glossary

Glossary

A	abcission zone	n.	A weakened layer of cells at the base of a leaf or fruit that allows the leaf or fruit to separate from the plant without injuring it.
	abscisic acid	n.	A plant growth regulator involved in the fruit ripening process.
	adventitious root	n.	Root that forms on shoot tissue.
	adventitious shoot	n.	Shoot that forms on root tissue.
	alkaloids	n.	Bitter-tasting compounds found in many plants, especially in the nightshade family (Solanaceae).
	allelopathy	n.	A form of chemical protection in which a plant produces substances that inhibit the growth of nearby plants.
	alternation of generations	n.	Describes the phenomenon in the plant kingdom in which plants alternate between a sporophyte phase and a gametophyte phase.
	amino acid	n.	Nitrogen-containing organic compounds; the building blocks from which proteins are formed.
	angiosperm	n.	Derived from the words for "vessel" and "seed"; a grouping of plants whose seeds are borne in protective structures.
	annual	adj.	Describes a plant that germinates, grows, flowers, and produces seeds all in one growing season.
	antitranspirants	n.	A substance sprayed on plant leaves to reduce the rate of transpiration and conserve moisture.
	apical bud	n.	A bud at the uppermost tip of a stem.
	apical dominance	n.	The suppression of growth in lower buds and branches by the uppermost, or apical, bud.
	apical meristem	n.	A region of actively-dividing cells at the tip of a root or stem; growth results in an increase in length.
	asexual propagation	n.	Any means of multiplying plants that do not involve the union of gametes, and depend on mitotic, rather then meiotic, cell division.
	asexual reproduction	n.	Propagation by means of plant parts; examples include new plants generated by creeping stems, bulb offsets, and layering.
	atom	n.	The basic unit of matter. The smallest unit into which a chemical element can be broken and still retain its characteristics.
	auxin	n.	A plant growth regulator that controls cell elongation; important in many plant growth responses such as phototropism and geotropism.
	axillary bud	n.	A bud located in the axil of a leaf, at the joint where the leaf meets the stem.
B	biennial	adj.	Describes a plant that grows for two years; it germinates and grows foliage the first season, and produces flowers and seeds the next season.
	binomial	adj.	Consisting of two names; for example, a botanical name consists of the genus name followed by the species epithet.
	bio-engineered	adj.	Organisms created using genetic engineering.
	bloom	n.	A powdery, bluish-white coating on some plants’ leaves and fruits. When a plant part’s waxy cuticle occurs in tiny rodlets that protrude from the surface, it results in a visible bloom. (Also, another word for flower.)
	budding	n.	A form of grafting in which a bud is inserted under the bark of another plant.
	bulb	n.	Modified stem consisting of fleshy leaf bases; used for food storage and asexual propagation.
C	carbohydrate	n.	An organic molecule consisting of a chain of glucose molecules; includes sugars, starches, and cellulose.
	cellulose	n.	A large molecule made up of a chain of glucose molecules; found primarily in plant cell walls.
	chilling requirement	n.	The number of hours a plant must be exposed to temperatures between 32�F and 45�F before it will break dormancy.
	chlorophyll	n.	A green plant pigment; found in chloroplasts and necessary for photosynthesis.
	chloroplasts	n.	Structures found within some plant cells; they contain chlorophyll and are the sites of photosynthesis.
	chlorotic	adj.	Describes abnormally pale, weak-looking foliage due to reduced chlorophyll content; often caused by a nitrogen or iron deficiency.
	chromatin	n.	The genetic material stored in a cell’s nucleus, made up of DNA and nuclear proteins.
	chromosomes	n.	Genetic material (chromatin) in a cell’s nucleus that has become condensed into strands in preparation for cell division.
	class	n.	A group of orders sharing similar characteristics.
	cloning	n.	The duplication of an organism by asexual means.
	commensalism	n.	Relationship of two or more organisms in which one organism benefits and the other is unaffected.
	compound	n.	A substance composed of one type of molecule.
	cork cambium	n.	A type of lateral meristem located just under the bark that gives rise to new outer bark.
	corm	n.	Swollen leaf base enclosed in scale-like leaves, used for food storage and asexual propagation.
	cotyledon	n.	A food storage structure within a seed, which provides nourishment for the embryo during germination.
	cultivar	n.	Short for cultivated variety. A unique plant that is the result of breeding efforts by horticulturists. Written in single quotes in plain text after species name.
	cuticle	n.	A protective waxy coating on the epidermis of leaves, herbaceous stems, and fruit.
	cutin	n.	The waxy substance that forms the cuticle layer, providing a protective coating on the epidermis of leaves, herbaceous stems, and fruit.
	cutting	n.	Propagation method that involves inducing adventitious roots or shoots on a plant part.
	cytokinin	n.	A plant growth regulator that stimulates cell division.
	cytoplasm	n.	The liquid component of a plant cell in which various structures are suspended.
D	dark reaction	n.	The second step in the process of photosynthesis, during which simple sugars are manufactured; light is not required.
	day-neutral	adj.	Describes plants for which flower initiation is not dependent upon day length.
	dicot	n.	A class of angiosperms in which the seeds’ cotyledons occur in pairs.
	dioecious	adj.	Describes plants in which the male and female flowers occur on separate plants.
	diploid	adj.	Describes cells in which the chromosomes occur in pairs; somatic cells, which make up the bulk of the cells in the plant body, are diploid. Often abbreviated as 2n.
	disaccharide	n.	A sugar made up of two monosaccharide molecules bound together; an example is sucrose, or table sugar.
	division	n.	A group of classes sharing similar characteristics.
	dominant trait	n.	A characteristic determined by a gene that hides, or masks, the comparable but recessive gene; this characteristic will be expressed if the dominant gene is present on one or both chromosomes.
E	element	n.	A substance composed of one type of atom.
	embryo	n.	Multi-celled structure resulting from the repeated cell division of the zygote.
	endosperm	n.	A temporary food storage tissue in seeds, created by the fusion of one sperm cell plus the two polar nucleu, and therefore often triploid.
	epidermis	n.	The outermost layer of cells on leaves, roots, and herbaceous stems.
	epiphyte	n.	A plant that grows on the body of another plant, but draws no nutrients from it.
	essential amino acid	n.	One of the eight amino acids the human body cannot synthesize, and therefore a vital nutrient in the human diet.
	ethylene	n.	A plant growth regulator produced by ripening tissues; stimulates cell walls to soften.
	etiolation	n.	The condition in which a plant has pale, underdeveloped leaves and extended internodes; ususally caused by insufficient light.
	expression	n.	The way a trait shows up in an organism.
F	F₁ or first filial generation	n.	The offspring resulting from a cross between two pure parent lines.
	F₂ or second filial generation	n.	The offspring resulting from cross- or self-pollination of the F₁generation.
	family	n.	A group or genera sharing similar characteristics.
	fertilization	n.	The successful union of egg and sperm.
	fibrous root system	n.	A root system consisting of highly branched, spreading roots.
	nitrogen fixation	n.	A process in which a type of soil-dwelling bacteria, in association with the roots of certain plants (such as legumes), convert nitrogen in the air into a form that plants can use.
	flower	n.	A specialized shoot of a plant bearing its reproductive structures.
	fruit	n.	The matured ovary of a plant; contains the seeds.
G	gametes	n.	Haploid cells (egg and sperm), the fusion of which results in the creation of a new organism. Also called reproductive cells or sex cells.
	gametophyte generation	n.	The phase of growth in which gametes, or sex cells, are produced.
	gene	n.	The basic unit of inheritance; occur along the chromosomes.
	genera	n.	The plural of genus.
	generative cell	n.	One of two cells that make up a pollen grain; upon successful pollination, it divides to form two sperm.
	genetic engineering	n.	The process of taking genetic material from one organism and inserting it into the nucleus of another organism, the result of which is an organism whose cells contain the introduced genes.
	genus	n.	The "generic" name of a plant; in plant classification, refers to a group of related plants.
	geotropism	n.	The bending of a plant organ in response to gravity; also called gravitropism.
	gibberellin	n.	A plant growth regulator that controls the elongation of internodes.
	glaucous	adj.	Describes a plant part with a visible bloom.
	grafting	n.	Propagation method in which two pieces of live plant tissue are united by placing their meristems in contact.
	gravitropism	n.	The bending of a plant organ in response to gravity; also called geotropism.
	guard cells	n.	Pairs of cells surrounding the stomata, or pores, on a leaf or stem. Swelling or shrinking of the guard cells opens or closes the stomata, depending on the needs of the plant and environmental conditions.
	guttation	n.	Exudation of excess water; appears as droplets on the tips and margins of leaves.
	gymnosperm	n.	Literally, "naked seed", a grouping of plants that produces seed that is borne exposed, rather than in a protective structure.
H	haploid	adj.	Describes cells in which the chromosomes occur singly (as opposed to occurring in pairs); reproductive cells are haploid. Often abbreviated as n.
	hardening off	n.	A process by which a plant is gradually acclimated to a new environment. The term often refers to the adjustment period necessary to allow indoor-grown plants to grow accustomed to the harsher (cooler, windier, sunnier) outdoor environment.
	herbaceous	adj.	Soft and green; describes primary growth tissues containing little or no woody growth.
	homologous	adj.	Describes the two similar chromosomes that form a pair in a diploid cell.
	hybrid	adj.	Offspring resulting from cross-breeding plants.
	hybrid	n.	Iin botany, offspring resulting from sexual reproduction between two plants; in horticulture, used to describe F1 crosses having mixed ancestry that are the products of plant breeding efforts, and do not grow true from seed.
	hybrid vigor	n.	The increase in vigor, size, fertility, or other positive characteristic of a hybrid compared with its parents.
	incomplete dominance	n.	Tthe relationship between two genes, neither of which fully masks the expression of the other.
	intercalary meristem	n.	A meristem located between non-dividing tissues, such as near the base of a blade of grass.
L	lateral meristem	n.	A region of actively-dividing cells located along the length of a root or stem; growth results in an increase in girth.
	layering	n.	Propagation method that induces rooting while daughter plant is still attached to parent plant.
	leaf	n.	A plant structure consisting of an outgrowth arising from a stem or branch. Most leaves are green and contain chlorophyll.The primary function of a leaf is to capture sunlight for photosynthesis.
	leaf blade	n.	The broad, flat part of a leaf whose primary function is to capture sunlight for photosynthesis.
	lenticel	n.	A pore on the surface of young woody stems; provides a pathway for air to reach inner tissues.
	light duration	n.	A measure of the amount of time a source of light is illuminated; usually represented by the number of hours of light in a 24-hour period.
	light intensity	n.	A measure of the brightness of light reaching a surface. Light intensity decreases as the distance from the source of the light increases.
	light quality	n.	An analysis of the color, or wavelengths, of light from a given source.
	light reaction	n.	The first step in the process of photosynthesis, which begins when the chlorophyll molecule absorbs a photon; light is required.
	lignin	n.	An important constituent of many secondary cell walls that increases the cell wall’s hardness and strength.
	lipid	n.	A category of organic macromolecules including fats and oils.
	long-day	adj.	Describes plants that initiate flowers when day length is longer than their critical day length.
M	macrofibril	n.	A structure made up of several microfibrils wound together into a "cable;" provide the framework for the plant cell wall
	macromolecules	n.	Relatively large molecules made up of smaller molecules bound together with chemical bonds.
	macronutrients	n.	The mineral nutrients that plants require in relatively large quantities; includes carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur.
	megaspore	n.	Haploid cells formed by meiosis in plants; divide by mitosis to form several daughter cells, one of which functions as the egg cell.
	meiosis	n.	Cell division that results in four haploid daughter cells.
	meristem	n.	A region of actively-dividing cells.
	mesophyll	n.	The tissue sandwiched between the epidermal layers of a leaf; containing both the palisade cells and the spongy cells.
	microfibril	n.	A structure made up of several cellulose molecules united into a thread-like strand
	micronutrients	n.	The mineral nutrients that plants require in relatively small quantities includes magnesium, iron, copper, zinc, manganese, molybdenum, and boron.
	microspore		Haploid cells formed by meiosis in plants; divide by mitosis to form pollen—precursor to the sperm cell.
	middle lamella	n.	A pectin-rich layer between adjoining plant cell walls, cementing them together.
	mitosis	n.	Cell division that results in two daughter cells that are genetically identical to the parent cell.
	molecule	n.	The smallest unit of a compound; consists of two or more different atoms in a specific ratio and configuration, held together with chemical bonds.
	monocot	n.	A class of angiosperms in which the seeds’ cotyledons occur singly
	monoecious	adj.	Describes plants with separate male and female flowers.
	monosaccharide	n.	A simple sugar made up of a chain or ring of carbon atoms to which hydrogen and oxygen atoms are attached.
	mutation	n.	A random genetic variation that is passed on to offspring.
			mutualism n. Relationship of two or more organisms in which both organisms benefit.
N	nastic movement	n.	Movement of plant parts not associated with a specific stimulus such as light or gravity.
	natural selection	n.	A process by which the healthiest, strongest, and most well-adapted organisms flourish and reproduce
	nodes	n.	Sites on a stem where the leaves and axillary buds are attached.
	nucleus	n.	A structure within a plant cell; controls cell functions, including inheritance.
O	osmosis	n.	The movement of water across a differentially permeable membrane, from a place where water concentration is higher to one where the concentration is lower.
	order	n.	A group of families sharing similar characteristics
	organic	adj.	Refers to substances containing carbon; pertaining to living organisms.
	ovary	n.	A female reproductive structure, containing ovules, usually found at the basal portion of the flower. After pollination, the ovary matures into a fruit; the ovules develop into seeds.
	ovule	n.	A female reproductive structure which, upon fertilization, develops into a seed.
P	palisade cells	n.	A layer of closely-packed, elongated cells located just beneath the upper epidermis of a leaf. These cells contain chloroplasts, and are the main sites of photosynthesis.
	parasite	n.	An organism that derives some or all its nutrients from another organism.
	pectin	n.	A gluey substance found in the middle lamella between adjoining cell walls that cements the adjoining cells together.
	perennial	adj.	Describes a plant that lives for more than two years; commonly used to describe herbaceous (non-woody) plants.
	petiole	n.	The stalk or support that attaches the blade of a leaf to the stem.
	phloem	n.	The food-conducting tissues of plants; part of the vascular system.
	photoperiodism	n.	The initiation of flowering based on the relative amounts of darkness and light in a 24-hour period.
	photosynthesis	n.	The process by which plants use light energy to manufacture sugars.
	phototropism	n.	The bending of a plant organ in response to light.
	pollen tube	n.	A long, hollow tube formed by the pollen grain’s tube cell that penetrates the pistil’s tissues to reach the egg cell.
	primary wall	n.	The initial layer of a plant cell wall.
	phytochrome	n.	A light-sensitive protein pigment involved in the photoperiodic response.
	plant growth regulators	n.	Chemical messengers within the plant body that control growth.
	plastids	n.	Structures found in plant cells; often contain pigments.
	pollinator	n.	Any organism responsible for transferring pollen to stigma of flowers, including bees and other insects, small rodents, and bats. Many plants require a specific pollinator.
	polysaccharide	n.	A carbohydrate composed of many monosaccharide units bound together in a long chain; examples include cellulose and starch.
	primary growth	n.	Growth arising from cell division and elongation in the regions of apical meristems.
	protein	n.	A category of organic macromolecules composed of many amino acids chemically bound together.
R	recessive trait	n.	A characteristic whose expression is masked by the presence of the comparable dominant gene; this characteristic will be expressed only if both genes are recessive.
	reproductive cells	n.	Haploid cells (egg and sperm), the fusion of which results in the creation of a new organism. Also called gametes or sex cells.
	respiration	n.	The process of breaking chemical bonds in carbohydrates to release the energy necessary to perform metabolic functions.
	rhizome	n.	Horizontal underground stem; may be fleshy or not. Used for food storage and asexual propagation.
	roots	n.	The plant part generally found underground; responsible for anchoring the plant as well as water and nutrient uptake.
S	saprophyte	n.	An organism that fills its nutritional needs from dead and decaying organic matter.
	secondary growth	n.	Growth arising from cell division and elongation in the regions of lateral meristems.
	secondary wall	n.	A second layer of cell wall laid down by the protoplast inside the primary wall.
	seed	n.	The fertilized and matured ovule of a flowering plant, containing an embryonic plant, and which, on being placed under favorable circumstances, develops into an individual similar to the one that produced it.
	seed coat	n.	The hard, protective coating covering a seed.
	seedless plants	n.	A category of evolutionarily primitive plants that do not form seeds. Includes mosses and ferns.
	seta	n.	In mosses, the tall, stem-like structures on which spore capsules are borne
	sexual reproduction	n.	The creation of offspring from the union of egg and sperm
	shoot system	n.	The above-ground portion of a plant, consisting of the stem and leaves.
	short-day	adj.	Describes plants that initiate flowers when day length is shorter than their critical day length.
	somatic cells	n.	Diploid cells that make up the bulk of the plant body; all cells in a plant that are not reproductive cells.
	species	n.	The "specific" name of a plant; used to describe a plant within a genus.
	specificity	n.	The degree to which two organisms must be compatible before a relationship will form.
	spongy cells	n.	A layer of loosely-packed cells located beneath the palisade cells of a leaf. The spaces between the cells allow for the exchange of gases necessary for photosynthesis.
	spore	n.	The product of meiosis in plants; germinates to form the gametophyte generation.
	sporophyte generation	n.	The phase of growth in which spores are formed.
	starch	n.	A carbohydrate composed of several hundred glucose units; the chief food storage substance in plants.
	stem	n.	The leaf- and flower-bearing part of a plant.
	stipule	n.	Small, leaf-like outgrowth found at the base of a leaf stalk.
	stolon	n.	Horizontal creeping aboveground stem; sprouts new plants at nodes.
	stomata	n.	Tiny pores in the epidermal cells of leaves and stems; most numerous on the undersides of leaves. (Singular: stoma or stomate. Plural: stomata or stomates)
	sucker	n.	Shoot arising from adventitious bud on underground root; sometimes used to describe any shoots arising at the base of a plant.
	symbiosis	n.	Relationship of two or more organisms living in close association.
T	taproot system	n.	A root system consisting of one or more prominent, swollen roots with few side roots; often a food-storage structure.
	thigmotropism	n.	The reaction of a plant in response to physical contact.
	tissue culture	n.	Propagation method that produces many plants from one or a few initial cells. Must be done under sterile, controlled conditions.
	trait	n.	An inherited physical or physiological characteristic.
	transgenic	adj.	Organisms created using genetic engineering
	transpiration	n.	The loss of water vapor from a plant; most of this water escapes from open stomata.
	triploid	adj.	Describes a plant cell in which the chromosomes occur in three’s.
	tube cell	n.	One of two cells that make up a pollen grain; upon successful pollination, it germinates and grows into the pollen tube.
	tuber	n.	Swollen tip of an underground stem, used for food storage and asexual propagation.
	tuberous root	n.	Enlarged secondary root, used for food storage and asexual propagation.
	tuberous stem	n.	Swollen section on underground portion of main stem, used for food storage and asexual propagation.
	turgor pressure	n.	The pressure within a plant cell; maintained by osmosis.
V	variegated	adj.	Describes leaves or petals exhibiting an irregular, inherited pattern of color.
	variety	n.	A population within a species that differs from other members of the species in some significant way. Written in italics after the species name.
	vascular cambium	n.	A type of lateral meristem that gives rise to new xylem (wood) and phloem (inner bark).
	vascular tissues	n.	Food- or water-conducting tissues.
	vernalization	n.	The promotion of flowering due to exposure to low temperatures, or chilling.
X	xylem	n.	The water-conducting tissues of plants; part of the vascular system.
Z	zygote	n.	The cell created by the union of egg and sperm; divides to become the embryo.