charged particle of an atom.

Element - one of more than 100 types of matter, most existing naturally but some human-made, each of which is composed of one kind of atom.

Embryo - immature sporophyte that develops from a zygote within an ovule or archegonium after fertilization.

Enation - one of the tiny, green leaves like outgrowths on the stems of whisk ferns.

Endocarp - the innermost layer of a fruit wall.

Endodermis - a single layer of cells surrounding the vascular tissue in roots and some stems; the cells have Casparian strips.

Endoplasmic reticulum - a complex system of interlinked double-membrane channels subdividing the cytoplasm of a cell into compartments; parts of it are lined with ribosomes.

Endosperm - a food-storage tissue that develops through divisions of the primary endosperm nucleus; it is digested by the sporophyte after germination in some species or before maturation of the seed in other species.

Endosymbiont hypothesis - the theory that mitochondria and chloroplasts were free-living bacteria that became incorporated in cells.

Energy - the capacity to do work; some forms of energy are heat, light and kinetic.

Enzyme - one of numerous complex proteins that speeds up a chemical reaction in living cells without being used up in the reaction.

Epicotyl - the part of an embryo or seedling above the attachment point of the cotyledon.

Epidermis - the exterior tissue, usually one cell thick of leaves, young stems and roots and other parts of plants.

Epigynous - having flower parts attached above the ovary.

Epiphyte - an organism that is attached to and grows on another organism without parasitizing it.

Ergotism - a disease resulting from consumption of goods made with flour containing ergot fungus.

Essential element - one of 18 elements generally considered essential to the normal growth, developmen6t and reproduction of most plants.

Ethylene - a simple. Naturally produced. Gaseous hormone that inhibits plant growth and promotes the ripening of fruit.

Etiolation - a condition characterized by long internodes. Poor leaf development and pale, weak appearance due to a plant's having been deprived of light.

Eukaryotic - pertaining to cells having distinct membrane-bound organelles, including a nucleus with chromosomes.

Eutrophication - the gradual enrichment of a body of water through the accumulation of nutrients. Resulting in a corresponding increase in algae and other organisms.

Evolution - the accumulation of genetic changes in populations of living organisms through many generations.

Exine - the outer layer of the wall of a pollen grain or spore.

Exocarp - the outermost layer of a fruit wall.

Explant - an excised portion of leaf or stem tissue used for tissue culture.

Extra nuclear DNA - DNA found outside the nucleus, typically in plastids and mitochondria.

Eyespot - a small. Often reddish structure within a motile unicellular organism; it appears to be sensitive to light.

F₁ - the offspring of a cross between two parent plants.

F₂ - the offspring of the F₁ generation.

FAD - flavin adenine dinucleotide, a hydrogen acceptor molecule involved in the Krebs cycle of respiration and in photosynthesis.

Family - a classification category between genus and order.

Fat - an organic compound containing carbon. Hydrogen and oxygen but with proportionately much less oxygen than is present in a carbohydrate molecule.

Fermentation - respiration in which the hydrogen removed from the glucose during glycolysis is transferred back to pyruvic acid. Creating substances such as ethyl alcohol or lactic acid.

Fertilisation - formation of a zygote through the fusion of two gametes.

Fibre - a long thick-walled cell whose protoplasm often is dead at maturity.

Filament - threadlike body of certain bacteria, algae, and fungi; also the stalk portion of a stamen.

Fission - the division of cells of bacteria and related organisms into two new cells.

Flagellum - a fine threadlike structure protruding from a motile unicellular organism or the motile cells produced by muilticelluar organisms; functions primarily in locomotion.

Floret - a small flower that is a part of the inflorescence of members of the Sunflower Family and the Grass Family.

florigen one or more hormones once thought from circumstantial evidence to initiate flowering but which have never been isolated or proved to exist.

Follicle - a dry fruit that splits along one side only.

Food chain a natural chain of organisms of a community wherein each member of the chain feeds on members below it and is consumed by members above it, with autotrophic organisms being at the bottom; interconnected food chains are referred to as food webs.

Foot - the basal part of the embryo of bryophytes and other plants; it is attached to and absorbs food from the gametophyte.

Fossil - the remains or impressions of any natural object that has been preserved in the earth's crust.

Frond - a fern leaf; term occasionally also applied to palm leaves.

Fucoxanthin - a brownish pigment occulting in brown and other algae.

Gametangium - any cell or structure in which gametes are produced.

Gamete - a sex cell; one of two cells that unite, forming a zygote.

Gametophores - a stalk on which a gametangium is borne.

Gametophyte - the haploid (n) gamete-producing phase of the life cycle of an organism that exhibits Alternation of Generations.

Gemma - a small outgrowth of tissue that becomes detached from the parent body and is capable of developing into a complete new plant or other organism; gemmae are produced in cuplike structures on liverwort thalli and are also produced by certain fungi.

Gene - a unit of heredity; part of a linear sequence of such units occurring in the DNA of chromosomes.

Gene bank - a collection of plants or seeds maintained for their germ plasma.

Generative cell - the cell of the male gametophyte of angiosperms that divides, producing two sperms; also, the cell of the male gametophyte of gymnosperms that divides, producing a sterile cell and a spermatogenesis cell.

Gene synthesizer - a machine that creates specific DNA sequences.

Genetic drift - a change in the genetic makeup of a population that may take place by chance alone.

Genetic engineering - the introduction, by artificial means. Of genes from one form of DNA into another form of DNA.

Genetics - the biological discipline involving the study of heredity.

Genome - the sum total of DNA in an organism's chromosomes.

Genotype - the genetic constitution of an organism; mayor may not be visibly expressed, as contrasted with phenotype.

Genus - a category of classification between a family and a species.

Germination - the beginning or resumption of growth of a seed or spore.

Germ-line mutation - a mutation in a cell from which gametes are derived; the mutation can be passed on to offspring.

Germ plasma - the sum total of all the genes of a species or group of organisms.

Gibberellin - one of a group of plant hormones that have a variety of effects on growth; they are particularly known for promoting elongation of stems.

Gill - one of the flattened plates of compact mycelium that radiate out from the stalk on the underside of the caps of most mushrooms.

Girdling - the removal of a band of tissues extending inward to the vascular cambium on the stem of a woody plant.

Gland - a small body of variable

Shape and size that may secrete certain substances but that also may be functionless.

Glycolysis - the initial phase of all types of respiration in which glucose is converted to pyruvic acid without involving free oxygen.

Graft (graft) the union of a segment of a plant, the scion.

Granum - a series of stacked thylakoid within a chloroplast.

Gravitational water - water that drains out of the pore spaces of a soil after a rain.

Gravitropism- growth response to gravity.

Ground meristem - meristem that produces all the primary tissues other than the epidermis and stele.

Growth progressive increase in size and volume through natural deve1opment.

Guard cell - one of a pair of specialized cells surrounding a stoma.

Guttation - the exudation from leaves of water in liquid form due to root pressure.

Gymnosperm - a plant whose seeds are not enclosed within an ovary during their development.

Half-life - the amount of time it takes for a radioactive element to lose half of its radioactivity (p. 276)

Haploid - having one set of chromosomes per cell, as in gametophytes; also referred to as having II chromosomes.

Haustorium - a protuberance of a fungal hypha or plant organ such as a root that functions as a penetrating and absorbing structure (p. 75)

Heartwood - nonliving, usually darker-coloured wood whose cells have ceased to function in water conduction.

Heirloom variety - a previously popular plant variety that is c1, 1rrently being maintained because of certain desirable qualities.

Herbarium - a collection of dried pressed specimens usually mounted on paper and provided with a label that gives collection information and identification.

Heterocyst - a transparent, thick-walled, slightly enlarged cell occurring in the filaments of certain cyanobacteria.

Heterosis - hybrid vigour; superior qualities of heterozygous off spring as compared with those of their homozygous parents.

Heterophony - the production of both microspores and megaspores.

Heterotrophic - incapable of synthesizing food and therefore dependent on other organisms for it.

Heterozygous - having two different alleles at the same locus on homologous chromosomes.

Hold fast - attachment organ or cell at the base of the thallus or filament of certain algae.

Homologous chromosomes - pairs of chromosomes that associate together in prophase I of meiosis; each member of a pair is derived from a different parent.

Homozygous - having two identical alleles at the same locus on a pair of homologous chromosomes.

Hormone - an organic substance generally produced in minute amounts in one part of an organism and transported to another part of the organism where it controls or affects growth and development.

Hybrid - heterozygous offspring of two parents that differ in one or more inheritable characteristics.

Hydathode - structure at the tip of a leaf vein through which water is forced by root pressures.

Hydrolysis - the breakdown of complex molecules to simpler ones as a result of the union of water with the compound; the process is usually controlled by enzymes.

Hydrosere - a primary succession that is initiated in a wet habitat.

Hygroscopic water - water that is chemically bound to soil particles and therefore unavailable to plants.

Hypha - a single, usually tubular, threadlike filament of a fungus; mycelium is a collective term for hyphae.

Hypocotyl - the portion of an embryo or seedling between the radicle and the cotyledon.

Hypodermis - a layer of cells immediately beneath the epidermis and distinct from the parenchyma cells of the cortex in certain plants.

Hypogynous - having flower parts attached below the ovary.

Hypothesis - a postulated explanation for some observed facts that must be tested experimentally before it can be accepted as valid or discarded if it proves to be incorrect.

Imbibition - adsorption of water and subsequent swelling of organic materials because of the adhesion of the water molecules to the internal surfaces.

Inbreeding - mating between individuals with a common ancestry.

Inbreeding depression - poor performance and low fertility of inbred individuals.

Incomplete dominance - a condition in which the heterozygous phenotype is intermediate to the two homozygous phenotypes as a result of one allele only partly masking another allele.

Indusium - the small, membranous, sometimes umbrella like covering of a developing fern sorus.

Inferior ovary - an ovary to which parts of the calyx, corolla, and stamens have become more or less united so they appear to be attached at the top of it.

Inflorescence - a collective term for a group of flowers attached to a common axis in a specific arrangement.

Inorganic - descriptive of compounds having no carbon atoms.

Integument - the outermost layer of an ovule; usually develops into a seed coat; a gymnosperm ovule usually has a single integument, and an angiosperm ovule usually has two integuments.

Intermediate-day plant - a plant that has two critical photoperiods; it will not flower if the days are either too short or too long.

Internodes - a stem region between nodes.

Inversion - a chromosome rearrangement as a result of a segment having been removed, rotated 1800, and then reinserted.

In vitro - "in glass"; growing or being maintained on artificial media, usually in glass test tubes or flasks.

Ion - a molecule or atom that has become electrically charged through the loss or gain of one or more electrons.

Isogamy - sexual reproduction in certain algae and fungi having gametes that are alike in size.

Isotope - one of two or more forms of an element that have the same chemical properties but differ in the number of neutrons in the nuclei of their atoms.

Kinetochore - specialized protein complexes that develop on the vertical faces of a centromere during late prophase; spindle fibres are attached to them.

Knot -a portion of the base of a branch enclosed within wood.

Laticifer - specialized cells or ducts resembling vessels; they form branched networks of latex-secreting cells in the phloem and other parts of plants.

Leaf - a flattened, usually photosynthetic structure arranged in various ways on a stem.

Leaf gap - a parenchyma-filled interruption in a stem's cylinder of vascular tissue immediately above the point at which a branch of vascular tissue leading to a leaf occurs.

Leaflet - one of the subdivisions, of a compound leaf.

Leaf scar - the suberin-covered scar left on a twig when a leaf separates from it through abscission.

Legume - a dry fruit that splits along two "seams," the seeds being attached along the edges.

Lenticel - one of usually numerous, slightly raised, somewhat spongy groups of cells in the bark of woody plants; lenticels permit gas exchange between the interior of a plant and the external atmosphere.

Leucoplast - a colourless plastid commonly associated with starch accumulation.

Light-dependent reactions - a series of chemical and physical reactions through which light energy is converted to chemical energy with the aid of chlorophyll molecules; in the process, water molecules are split, with hydrogen ions and electrons being produced and oxygen gas being released: ATP and NADPH also are created.

Light-independent reactions - a cyclical series of chemical reactions that utilizes cal-bon dioxide and energy generated during the light-dependent reactions of photosynthesis. Producing sugars, some of which are stored as insoluble carbohydrates, while others are recycled: the reactions are independent of light and occur in the stroma of chloroplasts.

Lignin - a polymer with which certain cell walls become impregnated.

Ligule - the tiny tongue-like appendage at the base of a spike moss or quillwort leaf.

Linked genes - genes located on the same chromosome.

Lipid - a general term for fats, fatty substances, and oils.

Locule - a cavity within an ovary or a sporangium.

Locus - the position of a gene on a chromosome.

Long-day plant (long-day plant) a plant in which flowering is not initialled unless exposure to more than a critical day length occurs.

Mass selection a plant breeding technique in which seeds of plants in a population are used to create each generation.

Maternal inheritance - inheritance in which the female gamete contributes extra nuclear genes to tale offspring.

Mega gametophyte - the female gametophyte of angiosperms, which, in approximately 70% of the species investigaled, 'contains eight nuclei.

Megaphyll - a leaf having branching veins: it is associated with a leaf gap.

Mega sporangium - a sporangium in which megaspores are formed.

Megasporocyte - a diploid cell that produces megaspores upon undergoing meiosis.

Meiosis - the process of two successive nuclear divisions through which segregation of genes occurs and a single diploid cell becomes four haploid.

Meristem - a region of un-differentiated cells in which new cells arise.

Mesocarp - the middle region of the fruit wall that lies between the exocarp and the endocarp.

Mesophyll - parenchyma tissue between the upper and lower epidermis of a leaf.

Metabolism - the sum of all the interrelated chemical processes occurring in a living organism.

Microfilament - a protein filament involved with cytoplasmic streaming and with contraction and movement in eukaryotic cells.

Macrophylla - a leaf having a single un-branched vein not associated with a leaf gap.

Mricropropagation - propagation of plants in vitro.

Micro shoots - of several to many shoots produced by a plant growing in vitro.

Microsporangium - a sporangium in which microspores are formed.

Microspore - a spore that develops into a male gametophyte.

Microsporocyte - a diploid cell that produces microspores upon undergoing meiosis.

Microsporophyll - a leaf usually reduced in size, on or within which microspores are produced.

Microtubule - an un-branched tube like proteinaceous structure commonly found inside the plasma membrane where it apparently regulates the addition of cellulose to the cell wall.

Middle lamella - a layer of material. Rich in pectin. That cements two adjacent cell walls together.

an organelle containing enzymes that function in the citric acid cycle and the electron transport chain of aerobic respiration.

Mitosis - nuclear division, usually accompanied by cytokinesis. During which the chromatics of the chromosomes separate and two genetically identical daughter nuclei are produced.

Molecule - the smallest unit of an element or compound retaining its own identity; consists of two or more atoms.

Monocotyledon - a class of angiosperms whose seeds have a single cotyledon; commonly abbreviated to monocot.

Monocots - having unisexual male flowers or cones and unisexual female flowers or cones both on the same plant.

Monohybrid cross - a cross involving a single pair of genes and heterozygous parents.

Monokaryotic - having a single nucleus in each cell or unit of the mycelium in club tungi.

Monomer - a simple individual molecular unit of a polymer.

Motile - capable of independent movement.

Multiple fruit - a fruit derived from several to many individual flowers in a single inflorescence.

Mushroom - a sexually initiated phase in the life cycle of a club fungus. Usually consisting of an expanded cap and a stalk.

Mutagen - an agent that causes a mutation to occur.

Mutation -a heritable change in a gene or chromosome.

N

N - Having one set of chromosomes per cell haploid.

NAD - nicotinamide adenine dinucleotide. A molecule that during respiration temporarily accepts electrons whose negative charges are balanced by also accepting protons and thereby hydrogen atoms.

NADP - nicotinamide adenine dinucleotide phosphate, a high energy storage molecule that temporarily accepts electrons from photosystern I in the light reactions of photosynthesis.

Nastic movement - a non-directed movement of a flat organ in which the organ alternately bends up and down.

Neutron - an uncharged particle in the nucleus of an atom.

Node - region of a stem where one or more leaves are attached.

Nuclear envelope - a porous double membrane enclosing a nucleus.

Nucleolus - a somewhat spherical body within a nucleus; contains primarily RNA and protein; there may be more than one nucleolus per nucleus.

Nucleotide - the structural unit of DNA and RNA nucleus - the organelle of a living cell that contains chromosomes and is essential to the regulation and control of all the cell's functions; also, the core of an atom.

Nutrient - a substance that furnishes the elements and energy for the organic molecules that are the building blocks from which an organism develops.

Oogamy - sexual reproduction in which the female gamete, or egg, is nonmotile and larger than the male gamete, or sperm, which is motile.

Oogonium -a female sex organ of certain algae and fungi; it consists of a single cell that contains one to several eggs.

Operculum - the lid or cap that protects the peristome of a moss sporangium.

Orbital - a volume of space in which a given electron occurs 90% of the time.

Order - a category of classification between a class and a family

Organelle - a membrane-bound body in the cytoplasm of a cell; there are several kinds, each with a specific function e.g. mitochondrion, chloroplast.

Organic - pertaining to or derived from living organisms and pertaining to the chemistry of carbon-containing compounds.

Osmosis - the diffusion of water or other solvents through a differentially permeable membrane from a region of higher concentration to a region of lower concentration.

Osmotic potential - potential pressure that can be developed by a solution separated from pure water by a differentially permeable membrane the pressure required to prevent osmosis from taking place.

Out crossing - crosspollination between individuals of the same species.

Ovary - the enlarged basal portion of a pistil that contains an ovule or ovules and usually develops into a fruit.

Ovule - a structure of seed plants that contains a female gametophyte and has the potential to develop into a seed.

Oxidation-reduction - reactions chemical reactions involving gain or loss of electrons to or from a compound.

Palisade mesophyll - mesophyll having one or more relatively uniform rows of tightly packed, elongate, columnar parenchyma cells beneath the upper epidermis of a leaf.

Papilla - a small, usually rounded or conical protuberance.

Parenchyma - thin-walled cells varying in size. Shape, and function; the most common type of plant cell.

Parental type - an offspring with the same combination of alleles as one of its parents.

Parthenocarpic - developing fruits from unfertilized ovaries; the resulting fruit is. Therefore, usually seedless.

Particle gun - a machine capable of changing the genetic makeup of plant tissue by shooting DNA-coated particles into it.

Passage cells a thin-walled cell of an endodermis.

Pectin - a water-soluble organic compound occurring primarily in the middle lamella; when combined with organic acids and sugar, it becomes a jelly.

Pedicel - the individual stalk of a flower that is part of an inflorescence.

Peduncle - the stalk of a solitary. Flower or the main stalk of an inflorescence.

Peptide bond - the type of chemical bond formed when two amino acid~ link together ill the synthesis of proteins.

Perennial - a plant that continues to Jive indefinitely after flowering.

Perianth - the calyx and corolla of a flower.

Pericarp - collective term for all the layers of a fruit wall.

Pericycle - tissue sandwiched between the endodermis and phloem of a root; often only one or two cells wide in transverse section; the site of origin of lateral roots.

Periderm - outer bark; composed primarily of cork cells.

Perigynous - having flower parts attached around the ovary; the flower parts are usually attached to a cup.

Peristome - one or two series of flattened, often ornamented structures arranged around the margin of the open end of a moss sporangium; the teeth are sensitive to changes in humidity and facilitate the release of spores.

pH - a symbol of hydrogen ion concentration indicating the degree of acidity or alkalinity.

Phenotype - the physical appearance of an organism.

Pheromone - something produced by an organism that facilitates chemical communication with another organism.

Phloem - the food-conducting tissue of a vascular plant.

Photon - a unit of light energy.

Photoperiodism - the initiation of flowering and certain vegetative activities of plants in response to relative lengths of day and night.

Photosynthesis the conversion of light energy to chemical energy; water, carbon dioxide, and chlorophyll are all essential to the process, which ultimately produces carbohydrate, with oxygen being released as a by-product.

photosynthetic unit - one of two groups of about 250 to 400 pigment molecules each that function together in chloroplasts in the light reactions of photosynthesis; the units are exceedingly numerous in each chloroplast.

Photosystem - collective term for a specific functional aggregation of photosynthetic units.

Phragmoplast - a complex of microtubules and endoplasmic reticulum that develops during telophase of mitosis.

Phytrochrome - protein pigment associated with the absorption of light; it is found in the cytoplasm of cells of green plants and occurs in interconvertible active and inactive forms it facilitates a plant's capacity to detect the presence and duration of light.

Pinna - a primary subdivision of a fern frond; the term is also applied to a leaflet of a compound leaf.

Pistil - a female reproductive structure of a flower, composed of one or more carpels and consisting of an ovary, style, and stigma.

Pit - a more or less round or elliptical thin area in a cell wall; pits occur in pairs opposite each other, with or without shallow, domelike borders.

Pith - central tissue of a dicot stem and certain roots; it usually consists of parenchyma cells that become proportionately less of the volume of woody plants as cambial activity increases the organ's girth.

Plankton free-floating aquatic organisms that is mostly microscopic.

Plant community - an association (plants inhabiting a common environment and interacting with one another.

Plant ecology the science that deals with the relationships and interactions between plants and their environment.

Plant geography - the botanical discipline that pertains to the broader aspects of the space relations of plants and their distribution over the surface of the earth.

Plant morphology - the botanical discipline that pertains to plant form and development.

Plant physiology - botanical discipline that pertains to the metabolic activities and processes of plants.

Plant taxonomy - the botanical discipline that pertains to the classification, naming, and identification of plants.

Plasma membrane - the outer boundary of the protoplasm of a cell; also called cell membrane, particularly in animal cells.

Plasmodium - minute strands of cytoplasm that extend between adjacent cells through pores in the walls.

Plasmolysis - the shrinking in volume of the protoplasm of a cell and the separation of the protoplasm from the cell wall due to loss of water via osmosis.

Plastid - an organelle associated primarily with the storage or manufacture of carbohydrates.

Plumule - the terminal bud of the embryo of a seed plant.

Pneumatophores - spongy root extending above the surface of the water, produced by a plant growing in water; pneumatophores facilitate oxygen absorption.

Pole - an invisible focal point toward each end of a cell from which spindle fibres extend in arcs during mitosis or meiosis.

Pollen grain - a structure derived from the microspore of seed plants that develops into a male gametophyte.

Pollen tube - a tube that develops from a pollen grain and conveys the sperms to the female gametophyte.

Pollination - the transfer of pollen from an anther to a stigma.

Pollinium - a cohesive mass of pollen grains commonly found in members of the Orchid Family.

Polymer - a large molecule composed of many monomers.

Polymerase - an enzyme that creates a polymer.

Polypeptide - a chain of amino acids.

Polyploidy - having more than two complete sets of chromosomes per cell.

Pome - a simple fleshy fruit whose flesh is derived primarily from the receptacle.

Population - a group of organisms, usually of the same species, occupying a given area at the same time.

Pressure-flow hypothesis - the theory that food substances in solution in plants flow along concentration gradients between the sources of the food and sinks.

Prickle- a pointed outgrowth from an epidermis or cortex beneath the epidermis.

Primary consumer - organism that feeds directly on producers.

Primary tissue - a tissue produced by an apical meristem.

Primordium - an organ or structure at its earliest stage of development.

Procambium - a tissue produced by the primary meristem that differentiates into primary xylem and phloem.

Producer - an organism that manufactures food through the process of photosynthesis.

Prokaryotic - having a cell or cells that lack a distinct nucleus and other membrane-bound organelles.

Promoter region - the DNA sequence to which RNA polymerase binds to initiate transcription.

Proplastid - a tiny, undifferentiated organelle that can duplicate it and that may develop into a chloroplast, leucoplast, or other type of plastid.

Protein - a polymer composed of many amino acids linked together by peptide bonds.

Protein sequencer - a machine that reveals the sequence of-amino acids in a protein.

Prothalus - the gametophyte of ferns and their relatives; also called prothallium.

Protoderm - the primary meristem that gives rise to the epidermis.

Proton - a positively charged particle in the nucleus of an atom.

Protonema - a green, usually branched, threadlike or sometimes plate like growth from a bryophyte spore; it gives rise to "leafy" gametophytes.

Protoplast - the unit of protoplasm in a plant cell wall.

Protoplast fusion - the process of combining in vitro two protoplasts in one cell.

Pyrenoids - a small body found on the chloroplasts of certain green algae and homworts; pyrenoids are associated with starch accumulation; they may occur singly on a chloroplast, or they may be numerous.

Pyruvic acid - the organic compound that is the end product of the glycolysis phase of respiration.

Quantitative trait - a trait controlled by several genes and influenced by the environment; it is usually measured on a continuous scale.

Quiescence - a state in which a seed or other plant part will not germinate or grow unless environmental conditions normally required for growth are present.

Rachis - the axis of a pinnately compound leaf or frond extending between the lowermost leaflets or pinnate and the terminal leaflet or pinna.

Radicle - the part of an embryo in a seed that develops into a root.

Ray - radically oriented tiers of parenchyma cells that conduct food, water and other materials laterally in the stems and roots of woody plants; they are generally continuous across the vascular cambium between the xylem and the phloem: the portion within the wood is called a xylem ray, while the extension of the same ray in the phloem is called a phloem ray.

Receptacle - the commonly expanded tip of a peduncle or pedicel to which the various parts of a flower are attached.

Recessive - a condition in which the phenotypic expression of one allele of a gene is masked by the phenotypic expression of another allele.

Recombinant DNA - a molecule created in vitro containing DNA trom at least two organisms.

Recombinant type - an individual offspring that due to recombination has a combination of alleles different from either of its parents.

Red tide - the marine phenomenon that results in the water becoming temporarily tinged with red due to the sudden proliferation of certain dinoflagellates that produce substances poisonous to animal life and humans.

Reproduction - the development of new individual organisms through either sexual or asexual means.

Resin canal - a tubular duct of many conifers and some angiosperms that is lined with resin-secreting cells.

Respiration - the cellular breakdown of sugar and other foods, accompanied by release of energy; in aerobic respiration, oxygen is utilized.

Restriction enzyme - an enzyme capable of severing a DNA molecule at a specific site.

Rhizoid - a delicate root- or root hair-like structure of algae, fungi, the gametophytes of bryophytes, and certain structures of a few vascular plants; functions in anchorage and absorption but have no xylem of phloem.

Rhizome - an underground stem, usually horizontally oriented, that may be superficially root like in appearance but that has definite nodes and internodes.

Ribosome - a granular particle composed of two subunits consisting of RNA and proteins; ribosomes lack membranes, are the sites of protein synthesis, and are very numerous in living cells.

RNA - the standard abbreviation for ribonucleic acid, an important cellular molecule that occurs in three forms, all involved in communication between the nucleus and the cytoplasm and in the synthesis of proteins.

Root (root) a plant organ that functions in anchorage and absorption; most roots are produced below ground.

Root cap - a thimble-shaped mass of cells at the tip of a growing root; functions primarily in protection.

Root hair - a delicate protuberance that is part of an epidermal cell of a root; root hairs occur in a zone behind the growing tip.

Root nodule - a small swelling associated with nitrogen-fixing bacteria that invade the roots of leguminous plants and alders.

Runner - a stem that grows horizontally along the surface of the ground; typically has long internodes.

Salt - a substance produced by the bonding of ions that remain after hydrogen and hydroxyl ions of an acid and a base combine to form water.

Samara - a dry fruit whose pericarp extends around the seed in the form of a wing.

Saprobe - an organism that obtains its food directly from nonliving organic matter.

Scion - a seglpent of plant that is grafted onto a stock.

Sclereid - a sclerenchyma cell that usually has one axis not conspicuously longer than the other; it may vary in shape and is heavily lignified.

Sclerenchyma - tissue composed of lignified cells with thick walls; the tissue functions primarily in strengthening and support.

Secondary consumer - an organism that feeds on other consumers.

Secondary tissue a tissue produced by the vascular cambium or the cork cambium.

Secretary cell - tissue cell or tissue producing a substance or substances that are moved outside the cells.

Seed - a mature ovule containing an embryo and bound by a protective seed coat.

Seed coat - the outer boundary layer of a seed; it is developed from the integument.

Semi conservative - replication DNA replication mechanism that ensures each daughter molecule has one parental strand and one new strand.

Senescence - the breakdown of cell components and membranes that leads to the death of the cell.

Sepal - a unit of the calyx that frequently resembles a reduced leaf; sepals often function in protecting the unopened flower bud.

Sessile - without petiole or pedicel; attached directly by the base.

Seta - the stalk of a bryophyte sporophyte.

Sexual reproduction involving the union of gametes.

Short-day plant a plant in which flowering is initiated when the days are shorter than its critical photoperiod.

Sieve plate - an area of the wall of a sieve tube member that contains several to many perforations that permit cytoplasmic connec1ions between similar adjacent cells, the cytoplasmic strands being larger than pla.5modesmata.

sieve tube - a column of sieve tube members arranged end to end; food is conducted from cell to cell through sieve plates

Sieve tube member a single cell of II sieve tube.

Silique - a dry fruit that splits along two "seams," with the seeds borne on a central partition.

Simple fruit - a fruit that develops from a single pistil.

Simple leaf - a leaf with the blade undivided into leaflets.

Slime moulds a simple organism that moves like an amoeba but resembles a fungus when reproducing.

Solvent - a substance capable of dissolving another substance.

Somatic hybrid - a plant produced by protoplast fusion.

Somatic mutation - a mutation in a somatic cell; such a mutation is not passed on to offspring.

Sorus - a cluster of sporangia; the term is most frequently applied to clusters of fern sporangia.

Speciation - the origin of new species through evolution.

Species - the basic unit of classification; a population of individuals capable of interbreeding freely with one another but because of geographic, reproductive, or other barriers, do not in nature interbreed with members of other species.

Sperm - a male gamete; except for those of red algae and angiosperms. Sperms are frequently motile and are usually smaller than the corresponding female gametes.

Spindle - an aggregation offiber-like threads that appears in cells during mitosis and meiosis; some threads are attached to the centromere of chromosomes, whereas other threads extend directly or in arcs between two invisible points designated as poles.

Spine - a relatively strong, sharp pointed. woody structure usually

Located on a stem; it is usually a modified leaf or stipule.

Spongy mesophyll - mesophyll having loosely arranged

Cells and numerous air spaces; it is generally confined to the lower part of the interior of a leaf just above the lower epidermis.

Sporangiophore - the stalk on which a sporangium is produced.

Sporangium - a structure in which spores are produced; it may be either unicellular or muilticelluar.

Spore - a reproductive cell or aggregation of cells capable of developing directly into a gametophyte or other body without uniting with another cell. Sexual spores formed as a result of meiosis are often called meiospores; spores produced by mitosis may be referred to as vegetative spores.

Sporocyte - a diploid cell that becomes four haploid spores or nuclei as a result of undergoing meiosis.

Sporophylls- a modified leaf that bears a sporangium or sporangia.

Sporophyte - the diploid (2n) spore-producing phase of the life cycle of an organism exhibiting Alternation of Generations.

Stamen - a pollen-producing structure of a flower; it consists of an anther and usually also a filament.

Stele - the central cylinder of tissues in a stem or root; usually consists primarily of xylem and phloem.

Stem - a plant axis with leaves or enalions.

Stigma - the pollen receptive area of pistil.

Stripe - the supporting stalk of seaweeds, mushrooms, and certain other stationary organisms.

Stipule - one of a pair of appendages of varying size, shape, and texture present at the base of the leaves of some plants.

Stock - the rooted portion of a plant to which a scion is grafted.

Stolon - a stem that grows vertically below the surface of the ground; it typically has relatively long internodes; see also runner.

Stoma - a minute pore or opening in the epidermis of leaves, herbaceous stems, and the sporophyte of horn warts; it is flanked by two guard cells that regulate its opening and closing and thus regulate gas exchange and transpiration.

Strobilus - an aggregation of sporophylls on a common axis; it usually resembles a cone or is somewhat cone like in appearance.

Stroma - a region constituting the bulk of the volume of a chloroplast or other plastid; it contains enzymes that in chloroplasts playa key role in carbon fixation, carbohydrate synthesis, and other photosynthetic reactions.

Style - the structure that connects a stigma and an ovary.

Subculture the Transfer of tissue culture plantlets or plant parts to a new medium, usual1y as a form of propagation.

Suberin - a fatty substance found primarily in the cel1 wal1s of cork and the Casparian strips of endodermal cells.

Succession - an orderly progression of changes in the composition of a community from the initial development of vegetation to the establishment of a climax community.

Sucrose - a disaccharide composed of glucose and fructose; the primary form in which sugar produced by photosynthesis is transported throughout a plant.

Superior ovary - an ovary that is free from the calyx, corolla, and other floral parts, so the sepals and petals appear to be attached at its base.

Symbiosis - an intimate association between two dissimilar organisms that benefit both of them or are harmful to one of them.

Syngamy - a union of gametes; fertilisation.

Tendril - a slender structure that coils on contact with a support of suitable diameter; it usually is a modified leaf or leaflet and aids the plant in climbing.

Thallus - a muilticelluar plant body that is usually flattened and not organized into roots, stems, or leaves.

Thorn - a pointed specialized stem.

Thylakoid - coin-shaped membranes whose contents include chlorophyll; they are arranged in stacks that form the grana of chloroplasts.

Tip layering - asexual propagation involving the burying of the tip of a flexible stem in soil to induce the formation of adventitious roots; the rooted portion is then cut from the parent plant and grown separately.

Tissue - an aggregation of cells having a common function.

Tissue culture - the culture of isolated living tissue on an artificial medium.

Totipotency - the potential of a cell to develop into a complete plant.

Tracheids - a xylem cell that is tapered at the ends and has thick walls containing pits.

Transcript - the RNA molecule formed by transcription.

Transcription - the copying of a sequence of DNA nucleotides into an RNA sequence.

Transformation - the transfer of DNA from one organism to another.

Transgenic plant - a plant containing recombinant DNA.

Translation - the process of decoding RNA into protein.

Translocation - a chromosomal rearrangement resulting from a segment of one chromosome being moved to another chromosome.

Transpiration - loss of water in vapour form; most transpiration takes place through the stomata.

Transposable genetic element - a DNA sequence capable of being moved from one chromosomal location to another.

Transposition - the movement of a transposable genetic element.

Tropism - response of a plant organ or part to an external stimulus, usually in the direction of the stimulus.

Tuber - a swollen, fleshy underground stem.

Turgid - firm or swollen because of internal water pressures resulting from osmosis.

The movement that results from changes in internal water pressures in a plant part.

Turgor pressure - pressure within a cell resulting from the uptake of water.

Unisexual - a term usually applied to a flower lacking either stamens or a pistil.

Vacuole membrane - the delimiting membrane of a cell vacuole; also called Tonoplast.

Vacuole - a pocket of fluid that is separated from the cytoplasm of a cell by a membrane; it may occupy more than 99% of a cell's volume in plants; also, food-storage or contractile pockets within the cytoplasm of unicellular organisms.

Vascular bundle - a strand of tissue composed mostly of xylem and phloem and usually enveloped by a bundle sheath.

Vascular cambium - a narrow cylindrical sheath of cells that produces secondary xylem and phloem in sterns and roots.

Vascular plant - a plant having xylem and phloem.

Vein - a term applied to any of the vascular bundles that form a branching network within leaves.

Velamen root - an aerial root with a multilayered epidermis believed to function in retarding moisture loss.

Venter - the site of the egg in the enlarged basal portion of an archegonium.

Vessel - one of usually very numerous cylindrical "tubes" whose cells have lost their cytoplasm; occur in the xylem of most angiosperms and a few other vascular plants; each vessel is composed of vessel members laid end to end; the perforated or open-ended walls of the vessel members permit water to pass through freely.

Vessel element - a single cell of a vessel.

Viability - capacity of a seed or spore to germinate.

Virus - a minute particle consisting of a core of nucleic acid, usually surrounded by a protein coat; it is incapable of growth alone and can reproduce only within, and at the expense of, a living cell.

Vitamin - a complex organic compound produced primarily by photosynthetic organisms; various vitamins are essential in minute amounts to facilitate enzyme reactions in living cells.

Water-splitting - a process in photosystem II of photosynthesis whereby water molecules are split with the release of oxygen.

Whorled - having three or more leaves or other structures at a node.

Xerosere - a primary succession that initiates with bare rock

Xylem - the tissue through which most of the water and dissolved minerals utilized by a plant are conducted; it consists of several types of cells.

Yield - a measure of crop quailty.

Zoospore - a motile spore occurring in algae and fungi.

Zygote -the product.