Botany definitions

[karmaxul]

Great link for terms and definitions ( a ten minute read, a couple have nothing to do with plants)

http://ecoport.org/ep?SearchType=ear...ource=Glossary

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c

karmaxul Reviewed by karmaxul on 03-16-2006. Botany definitions Great link for terms and definitions ( a ten minute read, a couple have nothing to do with plants) http://ecoport.org/ep?SearchType=earticleResourceView&earticleId=127&resource=Glossary One love c Rating: 5

[karmaxul]

Ill post all the good ones... maybe an hour or so (no need to read)

Autogamy 1. Self-fertilization, the fertilization of a flower by its own pollen. 2. The fusion of nuclei in paris within a single cell of the female organ but not accompanied by cell fusion.

Auxin An accessory growth-promoting substance in the food of plants, a hormone produced in the tips of plants which travels through the plant from cell to cell. Auxin veers away from light and causes the plant to grow faster on one side and curve toward light.

Autogamous Requiring only one individual to accomplish self-fertilization.

Autogamy 1. Self-fertilization, the fertilization of a flower by its own pollen. 2. The fusion of nuclei in paris within a single cell of the female organ but not accompanied by cell fusion.

One love
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[karmaxul]

Autogamy 1. Self-fertilization, the fertilization of a flower by its own pollen. 2. The fusion of nuclei in paris within a single cell of the female organ but not accompanied by cell fusion.

Auxin An accessory growth-promoting substance in the food of plants, a hormone produced in the tips of plants which travels through the plant from cell to cell. Auxin veers away from light and causes the plant to grow faster on one side and curve toward light.

Autogamous Requiring only one individual to accomplish self-fertilization.

Autogamy 1. Self-fertilization, the fertilization of a flower by its own pollen. 2. The fusion of nuclei in paris within a single cell of the female organ but not accompanied by cell fusion.

Actinomycete Gk. aktis - ray, mukes - fungus.

Group of heterotropic filamentous eubacteria tending to form extremely fine ramified mycelia. They multiply by mere breaking of the mycelium or by hyphae. The most common genera in soil (Streptomyces and Nocardia) are particularly able to degrade organic substances which cannot easily by decomposed, thereby producing vitamins and antibiotics. Being aerobic, their presence in a soil signifies good structure and good aeration. They can be symbiotic with some higher plants such as Alnus and Myrica

Albumen Nutritive material stored within the seed usually surrounding the embryo but not within the embryo, the nutritive matter in the seed used by the young plant until it develops roots and leaves; see ENDOSPERM.

Allele One of the forms of a gene.

Allogamous Requiring two individuals to accomplish sexual reproduction; habitually cross-fertilized although capable of self-fertilization

Allogamy Cross-fertilization; see geitonogamy; the opposite of autogamy.

Anthesis The period of flowering, the time of the expansion of a flower, the period of pollination.

Biotope The life area of the smallest space, a microhabitat within the phytocoenosis.

Bract 1. A relatively small leaf just below an inflorescence, flower, or flower part (see illustration morphology of flower heads). 2. A leaf or scale in whose axis an inflorescence, flower, or floral organ is produced. 3. A small rudimentary or imperfectly developed leaf. 4. A leaf subtending a flower.

Brix The Brix scale is a measure of the percent of sugar in the solution or of the number of grams of sucrose present per 100 grams of aqueous sugar solution. (50 Brix means 50 grams of solid per 100 gms of solution)

Bud The undeveloped state of a branch or flower cluster with or without scales, an undeveloped shoot or stem, the rudimentary or resting end or branch of a stem, an embryonic shoot, a growing point or undeveloped axis covered with the rudiments of leaves.

C3 Photosynthesis pathway Calvin cycle (aka Calvin-Benson Cycle or Carbon Fixation) (also referred to as a C-3 pathway) is a series of biochemical, enzyme-mediated reactions during which atmospheric CO2 is reduced and incorporated into organic molecules, eventually some of this forms sugars. The Calvin Cycle occurs in the stroma of chloroplasts. CO2 is captured by the chemical ribulose biphosphate (RuBP). Six molecules of CO2 enter the Calvin Cycle, eventually producing one molecule of glucose.
The first stable product of the Calvin Cycle is phosphoglycerate (PGA). The energy from ATP and NADPH energy carriers generated by the photosystems is used to attach phosphates to (phosphorylate) the PGA. Eventually there are 12 molecules of glyceraldehyde phosphate (also known as phosphoglyceraldehyde or PGAL), two of which are removed from the cycle to make a glucose. The remaining PGAL molecules are converted by ATP energy to reform 6 RuBP molecules, and thus start the cycle again.

Calyx The outer floral envelope of the flowering plants usually green in color and composed of sepals, the sepals considered collectively, the outer set of the floral envelope. When there is but one set, it is considered the calyx. See illustration morphology of flowers or morphology of apple flower and fruit.

Cambium The thin layer of formative tissue beneath the bark of dicotyledons and gymnosperms from which new wood and bark originate, a sheath of generative tissue ordinarily between the xylem and phloem, the meristematic zone from which new growth develops, the secondary tissue from which secondary growth arises in stems and roots. See illustration changes in a stem as it increases in age or details of stem structure.

Canopy 1. The layer of branches, twigs, and leaves formed by woody plants at some distances above ground level. 2. A characteristic membrane within the testa surrounding the free part of the nucleus.

Carbohydrate Any member of a large class of chemical compounds that includes sugars, starches, cellulose, and related compounds. Carbohydrates are produced naturally by green plants from carbon dioxide and water (see photosynthesis). Essential nutrients, they are the human body's main source of both quick and sustained energy. The three main classes of carbohydrates are monosaccharides, which are the simple sugars, e.g., fructose and glucose; disaccharides, which are made up of two monosaccharide units and include lactose, maltose, and sucrose; and polysaccharides, which are polymers with many monosaccharide units and include cellulose, glycogen, and starch.

Carpel One of the female reproductive organs of the flower, i.e. a unit of the gynoecium. See illustration main types of gynoecium, morphology of apple flower and fruit or morphology of citrus flower and fruit.

Cation exchange capacity The total number of negatively charged ion sites in a given volume of soil. These may be linked either to basic ions (e.g. potassium) or hydrogen ions. As the proportion of hydrogen ions increase so the acidity increases and the pH falls.

Cation exchange capacity The cation exchange capacity (CEC) is a measure of the soil's ability to retain cationic nutrients. It is also an index of the clay activity and mineralogy, which is important for calculating mineralisation rates, leaching rates and interaction with pollutants. It changes relatively slowly, and largely due to changes in the soil organic carbon and pH.
When dissolved in water, the nutrients are either positively charged or negatively charged. Examples of positively charged ions (cations) include: calcium (Ca++), magnesium (Mg++), potassium (K+), sodium (Na+), hydrogen (H+) and ammonium (NH4+). Soils have a slight excess of negative charge sites due to the presence of clay particles and organic matter. Thus the higher the clay content and organic matter content, the higher the CEC of the soil. Soils with a high CEC will tend to hold onto the positively charged nutrients better than soils with a low CEC.

Cellulose The carbohydrate which composes the cell walls; the primary cell-wall substance; an amorphous white compound which is isomeric with starch and insoluble in ordinary solvents; the raw material for the manufacture of paper, artificial silk, laquers, films, etc.

Chiasma The exchange of material between chromosomes during nuclear division, a crosswise fusion at one or more points of paired chromosomes or chromatids which are twisted about each other in meiosis; an exchange of partners in a system of paired chromatids, a visible genetic cross-over between chromosomes and chromatids; pl. chiasmata.

Chromosome A single DNA molecule, a tightly coiled strand of DNA, condensed into a compact structure in vivo by complexing with accessory histones or histone-like proteins. Chromosomes exist in pairs in higher eukaryotes. See chromosome walking.
Derives from: chroma + soma.

Coir Fibrous material derived from the outer husk of Cocos nucifera, the coconut palm; used as an environmentally friendly fibre.

Cortex 1. A cylinder of parenchymatous cells between the epidermis and the starch sheath (the endodermis) in a young stem and between the piliferous layer and the endodermis in a young root (see illustration primary plant body of a root or details of stem structure).
2. A similar cylinder in the older stems and roots, but less conspicuous.
3. A cellurar coating on the outide of the thalli of some algae.
4. The outer layers of the thallus in lichens and some fungi.

Cotyledon The seedleaf, a leaf-like organ within the seed, a leaf-like structure folded within a seed in which food for the new plant is usually stored. The number of cotyledons in a seed is the basis for the primary divisions of the seed plants into monocotyledons and dicotyledons. See illustration the body of a seed plant (common bean) or vascular connection between shoot and root.

Cross-pollination The deposition of pollen from one flower to the stigma in another by artificial or natural means.

Cultivar A botanical variety that has originated under cultivation.

Cuticle 1. A continous, non-cellular layer (covering the surface of the epidermis of the aerial parts of plants) consisting of cutin and containing no cellulose. See illustration morphology of leaves.
2. A water-repellant outer membrane of plant parts.
3. In fungi, a differentiated tissue consisting of a single layer of hyphae covering the pileus or stipe.
4. A pellicle.

[karmaxul]

Diallel Denoting hereditary lines which cross. A diallel cross involves all possible matings of several known males and females.

Dimorphism A difference in size, form, or colour, between individuals of the same species, characterising two distinct types.

Drip irrigation A planned irrigation system in which water is applied directly to the Root Zone of plants by means of applicators (orifices, emitters, porous tubing, perforated pipe, etc.) operated under low pressure. The applicators may be placed on or below the surface of the ground. Also see Irrigation Systems.

Embryo Derives from embryon, from bryein;
1. The young plant developed from the fertilized egg cell.
2. A rudimentary plant still enclosed in the seed, the young sporophyte resulting from the union of male and female sex cells. See illustration of cross section of fruits or vascular connection between shoot and root.

(I will include pictures if any after the definitons)

[karmaxul]

Embryo sac In seed the great, thinwaled cell in which the fertilization of the ovum and the development of the embryo takes place. See illustration the structure and main types of ovule.

[karmaxul]

Embryogenesis A physiological process leading to the formation of embryos.

Endocarp The usually woody-textured inner layer of the pericarp.

Endosperm 1. The multicellular food-storing tissue formed inside a seed of flowering plants following the double fertilization of the embryo sac by the second sperm nucleus. 2. The prothallus of the female gametophyte of gymnosperms.

Epicarp The outer layer of the ovary wall, the superficial layer of the pericarp especialy when it can be stripped off as a skin, the epicarpium.

Epidemiology The study of the dynamics of disease in populations. Generally has two aspects:
'Genetical' epidemiology in which the patterns of gene-flow in interacting populations of hosts and pathogens are studied. For example, a plant breeder may introduce a gene for resistance to disease. The resistance gene is first identified and evaluated in small experimental plots, and if found promising, it is then submitted to larger-scale field trials and subsequent release for commercial cultivation. The expression of disease in the host population carrying the new gene reflects the dynamic balance between adaptation and selection as the new host resistance gene exerts selection pressure on the pathogen population to try and adapt to overcome the newly introduced resistance gene. At first the pathogen population is at a disadvantage, facing a new situation (selection pressure) to which the pathogen had not been exposed previously. Consequently, most individuals in the pathogen population are not 'fit' and are epidemiologically 'incompetent' to cause disease. An observer seeing the field at this time will believe that the resistance mechanism introduced by the plant breeder is sucessful. However, since a pathogen population can pass through many hundreds more life cycles than its average host, and because the rate of adaptation is elicited and determined by the rate and nature of selection pressure, the pathogen population becomes progressively 'used to' the resistance gene by overcoming it.
Resistance genes can exert either qualitative or quantitative selection pressure. Just as there is, in chemistry, both (a1) [enzyme x substrate] specifcity; i.e. a qualitative lock-and-key recognition whereby a specific enzyme has its 'own' or a 'preferred' substrate, and (b1) quantitative variation in the rate at which enzymes after recognition, may catalyze a substrate, so too in plant disease, do (a2) vertical resistance genes in the host exert qualitative selection pressure that is usually, but not always or axiomatically more easily overcome by the pathogen; and (b2) do {{horizontal resistance}} genes exert quantitative selection pressure that is usually, but not always or axiomatically less easily overcome by the pathogen. Thus, the expression and erosion of vertical resistance may be compared to an athlete facing a pole vaulting hurdle: there is a single threshold that has to overcome after which there are no further obstacles. In contrast, the expression of horizontal resistance could be compared to mountain climbing in which every step of the route poses a small portion of the overall 'quantity' of the challenge that has to beovercome to succeed.
Host genes and pathogen genes do not interact directly, but do so through their intermedaries enzymes, proteins and other compounds determined by gene expression processes. Many of these are influenced by the environment, as are levels of pathogen population affected by external factors such as competition and, in agriculture, by factors such as crop spacing that influences micro-climate. This host x pathogen x environment (Hg x Pg x E) interaction, as it is viewed or interpreted from the perspective of genetics and plant breeding (hence the 'g' in (Hg x Pg x E) above, constitutes the 'genetical' component of epidemiology.
'Ecological epidemiology on the other hand, studies fluctuations in disease in populations due to ecological and abiotic factors that influence the host x pathogen interaction. Here too the (H x P x E) interaction is the centre of focus, but now the emphasis is on the many factors in the environment, such as weather effects, competition, density dependence etc., are the focus of study.
Ecological epidemiology is concerned with methods and procedures that measure the rates of disease in populations. It tries to identify the critical parameters; e.g. the {{incubation period}} and the latent period as well as abiotic factors such as relative humidity, rainfall, soil pH and others, that determine these rates, and then it tries to partition and ascribe the observed variation in in disease patterns to understand epidemics in terms of driving parameters and factors. The final purpose being the practical objective of reducing disease impact wthout causing environmental damage.

Epidermis The thin external layer of protective cells of a plant ; a sheath of closely united cells, usualy one cell thick, which forms a layer over the stems and leaves. It is usualy continuous except where stomata perporate it. See illustrations: leaf cross section, morphology of leaves, changes in a stem as it increases in age or primary plant body of a root.

[karmaxul]

Epistasis The dominant action of a different chromosome or at a different locus on the same chromosome.

Etiolation The blanched condition produced in plants by the lack of light or by disease.

Etiology The sciene of the causes of disease.

Evapotranspiration Amount of water transferred into the atmosphere by evaporation from the soil surface and by plant transpiration

Exodermis The outermost cortial layer of the adult root.

Fat Vegetable oils, non-nitrogenous reserves in seeds or the volatile oils which perfume many flowers and leaves. (I wonder if you could add smell by increasing the fat?-karmaxul)

Fiber Elongated sclerenchyma cells; slender, thick-walled cells many times longer than wide; prosenchyma.

Frond 1. A general term for the leaf of a fern which differs from a typical leaf in that it bears reproductive organs on its surface. 2. The leaf-like thallus of a liverwort or seaweed. 3. The leaf of a palm.

Fructose A fruit sugar, levulose, a keto-hexose sugar.
Simple sugar found in honey and fruit. Sweeter than sucrose, fructose is a carbohydrate with the same formula as glucose, but with a different structure (see isomer). An equimolar mixture of fructose and glucose, called invert sugar, is obtained by the breakdown of sucrose and is the major component of honey.

Gametophyte The phase in the life cycle of plants which bears the sex organs and gives rise to the gametes.

Gene The hereditary unit which controls the appearance of definite characters. The functional unit of heredity. A gene is a section of DNA that codes for a specific biochemical function in a living organism.

Genetic drift Random changes in gene frequency within a population resulting from sampling effects rather than natural selection, and hence of greatest importance in small populations.

Genome A complete haploid set of chromosomes as it is inherited from each parent, a genom.

Genotype 1. A group of individuals which are alike with respect to their hereditary factors.
2. The entire genetic constitution of an organism.
3. The single species upon which the genus is based.

Genus The principal subdivision of a family (plural: genera), a more or less closely related and definable group of plants comprised of one or more species. The generic name becomes the first word of the binomial employed in all member species.

Germ pore A pit on the surface of a spore membrane through which a germ tube makes its apperance. See illustration of pollen differentiation.

[karmaxul]

Germplasm Plants intended for use in breeding or conservation programmes

Glucose 1. The common sugar produced in plants. 2. A group of carbohydrates, crystallizable and soluble in water, occurring in fruits, as grape sugar. 3. A commercial term for syrups made from starch or gain.
Empirical formula: C6H12O6. White crystalline sugar; somewhat less sweet-tasting than sucrose (table sugar), it is found in fruits and honey. Glucose is the major source of energy in animal metabolism. It requires no digestion prior to absorption into the bloodstream. A monosaccharide (also see carbohydrate), glucose can be obtained by hydrolysis of a variety of more complex carbohydrates, e.g., maltose, cellulose, or glycogen. It is commercially made from cornstarch (see starch) and is used in sweetening candy, chewing gum, jellies, and various foods. Glucose present in urine may be a symptom of diabetes.

Halophyte A plant that can grow in a saline habitat.(kelp? - karmaxul)

Haustorium 1. An absorptive structure of a fungus mycelium or a modified root or shoot of a higher plant which serves as an attachment to obtain food through penetration of the host cells. 2. The foot of the embryo of a fern.

Heterosis Cross-fertilization, hybrid vigor, the increased growth vigor exhibited by a hybrid.
Refers to the phenomenon in which the Fl hybrid obtained by the crossing of two genetically dissimilar parents shows superiority over the best standard check prevailing at that time in one or a combination of characters.

Heterozygous Possessing both the dominant and the recessive genes of an allelomorphic pair.

Homozygous Having both parents transmit identical genes for a particular character, being genetically pure (for pairs of genes).

Hybrid The offspring of two different varieties, species, or genera; a heterozygote.

Hybrid vigour The increased vigor of a hybrid when it is greater than that of either of the parents.

Hybridization 1. The result of crossing of more or less dissimilar parents. 2. The act or process of hybridization.

hydromorphic Denoting areas with waterlogged soils (Grims Droopy-karmaxul)

Hypodermis hypo + dermis; The tissue just beneath the epidermis which serves to strengthen itself.

Inbreeding 1. In plants, self-fertilization (the most efficient and rapid method to produce homozygous genes to obtain a pure line). (result-karmaxul)

Inbreeding depression The reduction in vigor often observed in progeny from matings between close relatives. Inbreeding depression is due to the expression of recessive deleterious alleles and is usually severe in open-pollinated outcrossing species that occur in fairly high population densities.

Internode inter + nodus; The space between nodes or phalanges. See illustration morphology of grass plants (not posting the pic Im on a role everyone should know this one anyway)

Introgression The movement of genes from one population into another through hybridization followed by backcrossing. Usually refers to movement of genes from one species to another or among sub-species that have been geographically isolated then brought back together by changes in the species ranges or planting of exotic populations.

Lamina 1. A layer.
2. The blade or extended part of a leaf, the leafy portion or blade of the frond above, and attached to the petiole.

Lateral roots Lateral roots are the side roots which originate from the tap root. Lateral roots are mainly found only in the dicotyledonous plants.

Leaf area index The area of leaves exposed over a unit area of land surface.

Leaf scar The scar left on the twig at the point where a leaf has fallen. It is usually covered with a thin layer of corky tissue, periderm.

Leaflet One of the component parts of a compound leaf blade.

Lignified Lignified means that high amounts of the natural "cement" called ligninis deposited within the cellulose strands in the cell walls. This makes the cell walls very tough. Having tough, lignified cell walls is a unique feature of trees.Keslick (1997)

Lignin The substance which is deposited in cell walls to produce woody tissue, a secondary deposit which forms the greater part of the bulk of ordinary wood, lignine.

Lipase The enzyme which splits fats.

Lipoprotein Compounds found in membranes composed of protein and fats.

Locus 1. The position of a gene on a chromosome in a linkage group or on a chromosome map.

Meristem The undifferentiated formative or generative cells of plants which give rise to daughter cells capable of further division, the cells found in the cambium or growing points capable of further development.

Mesocarp The middle layer (between the endocarp and the exocarp) of the pericarp which consists of three layers. See illustration of cross section of fruits. ( wasnt sure if I should put in this picture but I need a bowl break and did not want to loose any info)

[karmaxul]

Molasses Molasses is a by product of the sugar refining industry. Cane and beet molasses are the end-products of the sugar manufacturing process and once no more sugar can be crystallised from the raw crop, the residual product is molasses. A hundred tonnes of sugar cane will give 10-11 tonnes of sugar and 3-4 tonnes of molasses, whilst 100 tonnes of sugar beet will give 11-12 tonnes of sugar and 4-6 tonnes of molasses.
Molasses is suitable for feeding as a supplement to grass and silage. It is difficult to predict the exact composition of molasses. Soil and climatic conditions, the variety and maturity of the cane or beet and the processing conditions in the factory all influence molasses composition. Consequently, considerable variation may be found in nutrient content, flavour, colour and viscosity. The average composition of molasses is 20% water, 35% sucrose, dextrose (glucose) 7%, levulose (fructose) 9%, other reducing substances 3%, other carbohydrates 4%, ash 12%, nitrogenous compounds 4.5%, non-nitrogenous acids 5%, wax, sterols and phospholipids 0.4%, pigments 0%, vitamins 0%.
Molasses is a rich source of minerals. In comparison to other commonly used sources of dietary energy, e.g. cereal grains, the calcium content of cane molasses is high (up to 1%), whereas the phosphorus content is low. Cane molasses is also high in sodium, potassium (which are present as chlorides), magnesium and sulphur. Beet molasses tends to be higher in both potassium and sodium but lower in calcium content. Molasses also contains significant quantities of trace minerals, copper for example (7ppm), zinc (10ppm), iron (200ppm), manganese (200ppm).

Monomorphic Producing spores of one form or kind.

Mycoplasma A mycoplasma is not a bacteria or virus; Rather, a mycoplasma is a mollicute with no cell-wall and is characterized as a virus-like infectious agent, somewhere in-between a virus and bacteria in complexity.
Mycoplasmas are unicellular, procaryotic disease-causing organisms of pleomorphic structure with no cell wall. In vitro they grow on special media and characteristically form "fried egg" shaped colonies. Like viruses, they are filtrable but are much larger. Transmission is affected by leafhoppers, planthoppers and psyllid vectors as well as by grafting and dodder.
Mycoplasmas are wall-less procaryotes, which can be pathogens of man, animal and plants.

Mycorrhiza A fungus attached to the roots of a plant, and in a symbiotic relationship with that plant.

Mycorrhiza A commonly mutualistic and intimate association between the roots of a plant and a fungus. See also Ectomycorrhiza and Vesicular arbuscular mycorrhiza.

Nitrogen fixation The conversion of elemental nitrogen in the atmosphere (N2) to a reduced form (e.g., ammonia and amino groups of amino acids) that can be used as a nitrogen source by organisms. The process is important since all organisms require a source of nitrogen for nutrition, and N2 cannot be used by the great majority of the biota to satisfy that need. Biological nitrogen fixation is carried out by a variety of organisms; however, those responsible for most of the fixation are certain species of bluegreen algae, the soil bacterium Azotobacter, and the symbiotic association of plants of the legume variety and the bacterium Rhizobium.

Nitrogen fixation The fixation of nitrogen by bacteria and fungi. Generally only those organisms which are prokaryotic in cell structure are able to fix nitrogen. Fixation of nitrogen by the living organisms is called biological nitrogen fixation. Generally, the conversion of inert Nitrogen (N2) into the combined form either as Ammonia (NH3) or Nitrate (NO3) is called nitrogen fixation. This form of combined nitrogen can be utilized by the plants for their nitrogen needs. This process of fixation of nitrogen is highly energy consuming. In crops like pea, the energy cost of nitrogen fixation has been worked out. A total of 9 â?? 10 kg of carbohydrates is required for each kilogram of nitrogen fixed. Biological Nitrogen Fixation (BNF) is limited by the photosynthetic capacity of the plants. This is because nitrogen fixation requires carbohydrates to provide electrons and ATP. Nitrogen fixation is also done industrially through the Haber-Bosch process wherein nitrogen is catalytically reduced under conditions of high temperature and pressure into ammonia. The process is represented as thus : (N2 + 3H2O -- 2NH3). Due to increasing costs of fuel and energy, more attention is being paid to biological nitrogen fixation systems as an alternative to industrial nitrogen fixation.
Biological Nitrogen Fixation is generally restricted to organisms with a cell structure which is prokaryotic in nature. These include the bacteria and blue green algae. There are in general three different systems of nitrogen fixation. Symbiosis. Associative symbiosis and Free living. Symbiotic systems are related to those bacteria which have a very close association with their host plants or live within the host plants. These host plants supply the energy requirements for the bacteria while in return the bacteria fixes atmospheric nitrogen by reducing the inert atmospheric nitrogen with the help of an enzyme called nitrogenase into ammonium (eg. Rhizobia). In Associative symbiosis, the organisms live in close association with the host roots. The root exudates from the host plants form the main energy source for the nitrogen fixing organisms eg. Azospirillum. The free living organisms which fix atmospheric nitrogen are either autotropic ie. photosynthetic or heterotropic ie. plant residues are the main source of energy. Free living nitrogen fixing rhizobacteria do not geneally contribute much to plant N nutrition. However it has been shown that inoculating cereals with such bacteria have been beneficial. (Dobereiner and Pedrosa, 1987); Okon and Hadar., 1987; Ishac 1989)

Node 1. The joint of a culm. 2. The place on the stem where leaves ordinarily arise

Nucleic acid An acid found in the nucleus which is rich in phosphorus. It is the nonprotein constituent of nucleoprotein. In RNA (ribonucleic acid) the sugar is ribose, in DNA (deoxyribonucleic acid) it is 2-deoxyribose. The DNA and RNA play an important part in protein synthesis and in the transmission of hereditary characters. (hmm K ay interesting - karmaxul)

Nucleic acids The two nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), are made up of long chains of molecules called nucleotides. See DNA, RNA, nucleotides.

Oospore The final stage of development after the fusion of unlike gametes in the Oomycetes. (the bond of spores - karmaxul)

Ortet The original plant from which a clone is started through rooted cuttings, grafting, or tissue culture, or other means of vegetative propagation. The original tree used to start a grafted clone for inclusion in a seed orchard is the ortet.

Ovary The enlarged base part of the pistil or carpel in which the ovules appear, the {{ovarium}}. See illustration

[karmaxul]

Ovule The unfertilized young seed in the ovary; the structure which, after fertilization, develops into a seed; the megasporangium of a seed plant which later develops into a seed; a rudimentary seed

Parenchyma The soft green undifferentiated cellular tissue made up of large, bluntended cells with thin cellulose walls found in many plant organs, particularly in the pulp of leaves and fruit and the pith of stems. The tissue is involved primarily with the distribution and storage of carbohydrates