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Galen - Aelius (Claudius) Galenus of Pergamon 129 - 216 AD was a renowned Greek physician, philosopher, anatomist and prolific author. His published herbal remedies incorporated plants from all over the (known) world, often based on earlier recipes and were an important influence in medicine into the 16th century. However, Galen's focus on the medicinal essences in plants provides little detail of morphology or taxonomy. Galen followed the Aristotelian doctrine of natural form following function, later expressed as the Doctrine of Signatures.
Galvanotropism - bending, growth or movement of a part under the influence of an electric current.
See also: Tropism.
Gamete - the male and female sexual cells that combine at fertilisation to form the zygote.
Gametophyte, Gametophore - the part of the plant which bears the gametes or sexual cells. The haploid state of life of a sexually reproducing plant.
Gamopetalous - (sympetalous), of a flower with the petals of the corolla more or less fused, to form a tube or funnel.
Gelatinous - a slimy and sticky jelly-like substance with a water base.
Geminate - arranged in pairs.
Gene - an inheritable factor, carried on the chromosomes, determining a character or trait in an organism.
Generic - pertaining to a genus.
Genetics - the study of inheritance of characteristics.
Genotype - the genetic characteristics of an organism.
Genus - (pl. Genera) a group of related species with sufficiently distinct unique characteristics in common to be treated as a separate unit. The name of the genus forms the first part of the binomial name of each species, and is always capitalised.
Geophyte - a perennial plant propagated by buds on underground bulbs, tubers, or corms that act as food storage organs and enable the plant to survive adverse conditions such as drought or Winter.
Geotropism - a growth response to gravitational forces causing bending, growth or movement of a part under the influence of a gravitational field.
See also: Tropism.
Germination - the sprouting of a seed. Development of a spore.
Gibberellin - a group of plant hormones based on gibberellic acid produced by seeds, mosses, ferns, algae and fungi. Gibberellins stimulate synthesis of nucleic acids and proteins and promote cell elongation, meristematic growth at the root and shoot tips, mobilisation of food reserves in seeds and other processes. Their absence results in the dwarfism of some plant varieties. These relatively expensive chemicals have been used commercially in the production of seedless grapes and navel oranges and in plant micropropagation from tissue culture and have been found to reverse the effects of some herbicides. Compare with auxins which inhibit root growth in high concentrations.
Gibbous - swollen on one side, usually near the base, to form a pouch or sack.
Glabrous - smooth, without hairs or protrusions.
Gland - a multi- cellular secretory structure producing oil, resin or other liquid, usually as a protruberance or appendage, but sometimes as part of a surface.
Glaucous - bluish grey or bluish green often as a result of a wax-like bloom.
Epithets: Glauca - Glaucum - denote plants with glaucous foliage.
Glaucescence - a fine bloom, blush or coating of whitish or bluish-white substances, usually microscopic particles of wax, easily rubbed off the surface.
Globose - spherical or spheroidal.
Glochids - spines or hairs, usually small, brittle and barbed. Occurring in tufts and characteristic of Opuntioideae.
See also: arachnoid, barbate, canescence, capillaceus, capillatus, ciliate, cephalium, coma, felt, lanate, lasiacantha, penicillate, pubescent, pubispina, scabrous, trichome villous, woolly
Glycoprotein - a diverse group of proteins which are modified by addition of short chains of typically 8-10 sugar residues covalently linked to their polypeptide structure.
Gracilis - slender.
Graft - a shoot, bud or other tissue joined to, and growing on, another compatible plant.
Greenhouse effect - the trapping of heat from sunlight by atmospheric gases ( greenhouse gases ), including carbon dioxide, methane and water, which raises planetary temperatures above those expected from a simple model of heat radiation received from the sun and re-radiated into space. The high surface temperature on the planet Venus is caused by an extreme form of greenhouse effect.
Grey Water - effluent water suitable for use in gardens, from light domestic use for baths, showers, washing clothes or dishes and containing less nitrogen and less likely to be a disease vector than water from toilets.
Guard cell - one of two crescent-shaped cells which surround and control the opening and closing of the aperture of the stoma and thereby regulate passage of gases and water vapour through a plant's epidermis.
Gum - material resulting from the breakdown of plant cells including their carbohydrates. On exposure to air, gums dry and harden.
Gummifera - bearing gum.
Guttation - exudation of liquid water from plants.
Guttered - of leaf margins folded inward.
Gynoecium - the female part of the flower consisting collectively of the carpel(s) or pistil(s).
Gymnosperm - with naked or unprotected ovules (seeds) e.g. conifers, cone-bearing plants such as Welwitschia. Gymnosperms do not produce flowers, but instead release pollen through the air to the female ovule, causing fertilization.
Gynostegium - a crown of united stamens and style protecting the gynoecium and typical of milkweeds (Asclepias).