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Glossary: A is for ... acorn, angiosperm, and autotroph.
by Ariadne Unst

Glossary of A...

abiotic factor (n.)
A non-living component (such as chemical elements, light, water, and wind). Contrast with biotic factor.

acaulescent (adj.)

achene (n.)
A small, dry, one-seeded fruit that does not split open; from an ovary with a single chamber.

acid rain (n.)
Sulphur and nitrogen oxides (released into the atmosphere by heavy industry and auto emissions) transform into acids, which fall to earth in rain and snow.

active layer (n.)
Upper zone of soil that (in higher latitudes) experiences daily and seasonal freeze and thaw.

acorn (n.)
The fruit of an oak; A one-seed nut fixed in a woody cup.

acyclic (adj.)
Having floral parts that are arranged spirally (instead of in whorls).

adiabatic (adj.)
A process where no heat enters or leaves the system. In the atmospherie, when air rises, it expands because of a reduction in pressure. In the absence of non-adiabatic processes (condensation, evaporation, radiation), expansion causes the air to cool at about 1 degree per 300 feet.

aerobic (adj.)
Able to live only in the presence of free oxygen.

A horizon (n.)
The soil horizon below the O horizon and above the B horizon . In this layer, humus and other organic materials are mixed with mineral particles, while finer particles and soluble substances are washed out.

akene (n.)
A small, hard, indehiscent one-seeded fruit from a 1-chambered ovary. Often it appears as a naked seed, such as a sunflower seed.

alate (adj.)
Having wings or wing-like structures.

alien species (n.)
A species that is not native to (i.e., not found in, unless imposed by humans) a region. "It is estimated that alien species now make up as much as 18 percent of the plant populations of the northeastern states" [ Jane Scott].

alkaline (adj.)
Soils that are basic rather than acidic with a PH value greater than 7.0. They contain large amounts of salts of sodium and potassium, and other soluble minerals.

allele (n.)
One of the possible variants of a polymorphic gene.

allelopathic (adj.)
Producing chemical compounds that inhibit the growth of other plants close by.

alternate (adj.)
A leaf arrangement in which the leaves along the axis are not opposite to each other and not whorled.

alpine zone (n.)
The region above timber line. Grassy slopes (moss and lichens at higher elevations) and tundra vegetation.

amino acids (n.)
Synthesized by plants from nitrogen, carbon, oxygen, and hydrogen. Used to construct proteins.

anaerobic (adj.)
Able to live in the absence of, or not requiring, molecular oxygen.

androecium (n.)
The male home of the flower consisting of several stamens. Usually a stamen has a thin stalk-like filament (stamen) with an enlarged end anther) where pollen is produced ("the male house").
Inside the carolla (of sepals) and the calyx (of petals).
Within is the gynoecium.

androgynous (adj.)
Having flowers with stamens and flowers with pistils in the same inflorescence.

angiosperm (n.)
A flowering plant whose seeds are enclosed in an ovary that ripens into a fruit. Angiosperms are divided into: monocotyledons and dicotyledons. Compare angiosperm with gymnosperm.

animal (n.)
Multicellular organism that includes: eukaryotic cell type, mitochondria, and a complex nervous system.

angiosperm (n.)
A plant whose seeds are enclosed completely in an ovary. Also (less scientifically), a flowering plant.

annual (n.)
A plant that completes its life cycle (from germination from a seed to the production of new seeds) in one year; then it dies.

anterior (adj.)
On the front side of the plant, away from the axis.

anther (n.)
The part of the stamen that develops and bears pollen.

aquifer (n.)
Sand, gravel, or porous rock through with groundwater flows.

arborescent (adj.)
Similar to the size and habit of a tree.

arctic climate (n.)
No month above 10ºC. Usually tundra. Also see climate.

arctic (or nirval) zone (n.)
Near and above the permanent snow line. Lichens on bare rock. A few hardy flowing plants.

arithmetic growth (n.)
Growth where the change in size or quantity (per unit of time) is constant; specifically it is independent of population size. Contrast with geometric growth.

atmosphere (n.)
The gases surrounding the earth. From the sea level to 8 miles up is the troposphere, in which the temperature decreases with height. Above that is the stratosphere, in which the temperature is constant.

austral (adj.)
Southern. Opposite of boreal.

autoecology (n.)
Ecology of individual organisms or species. More simple than synecology.

autogenic succession (n.)
Succession driven by the modification to the enviroment that the plant community itself causes.

autotroph (n.)
A "self-nourishing" organism. Any organism that obtains its energy from simple chemical reactions. Green plants, which make their own food through photosynthesis, are autotrophs.

axil (n.)
The upper angle (or cavity) at the junction between a leaf and stem, or two other structures or organs.