Alkaline Soil - A soil having alkaline pH. It is formed in areas of very high rainfall or dryness due to deposition of calcium salts in surface layers or on the soil. See pedocal.

Alkaloids - Used for cyclic Vegetable-bases, with a heterocyclic ring, and having nitrogen. They cause a physiological effect on animals. e.g., morphine and atropine. Sometimes include nitrogen bases which are not having a heterocyclic ring, e.g., caffeine.

Allele, Allelomorph, Allelomorphic Gene - Different forms of a gene, which have the same locus on homologous charomosomes, and are subject to Mendelian (alternative) inheritance.

Allelopathy - Releasing of some chemical by a plant into its surroundings which has been found to inhibit the growth of nearby plants. An example is that pine produces substances killing seedlings of same species growing near to the parent plant (autoallelopathy). Another example is the secretion of HCN by bitter almonds which inhibits seed germination of poppy.

Allocarpy - When fruiting takes place after cross-fertilization.

Allochronic Speciation - The formation of new species during the passage of time, tending to form a gradation from one species to the next.

Allogamy (Cross fertilisation exogamy). Used for the fusion of male and female gametes which are derived from two genetically different individuals of the same species.

Allometric Growth - Used fordescribing frowth rate ofa part ofan organism tothat ofwhole organism. All parts ofan organism rarely grow with same rate ofgrowth. Parts growing faster than the whole organism are said to exhibit positive allometry. Parts growing slower than the whole organism are said to exhibit negative allometry.

Allopatric Speciation - The formation ofnew species over a length oftime, by the geographical isolation ofgroups ofthe comhy;mon ancestor, e.g., by a mountain range.

Allopatry - Describing a population orspecies where two groups ofisolated organisms cannot breed with each other due to their separation by distance ornatural barriers e.g., water, deserts ormountain range. Population distributed in such a way (allopatric) may develop diffrent adaptations ofdifferent habitats and then they may fail tointerbreed even if barriers arebroken >(allopatric speciation).

Allophilic - Used forflowers ofan insect pollinated species ofthat can be pollinated by different types ofinsects.
Allopolyploidy - An artificial polyploid which is formed by the hybridization ofdifferent species, i.e., the individual is having two ormore sets ofchromosomes, which have different chromosome compliments.
Allosomal Inheritance - Inheritance ofcharacters which arecarried on an allosome.

Allosteric Enyme - A regulatory enzyme responsive tochanges in metabolic state ofthe cell ortissue. Its catalytic activity could be modified by non-covalent binding ofa specific metabolite at a site other than the enzyme active site. The mostcommon example ofsuch enzymes is the first enzyme ofsome enzyme sequences which gets inhibited specifically by the end product ofreaction sequence (feedback inhibition). Activity ofallosteric enzyme could be increased alsoby an allosteric modulator. Allosteric enzymes may be having more than one allosteric modulator also. Reactions involving allosteric enzymes are alwalys irreversible.

Allosteric Site - A regulatory site on an allosteric enyme which can reversibly undergo binding with a specific effecto or modulator. When bound to enzyme, modulator either inhibits (negative modulator) or activates (positive modulator) the enzyme by changing its shape. Some allosteric enzymes are having a site only for one modulator (monovaleu enymes) while others are having several allosteric sites (polyvalent enzymes).

Allosyndesis - (1) Used for the pairing in a cross of two polyploids, or of chromosomes derived from opposite parents.

(2) Pairing in an allopolploid between chromosomes which

are derived from ultimate diploid ancestors, opposed to

autosyndesis.

Allotetraploid - An allopolypoid which is formed by the doubling of the chromosome number in a diploid hybrid; i.e., a tetraploid having a diploid set of chromosomes from each parent.

Allotropous Flower - A flower which has the nectar freely exposed and available to a wide variety of insects.

Allotype - One of the original types for describing a new species.

Alluvial Soil - A soil which is derived from marine, esturine, or river deposits. A young soil, with an undeveloped profile. Usually has a high fertility.

Alpha-Ketoglutarate Oxidase - An lenzyme in the Citric Acid Cycle (Kreb's Cycle), which oxidises a ketoglutarate to succinic acid, by oxidative decarboxylation.

Alpine - A major biome (regiona plant community) in high mountaineous regions and on high level pleateaus. Plants growing in this stony soil are subjected to high wind and high light intensity. Certain drought resistant species e.g., grasses, sedges, mosses and lichens are common.

Alternate - Used for describing arrangement of leaves on stem in which one leave arises simply at each node. It is a common pattern in plants. Compare opposite, whorled.

Alternate Host - The host other that the main host of a pathogen on which it can survive in case the main host is not available. The term can also be used if pathogen is having more than one host.

Alternation of Generations - Describing the alternate production of independent haploid sexual, and diploid asexual, generations in a life-cyc1e. This may be further complicated in some Algae and Fungi. If the two generations look alike, the alternation is homologous, and if they do not look alike, the alternation is antithelic.

Alternative Host - One of the hosts of a plan t pathogen, usually referred to the wild host (s) of a disease-causing organism of a cultivated plant.

Alterne - A sudden change in a plant species which is spread over a wide area. Such a change is brought about by variation in the soil or other environmental conditions.

Alveole Alveolus - (1) A small surface pit.

(2) A pore of a polyporous fungus.

Ameiosis - Having one division (instead of two) of the nucleus at meiosis, so that the chromosome number of the mother-cell does not get reduced.

A mensalism - Used for describing association between two different types or organisms in which one organism harms the other by it activities but does not get any benefit by such activity.

Amino Acid - A derivative of acetic acid in which one hydrogen of the alkyl group has been replaced by an NH2 group. For example CH3.COOH is acetic acid while CH2 .CH2.COOH is amino-acetic acid (glycine). The substitution of a second hydrogen by one of a number of side-chains yields a series of amino acids, e.g. CH2NH2.CH2COOH, is alanine, Amino acids being synthesixed by autotrophic plants and ultimately are built up into proteins.