GLOSSARY 



409 



epidermis the outermost living layer that covers the 

 surface ol plants and animals with tissue or more 

 complex structural organization. 



epilimnion the wind-disturbed upper layer of a lake; 

 waters above the thermocline in a temperature- 

 layered lake. 



epiphyte an organism that grows upon a plant but does 

 not gain nutrients from the supporting plant. 



Epoch a subdivision of a geological time period, repre- 

 senting a lesser and more localized break in the time 

 sequence of the rocks; the time during which a rock 

 series was formed. 



Era any of the three major subdivision of Phanerozoic 

 time recognized by characteristic and dominant life 

 — the Cenozoic with modern mammals and flowering 

 plants, the Mesozoic with reptiles and gymnosperms, 

 and the Paleozoic with various invertebrates and, in 

 part, pteriodophytes; the time of a major rock group. 



erosion the process of wearing away and removal of 

 earth's crustal materials by natural phenomena. 



erratics drift, often limited to large rock particles. 



esker a long, narrow, winding ridge of sand and gravel 

 deposited by a stream within and, perhaps, in front of 

 a glacier. 



esophagus the food pipe; the part of the digestive tract 

 between the pharynx and stomach 



estuary an inlet of the ocean into a river mouth; especially 

 likely in places recently submerged by the sea, that is, 

 most places. 



Eucoelomata organisms with a coelom; the Lophophorata, 

 Schizocoela, and Enterocoela. 



eutrophic pertaining to bodies of water rich in nutrients 

 but perhaps seasonally poor in oxygen content; lakes 

 having abundant life. 



excretion any metabolic waste product that is cast out of 

 an organism's body, the process of forming such 

 materials. 



evaporation the conversion of a liquid into a gas at tem- 

 peratures below the boiling point, hence below- 

 normal occurrence of the gaseous state. 



evergreen any plant not losing all of its leaves as the end 

 of the growing season. 



evolution the process by which organisms change struc- 

 turally, functionally, and behaviorally through time; 

 in a broader sense, the change of living and nonliving 

 things through time. 



exoskeleton an external covering and/or supporting struc- 

 ture of an organism. 



exploitation symbiosis in which one organism is harmed 

 and the other benefits; predation and parasitism. 



family (1) a taxon ranking between order and genus; a 

 group of genera; (2) a major category in the classifica- 

 tion of clouds or soils; in soils, a category below an 

 order. 



fascicle a small cluster or bundle; in plants often refers 

 to leaf or flower arrangements. 



fault a break in rocks of the earth's crust along which 

 there has been and may be some horizontal to vertical 

 movement parallel to the break surface. 



fault line the portion of a fault seen on the surface of the 

 earth's crust; often restricted to the straight or linear 

 type. 



fauna the animal life of a particular area at a particular 

 time. 



Faunol Region or Realm a major unit in classifying the 

 distribution of animals on a world-wide basis. 



fecundity in a strict sense, the capability or rate at 

 which an organism produces reproductive units such 

 as gametes or spores. 



fertile pertaining to organisms or parts of organisms cap- 

 able of carrying on reproduction. 



fertility (1) in a strict biological sense, the capability or 

 rate at which an organism produces living offspring; 

 (2) the quality of a substrate in providing substances, 

 generally nutritive, required by organisms. 



fertilization the union of one gamete with another, 

 usually sperm and egg; the essential feature of sexual 

 reproduction. 



filament any threadlike structure. 



filter bridge a highway of temporary duration and lim- 

 ited size that restricts the numbers and kinds of or- 

 ganisms that can cross over it. 



fiord usually, a glacial valley submerged by the sea. 



fission (1) asexual reproduction of two daughter cells of 

 equal size by a single cell; (2) usually, binary fission 

 is the production of two daughter cells by mitosis and 

 multiple fission is the production of many daughter 

 cells by a sequence of mitoses, but amitosis (q.v.) may 

 be involved. 



flogellum any long, threadlike structure that is capable 

 of vibration; a structure typifying the Phylum Flagel- 

 lata. 



flood plain a plain roughly centered on a stream and 

 formed by erosion and deposition activities of the 

 stream. 



flora the plant life of a particular area at a particular 

 time. 



flow^er an organ system diagnosing the angiosperms that is 

 composed of leaves modified into sepals, petals, 

 stamens, and/or one or more pistils. 



foehn a warm, dry, sometimes destructive, wind blowing 

 down a mountain side. 



food chain a graphic or conceptual representation of the 

 dependence upon food of organisms being related to 

 other organisms in a sequence, e.g., producers 

 (plants), primary consumers (herbivores), and 

 secondary consumers (carnivores). 



food pyramid a graphic representation of a food chain 

 showing that the greatest number, weight, or produc- 



