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GLOSSARY 



phylum a major taxon forming a unit of a kingdom and 

 including one or more classes. 



physical in contrast to biological, pertaining to nonliving 

 things. 



physiology the study of life functions. 



pinna (1) in plants, a leaflet; (2) in animals, the append- 

 age of the external ear. 



pinnate featherlike, composed of parts arranged on two 

 sides of a central axis. 



pistil the central organ of a flower, usually consisting of 

 apical stigma, central style, and basal ovary. 



placenta (1) in higher mammals, the organ attaching the 

 later stages of the embryo (fetus) to the uterus of the 

 mother and serving in nourishment, excretion, and 

 respiration; (2) often applied to any parental structure 

 that nourishes an egg or developmental stage. 



plain (1 ) any relatively flat, level, and smooth land without 

 noticeable elevations or depressions; (2) one meaning 

 of "prairie." 



planet a heavenly body of size much smaller than a star, 

 which follows a definite elliptical path (orbit) about a 

 star; generally confined to the sun's planets. Mercury, 

 Venus, Earth, Mars, Jupiter, Saturn, Uranus, Nep- 

 tune, and Pluto, but includes asteroids and planets 

 about any other star. 



plankton passively floating, drifting, and weakly swim- 

 ming aquatic organisms; often microscopic. 



plasma (1 ) the fluid part of blood; (2) protoplasm. 



Plasmodium a slimy, naked, protoplasmic mass, contain- 

 ing many nuclei, that displays amoebid movement; the 

 vegetative body of a slime mold. 



plastid a prominent, often pigmented body (in the cyto- 

 plasm of many cells) that is associated with definite 

 functions; probably a special center of chemical 

 activity. 



plastron a shell or other external, protective structure, 

 usually skeletal, on the ventral surface of an animal 

 (e.g., a turtle). 



plateau a flat-topped, fairly large area that on one to all 

 sides lies above the surrounding land; a tableland. 



pollen a mass of pollen grains; each pollen grain is a de- 

 veloping male gametophyte enclosed within a spore 

 wall and was shed from the sporangium of a spermato- 

 phyte. 



pollen sac the male spore-forming sporangium of a 

 spermatophyte. 



pollen tube the structure, formed by a pollen grain upon 

 contacting a pistil stigma, that grows down to the 

 female gametophyte. 



polyp (1) the sedentary, vaguely plantlike adult stage 

 in the life cycle of most coclenterates; a sea anemone; 



(2) sometimes applied to any vaguely piantlike in- 

 dividual within a colony of a single animal species; 



(3) a swollen and projecting mass of tissue. 



polyphylletic pertaining to a single taxon in which all 

 species did not evolve from a common ancestor; two or 

 more natural groups. 



population a species or any localized species subunit 

 that may be recognized by preferential reproduction 

 within the group. 



porphyry any igneous rock containing scattered larger 

 crystals within its basic materials; often restricted to 

 such rocks with a considerable proportion (approxi- 

 mately 25 per cent or more) of scattered larger crystals. 



posterior at or near the hind or rear part of an organism, 

 usually the part facing backward when an organism is 

 moving or the part opposite the head. 



prairie loosely, any grassland area; specifically, an area 

 of tall (5 or more feet) grasses, in contrast to other 

 grasses. 



Preactuolistic Phase the portion of earth history having an 

 environment, especially an atmosphere, unlike the 

 present one; all time prior to about two billion years 

 ago. 



preadaptation those behavioral, functional, and structural 

 attributes that enable an organism to survive in 

 previously uninhabited conditions, e.g., habitats 

 created by geological change. 



predation symbiosis involving the killing of prey for food 

 by a predator. 



predator an organism that kills another (prey), usually 

 for food; generally a bulk-feeding flesh eater, a car- 

 nivore. 



pressure area any localized irregularity in air particles 

 number, hence air density or weight; a cyclone or 

 anticyclone. 



prey an animal killed by a predator; also any living animal 

 having high potential for being killed by a predator. 



primary pertaining to a natural history feature which 

 originated, formed, evolved, changed, or otherwise is 

 believed to have come first; often refers to a common or 

 primitive ancestor; not secondary. 



primitive pertaining to an early type or stage of an organ- 

 ism; generally implies simple rather than complex and 

 generalized rather than specialized; assumed to denote 

 features developed early in the evolution of life, primi- 

 tive features; not advanced. 



proboscis snout; any tubular prolongation of an animal's 

 head, generally nose, lips, or pharynx; many are ever- 

 sible or capable of being turned outward or inside out, 

 as in the finger of a glove. 



producer an organism capable of using solar (radiant) 

 energy to synthesize organic compounds from inor- 

 ganic materials; generally a photosynthetic organism. 



profundal any mass of deep water below the depth of 

 efTective light penetration. 



proglottid a body segment, not a true segment or somite, 

 of a tapeworm. 



