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GLOSSARY 



arete a sharp, narrow, irregular ridge that separates 

 two depressions carved by glaciers. 



asexual without sexual processes. 



aspect the appearance of a community at a given time. 



aspectation pertaining to the changing appearance of life 

 in a community from season to season. 



association a climax community. 



asteroid a small planet or planetlike body. 



astronomy the study of the heavens. 



atmosphere the gaseous envelope around a heavenly body. 



atoll a circular coral reef enclosing a body of water called 

 a lagoon. 



atom the smallest complete unit of a chemical element. 



autonomous (1) existing, reacting, or responding inde- 

 pendently; spontaneous reaction; (2) pertaining to re- 

 acting or the reaction due to an internal stimulus. 



autotroph an organism that manufactures its food from 

 inorganic substances; an organism practicing chemo- 

 synthesis or photosynthesis. 



autumnal pertaining to the fall season. 



axil the upper angle between a plant's stem and leaf or 

 branch. 



bar in geology, an offshore wave- or current-formed em- 

 bankment of more or less exposed materials. 



barchane a crescent-shaped sand dune with the crescent 

 pointing away from the wind. 



barrier any physical or biological feature restricting the 

 movement of an organism to a place outside its range. 



basalt a fine-grained, dark, igneous rock composed of 

 feldspar, pyroxene, and often olivine; generally any 

 dark lava whose crystals are not visible to the unaided 

 eve. 



basic in chemistry, pertaining to an alkali or a chemical 

 base. 



batholith the largest masses of igneous rock, formed 

 by magma flows deep underground; like a stock (q.v.), 

 but over 40 square miles in surface area. 



bay an inlet in the shore of an ocean or lake; the 

 largest bays grade into gulfs. 



beach the zone of unconsolidated rocks between the low- 

 est tide level of the sea and vegetation or clifTs of the 

 land; the seaward portion of a strand. 



bedrock the essentially solid, undisturbed rock either at 

 the surface or beneath soil, sand, or gravel. 



bench in geology, a generally flat, horizontal, long and 

 narrow surface that is bounded on one side by an 

 ascending slope and on the other bv a descending 

 slope. 



benthic pertaining to the bottom of a sea or lake. 



benthos the life on the bottom of a sea or lake. 



biennial an organism that completes ils life cycle, from 

 origin to death, in two years. 



bilateral symmetry the arrangement of a structure, es- 

 pecially an animal's body, so its parts can be halved in 



only one plane if mirror image halves are to be 

 formed. 



Bilateria the mostly bilaterally symmetrical animals 

 having an organ system basis of structure; animals 

 other than Porifera, Mesozoa, Coelenterata, and 

 Ctenophora. 



biogeochemical cycle the continuous circulation of the 

 chemical elements of protoplasm, as elements or in 

 various compounds, between organisms and their 

 environment; various subunits, also called cycles, 

 may be recognized, e.g., the nitrogen, carbon, and 

 water cycles. 



biogeography the study of the distribution of organisms. 



biological spectrum Raunkaier's means of characterizing 

 the plants of an area according to the relative per- 

 centage of various life forms. 



biology the study of living things. 



biome a plant formation and its animals, monerans, and 

 protistans. 



biome-class a group of biomes diagnosed by plant for- 

 mations of similar appearance; a formation-class, as 

 deciduous forest, boreal forest, or rain forest plus its 

 animals, monerans, and protistans. 



biosphere the part of earth containing life; in reference to 

 the life spectrum, may imply a single ecosystem in- 

 volving all life on our planet. 



Biotic District a continuous part of a Biotic Province 

 distinguished by ecological differences of lesser im- 

 portance than those separating biotic provinces. 



biotic potential the maximum possible rate at which a 

 species might reproduce itself in a particular environ- 

 ment; the inherent ability of a species to reproduce and 

 survive in its environment. 



Biotic Province a considerable geographic area character- 

 i7,cd by the occurrence of one or more relatively im- 

 portant stands, climax or not. 



biparental having two parents, usually one male and one 

 female. 



bipinnate leaves twice pinnate; pinnate subdivision of 

 each leaf part that in turn is a unit of a pinnate ar- 

 rangement. 



biradial symmetry the arrangement of a structure, par- 

 ticularly an animal s body, that is partly radial and 

 partly bilateral; a structure composed of two radially 

 arranged parts oriented half on one side and half on the 

 other side. 



bisexual pertaining to an organism with both male and 

 female sex organs; hermaphroditic. 



bivalved pertaining to a shell of two parts, as in clams. 



blade the usually flattened and expanded part of a leaf, 

 modified leaf (e.g., a sepal or petal), or leaflike 

 structure. 



bog a wet, spongy substrate that yields under the fool and 

 regularly is rich in decayed plant matter. 



