GLOSSARY 



407 



faces (crystal faces) are flat and symmetrically ar- 

 ranged. 



cuesta an elevation with one steep and an opposite 

 gentle slope, the dip of the gentle slope sometimes is 

 recognized as not surpassing 12 degrees; usually as- 

 sociated with fairly recent shorelines of emergence. 



cuticle a noncellular, external, protective covering; 

 especially found in plants and animals and formed by 

 the epidermis. 



Cycadeoldales fossil order (Permian to Middle Creta- 

 ceous of the Class Cycadae; mostly treelike-and palm- 

 like, seed-forming plants. 



cyclone an atmospheric pressure distribution or area in 

 which pressure decreases and winds travel toward the 

 center; a "Low"; generally characterized by moderate 

 to violent storms; hurricanes and typhoons are 

 violent types, of tropical origin. 



cyst a protective, resistant, and nonliving covering 

 about certain dormant monerans, protozoans, some 

 other small organisms, spores, and certain cells or 

 groups of cells; usually associated with asexual re- 

 production. 



cytology the study of cells, especially their structures 

 and functions. 



cytoplasm the portion of a cell surrounding the nucleus 

 and within the cell membrane. 



deciduous (1 ) to fall off, as leaves do in the autumn; (2) a 

 tree or shrub of such habit. 



decomposer an organism that breaks down organic mole- 

 cules into smaller molecules or atoms. 



decompound leaf one that is more than once divided; each 

 of the leaflets that would be the consequence of a single 

 compounding is in turn compounded at least once and 

 like a leaflet has the appearance of a leaf. 



degeneration evolutionary retrogression; the process of 

 losing features that typify a more complex or higher 

 body organization to assume a simpler or lower or- 

 ganization; typical of many parasites. 



delta the essentially triangular, mostly alluvial, de- 

 posits at the mouth (end) of a stream. 



dendritic much branched, as in a tree. 



deposition the laying down, accumulating, or placing into 

 position of thin sheets of sediments (beds), of materials 

 in cracks (veins), or of irregular masses. 



desert a generally rocky or sometimes sandy region 

 where evaporation is greater than precipitation and 

 vegetation is very sparse and often stunted. 



desert pavement the close-fitting gravel-to-boulder sub- 

 strate characterizing many deserts because wind re- 

 moves sand and finer particles. 



desert varnish a magnesium or iron oxide, brown to black, 

 typically shiny, thin stain on the surface of many 

 desert rocks; the varnish is polished by wind carried 

 materials or by being moved over the substrate by 

 wind. 



destructional land form any geological feature produced by 

 erosion; sometimes does not include land forms pro- 

 duced by the deposition of erosion products; may or 

 may not include features formed by organisms. 



detritis materials remaining after destruction of an object. 



dew point the temperature at which air with a known 

 moisture content will become saturated and with any 

 further cooling will deposit dew. 



diastrophism the processes whereby the earth's crust is de- 

 formed. 



differentiation the developmental changes, generally from 

 simpler structures and functions of early life cycle 

 stages, to greater complexity in the adult; often 

 implies the evolution of complex structures. 



differentiation area a geographic site that, owing to par- 

 ticular features such as isolation and a unique environ- 

 ment, is the place for the evolution of one or more 

 new species. 



diffusion movement of particles, owing to the energy 

 they contain, from sites of higher concentration to 

 those of lower concentration that tends to equalize 

 particle distribution throughout the system. 



dike any mass of igneous rock formed by magma filling a 

 crack in older rocks. 



dip the angle a geological feature (usually a stratum or 

 fault but also a vein, crack, or similar feature) makes 

 with a horizontal plain (the earth's surface) as 

 measured perpendicular to the strike of the geological 

 feature; see Figure 4.23, p. 62. 



dipleurula a hypothetical larval stage, presumed ancestral 

 to echinoderms. 



diplobiontic a life cycle in which diploid adults by 

 meiosis give rise to spores that grow to sexual, 

 haploid adults; the haploid adults produce the gametes 

 for the zygote formations that lead to asexual, diploid 

 adults. 



diplohaplontic a life cycle with two kinds of adults, the 

 diplobiontic life cycle. 



diploid pertaining to two of each kind or two sets of 

 chromosomes; twice the number typifying gametes or 

 twice the haploid number. 



diplontic a life cycle with all diploid adults, the gametes 

 being the product of meiosis. 



diplophase that part of a life cycle characterized by 

 diploid nuclei. 



disclimax any climax maintained by fire or animals. 



dissolve to cause to pass into solution by separating a 

 material into component parts. 



diurnal pertaining to the daylight hours; neither crepus- 

 cular nor nocturnal. 



diurnation the phenomenon of fluctuation in an organism's 

 or population's activity or a community's composition 

 within a 24-hour period. 



dominant any of the commonest (in terms of both surface 

 area covered and evenness of distribution) species of a 



