Russell M. Burns and Barbara H. Honkala

Acicular foliage- Needle-shaped leaves.

Acropetal- Developing upward from the base toward the apex.

Adventitious- Plant organs produced in an unusual or irregular position, or at an unusual time of development.

Aerobic- Capable of living only in the presence of free oxygen.

Afterripening- Enzymatic process occurring in seeds, bulbs, tubers, and fruit after harvesting; often necessary for germination or resumption of growth.

Air layering- Inducing root development on an undetached aerial portion of a plant, commonly by wounding it, treating it with a rooting-stimulant, and wrapping it in moist material under a waterproof covering, so that the portion so treated is capable of independent growth after separation from the mother plant.

All-aged- A condition of a forest or stand that contains trees of all or almost all age classes. It is generally a primary stand where individuals have entered at various times when and where space permitted. (See Uneven-aged).

Allele- One of an array of genes possible at a certain position (locus) on a given chromosome.

Allelopathy- The influence of plants, other than microorganisms, upon each other, arising from the products of their metabolism.

Allopatric- Occurring in different areas or in isolation. (Cf Sympatric).

Alluvial- A type of azonal soil which is highly variable and is classified by texture from fine clay and silt soils through gravel and boulder deposits.

Alluvium- Soil, usually rich in minerals, deposited by water, as in a floodplain.

Alpha pinene- A hydrocarbon of the terpene class occurring in many essential oils; it has a density of about 0.855 and an index of refraction of about 1.465, both at 25° C (77° F).

Anaerobic- Capable of living in the absence of, or not requiring, molecular oxygen.

Andesite- An extrusive usually dark grayish rock consisting essentially of oligoclase or feldspar.

Anemophilous- Normally wind-pollinated.

Anther- The part of the stamen that develops and contains pollen.

Anthesis-The time at which a flower comes into full bloom.

Apophysis- The rounded, exposed thickening on the scales of certain pine cones.

Appalachian Highlands- The lands of the Appalachian Mountains extending from central New York south to northeastern Alabama.

Arbuscula- A small or low shrub having the form of a tree.

Argillite- A compact argillaceous (clayey) rock differing from shale in being cemented by silica and from slate in having no slaty cleavage.

Arillate- Having an aril (an appendage, outgrowth, or outer covering of a seed, growing out from the hilum or funiculus).

Auxin- A natural hormone that regulates plant growth, generally identified with ß-indolylacetic acid (IAA), a heteroauxin.

Backcross- A cross between a hybrid and either one of its parents.

Basalt- A dark gray to black colored, dense to fine-grained igneous rock.

Basipetal- Developing toward the base from the apex.

Batture- Land between the river and the manmade levees that border it.

Berry- A simple, pulpy fruit of a few or many seeds (but no stones) developed from a single ovary.

Beta phellandrene- A terpene with a density of about 0.84 and an index of refraction of about 1.48, both at 25° C (77° F).

Beta pinene- A terpene with a density of about 0.867 and an index of refraction of about 1.477, both at 25° C (77° F).

Biomass- The total quantity, at a given time, of living organisms of one or more species usually expressed in weight per unit area.

Bisexual- Having both male and female sexual reproductive structures.

Bonsai- The culture of miniature potted trees, which are dwarfed by stem and root pruning and controlled nutrition.

Boreal forest- A coniferous forest of the northern hemisphere characterized by evergreen conifers such as spruce, fir, and pine.

Breast height- 1.37 rn or 4.5 ft above groundline on standing trees, a standard height in USA for recording diameter, girth, or basal area.

Campanulate- Bell-shaped.

Canadian Shield- The Precambrian nuclear mass centered in Hudson Bay around which, and to some extent upon which, the younger sedimentary rocks have been deposited.

Canopy- The more or less continuous cover of branches and foliage formed collectively by the crowns of adjacent trees.

Capsule- A dry usually many-seeded fruit composed of two or more fused carpels that split at maturity to release their seeds.

Carr- A deciduous woodland on a permanently wet, organic soil.

Catena- A sequence of different soils, generally derived from similar parent soil material, each of which owes its character to its peculiar physiographic position.

Catkin- A drooping elongated cluster of bracted unisexual flowers found only in woody plants.

Chromosome- A microscopic, usually rod-like body carrying the genes. Number, size, and form of chromosomes are usually constant for each species.

Cirque- A deep, steep-walled basin shaped like a half bowl, on a mountain.

Clearcut- The cutting method that describes the silvicultural system in which the old crop is cleared over a considerable area at one time. Regeneration then occurs from (a) natural seeding from adjacent stands, (b) seed contained in the slash or logging debris, (c) advance growth, or (d) planting or direct seeding. An even-aged forest usually results.

Cleft graft- The stock is cut off, split, and then one or more scions are placed in this cleft (split) making the cambium layers of the stock and scion match.

Climax community- The terminal stage of an ecological succession sequence which remains relatively unchanged as long as climatic and physiographic factors remain stable.

Clinal- Sloping.

Clone- Any plant propagated vegetatively and therefore considered a genetic duplicate of its parent.

Codominant- (a crown class)-Species in a mixed crop that are about equally numerous and vigorous; forming part of the upper canopy of a forest, less free to grow than dominants but freer than intermediate and suppressed trees.

Collenchyma- Flexible, supportive plant tissue usually of elongated living cells with unevenly thickened walls which are usually interpreted as primary walls.

Colluvium- Rock detritrus and soil accumulated at the foot of a slope.

Conglomerate- Made up of parts from various sources or of various kinds.

Corymb- A flat-topped floral cluster with outer flowers opening first.

Cotyledon- An embryonic leaf, which often stores food materials, characteristic of seed plants.

Crown class- Any class into which trees of a stand may be divided based on both their crown development and crown position relative to crowns of adjacent trees. The four classes commonly recognized are dominant, codominant, intermediate, and suppressed.

Culmination of mean annual increment- For a tree or stand of trees, the age at which the average annual increment is greatest. It coincides precisely with the age at which the current annual increment equals the mean annual increment of the stand and thereby defines the rotation of a fully stocked stand that yields the maximum volume growth.

Cultivar- A contraction of "cultivated variety." It refers to a plant type within a particular cultivated species that is distinguished by 1 or more characters.

Current annual increment (CAI)-The amount by which the volume of a tree or stand increases in 1 year.

Cymose- Bearing a cyme, a more or less flat-topped floral cluster with the central flowers opening first.

Cytokinins- A class of hormones that promote and control growth responses of plants.

Dehisce- To split open when ripe, usually along definite lines or sutures to release seeds.

Deliquescent branching- A mode of branching in trees in which the trunk divides into many branches leaving no central axis, as in elms. (See Excurrent branching.)

Destructive distillation- The decomposition of wood by heating out of contact with air, producing primarily charcoal.

Diallel cross- Complete: a mating design and subsequent progeny test resulting from the crossing of n parents in all possible n ² combinations including selfs and reciprocals. Incomplete: a partial sampling-any individual family or type of family may be omitted. In either type of cross, identities of both seed and pollen parents are maintained for each family.

Dichogamy- In a perfect flower, maturation of stamens and pistils occurs at different times, thus preventing self-pollination.

Dioecious- Having staminate (male) flowers and pistillate (female) flowers on different plants of the same species.

Diorite- A granular crystalline igneous rock commonly of acid plagioclase and hornblende, pyroxene, or biotite.

Diploid- An organism which has two sets of chromosomes in its cells, paternal and maternal.

Disclimax- A relatively stable ecological community often including kinds of organisms foreign to the region and replacing the climax because of disturbance.

DNA- Deoxyribonucleic acid, the carrier of genetic information (genes) in cells.

Dominant (a crown class)- One of four main crown classes recognized, on a basis of relative status and condition in the crop. Dominant trees have their crowns in the uppermost layers of the canopy and are largely free-growing.

Duff- The partially decomposed organic matter (litter of leaves, flowers, and fruits) found beneath plants, as on a forest floor.

Ecotone- Any zone of intergradation or interfingering, narrow or broad, between contiguous plant communities.

Ecotype- A subgroup within a species, which is genetically adapted to a habitat type that is different from the habitat type of other subgroups of that species. It normally has a large geographical distribution.

Ectotrophic mycorrhiza (ectomycorrhiza)- A mycorrhiza growing in a close web on the surface of an associated root; generally formed by basidiomycete fungi.

Edaphic- Pertaining to the soil in its ecological relationships.

Endocarp- The innermost differentiated layer of the pericarp, or fruit wall, as in the stoney part of a drupe.

Endosperm- A nutritive tissue in seed plants formed within the embryo sac.

Endotrophic mycorrhiza (endomycorrhiza)-A mycorrhiza penetrating into the associated root and ramifying between the cells; generally formed by phycomycete fungi.

Epicotyl- The portion of the axis of an embryo or young seedling above the point where the cotyledon(s) is attached.

Epigeal- The part of the seedling above the cotyledon(s). (Cf Hypogeal).

Epiphyte- An organism that grows on another plant but is not parasitic on it.

Even-aged management- The application of a combination of actions that results in the creation of stands in which trees of essentially the same age grow together. The difference in age between trees forming the main canopy level of a stand usually does not exceed 20 percent of the age of the level of a stand at maturity. Regeneration in a particular stand is obtained during a short period at or near the time that a stand has reached the desired age or size for regeneration, and is harvested. Cutting methods producing even-aged stands are clearcut, shelterwood, or seed tree.

Exalbuminous-Descriptive of seeds that lack endosperm.

Excurrent branching- Tree growth in which the main axis continues to the top of the tree from which smaller, lateral branches arise (as in conifers). (See Deliquescent branching.)

Fastigiate form- Strictly erect and more or less parallel vertical branches.

Fbm- Foot (feet) board measure (board foot [feet]).

Fen- A bog with springs as a water source other than precipitation.

Feral goats- Goats that have escaped from domestication and become wild.

Fluvial- Produced by stream action.

Frost rings- A zone of injured cambium tissue caused by frost.

Funiculus- The basal stalk of an ovule arising from the placenta in the angiosperms.

Gabbro- A dark, coarse-textured, heavy rock composed of calcium feldspar and augite with a small amount of quartz.

Gene- The smallest transmittable unit of genetic material consistently associated with a single primary genetic effect.

Genet- A single sexually produced individual.

Germinative capacity- Percentage of seeds that germinate during the normal period of germination.

Germplasm- Within an individual or group the collective materials that are the physical basis for inheritance.

Gibberellin- A plant hormone useful in regulating the growth characteristics of many plants.

Glade- An open space in a forest.

Gneiss- A metamorphic rock derived from either igneous or sedimentary formations.

Graft incompatibility- Said of plants which, when grafted together, fail to form a lasting union.

Granite- A very hard natural igneous rock formation.

Grood soils- Nut-structured soils characteristic of the transition zone between prairie soils and podzolic soils, i.e., prairie-forest soils.

Group selection- The cutting method which describes the silvicultural system in which trees are removed periodically in small groups resulting in openings that do not exceed 0.4 to 0.8 hectare (1 to 2 acres) in size. This leads to the formation of an unevenaged stand in the form of a mosaic of age-class groups in the same forest.

Growing stock level (GSL)- A numerical index. The residual square meters of basal area per hectare (square feet of basal area per acre) when the average stand diameter is 25 cm (10 in) or more in d.b.h. Basal area retained in a stand with an average d.b.h. of less than 25 cm. (10 in) is less than the designated level.

Haploid- An organism with one basic chromosome set symbolized by n.

Harden-off- The process of gradually reducing the amount of water and lowering the temperature for plants in order to toughen their tissues, making it possible for them to withstand unfavorable (usually cold) environmental conditions.

Hedging- Close-cropping.

Heptane- Any of several isometric hydrocarbons of the methane series.

Hermaphrodite (bisexual)- A flower with both functional male and female reproductive organs.

Heterozygote- An organism whose cells have one or more sets of unlike alleles.

High-lining- The underside of a forest canopy that is uniformly cropped by deer at the highest level they can browse. A browseline.

Hilum- The scar on a seed marking the point of attachment of the ovule.

Hybrid swarm- An extremely variable population derived from the hybridization of two different taxa and consisting of the products of subsequent segregation and recombination, backcrossing, and crossing between the hybrids themselves. It occurs where the range of inter-fertile species overlap.

Hydroponics- The cultivation of plants, without soil, in water solutions of nutrients required for growth.

Hydrosere- An ecological sere (plant community) originating in an aquatic habitat.

Hypanthium- A floral tube formed by the fusion of the basal portions of the sepals, petals, and stamens, and from which the rest of the floral parts emanate.

Hypocotyl- The part of an embryo or seedling below the cotyledon(s) and above the radicle (but sometimes including it).

Hypogeal- Describes seed germination in which the colytedons remain beneath the surface of the soil. (Cf Epigeal).

Hypogeous- Growing or developing below the soil surface.

Igneous rock- Formed by solidification of molten magma.

Imperfect flower- A flower which lacks either stamens or carpels.

Inbreeding- In plants, a breeding system in which sexual reproduction involves the interbreeding of closely related plants by self-pollination or backcrossing.

Individual tree selection- The cutting method that describes the silvicultural system in which trees are removed individually, here and there, each year over an entire forest or stand. The resultant stand usually regenerates naturally and becomes all-aged.

Indolebutyric acid (IBA)- A synthetic auxin widely used in horticulture to induce rooting of cuttings.

Inland Empire- A region in eastern Washington, northern Idaho, and western Montana, named for commercial purposes.

Intergeneric- Existing or occurring between genera.

Intermediate (a crown class)- A tree of the middle canopy dominated by others in the dominant and codominant crown classes.

Intermountain- In the Forest Service, an area that includes the States of Montana, Idaho, Utah, Nevada, and the western quarter of Wyoming.

Intraspecific- Refers to some relationship between the members of the same population or species.

Introgression- The entry or introduction of a gene from one gene complex to another.

Isoline- Isogram; a line on a map or chart along which there is constant value (temperature, pressure, or rainfall).

Isozymes (isoenzymes)- Any two or more chemically distinct but functionally like enzymes.

Jackstrawed fuel- Trees that have fallen in tangled heaps.

Juvenile cuttings- The youngest parts of the branches are severed from the plant and rooted to produce new plants.

Karyotype- The character of the chromosomes as defined by their size, shape, and number.

Knee- An abrupt bend in a stem or tree trunk, or an outgrowth rising from the roots of some swamp-growing trees such as baldcypress.

Krummholz- The stunted growth habit, literally crooked wood, caused by wind and found in certain tree species at their upper limit of distribution.

Cushion krummholz- Alpine trees exposed to severe wind conditions are wind-pruned to a cushion-like mat.

Flagged krummholz- The tallest trees protrude from the protective snow pack and become wind-battered "flags."

Lacustrine- Related to or growing in lakes.

Lake Agassiz Basin- A late glacial and early post-glacial lake area in southern North Dakota and western Minnesota.

Lake States- Those States bordering the Great Lakes, that is, Minnesota, Wisconsin, Illinois, Indiana, Michigan, Ohio, Pennsylvania, and New York.

Lammas- The part of an annual shoot that is formed after a summer pause in growth.

Layering- The rooting of an undetached branch, laying on or partially buried in the soil, which is capable of independent growth after separation from the mother plant.

Leaf area index (LAI)- Leaf surface area per unit of land surface area. For broad-leaf forests, the index is calculated using only one side of the leaf blade; for needle-leaf stands the total leaf surface is used; and, for mixed broad- and needle-leafed stands, a combination of the two is used.

Lightwood (fatwood, lightered wood or stumps, stumpwood)- Coniferous wood having an abnormally high content of resin and therefore easily set alight (afire).

Lignotubers- A woody swelling at ground level originating from the axils of the cotyledons from whose concealed dormant buds a new tree can develop if the old one is injured. Characteristic of many Eucalypts.

Limonene- A component of pine turpentine with a density of approximately 0.84 and an index of refraction of about 1.47, both at 25° C (77° F).

Litter- The uppermost layer of organic debris on a forest floor consisting essentially of freshly fallen or only slightly decomposed vegetable matter, mainly foliage but also bark, twigs, flowers, and fruits. The L-layer of the organic portion of the soil profile.

Loess- A uniform and unstratified fine sand or silt (rarely clay) deposit transported by wind (an aeolian soil). It is sometimes described as rock flour.

Lumen- Either the cell cavity or a unit of luminous flux equal to the light emitted by a uniform point source of one candle intensity.

Lye- A strong alkaline solution of sodium hydroxide, potassium hydroxide, or the leachate of wood ashes that is rich in potassium carbonate.

Maceration- The process of removing the fleshy tissue surrounding seeds, often by soaking in water.

Macronutrients- The nutritional elements, nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur, essential for normal plant growth, development, and reproduction. They are usually derived from the soil.

Mean annual increment (M.A.I. or m.a.i.)- The total increment of trees in a stand up to a given age, divided by that age, usually expressed in annual cubic meters of growth per hectare (cubic feet of growth per acre).

Megagametophyte- The female gametophyte which develops from the megaspore and produces the female gamete(s).

Megasporangium- The sporangium in which megaspores are produced; the nucellus of seed plants.

Megaspore- In plants having two types of haploid spores (microspores (male) and megaspores (female)), megaspores give rise to megagametophytes.

Meiosis- Reduction division resulting in the production of haploid gametes; a process consisting of two specialized nuclear divisions ultimately leading to the formation of eggs or sperm.

Meristem- Tissue primarily associated with protoplasmic synthesis and formation of new cells by division.

Mesic- Characterized by intermediate moisture conditions, neither decidedly wet nor decidedly dry.

Mesophyte- A plant whose normal habitat is neither very wet nor very dry.

Mesozoic- An era of geologic history marked by the cycads, evergreen trees, dinosaurs, marine and flying reptiles, and ganoid fishes.

Metamorphism- A pronounced change effected by pressure, heat, and water that results in a more compact and more highly crystalline condition.

Micronutrients (trace elements)- Nutritional elements necessary in minute quantities for normal plant growth, such as boron and manganese.

Micropyle- A minute opening in the integument of an ovule through which the pollen tube normally passes to reach the embryo sac, usually closed in the mature seed to form a superficial scar.

Microsporangium- In plants having two types of haploid spores (microspores and megaspores), the saclike structure in which microspores are produced.

Microspore- A haploid spore produced by meiosis of the microsporocyte and developing into the male gametophyte. The pollen grain of seed plants.

Mine spoil- Earth and rock excavated from a mine.

Mitosis- Normal division of a nucleus into two identical daughter nuclei by a process of duplication and separation of chromosomes.

Monadnock- A hill or mountain of resistant rock surmounting land of considerable area and slight relief shaped by erosion.

Monoecious- Having staminate and pistillate flowers in separate places on the same plant.

Montane- The biogeographic zone made up of relatively moist cool upland slopes below timberline that is characterized by large evergreen trees as a dominant life form.

Mor- A layer of organic material made up of largely unrecognizable plant debris and their decomposition products overlain by litter and lying on the surface of, and essentially unmixed with, the mineral soil. Earthworms are absent.

Muck- Highly decomposed organic material formed under conditions of waterlogging, with few recognizable remains of the original plants.

Mull- A soil whose upper mineral layer has become intimately mixed (mainly through the action of earthworms) with amorphous organic material, sometimes to a depth of 1.2 to 1.5 meters (4 to 5 feet).

Mycelium- The mass of threadlike filaments constituting the vegetative body of a fungus.

Natural pruning (self pruning)- The freeing of the stem of a standing tree of its branches by natural death, disintegration, and/or fall, from such causes as decay, or deficiency of light or water, or snow, ice, and wind breakage.

Naval stores- The products of the resin industry. In the United States they are turpentine, rosin, pine tars, and pitch. Gum naval stores refer specifically to gum turpentine and gum rosin; wood naval stores to wood turpentine and wood rosin.

Normal yield table- A table showing, for one or more species in a fully stocked stand, the growth pattern of a managed even-aged stand derived from measurements at regular intervals covering its useful life. It includes mean d.b.h. and height, number of stems, and standing volume per unit area. The table may also contain a variety of other useful data.

North Central- In the Forest Service, an area that includes Indiana, Illinois, Michigan, Wisconsin, Minnesota, Iowa, and Missouri.

Northeastern- In the Forest Service, an area that includes the New England States plus New York, New Jersey, Delaware, Maryland, Pennsylvania, Ohio, West Virginia, and Kentucky.

Nucellus- The tissue of an ovule, in which the female gametophyte (embryo sac) develops; the megasporangium.

Old growth- Stands of forest trees of either seral or climax species growing singly or in association with other tree species. The stands are usually well past the age of maturity as defined by the culmination of mean annual increment and often exhibit characteristics of decadence. These characteristics may include, but are not limited to: low growth rates, dead and dying trees, snags, and down woody material. The stands are usually characterized by large diameter trees relative to species and site potential, multi-layered canopies, a range in tree diameter sizes, and the presence of understory vegetation. The specific attributes of an old-growth stand are primarily dependent on plant associations and forest cover type.

Oleoresin- The nonaqueous secretion of resin acids dissolved in a terpene hydrocarbon oil which is produced in, or exuded from, the intercellular resin ducts of a living tree or accumulated, together with oxidation products, in the dead wood of weathered limbs or stumps. Commonly called pine gum, gum, pitch, or even sap.

Open-grown- In reference to trees, grown in the absence of woody competition.

Operculum- A caplike structure composed of fused sepals and petals that suggests a lid.

Organic soils layers
L-layer--Freshly fallen or only slightly decomposed leaves, twigs, flowers, fruit, and bark lying on the soil surface.
F-layer--Zone of active organic matter fermentation.
H-layer--Humidified zone. The more or less stable fraction from the decomposed soil organic material. Generally, it is amorphous, colloidal, and dark colored.

Ortet- An original plant from which a vegetatively propagated clone has been derived.

Overstory- That portion of the trees in a forest of more than one story forming the upper or uppermost canopy layer.

Ovulate- Bearing or possessing ovules.

Pacific Northwest- In the Forest Service, an area that includes the States of Washington and Oregon.

Pacific Southwest- In the Forest Service, the States of California, and Hawaii plus Guam and the Trust Territories of the Pacific Islands.

Parthenocarpy- The development of fruit without viable seed. It may be induced artificially, as by some foreign pollen, or with hormones.

Peat- Undecomposed or only slightly decomposed organic matter accumulated under conditions of excess moisture. Plant residues show little, if any, morphological change.

Peduncle- A stalk bearing a flower, flower cluster, or a fructification.

Perfect flower- A flower having both stamens and carpels; may or may not have a perianth.

Perianth- A collective term for the floral envelopes, usually the combined calyx and corolla, or tepals of a flower.

Pericarp- The wall of a ripened ovary (fruit) that is homogeneous in some genera and in others is composed of three distinct layers, exocarp, mesocarp, and endocarp.

Permafrost- Permanently frozen ground; generally refers to a layer at some depth below the soil surface. Any layer above it, which thaws in summer, is termed the active layer.

Phenotype- The plant as observed; the product of the interaction of the genes of an organism (genotype) with the environment.

Photoperiodism- The physiological response of an organism to the periodicity and duration of light and darkness which affects many processes including growth, flowering, and germination.

Phyllodes- A flat expanded petiole that replaces the blade of a foliage leaf and which functions in photosynthesis.

Pioneer- A plant capable of invading a newly exposed soil surface and persisting there until supplanted by successor species.

Pistil- Ovule-bearing organ of an angiosperm composed of ovary, style, and stigma. Collectively the pistils are called the genoecium.

Pistillate- Having only female organs. May apply to individual flowers or inflorescences, or to plants of a dioecious species in angiosperms.

Ploidy- Degree of repetition of the basic number of chromosomes.

Plus-tree- A phenotype judged, but not proven by test, to be unusually superior in some quality or qualities.

Podzol- A soil characterized by a superficial layer of raw humus above a generally grey A horizon of mineral soil depleted of sesquioxides of iron and aluminum and of colloids and overlying a B horizon wherein organic matter and/or sesquioxides of iron have accumulated.

Pole-size- A young tree with a d.b.h. of not less than 10.2 cm (4 in). A small pole has a maximum d.b.h. of 20.3 cm (8 in), and a large pole has a maximum d.b.h. of 30.5 cm (12 in).

Polygamo-dioecious- Bearing perfect and pistillate flowers on female trees and only staminate flowers on male trees.

Polygamous- Plants bearing both perfect and imperfect flowers.

Polymorph- One of several forms of an organism.

Primordium- An organ, a cell, or an organized series of cells in their earliest stage of differentiation, e.g., leaf primordium, sclereid primordium, vessel primordium.

Proembryo- Embryo in early stages of development, often the stages before the main body and suspensor become distinct.

Propagule- A plant part such as a bud, tuber, root, or shoot used to reproduce (propagate) an individual plant vegetatively.

Protandry- The termination of shedding of pollen by a flower prior to the stigma of the same flower being receptive.

Proteranthous- Having flowers appearing before the leaves.

Protogyny- The termination of receptivity prior to the maturation of pollen on the same plant or flower.

Provenance- The original geographic source of seed, pollen, or propagules.

Pumice- A volcanic glass full of cavities and very light in weight.

Pyrene- The pit or seed of a drupe which is surrounded by a bony endocarp.

Pyric- Resulting from, induced by, or associated with burning.

Ramet- An individual member of a clone, derived from an ortet.

Receptivity- The condition of the female flower that permits effective pollination.

Rocky Mountains- In the Forest Service, an area that includes the Dakotas, Nebraska, Kansas, Oklahoma, and Texas west of the 100th meridian, New Mexico, Arizona, Colorado, and the eastern three-quarters of Wyoming.

Saddle- A ridge connecting two higher elevations.

Samara- A dry, indehiscent, winged fruit, one-seeded as in Fraxinus and Ulmus or two-seeded as in Acer.

Sapling- A tree more than 0.9 in (3 ft) in height and less than 10.2 cm (4 in) in d.b.h.

Savannah- Essentially lowland tropical and subtropical grassland, generally with a scattering of trees and/or shrubs. If woody growth is absent it is termed a grass savannah; with shrubs and no trees, a shrub savannah; or with shrubs and widely irregularly scattered trees, a tree savannah.

Scarification (for seed)- Pregerminative treatment to make seed coats permeable to water and gases; accomplished usually by mechanical abrasion or by soaking seeds briefly in a strong acid or other chemical solution.

Schist- A metamorphic crystalline rock having a closely foliated structure divisible along approximately parallel planes.

Scion- An aerial plant part, often a branchlet, that is grafted onto the root-bearing part of another plant.

Sclerenchyma- A protective or supporting tissue in higher plants composed of cells with walls thickened and lignified and often mineralized.

Sedimentary- Formed by or from deposits of sediment.

Seed coat (testa)- The outer coat of the seed derived from the integument(s).

Seedling- A tree grown from seed that has not yet reached a height of 0.9 m (3 ft) or exceeded 5.1 cm (2 in) in d.b.h., which would qualify it as a sapling.

Seed tree- The cutting method that describes the silvicultural system in which the dominant feature is the removal of all trees except for a small number of seed bearers left singly or in small groups, usually 20 to 25 per hectare (8 to 10 per acre). The seed trees are generally harvested when regeneration is established. An even-age stand results.

Selection- See Group selection and Individual tree selection.

Self-pruning- See Natural pruning.

Selfing (self pollination)- The pollination of an individual or biotype with its own pollen, the offspring being termed selfs.

Sere- A sequence of plant communities that successively follow one another in the same habitat from the pioneer stage to a mesic climax.

Serotinous- Late in developing; particularly applied to plants that flower or fruit late in the season and to fruit and cones that remain closed for a year or more after the seeds mature, but also to bud opening, leaf shedding, etc.

Serpentine- A mineral or rock consisting essentially of a hydrous magnesium silicate. It usually has a dull green color and often a mottled appearance.

Serpentinite- A rock consisting almost wholly of serpentine minerals derived from the alteration of previously existing divine and pyroxene.

Sessile- Without a stalk; sitting directly on its base.

Shade-tolerance classes- Very intolerant, intolerant, intermediate, tolerant, very tolerant.

Shelterwood- The cutting method that describes the silvicultural system in which, in order to provide a source of seed and/or protection for regeneration, the old crop (the shelterwood) is removed in two or more successive shelterwood cuttings. The first cutting is ordinarily the seed cutting, though it may be preceded by a preparatory cutting, and the last is the final cutting. Any intervening cutting is termed a removal cutting. An even-age stand results.

Sialic- Light rock rich in silica and alumina, and typical of the outer layer of the earth.

Silvicultural system- A process whereby forests are tended, harvested, and replaced, resulting in a forest of distinctive form. Systems are classified according to the method of carrying out the fellings that remove the mature crop with a view to regeneration and according to the type of forest thereby produced. These are individual tree selection, group selection, shelterwood, seed tree, and clearcut.

Site class- A measure of the relative productive capacity of a site based upon the volume or height (dominant, codominate, or mean) or the maximum mean annual increment of a stand that is attained or attainable at a given age.

Site index (Sl)- A measure of site class based upon the height of the dominant trees in a stand at an arbitrarily chosen age, most commonly at 50 years in the East and 100 years in the West.

Skep- A woven straw beehive.

Soil orders- The 10 soil orders used by the Soil Conservation Service of the USDA in their basic system of soil classification are: Alfisol, Aridisol, Entisol, Histosol, Inceptisol, Mollisol, Oxisol, Spodosol, Ultisol, and Vertisol.

Solum- The upper and most weathered part of the soil profile, i.e., the A and B horizons.

Southeastern- In the Forest Service, an area that includes Virginia, the Carolinas, Georgia, and Florida.

Southern- In the Forest Service, an area that includes Alabama, Tennessee, Mississippi, Arkansas, Louisiana, and Oklahoma and Texas east of the 100th meridian.

Southern pines- Within the United States, the 10 species of hard pines with major portions of their ranges below the Mason-Dixon line, i.e., longleaf, shortleaf, slash, loblolly, spruce, Virginia, sand, pitch, Table Mountain, and pond pine.

Sporangium- A hollow, unicellular or multicellular saclike, spore-producing structure.

Sporophyll- A modified leaf or leaflike structure which bears sporangia, e.g., the stamens and carpels of the angiosperms.

Staminate- Having pollen-bearing organs (stamens) only. May apply to individual male plants of a dioecious species or to flowers, inflorescences, or strobili.

Stand density- A measure of the degree of crowding of trees within stocked areas, commonly expressed by various growing-space ratios such as crown length to tree height, crown diameter to diameter at breast height (1.37 m or 4.5 ft above the ground) (d.b.h.); crown diameter to tree height; or of stem (triangular) spacing to tree height.

Stemflow- Precipitation that is intercepted by vegetative cover and runs down the stem or major axes of such cover.

Steppe- Arid land with xerophilous vegetation usually found in regions of extreme temperature range and loess soil.

Stereome- A collective physiological term for all supporting tissues in a plant, such as sclerenchyma and collenchyma.

Sterigma- A peg-shaped projection to which the leaves of some conifers (as spruces) are attached on the twigs.

Stigma- The part of the pistil, usually the tip, often sticky, which receives the pollen and upon which the pollen germinates.

Stipe- A supporting stalk, such as the stalk of a pistil, a gill fungus, or the petiole of a fern leaf.

Stipule- A small structure or appendage found at the base of some leaf petioles, usually present in pairs. They are morphologically variable and appear as scales, spines, glands, or leaflike structures.

Stoma- A pore in the epidermis and the two guard cells surrounding it. Sometimes applied only to the pore.

Stool- A living stump capable of producing sprouts.

Stratification- A pregerminative treatment to break dormancy in seeds and to promote rapid uniform germination accomplished by exposing seeds for a specified time to moisture at near-freezing temperature sometimes with a preceding exposure to moisture at room temperature.

Strobilus- The male or female fruiting body of the gymnosperms.

Style- The stalk of a pistil which connects the stigma with the ovary.

Suppressed (a crown class)- Very slowly growing trees with crowns in the lower layer of the canopy and leading shoots not free. Such trees are subordinate to dominants, codominants, and intermediates in the crown canopy.

Sympatric- Species or populations inhabiting the same or overlapping areas. Cf Allopatric.

Sympodial- A branching growth pattern in which the main axis is formed by a series of successive secondary axes, each of which represents one fork of a dichotomy.

Taungya method- The raising of a forest crop in conjunction with a temporary agricultural crop.

Taxon- Any formal taxonomic group such as genus, species, or variety.

Tepal- Perianth parts undifferentiated into distinct sepals and petals.

Terpene- Any of various isometric hydrocarbons found especially in essential oils (as from conifers), resins, and balsams.

Testa- The outer coat of the seed derived from the integument(s).

Tetraploid (polyploid)- A cell, tissue, or organism having four sets of chromosomes.

Thermic soil temperature- The mean annual soil temperature is 15° C (59° F) or higher but lower than 22° C (72° C), and the difference between mean summer and mean winter soil temperature is more than 5° C (9° F) at a depth of 50 cm (20 in).

Throughfall- All the precipitation reaching the forest floor minus the stemflow, i.e., canopy drip plus direct precipitation.

Top-to-root ratio or root-to-shoot ratio- The relative weights or volumes of the epicotyl and the hypocotyl of a tree seedling, expressed as a ratio.

Tracheid- An elongated, thick-walled, nonliving conducting and supporting cell found in the xylem of most vascular plants.

Triploid- A cell, tissue, or organism having three sets of chromosomes.

T.S.I. (timber stand improvement)- A loose term comprising all intermediate treatments made to improve the composition, constitution, condition, and increment of a timber stand.

Tuff- A rock composed of the finer kinds of volcanic detritus usually fused together by heat.

Umbo- A blunt or rounded projection arising from a surface, as on a pine cone scale.

Uneven-aged- A condition of forest or stand that contains intermingled trees that differ markedly in age. By convention, a minimum range of 10 to 20 years is generally accepted, though with rotations of not less than 100 years, 25 percent (USA) of the rotation may be the minimum.

Variety- A subdivision of a species, usually separated geographically from the typical, having one or more heritable, morphological characteristics which differ from the typical even when grown under the same environmental conditions; a morphological variant.

Xerophyte- A plant that is adapted to dry or and habitats.