CULTURE To grow a crop; to grow fungi or bacteria on a prepared food material, such as agar or broth (the CULTURE MEDIUM). The entire process of obtaining an organism on prepared media is often called CULTURING.

CYTOPLASM (si-toe-plazm) The substance (protoplasm) of a cell exclusive of the nucleus and cell wall.

DAMPING-OFF A disease of seeds or young seedlings caused by fungi. The disease is most evident in young seedlings that topple over and die just after they emerge from the Soil (postemergence damping-off). Two other types of damping-off are often mistaken for poor seed rather than disease: Germination failure, in which a seed is invaded in the early stages of germination and fails to sprout; and preemergence damping-off, in which the young seedling is attacked before it pushes its way through the surface of the soil.

DIATOMACEOUS EARTH A whitish powder used as an absorbent in the manufacture of explosives, for filltering, for insulating, or as an abrasive in soap.

DIEBACK Death of branches or shoots beginning at their tips and moving back toward the trunk or stem.

DIPLOID (dip-loid) Having a double (2N) number of chromosomes. Compare HAPLOID.

DISEASE A condition in which any part of a living organism is abnormal; the condition of a plant that is being continuously affected by some factor that interferes with the normal activity of the plant's cells or organs. Injury, in contrast, results from a momentary damage.

DISINFECTANT Any material that kills micro-organisms.

DISINFECTANT An agent that removes or inactivates plant pests.

DISSEMINATION The spread of infectious material. Infectious agents causing plant disease are disseminated by wind, water, insects, man, animals, and machinery.

DISTAL Remote from the point of attachment or origin; away from the center of the body.

EMBRYO (em-bree-o) A young plant in its beginning, usually contained in a seed or surrounded by protective tissue.

ENCHYMA (eng-ki-ma) A suffix denoting type of cell tissue. Examples are collenchyma, plectenchyma, sclerenchyma.

ENDOSPERM Nutritive tissue formed within the seed of plants and on which the embryo feeds while germinating.

ENZYME (en-zim) A natural chemical, produced by plant and animal cells, that brings about changes in organic substances by influencing processes such as ripening, fermentation, or digestion. Some of the bacteria that cause plant diseases produce enzymes which cause some of the cells of the plant to grow more rapidly resulting in the formation of galls or tumors.

EPIDERMIS (ep-i-der-mis) The outermost layer of cells of a leaf or other plant part.

EPINASTY (ep-i-nas-tee) An abnormal downward curving growth or movement of a leaf resulting from more rapid growth of cells on the upper than on the lower side of the leaf stalk.

EPIPHYTE (ep-i-fight) A plant that grows upon another plant (or on a building or telegraph wire), which it uses as a mechanical support but not as a source of food. Some (such as Spanish-moss) may harm the plants they grow on, however, by excluding light or smothering them. Most orchids are epiphytes.

EPIPHYTOTIC (ep-i-fy-tot-ik) The sudden and destructive development of a plant disease, usually involving an extensive area. It corresponds to an epidemic of a human disease and the two words are used interchangeably by plant pathologists.

ESCAPE Pertaining to a plant which, in a given population of a species or variety of plants in which a disease is prevalent, remains free from disease although it possesses no natural inherent resistance to the disease. Sometimes plants escape attack because of the way they grow; for example, an early-maturing plant escapes late-season diseases. That kind of escape is called klendusity.

ETIOLATION (ee-tee-o-lay-shun) Yellowing of plants due to lack of light.

EXUDATE (ex-you-date) Any material or substance formed inside a plant and discharged through a natural opening or an injury; particularly a liquid discharge from diseased tissues. The presence of an exudate and its nature aid in diagnosis.

F₁ The first-generation offspring resulting from a given mating. F₂ second generation, etc.

FACTOR The causative agent transmitted from parent to offspring and determining the development in the offspring of a certain hereditary character; a gene.

FACULTATIVE PARASITE (fak-ul-to-tiv) An organism that can grow either on living or dead organic matter. Compare OBLIGATE.

FASCIATION (fash-e-ay-shun) A distortion of a plant caused by an injury to the cells of the bud or by an infection which results in flattened and sometimes spirally curved shoots. The plant may look as if several of its stems were fused.

FILIFORM (fil-i-form) Threadlike in shape.

FLAGELLUM (fla-jel-um) A tiny, whiplike filament of a cell which enables the cell to swim through a liquid. Plural: FLAGELLA; adjective: FLAGELLATED.

FRUCTIFICATION (fruk-ti-fi-kay-shun) (I) Production of spores by fungi. (2) The structure in or on which spores are formed.

FRUITING BODY A complex fungus structure that contains or bears spores and from which they are disseminated. The most important types are apothecia, perithecia, conidiophores, coremia, sporangia, pycnia or spermogonia, aecia, pycnidia, acervuli, and sporodochia.

FUMIGANT A liquid or solid substance that forms vapors which destroy pathogens, insects, etc. Fumigants are usually used in soils or in closed structures such as warehouses.

FUNGI IMPERFECTI ( fun -jye im-per-fek-tee) Imperfect fungi; one of the major groups of the fungi, for which no sexual production of spores is known. The group serves as a catchall: When the sexual stage of a fungus is dis, covered, the fungus is transferred to one of the. three other groups of fungi, depending upon' the characteristics of the sexual stage.

FUNGICIDE (fun-ji-side) A chemical that kills or inhibits fungi. Bordeaux mixture, lime-sulfur, and ferbam are fungicides.

FUNGUS (fung-gus) A low form of plant. life which, lacking chlorophyll and being incapable of manufacturing its own food, lives off dead or living plant or animal matter. The body of a fungus consists of delicate threads known as hyphae, many of which form branched systems called mycelia. The' mycelia, which may form inside or on the surface of the host, have different branching habits and structures which help to identify the fungus. In fungi (fun-jye) growth takes place at the ends of the hyphae. Many fungi multiply by forming spores at the ends of, within, or on specialized hyphae. The spores are tiny, microscopic bodies that function like the seeds of higher plants and are carried by wind, water, insects, man, animals, or machinery. A spore landing on a plant under the proper conditions can produce a. new fungus body. Many fungi produce both sexual and nonsexual spores. The manner Of production of the sexually formed spores is the basis of classification of fungi into three of their main groups, Phycomycetes, Ascomycetes, Basidiomycetes; in the Fungi Imperfecti, sexually produced spores have not been found. Spores are not known for some fungi, which are classified in a fifth group, the Mycelia Sterilia.

GALL A pronounced localized swelling; an outgrowth, often more or less spherical, of unorganized cells.

GAMETE (gam-eet) A matured sex cell.

GENE The unit of inheritance that is transmitted from parent to offspring and controls the development in the offspring of a characteristic of the parent; a factor.

GERM TUBE The threadlike filament (hypha) produced by a fungus spore when it begins to grow. It may grow into a plant through a natural opening or a wound or force its way through unbroken epidermis. In parasitic fungi it is also called an infection thread. It grows and gives off branches which form the body of the "new" fungus.

GERMICIDE A substance that kills microorganisms.

GERMINATION The beginning of growth.

GLUME (gloom) A small, dry, light leaf next to the flower of a grass.

GRAFT INDEXING A procedure used to determine the presence or absence of a virus in a plant. The plant is grafted to another plant that is known to show symptoms if affected by the disease in question. The method is used to detect the presence of viruses that are not readily transmitted mechanically.

GRAM-NEGATIVE Not being stained by the crystal violet dye (GRAM STAIN) used in a method of classifying bacteria. Bacteria that retain the stain are GRAM-POSITIVE.

GUTTATION (guh-tay-shun) The normal, physiological process of plants of exuding moisture from an uncut surface: the forcing out of cell sap on a free surface.

GYNOPHORE (jyn-o-fore) The stalk which bears the pistils of a flower.

HAPLOID (hap-loid) Single in appearance or arrangement; specifically, having the basic (or N) number of chromosomes for the species. Compare DIPLOID.

HAUSTORIUM (hos-tor-e-um) (1) A special filament (hypha) of a fungus that penetrates the cells of the host plant and absorbs food from them. (2) A rootlike absorbing organ connecting a parasitic seed plant to the food-conducting system of its host.

HETEROECIOUS (het-er-ee-shus) Pertaining to the rust fungi: Passing through the various stages of the life cycle on more than one kind of host. Compare MONOECIOUS.

HETEROZYGOTE (het-er-o-zve-gote) An organism to which its two parents have contributed unlike genes with respect to any given contrasting pair of chromosomes (for example, one parent contributes the characteristic of tallness, the other, shortness) and which produces two kinds of germ cells with respect to the characteristics.

HILUM (high-lum) (I) A small depression OF a cell in which the flagella (the whiplike filament that enables the cell to swim through a liquid) is inserted. (2) A small depression of an organ, such as a seed, which usually marks the point at which the organ was attached to its base.

HOST The plant which is invaded or parasitized by a disease-producing agent and from which the parasite obtains its sustenance. The HOST RANGE of a parasite is the various kinds of plants that may be affected by it.