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Home >>Botany Dictionary>>Wallace Effect - Wracks
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Wallace Effect - The idea postulated by A.R. Wallace that the reproductive barriers may be developing within a species and subsequently improve by selection. The intermediate phenotypes between optimum phenotopes (favoured by selection) have been found to be less suited in the particular environ-ments of the areas and will get eliminated by selection. Hence, hybrids between optimum species become disadvantageous and hybridization shall be selected against.
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Wall Pressure - The force which is exerted by cell wall on the cellcontents. It is equal and opposite to the turgour pressure.
Warburg Effect - Used for the inhibition of carbon dioxide assimilation and photosynthesis by atmospheric oxygen given by O. Warburg in 1920. Later it had been found to be due to photorespiration.
Weismannism - The theory postulated by A. Weismann in 1886. It postulated the continuity of germ plasm and opposed the idea of inheritance of acquired characteristics. The body of organism is known as soma and the reproductive cells the germ plasm. Only germ plasm are involved in the inheritance of characteristics. Weismann postulated that germ plasm was set aside during early development and was not influenced by subsequent changes in the soma.
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Wart - A small blunt-tipped rounded up growth caused by a fungusdisease.
Water Balance - The relation between the water taken in by a plantand the water given out by it.
Water Bloom, Water Flower - Development of large masses of
algae, mostly Myxophyceae suddenly on bodies of freshwater.
Weight A differential value. which has been assigned for estimating a quantity, relative to other estimates of the same quantity, for the purpose of combing the estimates, Generally its invariance or amount of informationhas been taken as the weight for each estimate of a series for the purpose of combining the estimates. Generally its invariance or amount of information has been taken as the weight for each estimate of a series.
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Water Culture - An experimental set up for determining the mineral requirement of a plant. The plant is made to grow with its roots dipping in solutions of known composition.
Water Moulds - Used for members of order Saprolegniales of Oomycetes having about 32 genera and 240 species which are aquatic, mainly saprophytic fungi and often with diplanetic zoospores. Some act as parasites on fish e.g., Saprolegnia parasitica which often attacks salmon and goldfish.
Wax - A mixture of esters of higher fatty acids with higher monohydric alcohols or sterols. It may also have odd - carbon alkanes, long, chain monoketones, β-hydroxyketones and secretory alcohols. These are important constituents of waxy cuticle which is covering the plant organs and are manufactured as oil droplets in epidermal cells from where they get migrated to the outer surface of the plant via tiny canalculi in cell wall and crystallize as rods and platelets. The main function of wax is to maintain water balance.
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Water Potential - Symbol ψ. The potential which is responsible for movement of water molecules from one place to another place. As water potential of pure water at normal temperature and pressure is considered to be zero and addition of solute lowers the water potential, it means that the water potential of a solution is always negative. Water tends to move from high water potential towards the lower water potential. In an osmotic system, water potential is given as follows:
water potential (ψ) = osmotic potential (ψo) + matric potential (ψm) + pressure potential (up).
The term 'water potential' has now replaced the osmotic pressure. It differs from osmotic pressure in taking capillary and imbibitional forces into account.
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Weed - Any wild plant of no use to man which makes its way into farm fields and gardens where it is not desired.
Weighted Mean - A mean obtained if different classes of observation or quantities give different weights in calculation.
Wet Rot - A plant disease which gets characterized by disintegration of tissues and release of cell fluids e.g. Brown rot of stored fruits like apples and plums is caused by members of Sclerotinia and wet rot of timber by various fungi such as Coniophora Puteana and Poria vaillanui.
Wild (of a plant or animal). Not cultivated or domesticated being of a sort produced without the help or care of man, living, having growth in natural conditions.
Whorl - Used for the arrangement of organs in such a way that theyarise from another organ at a common level.
Wilt (of a plant, leaf or stem). Become soft and undergo a stopping
of growth because the loss of water is not made up by intake,as in very dry weather.
Wilting Coefficient - The percentage of water present in the earthwhen plants rested in it undergo wilting.
Wilting Point - The pF value if the soil cannot supply water repidly
enough for making up the losses by transpiration.
Wind Dispersal - The occurring of dispersal of spores, seeds andfruits bywind.
Wind Pollination - The conveyance of pollen from anther to stigmas by wind.
Wing - (1) One of lateral petals in the Papilionaceae.
(2) A flattened outgrowth from a fruit or seed which increases, the area without increasing the weight. It takes part in wind dispersal.
(3) The downwardly continuing base of a decurrent leaf.
Winter Annual - A plant living for a short duration. It grows, and sets its seeds in the colder parts of the year, dies, and survives the rest of the year as seed.
Winter - Green Plants - Small plants retaining their green leavesthroughout the winter.
Witches Broom - A dense tuft of weak branches which is formed ona woody plant attack by a parasite.
Wood - Xylem which is made chiefly of compounds or lignin and cellulose mixed with some inorganic substances.
Wood Fibre - A thick - walled elongated dead element occurring in wood. It gets developed by the elongation and lignification of the wall of a single cell. It is different from a tracheid in its thicker wall, and general inability for conducting water.
Wort - A liquid made from malt which is used in making cultures
of bacteria.
Wound Cork - A layer of cork cambium and cork which is formed
below and around wounds. It heals the damage, and does notall the entry of parasites into the plant.
Wound Hormone - A substance formed in wounded tissue, whichmay affect the subsequent development of parts of the plant.
Wound Parasite - A parasite which can only enter into the body ofa plant through a wound.
Wound Tissue - A pad of parenchymatous cells which are formedby a cambium after wounding. It may result in the formationof groups of meristematic cells from roots and buds form.
Wound wood - A mass of parenchymatous cells which are formed at a wounded surface.
Wracks - Used for members of order Fucales of brown algae (Phaeophyta). They are solely marine and consist of large proportion of the vegetation of coastal littoral zone. Thallus is parenchymatous and gets modified variously. Reproduction is cogamous and gametangia get developed in specialized conceptacles. The life cycle of plants has been diplontic
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