4vBFusiform
Referring to the shape of a cell which is characteristically elongated with taperĊv!de walls.
Gamete
Haploid)@&ductive cells (egg or sperm) produced in plants by mitosis from a gametophyte.
Gametophyte
That plan[&generation which gives rise to the gametes by me,`!n!mitosis. Typically haploid.
Gap
In a siphonos/{d-uhe parenchymatous region in the vascular cylinder above the position where the leaf-trace (or branch trace) enters a leaf (or branch).
GelaTqt!fiber/layer
A non-lignified fiber which appears gelatinous-like with light microJnx! Layers of such fibers comprise reaction wood.
The smaller haploid cell in a pollen grain that divides (most ofteIH=he pollen tube) to form two sperm cells.
Geron :t
A type of chromoplast typically found in senescent cells.
Gland
A multicellular secretory structure.
A trichome with an enlarged unicellular, or mul[ocellular secreto}dms, at the terminus.
Glutaraldehyde
A five-O|n!dialdehyde commonly used as a primary chemical fixative for light and electron microscopyf"Q
Golgi apparatus
A system of interconnevz!hctyosomes of similar function in a cell.
Granum(TQ1C
Stack(s) of chloroplast thylakoids.
Gravitropi\k<! =DD>A directional growth response to the influence of gravity. Induced by mechanical and hormonals`u growth regulator) influences.
Ground epir8rh=/B>
Cells of the epidermis of stems and leaves not possessing trichomes and not diff>qu`ted as guard cells. Also designated as "pavement cells."
Ground meristem
A primary meristem derived from the apical meristem and giving rise to primarV&ground tissues.
Ground tissue
Tissues derived from the ground meristem (e.g. pith or cortex).
Growth ring
A circular layer of secondary xylem (or, in some cases, secondary phloem) which is the result of seasonal growth in perennial stems or roots. Typically observed in cross-sectional view.
Guard cells
A specialized pair of epidermal cells surrounding and adjusting the size of a stomatal pore.
Guttation
The exudation of liquid water from hydathodes fed by vascular xylem traces.
Gymnosperms
Seed plants in which the seeds are not enclosed in an ovary.
Gynoecium
All of the carpels in a flower; or that part of the flower in which megasporogenesis occurs.
Half-bordered
Referring to pit-pairs in which one is bordered, and the adjacent one is simple.
Half-inferior ovary
An ovary in which the hypanthium is adnate only to the lower half of the ovary.
Hardwood
General non-specific term for the wood of dicotyledons.
Hartig net
In ectomycorrhizae, hyphae which penetrate between the outermost root cells where they form a mycelium.
Haustorium
A modified root that penetrates host tissues for the purpose of absorbing nutrient materials.
Heartwood
Inner, non-functional wood characterized by a darker color than the surrounding sapwood. Often becomes prone to decay or degradation by biotic agents.
Hemicelluloses
Soluble and loosely organized polysaccharides in the cell wall matrix.
Heterocellular ray
A vascular ray composed of more than one type of cell.
Heterochromatin
Chromatin which is condensed and in light and electron micrographs appears dense in relation to euchromatin. Believed to be in an inactive state for transcription.
Heterotrophic
An organism incapable of producing organic compound from inorganic materials and thus must rely on other living or dead organisms for its food supply.
Hilum
Seed scar where the funiculus was once attached. Also may designate the central part of a starch grain.
Histogen
An older term for root or shoot apical meristems which are initials that form definite tissue systems in the plant body. See Primary meristem.
Histogenesis
The process of tissue formation.
Homocellular ray
A vascular ray composed of only one type of cell.
Homology
Being derived of the same evolutionary or phylogenetic origin, but not necessarily sharing the same function or structure.
Hydathode
Pore in the margin of a leaf through which the exudation of water in liquid form takes place, usually by the process of guttation.
Hydrophyte
A plant adapted to growing in or under the surface of water.
Hypanthium
A ringlike, cup-shaped, or tubular structure of a flower on which the sepals, petals, and stamens are borne, as in the flowers of the rose or cherry.
Hyperplasia
Excessive, and usually abnormal, enlargement of plant structure due to continuous cell division.
Hypertrophy
Abnormal enlargement.
Hypocotyl
That part of the embryo or seedling located below the site of cotyledon attachment.
Hypodermis
One or more layers of cells beneath the epidermis and distinctly different from the cortex or other ground tissue.
Hypogeal
Type of germination in which the cotyledons remain beneath the surface of the ground.
Hypogyny
Floral structure in which the sepals, petals and stamens are attached below the ovary (which is said to be superior).
Hypophysis
The top cell of a suspensor which gives rise to the development of the root in the embryo of angiosperms.
Hypsophylls
Leaves located at high levels on the stem resembling floral bracts.
Hypostomatous
Having stomates only on the abaxial surface of a leaf.
Idioblast
An unusual cell in a tissue which is distinctly different in form, size or content from the surrounding cells.
Imperfect flower
Flower lacking in either stamens or carpels.
Indehiscent
Fruits which do not open spontaneously upon maturity and drying.
Indeterminate growth
Continued growth due to continuing activity of the apical and lateral meristems.
Inferior ovary
Floral structure in which the sepals, petals and stamens are attached above the ovary.
Initial
A cell which normally gives rise to two cells, one of which remains in the meristem and the other is added to the plant body.
Inner bark
Region in stems or roots from vascular cambium through cork cambium. Includes living tissues.
Integument
Cell layers enveloping the nucellus of an ovule, and which will become the seed coat.
Intercalary growth
Growth by cell division occurring away from the site of the (apical) meristem from which it originated.
Intercalary meristem
Meristematic tissue located at some distance away from the meristem that gave rise to it.
Intercellular space
Space between two or more cells in a tissue.
Interfascicular cambium
Vascular cambium that develops between the sites of vascular bundles and in the ground tissue.
Interfascicular region
Sites of ground tissue located between the vascular bundles in a stem.
Interphase
The non-divisional stages of the cell cycle. Although mitotic activity and cytokinesis do not occur in interphase, replication of DNA does.
Internal phloem
Primary phloem located internally from the primary xylem.
Internode
Regions of a stem between nodes.
Interxylarly
Within, or enclosed by, the xylem tissue.
Intine
The inner wall of a pollen grain which does not contain sporopollenin.
Intraxylarly
Inside the region of the xylem.
Introrse
An orientation towards the floral axis.
Intrusive growth
Growth of cells which invade between existing ones by interpositioning themselves.
Intussusception
Growth of cell walls by the deposition of new wall material within the existing wall.
Isobilateral leaf
Leaf in which the palisade mesophyll occurs on both sides.
Isodiametric
Essentially uniform in diameter.
Isotropic
Having similar refractive properties with regard to the optical transmission of light.
Karyokinesis
Nuclear division, as opposed to cytoplasmic division.
Kranz anatomy
Radially-oriented mesophyll cells which surround the vascular bundles in plants with C4 pathway of photosynthesis. (Kranz = wreath)
Lacuna(e)
Normally, an air space between cells.
Lacunar collenchyma
Collenchyma cells with intercellular spaces adjacent to cell wall thickenings.
Lake
The combination of a dye and a mordant.
Lamella(e)
Used in various contexts to refer to layer(s).
Lamellar collenchyma
Collenchyma cells with cell wall thickenings on the tangential surfaces. Also, sometimes designated "plate collenchyma."
Lamina
The blade of a leaf.
Late wood
Secondary xylem that forms late in the growing season.
Lateral meristem
Those meristems, such as vascular cambium or cork cambium, which are located in a cylinder around the periphery, or parallel to it.
Latex
Milky-like fluid produced in laticifers.
Laticifer(s)
One or more cells containing latex.
Laticiferous cell
A non-articulated laticifer.
Laticiferous vessel
An articulated laticifer in which the cell walls between cells are partially or wholly lacking.
Leaf buttress
The initial formation of a leaf primordium characterized by a protrusion of tissues below the shoot apical meristem.
Leaf fibers
Fibers derived from monocot leaves.
Leaf gap
A region where a portion of the vascular materials connecting the stem to the leaf is interrupted.
Leaf trace
The vascular bundle connecting the vasculature of the stem with that of the leaf. There may be multiple leaf traces per leaf.
Leaves
The most transient and variable vegetative organ of higher plants. Typically adapted for photosynthesis, they also include cotyledons.
Lens
A piece of glass, or a medium (e.g. electromagnetic), which serves to focus radiant energy by refraction.
Lenticel
An opening, usually characterized as an eruption of the periderm through which gaseous exchange may occur in stems.
Leucoplast
A plastid lacking in pigmentation.
Libriform fiber
A very long xylem fiber with thick walls and simple pits.
Lignification
The process of depositing lignin in cell walls, primary or secondary.
Lignin
Mixed organic polymers of complex structure with units derived from phenylpropane and other complex phenolics. A component of many plant cell walls--especially in secondary wall structure.
Lithocyst
A cell that contains a crystal known as a cystolith.
Locule
An opening or cavity within a sporangium, as in anthers and ovules.
Lysigenous
An intercellular space derived by the dissolution of cells.
Maceration
The breakdown of a tissue into individual cells by the digestion, or hydrolysis, of the middle lamella with chemical or enzymatic agents.
Macrosclereid
An elongated sclereid with randomly thickened secondary walls.
Marginal growth
The growth along the edges of a leaf primordium which gives rise to the leaf blade. A combination of mitosis and cell enlargement.
Margo
The pit membrane around the torus in bordered pits of conifers.
Matrix
A medium in which something is embedded.
Mechanical tissue
Supporting tissue.
Medulla
Pith.
Medullary bundles
Vascular bundles distributed in the pith.
Megagametogenesis
The process of forming a female gamete, and egg, through mitotic division.
Megagametophyte
The female gametophyte which is the embryo sac in angiosperms.
Megaphyll
A foliage leaf in ferns and seed plants that has branched or parallel vascular bundles within the lamina and is associated with a leaf gap.
Megaspore
A haploid cell that develops into a female gametophyte.
Megasporocyte
The diploid cell that gives rise by meiosis to four haploid megaspores,of which only one survives to become a megaspore.
Megasporogenesis
Process of forming the female megaspore as a consequence of meiosis.
Membranes
Partitional structures limiting the surface of cells and comprising the structural organization of most organelles of cells. Typically comprised of a bi-layer of lipids with various protein and glycoprotein components.
Meristem
Region of actively dividing cells giving rise to new tissues.
Mesarch xylem
Xylem strand in which the protoxylem is in the center and metaxylem differentiates from the center.
Mesocarp
The central layer of a pericarp.
Mesogeny
Process of common developmental origin between subsidiary cells and guard cells of the epidermis.
Mesoperigeny
Partial common origin of subsidiary cells and neighboring guard cells in epidermis.
Mesophyll
Leaf parenchyma cells active in photosynthesis and located within the two epidermal layers.
Mesophytic
A plant living in a temperate environment and receiving average amounts of moisture.
Mestome sheath
An inner layer of cells around vascular bundles of grass leaves characterized by sclerenchyma cells.
Metachromatic (Metachromasia)
The effect of producing different colors from use of a single dye due to different pH or the binding of dimers or polymers of the dye at certain locations.
Metaphase
That phase of mitosis or meiosis in which the chromosomes are aligned on an equatorial plane prior to separation of the chromatids. Chromosomes are at their shortest length during this phase.
Metaphloem
That phloem which matures after the establishment of the protophloem and before the secondary phloem.
Metaxylem
That xylem which matures after the establishment of the protoxylem and before the secondary xylem.
Micelles
Typically used to refer to the ordered crystalline-like organization of cellulose molecules.
Microbody
A small subcellular organelle, enclosed with a single membrane, and containing a variety of non-hydrolytic enzymes.
Microfibril (microfilaments)
Long, thin proteinaceous fibers in the cytoplasm which can only be resolved structurally with the aid of transmission electron microscopy. The term microfibril is also used in reference to the grouping of cellulose molecules in the cell wall.
Microgametogenesis
The formation of male gametes (sperm) through mitosis.
Microgametophyte
The male gametophyte--pollen grains in seed plants.
Micrometer
Same as micron, one-thousandth of a millimeter.
Micropyle
The opening in the integument of an ovule through which the pollen tube may pass and enter the embryo sac.
Microscope
An optical instrument capable of producing a magnified image of an object. Also adapted as electron, x-ray, and sonic microscopes among others.
Microsporangium
A sporangium in which microspores are formed--the anther in angiosperms.
Microspore
A haploid spore that develops into the male gameophyte, e.g. the first stage of a pollen grain.
Microsporocyte
Diploid cell that undergoes meiosis and forms four haploid microspores. Same as microspore mother cell.
Microsporogenesis
Process of forming haploid male microspores through meiosis.
Microtome
A machine designed for cutting uniform sections of specimens..
Microtubules
Proteinaceous tubules in the cytoplasm of cells which appear hollow and are approx. 25 nm in diameter. These structures form to guide chromosomes in nuclear divisions, establish the cell plate, and in providing a framework for the cell prior to cell wall establishment.
Middle lamella
A "cementing" layer of pectic materials holding together the primary cell walls of adjacent cells.
Mitochondrion
Double-membrane-limited subcellular organelle actively involved in functions of aerobic respiration.
Mitosis
Division of the cell's nucleus into two daughter nuclei--each with the same number of chromosomes as the original parent nucleus.
Mordant
A substance that combines with a dye to form a lake that serves to produce a fixed color, or stain, in a tissue.
Morphogenesis
The development of tissues and organs.
Morphometry
The quantification of structure from sectional planes. Used at both light and electron microscopic levels to determine the absolute and relative composition of subunits of structure.
Mucilage
Gums and other carbohydrates which swell in water.
Multiple epidermis
Two or more layers of epidermal tissue derived from protoderm.
Multiple fruit
Fruit composed of several matured ovaries, each from a separate flower.
Multiseriate ray
A phloem or xylem ray which is several cell layers in width.
Mycorrhiza
The symbiotic association of fungi with roots of higher plants.
Nacreous wall
A cell wall of pearly luster characteristic of sieve tube elements which have non-lignified wall thickenings.
Nanometer
One millionth of a millimeter.
Nectary
A glandular structure in flowers or on vegetative structures that secretes insect-attracting substances, usually containing sugars.
Node
The position on a stem at which one or more leaves are attached.
Nonarticulated laticifer
A single, often multinucleate, cell that may be branched and transports latex.
Nonporous wood
Wood with no vessel elements.
Nonstoried
Typically, secondary growth in which the cells and rays are not found to be synchronously developed in tiers.
Nonstratified
Same as nonstoried (see above).
Nucellus
The internal region of an ovule in which the embryo sac develops.
Nuclear envelope
The double membranes limiting the boundary of a nucleus in eukaryotic cells.
Nucleolus
An irregularly dense region of a nucleus responsible for the development of ribosomes.
Nucleus
The double membrane-limited organelle of eukaryotic cells which contains the hereditary materials.
Objective lens
The lens in a light or transmission electron microscope that creates the initial magnification of a specimen.
Obturator
A growth in the style or its canal that brings the pollen tubes and conducting tissue near to the micropyle.
Ontogeny
The development of an individual from embryo to maturity.
Organ
A unique structure composed of tissues which possesses common functions,e.g. leaves,stems and roots are vegetative organs.
Organelle
Characteristic subcellular structures, usually membrane limited, that have a specific function within the cell.
Orthic tetrakaidecahedron
A 14-sided geometric figure often considered to represent the average cell form of closely-compacted parenchyma cells.
Orthoptropous
An ovule that is upright, or not bent over.
Osmium tetroxide
A heavy-metal containing compound used in the chemical fixation of lipids and some amino acids. It not only fixes, but adds contrast to the image in transmission electron microscopy.
Osteosclereid
A bone-shaped sclereid, swollen at the ends.
Outer bark
The "dead" bark lying outside of the phellogen, or cork cambium.
Ovary
Basal region of a carpel or simple pistil containing ovules and developing into a fruit.
Ovule
Structure in the flower which contains the female gametophyte and which develops into a seed.
P-protein
A network of protein filaments found in sieve tube elements. Formerly called "slime."
Palisade parenchyma
Leaf chlorophyllous mesophyll cells which are elongated with their long axis perpendicular to the leaf surface. Typically, the primary photosynthetic tissue.
Palmate
Radiating from a point, as fingers radiating from the palm of a hand.
Papilla
A non-lignified modified trichome appearing as a protruberance on an epidermal (usually leaf or petal) cell.
Paracytic stoma
An arrangement of epidermal subsidiary cells in which one or more are parallel with the guard cells.
Paradermal
Refers to a plane of sectioning that is parallel to the epidermal layer (or surface of the leaf).
Paratracheal parenchyma
Wood parenchyma associated in some form with vessel members.
Parenchyma cell
An unspecialized plant cell which usually has thin walls with no secondary wall development.
Parietal cytoplasm
That which is located adjacent to the cell wall.
Parthenocarpy
Development of a fruit (typically seedless) without fertilization.
Passage cell
Endodermis cell that remains thin-walled when others in the tissue are thick-walled. Still has Casparian strip.
Pavement cells
Ground cells of an epidermis, not a part of a stomatal complex or trichome.
Pectic substances
Carbohydrate compounds which are an important part of the middle lamella and which are derived from polygalacturonic acid.
Pedicel
The stalk of an individual flower.
Peduncle
The stem of an inflorescence.
Peltate trichome
A flattened disc-shaped plate of cells that may or may not have a stalk for attachment to an epidermal layer.
Pepo
A fleshy fruit with a firm rind, characteristic of cucurbits (squash family).
Perfect flower
Flower containing both stamens and carpels.
Perforation plate
That region of a cell wall which is perforated, and found in a vessel member.
Perianth
Collectively, the petals and sepals (or tepals) of a flower.
Periblem
The meristem which forms the cortex and the initials that form the root ground meristem.
Pericarp
The wall of a fruit which was derived from an ovary wall.
Periclinal
A plane of division or cell wall establishment which is parallel with the surface of the organ.
Pericycle
A tissue typically of roots which is found between the endodermis and the phloem, and which gives rise to branch roots.
Periderm
A secondary tissue that replaces epidermis in roots and stems, and which consists of phellem, phellogen, and phelloderm.
Pericyclic fibers
Same as perivascular fiber (below).
Perigenous
Ontogeny in stomatal complexes where there is no common origin of guard and subsidiary cells.
Perivascular fiber
A fiber, not of phloem origin, which is located at the outer periphery of a vascular cylinder or even towards the margin of a stem.
Petal
A non-reproductive modified leaf which is a component of the corolla of a flower.
Petiole
Stalk of a leaf which is the attachment to a stem.
Petiolule
The modified petiole of a leaflet in a compound leaf.
Phellem
Corky tissues characterized by non-living suberized cells produced in a centrifugal manner by the cork cambium (phellogen).
Phelloderm
Parenchyma-like cells produced in a centripetal manner (to the inside) by the cork cambium (phellogen).
Phelloid
Idioblasts of the phellem that may be sclerified or containing other wall materials than suberin.
Phellogen
The cork cambium which produces cork to the outside (centrifugal manner),and phelloderm to the inside (centripetal manner).
Phenotype
The physical appearance of an individual formed from its genetic makeup and the influence of the environment.
Phloem
Food-conducting tissue of a plant composed of sieve elements, companion cells, and various parenchyma and fibers.
Phloem ray
A vascular ray found in the secondary phloem.
Photoautotrophic
Capable of synthesizing food products (based on molecules of carbon) using light energy.
Photorespiration
The production of glycolic acid in chloroplasts in the light. The glycolic acid may be oxidized by enzymes of peroxisomes.
Phragmoplast
A disk or plate-like structure composed of microtubules and microfilaments which defines the site of new wall formation following mitosis or meiosis.
Phyllotaxy
The pattern of leaf arrangement on a stem.
Phylogeny
The sequence of evolutionary changes that have occurred in the development of a species or taxonomic group.
Pistil
A gynoecium composed of ovary, style, and stigma.
Pit
A small region of the cell wall in which the primary wall is not covered with secondary wall material.
Pit aperture
Opening into a pit from the interior of a cell.
Pit membrane
The compound middle lamella separating two pits.
Pit-pair
Two adjacent pits from opposing cells sharing a common pit membrane.
Pith
Ground tissue in the center of a root or stem originating from ground meristem.
Placenta
Site of attachment of the ovule to the ovary wall.
Plasma membrane
The outer limiting membrane of a cell.
Plasmalemma
Synonymous with cell membrane or plasma membrane.
Plasmodesma
The connecting strands of protoplasm between the cytoplasm of adjacent cells which forms canals through the cell walls. It may contain a desmotubule which links the endoplasmic reticulum of the adjacent cells.
Plasmodesmatal field
An aggregation of plasmodesmata at a particular site.
Plastid
A cellular organelle containing photosynthetic and/or ancillary pigments in its internal membranes and limited by a pair of membranes.
Plastoglobule
Oil-containing droplets in the stroma of a plastid, often associated with senescence.
Plate collenchyma
Same as lamellar collenchyma.
Pleomorphic
Having no regular form or distinctive shape, but one that varies.
Plerome
An apical meristem region giving rise to the vascular tissues and the root procambium.
Plicate cell
A cell with infoldings of the cell wall extending into the cytoplasm.
Polar nuclei
The two central nuclei which migrated from the opposite poles of an embryo sac.
Pollen grain
A mature microspore in a seed plant with a distinctive cell wall exine and containing sperm.
Pollen sac
The locule in an anther containing pollen grains.
Pollen tube
A hypha-like germination tube from a pollen grain that transmits the male (micro)gametophytes to an embryo sac in an ovule.
Pollination
The transfer of pollen from an anther to the stigma of the same species.
Polyarch
The primary xylem of a root with many protoxylem strands.
Porous wood
The appearance of secondary xylem in cross-section with vessels.
Pre-prophase
Stages of events in a cell occuring prior to the visible recognition of prophase in mitosis or meiosis.
Primary body
A plant body arising from the embryo and apical meristems.
Primary cell wall
Cell wall developing during the growth of a cell in which the wall microfibrils are layered in various, often random, orientations.
Primary growth
Plant growth derived from the tissues of apical meristems.
Primary meristems
Root or shoot apical meristems which form definite tissue systems in the plant body. See Histogens (older term).
Primary phloem
Phloem derived from procambium and divided into the earlier protophloem, and the later metaphloem.
Primary pit field
A thin area of a primary wall in which a number of pits develop as the secondary wall is deposited.
Primary xylem
Xylem derived from procambium and divided into the earlier protoxylem,and the later metaxylem.
Primexine
An early exine wall stage in which sporopollenin is deposited over the stretching wall.
Procambium
That primary meristem which develops into primary vascular tissue.
Procumbent ray cell
A secondary vascular ray cell with its long axis in the horizontal (ray) direction.
Proembryo
A very early stage of plant embryo development, before protoderm and suspensor are formed.
Prophase
The first recognizable stage of mitosis or meiosis when the structural organization of chromosomes becomes visually evident with light microscopy.
Projector lens
The final lens in an electron microscope that creates additional magnification from that generated by the objective lens.
Prokaryotic
Organisms whose cells have no membrane-limited nucleus or organelles. Mostly, bacteria and cyanobacteria.
Promeristems
Of an apical meristem, the initial and early derivatives at the root or shoot apex.
Prop roots
Aerial adventitious roots which usually provide support.
Proplastid
The early stage of plastid development.
Protoderm
The primary meristem that gives rise to epidermis.
Protophloem
Initial phloem elements produced in primary growth.
Protoplasm
All of the living contents of a cell, including the cytoplasm and nucleus.
Protoplast
All cell components, but lacking the cell wall.
Protostele
A simple stele with phloem outside of a solid column of xylem.
Protoxylem
The first formed primary xylem.
Pulvinus
An enlargement of a leaf petiole at its base which may regulate leaf movement.
Quiescent center
That region of apical meristems, particularly in roots, in which there is relatively little (or no) mitotic activity.
Radial section
A longitudinal section along a radial plane.
Radial system
Components of structure and growth in a radial axis.
Radicle
An embryonic root.
Ramified
Showing one or more branches.
Ramiform pit
A pit that is branched due to two or more simple pits having fused.
Raphe
A ridge on the surface of a seed formed from the fusion of a funiculus to the outer ovule wall surface.
Raphides
Slender, needle-like crystals.
Raster
The formation of an image composed of many image points scanned in a series of parallel lines. The scanning electron microscope produces images in this manner, and confocal microscopes may employ a rastering system of light or laser beam.
Ray
Tissue extending radially in the secondary xylem and phloem.
Ray parenchyma
Parenchyma cells of a ray.
Reaction wood
Wood showing stress formations due to compression, leaning, or uneven growth of a stem.
Receptacle
A modified stem upon which the floral organs are borne.
Rectilinear
A straight line, as in the projection of light rays.
Refractive index
The speed of light in a vacuum as opposed to its speed in a medium. Also measured as the sine of the angle of bending from one medium to another.
Refraction
The deflection from a straight path encountered by a photon of light, an electron, etc. in passing from one medium to another.
Resin duct
A duct formed by the breakdown of cell walls of end members, lined with epithelial cells, and transporting resin.
Resolution
The finest detail observable with an optical device. Often defined as the ability to observe two object points very close to one another. The measure of the finest distance between the points is referred to as the resolution of an instrument.
Reticulate
Having a net-like pattern.
Rexigenous
An intercellular space originating as a consequence of cell rupture.
Rhizodermis
Primary surface layer of the root, similar to epidermis but of different origin and function.
Rhytidome
Outer bark.
Rib meristem
Meristematic tissue in which the cells divide perpendicular to the longitudinal axis of an organ (usually a stem) to produce parallel vertical rows of cells.
Ribosome
A very small non-membranous cell organelle composed of protein and RNA that is the site of protein synthesis, and is found in the nucleus, cytoplasm, mitochondria and plastids of a cell.
Ring-porous wood
Secondary wood of hardwood species which have large diameter vessel elements located primarily in the early wood.
Root hair
An extension of cells of the rhizodermis, increasing surface area for absorption.
Rootcap
The mass of cells covering and protecting the root apical meristem.
Roots
The (typically) underground vegetative organ of plants derived from the root apical meristem. Capable of storage, support, mutualistic associations with microorganisms and secondary growth in many cases.
Sapwood
The outer part of the secondary xylem which still contains some living cells, and in which water conduction takes place.
Scalariform
Having a ladder-like pattern.
Schizo-lysigenous
Intercellular spaces formed by a combination of wall separation, and the degradation of cell walls.
Schizogenous
Intercellular spaces formed by the separation of cell walls of adjacent cells along their middle lamellae.
Sclereid
A relatively short sclerenchyma cell characterized by thick lignified secondary walls with many simple pits.
Sclerenchyma
A tissue composed of sclerenchyma cells which have thick, lignified cell walls, and may or may not have living contents.
Secondary cell wall
Cell wall material formed after the cell ceases to enlarge, and in which the wall microfibrils have one or more sets of parallel orientation.
Secondary electrons
Electrons generated out of a specimen in order to show an image in a scanning electron microscope. Defined as electrons with <50 eV energy.
Secondary growth
Growth originating from a vascular cambium and/or phellogen that gives rise to an increase in girth.
Secondary phloem
Phloem derived from vascular cambium.
Secondary xylem
Xylem derived from vascular cambium.
Secretory structure
A structure that produces a secretion.
Seed
A ripened ovule containing a multicellular embryo plant, endosperm and a protective seed coat.
Seed coat
The outer coat, or testa, of a seed that is derived from the integument.
Sepals
Outermost vegetative organs of a flower, collectively called a calyx.
Septum
A partition.
Sessile
A leaf lacking a petiole, or a flower lacking a pedicel.
Sexine
An outer layer of the exine.
Sieve area
A pit-like area in the wall of a sieve element whose pores are lined with callose.
Sieve cell
A type of sieve element with undifferentiated sieve areas and no sieve plates.
Sieve element
A phloem cell involved with food conduction, either a sieve cell or a sieve tube member.
Sieve plate
Wall of a sieve element with sieve areas.
Sieve pores
Openings in a sieve plate or sieve area.
Sieve tube
A series of sieve elements arranged end-to-end, and interconnected through sieve plates.
Sieve tube member
A cell component of a sieve tube.
Simple pit
A pit in which the cavity remains uniform in width or gradually becomes either wider or narrower during growth in thickness of the secondary wall.
Siphonostele
A stele in which the vascular cylinder has a core of pith.
Soft wood
That wood lacking vessel members, typically used to refer to gymnosperm wood.
Sperm
Male gametes formed by mitosis in plants.
Spindle apparatus/fibers
An aggregation of microtubules that aid in the movement of chromosomes during mitosis or meiosis.
Spongy mesophyll
Leaf parenchyma cells of irregular shape and with large air spaces surrounding. Primary function is in gaseous exchange.
Spore
A reproductive cell in plants that is produced by meiosis and gives rise to the gametophyte generation.
Sporophyte
The diploid phase of the life cycle of plants that gives rise to the production of spores by means of meiosis. In higher plants it is the dominant phase of the life cycle.
Sporopollenin
The highly resistant material comprising the exine of a pollen grain.
Spring wood
Same as early wood.
Stain
A compound used to add selective or non-selective color to a specimen in light microscopy, or contrast in transmission electron microscopy.
Stamen
Floral organ producing pollen and typically composed of a filament and an anther.
Staminate
Referring to having stamens.
Statolith
Starch or carbonate-containing structure (often plastids) in a rootcap cell believed to be involved in sensing gravitational pull.
Stele
The vascular system of a plant body and its associated ground tissues.
Stellate
Star-shaped.
Stems
Typically, the aerial portion of the plant structure bearing leaves. The most complex vegetative organ of the plant.
Stereology
The method of quantifying volume and surface area components in a structure.
Stigma
The terminal portion of a style morphologically adapted to holding and germinating pollen.
Stigmatoid tissue
Tissue of the style which provides a pathway and nutrition for growing pollen tubes.
Stomatal crypt
A leaf depression in which the stomate(s) and guard cells are found.
Stoma/Stomate
An opening in an epidermal layer (usually in leaves and stems) which is bordered by two guard cells.
Stomium
An opening, often slit-like, in an anther that dehisces upon drying to release pollen.
Stone cell
A brachysclereid.
Storied
Stratified (often found in cambium, wood and rays).
Stroma
The non-membranous matrix material of a chloroplast containing enzymes of the Calvin-Benson cycle.
Style
A filamentous portion of the ovary through which pollen tubes may grow.
Suberin
A fatty substance found in the cell wall of cork cells, and the Casparian strip of endodermis tissue.
Subsidiary cell
A morphologically distinguishable cell associated with a stomate and its guard cells.
Summer wood
That secondary xylem formed late in the growth season for temperate plants. Also called "late wood."
Superior ovary
An ovary located above other floral parts on the floral axis.
Suspensor
A cellular filament that anchors the embryo into the endosperm.
Symplast
The living cell contents of tissues (which may be connected from cell to cell by plasmodesmata).
Synaptonemal complex
A railroad track-like image in electron micrographs representing the nuclear sites where homologous chromosomes have paired during meiosis.
Synergids
A pair of "sister" cells associated with the egg at the micropylar end of an embryo sac.
Syngamy
The process of fertilization, or union of gametes.
Tabular cells
Early cells of an abscission zone in a leaf petiole which possess a rectangular outline.
Tangential
A plane of sectioning at right angles to the radial plane or parallel to the surface of a flattened structure (as a leaf).
Tannin
Any of a group of polyphenolic compounds used in tanning and dyeing. Typically makes a strong preservative solution in water.
Tapetum
A layer of (often binucleate) cells lining the locules of anthers and which provide nutrition to the developing pollen. May become coenocytic and plasmodial in later stages of development.
Taproot
A root that is not highly branched and may be adapted for food storage.
Telophase
the divisional stage when chromosomes have moved to opposite poles of the cell and have begun to decondense.
Tension wood
A type of reaction wood in dicotyledons in which there is less lignification and more gelatinous fibers.
Tenuinucellate ovule
Ovule in which the megagametophyte is located immediately adjacent to the epidermis of the nucellus.
Tepal
Units of calyx and corolla that cannot be differentiated from each other.
Testa
Seed coat.
Tetrarch
Primary xylem of a root with four protoxylem poles.
Thylakoid
A membrane element, usually in stacked orientation, within the stroma of a plastid, usually a chloroplast.
Tissue
Groups of cells associated in large numbers, and of common origin, common structure and common function.
Tonoplast
The limiting membrane surrounding a vacuole.
Torus
A central thickened portion of a pit membrane in a bordered pit of gymnosperms.
Tracheary elements
Cells of the xylem involved with water conduction. May be tracheids or vessel members.
Tracheid
A tracheary element with no perforations, and often intermediate between a vessel member and a fiber.
Trans-face
The secretory side of the cisternae in a dictyosome.
Transfer cell
Parenchyma cell with wall invaginations that aid in the transfer of solutes.
Transfusion tissue
Tracheids and parenchyma cells that surround the vascular tissues in leaf veins of gymnosperms.
Transverse section
Same as cross-section.
Triarch
Primary xylem of a root in which there are three protoxylem poles.
Trichoblast
A rhizodermal cell that develops a root hair.
Trichome
A hair or scale, usually multicellular, of a leaf or stem epidermis that may be glandular.
Trichosclereid
A branched sclereid extending into intercellular spaces.
Tubulin
A globular polypeptide which, in the dimer form, represents the building block of microtubules.
Tunica-corpus
Concept of the two-layered structural organization of a shoot tip in angiosperms.
Tylose
An outgrowth of a parenchyma cell extending through a pit cavity into a tracheary cell. It usually blocks the lumen of the vessel and therefore the movement of materials.
Ultrastructure
The type of structural detail at high resolution and high magnification that is typical of images observed with the transmission electron microscope.
Unifacial leaf
A leaf in which one face, typically the adaxial face has fused, so that both faces are abaxial, as in Iris.
Uniseriate ray
A ray (xylem and/or phloem) that is only one cell in thickness (width).
Vacuole
Nonliving region within a cell that is membrane-bound and is filled with water, storage and waste products.
Vacuome
Collectively, all the vacuoles of a cell.
Vascular bundle
A strand of xylem and phloem originating from primary meristems.
Vascular cambium
Lateral meristem which gives rise to secondary vascular tissues in stems and roots.
Vascular cylinder
Same as stele, but excluding associated ground tissues.
Vegetative cell
The larger haploid cell of a pollen grain that forms the pollen tube.
Vein
A strand of vascular tissue in a flat organ such as a leaf.
Vein rib
Ground tissue associated with a vein and usually occurring on the abaxial side of a leaf.
Velamen
Multiple epidermis found on aerial roots of tropical orchids.
Vessel
A tube-like series of vessel members which have perforations in their common end walls.
Vessel member
A single cellular component of a vessel.
Vesicles
Small membrane-limited bodies often derived from dictyosomes and carrying structural or enzymatic materials for deposition at a more remote location, such as the cell surface or cell plate.
Wall
Generally referring to cell wall.
Warts
Small deposits on the inner walls of the S3 layer in secondary walls. Believed to be derived from final decomposition of the protoplast.
Wood
The secondary xylem of seed plants.
Wound periderm
A periderm formed in response to injury.
Xeromorphic leaves
Leaves with special structural adaptations to living in a dry environment.
Xerophyte
A plant adapted to growth and survival in a dry environment.
Xylem
Water conducting tissue containing tracheary elements.
Xylem elements
Cells comprising the xylem.
Xylem ray
That portion of a vascular ray which is found in the xylem.
Xylotomy
The anatomical study of wood.
Zygomorphic
An irregular flower which may be bilaterally symmetrical.
Zygote
The diploid cell produced after an egg cell is fertilized. Beginning of the new sporophyte plant.