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Abaxial
Facing away from the axis of stem or root (as opposed to adaxial). Also, typically the lower surface of leaves.
Abscission
The dropping of leaves and fruits or floral structures upon maturation or at the end of a growing season.
Abscission layer
The layer of cells which transverses the structure (e.g. petiole) which is separated in the process of abscission.
Accessory bud
A bud, secondary in nature, which is located adjacent to a main axillary bud.
Accessory fruit
A fruit composed primarily from tissues other than the ovary.
Acicular crystal
Typically, an inorganic crystal which is elongated into a needle-shape, such as raphides.
Acropetal
Directed towards the apex of an organ, e.g. the tip of a stem or root.
Actin
A globular protein often organized into two filamentous strands wound around each other. An important component of the cell cytoskeleton.
Actinocytic
A stomate surrounded by a circle of radiating subsidiary cells.
Actinomorphic
Floral parts which are radially symmetrical.
Actinostele
A protostele that is star-shaped in cross-sectional view.
Adaxial
Facing toward the axis of stem or root (as opposed to abaxial). Used to describe the upper surface of leaves.
Adnation
Fusion of stamens, pistils or petals in a flower involving different whorls.
Adventitious
Anomalous growth of tissues or organs as in the growth of roots directly from stems and/or leaves.
Aerenchyma
Parenchymatous tissue characterized by air-spaces between cells.
Aggregate fruit
One developing from a single flower, but with multiple carpels.
Aggregate ray
In woody tissues, several adjacent simple rays clustered together so as to appear as a single large ray.
Albuminous cells
Found in gymnosperm phloem where cells which are functionally and structurally similar to companion cells exist, but do not originate from the same precursors as do the companion cells in angiosperms.
Aleurone layer
The outermost layer of the endosperm in grass seeds which are characterized by large protein deposits and enzymes which can degrade the endosperm.
Aminopeptidase
An enzyme that acts by hydrolysis of the amino groups of amino acids in proteins.
Amphicribral vascular bundle
A concentric vascular bundle in which the phloem surrounds the xylem tissue.
Amphiphloic siphonostele
A stele in which the vascular system appears as a tube with the phloem located on both the external and internal sides of the xylem.
Amphistomatous leaves
Having stomata on both adaxial and abaxial surfaces of a leaf.
Amphivasal vascular bundle
A vascular bundle in which the xylem surrounds the phloem.
Amphoteric
A molecule which may be either acidic or basic depending on the pH of the medium which affects the overall charge on the molecule.
Amyloplast
A colorless plastid containing starch grains; often found in root parenchyma.
Analogous
Having the same function, but a different phylogenetic origin from another cell/tissue.
Anaphase
That phase of mitosis or meiosis in which the separation of chromatids takes place to opposite poles of the cell.
Anastomosis
Interconnection or fusion of cells or tissues.
Anatomy
The study of biological structure of individuals at the tissue/organ level (gross), and at the cell/subcellular level (microscopic). Plant anatomy is generally considered to primarily be concerned with microscopic structure.
Anatropous
A configuration of an ovule in which it is bent downwards with the micropyle adjacent to the funiculus.
Androecium
Collectively, all of the stamens in the flower of a seed plant.
Angiosperm
Higher plants in which seeds are borne within a mature ovary.
Angular collenchyma
Collenchyma cells in which the primary wall is thickened at intercellular sites with adjacent cells.
Anisocytic
A type of stomatal complex in which three subsidiary cells are unequal in size.
Annual ring
The growth of xylem tissues formed in a single growing season as observed in transectional view.
Annular cell wall thickenings
Secondary wall thickenings appearing as rings in xylem tracheary cells.
Annular collenchyma
Collenchyma cell in which the primary wall is uniformly thickened.
Anomocytic stoma
A stomatal opening with guard cells, but without subsidiary cells.
Anther
The pollen sack typically at the terminus of a stamen.
Anthocyanin
A red, purple or reddish-blue water-soluble pigment found in the cell vacuole.
Anticlinal
A plane of growth or development at right angles to the nearest surface.
Antipodals
In angiosperms, the cells at the opposite end of the embryo sac from the site of the zygote.
Aperture
A thin plate of exine covering an opening through which the pollen tube may emerge (in pollen). May also be an opening into a pit from the interior of a cell.
Apex
The terminus, or tip of a structure (e.g. shoot or root).
Apical cell
A cell found at the apex which is typically the origin, or initial, of a meristem.
Apical meristem
A group of mitotically dividing cells found in the apical region of a root or shoot, and which give rise to primary tissues.
Apocarpy
The lack of fusion between carpels in a flower (also, free carpels).
Apomixis
Embryonic reproduction with no meiosis or gametic fusion.
Apoplast
Region of the plant body outside of the living cell contents; typically limited to the cell wall and intercellular spaces.
Apotracheal parenchyma
That parenchyma in wood which is not closely associated with vessel members.
Apposition
Growth of cell wall by successive deposition of layers of wall material.
Areole
A leaf mesophyll region limited by vascular tissues around it.
Articulated laticifer
Fusion of two or more cells in a laticifer in which the partitioning walls are partly or wholly lacking.
Aspirated pit
A bordered pit in gymnosperm wood in which the pit membrane is displaced to one side, and the torus blocks the aperture.
Astrosclereid
A branched sclereid.
Atactostele
A stele with the vascular bundles scattered throughout the ground tissue.
Atrichoblast
A rhizodermal cell that does not give rise to a root hair.
Autoradiograph
A photo image created by exposure to a radioactive substance incorporated into a tissue. It shows the location and intensity of the radioactive substance.
Autotroph
An organism capable of making its own food substances from (usually) light energy, and producing organic material from CO2 as a raw material.
Auxochromic group
Chemical group on a dye molecule that enables the dye to become attached to substrate and to dissolve and dissociate in water or other solvent.
Axial parenchyma
That parenchyma found in the vertical axis of a plant, not associated with rays.
Axial system
Secondary vascular cells derived from cambial initials, and with their axis running parallel with the axis of the stem or root.
Axial tracheid
Tracheids in the axial system of secondary xylem; as contrasted to ray tracheids.
Axil
The upper (and usually smaller) angle between a stem and the petiole of a leaf.
Axillary bud
A bud found in the axil of a leaf.
Axillary meristem
The meristematic region in the axil of a leaf that gives rise to an axillary bud.
Bark
A general term for all tissues outside of the vascular cambium.
Basipetal
Development or differentiation occurring in a downwards direction or toward the base of an organ. Opposite of acropetal.
Bast fiber
Any fibrous tissue outside of the xylem; primarily phloem fibers.
Bicollateral vascular bundle
A vascular bundle with phloem on two sides of the xylem.
Bifacial leaf
Leaf with palisade mesophyll on one side of the leaf (within the epidermis), and spongy mesophyll on the other.
Bilateral symmetry
Floral structure showing two sides of similar structure, as opposed to radial symmetry.
Biseriate ray
A vascular tissue ray that is two cells wide.
Blind pit
A pit without an adjacent complementary one in the joining wall.
Bordered pit
A pit in the secondary wall which overarches the pit membrane.
Bordered pit-pair
The pairing of bordered pits from adjacent cells.
Brachysclereid
A thick-walled sclereid that is nearly isodiametric.
Branch gap
The region in a stem above where leaf traces are found that in transverse sectional view does not show the presence of vascular components.
Branch root
A root arising from the pericycle of the primary root.
Branch traces
Vascular bundles connecting the vascular tissue of the main stem to its branches.
Bulliform cell
In grasses, it appears as a large epidermal cell arranged in a row that may regulate the rolling or unrolling of the leaf.
Bundle sheath
One or more layers of cells which enclose a vascular bundle in a leaf. While usually parenchyma cells comprise the bundle sheath, they may also be composed of sclerenchyma cells.
Bundle sheath extension
An extension of the bundle sheath cells that extends to one or both of the epidermal layers in a leaf.
Callose
Depositions of ▀-1,2 glucan (a carbohydrate which can be hydrolyzed to glucose residues) on sieve plates in phloem, as partitions in pollen tubes, and occasionally in parenchyma cells.
Callus
A mass of undifferentiated parenchyma cells produced in tissue culture, or as a response to injury or grafting.
Calyptra
A rootcap.
Calyptrogen
Meristematic cells (histogen) of the root tip which give rise to the rootcap. Characteristic of monocots.
Calyx
Collectively, all the sepals of a flower.
Cambial initials
Cells of the vascular cambium which give rise through periclinal divisions to either phloem or xylem (fusiform initials), or to rays (ray initials).
Cambium
Lateral meristematic cells of either vascular cambium or cork cambium.
Capitate
A globular, head-like structure.
Carboxypeptidase
An enzyme hydrolyzing a protein by acting on the carboxyl group of amino acids.
Carpel
Highly modified leaf-like organs in angiosperm flowers that produce one or more ovules.
Casparian strip
Deposits of suberin and lignin on the radial and transverse anticlinal walls of the root endodermis which limits the flow of water and solutes through the apoplast.
Cathepsins
Proteolytic enzymes often found in microbodies and/or lysosomes of cells.
Cauline
Pertaining to the stem of a plant.
Cell plate
The partition of cell wall material that appears during the latter stages of mitosis and which become the new primary cell wall that separates the daughter cells.
Cell wall
The non-living materials deposited outside of the plasmalemma which give rigidity, form and protection to the cell. Typically composed of cellulose and other organic materials that may contain extracellular enzymes and other substances.
Cellulose
A polysaccharide component of primary cell walls consisting of a glucan polymer of indeterminate length, typically gathered into bundles forming microfilaments. A principal component of primary cell walls and the scaffolding for secondary walls.
Central cell
A large bi-nucleate cell of the megagametophyte that will develop into endosperm after double fertilization.
Central cylinder
The vascular system in a root including the pericycle and pith if present, but not including the endodermis or outer tissues. Same as stele.
Centric
Morphology of monocot leaves that are cylindrical in cross-sectional view.
Centric mesophyll
Occurs in thin or narrow leaves, in which the mesophyll is palisade on both abaxial and adaxial surfaces, and they are continuous.
Centrifugal
Refers to movement or development progressively away from the center.
Centripetal
Refers to movement or development progressively toward the center.
Chalaza
The site of an ovule opposite the micropyle, and adjacent to the stalk region.
Chemoautotrophic
An autotrophic organism which uses energy from chemical degradation as opposed to light energy. Found among microorganisms.
Chimera
A plant organ consisting of different tissue layers comprised of different ploidy levels, or other consistent differences in genetic composition.
Chlorenchyma
Any parenchyma tissue containing chloroplasts.
Chloroplast
A photosynthetically active organelle with chlorophyll pigments organized into thylakoid membranes usually arranged in stacks. The organelle is typically bounded by two membranes and is found in eukaryotic plants.
Chromatid
One of two genetically identical halves of a chromosome.
Chromatin
DNA and associated protein of a cell which is (typically) not in a chromosomal state, i.e. in an interphase nucleus. May be euchromatin or heterochromatin.
Chromophoric group
Chemical group of a dye molecule that imparts color to the dye.
Chromoplast
A plastid containing pigments other than chlorophyll, usually carotenoids.
Chromosome
Rod-like structure containing units of genetic information as DNA in association with histone proteins. Formed within the nucleus of eukaryotic cells.
Cicatrice
Scar tissue formed when one plant part separates from another, as in leaf and fruit abscission.
Circular bordered pit
A bordered pit with a circular aperture.
Cis-face
The forming face of a dictyosome.
Cisterna(e)
A generic term for any flattened membrane sac within cells, including those of the endoplasmic reticulum, thylakoids of chloroplasts, etc.
Cladophyll
A flattened stem, functioning and appearing much as a leaf.
Clathrin
A fibrous protein which, together with smaller peptides, forms a coat over vesicles, as from dictyosomes. The clathrin may act in binding to specific receptors on other membranes such as the plasma membrane of a cell.
Closed vascular bundle
A vascular bundle with no cambium tissue.
Closed venation
A situation occurring in leaves in which the vein endings fuse with each other so that there are no free endings to the minor veins.
Coagulate
To form a dense mass, often from proteins through the removal of the water of hydration which allows for reactive sites on the protein molecule to act with one another.
Coenocyte
Refers to usually large, multinucleate cells in plants.
Coleoptile
In grasses, a leafy sheath which encloses the epicotyl of the embryo.
Coleorhiza
In grasses, a sheath that encloses the radicle of the embryo.
Collateral vascular bundle
A vascular bundle with phloem on the abaxial side of the xylem. The most common situation.
Collenchyma
Elongated cells with uneven primary cell walls and containing no lignin. Usually found in early development of stems and leaf petioles.
Colleter
A multicellular trichome of a leaf or bud scale that produces a sticky secretion.
Columella
The central part of a rootcap in which the parenchyma cells are arranged in a series of columns.
Commissural vascular bundle
A small vascular bundle which tends to connect the larger, parallel vascular bundle bundles of grass leaves.
Companion cell
A living phloem parenchyma cell in angiosperms which is associated with a sieve tube member, and was derived from the same mother cell.
Complete flower
A flower containing all of the typical associated floral parts.
Compound light microscope
An optical instrument designed for producing magnified images of objects using two or more glass lenses.
Compound middle lamella
A general term referring collectively to the middle lamella and the primary cell walls of two adjacent cells.
Compound sieve plate
A sieve plate composed of several patchy sieve areas.
Compression wood
A reaction wood in conifers characterized by dense structure due to stress.
Concentric vascular bundle
A vascular bundle with concentric layers of xylem and phloem, either amphicribral or amphivasal.
Condenser
A lens which efficiently focuses rays of illumination onto and/or through a specimen. In light and transmission electron microscopes, the rays usually continue into the objective lens.
Confocal
A type of light microscopy in which a point of illumination is projected or rastered over a specimen, and the reflected illumination is screened through an exit aperture in order to eliminate light from out-of-focus planes.
Conjunctive tissue
Secondary growth in which scattered vascular bundles are found within a parenchyma tissue.
Connective
A band of parenchyma cells that unites the lobes of an anther.
Coordinated growth
Tissue growth in which there is no separation of the adjacent cell walls.
Cork
Nonliving cells with suberized walls and formed from cork cambium (phellogen). Also known as phellem.
Cork cambium
A lateral meristem producing cork centripetally in stems and sometimes roots.
Corolla
Refers to all the petals of a single flower.
Corpus
A mass of meristematic cells in the apical meristem of roots and shoots which is covered by a less meristematically active tunica, and in which divisions occur in various planes.
Cortex
Region found between the epidermis and the vascular system in roots and stems.
Cotyledon
The first leaf/leaves generated from a plant embryo.
Cotyledonary trace
A vascular connection between the root and hypocotyl in angiosperms, resembling a leaf trace.
Crassinucellate ovule
An ovule in which the megagametophyte is located deep in the nucellus, away from the epidermis.
Crassulae
Ridge-like thickenings of the compound middle lamellae in tracheids of certain conifers. Appear near bordered pits, normally.
Crista(e)
The infolding(s) of the inner mitochondrial membrane possessing the electron transport mechanism.
Crystalloid
Term for protein crystals which show fine regularity of structure in the transmission electron microscope. A repetitive lattice of molecular layers can often be observed as opposed to inorganic mineral crystals which have no such layering.
Cuticle
A layer of water-impervious material (cutin) deposited on the outer surfaces of epidermal cell walls, particularly in leaves.
Cuticularization
An obscure process of cuticle deposition on the surface of epidermal cell walls.
Cutin
The primary material of the cuticle which is hydrophobic and containing complex fatty substances.
Cyclosis
Cytoplasmic streaming, generally unidirectional and around a large, central vacuole.
Cystolith
Inorganic deposits (usually calcium carbonate) on the inner surface of the cell walls of lithocysts.
Cytokinesis
The division of the remaining cytoplasmic substances in a cell aside from the nuclear events of mitosis.
Cytoplasm
All the living contents of a cell aside from the nucleus. Does not include vacuole or cell wall substances.
Cytoplasmic sleeve
Cytoplasmic content of a plasmodesma surrounding the desmotubule.
Cytoskeleton
A network of protein filaments (microfibrils and microtubules) that give eukaryotic cells shape and movement. Are involved in directing chomosome movement, cell plate formation, orientation of chloroplasts, etc.
Decussate
A leaf arrangement on stems in which alternating leaves are at right angles to one another.
Dedifferentiation
A loss of differentiation in which a cell or tissue may resume mitotic activity.
Dehiscence
The process of splitting open to release enclosed spores, seeds or other reproductive structures.
Dendritic
Branching in a tree-like manner.
Dendroid venation
A venation pattern in which the minor veins of leaves do not form isolated regions of the mesophyll tissue, but rather leave open confluent spaces.
Derivative
A cell which comes from a meristem and undergoes differentiation into a specialized tissue. The sister cell from the mitosis in the meristem may or may not also become a derivative.
Dermal tissue system
The tissue which covers the outer surface of a plant, typically the epidermis or the periderm.
Dermatocalyptrogen
A histogen giving rise to protoderm and rootcap.
Dermatogen
A primary meristem (from the apical meristem) which produces the epidermis or rhizodermis.
Desmogen
Meristematic cells from primary or secondary meristem that are destined to become vascular.
Desmotubule
A cylindrical membrane within a plasmodesma that connects the endoplasmic reticulum system of adjacent cells.
Determinate growth
Development to a point characterized by a fixed number of leaves or other lateral organs.
Development
Growth and maturation of an organism or some part of it.
Diacytic stoma
A stomatal complex in which one pair of subsidiary cells at right angles to the guard cells surrounds the stomatal opening.
Diarch
Primary xylem of the root showing two strands or poles of protoxylem in cross-sectional view.
Dichotomous venation
Branching of veins within a leaf blade resulting in two new veins from each existing one. Found in grasses and in Ginkgo.
Dicotyledonous plants
Members derived from the Magnoliopsida that possess two cotyledons. Believed to be ancestral to monocotolydenous plants.
Dictyosome
A functional unit of a Golgi apparatus. Characterized by a stack of membranes involved with secretory activities.
Dictyostele
Vascular system in which the phloem surrounds the xylem in anastomosing strands defined by a series of leaf gaps.
Differentiation
The development of a cell, tissue, organ or plant from simple, early organization to more complex mature organization.
Diffuse porous wood
Wood characterized by a relatively uniform distribution of xylem vessels in the annual rings, so that the change from one year to the next is not easily distinguished.
Dilatation
An increase in the diameter of a stem or root due to mitotic division of the parenchyma cells in tissues such as pith or rays.
Distal
The position of an object farthest away from the site of attachment or origin.
Distichous
The arrangement of leaves in two vertical rows on a stem.
Dorsiventral
A leaf characterized by having palisade mesophyll on one side and spongy mesophyll on the opposite side.
Double fertilization
The process of two sets of nuclear fusions in an embryo sac occurring at the same time, involving the fusion of egg and sperm as well as the fusion of a second male gamete with the two polar nuclei.
Druse
A globular inorganic crystal, usually with many spike-like processes on the surface. The presumed composition is typically calcium oxalate.
Duct
A space within a tissue where secretion often occurs, formed by the separation of cells or their dissolution.
Dye
A compound that imparts a specific color to substrate materials.
Early wood
The same as spring wood, which is formed first in the growing season and is often characteristically distinctive from the late (or summer) wood.
Ectophloic siphonostele
A stele characterized by xylem enclosing a pith region, and with phloem outside of the xylem.
Elaioplast
A leucoplast containing oil as the storage product in place of starch.
Elaiosome
An outgrowth of a seed or fruit which contains a rich store of oil.
Elastic
Capable of recovering size and shape after deformation, as in an elastic rubber band.
Embryo sac
In angiosperms, the female gametophyte which is multinucleate/multicellular.
Enation
Outgrowths of the stem in simple, primitive land plants. May be called microphylls to distinguish them from megaphylls which are true primitive leaves derived from a system of branches.
Endarch xylem
A xylem system in which the progression of development occurs to a direction away from the axial center. Typical of most seed plants.
Endocarp
The innermost layer(s) of the pericarp.
Endodermis
The innermost layer of ground tissue in a root representing modified cortex,and possessing a Casparian strip on its anticlinal walls.
Endogenous
Arising from a deep tissue in the plant's organization, such as the development of branch roots from the pericycle of a primary root.
Endoplasmic reticulum
A series of (usually) flattened sac-like membranes that extend throughout the cytoplasm of cells. Site of lipid and lipoprotein production. May be rough (with ribosomes attached), or smooth (with no ribosomes).
Endosperm
Typically a 3n tissue in the seeds of angiosperms formed by the fusion of a sperm nucleus with the two polar nuclei in an embryo sac. The endosperm is rich in proteins and carbohydrates that serve as a food substance for the early growing embryo.
Endothecium
In anthers, it is a wall layer adjacent to the tapetum that lines the locules (or pollen sacs), and is characterized by secondary wall thickenings.
Endothelium
The innermost layer of the integument lining an embryo sac.
Enucleate
Lacking a nucleus.
Ephedroid
Pollen without many ridges of the exine, similar to Ephedra.
Epiblast
A small structure opposite the scutellum present in grass embryos.
Epiblem
The "epidermis" of a root, also called rhizodermis.
Epicotyl
The shoot of an embryo above the cotyledons.
Epicuticular wax
Wax deposits on the outer surface of epidermal cuticle in stems and leaves.
Epidermis
The outer layer of cells of a plant body derived from protoderm.
Epigeal
Growth of an embryo plant characterized by having the cotyledon(s) raised above the level of the ground.
Epigyny
A flower structure organized with the petals, sepals and stamens above the ovary. In this case, the ovary is said to be inferior.
Epiluminescence
Illumination for microscopy in which the light source is above the specimen. Commonly used in confocal microscopy.
Epipetalous stamen
Stamen(s) that are attached to the corolla.
Epistomatic leaves
Possessing stomata only on the upper (adaxial) surface of a leaf.
Epithelium
Cells lining a duct or cavity, which are typically secretory in nature.
Epithem
Modified leaf mesophyll cells between minor vein endings and a hydathode pore. Cells may structure as transfer cells.
Ergastic matter
Non-living products of protoplasmic structures (organelles), such as fat globules, crystals, starch grains, etc.
Etioplast
A plastid developed in the dark or under very low light levels and having a prolamellar body with no chlorophyll.
Euchromatin
The portion of the nuclear genome that may be more structurally diffuse and active in transcription.
Eukaryotic
Refers to cells and/or organisms that possess true nuclei, and contain organized chloroplasts.
Eumeristem
A meristem that is characterized by small, compact cells that are uniform in size and diameter.
Eustele
A stele in which the primary vascular tissues is arranged in strands around the pith.
Exalbuminous seed
A mature seed lacking endosperm.
Exarch xylem
A xylem in which the oldest members are located away from the axis, as in most roots.
Exine
The outer, rather rigid and resistant wall of pollen grains, primarily composed of sporopollenin.
Exocarp
The outer layer of pericarp.
Exocytosis
The release of vesicular materials to the outside of a cell. The opposite of endocytosis.
Exodermis
The outer layer of root cortex cells functioning as a hypodermis.
Exogenous
Developing from superficial tissue.
External phloem
Primary phloem located outside, or external to, the primary xylem.
Extrafloral nectary
A nectary occurring outside of a flower.
Extraxylary fibers
Fibers found in regions outside of the xylem.
Fascicle
A bundle, usually vascular.
Fascicular cambium
That vascular cambium derived from a vascular bundle.
Fertilization
The fusion of male and female gametes to produce a 2n (diploid) zygote.
Fiber
An elongated narrowly tapered sclerenchyma cell with thickened cell wall and typically no living cytoplasm at maturity.
Fiber-sclereid
A cell intermediate between a fiber and a sclereid, with characteristics of both.
Fiber-tracheid
A cell intermediate between a fiber and a tracheid, with characteristics of both.
Fibril
Thin, solid strands in the cytoplasm of cells composed of protein and/or polysaccharide.
Fibrous roots
Roots characterized by many similar branching roots of common length and thickness. Generally not highly adapted for food storage.
Filament
The stalk of a stamen which supports the anther.
Filiform
Thread-like.
Filling tissue
Loose tissue formed by a lenticel phellogen toward the outside.
Fine structure
The type of structural detail at high resolution and high magnification that is typical of images observed with the transmission electron microscope. Also designated "ultrastructure."
Floral tube
A tube or cup-like structure composed of the unified sepals, petals and stamens in flowers.
Follicle
A dry fruit derived from a single carpel, dehiscent along a single axis.
Foraminate
Having a number of circular openings, as in perforation plates.
Freeze-substitution
A preparation technique for microscopy involving the rapid freezing of a specimen, and its subsequent immersion into a very cold organic fluid (e.g. acetone or methanol) that gradually substitutes for the frozen water in the specimen. The specimen is then chemically fixed at low temperature before warming to ambient temperature for embedment.
Fruit
A mature ripened ovary containing seeds in angiosperms. May also include associated floral tube.
Funiculus
The stalk of an ovule.
Fusiform
Referring to the shape of a cell which is characteristically elongated with tapering end walls.
Gamete
Haploid reproductive cells (egg or sperm) produced in plants by mitosis from a gametophyte.
Gametophyte
That plant generation which gives rise to the gametes by means of mitosis. Typically haploid.
Gap
In a siphonostele, the parenchymatous region in the vascular cylinder above the position where the leaf-trace (or branch trace) enters a leaf (or branch).
Gelatinous fiber/layer
A non-lignified fiber which appears gelatinous-like with light microscopy. Layers of such fibers comprise reaction wood.
Generative cell
The smaller haploid cell in a pollen grain that divides (most often in the pollen tube) to form two sperm cells.
Gerontoplast
A type of chromoplast typically found in senescent cells.
Gland
A multicellular secretory structure.
Glandular hair (trichome)
A trichome with an enlarged unicellular, or multicellular secretory cells, at the terminus.
Glutaraldehyde
A five-carbon dialdehyde commonly used as a primary chemical fixative for light and electron microscopy.
Golgi apparatus
A system of interconnected dictyosomes of similar function in a cell.
Granum(a)
Stack(s) of chloroplast thylakoids.
Gravitropism
A directional growth response to the influence of gravity. Induced by mechanical and hormonal (plant growth regulator) influences.
Ground epidermis
Cells of the epidermis of stems and leaves not possessing trichomes and not differentiated as guard cells. Also designated as "pavement cells."
Ground meristem
A primary meristem derived from the apical meristem and giving rise to primary 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.
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