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GLOSSARY 



taiga the northern area of open and stunted, mostly conif- 

 erous, trees adjacent to the tundra; sometimes includes 

 the adjacent northern coniferous forest. 



taxon any taxonomic category; plural, taxa. 



taxonomic category any unit of organism classification 

 based as much as possible on natural relationships 

 through evolution; generally, anything above a species 

 is called a higher category. 



taxonomy the study of classification, usually as limited to 

 organisms. 



tendril loosely, a slender, branched or unbranched struc- 

 ture in an organism; generally restricted to a plant 

 stem, leaf, or leaf part modified into a hairlike struc- 

 ture that coils about an object and thus supports the 

 plant. 



tentacle a slender, flexible, often sensory and anterior, 

 animal organ of various functions (e.g., locomotion, 

 grasping, holding, and/or food-getting). 



territory the portion of a home range actively defended by 

 an animal against intruders. 



testis in animals, a male sex organ; plural, testes. 



thallophyte once a taxon of "plants,"" including bacteria, 

 fungi, and algae; now usually used to indicate such 

 organisms. 



thallus a relatively simple plant body lacking roots, stems, 

 or leaves; generally any algae or bryophyte body; also 

 any thallophyte body. 



theory a group of interrelated and much-tested hypotheses 

 that are consistent with one another and observed 

 phenomena. 



thermocline a layer or zone of rapid temperature decrease 

 with depth (generally more than 1 degree centrigrade 

 per meter) found in temperature-layered lakes. 



thorax the major part of an animal "s body behind the 

 head (or neck) and in front of the abdomen; in birds 

 and mammals, the part enclosed by ribs. 



till unsorted, unlayered, and generally unconsolidated ma- 

 terials deposited by ice; glacial drift or erratics. 



tissue a group of similar cells performing similar functions. 



tolerance the ability and capacity of an organism to live 

 under a range of conditions of one or more environ- 

 mental factors. 



topsoil the uppermost layer of soil that is lighter in color 

 but richer in humus than the underlying subsoil. 



tracheae a system of small air-conducting tubes present 

 and involved in the respiration of many land arthro- 

 pods. 



transformer often not distinguished from a decomposer; 

 an organism that uses and alters the products of de- 

 composers to molecules, generally even smaller ones, 

 that can be used by plants. 



transpiration the loss of water, generally as vapor, from the 

 aerial parts of plants; may be a type of evaporation. 



trichocyst a protistan organelle, particularly in ciliate 



protozoans, that occurs near the body surface and 

 produces hairlike fibers that function in predation, 

 protection, and attachment. 



triploid the presence of three complete sets of chromo- 

 somes in a nucleus. 



trochophore a ciliated and free-swimming, marine larva 

 typical of the Schizocoela. 



tuber a short, thick, and fleshy, underground stem con- 

 taining buds, e.g., a potato. 



tundra ranging from bare areas to those consisting of 

 various lichens, mosses, herbs, and dwarf shrubs (but 

 not trees) in arctic or alpine regions. 



unconformity the surface occurring between two distinctly 

 different rock layers and representing a time of ero- 

 sion and/or no deposition. 



unicellular pertaining to a single cell. 



univalved pertaining to a shell of one solid part as in 

 snails. 



vacuole a cavity within protoplasm bounded by a mem- 

 brane and containing liquids and/or solids. 



valve (1) in anatomy, a structure closing an opening or 

 directing movement in one direction; (2) in botany, a 

 covering or lidlike part of a larger structure; any of the 

 units formed from normal separation of parts of a 

 single plant structure, usually a reproductive one; (3) 

 in zoology, any separate piece of a shell as found in 

 mollusks, branchiopods, and barnacles. 



vascular bundle a plant vein. 



vascular plant any plant containing veins. 



vegetative reproduction any asexual reproduction by means 

 of reproductive bodies other than true buds. 



vegetative structure any part of an organism without re- 

 productive structures. 



vein (1) in plants, a strand of conducting tissue, xylem 

 and phloem; a vascular bundle, stele, or central cyl- 

 inder; (2) in animals, a tube or vessel carrying blood 

 to the heart; (3) in geology, a crack filled with a min- 

 eral or rock deposit. 



vellum a washer-like ring attaching by its outer margin to 

 to the undersurface of the medusa stage of the Hydro- 

 zoa, especially prominent in hydromedusans. 



ventral pertaining to the belly or away from the back. 



vernal pertaining to the spring season. 



vestigeal degenerate; pertaining to an incompletely formed 

 structure that was fully formed during development or 

 in ancestors of the organism bearingthe structure. 



viscera the internal organs of an organism. 



weather the atmospheric conditions (precipitation, tem- 

 perature, humidity, cloudiness, wind, pressure, and 

 so on) at a given time. 



weathering erosion by atmospheric agents causing physi- 

 cal and chemical disintegration of rocks. 



weed any undesirable or troublesome, usually exotic, 

 plant growing without cultivation by man. 



