e- (L. e: outside of, coming from inside, without) prefix. Meaning without, or free from, or away from or out of.

ear n. The seed bearing spike of a grass.

eared See auriculate.

earlet See spikelet.

early wood The wood formed early in a growth period, typically relatively low in density and with large cells.

ebeneous (Gr. ebenos: ebony) adj. Ebony in color; black.

ebracteate (L. e: without: bractea: thin metal plate) adj. Without bracts.

ebracteolate (L. e: without: bractola: thin and small metal plate) adj. Without bracteoles.

eburneous (L. eburneus: of ivory) adj. Ivory-white.

ecad n. A habitat form. An organism showing somatic adaptations to a certain environment that are not hereditary. Cf. phenotype, ecotype. Syn. ecophene, environmental form.

eccentric (L. eccentros: eccentric) adj. Off-center; not positioned directly on the central axis.

ecesis (Gr. oikŕsis: an inhabiting, an establishing) n. The successful establishment of a plant or animal in a new habitat.

echard n. Soil water not available for absorption by plants.

echinate (L. echinus: hedgehog, sea urchin) adj. Set with prickles; prickly, like a hedgehog; having sharp points; roughened by blunt spiny projections.

echinulate (L. echinus: hedgehog, sea urchin) adj. With very small prickles or spines

eciliate (L. e: outside of, coming from inside, without; cilium: eyelid, eyelash) adj. Lacking cilia.

ecize v. To become established, to spread, to invade. Cf. ecesis.

ecocline n. The rate of increase or decrease of a variable character in the adaptation of a species, associated with environmental changes. Cf. geocline. The group exhibiting such a gradient. A gradient of ecosystems along an environmental gradient, including both the gradient of natural communities and the complex gradient of environmental conditions. Cf. coenocline.

ecological adj. See ecology.

ecologically adj. See ecological.

ecological amplitude The variety of environmental conditions within which an organism can survive and replace itself, or a process can function. Cf. tolerance, optimum, pessimum. Also ecological valence.

ecological bonitation The numerical statement of well-being of an organism or group during a season or in a specific locality. Cf. bonitation, biotic potential.

ecological efficiency A mathematical statement of the ratio between the energy available to an organism or group or group processes, and the energy actually expended. For example, a bear may use less calories to hunt a rabbit during the summer than the calories gained from the rabbit, but winter hunting expends more than is gained, so it is more ecologically efficient for bears to hibernate. A 10 percent gain is average, 20 percent very good, 5 percent typical of the top of the food chain.

ecological equilibrium See the balance of nature, dynamic equilibrium.

ecological equivalence The case in which two or more species have enough similarities so that any could replace the other in a specified habitat. Cf. ecological amplitude, niche.

ecological equivalent An organism capable of replacing another in a habitat. Cf. ecological equivalence, vicariation.

ecological factor Any variable of the environment that impacts the life of one or more organisms. May be classified into A: climatic, physiographic, edaphic and biotic factors; or B: direct, indirect, and remote factors. Cf. biotic, limiting factor, density dependent factor.

ecological longevity Life span; the average length of life of a species under stated conditions.

ecological pyramid The concept that in most food chains, the number of individuals decreases at each stage, with huge numbers of tiny individuals at the base and a few large individuals at the top, as displayed by millions of plankton, a moderate number of large fish, and a few eagles. Also Eltonian pyramid.

ecological valence See ecological amplitude.

ecologic dominance The state in communities in which one or more species, by their size, number or coverage, exert considerable influence or control over the associated species.

ecology (Gr. oikos: house; logos: word) n. Branch of science concerned with the interrelationships of organisms and their environments esp. as manifested by natural cycles and rhythms, community development and structure, interaction between different kinds of organisms, geographic distributions and population alteration.

ecophene See ecad.

ecorticate adj. Without a cortex.

ecospecies n. A taxonomic species described in terms of its ecological characteristics, usually including two or more ecotypes capable of interbreeding.

ecostate (L. e: without; costa: rib) adj. Without a midrib (costa).

ecosystem (eco[logy]) + system) n. A community of plants and animals within a particular physical environment which is linked by a flow of materials through the non-living (abiotic) as well as the living (biotic) sections of the system. Thus, ecosystems can range in size from the whole earth to a drop of water, although in practice, the term ecosystem is generally used for units below the size of biomes, such as sand dunes, or an oak woodland.

ecotone (eco[logy]) + Gr. tonos: tension) n. The transition zone between two different plant communities, as that between forest and prairie.

ecotype (eco[logy]) + Gr. typos: mark) n. A distinct form of a species occupying a particular habitat; those individuals adapted to a specific environment. See also ecad.

ectexine n. The outer part of the exine, which stains positively with basic fuchsin in optical microscopy and has higher electron density in conventionally prepared TEM sections, includes the foot layer (nexine 1), if present. Also ektexine.

ectocarp (Gr. ektos: outside; karpos: fruit) See exocarp.

ectomycorrhiza n. The mutualistic association between fungi and roots in which fungal hyphae invest the roots and weave between between the cells, but do not penetrate them.

ectoparasite n. A parasite that lives on the outer surface of the body, such as fleas, lice, or ticks.

ectophloic (Gr. ektos: outside; phloios: [inner] bark) adj. having phloem only on the outer side of the stele; cf. amphiphloic.

ectophyte (Gr. ektos: outside; phyton: plant) n. a parasitic plant growing on an animal or another plant.

ectotrophe n. See ectotrophic.

ectotrophic (Gr. ektos: outside; trophŕ: food) adj. Of a mycorrhiza growing outside the root or between the cells. Cf. endotrophic, mycorrhiza. Describes an organism that gets its nutrients from the outside surface of its host.

eczema n. A noncontagious inflammation of the skin, characterized chiefly by redness, itching, and the outbreak of lesions that may discharge serous matter and become encrusted and scaly.

edaphic (Gr. edaphos: soil) adj. Relating to, or determined or influenced by the conditions of the soil. Edaphic factors that influence soil organisms are derived from the development of soils and are both physical and biological (e.g. mineral and humus content, and pH).

edaphically See edaphic.

edaphic climax See edaphic community.

edaphic community A climax stage determined by factors related to the soil, pH, drainage, salinity, etc. Cf. physiographic climax, biotic climax. Also edaphic climax.

edaphic factor A condition of the soil that is physical, chemical, or biological that influences organisms growing there. Cf. biotic, climatic, ecological factor

edaphology (Gr. edaphos: soil; logos: word) n. The study of soils; the science that deals with the influence of soil and other media on the growth of plants.

edaphon (Gr. edaphos: soil) n. An organism that lives in the soil, such as a fungus, nematode, bacterium, etc. The aggregate of organisms in the soil, with the exception of plant parts like roots. CF. plankton.

edema n. An abnormal excess accumulation of serous fluid in connective tissue or in a serous cavity, called also dropsy. Also oedema.

edentate (L. edentatus: without teeth) adj. Without teeth, i.e. with entire leaf margins.

edge effect The impact of two diverse communities where they abut, such as where a stream adjoins a prairie. Cf. ecotone.

effective temperature range The spread between the highest and lowest temperatures in which an organism can survive and reproduce. Cf. ecological amplitude, tolerance.

effigurate adj. In lichens, of pseudocyphellae, particularly on the upper surface, having a definite form or figure.

efflorescence (L. efflorescere: to flower) n. The production of flowers; the period of flowering.

effuse (L. effusus: spread) adj. Of an inflorescence etc., spreading loosely; stretched out flat especially as a film-like growth. See patulous.

egg apparatus The egg cell or female gamete and two associated synergid cells at the apex of the embryo sac immediately adjacent to the micropyle.

egg cell See oosphere.

eglandular (L. e: without; gland, glandis: acorn) adj. Without glands.

Eifelian n. 1. An age in the Middle Devonian epoch preceded by the Emsian, followed by the Givetian, and dated at 386.0 to 380.8 million years ago. 2. The name of the corresponding European stage, which is roughly contemporaneous with the upper Cunninghamian (Australia) and upper Onesquethawian (N. America).

ektexine See ectexine.

elaioplast n. A protoplasmic body in plants in which oil is formed and stored; an unpigmented type of plastid modified as an oil-storage organelle. Cf. plastid.

elaiosome (Gr. elaion: oil; s˘ma: body) n. An appendage of a seed, usually rich in oil, not essential for the viability of the seed but attractive to fauna (especially ants) as a food for larvae etc. and hence an aid to dispersal by such fauna. See myrmecochory.

elaminate (L. e: without; lamina: leaf, plate) adj. Without a blade.

elater (Gr. elatŕr: driver) n. Structures attached to spores to aid in dispersal; an elongated, spirally thickened, hygroscopic cell in the capsule of a liverwort, derived from sporogenous tissue and assisting in spore dispersal; an appendage to the spore of Equisetum.

elaterocyte n. Diploid cell within most liverwort and all hornwort capsules that differentiates into an elater (liverworts) or undergoes a few mitotic divisions to form a pseudoelater (hornworts).

elaterophore n. A tuft or brush-like cluster of elater-like cells attached to either the base or apex of a capsule in a few liverworts; e.g. Riccardia, Pellia.

eligulate (L. e: outside of, coming from inside, without; ligula: small tongue) adj. Without strap organs, without ligule.

elimbate adj. Lacking a border; referring to leaves without strongly differentiated marginal cells.

elite tree A plant of proved good combining ability.

ellagic acid A lactone, a hydroxy acid formed by the hydrolysis of some tannins, for the combined state.

ellagitannin A hydrolyzable tannin, ester involving dimers of gallic acid.

ellipsoid (Gr. elleipsis: omission; eid˘: to seem) n. A solid with an elliptical outline, i.e. elliptic in long section and circular in cross section.

ellipsoidal (Gr. elleipsis: omission; eid˘: to seem) adj. In the form of an ellipse, an oval solid.

elliptic (Gr. elleipsis: omission) adj. An outline that is oval, narrowed to rounded at the ends and widest at about the middle (as the outline of a football). Also elliptical.

elliptical (Gr. elleipsis: omission) adj. Having the outline of an ellipse, broadest at middle and narrower at each end, oblong with convex sides or ends. Also elliptic.

elongate (Lat. elongare, to lengthen) adj, v. To lengthen, prolong, to be of slender or tapering form. Much longer than wide; drawn out; lengthened; stretched out.

elongated adj. See elongate.

Eltonian pyramid See ecological pyramid.

eluvial layer See A horizon.

emarginate (L. e: withaout; margo, marginis: edge) adj. Said of leaves, sepals, or petals, and other structures that are notched at the apex; e.g. Tortula.

emasculation The Removal of the anthers from a flower.

embedded adj. Said of an anther when the thecae are surrounded by and embedded in a well-developed connective for more or less their entire length.

embracing adj. Clasping at the base.

embryo (Gr. embryon: any new-born being) n. The young plant within a seed. The structure in plants that develops from the zygote prior to germination. In seed plants the zygote is situated in the embryo sac of the ovule. It divides by mitosis to form the embryonic cell and a structure called the suspensor, which embeds the embryo in the surrounding nutritive tissue. The embryonic cell divides continuously and eventually gives rise to the radicle (young root), plumule (young shoot), and one or two cotyledons (seed leaves). Changes also take place in the surrounding tissues of the ovule, which becomes the seed enclosing the embryo plant.

embryogenesis (Gr. embryon: any new-born being; genesis: creation, production) n. The mechanism of development of organisms; the formation and subsequent development of plumule, radical, and cotyledons in a plant, i.e. the process of embryo development.

embryogenetics The heredity and variation of embryos; the genetics of embryos.

embryophyte (Gr. embryon: any new-born being; phyton: plant) n. Synonym for the Plantae, as here defined. It includes all green photosynthetic organisms which begin the development of the sporophyte generation within the archegonium.

embryo sac A large cell that develops in the ovule of flowering plants. It is equivalent to the female gametophyte of lower plants, although it is very much reduced. Typically, it contains eight nuclei formed by division of the megaspore mother cell. The oosphere (egg cell), which is associated with two synergid cells to form the egg apparatus, is fertilized by a male nucleus and becomes the embryo. The two polar nuclei fuse with a second male nucleus to form a triploid nucleus that gives rise to the endosperm. The three remaining nuclei form the antipodal cells.

embryotega n. A callus near the hilum of certain seeds, which is detached during germination; a small circular thickening near the seed scar on the seeds of some plants, such as members of the spiderwort family.

emerge (L. emergere: to rise up, rise out) vt. To rise out of a fluid or other covering.

emergence (L. emergere: to rise up, rise out) n. Refers to outgrowths on the surface of an organ, such as warts, prickles, etc.

emergent (L. emergere: to come out, to rise) adj. Applied to any of various plants (as a cattail) rooted in shallow water and having most of the vegetative growth above the water; partially exposed, referring to capsules or perianths only partly projecting beyond the tips of perichaetial leaves. Cf. exserted, immersed.

emersed (L. emersus: come out, risen) adj. Standing out of or rising above a surface as an aquatic plant with flower stalk standing out of water.

emersed plants Plants growing with their roots and a portion of the shoot below the water and the remainder of the shoot above the surface of the water.

emetic (L. emeticus: that induces vomiting) adj, n. (Of) a herbal medicines that can induce vomiting. Direct, or gastric, emetics, which act directly on the stomach, include syrup of ipecac, sulfate of zinc or copper, alum, ammonium carbonate, mustard in water, or copious quantities of warm saltwater. Indirect, or systemic, emetics, such as apomorphine, induce vomiting by acting indirectly through the blood on the brain center that controls vomiting. Emetics are not used to treat poisoning by strong acids or alkalis, petroleum distillates such as kerosene, or substances causing convulsions

emmenagogue (Gr. emmŕnos: that come back ebvery month, entrula flow; agogŕ: driving) n. A drug or agent that induces or hastens menstrual flow.

emollience n. See emollient.

emollient (L. emollire: to soften up) adj., n. (Of) an agent that will soften, soothe and protect the part when applied locally. Usually confined to agents affecting the surface of the body e.g., ointment of rose water, olive oil petrolatum.

emollition n. See emollient.

Emsian n. 1. An age in the Early Devonian Epoch preceded by the Siegenian, followed by the Eifelian, and dated at 390.4 to 386.9 million years ago. 2. The name of the corresponding European stage, which is roughly contemporaneous with the lower Cunninghamian (Australia) and part of the Onesquethawian (N. America).

enantiomorphous adj. Said of asymmetric flowers with mirror image morphologies, as of the flowers borne along the stem of species of Chamaechrista or the paired flowers in inflorescences of Marantaceae.

enantiomer n. Either one of a pair of compounds (crystals or molecules) that are mirror images on each other but are not identical, Synonym: enantiomorph.

enantiomorph See enantiomer.

enantiostylous adj. Refers to flowers whose stamens bend to the left or right, with the styles in the opposite direction.

enation (L. enatus: born, grown) n. An abnormal growth of an organ or of an excresence upon any part of a plant; an epidermal outgrowth; a projection or outgrowth from the surface of an organ or structure.

enation theory The theory that accounts for the origin of the fern leaf by suggesting that it arose from the development of simple outgrowths (enations). Any such theory has to account for the large, branching fronds of a fern with branching veins (a 'megaphyll') and also for the small leaves with one or two veins ('microphyll').

encina n. The live oak Quercus virginiana.

encinal adj. Refers to a grove or forest of evergreen oaks. See encina.

encyst (Gr. en: in; kystis: swollen sac, bladder v. To become enclosed in a cyst.

encystation n. See encyst.

encystment (Gr. en: in; kystis: swollen sac, bladder n. A state of inactivity of an organism surrounded by a protective case; metabolism is lowered while resistance is raised to unfavorable environmental conditions. A process which, among some of the lower forms of life, precedes reproduction by budding, fission, spore formation, etc. Cf. cyst.

end- prefix. (Before a vowel.) Meaning inner.

endangered See endangered plant.

endangered plant A species adjudged to be threatened with extermination.

endarch n. A type of xylem maturation in which protoxylem is internal to metaxylem and development prodeeds centrifugally (from the inside out); for comparison see exarch and mesarch.

endemic (Gr. endŕmos: native) adj. A plant that is native to a particular, specific country or region or geographic area or edaphic type; not introduced or naturalized. Describing a plant or animal species that is restricted to one or a few localities in its distribution. Endemic species are usually confined to islands and are vulnerable to extinction. Describing a disease or a pest that is always present in an area. For example, malaria is endemic in parts of Africa.

endemism (Gr. endŕmos: native) n. The occurrence of highly adapted plants or animals in an area. Cf. endemic.

endexine n. The inner part of the exine, which stains.

endo- prefix. Meaning inner.

endocarp (Gr. endo: inside; karpos: fruit) n. The innermost layer of the pericarp. The inter layer of the wall of a matured ovary; when its texture differs from the outer wall, it may be hard and stony, membranous, or fleshy. In a drupe, the stony layer surrounding the seed. adj. Of a lichen having the apothecia embedded in the thallus.

endochory (Gr. endo: within; kh˘re˘: to move) n. Dispersal of an organism, particularly a seed, by an animal which carries it from one place to another, often in its digestive tract. Syn. endozoochory.

endodermis (Gr. endon; inside; derma: skin) n. Literally 'inner skin", this is a layer of cells which surrounds the central core of vascular tissue, and which helps to regulate the flow of water and dissolved substances. The thin sheath of cells bounding the stele and separating it from the cortex. The inner layer of the pericarp of a fruit. cf mesocarp and exocarp. See endogamous.

endogamous (Gr. endo: within; gamos: marriage) adj. Self-pollinating. See endogamy. Syn. endogamic.

endogamy (Gr. endo: within; gamos: marriage) n. Pollination between two flowers from the same plant. Cf. exogamy.

endogenous (Gr. endo: within; genna˘: to produce) adj. Describing a substance, stimulus, organ, etc., that originates from within an organism; originating from internal rather than superficial cells or tissues, e.g. the endogenous branches in some liverworts. For example, growth rhythms not directed by environmental stimuli are termed endogenous rhythms. Lateral roots, which always grow from inside the main root rather than from its surface, are said to arise endogenously. Cf. exogenous.

endohydric adj. Having water transport essentially internal. Cf. exohydric, mesohydric.

endolithic aj. Immersed in rock.

endomycorrhiza n. The mutualistic association between zygomycetous (usually) fungi and roots in which the fungal hyphae penetrate the root cells.

endonuclease n. Any of a group of enzymes that catalyze the hydrolysis of bonds between nucleic acids in the interior of a DNA or RNA molecule.

endoperidia See endoperidium.

endoperidium n. (pl. endoperidia) The inner layer of a multilayered peridium.

endophloeodal adj. Immersed in bark.

endophyte (Gr. endo: within; phyton: plant) n. A plant living within another plant. Growing within the tissue of a plant. Syn. entophyte.

endophytic (Gr. endo: within; phyton: plant) See endophyte.

endophytically See endophytic.

endophytous See endophytic.

endoplasm (Gr. endo: within; plasma: something molded) n. The inner cytoplasm that in many cells is more granular and fluid than the outer cytoplasm. The inner granular layer of protoplasm in ovum development. Syn. endoplasma, entoplasm, endosarc. Cf. ectoplasm.

endoplasma See endoplasm.

endosarc See endoplasma.

endosmosis (Gr. endo: within; ˘smos: pushing) n. The flow of a substance from a area of lower concentration to one of greater concentration. Cf. exosmosis.

endosperm (Gr. endo: within; sperma: seed) n. The nutritive tissue surrounding the embryo of a seed derived from the fusion of a sperm cell with the polar nuclei of the embryo sac. Nutrients enclosed in the seed to sustain early growth of the embryo. A nutritive tissue, characteristic of flowering plants, that surrounds the developing embryo in a seed. It develops from nuclei in the embryo sac and its cells are triploid. In endospermic seeds it remains and increases in size; in nonendospermic seeds it disappears as the food is absorbed by the embryo, particularly the cotyledons. Many plants with endospermic seeds, such as cereals and oil crops, are cultivated for the rich food reserves in the endosperm. See perisperm.

endospermic adj. Relating to, accompanied by, or containing, endosperm.

endosporal adj. Related to the endospore.

endospore (Gr. endo: within; spora: seed) n. An asexual spore developed within the cell especially in bacteria. A (usually) resistant spore formed within the cell of a bacterium, allowing it to survive in unfavourable conditions. The resting stage of certain bacteria, formed in response to adverse conditions. The bacterial cell changes into a partially dehydrated core, enclosed in a multilayered protein coat. On return to favourable conditions the spore germinates and reverts to the normal vegetative form of the organism. Endospores can remain viable for long periods, perhaps several thousands of years. There are even reports of successful germination of endospores obtained from the guts of prehistoric bees preserved in amber for 25-40 million years. The inner coat of a spore. Syn. endosporium.

endosporia See endosporium.

endosporic adj. Of the occurrence of one or more mitotic divisions within the confines of the spore wall to produce a multicellular protonema prior to spore wall rupture; e.g. Pellia, Dicnemon, Drummondia. Also endosporal.

endosporium n, (pl. endosporia) See endospore.

endosporous adj. Related to the endospore.

endosporously See endosporous.

endostomal n. Where the micropyle of an ovule is formed from the inner integument alone.

endostome (Gr. endo: within; stoma: mouth) n. The inner row of teeth of a peristome; the inner circle of a diplolepidous peristome, formed from contiguous periclinal wall-pairs of the primary and inner peristomial layers; typically a weak membranous structure consisting of a basal membrane bearing segments and cilia. The endostome is homologous with the haplolepidous peristome.

endosubstratic adj. Growing within the substratum.

endosymbiosis (Gr. endo: within; syn: with, together; bios: life) n. When one organism takes up permanent residence within another, such that the two become a single functional organism. Mitochondria and plastids are believed to have resulted from endosymbiosis.

endotesta n. The delicate, innermost layer of the integument in some seeds; cf. sarcotesta and sclerotesta.

endothecia See endothecium.

endothecial adj. See endothecium.

endothecium (Gr. endo: within; thŕkŕ: case, box) n. (pl. endothecia) The lining of the cavity of an anther; in mosses, the central mass of cells in the rudimentary capsule, from which the archespore is generally developped; in bryophytes, the central mass of cells in the capsule, including the spores and columella; in Sphagnum and hornworts the endothecium only produces the columella.

endothelia Seeendothelium.

endothelium n. (pl. endothelia) The cells of the inner epidermis of the inner (or only) integument of the ovule that are radially elongated and metabolically very active.

endotrophic adj. Refers to fungi that grow within roots; nourished or receiving nourishment from within; for example, fungi or their hyphae receiving nourishment from plant roots in a mycorrhizal association. See ectotrophic, mycorrhiza.

endozoochore (Gr. endo: within; z˘on: animal; kh˘re˘: to move) n. A propagule like a seed that is dispersed by being carried inside an animal's body, such as a cherry seed, Prunus, being swallowed by a bird and dropped in feces.

endozoochory (Gr. endo: within; z˘on: animal; kh˘re˘: to move) n. Dispersal of seed through animal ingestion and excretion, e.g. Fragaria. Syn. endochory.

enema n. The injection of a fluid into the rectum to cause a bowel movement. The fluid injected.

enervate adj. Lacking a costa. Cf. ecostate

enphytotic adj., n. An endemic disease of plants; (of) a plant disease regularly affecting but not destroying the plants in a given area; occurring regularly among the plants of a region, such as an endemic fungus; any enphytotic disease. Cf. epiphytotic.

enrichment zone The cluster of flowers that terminates a lateral branch of a synflorescence.

ensiform (L. ensis, sword) adj. Having sharp edges and tapering to a slender point; having a shape suggesting a sword (as an Iris leaf); xiphoid.

entheogen n. A psychoactive substance used in a religious or shamanic context. Historically, entheogens are derived primarily from plant sources and have been used in a variety of traditional religious contexts. With the advent of organic chemistry, there now exist many synthetic substances with similar properties. More broadly, the term entheogen is used to refer to such substances when used for their religious or spiritual effects, whether or not in a formal religious or traditional structure. This terminology is often chosen to contrast with recreational use of the same substances. These spiritual effects have been demonstrated in peer-reviewed studies, though research remains difficult due to ongoing drug prohibition. The word entheogen is derived from two Ancient Greek words, entheos and genesthai. Entheos means literally 'in God", and, more freely translated, inspired. The Greeks used it as a term of praise for poets and other artists. Genesthai means 'to cause to be'. So an entheogen is 'that which causes (a person) to be in God'.

entheogenic adj. See ethneogen.

entire adj. Having a margin devoid of any indentations, notches, teeth, or lobes; without toothing or division; note that lobed leaves can also have entire margins.

entomophagous (entomos: insect; phagos: glutton) adj. Insect-eating; insectivorous.

entomophilous (Gr. entomos: insect; philos: friend, loved) adj. Pollinated by insects. See entomophily.

entomophily (Gr. entomos: insect; philos: friend, loved) n. Pollination of a flower in which the pollen is carried on an insect. Entomophilous flowers are usually brightly coloured and scented and often secrete nectar. In some species (e.g. primulas) there are structural differences between the flowers to ensure that cross-pollination occurs. Other examples of entomophilous flowers are orchids. Cf. anemophily, hydrophily.

entophyte (Gr. entos inside; phyton: plant) n. A plant living within another plant. Growing within the tissue of a plant. Syn. endophyte.

entoplasm See endoplasm.

entotrophe n. See entotrophic.

entotrophic (Gr. endo: inside; trophŕ: food) adj. Of a mycorrhiza growing inside the cells of the root.

enzyme n. Complex protein which helps to speed biochemical reactions. Enzymes are important in the construction and degradation of other molecules.

Eocene (Gr. e˘s: dawn; kainos: new) n. Tertiary epoch which began at the end of the Palaeocene (56.5 million years ago) and ended at the beginning of the Oligocene (35.4 million years ago). It is noted for the expansion of mammalian stocks (horses, bats, and whales appeared during this epoch), and the local abundance of Nummulites (marine protozoans of the Foraminiferida). The Eocene Epoch is divided into the Ypresian, Lutetian, Bartonian, and Priabonian Ages.

eolian See aeolian.

eon (Gr. ai˘n: long space of time) n. The largest geologic-time unit, incorporating a number of eras. The equivalent chronostratigraphic unit is the eonothem. Originally, two eons were proposed in 1930 by G. H. Chadwick. The younger was the Phanerozoic Eon (time of evident life), comprising the Cenozoic, Mesozoic, and Palaeozoic Eras, and this term is still used. The term suggested for the preceding eon was the Cryptozoic (time of hidden life). This time has also been called the Archaeozoic (time of most ancient life), but most commonly has been known simply as the Precambrian. Three eons have been proposed for Precambrian time: the Priscoan for time before 4000 million years ago; the Archaean for 4000 to 2500 million years ago; and the Proterozoic for 2500 to 590 million years ago; the term 'Precambrian' is still in frequent use but is informal. Syn. aeon.

eonothem An eonothem is a chronostratigraphic unit greater than an erathem. The geochronologic equivalent is an eon. Three eonothems are generally recognized, from older to younger, the Archean, Proterozoic and Phanerozoic eonothems. The combined first two are usually referred to as the Precambrian. The eons take the same name as their corresponding eonothems. At present it is a little-used term.

eophyll n. The first leaf (or leaves) produced by the seedling.

epappose (L. e: out of; pappus: down of thistle) adj. Without a pappus.

epetiolate (L. e: out of; petiolus: petiole, peduncle) adj. Without a petiole, as in a sessile leaf.

epetiolulate (L. e: out of; petiolus: petiole, peduncle) adj. Without a petiolule, as in a sessile leaflet.

epharmone n. A growth form adopted to the environment. An organism which is adapted to changes in its environment. Cf. ecad, epharmony.

epharmony n. The changes of processes or shape of structures by which an organism adapts to an altered environment; a development in complete harmony with environment; harmonic relation between structure and environment. Cf. adaptation, epharmone, ecad.

ephedrine n. A protoalkaloid.

ephemeral (Gr. ephemeros: lasting one day) n. Referring to an organ living a very short time, usually a day or less; lasting a very short time.

ephemerally adv. See ephemeral.

ephemeralness n. See ephemeral.

epi- (Gr. epi: upon, above) prefix. Meaning upon, above.

epibenthic (Gr. epi: upon, above; benthos: bottom, depth) adj. Living on the surface of bottom sediments in a water body; living above the bottom. Also demersal.

epibiosis (Gr. epi: upon, above; bios: life) n. Any relationship between two organisms in which one grows on the other but is not parasitic on it. Cf. o: epiphyte, epizoite.

epibiotic (Gr. epi: upon, above; bios: life) adj., n. An endemic surviving from a former habitat; a relic. Cf. epibiosis.

epiblast (Gr. epi: upon, above; blasti, blastos: bud, sprout) n. A small flap of tissue on the embryo of some members of the grass family.

epicalyx (Gr. epi: upon, above; kalyx: calyx) n. A whorl of bracts, just below a flower, looking like a second calyx, as in Malva.

epicarp (Gr. epi: upon, above; karpos: fruit) n. The outer layer of the wall of a fruit, i.e. the 'skin', i.e. the outermost layer of the pericarp. See exocarp.

epichil n. The terminal part of the lip in some orchids, distinctly different from the form of the basal part, as in the genus Stanhopea. Also epichile, epichilium.

epichile See epichil.

epichilia See epichilium.

epichilium n. (pl. epichilia) See epichil.

epicormic (Gr. epi: upon, above; kormos: piece [of wood]) adj. Of buds, shoots or flowers, borne on the old wood of trees (applied especially to shoots arising from dormant buds after injury or fire).

epicortex n. In lichens, a thin, homogeneous polysaccharide layer over the surface of the cellular cortex, which may have regular pores or breaks (using the scanning electron microscope).

epicortical (Gr. epi: upon, above; L. cortex: bark) adj. On top of the bark, i.e. outside the bark.

epicorticate adj. Covered by epicortex; of apices of isidia, eroding or breaking open very easily and often appearing hollow or erumpent, or becoming pustulate.

epicotyl (Gr. epi: upon, above; kotylos: cup) n. That portion of the embryonic stem above the cotyledons, i.e. the part of the embryo of a germinating seed that is above the point of insertion of the cotyledons. The epicotyl comprises the plumule, which gives rise to the shoot system. See plumule.

epicuticular adj. Onto the cuticle,

epicuticular wax Wax of variable composition and morphology found on the outer surfaces of the above-ground parts of plants.

epicutis n. The outermost layer of the pellis (cuticle), properly called suprapellis.

epidermis (Gr. epi: upon, above; derma: skin) n. The outermost layer of cells of an organ, usually only one cell thick, frequently fragile and ephemeral.

epigaeous adj. See epigeal.

epigeal (Gr. epi: upon, above; gŕ: earth); adj. Describing seed germination in which the seed leaves (cotyledons) emerge from the ground and function as true leaves. Examples of epigeal germination are seen in sycamore and sunflower. Cf. hypogeal. Syn. epigaeous, epigeous.

epigenetic adj. Of a change in some morphological character as a result of localized influences different from the normal or usual pattern that occurs after development of an organism is initiated; a term used in connection with changes that result from plant tissue culture or animal embryological studies (used in apposition to genetic).

epigenous (Gr. epi: upon; genna˘: to produce) adj. Growing on the surface, as a fungus growing on the surface of a leaf.

epigeous adj. See epigeal.

epigonia See epigonium.

epigonianthus n. (pl. epigonianthi) A three-keeled perianth with two lateral and one dorsal (antical) keels. Cf. hypogonianthus.

epigonium n. (pl. epigonia) The protective envelope of the embryo or young sporophyte, derived primarily from the archegonial venter, in most mosses it ruptures into two parts, a vaginula that encircles the seta base and the foot, and a calyptra that is carried aloft as a covering on the capsule; i.e. Bryobartramia has a persistent epigonium.

epigynous (Gr. epi: upon; gynŕ: woman) adj. Growing upon the top of the ovary or seeming to do so, as petals, sepals, and stamens, i.e. with the ovary inferior to the other floral parts. Cf. hypogynous, perigynous.

epigyny (Gr. epi: upon; gynŕ: woman) n. The condition of being epigynous. A floral arrangement in which the ovary is completely enclosed by the receptacle so that the stamens and perianth arise above it, from the top of the receptacle; i.e. the ovary is inferior. The perianth and stamens are said to be epigynous with respect to the ovary, as seen in the daffodil. Cf. hypogyny, perigyny.

epihymenia See epihymenium.

epihymenium n. (pl. epihymenia) The uppermost (often pigmented) layer of the hymenium, above the asci.

epilithic (Gr. epi: upon; lithos: stone) adj. Of plants growing on stones, on surface of rocks. Cf. saxicolous. Also lithophytic.

epinastic (Gr. epi: upon; nastos: pressed) adj. Growing faster on one side of a leaf or stem than on the other. See epinasty.

epinasty (Gr. epi: upon; nastos: pressed) n. Increased growth on the upper surface of an organ or part, causing it to bend downwards.

epipetalous (Gr. epi: upon; petalon: leaf) adj. Attached to the petals. Of a flower having the stamens inserted on the petals.

epipetreous See epipetric.

epipetric (Gr. epi: upon; petros: stone) adj. Growing on a rock. Also epipetreous. Cf. saxicolous, epilithic.

epiphloedal (Gr. epi: upon; phloios: bark) adj. Growing on bark, as lichens. Syn. epiphloedic.

epiphloedic adj. See epiphloedal.

epiphragm n. (pl. epiphragmata) A circular membrane positioned horizontally over the capsule mouth of some mosses, attached to the tips of the peristome teeth and partially closing the mouth of the deoperculate capsule; e.g. Polytrichum and Funaria. A membrane covering the mouth of a deoperculate capsule.

epiphragmata See epiphragm.

epiphyll (Gr. epi: upon, above; phyllon: leaf) n. An epiphyte that grows on the surface, especially the upper surface, of leaves, as a lichen.

epiphyllous (Gr. epi: upon, above; phyllon: leaf) adj. Growing on leaves, e.g. applied to vegetatively propagated plantlets in some Crassulaceae. lichens, growing on the surface (usually upper) of leaves, the mycobiont not penetrating the leaf surface.

epiphyte (Gr. epi: upon, above; phyton, plant) n. A plant growing on, but not parasitic on, another plant, and merely uses the plant for structural support, or as a way to get off the ground and into the canopy environment (often loosely applied to plants, such as orchids, that grow on vertical rock faces). An epiphytic plant then derives its moisture and nutrients from the air and rain. Many orchids and bromeliads are epiphytes. Cf. parasite, saprophyte.

epiphytic (Gr. epi: upon, above; phyton, plant) adj. Of, relating to, or being an epiphyte. Living on the surface of plants, usually trees, without deriving or contributing nutritional benefit from them. See epiphyte.

epiphyton (Gr. epi: upon, above; phyton, plant) n. A collection of organisms scattered over surfaces submerged in water, that may later become mechanically associated. Cf. lasion, periphyton.

epiphytotic adj., n. Of, relating to, or characterized by a sudden or abnormally destructive outbreak of a plant disease, usually over an extended geographic area; common, even epidemic, among plants in general, as some fungus diseases like mildew. Cf. enphytotic.

epipsamma n. In lichens, a granular zone (usually pigmented) permeating upper parts of hymenium but more or less distinct from epithecium, especially in Rhizocarpon.

episepalous (Gr. epi: upon, above; sepalous: see sepal) adj. Borne on or attached to the sepals.

epispastic adj., n. (Of) a herbal medicine which can cause blisters when applied to the skin, and causes sloughing.

episporia See episporium.

episporial adj. Of the episporium.

episporium n. (pl. episporia) The thin outer covering of a spore. Cf. exosporium.

epistase n. A structure in the ovule made up of thick-walled cells at the tip of the nucellus.

epistasis n. The interaction between nonallelic genes in which one gene has a dominant effect on the expression of the other; the suppression of the effect of a gene by another, nonallelic gene. The gene suppressed is said to be hypostatic. More generally, the term epistasis is used to describe all types of inter-allelic interaction whereby manifestation at any locus is affected by genetic phase at any or all other loci.

epistatic adj. Of lobules of male bracts not overlapping ventrally. Cf. hypostatic.

epistemonous (Gr. epi: upon, above; L. stamen: thread) adj. Attached to the stamens.

epithecia See epithecium.

epithecial adj. See epithecium.

epithecium (Gr. epi: upon, above; thŕkŕ: case, box) n. (pl. epithecia) The surface layer of tissue of the apothecium of lichen andu fungi, formed by the union of the tips of the paraphyses over the asci.

epithelia See epithelium.

epithelium (Gr. epi: upon, above; thŕlŕ: nipple) n. (pl. epithelia) Any tissue which covers a surface, or lines a cavity or the like, and which performs protective, secreting, or other functions, as the epidermis, the lining of blood vessels, etc. adj. Of the epithelium.

epithem n. The mesophyll of an hydathode involved in the secretion of water.

epithet (Gr. epithetos: added) n. The part of a scientific name designating a species or lower division of a genus. For example, in Cyranthus mackenii var. cooperi, mackenii is the species epithet and cooperi is the variety epithet.

epithetic adj. See epithet.

epitropous adj. Said of the curvature of an ovule with respect to the ovary axis, adaxial.

epixylous (Gr. epi: upon, above; xylon: bois) adj. Growing on wood, as certain fungi.

epizoa n. Any external parasitic organism, as fleas.

epizoan adj., n. An epiphyte animal; epibionts can be broken down into their plant (epiphyte) and animal (epizoan) components; of or relating to epizoa; an epizo÷n.

epizoochory (Gr. epi: upon, above; z˘on: animal; kh˘re˘: to move) n. Dispersal of seed attached to the fur of animals, etc., e.g. Carex, Tribulus.

epizo÷n (Gr. epi: upon, above; z˘on: animal) n. (pl. Epizoa) One of the artificial group of invertebrates of various kinds, which live parasitically upon the exterior of other animals; an ectozo÷n. Among them are the lice, ticks, many acari, the lerneans, or fish lice, and other crustaceans.

epoch (Gr. epokhŕ: time interval) n. One of the intervals of geologic time recommended by the International Subcommission on Stratigraphic Terminology. An epoch is ranked as a third-order time unit, and is the equivalent of the chronostratigraphic unit series. Several epochs form a period; several periods an era. Epochs are themselves subdivided into ages. When used formally, the initial letter is capitalized, e.g. Early Devonian Epoch.

epruinose (L. e: outside of, coming from inside, without; pruinosus: frost covered) adj. Lacking bloom or powdery coating upon the surface of the leaf, stem or other plant part; not pruinose.

epulvinate adj. Without a swelling at the base; used of a leafstalk. See pulvinate.

equal (L. Šqualis: equal) adj. Of the same length, as in 'sepals equal petals' means the two are the same length, not that they cannot be told apart as in plants where the two are so inseparable as to be called tepals.

equalling See equal

equidistant adj. Regularly separated or spaced.

equilateral (L. [Šquilateralis: equilateral] Šquus: equal; lateralis: of the side) adj. With sides of equal shape and length. Of stamens, with anthers regularly spaced around the style.

equinoctial (L. [Šquinoctialis: equinoctial] Šquus: equal; nox, noctis: night) adj. With flowers that open regularly at a particular hour of the day. Happening at or near the time of an equinox.

Equisetaceae (L. [equiseta: horsetail] equus, equi: horse; seta: bristle, horse mane) n. A family of the phylum Filicinophyta.

equisetoid (L. equiseta: horsetail; Gr. eid˘: to look like) adj. Resembling Equisetum.

Equisetopsida n. A phylum of the kingdom Plantae. Syn. Sphenophyta.

equisetum (L. [equiseta: horsetail] equus, equi: horse; seta: bristle, horse mane) n. Any plant of the genus Equisetum.

Equisetum (L. [equiseta: horsetail] equus, equi: horse; seta: bristle, horse mane) n. A genus of the family Equisetaceae.

equitant (L. equitare: to ride) adj. Of leaves, folded in half along the midline so that the adaxial surface disappears, and overlapping the edges of a similarly folded leaf on the opposite side of the stem, i.e. of leaves whose bases overlap the leaves within or above them, as in the Iris; referring to conduplicate and strongly sheathing leaf bases; e.g. Fissidens.

era (L. era: era, epoch) n. First-order geologic time unit composed of several periods. The Mesozoic Era, for example, is composed of the Triassic, Jurassic, and Cretaceous Periods. When used formally, as above, the initial letter of the term is capitalized.

eramous (L. e: without; raus: branch) adj. With unbranched stems.

erathem n. The chronostratigraphic unit that is equivalent to the geologic-time unit era. An erathem comprises a number of systems grouped together and takes its name from the corresponding era, e.g. the Mesozoic Erathem would refer to the rocks laid down during the Mesozoic Era. At present it is a little used term.

erect (L. erectus: erect) adj. Vertical or upright; with leaves directed toward stem apex; with leaf margins curved upward (adaxially); with capsules straight, not curved.

erectopatent See erecto-patent.

erecto-patent adj. Midway between erect and patent; spreading at an angle of 45║ or less. Cf. spreading, patent.

eremean (Gr. erŕmos: desert, empty) adj. Pertaining to regions of low, irregular rainfall.

eremophyllous (Gr. erŕmos: desert, empty; phile˘: to like) n. Living in desert.

eremophyte (Gr. erŕmos: desert, empty); phyton: plant) n. A plant that grows in a desert.

ergastic substances The metabolic products of the protoplastl such as starch grains, crystals, fat globules, fluids, etc., that are found in various parts of the cell, including the cell wall.

ergot n. The dark hard-walled mass of hyphae produced by the fungus Claviceps purpurea (see Ascomycota) in the grain of the cereals and other grasses that it parasitizes. Ergots are the sclerotia of this species - resting bodies that germinate in favourable conditions to produce mycelia or ascocarps. They contain alkaloids related to LSD, which cause blood vessels to constrict and are used therapeutically in the treatment of migraine and haemorrhage. Ingestion of infected grain can result in ergot poisoning (ergotism), with symptoms of gangrene and hallucinations - known as 'St Anthony's fire' in the Middle Ages.

ericaceous (L. erice: heather; Gr. ereikŕ: heather) adj. Refers to plants of the family Ericaceae that require an acid soil, generally with a pH of 6 or less. Also ericoid.

ericoid (Gr. ereikŕ: heather; eidos: shape, appearance) adj. Related to the Ericaceae family, resembling one of its genera. See ericaceous.

eriophyllous adj. Having leaves covered with a woolly pubescence.

eroded adj. Irregularly bounded, as if gnawed.

erose (L. erosus: gnawed, nibbled) adj. Having small irregular notches in the margin, as if gnawed; with a margin irregularly incised, finely and irregularly eroded or toothed; of leaves and perianths irregularly notched or ragged, as though gnawed, frequently through abrasion of lamina.

erosulate (L. erosus: gnawed, nibbled) adj. More or less erose.

errant vascular hydrophyte Free-moving water plant. These are the floating aquatic plants.

errhine (Gr. medicine snuffed up the nostrils) adj., n. Designed to be snuffed into the nose; occasioning discharges from the nose; substance, medicine applied to lining of the membrane of the nostrils to create a discharge of mucous.

erucic acid A type of unsaturated fatty acid, a major constituent of most rapeseed and mustard oils.

erumpent (L. erumpere: to break out, to burst) adj. Prominent, as if bursting through the epidermis; appearing to be ready to break throug.

erysipelas n. An acute disease of the skin and subcutaneous tissue caused by a species of hemolytic streptococcus and marked by localized inflammation and fever. Also called Saint Anthony's fire.

escape n. An exotic plant that has spread from cultivation and grows successfully in the wild; a plant originally cultivated, but now growing wild.

escapee n. A plant that has escaped from cultivation and now reproduces on its own. Also escape.

eschar n. A dry scab or slough formed on the skin as a result of a burn or by the action of a corrosive or caustic substance.

escharotic adj., n. Producing an eschar. A caustic or corrosive substance or drug.

esculent (L. esculentus: edible, eatable) adj. Suitable for use as food; edible.

esculetin n. A coumarin.

esorediate (L. e: outside of, coming from inside, without; s˘ros: heap) adj. Lacking soredia.

essential flower parts The stamen and pistil organs of the flower that are required for pollination.

essential oil See essential oils

essential oils Substances with a characteristic scent produced by the glands of aromatic plants. Essential oils may be extracted by distillation, mechanical pressing, or organic solvents and are used in perfumes, food flavourings, and medicines. Examples include attar of roses, lavender oil, and clove oil.

ester n. Any of a class of organic compounds corresponding to the inorganic salts and formed from an organic acid and an alcohol.

estipellate (L. e: without; stipula: stalk, straw) adj. Without stipels.

estipitate (L. e: without; stipes: post, trunk) adj. Without a stipe.

estipulate (L. e: without; stipula: stalk, stem) See exstipulate.

estival See aestival.

estivation (L. Šstivus: of the summer) n. Stagnating or otherwise nonfunctional during the summer months. See also: hibernation. Syn. aestivation.

estrogen n. Any of several major female sex hormones produced primarily by the ovarian follicles of female mammals.

estrogenic adj., n. Promoting or producing estrus. Herbal medicine that stimulates female hormone production or replaces it with plant hormones.

estrous n. See oestrus.

estrum n. A variant of oestrus, oestrum and estrus; see that last word.

estrus (L. ­strus: prophetic or poetic frenzy) n. The period of rut, the period of maximal receptivity of the female. The periodic state of sexual excitement in the female of most mammals, excluding humans, that immediately precedes ovulation and during which the female is most receptive to mating; heat. Also oestrus, oestrum, estrum.

etaerio (Gr. etaireia: association of friends) n. A cluster of fruits formed from the unfused carpels of a single flower. For example, the anemone has an etaerio of achenes, larkspur an etaerio of follicles, and blackberry an etaerio of drupes.

ethene See ethylene.

ethereal oils The more or less volatile and often aromatic susbtances made up of various kinds of terpenes, including diterpenes, sesquiterpenes, etc.

ethnobotany (Gr. ethnos: race, people, nation; botanŕ: herbe) n. The plant lore and agricultural customs of a people; the systematic study of such lore.

ethnopharmacology (Gr. ethnos: race, people, nation; pharmakon: drug, medicine; logos: word) n. The study and practice of medicines used by a people.

ethology (Gr. ethos: custom, habit; logos: word) n. The study of animal behaviour. A major principle of ethology is that animal behaviour has been subject to the process of evolution by natural selection. The behaviour of animals has evolved in such a way that it promotes the chances of the survival of their offspring. For example, the adults of many ground-nesting birds will put themselves at risk by distracting a predator from eggs or chicks. See altruism.

ethylene n. A colourless gaseous hydrocarbon, C2H4, that occurs naturally in plants and acts as a growth substance in a variety of physiological roles. It seems not to be required for normal growth, but is produced in response to stresses, such as water shortage, or when the concentration of auxins is elevated. The best known effect is the stimulation of fruit ripening: fruits such as bananas, apples, and avocados naturally produce ethylene during the later stages of ripening, and ethylene gas is used to promote the ripening of fruits, such as bananas, that are picked and shipped 'green'. Ethylene generally suppresses flowering, except in members of the pineapple family (Bromeliaceae) - hence flowering of pineapples may be synchronized by releasing ethylene into the growing crop. Studies have shown varied and often contradictory effects of ethylene on vegetative growth. For example, in rice it acts with gibberellins to promote stem elongation, while in peas ethylene inhibits root and shoot elongation. Seed germination, bud opening, and root initiation may also be promoted by ethylene. Syn. ethene.

etiolate v. To cause a plant to whiten by excluding light; plants that whiten trough lack of light.

etiolated adj. Drawn out or elongate stems or thalli, usually pale in color; in bryophytes such errant growth can be a response to exceedingly high or low light regimes. Cf. etiolation.

etiolation n. A physiological response in plants which are grown in the absence of light. Etiolated plants are yellowed, lacking chlorophyll, and are elongated and spindly. Light is essential for chlorophyll synthesis and also inhibits the synthesis of gibberellin, which causes cell elongation in shoots.

etiology n. The science and study of the causes of disease and their mode of operation.

eu- (Gr. eu: good) prefix. Meaning true or real

eucamptodromous adj. Of leaves, with a pinnate venation in which the secondary veins do not terminate at the margins but which gradually diminish inside the margin, connected to the superadjacent secondary veins by a series of cross-veins without forming prominent marginal loops. Cf. acrodromous, brochidodromous, semicraspedodromous.

eucarpic (Gr. eu: good; karpos: fruit) adj. Of a fungus having only part of the thallus converted into fructifications. Syn. eucarpous. See holocarpic.

eucarpous See eucarpic.

Eucaryota (Gr. eu: good; karyon: nut, nucleus) n. The domain which contains the eukaryotic kingdoms, i.e. plants, animals, fungi, and protists.

eucaryote See eukaryote.

Euglena n. A genus of single-celled organisms found in fresh water. They contain the green pigment chlorophyll and can make food by photosynthesis. However, if deprived of sunlight many species of Euglena can utilize ready-made foods from their surroundings. All species have two long, whip-like flagella with which they propel themselves through the water. They are now usually classified as a phylum, Euglenophyta, of the kingdom Protoctista.

Euglenophyta n. A phylum of the kingdom Protoctista.

Eukarya See Eucaryota.

eukaryote (Gr. eu: good; karyon: nut, nucleus) n. An organism consisting of a cell or cells having DNA in the form of chromosomes, a distinct nucleus with a membrane, and other specialized organelles. This includes all organisms apart from bacteria and blue-green algae Cf. prokaryote.

eukaryotic (Gr. eu: good; karyon: nut, nucleus) adj. Describing a cell (a eukaryote) that contains a nucleus bounded by a double plasma membrane and other membrane-bound organelles such as chloroplasts and mitochondria. Prokaryotic cells lack these features. The distinction between these two cell types represents a fundamental division in the levels of organization of living organisms. Eukaryotic organisms comprise the multicellular kingdoms of plants, animals and fungi, and the unicellular kingdom of protoctistans, which includes yeasts.

Eumetazoa See Metazoa.

Euphyllophytina n. Clade comprising the seed plants, sphenopsids, ferns and Ps ilophyton; synapomorphies for the clade include among others a basically helical arrangement of small, pinnule-like vegetative branches, recurvation of branch apices and paired sporangia grouped into terminal branches

euploid (Gr. eu: good; eidos: shape) adj., n. (Of) a cell having a chromosome number that is an exact multiple of the monploid or haploid (1n) number for the species; terms used for a euploid series are haploid (1x), diploid (2x), triploid (3x), tetraploid (4x), etc.

euploidion n. A species sexually reproduced (i.e., apomixis is not present) and composed of segments with a common origin arranged in a euploid series; the segments are morphologically separable but are similar and tend to intergrade.

euploidy n. See euploid.

Euryarchaeota n. The more derived (see Apomorph) of the two kingdoms of Archaea, comprising a broad range of phenotypes including methanogens, halophiles, and sulphur-reducing organisms. Members of the Euryarchaeota show less genetic similarity to those belonging to the domains Eucaryota and Bacteria than do those of the Crenarchaeota.

eusporangiate (Gr. eu: good; spora: seed; aggeion: vase, bowl, container) adj. Of ferns, having sporangia with walls more than one cell thick. Cf. eusporangium, leptosporangiate.

eusporangia See eusporangium.

eusporangium (Gr. eu: good; spora: seed; aggeion: vase, bowl, container) n. (pl. eusporangia) A thick-walled sporangium originating from several epidermal cells. This is the primitive character state in vascular plants; cf. leptosporangium.

eusporia See eusporium.

eusporium n. (pl. eusporia) The inner set of firm and resistant layers of the basidiospore wall, consisting of episporium and endosporium.

eustele (Gr. eu: good; stŕlŕ: stele) n. When a plant's vascular tissue develops in discrete bundles, it is said to have a eustele; an eustele is similar to a dictyostele except that the bundles lack an endodermis and are collateral; collateral bundles have xylem on one side and phloem on the other, and the absence of an endodermis. the bundles are arranged in one circle around the axis; a eustele is characteristic for dicot stems. See also stele.

eutrophe n. See eutrophic.

eutrophic (Gr. eu: well; trophe: food) adj. The gradual increase in nutrients in a body of water. Natural eutrophication is a gradual process, but human activities may greatly accelerate the process. Cf. oligotrophic.

eutrophication (Gr. eu: well; trophe: food) n. The process by which ecosystems, usually lakes, become more fertile environments as detergents, sewage, and agricultural fertilizers flow in. The response to this enhanced fertility in a lake is algal bloom, which inhibits the penetration of light into the water, thus restricting photosynthesis. The consequent loss of an oxygen input into the water causes widespread death of all species unable to survive in an anaerobic environment. In an attempt to reverse the effects of eutrophication in Cockshoot Broad, the Norfolk Broads Authority has dredged the broad to remove phosphates in the mud. Some increase in oxygen content of the water and species diversity has been observed.

eutrophicated adj. Said of nutrient-enriched water.

evanescent (L. evanescere: disappear, vanish, fade) adj. Fleeting; remaining only a very short time.

even-pinnate adj. Pinnately compound with a terminal pair of leaflets or a tendril rather than a single terminal leaflet, so that there is an even number of leaflets, Said of compound leaves having an even number of leaflets, i.e. lacking a terminal leaflet; this is usually easily determined because there is a pair terminally. See pinnate.

evergreen n., adj. Opposite of deciduous, i.e. evergreen plants do not shed all their leaves annually, but shed and grow new leaves continually; most conifers are evergreen, but the evergreeen habit is not restricted to conifers.

everted adj. Turned inside out.

eviction n. Said of growth, the process by which a terminal inflorescence becomes lateral and leaf-opposed by the vigorous growth of an axillary bud immediately below it.

evolution (L. evolutio: unfolding, unrolling) n. Darwin's definition: descent with modification. The term has been variously used and abused since Darwin to include everything from the origin of man to the origin of life. The process by which living organisms have developed from earlier ancestral forms. Evidence of evolution comes indirectly from studies of fossil records, comparative anatomy, biochemistry and physiology, and directly by various experiments observing the behaviour and survival of organisms in their natural environments. Various theories of evolution have been proposed, but the most widely accepted mechanism is natural selection (See Darwinism). Darwin's explanation of evolution remains the central theme of current evolutionary thinking. It has now been assimilated with modern genetics to form what is referred to as neo-Darwinism, in which evolution may be defined as the change in gene frequency in a population over time. In speciation, new species arise when the genetic difference between populations that have been subjected to different patterns of natural selection is sufficiently different to prevent interbreeding between the populations. Two main additional lines of thinking have recently been applied to the evolutionary debate. The first of these seeks to explain the major breaks in the fossil record, such as that at the end of the Cretaceous period which signalled the end of the dinosaurs, by suggesting that long periods of stability have been interrupted by relatively short bursts of rapid evolutionary change, and is referred to as punctuated equilibrium. The second reinforces the basic idea of natural selection, and sees the evolutionary process as being driven by the accumulation of random mutations which produce small but significant changes in an organism's phenotype; this has been tested by mathematical and computer models. Evolution is a major unifying concept in virtually all areas of biology. See ethology.

evolutionary adj. Related to evolution.

evolutionary grade Same as paraphyletic group; showing similarities in morphology, ecology or life history.

evolutionary lineage Line of descent of a taxon from its ancestral taxon. A lineage ultimately extends back through the various taxonomic levels, from the species to the genus, from the genus to the family, from the family to the order, etc. See also Classification.

evolutionary species See chronospecies.

evolutionary systematics Same same as synthetic systematics; a way to determine natural relationships of organisms by studying a group in detail and comparing degree of similarity; evolutionary systematics does not have an explicit methodology, but rather relys on the expertise of authorities very familiar with the group in question; compare to phenetics or numerical taxonomy and phylogenetic systematics or cladistics.

evolutionary tree A diagram which depicts the hypothetical phylogeny of the taxa under consideration. The points at which lineages split represent ancestor taxa to the descendant taxa appearing at the terminal points of the cladogram.

ex- (L. ex: out of) prefix. Same as e-.

exalate (L. ex: out of; alatus: winged) adj. Lacking wings or wing-like appendages; not alate.

exalbuminous (L. ex: out of; albumen: the white of an egg) adj. Without albumen.

exannulate adj. Lacking an annulus.

exapophysate adj. Not having an apophysis.

exarch n. A type of xylem maturation in which protoxylem is external to metaxylem and development proceeds centripetally (from the outside in); cf. endarch and mesarch.

exarillate adj. Having no aril; said of certain seeds, or of the plants producing them.

exasperate (L. exasperatus: made rough, inequal) adj. Roughened with short, stiff points.

excavate adj. Deeply concave.

excavated (L. excavatus: hollowed out) adj. Hollowed out or concave, as the surface of some seeds.

excentric See eccentric.

exciple (L. excipulum: [a kind of] vase, bowl) n. In certain lichens, the rim or outer covering of the apothecium. Syn. excipule, excipulum.

excipula See excipulum.

excipulum n. (pl. excipula). See exciple.

excrescence (L. excrescentia: excrescence) n. A abnormal or morbid outgrowth on the body or a plant; a disfiguring addition; an irregular growth or protuberance.

excrescent adj. See excrescence.

excurrent (L. excurrere: to run out, run forth, project, continue) adj. A growth habit with a single vertical trunk, the branches obviously secondary, as in spruces and some other conifers. Running out, as a costa (nerve) of a leaf running out, projecting beyond the lamina of a leaf, beyond the margin. Projecting beyond the apex (tip), as the midrib of a leaf or bract, e.g. an awn formed by a protruding costa, used especially of the midrib of a mucronate leaf.

excurved (L. ex: out of; curvus: curved) adj. Curving outward, away from the axis.

exfoliate (L. ex: out of; folium, leaf) vt. Peeling off in thin layers, shreds, or plates, as the bark of some trees; shedding (material) in flakes, scales or layers.

exfoliating (L. ex: out of; folium, leaf) adj. Cleaving off in thin layers; losing outer cortex through peeling or cracking. See exfoliate.

exfoliation n. See exfoliate.

exindusiate adj. Lacking indusia.

exine (L. ex: outside) n. The outer, decay-resistant, of two layers forming the wall, coat, of certain spores or pollen grains, sporopollenin, an inert polymer; the exine is characteristic for different plant families and genera, and sometimes even for different species; hence it forms the basis for the identification and quantitative analysis of the vegetation composition of peats and other suitable sedimentary deposits dating back many thousands of years; also called exosporium.

exo- prefix. Meaning outer.

exocarp (Gr. exo: outside; karpos, fruit) n. The outer layer of the wall of a matured ovary, i.e. the outer layer or 'skin' of a pericarp. Cf. mesocarp, endocarp. Syn. ectocarp.

exodermis (Gr. exo: outside; derma: skin) n. A temporary layer of cells in some roots, as in certain orchids. See hypodermis.

exogamic See exogamous.

exogamous (Gr. exo: outside; gamos: marriage) adj. Pollination between genetically different plants. Syn. exogamic. See exogamy.

exogamy (Gr. exo: outside; gamos, marriage) n. The fusion of reproductive cells from distantly related or unrelated individuals, i.e. the union of gametes of unrelated parents.

exogenism n. See exogenous.

exogenous (Gr. exo: outside; genna˘: to produce) adj. Describing substances, stimuli, etc., that originate outside an organism; for example, vitamins that cannot be synthesized by an animal are said to be supplied exogenously in the diet. Of plants, as the dicotyledons, having stems which grow by the addition of an annula layer of wood to the ouside, beneath the bark. Cf. endogenous.

exogenously adv. See exogenous.

exohydric adj. Having water transport essentially external by surface flow, including capillary flow between leaves or through surface papillae. Cf. endohydric, mesohydric.

exomorphic (Gr. exo: outside; morphe: shape) adj. Pertaining to the external form.

exon n. That part of a gene sequence that is transcribed and translated.

exoperidia See exoperidium.

exoperidium (Gr. exo: outside; pŕridion: small bag, small pouch) n. (pl. exoperidia) The outer of the two layers into which the peridium is divided.

exoskeleton n. A hard outer structure, such as the shell of an insect or crustacean, that provides protection or support for an organism.

exosmosis (Gr. exo: outside; ˘smos: pushing) n. The flow of a substance from a area of greater concentration to one of lower concentration. Cf. endosmosis.

exosporal adj. See exosporic.

exospore (Gr. exo: outside; spora: seed) n. The outer coat of a spore.

exosporia See exosporium.

exosporic adj. Of spore germination where the first mitotic division occurs after rupture of the spore wall and outside the spore; gametophyte development outside the spore wall, i.e. the development of a free-living, multicellular gametophyte. Cf. endosporic. Also exosporal, exosporous.

exosporium n. (pl. exosporia) In lichens, a thin or thick outer covering of a spore (especially in Pannariaceae). Cf. episporium.

exosporous adj. See exosporic.

exostomal adj. Said where the micropyle of an ovule is formed from the outer integument alone.

exostome n. The outer circle of the diplolepidous peristome, formed from contiguous periclinal wall-pairs of the outer and primary peristomial layers; missing or rudimentary in haplolepidious peristomes.

exothecia See exothecium.

exothecium n. (pl. exothecia) The outermost layer of the capsule wall, consisting of exothecial cells; the capsule epidermis.

exotic (L. exoticus: foreign) adj. Not native; introduced from elsewhere, but not completely naturalized.

expectorant adj., n. Promoting the secretion of fluid from the repiratory tract; a medicine which can loosen mucus from the throat.

explanate (L. explanatus: spread) adj. Spread out flat; flattened, spread.

expressivity n. The degree of manifestation of a genetic character.

exsert (L. exserere: to pull out) vt. To put forth; to thrust out; to protrude.

exserted (L. exsertus: proeminent, protuberen) adj. Sticking out; extending beyond (some enclosing part); protruding, e.g. of stamens with respect to a corolla tube; projecting beyond the surrounding part; projecting and exposed; e.g. capsules or perianths held clear of the tips of perichaetial leaves. Cf. emergent.

exsiccata See exsiccatum.

exsiccated (L. exsiccare: to dry) adj. Dried.

exsiccatum (L. exsiccare: to dry) n. (pl. exsiccata) Dried plant; usually referring to widely distributed sets of specimens, with printed labels, that are used as standards for comparison.

ex situ conservation This involves the conservation of genetic resources of plants away from the ir area of origin or development. Ex situ conservation occurs mainly in gene banks that can be categorized into four principal types: Seed gene banks, Field gene banks, in vitro gene banks and Cryo-preserved gene banks.

exstipellate See estipellate.

exstipitate adj. Lacking a stipe.

exstipulate (L. ex: out of, without; stipula: stalk, stem) adj. Without stipules. Syn. estipulate.

exsudate See exudate.

extant adj. Still in existence; not extinct.

extensile adj. Capable of enlargement or extension.

extinct adj. No longer living; no longer in existence.

extinction (L. exstinctio: extinction) n. When all the members of a clade or taxon die, the group is said to be extinct.

extirpated (L. extirpare: to uproot) adj. Literally, plucked up by the roots, exterminated. Often used to indicate that a species once lived in an area, and no longer does, usually because of changes in habitat.

extirpation (L. extirpare: to uproot) n. Wiped out, completely destroyed. Carries the connotation of differing from extinction in that it is more often due to human causes.

extra- (L. extra: outside) prefix. Meaning outside or beyond.

extra-axillary (L. extra: outside; axilla: armpit) adj. Outside of but close to the axil. Arising on side of a stem outside of or opposite to an axil.

extrafloral See extra-floral.

extrafloral nectary A gland found on the outside of the flower (and then sometimes called an extranuptial nectary that is supplied both by tracheids and phloem.

extra-floral (L. extra: outside; flos, floris: flower) adj. Beyond the essential parts of the flower, as nectaries, bracts, etc.

extrastaminal (L. extra: outside; stamen, inis: thread) adj. Outside of the stamens.

extravaginal (L. extra: outside; vagina: sheath) adj. Of a shoot, arising from an axillary bud which breaks through the sheath of the subtending leaf, as the young shoots of certain grasses..

extrorse (extrorsus: outwards) adj. Facing outwards. Of anthers, opening away from the centre of the flower. Cf. introrse.

exudate (Lat. exsudare: to drip, ooze) n. A substance exuded or excreted from a plant, that has oozed forth. Also exsudate.

exudation n. The process of exuding.

exude (Lat. exsudare: to drip, ooze) v. Of a liquid, moisture, etc.: to escape or cause to escape gradually; to ooze out; to give off.