GLOSSARY 



417 



profonema a hairlike, often branching stage, resembhng 

 certain algae, in the early development of bryophytes, 

 particularly mosses; often with a gametophore con- 

 sidered two gametophyte stages, but the protonema 

 buds one or more gametophores. 



protoplasm (1) collective term for living substance 

 regardless of its organization; (2) here also used to 

 imply Monera organization, which lacks at least com- 

 plete structural organization of a nucleus. 



pseudocoel an animal body cavity called a "false body 

 cavity" because it lacks a complete membranous 

 lining derived from mesoderm; the basis for defining 

 Pseudocoelomata, the Acanthocephala, Aschelminthes, 

 and Entoprocta. 



pseudopodium a flowing protoplasmic extension of a cell 

 or protistan that functions in locomotion (amoeboid 

 movement) and feeding. 



pteridophyte a collective term, meaning fern plant, for 

 vascular plants that do not produce true seeds; some- 

 times considered a major taxon, usually a phylum or 

 class, of plants; most likely not a natural group. 



Pterldospermae fossil order (Early Mississippian, perhaps 

 upper Devonian, to Jurassic) of fernlike herbs, trees, 

 or vines that produce true seeds; the seed ferns. 



pupa an immature stage between larva and adult in in- 

 sects displaying complete metamorphosis; a "resting" 

 stage featuring great developmental changes and 

 minor body movements but neither feeding nor loco- 

 motion. 



quarrying the erosion process whereby water or ice re- 

 moves and transports large masses of rock. 



radial symmetry the arrangement of structure, particularly 

 an animal body, so its parts can be divided into two 

 approximate images by an infinite number of vertical 

 cuts, so long as each cut is through the center. 



Radiata the mostly radially or biradially symmetrical 

 animals of tissue organization, the Coelenterata and 

 Ctenophora. 



radioactivity the spontaneous emission of charged particles 

 by decay or disintegration of certain, usually heavy, 

 elements. 



radula the horny, rasping organ, generally used in food 

 getting, in the anterior part of the digestive tract of 

 many mollusks. 



rain forest a forest of tall, mostly broadleaved trees, often 

 of different heights and in more »han one layer as 

 determined by size; generally restricted to equatorial, 

 evergreen trees in areas lacking a dry season, but is 

 also applied to similar temperate forests (e.g., the 

 Olympic Peninsula forests of Washington state) and 

 similar forests in tropical areas having a dry season. 



rain shadow an area occurring on the leeward side of a 

 mountain and having little or no rainfall because the 

 mountain traps most of the moisture from the winds. 



receptacle in plants, a structure bearing reproductive 

 structures, e.g., the stalk for the sex organs of certain 

 liverworts, for the sori of ferns, or for the flower of 

 angiosperms. 



regeneration healing, ranging from the limited extent in 

 man to restoration of half or more of an organism's 

 body. 



regression used in the usual sense of a return to earlier 

 stages of development but often, as stated, not to the 

 exact features or conditions of an earlier stage. 



relative humidity the percentage of water vapor in any size 

 sample of air in relation to the amount that could be 

 held at the same temperature. 



relict a remnant of a species, community, flora, or fauna 

 from a time when it was more numerous in individuals 

 and, (where pertinent) species and was more wide- 

 spread. 



reproduction the processes involved in the perpetuation of 

 species. 



respiration the processes involved in releasing energy from 

 fuel; often restricted to processes within cells, but may 

 include other functions such as those in obtaining 

 oxygen from the environment and releasing carbon 

 dioxide; may or may not involve oxygen. 



rhizome a rootstock, or underground (usually horizontal) 

 stem. 



rock refer to pp. 68-69. 



Rock Group two types are recognized, major and minor; 

 a major rock group is less frequently recognized but 

 consists of rocks formed during an era; a minor rock 

 group is a local unit composed of two or more forma- 

 tions sharing some local peculiarity, in which upper 

 and lower limits vary in age geographically, thus have 

 no corresponding time unit. 



Rock Series a geographically localized unit within a rock 

 system that represents a single geological time unit, an 

 epoch. 



Rock Stage a geographically localized unit within a rock 

 series that represents the smallest geological time unit, 

 the Age. 



Rock System the natural rock unit formed during a geo- 

 logical time period and is separated from overlying and 

 underlying rocks by general differences in rocks or a 

 major structural change in rocks and by a distinct 

 change in fossils; separations imply a marked change 

 in environment. 



root a vascular plant organ having neither leaves nor 

 modified leaves; functions in water absorption, as a 

 food reservoir, and as a means of support. 



rootstock a rhizome. 



salt a compound formed by the replacement of one or 

 more hydrogen atoms of an acid by metal atoms or 

 certain other groups of atoms. 



