Abrasion - (1) A superficial injury caused to the skin or the mucous lining (2) The wearing away of part of the earth's surface by the action of water, wind or ice.

Abrasive - Substances which are able to facilitate the machanical transmission of certain viruses. They tend to increase the number of wounds and also the type of injury conducive to successful establishment of infection.

Abscisic Acid - A plant hormone which has growth inhibiting action, and promotes abscission. It is associated with the onest and maintenance dormancy.

Abscission - (1) The term used for the shedding of leaves, foliage branches, floral parts, fruits or bark by the layingdown of ail abscission layer. (2) Also, refers to the liberation of a fungus spore by the disappearance of an adjoining layer or wall.

Absolute Drought - The term used for a period of atleast fifteen consecutive days, none of which has received as much as 0.25 milimeters of rain.

Absolute Growth Rate - Defined as the rate of increase in size of a growing plant (or a part of it) in a given time, under specified conditions.

Absolute Humidity - Refers to the mass of water vapour present in a unit volume of air. It may be expressed as grams per cubic meter.

Absolute Transpiration - The term used for the rate of water loss from a plant determined experimentally.

Absolute Water Requirement - Means the quantity of water in acre­ inches per crop season which is absorbed by the crop together with the evaporation from the crop producing land. Also called 'consumptive use of water'.

Absolute Weed - One of no use to farners under any circumstances.

Absorbed Water - Water which is held mechanically in a soil mass and possessing physical properties which is not substantially different from ordinary water at the same temperature and pressure.

Absorptiometer - An instrument used for measuring the absorption of nearly monochromatic radiation in the visible range by a gas or a liquid, and so is used to find out the concentration of the absorbing constituents in the gas or liquid.

Abstraction Licence - A licence issued by a water authority for the abstraction of water from a water source for domestic or commercial use, after for irrigation purposes.

Acaricides - Substances that are able to destroy acarids (ticks and mites). They find use in the treatment of acariasis.

Acarologist - Specialist in mites.

Acarology - Deals with the study of acarina which is a large order of small to microscopic arachnids including ticks and mites.

Acclerated Erosion - Refers to the erosion of soil material which takes place at a rate greater than that of normal erosin. It is caused due to the destruction of vegetative cover or due to some activity of man.

Accession - (1) Refers to a cultivar which is registered at a genetic resources centre (2) Any entry which has been newly received in a crop improvement programme.

Accession Collection - Refers to the collection in which seed of every entry has been saved. This reduces the chance that genetic loss will take place through elimination of apparent 'duplicates' and the masking of useful traits by bulking.

Accessory Pigments (Photosynthesis) - Pigments such as carotenoids and phycobiliptoteins which obtain light energy and transfer it to the reaction centres.

Acclimatization. The term used for the process by which human beings, animals and plants get adapted to an unfamiliar set of climatic conditions.

Acclimatisation Value - The extra worth of a flock of sheep acclimatised to a farm, over an imported flock which may stray, with loss of sheep, (Hefted Sheep).

Acc1imatised Sheep - Sheep which are long accustomed to their local environment. They will normally not stray beyond the farm boundary, unlike an imported flock.

Accredited Herds Scheme - Brucellosis (Accredited Herds) Scheme. Accredittd Milk. Milk sold by a producer retailer from herd accredited as free from Brucellosis.

Acetonaemia - Bovine Ketosis.

Accrescent - Enlarged and persistent. Especially of a calyx which becomes enlarged as the fruit ripens.

Accretion - (1) Refers to the process of growth in which material has been added to the outside in non living matter (2) Also, refers to the gradual addition of new land to old by the deposition of sediment carried by the water of a system.

Accumulation or Summation Curve - Curve which is obtained by plotting settling time on the abscissa and the weight of the deposited particles on the ordinate. It is representing the total amount of accumulated material at various time intervals.

Acenapthene - Chemical agent which is able to induce polyploidy, C1oH6(CH2)2' .

Acentric - Whole or part of a chromatid or chromosome which lacks centromere.

Acephalous - Lacking a head. Said of a style lacking a well developed stigma.

Acetabularia - It is the genus of tropical or subtropical marine algae of the division Chlorophyta.

Acetic Acid Bacteria - Bacteria which are able to produces acetic acid from alcohol.

Acetobacter - It is the genus of gram negative, chemoorganotrophic, aerobic, ovoid or rod shaped non spring bacteria. They are able to oxidize ethanol to acetic acid and acetic acid to carbon dioxide.

Acetomonas - It is the genus of gram negative, aerobic, chemoor ganotrophic, ovoid or rod shaped polarly flagellate (or non motile) non spring bacteria belonging to the family Pseudo monadaceae.

Acetonemia - The term used for the metabolic disorder of cattle which causes an abnormal quantity of ketone bodies in the blood and urine. It is responsible for a distinctive flavour to milk. It is associated with poor quality of ration.

Achene - A small, dry, one-seeded Fruit fonned from a single Carpel, which does not split open on ripening but rots gradually with seed gennination. The pips on strawberries are achenes.

Achrodextrins - Dextrins which are produced when the hydrolysis of starch has carried out to the stage that it imparts no colour with iodine.

Achromatin - Non staining basic substance of the nucleus excluding the chromatin. .

Acid Fast Bacteria - Bacteria keeping carbol fuchsin stain after addition of 25% sulphuric acid.

Acid Fast Organisms - Micro organisms which, once effectively stained, cannot get decolorized when treated with mineral acids or mixtures of ethanol and acid.

Acid Forming Fertilizer - A fertilizer leaving acid residue in the soil when applied.

Acid Scarification - Its purpose is to modify hard or impermeable seed coverings. Soaking seeds in concentrated sulphuric acid is considered to be an effective method of doing this.

Acid Soil - Soil having a preponderance of hydrogen ions, and probably of aluminium in proportion of hydroxyl ions. Specifically, it is a soil with a pH value less than 7.0.

Acidosis - The term used for the pregnancy disease of animals which involves a metabolic disorder, a decreased alkalinity of blood and tissues due to the presence of excessive amount of acids in the system.

Acinetobacter - It is the genus of gram negative, aerobic, chemoorganotrophic, asporogenous, aflagellate bacteria of the family Neisseriaceae.

Acquired Immunity - Means specific immunity which is acquired through exposure to the antigen. .

Acre - A measure of land. 4840.sq. yds. Equal to 4 Roods, or 10 square Chains. (Scottish acre, 6150.4 sq. yds; Irish acre, 7840 sq. yds both obsolete.) Also equivalent to 0.405 Hectares. Originally, the amount of land that could be ploughed in a day by a team of oxen.

Acre Foot of Water - Defined as the amount of water that would cover an acre of land to a depth of one foot, provided that there occurs no seepage, evaporation and runoff losses.

Acre-inch - A unit of measurement used in Irrigation works. The amount of water required to cover an acre to a depth of 1 in.(25.4 mm per hectare) equivalent to 101 tons or 22460 gallons.

Actinobacillosis - An animal disease mainly of cattle and pigs. It is caused by bacteria (Actinobacillus lignieres) causing swelling and hardening of tongue and face. It is also known as Wooden Tongue. The disease is also found in sheep and is sometimes called' Cruels' .

Actinomycin D - An antibiotic that is able to inhibit the elongation of RNA chains.

Actinomycosis - An animal disease which is caused by the micro scopic 'ray fungus' (Actinomyces bovis) that penetrates through small mouth wounds (caused by barley awns, foreign bodies, during change of teeth, etc.) resulting in the swelling of the jawbone with ultimate suppuration. Also known as Lumpy Jaw.

Activated Sludge - Refers to the thick or thin watery suspension of sewage and associated protozoans, micro-metazoans and bacteria in certain sewage treatment processes. When the suspension is constantly stirred and air is blown through it, the organisms convert much of the organic fraction into gases, salts, and inert organic compounds.

Active Immunity - Refers to the specific immunity which is afforded by the body's own immunological defence mechanism follow ing exposure to antigen.

Active Ingredient - Refers to an active component of a formulated product like a fungicide. For example Ridomil 25 WP has 25% of the active component acylalenine and 75% inert material. The ridomil has 25% a.i.

Acute Exposure - Term used for radiation exposure of short duration. Adaptive Enzyme. An enzyme which is able to synthesize only in the presence of an inducing agent, such as its substrate.

Additives - (1) Substances added to Feedingstuffs or Concentrates during manufacture, which are not principal nutrient sources. Examples include Vitamins, minerals, Trace Elements, certain Antibiotics, etc. (2) Substances added to pesticides to improve their efficiency and efficacy. They include Surfactants (wetters), Adjuvant Oils and drift retardants.

Additive (Fertilizer) - A substance which is added to fertilizer to improve its chemical or physical condition.