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dictionary of 

by Herbert c. hanson 

Dictionary of 


This practical dictionary is for the use 
of students, teachers, and investigators 
in ecology and related fields such as 
range management, forestry, wildlife, 
conservation, agronomy, and limnology. 
It is also designed for use by the general 
public for the better understanding of 
widely used ecological terms. The Dic- 
tionary includes not only strictly ecologi- 
cal terms but also those that have been 
adopted from related fields. The aim is 
not to define words with final fixity but 
rather to give clear, concise statements 
indicating present-day usage. The defi- 
nitions will be useful, not only in facili- 
tating the comprehension of ecological 
concepts, but also in furthering the re- 
finement of both concepts and defini- 

The author is Plant Ecologist, Ber- 
thoud, Colo., formerly Research Profes- 
sor, Dept. of Biology, The Catholic 
University of America. 


From the collection of the 


^ m 

o PreTinger 
v JJibrary 

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San Francisco, California 




The Catholic University of America 
Washington, D. C. 


Copyright, MCMLXII 

by Philosophical Library, Inc. 

Printed in the United States of America 

Library of Congress Catalog Card Number 60-15954 

This edition published by Bonanza Books, 

a division of Crown Publishers, Inc., 
by arrangement with Philosophical Library, Inc. 
b c d e f g h 



cf. confer, compare this definition with the definition of 
words that follow. 

q. v. quod vide, indicating that it is desirable to look up 
the definition of the preceding word in order to under- 
stand more fully the definition being considered. 

Syn. Synonym. 

Italicized words indicate that they are defined in this book, 
or that such words form the scientific name of a plant or 


The aim of this dictionary is to fill the need for defini- 
tions of many new terms that have come into usage during 
the past thirty years and also to include many of the old 
terms that are used in current literature. It has not seemed 
desirable to include many words that are rarely if at all 
used at present and which are in the older glossaries. Many 
words from fields closely related to ecology such as forestry, 
range management, agronomy, soils, and genetics are in- 
cluded because of their wide usage in ecological literature. 

The definitions are usually those that are in accord with 
present general usage. It has not seemed wise to attempt to 
pronounce judgment on the desirability of, or the need for, 
certain terms since such decisions are made by usage as a 
language grows. The inclusion of certain words in this dic- 
tionary does not necessarily imply that the author approves 
or recommends their use. 

Words are tools of thought. Clarification of the meaning 
of terms, precision in their use, and uniformity in usage 
among workers in ecology and related fields are essential 
in the growth of a science. When a concept or process can 
be expressed precisely in ordinary language it appears un- 
necessary, and indeed detrimental to the growth of a science, 

to coin a new term. It is worth while to make ecological 
literature intelligible to as wide a field of readers as possible. 
As concepts and techniques become clearer and more precise 
new terms are often needed, and when a new word is 
accepted hi one branch of science it should be accepted in 
other branches. 

Definitions are not immutable. As knowledge increases 
the meanings of terms change. It is hoped that this volume 
will aid in the development of an increasingly useful ecologi- 
cal terminology. 

A list of references are given below, many of which will 
be found useful in securing further amplification of the 
meaning of words in this dictionary. 



A mosaic of high moor and low moor, consisting of 
circular or elongated mounds covered with dwarf shrubs 
and sphagnum and depressions occupied by mostly sedges 
and sphagnum. 


The non-biotic elements of a habitat. 


See Seston. 

Abrasion Platform 

The part of the continental shelf and terrace on which 
a horizontal plain is formed by long continued wave action. 

Absolute Extremes 

The highest (absolute maximum) and lowest (absolute 
minimum) values of a meteorological element, especially tem- 
perature, that have ever been recorded at a station. 

Absolute Humidity 

See Humidity, absolute. 

Absorption Loss 

The initial loss of water from a canal or reservoir by 
capillary action and percolation. 

Abstract Community 

A generalized category comprising a number of similar 
units or stands of vegetation and including animal life. 


The total number of individuals of a species in an area, 
population, or community. The index of relative abundance 
gives a useful approximation of numbers relative to time or 
space, e.g., the number of rabbits seen in an hour in a certain 
place, cf. Density. 


Refers to the deepest region of the ocean and often used 
for the zone in lakes below the profundal (q. v.). See 

Abyssal-benthic (Abyssobenthic) 

The lower part of the abyssal region, below about 3300 
feet (1000 meters). 


The symbiotic relationship of mites and plants. 


Refers to a plant with inconspicuous, or seemingly absent, 
stem above the ground. 

Accelerated Erosion 

Washing away or blowing away of soil material in excess 
of normal erosion (q. v.), resulting from changes in the 
vegetation cover or ground conditions. 


A species that occurs with a low degree of Fidelity in a 


The increased tolerance or physiological adjustment of an 
organism to a change in its environment. 


Modification of the focus of the eye. 


Refers to plants which continue to grow after flowering. 

Accumulator Plant 

A plant that absorbs certain elements which accumulate 
in its tissues to a much higher degree than in most plants, 
e.g., Equisetum concentrates large amounts of silica, cf. 


A short-lived type of vegetation, characterized chiefly 
by mustards and grasses, in the Italian Sahara. 


A one-seeded, dry, non-opening fruit in which the seed 
is not attached to the wall of the fruit, e.g., sunflower 


Coniferous vegetation with small, evergreen, needle-like 

Acid Bog 

See Bog. 


Refers to organisms that grow well or exclusively on soil 
or in a medium that is acid in reaction. 

Acid Soil 

A soil with an acid reaction, containing more hydrogen 
than hydroxyl ions; for practical purposes with a pH below 


Refers to organisms that feed on food having an acid 

Acquired Character 

A modification of structure or function appearing during 
the lifetime of an individual, caused by environmental con- 
ditions, e.g., broad leaves of some plants growing in shade. 


The quantity of water that will cover one acre one 
foot deep. 


The quantity of water that will cover one acre one 
inch deep. 


Structures on plants that shelter mites. 


Refers to the development of organs in plants, the oldest 
at the base, the youngest at the tip. cf. Basipetal. 


Plant communities in alpine regions. 


Refers to the part of the seashore between tide marks. 
See Littoral. 


An instrument which measures radiant energy, especially 
the property that produces chemical effects. 


The measurement of chemical reactions caused by 


A group of organisms possessing very fine hyphae or 

threads, classified with bacteria or fungi. Various kinds 
cause decomposition, disease, or produce antibiotics such as 
streptomycin (q.v.). 


The impingement of environmental factors such as heat 
or light upon organisms. 


A plant-animal community on a rocky seashore. 

Activated Sludge 

Material composed chiefly of bacteria and protozoa, used 
in one method of sewage disposal. 


Refers to organisms that grow well on rocky seashores. 


Capability of an organism to make changes which fit it 
better to its environmental conditions. 


Refers to the adaptability of an organism. 


(1) The process or processes by which an organism be- 
comes apparently better suited to its environment or for 
particular functions. (2) The structures or activities of an 
organism, or of one or more of its parts, which tend to fit it 
better for life in its environment. (3) The adapted form. 


The sum of genetic characters by which an organism 
is suited to its environment. 


See Adaptation. 

Adaptive Radiation 

The evolution of taxa (q. v.) as they become adapted to 


new habitats, applicable also to the development of a new 

Adaptive Selection 

The evolution of more or less similar forms in separate 
but ecologically similar areas. 


A material added to a fertilizer, or to another substance, 
to improve its chemical or physical condition. 


Refers to an occurrence in which heat is neither gained 
nor dissipated. 


Processes by which an organism becomes better fitted to its 
environment; functional, never structural, cf. Adaptation. 


A fine calcareous clay or silt, may be mixed with water 
to make bricks for construction purposes, cf. terron. 


The attachment of molecules or ions to surfaces or inter- 
faces such as solid-liquid, solid-gas, and liquid-gas boundaries. 

Advance Growth 

Young trees in openings or under the canopy in forests 
before cutting or regeneration operations are started, syn. 
Advance reproduction, cf. Second growth. 

Adventicous Species 

Organisms which have invaded from a distance. 


An organ growing out of its usual location, e.g., root 
from a stem; a species which has invaded from another area 
and has become more or less naturalized. 


A plant growing spontaneously, not native, ephemeral or 
not spreading appreciably. 


Refers to dissemination by wind. 


Refers to the wind, or to soil materials which have been 
moved by the wind or are subject to such movement. 


The processes by which air and other gases in a medium 
are renewed or exchanged. 


An organism capable of living only in the presence of 
free oxygen. 


Tissue with thin-walled cells and large air spaces, espe- 
cially common in aquatic plants. 

Aerial Photograph 

A vertical or oblique photograph taken from the air. 


Refers to life or a process occurring only in the presence 
of free oxygen. See Aerobe. 


Life in the presence of free oxygen in the medium. 


See Epiphyte. 


Microorganisms floating in the air, cf. Plankton. 


Involuntary response of an organism to a gas, such as 


the curving of a plant toward a higher concentration of 


Woodland characterized by mixed evergreen-deciduous 


Forest or woodland in which the woody plants are leafless 
in winter and buds are protected by scales, e.g., beech forest. 


See Estival. 


The relationship between organisms that indicates a 
common origin; used occasionally to denote similarity of 


The process of establishing a forest on an area, especially 
where forest was not present previously, cf. reforestation. 


The regrowth of plants after mowing. 


The dormancy period, following formation of the seed 
that is required for changes in the embryo to occur prior 
to germination. 


See Agamospecies. 




Asexual reproduction, parthenogenesis (q. v.). 


An aggregation of individuals in which reproduction oc- 


curs almost exclusively by asexual means, syn. Agameoo, 


Production of seed asexually, exclusive of vegetative 
reproduction, cf. apomixis. 

Age and Area 

Willis* hypothesis that the older a species is, the larger is 
the area that it occupies. 

Age Class 

A stand in which all of the trees originated in the same 
regeneration period, cf. Even-aged. 

Age Distribution 

The classification of individuals of a population accord- 
ing to age classes or periods such as prereproductive, repro- 
ductive, and postreproductive. 


Formation of clumps of microorganisms or cell inclusions. 


Building up of a portion of the earth's surface toward 
uniformity of grade by deposition, as on the bottom of a lake. 


A cluster of particles as a crumb of soil; to collect particles 
into a cluster. 


The coming together of organisms into a group, e.g., 
offspring clustered about the parents. The condition of 
being collected into a cluster or group, cf. Community. 

Agonistic Behaviour 

An activity such as fighting, feigning, and escaping, con- 
nected with conflict between animals. 


Agrarian Zone 

The portion of a country that can be cultivated. 


Refers to an organism that grows in arable ground. 


The study of soils. See Edaphology. 


The study of the production, processing, and use of farm 


Refers to organisms that grow well in grain fields or other 
areas resulting from man's activities. 


The branch of systematic botany dealing with grasses. 

A Horizon (Soil) 

The stratum of soil consisting of one or more of the 
following layers. (A horizon, partly decomposed or matted 
plant remains lying on top of the mineral soil. A 00 horizon, 
the relatively fresh leaves and other plant debris, generally 
of the past year, lying on the A horizon.) AI horizon, the 
surface mineral layer, relatively high in organic matter, 
usually dark in color. A 2 horizon, below the A x horizon, in 
places the surface layer, usually lighter in color than the 
underlying horizon, in which leaching of solutes and sus- 
pended materials occurs. A 3 horizon, transitional to the B 
horizon, more like A than B, sometimes absent. 



Air layering 

A method for producing roots on a stem in an aerial 



Thin-walled structures, containing air, in birds and in 
some insects. 

Alar, Alary, Alate 



Complete or almost complete absence of pigment, result- 
ing in plants that are white in whole or in part, and in 
animals with milky-white skin, light hair, and red pupils 
in eyes. 


An organism deficient in pigment. 

Alice's Principle 

The extent of aggregation and the degree of density 
of a population most favorable for optimum growth and 
survival varies according to the species and environmental 
conditions. Either deficiency or excess may be detrimental. 


A weed growing in a mesic (q. v.) habitat. 


The simplest kind of green plants, usually growing in 
water or damp places, consisting of several phyla, formerly 
classified in the Thallophytes (q. v.). 


Resembling an alga. 


The study of Algae. 


An introduced plant which has become naturalized. 



The constant of temperature for a certain stage in the 
life-cycle of an organism. See Temperature summation. 

Alkali Reserve 

The total amount of dissolved salts or other substances 
which tend to maintain the normal alkalinity of a natural 
water or the internal body fluid of an organism. 

Alkali Soil 

A soil that has such a high degree of Alkalinity (pH 8.5 
or higher), or such a high percentage of exchangeable sodium 
(15 per cent or more), or both, that the growth of most crop 
plants is reduced or prevented. See Black alkali, Saline soil. 

Alkaline Soil 

A non-acid soil which contains more hydroxyl ions than 
hydrogen ions; precisely, a soil with pH 7.0 or higher; for 
practical purposes, with pH 7.3 or higher. 


The chemical state of water or other substance in which 
the hydroxyl ions exceed the hydrogen ions, usually with 
pH 7.0 or higher, cf. Salinity. 

Alleghanian Life Zone 

One of the divisions of Merriam's Austral life zone (q. v.), 
east of the 100th meridian. See Life zone. 

Allelarkean Society 

An independent, dense, fixed, civilized society, cf. 
Autarkean society. 


One of the two forms of a gene located at a certain 
position (locus) on a homologous chromosome (q. v.). If one 
allele of a pair is dominant to the other it largely controls 
the character, e.g., greenness is dominant over albinism 
(q. v.) in seedlings. 


Allelomimetic Behaviour 

Two or more animals, mutually stimulated, acting sim- 
ilarly. See Mimetic. 


See Allele. 


Influence of plants, exclusive of microorganisms, upon 
each other, caused by products of metabolism. 

Allen's Principle (Rule) 

Appendages of animals tend to be shorter in cold regions, 
resulting in reduced loss of heat. Cf. Bergmann's, principle. 


A substance which induces allergy, or causes symptoms to 
show, e.g., Pollen. 


Sensitivity resulting in pathologic condition in certain 
people to substances such as pollen, food, hairs; or may be 
caused by mental or environmental conditions. 


A group of plant associations according to Braun- 
Blanquet classified together on the basis of similarity in 
floristic and sociological characteristics. See Association. 


Refers to a species occurring in two or more similar 
communities in the same region. 


Refers to deposits of material that originated elsewhere, 
e.g., drifted plant materials on the bottom of a lake. cf. 


Cross-fertilization (q. v.). See Outbreeding. 


Aliogenic Succession 

The kind of succession (q. v.) in which one kind of 
community replaces another because of a change in the 
environment which was not produced by the plants them- 
selves, e.g., decrease in soil moisture by improved drainage, 
cf. Autogenic succession. 


Relationships in the evolutionary development of organs 
or other characters of organisms which may bring about 
disharmony, e.g., disproportionate development of antlers 
and neck muscles of deer or moose. 


Refers to organisms originating in or occupying different 
geographic areas, cf. Sympatric. 


A polyploid (q. v.) which originated by the addition of 
unlike sets of chromosomes, cf. Autopolyploid, Amphiploid. 


Refers to organisms occurring at any depth in the sea. 


Refers to lakes or ponds that receive organic material 
by drainage from the adjacent land. cf. Autotrophic. 

Alluvial Fan 

A fan-shaped deposit of sand, gravel, and fine material 
from a stream where its gradient lessens abruptly. 

Alluvial Soil 

Soil that has developed from transported and relatively 
recently deposited material (alluvium), characterized by 
little or no modification of the original material by soil- 
forming processes. 



Sediments, usually fine materials, deposited on land by 

a stream. 


A high mountain meadow, alpine or subalpine. 

Aim's Fb Coefficient 

The relationship of fish caught per hectare to the live 
weight of the bottom fauna per hectare. 


A mountain or upland pasture of natural plants grazed 
by animals at the height of summer. See Aim. 

Alpha Particle, * Particle 

A helium nucleus, given off by nuclei of certain radio- 
active substances. 

Alpha Radiation 

A kind of ionizing radiation (q. v.) in which alpha 
particles are given off. 

Alpha Ray 

A stream of alpha particles (q. v.) cf. Beta ray. 


Refers to parts of mountains above tree growth or to 
organisms living there. 

Alternating Communities 

See Twin communities. 

Alternation of Generations 

The alternation of different forms in the life cycle of an 
organism, especially a sexual (gamete-producing) form with 
a non-sexual (spore-producing) form; occurs in most plants 
and in many animals. 



Two or more communities alternating with each other 
in a more or less restricted area. 


Communities with tall herbs, especially in denuded forest 


An instrument for determining altitude, e.g., aneroid 


Refers to the condition of delay after birth or hatching in 
the attainment of a completely independent mode of self 
maintenance, cf. Precocial. 


A vegetation type consisting of dwarf shrubs resembling 
steppe, in Sweden. 


Pitted, appearing like a honeycomb. 

Ama nthophi lous 

Refers to organisms living in sandy areas. 


Refers to adaptations for walking in contrast to running, 
associated with forest animals, cf. Fossorial, Scansorial. 


Any material such as lime or synthetic conditioners that 
is worked into the soil to make it more productive; usually 
restricted to materials other than fertilizers. 


The state or interaction in which one organism is in- 
hibited while the other is not influenced, cf. Commensalism. 



A pendulous, spike-like cluster of flowers as in the oaks, 
willows, and birches, syn. Catkin. 


Refers to plants with aments or catkins. 


Refers to a parasite that is restricted to a single host. 

Amino Acid 

A class of organic compounds containing nitrogen, large 
numbers of which become linked together to form proteins 
(q. v.); each one containing at least one amino group (-NH 2 ) 
and at least one carboxyl (-COOH) group. 


Direct division of the nucleus of the cell without mitosis 
(q. v.). 


A compound of ammonium sulfate used as an herbicide 
(q. v.). 


Refers to an organism that grows in sand. 


The formation of ammonium compounds from organic 
materials containing nitrogen. 


See Ammocolous. 


Refers to organisms inhabiting sandy banks of rivers. 


An animal such as reptile, bird, or mammal the embryos 
of which develop within a fluid-filled sac. 



A Protozoan (q. v.) in the genus Amoeba. 


A cell possessing movement similar to that of Amoeba. 


Refers to movement similar to that of Amoeba. 


Refers to structures in which differentiation is not ap- 
parent, shapeless. 


A class of vertebrates (q. v.) comprising frogs, toads, 
salamanders, newts, and related animals, most of which 
spend part of the life-cycle in water. 


Refers to organisms that can live in water or on land. 


Refers to plants with two kinds of fruit. 


The appearance on a plant of flowers with different colors 
in different seasons. 


A marsh plant with amphibious vegetative parts. 


See Amphiploid. 


An organism that is native to both the old and new 


The union of gametes to form a Zygote (q. v.). 



Refers to an organism or a generation that produces 


Sexual reproduction in contrast to apomixis (q. v.). It 
includes Allogamy (q. v.), Autogamy (q. v.), or a mixture of 
these two. 


Refers to an animal having feet for walking and feet for 


A plant growing in the border zone of wet land and 
water, with amphibious characteristics. 

Amphiploid (Amphidiploid) 

A kind of Polyploid (q. v.) in which there are two sets 
of chromosomes, each set derived from a parent in different 


Refers to an organism with two noses. 


Refers to the capacity of a substance to react either as 
a base or an acid. 


Refers to clasping or twining for support, e.g., tendril. 


Refers to an organ clasping or growing around a stem 
such as the base of a leaf. 

Amplitude (Ecological) 

The range of an environmental condition or complex of 


conditions in which an organism can exist or in which a 
process occurs, cf. Tolerance. 


A perennial plant that produces flowers and fruits many 


Revival of an organism after apparent death, as for 
example by dessication. 


The synthesis of complex organic substances from simple 
materials in organisms, cf. Catabolism, Metabolism. 


Refers to animals having Anadromy. 


The behaviour of animals such as eels and salmon which 
live in the sea and migrate into fresh water to breed. 


An organism living in the absence of free oxygen, cf. 


Refers to life or activity in the absence of free oxygen. 


The existence of life under anaerobic conditions. 


The anaerobic flora of the soil. 


Refers to an organ of one organism that corresponds in 
function to an organ of another animal or plant but which 
is not Homologous (q. v.), e.g. petioles of clematis and 
leaflets of peas as twining structures, wings of birds and 



An animal lacking an embryonic membrane or amnion 
(q. v.), e.g. frogs, fishes, cf. Amniote. 


Refers to flowers lacking stamens. 


The branch of biology that deals with the structure of 
plants or animals. 


Ice that has formed on the bottom of a stream. 


Refers to the Andes Mountains of South America. 


Modified scales on wings of Lepidopterons (q. v.), produc- 
ing a sexually attractive odor. 


Refers to the presence of flowers with only stamens and 
flowers with both stamens and pistils on separate plants, 
cf. Andromonoecious. 


The stamens of a flower, collectively. 


A substance causing the formation or maintenance of 
male sexual characteristics in certain animals. 


Refers to flower clusters in which the staminate flowers 
are attached above the pistillate flowers, e.g. certain sedges. 


Refers to the presence of flowers with only stamens and 
flowers with both stamens and pistils on the same plant, 
cf. Androdioecious. 



A plant that grows in the vicinity of man and his 


A species of which the seeds, spores, or other parts capable 
of reproducing offspring are dispersed by wind, e.g. dande- 
lion, cf. Diaspore, Disseminule. 


A continuous record of wind velocity made by an 


A self-recording instrument for recording the velocity 
of the wind. 


An instrument that measures the velocity of the wind. 


Refers to plants in which the pollen or other spores are 
scattered almost exclusively by wind, e.g., willows, cf. 


Plankton (q. v.) that are transported by wind. 


The reaction to wind by the movement of a free organism. 


The reaction to wind by the movement of an attached 

Aneroid Barometer 

An instrument that registers atmospheric pressure in 
such a way that altitude may be calculated. 


Refers to the presence of an irregular number of chromo- 


somes, fewer or greater than the multiple of the Haploid 
(q. v.) number, cf. Euploid. 


The subdivision of Spermatophytes (seed-plants) in which 
seeds are produced within the ovary, includes Monocotyle- 
dons and Dicotyledons. 

Angle of Repose 

The maximum slope on which soil or loose rock remains 
stable, syn. Critical slope. 


Refers to a substance that does not contain water, e.g. 
anhydrous ammonia. 

Animal Unit 

A measure of converting kinds of livestock to a common 
standard in relation to forage resources on the equivalent 
of a mature cow (live weight of about 1000 pounds). One 
animal unit in western range country equals about one head 
of cattle, one horse, one mule, five sheep, five swine, or five 

Animal Unit Month 

A measure of forage or feed requirement to maintain 
one animal unit for 30 days. 

Animation, Suspended 

Animals of simple organization such as some nematodes, 
snails, and rotifers which can endure long periods of drying 
in an inactive condition. 


A negatively charged ion, e.g., chlorine, cf. Cation. 


The presence of two kinds of leaves on one plant as in 
Selaginella and some junipers. 



An animal belonging to the phylum Annelida such 
as earthworms, leeches, and marine worms; showing 

Annual Heat Budget 

See Heat budget. 

Annual Plant 

A plant which completes its life-cycle and dies in one 
year or less; a winter annual starts growth in late summer or 
fall and completes its life-cycle the following spring or early 
summer, a summer annual begins growth in the spring or 
early summer and completes its life-cycle before the follow- 
ing winter, cf. Biennial, Perennial. 

Annual Production 

The amount of substance formed in a year by an organ- 
ism or a group of organisms. 

Annual Ring 

The layer of wood (Xylem) added each year to stems and 
roots of woody plants, which indicate the age of the plant. 
Occasionally more than one layer may be formed in one 
year. See Growth layer. 

Annual Seasons 

The chief climatic periods of the year; Vernal/ Estival, 
Autumnal. (Serotinal), and Hibernal (q. v.). 

Annual Succession 

The successive occurrence of plants or animals in an area, 
or their activities, during the year, such as summer-flowering 
plants replacing the spring-flowering ones; or the various 
reproductive stages in animals. 

Annual Turnover 

The total quantity of living organisms (Biomass) (q. v.) 
produced in one year in an area. 



The variation from year to year in abundance or behav- 
iour of organisms caused often by differences in environ- 
mental conditions, especially precipitation and temperature. 


A ring-like structure characteristic of certain plant parts 
such as the stalk of mushrooms or on the spore-case of ferns. 
In certain animals, notably fishes, a ring, arrangement of 
rings, or other markings formed once a year and used in the 
determination of age and rate of growth. 


The period in animals when sexual desire or breeding is 


The condition of oxygen deficiency as in the tissues of 
an organism. 


The depressive effect of one organism upon another 
one such as certain grasses upon the growth of alfalfa, or 
the excretion of antibiotic substances such as penicillin by 
a mold. 


The Australian zoogeographical region, excluding New 
Zealand and Polynesia. 

Antecedent Moisture 

The degree of wetness of the soil at the beginning of a 
run-off period. 


The pollen-producing part of the stamen in a flower. 


The organ in which sperms are produced, found in 


several groups of plants such as the algae, fungi, mosses, 
and ferns. 


The period when a flower is fully expanded or when fer- 
tilization occurs. 


Water-soluble pigments, usually red, blue, or violet in 
the cell-sap of leaves, stems, flowers, and fruits of plants. 

Anthropic (Anthropeic) 

Refers to the influence of man in contrast to natural 
influences, e.g. a fertilized soil under crop rotation. 


A species that is regularly disseminated by man, e.g. 
weeds, crop plants, cf. Anemochore. 


Refers to influences caused by man, e.g. cultivation. 


The mode of thought or expression which attributes 
characteristics of man to non-human objects. 


Refers to plants which grow in proximity to man such 
as weeds in cultivated lands or on paths. 


The interaction between organisms produced by an 
Antibiotic (q. v.). 


A substance produced by organisms, especially bacteria 
and fungi, which passes into the surrounding medium and 
is toxic to other organisms, e.g., penicillin from the mold 
Penicillium notatum destroys many kinds of bacteria. 



A substance such as Antitoxin produced in an animal 
when foreign material (Antigen) is introduced into the body. 
The antibody counteracts the effect of the antigen. 


A geological structure or arch formed by strata from 
opposite sides dipping upward toward a common line. cf. 


Refers to coloration which facilitates aggressive action 
of an animal. 


A mass of air of high atmospheric pressure compared to 
adjacent areas, in which the circulation of the air is clock- 
wise in the northern hemisphere, anti-clockwise in the 
southern hemisphere. 


Parasites, substances produced by them, enzymes, toxins, 
or proteins which cause the formation of antibodies in the 
body of an animal. 


An Antibody (q. v.) that counteracts a Toxin (q. v.), e.g., 
antitoxin serum used in treatment of diphtheria. 


The coloration of an animal that causes it to resemble 
physical features of the habitat. 


The irregular occurrence of phenomena, cf. Periodicity. 


Refers to flowers that lack petals. 



A plant louse, an insect in the family Aphides, feeds by 
sucking juices of plants, e.g., green-peach aphid (Myzus per- 
sicae) which transmits more than 50 different plant viruses. 

Aphotic Zone 

The deeper portions of bodies of water to which daylight 
does not penetrate with sufficient intensity to influence or- 
ganisms, cf. Disphotic, Euphotic, Photic zones. 


The response of an organism by which it turns away from 
the source of light, cf. Phototropic. 


Refers to plants lacking leaves. 

Aphytal Zone 

The part of a lake floor that lacks plants, includes the 
sublittoral and profundal zones. 


Refers to flowers in which the carpels (q. v.) are not 
joined together, e.g. buttercup flowers. 


The reproduction of an organism without Fertilization 
(q. v.). cf. Apomixis, Parthenocarpy. 


The response of an organism by turning away from the 
earth, cf. Geotropism. 

Apomict Population 

A population of organisms produced asexually. 


Asexual reproduction of organisms in contrast to Amphi- 
mixis (q. v.). It includes Vegetative propagation (q. v.) and 


reproduction resembling sexual reproduction but in which 
the egg and sperm do not fuse. cf. Apogamy, Parthenogenesis. 


Refers to organisms that possess coloration associated with 
harmful or distasteful contents, and therefore such organism 
may be avoided by predators. 

Appetitive Behaviour 

The reaction of an animal by which it becomes located 
or in a suitable condition to satisfy its needs. 


A layer of material such as concrete or timber to protect 
a surface from erosion, e.g., pavement below a spillway. 


Refers to organisms or organs lacking wings, cf. Alar. 


A conduit for water, e.g., canal, pipe, tunnel, or a 


The use of artificial means to increase the production 
of fish, oysters, crabs, etc., in fresh or salt waters. 

Aquifer (Aquafer) 

A porous soil or geological formation lying between 
impermeable strata in which water may move for long 
distances, yields ground water to springs and wells. 


Communities of herbs occurring in ponds and swamps. 


Communities of plants where ground water is an impor- 
tant factor, e.g., wet meadows. 


Arable (land) 

Land suitable for cultivation by plowing or tillage, does 
not require clearing or other modification. 


An animal in the class Arachnida which includes spiders, 
mites, ticks, scorpions, and king-crabs. 


Refers to an Arachnid, particularly spiders or spider- 
webs; cobwebby. 


A weed introduced in prehistoric time into cultivated 


The organ producing the egg in many groups of plants 
such as mosses, ferns, and most Gymnosperms. 


Refers to the Archibenthic zone. 

Archibenthic Zone 

The layers of the ocean between depths of about 200 feet 
and 3300 feet, the upper part of the Abyssal zone (q. v.). 


Refers to the regions in high latitudes from which tree 
growth is usually absent because of the shortness of the grow- 
ing season and other unfavorable environmental conditions; 
may also be used as a noun for the region. 


Refers to the arctic and alpine regions jointly. 

Arctic Life Zone 

One of Merriam's life zones (q. v.), the portion of the 
Boreal life zone (q. v.) north of the limits of tree growth, 


southern limit marked by a normal mean temperature of 
50 F. during the six hottest weeks of summer. 


The faunal realm which includes the Ethiopian, Oriental, 
Palearctic, and Nearctic regions (q. v.). syn. Megagea. 


The total territory or range in which a Taxon or Com- 
munity occurs, cf. Basal area, Coverage. 


A sand desert. 


Refers to a sandy substratum. 


Refers to organisms inhabiting sandy substrata. 


The study that deals particularly with area. 


A small area of a leaf surrounded by intersecting veins. 


Refers to clayey material. 


Refers to regions or climates which lack sufficient mois- 
ture for crop production without irrigation; precipitation 
10 inches or less in cool regions, up to 15 or 20 inches in 
tropical regions, cf. Semiarid. 


The condition of dryness. See Arid. 

Arid Transition Life Zone 

The western part of Merriam's Transition zone, lying 
west of the 20-inch annual precipitation line. 



A special covering on a seed, arising from base of the 
ovule or the stalk, sometimes pulpy or brightly colored as 
in the bittersweet. 


Refers to the activity of an organism which occurs during 
both day and night, cf. Diurnal, Nocturnal. 


A stream channel or gully in an arid country, usually 
with steep banks, dry much of the time. 


An animal in the phylum Arthropoda such as insects, 
crabs, spiders, centipedes. 


(1) A substance or appearance of a specimen of an organ- 
ism or preparation of part of an organism which is not 
present in the living tissue. (2) Something made by man 
especially primitive man. 

Artificial Selection 

Selection by man of plants or animals which possess 
desired qualities for reproduction and for the improvement 
of the properties of the organisms, cf. Natural selection. 

Artificial Stocking 

The introduction of animals from another region, or the 
artificial propagation of animals, into an area, e.g., stocking 
streams with fish or introducing quail into an area where 
they are scarce or lacking. 

Asexual Reproduction 

Reproduction of organisms without the fusion of gametes, 
cf. Apomixis. 



(1) One of the seasonal appearances of vegetation. See 
Aspection. (2) The direction toward which a slope faces. 


The variability in the appearance of vegetation or of its 
constituent parts such as blooming, fruiting, foliation, and 
defoliation during the various seasons of the year. Chief 
seasons are Prevernal* Vernal, Estival, Serotinal, and Hibernal 
(q. v.). 


The synthesis of protoplasm and other complex sub- 
stances by organisms. 


A term with a number of usages, some of which are 
defined. (1) An actual or Concrete community, Stand, or 
group of organisms characterized by a definite floristic com- 
position, presenting uniformity in physiognomy and struc- 
ture, and growing under uniform habitat conditions. (2) In 
an abstract sense, a group of concrete communities or stands 
that are classified together because they meet certain stand- 
ards of similarity. See Association type, Index of similarity. 
(3) In the Clements' sense, a Climatic climax (q. v.) unit 
that includes all of the successional stages preceding or 
associated with it. Plant association and animal association 
emphasize populations of plants or animals respectively 
within an area. 

Association, Coefficient of 

A measure of the frequency of occurrence together of 
two species not due to chance, calculated by dividing the 
number of samples in which both occur together by the 
number of samples in which it is expected they would occur 
by chance alone. 


Association Complex 

A group of associations which occupies a definitely cir- 
cumscribed area. 

Association Fragment 

A stand or group of plants that lacks some of the charac- 
teristics of its community type. 

Association, Index of 

A measure of the occurrence together of one species with 
another, calculated by dividing the number of samples in 
which one species occurs by the number of samples in which 
both occur. 

Association, Interspecific 

The occurrence together of two or more species, e.g., 
a parasite on a host, a grass and a legume mutually benefit- 
ing by growing in proximity to each other. 

Association Segregate 

A Climax community which has become differentiated 
out of a mixed or undifferentiated vegetation under the in- 
fluence of climatic change, e.g., the beech-maple association 
arising as a segregate from the mixed deciduous forest in 
southeastern United States. 

Association Table 

A listing of species occurring in several stands of an 
Association or Community -type, and including data on such 
characteristics as abundance, cover, vitality, etc. syn. Syn- 
thesis table, cf. Stand table. 


A group of similar associations. 


In the Clements' usage a temporary, developmental com- 
munity, cf. Association (3). 


Assortative Breeding (mating) 

Pairing of male and female organisms that involves more 
than chance so that mating of similar parents is favored. 

Asymptotic Population 

The maximum size reached by a population under pre- 
vailing environmental conditions, no matter how long repro- 
duction continues. 


The appearance in an organism of an ancestral character 
after a period of several generations. 

Atlantic Period 

See Sub-boreal period. 


Any instrument for measuring evaporation such as a 
porous porcelain sphere or open pan of water. 


A body of water, lagoon, surrounded by a coral reef in 
the ocean. 


Adenosine triphosphate, an energy-rich phosphate com- 
pound in organisms, important in the transfer of energy. 


Reduction in size or contents of an organ, tissue, or cell. 

Audiogenic Seizure 

Convulsion in an animal caused by a high-pitched noise. 

Aufnahme (G) 

See Sample area, Quadrat. 

Aufwuchs (G) 

See Periphyton. 



The Antibiotic formed by the mold Streptomyces 


Refers to the dawn or the morning Crepuscular period. 

Austral Life-zone 

One of Merriam's life-zones comprising most of non- 
montane United States and Mexico, bounded on the north 
by a growing season of accumulation of 1 0,000 F. above 43 F. 
and on the south by 26,000 F., with a mean daily tempera- 
ture of 64.4 F. during the six hottest weeks at the northern 

Australian Region 

The faunal region comprising Australia and New Guinea, 
with Tasmania and smaller islands, in the realm Notogea 
(q. v.). 

Austroriparian Life-zone 

A subdivision of the Lower Austral life-zone, east of the 
100th meridian. 

Autarkean Society 

A simple, independent, economic human society consist- 
ing of nomadic or sparsely distributed individuals, cf. Allelar- 
kean society. 


The study of the individual, or members of a species 
considered collectively, in relation to environmental condi- 
tions, cf. Ecology, Synecology. 


A species in which the action of the parent plant is the 
chief force of dissemination, e.g., the mechanical projection 
of seeds in vetch, cf. Anemochore, Diaspore. 



Refers to local origin, e.g., an Indigenous species, deposits 
produced within a lake. cf. Index species f Allochthonous. 


Refers to parasites which pass all stages of their life-cycle 
within or on the same host, e.g., certain rust fungi, cf. 


(1) Self- or close-pollination leading to self-fertilization 
in plants, cf. Geitonogamy, Xenogamy, Cleistogamous. (2) 
Division of the nucleus into two parts followed by the union 
of these parts in the same cell, occurs in some diatoms and 

Autogenic Succession 

A successional series in which one stage modifies the 
habitat in such a way that it is replaced by another stage, 
e.g., deciduous forest replacing a pine forest, cf. Allogenic 
succession, Succession. 


The dissolution or digestion of an organism or parts 
thereof by its own enzymes. 


Refers to processes or activities arising from internal 
causes, spontaneous, self-governing, e.g. Mutation (q. v.). 


Refers to organisms, especially plants with chlorophyll, 
that are Autotrophic (q. v.). Also used as syn. of Autonomic. 


An Autotrophic plant. 


A Polyploid (q. v.) in which three or more sets of like 


(homologous) chromosomes have been derived from the same 
species, cf. Amphiploid, Allopolyploid. 


Loss of a part of the body of an organism by self-amputa- 
tion followed usually by regeneration of the part, as in 
certain arthropods and lizards. 


(1) Refers to organisms which are capable of producing 
organic substances from inorganic materials by means of 
energy received from outside of the organisms, e.g., plants 
with chlorophyll and certain bacteria, cf. Parasitic, Sapro- 
phytiCj Heterotrophic, Holophytic. (2) Refers to a pond or 
lake that is restricted in its supply of organic material to that 
produced within its own confines. 


Refers to the fall season or Aspect (q. v.). 


A non-essential organic substance such as an extract 
secured from dung, of unknown chemical composition, which 
stimulates the growth of certain plants such as duckweeds. 


A substance, natural or synthetic, that controls the growth 
of plants, cf. Hormone. 

Available Nutrient in Soil 

The part of the supply of nutrient materials such as 
phosphates in the soil that can be absorbed by plants at rates 
and amounts required for growth. 

Available Water (in soil) 

The part of the water in the soil that plants can absorb. 

Available Water-holding Capacity (of soil) 

The amount of water available in the soil between the 


amount held at Field capacity (q. v.) and the amount at the 
Permanent Wilting percentage (q. v.). 

Avalanche Cone 

Materials such as rocks, snow, ice, trees, deposited at the 
base of the path of an avalanche. 

Avalanche Wind 

A wind, often destructive over a distance, produced by 
an avalanche. 

Average Distance 

The distance between plants determined by dividing the 
square root of an area by the density of each species within 
the area. 


An unhealthy condition or disease caused by a deficiency 
of vitamins. 


A bristle-like structure attached to plant parts such as on 
Floret parts of grasses. 

Azonal (soil) 

A soil without a well-developed profile, occurring in any 
soil zone, consisting largely of Parent material (q. v.), e.g., 
recently deposited Alluvium, dune sand. 



The mating or crossing of a hybrid with either one of 
its parents or parental stocks. 


A fire started purposely ahead of an advancing fire to 
remove inflammable material and thus control the main fire. 


The movement of a poison through root grafts from 
trees that have been treated with poison to non-treated trees. 


A virus which destroys bacteria. 


The nodules on the roots of most legumes and on some 
other plants such as alders which contain bacteria that can 
use atmospheric nitrogen in synthesizing organic compounds. 


Areas of rough, irregular, eroded land on which most of 
the surface is occupied by ridges, gullies, and deep channels, 
with sparse vegetation. 


Baermann Funnel 

A modification of the Berlese funnel (q. v.) for forcing 
nematodes out of soil or debris. The funnel is filled with 
warm water which forces the nematodes into a vessel below. 


An obstruction placed in the path of water moving at a 
high velocity, e.g., a pier on the Apron of an over-flow dam. 


A set of vanes, guides, or similar devices placed in a con- 
duit to check eddy currents below them, and provide a more 
uniform distribution of velocities. 

Bag Limit 

The maximum number of individuals of a species that a 
hunter may take legally. 


A tropical cyclone or Typhoon, a term used in the 
Philippine Islands. 


Outwash slopes with long straight longitudinal profiles, 
occur in southwestern United States. 

Balance of Nature (Ecological Balance) 

The state in an Ecosystem (q. v.) when the interrelation- 
ships of organisms to one another and to their environment 
are harmonious or integrated to a considerable degree, e.g., 
a climax forest. This balance may be upset in many ways 
such as by a drastic change in environmental conditions (ero- 
sion followed by death of many plants) or by a great increase 
in numbers of a certain organism (grasshoppers in grass- 
lands). See Dynamic equilibrium. 


Refers to barnacles. 



A treeless area in a forest vegetation, especially in the 
southern Appalachians, occupied by grasses or shrubs usually. 


Shallow swamps in Paraguay. 

Bancroft's Law 

A generalization that organisms and communities tend 
to come into a state of Dynamic equilibrium (q. v.) with 
their environment. 


A general term for a social group of two or more mobile 
animals of the same species, e.g., a herd of deer, pack of 

Bank Storage 

Water absorbed by the bed and banks of a stream and 
returned in whole or in part after the Ground-water level 


(1) A deposit of sand or rock particles forming a ridge 
along the coast, usually at the mouth of a stream or across 
a bay. (2) A unit of atmospheric pressure equivalent to 29.53 
inches (750.1 mm) of mercury at 32 F. in latitude 45. 


A species in which the seed, fruit, or other Propagule is 
disseminated largely by its own weight, e.g., walnut fruit, 
cf. Autochore, Diaspore. 


A distinctive isolated sand dune which is crescent-shaped 
with the ends projecting leeward, common in Turkestan. 


A general term for all the tissues outside of the cambium 
in stems of trees; outer part may be dead, inner part is living. 



The continuous record made by a self-registering 


A self-registering barometer. 


An instrument for measuring the atmospheric pressure, 
cf. Aneroid barometer. 


Response by locomotion of an organism or part of an 
organism in response to a barometric stimulus. 


Reaction by growth curvature of a plant or a sedentary 
animal in response to a barometric stimulus. 


An area in which vegetation is absent or poorly developed. 


(1) A topographic feature or a physical or biological con- 
dition that restricts or prevents migration of organisms or 
prevents establishment of organisms that have migrated. 
(2) A condition that prevents or appreciably reduces cross- 
breeding of organisms. 

Barrier Beach 

See Beach. 

Basal Area 

(1) The area of the cross section of a tree at height of 
4.5 feet above* the ground, usually expressed as the summa- 
tion of the basal area of the trees in a forest in square feet 
per acre. (2) The surface of the soil actually covered or 
occupied by a plant, especially the basal part, as compared 
to the full spread of the herbage; in grassland ecology often 


measured at one inch above the ground surface, syn. Basal 
cover, Ground cover, cf. Cover. 

Basal Cover 

See Basal area (2). 

Basal Metabolism 

The rate of physiological processes in an organism when 
it is carrying on a minimum of its life processes such as 
respiration in order to remain alive. 

Base Exchange Capacity 

A measure of the absorptive capacity of a soil for bases, 
or exchangeable cations. A soil with a high base exchange 
capacity will retain more plant nutrients and is less subject 
to leaching than one with a low exchange capacity. 

Base Flow 

Stream flow originating from subterranean sources in 
contrast to flow from surface run-off. 

Base Level 

The lowest level to which a land surface can be reduced 
by streams; the permanent base level is the level of the sea. 

Base Number 

The Haploid (q. v.) number of chromosomes (as found 
in sperms or eggs, gametes) in those species with the lowest 
number in a Polyploid series, or sometimes postulated for 
a species that is extinct or unknown. 

Base Saturation 

The proportion of the Base exchange capacity that is 
saturated with metallic cations. 

Basin Irrigation 

A method of irrigation in which a level area is sur- 
rounded by an earth ridge so that a shallow body of water 
may accumulate prior to infiltration. 


Basin- Listing 

Alkind of land tillage in which small dams at intervals 
of 15 to 25 feet are formed across furrows to form basins 
for collecting water after precipitation, thus retarding runoff 
and erosion. 


Refers to the development of organs in plants in which 
the oldest are at the apex, the youngest at the base. cf. 


Refers to organisms which possess adaptations for life 
in alkaline soil or in an alkaline medium, e.g. A triplex spp. 

Bathyal Zone 

The deep part of the ocean into which light does not 
penetrate effectively. 


Refers to life in the Bathyal zone. 


Refers to deep portions of the ocean, not including the 


A structure consisting of a spherical chamber in which 
man can descend deep into the ocean to make observations. 


A marshy body of water caused by seepage, lack of 
drainage, or floods, tributary to a stream or lake, in flat 
country. A term used in the Gulf Coast region and in the 
lower Mississippi River basin. 


The line or zone of demarcation between land and water 
of lakes, seas, etc. Barrier beach; a ridge of deposits separated 
from the mainland by an interval of water. 


Beach Pool 

(1) Barrier beach pool is a shallow lagoon formed inland 
from Barrier beaches. (2) Sand spit beach pool is a shallow 
lagoon generally sigmoid-shaped inland from a sand Spit, 
characteristically on the protected side of a headland. 

Beaufort Scale 

A series of numbers devised by Francis Beaufort in 1805 
to designate approximate wind velocities ranging from for 
a calm to 12 for a hurricane with wind velocity in excess of 
75 miles per hour. 

Beckmann Thermometer 

A thermometer graduated to 0.01 degree and covering a 
scale of 6 to 7 degrees. 

Bed Load 

Soil, rocks, and other debris rolled along the bottom of 
a stream by moving water, in contrast to "silt load" which 
is carried in suspension. 


The solid rock underlying soils or other surface materials. 

Behaviour, Appetitive 

A reaction of an animal that aids in the satisfaction of 
its needs. 

Behaviour, Displacement 

The reaction of an animal that is not pertinent to the 
stimulus, as when it cannot respond appropriately or when 
two or more incompatible drives are present. 

Behaviour, Instinctive 

A fixed pattern of action that is inherited. 


A comparatively narrow area or strip of vegetation with 
distinctive characteristics from adjoining areas or vegetation. 

cf . Zone. 


Belt Transect 

A strip of vegetation, usually a few inches or feet wide, 
in which the constituent plants are recorded or mapped. 

Bench Mark 

A point of reference used in elevation surveys. 

Bench Terrace 

A shelf-like embankment of earth constructed along the 
contour of sloping land to control run-off and erosion, cf. 
Ridge terrace. 


Refers to the bottom of any body of water. In the ocean 
the benthic division is divided into the Littoral, Sublittoral, 
Archibenthic, Abyssal-benthic zones, (q. v.). cf. Pelagic. 


Organisms which live on or in the bottom of the ocean or 
bodies of fresh water, from the water's edge down to the 
greatest depths, cf. Nekton. 

Bergmann's Principle (Rule) 

The generalization which states that Homoiothermal 
(q. v.) animals such as birds and mammals in cold regions 
tend to be larger in size and have a lower ratio of body 
surface to body weight than related animals in warmer 
climates. The reverse relationship is shown by Poikilo- 
thermous animals, especially amphibians and reptiles, cf. 
Allen's principle. 

Berlese Funnel 

An apparatus in which soil or debris is placed in a funnel, 
heat and light applied from above as a rule, which forces 
mites, collembolons, etc., into a vessel below, cf. Baermann 
funnel, Tullgren funnel. 

Beta Particles 

High-speed electrons given off by radioactive substances. 


Beta Ray 

A stream of Beta particles with greater power of penetra- 
tion in the tissues of organisms than Alpha rays (q. v.). 

B Horizon 

A master soil horizon between A and C Horizons (q. v.), 
a layer of Illuviation (q. v.) in which materials from overlying 
horizons are deposited. B! is transitional between A 3 and B 2 , 
but more like B than A. B 2 is the layer of maximum illuvia- 
tion especially of silicate clay materials, or of iron and 
organic materials, or with maximum development of blocky 
or prismatic structure. B 3 is transitional between B and C 
horizons, often absent. 


Refers to a Taxon (q. v.) with two centers of dispersion 
or evolution. 


A plant that lives for two years, usually blooming and 
fruiting only in the second year and then dying, e.g. carrot. 


A plant that flowers in both spring and autumn. 

Bilateral Symmetry 

An organism which can be divided so that each half is 
the mirror image of the other, e.g., vertebrates, snapdragon 
flower, syn. zygomorphy. cf. symmetry. 

Binary Name 

See Binomial. 


See Agamospecies. 


A name of organisms consisting of two words, e.g., 
Quercus alba, the white oak; the first name is the genus, the 
second the species. 



The employment of living organisms to test the effects 
of a substance such as feeding rats with food containing 
herbicide residues. 


See Biocoenosis. 

Biochemical Oxygen Demand (B.O.D.) 

A test for the detection and measurement of pollution in 
which the quantity of oxygen that has been used by oxidiz- 
able materials under standardized conditions is determined. 


A subdivision of the Biocycle (q. v.) It comprises a group 
of Biotopes (q. v.) which resemble one another. The princi- 
pal biochores are grassland, forest, savanna, and desert. The 
desert biochore includes sandy desert and stony desert bio- 
topes, cf. Biosphere. 


See Microclimate. 

Bioclimatic Law (Hopkins) 

The generalization that in temperate North America 
Phenological events generally occur at the average rate of 
four days to each degree of latitude, 5 of longitude, and 
400 feet of altitude; later northward, eastward, or upward 
in spring and early summer, and earlier in late summer and 


The study of the interrelations of organisms and climate. 


The study of communities including qualitative and 
quantitative analyses; the Synecology, Synchorology, Dynam- 
ics, and classification of communities. 


Biocoenosis (Biocoenose) 

The aggregate of interacting organisms living together 
in a particular habitat, e.g., an oyster-bed community, usually 
containing producer, consumer, reducer, and transformer 
organisms, cf. Ecosystem, Community, Association. 


See Biocoenology. 


A subdivision of the Biosphere (q. v.). Biocycles usually 
recognized are saltwater, freshwater, and land; each consist- 
ing of Biochores (q. v.) cf. Biotope. 


The mathematical treatment of population problems. 


The branch of biology that deals with the interrelations 
of organisms among themselves and with their environments, 
stressing the inclusion of both plants and animals, cf. Ecology. 


The principle that living organisms can originate only 
from other living organisms, cf. Spontaneous generation. 


Refers to biological origin. 

Biogeochemical Cycle 

The circulation of chemical elements such as nitrogen, 
carbon, etc., in specific ways from the environment into 
organic substances in animals and plants and back again into 
the environment. 


A concrete or actual Ecosystem (q. v.), e.g., a certain bog. 

Biogeographic Region 

See Biome. 



The branch of biology that deals with the geographic 
distribution of plants and animals, cf. Plant geography, 
Zoogeography, Chorology. 


Preliminary treatment for seeds with chemicals to stim- 
ulate growth. 

Biological Clock 

The rhythmic occurrence of processes in organisms at 
periodically timed intervals, e.g., the ejection of spores by 
the fungus Pilobolus sphaerosporus. 

Biological Control 

The use of organisms or viruses to control parasites, 
weeds, or other pests, e.g. control of the cottony-cushion scale 
by the lady beetle, prickly pear cactus in Australia by the 
insect Cactoblastis cactorum. 

Biological Efficiency 

The ratio of the productivity of an organism, or a group 
of organisms, to that of its supply of energy, cf. Productivity. 

Biological Equilibrium 

See Biotic balance. 

Biological Factor 

An influence resulting from biological as distinct from 
physical and chemical agents, including both Biotic factors 
(q. v.) and physiologic factors such as Hormones. 

Biological Race (Strain) 

A group of organisms which differ only in their physio- 
logical or ecological behaviour from other groups in the same 

Biological Spectrum 

A tabulation by percentages of the plants of a community 


or region into the life-form classes according to Raunkiaer's 
classification (q. v.). 


Biological products such as vaccines, serums, etc. 


Emission of light by living organisms such as fireflies, 
jelly fish, etc., popularly "phosphorescence." 


The total quantity at a given time of living organisms of 
one or more species per unit of space (species biomass), or of 
all the species in a community (community biomass). cf. 
Yield, Productivity , Standing crop. 


A major biotic community composed of all the plants and 
animals and communities, including the successional stages 
of an area; the communities possess certain similarities in 
physiognomy and in environmental conditions. Similar to 
Formation (q. v.), e.g., the North American grassland, cf. 
Biotic province, Biome-type. 


A group of similar Biomes, e. g., the temperate deciduous 
biome-type which includes the deciduous forests of eastern 
North America, China and Manchuria, and Europe. 


The application of the science of statistics to the study 
of organisms. 


The study of organisms in relation to each other and to 
the environment, cf. Ecology. 


See Biome-type. 



Plant and animal life. 


The living components of the Seston (q. v.). 

Biosocial Facilitation 

See Facilitation, social. 


The portion of the earth and its atmosphere that is ca- 
pable of supporting life; may be subdivided into Biocycles, 
Biochores, Biotopes (q. v.). 


See Ecosystem. 


The study of living organisms for the purpose of recog- 
nizing and differentiating biotic units and their classification 
into taxa on the basis of genetic relationships. 


All of the species of plants and animals occurring within 
a certain area or region. 

Biothermal Zones 

The divisions according to Merriam of the flora and 
fauna of North America on the basis of temperature data. 


Refers to life, living. 

Biotic Area 

A general term to denote any large area that can be delim- 
ited from adjacent areas on the basis of the composition of 
its Biota. 

Biotic Balance (Biological Equilibrium) 

The state of more or less self-regulation of the- numbers 


of plants and animals in a community, brought about by 
interactions within and between species and by the effects of 
environmental conditions, cf. Life-cycle, Balance of nature, 
Pyramid of numbers. 

Biotic Climax 

See Climax. 

Biotic District 

According to Dice a subdivision of a Biotic Province, dis- 
tinguished by ecologic differences of less importance than 
those that separate biotic provinces. 

Biotic Environment 

The living parts of the environment of an organism or 
group of organisms. 

Biotic Equilibrium 

See Biotic balance, Balance of nature. 

Biotic Factor 

Environmental influences caused by plants or animals 
such as shading by trees or trampling by animals, sometimes 
used to include effects of non-living organic matter, cf. Bio- 
logical factor, Coaction. 

Biotic Formation 

See Biome. 

Biotic Influence 

See Biotic factor. 

Biotic Potential 

The inherent capacity of an organism to reproduce and 
survive, which is pitted against limiting influences of the 
environment, cf. Reproductive potential, Environmental 

Biotic Pressure 

The activities of an enlarging population to maintain 


itself and spread, or the tendency of one or more species to 
extend its range, cf. Population pressure. 

Biotic Province 

A major ecologic portion of a continent, occupying a 
continuous geographic area, containing one or more regional 
communities of plants and animals, e.g., Hudsonian biotic 
province which occupies most of Canada and Alaska (Dice), 
cf. Biome, Formation. 

Biotic Succession 

See Succession. 


A growth-promoting or stimulatory substance (vitamin 
H), a member of the vitamin B complex. 


The smallest geographic unit of a habitat, characterized 
by a high degree of uniformity in the environment and in its 
plant and animal life, e.g., a decaying stump, a sandy beach, 
cf. Biochore. 


A group of individuals occurring in nature, all with 
essentially the same genetic constitution. A species usually 
consists of many biotypes. cf. Ecotype. 

Bipolar Distribution 

Discontinuous distribution of a Taxon in the northern 
and southern hemispheres. 

Birge's Rule 

A generalization which states that the Thermocline (q.v.) 
is the transition stratum in lakes in which the temperature 
decreases at the rate of at least 1C. per meter of depth. 


A line transect which shows the vertical and lateral dis- 


tribution of roots along the side of a trench in the soil and 
the above-ground parts of the plants along the line. 


The presence of functional male and female organs in 
the same plant or animal, cf. Hermaphrodite, Dioecious, 


A pair of Homologous chromosomes in a certain stage of 
cell division. 


Refers to organisms with two generations a year. cf. Uni- 
voltine, Multivoltine. 

Black Alkali 

Highly alkaline soil covered with a dark incrustation of 
carbonates of sodium or potassium, cf . A Ikali soil, Saline soil. 

Black Earth 

See Chernozem. 


A storm in which the cold wind, usually of high velocity, 
drives fine snow and often ice crystals; the visibility is greatly 


(1) A fine pale gray granular layer, often waxy, occurring 
commonly on the surface of plant organs such as leaves and 
fruits, e. g., the grape fruit. (2) A sudden appearance of brief 
duration of large numbers of minute organisms, usually 
algae, in bodies of water. 


An excavation in loose soil, usually sand, produced by 


Blytt-Sernander Scheme 

The chronological series of floras and kinds of vegetation 
following the last glaciation in Scandinavia; comprising the 
boreal, Atlantic, sub-boreal, and sub-Atlantic stages. 


An undrained or imperfectly drained area, with a vegeta- 
tion complex composed of sedges, shrubs (Ericaceous, espe- 
cially), and sphagnum mosses, typically with peat formation; 
often with an area of open water. Frequently used in various 
meanings, in the sense of Marsh, Swamp, Moor, Fen. cf. 
Muskeg, Heath, Raised bog. 

Bog Soil 

A mucky or peaty surface horizon underlaid by peat. 


The unbranched trunk or stem of a tree. 


A depression lacking exterior drainage in an arid or semi- 
arid region, term used in southwestern United States and 


The state of well being of a population, as indicated by 
the number of individuals, cf. Ecological bonitation. 

Border Dike 

Ridges of earth constructed to hold irrigation water 
within certain limits in a field. 

Border Irrigation 

Flooding areas in fields by the use of Border dikes. 

Border Strip 

A zone or strip surrounding a sample plot, usually given 
the same treatment as the plot. 



A tidal wave with an abrupt front often three or more 
feet high, advancing upstream in a narrow river estuary. 

Boreal Forest 

The forest consisting chiefly of conifers extending across 
northern North America from Newfoundland to Alaska. 

Boreal Life Zone 

One of Merriam's life zones including northern North 
America, Boreal forest and Tundra vegetation, bounded at 
its southern limit by growth-season accumulated temperature 
above 43 F. of 1 0,000 F. and a mean daily temperature of 
64.4 F. for the six hottest weeks. Subdivided into the Arctic, 
Hudsonian, and Canadian life zones. 

Boreal Period 

The climatic period from about 7500 to 5500 B. C., 
characterized by warm, dry conditions; preceded by the 
Preboreal period (8000-7500 B. C.) with variable climate, and 
the Subarctic period (9000-8000 B. C.) with cold, dry climate, 
cf. Sub-boreal period. 

Bottom Deposits 

Organic and inorganic materials deposited beneath water 
and upon the original basin or channel floor. 

Bottom Fauna 

Animal components of the Benthos (q. v.). 


See Flood plain. 


Unstratified clay intermixed with many stones, deposited 
by glaciers, cf. Till, Drift. 


Refers to organisms with short wings. 


Breast Height 

A height of 4.5 feet (1.3 meters) above the average ground 
surface or above the root collar, diameters of standing trees 
are ordinarily measured at this height. (Abbreviation is 
d. b. h.). 


A rock composed of angular pieces in a matrix. 

Breeding (Plants, Animals) 

The application of genetics and other sciences in the 
systematic improvement of a Taxon or a population. 

Breeding Potential 

See Reproductive potential. 

Broad-base Terrace 

A terrace 10 to 20 inches high, 15 to 30 feet wide, with 
gently sloping sides, a rounded crown, and a dish-shaped 
channel on the upper side, built to divert run-off water along 
the contour. 

Broadcast Seeding 

Scattering seed on the surface of the soil as contrasted to 
seeding with a drill in rows. cf. Drill seeding. 

Brown Forest Soils 

A group of soils with dark brown surface horizons, rela- 
tively rich in humus, becoming lighter colored below, 
slightly acid or neutral, with moderate amount of exchange- 
able calcium; commonly developed under deciduous forests 
that are relatively rich in bases, particularly calcium. 

Brown Podzolic Soils 

A group of soils with thin mats of partly decayed leaves 
above a thin, grayish brown layer containing mineral matter 
and humus; overlying yellow or yellowish brown acid B 
horizons; developed under deciduous or mixed deciduous- 
coniferous forests in cool temperate, humid regions. 


Brown Soils 

A group of soils with brown surface horizon, becoming 
lighter in color with depth; accumulation of calcium carbon- 
ate at depth of one to three feet; developed under grassland 
and shrubs in temperate to cool semiarid climate. 


(1) Twigs or shoots, with or without attached leaves, of 
shrubs, trees, or woody vines grazed by livestock. (2) To 
graze plant parts as in (1). 


A line marking the height to which browsing animals 
have removed the Browse from shrubs, trees, or vines. 

Bruckner Cycle 

The cycle of about 35 years in average length (25 to 50 
years) which includes an alternation of a warm dry period 
and a cold damp period. 


An area characterized by shrubby vegetation. 

Brush Matting 

(1) A matting of branches placed on eroded land to con- 
serve moisture and reduce erosion while trees or other vegeta- 
tion is being established. (2) A matting of mesh wire and 
brush used to retard streambank erosion. 

Brush Pasture 

A pasture with a natural cover of trees and shrubs, where 
a large part of the forage secured by livestock comes from 
browsing woody plants. 


A small animal such as a tardigrade, rotifer, and nema- 
tode which live among moss plants. 


A plant in the phylum Bryophyta comprising mosses, 
liverworts, and hormvorts. 



(1) A form of grafting, by inserting a bud with a small 
amount of tissue at its base into a slit made in the stem of 
the stock plant. (2) A form of asexual reproduction in which 
a new cell grows out from the parent cell, e.g., yeast plants. 

Buffalo Wallow 

A depression in grassland made by buffalo or cattle while 
trampling or wallowing, followed by denudation and loss of 


The modification of environmental conditions by vegeta- 
tion or topographic features, e.g., shading, cf. Reaction. 

Buffer Species 

A plant or animal which may provide an alternative food 
for another animal and thus reduce the demand for certain 
food items. 

Buffer Strip 

A strip of grassland or other erosion-resistant vegetation 
planted on the contour between or below cultivated strips 
or fields. 

Buffer Zone 

(1) An area or strip surrounding a study-area or other 
specific area in part or entirely to protect the inner area from 
ecological disturbance by influences from the outside. (2) 
A publicly owned range area adjoining a privately owned 
range tract, which may be used to supplement the range 
on the latter. 


A small bulb or modified bulb by which the plant is 

Bulk Density 

The mass or weight of oven-dry (100-1 10C.) soil per unit 
of bulk volume, including air space. 


Bunch Grass 

A grass which forms a tuft or bunch, many stems arising 
from the root-crown in a dense mass, e.g., orchard grass, 

Bunt Order 

Rank of dehorned cattle in a herd, determined by aggres- 
sive behaviour. 

Buoyancy Theory 

An explanation of the role of morphological features that 
decrease the rate of sinking of plankton. 

Buried Soil 

One or more layers of soil which was formerly at the 
surface followed by covering with ash, sand, or some other 
form of deposition. 

Burn Scar 

A scar on a tree where the tissues were damaged by fire, 
it may be partly or entirely covered by later-formed tissues. 


(1) a shrub. (2) An area covered by shrubs or forest, 
especially in Australia and South Africa; also used for any 
uncleared land. 


An isolated hill with steep sides and a comparatively 
flat top, smaller than a Mesa, term used in western United 
States especially. 


A lateral plank-like extension near the base of some trees, 
gives additional support to the tree. 



A type of vegetation consisting of thorn scrub in north- 
eastern Brazil. 


Resembling a cactus, e.g., Euphorbia spp. in northern 


Special adaptations of embryonic or young stages of an 
animal to environmental conditions, which are more recent 
in evolution than adaptations in the adult, e.g., mosquito 
larvae with special spiracular openings, cf. Deuterogenesis. 

Caingin Clearing 

An area denuded of vegetation and used for agriculture 
in southeast Asia. 


A pile of stones used as a landmark. 


Refers to material containing calcium in moderate to 
large amounts, especially soil with calcium carbonate, 


Calcareous Ooze 

Partially decomposed, soft, organic material mixed with 
a considerable proportion of calcareous material on the bot- 
tom of some bodies of water. 


An organism, usually a plant, growing in soil rich in 


A soil process in which the surface soil is supplied with 
calcium by the decomposition of plants or in which a 
calcareous layer is formed in the soil. cf. Podzolization. 


A plant that grows best in acid soil. See Acidophilous. 


A plant that grows best in calcareous soil. See Basophilous. 


An Acidophilous (q. v.) plant. 


A large basin-like depression with steep sides in the top 
of a volcanic mountain, e.g., Crater Lake, Oregon. 


A calcareous hardpan in southwestern United States, also 
applied to deposits of sodium nitrate in Chile and Peru. 


The outer whorl of flower parts, made up of sepals, 
usually green and resembling leaves or bracts, or with other 
colors in some flowers. 


A layer of Meristem (q. v.) cells and the undifferentiated 
daughter cells; used preferably for vascular cambium (which 


gives rise to parenchyma, secondary xylem, and secondary 
phloem in dicotyledons and gymnosperms) and for cork 


Refers to the oldest geological period in the Paleozoic 
era, about 500 million years ago. 

Campo Cerrado 

A vegetation type in Brazil composed of scattered trees 
in dense grassland. 


Grasslands or savanna located south of the equatorial 
forests in Brazil. 

Canadian Life Zone 

The southern half of the coniferous forest area of the 
Boreal life zone (q. v.). 


The uppermost layer consisting of crowns of trees or 
shrubs in a forest or woodland. 

Canopy Trees 

Trees with crowns in the uppermost layer of forest or 


See Land capability. 

Capacity, Adaptive 

The genetically determined range (or plasticity) of reac- 
tions of an organism which enable it to respond in different 
ways to a variety of conditions. 

Capacity Formula 

A formula used in hydraulics to calculate the capacity 
or discharge volume of a channel. 


Capillary Porosity 

The aggregate volume of small pores within the soil 
which retain water against the force of gravity. 

Capillary Water 

The portion of soil water which is held by cohesion as a 
continuous film around particles and in spaces; most of it 
is available to plants. 


The process of Pollination by wasps in the commercial 
fig plants. 


(1) A dry, dehiscent fruit consisting of several Carpels. 
(2) A sac-like tissue surrounding an organ. (3) Organs in some 
plants such as mosses in which spores are produced. 


A hard case or shield covering part of the body of some 
animals, e.g., crabs. 


An organic compound consisting of carbon, hydrogen, 
and oxygen, such as sugars, starch, and cellulose. 

Carbon Assimilation 

See Photosynthesis. 

Carbonate Zone 

A layer in the soil with a concentration of carbonates, 
chiefly calcium carbonate, found especially in arid regions. 

Carbon Cycle 

The circulation of carbon from carbon dioxide in the 
atmosphere into sugar by photosynthesis in plants, synthesis 
of more complex organic compounds in plants and animals, 
and the return by respiration or death and decay of plant 
and animal tissues to carbon dioxide. 


Carbon- 14 Dating 

The use of radioactive carbon which has an atomic mass 
of 14 and an approximate half-life of 5,500 years, for deter- 
mining approximately the age of soils, buried materials 
such as wood, and other organic materials. See Radiation, 


Refers to the Pennsylvanian (Upper Carboniferous) and 
the Mississippian (Lower Carboniferous) geological periods 
in the upper part of the Paleozoic era, about 200-260 mil- 
lion years ago. 


A substance that produces cancer. 

Cardinal Points 

The four chief directions of the compass; south, east, 
north, and west. 


An animal in the order Carnivora such as the dog, cat, 
bear, and seal. 


Refers to carnivores or to plants such as the sundew that 
trap and digest insects and other small animals. 

Carolinian Life Zone 

One of the divisions of the Upper Austral life zone. See 
Austral life zone. 

Carotene (Carotin) 

An orange-yellow pigment, a hydrocarbon, which occurs 
commonly in plants, especially in the roots of carrots, a 
precursor of vitamin A. 


The part of the flower, usually consisting of stigma, style, 


and ovary, the latter producing one or more ovules which 
develop into seeds, syn. simple pistil. Two or more carpels 
may be fused to form a compound pistil. 


See Fen. 

Carrying Capacity 

(1) The maximum number of a wildlife species which 
a certain territory will support through the most critical 
period of the year. (2) The maximum quantity of the 
Standing crop (q. v.) which can be maintained indefinitely 
on an area. (3) See Grazing capacity. 


(1) A protuberance, usually fleshy, near the hilum of a 
seed such as the castor bean. (2) A fleshy, naked outgrowth 
on the head and neck of certain birds, e.g., wattles of the 


An indehiscent, dry, one-seeded fruit in which the peri- 
carp (ovary wall) and seed coats are united, e.g., grain of corn. 


One of the kinds of specialized individuals in social 
insects such as termites, ants, and bees, e.g. drones, workers. 

Casual Species 

Species which occur rarely or without regularity in a 


The aggregate of metabolic processes such as respiration 
and digestion by which organic compounds are changed into 
simpler substance's, cf. Anabolism, Metabolism. 


Refers to the migration of organisms, usually fish, from 
fresh to salt water to spawn, e.g., eel. 



The condition of muscular rigidity in which the body 
and limbs maintain the position in which they are placed. 


An animal derived by crossing cattle and buffalo. 


Refers to an aquatic habitat in which slow decomposition 
of organic matter is taking place, organic substances are given 
off into the medium, and much oxygen is used but not 
enough to prohibit the occurrence of aerobic organisms, cf. 
Oligosaprobic, Polysaprobic, Mesosaprobic. 

Catch Crop 

A crop grown incidentally to the main crop of a farm 
and usually occupying the land for a short period; or a crop 
grown to replace a main crop which has failed. 

Catchment Basin 

A unit watershed, an area from which all the drainage 
water passes into one stream or other body of water. 


A group of soils within a specific soil zone, formed from 
similar parent materials but with unlike characteristics 
because of differences in relief and drainage. 


An ion carrying a positive charge of electricity such as 
calcium, sodium, and hydrogen, cf. Anion. 

Cation Exchange 

The exchange of cations held by soil absorbing materials 
such as calcium replacing sodium when calcium sulfate is 
added to a sodium-rich soil. 

Cation-exchange Capacity 

A measure of the total quantity of exchangeable cations 
that a soil can hold; preferable to base-exchange capacity. 



See Ament. 


Refers to the tail of an organism. 


Refers to the possession of a tail by an organism. 


Refers to a plant which has a readily perceived stem 
above ground. 


Refers to a woody plant that produces an Inflorescence 
directly from the trunk or one of the chief branches, e.g., the 
fig tree. 


Refers to the stem of a plant. 


An organism that lives in a cave. 


A gall produced by an insect or a fungus on a plant. 

Cell Sap 

The solution in water of organic and inorganic substances 
in the Vacuole of a plant cell. 


The principal component of cell walls of plants, a com- 
plex Carbohydrate. 


A group of species in nature distinguished only by factors 
external to the organisms, or the various forms of a species 
under domestication, a "superspecies." 



Refers to the geological era extending from 40 million 
years or more ago to the present era which began about one 
million years ago. 

Center of Dispersal 

The area from which a Taxon has spread or is spreading. 

Center of Origin 

The area in which a Taxon originated and from which 
it has spread. 

Cephalic Index 

A measure of the conformation of the human head, the 
breadth in percentage of the length (front to back). 


A plant in the grass family, Gramineae, the grains of 
which are used for human food, e.g., maize, wheat, and oats. 

Certified Seed 

Seeds that have been approved by a certifying agency as 
qualifying under established standards of germination, free- 
dom from diseases and weeds, and trueness to variety. 

Cespitose (Caespitose) 

Refers to plants with branches, short stems that are 
usually covered with leaves, forming dense tufts or cushions. 


An animal in the class Cestoda, including the tapeworms. 


A Mammal in the order Cetacea, including whales, 
dolphins, and porpoises. 


(1) A dry, thin scale found especially as bracts in flower 


heads of many Composites. (2) The outer layers of cells of 
grains removed during threshing. 


A gray or white form of limestone composed mostly of 
the remains of small marine organisms, with a very high 
content of calcium carbonate. 


One of the classes of Raunkiaer's life-forms, consisting 
of plants whose Perennating buds are located between the 
surface of the ground and a height of 10 inches (25 cm.). 


Low and often dense scrub vegetation characterized by 
shrubs or dwarf trees with mostly evergreen and often hard 
leaves such as oaks and buckbrush, cf. Maquis. 


An attribute or property of an organism, functional or 
structural, modifiable by environmental conditions within 
genetically determined limits. 

Character (Characteristic) Species 

The species in classes 3, 4, and 5 of Braun-Blanquet's 
fidelity classification. Class 5 includes species occurring ex- 
clusively or almost so in a particular kind of plant com- 
munity; class 4 contains species that show a strong preference 
for one kind of community but occurs sparingly in others; 
class 3 contains species that often occur in several kinds of 
communities but the optimum growth is found in only one 
kind. cf. Fidelity. 

Characteristic Species-combination 

A group of species in a community-type, which comprises 
the Character species and other species that have a Constancy 
rating above 80 per cent (varies with authors from 60 to 90 
per cent). 


Chart Quadrat 

A chart or map of a sample area showing the location 

and area of each plant. 


A plant growing in the crevice of rocks, e.g., saxifrages, 
cf. Chomophyte. 

Check Dam 

A small low dam constructed in a watercourse to decrease 
the velocity of stream flow and to promote the deposition of 
eroded material. 

Chemical Stratification 

A condition found in temperate lakes of the second order 
during the summer and winter stagnation periods in which 
certain horizontal strata become different chemically from 
adjacent ones, often with abrupt transitions. 


The kind of nutrition found in various bacteria in which 
energy is secured from the oxidation of inorganic materials. 


Movement of an organism induced by a chemical 


Refers to an organism that obtains energy from a chemi- 
cal reaction, excluding light, e.g., sulfur bacteria, cf. Hetero- 
trophic, Autotrophic, Phototrophic. 


Growth of an organism in response to a chemical 


A zonal group of soils with deep, dark brown to black, 
fertile surface soil, rich in organic matter, grading into lighter 


colored soil below, and containing a calcium carbonate layer 
at a depth ranging from 1.5 to 4 feet. Associated with tall 
grassland in a temperate to cool, subhumid climate. 

Chestnuts Soils 

A zonal groups of soils with dark brown surface horizons 
grading into lighter colored soil below, and a calcium carbon- 
ate layer varying in depth from 1 to 4 feet. Associated with 
grassland in temperate to cool and subhumid to semiarid 
climates, in moister regions than Brown soils, drier than 


A plant that can endure long-lasting snow-cover during 
winter and spring, or one that requires snow-cover in winter. 


A plant that cannot tolerate long-lasting snow-cover, or 
one that can live with little or no snow-cover during winter. 


The condition in animals caused by exposure to low tem- 
perature in which most of the physiological processes have 
been slowed down or arrested. 


An organ with genetically different tissues adjacent to 
each other, e.g., a green leaf with an area of white tissue. 


A warm, dry wind descending the eastern slopes of the 
Rocky Mountains in North America onto the adjacent 
plains, cf. Foehn. In Washington and Oregon coast country 
a warm, moist, southwest wind. 


See Subsoiling. 


A nitrogen-containing polysaccharide forming a hard 


outer layer in many Invertebrates, especially insects; found 
also in the cell walls of many fungi. 

Chlorenchyma Tissue 

In plants Parenchyma cells containing Chloroplasts. 


The chloride content of a solution, the average in sea- 
water is 19.3 per cent. 


A mixture of chlorophyll a and chlorophyll b, the green 
pigments contained in Chloroplasts in plants, except in the 
blue-green algae. Photosynthesis is carried on in chlorophyll. 


The protoplasmic body or plastid in the cells of plants 
that contains the Chlorophyll. 


The condition of plants when chlorophyll fails to develop, 
the plants are yellowish white to white arid poorly developed. 


Refers to a plant that has Chlorosis. 


A plant that grows in a fissure or crevice in rock, or 
on ledges where rocks have accumulated, cf. Chasmophyte. 


See Mitochondrion. 


An animal in the phylum Chordata, characterized by a 
notochord, a dorsal central nervous system, and gill slits, 
e.g., the Vertebrates. 


A corolla consisting of separate petals, syn. polypetalous. 


C Horizon 

In soils the unconsolidated, partly weathered rock frag- 
ments from which the upper A and B Horizons (q. v.), have 
developed; occasionally lacking, cf. D horizon. 


The study of regions or areas, cf. Synchorology. 


A term occasionally used for the water in soil that is 
available to plants for absorption. 


One of the halves of a divided Chromosome. 


Material in the nucleus and chromosomes which stains 
deeply with certain dyes. 


(1) A Plastid (q. v.) which contains pigment in a plant 
cell, e.g., Chloroplast, Chromoplast. (2) In animals a cell or 
group of cells with pigment which has the capability of 
changing color. 


Refers to the capability of an organism to produce color 
in a substance, e.g., certain bacteria. 


A plastid other than a Chloroplast, containing pigment, 
usually yellowish or red in color. 


The threadlike or rodlike bodies bearing genes in the 
cells of plants and animals, formed from chromatin during 
the process of cell division. 


See Pupa. 



A vortical disturbance in the vicinity of the Gulf of 
California, resembling Dust whirls on land and Waterspouts 
over water; reaches rather great heights and becomes violent 
enough to capsize small craft. 


A high-velocity conduit for conveying water to a lower 
level without causing erosion because of excessive velocity 
and turbulence. 


Refers to stems that are fleshy, e.g., cactus stem. 


Refers to leaves that are fleshy, e.g., agave leaves. 


A semi-fluid substance, the partly digested food passing 
from the stomach into the duodenum. 


Refers to a row of minute hairs along the margin of a 
structure or organ of organism. 


The hairlike, protoplasmic outgrowths on the surface of 
a cell. 


Refers to color that resembles ashes. 

Circle of Vegetation 

All of the species and communities that are restricted, or 
nearly so, to a natural vegetation unit, the highest unit of 
floristic classification according to Braun-Blanquet. 


One of the concentric circles or ridges on a fish scale. 



Refers to organisms occurring in North ' America and 


Refers to organisms that occur in the polar regions of 
both hemispheres. 


A deeply eroded depression with steep slopes in areas 
which have been glaciated, syn. Corrie. 


See Cladophyll. 


A modified stem that has the appearance and the func- 
tions of a leaf, e.g., asparagus, syn. Phylloclade. 


A group of animals that includes several interrelated 
families, or a group of plants arising from a common pro- 
genitor such as a group of young plants around the parent. 
cf. Colony. 


A unit of classification of organisms, composed of orders, 
e.g. Monocotyledons, Mammals. 


Club-shaped, larger at one end. 


A bone in the shoulder girdle of many vertebrates. 


(1) Small mineral particles of the soil, less than 0.002 
mm. in diameter. (2) Soil material that contains 40 per cent 
or more of clay particles, less than 45 per cent of sand, and 
less than 40 per cent of silt. 


Clay Loam 

Soil material that contains 27 to 40 per cent of clay 
particles and 20 to 45 per cent of sand, the rest of silt. 


A layer of compact and relatively impervious clay, not 
cemented, but hard when dry and plastic or stiff when wet; 
similar to a true hardpan in that it may interfere with the 
movement of water or with the development of roots. 

Clean Tillage 

Cultivation of a field to prevent the growth of all plants 
except the particular kind of crop wanted. 

Clear Cutting (Felling) 

The felling of all merchantable trees in an area in one 
operation, cf. Selective cutting. 


(1) An area of land from which trees and shrubs have 
been removed. (2) One of the steps in the preparation of a 
tissue for microscopic observation. 


Refers to Self-pollination (q. v.) in flowers that do not 
open, e.g., some violets. 


A great change in a physiologic process, e.g., a pro- 
nounced rise in the respiration rate at about the time that 
some fruits such as the apple are picked, or the menopause 
in human beings. 


See Climograph. 


The aggregate of all atmospheric or meteorological influ- 
ences, principally moisture, temperature, wind, pressure, and 
evaporation, which combine to characterize a region, cf. 


Weather. Continental climate is the characteristic climate 
of land areas separated from the moderating influence of 
the oceans by distance or mountain barriers, marked by 
relatively large daily and seasonal changes in temperature. 
Oceanic climate is the characteristic type of climate of land 
areas near oceans which have a moderating influence on the 
range of variations in temperature. 

Climatic Climax 

The Climax (q. v.) that develops on land (moderately 
rolling to level) that is neither excessively nor inadequately 
drained in a region, so that the major environmental condi- 
tions affecting organisms are climatic, e.g., the beech-maple 
forest in southern Michigan. Theoretically, the ultimate 
phase of ecological development of communities that the 
climate of a given region will permit, cf. Monoclimax, 
Edaphic climax, Polyclimax. 

Climatic Factors 

Atmospheric or meteorological conditions which collec- 
tively make up the Climate (q. v.) cf. Biotic factor, Edaphic 
factor, Factor ecological. 

Climatic Formation 

(1) The major vegetation type in a region, e.g., the 
temperate climatic grassland comprising the prairie and 
plains grassland in the United States and Canada, cf. Biome. 
(2) A complex of communities which are geographically 
linked with one another because of climatic conditions, an 
extremely complex vegetation unit. cf. Climatic climax. 

Climatic Region 

One of the main portions of the earth's surface delimited 
on the basis of Climate such as the polar, temperate, sub- 
tropical, and tropical; each with subdivisions. 


See Climograph. 



The study of Climates and their influences. 


The kind of community capable of perpetuation under 
the prevailing climatic and edaphic conditions; the terminal 
stage of a Sere under the prevailing conditions. The physi- 
ographic climax is a climax determined in large measure by 
the nature of the topography or soil, e.g., a forest climax on 
a north-facing slope while grassland is the climax on the 
south-facing slope of the same ridge. The edaphic climax 
is a climax determined largely by the nature of the soil 
conditions, e.g., a saltgrass marsh in a poorly drained alkaline 
depression in grassland. A biotic 'climax is a climax caused 
by a permanent influence or combination of influences caused 
by one or more kinds of organisms, including man. cf. 
Climatic climax, Succession. 

Climax Area 

A region occupied by the same Climax. 

Climax Community 

See Climax. 

Climax Complex 

The totality of Seres that lead to a Climatic climax 
(q. v.), occupying a large area corresponding to a Climatic 

Climax Formation 

A major Climax occupying a large area, e.g., the decidu- 
ous forest formation, cf. Climatic formation. 

Climax Units 

The units of a Climatic climax (q. v.); Association, Con- 
sociation, Society, Clan. 

Climax Vegetation 

A pattern or complex of Climax (q. v.) stages correspond- 


ing to the pattern of environmental gradients or habitats. 


A chart in which one climatic factor such as the mean 
monthly temperature is plotted against another factor such 
as the mean monthly precipitation or the mean relative 


A series of climatic data for different places in an area. 


A gradation in genetic properties of a population along 
an environmental gradient. 


An instrument for measuring the angle of a slope. 


A series of different Climaxes (q. v.) in a particular area 
resulting from changes in climate, e.g., the succession of 
climaxes during post-glacial time in north central United 


The terminal portion of the gut into which reproductive 
and kidney ducts open, as for example in most Vertebrates 
such as birds, amphibians, reptiles, and many fishes. 


A mass of soil produced by plowing or digging. 


Refers to a clone. 


The progeny produced vegetatively, by Apomixis, or by 
Parthenogenesis, from a common ancestor, cf. Ortet, Ramet. 


Closed Community 

A Community in which the Niches are so well occupied 
by organisms that invasion by other organisms is difficult or 

Closed Society 

A Society (q. v.) in which strangers are rarely admitted, 
e.g., many kinds of insect societies including bees. 


A sudden and extremely heavy downpour of rain, espe- 
cially in mountainous regions. 

Cloud Forest 

A forest occupying the parts of mountainous regions 
where cloudiness or moisture condensation occurs regularly, 
e.g., laurel forest in the Canary Islands. 

Cloud Seeding 

The placing of materials such as silver iodide in the 
clouds to produce precipitation. 


The aggregate of eggs or the young of birds. 


An Interaction (q. v.) among organisms, e.g., Competi- 
tion, Cooperation, Symbiosis. 


The correlated modification of two or more mutually 
dependent organs or organisms, e.g., the structure of a 
flower and the proboscis of an insect. 

Coastal Plain 

A plain between the sea and higher land, usually at a 
low altitude. 



A disease in poultry, rabbits, etc., caused by certain micro- 
organisms (Sporozoa). 


One of two or more of the dominants in a community. 

Coefficient of Association 

A measure of the joint occurrence of any two species not 
due to chance, obtained by dividing the number of samples 
in which both species occur by the number of samples in 
which it is expected they would occur only by chance. 

Coefficient of Community 

The ratio of the number of species common to two com- 
munities or areas to the total number of species occurring 
in each of the communities, cf. Index of similarity. 

Coefficient of Variation 

The standard deviation expressed as a fraction of the 
mean, or as a percentage. 


An animal in the Invertebrate phylum Coelenterata, e.g., 
corals, sea-anemones, jellyfish. 


The body cavity in many invertebrate and vertebrate 
groups of animals. 

Coenobiology (Cenobiology) 

See Biocoenology. 


A colony of organisms held together in a common sub- 
stance, e.g., Volvox. 


The sequence of natural communities in relation to 


environmental gradients; the distribution of natural com- 
munities in an Ecocline (q. v.). 


A group of protoplasmic units; a structure with many 
nuclei and no cross walls as occurs in a number of algae and 


A group of Species in which hybridization is possible, cf. 
Superspecies, Syngameon. 


A barrier constructed in a body of water so as to form 
an enclosure from which the water is pumped, to permit free 
access to the area within. 


An artificial Savanna of cogongrass (Imperata spp.) in the 


A high pass in a mountain range. 


An alkaloid that inhibits Mitosis, obtained from the 
autumn crocus (Colchicum autumnale), used to produce 
polyploidy artificially. 

Cold-air Drainage 

The settling of cold air in low places displacing the 
less dense warm air, as at the mouth of a mountain canyon. 

Cold Desert 

Land covered with snow and ice. 

Cold Front 

The boundary of a mass of cold air and a mass of warm 


Cold Hardiness (Resistance) 

The capacity of an organism to tolerate low temperatures. 


An insect in the order Coleoptera, the beetles. 


The sheath surrounding the Plumule in the early seed- 
ling stage of plants in the grass family. 


The sheath surrounding the Radicle in the early seedling 
stage of plants in the grass family. 


A small primitive insect in the order Collembola, the 


Elongated, living cells with walls usually thickened 
mostly in the corners, common in stems of herbaceous plants. 


A substance in the colloidal state in which the dispersed 
particles are larger than those in a true solution, ranging 
from 0.001 to 0.1 micron in diameter. 


Mixed deposits of soil material near the base of rather 
steep slopes, accumulations from slides, soil creep, frost 
action, and local wash. 


The part of the large intestine excluding the rectum, of 


Refers to organisms that form Colonies (q. v.). 



Occupation of an area by a group of organisms, cf. 


A group of individuals of one species, with a more or less 
permanent location, e.g., a prairie dog "town." 

Columnar Structure 

The arrangement of soil particles in elongated, vertical, 
blocky pieces with rounded tops. cf. Soil structure. 

Combination of Species, Characteristic 

See Characteristic combination of species. 


One of the organisms reacting in Commensalisrn (q. v.). 


The living together of two or more organisms with benefit 
usually to one and with injury to none. cf. Symbiosis, 


A measure of the extent to which ranches should share 
in grazing privileges on nearby public land or cooperatively 
controlled range, as determined by the forage resources of 
the privately controlled property of the ranches involved. 


A group of one or more populations of plants and animals 
in a common spatial arrangement; an ecological unit used 
in a broad sense to include groups of various sizes and de- 
grees of integration, cf. Association, Biocoenosis, Concrete 
community, See Stand. An Abstract community or Commu- 
nity-type is an assemblage of stands, e.g., the oak-hickory 
community-type, cf. Association. A Microcommunity is a 
community or stand occupying a small area such as an area 


of mosses between clumps of grass and a Microcommunity- 
type consists of an assemblage of microstands. cf. Closed 

Community Complex 

A mixture of concrete communities or Stands, including 
transitional stands, e.g., a sand-dune complex. 

Community Dynamics 

The aggregate of changes that take place within and be- 
tween communities, cf. Succession, Syngenetics, Fluctuation. 

Community Mosaic 

The arrangement of two or more microstands making up 
the plant and animal life of an area, such as the different 
kinds of vegetation on the mounds and in the depressions in 
a marsh or bog. 

Community Regulation 

See Homeostasis. 


(1) See Abstract community. (2) -A group or class of 
similar abstract communities. 

Companion (Species) 

According to Braun-Blanquet's Fidelity classification the 
species of plants that are not restricted to any definite kind 
of vegetation unit. 

Companion Crop 

A crop which is grown with another crop, usually applied 
to a small grain crop ("nurse crop") with which forage crops 
are sown. 


The capacity of two organisms to crossbreed successfully. 

Compensation Intensity 

The intensity of light at which the amount of oxygen 


produced by Photosynthesis of a plant equals the oxygen 
absorbed in Respiration. 

Compensation Level (Point) 

The depth in a body of water at which the Compensation 
intensity of a given plant occurs. 


The condition that exists when the requirements of one 
or more of the organisms living in a community cannot be 
obtained from the available supply of resources, cf. Exploita- 
tion, Interference. 

Competitive Exclusion Principle 

A generalization "that states that as a result of competition 
two similar species rarely if ever occupy the same ecological 
Niche. Also termed Cause's principle, Grinnell's axiom. 


An organism competing with one or more other organ- 

Complementary Genes 

Two or more genes that by their joint action produce a 

Complete Flower 

A flower that has all of the usual parts; sepals, petals, 
stamens, and one or more pistils. 


See Community complex. 

Complex Gradient 

A gradient comprising a mixture or a combination of 
environmental conditions, cf. Ecocline. 


A plant in the family Compositae, e.g., aster, sunflower. 



A pile of decomposing organic matter of plant or animal 
origin in which soil or other amendments such as lime, nitro- 
gen, and phosphorus may be mixed. 

Concealing Coloration 

Color of plumage, pelage, scales, scutes, skin, or other 
body covering which brings about some degree of conformity 
in the appearance of an animal with its biotic or inanimate 


Feed that has a high content of total digestible nutrients 
and low fiber content, e. g., grain and grain by-products. 

Conditioned Reflex 

See Reflex. 


A substance that modifies the characteristics of a ma- 
terial or medium to which it is added. 

Condition Factor 

A numerical index, usually applied only to fishes, which 
represents the relationship between length and weight of the 

Conditioning, Environmental 

The modification of the environment of one or more or- 
ganisms by their activities including Reactions and Coac- 
tions, e. g., liberation of oxygen by water plants in an 


The total electrolytic content of natural waters, deter- 
mined by measuring the electrical conductivity. 


The splitting of rocks caused by frost. 



Refers to plants or animals in the same genus, e. g., 
Quercus alba and Q. rubra. 


Any plant in the order Coniferales, e. g., pine, spruce, fir, 
juniper, etc. 


Refers to a Conifer, or to the order, Coniferales. 

Conjunctive Symbiosis 

See Symbiosis. 


Usage or the aggregate of practices and customs of man 
that permit the perpetuation and sustained yield of renew- 
able resources and the prevention of waste of non-renewable 


In the Clements usage a morphological part of a Climax 
Association, characterized by the presence of one dominant, 
e. g., the little bluestem and needlegrass consociations in 
climax tall grass or true prairie. 


In the Clements sense a morphological part of an As- 
socies (q. v.), a developmental unit, characterized by the 
presence of a single dominant, e. g., a stand of Russian thistle 
in the first weed stage in secondary Succession. 


See Symbiosis. 


See Constancy. 


The percentage of occurrence of a species in the total 


number of plots, uniform in area, located in a number of 
stands of one kind of Community-type or Abstract commun- 
ity, cf. Presence. 

Constants of a Community or Association 

The species which show the highest degrees of Con- 
stancy (q. v.); the most usual lower limit is 80 per cent, but 
varies from 50 to 90 per cent, according to various schools. 

Constructive (Species) 

Refers to plants whose Reactions or Coactions aid in the 
development or persistence of a Community. 

Consumer Organisms (Consumers) 

Organisms which ingest other organisms or food par- 
ticles, may be classified as primary, secondary, etc., depend- 
ing upon their position in the Food chain (q. v.) or the 
Trophic level (q. v.). cf. Producers. 

Consumptive Use 

The quantity of water used and transpired by vegetation 
plus the amount lost by evaporation, syn. Evapotranspiration. 

Contagious Dispersion 

The non-random (above normal) occurrence of indi- 
viduals of a species, forming aggregations, syn. over-disper- 
sion, Hyperdispersion. cf. Normal dispersion, Hypodisper- 

Continental Bridge Hypothesis 

The hypothesis that the present-day continents were 
once connected by isthmuses, or other areas of land. 

Continental Drift Hypothesis 

The hypothesis, advanced especially by Wegener, that 
the presentnday continents were displaced horizontally from 
the original mass of land to their present positions. 


Continental Platform 

The parts of the world comprising the lower areas of con- 
tinents and the continental shelves (q. v.). 

Continental Shelf 

The shallow, gently sloping portion of the seabottom 
bordering a continent, down to a depth of about 100 fathoms. 

Continental Slope 

The steeply sloping portion of the sea-bottom extending 
seaward from the Continental shelf. 

Continuous Grazing 

The practice of grazing the vegetation of an area without 
interruption throughout the season, cf. Deferred grazing, 
Rotation grazing. 

Continuum (Vegetation and Animal Life) 

The occurrence of populations of organisms along a 
gradient, forming a distribution pattern of intergrading pop- 


(1) An imaginary line on the surface of the land which 
connects points of the same altitude. (2) A line on a map 
to show the location of points of the same altitude. 

Contour Farming 

The performance of farming operations such as plow- 
ing, seeding, and cultivating along contour lines. 

Contour Furrows 

Furrows located along contour lines on range or pasture 
land to prevent or retard runoff and permit the infiltration 
of water into the soil. 

Contour Interval 

The vertical distance between two contour lines. 


Contour Strip Cropping or Farming 

The growing of crops on the strips between contour lines, 
at right angles to the slope. Strips of grass or other plants may 
be grown in alternation with the cultivated crops. A con- 
servation practice to control or eliminate runoff and erosion, 
and permit greater infiltration of water. 

Control Factor 

The chief limiting factor or condition influencing an or- 
ganism, e. g., wilting of a plant caused by insufficient soil 

Control Flume 

An open conduit or artificial channel arranged for meas- 
uring the flow of water. 

Controlled Burning 

See Prescribed burning. 


The increase in similarity of different Seres as Succession 
proceeds from early to late stages. 

Convergent Evolution 

The development of similarity in characteristics of or- 
ganisms that were originally more different. 


The kind of reaction between organisms which are bene- 
ficial and non-obligatory to those participating, cf. Disopera- 
tion, Protocooperation, Coaction. 


An animal in the order Copepoda, minute Crustaceans 
in salt and fresh water. 


A grove in which the trees are regularly cut, new growth 
arising from the base. 



Refers to organisms that feed on dung. 


See Coppice. 

Coral Reef 

A series of calcareous rocks formed chiefly by corals, 
partly by algae, at or near the surface in some warm parts of 
the sea. 


A system of mountain ranges, e. g., the Andes Mountains 
in South America. 


Refers to structures that are leathery such as leaves. 


A short, firm, enlarged, fleshy underground stem as in 
the crocus. 


A plant that has a stem and roots, cf. Thallophyte. 


Refers to a structure that is horny in texture. 


The whorl of parts, usually colored, of a flower, composed 
of petals, within the calyx. 


The process by which flowing water carrying solid ma- 
terial wears away underlying rock, e. g., a stream carrying 
gravel and sand. 


^ A broad, continuous land connection enduring a long 
time and thus permitting the extensive interchange of or- 


ganisms by migration as at the present time between Asia 
and Europe, cf. Filter bridge, Sweepstakes bridge. 


A series of Moraines, a term used in Western United 


A closed social group of animals, individuals of which de- 
fend their common territory against members of other 


A primary leaf of the embryo in seeds, only one in the 
Monocotyledons, two in Dicotyledons. In many of the latter 
such as the bean they emerge above ground and appear as 
the first leaves. 


(1) The plants or plant parts, living or dead, on the sur- 
face of the ground. Vegetative cover or herbage cover is com- 
posed of living plants, litter cover of dead parts of plants. 
cf. Basal area. (2) The area of ground covered by plants of 
one or more species. 

Cover, Vegetation 

The area of ground covered by the sum total of plants 
in an area. 


The percentage of the area of a community covered by 
a plant or an animal that is attached to the substratum, as 
seen from above, cf. Cover. 

Cover Crop 

A crop growing close to the ground for the chief pur- 
pose of protecting the soil from erosion and also for the 
improvement of its fertility, between periods of regular pro- 


duction of the main crops, or between trees and vines in 
orchards and vineyards. 


A place of concealment for an animal, e.g., a hedge row. 

Cover Type 

The present vegetation on an area, a community form- 
ing the Cover at the present time. 

Cow Month 

The quantity of feed or forage required for the main- 
tenance of a mature cow in good condition for 30 days. cf. 
sheep month. 


A group of young animals after leaving their nests. 


A stream that is intermediate between a river and a 

Creep, Soil 

The slow, downward, mass movement of soil on a slope. 

Crepuscular Periods 

The periods of dusk before sunrise and after sunset, cf. 
Auroral, Vesper al, Diurnal, Diel, Nocturnal. 


The most recent geological period of the Mesozoic era, 
which began abont 135 million years ago and lasted for about 
60 million years. 

Critical Factor 

See Limiting factor. 

Critical Slope 

See Angle of repose. 



Land that is used regularly for the growing of crops (ex- 
cept forest crops and permanent pasture). Includes orchards, 
cultivated summer fallow, rotation pasture, and land that 
is temporarily idle but customarily used for production of 

Crop Residue 

The parts of plants, or a crop, left in the field after har- 
vesting the desired part such as grain or fruit, e. g., Stubble. 

Crop Rotation 

The growing of different crops in recurring succession 
on the same piece of land. 

Crop, Standing 

The total amount of organic material of one or more 
species in a certain space at a given time; e. g., the trees in 
a stand that are useful for lumber or other products, cf. 


See Hybrid. 


Sexual reproduction by means of two separate organisms, 
cf. Self-pollination, Cross-pollination. 


The interchange of parts of Chromatids (q. v.) of Ho- 
mologous chromosomes during pairing in Meiosis. 


The transfer of pollen from the anther in the flower of 
one plant to the stigma in the flower of another plant. Syn. 
Xenogamy, cf. Self-pollination. 


Strips of oak forest at right angles to the river systems 
in Oklahoma and Texas. 


Crown Canopy 

See Crown cover. 

Crown Class 

The trees occupying a similar layer or position in the 
crown cover such as the dominant crown class consisting of 
dominant trees in the canopy layer; co-dominant crown class, 
trees with less well developed crowns but in the canopy 
layer; intermediate crown class, trees with crowns mostly 
below the canopy layer but extending into it; and overtopped 
crown class, trees with crowns entirely below the canopy 
layer, crowns poorly developed, or trees are suppressed, dying, 
or dead. 

Crown Cover 

The canopy formed by the trees in a forest. 

Crown Density 

The percentage of the total area of land that has a com- 
plete crown cover. 


A plant in the mustard family, Cruciferae, e. g., radish. 


A survey of forest land to locate and estimate the volume 
and grades of the standing timber; or an estimate secured 
in such a survey. 

Crumb Structure 

The condition of a soil that contains irregularly shaped 
and highly porous aggregates. 


An Arthropod in the class Crustacea, e. g., crab, shrimp. 

Crustal Movement 

A movement of the outer solid part of the earth such as 
an earthquake. 



A plant growing on snow or ice, e. g., "red snow," an 
alga, Chlamydomonas sp. 


Land erosion or reduction by intensive frost action. 


A plant in any of the groups; Thallophytes, Bryophytes, 
and Pteridophytes. cf. Phanerogam. 


A plant in one of the Life-form classes of Raunkiaer in 
which the buds are covered with soil or water; includes 
Geophytes, Helophytes, and Hydrophytes (q. v.). 


Refers to animals living in darkness as under stones or in 


A plant in the gourd family, Cucurbitaceae, e. g. squash, 

Cuesta (Spanish) 

A kind of ridge with a gentle slope on one side and a 
steep slope on the other. 

Culled Forest 

A cut-over forest from which only certain individuals 
or species have been removed, e. g., a forest culled for pines 
of a certain minimum diameter. 


A stem, especially the grass stem with nodes and inter- 


Empty shells and other kinds of material dumped into 


spawning areas to provide a suitable substratum for growth 
of oysters. 


A plant or a group of plants that is grown only under 
cultivation so far as is known, e. g., cabbage, cf. Indigen. 


A strain, variety, or race which originated and is main- 
tained under cultivation; not necessarily a species. 

Culture Community 

A Community brought about by man's activity, e. g., a 
seeded meadow; or a natural community greatly altered by 
man. cf. Hemerocology, Secondary succession. 


The basic measure or unit of radioactivity of a substance, 
the disintegration of a Radioactive Isotope at the rate of 3.7 
times 10 10 atoms of material per second. 

Cushion Plant 

An herbaceous perennial plant that produces a form with 
a dense mass of short stems and many leaves. 


A covering of fairly water-proof material composed of 
Cutin in higher plants, or chitin and/or protein in many 


A mixture of waxlike materials forming the Cuticle of 
higher plants. 

Cut-over Forest 

A forest from which some or all of the merchantable trees 
have been removed, cf. Culled forest, syn. Logged-over. 



The study of kinds of communication and control sys- 
tems in human beings and in machines. 

Cycle (Population) 

The regular or approximately regular oscillation in the 
abundance of a population or species. An Intrinsic cycle is 
caused by the interactions within populations of one or more 
species, an Extrinsic cycle is caused by changes in the physical 
or biotic environment. 

Cycle of Erosion 

The changes brought about by erosion from youthful to 
mature to old-age Topography. 


The change in form of some animals in accord with the 
season of the year as occurs in Cladocera. 


The streaming of Cytoplasm in plant cells. 


The combination of Cytology and Genetics in the study 
of variation in organisms. 


The study of cells of organisms, a branch of biology. 


The disintegration of a cell. 


The Protoplasm of the cell excluding the Nucleus. 


The combination of Cytology and Taxonomy in the 
study of classification of plants. 



The sudden wilting and death of seedling plants, caused 
by microorganisms. 


The sum of degrees of heat above a threshold, such as the 
sum of the degrees above a daily mean of 43 F. for the grow- 
ing season, or for some other period, cf. Temperature sum- 

Day-neutral Plant 

A plant that blooms when the length of day is either 
long or short, cf. Photoperiodism. 

D. B. H. 

See Breast height. 


An Insecticide (q. v.), dichloro-diphenyl-trichlorethane. 


Removal by leaching or by chemical treatment of ex- 
changeable sodium from the soil. cf. Alkali soil. 



An animal in the order Decapoda, class Crustacea, e. g., 
lobster, crab, shrimp. 


Communities consisting of trees or shrubs with deciduous 


Refers to the losing of parts of an organism such as leaves 
of trees or antlers of deer at certain seasons. 

Decomposer Organism 

An organism, usually a bacterium or a fungus, that 
breaks down the bodies or parts of dead plants and animals 
into simpler compounds. 


A species that decreases in Population density or Cover 
under continued grazing, cf. Increaser. 

Deferred Grazing 

The postponement in the grazing of vegetation after 
growth has started until a certain stage of development has 
been attained in order to promote vigor of the plants, cf. 
Continuous grazing, Rotation grazing. 

Deficiency Disease 

A disease or malfunctioning of an organism caused by the 
lack or insufficiency of some food substance such as a certain 
vitamin or a mineral. 


The separation of soil aggregates containing clay into 
individual particles. 

Degradation (Soil) 

The change in a soil that occurs in leaching, e. g., a 
Chernozem into a Podzol. 



Refers to a structure that breaks open at maturity, e. g., 
a pea pod. cf. Indehiscent. 


One or more populations of a Taxon, an interbreeding 


The study concerned with the analysis of populations in- 
cluding births, deaths, age, etc. 


The dating of events or historical periods by the study 
of growth rings of trees. 


The study of trees. 


The change of nitrogenous compounds by certain bac- 
teria in which free nitrogen is formed. 

Density (Population, Species) 

The number of individuals in relation to the space in 
which they occur, refers to the closeness of individuals to 
one another, cf. Population density, Abundance, Cover. 

Density-dependent Factor 

An influence that is dependent upon a certain density 
of individuals in order to be fully effective, e. g., a limited 
number of prey animals for the number of predators present 
in an area. 

Density-independent Factor 

An influence that is effective without regard to the den- 
sity of individuals in a population, e. g., very unfavorable 
weather such as a blizzard. According to Andrewartha (1954) 
and Birch this factor is non-existent. See Non-reactive factor. 



(1) The processes by which the surface of the earth is 
worn away, including rainfall, wind, erosion, waves, tides, 
frost action, heating by the sun, etc. (2) The total destruction 
of plant and animal life in an area by physical or biotic 


A relationship between organisms in which one organism 
receives benefit from the other, not reciprocal, cf. Competi- 
tion, Symbiosis, Coaction. 

Dependency Zone (Range) 

A certain area surrounding -an area of private land, 
within which the use of the private land may be supple- 
mented by use of the public' land. 

Dependent Property (Range) 

Privately owned or controlled land or water judged to 
have special claims for companionate use with certain public 
or cooperatively controlled range land. 


See Allochthonous, Autochthonous, Terrigenous. 

Depth, Effective Soil 

The depth of the soil which roots of plants can penetrate 
readily to obtain water and plant nutrients, cf. Working 


Removal of salts from a saline soil, usually by leaching. 


An area of land which has an arid, hot to cool climate, 
with vegetation that is very sparse and usually shrubby. 


Various kinds of vegetation found in areas and on sub- 
strata that are poor in available water for plant growth such 


as dry deserts, salt deserts, cold deserts, strand vegetation, 
dune communities, and rock communities. 

Desert Grassland 

The extensive grassland in southwestern United States 
and Mexico, characterized in part by several species of grama- 
grass, three-awn grass, and curly mesquite. 

Desert Pavement 

The stony or pebbly surface of land after the fine ma- 
terials have been removed by wind or water action. 


See Siccation. 

Desilting Area 

An area occupied by vegetation such as grasses or shrubs 
used solely for the deposition of silt and other debris from 
flowing water, located above a reservoir, pond, or field which 

needs protection from accumulation of sediment. 


Desilting Basin 

See Settling basin. 

Detention Dam 

A dam built for the purpose of storing streamflow or 
surface runoff, and to control the release of such stored water. 


The development of adaptive characteristics in late stages 
of the life-cycle, e. g., wings of insects, cf. Caenogenesis. 


A geological period in the Paleozoic era, which began 
about 325 million years ago and lasted about 45 million 


The temperature at which a certain body of air is capable 
of holding no additional water vapor, so that any decrease 


in temperature or any increase in water vapor will result in 
condensation of the vapor into liquid water; at this point 
the Relative humidity (q. v.) is 100 per cent and the Satura- 
tion deficit (q. v.) is zero. 

D Horizon 

The stratum in the soil below the depth of weathering, 
composed of undifferentiated and unconsolidated parent ma- 
terials, immediately below the C horizon, cf. A horizon, B 

Diameter Breast High 

See Breast height. 


A period of suspended growth or development and re- 
duced metabolism in the life-cycle of many insects, in which 
the organism is more resistant to unfavorable environmental 
conditions than in other periods. 


A portion of a plant such as a seed, spore, bud or other 
part that undergoes dispersal and can give rise to a new 
plant, cf. Disseminule. 


Dislocation of the earth's crust such as folding, resulting 
in the formation of mountains, sea basins, etc. 


A one-celled, microscopic alga in the class Bacillariaceae, 
with siliceous walls. 

Diatomaceous Earth 

A deposit of the siliceous remains of diatoms. 

Diatomaceous Ooze 

Material consisting of siliceous remains of diatoms found 
in cold seas. 


2, 4-Dichiorophenoxyacetic Acid (2, 4-D) 

A compound used to destroy undesirable plants, applied 
as a dust or spray to the foliage. 


The maturing of stamens and pistils of a flower at dif- 
ferent times. 

Diclinous (Diclinic) 

Refers to plants that have stamens and pistils in separate 
flowers, cf. Monoecious, Dioecious, Monoclinous. 


A Vascular plant in the subclass Dicotyledoneae, class 
Angiospermae (flowering plants), which have seeds contain- 
ing two seed-leaves or cotyledons, e. g., peas, beans, cf. 


Refers to the 24-hour period of day and night, cf. Di- 
urnal, Nocturnal, Crepuscular. 

Differential Species (Differentiating Species) 

A species, because of its greater Fidelity (q. v.) in one 
kind of community than in other kinds can be used in dis- 
tinguishing vegetation units. 


(1) The development of a cell, organ, or immature or- 
ganism into a mature organism. (2). The development of 
different kinds of organisms in the course of evolution. 


The conversion of complex, usually insoluble organic 
substances into simpler and usually soluble compounds by 

Dihybrid (Cross) 

An organism resulting from the breeding of parents that 


differ in two characters such as color of flowers and length of 
stems, cf. Monohybrid. 


The state of organs of a plant or animal or individuals 
in a population occurring hi two forms or colors, e. g., a 
plant with leaves of two forms, cf. Polymorphism. 


A motile organism hi the class Dinophyceae of the algae; 
great abundance of some forms ("red tides") along coasts 
causes death of many fish. 


Refers to plants with pistillate and staminate flowers in 
separate plants, e. g. willows, cf. Monoecious. Diclinic. In 
animals refers to unisexual organisms, cf. Hermaphrodite. 


Refers to the presence of chromosomes in pairs or in two 
sets, resulting from the union of two Gametes, each with a 
single set (Haploid, q. v.). 


Refers to an insect in the order Diptera which possess 
two wings (except parasitic forms), e. g., housefly, mosquito. 


An enduring Climax (q. v.) community altered by dis- 
turbance by man or domesticated livestock, e. g., a grassland 
which has replaced a deciduous forest, cf. Plagioclimax. 


The existence of a gap in the geographic distribution of 
a Taxon. cf. Distribution, Disjunct. 


Refers to the absence of a connection as in the geographic 
distribution of a Taxon or a community, cf. Discontinuity. 



See Discontinuity. 

Disjunctive Symbiosis 

See Symbiosis. 


An interaction between organisms in which one or all 
are harmed, e. g. Competition resulting in stunted growth. 


(1) The actual transfer or movement of Disseminules or 
organisms from one place to another. (2) The history of the 
movement of a group of organisms, cf. Migration, Establish- 
ment, Spread. 


The pattern of Distribution of individuals of a Popula- 
tion, especially in regard to probability. 

Dispersion (Soil) 

The breaking down of soil aggregates, resulting in single 
grain structure; usually the more easily a soil is dispersed 
the more credible it is. 

Disphotic Zone 

The depths in bodies of water where light is inadequate 
for photosynthesis in plants but adequate for animal life. cf. 
Aphotic zone, Euphotic zone. 

Displacement Theory 

See Continental drift hypothesis. 


The processes by which organisms or their parts, espe- 
cially spores, seeds, or fruits are scattered, cf. Diaspore, Dis- 
persal, Disseminule. 



A detachable part of a plant which is capable of Dis- 
persal and of giving rise to a new plant, cf. Diaspore. 


(1) The geographic range (continuous or discontinuous) 
of a Taxon at any one time. (2) The pattern of occurrence of 
individuals of a taxon in an area such as Random or Pots- 
son (Normal) distribution; non-random or above normal, 
Contagious dispersion (Over-dispersion, Hyperdispersion); 
and non-random, below normal, Hypodispersion or even- 

Distribution, Center of 

See Center of dispersal. 


Refers to daytime in contrast to Nocturnal, cf. Diel, 


The condition in which Seres of a similar origin become 
increasingly unlike as Succession proceeds toward the Cli- 
max. See Convergence. 

Diversion Dam 

A dam constructed for the purpose of diverting part or 
all of the water in a stream into a different course. 

Diversity Index 

The number of species in an area divided by the number 
of individuals of all these species. 

Division of Labor 

The specialization of parts of an organism or members 
of a species for carrying on certain processes, e. g., in birds 
the wings for flying and the legs for walking, in bees the 
workers and drones, in plants the various kinds of tissues for 
carrying on different functions. 



Deoxyribonucleic acid, the chief constituent of chromo- 
somes which apparently is the material constituting the 


The equatorial belt of calm or light variable winds, low 
atmospheric pressure, lying between two trade- wind belts. 


A rock containing a high percentage of calcium and mag- 
nesium carbonates. 


A small structure on certain plants, particularly on the 
leaves, which forms a shelter for organisms such as insects 
or fungi. 

Dominance Classes 

The five groups of species in a classification based on 
Coverage (q. v.). 

Dominance, Ecologic 

The condition in communities or in vegetational strata 
in which one or more species, by means of their number, 
coverage, or size, have considerable influence or control upon 
the conditions of existence of associated species. 

Dominance, Genetic 

The influence exerted by a dominant character or Allele 
e.g., redness of petals in certain flowers is dominant over 
white, cf. Recessive. 

Dominance, Social 

The determination of the behaviour of one or more ani- 
mals by the aggressive behaviour or otherwise of other indi- 
viduals, resulting in the establishment of a social Hierarchy. 

Dominant (Character) 

See Allele. 


Dominant (Species) 

A species that manifests Ecologic or Social dominance. 
cf. Secondary species. 


A gully with steep sides or a dry watercourse, a term used 
in South Africa. 


The condition in an organ or in an organism where 
metabolic processes are relatively inactive as a result of in- 
ternal causes, e. g., many kinds of seeds, overwintering stages 
of insects, cf. Hibernation, Estival, Diapause. 

Double Fertilization 

The process, unique in Angiosperms, in which one male 
nucleus fertilizes the egg nucleus to form the Zygote which 
develops into the Embryo, and the other male nucleus joins 
with two other nuclei in the embryo sac to form the Endo- 
sperm, e. g., in corn and other grasses. 


An area of open, treeless upland with a thin covering of 
soil, used mostly for sheep grazing; especially the chalk hills 
of southern England. 


Temperate grasslands in Australia and New Zealand. 

Drainage Basin 

The largest natural drainage area subdivision of a con- 
tinent, such as the Mississippi, Columbia, and Colorado 
basins, cf. Watershed. 

Drainage Terrace 

A Graded terrace constructed to have a relatively deep 
channel and a low ridge primarily for drainage of a hillside. 



A natural depression or swale; a small natural drainage- 

Drift (Geology) 

Material of any kind which is deposited in one area after 
having been moved from another, most commonly used in 
reference to glacial drift, the material deposited by glacial 
action. Glacial drift includes Till (q. v.) and stratified out- 
wash materials, cf. Loess, Boulder-clay, Drumlin. 

Drift Barrier 

An open structure constructed across a stream channel to 
catch driftwood, such as a wire fence. 

Drift Fence 

A fence for the purpose of preventing livestock from 
going from their regular range to another, often used in con- 
nection with natural barriers. 

Drift, Genetic 

Random changes in the characteristics or attributes of 
populations that are usually isolated, or in the frequencies 
of certain genes, which cannot be attributed to selection, mu- 
tation, or migration, cf. Natural selection. 

Drift Ice 

Portions of icebergs or ice-floes in the open sea outside 
of the areas of pack-ice. 

Drill Seeding 

Sowing seeds with a drill usually in rows that are less 
than one foot apart as in seeding grains, cf. Broadcast seed- 

Drip Point 

The long, attenuate tip of many leaves in the Rain 
forest of the Tropics. 



The complex of internal and external states and stimuli 
leading to a certain behaviour in an animal. 

Driveway, Stock 

A strip of land set aside for the movement of livestock 
from one place to another. 


A genus of flies, order Diptera, much used in research in 
genetics, e. g. fruit-fly. 


An extended period of dryness; usually any period of 
moisture deficiency that is below normal for a specific area. 

Drought Resistance 

The capability of an organism to survive drought with 
little or no injury. 


An oval-shaped hill composed of glacial Drift, usually 
compact and not stratified, commonly with its longer axis 
parallel to the movement of the ice when deposition oc- 


A fleshy fruit in which the single seed is within a stony 
inner cover (endocarp) which is surrounded by a fleshy layer 
(pericarp), e. g., plum, cherry. 


A small drupe, e. g., the raspberry fruit is a cluster of 

Dry Farming 

(1) Cultivation of land and other farming operations in 
semi-arid or arid regions without irrigation. (2) A system of 
cultivation of the land in which Fallow and Mulch are used 
to absorb and retain much of the precipitation that occurs. 



An implement with horizontally spreading V-shaped 
blades which provide shallow cultivation without turning 
over the surface soil or entirely burying crop residues. 

Ductless Glands 

See Endocrine gland. 


A general term for vegetal material in forests, including 
the fresh litter and well decomposed organic material and 
humus. See A horizon. 


A mound or ridge of sand piled up by the winds, com- 
monly found where sand is abundant as along lake shores, 
sea shores, and in desert and semi-desert areas. 

Dune Sand 

(1) An area of sand accumulated by wind action into 
dunes or hummocks, usually free from vegetation or sparsely 
vegetated and undergoing erosion and redeposition by the 
wind. (2) Refers to sand that has texture size of 0.1 to 0.4 
mm. in diameter which has been piled up by the wind. 


Vegetation consisting of herbaceous plants whose above- 
ground parts die during winter, e. g., grasslands. 


Vegetation consisting of broad, hard-leaved Sclerophyll 
trees or shrubs, e. g. chaparral, (q. v.). 

Dust Mulch 

A shallow layer of loose surface soil. 

Dust Whirl (Dust Devil) 

A small, intense, vortical disturbance, usually only a few 
yards in diameter, in which large volumes of dust and debris 


are carried upward; occur usually in arid and semi-arid 

Dynamic Equilibrium 

A system that is maintained in approximately the same 
condition because of the action of opposing processes or ac- 
tivities proceeding at about equal rates, cf . Balance of nature. 

Dynamics, Community 

See Community dynamics. 

Dynamics, Population 

See Population dynamics. 


Refers to any influence that is detrimental to the genetic 
properties of a population, cf. Eugenics. 


A type of lake or pond which contains brown water with 
much humic material in solution and with a small bottom 
fauna characterized by pronounced oxygen consumption. 
Cf. Eutrophic. 



A habitat form; an organism showing Somatic adapta- 
tions to a specific environment, not hereditable, cf. Pheno- 
type, Ecotype. 


See Establishment, Spread, Invasion. 


A term occasionally used to denote the water in the soil 
below the permanent Wilting percentage (q. v.); not avail- 
able for absorption by plants. 


A marine animal in the phylum Echinodermata such as 
starfish, sea-cucumbers, and sea-urchins. 


The ability of certain animals, especially bats, to orient 
themselves by emitting high-frequency sounds and detect- 
ing their echoes; acoustic orientation. 


To undergo Ecesis (q. v.). 



(1) A gradation or Cline (q. v.) in the adaptations of a 
species that is associated with an environmental gradient, cf. 
Geocline. (2) A gradation of ecosystems along an environ- 
mental gradient, comprising both the gradient of natural 
communities (Coenocline) and the Complex gradient of en- 
vironmental conditions. 

Ecological Amplitude 

The range of one or more environmental conditions in 
which an organism or a process can function, cf. Tolerance, 
Optimum, Pessimum. 

Ecological Bonitation 

The estimate of the numerical abundance of an organism 
in a locality or a season, cf. Bonitation, Biotic potential. 

Ecological Efficiency 

The ratio between the energy available to one or more 
organisms or processes and the energy that is actually util- 

Ecological Equilibrium 

See Balance of nature, Dynamic equilibrium. 

Ecological Equivalence 

The situation or condition in which two or more species 
because of their similarity in Ecological amplitude can oc- 
cupy the same ecological Niche, thus being able to replace 
each other. 

Ecological Equivalent 

An organism which participates in Ecological equivalence 
(q. v.). cf. Vicariation. 

Ecological Factor 

Any part or condition of the environment that influences 
the life of one or more organisms; often classified into A; 


climatic, physiographic and edaphic, and biotic factors, or B; 
direct, indirect, and remote factors, cf. Limiting factor. 

Ecological Indicator 

See Indicator. 

Ecological Longevity 

The average length of life of individuals of a population 
under stated conditions, cf. Life-span. 

Ecological Niche 

See Niche. 

Ecological Pyramid 

See Pyramid of numbers. 

Ecological Race 

See Eco type. 

Ecological Sociology 

See Synecology. 

Ecological Structure 

See Structure. 

Ecological Succession 

See Succession. 

Ecological Valence 

See Ecological amplitude. 


The study of the interrelationships of organisms to one 
another and to the environment, cf. Autecology, Synecology, 
Bioecology, Sociology, Plant sociology. 


See Ecad. 


A Taxon of plants consisting of one or more Ecotypes 


(q. v.) within a Coenospecies (q. v.), capable of reproduction, 
approximately equivalent to Species (q. v.). 


The Community (q. v.), including all the component 
organisms together with the abiotic environment, forming an 
interacting system, e. g., a marsh, cf. Biogeocenose. 


A transition line or strip of vegetation between two com- 
munities which has characteristics of both kinds of neighbor- 
ing vegetation as well as characteristics of its own. cf. Edge- 


The smallest Taxon (q. v.) or group of similar Bio types 
(q. v.) within an Ecospecies (q. v.), each one adapted to a 
certain combination of environmental conditions. Differ- 
ences between ecotypes may be morphological, or only physi- 
ological, cf. Habitat form, Ecad. 


A Parasite living on the outside surface of another or- 
ganism, e. g., a flea. cf. Endoparasite. 


Refers to an organism that feeds from the outside of the 
structure it is consuming such as a deer feeding on leaves of 
a plant, cf. Entophagous. 


Refers to fungi that grow on the surface of roots, cf. 
Endotrophic, Mycorrhiza. 


Refers to the soil, cf. Edaphic factor. 

Edaphic Climax 

See Climax. 


Edaphic Factor 

A condition or characteristic of the soil, physical, chem- 
ical, or biological that influences organisms, cf. Biotic, Cli- 
matic, Ecological factor. 


The study of soils. 


The aggregate of organisms in the soil except the roots 
or underground stems of plants, cf. Plankton. 

Edge Effect 

The influence of two communities upon their adjoining 
margins or fringes, affecting the composition and density of 
the populations in these bordering areas, e. g., a forest edge 
bordering a grassland, cf. Ecotone. 

Effective Temperature Range 

The range between the highest and the lowest tempera- 
ture in which an organism can live. cf. Ecological amplitude, 


The outflow of water from subterranean storage, cf. In- 


A Plastid in which oil is formed and stored. 


Salts, acids, or bases that in a solution conduct an electric 
current, e. g., sodium chloride dissolved in water. 


(1) Organisms that are typical or characteristic of a cer- 
tain region, but may occur outside of it, e. g., a group of 
prairie species occurring in the eastern part of the United 
States. (2) See Ecological factor. 


Elementary Species 

See Ecotype. 

Elfin Forest 

See Krummholz. 

Eltonian Pyramid 

See Pyramid of numbers. 

Eluvial Layer 

See A horizon. 


The removal of material from a soil horizon by down- 
ward or lateral movement in solution and to a lesser degree 
in colloidal suspension, cf. Illuviation. 


In plants the removal of anthers or flowers bearing sta- 
mens to prevent self-pollination. In animals the removal of 
sperm-producing organs. 

Embryo Sac 

The structure within the ovule of a flowering plant, in 
which Fertilization occurs. 


The Migration of an organism out of a locality, usually 
without the probability of returning, cf. Immigration. 


A grove or forest of evergreen oaks. 


An area fenced to include certain kinds of animals, cf. 


The state of inactivity of an organism in which it is sur- 
rounded in a protective case; metabolism is reduced, resist- 
ance to unfavorable environmental conditions increased. 



A Taxon confined to a certain country or region and with 
a comparatively restricted distribution. 


The occurrence of endemics in an area. 


The existence of a Parasite within the body of another 

Endocrine Gland 

A gland in animals that produces hormones, e. g., the 
Pituitary gland. 


Refers to a substance or process that originated within 
an organism or a cell. 


A Parasite living inside of another organism, e. g., a tape- 


A plant which grows within another plant such as a 
fungus Endoparasite; a plant which can penetrate a rock, 
e. g., lichen. 


The supporting framework inside the body of animals 
such as Vertebrates, cf. Exoskeleton. 


The nutritive tissue that surrounds the growing embryo, 
and which is present in the mature seed in many kinds of 
Spermatophytes such as the grasses. 


Refers to fungi that grow within roots, cf. Ectotrophic, 



A Propagule such as a seed or a spore which is dispersed 
by being transported inside of an animal's body. 

Energy Flow 

The intake, conversion, and passage of energy through 
organisms or through an Ecosystem (q. v.). 

Energy Transformers 

Plants and animals which convert and pass on energy, 
originally secured from sunlight by plants, from one or- 
ganism to another as in a food-chain, cf. Energy flow. 


Refers to plants that are pollinated by insects, e. g., 
orchids, cf. Anemophilous. 


Animals that feed inside of dead leaves and roots, cf. 


The degradation of energy, a measure of the degree of 
disorder of a system. 


The sum total of all the external conditions which may 
influence organisms, cf. Habitat, Site. 

Environment, Fitness of 

The suitability of an environment or habitat for main- 
taining life. 

Environmental Clock 

The influence of environmental factors to initiate proc- 
esses or activities of organisms, e. g., the initiation of flower- 
ing in the cocklebur by the Photoperiodic influence of short 
days and long nights. 


Environmental Conditioning 

See Conditioning, environmental. 

Environmental Form 

See Ecad. 

Environment, Holocoenotic 

The concept that the environmental factors act as a 
whole or aggregate in their effect upon one or more or- 

Environmental Resistance 

The restriction caused by environmental factors upon 
the increase in numbers of individuals in a population, cf. 
Biotic potential, Reproductive potential. 


An organic catalyst, produced by living cells, each kind 
determining a specific chemical reaction, e. g., diastase which 
digests starch. 


The second geological epoch in the Cenozoic Era, Ter- 
tiary period, began about 58 million years ago and lasted for 
about 19 million years. 


See Aeolian. 


Great alterations in the level of the crust of the earth 
such as the elevation or lowering of the surface of con- 


An organism which has been subjected to Epharmony 
(q. v.). See ecad. 



The acquirement by an organism of processes or morpho- 
logical structures by which it is enabled to exist in an 
altered environment, cf. Adaptation. 


The process of gradual adaptation of a species to a 
change of environment. 


Refers to short-lived existence. 


An endemic surviving from a former flora, a Relic. 

Epicole (Epibiont) 

An organism living attached to another organism with- 
out benefit or harm to the latter, e. g., barnacles attached to 
corals, algae on the bark of trees, cf. Commensalism, Epi- 


The widespread occurrence in greater numbers than 
usual of a species that is usually parasitic or predatory. 


The outermost layer of cells of animals and plants; cork 
cells replace the epidermis in stems and roots of older woody 


Refers to an organism that lives close to the ground, e. g., 
some insects, cotyledons on seedlings such as the navy bean, 
cf. Hypogeal. 


A community of Epiphytes (q. v.). 



The upper layer of lakes, subject to disturbance by winds, 
lying above the Thermocline, (q. v.). cf. Hypolimnion. 


The downward curvature of a plant organ such as a leaf, 
caused by the greater growth on the upper surface than on 
the lower. 


A natural group or entity consisting of individual or- 
ganisms, e. g., a society of termites, a stand or community- 
type, syn. supraorganism. 


An Epiphyte (q. v.) growing on a leaf, e. g., certain 


A plant growing upon or attached to another plant, or 
often, on some non-living support, deriving no sustenance 
from the supporting structure, e. g., Spanish moss on a live 


An assemblage of organisms scattered on submerged sur- 
faces which later may become mechanically associated, cf. 
Periphyton, Lasion. 


An Epidemic disease in plants, e. g., wheat rust. 


The upper layer, above the Thermocline, where Thermal 
stratification occurs in the ocean. 


A non-parasitic animal living attached to another, cf. 



A Propagule such as a spore or a seed that is carried on 
the body of an animal. 


An Epidemic disease in animals, cf. Epiphytotic. 

Equilibrium, Community 

The condition in which a community is maintained with 
only minor fluctuations in its composition within a certain 
period of tune. 

Equilibrium, Ecologic 

See Balance of nature, Dynamic equilibrium. 

Equivalence, Ecologic 

See Ecological equivalence. 

Eremean (Eremic) 

Refers to desert vegetation, 


Refers to organisms living in deserts. 


A plant growing in a desert. 


The part of the Sahara desert covered with sand dunes. 


A disease of cereals, especially rye, and other grasses, 
caused by the fungus Claviceps pur pur ea; in which dark- 
colored structures replace the grain. 


Refers to the heath family of plants, Ericaceae. 


A member of the heath family, Ericaceae, e. g., blue- 



A type of vegetation in which ericaceous plants are dom- 
inant or very abundant. 


A substance, especially soil, that is susceptible to erosion, 
cf. Erosive. 


The detachment and movement of particles of the land 
surface by wind, water, ice, or earth movements such as land- 
slides and creep, cf. Accelerated erosion, Normal erosion. 
Sheet erosion. 

Erosion Class 

One of several categories in a classification indicating the 
degree of erosion. 

Erosion Pavement 

A layer of stones or gravel on the surface of the ground 
after fine particles have been removed by erosion. 


Refers to the tendency of an agent such as water or wind 
to cause erosion. Erosive is preferred when referring to the 
agent, Erodible when referring to the substance that is 


A plant found wild but which originated from a culti- 
vated ancestor. 

Escape Covert 

Vegetation which is intended or used for protection by 
animals from attack by enemies. 

Escape Mechanism 

A structure, behaviour, or process that enables an or- 
ganism to survive unfavorable conditions, e. g., shedding of 
leaves, burrowing, development of cysts. 



A long, inland cliff or steep slope, usually high, formed 
by erosion or possibly by faulting, syn. scarp. 


A long, narrow ridge of gravel and sand deposited by a 
stream flowing under or within a glacier, cf. Kame. 

Esophagous (Oesophagous) 

The portion of the alimentary tract between the pharynx 
and the stomach. 


A thorny woodland. 

Essential Element 

A chemical element required by green plants for normal 
growth, such as the primary essential elements: hydrogen, 
oxygen, nitrogen, phosphorus, and potassium; secondary 
essential elements: sulfur, calcium, and magnesium; and the 
trace or minor elements: iron, boron, manganese, copper, 
zinc, and molybdenum. The last six, and traces of other 
elements, are required in only minute quantities. 


The successful growth of an organism in a new location, 
syn. Ecesis. cf. Invasion, Spread, Dispersal. 


Refers to the summer season, cf. Aspection. 


The condition in which an organism may pass the sum- 
mer and in which its normal activities are greatly curtailed 
or temporarily suspended, cf. Dormancy, Hibernation. 


An arm of the sea at the mouth of a river, in which the 
current of the river meets the tide. 


Ethiopian Region 

The faunal region in the realm Megagea (Arctogea); it 
includes all of Africa except the northern corner and part of 
southern Arabia. 


The study of the use of plants by any race or group of 
people, cf. Paleobotany, Paleontology. 


The study of the distribution and characteristics of the 
divisions of mankind. 


The comparative study of the Behaviour of animals. 


The development of a plant grown without light, result- 
ing in the loss of chlorophyll, a weak elongated stem, and 
abnormal leaves. 


The study of the causes of diseases. 


See Index species. 


The study of the improvement of the genetic constitu- 
tion of a population or species, especially the human race. 


The shoreward part of the Benthic zone in lakes and 
oceans; the landward part of the littoral zone, including all 
of the inter tidal region, cf. Littoral. 

Euphotic Zone 

The uppermost portion of a body of water which re- 
ceives sufficient light for Photosynthesis, cf. Aphotic, Dis- 
photic, Photic zones. 



Animal components of the Plankton (q. v.). 


Refers to the presence of a regular number of chromo- 
somes, a multiple of the Haploid number, cf. Aneuploid. 


The capacity of an organism to live under a wide range 
of environmental conditions, syn. Eurytopic. cf. Ecological 
amplitude, steno-. 


See Euroky. 


The study dealing with the improvement of living con- 
ditions in order to secure better human beings, cf. Eugenics. 


Refers to bodies of water, accumulations of peat, etc., 
which are rich in mineral nutrients and organic materials, 
therefore productive. Oxygen may be deficient seasonally in 
lakes or ponds, cf. Oligotrophic, Dystrophic. 

Evaporative Power of the Air 

The environmental factor complex including factors such 
as temperature, relative humidity, and wind that influence 
the evaporation of water from organisms and from other 
bodies containing water. 


An instrument to measure the Evaporative power of the 
air such as an open pan of water or an Atmometer (q. v.). 


The sum total of water lost from the land by evaporation 
and plant Transpiration. 



A soil-filled container covered with living vegetation and 
supplied with water to measure transpiration and evapora- 


Refers to a stand of trees in which only small differences 
in age occur between the individuals; in young stands dif- 
ferences should not exceed 10 to 20 years, in mature stands 
not more than 30 to 40 years, cf. Age-class. 


The process of Natural or Artificial selection acting upon 
genetic diversity in organisms. 

Evolution, Convergent 

The development during the course of evolution of simi- 
lar structures or habits in organisms that are not closely re- 
lated taxonomically. cf. Taxonomy. 

Exchange Capacity 

See Cation-exchange capacity. 


An area fenced to exclude certain kinds of organisms, cf. 

Exclusive Species 

A species belonging to the highest Fidelity class (Braun- 
Blanquetj, one which occurs exclusively or almost so in "a 
specific kind of vegetation unit. 


The degree in which a particular species is restricted to 
a particular kind of community to the exclusion of other 
communities, cf. Exclusive species, Fidelity. 


The elimination of substances from the bodies of or- 



A plant with one main stem, the lower branches longer 
than the upper, e. g., a spruce tree. 

Exempt Stock 

Livestock such as work or saddle horses and milk cows 
which are permitted to graze on National Forests or the 
Public Domain free of charge. 


The peeling off of material in thin layers from the sur- 
face of rocks or the flaking off of scales or other parts of 


A hard, supportive structure in the outer part of the body 
of many kinds of animals, e. g., shell of a crab. 


Refers to the release of heat. 


Refers to any organism that is not native in the area 
where it occurs; introduced, cf. Endemic, Indigenous. 

Experimental Design 

The plan of an experiment, especially to insure that the 
data to be secured will be suitable for statistical analysis. 


The ability of an organism to find, occupy, and retain 
unused vital resources, cf. Competition, Interference. 


Dried, preserved specimens of plants. 


The process of promoting the development of desert con- 
ditions through human activity or climatic change, cf. Sicca- 



Refers to something outside of a cell, but may be within 
a multicellular organism, cf. Intracellular. 


Refers to an organism or a population that is not part 
of a Cline (q. v.). 


Refers to the presence of an organism near the border 
of its range or nearer the margins than the Center of dis- 

Extrinsic Cycle 

See Cycle. 


The nest or brood of a bird of prey such as an eagle or 



A part of a Climax Association (sensu Clements) which 
lacks some of the dominants of the association because of 
slight differences in environmental conditions, cf. Lociation. 


(1) See Faciation. (2) The general appearance or aspect 
of a plant, population, or community, cf. Aspection. (3) A 
modification of the Bio tope, differing recurrently from the 
typical conditions in minor ways. (4) A variation in a com- 
munity such as a dogwood or mountain laurel shrub facies 
in an oak forest. 

Facilitation, Social 

The effect of the presence of one organism upon the 
behaviour of another. 

Factor, Ecological 

Any part of the environment that influences the life of 
an organism, cf. Biotic, Limiting, Density-dependent factors. 


Refers to the capability of an organism to live under 


various conditions such as parasitism and saprophytism. cf. 
Obligate parasite. 

Fairy Ring 

A circle of mushrooms arising from underground mycelial 
growth, usually accompanied by a luxuriant ring of vegeta- 
tion, fairly common in grasslands. 

Fall Line 

A line connecting the points where rivers leave the 
uplands for the lowlands, marked by an increased slope and 
waterfalls, e.g., the Atlantic coastal plain adjoining the Ap- 
palachian Mountains. 


The dropping to the earth from the air of solid material, 
particularly the radioactive dust from atomic explosions. 

Fall Overturn 

See Spring overturn. 


Refers to cropland left idle except for tillage in order to 
destroy weeds and accumulate water and nutrients for use 
of a crop to be planted later, cf. Summer fallow. 

False Annual Ring 

More than one of the Growth rings that may be produced 
in woody plants in a single season. 


In the classification of organisms a group of one or more 
related genera, e.g., the rose family in which the roses, straw- 
berries, etc., are classified. In ecology it has been used for a 
community comprising individuals of a single species. 


The condition in plants in which stems and branches 
have grown together to form a malformed and flattened 



A dense cluster or bundle such as three to five leaves 
in groups on pine trees. 


A collective term to include all the kinds of animals in 
an area or in a geological period. 

Fauna! Region 

An area containing characteristic kinds of animals, e.g., 
the Oriental Region, (q. v.). 


Capability of an organism to produce reproductive units 
such as eggs, sperms, or asexual structures, cf. Fertility. 


Harvested forage including hay or fodder, or grain, grain 
products, and other foodstuffs that are processed for feeding 


The return of a substance to a former condition or loca- 
tion, such as the absorption of calcium by plants and the 
return to the soil when the leaves fall to the ground and 

Fell, Fell-field 

A tract of bare, elevated country which is in more or 
less uncultivated condition. 


In selective felling only certain trees are cut down in a 
forest, in clear felling all are taken. 


A tract of low, marshy ground containing peat, relatively 
rich in mineral salts, alkaline in reaction, situated in the 
upper parts of old estuaries and around fresh-water lakes, 
vegetationally distinct from Moors (q. v.). 



Refers to an organism that has escaped from cultivation 
or domestication and become wild again. 


The chemical alteration of organic substances by organ- 
isms, especially yeast and bacteria, e.g., alcoholic fermentation 
in which sugar is changed to alcohol and carbon dioxide by 
the enzyme zymase, produced by yeast. 


Refers to the capability of an organism or organ such as 
a stamen, pistil, or ovary to carry on reproductive functions. 


(1) The capability of an organism to produce living off- 
spring, cf. Fecundity. (2) The quality of a soil which enables 
it to provide substances in adequate amounts properly bal- 
anced and available for the growth of specified plants when 
other environmental factors are favorable. 


The union of egg and sperm, or of two Gametes (q. v.). 


Any material added to soil to supply one or more plant 
nutrients, usually not including lime or gypsum. 

Fibrous Root System 

The aggregate of the numerous, similar roots arising from 
the base of the stem such as occurs in corn and the grasses. 
cf. Tap root system. 


The degree of regularity or "faithfulness" that a species 
occurs in certain plant communities, expressed in a 5-part 
scale: (5) Exclusive, (4) Selective, (3) Preferential, (2) Com- 
panion, indifferent, (1) Accidental, strangers (q. v.). 


Field Border Plantings 

Vegetation established on the borders of fields to conserve 
soil and to provide cover and food for wildlife, e.g., a strip 
of multiflora rose. 

Field Capacity 

The moisture content of a soil, expressed as the per- 
centage of oven-dry weight (100-110 C.) after the Gravita- 
tional water has drained away; the field moisture content 
two or three days after a soaking rain. cf. Capillary water, 
Water-holding capacity. 

Field Crops 

Crops such as grain, hay, root, and fiber in contrast to 
vegetable (truck) and fruit crops. 

Field Layer 

The stratum of vegetation formed by grasses, forbs, and 
dwarf shrubs. 

Field Strip Cropping 

The kind of Strip cropping in which crops are grown 
in parallel strips across a slope but which do not follow 
contour lines, and strips of grass or other close-growing plants 
are grown alternately with the strips of cultivated crops. 

Field Test 

An experiment conducted under ordinary field condi- 
tions, usually less subject to control than a precise experi- 


The stalk of an Anther or of a down-feather. 

Filter Bridge 

A land connection, temporary in duration and restricted 
in extent, limiting the kinds of organisms which can migrate 
over it, e.g., the Bering Strait in the Pleistocene, cf . Corridor, 
Sweepstakes bridge. 

Filter Strip 

A strip of permanent vegetation sufficiently wide and 
dense above a farm pond, diversion terrace, etc., so it will 
retard run-off and cause deposition, thus preventing silting 
in the water or structure below. 

Fine-textured Soil 

A soil that consists mainly of silt and clay. 

Fiord (Fjord) 

A narrow, often long and deep inlet of the sea as in the 
coasts of Norway and Alaska, very likely formed by glaciers. 


A strip of land from which inflammable materials have 
been removed in order to check or stop a creeping or 
running fire. 

Fire Control Line 

The line along which efforts are made to stop the advance 
of a fire or from which to start to backfire. 

Fire Hazard 

The risk of probabilities that a fire may start because 
of the inflammability of materials under the prevailing 
climatic conditions. 


See N4v4. 

First Bottom 

The Flood plain that is most immediate to a stream, or 
at the lowest elevation above a stream, consequently some 
are frequently flooded. 


A long, narrow arm of the sea or lower portion of an 
estuary, especially in Scotland. 



A sloping structure over which water flows, to enable 
fish to ascend a stream around a dam or other obstruction; 
a fish ladder. 


(1) Reproduction of a unicellular organism by simple 
division into two parts. (2) Refers to atomic bombs in which 
elements such as uranium and plutonium are split into 
products as, for example, Sr 90 , I 131 , and Cs 157 , which are 
formed during the explosion. 


The degree of Adaptedness (q. v.) to the environment 
that an organism possesses. 

Fitness of the Environment 

The suitability of environmental conditions such as the 
nature of the water, gaseous composition of the atmosphere, 
and temperatures for the maintenance of life or for the 
activities of a certain organism. 

Fixation (in Soil) 

The conversion of a soluble substance such as phos- 
phorus from a soluble or exchangeable form to a relatively 
insoluble form. 

Fjaeld (Fjeld) 

A more or less barren upland area (Scandinavia). See Fell. 


A moor with a flat or even slightly concave surface and 
soil poor in salts and acid in reaction. 


A member of the phylum Platyhelminthes, e.g., flukes, 


F Layer (Soil) 

Sometimes used to designate the partially decomposed 
litter which can still be recognized as to origin and age. 
cf. A horizon, H layer, L layer. 


The aggregation of suspended colloidal material or very 
fine particles into larger masses or floccules. 

Flood Plain 

The nearly level land forming the bottom of a valley 
in which a stream is present and usually subject to flooding, 
cf. First flood plain. 


A channel usually bordered by levees for the purpose 
of carrying flood water. 


The sum total of the kinds of plants in an area at one 
time. cf. Vegetation, Fauna. 

Floral Region 

See Floristic region. 


The small flower of grasses or Composites. 


A hormone evidently made in the leaves which after 
translocation to apical Meristem initiates the formation of 

Floristic Area 

An area in which a certain degree of homogeneity exists 
because of similarities in the areas occupied by various 


Florlsttc Composition 

The kinds of plant species, in the aggregate, that occur 
in a community or in an area. 

Floristic Element 

Species that are characteristic of a certain territory but 
occur also in a different one, e.g., an arctic species growing 
in the high Rocky Mountains is an arctic element in the 
flora of the Rockies. 

Floristic Region 

A portion of the earth's surface supporting a characteristic 
flora which developed largely within this portion, e.g., the 
Atlantic North American Region of the Boreal Kingdom. 

Floristic Territory 

A geographic area characterized by the common occur- 
rence of a number of species which are more or less confined 
to it, but other species may also be present. 


The organ of the class Angiospermae, flowering plants, 
consisting of one or more pistils (carpels) or stamens, or both, 
and usually a calyx (composed of sepals) and a corolla (com- 
posed of petals). 

Flower Induction 

The stimulation, presumably by Florigen (q. v.) which 
initiates the production of flowers. 


A relatively irregular departure from more normal or 
average conditions, cf. Community dynamics. 


A parasitic flatworm in the class Trematoda, phylum 
Platyhelminthes, e.g., the liverfluke in sheep. 


An open conduit of wood or other material for carrying 


water or other liquids across a creek, ravine, or other depres- 
sion which lies across the course of a canal or ditch location. 


A migration route of birds, e.g., the Mississippi River 



The dried, cured plants of crops such as corn and sor- 
ghum, including all parts above ground including the grain, 
cf. Stover, Hay. 


A dry wind which is warm for the season. It blows down 
leeward slopes of mountains, especially in the Alps. cf. 


The condensation of water vapor on particles of dust or 

smoke particles. 


Refers to structures that are leafy or leaf-like, thin. 

Foliage Cover 

See Cover. 

Foliar Diagnosis 

Evaluation of the status of plant nutrients in a plant, 
or the plant-nutrient requirements of a soil, by the analysis 
of leaves. 


A dry, many-seeded fruit developed from a simple ovary 
which when ripe splits along a single line, e.g., the larkspur 


A figure of speech for the dependence for food of organ- 


isms upon others in a series, beginning with plants or 
scavenging organisms and ending with the largest carnivores. 


All the interconnecting Food-chains in a community, 
syn. food-web. 


The particular location of an organism in a Food-cycle. 


A graphic representation of the food chain which indi- 
cates the large numbers of producer organisms at the base 
and the progressively decreasing numbers of herbivores and 
carnivores above. 


See Food-cycle. 


Unharvested plant material available as food for domestic 
animals, may be cut for hay or grazed; after cutting it is 
called Feed. cf. Fodder. 


A theoretical concept, the quantity of forage on an acre 
of land which is completely covered with herbage and com- 
pletely utilized under proper management. 

Forage-acre Requirement 

The number of forage acres needed for the maintenance 
of a mature grazing animal for a certain period of time. 

Forage Fish 

Small kinds of fish which reproduce prolifically and are 
used as prey by predatory fishes. 

Forage Ratio 

This is the ratio of the percentage of a certain prey 


organism present in the food of a predator divided by the 
percentage of this prey that is present in the habitat. 

Forage Volume 

(1) The parts of a plant within reach of animals for 
grazing. (2) A measure of the yield of Forage, the total 
amount of forage produced on a range area during a year. 


An herbaceous plant that is not a grass nor grasslike such 
as a sedge, e.g., sunflower, geranium. 


A low dune, often occupied by a sand-binding grass, 
bordering the sandy shore of a sea or lake. 


The portion of the shore occupied daily by tides. 


A stand of trees growing close together with associated 
plants of various kinds. 

Forest Cover 

The living plants and dead organic material occupying 
the surface of a forest, often restricted to the woody plants 
covering the ground, cf. Basal cover. 

Forest Edge 

The border, or Ecotone, of a forest with another kind 
of vegetation such as grassland. 

Forest Floor 

The deposits of plant material such as leaves and branches 
on the ground in a forest. 

Forest Influences 

All the effects or Reactions of a forest upon the habitat 
or the environmental conditions, e.g., aiding in maintenance 
of uniform stream flow, shading the ground. 


Forest Type 

A forest stand that is essentially similar throughout its 
extent in composition under generally similar environmental 
conditions. It includes temporary, permanent, climax, and 
cover types. 


A botanical taxonomic category based upon more trivial 
characteristics and with a less distinct geographical range 
than those of the Subspecies or Variety. 


One of the largest subdivisions of the vegetation of the 
earth, usually of great geographical extent, composed of com- 
munities that are similar in physiognomy and broad environ- 
mental relations, e.g., the deciduous forest of eastern North 
America, cf. Climax, Biome. 


A series of related forms distinguished geographically 
and which originated entirely or primarily by geographic 


Refers to animals that burrow in the soil, e.g., the mole, 
cf. Ambulatorial. 

Fragment (of a Community) 

A stand so small that it lacks the species composition 
and other characteristics of the Community. 

Fragmented Structure (Soil) 

A soil composed largely of particles that have well defined 
faces and edges, cf. Granular structure. 


A sexually imperfect female calf, sterile usually, born as 
a twin of a male animal. 



See Frequency. 


The degree of uniformity with which individuals of a 
species are distributed in an area, and more specifically in 
a Stand, cf. Constancy. 

Frequency Class 

One of the small groups into which the Frequency indices 
of the various species in a stand may be classified. 

Frequency Index 

The quantitative expression in percentage of Frequency, 
e.g., a species occurring in 15 of 20 sample areas in a stand 
has a frequency index of 75 per cent. 

Frequency, Law of 

The generalization which states that when Frequency 
indices of species in a stand are classified into five main 
classes a double peak occurs in homogeneous vegetation, i.e. 

Frigid Zone 

The portions of the earth north of the Arctic Circle and 
south of the Antarctic Circle. Cf. Temperate zone. Tropics. 


Tundra or cold arctic and alpine, open communities. 

Fringing Forest 

A strip or zone of forest along a stream bed. cf. Gallery 


The border of cold and warm air masses at the earth's 


(1) The act or state of freezing, or injury to organisms 


because of low temperatures, especially near the beginning 
or the end of the growing season. (2) Particles of frozen water 
or dew (hoarfrost) appearing on the earth's surface at 32 F. 
or lower. 

Frostless Season 

The period between the last frost in the spring and the 
first one in the autumn. 

Frost Resistance 

The capability of plants to survive the formation of ice 
crystals in their tissues. 


The ripe ovary or group of ovaries with any other parts 
that may be regularly associated with it, e.g., a grain of corn, 
a gooseberry fruit, an apple pome. 


Resembling a shrub somewhat. See Fruticose. 


Vegetation types consisting of scrub forests. 


Shrubby, cf. Suffruticose. 

Fruticose Lichen 

A Lichen with a Thallus ten cm. or more tall, e.g., 
Cladonia rangiferina, the reindeer "moss." 


Resembling a seaweed, especially Fucus. 


Refers to a structure that falls or separates early from a 
plant, e.g., sepals or petals of some flowers. 

Fully Stocked 

Refers to a stand which contains as many trees or as much 


material of the species and of the age as the Site can support. 
Cf. Overstocked, Understocked. 


A hole in the earth from which gases such as CO 2 and 
steam escape under pressure, as seen in the Valley of Ten 
Thousand Smokes, Alaska. 


A substance that is toxic to fungi, e.g. Paris green. 


Refers to organisms which consume fungi, e.g., some 
Collembolons and mites. 


Resembling a fungus. 


One of the true fungi, belonging to the phylum Eumyco- 
phyta; plants lacking Chlorophyll such as the molds, yeasts, 
mildews, rusts, and mushrooms. They may be either Parasitic 
or Saprophytic. 


The stalk of the Ovary in plants. 

Furrow Dam 

A small earth dam for the purpose of holding water 
within a furrow, cf. Lister. 


Sclerophyllous vegetation on plateaus and mountains in 
South Africa, ecologically equivalent or similar to Macchia of 
the Mediterranean region and the Chaparral of California. 


Gallery Forest (Galleria) 

Woods or a narrow zone of forest along a stream in grass- 
land, savanna, or other open vegetation. 

Game Management 

The practice of producing sustained annual crops of wild 
game on land. cf. Range management. 

Game Refuge 

An Enclosure for the purpose of controlling or prohibit- 
ing the hunting, fishing, or otherwise destroying game ani- 
mals, birds, fish, and other animals. 


A sex cell, a sperm or egg; in some of the simplest 
organisms the gametes are not differentiated into egg and 


An Herbicide that prevents development of or destroys 


The plant or generation in organisms that produces 
gametes, contains the Haploid number of Chromosomes. 


Gamma Radiation 

One kind of ionizing radiation, electromagnetic, readily 
penetrates biological materials. 


Refers to flowers that have more or less united Petals. 


Refers to flowers that have more or less united Sepals. 

Garique (Garrique) 

Open vegetation consisting of dwarf, evergreen Scrub on 
poor land in the Mediterranean region, cf. Maquis. 


An animal in the class Gastropoda, phylum Mollusca, 
e.g., slug, snail. 

Cause's Principle 

The generalization that states that two species do not 
occupy exactly the same Niche. See Competitive exclusion 
principle, GrinnelVs axiom. 

Geiger Counter 

An instrument for detecting Ionizing radiation. 


The Pollination of a flower by pollen from another flower 
on the same plant, cf. Autogamy, Cleistogamous^ Xenogamy. 


A structure consisting of a few cells which becomes 
separated from the parent and grows into a new plant, found 
in certain liverworts. 


A localized unit of genetic material with a specific func- 
tion in transmitting characters from one generation to the 
following one. 



The study of population genetics in relation to the 
habitat conditions; the study of species and other taxa by the 
combined methods and concepts of ecology and genetics. 

Gene Flow 

The duplication and dispersal of genes in a population. 

Gene Pool 

In a narrow sense, the genie material of a local inter- 
breeding population at the present time. In a broad sense, 
the total genie resources or materials of a species throughout 
its geographical range. 


Refers to Genus. 

Generic Coefficient 

The ratio of the number of genera to the number of 
species in an area. 

Genetic Drift 

Accidental fluctuations in the proportions of a particular 
Allele so that exact Mendelian ratios do not occur, which 
may result in the fixation or loss of certain genes in small 
populations without reference to selective value, cf. Natural 


The branch of biology dealing with Heredity in all its 

Genome (Genom) 

The set of different Chromosomes, as found in a Gamete, 
or Haploid nucleus; the Diplod nucleus contains two 
genomes, Polyploids more than two. 


The entire genetic constitution, or the sum total of genes, 
of an organism, in contrast to the Phenotype. 



A group of related species, or occasionally only one 
species, used in the classification of organisms, e.g., the white 
and Scotch pines belonging to the genus Pinus. 


An organism that spends all its life in the soil, e.g., 
certain fungi, protozoa, and nematodes. 


The study of biological and meteorological events in 
relation to time. 


A gradation or Cline (q. v.) based on topographic or 
spatial separation, cf. Ecocline. 


An organism that spends a portion of its life in the soil, 
e.g., certain mammals, reptiles, and other animals, cf. Geo- 
biont, Geoxene. 


See Geotype. 

Geographic Race 

A Race restricted to a certain geographic area. cf. Ecotype. 

Geological Erosion 

See Normal erosion. 


The branch of physical geography that deals with the 
form and arrangement of the earth's crust. 


See Geocole. 


One of Raunkiaer's Life-form classes of plants in which 
the buds or other Perennating parts surviving unfavorable 


seasons are buried in the surface soil, e.g., plants with bulbs, 
tubers, or rhizomes. 


A series of Climax Formations throughout geological 
time in an area. 


A Taxis (q. v.) in response to gravity. 


An instrument for securing soil samples. 


A Tropism (q.v.) in response to gravity, e.g., the main 
roots of plants growing downward, the main stems upward. 


A genotypic population occurring in a habitat which is 
partly isolated by topographic barriers; includes most geo- 
graphical Races and Subspecies. Syn. geoecotype. cf. 


An organism that occurs accidentally in the soil. cf. 


The process of growth renewal of a seed or spore; a seed 
is considered to have completed germination in some in- 
stances when the Hypocotyl projects outside of the seed coat, 
in other instances when the seedling appears above ground. 

Germ Plasm 

The protoplasm which transmits the hereditary characters 
or Genes (q. v.). 

Gestation Period 

The period of time that the embryo and fetus are in the 
uterus of an animal. 


G Horizon 

A soil layer developed wholly or partly in Gley (q. v.) soil, 
characterized by the presence of ferrous iron and usually by 
neutral gray colors. 

Gigantism (Giantism) 

A plant showing excessive vegetative growth. 


The type of microrelief characterized by a succession of 
micro-basins and micro-knolls or many small ridges in nearly 
level areas on clay soil having high coefficients of expansion 
and contraction with changes in moisture content; "pits- 


The removal of a ring of bark or tissues from a stem, 
causing the death of the plant. 

Glacial Drift 

See Drift. 


The covering of an area by a glacier or by an ice-sheet, 
or the geological action of the glacial ice upon the land. 


The soil-forming process in which Gley soil is formed. 

Gley (Glei) Soil 

A soil formed under the influence of water-logging and 
lack of oxygen; usually neutral gray in color and containing 
reddish brown deposits of ferrous hydroxide, cf. G horizon. 

Gloger's Rule 

The generalization which states that animals in warm 
climates tend to be darker in color than those in arid or cool 



A plant growing in soil that is low in salt content, in 
contrast to Halophyte, e.g., American elm. 

Graded Terrace 

A terrace having a continuous slope along its length, cf. 
Level terrace. 


An Indehiscent fruit in which the coat of the single seed 
is united with the ovary wall, e.g., wheat. 


Refers to the grass family, Gramineae. 


Refers to an animal that eats grass. 


Refers to an herb with long, narrow leaves. 

Granular Structure (Soil) 

A soil made up chiefly of particles or aggregates that have 
rather indistinct faces and edges, cf. Fragmented structure. 


A plant in the family Gramineae with characteristically 
reduced flowers of florets, grain type of fruit, and with nar- 
row, usually elongated leaves which are attached in two 
ranks to the jointed stem or culm. 

Grassed Waterway 

A natural or artificially made course for the flow of 
water, usually shallow, on which erosion-resistant grasses are 
grown, to permit water to run off fields thus reducing 
erosion where the crops are growing. 


Vegetation consisting chiefly of grasses or grasslike plants, 
cf. Steppe, Prairie, Pampas, Meadow, Veld, Savanna. 


Grasslike Plant 

A plant which resembles a true grass, e.g., sedges, rushes. 

Gravitational Water 

Water in large pores in the soil which drains away under 
the force of gravity when underdrainage is free. 

Gray-Brown Podzolic Soil 

A major soil group having a thin organic and thin 
organic-mineral layers over a grayish brown leached layer 
which rests upon a brown B horizon richer in clay than the 
horizon above; formed under deciduous forests in a moist 
temperate climate. 


The feeding by livestock and game animals on live or 
standing plants other than Browse. 

Grazing Capacity 

The maximum number of animals or animal units per 
acre, or acres per animal, that a grazing area can support 
without deterioration, cf. Carrying capacity. 

Grazing District 

An administrative unit of the Federal rangeland estab- 
lished by the Secretary of the Interior under provisions of 
the Taylor Grazing Act of 1934, as amended; or an adminis- 
trative unit of a state, private, or other range lands, estab- 
lished under state laws. 

Grazing Land 

Land used regularly for grazing; not necessarily restricted 
to land suitable only for grazing but cropland and pasture 
used in connection with a system of farm crop rotation are 
usually not included, cf. Range. 

Grazing Permit 

An authorization for the grazing on public or other lands 


under specified conditions, issued to a livestock operator by 
the agency in charge of the lands. 

Grazing Preference 

The criteria used in the administration of public grazing 
lands for the issuance of grazing permits and licenses. 

Grazing Unit 

A division of the Range for the facilitation of adminis- 
tration or the handling of livestock. 

Green Manure Crop 

A crop grown for the purpose of turning under while 
it is still green, or shortly after maturity, in order to improve 
the soil. 


The tendency of organisms to congregate or form groups, 
e.g., reindeer, cattails. See Sociability. 

Grinnell's Axiom 

The generalization stating that no two species in the same 
general territory can occupy for a long time the same 
ecologic Niche, cf. Cause's principle. 

Ground Cover 

See Cover. 

Ground Water 

Water standing in or moving through the soil and under- 
lying strata, Gravitational water, the source of water in 
springs and wells, cf. Runoff. 

Group Control 

The control or influence of the behaviour of a group of 
animals, by means of the cue behaviour or a signal of specific 

Growing Point 

One of the sections of a plant body in which growth is 
localized, especially the tips of stems and roots. 


Growing Stock 

The total number or total volume of all the trees in an 

Growth Form 

The characteristic shape or appearance of an organism 
as a result of its development in response to the impinging 
environmental conditions within its genetic constitution, cf. 
Habitat form, Phenotype, Genotype. 

Growth Layer 

A layer of Xylem and Phloem produced in woody stems 
usually during each growing season, cf. Annual ring. 

Growth Ring 

A Growth layer seen in the cross section of a woody stem. 

Growth Substance 

Any chemical produced by a plant, or synthetically, that 
regulates plant growth, cf. Hormone. 


A channel or small valley formed by running water which 
usually flows only during and immediately after heavy rains 
or the melting of snow; it may be branched or linear and 
fairly long, narrow, and uniform in width; smaller than a 
ravine, deeper than a rill. 

Gully Erosion 

Removal of stones, gravel, and finer material by running 
water with the formation of channels that cannot be smoothed 
out completely by ordinary cultivation. 


The exudation of water in liquid form from plants 
through HydathodeSj (q. v.). cf. Transpiration. 


A plant in the class Gymnospermae of the seed plants, 
Spermatophytes, in which the seeds are not enclosed within 
an ovary, e.g., pine, spruce, cf. Angiosperm. 



An organism containing both male and female character- 
istics, e.g., certain insects, cf. Hermaphrodite. 


Refers to plants in which the stamens are fused with the 
pistil, e.g., certain orchids. 

Gynoecium (Gynaecium) 

The Carpels or Pistils of a flower considered collectively. 


Refers to plants growing characteristically on soils rich 
in gypsum. 


The jelly-like ooze on lake bottoms. 




The general appearance of a plant such as tall and erect 
or decumbent and trailing, cf. Life-form. 


The sum total of environmental conditions of a specific 
place that is occupied by an organism, by a population, or a 
community, cf. Environment, Niche, Site, Microhabitat, 
Standort, Station. 

Habitat Form 

The Growth form or appearance of an organism which 
is characteristic of a certain Habitat, cf. Epharmony, Life- 
form, Eco type. 


The relatively waning response of an organism resulting 
from repeated stimulation which is not followed by any 

Hadal Zone 

The very deep part of the ocean, below 6000 meters, 
cf. Abyssal. 



Refers to saline conditions present in the soil at the 
beginning of a Halosere (q. v.). 


A perennial plant that is partly woody, usually at the 
base, and partly herbaceous, e.g., Artemisia frigida. 


Refers to saline soil or to plants growing in such soil. 


A plant growing in soil with a high content of salts. 


Any organism that grows in a Saline habitat. 


Refers to a soil found in poorly drained depressions in 
arid and semi-arid regions, cf. Hydromorphic, Solonchalk, 


A plant growing in Saline soil. 


The series of stages in Succession originating on a Saline 
area. cf. Sere, Hydrosere, Xerosere, Halarch. 

Hammada (Hamada) 

Rocky uplands in deserts, bare of fine soil or sand because 
of wind action, used especially in the Sahara. 


A mesic area occupied by a community of hardwoods 
(Florida) or an island in a swamp (Okefinokee swamp). 


The condition occurring in some Arthropods in which 
males develop from unfertilized eggs and females from 
fertilized eggs. 



Refers to an organism or part of one in which the nuclei 
contain a single set of Chromosomes, i.e., one Genome (q. v.), 
e.g., Spores, Gametes, Gametophytes, certain male animals 
such as bees. cf. Diploid, Tetraploid, Polyploid. 


The increase in resistance to frost in a plant tissue. 


The capability of plant tissue to survive the formation of 
ice crystals within them. cf. Frost resistance. 


A cemented, hardened layer in the soil, cemented by iron 
oxide, silica, organic matter, or some other substance, cf. 

Hard Seed 

The condition of some seeds in which water absorption 
and germination do not occur although the environmental 
conditions are favorable, e.g., seeds of many legumes and 


The wood of a tree in the Angiosperms (q. v.), e.g., the 
oak, in contrast to Softwood (q. v.). 


A specialized organ of certain parasitic plants which 
penetrates the Host and absorbs food from its tissues, e.g., 
special hyphal branch, a specialized structure in dodder. 


The dried, mowed stems and leaves, often including also 
flowers or fruits and seeds, of grasses and forage legumes 
such as alfalfa and clovers, cf. Fodder, Stover. 


The main center or centers of activity of an animal, e.g., 


the larvae of the longicorn beetle in dying or dead wood, 
cf. Habitat, Niche. 

Heat Budget 

The amount of heat expressed in gram calories that is 
necessary to raise the temperature of a body of water from 
the winter to summer temperatures. 


A community usually occurring in cool climates, often 
dry, usually without trees and uncultivated, characterized by 
low shrubby plants mostly in the family Ericaceae, cf. Moor, 
Bog, Marsh, Swamp. 


The partial raising of plants out of the ground resulting 
from the freezing and thawing of the soil during the winter, 
often breaking the roots. 


A strip of shrubs or small trees, often planted, enclosing 
a field or other area. 


Placing young plants such as fruit trees in a temporary 
trench with soil over the roots to protect them from drying 
until they are permanently planted. 


A plant growing in a cold region, which requires less 
heat than other kinds of plants, growing where the average 
temperature for the warmest month of the year is less than 
50 F., e.g., mosses, lichens, sedges, etc., in the Arctic, cf. 
Megatherm, Mesotherm, Microtherm. 


Refers to organisms that grow best in full sunlight. 


A Heliophyllous organism. 



Refers to organisms which grow best in the shade. Syn. 
Sciophyllous, Shade plant. 


See Phototropic. 


A worm, usually parasitic. 


One of Raunkiaer's Life- form classes, consisting of marsh 
plants whose Perennating parts are in the soil under water, 
e.g., arrow-head, cf. Geophyte, Hydrophyte. 


A term that has been used for the interaction of two 
organisms such as an alga and fungus in a lichen. See Mutual- 
ism, Parasitism, Symbiosis. 


Refers to reef-building corals which contain zooxanthellae 
and algal Symbionts. 


The ecology of land that is modified by man such as 
gardens, parks, fields, cf. Culture community. 


A plant introduced into an area by man. cf. Culture 
community, Exotic, RuderaL 


One of Raunkiaer's Life-form classes in which the buds 
or Perennating parts of plants surviving unfavorable periods 
are located at the soil surface, cf. Cryptophyte, Geophyte, 


A plant that is Epiphytic (q. v.) for only part of its life- 



An organism which is intermediate between an Epiphyte 
(q. v.) and a Parasite (q. v.). 


A plant which is intermediate between a Saprophyte 
(q. v.) and an Autotrophic (q. v.) organism. 


Refers to the liver or to a Liverwort, (q. v.). 


A plant with one or more stems that die back to the 
ground each year; grasses and Forbs (q. v.) as distinct from 
shrubs and trees. 


Refers to plants with characteristics of an herb. 


Herbs in a collective sense, and any other plant material 
used as forage by animals, especially Pasturage. 


A collection of preserved, classified plants. 


A chemical substance used for killing plants particularly 
weeds, e.g., 2,4-D. cf. Insecticide. 


An organism that eats plants, e.g., rabbit, sheep. 


Refers to a herbivore. 


Vegetation consisting of non-woody plants. 



A group of animals, especially cattle or big game. cf. 


Herding, Close 

Handling a band of sheep or goats in a compact group 
and restricting the spread of the animals while grazing. 

Herding, Open 

Handling a band of sheep or goats so the individuals 
are allowed to spread freely while grazing. 


The transmission of characters or directions from parents 
to offspring, or the sum total of such characters. 


A plant with stamens and pistil in the same flower or an 
animal that produces both male and female Gametes, e.g., 
the rose, earthworm, cf. Dioecious, Gynandromorph. 


Refers to reptiles or amphibians. 


The branch of zoology concerning reptiles and 


Refers to organisms having stages of its life-cycle on 
different hosts, e.g., wheat rust which attacks wheat and the 


(1) The production of unlike Gametes (egg and sperm), 
cf. Isogamy. (2) Alternation of generations (q. v.). 


See Alternation of generations. 



Refers to Alternation of generations (q. v.) in which 
forms in different stages are unlike. 


Refers to animals which eat several kinds of food. cf. 


A Saprophyte or Parasite (q. v.). See Heterotrophic, 
Autotrophic, Holophytic. 


Refers to a population comprising Aneuploid, Diploid, 
and Euploid members. 


The increase in vigor or the growth of offspring resulting 
from the crossing of genetically different parents, syn. Hy- 
brid vigor. 


Refers to an organism in which complex materials, espe- 
cially organic foods, are the chief source of nutrition, in con- 
trast to Autotrophic (q. v.) organisms, e.g., animals, Parasites, 
Saprophytes, cf. Holozoic, Mixotrophic. 


Refers to an animal which may wander into a com- 
munity and play an important or unimportant part while 
present, but eventually dies if it does not move into a more 
favorable environment, cf. Index species, Tychocoen. 


Refers to an organism that originated from the fusion of 
gametes containing unlike Genomes (q. v.). cf. Homozygous. 


(1) The habitat Niche where certain animals overwinter. 
(2) An overwintering bud of an aquatic plant. 



Refers to winter, especially the winter season in contrast 
to the Vernal, Estival, and other seasons, cf. Aspection. 


A state of Dormancy especially during winter, cf. 


See Hibernal. 


Monsoon forest which merges into savanna or park land 
in a tropical-continental climate; woody plants lose their 
small xerophytic leaves during the hot and dry summers. 


A social rank-order of animals formed through passive 
submission, direct combat, or threat. 

High Grass 

A class of grasses, 6 to 8 feet high or more, e.g., Panicum 
virgatum. cf. Medium-height grass, Short grass. 


The division of biology that deals with microscopic 
structures or tissues of organisms. 

H Layer 

A layer of completely decomposed litter, unrecognizable 
as to origin, on the surface of the mineral soil. See A horizon, 
F layer, L layer. 

Hoar Frost 

A deposit of ice crystals formed directly from water vapor 
in the air. cf. Rime. 


A moor that rises from the edge towards the middle, so 


that the upper surface is convex in section, caused by the 
growth of Sphagnum. 


A ridge with a narrow summit and steep slopes. 

Hohenheim System 

A system of grazing followed by resting small pastures 
or paddocks for short periods in rotation. 


Refers to the combined Palearctic (q. v.) and Nearctic 
(q. v.) regions of the faunal realm Megagea (Arctogea) (q. v.). 


A term used occasionally to designate the total water con- 
tent of the soil. 


The doctrine that life hi all its forms and the inorganic 
environment form an interacting, integrated system, cf. 


Equivalent to Ecosystem (q. v.). 


Refers to the joint action and interaction of a numbei 
of environmental factors upon organisms. 


An organism that is wholly parasitic, e.g., wheat rust. 


Refers to an organism that utilizes light as the primary 
source of energy, e.g., green plants, purple bacteria, cf. Auto- 
trophic, Chemotrophic, Heterotrophic, Holozoic. 


An organism that is in the Plankton (q. v.) during its 
entire life-cycle, e.g., Copepod. cf. Meroplankton. 



Refers to a heterotrophic animal that ingests solid food, 
digesting it internally. 


The maintenance of constancy or a high degree of uni- 
formity in functions of an organism or interactions of indi- 
viduals in a population or community under changing 
conditions, because of the capabilities of organisms to make 
adjustments. Perceptual homeostasis is the state of maximum 
predictability and control of environmental stimuli by an 
organism, cf. Steady state, Stabilization. 


See Homoiotherm. 

Home Range 

The area around an animal's established home which is 
traversed in its normal activities, cf. Territory. 


The location of the nest or resting place that is in 
regular use by an animal. 


The reaction of an animal to return to a given place 
after displacement, e.g., homing pigeons. 


Refers to the regularity in the distribution and abun- 
dance of the species in a community or area. cf. Frequency, 


An animal which is able to maintain the temperature 
of the body at an approximate constant level independent 
of the surrounding medium, "warm-blooded," e.g., birds, 
mammals, cf. Poikilo therm. 



Refers to structures of organisms that possess the same 
phylogenetic origin, e.g., wings of bats and forelimbs of 
a rabbit. 

Homologous Chromosomes 

The two Chromosomes (q. v.) occurring in each pair in 
Diploids, each derived from a separate parent. 


A pair of Homologous chromosomes, (q. v.). 


Refers to organisms which have organs resembling each 
other because of the evolution along similar paths, but the 
organs are not Homologous, e.g., Lagomorphs and Rodents. 

Homoteneity (Homotony) 

The Homogeneity (q. v.) of a Vegetation type in contrast 
to that of a Stand. 


Refers to an organism resulting from the fusion of 
Gametes carrying the same genes, cf. Heterozygous. 

Hook Order 

A social order or rank in horned animals determined by 
the aggressive use of horns. 

Hopkins Bioclimatic law 

See Bioclimatic law. 

Horizon (Soil) 

A layer of soil approximately parallel to the soil surface, 
with distinct characteristics produced by soil-forming proc- 
esses. See A horizon, B horizon, C horizon. 


A chemical substance produced in one part of an organ- 


ism and usually transported to another part where it causes 
an effect, cf. Auxin. 


An organism that furnishes food, shelter, or other bene- 
fits to another organism of a different species, cf. Parasite, 
Symbiont, Mutualism. 

Hudsonicm Life Zone 

One of Merriam's Life zones, includes the northern part 
of the Boreal forest and coniferous forest on mountains 
farther south; southern boundary delimited by the 57.2F. 
isotherm for the six hottest weeks of the year. 

Humidity, Absolute 

The actual quantity of water vapor present in a given 
volume of air, usually expressed in grams per cubic meter. 

Humidity, Relative 

The ratio of the actual amount of water vapor present in 
a unit portion of the atmosphere to the quantity which would 
be* present when saturated, cf. Psychrometer, Hygrometer. 


The process of decay of organic material to Humus. 


(1) Organic matter in a more or less stable advanced 
stage of decomposition, dark in color, with a high nitrogen 
content, a carbon-nitrogen ratio near 10:1, and other chemi- 
cal and physical properties such as a high Base exchange 
capacity, water absorption, and swelling. (2) Residues in the 
soil of plants and animals that have undergone an appreci- 
able degree of decomposition. 

Humus, Raw 

See M or. 



(1) A tropical cyclone, especially one in the West Indian 
region; with winds of hurricane force which blow around 
the central calm area or "eye" which is very low in atmo- 
spheric pressure. (2) The highest wind velocity on the 
Beaufort scale (q. v.), a wind greater than about 75 miles per 


(1) Genetic; an organism resulting from a cross between 
parents with different Genotypes (q. v.). (2) Taxonomic; a 
cross between parents of different Taxa (q. v.). 


The crossing or breeding of unlike individuals to produce 

Hybrid Segregate 

A form produced in the second or later generation after 

Hybrid Swarm 

A population of organisms derived through hybridiza- 
tion, comprising various generations of hybrids and back- 
crosses; often varying greatly, cf. Back-crossing. 

Hybrid Vigor 

See Heterosis. 


A pore or gland, usually in leaves, that exudes water. 
cf. Guttation. 


Refers to a Succession or Sere which begins in wet habi- 
tats such as a pond. cf. Hydrosere, Xerarch. 

Hydraulic Equilibrium 

The condition of absence of flow rate of water in soil, 


when the pressure gradient force is equal and opposite to 
the gravity force. 


(1) Refers to, or containing hydrogen, e.g., hydric oxide. 
(2) Sometimes used wrongly in the sense of "wet" as a 
substitute for Hydrophyte (q. v.). See Hygric. 


A plant whose Diaspores (q. v.) are disseminated primarily 
by water, e.g., water lilies, cf. Anemochore. 


A graph in which monthly temperature data are plotted 
against data on salinity in the form of a polygon. 


An animal living in water, cf. Hygrocole, Hydrophyte, 
Mesophyte, Xerocolous. 

Hydrogen-ion Concentration 

The concentration of free hydrogen ions in a solution, 
commonly expressed as the logarithm of the reciprocal of 
the normality of free hydrogen ions in which pH 7.0 is 
neutral, values higher than 7.0 indicate alkalinity, below 
this acidity, cf. Reaction. 


The study of natural bodies of water such as lakes, rivers, 
and seas, especially their physical characteristics in contrast 
to the biological qualities. 

Hydrologic Cycle 

The cycle of the movement of water from the atmosphere 
by precipitation to the earth and its return to the atmosphere 
by interception, evaporation, run-off, infiltration, percola- 
tion, storage, and transpiration. 



The science dealing with water and snow, including their 
properties and distribution. 


(1) Refers to soil occurring in poorly drained depressions 
in humid regions, cf. Halomorphic. (2) Refers to cellular 
features typical of Hydrophytes. 


Refers to a plant that grows well in water or wet land. 


A plant which grows wholly or partly immersed in water, 
cf. Hygrophilous, Xerophilous, Mesophyte. 


The growing of plants so that the roots are immersed 
in a water solution of nutrient salts or in some inert mate- 
rial such as vermiculite which is supplied with a nutrient 


A collective term which includes all the stages in a 
Succession beginning in water, cf. Hydrarch, Xerarch, Sere. 


The parts of the earth covered with water, including 
streams, lakes, oceans, cf. Lithosphere, Biosphere. 


A growth response of plants to water as a stimulus. 


A form of self-recording Rain gage. 


Refers to a wet or moist condition of a habitat, cf. 
Hygrophilous, Xerophilous. 



A seed pod that opens in humid air and closes in dry 
air. cf. Xerochase. 


An animal living in a moist place, cf. Hydrocole, Hygro- 
philous, Xerocolous. 


A record made by a Hygrograph. 


A self-recording Hygrometer. 


An instrument for measuring the Relative humidity of 
the air. 


Refers to an organism that inhabits steep and wet rock 


A plant which grows in moist or wet places, cf. Hygro- 
cole > Xerophilous, Mesophyte. 

Hygroscopic Coefficient 

The moisture in percentage of oven-dry (100-110 C.) 
weight that a soil will absorb in a nearly saturated atmos- 
phere (relative humidity of 98 per cent at 25C.). 

Hygroscopic Water 

Water held so firmly by the attraction of soil particles 
that it can be removed only by heating above 100C. It is 
not available to plants. 


An instrument that makes a simultaneous record of 
both relative humidity and temperature, cf. Hygrograph, 



An order of insects which includes the bees, ants, wasps, 
and ichneumon flies. 


A pattern of distribution of individuals of a species in an 
area which is characterized by clumping, or the occurrence 
of denser aggregations in some spots than in others. Syn. 
Contagious distribution, Over-dispersion, cf. Hypodispersion, 
Normal dispersion. 


An organism that is parasitic upon another Parasite. 

Hyperplasy (Hyperplasia) 

An abnormal increase in the number of cells in an 
organism, e.g., certain plant galls, tumors in animals. 


Usually used to mean an abnormal enlargement, in re- 
spect to an organism it may include both enlargement of cells 
and Hyperplasy (q. v.). 


A filament or thread-like structure of a Fungus. 


Refers to a Hypha. 


The portion of a seed or a seedling between the attach- 
ment of the Cotyledons and the Radicle. 


The layer of cells adjacent to the epidermis in certain 
plants, in some species the cells are thick-walled, in others 
used for water storage. 


A pattern of distribution of individuals of a species in 


an area which shows more even spacing than can be expected 
by chance. Syn. Under-dispersion. cf. Hyper dispersion, Nor- 
mal dispersion. 


Refers to Cotyledons which remain underground after 
seed germination, e.g., the pea seed. cf. Epigeal. 


The non-circulating body of water in lakes below the 
Thermocline. cf. Epilimnion. 


The more rapid growth of the under side of an organ 
such as a leaf than of the upper side. 

Hypoplasy (Hyperplasis) 

The reduction in the number of cells in an organ, e.g., 
in certain plant galls. 


An instrument for measuring the height of an object, 
especially a tree. 


A graphic presentation of climatic conditions in which 
one coordinate is the mean monthly temperature and the 
other is the mean monthly precipitation, cf. Climagraph. 


Ice Age 

A glacial epoch in which glaciers and ice sheets occupied 
large areas of continents, as occurred in the Quaternary 


The branch of zoology which deals with fishes. 


A pictorial diagram of an object in which relationships 
are shown between measurements of various characteristics. 


The study of the individual organism, cf. Autecology, 
Synecology, Individual ecology. 


Syn. Light intensity. A unit of illuminance is the lumen 
per square foot, equivalent to the foot-candle when Light 
intensity is used. cf. Illumination value. 

Illumination Value 

The illumination capacity or brightness of light as per- 


ceived by the human eye; on a clear summer day it is 8000 
to 10,000 foot-candles at noon. cf. Irradiance. 


The accumulation of material in a soil horizon by precip- 
itation from solution or from suspension from a layer above, 
cf. Eluviation, B horizon. 


The adult, sexually mature stage of an insect. 

Immature Soil 

A soil in which development is not complete because of 
insufficient time since deposition or exposure to the action 
of the physical environment and organisms on the Parent 
material (q. v.). 


A plant or an animal of a species which has recently 
invaded an area, whose role is still uncertain, cf. Emigration. 


The Migration (q. v.) of an organism into an area where 
it did not occur previously, cf. Emigration. 


The capability of an organism to resist infection by a 
Parasite or one of its products. 

Imperfect Flower 

A flower lacking pistils or stamens. 

Impervious Soil 

Refers to soil or a certain layer in which the penetration 
of water, and usually air and roots as well, occurs slowly 
or not at all. 


An artificial lake or pond. 



A form of rapid and stable learning in a young animal 
when it is exposed to a meaningful stimulus. 


The residence of flocks and herds upon Alpages (q. v.). 


The mating of closely related organisms, cf. Outbreeding. 


A failure or partial failure of some process which results 
in lack of Fertilization. See Self -incompatibility. 


A plant already present in a community or area which 
increases in abundance under overgrazing, cf. Decreaser. 


The increase in the Basal area (q. v.), diameter, height, 
volume, quality, or value of a tree or a Stand. 

Increment Borer 

An instrument used for securing from the trunk of a 
tree a core which shows the Growth rings. 


Refers to a structure, especially fruits of plants, that do 
not break open when ripe. cf. Dehiscent. 

Index, Frequency 

See Frequency index. 

Index of Similarity 

The ratio of the number of species found in common in 
two communities to the total number of species that are 
present in both, cf. Coefficient of community. 

Index Species 

An organism that is so well adapted to its habitat it 


seldom occurs elsewhere, therefore useful in characterizing 
the environmental conditions as a living label, cf. 


An organism, species, or community which indicates the 
presence of certain environmental conditions, cf. Exclusive 

Indifferent Species 

A species occurring in many different communities, a 
Companion species (q. v.). See Fidelity. 


An indigenous species, cf. Cultigen. 


Refers to an organism that is native, not introduced, in 
an area. cf. Endemic, Exotic. 

Individual Ecology 

See Autecology, Idiobiology, Synecology. 


The establishment of a Parasite upon an organism. 


The establishment of an organism in numbers as para- 
sites upon another plant or animal, e.g., aphids infesting 
a rose bush. 


The penetration of water into soil or other material, 
cf. Percolation. 

Infiltration Capacity 

The maximum rate of Infiltration under a given set 
of conditions. 



A mechanism for measuring Infiltration into the soil in 
which water is applied by sprinkling or flooding. 


The flower-cluster in plants, including the flowers, bracts, 
and stems. 


(1) An organism which has important interactions (Reac- 
tions, Coactions) within a community, but is not a dominant. 
(2) The flow of water from a channel into subterranean 
storage, cf. Effluent. 


Animals which are supported by the lower surface of the 
film of water on lakes and ponds, e.g., mosquito larvae, cf. 
Neuston, Supraneuston. 


Used formerly in the sense of all microscopic organisms 
occurring in infusions of organic matter; now used chiefly 
for ciliated Protozoans (Ciliophora). 

Ingestive Behaviour 

The actions of an organism when eating or drinking. 


See Heredity. 

Inheritance of Acquired Characters 

The outmoded theory of evolution tfyat modifications 
produced during the lifetime of an individual, because of 
use or disuse, new needs, or because of the direct action of 
the environment are inherited by the offspring and are 
cumulative with time. 

Initial Cause of Succession 

The process or agent which produces denuded or partly 


denuded areas on which ccologic Succession is initiated, e.g., 
Erosion, Deposition. 

Innate Releasing Mechanism 

A device (postulated) in the nervous system which 
initiates a certain reaction when an animal receives a par- 
ticular stimulus. 


To introduce a microorganism, virus, serum, etc., into 
an organism. 


A material used for destroying insects, e.g., DDT, rote- 
none. cf. Herbicide, Fungicide. 


An animal in the order Insectivora, a primitive Insecti- 
vorous group in the class Mammalia, e.g., mole, shrew. 


Refers to an organism that eats insects. 

Insect Vector 

An insect by which a disease-producing organism or a 
parasite is disseminated, e.g., aphids and leafhoppers trans- 
mitting plant diseases. 


Solar radiation received by the earth or other planets 
from the sun, or exposure to rays of the sun. 


A form in the larval development of insects between 
two moults. 


An inherited and adapted system of co-ordination within 
the nervous system as a whole, which when activated finds 
expression in behaviour culminating in a fixed action pattern. 



An interrelationship between organisms, between organ- 
isms and the environment, or between environmental factors, 
e.g., Competition, grazing, wilting of a plant, Relative 
humidity decreased by heat. See Coaction, Reaction. 


Refers to the position between cells of an organism, e.g., 
air-spaces between cells in leaves. 


The process by which precipitation is retained by leaves, 
branches, and other organs of plants before the moisture 
reaches the ground. 


The ability of a species to damage another either directly 
by attacking its individuals or indirectly by harming its 
resources or blocking access to them. cf. Competition, 


A ridge between river valleys. 

Internal Drainage (Soil) 

The quality of a soil that permits downward flow of 
excess water through it, determined by the texture, structure, 
depth to the Water table, etc. cf. Gravitational water. 

Internal Environment 

The conditions within an organism or cell that influence 
its processes, e.g., the oxygen content in body fluids in ani- 
mals or in air-spaces in plants. 


Refers to relations or conditions between species, cf. 

Interspecific Association 

See Association, interspecific. 



The irregular occurrence of plant communities and 
species which provide cover for animals within a limited 
area. cf. Mosaic. 

Intertidal Zone 

See Tidal zone. 


Refers to the location or position of a substance or 
structure within a cell. 


Refers to the presence of organisms such as Ecotypes 
(q. v.) within a Cline (q. v.). 


Refers to the period of a single 24-hour day. 


The presence of individuals of a species toward the center 
of its entire area of distribution, cf. Extraneous. 


Refers to relations or conditions between individuals 
within a species, cf. Interspecific. 

Intrazonal Soil 

A group of soils having characteristics caused by the 
preponderant influence of local relief or parent material over 
the normal influences of the prevailing climate and vegeta- 
tion, cf. Zonal soil. 

Intrinsic Cycle 

See Cycle. 


See Introgressive hybridization. 

Introgressive Hybridization 

The infiltration of genes of one species by the inter- 


mediacy of Hybrids into another species, resulting in the 
genetic modification of the latter. 


The Migration (q. v.) and Establishment (q. v.) of an 
organism in a new location. 

Inverse Stratification 

The condition in which the water just beneath the ice 
in a body of water is near the freezing temperature and 
within a short distance below shows a rapid rise to 3C., 
and further below a gradual increase to 4C., or to the 
maximum temperature of the lake or pond. cf. Thermal 

Inversion, Temperature 

An increase in air temperature with an increase of alti- 
tude, instead of the normal decrease. 


An animal lacking a spinal column, e.g., insects. 

In Vitro 

Refers to experiments on cells, etc., which are carried 
on when they are separated from the living organisms, e.g., 
tissue cultures, cf. In vivo. 

In Vivo 

Refers to location within the living system, cf. In vitro. 


A number of closely associated bracts subtending a flower 
or flower cluster. 


(1) The diminution in the size of an organ, cf. Hyper- 
plasy, Hypertrophy. (2) The formation of abnormal yeasts, 
bacteria, etc. 


Ion Exchange 

The replacement of one kind of ion by another, e.g., 
hydrogen ions replacing calcium ions in certain soil solutions. 
See Exchange capacity. 


The process of ion formation. 

Ionizing Radiation 

Radiation that takes electrons from atoms and attaches 
them to other atoms, e.g., Alpha, Beta, Gamma radiation, 
(q. v.). 


The receipt of radiant energy per unit area per unit of 
time. On a clear summer day solar radiant energy equals 
1.2 to 1.5 gram-calories per square centimeter per minute 
at noon. cf. Illuminance, Light intensity. 


The exposure of an object to radiation such as sunlight, 
Ionizing radiation, etc. 


The characteristic capability of an organism to respond 
to a stimulus, e.g., a plant growing towards the light. 


An abrupt, irregular increase in population number or 


A line drawn on a map or chart connecting places of 
equal barometric pressure. 


A line drawn on a map connecting points of equal depth 
on the bottom of the sea. 



A line drawn on a map connecting regions that possess 
similar Biological spectra (q. v.). 


A group of Synusiae (q. v.) that show Physiognomic 


A line drawn on a map connecting regions possessing an 
equal number of species within a genus or a family. 


The production of similar Gametes (q. v.), occurs in 
certain algae (Ulothrix), fungi, and protozoa, cf. Heterogamy. 


Refers to organisms that occur in the same region. 


See Isotherm. 


The line or layer within a body of water which has the 
same Salinity at a certain time or the same mean salinity 
over a certain period. 


A line drawn on a map connecting places with equal 
duration of sunshine. 


A line drawn on a map connecting places with equal 
quantity of rainfall. 


The separation of populations from other populations of 
the same species by geographic, ecologic, climatic, physiolo- 
gic, or other barriers, cf. Natural selection. 


Isolation Transect 

An Exclosure (q. v.) which is divided into plots, one of 
which is opened to grazing each year, and another plot which 
has been grazed is added. 


A line drawn on a chart connecting areas of a community 
that show equal Frequency indices of a species. 


A line drawn on a chart connecting areas where events 
in the life history (e.g., egg-laying, flowering) of an organism 
occur at the same time. cf. Aspection. 


A line drawn on a map or chart connecting places having 
the same value of a certain factor, cf. Isohyet, Isotherm. 


An animal in the order Isopoda, class Crustacea, e.g., 
woodlice, pillbug. 


The state of general equilibrium between the upland 
and lowland areas of the earth, with indications that the 
rock materials under the oceans are heavier than those under 
continental protuberances, cf. Tectonic. 


A line drawn on a map or chart connecting places with 
the same temperature at a particular time or for a certain 


Forms or atoms of the same element that differ in atomic 
weight and in the constitution of the atomic nucleus. Some 
elements in nature such as radium and uranium have Radio 
isotopes (q. v.). 



An instrument arranged at the entrance of a bird's nest 
for the automatic recording of the number and direction 
of visits made by the parents. 



See Vernalization. 


A Microspecies (q. v.). 

Jordan's Rule 

The generalization that fishes living in waters of low 
temperatures tend to have more vertebrae than do those in 
warm waters. 


A geological period in the Mesozoic era which began 
about 165 million years ago and lasted about 30 million. 



A short ridge or mound of sand or gravel desposited by 
a stream under a glacier, cf. Esker. 


Refers to a limestone region with a dry, barren surface 
from which most or all of the drainage is through under- 
ground channels. 

Kar Herbage 

An aggregation of tall herbs growing in fertile soil in 
hollows high in mountainous regions. 


An open vegetation type in South Africa consisting of 
succulent and sclerophyllous shrubs, where the precipitation 
amounts to 3 to 14 inches annually, but which falls mostly 
in the summer. 


See Mitosis. 


The gross appearance, i.e., the size, number, and shape, 
of the set of Somatic chromosomes. 


Key-industry (Animals) 

Herbivorous animals which are so numerous that a large 
number of other animals are dependent upon them for food 
(e.g., Copepods. cf. Food-chain, Pyramid-oj '-numbers. 

Key Areas 

Critical areas of range land which represent range that 
is most likely to be overgrazed; used as criteria or indices 
of proper use of the range. 

Key Species 

Any species of plants which because of palatability, abun- 
dance, or other characteristics may be used in estimating 
degree of utilization, trend, or condition of the range, cf. 

Krebs Cycle 

The aerobic portion of Respiration, in which pyruvic 
acid is oxidized, usually to carbon dioxide and water as end 


The behaviour of an animal resulting from unoriented 
reflex action of the entire animal. 


The capability of an otherwise susceptible variety of 
a species to escape infection because of the way it grows, 
e.g., plants that mature early and thus escape late-season 


The random turning movements of an organism which 
increase in rate as it nears an unfavorable environment, cf. 

Klinotaxis, Orthokinesis. 


A sudden movement away from an unfavorable en- 


vironment, directed by the organism, cf. Klinokincsis, 


See Coprophagous. 


Irregular, tubular streaks within one soil horizon, con- 
sisting of material transported from another horizon; caused 
by filling of tunnels made by burrowing animals, especially 


Scrubby, stunted growth-form of trees, often forming a 
characteristic zone at the limit of tree growth in mountains. 



Refers to a lake. 


See Raised bog. 


An animal in the order Lagomorpha, class Mammalia, 
e.g. rabbit. 


The doctrine regarding the inheritance of Acquired 
characters (q. v.) propounded by J. B. Lamarck. 

Lambing Range 

The area used by bands of sheep during the lambing 

Land Bridge 

A land connection between two bodies of land over which 
migration of organisms has occurred. 

Land Capability 

The suitability of land for use of some kind without 


Land-capability Class 

One of the eight classes of land in the land-capability 
classification, ranging from (1) land that is very good for 
cultivation to (8) land that is not suitable for cultivation, 
grazing, or forestry. 


The pre-adult, usually self-feeding, but not sexually repro- 
ducing form of an animal, passes through metamorphosis 
to the adult stage, e.g., caterpillar of a moth, tadpole of a 


A Periphyton (q. v.) in which the organisms are asso- 
ciated in a more or less dense growth and are interdepend- 
ent, cf. Epiphyton. 


A red, highly weathered soil characteristic of damp 
tropical regions such as equatorial Africa, cf. Laterization. 


Weathering which tends to produce Laterite, essentially, 
the removal of silica and consequent increase in alumina and 
iron oxide content, and a decrease in the Base exchange 
capacity of the soil. cf. Podzolization. 


Laurel forests or subtropical rain forests, often with 
Dicotyledonous and Gymnospermous dominants, cf. Lignosa. 


The horizontal part of a community in which the plants 
are of about the same height, e.g., tree layer, herb layer. 
Also applicable to depth in the soil. syn. Stratum, cf. Layer- 
ing, Synusia. 


The propagation of plants by inducing formation of 
roots on stems that are attached to the plant. 



The appearance of plants or plant parts, or their remains, 
in horizontal divisions, syn. Stratification. 


The removal by percolating water of soluble constituents 
from the soil or other material. 


The lower layer of the A horizon, lying on the mineral 
soil, consisting mostly of well-decomposed, finely-divided 
organic material. 

Leaf-size Classes 

The arbitrary groups of leaves based on the area of 
blades, as proposed by Raunkiaer, in square mm: Leptophyll 
25, Nanophyll 225, Microphyll 2025, Mesophyll 18,225, 
Macrophyll 164,025, Megaphyll larger than 164,025. 


(1) A plant belonging to the family Leguminosae, e.g., 
pea, alfalfa. (2) The fruit of Leguminosae. 


Refers to the pea family, Leguminosae. 


One of the small rodents in genus Lemmus or Die- 
rostonyx, order Rodentia, of circumpolar distribution. 


See Photoperiodism. 


Refers to the standing-water series; lakes, ponds, swamps. 
cf. Lotic. 


A pore on the surface of woody stems or roots, filled 
with loosely arranged cells that permit diffusion of gases 
between the atmosphere and the interior of the plant. 



An insect in the order Lepidoptera (e.g.) moth. 


See Leaf-size classes. 

Lethal Gene 

A gene (q. v.) that causes death of an organism. 


A colorless Plastid in which starch often forms, located 
in the Cytoplasm in plant cells. 

Level Terrace 

A terrace that strictly follows the contour, in contrast to 
the Graded terrace (q. v.). 


An English term for land that is temporarily under grass, 
legumes, or mixtures of these. 

Liana (Liane) 

A climbing or twining plant. 


A Symbiotic association or relationship of an alga and a 
fungus, which forms crustose, foliose, or fruticose bodies. 

Liebig's Law of the Minimum 

The generalization that states the growth and reproduc- 
tion of an organism is dependent on the nutrient substance, 
such as nitrogen, oxygen, carbon dioxide, that is available 
in minimum quantity. 

Life Belt 

A vertical subdivision of plant and animal life, deter- 
mined largely by altitudinal influences, part of a Bio tic 
province (q. v.). 

Life Cycle 

The phases, changes, or stages an organism passes through 


from the fertilized egg to death of the mature plant or 

Life Expectancy 

The average duration of life that a given individual is 
expected to live after having reached a certain age. cf. 
Life table. 


The characteristic form or appearance of a species at 
maturity, e.g., tree, herb, worm, fish. cf. Growth form, 
Habitat form, Raunkiaer's life-form classification. 

Life-form Class 

One of the groups in Raunkiaer's classification of life- 
forms, e.g., Geophyte, Therophyte. 

Life-form Dominance 

The condition in which several species of the same Life- 
form dominate a plant community, cf. Dominance, ecologic. 

Life Span 

The maximum duration of life of an individual of a 

Life Table 

A statistical tabulation presenting complete data on the 
mortality of a population, cf. Ecological longevity, Life 

Life Zone 

An altitudinal or latitudinal biotic region or belt with 
distinctive faunal and floral characteristics, cf. Alleghenian, 
Hudsonian life zones. 

Light Intensity 

See Illumination value. 

Light Quality 

The wave-length composition of light. 



A complex organic compound in the walls of certain cells, 
especially in woody tissue. 


The process of impregnating cell walls of a plant with 


Woody vegetation. 

Lime Requirement 

The amount of standard ground limestone needed to 
change the upper 6.6-inch layer of an acre of acid soil to some 
lesser degree of acidity, usually stated in tons per acre. 

Limiting Factor 

The environmental influence by which the limit of tolera- 
tion of an organism is first reached and which therefore 
acts as the immediate restriction to one or more of its func- 
tions or activities or in its geographic distribution. 


Refers to the open water of a pond or lake. cf. Benthic. 


The branch of biology that deals with fresh waters and 
organisms in them. 

Lincoln Index 

The use of marked animals to estimate the size of a 

Line-intercept Method 

The sampling of vegetation by recording the plants inter- 
cepted by a measured line placed close to the ground, or by 
vertical projection to the line. cf. Transect. 


Line-plot Survey 

The sampling of vegetation by means of plots of uniform 
size located at regular intervals along a line. 

Line Transect 

Sampling vegetation by recording kinds of plants or 
communities intercepted by a measured line. cf. Line- inter- 
cept method, Transect. 


The association of certain characters in such a way that 
they are inherited together, because the controlling genes 
are in the same Chromosome. 


Refers to the work or the concepts of Carolus Linnaeus. 


A species according to the nomenclature of Linnaeus, a 
broad category, often containing variable forms. 


An implement consisting of a double plow, in which the 
shares push the soil in opposite directions, forming a series 
of alternate ridges and furrows. The -Basin lister has an 
attachment that forms low dams of soil across the furrows 
at intervals of 15 to 25 feet, so that basins are formed which 
can hold large amounts of water. 

List Quadrat 

A rectangular sample area in vegetation in which organ- 
isms are merely tabulated according to species. 


According to the metric system the volume of pure water, 
free of air, at 760 mm. pressure and 4C., equivalent to 1.057 
U. S. liquid quart. 



A plant growing on a rock, e.g., many lichens and mosses. 


All of the stages of a successional sequence that originated 
on rock. cf. Succession, Xerosere, Hydrosere. 


A soil consisting mainly of partly weathered rock frag- 
ments or of nearly bare rock. 


The earth's crust, consisting of the surface soil lying upon 
the hard rock which is several miles thick, cf. Hydrosphere, 


(1) The uppermost organic materials, partly or not at all 
decomposed, on the surface of the soil. cf. A 00 horizon. (2) 
The group of young born at one time by a Multiparous 
animal as a cat. 


Refers to the zone in a lake or a pond that extends from 
the shore to the depth at which plants are rooted. In the 
ocean the zone extends to about the depth to which tides, 
wave action, and light penetrate. 


A Fluke (q. v.) parasitic on sheep, cattle, and other ani- 
mals, causing liver-rot. 


A plant in the class Hepaticae, phylum Bryophyta, 
usually growing in moist places, e.g., Marchantia. 


A tropical Savanna (q. v.) or grassland north of forests 
of the Amazon River basin in South America. 


L Layer 

Used at times for the A w horizon (q. v.). 


A winter fog caused by the invasion of cold air during 
"northers" along the shores of the Gulf of California. 


(1) A soil containing relatively equal amounts of sand 
and silt and a somewhat smaller proportion of clay. (2) 
Specifically, soil material containing 7 to 27 per cent clay, 
28 to 50 per cent silt, and less than 52 per cent sand. 


Refers to a relatively small area, a few square miles as 
a maximum. 


The behaviour of an animal where it becomes associated 
with a particular area. 

Local Race 

A group of individuals of a species with better genetic 
adaptation to a given environment than other groups, cf . 
Eco type. 


A local variation of a Climax community, differing from 
it in the kinds of Subdominants. cf. Faciation. 


Similar to Lociation but applies to a Serai community. 


A deposit of relatively uniform, fine soil material, mostly 
Silt, presumably transported to its present position by wind. 


See Cut-over forest. 


Logistic Curve 

A graph that represents the growth of an individual or 
a population, typically S-shaped. 

Long-day Plant 

A plant that blooms under long periods of light and short 
periods of darkness, e.g., red clover, cf. Photoperiodism. 


The loss in weight of a soil (or other material), pre- 
viously dried at 100C., heated to redness hi a crucible; often 
used to represent the organic content. 


Refers to running water as in a creek, cf. Lentic, 

Lower Austral Life Zone 

See Austral life zone. 

Lower Sonoran Life Zone 

See Sonoran life zone. 


The emission of light that is not caused by high tempera- 
ture, cf. Bioluminescence. 

Lunar Periodicity 

The correlation of activities of certain organisms with 
periods of the moon, e.g., Bioluminescence of the Bermuda 
fireworm at the time of full moon. 


A plant in the subphylum Lycopsida (club-mosses) in 
the phylum Tracheophyta, e.g., Selaginella. 


An apparatus used to collect and measure the amount 


of water that percolates through a quantity of soil and for 
measuring the amount of Leaching. 


A substance that causes bacteria, blood corpuscles, and 
other organic bodies to dissolve. 




Vegetation consisting of dense evergreen brush (shrubs 
and small trees) in the Mediterranean region, denser than 
Garique (q. v.), similar to Chaparral (q. v.). Syn. Maquis. 

Macronutrient (Macrometabolic Element) 

An element or a compound required by organisms in 
relatively large quantity, e.g., calcium by clams, phosphorus 
salts by clovers, cf. Micronutrient. 


See Leaf-size class. 


Refers to large aquatic plants, e.g., kelps, water cress. 


Refers to an animal with unusually large wings or fins, 
cf. Micropterous. 


See Linneon. 


A northwesterly wind in the central Mediterranean 



Refers to ferromagnesian minerals in a rock. 


The division of zoology that deals with mollusks. 


Scrub vegetation composed largely of various species of 
Eucalyptus, about 2 to 10 meters high, in dry, subtropical 
parts of southwest and southeast Australia. 


Refers to the doctrine of T. R. Malthus that organisms 
tend to increase in geometrical progression while the food 
supply increases in arithmetical progression, so that the in- 
crease in the size of a population tends to be at a more rapid 
rate than the increase in available food. cf. Competition. 


An animal in the class Mammalia, subphylum Vertebrata, 
e.g., rabbit, deer. 


A type of vegetation that is worldwide on tropical and 
subtropical saline, tidal mud flats, consisting usually of low 
trees or shrubs in genera Rhizopora, Avicennia, and 


See Macchia. 


A deposit of chiefly calcium carbonate, mixed with clay 
or other material, and formed chiefly in fresh water lakes 
by organisms such as Chara. 


A Swamp in which grasses, sedges, cattails, or rushes form 
the dominant vegetation, cf. Bog. Moor. 


Marsh Gas 

See Methane. 


An animal in the subclass Marsupalia, class Mammalia, 
e.g., kangaroo, opossum. 


A principal, relatively uniform mountainous mass with 
peaks on top. 

Mass Selection 

The choosing of individuals that possess a certain char- 
acteristic in common from a population such as a corn field, 
and then bulking the seeds or propagules for later planting. 


Nuts such as acorns, beechnuts, and others, in a collective 
sense, especially when the nuts are used as food for animals. 

Mature Soil 

A soil that is in good adjustment with environmental 
conditions, in many regions with well-developed horizons, 
cf. Podzol, Chernozem. 


A grassland, usually in a low, moist area; often mowed 
for hay. cf. Pasture, Range. 

Mean Sample Tree 

A tree selected for its representative form and that is 
average hi diameter, height, and volume of the other indi- 
viduals of the species in a stand. 

Mechanical Analysis 

A laboratory procedure for determining the percentages 
of clay, silt, and sand in a sample of soil. 

Mediterranean Climate 

The climatic conditions that prevail in lands bordering 


the Mediterranean Ocean, characterized by hot, dry summers 
and cool, rainy winters. 

Medium-height Grass 

In the classification of grasses according to height, the 
class that ranges from 2 to 5 feet in height, includes Mid- 
grasses (q. v.). cf. Highgrass, Shortgrass. 

Megagea Realm 

One of the three classes of the earth's fauna, which 
includes the Ethiopian, Oriental, Palearctic, and Nearctic 
regions, cf. Neogea, Notogea. 


A group of plants in Raunkiaer's life-form classification 
which includes trees, lianas, and epiphytes over 30 meters 


See Leaf-size classes. 


The larger of two kinds of spores produced by plants such 
as Selaginella and the Spermatophytes (q. v.). cf. Microstore. 


An organism that requires continuously high tempera- 
tures, and according to some usage abundant moisture, e.g. 
sugarcane, cf. Mesotherm, Microtherm, Hekisto therm. 


The two successive divisions of the nucleus in which the 
Chromosome number is halved, from the Diploid (q. v.) to 
the Haploid (q. v.) number. 


The unusual development of a dark pigment in an 



Cells in certain animals that contain black pigment, 
melanin, as in the chameleon. The contraction of the cells 
makes the animal appear light in color, expansion makes it 
appear dark. 


Refers to an organism that feeds on honey. 


Refers to Mendel's laws (q. v.). 

Mendelian Population 

A group of individuals of a species that share in a 
common Gene pool through reproduction, cf. Species, 


The knowledge of inheritance according to Mendel's 

Mendel's Laws 

The rules according to which characteristics of organisms 
are inherited as stated by Gregor Mendel, such as characters 
or factors (genes) act as units, dominance and recessiveness 
of characters, the segregation of Alleles during meiosis, and 
the independent assortment of alleles in each Gamete. 

Mercator's Projection 

A method of mapping in which the parallels of latitude 
are drawn as straight lines of the same length as the equator. 


A tissue in plants that is concerned with division to form 
new cells, located in various places such as root tips, stem 
tips, and buds. cf. Cambium. 


An organism that is in the Plankton (q. v.) during part 
of its life cycle, cf. Holoplankton. 


Merriam's Life Zones 

A series of belts or Life zones (q. v.) based originally on 
criteria of temperature according to C. Hart Merriam. See 
Alleghanian, Carolinian, Hudsonian, Sonoran, Transitional, 
Tropical Life zones. 


A flat or nearly flat table land with steep sides. 


Refers to a successional series that begins in a moderately 
moist habitat, cf. Hydrarch, Xerarch. 


The greatly eroded, broad plateau in the interior part 
of Spain, crossed by a few mountain ridges. 


Refers to environmental conditions that are medium in 
moisture supply, cf. Mesophytic, Hygric, Xeric. 


See Thermocline. 


One of the groups of plants in Raunkiaer's life form 
classification, consisting of trees, lianas, and epiphytes, 8 to 
30 meters tall. 


The palisade and sponge cells between the upper and 
lower epidermises in a leaf. 


A plant that grows in environmental conditions that are 
medium in moisture conditions, e. g., corn. 


Refers to a Mesophyte. 



Refers to an aquatic environment in which the oxygen 
content is considerably reduced and in which much decom- 
position of organic materials is taking place, cf. Catarobic, 


An organism that requires moderate warmth and mod- 
erate moisture, e. g., corn, hickory, cf. Megatherm, Micro- 
therm, Hekistotherm. 


Refers to a swamp supplied with a moderate amount of 


One of the great geological eras, preceding the Cenozoic 
era, began about 205 million years ago and lasted about 130 
million years; divided into the Triassic, Jurassic, and Cre- 
taceous periods. 

Metabolic Water 

The water obtained from the chemical breakdown of 
foods by some organisms such as the clothes moth. 


The sum total of chemical processes occurring within 
an organism or a portion of it, includes Anabolism and 
C atabolism (q.v.). Basal metabolism is the rate of expendi- 
ture of energy while an animal is at rest. cf. Autotrophic, 


Any substance that plays a part, directly or indirectly, 
in Metabolism. 


See Alternation of generations. 



See Thermocline. 


The change of an animal from one form to another in its 
postembryonic development, e. g., larva of an insect to a 


The differential effect of pollen from different varieties 
on the development of the fruit. 


An animal in the group Metazoa which includes all mul- 
ticellular animals as opposed to the unicellular Protozoan 


An apparatus for automatically recording simultaneously 
two or more meteorological elements. 


The study that deals with physical processes occurring in 
the atmosphere such as precipitation, winds, and tempera- 


CH 4 , often called marsh gas, an odorless, inflammable 
gas, and explosive when mixed with air. Develops from de- 
composing organic matter in marshes and in coal-mines. 

Micelle (Micella, Micell) 

A particle composed of complex molecules that forms the 
units of structure in many organic substances such as cellu- 
lose and starch. 


The abstract class or type of community in which similar 
Microstands are grouped, e. g., microstands of certain kinds 


of annual weeds that form a zone around carpenter-ant 
mounds in a shortgrass association or community-type. 


A Microorganism (q. v.). 


The climatic conditions within a Microhabitat (q. v.). 
cf. Local. 


A small Community (q. v.) such as the plants and animals 
living in and on a decaying stump in a forest. 


A miniature world, organisms plus the environmental 
conditions, cf. Ecosystem. 


The procedure in which organisms or cells are studied 
through a microscope by means of a mechanically operated 


A small Habitat (q. v.), e. g., a tree stump or a space 
between clumps of grass. 


A metric measure, one-millionth part of a Micron (q. v.). 


A metric measure, one-millionth part of a millimeter. 


A metric measure, one thousandth part of a millimeter. 


A chemical substance required by an organism in very 
small quantity, e.g., boron by many plants, cf. Essential ele- 
ment, Macronutrient, Vitamin, Deficiency disease. 



An organism that is microscopic in size, e. g., bacteria, 


Refers to an animal that feeds on particles that are very 
small in comparison to its own size, e.g., certain whales feed- 
ing on plankton. 


A group of plants in Raunkiaer's life-form classification, 
includes trees, shrubs, lianas, and epiphytes, two to eight 
meters tall. 


See Leaf-size classes. 


Refers to a plant that has small leaves. 


Refers to a fish with small fins or to an insect with small 
hind wings, cf. Macropterous. 


Minor differences in topography such as small mounds 
or pits with differences in elevation of about three feet or 


A series of successful stages that occur within a micro- 
habitat such as a tree-stump. 


A minute, RNA-rich particle in the cytoplasm of a cell, 
the center of protein synthesis. 


A Species that is less inclusive than the Linneon (q. v.), 
similar to Subspecies (q. v.). Syn. Jordanon. 



The smaller of two kinds of spores produced by plants 
such as Selaginella and the Spermatophytes, e. g., pollen 


A group of plants that occupies a Microhabitat (q. v.). 
cf. Stand. 


An organism that can develop in cool and short sum- 
mers, e. g., barley, spruce trees, cf. Megatherm, Mesotherm, 


An instrument for cutting very thin sections of tissue 
for microscopic study. 


A heterogeneous mixture of species such as occurs often 
in a transition zone between two kinds of stands. 


A grass two to four feet tall, in contrast to a tallgrass 
which is five feet or more tall, e. g., Koeleria cristata. cf. 
Medium-height grass, Shortgrass, Highgrass. 


An organism that is undergoing Migration (q. v.). 


(1) The movement of a plant or one or more of its parts, 
such as fruits, from one area to another. (2) The movement 
of an animal beyond its regularly occupied geographic loca- 
tion or Home range (q. v.). cf. Emigration, Immigration, In- 


See Diaspore. 



An area one-thousandth part of an acre, containing 
43.56 square feet, often used as a plot 6.6 feet square. 


A unit of atmospheric pressure, 1000 millibars repre- 
sents a pressure of about 29.53 inches (750.1 mm.) of mer- 


One-thousandth part of a Curie (q. v.). 


One-thousandth part of a gram. 


One-thousandth part of a liter. 


One-thousandth part of a meter, 0.0394 inch. 

Millimicron (mu) 

One-thousandth part of a Micron (q. v.). 

Mima-type Microrelief 

A type of microrelief characterized by low mounds or 
soil pimples, named after the mounds in Mima prairie in 
western Washington. 


The kind of behaviour in which like elicits like, involv- 
ing hereditary patterns. 


Refers to mimicking behaviour, cf. Allelomimetic. 


(1) Batesian: The kind of behaviour in which an edible 
species escapes death by its close resemblance in appearance 
to an inedible species. (2) Mullerian: The kind of be- 


havior in which both species are inedible but are similar 
in appearance, so avoidance learned by predators in tasting 
one is extended to the other. The term mimicry is often 
restricted to the former. 


The decomposition of organic substances to mineral 
forms, e. g., proteins to nitrates, phosphates, etc. 

Mineral Soil 

Soil composed mainly of inorganic materials and with 
only a relatively low amount of organic material. 

Minimal Area 

The smallest area on which a community develops its 
Characteristic species-combination (q. v.). 

Minimalraum, Minimiareal 

See Minimal area. 

Minimum, Law of 

See Liebigs law of the minimum. 

Minimum Quadrat Area 

For a given number of samples in a stand the size of 
quadrat in which the Species-area curve (q. v.) becomes 
nearly horizontal, and the use of a larger size to secure 
greater accuracy is not justified by the time and labor in- 

Minimum Quadrat Number 

For a given size of quadrat used to sample a stand the 
number of quadrats at which the number of species-number 
of quadrats curve becomes nearly horizontal, and the use of 
more quadrats to secure greater accuracy is not justified by 
the time and labor involved. See Species-number curve. 

Minor Element 

See Essential element, Micronutrient. 



A geological epoch which began about 28 million years 
ago and lasted about 16 million years, in the Tertiary pe- 
riod of the Cenozoic era. 

Mississippian Period 

A geological period in the Paleozoic era (q. v.), which 
began about 280 million years ago and lasted for about 25 
million years. 


A cold, northerly wind along the northwest Mediter- 
ranean coast, especially during winter. 


An animal in the order Ac&rina, class Arachnida, phylum 
Arthropoda; including both free-living and parasitic forms. 


A minute body in the cytoplasm in cells, the chief loca- 
tion of respiratory enzymes, syn. Chondriosome. 


The ordinary division of a nucleus that includes the 
longitudinal doubling of chromosomes to form pairs of 
chromatids, separation of each pair to form two daughter 
nuclei; so a constant number of chromosomes is maintained. 


Refers to Mitosis. 

Mixed Forest 

A forest composed of trees of two or more species, usu- 
ally at least 20 per cent of the trees are of other than the 
leading species. 

Mixed Prairie 

An extensive grassland type lying west of the tall-grass or 
True prairie in North America, consisting of a mixture of 
tall-, short-, and midgrasses, and other herbaceous plants. 



Refers to an organism that is both Autotrophic (q. v.) 
and Heterotrophic (q. v.), e. g. Insectivorous plants. 


The organism that in Mimicry is imitated. 


A non-inheritable, Phenotypic variation of a character- 
istic of an organism, caused by the environment, e. g., taller 
growth of a plant in the shade than in the sun. cf. Acquired 

Moisture Equivalent 

The percentage of moisture retained by a small sample 
of saturated soil after being subjected to a centrifugal force 
1000 times that of gravity for a definite period of time, usu- 
ally one-half hour. 

Moisture Stress 

The tension at which water is held in the soil. 

Moisture Tension 

The force at which water is held in the soil. 


An organism in the large phylum Mollusca, e. g., snail, 


An erosion remnant such as a hill or a mass of rock rising 
above the surrounding land. 


The mating of a female with only one male, or the 
presence of only one stamen in a flower. 

Monoclimax (Theory) 

As postulated by F. . Clements, ecologic succession will 


in time culminate in a single Climax (q. v.) within a climatic 
region, cf. Polydimax. 

Monoclinous (Monoclinic) 

Refers to plants that have perfect flowers, i. e., stamens 
and pistil in the same flower, e. g., a rose flower, cf. Di- 


A vascular plant in the subclass Monocotyledoneae, class 
Angiospermae (flowering plants), e. g., grasses, orchids, cf. 


(1) Refers to a plant with some flowers containing only 
stamens and other flowers with only one or more pistils on 
the same plant, e. g., corn. cf. Dioecious. (2) A unisexual 

animal or plant, cf. Hermaphrodite. 


The mating of an animal with only one member of the 
opposite sex. cf. Polygamy. 


The mating of a male with only one female, cf. Poly- 


A cross or Hybrid resulting from the mating of parents 
differing in only one character, cf. Dihybrid. 

Monolith (Soil) 

A sample of a vertical section of a soil profile a few inches 
thick, removed from the soil with as little disturbance as 
possible, cf. Profile (soil). 


Refers to an organism that subsists on a few or only one 


kind of food, e. g. many caterpillars, cf. Steno-, Euroky. 


See Haploid. 


Refers to a single area such as in the restricted area of 
distribution of a species. 


An animal in the primitive order Monotremata, egg- 
laying mammals, restricted to the Australian faunal region, 
e. g., platypus. 


A wind system that reverses its direction with the season, 
mostly in southeast Asia. 

Monsoon Forest 

A tropical forest of deciduous trees in regions where sea- 
sons of heavy rainfall alternate with long droughts. 


Refers to mountains. 

Moor (Moorland) 

Primarily high-lying, unenclosed land occupied by 
heather and other ericaceous dwarf shrubs, including boggy 
areas, cf. Bog, Heath, Marsh, Swamp. 


A layer of Humus material, usually compacted or matted 
or both lying on the mineral soil. cf. H-layer. 


The accumulation of rock material by a glacier, occurs 
in various topographic forms such as ridges or more level 
areas according to the manner of formation. Various kinds 
are lateral, terminal, medial, and ground moraines. 



The general behavioural attributes of motile organisms, 
or groups of animals possessing particular ecological charac- 


The origin and development of the form and structure 
of an organism or one of its parts. 


The study of the form, structure, and development of 

Morphology (Soil) 

The constitution of the soil including texture, structure, 
and other properties. 


(1) A pattern of vegetation in which two or more kinds 
of communities are interspersed in patches, e. g., clumps of 
shrubs with grassland between. (2) A symptom of some kinds 
of virus disease. 


(1) A plant in the class Musci, phylum Bryophyta. (2) 
A Bog. 


An organic soil consisting of fairly well decomposed un- 
recognizable organic material that is finely divided, dark in 
color, and with a relatively large content of mineral matter. 


A natural or artificial layer of plant residue or other 
material such as sand or paper on the soil surface, cf. Dust 

Mulch Tillage 

Working of the soil so that plant residues are left on 
the surface. 



A scrub thicket consisting mostly of Acacia. 


A layer of Humus that is granular in structure, more or 
less friable, slightly or not at all matted, and with a gradual 
transition to the mineral soil below, cf. M or. 


Refers to an animal that produces more than one young 
at birth, cf. Uniparous. 

Multiple Use 

The policy of using a resource in several ways such as the 
use of forests for the production of timber, forage, water 
supplies, and game animals, and also for recreation. 


Refers to an organism that has several generations dur- 
ing a single season, cf. Univoltine. 


A Bog in the northern part of North America charac- 
terized by an abundance usually of Sphagnum moss and a 
greater or lesser abundance of shrubs and low trees such as 
black spruce. 


An influence that induces Mutation (q. v.) in organisms, 
e. g., Ionizing radiation. 


An organism, characteristic, or gene resulting from Mu- 


A sudden, inheritable variation in an organism resulting 
from changes in a Gene, or in alterations of the structure 
or number of Chromosomes. 



The kind of interspecies relationship, Coaction, or Sym- 
biosis that is obligatory and beneficial to the two or more 
participating organisms, e. g. a fungus and an alga in a 


The relationship where mutual benefit or dependence 
occurs because of the proximity of organisms to one another. 


The mass of Hyphae (q. v.) of a fungus, e. g., bread mold. 


Refers to an organism that eats fungi, e. g., a Collem- 
bolon that eats Hyphae. 


See Myxomycete. 


The branch of botany that deals with fungi. 


The symbiotic relationship of a fungus with the roots of 
certain plants, cf. Mutualism, Endotrophic, Ectotrophic. 


The association of a fungus with a Rhizome. 


The association of a fungus with a Thallus. 


Refers to a plant with Mycorrhiza. 


An animal in the group Myriapoda comprising classes 
Chilopoda (centipedes) and Diplopoda (millipedes), phylum 



Structures on plants in which ants or termites live. 


Refers to an organism that lives in ant or termite gal- 


Refers to plants that are inhabited by ants or termites. 
cf. Trophobiosis. 


Refers to plants that repel ants or termites. 


A plant that has structures adapted for the shelter of ants 
or termites and usually also has extrafloral nectaries or 
glands producing nutritious substances, e. g. Acacia spp. 


A slime mold. An organism possessing both animal and 
plant characteristics, classified in the phylum Myxomyco- 
phyta in the Fungi, syn. Mycetozoa. 




The dwarfed appearance of plants, as at tree-line in 


A subdivision of the Phanerophytes (q.v.) in Raunkiaer*s 
life-form classification, comprising shrubs 0.25 to 2 meters in 


See Leaf-size classes. 


Very minute Plankton (q. v.), those that pass through 
meshes of a No. 20 silk bolting cloth (0.03 to 0.04 mm.). 

Nastic Movement 

A response in plants caused by a diffuse stimulus (not 
received from a definite direction) or when the response to 
a diffuse or lateral stimulus is determined exclusively by the 
irritable organ, e. g., drooping of the leaves of Mimosa 
pudica when it is touched, cf. Tropism. 



The production of offspring by organisms. 


Refers to the swimming capacity of an organism. 

Natural Area 

An area of land in which organisms and geological proc- 
esses are undisturbed by man, with as few controls as pos- 
sible, cf. Primitive area. 

Natural Selection 

The agent of evolutionary change by which the organisms 
possessing certain characteristics in a given environment give 
rise to more offspring than those lacking such characteristics. 
cf. Drift, genetic; Mutation. 

Nature Reserve 

See Natural area. 

Nature Sanctuary 

See Natural area. 

Neap Tides 

The lowest tides during a month, occurring about the 
time of the moon's first and last quarters. 


One of the faunal regions of the earth, in the realm 
Megagea, includes North America except the tropical part 
of Mexico. 


The death of an organism or one of its parts. 


The sweet liquid secreted by special glands in flowers or 
in other parts of plants, attractive to insects, cf. Nectary. 


Refers to a flower or plant that produces nectar. 



A gland in a flower or on a vegetative organ that pro- 
duces nectar. 


The strong-swimming animals in water, e. g., fish. cf. 
Benthos, Plankton. 


An animal in the class Nematoda, phylum Nemathel- 
minthes, e. g., hookworm, eelworm in potatoes. 


The doctrine of modern evolution that combines Gen- 
etics with Natural selection (q. v.). 


The faunal realm, containing only one region, the Neo- 
tropical which includes South and Central America and the 
tropical parts of Mexico, cf. Megagea, Notogea. 


The theory of evolution that includes modern-day modi- 
fications of the doctrines of Lamarckism (q. v.). 


The cultural stage, beginning about ten thousand years 
ago, in human history, following the Paleolithic, during 
which cultivation of plants and domestication of animals 
were started. 


An abnormal increase in the number of cells in some 
part of an organism, often malignant. 


The occurrence of larval or other juvenile characters in 
the adult stage of an organism, or the presence of an adult 
character in the larval stage, e. g., larval form of the adult 


female glowworm, cf. Paligenesis, Caenogenesis, Paedo- 


See Neogea. 


An instrument for measuring the percentage of sky that 
is overcast. 


An instrument for measuring the direction and speed of 
the movement of clouds. 


Refers to the portion of the sea lying above the conti- 
nental shelf, usually to a depth of 200 meters, cf. Oceanic 
province, Pelagic, Littoral, Sub littoral. 

Nested Quadrats 

An arrangement of placing Quadrats in one area so that 
the size of the area sampled becomes progressively larger, 
to determine the proper size of quadrat to use for the par- 
ticular kind of vegetation. 

Net-Assimilation Rate 

The rate of increase in dry weight of the whole plant in 
relation to the unit leaf-area or unit leaf-rate. 


Refers to the nervous system or to a nerve. 


The organisms in a collective sense that are associated 
with or dependent upon the surface film of water, e. g., 
mosquito larvae. 


The occurrence of two or more populations in an area 
and neither influences the other. 


Granular, compacted snow at the head of a glacier, or 
similar snow elsewhere, syn. Firn. 


(1) Ecological niche: the role of an organism in the en- 
vironment, its activities and relationships to the biotic and 
abiotic environment. (2) Habitat niche: the specific part 
or smallest unit of a Habitat occupied by an organism, cf. 


Refers to young, undeveloped birds that remain in the 
nest for a time after hatching. 


Refers to young, undeveloped birds that leave the nest 
soon after hatching. 


The oxidation of ammonia and ammonium compounds 
to nitrites and then to nitrates by certain bacteria, cf. Nitro- 
gen cycle. 

Nitrogen Cycle 

The circulation of nitrogen, chiefly by means of organ- 
isms from the inorganic nitrogen in the atmosphere to ni- 
trates, into proteins and protoplasm in plants and animals, 
to ammonia, and return to nitrites and nitrates, cf. Nitrogen 
fixation, Nitrification. 

Nitrogen Fixation 

The assimilation of free nitrogen of the atmosphere 
by microorganisms in the soil or by bacteria in the nodules 
of certain plants, especially legumes, into organic nitro- 
genous compounds. 


Refers to plants that grow well in soil that is rich in 
nitrogen, e. g., many barnyard weeds. 



A kind of erosion caused by the action of snow, e. g. 


Refers to night time. cf. Crepuscular, Diel, Diurnal. 


A structure formed on the roots of most legumes and a 
few other species containing bacteria that carry on Nitrogen 


An abstract unit of vegetation such as Association, Socia- 
tion, and Alliance; corresponds to Taxon in Systematic*. 


A member of a group, especially of primitive people, who 
change their dwelling place frequently. 

Nomina Conservanda 

Names of organisms whose usage is maintained by agree- 
ment of systematists although the names may be contrary to 
the rules of nomenclature. 

Non-available Water 

The amount of water in the soil when a plant wilts 
permanently, cf. Wilting. 

Non-reactive Factor 

An environmental factor such as weather conditions 
which are not influenced by the density of individuals in a 
population, but may produce increasingly adverse effects 
with increasing density, cf. Density-independent factor, Den- 
sity-dependent factor. 

Normal Dispersion, Normal Distribution 

The distribution in an area of individuals of a popula- 
tion that is at random. 


Normal Erosion 

The Erosion that occurs on land under natural environ- 
mental conditions not disturbed by human activities, cf. 
Accelerated erosion. 

Normal Spectrum 

See Biological spectrum. 

Norther (Norte in Central America) 

A northerly wind, especially a strong one, that begins 
suddenly during the colder half of the year in the region 
from Texas southward, including the Gulf of Mexico and 
the western Caribbean. 


One of the three continental fauna! realms. It includes 
the Australian region (q. v.). cf. Megagea, Neogea. 


Refers to nut-bearing plants. 


A body of land, such as a mountain, projecting at some 
time above a mass of ice and snow, or above a glacier. 

Nurse Crop 

See Companion crop. 


A circular or spiral movement of the growing portions 
of plants such as stems or tendrils. 

Nutrient (Plant) 

Any substance absorbed by a plant that is used in its 


The movement of a plant organ in response to alterna- 
tion of night and day as in clover leaflets. 



See Nyctinasty. 


A stage in the Metamorphosis of certain insects between 
the larval and adult forms. 


Obligate Parasite 

A Parasite that cannot attain complete development inde- 
pendent of its Host. 

Oceanic Province 

The portion of the ocean seaward from the Continental 
shelf, having a depth greater than 200 meters, cf. Neritic. 


The science dealing with all aspects of the ocean; physi- 
cal conditions, plant and animal life, etc.; sometimes re- 
stricted to the study of physical conditions only. 


See Ecology. 


See Esophagous. 

Oestrus (Estroys) cycle 

The period in mature females in many kinds of mam- 
mals when the desire for mating occurs; it varies in length, 
is controlled by hormones, and is often accompanied by 
bodily changes. 



A short, basal stem by which some plants propagate. 


Refers to the production or presence of oil in a plant 
organ, e. g., olive fruit. 


The geological epoch near the middle of the Tertiary 
period in the Cenozoic era which began about 39 million 
years ago and lasted for about 11 million years. 


Refers to an aquatic habitat that is high in content 
of oxygen, low in dissolved organic matter, and with very 
little decomposition of organic substances that are present, 
cf. Catarobic, Polysaprobic, Mesosaprobic. 


Refers to ponds or lakes that are low in content of basic 
nutritive substances for plants, lacking a distinct stratifica- 
tion of dissolved oxygen in summer or winter, cf. Eutrophic. 


Refers to plants that endure much rain, with leaves that 
are easily wetted. 


Refers to plants that do not endure much rain, with 
unwettable leaves. 


Refers to an animal that eats both plant and animal food, 
cf. Carnivorous, Herbivorous. 


A gradation in phenotypic characteristics such as color or 
form appearing at different times in the life cycle of an ani- 
mal, may be related to the Ecocline (q. v.). 



The development of an individual, or a part of it, from 
the Zygote to the adult, cf. Phytogeny. 


Sexual reproduction by means of eggs and sperms, cf. 

Open Community 

A community in which the plants are more or less scat- 
tered, in which invasion may readily occur. 

Open Pollination 

Pollination (q. v.) by wind, insects, etc., not directly by 

Open Range 

An extensive grazing area on which the movements of 
livestock are unrestricted. 

Open Woodland 

A parkland type of vegetation in which trees do not form 
an open canopy. 

Optimum (Conditions) 

The range of conditions which is most favorable for an 
organism, or for a certain function of an organism, cf. Eco- 
logical amplitude. 


In plant and animal Taxonomy, a group or Taxon of 
related families, e. g. Resales. In phytosociology, a group of 
similar Alliances. In classification of soils, the highest cate- 
gory comprising Zonal, Intrazonal, and Atonal soils. 


A geological period in the early pan of the Paleozoic 
era, which began about 425 million years ago and lasted 
about 65 million years. 



A distinct part of a plant or animal which carries on one 
or more particular functions, e. g., a leaf, wing of a bird. 


Any part of a cell of an organism. 

Organic Matter (In Soil) 

Materials derived from plants or animals, much of it in 
a more or less advanced stage of decomposition, cf. Humus. 

Organic Soil 

A soil composed mainly of organic matter on a volume 
basis; containing 20 per cent or more on weight basis, e. g., 
Muck, Peat. 

Organismic (Organismal) 

Refers to the concept that a group of organisms such as 
a community has qualities of a higher level of organization 
than the constituent organisms have individually; changes 
occurring in a community are related more to the qualities 
of the group than to those of the individual plants and 

Oriental Region 

One of the four continental faunal regions in the realm 
Megagea; it includes tropical Asia and the associated con- 
tinental islands. 


The division of zoology that deals with birds. 


Refers to flowers that are pollinated by birds such as the 


The process of mountain formation by changes in the 
earth's crust. 



Refers to mountains, or to relief characteristics of the 



The plant from which members of a Clone (q. v.) were 

derived, cf. Ramet. 


The trend in the evolution of organisms in a particular 
direction for a long time. cf. Genetic drift, Sewall Wright 


The random movements of an organism that decrease 
in rate from one part of an environmental gradient to an- 
other part, e. g., a meal worm moving from the moist part 
of a gradient and congregating in the drier part. cf. Klino- 
kinesis, Klinotaxis, Photokinesis. 


An insect in the order Orthoptera, e. g., cricket, grass- 


The trend in the evolution of organisms which is in a 
particular direction under the influence of selection, cf. 
Orthogenesis, Natural selection. 


A strongly compacted, indurated layer (Pan) of soil in 
which the particles are cemented together with iron and or- 
ganic matter. 


The adjustment in the osmotic concentration of solutes 
in fluids in organisms to environmental conditions, e. g., 
when eels migrate from salt to fresh water. 



The diffusion of a solvent (especially water) across a dif- 
ferentially permeable membrane separating two solutions or 
separating a solution and a solvent. 

Osmotic Concentration 

The concentration of salts in a solution. 

Osmotic Pressure (of a Solution) 

The rating or index of potential maximum pressure 
which can develop in a given solution when it is exposed to 


The study of the development and nature of bones in 
vertebrate animals. 


A valley that contains water in rainy seasons (Arabian). 


The occurrence of an organism in large numbers or in 
sufficient number to cause serious damage over an appreci- 
able area. 


The mating of individuals that are not closely related, 
cf. Inbreeding. 


A geological stratum that is exposed on the surface of 
the earth. 

Outwash, Glacial 

Material carried by streams of melt water from a glacier 
and deposited in the form of plains, deltas, and Valley 



(1) The portion of the Pistil or Carpel of a flower that 
contains one or more ovules (q. v.). (2) The organ in female 
animals that produces the egg or ovum. 


See Contagious dispersion. 


Grazing so intensively that it reduces the capacity of 
plants to continue production of forage and also causes de- 
terioration by damaging plants or soil or both. cf. Under- 


A population-density in excess of the capacity of the en- 
vironmental resources to supply the requirements of the in- 
dividual organisms, usually accompanied by a high mortality 
rate because of inadequate nutrition, insufficient shelter, and 
increased predation, disease, or parasitism, cf. Malthusian. 


(1) Refers to stands of trees in which the large number 
may retard growth. (2) A population of animals in which the 
number is in excess of the resources of the habitat to provide 
food and shelter, cf. Fully stocked. 


The placing of more livestock on a range than its re- 
sources can support through the grazing season without 


The layer of trees in a forest that forms the Canopy, cf. 


The spring and fall circulation in lakes induced by the 


wind when thermally different strata become mixed, cf. 


Refers to an animal that lays eggs in which embryos 
show little or no development, e. g., most fishes, cf. Vivi- 
parous, Ovoviparous. 


A specialized structure in insects for depositing eggs. 


Refers to an animal that keeps ova or eggs within the 
body until they are ready to hatch, requiring internal fer- 
tilization, as in birds, cf. Oviparous, Viviparous. 


The structure within the Ovary of a flower that after 
Fertilization of the egg within it develops into a seed. 


A female Gamete (q. v.) or egg. 

Oxbow Lake 

A more or less semicircular lake or pond formed when 
a meander of a river is separated from the main stream. 

Oxidation-reduction Potential 

The potential of a given material, in comparison with 
other materials, to release electrons (oxidation), or to receive 
electrons (reduction); symbolized by E h . syn. Redox poten- 


See Acidophilous. 


See Acidophilous. 



See Basophilous. 


The stages of a successional series that began in water or 
soil that is appreciably acid. cf. Succession, Hydrosere. 



A small Enclosure in a grassland. 


Reproduction occurring in larval or other young stages 
of an animal. cf. Neoteny. 


The evolutionary process in which a character of an im- 
mature stage of an organism appears in the adult stage, cf. 


The acceptability of food by domestic or wild animals as 
shown by their preferences; in range management often used 
for utilization of forage, especially the proper degree of use 
under good management, cf. Proper use factor. 


One of the four continental faunal regions in the realm 
Megagea (q. v.). It includes Eurasia north of the Tropics and 
the northernmost part of Africa. 


PQ looDoto ny 

The study of fossil plants, cf. Paleontology, Paleozoology. 


The earliest geological epoch in the Tertiary period of 
the Cenozoic era, which began about 75 million years ago 
and lasted for about 17 million years. 


The study of Ecology of former geological periods. 

Paleogenic (Palaeogenic) 

See Paleozoic. 


Refers to the period of human history characterized by 
food-gathering, fishing, and hunting, without cultivation; 
and by the use of stone implements. 


The study of the life of former geological epochs by 
means of fossils, cf. Paleobotany, Paleozoology. 


One of the major geological eras, preceding the Mesozoic, 
which began about 505 million years ago and ended about 
205 million years ago. 


The study of animal fossils, cf. Paleontology, Paleobotany. 


The appearance during the development of an organism 
of stages or structures which occurred in earlier forms dur- 
ing its evolution, cf. Caenogenesis, Recapitulation. 


Refers to marshes. 



The study of Pollen and other microfossils, especially 
from deposits in lakes and other bodies of water, to deter- 
mine the age of strata and the kind of plant life existing 
in former periods, cf. Paleobotany. 


Extensive grasslands in South America, particularly in 
Argentina, large portions of which are now cultivated, cf. 
Prairie, Steppe, Veld. 


A suddenly arising, violent, southwesterly wind on the 
Pampas of South America, most prevalent from July to Sep- 


(1) A layer in the soil that is strongly compacted and 
indurated, or with a very large clay content, cf. Ortstein. 
(2) A shallow, basin-like depression without vegetation or 
outlet for drainage. 


According to F. E. Clements two or more related cli- 
maxes that have the same life-form, common genera of dom- 
inants, and the same general climatic factors, cf. Formation. 


Refers to something which has a wide occurrence such as 
a disease. 


The wide interbreeding of individuals of a population, 
where each individual has the potential capacity of mating 
with any other individual. 


The feeding of swine in woods, or the food such as 


acorns that is secured. A term used in England especially. 


A fresh-water or brackish marsh in Argentina. 


A drafting instrument used in copying maps or charts, 
adapted for charting the location and area of plants in a 
Quadrat (q. v.). 


A violent northeasterly wind of the Pacific coast of Cen- 
tral America. 


Refers to the butterfly-like flower of many species in the 
pea family, Leguminosae. 


An alpine type of vegetation, or the sparsely vegetated 
land, in high mountains in the Andes and in northern South 
America, cf. Tundra. 


A type of mixed vegetation composed of species differing 
in height, which occurs on areas following the repeated cut- 
ting of forest in southeast Asia. 


The interaction or Coaction in which one or more or- 
ganisms, the Parasite, benefits while feeding upon, securing 
shelter, or otherwise injuring one or more other organisms, 
the Host; often the term is restricted to nutritive relations, 
cf. Symbiosis, Saprophyte. 


Refers to movements of plants such as tropic or nastic 
movements induced by an external stimulus, cf. Tropism, 
Nastic movement. 


Parch Blight 

The kind of injury to plants, especially evergreens that 
have been exposed to strong, drying winds in winter. 


(1) A common tissue in the soft parts of plants consisting 
of thin-walled, cubical cells, e. g. pith, fleshy fruits. (2) The 
loose tissue that forms a large part of the body of flat-worms. 

Parent Material (Soil) 

The C horizon (q. v.) of the soil. 

Parent Rock (Soil) 

The rock from which the parent material of the soil has 
been formed. 


The type of landscape in which trees occur in clumps in 


The development of the fruit of a plant without Fertili- 
zation, e. g., as in the banana. 


The development of the egg of an organism into an em- 
bryo without Fertilization, cf. Apomixis. 


Herbage of an area taken by an animal when grazing, the 
yield of a Pasture. 


An area of vegetation used for grazing, sometimes re- 
stricted to areas of cultivated land which, have been seeded 
and then used for grazing, cf. Range. 


An animal that spends its normal life in the debris of the 
forest floor stratum. 



(1) A montane grassy slope (Ceylon). (2) A grassy slope 
with a moderate supply of moisture, resembling a Savanna. 


An organism or virus that causes disease. 


The study of diseases. 


An animal that spends a regular part of its normal life 
outside of the forest floor but lives transiently in it. 


An animal that occurs accidentally in the litter of the 
forest floor. 


The arrangement formed by the occurrence of indivi- 
duals or groups of organisms in an area, such as Contagious 
dispersion, Hypodispersion, and Normal dispersion (q. v.). 


An organic soil consisting of partially decomposed or- 
ganic remains which can be identified as to the kind of con- 
stituent plants. It accumulates in water or under wet condi- 
tions, cf. Muck. 


The dominance of one bird over another in a flock, ap- 
plied also to other animals, cf. Social dominance. 


The order of dominance of some birds over others in a 
flock, applied also to other animals. 


The dominance of one bird over all the others iri a flock. 



An individual soil aggregate occurring naturally. 


The kind of soil in which alumina and iron oxides move 
downward in the soil profile and in which no accumulation 
of calcium carbonate occurs, cf. Pedocal, Laterite. 


A record of the ancestry of an individual. 


A gradual slope covered with scattered rock adjacent to a 
mountain in semi-arid and arid regions. 


A type of soil in which a layer of accumulated carbonates 
occurs, cf. Pedalfer, Laterite. 


Refers to effects caused by soil factors. 


The science dealing with soils. 


A Community dependent on the bottom in lakes, cf. 


Refers to the open water of the ocean, lacking associa- 
tion with the shore or the bottom, cf. Abyssal, Neritic, Ben- 
thic, Littoral. 


A land surface worn down by erosion to almost Base 
level so that most of it appears as a plain. 


An Antibiotic (q. v.) produced by the mold Penicillin 



A geologic period in the latter part of the Paleozoic era 
which began about 255 million years ago and lasted for about 
25 million years. 

Perched Water 

The body of free ground water in a zone of saturation, 
separated from an underlying body of ground water by an 
unsaturated layer of material. 


The downward movement of water in the soil, especially 
in saturated or nearly saturated soil, cf . Infiltration. 


The continuance of life in an organism from year to year 
as in a Rhizome or seed. 


A plant that lives for three or more years, cf. Annual, 



Refers to flowers containing one or more stamens and 


The flower parts surrounding the stamens and petals; the 
petals and/or sepals of a flower; much reduced in some 


The repeated occurrence of events at fairly frequent and 
regular intervals, cf. Aspection, Phenology. 


The assemblage of organisms attached to surfaces sub- 
merged in water, above the bottom, cf. Benthos, Plankton. 



Permanently frozen ground in arctic and subarctic re- 

Permanent Pasture 

Grazing land that remains under grazing use for many 
years, cf. Rotation Grazing, Range. 

Permanent Quadrat 

A marked sample area or quadrat (q. v.) in which the 
vegetation is recorded over a period of many years. 

Permanent Wilting Percentage 

The quantity o water in the soil on a dry weight basis 
when plants growing in it have reached the condition of 
permanent Wilting. 


(1) The property or condition of the soil that relates to 
the passage of water or air through it. cf. Percolation. (2) 
The rate of diffusion of molecules of a substance through a 
membrane, cf. Osmosis. 


An animal in a terrestrial community which has great 
motility, e. g., a bird. 


The latest geological period in the Paleozoic era which 
began about 230 million years ago and lasted for about 25 
million years. 


The conditions of the environment outside of the Opti- 
mum which an organism can endure, cf. Ecological ampli- 


An agent or substance that destroys pests, e. g., a fungi- 
cide or insecticide. 



One of the parts of the Corolla of a flower. 


The stalk of a leaf. 


Refers to the Rocky Mountains. 


The formation of fossils by the replacement of organic 
substances in dead organisms by minerals. 


A measure of the energy by which a soil holds water; 
soil dried at 100-110 C has a pF of 7.0, the tension de- 
creases as the water content increases. 


A measure of the acidity or alkalinity of a solution, or 
the concentration of H or OH ions, ranging from to 14. 
Values above 7 are alkaline, below 7 are acid. cf. Reaction 


See Bacteriophage. 


A cell that engulfs bacteria or other particles, e. g., white 
corpuscles in the blood. 


The engulfing of particles by a Phagocyte. 


See Spermatophytes. 


One of Raunkiaer*s life-form classes (q. v.) in which the 
buds or other perennating parts are more than 25 cm. above 
the ground, especially trees and shrubs. 



The study of the periodic phenomena of animal and 
plant life and their relations to the weather and climate, 
e. g. the time of flowering in plants, cf. Periodicity, Aspec- 


The expression of the characteristics of an organism as 
determined by the interaction of its genie constitution and 
the environment, cf. Genotype, Ecad. 


The tissue in plants that conducts foods such as sugar 
which is performed especially by the sieve tubes. 


The transport of one organism by another, e. g., mites 
carried by insects. 


See Bioluminescence. 


See Nyctinasty. 

Photic Zone 

The upper portion of bodies of water into which light 
penetrates in sufficient intensity to influence plants or ani- 
mals, cf. Aphotic zone. 


Refers to the capacity of a substance to produce light, 
cf. Bioluminescence. 


The undirected locomotion of many lower organisms in 
response to light, accomplished by their capacity to influ- 
ence the speed of their movements, cf. Phototaxis, Ortho- 



An instrument for measuring the intensity of light. 


One of the particles in a beam of radiant energy, cf. 


The response of an organism or organ to a diffuse light 
stimulus, e. g., closing of oxalis flowers in the evening. 


The duration of light during a 24-hour period. 

Photoperiodism (Photoperiodicity) 

The response of plants and animals to the relative dura- 
tion of light and darkness, e. g. a chrysanthemum blooming 
under short days and long nights. 


The synthesis of carbohydrates from carbon dioxide and 
water by Chlorophyll using light as energy with oxygen as a 


The directed movement of a motile organism in response 
to a light stimulus, cf. Photokinesis. 


Refers to organisms that can obtain energy from sunlight, 
cf. Autotrophic, Heterotrophic, Chemotrophic. 


The growing or turning of an organ of a plant when un- 
equally illuminated, toward the light of greater intensity. 


The process of opening or closing holes by animals, e. g., 
an ant closing its entrance to the nest in a plant stem. 



A plant that absorbs its water from a permanent supply 
in the ground, e. g., willows along a stream. 


See Algology. 


A phylogenetic group of closely related species. 


See Cladophyll. 


The evolutionary development and relationships of a 
group of organisms such as rodents or species of rose. cf. 


One of the major subdivisions used in classifying plants 
and animals, e. g., Tracheophyta (vascular plants), Arthro- 
poda (arthropods). 

Physiognomic Dominance 

Dominance (ecologic) (q. v.) caused by the similarity of 
a number of species in a certain life-form rather than be- 
cause of greater cover, number, or size of one or a few 
species, e. g., a weed patch consisting of many species of 
annual weeds similar in form. 


The appearance of vegetation as determined by the life- 
form of the dominant plants, e. g., a grassland, pine forest. 

Physiographic Climax 

See Climax. 


The branch of physical science that deals with the physi- 
cal features of the earth, cf. Geomorphology. 


Physiological Drought 

The conditions that obtain when a plant wilts or suffers 
from insufficient water although the habitat contains ample 
water, cf. Aridity, Cold desert. 

Physiological Form 

See Biological race. 

Physiological Isolation 

The condition of organisms that have become isolated 
because of their physiological requirements rather than be- 
cause of other kinds of Barriers, cf. Isolation. 


The branch of biology that deals with the functions and 
processes carried on by plants and animals. 


The condition in some insects in which the body be- 
comes swollen, soft, and white, as in some beetles. 


A chemical substance that exerts a differential killing 
effect within a crop, e. g., one variety but not the other 
varieties killed by DDT in a barley crop. 


The totality of plants in a stand of vegetation, the entire 
plant Community, cf. Biocoenosis. 


The term preferred by Gams in place of Plant sociology. 


See Plant geography. 


A polygonal diagram that expresses several kinds of com- 
munity characteristics such as numerical abundance, fre- 
quency index, size classes, and basal area on various axes for 
a certain species of tree in a forest. 



A plant such as the sunflower, used to measure environ- 
mental conditions. 


The study of plant diseases. 


See Herbivorous. 


The plants occurring in Plankton (q. v.), e. g. diatoms. 


See Plant sociology. 


An extensive set of rooms used for growing plants under 
controlled environmental conditions. 


A plant, animal, or community that first invades a bare 
area, e. g., willows on a newly formed sandbar. 


The growing of fish. 


See Carpel 


Refers to the pistil, e. g. pistillate flower. 


The making of shallow pits or depressions, especially in 
rangeland, with an offset disk or pitting machine, in order 
to retain rain water or snowmelt. 


The gland inside the skull of vertebrates which is of 


major importance in the secretion of Hormones, many of 
which control the activity of other Endocrine (q. v.) glands. 


A type of Climax (q. v.) vegetation which is the result of 
man's activity, a biotic climax, e. g., an apparently stable 
community caused by continued mowing or grazing, cf. Dis- 
climax, Proclimax, Sub climax, Plagiosere, Ser climax. 


A Sere (q. v.) deflected from its undisturbed course by the 
constant intervention of man in such activities as burning, 
grazing, and mowing, resulting in a Plagioclimax. 


An extensive tract of nearly level or gently undulating 
land that is usually occupied by grassland vegetation. 

Plane Table 

A surveying , instrument used for making a sketch-map 
of a small area. 


An instrument used to determine the area of a plane fig- 
ure or object such as a leaf by tracing the boundaries. 

Plankter (Plankt, Planktont) 

An individual organism in the Plankton (q. v.). 


The floating or weakly swimming animal and plant or- 
ganisms occurring at any depth in lakes, ponds, streams, or 
seas; often microscopic in size. 


An Intrazonal group of soils with eluviated surface hori- 
zons underlain by clay pans or fragipans, developed on nearly 
flat or gently sloping uplands in humid or subhumid cli- 
mates, cf. Eluviation. 


Plant Association 

See Association. 

Plant Community 

See Community. 

Plant Cover 

See Cover. 

Plant Formation 

See Formation. 

Plant Geography 

The science that deals with the geographic distribution 
of plants and the causes of their distribution and dispersal, 
syn. Phytogeography, Synchorology. 

Plant Nutrient 

The substances or elements absorbed by a plant and used 
in its metabolism, e. g., nitrates, phosphates, cf. Essential 

Plant Unit 

The part of a vegetatively propagating plant which is con- 
sidered as a unit in analyzing vegetation, e. g., each stalk of 
plant that has rhizomes. 


An animal that walks on the entire bottom of the feet, 
e. g., bear, man. 

Plant Sociology 

The study of plant communities, including their origin, 
composition, structure, characteristics, distribution, dy- 
namics, and classification, syn. Phytogeography. 


Gene-like, non-Mendelian carriers of hereditary charac- 
ters, located in the Cytoplasm. 



The mass of cytoplasm containing many nuclei that is 
enclosed by a single plasma membrane, occurring in Slime 
molds (q. v.). cf. Syncytium, Coenocyte. 


The shrinking of the Cytoplasm from the cell wall, 
caused by osmosis of water out of the cell. 


(1) The capacity of an organism to adapt itself to various 
environmental conditions. (2) The capacity of a soil to be 
changed in shape under applied stress and to retain the im- 
pressed shape after removal of the stress. 


A protoplasmic body in the Cytoplasm in cells of plants, 
e. g., Chloroplast, Leucoplast, Chromoplast. 


Undrained, flat, barren basins that are usually dry and 
often saline, in arid and semiarid regions. 


The geological epoch preceding the Recent in the Quat- 
ernary period of the Cenozoic era, which began about one 
million years ago and lasted for about one million years. 


Refers to an organism that has two or more forms in its 
life cycle, cf. Polymorphism. 


A one-layered community of plants that float on or 
within bodies of water, cf. Plankton. 


The latest geological epoch in the Tertiary period of the 


Cenozoic era which began about 12 million years ago and 
lasted for about 1 1 million years. 


Refers to the number of sets of Chromosomes in a cell, 
e. g., Diploid, Polyploid (q. v.). 


An area of land that is studied or used for experimental 
purposes, in which sample areas are often located. 


A compacted layer formed in the soil immediately below 
the depth of plowing, syn. Plowsole. 


The portion of the embryo of a seed, above the place of 
attachment of the cotyledons, consisting of the stem tip and 
a few embryonic leaves. 


Refers to rain. 


Vegetation that includes rain forest (Pluviisilvae) which 
is dominated by evergreen broad-leaved trees, and rain bush 


(1) A special structure on an aquatic or marsh plant that 
extends above the water making a direct connection of the 
tissues with the aerial environment. (2) Air sacs exposed to 
the aerial environment occurring in some aquatic insects. 


A bog in shallow, undrained depressions in savannas in 
the southeastern part of the United States. 

Podzol (Podsol) 

A Zonal group of soils having surface organic layers and 


thin, organic mineral horizons above gray, leached horizons 
upon illuvial, dark brown horizons; developed under coni- 
ferous or mixed forests or heath vegetation in cool-temperate, 
moist climates. 


Refers to soils that have part or all of the characteristics 
of Podzol. 


The process by which soils are depleted of bases, becom- 
ing more acid, and develop leached surface layers from which 
clay is removed, cf. Laterization, Calcification, Solonization. 


An animal that lacks capacity to control its body tempera- 
ture which is approximately that of the environment, e. g., 
a frog. 

Point-contact Method (Point-frame) 

A technique for determining the area of herbage cover by 
listing the number of times that various species are touched 
by the point of a rod or pin. Numerous contacts are used in 
each Stand or Plot. 

Poisson Distribution 

See Normal dispersion. 

Polar Front 

The boundary between the cold air of a polar region and 
the warmer air of lower latitudes, cf. Warm front. 


The property of an organism to respond differently in its 
various ends or in contrasting parts of its body to stimuli. 


An area of land reclaimed from the sea or from a lake by 
dams or dikes, especially in Holland. 



The Microspores which give rise to the male Gameto- 
phytes in seed plants, cf. Pollination. 

Pollen Analysis 

The identification and determination of abundance of 
pollen in soil deposits, particularly in peat. cf. Palynology. 

Pollen Profile 

A tabular or graphic expression of the occurrence of vari- 
ous kinds of pollen in deposits of peat or other materials at 
different depths. 

Pollen Spectrum 

The expression in percentage of the kinds of pollen in 
one sample of a Pollen analysis (q. v.). 

Pollen Tube 

The tubular growth, male Gametophyte containing the 
sperms, produced by a pollen grain when it germinates on 
the stigma and extends into the style of the pistil of a flower. 


The transportation of pollen by wind, insects, or other 
agent from an anther to a stigma in flowering plants; usually 
by wind from a pollen-bearing cone to the Ovw/e-bearing 
cone in conifers. 


Contamination of a habitat with substances which make 
it less favorable for organisms. 


A plant form resembling a cushion, consisting of closely 
packed stems, dead leaves, and often roots, e. g., many saxi- 
frages, mosses. 


The mating of a single female animal with several males, 
cf. Monogynous. 



The concept that several Climaxes (q. v.) constitute the 
vegetation in an area as the result of Succession (q. v.). 


In animals the development of more than one embryo 
from a fertilized egg; in plants the development of more than 
one embryo within a single Ovule of a plant. 


The mating of one male animal with several females, 
cf. Monogamy, Polygyny. 

Polygonal Soil 

The surface configuration of soil characterized by poly- 
gons, common in arctic regions. 


Mating by Polyandry or Polygamy (q. v.). 


The presence of several distinct forms in a species, 
particularly within a certain habitat or population, cf. 


An organism or a cell that contains more than the 
Diploid number of Chromosomes per cell. cf. Haploid, 


Refers to an aquatic habitat that is characterized by con- 
siderable decomposition of organic material and low con- 
centration or absence of free oxygen, cf. Catarobic, Mesosa- 
probic, Oligosaprobic. 


Refers to a species that occurs in more than one area, 
especially to Discontinuities (q. v.). 



Refers to a species that occurs in various forms in differ- 
ent parts of its range. 


A multicarpellate fruit in which the fleshy part surround- 
ing the ovary is formed from the receptacle, e.g., apple fruit. 


A group of interacting individuals of the same species or 
smaller Taxa in a common spatial arrangement. 

Population Cycle 

The recurrent changes in the size of a population from 
low to high numbers and the return to low numbers as in 
the cycle of the snowshoe hare. 

Population Density 

The number of individuals in a population per unit area. 

Population Dynamics 

The totality of changes that take place during the life 
of a population. 

Population Pressure 

The combined forces of the individuals of a population 
upon the organisms in a community and upon the environ- 
ment, cf. Biotic pressure. 

Pore Space 

The fraction of the volume of soil or rock that is not 
occupied by solid particles. 


The state of matter which contains Pore spaces. 


The increase in Adaptation in a Preadapted organism 
after its invasion into a given environment. 



A Climax community (q. v.) that requires more mesic 
conditions than obtain generally in the region where it is 
present, often considered a remnant of a former widespread 
Climatic climax (q. v.). 

Potential, Biotic 

See Biotic potential. 


A hole formed in rock by the grinding action of a stone 
kept in motion by a stream. 


An instrument used to measure the absorption of water 
by plants. 


Grassland vegetation, particularly the extensive tract of 
nearly level or rolling land in North America occupied by 
tall grasses. 

Prairie Soils 

A Zonal group of soils with dark surface horizons grad- 
ing through brown to lighter colored parent material at two 
to five feet, formed under tall grasses in a temperate, humid 
climate, cf. Chernozem. 


The possession by an organism of characteristics that 
enable it to survive when exposed to new ("prospective") 
conditions, e.g., the possession of a disease-resistant gene in 
an organism not yet exposed to the disease, cf. Postadaptation. 

Preboreal Period 

See Boreal period. 


The geological time preceding the Cambrian period, the 
oldest period of the Paleozoic era. 



(1) A general term for all forms of falling moisture in- 
cluding rain, snow, hail, sleet, or modifications of them. 
(2) The quantity of water that is precipitated. (3) The process 
in which water as a liquid is discharged from the atmosphere 
upon land or water. 

Precipitation-effectiveness Ratio 

The total amount of precipitation for a certain period of 
time divided by the total amount of evaporation, both in 
liquid form. 

Precipitation Rose 

A radial diagram expressing the amounts of precipitation 
by months or other intervals of time. 


A Climax community (q. v.) that occurs usually in more 
Xeric conditions than obtain generally in the region where 
it is present, often considered a stage in succession preceding 
the full development of a climax, cf. Postclimax. 


Refers to young animals that do not need parental care 
after birth or hatching, cf. Altricial. 


The behaviour of animals, Predators, in killing other 
animals, Prey. 


An animal that attacks other animals, Prey, e.g., a fox 
that kills mice or other prey. 


Refers to organisms that are of outstanding abundance 
or conspicuous importance in a community. 


The preferred or "selected" conditions of a motile organ- 


ism when exposed to a gradient of one or more environ- 
mental conditions, cf. Optimum, Minimum, Pessimum, 

Preferential Species 

Species in Class 3 of Braun-Blanquet's classification of 
Fidelity (q. v.); species occurring more or less abundantly, 
but predominantly or with greater vitality, in a certain 

Premature Grazing 

The grazing of vegetation before the most important 
forage species have grown sufficiently, or before the soil has 
become dry and firm enough, to prevent cumulative injury 
to the range, cf. Range readiness. 

Prescribed Burning 

The use of fire under control to improve growth condi- 
tions in vegetation. 


The degree of occurrence of a species in Stands of a 
Community-type, cf. Constancy. 

Pressure, Biotic 

See Biotic pressure. 


Refers to early spring, cf . Aspcction. 


An animal that is attacked and killed by another, Pre- 
dator (q. v.), e.g., a ground squirrel killed by the coyote as a 

Primary Succession 

Succession (q. v.) beginning on a bare area such as a lava 
flow, not previously occupied by plants or animals, cf. 
Secondary succession. 



An animal in the order Primates which includes lemurs, 
monkeys, apes, man, and others, in the class Mammalia. 


Refers to vegetation, geological features, and other 
natural phenomena, in original condition, before any modi- 
fication has been made through the influence of modern 
man, e.g., a primeval forest. 


Refers to an organism, organ, or behaviour that is char- 
acteristic of an early stage in evolution, not specialized or 
advanced in evolution. 

Primitive Area 

An area in which conveniences for transportation and 
living are kept simple and not modernized, cf. Natural area. 


A part of an organism where growth is initiated. 


See Primary succession. 


According to F. E. Clements any community that re- 
sembles a climax in permanence or extent such as a Post- 
climax and Preclimax (q. v.). cf. Subclimax, Plagioclimax, 


An organism that can utilize radiant energy to synthesize 
organic substances from inorganic materials, cf. Consumer 


(1) The total quantity of organic material produced 
within a given period by organisms, or the energy that this 


represents such as gram-calories per square centimeter per 
year. (2) The innate capacity of an environment to produce 
plant and animal life. (3) The capacity of a soil to produce 
a certain kind of crop under a defined set of management 

Profile (Soil) 

A vertical section of soil through all its horizons into 
the parent material, cf. A horizon. 

Profundal (Zone) 

The body of deep water and the bottom of lakes below 
the depth of effective penetration of light, cf. Abyssal. 


The rapid development of new growth such as the pro- 
duction of new parts from buds, offsets, and other organs. 


Refers to the ready vegetative reproduction by means of 
organs such as buds and offsets; the development of leafy 
shoots from a flower or flower head or other organ. 


To increase the number of plants vegetatively by bulbs, 
conns, cuttings, or other plant parts. 


Any part of a plant that when it is separated from a plant 
will give rise to a new individual, cf. Diaspore, Disseminule. 

Proper Stocking 

The number of individual livestock in a grazing unit that 
utilizes the herbage without permanent deterioration of the 
vegetation or the soil. cf. Overstocking. 

Proper Use Factor 

The maximum percentage of the total amount of annual 
forage production of a species in a given area within easy 


reach of the livestock that may be grazed without permanent 
deterioration of the plants of this species or associated 
species nor of the soil. cf. Overstocking. 


Refers to a flower that produces pollen before the stigma 
is receptive, e.g., fireweed; or to animals that produce sperms 
sooner than eggs are produced by the same animal, e.g., 
certain nematodes. cf. Protogynous. 

Protective Coloration 

The concept that coloration in animals benefits the 
individual by affording concealment from predators or from 
prey animals, cf. Mimicry. 


A nitrogenous organic compound of large molecular size 
and complex structure, formed from amino acids. 


The geological era preceding the Paleozoic which began 
about 2,000 million years ago and lasted for about 1,500 
million years. 


The vegetative structure of the Gametophyte (q. v.) gen- 
eration that is part of the life cycle of ferns and their allies, 
cf. Thallus. 


A group including all one-celled organisms such as one- 
celled algae, bacteria, and protozoans; suggested as a third 
kingdom of living organisms, the other two being plants 
and animals. 


An interaction between organisms that is mutually bene- 
ficial but not obligatory to those participating, not appli- 


cable to conscious cooperation of human beings, cf. Com- 
mensalism, Symbiosis. 


Refers to a flower that produces pollen when its stigma 
is no longer receptive to pollen, cf. Protandrous. 


The branched filament of the Gametophyte (q. v.) gen- 
eration that develops from a spore in mosses, and produces 
leafy branches. 


The living material in cells of animals and plants, usually 
differentiated into nucleus and cytoplasm. 


The organized protoplasmic contents of a cell, used par- 
ticularly in plants to distinguish the cell wall from the parts 


An animal, unicellular or non-cellular in the phylum 


The place of origin of seeds or other Propagules. 


The sandy shore of a lake. 


The assemblage of organisms that live in the water in 
the interstices between sand grains in the Psammolittoral 
(q. v.). 


A plant that grows in sandy soil. cf. Hydrophyte. 



All the stages of a successional series or Sere (q. v.) orig- 
inating in sandy soil. cf. Hydrosere. 


An instrument used to measure the Relative humidity of 
the atmosphere by means of the effect of temperature differ- 
ences of the wet and dry bulb thermometers, cf. Hygrometer. 


A Vascular plant in one of the subphyla of the phylum 
Tracheophyta, exclusive of the seed plants, e.g., fern, club- 
moss, horsetail. 

Public Domain 

Land for which the title was originally vested in the 
Government of the United States by virtue of its sovereignty. 
More than half of the original public domain has been 
granted to states, homesteaders, railroads, or has been sold. 
The remainder is set aside for national forests, national 
parks, national monuments, Indian reservations, grazing dis- 
tricts, and similar purposes. 

Puddled (Soil) 

Dense, massive soil artificially compacted when wet, hav- 
ing no regular structure. 


The process of destroying the structure of the soil during 
which the porosity and permeability are reduced. 


The sudden appearance of a great abundance of plant 


The cold, bleak portions of the high plateau region in 
the central part of the Andes in South America. 



The stage in the Metamorphosis of an insect between the 
larval and adult stages. 


The process during the Metamorphosis of an animal 
when the Pupa is formed. 

Pure Line 

A series of generations of individuals which orginated in 
a Homozygous ancestor. 


A grassland type of vegetation in the Plains of Hungary, 
cf. Steppe, Prairie. 

Pyramid of Numbers 

The concept of C. Elton that in most Food-chains the 
number of individuals decreases in each succeeding stage, 
large numbers of animals occur at the base, a few large ones 
at the top. 


An instrument for measuring solar radiation. 


Refers to fire. 


Qio Rule, Van't Hoff Rule 

The rate of response of a process in an organism is often 
doubled or more for each increase of 10C. of temperature 
within certain limits. 


A sampling area, originally square, most commonly one 
square meter, used for analyzing vegetation. A major quadrat 
is usually 10 meters square, cf. Plot, Permanent quadrat. 


An animal with four feet, e.g., cow. 


Soft, wet, boggy ground which quakes or yields underfoot, 
cf. Bog. 


A unit of energy that is emitted by a Photon (q. v.). 


The latest geologic period of the Cenozoic era which 
began about one million years ago, includes the Recent and 
Pleistocene epochs. 

Quotient of Similarity 

See Index of similarity. 


(1) Biology. A Population within a species that differs in 
one or more inherited characteristics from other populations 
but not sufficiently distinct to rate as a Taxon (q. v.). (2) A 
rapid movement of the tide through a narrow channel. 


The line where waves break in lakes, the places where 
wave action and undertow cause the greatest turmoil. 


The dose or unit of ionizing radiation absorbed by tissues 
of an organism, equal to 100 ergs of energy per gram. 


(1) The emission and transmission of energy from a 
source, e.g., Ionizing radiation (q. v.), solar radiation by 
electromagnetic waves such as light, x-rays, gamma-rays. (2) 
See Adaptive radiation. 


The lower end of the axis of the embryo in a seed and 
which develops into a root during germination. 



The spontaneous breakdown of certain atomic nuclei 
usually resulting in the emission of radiant energy in the 
form of Alpha or Beta particles, or Gamma rays. 


A representation of an object containing radioactive 
Isotopes (q. v.) such as a leaf on a photographic negative to 
show the distribution of the radioactive material. 

Radiocarbon Dating 

Determination of the age of organic remains such as 
long-buried wood by measuring its radioactivity caused by 
C 14 , which has a half-life of 5568 years and begins to break 
down upon the death of organisms. 


An Isotope (q. v.) that is unstable, disintegrates, and 
emits radiations, e.g., uranium-235 which emits alpha and 
gamma rays. 


An instrument that measures the intensity of solar Radia- 
tion, cf. Pyrheliometer. 


The sensitivity, or lack of tolerance of organisms to 
endure Ionizing radiation (q. v.). 


A free balloon with attached instruments and radio trans- 
mitter for securing measurement of temperature and atmos- 
pheric pressure. 


The total amount of Precipitation including rain, snow, 
hail, and other forms. 

Rain Forest 

A type of vegetation consisting of tall, evergreen trees, 


mostly broadleaved, occurring in equatorial regions with 
much rainfall and no, or very short dry seasons. 

Rain Gage 

An instrument to measure the amount of rainfall. 

Rain Shadow 

Refers to an area in which little or no rain falls because 
it is located to the leeward of mountains which on the 
opposite side are exposed to moisture-laden winds. 

Raised Beach 

The shore of a former lake or sea that has been elevated 
by a movement of the earth to form a narrow plain. 

Raised Bog 

A Bog with vegetation of Sphagnum spp. and associated 
plants that is typically convex and gently sloping from the 
center toward the steep margins, and bordered by a ditch 
or a watercourse (lagg). 


An individual member of a Clone (q. v.). cf. Ortet. 

Random Sample 

A sample of plant or animal life, soil, or other material 
or objects in an area in which the sample is located spatially 
by chance or at random; in contrast to selected samples or 
Systematic sampling (q. v.). 

Random Searching 

The hypothesis that populations obtain food, suitable 
niches, and mates by entirely unorganized search, in contrast 
to systematic searching. 


(1) The extent of the geographic area in which a plant 
or animal occurs. (2) Land covered with plants that are 
suitable for grazing; usually extensive in area and not suit- 
able for cultivation, especially in arid, semiarid, or forested 


regions, cf . Pasture. (3) A unit of grazing land used by a given 
herd of livestock. 

Range Condition 

The status of vegetation and soil of a given range area 
in relation to the optimum status (considered by some the 
Climax) obtainable under the prevailing environmental 

Range, Home 

See Home range. 

Range Improvement 

Any procedures that are used to increase the value and 
ease of management of the range such as the development of 
water supplies, fencing, revegetation, and control of unde- 
sirable plants. 

Range Management 

The handling of range land to obtain the continuous pro- 
duction of forage and livestock, consistent with uses of the 
land for other important purposes, cf. Proper stocking. 

Range Readiness 

The degree of growth of important forage plants on the 
range and the condition of the soil so that livestock may 
graze without undue compacting of the soil or decreasing the 
capability of the plants to maintain themselves, cf. Pre- 
mature grazing. 

Range Survey 

A systematic and comprehensive analysis and inventory 
of the resources of a range area and the related problems of 
management, and the formation of plans for management of 
these resources. 


Refers to a predatory animal that has feet with curved, 
sharp claws adapted for seizing Prey, e.g., eagles. 



Refers to an animal that usually scratches the ground 
for food, e.g., barnyard fowl. 


A series of races in which distinct forms of a Polytypic 
species replace each other in a geographic progression, cf. 
Race (1). 


A shoot from a perennial plant such as sugarcane. 

Raunkider's Law of Frequency 

See Frequency, law of. 

Raunkider's Life-form Classification 

A system of classification of Life-forms of plants based on 
the kinds and position of the organ with respect to the soil 
level that survives unfavorable environmental periods, cf. 
Phanerophyte, Geophyte. 


An elongated, narrow depression, larger than a gully, 
usually formed by running water. 

Rdw Humus 

See Mor. 


(1) The effects which one or more organisms produces 
upon its habitat, cf. Interaction. (2) The degree of acidity or 
alkalinity of a substance, usually expressed as pH (q. v.). cf. 
Hydrogen-ion concentration. 

Reaction Time 

The time required by an organism for the manifestation 
of a response to a stimulus. 


One of the major divisions in the classification of con- 


tinental Faunas according to P. J. Darlington, Jr., e.g., 

Megagea (Arctogea), Neogea, Notogea (q. v.). 


The theory that in the development of an individual 
the stages of earlier forms in its evolution are repeated, 
e.g., gill slits in the embryo of a pig. cf. Palingenesis. 


Refers to a Gene that has no effect on the appearance of 
an organism unless it is Homozygous (q. v.), i.e., the domi- 
nant gene is not present, cf. Allele. 


See Oxidation-reduction potential. 

Red Tide 

See Dino flagellate. 

Reduction Division 

See Meiosis. 

Reed Swamp 

A community of plants such as cattail or bulrush that 
grows in shallow water and often extends landward on wet 
soil where the water table is near the surface. 


A series of rocks close to the surface of a body of water, 
may be exposed at low tide. 


An innate, simple, stereotyped response, located in the 
nervous system, occurring very shortly after the stimulus has 
been received by an animal. 


The establishment of a forest on previously cleared land, 
cf. Afforestation. 



An area designated for the maintenance of animals 
within which hunting or fishing is prohibited or strictly 
controlled, cf. Natural area. 


An area that has not been exposed to great changes under- 
gone by the region as a whole, and as a result provided 
conditions suitable for the survival of Relic (q. v.) species, 
cf. Nunatak. 


Parts of the Sahara desert with a gravelly or stony surface 
because the fine materials have been blown away. 


The process occurring in some animals by which a part 
of the body which has been lost may be restored, e.g., a 
crayfish growing a new appendage, growth of new tissue in 
the wound of a mammal. 

Regional Climax 

See Climatic Climax. 


The concept of the integration of relations in human 
society to the particular conditions and resources that obtain 
in a region such as the Columbia River basin or the northern 
Great Plains. 


The unconsolidated mantle of soil material and weathered 
rock on the surface of the earth. 


A deep soil consisting of loose material without stones 
and shows only slight development of a Profile (q. v.). 



(1) A statistical method for the study and expression of 
the change in one variable associated with and dependent 
upon changes in another related variable or group of vari- 
ables. (2) See Retrogression. 

Regulatory Mechanism 

Any influence in the physical or biotic environment of a 
population that tends to maintain the number of individuals 
which the resources of the habitat can support, cf. Reaction, 
Coaction, Predation, Parasitism. 

Relative Humidity 

See Humidity, relative. 


An analysis sample of a Stand of vegetation in which are 
given the data on characteristics such as kinds of species, 
Cover, Density, and sometimes others, cf. Sample area. 

Relic (Relict) 

(1) A remnant or fragment of a flora or fauna that re- 
mains from a former period when it was more completely 
developed. (2) A remnant of the population of a species that 
was formerly more widespread. 


The inequalities in the elevation of the land surface, cf . 


An Intrazonal group of soils usually with brown or 
black, friable surface horizons and light gray or pale yellow 
calcareous material below, formed under grassland or mixed 
grassland-forest in humid or semiarid regions, cf. Prairie 

Replacement Control 

The substitution of one kind of plant by another kind, 
chiefly as a result of competition, e.g., downy bromegrass 


which is resistant to leafhoppers replacing Russian thistle 
and mustards which are susceptible to the insect, cf. Suc- 

Reproduction, Vegetative 

Propagation of a plant by stems, roots, or other asexual 
organs, e.g., strawberry plant increasing in number by means 
of runners, cf. Propagate, Sexual reproduction, Asexual 
reproduction, Apomixis. 

Reproductive Isolation 

The separation of populations or organisms so that inter- 
breeding cannot occur. 

Reproductive Potential 

The maximum rate of increase in numbers of individuals 
of a species or a population under the most optimum condi- 
tions, in contrast to the actual reproduction obtained under 
existing conditions, cf. Biotic potential, Environmental 


An animal in the class Reptilia of the subphylum Verte- 
brata. e.g., snakes, crocodiles. 


The group of meteorological stations operating under a 
common direction or in the same territory. 

Residual Soil 

A kind of soil formed in place by the disintegration and 
decomposition of rocks and the consequent weathering of 
the mineral materials, cf. Alluvium. 

Residual Stand 

See Second growth. 


The capacity of an organism to remain relatively un- 
affected by insects, disease-causing bacteria or fungi, or 


severe conditions in the physical environment because of 
inherent qualities that it possesses. 


The complex series of chemical reactions in all living 
organisms by which the energy in foods is made available for 
use. In aerobic respiration free oxygen is utilized and carbon 
dioxide is liberated; in anaerobic respiration, free oxygen is 
not required. 

Respiratory Quotient 

The ratio of the volume of carbon dioxide given off by 
an organism to the volume of oxygen used in a unit of time. 


The state in a forest in which replacement of important 
trees is taking place by natural or artificial means, cf. 


The change from a more highly organized individual, 
group, or state of organization to one on a lower level, as in 
a Succession (q. v.) that recedes from the Climax. 


A structure or obstacles placed along the margins of a 
stream in order to protect the bank from erosion. 


The division of Limnology (q. v). dealing with running 
waters, their physical, chemical, and biological conditions 
and interrelationships, cf. Lotic. 


A plant that grows in running water, cf. Hydrophyte. 


The orientation in the locomotion of organisms in 
streams with reference to the current. 



The response of an organism to a current. 

Rhesus Factor 

See RH factor. 

RH Factor 

An Antigen (q. v.) found in the blood of a large number 
of human beings who consequently possess Antibodies against 
the antigen. Syn. Rhesus factor. 


An organ that serves for the attachment of certain organ- 
isms such as the many intergrown filaments in many lichens. 


Bacteria that occur in the nodules of certain plants, 
especially in the pea family, Leguminosae, and fix free litro- 
gen into forms useful to the Host. 


A filamentous organ, one cell thick, found in mosses, 
fern Gametophytes, and other plants, used for attachment 
and probably also for absorption of water and nutrient salts. 


An underground stem that produces shoots and roots at 
the nodes, cf. Rootstock, Runner. 


The portion of the soil close to and under the influence 
of the root of a plant. 


The more or less regular recurrence of phenomena such 
as day and night, differences in animal behaviour, cf. 

Ridge Terrace 

A long, low ridge with gently sloping sides and a shallow 
channel along the upper side for the purpose of collecting 


run-off water and diverting the flow across the slope, thus 
controlling erosion, cf. Bench terrace. 

Rift Valley 

A long, narrow valley between two approximately parallel 
geological faults, e.g., the extensive one extending from 
Lake Nyasa northward in the eastern part of Africa. 

Rill Erosion 

The removal of soil by running water resulting in the 
formation of shallow channels that can be smoothed com- 
pletely by cultivation in the normal manner, cf. Gully ero- 
sion, Sheet erosion. 


A feathery or rough layer of ice deposited on plants and 
other objects by a fog. cf. Hoarfrost. 


Refers to land bordering a stream, lake, or tidewater. 


Stones placed on the face of a dam or on stream banks 
or other land surfaces in order to protect them from erosion; 
often applied also to other materials that are used for erosion 


Barren alluvial land exposed along streams at low water 

RNA (Ribose Nucleic Acid, Ribonucleic Acid) 

A nucleic acid occurring in the cytoplasm of plant and 
animal cells. 

Roaring Forties 

Strong westerly winds over the ocean between latitudes 
40 S. and 50 S., or the region in which these winds occur. 


Rock Flour 

Fine material formed by the action of a glacier grinding 
rocks in its base as it moves forward. 


An animal in the order Rodentia in the class Mammalia, 
e.g., mouse. 


(1) A unit of measurement of radiation caused by Gamma 
rays and X-rays, very similar to Rad (q. v.). (2) Refers to 


To remove undesired individuals from a population to 
prevent their reproduction. 


The breeding place of a group of birds or seals. 

Root Climber 

A plant that ascends by means of roots attached to a 
support, e.g., poison ivy on the trunk of a tree. 

Root Nodule 

See Nodule. 


See Rhizome. 

Root Sucker 

A sprout arising from a root. 

Root Zone 

The part of the soil occupied by roots, or subject to such 
occupation under normal conditions, cf. Rhizosphere. 

Rotation Grazing 

The orderly alternation in the use of two or more por- 
tions of a range or pasture. 



An aquatic animal in the phylum Rotifera, possesses cir- 
cles of cilia at the anterior end. 

Rouches Moutonnees 

Mounds of smoothed rock marked by striations caused 
by a glacier passing over them. 


Feed for animals consisting of plants or plant parts con- 
tains a high fiber content and low total digestible nutrients, 
e.g., hay, Stover. 

Rough Grazings 

Grasslands, largely on hills and mountains in Great 
Britain, which have replaced forest by natural processes, 
maintained as grassland by grazing, in contrast to pastures 
seeded by man. 


See Nematode. 

Row Crop 

A crop such as corn planted in rows relatively far apart, 
usually two to four feet, to permit cultivation between the 


A plant inhabiting fields or waste places, cf. Weed, 


Refers to an organism or part of one that is in an early 
stage of development or evolution. 


The first stomach of a Ruminant (q. v.). 


An animal in the order Artiodactyla, even-toed ungulates, 


class Mammalia, that lacks upper incisor teeth and chews the 
cud, e.g., giraffe, ox, deer. 


An above-ground, more or less horizontal stem that forms 
roots and shoots at some of the nodes under favorable 
conditions, e.g., the strawberry plant, Bermudagrass. cf. 
Rhizome, Stolon. 


The part of Precipitation which as surface run-off flows 
off the land without sinking into the soil and the part that 
enters the ground and passes through into surface streams as 
groundwater run-off. 


Sabdlicm Life Zone 

The portion of the Austral life zone (q. v.) which borders 
the Gulf of Mexico from the southern tip of Florida to the 
17th meridian. 


A sand-dwelling insect. 


A salt flat. 

Saline Soil 

A soil that contains soluble salts, usually chlorides and 
sulfates in high enough concentration so that the growth of 
most crop plants is reduced, pH is less than 8.5, often called 
"white alkali" because of the presence of a white or gray 
crust on the surface, cf. Alkali soil, Solonchalk. 


The quality of saltness in seawater or fresh water, most 
commonly expressed in parts of dissolved salt per 1000 parts 
of water, e.g., salinity of seawater is 35 parts per thousand. 
cf. Alkalinity. 



The formation of a saline soil by the addition of salts 
to a non-saline soil, as occurs often in irrigating land with 
water of a high degree of Salinity. 


A sudden change. 

Saltatorial (Saltatory) 

Refers to leaping or dancing, e.g., the hind limbs of a 
kangaroo adapt it to saltatorial motion. 

Salt Grounds 

Places in a pasture or on a range where salt is placed for 
consumption by livestock. 


Refers to an animal possessing legs that are adapted for 
leaping, e.g. kangaroo rat. 

Salt Marsh 

A Marsh in which the water is salty or brackish, with 
greater Salinity than fresh water. 

Salt Pan 

A depression in a salt marsh, usually bare of vegetation. 

Sample Area 

A portion of an area of vegetation or of a plot that is 
used for sampling purposes, cf . Plot, Quadrat. 

Sample Plot 

A measured area in vegetation used for sampling or an 
area of land used for experimentation. 

Sample, Random 

A sample taken without bias from an area or from a 
population in which every part of the area or population has 
an equal chance of being taken. 


Sample, Representative 

A sample taken that is typical of or that represents a fair 
value of the area or population from which it is taken. 

Sand Binder 

A plant that holds sand from being blown away. 


A tree that is more than three feet in height and less 
than 4 inches in diameter at breast height. 


An organism that lives on dead organisms or on decaying 
organic material. 


A plant that obtains food from dead or decaying organic 
material, cf. Parasite, Heterophyte. 


The outermost part of the wood or xylem of the trunks 
of trees, generally lighter in color than the heartwood, con- 
tains living cells, active in translocation of water and mineral 

Saturation Deficit 

The difference between the pressure of water vapor in the 
atmosphere at a given time and the maximum that it could 
contain at the same temperature, expressed in millimeters 
of mercury; or sometimes expressed as the difference between 
the relative humidity and the humidity at saturation. 

Saturation Point 

The density of a given population above which it no 
longer increases. 


Refers to a lizard. 


Savanna (Savannah) 

An area of grassland in which are scattered trees or shrubs 
but little or no breaks in the continuity of grassland cover. 


Refers to organisms growing on or among rocks, e.g., 
many mosses and saxifrages. 




Refers to an organism that has adaptations for climbing, 
e.g., a Liana such as Virginia creeper, cf. Ambulatorial, 


See Escarpment. 


The study of Scats, identification, determination of con- 
tents, etc. 


Animal feces or droppings such as pellets of rabbit dung. 


An animal that eats animal wastes and dead bodies of 
animals not killed by itself, e.g., vulture. 


A plant in the phylum Schizomycophyta, bacteria. 


Any aerial plant part, often a small branch, that is 
grafted onto the root-bearing part (Stock) of another plant. 


See Heliophyllous. 



Thick walled cells, fibers or stone cells, constituting 
strengthening tissue in plants. 


Plants with stiff, leathery, evergreen leaves, may be 
broad-leaved as the holly, or narrow-leaved as the pine. cf. 


The hardening of tissue by an increase in the content of 
lignin in plants, or an increase in collagen in animals. 


A hard, compact, rounded mass of hyphae serving as a 
dormant stage for carrying a fungus through an unfavorable 
environmental period; it may survive many winters in the 


See Talus. 


Densely growing, low, often stunted bushes or trees, cf. 
Fruticeta, Bush, Chaparral. 


See Random searching. 

Season, Critical 

The part of the year when a species suffers greatest 
mortality, e.g., the migration time of some migratory birds. 

Seasonal Aspects 

See Aspection. 


An alga, usually large, growing in the sea, e.g., kelps. 


Refers to fatty material, particularly to the gland in the 
skin of mammals that secretes sebum. 


Secondary Sexual Character 

A characteristic, not directly associated with the char- 
acters directly connected with reproduction, in which the 
male and female animals differ, such as the difference in 
coloration of many male and female birds. 

Secondary Species 

The species in a community that are subordinate to the 
Dominant species (q. v.), e.g., dogwood shrubs or trees in a 
white oak forest. 

Secondary Succession 

The kind of Succession (q. v.) which takes place follow- 
ing the destruction of part or all of the vegetation in an 
area, usually caused directly or indirectly by man. cf . Primary 
succession, Sere, Plagiosere, Sub sere. 


A measuring unit for the volume of the flow of water 
expressed in cubic feet per second. 

Second Growth 

(1) A forest which comes up after the removal of the old 
stand by cutting, fire, or other cause; actually Young growth. 
(2) The smaller trees left after cutting all the merchantable 
trees, actually Residual stand, cf. Virgin forest, Advance 


The process of passing substances made within a cell, par- 
ticularly gland cells, to the outside of the cell; or the sub- 
stance itself, e.g., nectar from nectar glands in flowers. 


Refers to an animal that has little tendency to move 
about, e.g., certain spiders, cf. Sessile. 


A plant, resembling a grass in vegetative appearance, in 


the family Cyperaceae, with usually solid stems, three-ranked 
leaves, and closed leaf sheaths. 

Sedimentary Rock 

Rock formed from materials such as pebbles, sand, and 
clay in rivers, lakes, and seas; usually in distinct layers, e.g., 
conglomerate, sandstone, limestone. 


The process of depositing materials from a liquid, espe- 
cially in bodies of water, cf. Sedimentary rock, Alluvium. 

Sediment Delivery Ratio (Percentage) 

The relation of the annual Sediment yield to the annual 
gross amount of erosion. 

Sediment Yield 

The total sediment outflow from a watershed, includes 
coarse and fine materials, bedload, and suspended materials; 
a part of the gross erosion from an area. 


The reproductive structure in Spermatophytes (flowering 
plants and conifers) formed from the Ovule (q. v.), contain- 
ing an Embryo, seed coat, and, in many kinds of plants, an 

Seed Leaf 

See Cotyledon. 


A young plant produced from a seed. Usage in forest 
nurseries; a tree which is still growing in the nursery, not 
transplanted. Usage in forest reproduction; a tree grown 
from seed and less than three feet in height. < 

Seed Plant 

A Spermatophyte (q. v.). 


Seed Tree 

A tree purposely left standing at the time of cutting a 
forest, for the purpose of producing seed for reproduction 
of trees in the surrounding area. 

Seed Year 

A year in which a given species bears seed in large 


(1) The water that passes through or emerges from the 
ground along a line or surface in contrast to a spring where 
the water emerges from a localized spot. (2) The process 
by which water passes through the soil. 


Separation of the Gene pairs (Alleles) and distribution 
of each gene into separate cells during Meiosis (q. v.). 


An oscillation in the level of the surface of a lake or 
inland sea. 


See Artificial selection, Natural selection. 

Selection Pressure 

A criterion of the results of Natural selection (q. v.) upon 
a population. 

Selective Cutting (Felling) 

The system of removing certain trees such as the largest 
ones in a forest, cf. Clear cutting. 

Selective Grazing 

The habit of grazing animals to eat certain plants in 
preference to others, cf. Palatability. 

Selective Species 

The group of Characteristic species (q. v.) in Braun- 


Blanquet's scheme of classification that contains species oc- 
curring most frequently in only one kind of community, but 
may rarely occur in others also. 


Refers to soils, plants, and other substances that contain 
a relatively high concentration of selenium. Some species of 
Astragalus are toxic to livestock because of accumulations of 
selenium in the tissues. 


Refers to an organism in which Self-fertilization occurs. 


The process by which eggs of an organism can be ferti- 
lized by sperms produced by itself, cf. Hermaphrodite, Self- 


The condition where pollen of a plant fails to develop 
effectively on a Stigma of the same plant, cf. Compatibility, 


A process of causing Self-pollination. 


The transfer of pollen from an Anther to the Stigma in 
flowers on the same plant, cf. Cross-pollination. 


The death and falling of branches, especially the lower 
ones, of living trees. 


The failure of an egg of an organism to be fer- 
tilized by a sperm produced by the same organism, cf. 



An equatorial Rain forest in the Amazon River basin in 
South America. 


Refers to an organ, odor, color, or other attribute of an 
animal that may serve as a warning to other animals. 


Refers to a region or climate that is intermediate between 
Arid and Subhumid, with Precipitation-effectiveness ratios 
ranging between 16 and 32, and supporting grassland or 
shrub types of vegetation. 


Refers to seed or semen. 

Seminatura! Community (Vegetation) 

A community in which the development or character- 
istics have been modified in part by man's influence, e.g., 
a successional community on an area where sagebrush was 
burned by man. 


Refers to a membrane that permits certain substances 
to pass through readily while others pass through slowly or 
not at all; differentially permeable. 


The process of aging. 


The state of old age. 


Refers to the capacity or sense-organ of an animal by 
which it receives stimuli. 


See Calyx. 



Refers to Sere (q. v.). 


A stage in a Sere before the Climax is reached and re- 
mains in that stage indefinitely, e.g., tule marshes in Califor- 
nia, cf. Subclimax, Plagioclimax. 


The series of stages that follow one another in an ecologic 
Succession (q. v.). cf. Hydrosere, Xerosere, Subsere, Primary 


The study of the reactions of blood serums to the intro- 
duction of foreign substances into the body of organisms. 


Refers to the latter part of the summer season, cf. Aspec- 
tion, Estival. 


Refers to late opening such as cones of some pine trees 
which remain on the trees for several years without opening. 


A rock or mineral consisting of hydrated magnesium 


An organism that is attached to an object or is fixed in 
place, e.g., barnacles, cf. Sedentary. 


The aggregate of substances and organisms that float or 
swim in water, including the Bioseston (living organisms) 
and the Abioseston (non-living). 


Settling Basin 

The widening or deepening of a stream so that materials 
carried in suspension will be deposited. 

Sewall Wright Effect 

The postulate that if a population is subject to cyclical 
fluctuations in abundance, the evolutionary trend of the 
species is influenced by the size (population density and 
area inhabited) of the minimum breeding population, cf. 
Natural selection. 

Sex Chromosome 

A Chromosome (q. v.) that determines the sex of the 
offspring of an organism. 


The connection or association of certain Genes or attri- 
butes of an organism with the Sex chromosome, e.g., certain 
kinds of color blindness. 

Sex Ratio 

The relationship of the numbers of males and females 
in a population, approximately 1 : 1 in most kinds of animals. 

Sexual Dimorphism 

The condition in which marked differences in character- 
istics such as color, size, and form occur between male and 
female animals in the same species. 

Sexual Reproduction 

The production of offspring resulting from the fusion of 
sex cells (Gametes, eggs and sperms), cf. Asexual reproduc- 
tion, Propagate. 

Sexual Selection 

A theory to explain certain kinds of evolution based upon 
selective mating such as the choosing of a certain mate by a 


female animal because of attractive features such as the 
bright coloration of the male. 

Shade Plant 

A plant that can grow in the shade, cf. Heliophyllous. 


An easily splitting sedimentary rock formed from clay 
or silt. 


A wind that blows with considerable constancy, carrying 
much dust, in Iraq. 

Sheep Month 

The amount of forage or feed required for maintenance 
by a mature sheep or an ewe and its suckling lamb for 30 
days, usually figured as equivalent to one-fifth of a Cow 
month (q. v.). 

Sheet Erosion 

The erosion or removal of a rather uniform layer of soil 
from the surface of the land by rainfall and Run-off water, 
cf. Gully erosion, Rill erosion. 


The conditions, objects, or material that provide organ- 
isms suitable resting places or protection from attack by 
predators or from unfavorable conditions of the physical 
environment, cf. Covert. 


A long Windbreak of living trees and shrubs extending 
over an area larger than a single farm. 


More or less rounded pebbles varying in size, often mixed 
with sand, on seashores. 



Vegetation consisting of dwarf oaks as dominants, espe- 
cially in sandy areas in the southern Great Plains. 


An animal of the Lamellibranchiata (clams), especially 
Teredo navalis which burrows in submerged wood. 

Shock Disease 

The deterioration in overcrowded populations of an or- 
ganism in which the activity of the Endocrine glands (q. v.) 
is abnormal and the general condition and viability of the 
animals are reduced, which may result in a rapid decline 
(crash) in the number of individuals. 


The stem and leaves of a plant taken collectively, cf. 

Shore, Depositing 

The addition of sand, silt, and clay, or the removal of 
rock, to the land adjacent to a body of water by the action 
of water or wind. 

Short-day Plant 

A plant that blooms when periods of light are short and 
periods of darkness are long, e.g., chrysanthemum, cf. 

Short Grass 

Grasses that grow only a few inches high, particularly 
blue gramagrass and buffalograss. cf. High grass, Medium- 
height grass. 


A perennial woody plant that differs from a tree by its 
low growth and the possession of several stems arising from 
the base. 


Siblings (Sibs) 

The offspring, brothers and sisters taken collectively, from 
the same parents. 


Shrub vegetation on deforested land in the Balkan 


Processes that include the diminution of rainfall (desicca- 
tion) and the drying out of the earth's crust and atmosphere. 
(Exsiccation, q. v.) 


Dry areas such as steppe and desert occupied by open 


See Xerophilous. 


A Zonal group of soils with brownish gray surface hori- 
zons that grade through lighter colored material to a layer 
with accumulated calcium carbonate, in arid temperate 
climates where vegetation usually is shrubby. 


A chain of mountains with jagged tops. 

Sieve Tube 

A tube of cells connected end to end, part of the Phloem 
tissue in plants, used to conduct food. 


The partly fermented above-ground parts of crops such 
as corn, sorghum, legumes, or grasses preserved in a succulent 
condition for feeding livestock. 


Mineral particles in the soil, intermediate between clay 


and sand; 0.5 to 0.002 mm. in diameter according to the 
U. S. Department of Agriculture system, 0.02 to 0.002 mm. 
in diameter according to the International system. (2) In a 
general sense waterborne sediment in which the diameters 
of individual grains are similar to those of silt (1). (3) Soil 
material containing 80 per cent or more of silt (1) and less 
than 12 per cent of clay. 

Silting (Siltation) 

The deposition of water-borne sediments in bodies of 
water, caused usually by a decrease in the velocity of the 
water movement. 


One of the geological periods in the Paleozoic era, which 
began about 360 million years ago and lasted for about 35 
million years. 


The aggregate of the forest trees in an area or country. 


The production and care of forest trees. 


Refers to monkeys and apes, particularly anthropoid apes; 
or used as a noun especially for the latter. 


An intensely hot, dry wind of Arabian and Saharan 
deserts, usually carrying much sand. 


A hole into which water drains and passes into an under- 
ground channel, occurring usually in limestone regions. 


Deposits, mainly siliceous and calcareous (Travertine), 
formed in lakes or springs by evaporation, e.g., terraces of 


siliceous sinter around hot springs in Yellowstone National 


A plant in the abstract as compared to the concrete plant. 


A hot, south wind, occasionally dust laden, blowing from 
the Sahara in the Mediterranean region. 


An area delimited by fairly uniform climatic and soil 
conditions, essentially equivalent to Habitat (q. v.). 

Site Index 

A numerical evaluation of the quality or productivity of 
land, especially used in forest land where it is determined 
by the rate of growth in height of one or more of the tree 

Site Quality 

The capacity of a Site to produce vegetation, particularly 
timber or forage. 


See Heliophobous. 


A damp hollow, or low area, among sand dunes. 


The branches, cull logs, uprooted trees, and other waste 
material left on the ground after an area has been logged off. 


An area of forest that has been logged off and where the 
Slash remains. 


A fine-grained, dense rock produced from clay or shale 
by compression, splitting readily into thin plates. 



(1) In the United States, frozen or partly frozen raindrops 
in the form of particles of clear ice. (2) In British use, snow 
and rain falling together. 

Slick (Slick Spot) 

A small area of Alkali or Solonetz (q. v.) soil. 

Slime Mold 

An organism in the phylum Myxomycophyta, character- 
ized in part by a naked, fluid mass of protoplasm that can 
move with a flowing motion, cf. Wasting disease. 


The downhill movement for a short distance of a mass 
of wet or saturated soil. 


The inclination of the surface of the land from the hori- 
zontal. Level 0-3.0 (0-5%), gentle 3.0-8.5 (5-15%), moderate 
8.5-16.5 (15-30%), steep 16.5-26.5 (30-50%), very steep 
26.5-45 (50-100%), precipitous above 45 (over 100%). 


A wet depression with deep mud. cf . Swamp, Marsh, Bog. 


Muddy, ooze-like sediments in a river bed, tidal flat, or 
similar location. 


A polluted atmosphere in which products of combustion 
such as hydrocarbons, soot, sulfur compounds, etc., occur in 
detrimental concentrations for human beings and other 
organisms, especially during foggy weather. 

Snow Density 

The water content of snow expressed as a percentage by 
volume. In snow surveys, the ratio of the scale reading 
(inches of water) to the length of the core of snow in inches. 



A fence of slats and wire or other material used to inter- 
cept drifting snow. 


An area or mass of snow that remains throughout the 


A deposit of soil material accumulated in a mass of snow 
following melting of the snow. 

Snow Line 

A line marking the lower limit of perpetual snow. 


An area in which snow melts late in the year and where 
Snowflush forms and vegetation is characteristic of such a site 
or is lacking. 

Snow Sample 

A core taken in an accumulation of snow from which the 
depth and density of the snow may be determined. 

Snow Survey 

A series of measurements of the depth and density of 
the accumulation of snow, usually for the purpose of deter- 
mining the amount of water that is stored in the form of 
snow on a drainage basin, as a means of forecasting the later 


The distribution of organisms in relation to one another 
as individuals or as groups within a community. J. Braun- 
Blanquet recognizes five classes of sociability, ranging from 
isolated individuals to dense masses. 

Social Behaviour 

The activity of an animal caused by another animal or 


that influences another animal; the reciprocal interactions 
of two or more animals. 

Social Dominance 

The behaviour pattern in which one or more animals 
dominate other individuals in the group, cf. Peck-dominance. 

Social Facilitation. 

See Facilitation, social. 

Social Hierarchy 

See Hierarchy. 


A vegetation type characterized by Dominant species in 
the various strata; a subdivision of the Association (4) (q. v.) 
in the Scandinavian School of Phytosociology. 


According to F. E. Clements a group of one or more 
kinds of subdominant plants in a stage of Succession preced- 
ing the Climax, cf. Associes, Society. 


(1) A social group of individuals of one species which 
cooperate in their activities. (2) According to F. E. Clements 
a group of subdominant plants in Climax vegetation, cf. 
Association, Socies. 


The study of the development, composition, character- 
istics, and interactions of groups of organisms or communi- 
ties, cf. Plant sociology. Ecology. 


A surface layer of soil matted or bound together by 
roots and rhizomes of grasses and other herbs, especially by 
Sod grasses. 


Sod Grass 

A grass that forms a Sod, e.g., Kentucky bluegrass. 


The wood of a coniferous tree, e.g., pine, in contrast to 
Hardwood (q. v.). 


The aggregate of weathered minerals and decaying 
organic material that covers the earth in a thin layer in which 
plants grow. 

Soil Creep 

The very slow movement of surface soil down a slope. 

Soil Erosion 

The loosening and movement of particles of soil from 
the surface of the land by wind or flowing water, including 
Accelerated erosion and Normal erosion, cf. Gully erosion, 
Rill erosion, Sheet erosion, Splash erosion. 

Soil Horizon 

A layer of soil with characteristics resulting from soil- 
building processes. See A, B, C horizons, Podzolization. 


The feeding of livestock with mowed, fresh forage such 
as bromegrass or legumes, in contrast to their grazing on a 

Soil Productivity 

The capacity of a soil to produce plant growth because 
of its chemical, physical, and biological properties. 

Soil Profile 

A vertical section of the soil from the surface through 
all its horizons into the parent material, cf. Soil horizon. 

Soil Reaction 

The acidity or alkalinity of the soil usually expressed 
as pH (q. v.). 


Soil Structure 

The arrangement of particles in the soil, e.g., single 
grain, granular, columnar. 

Soil Texture 

The relative proportions of the various sizes of mineral 
particles (gravel, sand, silt, clay) in the soil. cf. Silt. 

Soil Type 

An area of soil which is relatively uniform in profile 
characteristics and in texture of the surface soil, a sub- 
division of a soil series, e.g., Cecil sandy loam and Cecil clay 
loam are soil types in the Cecil series. 

Solar Constant 

The energy received from the sun above the upper limit 
of the atmosphere, equal to 1.94 gram-calories per minute 
per square centimeter. 


The inhibiting effect of extremely high light intensities 
on Photosynthesis. 


The flow of saturated soil upon an impermeable layer 
or on frozen ground, especially under conditions of alternate 
freezing and thawing. 


A type of soil that has a high concentration of soluble 
salts in relation to other soils, usually light-colored, "white 
alkali." cf. Saline soil. 


A type of soil in which the surface horizons of varying 
friability are underlain by dark-colored, hard soil which is 
usually highly alkaline and columnar in structure, "black 
alkali." cf. Alkali soil, Solonchalk. 



The process of soil formation in semiarid and arid 
climates where Saline soil (q. v.) or Solonetz is formed, cf. 
Podzolization, Calcification. 


The time of the year when the sun is above the point 
which is farthest north or south of the equator, in the 
northern hemisphere the summer solstice is about June 21, 
the winter solstice about December 22. 


The upper part of the Soil profile (q. v.) above the parent 
material, usually the A and B horizons; often considered the 
true soil because of its development by soil-building forces. 
cf. Soil. 


The cells of an organism exclusive of those concerned 
with Sexual reproduction. 


Refers to the Soma, or the non-reproductive parts of an 

Sonoran Life Zone 

The part of the Austral life zone (q. v.) lying west of the 
100th meridian, divided into Transition, Upper Sonoran, 
and Lower Sonoran zones. 


A juvenile form of a bivalve mollusk such as the oyster. 


(1) The eggs of frogs, fishes, oysters and other aquatic 
animals. (2) The Mycelium (q. v.) of certain fungi especially 
of the mushroom in which it is used for propagation. 


To remove the ovaries from a female animal. 



Refers to an organism, or part thereof, that is adapted to 
a particular kind of life or to a certain combination of 
environmental conditions; more limited than an unspecial- 
ized organism. 


The processes in evolution by which new species are 
formed, cf. Mutation, Natural selection. Sub spe elation. 


A unit of classification of plants and animals, consisting 
of the largest and most inclusive array of sexually reproduc- 
ing and cross-fertilizing individuals which share a common 
gene pool; the most inclusive Mendelian population (q. v.), 
e.g., the white pine (Pinus strobus) and ponderosa pine 
(Pinus ponderosa) are two species in the genus Pinus. cf. 
Jordanon, Ecospecies, Coenospecies, Taxon, Syngameon, 

Species-area Curve 

A graph showing the number of species on the vertical 
axis and the area of the sampling-unit or Quadrat on the 
horizontal axis; used to determine the most suitable area 
of quadrat to use in sampling vegetation. 

Specific Gravity (Soils) 

The ratio of the weight of a given volume of soil, pore 
space excluded, to the weight of an equal volume of water; 
the average specific gravity of tilled surface soil is about 2.65. 


The limitation of an organism to restricted, definite set 
of environmental conditions, a single kind of food plant or 
animal host, or other set of circumstances. 

Spectrum, Biological 

See Biological spectrum. 



The study of the conditions and the life in caves. 


The male sex cell or Gamete. 


The formation of sperms in an organism. 


The seed-bearing plants, Spermatophyta, a section of the 
subphylum Pteropsida, phylum Tracheophyta. It includes 
the Gymnosperms and the Angiosperms (q. v.). 


A highly motile Sperm occurring in animals. 


Plant communities with abundance of Sphagnum and 
with peat in the substratum, cf. Bog. 


A genus similar to the true mosses, in the subclass 
Sphagnobrya, class Musci, phylum Bryophyta; usually occur- 
ring in bogs. 

Sphagnum Bog 

A kind of community characterized by the presence, and 
often the abundance, of Sphagnum, acid substrata, and the 
accumulation of peat. cf. Bog. 


One of the main parts of the inflorescence of a grass or 
a sedge, containing one or more flowers (Florets) and asso- 
ciated bracts or scales. 


A passageway for the escape of excess water around a dam. 

Spinney (Spinny) 

A copse or small grove. 



One of the external openings of the Trachea (q. v.) of 
most terrestrial Arthropods. 

Spirochete (Spirochaete) 

A microorganism which moves by undulating its body 
(not by cilia), parasitic or free-living, classified usually with 
the bacteria, e.g., the organism causing syphilis. 


A long, narrow strip of land extending into the sea, 
attached to the mainland at one end. 

Splash erosion 

The direct effect of the impact of rain drops on the 
ground surface or on a thin film of water causing detachment 
of soil particles which are then readily available for washing 
away. cf. Erosion, Sheet erosion, gully erosion. 


An animal in the phylum Porifera. 

Spontaneous Generation 

The belief that organisms, even complicated ones, orig- 
inated directly from non-living substances, cf. Biogenesis. 


A case-like structure in plants in which spores are 


An asexual, Haploid (q. v.), one- or few-celled, reproduc- 
tive body produced by organisms, cf. Spore-mother cell. 

Spore-mother Cell 

A Diploid (q. v.) cell in plants that gives rise to four 
Haploid spores. 


A leaf or leaf-like structure or scale that produces one 
or more Sporangia^ e.g., leaves of many ferns, a Stamen. 



The part, or asexual generation, of the life cycle of 
plants in which the cells contain the Diploid (or Polyploid) 
number of chromosomes, begins with Fertilization, pro- 
duces Spores, e.g., a flowering plant, a fern. 


A vegetative or Somatic Mutation (q. v.) in an organism, 
e.g., a shoot differing from other shoots arising from a bud 
on a plant. 


The rapid formation of Spores by fission as in many 
bacteria, molds, algae, and protozoons. 


The combined results of dispersal and of the establish- 
ment of the individual and then the species in a new place, 
cf. Dispersal, Establishment. 


The planting of a part of the stem and root system of 
a grass. 

Spring Overturn 

The mixing of water in lakes after the ice melts, result- 
ing in a uniform temperature from the surface to the bottom. 
Another mixing occurs in the autumn, the Fall overturn. 


See Collembolon. 

Spring Wood 

The portion of the annual woody growth of a tree or 
a shrub that is formed in the early part of the growing 
season; it is more porous than the Summer wood (q. v.). 


The first growth or shoot from a seed, root, or other plant 
part; or a tree that has grown from a stump or root. 


Square-foot Method 

A method used to determine the species composition and 
the cover of range vegetation by means of systematically 
located sample areas one square foot in area. 


(1) The state in the interrelationships of organisms in 
which integration and adjustment between the organisms 
and between them and the prevailing environment is being 
attained, maximum stabilization occurs in climax com- 
munities usually. (2) In oceanography the condition in a 
mass of water in which a density gradient has become estab- 
lished such as when a Thermocline occurs. 


The part of a flower that produces pollen, consisting of 
an Anther (contains the pollen) and a filament (the stalk). 


Refers to a flower that bears stamens. 


A general term for an aggregation of plants with more 
or less uniformity in Physiognomy, composition, and habitat 
conditions; a local example of a Community-type or Associa- 
tion (q. v.). 

Standing Crop 

The total amount of the Biomass (q. v.) of organisms of 
one or more species within an area. cf. Productivity, Yield. 


The influence in the aggregate of all factors (climatic, 
edaphic, biotic, orographic) upon a geographically delimited 
locality, cf. Habitat. 

Stand Table 

A listing of species that occur in a stand, including data 


on characteristics such as Cover, Vitality, and Frequency. 
cf. Association table. 


A particular location comprising a stand, part of a stand, 
or a locality, cf. Habitat, Standort. 

Steady State 

See Homeostasis. 


The central part of the stem or root of plants, includes 
the pericycle, Phloem, Xylem, and pith when present. 


A prefix denoting a narrow range of Ecological amplitude 
(q. v.) of an organism, e.g., stenothermal refers to tempera- 
ture, stenophagous to variety in the diet, stenoky to number 
of factors, stenohaline to salinity, stenohydric to water, cf. 


An extensive area of natural, dry grassland; usually used 
in reference to grasslands in southwestern Asia and south- 
eastern Europe, cf. Prairie, Pampas. 


See Thigmotaxis. 

Stereo tropisiii 

The growth of a plant organ in response to contact with 
an object, e.g., tendrils of vines coiling around a stem. 


The lack of ability of an organism to carry on Sexual 


The upper part of the pistil (carpel) of a flower, receives 
the pollen and aids in its germination, cf. Pollination. 


Stilling Basin 

An excavation or structure below a waterfall or rapids 
that reduces the velocity and turbulence of the current. 


An influence that causes a response in an organism or 
in a part of it. 


(1) The parts of a plant, usually a portion of the stem 
and the root system, to which a Scion is grafted. (2) Live- 
stock. (3) See Standing crop. 


Placing animals such as deer or domestic livestock on 
an area of vegetation. 


A horizontal stem on the surface of the ground where it 
propagates vegetatively by forming new Shoots and roots at 
the nodes, e.g., Bermuda grass, cf. Runner, Rhizome. 

Stoma (Stomate) 

A minute pore and two surrounding guard cells occurring 
in the epidermis of leaves, young stems and fruits, and other 
organs, through which diffusion of gases occurs. 


The base of a plant from which shoots arise, or the base 
including the shoots, cf. Tiller. 


The dry, cured stems and leaves of grain crops such as 
corn and sorghum after the removal of the grain, cf. Fodder, 
Forage, Feed. 


A group of organisms having distinctive attributes and a 
common lineage which differs from other groups, but which 
is not sufficiently distinct to form a breed or Variety. 



(1) The area of bare beach above the level of high water, 
which is subject to the action of wind. (2) The intertidal 
portion of a beach. 


See Layering, Thermal stratification. 

Stratified Sampling 

In sampling vegetation or a geographic complex the 
separation into types or blocks in order to secure the maxi- 
mum degree of Homogeneity in the area to be sampled. 


The upper region of the atmosphere beginning about 
six miles above the surface of the earth, in which water-vapor 
clouds do not form and where no marked changes in temper- 
ature take place as the altitude increases. 


See Layer. 


A general term for water flowing in one direction such 
as a rill, rivulet, brook, creek, and river. 


An Antibiotic (q. v.) produced by the mold, Streptomyces 


(1) Systemic. According to Selge the condition of an 
animal in which large parts of the body deviate from their 
normal resting state, either because of their activity or 
because of an injury. (2) The total energy with which water 
is held in the soil. 


A stimulus causing systemic stress. 



The making of shrill sounds by certain insects such as 
crickets by rubbing one organ against another. 

Strip Cropping 

The growing of crops in narrow fields or strips so that 
wind and water erosion is reduced or prevented, cf. Buffer 

Strip Survey 

The use of continuous narrow strips as sampling units, 
especially in forestry. 

Strobilus (Strobile) 

A cluster of Sporophylls; the cone of conifers in which 
seeds or pollen grains are produced. 


(1) An expression of the composition, abundance, spac- 
ing, and other attributes of plants in a community, cf. 
Layering, Life-form. (2) The composition of a population 
with reference to age-classes, or to some other criterion. (3) 
See Soil structure. 

Struggle for Existence 

Refers to the processes used by an organism to maintain 
life and to reproduce, especially in an unfavorable environ- 
ment or where Competition (q. v.) is severe, cf. Natural 


The lower parts of plants that remain after the tops have 
been removed in harvesting operations; may also be applied 
to the parts left ungrazed on range or pasture. 

Stubble Crop 

(1) A crop that is produced from Stubble of the previous 
season. (2) A crop sowed in the grain Stubble after the grain 


crop such as wheat has been harvested; for the purpose of 
plowing it under the following spring to increase organic 
matter in the soil. 

Stubble Mulch 

The residues of a crop left on the soil surface as a mulch 
to prevent or reduce erosion when preparing the land for 
planting another crop. 


The value of timber as it stands in a forest; the uncut 


The portion of the pistil between the stigma and the 
ovary in a flower. 


Refers to the region or zone in mountains below the 
treeless Alpine (q. v.) region, characterized in North America 
by coniferous forests, especially spruce and fir. 


(1) Refers to the region south of the Arctic (q. v.) region 
and includes the northern part of the region south of the 
geographical timber line. (2) Boreal. 

Sub-boreal Period 

The climatic period from about 2500 B. C. to about 
700 B. C. according to Blytt and Sernander, a period drier 
than the preceding Atlantic (5500-2500 B. C.) and the follow- 
ing Subatlantic (700 B.C. to the present) periods, cf. Boreal 


A subfinal stage in Succession in which further develop- 
ment is inhibited because of the influence of some factor 
other than the climatic factors, cf. Proclimax, Serclimax. 



A species in a community that exerts much less Domi- 
nance (q. v.) than the Dominant species. 


The waxy material found in walls of chiefly cork cells 

in plants. 


The process of Suberin formation in plants. 


Refers to climatic regions where the moisture conditions 
range from 20 inches in the cool parts to 60 inches in the 
hot parts; and where the natural vegetation consists chiefly 
of tall grasses, and where many kinds of crops can be grown 
without irrigation, or dry farming procedures. 


An organism that has less effect than an Influent in a 
community and is present usually for only a part of the year. 


The control of the water table so as to raise it near or 
into the root zone. 


The lower division, at a depth from about 40 or 60 
meters to about 200 meters in the sea, of the Neritic or Ben- 
thic zone, below the Littoral division. These terms apply 
also in a general way to lakes. 

Subpolar Region 

Approximately the region south of the Tundra, occupied 
by Boreal forest. 

Subsequent Reproduction 

Trees which have grown up in openings in the forest 


or under the canopy following cutting or after regeneration 
operations have been started. 


See Secondary succession. 


Approximately the B horizon in soils that have distinct 
profiles; where the profile development is weak the subsoil 
is below the plowed soil, or its equivalent, in which roots 
normally grow, a vague term. 


Tillage of the Subsoil (q. v.) or the soil below the normal 
depth of plowing, cf. Chiseling. 


The formation within a species of populations that differ 
consistently one from another in Genotypic constitution and 
in the resulting Phenotypes. Isolation of such Subspecies 
may in time give rise to new Species, cf. Speciation. 


A Taxon of distinct, geographically separated complexes 
of genes, immediately below Species and above Variety (if 
varieties are recognized in a species), sometimes considered 
as synonymous with variety, or as an incipient species. 

Substitute Species 

See Vicariation. 


(1) The base, or substance upon which an organism is 
growing. (2) A vague term for the C horizon (q. v.). 


Refers to the region between the Tropics and the Tem- 
perate zone, with distinct summer and winter seasons and 
with greater heat than the Temperate zone. 


Succession (Ecological) 

The replacement of one kind of Community by another 
kind; the progressive changes in vegetation and in animal 
life which may culminate in the Climax (q. v.). cf. Allogenic, 
Autogenic, Primary succession, Secondary succession, Sere. 


The condition of a plant that contains much tissue rich 
in cell sap and is therefore fleshy or juicy, e. g., cactus. 


(1) In some animals an organ of attachment and also 
often used for the absorption of food. (2) See Haustorium. 
(3) In many plants a shoot arising from the lower parts of 
the stem or from the root. cf. Tiller, Sprout. 


An extensive Marsh type of vegetation characterized by 
the Dominance of papyrus (Cyperus papyrus) along the 
upper White Nile River, large masses of which may break 
loose and float down the river. 


Refers to Perennial plants that normally are somewhat 
woody at the base so they do not die down to the ground 
each year. 


Refers to Perennial plants that are distinctly woody at 
the base, herbaceous above (Under shrubs), intermediate to 
Suffrutescent and Fruticose (q. v.). 


The Mineralization (q. v.) of organic compounds in 
dead remains of plants and animals to inorganic compounds 
containing sulfur such as calcium sulfate which can again 
be absorbed by plants. 


Summation Temperature 

See Temperature summation. 

Summer Fallow 

The cultivation of a field in which crops have not been 
planted in order to control weeds and to accumulate soil 
moisture for the growth of a crop subsequently, cf. Fallow. 

Summer Wood 

The less porous and harder portion of the Xylem (q. v.) 
of a growth layer in woody plants produced in the latter part 
of the growing season, cf. Spring wood. 

Sun Plant 

A plant that grows well in full sunlight, cf. Heliophyllous. 


Death of tissues of a plant caused by high temperature 
and loss of water in organs exposed to bright sunshine. 

Sunspot Cycle 

The alternation in occurrence of a period of numerous 
spots on the surface of the sun and a period with fewer 
spots; one cycle averages about 11 years. 


See Epiorganism. 


A secondary Parasite, i. e., a parasite using another as its 


Refers to vibrations exceeding 20,000 per second, not 
audible to the human ear. 


A group of related Species that are geographically iso- 
lated; without any implication of natural Hybridization 
among them. cf. Syngameon. 


Supralittoral (Zone) 

The portion of the shore immediately adjacent to the 
tidal zone. 


Collectively, the minute organisms associated with the 
upper surface of the film of water in lakes, streams, ^etc. e. g., 
the water-strider. 


See Epiorganism. 

Surface Run-off 

See Run-off. 

Surface Soil 

The upper part of cultivated soil, usually stirred during 
tillage operations, or the equivalent depth of 5 to 8 inches 
in non-cultivated soils. 

Surplus Stock 

The portion of the population of game animals or fish 
at the time of harvest that are in excess of the number needed 
to maintain an adequate breeding stock. 

Survival Potential 

The capacity of an organism to survive in a given en- 


An arei of low, wet land; a low meadow. 


A land area containing excessive water much of the 
year and covered with dense, native vegetation that includes 
trees; but the term is used with various meanings, cf. Marsh, 


An area of grassland, especially one composed of sod- 
grasses, cf. Turf. 



A dense aggregation of minute aquatic organisms, or of 
certain insects such as bees and midges. 

Sweep-net Method 

A technique for determining an evaluation of the density 
of insects and other invertebrates in an area by making a 
certain number of swings of a standard entomological sweep 

Sweepstakes Bridge 

The accidental transportation of organisms across a bar- 
rier from one area to another, usually where no land connec- 
tion occurs, e. g., the migration of a few kinds of animals 
from Africa to Madagascar, cf. Filter bridge, Corridor. 


In a broad sense an organism that lives in close associa- 
tion with another, cf. Symbiosis. 


In a broad sense the living together of two or more or- 
ganisms of different species; including Parasitism, Mutual- 
ism, and Commensalism (q. v.). cf. Coaction. In a narrow 
sense synonymous with mutualism. 


The condition of similarity in form or structure in the 
parts of an organism on each side of an axis dividing it. 
cf. Bilateral symmetry, Zygomorphy. 


Refers to the origin or area of occupation of two or more 
closely related species in the same geographical area. cf. 


One of the places in the nervous system of animals where 


nerves touch one another and where stimuli are transmitted 
from one nerve cell to another. 


The pairing of Homologous chromosomes (q. v.) in early 
stages of Meiosis (q. v.). 


The branch of Plant sociology dealing with the occur- 
rence and distribution of communities, cf. Plant geography. 


A geological structure or fold formed by strata from op- 
posite sides dipping downward toward a common line. cf. 


A kind of fleshy fruit in which the seeds are produced 
on the inner surface of the concave or hollow receptacle, 
e. g., fig. 


In certain animals a mass of cytoplasm containing many 
nuclei within a single plasma membrane, cf. Coenocyte, 


The condition in which two or more digits are at least 
partly joined. 


The study of the environmental relations of communi- 
ties, a branch of Plant sociology. 


The total activity of separate agents such as various drugs 
producing an effect which may be greater than the sum of 
the effects of the individual agents. 



The sum total of species linked by frequent or occasional 
Hybridization in nature; a hybridizing group of species; the 
most inclusive interbreeding population. 


The fusion of Gametes; the Fertilization of an egg* by a 


The branch of Plant sociology dealing with the origin 
and development of communities, cf. Succession, Community 

Synthesis Table 

See Association table. 


An aggregation of plants belonging to the same Life-form 
having similar environmental requirements and occurring 
in a similar Habitat, e. g., a layer of moss plants, a group 
of floating herbs such as water lilies. 

Systematic Plant Sociology 

The branch of Plant sociology that deals with the de- 
limitation and description of communities, followed by 
grouping them into categories such as Sociation, Association, 
Alliance, Order, and Class. 

Systematic Sampling 

A method of sampling in which the samples are dis- 
tributed in a regular manner so that the sampling units will 
be located as uniformly as possible over the area under 


The science of classification; including the description, 
naming, and grouping of organisms in categories such as 


species, genus, family, order, and class; with especial con- 
sideration of evolutionary relationships. 


Refers to the entire body of an organism, e. g., the whole 
body of an organism being affected by a disease. 



A broad, elevated area of land bounded by steep slopes 
or cliffs, cf. Mesa. 


The open forest, usually coniferous, adjacent to the arctic 
Tundra (q. v.) cf. Boreal Forest. 


Accumulations of coarse rock debris from which the finer 
materials have been removed during mining operations. 

Tallgrass Prairie 

See True prairie. 


Accumulations of rock fragments below steep slopes or 
cliffs, caused by the effect of gravity. 

Tame Pasture 

An area of land once cultivated and seeded to cultivated 
plants, used for grazing, cf. Range, Ley. 


Tank, Earth 

A structure made by an excavation and an earthen dam 
across a drainage course for the purpose of impounding 
drinking water for livestock. 


A flatworm in class Cestoda, phylum Platyhelminthes, 
parasitic in the adult stage in the intestines of Vertebrates. 

Taproot System 

A root system in plants characterized by a large primary 
root (the taproot) that extends deep into the soil and has 
many smaller branches, e. g. alfalfa, cf. Fibrous root system. 


A small lake or pool in the mountains. 


An area cleared of vegetation and undergoing Secondary 
Succession in Burma. 


Movement of an organism directly towards or away from 
a stimulus, e. g. Phototaxis, (q. v.) 


A series of gradations in taxonomic status of organisms 
in which hybridization is involved. 


Any taxonomic category, e. g., species, genus, variety. 


The science of classification of organisms; the arrange- 
ment of organisms into systematic groupings such as Species, 
Genus, Family, and Order, cf. Systematics. 


Refers to processes that cause the formation of features 
of the earth's crust, e. g., upwarping. cf. Isostasy. 



The belief that the processes of nature are directed to- 
wards some end or goal such as plants store starch for the 
purpose of surviving. 


The direct orientation of an organism to the gradient of 
a stimulus, known only in response to light, cf. Taxis, Tropo- 

Temperate Zone 

The portions of the earth in the northern and southern 
hemispheres between the Tropics (q. v.) and the polar circles 
2327' from the poles, cf. Frigid zone. 

Temperature Coefficient 
See Q 10 . 

Temperature, Effective 

The temperature above a certain minimum, at which 
physiological processes such as growth of an organism are 
active, considered 5C (41 F.) for many plants. 

Temperature Inversion 

See Inversion, temperature. 

Temperatures, Cardinal 

The minimum, optimum, and maximum temperatures 
for the growth of an organism or organ, or for a process or 

Temperature Summation 

The summing of effective temperatures or Day-degrees 
(q. v.) for a period of time or for the length of time required 
for the development of an organism or organ. See Aliquote. 

Temperature Zero 

The temperature below which a number of physiological 
processes of an organism cease or are carried on at a very 
slow rate. cf. Temperature, effective. 


Temporary Pasture 

A pasture used for grazing for only a short period, usu- 
ally composed of annual plants, cf. Tame pasture. 


A band of dense, fibrous tissue connecting a muscle to 
some other part, usually a bone, in an animal. 


A stem, leaf, leaflet, or stipule of a plant, modified into 
a slender structure that coils around an object thus giving 
support to the plant bearing the tendril, e. g., pea vines, 


An instrument for measuring the tension with which 
water is held in the soil. cf. Stress. 


A slender, flexible organ, usually tactile, attached to the 
head of many kinds of animals such as insects, jellyfish, and 
snails; also the hair-like structures on the insectivorous sun- 
dew plant which traps insects. 


The study that deals with monstrosities and malforma- 
tions in organisms, especially in man. 


A mound constructed and inhabited by termites. 


Animals in the order Isoptera (white ants), resembling 
true ants, forming large, complex colonies with a highly de- 
veloped social system, occurring especially in the Tropics. 


An organism inhabiting a termite nest. 


An organism living with termites in their galleries. 



(1) Flat or undulating land usually with a steep face 
bordering a stream, lake, or sea cf. Floodplain. (2) An em- 
bankment of earth built across a slope to control Run-off and 
reduce erosion. 


Refers to the land. 


Refers to deposits derived from the land. cf. Allochtho- 
nous, Autochthonous. 


Herbaceous types of vegetation on dry land, e. g., Steppe, 


The behaviour of an animal when it defends an area from 
intruders, e. g., various birds and fishes. 


(1) The area occupied by an individual or group of or- 
ganisms. (2) The area which an animal defends against in- 
truders, cf. Home range. 


An earthen construction made of bricks that have been 
cut directly from the natural sod of sedge meadows and dried 
in the sun. cf. Adobe. 


The first of two geological periods in the Cenozoic era 
comprising the Paleocene, Eocene, Oligocene, Miocene, and 
Pliocene epochs; in order from the oldest to the most recent. 


The outer covering or coat of seeds. 



An organism or part of one having four sets of chromo- 
somes in its nuclei, cf. Haploid, Diploid, Polyploid. 

Texture (Soil) 

The property of the composition of soil that deals with 
the relative proportions of various sizes of separates or min- 
eral particles including clay, silt, sand, and gravel, cf. Struc- 

Thai lop hyte 

A plant in any one of the phyla of algae and fungi, for- 
merly classified in the division Thallophyta. 


A plant body that is not differentiated into leaves, stems, 
and roots; one- to many-celled, e. g., Thallophytes. 

Thermal Constants 

The sum of Day-degrees (q. v.) of temperature that is re- 
quired fqr a plant to mature after planting, cf. Temperature 

Thermal Stratification 

The condition of a body of water in which the successive 
horizontal layers have different temperatures, each layer 
more or less sharply differentiated from the adjacent ones, 
the warmest at the top. cf. Epilimnion, Hypolimnion, In- 
verse stratification, Thermocline. 

Thermal Zone (Belt) 

A well defined area or zone, occurring on some mountain- 
sides, in which the vegetation is exceptionally free from frost 
in the spring and fall. 


The layer in a thermally stratified body of water within 
which the temperature decreases rapidly with increasing 


depth usually at a rate greater than 1 C. per meter of depth, 
cf. Thermal stratification. 

Thermodynamics, Laws of 

(1) Energy and work are transformable from one to an- 
other kind, e. g., sunlight to chemical energy. (2) Spon- 
taneous transformation of energy is accompanied by dis- 
persal of a part into non-available heat such as in respiration. 
(3) The absolute zero temperature is not attainable. 


The production of heat as occurs in an organism during 


The continuous record of temperature made by a 


A self-recording thermometer. 


The response of an organism to a general diffuse change 
in temperature, e.g., the opening of flowers as the tempera- 
ture rises. 


The effects of the alternation of temperature such as 
occurs during day and night alternations upon organisms. 


Refers to organism that grows well in high tempera- 
tures, e.g., bacteria in hot springs. 


The movement of an organism toward heat or cold as a 



One of the classes of life-forms of Raunkiaer that includes 
the annual plants. 


A vitamin (Bj) required by numerous organisms, but 
formed only in green plants and in some microorganisms. 


Vegetation that is dominated by a dense growth of small 

trees and shrubs. 


The movement of an organism to secure close contact 
with an object, syn. Stereotaxis. 


The response of a plant or a portion of it to a con- 
tact stimulus, e.g., a tendril growing around a stem. syn. 


(1) The part of the body in higher Vertebrates, contain- 
ing the heart and lungs. (2) The middle portion of the body 
of insects, bearing the legs and wings (when present). 


A stiff, pointed, modified branch in plants such as the 

Thorn Forest 

A vegetation type in the Tropics or Sub tropics consisting 
mostly of thorny trees, shrubs, and vines; Xerophytic in 
aspect, and subject to long droughts. 


See Nematode. 



The duration or intensity of a stimulus that is required 
to produce response in an organism. 


The coagulation or clotting, as of blood, in the vascular 
and lymphatic systems of living animals. 


One of the Endocrine glands (q. v.) found in Vertebrates, 
secretes a Hormone containing iodine. 


The substance containing iodine produced by the Thy- 
roid gland. 


An animal in the order Acarina, class Arachnida, which 
sucks blood, e.g., the fever tick on cattle. Also used for some 
parasitic dipterous insects such as the sheep tick. 

Tidal Flat 

An essentially barren, nearly flat, muddy area, periodi- 
cally covered by tides, the lower parts daily, the higher parts 
only during exceptionally high tides. 

Tidal Marsh 

A low flat marshland that is intersected by channels and 
tidal sloughs, usually covered by high tides, with vegetation 
consisting of rushes, grasses, and other low, salt-tolerant 

Tidal Zone 

The area of a shore between the levels of high and low 
tides, syn. Intertidal zone. 


An unstratified deposit of gravel, boulders, sand, and 
finer materials which has been transported by a glacier, cf. 
Drift, Colluvium. 



The operations such as plowing, harrowing, and disking 
that are used in cultivating the soil in order to make condi- 
tions more suitable for the growth of crop plants. 


A Shoot arising from the base of a plant as in wheat and 

other grasses. 

Till Plain 

A more or less level land area covered with glacial Till. 

Tilth, Soil 

The physical condition, particularly Structure, of soil with 
reference to favorableness for growth of crops; characterized 
by friability, high degree of non-capillary porosity, and stable 
granular structure. Soil in poor tilth is non-friable, hard, 
non-aggregated, and difficult to cultivate properly. 


This term usually denotes the upper limit of tree growth 
in mountains or poleward in latitude, cf. Tree limit. 


A organized, usually compact group of cells that have 
similar structure and function, e.g., cork tissue in plants, 
bone tissue in animals. 

Tissue Culture 

The growth in a suitable medium of a portion of tissue 
separated from a plant or animal body. 


The capacity of an organism to live under a given set 
of conditions within its range of Ecological amplitude (q. v.), 
between the Maximum and the Minimum (q. v.) (the limits 
of tolerance), cf. Preferendum. 


A general term to include characteristics of the ground 


surface such as plains, hills, and mountains; degree of Relief, 
steepness of slopes; and other physiographic features. 


The uppermost portion of the soil, often considered the 
layer six or seven inches in thickness, which is richer in 
organic material and lighter in texture than the material 
below. In uniform material the topsoil includes the layer 
that is usually plowed up. cf. Subsoil. 


(1) A violent vortex, with a diameter usually of about 
0.25 mile, in the atmosphere, accompanied by a pendulous, 
more or less funnel-shaped cloud. (2) In West Africa a 
violent thundersquall. 


Refers to the rapid and violent movement of materials 
such as water in a stream, heavy rainfall, sliding of gravel, 
etc.; or to organisms living in swift streams. 

Torrid Zone 

See Tropics. 

Total Digestible Nutrients (T. D. N.) 

The standard evaluation of the digestibility of materials 
in the feed of livestock, including proteins, fats, nitrogen- 
free extract, and fiber content. 

Total Estimate 

The combined estimates of abundance and cover char- 
acteristics of vegetation; used commonly in England. 


A poison produced by an organism. 

Trace Element 

See Essential element. 



A Radioisotope isotope (q. v.) used to follow the course 
of or to determine the location of a normal element in an 


(1) A Vessel in the Xylem (q. v.) in plants. (2) The tube 
from the throat to the lungs in Vertebrates. (3) One of the 
small tubes that conduct air in the bodies of most Ar- 
thropods, especially in insects, opening to the exterior 
through Spiracles (q. v.). 


A long, thick-walled cell, without perforations, with 
tapering ends, that conducts water and gives support, located 
in the Xylem of plants, especially Conifers. 


A member of the Tracheophyta (vascular plants) com- 
prising four subphyla; Psilopsida (the most primitive), 
Lycopsida (the clubmosses), Sphenopsida (the horsetails), and 
the Pteropsida (the ferns, conifers and their allies, and the 
flowering plants). 

Trade Winds 

Winds that blow regularly from subtropical areas of high 
pressure towards areas of low pressure along the equator, 
in the northern hemisphere from the northeast, in the south- 
ern hemisphere from the southeast; important in producing 
ocean currents. 


A species, or closely related species, that exist on both 
sides of a barrier and consequently must have extended across 
it at one time. 


A long, narrow sample area, or a line, used for analyzing 


vegetation; essentially a cross section of the vegetation, cf. 
Line-intercept method. Quadrat. 


The change of one type of bacterium to another type, 
as when DNA from Type I of Pneumococcus is transferred 
to Type II it replaces some of the Chromatin in the latter 
whose characteristics such as resistance to Penicillin may 
thus be modified. Genetic information is thus transferred. 


Species that regularly occur in an upper layer in a com- 
munity found also in a lower stratum. 


The periodic and alternating movement of livestock 
between two regions that differ in climate. 

Transient Species 

A species that migrates through a locality without breed- 
ing or over-wintering. 

Transition Life-Zone 

The northern part of the Austral life-zone (q. v.). 


(1) The movement of materials in solution from one 
part of a plant to another part. cf. Xylem, Phloem. (2) The 
separation of a part of a Chromosome and its attachment to 
another one. 


The loss of water in vapor form from a plant, mostly 
through the stomata and lenticels. cf. Stoma, Lenticel. 

Transpiration Coefficient 

The ratio of the oven-dry material produced by a plant 
during a more or less extended period of time (usually the 
entire growth period) to the total amount of water transpired 
during the same period. 


Transpiration Efficiency 

The amount in grams of dry substance produced by a 
plant for every kilogram of water transpired. 


A seedling, or young plant, that has been moved from one 
location to another; in forestry practice a seedling that has 
been transplanted one or more times in the nursery. 

Transportation (in Soil Erosion) 

The movement of detached particles or masses of soil 
across the land or through the air by wind, water, or gravity. 

Trap Line 

A series of traps arranged in a more or less linear arrange- 
ment to secure a sample of the mammals in an area, or for 
securing animals for their fur, or some other purpose. 


Refers to a shock or a wound, or the resulting condition 
in an organism. 


A calcareous, concretionary limestone that has been 
formed in water, cf. Sinter, Tufa. 


A woody plant that has a single main stem and commonly 
more than eight or ten feet tall. cf. Shrub. 

Tree Limit (Line) 

The altitude in mountains, or the southern or northern 
latitude, at which only isolated trees grow and beyond which 
only stunted forms, Krummholz (q. v.), or Tundra (q. v.) 
occur, cf. Timber line. 


cf. Fluke. 



The oldest geologic period in the Mesozoic era; it began 
about 205 million years ago and lasted for about 40 million 


A group of plants of related genera, a division of the 
Family, e.g., the tribe Festuceae includes the genera Poa, 
Festuca, Bromus, and others. 


An organism or one of its parts that has three times the 
Haploid set of Chromosomes in the nucleus, cf. Polyploid. 


Refers to an organism that has one more Chromosome 
than the Diploid (q. v.) number; occurs in barley, and peas. 

Tristat Method 

A method of photographing the same area at successive 
periods of time by permanently marking the spot where 
each leg of the tripod is set 

Trophic (-trophy) 

Refers to nutrition. 

Trophic Level 

One of the parts in a nutritive series in an Ecosystem 
(q. v.) in which a group of organisms in a certain stage in 
the Food chain secures food in the same general manner. 
The first or lowest trophic level consists of Producers 
(green plants), the second level of Herbivores, the third 
level of primary Carnivores, the fourth level of secondary 
Carnivores. Bacteria and fungi are organisms in the Decom- 
poser trophic level. 


A type of association of species involving aphids and 
coccids with ants. cf. Myrmecophilous. 



The exchange of food, or the interchange of a stimulus 
response concerning food, between animals, especially in the 
social insects. 

Tropical Cyclone 

See Hurricane. 

Tropical Life Zone 

The portion of Central America south of the Austral 
life zone (q. v.), bounded on the north by an accumulation 
of temperatures during the growing season above 43 F. of 
26,000F. cf. Life zone. 


The Tropic of Cancer, 2327' north latitude, and the 
Tropic of Capricorn, 2327 / south latitude; or the region 
between these parallels. 


The curvature response of an organ to a stimulus, e.g., 
a stem growing towards a source of light and roots away from 
the light. 


An Obligate parasite (q. v.) that regularly lives as a non- 
parasite during part of its life cycle. 


The uppermost portion of the Troposphere (q. v.). 


A plant that can live under moist conditions pan of the 
year and under dry conditions during another part, e.g., 
woody plants that lose their leaves during the dry parts of 
the year or during winter. 


The part of the atmosphere extending upward about 


six miles to the Stratosphere (q. v.), in which clouds of 
moisture form and the temperature decreases with increas- 
ing altitude. 


The direct orientation of an organism in response to two 
lights that are moving toward or away from the midpoint 
between them. cf. Telotaxis. 

True Prairie 

The prairie grassland characterized by tall grasses (five 
to six or more feet tall) and mid-grasses (two to four feet 
tall) in the central part of the United States, cf. Pampas. 


Underground fungi in the genus Tuber, class Ascomy- 
cetes, or their fruiting bodies, edible. 

Truncated Soil Profile 

A Soil profile (q. v.) which has lost part or all of the 
A and B horizons (q. v.) by accelerated erosion or by 


A flagellated Protozoan in the genus Trypanosoma, 
parasitic in the blood of various Vertebrates, and causing 
serious diseases in man and other animals such as sleeping 

Tsetse Fly 

A dipterous insect in the genus Glossina, sucks blood and 
transmits diseases caused by Trypanosomes such as sleeping 


A high wave on shore areas, particularly bordering the 
Pacific Ocean, caused by an earthquake in the ocean floor. 



An enlarged, underground stem, tending to be oval or 
spherical in shape, usually rich in starch, and capable of 
vegetative reproduction of the plant, e.g., a potato tuber. 


A porous rock formed by the deposition of material, 
especially calcium carbonate from water, as in springs, cf. 
Travertine, Sinter. 


A disease in rabbits, rodents, and man, caused by the 
microorganism Pasteurella tularensis, which is transmitted 
by insects. 

Tullgren Funnel 

A modification of the Berlese funnel (q. v.) for separating 
Collembolons (q. v.), Mites, larvae, and other small organisms 
from the soil. cf. Baerman funnel. 


The treeless land in arctic and alpine regions, varying 
from bare area to various types of vegetation consisting of 
grasses, sedges, forbs, dwarf shrubs, mosses, and lichens. 


The condition of a body of water that contains suspended 
material such as clay or silt particles, dead organisms or their 
parts, or small living plants and animals. 


The layer of low, dense grassland, comprising the above- 
ground portions and the upper roots and rhizomes with at- 
tached soil particles, cf. Sward, Sod. 


The condition of a cell or a tissue when it is swollen 
with water causing Turgor pressure (q. v.). 


Turgor Pressure 

The actual pressure of the sap within a cell against the 
cell wall resulting from the intake of water by Osmosis 

(q. v.). 


A winter bud on some water plants that becomes de- 
tached, overwinters, and under favorable conditions develops 
into a new plant. 


(1) The mixing of layers of water in lakes in the spring 
and autumn, cf. Thermal stratification. (2) The period of 
time required for an organism to grow, mature, die, and 
undergo decomposition. 


A plant-form that is tufted, bearing many stems arising as 
a large, dense cluster from the crown, e.g., a large bunch 
grass such as Arizona fescue. 

Twin Communities 

Communities that are similar in a dominant or com- 
bining layers, or in Synusiae (q. v.), but vary in others. 


See Ubiquist. 


(1) A kind of vegetation, e.g., Community-type, forest 
type, birch type. (2) The one or more specimens of a species, 
subspecies, or variety on the basis of which the Taxon was 
described. (3) One of the groups of soils in a soils series, 
e.g., Miami silt loam type in the Miami series. 


A Tropical cyclone or Hurricane (q. v.) in the Far East, 
particularly in the China Seas. 



Ubiquist (Ubiquitist) 

An organism that flourishes in several kinds of commu- 
nities or ecosystems, e.g., the raven, red maple tree. 


Refers to a Ubiquist. 


See Supersonic. 

Ultraviolet Radiation 

The electromagnetic waves not perceptible to the human 
eye, between violet light waves and X-rays, from about 
390 mu to 10 mu in length. 


An irregular line of contact between two geological strata 
caused by exposure to erosion of the lower one before sub- 
mersion and consequent deposition of the second stratum. 


See Hypodispersion. 


An intensity of grazing by livestock in which the forage 


available for consumption under good management practices 
is not used sufficiently, thus causing loss of forage. 


Collectively the shrubs, sprouts, seedling and sapling 
trees, and all herbaceous plants in a forest. 


A size of population so low in number of individuals that 
mortality is greater than in denser populations largely 
because of increased exposure to unfavorable environmental 


A low shrub. 


Refers to a range area on which a smaller number of 
livestock is present than it is capable of supporting ade- 
quately for a given season, cf. Fully stocked. Overstocked. 


Collectively the trees in a forest below the upper canopy 
cover, cf. Overstory. 


Refers to a forest in which considerable differences in 
the ages of trees occur. 


A Mammal with hooves, e.g., horse, cow, swine, elephant. 


Refers to an organism that consists of only one cell, 
e.g., blue-green algae, Protozoans. 


A homogeneous grouping of plant species within a given 
stratum or of the same or closely similar life-forms, cf. 



Refers to an animal that produces only one egg or one 
offspring at one time. 


Refers to an organism that is either male or female, cf. 


Refers to an organism that has only one generation in a 
year. cf. Multivoltine , Diapause. 


Refers to plants and other kinds of food that are not 
readily eaten by animals. 


Not Specialized (q. v.). 

Upper Austral Life Zone 

One of the divisions in Merriam's Austral life zone (q. v.). 

Upper Sonoran Life Zone 

See Sonoran life zone. 

Use, Actual 

The total number and period of time livestock graze 
on a range, usually expressed as animal-unit months, cow 
months, or sheep months. 

Use, Common 

The practice of grazing a given range by more than one 
kind of livestock within the same grazing year. 

Use, Dual 

The grazing of a range area by more than one kind of 
livestock at the same time, such as cattle and sheep. 

Use, Proper 

The utilization of a Range so that the Condition is 
maintained in a good to excellent rating. 



Refers to a cell that contains one or more Vacuoles. 


A space within a cell, enclosed by a membrane and 
containing a watery solution, the cell sap, surrounded by 

Vacuole, Contractile 

A structure in some one-celled organisms that excretes 
water by means of energy supplied by the Cytoplasm. 


The capability of an organism for Dispersal (q. v.). 

Valence, Ecological 

See Ecological amplitude. 

Valley Train 

Materials carried beyond a glacial ice-front by streams 
of melt water and deposited over a narrow area within a 

Van't Hoff Rule 


Vopor Pressure Deficit 

The difference between the actual vapor pressure in the 
atmosphere in a certain space and the vapor pressure at 


An organism, community, types of soil, etc., that differs 
sufficiently in its attributes from the typical specimen or 
norm to be classified as a variation of the group as a whole. 


The attribute or characteristic such as height and weight 
that is used in statistical measurements of Variation. 


Divergences in the characteristics of organisms, or other 
objects, of the same kind caused either by the environment 
or by differences in the genetic constitution of the organism, 
cf. Phenotype, Genotype. 


The irregular occurrence of patches, bands, or other 
areas on the surface of organs of plants and animals, such as 
leaves, caused chiefly by the lack of pigment in the cells of 
these areas or beneath them. 


A taxonomic group or Taxon (q. v.) within a Species, or 
a Subspecies, e.g., Juniperus communis L. var. sibirica 
(Burgsd.) Rydb. cf. Cultivar. 


A layer in a mass of lacustrine sediments, which may 
consist of coarser and finer sediments, deposited annually 
in a lake or sea. 


Refers to vessels or ducts that conduct fluids in organisms. 


Vascular Bundle 

A strand consisting of Xylem (q. v.) and Phloem (q. v.) 

in plants. 

Vascular Cylinder 

A vascular bundle with associated tissues in stems and 
roots of plants, cf. Stele. 

Vascular Plant 

A plant in the phylum Tracheophyta which includes the 
pteridophytes (ferns and their allies) and the spermatophytes 
(seed plants). 


An organism, usually an insect, that transmits a patho- 
genic virus, bacterium, protozoon, or fungus from one organ- 
ism to another, e.g., Tsetse fly (q. v.). 

Vegetable Ball 

A more or less spherical mass of plant material consist- 
ing of algae, other water plants, needles of trees, etc., formed 
by wave action in shallow water on sandy shores. 


See Vegetative. 


Plants in general, or the sum total of plant life in an 
area. cf. Flora, Floristic, Community. 


Refers to Vegetation, in contrast to Vegetative (q. v.). 

Vegetation (Vegetational) Cover 

The sum total of plants and plant materials such as 
leaves, stems, and fruits that forms coverage on the surface 
of the soil; sometimes used in a more restricted sense to 
designate the sum of living plants on an area. 


Vegetation (Vegetational) Type 

A kind of Vegetation (q. v.) or the kind of Community 
(q. v.) of any size, rank, or stage of Succession. 

Vegetative (Vegetal) 

Refers to the nutritive and growth functions or structures 
of plants in contrast to the reproductive functions or struc- 
tures; not to be confused with Vegetation or Vegetational 
(q. v.). cf. Somatic. 

Vegetative Propagation 

The propagation, or increasing the number, of plants by 
the use of Vegetative parts such as rhizomes (q. v.), runners 
(q. v.), gemmae, or other parts, cf. Asexual reproduction. 


(1) See Vascular bundle. (2) A Vessel in animals that 
carries blood from the capillaries to the heart. (3) A thick- 
ened structure that gives support to wings of insects. 


A tissue in the outer part of aerial roots of certain plants, 
especially orchids, that absorbs water rapidly. 

Veld (Veldt) 

A tract of open country in South Africa occupied by 
grasslands at the higher elevations and by Scrub or Savanna 
at the lower elevations. 


The arrangement of Veins in a leaf blade or in a wing 
of insects. 


The long, dry period of the year in tropical America. 


Refers to a shape of an object that is similar to a worm. 



Refers to spring, cf. Aspection. 


The process of hastening the flowering phase of plants 
by subjecting young seedlings or other parts to low tempera- 
ture, less commonly to a high temperature. 


The general slope of a mountain range or a landscape. 


An animal in the subphylum Vertebrata, phylum Chor- 
data, e.g., mammals, fishes, reptiles, birds. 


Refers to evening time. cf. Crepuscular. 


A series of cells forming a tube-like structure in the 
Xylem (q. v.) of plants, conducts water and substances in 


Refers to a structure, function, or behavioural act of an 
organism that has so decreased in importance during the 
course of evolution that only a trace remains, e.g., the vermi- 
form appendix in man. cf. Primitive. 


The capability of a seed, spore, egg, or other organ of a 
plant or animal to continue or resume growth when it is 
exposed to favorable environmental conditions, cf. Dormancy. 


Refers to the state of being alive, cf. Viability. 

Vicariad (Vicarious Species) 

One of a pair of closely related species, variety, or other 
Taxon that replace each other geographically. 



The phenomenon of ecologically equivalent species, or 
taxonomically corresponding species, replacing (or "substi- 
tuting") each other in similar environments in different 
geographic areas, e.g., caribou in North America and rein- 
deer in Eurasia. 


The condition of variation in a population or in an 
individual resulting from growing in close proximity to 
other organisms. 

Virgin (Forest, Community, Region, etc.) 

Refers to objects or aggregations, especially vegetation, 
essentially uninfluenced by human activity. 


The branch of biology dealing with viruses. 


A submicroscopic parasite in organisms consisting of 
nucleic acid and protein, incapable of increasing in number 
outside of the host cell, causing various diseases in plants 
and animals. 


The doctrine that life processes are caused by some force 
that cannot be measured, in addition to the operation of the 
laws of chemistry and physics. 


The condition of vigor of organisms; the capacity to live 
and complete the life cycle. Braun-Blanquet classified plants 
according to states of vitality into four categories. 


Organic substances required in minute quantities by 
plants and animals in their metabolic processes, cf . Thiamine. 



The cultivation and production of grapes. 


(1) Refers to an animal in which the embryo develops 
within its body and which produces living offspring, e.g., 
most mammals, cf. Oviparous. (2) Refers to a plant in which 
the embryo within the Ovary continues development without 
interruption, e.g., the mangrove; or the production of 
Bulbils or small plants instead of flowers and seeds, e.g., 
bulbous bluegrass. 

Volume Weight 

A figure denoting the number of times heavier a dry 
soil, including the pore space, is than an equal volume of 
water, cf. Bulk density. 



Wadi (Wady) 

A watercourse in deserts, dry except after rains, term 
used in southwest Asia and the Sahara, cf. Arroyo, Wash. 

Wallace's Line 

The line established by A. R. Wallace (1860) as a 
boundary between the Oriental and the Australian Faunal 
regions (q. v.). 


See Honuoio therm. 

Warm Front 

The border between a mass of warm air advancing into 
or above a mass of colder air. cf. Cold front. 

Warning Coloration 

See Aposematic. 


In southwestern United States, a dry bed of an inter- 
mittent stream, usually sandy and gravelly. 

Wasting Disease 

A disease of eelgrass (Zostera marina) often producing 
serious epidemics, caused by a Slime mold (Labyrinthula sp.). 


Water Gap 

A narrow valley or gorge in a ridge of mountains or 
hills, eroded by a stream, e.g., the Delaware Water Gap. 

Water-holding Capacity 

The amount of water, stated as the percentage of oven-dry 
soil, that is retained by the soil after the gravitational water 
has drained off. cf. Field capacity. 


The condition of a soil in which all the pore spaces are 
filled with water. 

Water Requirement 

The ratio of the number of units of water absorbed by 
a plant during the growing season to the number of units 
of dry matter produced by the plant during the same time, 
cf. Transpiration coefficient. 


(1) The total area of land above a given point on a 
waterway that contributes run-off water to the flow at that 
point. (2) A major subdivision of a drainage basin. 


A tornado-like vortex and cloud occurring over a body 
of water. 

Water Spreading 

The application by means of stream diversion or other- 
wise of water over the land in order to increase the soil 
moisture supply for the growth of plants or to store it under- 
ground for subsequent withdrawal by pumping. 

Water Table 

The upper surface of the free ground water in a zone 
of saturation, except where it is separated by an underlying 
body of ground water by unsaturated material. 


Water Table, Perched 

The upper surface of a body of free ground water in a 
zone of saturation, separated by unsaturated material from 
another body of ground water in a saturated zone beneath, 
cf. Perched water. 


The state of the atmosphere at any given time with re- 
gard to precipitation, temperature, humidity, cloudiness, 
wind movement, and barometric pressure, cf. Climate. 


The process of the physical and chemical disintegration 
of rocks and minerals. 


A general term for any troublesome or otherwise unde- 
sirable plant, usually introduced, grows without intentional 

Wegener's Hypothesis 

See Continental drift. 


A dam across a water channel for diverting or for measur- 
ing the flow of water. 


Winds that blow prevailingly from the southwest in the 
northern hemisphere, from the northwest in the southern 
hemisphere, located between the high pressure areas of the 
Subtropics and the arctic or antarctic circles. 

White Alkali 

See Saline soil. 

Wilderness Area 

See Natural area. 



Collectively the non-domesticated vertebrate animals, 
except fishes, such as deer, moose, birds, etc. 


A seedling or a young plant that grew under natural 
conditions, not cultivated, outside of a nursery, and that 
has been dug for use as planting stock. 


A sudden blast of wind descending from mountains to 
the sea, especially in the Straits of Magellan. 


A violent storm of rain and wind on the northwest coast 
of Australia; also applied in some parts of Australia to a 
local Dust whirl (q. v.). 


The temporary or transient loss of turgidity in a plant 
caused by a rate of transpiration in excess of the rate of 
absorption of water. Permanent wilting: wilting to such a 
degree that plants do not recover unless water is added to 
the soil soon after wilting occurs. Permanent wilting per- 
centage (wil ting-point, wil ting-coefficient): the water remain- 
ing in the soil in percentage of dry weight of the soil when 
the plants are in a condition of permanent wilting. 


A planting of trees and shrubs, usually in three or more 
rows to serve as a barrier to reduce or check the velocity of 
the wind. cf. Shelterbelt. 

Winter Annual 

A plant that germinates in the autumn, lives through 
the winter as a small plant usually, renews growth in the 
spring, flowers, produces fruit, and then dies. 



The larva of certain slender beetles as in the genus 

Witches' Broom 

The abnormal brushlike production of numerous weak 
shoots toward the tip of a branch of a tree or a shrub, caused 
by a fungus or a mite. 


Any land used for the growth of trees and shrubs such 
as permanent woodland cover, plantings along roadsides and 
stream banks, Shelterbelts, farm Woodlots, etc. 


A small area of land occupied by trees. 

Working Depth (Roots) 

The depth in the soil to which a large number of roots 
of a plant penetrate, cf. Depth, effective soil. 



An effect produced in the offspring in the endosperm of 
a seed brought about by the fusion of one of the sperms with 
the Diploid fusion nucleus in the Ovule. 


See Cross-pollination. 


Refers to a successional sequence (Sere) which begins in 
a dry habitat, cf. Xerosere, Hydrarch. 


Refers to a dry habitat, cf . Xerocolous, Xerophyte, Hygric, 


A seed pod that opens in dry air. and closes in moist air, 
e.g., carrot seed pods. 


Refers to animals living in dry places, cf. Xerophilous, 



The structure or form characteristic of organs of Xero- 
phytes (q. v.), e.g., tough, leathery leaves on some desert 

Xerophilous, Xerophytic 

Refers to a plant that is capable of growing in dry places, 
e.g., cactus, cf. Xerophyte, Hydrophilous, Mesophyte. 


A plant that can grow in dry places, e.g., creosote bush, 
cactus, cf. Xerophilous. 


Refers to characteristics which are developed under the 
influence of drought. 


A series of successional stages beginning in a dry area, 
cf. Hydrosere, Sere, Xerarch. 


Refers to a dry and warm climatic period, e.g., one of 
the postglacial periods. 


Electromagnetic rays, 0.1 to 50 mu, shorter than Ultra- 
violet and longer than Gamma rays. 


Woody tissue in the Stele (q. v.) of plants, conducts water 
and substances in solution. 


Refers to organisms that consume wood. 



One-celled plants in the class Ascomycetes, phylum Eumy- 
cophyta, the true fungi, reproduce vegetatively by budding, 
and convert sugar to alcohol and carbon dioxide in An- 
aerobic respiration. 


The part of the production or Productivity (q. v.) of a 
group of organisms that is removed or expected to be re- 
moved by man, e.g., the number of deer killed during a 
hunting season, the timber produced by a stand of trees. 

Yield Table 

A table showing the volumes of timber that a stand of 
trees will produce at different ages (usually in ten-year 
periods) per unit of area. 

Young Growth 

See second growth. 



Refers to Zone. 

Zonal Soil 

A kind of soil that has a permanent type of profile, 
characteristic of the prevailing conditions of the climate and 
vegetation, e.g., Chernozem (q. v.). cf. Intrazonal soil. 


(1) Vegetation occurring in more or less well marked belts 
or areas much longer than wide, usually fairly uniform in 
physiognomy, as along lake shores, mountain sides, and sea 
shores. (2) One of the five great climatic belts of the earth; 
the two frigid zones, two temperate zones, and the torrid 


An organism that is normally disseminated by an animal, 
cf. Diaspore. 


The science that deals with the geographic distribution 
of animals, cf. Biogeography, Plant geography. 



The study of animals. 


Refers to organisms that feed on substances of animal 


Animals occurring in Plankton (q. v.). 


A motile spore, possessing one or more flagella, in certain 
algae and fungi. 


See Bilateral symmetry. 


The product resulting from the union of two gametes; 
the fertilized egg. 


Alee, W. C., A. E. Emerson, O. Park, T. Park, and K. P. 
Schmidt. Principles of Animal Ecology, W. B. Saunders 
& Co., Philadelphia, Pa., 1949. 

Andrewartha, H. G., and L. C. Birch. The Distribution and 
Abundance of Animals, University of Chicago Press, 
Chicago, 111., 1954. 

Becking, R. W. The Zilrich-Montpellier School of Phytoso- 
ciology, Botanical Review, vol. 23 (1957), pages 411488. 

Braun-Blanquet, J. Plant Sociology, McGraw-Hill Book Co., 
Inc., New York, N. Y., 1932. 

Brown, Dorothy. Methods of Surveying and Measuring 
Vegetation, Bulletin 42, Commonwealth Bureaux Pas- 
tures and Field Crops, Hurley, Berks, England, 1954. 

Cain, S. A. Foundations of Plant Geography, Harper and 
Bros., New. York, 1944. 

Cain, S. A., and Q. M. de Oliveira Castro. Manual of Vegeta- 
tion Analysis, Harper and Bros., New York, N. Y., 1959. 

Clarke, G. L. Elements of Ecology, John Wiley & Sons, Inc., 
New York, N. Y., 1954. 

Clements, F. E. 'Plant Succession, Carnegie Institute of Wash- 
ington Publication 242 (1916), Washington. D. C. 


Clements, F. E., and V. E. Shelford. Bioecology, John Wiley 

& Sons, New York, N. Y., 1939. 
Dansereau, P. Biogeography. An Ecological Perspective, The 

Ronald Press, New York, N. Y., 1957. 
Darlington, P. J., Jr. Zoogeography: the Geographical Dis- 
tribution of Animals, John Wiley & Sons, New York, 

N. Y., 1957. 
Daubenmire, R. F. Plants and Environment, a Textbook of 

Plant Autecology, John Wiley & Sons, Inc., New York, 

N. Y., 1959. 2nd Edition. 
Dayton, W. A. Glossary of Botanical Terms Commonly Used 

in Range Management, U. S. Dept. of Agriculture Miscl. 

Publication No. 110 Revised (1950). 
Dice, Lee R. Natural Communities, University of Michigan 

Press, Ann Arbor, Mich., 1952. 
Dodson, E. D. Evolution: Process and Product, Reinhold 

Publishing Corporation, New York, N. Y., 1960. 
Ecological Society of America. Reports 1, 2, 3, of the 

Committee on Nomenclature, (1933, 1934, 1935). 

Eggleton, F. E. Report of the Committee on Nomenclature 

of the Ecological Society of America, Revised. (1952). 

Esau, Katherine. Anatomy of Seed Plants, John Wiley & Sons, 

Inc., New York, N. Y., 1960. 

Giese, A. C. Cell Physiology, W. B. Saunders Co., Philadel- 
phia, Pa., 1957. 
Good, R. The Geography of Flowering Plants, 2nd Edition, 

Longmans, Green & Co., London, England, 1953. 
Hanson, Herbert C. Ecology of the Grassland H, Botanical 

Review, vol. 16 (1950), pp. 283-360. 

Hanson, Herbert C., and E. D. Churchill. The Plant Com- 
munity, Reinhold Publishing Corporation, New York, 

N. Y., 1961. 
Hawley, A. H. Human Ecology, The Ronald Press Co., New 

York, N. Y., 1950. 


Jackson, B. D. A Glossary of Botanic Terms With Their 
Derivation and Accent, Lippincott, Philadelphia, Pa., 

Macfadyen, A. Animal Ecology, Aims and Methods, Sir Isaac 
Pitman & Sons, Ltd., London, England, 1957. 

Mayr, E. (Editor). The Species Problem (A Symposium), 
American Association for the Advancement of Science 
Publ. No. 50, Washington, D. C., 1957. 

McDougall, W. B. Plant Ecology, 4th Edition, Lea & Febiger, 
Philadelphia, Pa., 1949. 

Meyer, B. S., D. B. Anderson, & R. H. Bohning. Introduction 
to Plant Physiology, D. Van Nostrand Co., Inc., Princeton, 
N. J., 1960. 

Odum, E. P. Fundamentals of Ecology, 2nd Edition, W. B. 
Saunders Co., Philadelphia, Pa., 1959. 

Costing, H. J. The Study of Plant Communities, 2nd Edition, 
W. H. Freeman & Co., San Francisco, Calif., 1956. 

Pearse, A. S. Animal Ecology, 2nd Edition, McGraw-Hill 
Book Co., Inc., New York, N. Y., 1939. 

Sampson, A. W. Range Management, Principles and Prac- 
tice, John Wiley and Sons, Inc., 1952. 

Scott, J. P. Animal Behaviour, The University of Chicago 
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Soil Conservation Society of America, Soil and Water Con- 
servation Glossary, Journal of Soil and Water Conserva- 
tion, vol. 7 (1951-1952), pp. 1-37. 

Stoddart, L. A. Range Management, McGraw-Hill Book Co., 
Inc., New York, N. Y., 1943. 

Swanson, C. P. The Cell, Prentice-Hall, Inc., Englewood 
Cliffs, N. J., 1960. 

Tansley, A. G. The British Islands and Their Vegetation, 
2 vols. Cambridge University Press, Cambridge, England, 

U. S. Department of Agriculture. Soils, the Yearbook of 
Agriculture, 1957, U. S. Government Printing Office, 
Washington, D. C., 1957. 


U.S. Soil Survey Staff. Soil Survey Manual, U.S. Government 
Printing Office, Washington, D.C., 1951. 

Weaver, J. E., and F. E. Clements. Plant Ecology, 2nd Edi- 
tion, McGraw-Hill Book Co., Inc., New York, N. Y., 1938. 

Welch, Paul S. Limnology, McGraw-Hill Book Co., Inc., 
New York, N. Y., 1935. 

Woodbury, A. M. Principles of General Ecology, McGraw- 
Hill Book Co., Inc. New York, N. Y., 1954. 


Pictorial History 
of Philosophy 


Here, in vivid pictures and illuminating 
text, are more than three thousand years of 
world philosophy. From Socrates to Suzuki 
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The editor, Dr. Dagobert D. Runes, has 
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ages will enrich anyone's enjoyment and ap- 
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Distributed to the trade by: 

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a division of Crown Publishers, Inc. 
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Dean, Graduate School, 

Duquesne University