Alkali
A soil contains sufficient exchangeable sodium to interfere with the growth of most crops plants, either with or without appreciable quantities of soluble salts.

Alkaline
A soil for which the pH reading of the saturated soil paste is higher than 7.

Anions
Anions are negatively charged ions such as sulfate SO₄^- and phosphate PO₄^-

Annual
Maturing and living one season only.

Areole
A round or elongated often raised or depressed area on a cactus which is equivalent to a bud and from which spines, flowers, stems, or roots grow

Available Nutrient That quantity of a nutrient element or compound in the soil that can be readily absorbed and assimilated by growing plants.

Awn
A slender bristle at the end or on the back or edge of an organ. In grasses, the awn is usually a continuation of the mid nerve of the glumes or lemmas, rarely of the palea.

axil
Latin: the angle between a branch or leaf and the axis from which it originates.

Bract
The reduced leaves of the inflorescence and upper part of a shoot.

Bud
A structure of embryonic tissues, which will become a leaf, a flower, or both, or a new shoot. Especially the stage in which a growing point spends the winter or a dry season. May be naked or enclosed in bud scales.

Bud Scale
A modified leaf or stipule (there may be one, a few, or many) protective of the embryonic tissue of the bud.

Callus Tissue Wound tissue

Cambium
A thin layer of meristematic cells between the bark and wood that gives rise to new phloem and xylem cells.

Carbon-Nitrogen ratio The ratio of the weight of organic carbon to the weight of total nitrogen (mineral plus organic forms) in soil or organic material.

Cations
Cations are positively charged ions such as calcium Ca⁺, Magnesium Mg⁺, and Sodium Na⁺².

Cation Exchange Capacity(CEC) The clay and organic components of the soil have a negative charge. As a result of these charges, positively charged ions (cations) such as hydrogen H⁺, potassium K⁺, ammonium NH⁺₄, calcium Ca²⁺, magnesium Mg²⁺, aluminum Al³⁺, etc. may be held at the surface of the clay or organic particles and exchanged with other ions in the solution or with ions at the plant root's surface.
This ability of a soil to hold cations is termed its cation exchange capacity (CEC). Since many cations are plant nutrients the cation exchange capacity is a measure of the soil's ability to hold such nutrients. Expressed in milliequivalents per 100 grams or per gram of soil (or other exchangers such as clay).

Chlorosis
A condition in plants resulting from the failure of chlorophyll to develop caused by a deficiency of an essential nutrient. Leaves of chlorotic plants range from light green through yellow to almost white.

Cleistothecia
Cleistothecium (singular). The characteristic fruiting structure of powdery mildew fungi. This is a tiny sphere usually 0.1 to 0.2 mm in diameter. At maturity the cleistothecia liberate ascospores from microscopic sacs (asci) that develop within the sphere. Cleistothecia are at first colorless, then yellow, brown, and finally black in most species.

Corm
A solid, swollen part of a stem. This is typically underground. Plants with corms include Crocus and Gladiolus.

Cultivar
A cultivated variety.

Deciduous
Having leaves that fall at the end of a growing season.

Dieback
Progressive dying from the extremity of part of the plant.

Epicormic Branches
Epi - upon; cormic - stem

Epicormic branches develop from two types of buds:

from dormant buds that developed when the twig was still small and have moved outward with the cambium as the diameter of the branch has enlarged.
from new buds that develop de novo within the cambial zone as needed.

When the stem is injured or a reduction in energy reserves occurs, these buds begin to develop. The resulting branches are weakly attached to the stem.

Floret
The Lemma and Palea with included flower (stamens and pistil).

Frass
Wood fragments mixed with excrement produced by insect larvae.

Genus
Genus - singular; Genera - plural). A category of related organisms, usually containing several species; the first name of an organism in the binomial system of classification.

Glume
The pair of bracts at the base of a spikelet.

Green Manure
Any crop that is grown expressly to be plowed or dug under so as to improve the soil.

Haustoria
{Latin - haurire, to drink} Haustorium, singular; Haustoria, plural. An outgrowth of stem, root, or hyphae of certain parasitic plants which serves to draw food from the host plant.

Heading Back
Also called stubbing, dehorning, or lopping. Main branches are cut to stubs with little regard for their location. Regrowth from below the cuts is dense, vigorous, and upright. The new shoots create a dense head and shade and are weakly attached. While this pruning method is often used to reduce the height of large trees, it is not recommended.

Heartwood
The nonliving inner core of wood, usually darker than sapwood.

Herbaceous
Having no persistent woody stem above ground.

Honey Dew
The sugary deposit forming on plant parts from the droppings of certain insects, such as aphids, mealy bugs, whiteflies and scale insects.

Host
A plant that is invaded by a parasite and from which the parasite obtains its nutrition.

Included Bark
This problem occurs at branch attachments when bark becomes embedded between the branch and stem. This included (embedded) bark creates a weak branch attachment, one which is susceptible to breakage.

Imperfect Stage
A stage in the life cycle of a fungus in which spores are produced without a previous sexual fusion; also called imperfect stage. See Perfect Stage.

Infection
The establishment of a parasite within a host plant.

Inoculum
The pathogen or its parts that can cause infection. That portion of individual pathogens that are brought into contact with the host.

Instar
The period or stage between molts in a larva. These are usually numbered such as 2nd instar.

Larva, Larvae (plural)
A young insect that hatches from the egg and differs fundamentally in form from the adult. A maggot, the larval stage of a fly, is a good example of this difference.

Lemma
The bract of a spikelet above the pair of glumes.

Lenticles
Lenticles are small corky spots on the surface of stems and roots made of loosely packed cells, providing gaseous exchange between the inner tissues and the atmosphere.

Monocarpic
Bearing fruit once and then dying.

Mottled
Spots or blotches of different colors or shades of color interspersed with the dominant color.

Mycelial mat
Fungi that produce hyphae can form a macroscopic surface layer. This is call a mycelial mat. In nature, these may form between the bark and wood of trees, or over the surface of the plant tissue. These are often used to identify the plant disease organism.

Mycelium
The mass of interwoven filaments (hyphae) that makes up the vegetative body of a fungus. This is the portion of the fungus that absorbs nutrients.

Necrotic
From Greek nekrOsis: localized death of living tissue

Palea
The inner bract of a floret.

Parasite
An organism that lives on or in another living organism (called a host). The parasite obtains its food supply from the host. See saprophyte.

Pathogen
Any organism capable of causing disease.

Perennial
Of three or more seasons duration.

Perfect Stage
The stage in the life cycle of a fungus in which spores are produced after sexual fusion. Also known as sexual stage. See imperfect stage.

Periderm
A secondary protective tissue replacing the epidermis; it is made up of cork, cork cambium, and phelloderm

Petiole
The slender stem that supports the blade of a leaf.

Phloem
Inner bark tissue responsible for translocation of foodstuffs (e.g. sugars and starches) produced by green tissue to the roots and other parts of the plant.

Pistil; also pistal
The seed-bearing organ of a flower consisting of ovary, style and stigma; gynoecium.

Pollarding
A training system used on some large-growing trees to keep them to a modest size or to give the landscape a formal look. These trees are severely headed back annually or every few years.

Pollen
The powder produced by anthers, consisting of pollen grains. The male gametophyte is confined to the pollen grain. Each pollen grain contains two cells: the vegetative cell from which the pollen tube develops and the generative cell which produces sperm.

Rhizome
An underground stem. The rhizomes of grasses are usually slender and creeping.

Salts
The soluble salts in soils are mostly combinations of the cations (+ charged ions) sodium, calcium, magnesium and potassium, and the anions (- charged) bicarbonate, chloride and sulfate. When dissolved in water these compounds dissociate (separate) into their respective cations and anions. For example, calcium sulfate (gypsum) will dissociate into calcium cations and sulfate anions.

Dissociation of gypsum

Saprophyte
An organism that uses dead organic matter as its source of food. Different from Parasite.

Sapwood
Living outer layers of wood, usually light in color.

Scalping
Removing an excessive quantity of functioning, green leaves at any one mowing; exposes crowns, stolons, dead leaves and even bare soil resulting in a shabby appearance.

Sodium Adsorption Ratio
A ratio of sodium, magnesium and calcium that is used to express the relative activity of sodium ions in exchange reactions with soil. When the SAR exceeds a certain level (i.e. 10 for most woody plants) the exchangeable soil sodium would be toxic to the plant.

Soil Buffer Compounds
The clay, organic matter, and compounds such as carbonates and phosphates that enable the soil to resist appreciable change in pH.

Sooty Mold
The sooty molds include several species of fungi such as Capnodium and Limacinia that live off "honey dew". While the sooty molds are not parasitic, their black mycelial growth may become so abundant that they can give the leaf and other plant parts a black, sooty appearance. Sooty molds may interfere with the amount of light that reaches these plant parts. Since these fungi live on the excretions of insects, control of the particular insect also results in the elimination of the sooty mold fungi.

Species
A natural group of plants composed of individuals similar in structure and physiology capable of producing similar fertile offspring; usually including several minor variations (subspecies). Different in structure and/or physiology from other such groups and normally do not interbreed with them. A sub component of a genus.

Spore
In fungi, the microscopic reproductive unit consisting of one or more cells; it is analogous to the seeds of green plants.

Sprinkler Zone
A sprinkler zone is a single line of pipe with sprinkler heads attached controlled by a manual or electric valve. The valve provides water to all of the sprinkler heads fed by that zone.

Stigma
The portion of the pistil that receives pollen.

Stomate
An opening or pore on the upper (i.e. water lilies) and/or lower leaf surface through which gas exchange occurs (i.e. oxygen and carbon dioxide) and moisture vapor moves. The size of this opening of the stomate is controlled by `guard cells'. A similar gaseous exchange site (lenticle) exists on stems.

Suberin
A fatty substance present in the cell walls of cork and other plant tissues.

Suberization
The impregnation of plant cell walls with suberin, resulting in cork-like tissue.

Tilth
The state of a soil which makes it suitable to plant growth.

Top dressing
A prepared soil mix added to the turf surface; usually incorporated into the soil by raking or irrigating.

Tuber
A short, thick, usually but not always subterranean stem or branch bearing buds or "eyes" and serving as a storage organ.

Turgor
Plant Physiology: the normal distention or rigidity of plant cells, resulting from the pressure exerted from within against the cell walls by the cell contents.

Turgid: Swollen to firmness.

Virescence
{Latin - virescere, to grow green}. The production of green color in petals instead of the usual pigments.

Winter Annual
Germinates at the end of the summer and over winter as small dormant, but green plants. These plants usually complete their life cycle by the mid summer.

Xylem
The principal strengthening and water/nutrient conducting tissue of branches, stems and roots. The wood of woody plants.

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