gall - abnormal growths that form on plant roots, shoots, and leaves. Galls often result from infection by a fungus, bacteria, etc. or insect infestation such as a certain types of spider mites.

As part of certain insect's life cycle, when they lay their eggs on the leaf or stem of certain plants, they also inject a chemical that stimulates the growth of a gall. Inside the gall, the egg hatches and the new creature feeds inside for a while before emerging to fly away. That is why, on certain gall such as many that grow oak trees, by the end of the season you will find a nice hole in them.
general use pesticide - a pesticide which can be purchased and used by the general public without any special training or licensing.  See Restricted Use Pesticide
genetic - referring to characteristics or groups of chromosomes inherited through the process of sexual reproduction i.e. seeds in plants.
genotype - the genetic makeup of a plant which is inherited through the process of sexual reproduction i.e. seeds. It is expressed in the DNA of the plant. See phenotype.
genus - in the hierarchy of the binomial nomenclature system, plants are grouped because they share certain characteristics. The most closely related plants are in the species, a little broader grouping is the genus and the next wider group is the family. Common characteristics of members of a genus are the similarities of flowers and fruits. The plural is genera.

For example, in the name Hosta sieboldiana,  Hosta is the genus name while sieboldiana is an example of a species (specific epithet).

The proper format is that the genus name is always capitalized and in italics if in print or underlined if hand written.
 
geotropism - growth oriented with respect to the force of gravity. A hormone regulated response of stems and roots to gravity. It is why most plant roots grow down into the earth while the stems grow upwards.
germinate - refers to the initiation of active growth in a seed which occurs when the initial root and stem emerge. In fungi, it is when the germ tube emerges from the spore.
germplasm - a collection of genetically diverse plants, including wild specimens, which can be used to improve future cultivated plants through cross breeding
giant size - according to the The American Hosta Society, there are five size categories of hosta including Giant, Large, Medium, Small and Miniature.

Giant hostas are those where the mound reaches a height of over 28 inches and an area of greater than 144 square inches. Hostas of this size are also occasionally called specimen size.
gibberellin - (gibberellic acid)  a naturally occurring growth hormone that stimulates stem elongation. In some cases, plants that are grown as standards such as Pelargoniums, have stems that were treated with giberellin.
 
girdle or girdling - generally refers to the destruction of the cambium layer around the circumference of a trunk or branch. This can occur when a notch is cut through the bark of a tree with an ax or saw or other physical damage. The cambium layer is broken and interrupted with stops the production of new vascular tissue resulting in death. Other things that can girdle a tree include borer insects (Emerald ash borer) and, sometimes, cankers.
girdling root - trees grown in containers will occasionally develop a root that begins to wrap around the circumference of the pot. If this root is not cut at the time of transplanting, it will continue to curl around the base of the tree and will grow in girth. As the tree trunk also grows in girth, eventually, the root will start to strangle the trunk and will interrupt the cambium layer.

A tree with a girdling root may not show any symptoms for many years after being transplanted. Then, it will begin to lose vigor and decline. The tree will develop fewer and fewer leaves and branches will die. Over time, the entire tree may also die. This is most common on shallow rooted trees such as maples.
glabrous - describes a smooth, hairless leaf texture.
glaucous - a glaucous leaf or stem has a waxy coating or bloom which produces a whitish to blue coloring of leaves or needles. As the growing season progresses, the coating may rub or wash off especially in hot, dry conditions. Many blue hostas will turn green by the end of the summer. This does not hurt the plant but may change the color design combinations in the garden.
glyphosate - this is the active ingredient in many common herbicides including RoundUp, KleenUp, Rodeo and others. It is a non-selective, systemic herbicide with very little carryover. It must be applied to actively growing, green plant tissue and it kills plants by preventing the photosynthesis process.
 
graft - propagation method in which a scion (stem piece or bud) is inserted into a rootstock (stock) so that their cambium layers align and they grow together to form a new plant. If the cambium layers are not properly aligned or it is allowed to dry out, the graft will fail.
graft union - the point where the scion and rootstock (stock) are joined together during grafting.
grass Images of Grass Plants.
green manure - a temporary, cover crop of plants such as certain grains, grasses or legumes that is incorporated (buried) into the soil to add nutrients and organic matter for succeeding crops.
groundcover - a plant whose major roll is to blanket an area of soil with foliage. They often have the characteristic of being able to spread by rhizomes or seeds to rapidly fill the area. See invasive.
growing medium - in this context, a media or medium, refers to the mixture of particles in which seeds germinate or plants are grown (usually in containers). Although it could be a mixture of soils, this usually refers to soilless mixtures used for pot grown plants in greenhouses. This media will consist of various proportions of peat moss, vermiculite, perlite, compost and other materials.
 
growth regulator - either a natural or synthetic compound that controls or modifies the growth process of a plant or insect. In plants, these may be used to keep flowering plants small during greenhouse production. Other regulators such as gibberellin may be used to make stems artificially tall.

Some insecticides act by preventing the insect from moving through its natural growth cycles resulting in its death.
grub - the soil-inhabiting larva of many beetles. Some grubs stay in the soil for one year before becoming beetles while others may take up to 3 years to mature. European chafer grubs have caused widespread damage to turfgrass. Japanese beetle grubs will cause damage in irrigated areas.
guard cells - one of a pair of cells surrounding a stoma usually located on the bottom of leaves. These allow the stoma to open or close to regulate the water loss through the leaves.

Lenticels are similar openings often found on stems but they do not have guard cells so they stay open all the time.
gummosis - oozing of plant sap, often from a plant wound or canker. Gummosis may occur as a result of infection or insect infestation. This is common on peach trees.
guttation - this refers to a water soaked area of a leaf caused by the excessive uptake of water by a plant. This is more common on indoor plants when they are moved from a high humidity situation to a low humidity area.
gymnosperm - a plant with seeds not enclosed in an ovary. They are also called "naked-seed" plants and include the conifers which are plants with generally needlelike foliage and which usually bearing cones such as pines, juniper, and spruce.

See angiosperm.
 

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