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MAGILLS ENCYCLOPEDIA OF SCIENCE
P L A N T L I F E
MAGILLS ENCYCLOPEDIA OF SCIENCE
P L A N T L I F E
Volume 3Microbial Nutrition and Metabolism–Sustainable Agriculture
EditorBryan D. Ness, Ph.D.Pacific Union College, Department of Biology
Project EditorChristina J. Moose
Salem Press, Inc.Pasadena, CaliforniaHackensack, New Jersey
Copyright © 2003, by Salem Press, Inc.All rights in this book are reserved. No part of this work may be used or reproduced in any manner what-
soever or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording,or any information storage and retrieval system, without written permission from the copyright ownerexcept in the case of brief quotations embodied in critical articles and reviews. For information address thepublisher, Salem Press, Inc., P.O. Box 50062, Pasadena, California 91115.
Some of the updated and revised essays in this work originally appeared in Magill’s Survey of Science: LifeScience (1991), Magill’s Survey of Science: Life Science, Supplement (1998), Natural Resources (1998), Encyclopediaof Genetics (1999), Encyclopedia of Environmental Issues (2000), World Geography (2001), and Earth Science (2001).
∞ The paper used in these volumes conforms to the American National Standard for Permanence ofPaper for Printed Library Materials, Z39.48-1992 (R1997).
Library of Congress Cataloging-in-Publication Data
Magill’s encyclopedia of science : plant life / edited by Bryan D. Ness.
p. cm.Includes bibliographical references (p. ).
ISBN 1-58765-084-3 (set : alk. paper) — ISBN 1-58765-085-1 (vol. 1 : alk. paper) —ISBN 1-58765-086-X (vol. 2 : alk. paper) — ISBN 1-58765-087-8 (vol. 3 : alk. paper) —ISBN 1-58765-088-6 (vol. 4 : alk. paper)
1. Botany—Encyclopedias. I. Ness, Bryan D.QK7 .M34 2002580′.3—dc21
2002013319
First Printing
printed in the united states of america
Editor in Chief: Dawn P. DawsonManaging Editor: Christina J. Moose
Manuscript Editor: Elizabeth Ferry SlocumAssistant Editor: Andrea E. MillerResearch Supervisor: Jeffry Jensen
Acquisitions Editor: Mark Rehn
Photograph Editor: Philip BaderProduction Editor: Joyce I. BucheaPage Design and Graphics: James HutsonLayout: William ZimmermanIllustrator: Kimberly L. Dawson Kurnizki
TABLE OF CONTENTS
List of Illustrations, Charts, and Tables . . . . xlixAlphabetical List of Contents . . . . . . . . . . liii
Microbial nutrition and metabolism . . . . . . 663Microbodies . . . . . . . . . . . . . . . . . . . . 666Microscopy . . . . . . . . . . . . . . . . . . . . 668Mitochondria . . . . . . . . . . . . . . . . . . . 672Mitochondrial DNA . . . . . . . . . . . . . . . 675Mitosis and meiosis . . . . . . . . . . . . . . . 677Mitosporic fungi . . . . . . . . . . . . . . . . . 681Model organisms . . . . . . . . . . . . . . . . . 682Molecular systematics . . . . . . . . . . . . . . 686Monocots vs. dicots . . . . . . . . . . . . . . . 688Monocotyledones . . . . . . . . . . . . . . . . . . 690Monoculture . . . . . . . . . . . . . . . . . . . 692Mosses . . . . . . . . . . . . . . . . . . . . . . . 694Multiple-use approach . . . . . . . . . . . . . . 697Mushrooms . . . . . . . . . . . . . . . . . . . . 699Mycorrhizae. . . . . . . . . . . . . . . . . . . . 702
Nastic movements . . . . . . . . . . . . . . . . 704Nitrogen cycle . . . . . . . . . . . . . . . . . . 706Nitrogen fixation . . . . . . . . . . . . . . . . . 709Nonrandom mating . . . . . . . . . . . . . . . 712North American agriculture. . . . . . . . . . . 714North American flora . . . . . . . . . . . . . . 718Nuclear envelope . . . . . . . . . . . . . . . . . 722Nucleic acids . . . . . . . . . . . . . . . . . . . 723Nucleolus . . . . . . . . . . . . . . . . . . . . . 727Nucleoplasm . . . . . . . . . . . . . . . . . . . 729Nucleus . . . . . . . . . . . . . . . . . . . . . . 730Nutrient cycling . . . . . . . . . . . . . . . . . 732Nutrients . . . . . . . . . . . . . . . . . . . . . 734Nutrition in agriculture . . . . . . . . . . . . . 737
Oil bodies . . . . . . . . . . . . . . . . . . . . . 740Old-growth forests . . . . . . . . . . . . . . . . 741Oomycetes. . . . . . . . . . . . . . . . . . . . . 743Orchids . . . . . . . . . . . . . . . . . . . . . . 745
Organic gardening and farming . . . . . . . . 747Osmosis, simple diffusion, and
facilitated diffusion . . . . . . . . . . . . . . 751Oxidative phosphorylation . . . . . . . . . . . 755Ozone layer and ozone hole debate . . . . . . 757
Pacific Island agriculture . . . . . . . . . . . . 761Pacific Island flora . . . . . . . . . . . . . . . . 765Paclitaxel . . . . . . . . . . . . . . . . . . . . . 768Paleobotany . . . . . . . . . . . . . . . . . . . . 770Paleoecology . . . . . . . . . . . . . . . . . . . 774Parasitic plants . . . . . . . . . . . . . . . . . . 777Peat. . . . . . . . . . . . . . . . . . . . . . . . . 779Peroxisomes . . . . . . . . . . . . . . . . . . . . 782Pesticides . . . . . . . . . . . . . . . . . . . . . 783Petrified wood . . . . . . . . . . . . . . . . . . 787Pheromones . . . . . . . . . . . . . . . . . . . . 790Phosphorus cycle . . . . . . . . . . . . . . . . . 791Photoperiodism. . . . . . . . . . . . . . . . . . 794Photorespiration . . . . . . . . . . . . . . . . . 796Photosynthesis . . . . . . . . . . . . . . . . . . 800Photosynthetic light absorption. . . . . . . . . 804Photosynthetic light reactions. . . . . . . . . . 807Phytoplankton . . . . . . . . . . . . . . . . . . 809Pigments in plants . . . . . . . . . . . . . . . . 812Plant biotechnology . . . . . . . . . . . . . . . 815Plant cells: molecular level . . . . . . . . . . . 821Plant domestication and breeding . . . . . . . 826Plant fibers . . . . . . . . . . . . . . . . . . . . 829Plant life spans . . . . . . . . . . . . . . . . . . 831Plant science. . . . . . . . . . . . . . . . . . . . 835Plant tissues . . . . . . . . . . . . . . . . . . . . 839Plantae . . . . . . . . . . . . . . . . . . . . . . . 843Plants with potential . . . . . . . . . . . . . . . 849Plasma membranes. . . . . . . . . . . . . . . . 851Plasmodial slime molds . . . . . . . . . . . . . 854Poisonous and noxious plants . . . . . . . . . 857Pollination. . . . . . . . . . . . . . . . . . . . . 862Polyploidy and aneuploidy . . . . . . . . . . . 865
xlvii
Population genetics . . . . . . . . . . . . . . . 868Prokaryotes . . . . . . . . . . . . . . . . . . . . 870Proteins and amino acids . . . . . . . . . . . . 873Protista . . . . . . . . . . . . . . . . . . . . . . . 875Psilotophytes . . . . . . . . . . . . . . . . . . . 879
Rain-forest biomes . . . . . . . . . . . . . . . . 883Rain forests and the atmosphere . . . . . . . . 885Rangeland . . . . . . . . . . . . . . . . . . . . . 889Red algae . . . . . . . . . . . . . . . . . . . . . 892Reforestation . . . . . . . . . . . . . . . . . . . 894Reproduction in plants. . . . . . . . . . . . . . 897Reproductive isolating
mechanisms . . . . . . . . . . . . . . . . . . 899Resistance to plant diseases . . . . . . . . . . . 901Respiration . . . . . . . . . . . . . . . . . . . . 904Rhyniophyta . . . . . . . . . . . . . . . . . . . . 907Ribosomes . . . . . . . . . . . . . . . . . . . . . 909Rice. . . . . . . . . . . . . . . . . . . . . . . . . 912RNA . . . . . . . . . . . . . . . . . . . . . . . . 914Root uptake systems . . . . . . . . . . . . . . . 917Roots . . . . . . . . . . . . . . . . . . . . . . . . 920Rubber . . . . . . . . . . . . . . . . . . . . . . . 925Rusts . . . . . . . . . . . . . . . . . . . . . . . . 929
Savannas and deciduous tropical forests . . . 932Seedless vascular plants . . . . . . . . . . . . . 934Seeds . . . . . . . . . . . . . . . . . . . . . . . . 937Selection . . . . . . . . . . . . . . . . . . . . . . 941Serpentine endemism . . . . . . . . . . . . . . 943Shoots . . . . . . . . . . . . . . . . . . . . . . . 944Slash-and-burn agriculture . . . . . . . . . . . 946Soil . . . . . . . . . . . . . . . . . . . . . . . . . 949Soil conservation . . . . . . . . . . . . . . . . . 955Soil contamination . . . . . . . . . . . . . . . . 957Soil degradation . . . . . . . . . . . . . . . . . 959Soil management . . . . . . . . . . . . . . . . . 962Soil salinization . . . . . . . . . . . . . . . . . . 963South American agriculture . . . . . . . . . . . 965South American flora . . . . . . . . . . . . . . 969Species and speciation . . . . . . . . . . . . . . 973Spermatophyta . . . . . . . . . . . . . . . . . . . 976Spices . . . . . . . . . . . . . . . . . . . . . . . 977Stems. . . . . . . . . . . . . . . . . . . . . . . . 980Strip farming . . . . . . . . . . . . . . . . . . . 983Stromatolites . . . . . . . . . . . . . . . . . . . 985Succession . . . . . . . . . . . . . . . . . . . . . 988Sugars . . . . . . . . . . . . . . . . . . . . . . . 991Sustainable agriculture. . . . . . . . . . . . . . 993
xlviii
Magill’s Encyclopedia of Science: Plant Life
PUBLISHER’S NOTE
Magill’s Encyclopedia of Science: Plant Life is de-signed to meet the needs of college and high schoolstudents as well as nonspecialists seeking generalinformation about botany and related sciences. Thedefinition of “plant life” is quite broad, covering therange from molecular to macro topics: the basics ofcell structure and function, genetic and photosyn-thetic processes, evolution, systematics and classi-fication, ecology and environmental issues, andthose forms of life—archaea, bacteria, algae, andfungi—that, in addition to plants, are traditionallystudied in introductory botany courses. A numberof practical and issue-oriented topics are covered aswell, from agricultural, economic, medicinal, andcultural uses of plants to biomes, plant-related en-vironmental issues, and the flora of major regionsof the world. (Readers should note that, althoughcultural and medicinal uses of plants are occasion-ally addressed, this encyclopedia is intended forbroad information and educational purposes.Those interested in the use of plants to achievenutritive or medicinal benefits should consult aphysician.)
Altogether, the four volumes of Plant Life survey379 topics, alphabetically arranged from Acid pre-cipitation to Zygomycetes. For this publication, 196essays have been newly acquired, and 183 essaysare previously published essays whose contentswere reviewed and deemed important to include ascore topics. The latter group originally appeared inthe following Salem publications: Magill’s Survey ofScience: Life Science (1991), Magill’s Survey of Science:Life Science, Supplement (1998), Natural Resources(1998), Encyclopedia of Genetics (1999), Encyclope-dia of Environmental Issues (2000), World Geography(2001), and Earth Science (2001). All of these previ-ously published essays have been thoroughly scru-tinized and updated by the set’s editors. In additionto updating the text, the editors have added newbibliographies at the ends of all articles.
New appendices, providing essential researchtools for students, have been acquired as well:
• a “Biographical List of Botanists” with briefdescriptions of the contributions of 134 fa-mous naturalists, botanists, and other plantscientists
• a Plant Classification table
• a Plant Names appendix, alphabetized bycommon name with scientific equivalents
• another Plant Names appendix, alphabetizedby scientific name with common equivalents
• a “Time Line” of advancements in plant sci-ence (a discursive textual history is also pro-vided in the encyclopedia-proper)
• a Glossary of 1,160 terms
• a Bibliography, organized by category of re-search
• a list of authoritative Web sites with theirsponsors, URLs, and descriptions
Every essay is signed by the botanist, biologist,or other expert who wrote it; where essays havebeen revised or updated, the name of the updaterappears as well. In the tradition of Magill reference,each essay is offered in a standard format that al-lows readers to predict the location of core informa-tion and to skim for topics of interest: The title ofeach article lists the topic as it is most likely to belooked up by students; the “Category” line indi-cates pertinent scientific subdiscipline(s) or area(s)of research; and a capsule “Definition” of the topicfollows. Numerous subheads guide the reader
vii
through the text; moreover, key concepts are itali-cized throughout. These features are designed tohelp students navigate the text and identify pas-sages of interest in context. At the end of each essayis an annotated list of “Sources for Further Study”:print resources, accessible through most libraries,for additional information. (Web sites are reservedfor their own appendix at the end of volume 4.) A“See also” section closes every essay and refersreaders to related essays in the set, thereby linkingtopics that, together, form a larger picture. For ex-ample, since all components of the plant cell arecovered in detail in separate entries (from the Cellwall through Vacuoles), the “See also” sections forthese dozen or so essays list all other essays cover-ing parts of the cell as well as any other topics of in-terest.
Approximately 150 charts, sidebars, maps, ta-bles, diagrams, graphs, and labeled line drawingsoffer the essential visual content so important tostudents of the sciences, illustrating such core con-cepts as the parts of a plant cell, the replicationof DNA, the phases of mitosis and meiosis, theworld’s most important crops by region, the partsof a flower, major types of inflorescence, or differentclassifications of fruits and their characteristics. Inaddition, nearly 200 black-and-white photographsappear throughout the text and are captioned tooffer examples of the important phyla of plants,parts of plants, biomes of plants, and processes ofplants: from bromeliads to horsetails to wheat; fromArctic tundra to rain forests; from anthers to stemsto roots; from carnivorous plants to tropisms.
Reference aids are carefully designed to alloweasy access to the information in a variety of modes:The front matter to each of the four volumes in-
cludes the volume’s contents, followed by a full“Alphabetical List of Contents” (of all the volumes).All four volumes include a “List of Illustrations,Charts, and Tables,” alphabetized by key term, toallow readers to locate pages with (for example)a picture of the apparatus used in the Miller-UreyExperiment, a chart demonstrating the genetic off-spring of Mendel’s Pea Plants, a map showing theworld’s major zones of Desertification, a cross-section of Flower Parts, or a sampling of the manytypes of Leaf Margins. At the end of volume 4 isa “Categorized Index” of the essays, organizedby scientific subdiscipline; a “Biographical Index,”which provides both a list of famous personagesand access to discussions in which they figureprominently; and a comprehensive “Subject Index”including not only the personages but also the coreconcepts, topics, and terms discussed throughoutthese volumes.
Reference works such as Magill’s Encyclopediaof Science: Plant Life would not be possible withoutthe help of experts in botany, ecology, environmen-tal, cellular, biological, and other life sciences; thenames of these individuals, along with their aca-demic affiliations, appear in the front matter tovolume 1. We are particularly grateful to the pro-ject’s editor, Bryan Ness, Ph.D., Professor of Biol-ogy at Pacific Union College in Angwin, California.Dr. Ness was tireless in helping to ensure thorough,accurate, and up-to-date coverage of the content,which reflects the most current scientific knowl-edge. He guided the use of commonly acceptedterminology when describing plant life processes,helping to make Magill’s Encyclopedia of Science:Plant Life easy for readers to use for reference tocomplement the standard biology texts.
viii
Magill’s Encyclopedia of Science: Plant Life
CONTRIBUTOR LIST
About the Editor: Bryan Ness is a full professor in the Department of Biology at Pacific Union College, afour-year liberal arts college located atop Howell Mountain in the Napa Valley, about ninety miles north ofSan Francisco. He received his Ph.D. in Botany from Washington State University. His doctoral work focusedon molecular plant systematics and evolution. In addition to authoring or coauthoring a number of scientificpapers, he has contributed to The Jepson Manual: Higher Plants of California, The Flora of North America, amultivolume guide to the higher plants of North America, and more than a dozen articles for various SalemPress publications, including Aging, Encyclopedia of Genetics, Magill’s Encyclopedia of Science: Animal Life,Magill’s Medical Guide, and World Geography. For four years he managed The Botany Site, a popular Internetsite on botany. He is currently working on a book about plant myths and misunderstandings.
Stephen R. AddisonUniversity of Central Arkansas
Richard AdlerUniversity of Michigan, Dearborn
Steve K. AlexanderUniversity of Mary Hardin-Baylor
Michael C. AmspokerWestminster College
Michele ArduengoIndependent Scholar
Richard W. ArnsethScience Applications International
J. Craig BaileyUniversity of North Carolina,
Wilmington
Anita Baker-BlockerApplied Meteorological Services
Iona C. BaldridgeLubbock Christian University
Richard BeckwittFramingham State College
Cindy BenningtonStetson University
Alvin K. BensonUtah Valley State College
Margaret F. BoorsteinC. W. Post College of Long Island
University
P. E. BostickKennesaw State College
J. Bradshaw-RouseIndependent Scholar
Thomas M. BrennanDickinson College
Alan BrownLivingston University
Kenneth H. BrownNorthwestern Oklahoma State
University
Bruce BruntonJames Madison University
Pat CalieEastern Kentucky University
James J. CampanellaMontclair State University
William J. CampbellLouisiana Tech University
Steven D. CareyUniversity of Mobile
Roger V. CarlsonJet Propulsion Laboratory
Robert E. CarverUniversity of Georgia
Richard W. Cheney, Jr.Christopher Newport University
John C. ClauszCarroll College
Miriam ColellaLehman College
William B. CookMidwestern State University
J. A. CooperIndependent Scholar
Alan D. CopseyCentral University of Iowa
Joyce A. CorbanWright State University
Mark S. CoyneUniversity of Kentucky
Stephen S. DaggettAvila College
William A. DandoIndiana State University
ix
James T. DawsonPittsburg State University
Albert B. DickasUniversity of Wisconsin
Gordon Neal DiemADVANCE Education and
Development Institute
David M. DiggsCentral Missouri State University
John P. DiVincenzoMiddle Tennessee State University
Gary E. DolphIndiana University, Kokomo
Allan P. DrewSUNY, College of Environmental
Science and Forestry
Frank N. EgertonUniversity of Wisconsin, Parkside
Jessica O. EllisonClarkson University
Cheryld L. EmmonsAlfred University
Frederick B. EssigUniversity of South Florida
Danilo D. FernandoSUNY, College of Environmental
Science and Forestry
Mary C. FieldsMedical University of South Carolina
Randy FirstmanCollege of the Sequoias
Roberto GarzaSan Antonio College
Ray P. GerberSaint Joseph’s College
Soraya GhayourmaneshIndependent Scholar
Carol Ann GillespieGrove City College
Nancy M. GordonIndependent Scholar
D. R. GossettLouisiana State University,
Shreveport
Hans G. GraetzerSouth Dakota State University
Jerry E. GreenMiami University
Joyce M. HardinHendrix College
Linda HartUniversity of Wisconsin, Madison
Thomas E. HemmerlyMiddle Tennessee State University
Jerald D. HendrixKennesaw State College
John S. HeywoodSouthwest Missouri State University
Jane F. HillIndependent Scholar
Joseph W. HintonIndependent Scholar
Carl W. HoagstromOhio Northern University
Virginia L. HodgesNortheast State Technical Community
College
David Wason Hollar, Jr.Rockingham Community College
Howard L. HosickWashington State University
Kelly HowardIndependent Scholar
John L. HowlandBowdoin College
M. E. S. HudspethNorthern Illinois University
Samuel F. HuffmanUniversity of Wisconsin, River Falls
Diane White HusicEast Stroudsburg University
Domingo M. JarielLouisiana State University, Eunice
Karen N. KählerIndependent Scholar
Sophien KamounOhio State University
Manjit S. KangLouisiana State University
Susan J. KarcherPurdue University
Jon E. KeeleyOccidental College
Leigh Husband KimmelIndependent Scholar
Samuel V. A. KisseadooHampton University
Kenneth M. KlemowWilkes University
Jeffrey A. KnightMount Holyoke College
Denise KnotwellIndependent Scholar
James KnotwellWayne State College
Lisa A. LambertChatham College
Craig R. LandgrenMiddlebury College
x
Magill’s Encyclopedia of Science: Plant Life
John C. LandoltShepherd College
David M. LawrenceJohn Tyler Community College
Mary Lee S. LedbetterCollege of the Holy Cross
Donald H. LesUniversity of Connecticut
Larry J. LittlefieldOklahoma State University
John F. LogueUniversity of South Carolina, Sumter
Alina C. LopoUniversity of California, Riverside
Yiqi LuoUniversity of Oklahoma
Fai MaUniversity of California, Berkeley
Jinshuang MaArnold Arboretum of Harvard
University Herbaria
Zhong MaPennsylvania State University
Dana P. McDermottIndependent Scholar
Paul MaddenHardin-Simmons University
Lois N. MagnerPurdue University
Lawrence K. MagrathUniversity of Science and Arts of
Oklahoma
Nancy Farm MännikköIndependent Scholar
Sergei A. MarkovMarshall University
John S. MechamTexas Tech University
Roger D. MeicenheimerMiami University, Ohio
Ulrich MelcherOklahoma State University
Iain MillerWright State University
Jeannie P. MillerTexas A&M University
Randall L. MilsteinOregon State University
Eli C. MinkoffBates College
Richard F. ModlinUniversity of Alabama, Huntsville
Thomas J. MontagnoSimmons College
Thomas C. MoonCalifornia University of Pennsylvania
Randy MooreWright State University
Christina J. MooseIndependent Scholar
J. J. MuchovejFlorida A&M University
M. MustoeIndependent Scholar
Jennifer Leigh MykaBrescia University
Mysore NarayananMiami University
Bryan NessPacific Union College
Brian J. NichelsonU.S. Air Force Academy
Margaret A. OlneyColorado College
Oghenekome U. OnokpiseFlorida A&M University
Oluwatoyin O. OsunsanyaMuskingum College
Henry R. OwenEastern Illinois University
Robert J. ParadowskiRochester Institute of Technology
Bimal K. PaulKansas State University
Robert W. PaulSt. Mary’s College of Maryland
Kenneth A. PidcockWilkes College
Rex D. PieperNew Mexico State University
George R. PlitnikFrostburg State University
Bernard Possidente, Jr.Skidmore College
Carol S. RadfordMaryville University, St. Louis
V. RaghavanOhio State University
Ronald J. RavenState University of New York
at Buffalo
Darrell L. RayUniversity of Tennessee, Martin
Judith O. RebachUniversity of Maryland,
Eastern Shore
David D. ReedMichigan Technological University
xi
Contributor List
Mariana Louise RhoadesSt. John Fisher College
Connie RizzoPace University
Harry RoyRensselaer Polytechnic Institute
David W. RudgeWestern Michigan University
Neil E. SalisburyUniversity of Oklahoma
Helen SalmonUniversity of Guelph
Lisa M. SardiniaPacific University
Elizabeth D. SchaferIndependent Scholar
David M. SchlomCalifornia State University,
Chico
Matthew M. SchmidtSUNY, Empire State College
Harold J. SchreierUniversity of Maryland
John Richard SchrockEmporia State University
Guofan ShaoPurdue University
Jon P. ShoemakerUniversity of Kentucky
John P. ShontzGrand Valley State University
Nancy N. ShontzGrand Valley State University
Beryl B. SimpsonUniversity of Texas
Sanford S. SingerUniversity of Dayton
Susan R. SingerCarleton College
Robert A. SinnottArizona Agribusiness and Equine
Center
Elizabeth SlocumIndependent Scholar
Dwight G. SmithConnecticut State University
Roger SmithIndependent Scholar
Douglas E. SoltisUniversity of Florida
Pamela S. SoltisIndependent Scholar
F. Christopher SowersWilkes Community College
Alistair SponselImperial College
Valerie M. SponselUniversity of Texas, San Antonio
Steven L. StephensonFairmont State College
Dion StewartAdams State College
Toby R. StewartIndependent Scholar
Ray StrossState University of New York at Albany
Susan Moyle StudlarWest Virginia University
Ray SumnerLong Beach City College
Marshall D. SundbergEmporia State University
Frederick M. SurowiecIndependent Scholar
Paris SvoronosQueen’s College, City University
of New York
Charles L. VigueUniversity of New Haven
James WaddellUniversity of Minnesota, Waseca
William J. WassermanSeattle Central Community College
Robert J. WellsSociety for Technical Communication
Yujia WengNorthwest Plant Breeding Company
P. Gary WhiteWestern Carolina University
Thomas A. WikleOklahoma State University
Donald Andrew WileyAnne Arundel Community College
Robert R. WiseUniversity of Wisconsin, Oshkosh
Stephen L. WolfeUniversity of California, Davis
Ming Y. ZhengGordon College
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Magill’s Encyclopedia of Science: Plant Life
LIST OF ILLUSTRATIONS, CHARTS, AND TABLES
Volume-pageAcid Precipitation pH Scale (bar graph). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-3Africa, Desertification of (map) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-301African Countries with More than 15 Percent Arable Land, Leading Agricultural Crops of (table) . . . I-15African Rain Forests (Sidebar) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-884Africa’s Agricultural Products (map) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-13Air Pollutant Emissions by Pollutant and Source, 1998 (table) . . . . . . . . . . . . . . . . . . . . . . . . I-45Algae, Classification of (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-49Algae, Types of (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-48Angiosperm, Life Cycle of an (drawing). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-66Angiosperms and Continental Drift (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-63Antibiotic Resistance, The Growth of (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-122Ants and Acacias (sidebar). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-254Asian Countries with More than 15 Percent Arable Land, Leading Agricultural Crops of (table) . . . . I-93Australia, Selected Agricultural Products of (map) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-103
Bacillus thuringiensis and Bacillus popilliae as Microbial Biocontrol Agents (table) . . . . . . . . . . . . . I-155Bacterial Diseases of Plants, Some (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-115Biomes and Their Features (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-148Biomes of the World (map) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-151Biomes (percentages), Terrestrial (pie chart) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-152Brown Algae (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-165
Cacao: The Chocolate Bean (sidebar) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-211Carbon Cycle, The (flow chart) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-184Carnivorous Plants (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-194Cell, Parts of a Plant (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-822Cell, Parts of the Plant (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-286Central America, Selected Agricultural Products of (map) . . . . . . . . . . . . . . . . . . . . . . . . . I-208Central American Countries, Leading Agricultural Crops of (table) . . . . . . . . . . . . . . . . . . . . I-209Chromosome, Schematic of a (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-229Conifer Leaves (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-270Conifers, Classification of (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-271Corn-Producing Countries, 1994, Leading (bar graph) . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-275Crop Yields, Declining with Successive Harvests on Unfertilized Tropical Soils (bar graph). . . . . . III-948Crops and Places of Original Cultivation, Major (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-26Crops of African Countries with More than 15 Percent Arable Land (table) . . . . . . . . . . . . . . . . I-15Crops of Asian Countries with More than 15 Percent Arable Land (table) . . . . . . . . . . . . . . . . . I-93Crops of Central American Countries (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-209Crops of European Countries with More than 20 Percent Arable Land (table) . . . . . . . . . . . . . . II-387Crops of Pacific Island Nations (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-763Cycads, Classification of (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-283
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Darwin and the Beagle, Charles (sidebar/map) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-402Deforestation, Results of (flow chart) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-295Deforestation by Country, 1990-1995, Percentage of Annual (map). . . . . . . . . . . . . . . . . . . . . I-294Desertification of Africa (map) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-301Diatoms (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-308Dicot (Eudicot) Families, Common (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-74Dinoflagellates (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-312Diseases, Symptoms of Plant (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-314DNA, The Structure of (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-323DNA Replication, Stages in (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-330Drought, Impacts of (sidebar). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-336
Endangered Plant Species, A Sampling of the World’s (table) . . . . . . . . . . . . . . . . . . . . . . . II-352Endocytosis (drawing). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-356Endomembrane System, The (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-359Eudicot (Dicot) Families Common in North America (table) . . . . . . . . . . . . . . . . . . . . . . . . II-376Eukarya, Classification of Domain (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV-1106Eukaryotic Cell, Parts of a (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-383Europe, Selected Agricultural Products of (map) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-386European Countries with More than 20 Percent Arable Land, Leading Agricultural
Crops of (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-387Evolution of Plants (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-411Exocytosis (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-357
Ferns, Classification of (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-420Flower, Parts of a (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-429Flower Shapes: Perianth Forms (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-433Flower Structure, Variations in (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-430Forest Areas by Region (pie chart) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-455Forest Loss in Selected Developing Countries, 1980-1990 (bar graph) . . . . . . . . . . . . . . . . . . . I-296Fruit Types (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-465Fruit Types and Characteristics (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-466Fungi: Phyla and Characteristics (table). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-472
Garden Plants and Places of Original Cultivation (table) . . . . . . . . . . . . . . . . . . . . . . . . . . II-475Genetically Modified Crop Plants Unregulated by the U.S. Department of Agriculture (table) . . . . II-496Germination of a Seed (drawing). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-510Ginkgophyta, Classification of Phylum (table). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-513Gnetophytes, Classification of (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-518Grasses of the United States, Common (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-523Greenhouse Effect (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-535Greenhouse Gas Emissions, 1990-1999, U.S. (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-536Growth Habits (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-542Gymnosperms, Classification of (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-544
Hormones and Their Functions, Plant (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-575Hornworts, Classification of (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-579
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Horsetails, Classification of (table). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-581Hydrologic Cycle (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-594
Inflorescences, Some Common (drawing). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-601Invasive Plants: Backyard Solutions (sidebar) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-606
Land Used for Agriculture by Country, 1980-1994, Increases in (map) . . . . . . . . . . . . . . . . . . . I-38Leading Peat-Producing Countries, 1994 (bar graph) . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-780Leaf, Parts of a (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-617Leaf Arrangements, Common (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-620Leaf Bases (drawing). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-626Leaf Lobing and Division, Common Patterns of (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . II-623Leaf Margins (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-624Leaf Shapes, Common (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-628Leaf Tips (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-625Leaf Tissue, Cross-Section of (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-618Leaves, Types of (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-622Liverworts, Classification of (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-641Lumber Consumption, U.S. (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV-1062Lycophytes, Classification of (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-646
Meiosis: Selected Phases (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-679Mendel’s Pea-Plant Experiments, Results of (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-501Mendel’s Pea Plants (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-500Miller-Urey Experiment (drawing). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-405Mitochondrion, Structure of a (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-673Mitosis (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-678Monocot Families, Common (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-73Monocot Families Common in North America (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . III-690Monocots vs. Dicots, Characteristics of (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-688Mosses, Classification of (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-695
Nastic Movement (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-704Nitrogen Cycle (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-707No-Tillage States, 1994-1997 (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-369North America, Selected Agricultural Products of (map) . . . . . . . . . . . . . . . . . . . . . . . . . III-715Nutrients, Plant (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-735
Osmosis, Process of (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-752Ovule, Parts of an (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-70Ozone Hole, 1980-2000, Average Size of the (graph) . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-758
Pacific Island Nations, Leading Agricultural Crops of (table) . . . . . . . . . . . . . . . . . . . . . . . III-763Persons Chronically Undernourished in Developing Countries by Region,
Number of (bar graph) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-39Phosphorus Cycle, The (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-792
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Photoperiodism (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-794Photosynthesis (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-801Plant, Parts of a (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-840Plantae, Phyla of Kingdom (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-844Poisonous Plants and Fungi, Common (table). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-858Pollination (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-864Population Growth, 1950-2020, World and Urban (bar graph) . . . . . . . . . . . . . . . . . . . . . . . II-587Prokaryotic Cell, A (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-871Protista, Phyla of (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-876
Rain Forests, African (Sidebar) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-884Rice-Producing Countries, 1994 (bar graph) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-913Root, Parts of a (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-921Root Systems, Two (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-923Roots, Water Uptake by (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-637Rubber, End Uses of Natural (pie chart) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-928
Seed, Germination of a (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-510Seedless Vascular Plants: Phyla and Characteristics (table) . . . . . . . . . . . . . . . . . . . . . . . . III-935Seeds: Eudicots vs. Monocots (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-938Seeds of Dissent (sidebar) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-497Shoot, Parts of the (drawing). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-945Silvicultural Methods, Environmental Effects of Select (flow chart) . . . . . . . . . . . . . . . . . . . . II-452Soap and Water (sidebar). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-123Soil Horizons (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-950Soil Limits to Agriculture, by Percentage of Total Land Area (pie chart) . . . . . . . . . . . . . . . . . III-961Soil Orders in the U.S. Classification System, The Twelve (table) . . . . . . . . . . . . . . . . . . . . . III-952South America, Selected Agricultural Products of (map) . . . . . . . . . . . . . . . . . . . . . . . . . III-966Stem Structure (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV-1018
Time Line of Plant Biotechnology (table). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-816Tissues, Plant (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-842Transformation of Sunlight into Biochemical Energy (flow chart) . . . . . . . . . . . . . . . . . . . . . II-365Transport Across Cell Membranes, Mechanisms for (table) . . . . . . . . . . . . . . . . . . . . . . . . III-852Tropical Soils, Declining Crop Yields with Successive Harvests on Unfertilized (bar graph). . . . . . III-948Tropisms (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV-1028
Water Through a Plant, The Path of (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV-1049Water Uptake by Roots (drawing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-637Welwitschia: The Strangest Gymnosperm (sidebar). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . II-545Wheat-Producing Countries, 1994 (bar graph) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IV-1055Wheat Stem Rust: Five Stages (table) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III-931World Food Production (bar graph) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-40
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ALPHABETICAL LIST OF CONTENTS
Volume 1
Acid precipitation . . . . . . . . . . . . . . . . . . 1Active transport . . . . . . . . . . . . . . . . . . . 4Adaptations . . . . . . . . . . . . . . . . . . . . . 7Adaptive radiation. . . . . . . . . . . . . . . . . 10African agriculture. . . . . . . . . . . . . . . . . 12African flora . . . . . . . . . . . . . . . . . . . . 17Agricultural crops: experimental. . . . . . . . . 20Agricultural revolution . . . . . . . . . . . . . . 23Agriculture: history and overview. . . . . . . . 24Agriculture: marine . . . . . . . . . . . . . . . . 29Agriculture: modern problems . . . . . . . . . . 31Agriculture: traditional . . . . . . . . . . . . . . 34Agriculture: world food supplies . . . . . . . . 37Agronomy . . . . . . . . . . . . . . . . . . . . . 42Air pollution . . . . . . . . . . . . . . . . . . . . 43Algae . . . . . . . . . . . . . . . . . . . . . . . . 47Allelopathy . . . . . . . . . . . . . . . . . . . . . 51Alternative grains . . . . . . . . . . . . . . . . . 52Anaerobes and heterotrophs . . . . . . . . . . . 54Anaerobic photosynthesis . . . . . . . . . . . . 56Angiosperm cells and tissues. . . . . . . . . . . 58Angiosperm evolution . . . . . . . . . . . . . . 61Angiosperm life cycle . . . . . . . . . . . . . . . 65Angiosperm plant formation . . . . . . . . . . . 69Angiosperms . . . . . . . . . . . . . . . . . . . . 72Animal-plant interactions. . . . . . . . . . . . . 78Antarctic flora . . . . . . . . . . . . . . . . . . . 81Aquatic plants . . . . . . . . . . . . . . . . . . . 82Archaea . . . . . . . . . . . . . . . . . . . . . . . 84Arctic tundra . . . . . . . . . . . . . . . . . . . . 88Ascomycetes . . . . . . . . . . . . . . . . . . . . 90Asian agriculture. . . . . . . . . . . . . . . . . . 92Asian flora . . . . . . . . . . . . . . . . . . . . . 96ATP and other energetic molecules. . . . . . . 100Australian agriculture . . . . . . . . . . . . . . 103Australian flora . . . . . . . . . . . . . . . . . . 105Autoradiography . . . . . . . . . . . . . . . . . 109
Bacteria . . . . . . . . . . . . . . . . . . . . . . 112Bacterial genetics . . . . . . . . . . . . . . . . . 119Bacterial resistance and super bacteria . . . . . 121Bacteriophages . . . . . . . . . . . . . . . . . . 125Basidiomycetes . . . . . . . . . . . . . . . . . . . 127Basidiosporic fungi . . . . . . . . . . . . . . . . 129Biochemical coevolution in
angiosperms. . . . . . . . . . . . . . . . . . 131Biofertilizers. . . . . . . . . . . . . . . . . . . . 134Biological invasions . . . . . . . . . . . . . . . 136Biological weapons . . . . . . . . . . . . . . . . 139Bioluminescence . . . . . . . . . . . . . . . . . 142Biomass related to energy . . . . . . . . . . . . 144Biomes: definitions and determinants . . . . . 147Biomes: types . . . . . . . . . . . . . . . . . . . 150Biopesticides . . . . . . . . . . . . . . . . . . . 154Biosphere concept . . . . . . . . . . . . . . . . 157Biotechnology. . . . . . . . . . . . . . . . . . . 158Botany . . . . . . . . . . . . . . . . . . . . . . . 161Bromeliaceae . . . . . . . . . . . . . . . . . . . . 162Brown algae . . . . . . . . . . . . . . . . . . . . 164Bryophytes . . . . . . . . . . . . . . . . . . . . 166Bulbs and rhizomes . . . . . . . . . . . . . . . 169
C4 and CAM photosynthesis . . . . . . . . . . 172Cacti and succulents . . . . . . . . . . . . . . . 175Calvin cycle . . . . . . . . . . . . . . . . . . . . 178Carbohydrates . . . . . . . . . . . . . . . . . . 180Carbon cycle . . . . . . . . . . . . . . . . . . . 183Carbon 13/carbon 12 ratios . . . . . . . . . . . 186Caribbean agriculture . . . . . . . . . . . . . . 188Caribbean flora . . . . . . . . . . . . . . . . . . 190Carnivorous plants . . . . . . . . . . . . . . . . 192Cell cycle . . . . . . . . . . . . . . . . . . . . . 195Cell theory. . . . . . . . . . . . . . . . . . . . . 197Cell-to-cell communication . . . . . . . . . . . 199Cell wall . . . . . . . . . . . . . . . . . . . . . . 201
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Cells and diffusion . . . . . . . . . . . . . . . . 203Cellular slime molds . . . . . . . . . . . . . . . 205Central American agriculture . . . . . . . . . . 207Central American flora. . . . . . . . . . . . . . 210Charophyceae . . . . . . . . . . . . . . . . . . . . 211Chemotaxis . . . . . . . . . . . . . . . . . . . . 213Chlorophyceae . . . . . . . . . . . . . . . . . . . 216Chloroplast DNA. . . . . . . . . . . . . . . . . 218Chloroplasts and other plastids. . . . . . . . . 220Chromatin . . . . . . . . . . . . . . . . . . . . . 223Chromatography . . . . . . . . . . . . . . . . . 225Chromosomes. . . . . . . . . . . . . . . . . . . 228Chrysophytes . . . . . . . . . . . . . . . . . . . 230Chytrids . . . . . . . . . . . . . . . . . . . . . . 233Circadian rhythms . . . . . . . . . . . . . . . . 236Cladistics . . . . . . . . . . . . . . . . . . . . . 238Climate and resources . . . . . . . . . . . . . . 241Clines . . . . . . . . . . . . . . . . . . . . . . . 243Cloning of plants . . . . . . . . . . . . . . . . . 245Coal . . . . . . . . . . . . . . . . . . . . . . . . 247Coevolution . . . . . . . . . . . . . . . . . . . . 252Community-ecosystem interactions . . . . . . 255Community structure and stability. . . . . . . 257Competition . . . . . . . . . . . . . . . . . . . . 260
Complementation and allelism:the cis-trans test . . . . . . . . . . . . . . . . 263
Compositae . . . . . . . . . . . . . . . . . . . . . 265Composting . . . . . . . . . . . . . . . . . . . . 267Conifers . . . . . . . . . . . . . . . . . . . . . . 270Corn . . . . . . . . . . . . . . . . . . . . . . . . 273Cryptomonads . . . . . . . . . . . . . . . . . . 276Culturally significant plants. . . . . . . . . . . 278Cycads and palms . . . . . . . . . . . . . . . . 281Cytoplasm. . . . . . . . . . . . . . . . . . . . . 285Cytoskeleton . . . . . . . . . . . . . . . . . . . 289Cytosol. . . . . . . . . . . . . . . . . . . . . . . 291
Deforestation . . . . . . . . . . . . . . . . . . . 293Dendrochronology . . . . . . . . . . . . . . . . 297Desertification . . . . . . . . . . . . . . . . . . 300Deserts . . . . . . . . . . . . . . . . . . . . . . . 303Deuteromycetes. . . . . . . . . . . . . . . . . . 306Diatoms . . . . . . . . . . . . . . . . . . . . . . 307Dinoflagellates . . . . . . . . . . . . . . . . . . 311Diseases and disorders. . . . . . . . . . . . . . 313DNA: historical overview . . . . . . . . . . . . 316DNA in plants. . . . . . . . . . . . . . . . . . . 322DNA: recombinant technology . . . . . . . . . 326
Volume 2
DNA replication . . . . . . . . . . . . . . . . . 329Dormancy . . . . . . . . . . . . . . . . . . . . . 331Drought . . . . . . . . . . . . . . . . . . . . . . 334
Ecology: concept . . . . . . . . . . . . . . . . . 337Ecology: history. . . . . . . . . . . . . . . . . . 339Ecosystems: overview . . . . . . . . . . . . . . 341Ecosystems: studies . . . . . . . . . . . . . . . 344Electrophoresis . . . . . . . . . . . . . . . . . . 348Endangered species . . . . . . . . . . . . . . . 350Endocytosis and exocytosis . . . . . . . . . . . 355Endomembrane system and
Golgi complex . . . . . . . . . . . . . . . . . 358Endophytes . . . . . . . . . . . . . . . . . . . . 361Endoplasmic reticulum . . . . . . . . . . . . . 363Energy flow in plant cells . . . . . . . . . . . . 364Environmental biotechnology. . . . . . . . . . 367Erosion and erosion control . . . . . . . . . . . 369
Estrogens from plants . . . . . . . . . . . . . . 371Ethanol. . . . . . . . . . . . . . . . . . . . . . . 374Eudicots . . . . . . . . . . . . . . . . . . . . . . 375Euglenoids . . . . . . . . . . . . . . . . . . . . 378Eukarya. . . . . . . . . . . . . . . . . . . . . . . 380Eukaryotic cells . . . . . . . . . . . . . . . . . . 382European agriculture. . . . . . . . . . . . . . . 385European flora . . . . . . . . . . . . . . . . . . 389Eutrophication . . . . . . . . . . . . . . . . . . 393Evolution: convergent and
divergent . . . . . . . . . . . . . . . . . . . . 396Evolution: gradualism vs.
punctuated equilibrium . . . . . . . . . . . 398Evolution: historical perspective . . . . . . . . 400Evolution of cells . . . . . . . . . . . . . . . . . 404Evolution of plants . . . . . . . . . . . . . . . . 409Exergonic and endergonic reactions . . . . . . 412Extranuclear inheritance. . . . . . . . . . . . . 414
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Farmland . . . . . . . . . . . . . . . . . . . . . 417Ferns . . . . . . . . . . . . . . . . . . . . . . . . 419Fertilizers . . . . . . . . . . . . . . . . . . . . . 423Flagella and cilia . . . . . . . . . . . . . . . . . 426Flower structure . . . . . . . . . . . . . . . . . 428Flower types . . . . . . . . . . . . . . . . . . . 432Flowering regulation . . . . . . . . . . . . . . . 435Fluorescent staining of cytoskeletal
elements . . . . . . . . . . . . . . . . . . . . 438Food chain. . . . . . . . . . . . . . . . . . . . . 440Forest and range policy . . . . . . . . . . . . . 443Forest fires. . . . . . . . . . . . . . . . . . . . . 447Forest management . . . . . . . . . . . . . . . 450Forests . . . . . . . . . . . . . . . . . . . . . . . 454Fossil plants . . . . . . . . . . . . . . . . . . . . 458Fruit crops . . . . . . . . . . . . . . . . . . . . . 461Fruit: structure and types . . . . . . . . . . . . 464Fungi . . . . . . . . . . . . . . . . . . . . . . . . 469
Garden plants: flowering . . . . . . . . . . . . 474Garden plants: shrubs . . . . . . . . . . . . . . 478Gas exchange in plants. . . . . . . . . . . . . . 481Gene flow . . . . . . . . . . . . . . . . . . . . . 483Gene regulation. . . . . . . . . . . . . . . . . . 486Genetic code. . . . . . . . . . . . . . . . . . . . 488Genetic drift . . . . . . . . . . . . . . . . . . . . 490Genetic equilibrium: linkage . . . . . . . . . . 491Genetically modified bacteria . . . . . . . . . . 494Genetically modified foods . . . . . . . . . . . 496Genetics: Mendelian . . . . . . . . . . . . . . . 499Genetics: mutations . . . . . . . . . . . . . . . 503Genetics: post-Mendelian . . . . . . . . . . . . 505Germination and seedling development. . . . 509Ginkgos . . . . . . . . . . . . . . . . . . . . . . 512Glycolysis and fermentation . . . . . . . . . . 515Gnetophytes. . . . . . . . . . . . . . . . . . . . 517Grains . . . . . . . . . . . . . . . . . . . . . . . 520Grasses and bamboos . . . . . . . . . . . . . . 522Grasslands. . . . . . . . . . . . . . . . . . . . . 525Grazing and overgrazing . . . . . . . . . . . . 527Green algae . . . . . . . . . . . . . . . . . . . . 530Green Revolution . . . . . . . . . . . . . . . . . 532Greenhouse effect. . . . . . . . . . . . . . . . . 534Growth and growth control . . . . . . . . . . . 537Growth habits. . . . . . . . . . . . . . . . . . . 541Gymnosperms . . . . . . . . . . . . . . . . . . 544
Halophytes . . . . . . . . . . . . . . . . . . . . 548Haptophytes . . . . . . . . . . . . . . . . . . . 551Hardy-Weinberg theorem . . . . . . . . . . . . 554Heliotropism . . . . . . . . . . . . . . . . . . . 557Herbicides . . . . . . . . . . . . . . . . . . . . . 558Herbs. . . . . . . . . . . . . . . . . . . . . . . . 561Heterokonts . . . . . . . . . . . . . . . . . . . . 564High-yield crops . . . . . . . . . . . . . . . . . 566History of plant science . . . . . . . . . . . . . 569Hormones . . . . . . . . . . . . . . . . . . . . . 575Hornworts. . . . . . . . . . . . . . . . . . . . . 578Horsetails . . . . . . . . . . . . . . . . . . . . . 581Horticulture . . . . . . . . . . . . . . . . . . . . 583Human population growth . . . . . . . . . . . 586Hybrid zones . . . . . . . . . . . . . . . . . . . 589Hybridization . . . . . . . . . . . . . . . . . . . 591Hydrologic cycle . . . . . . . . . . . . . . . . . 593Hydroponics . . . . . . . . . . . . . . . . . . . 597
Inflorescences . . . . . . . . . . . . . . . . . . . 600Integrated pest management . . . . . . . . . . 602Invasive plants . . . . . . . . . . . . . . . . . . 604Irrigation . . . . . . . . . . . . . . . . . . . . . 607
Krebs cycle . . . . . . . . . . . . . . . . . . . . 610
Leaf abscission . . . . . . . . . . . . . . . . . . 613Leaf anatomy . . . . . . . . . . . . . . . . . . . 616Leaf arrangements . . . . . . . . . . . . . . . . 619Leaf lobing and division . . . . . . . . . . . . . 621Leaf margins, tips, and bases . . . . . . . . . . 624Leaf shapes . . . . . . . . . . . . . . . . . . . . 627Legumes . . . . . . . . . . . . . . . . . . . . . . 629Lichens. . . . . . . . . . . . . . . . . . . . . . . 632Lipids . . . . . . . . . . . . . . . . . . . . . . . 634Liquid transport systems . . . . . . . . . . . . 636Liverworts. . . . . . . . . . . . . . . . . . . . . 640Logging and clear-cutting . . . . . . . . . . . . 643Lycophytes . . . . . . . . . . . . . . . . . . . . 645
Marine plants . . . . . . . . . . . . . . . . . . . 649Medicinal plants . . . . . . . . . . . . . . . . . 652Mediterranean scrub . . . . . . . . . . . . . . . 655Membrane structure . . . . . . . . . . . . . . . 658Metabolites: primary vs.
secondary . . . . . . . . . . . . . . . . . . . 659
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Volume 3
Microbial nutrition and metabolism . . . . . . 663Microbodies . . . . . . . . . . . . . . . . . . . . 666Microscopy . . . . . . . . . . . . . . . . . . . . 668Mitochondria . . . . . . . . . . . . . . . . . . . 672Mitochondrial DNA . . . . . . . . . . . . . . . 675Mitosis and meiosis . . . . . . . . . . . . . . . 677Mitosporic fungi . . . . . . . . . . . . . . . . . 681Model organisms . . . . . . . . . . . . . . . . . 682Molecular systematics . . . . . . . . . . . . . . 686Monocots vs. dicots . . . . . . . . . . . . . . . 688Monocotyledones . . . . . . . . . . . . . . . . . . 690Monoculture . . . . . . . . . . . . . . . . . . . 692Mosses . . . . . . . . . . . . . . . . . . . . . . . 694Multiple-use approach . . . . . . . . . . . . . . 697Mushrooms . . . . . . . . . . . . . . . . . . . . 699Mycorrhizae. . . . . . . . . . . . . . . . . . . . 702
Nastic movements . . . . . . . . . . . . . . . . 704Nitrogen cycle . . . . . . . . . . . . . . . . . . 706Nitrogen fixation . . . . . . . . . . . . . . . . . 709Nonrandom mating . . . . . . . . . . . . . . . 712North American agriculture. . . . . . . . . . . 714North American flora . . . . . . . . . . . . . . 718Nuclear envelope . . . . . . . . . . . . . . . . . 722Nucleic acids . . . . . . . . . . . . . . . . . . . 723Nucleolus . . . . . . . . . . . . . . . . . . . . . 727Nucleoplasm . . . . . . . . . . . . . . . . . . . 729Nucleus . . . . . . . . . . . . . . . . . . . . . . 730Nutrient cycling . . . . . . . . . . . . . . . . . 732Nutrients . . . . . . . . . . . . . . . . . . . . . 734Nutrition in agriculture . . . . . . . . . . . . . 737
Oil bodies . . . . . . . . . . . . . . . . . . . . . 740Old-growth forests . . . . . . . . . . . . . . . . 741Oomycetes. . . . . . . . . . . . . . . . . . . . . 743Orchids . . . . . . . . . . . . . . . . . . . . . . 745Organic gardening and farming . . . . . . . . 747Osmosis, simple diffusion, and
facilitated diffusion . . . . . . . . . . . . . . 751Oxidative phosphorylation . . . . . . . . . . . 755Ozone layer and ozone hole debate . . . . . . 757
Pacific Island agriculture . . . . . . . . . . . . 761Pacific Island flora . . . . . . . . . . . . . . . . 765
Paclitaxel . . . . . . . . . . . . . . . . . . . . . 768Paleobotany . . . . . . . . . . . . . . . . . . . . 770Paleoecology . . . . . . . . . . . . . . . . . . . 774Parasitic plants . . . . . . . . . . . . . . . . . . 777Peat. . . . . . . . . . . . . . . . . . . . . . . . . 779Peroxisomes . . . . . . . . . . . . . . . . . . . . 782Pesticides . . . . . . . . . . . . . . . . . . . . . 783Petrified wood . . . . . . . . . . . . . . . . . . 787Pheromones . . . . . . . . . . . . . . . . . . . . 790Phosphorus cycle . . . . . . . . . . . . . . . . . 791Photoperiodism. . . . . . . . . . . . . . . . . . 794Photorespiration . . . . . . . . . . . . . . . . . 796Photosynthesis . . . . . . . . . . . . . . . . . . 800Photosynthetic light absorption. . . . . . . . . 804Photosynthetic light reactions. . . . . . . . . . 807Phytoplankton . . . . . . . . . . . . . . . . . . 809Pigments in plants . . . . . . . . . . . . . . . . 812Plant biotechnology . . . . . . . . . . . . . . . 815Plant cells: molecular level . . . . . . . . . . . 821Plant domestication and breeding . . . . . . . 826Plant fibers . . . . . . . . . . . . . . . . . . . . 829Plant life spans . . . . . . . . . . . . . . . . . . 831Plant science. . . . . . . . . . . . . . . . . . . . 835Plant tissues . . . . . . . . . . . . . . . . . . . . 839Plantae . . . . . . . . . . . . . . . . . . . . . . . 843Plants with potential . . . . . . . . . . . . . . . 849Plasma membranes. . . . . . . . . . . . . . . . 851Plasmodial slime molds . . . . . . . . . . . . . 854Poisonous and noxious plants . . . . . . . . . 857Pollination. . . . . . . . . . . . . . . . . . . . . 862Polyploidy and aneuploidy . . . . . . . . . . . 865Population genetics . . . . . . . . . . . . . . . 868Prokaryotes . . . . . . . . . . . . . . . . . . . . 870Proteins and amino acids . . . . . . . . . . . . 873Protista . . . . . . . . . . . . . . . . . . . . . . . 875Psilotophytes . . . . . . . . . . . . . . . . . . . 879
Rain-forest biomes . . . . . . . . . . . . . . . . 883Rain forests and the atmosphere . . . . . . . . 885Rangeland . . . . . . . . . . . . . . . . . . . . . 889Red algae . . . . . . . . . . . . . . . . . . . . . 892Reforestation . . . . . . . . . . . . . . . . . . . 894Reproduction in plants. . . . . . . . . . . . . . 897Reproductive isolating mechanisms . . . . . . 899
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Resistance to plant diseases . . . . . . . . . . . 901Respiration . . . . . . . . . . . . . . . . . . . . 904Rhyniophyta . . . . . . . . . . . . . . . . . . . . 907Ribosomes . . . . . . . . . . . . . . . . . . . . . 909Rice. . . . . . . . . . . . . . . . . . . . . . . . . 912RNA . . . . . . . . . . . . . . . . . . . . . . . . 914Root uptake systems . . . . . . . . . . . . . . . 917Roots . . . . . . . . . . . . . . . . . . . . . . . . 920Rubber . . . . . . . . . . . . . . . . . . . . . . . 925Rusts . . . . . . . . . . . . . . . . . . . . . . . . 929
Savannas and deciduous tropical forests . . . 932Seedless vascular plants . . . . . . . . . . . . . 934Seeds . . . . . . . . . . . . . . . . . . . . . . . . 937Selection . . . . . . . . . . . . . . . . . . . . . . 941Serpentine endemism . . . . . . . . . . . . . . 943Shoots . . . . . . . . . . . . . . . . . . . . . . . 944Slash-and-burn agriculture . . . . . . . . . . . 946
Soil . . . . . . . . . . . . . . . . . . . . . . . . . 949Soil conservation . . . . . . . . . . . . . . . . . 955Soil contamination . . . . . . . . . . . . . . . . 957Soil degradation . . . . . . . . . . . . . . . . . 959Soil management . . . . . . . . . . . . . . . . . 962Soil salinization . . . . . . . . . . . . . . . . . . 963South American agriculture . . . . . . . . . . . 965South American flora . . . . . . . . . . . . . . 969Species and speciation . . . . . . . . . . . . . . 973Spermatophyta . . . . . . . . . . . . . . . . . . . 976Spices . . . . . . . . . . . . . . . . . . . . . . . 977Stems. . . . . . . . . . . . . . . . . . . . . . . . 980Strip farming . . . . . . . . . . . . . . . . . . . 983Stromatolites . . . . . . . . . . . . . . . . . . . 985Succession . . . . . . . . . . . . . . . . . . . . . 988Sugars . . . . . . . . . . . . . . . . . . . . . . . 991Sustainable agriculture. . . . . . . . . . . . . . 993
Volume 4
Sustainable forestry . . . . . . . . . . . . . . . 997Systematics and taxonomy . . . . . . . . . . . 999Systematics: overview . . . . . . . . . . . . . 1004
Taiga . . . . . . . . . . . . . . . . . . . . . . . 1007Textiles and fabrics . . . . . . . . . . . . . . . 1009Thigmomorphogenesis . . . . . . . . . . . . . 1013Timber industry . . . . . . . . . . . . . . . . . 1015Tracheobionta . . . . . . . . . . . . . . . . . . . 1017Trimerophytophyta . . . . . . . . . . . . . . . . 1021Trophic levels and ecological niches . . . . . 1023Tropisms . . . . . . . . . . . . . . . . . . . . . 1027Tundra and high-altitude biomes . . . . . . . 1030
Ulvophyceae. . . . . . . . . . . . . . . . . . . . 1033Ustomycetes. . . . . . . . . . . . . . . . . . . . 1035
Vacuoles . . . . . . . . . . . . . . . . . . . . . 1037Vegetable crops . . . . . . . . . . . . . . . . . 1039Vesicle-mediated transport. . . . . . . . . . . 1043Viruses and viroids . . . . . . . . . . . . . . . 1045
Water and solute movement in plants . . . . 1048Wetlands . . . . . . . . . . . . . . . . . . . . . 1051
Wheat. . . . . . . . . . . . . . . . . . . . . . . 1054Wood . . . . . . . . . . . . . . . . . . . . . . . 1056Wood and charcoal as fuel resources . . . . . 1058Wood and timber . . . . . . . . . . . . . . . . 1060
Yeasts . . . . . . . . . . . . . . . . . . . . . . . 1065
Zosterophyllophyta . . . . . . . . . . . . . . . . 1067Zygomycetes. . . . . . . . . . . . . . . . . . . 1069
Biographical List of Botanists . . . . . . . . . 1073Plant Classification . . . . . . . . . . . . . . . 1105Plant Names: Common-to-
Scientific . . . . . . . . . . . . . . . . . . . . 1115Plant Names: Scientific-to-
Common . . . . . . . . . . . . . . . . . . . 1130Time Line. . . . . . . . . . . . . . . . . . . . . 1199Glossary . . . . . . . . . . . . . . . . . . . . . 1207Bibliography . . . . . . . . . . . . . . . . . . . 1244Web Sites . . . . . . . . . . . . . . . . . . . . . 1254
Biographical Index. . . . . . . . . . . . . . . . . IIICategorized Index . . . . . . . . . . . . . . . . VIIIndex . . . . . . . . . . . . . . . . . . . . . . . XVII
xxi
Alphabetical List of Contents
MICROBIAL NUTRITION AND METABOLISM
Categories: Algae; bacteria; fungi; microorganisms; nutrients and nutrition; Protista
The diverse metabolic activities of microorganisms make them a critical component of all the earth’s ecosystems and asource of many useful products for human industry.
Microorganisms—bacteria, fungi, algae, andprotists—are found in every environment onthe earth that supports life. Microorganisms havebeen found in hot springs where temperatures ex-ceed 80 degrees Celsius as well as in rocks of Ant-arctic deserts. To ensure survival in a variety of hab-itats, microorganisms have developed a fascinatingvariety of strategies for survival. The study of mi-crobial ecology involves consideration of the mech-anisms employed by microorganisms to obtain nu-trients and energy from their environment.
Nutritional ModesTo maintain life processes and grow, all cellular
organisms require both a source of carbon (the prin-cipal element in all organic molecules) and a sourceof energy to perform the work necessary to trans-form carbon into all the molecular components ofcytoplasm. Among plants and animals, two mainnutritional modes have evolved to meet these re-quirements. All plants are photoautotrophs, fixingcarbon from inorganic carbon and obtaining energyfrom light. All animals are chemoheterotrophs, meet-ing their carbon needs by taking preformed organicmolecules from the environment and extracting en-ergy from chemical transformation of the same or-ganic molecules.
Both of these nutritional modes, photoauto-trophy and chemoheterotrophy, are found amongmicroorganisms; for example, all algae are photo-autotrophs, while all fungi are chemoheterotrophs.In addition, certain specialized bacteria exhibit amode of nutrition, chemoautotrophy, found in nohigher organisms. Like photoautotrophs, chemo-autotrophs are able to use carbon dioxide for allof their carbon requirements; however, they donot use light as an energy source. Instead, chemo-autotrophic bacteria capture energy from inorganic
chemical reactions, such as the oxidation of ammo-nia. Chemoautotrophic bacteria are highly special-ized and can be found in unusual environments.The most spectacular display of chemoautotrophicenergy metabolism is exhibited at the hydrother-mal vents found in certain locations on the oceanfloor. There, where sunlight cannot penetrate, che-moautotrophic bacteria serve as the producers for arich and diverse ecosystem.
An appreciation of the metabolic diversity dis-played by microorganisms enhances understand-ing of the ways in which matter and energy aretransformed in the biosphere. Consideration of mi-crobial contributions to the flow of carbon, nitro-gen, and other elements is critical to defining thebalance of ecosystems and the effects of changes inenvironmental chemistry and species composition.Microorganisms are, by definition, unseen, andmany people become aware of them only in theirnegative manifestations as agents of disease andspoilage. In fact, however, the diverse metabolic ac-tivities of microorganisms make them a criticalcomponent of all the earth’s ecosystems and a sourceof many useful products for human industry.
Cellulose DigestionEven among chemoheterotrophs, microorgan-
isms possess metabolic capabilities unknown inhigher organisms. These include the ability of somebacteria and fungi to digest cellulose, a linear poly-mer of glucose that is the principal molecular con-stituent of paper. Sixty percent of the dry mass ofgreen plants is in the form of cellulose, although noanimal that eats the plants is directly able to obtaincarbon or energy from cellulose. Microorganismsthat digest cellulose do so by secreting exoenzymes,proteins that cause cellulose to be broken into sim-pler molecular units that are absorbed by the micro-
Microbial nutrition and metabolism • 663
organism. Cellulose-digesting microorganisms arefound in most terrestrial ecosystems and in the di-gestive tracts of animals, such as cattle and ter-mites, that depend on cellulose-rich plant materialas a nutrient source. By breaking down celluloseand other complex organic polymers, microorgan-isms make a significant contribution to the cyclingof carbon in ecosystems.
Nitrogen FixationDigestion of complex organic polymers is only
one of the ways in which microorganisms contrib-ute to the cycling of elements in the environmentsthey inhabit. Microorganisms also perform chemi-cal transformations involving nitrogen, which isfound in all cellular proteins and nucleic acids.Plants incorporate nitrogen from the soil in theform of nitrate or ammonium ions, and animals ob-tain nitrogen from the same organic compoundsthey use as carbon and energy sources.
When dead plant and animal tissue is decom-posed by chemoheterotrophic microorganisms, thenitrogen is released as ammonia. A group ofchemoautotrophic bacteria, the nitrifying bacteria,obtain their metabolic energy from the conversionof ammonia to nitrate; in this way, the nitrifiers con-vert the nitrogen released during decomposition toa form readily used by plants, thus contributing tosoil fertility. Asecond group of bacteria converts ni-trate to atmospheric nitrogen gas, which cannot beused by plants; these bacteria are called denitrifiersbecause (in contrast to the nitrifiers) their metabolicactivities cause a net loss of nitrogen from the soil.
Nitrogen lost from the environment by deni-trification is replaced by ammonia released duringdecomposition and by the metabolic activity ofnitrogen-fixing bacteria, so called because they “fix”nitrogen gas from the atmosphere in the form ofammonia. Nitrogen fixation requires a great quan-tity of energy, and nitrogen-fixing bacteria are often
664 • Microbial nutrition and metabolism
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found in symbiotic association with plants, espe-cially legumes. The bacteria provide nitrogen in ausable form to the plant, while the plant providescarbon and energy in the form of organic com-pounds to the chemoheterotrophic nitrogen-fixingbacteria. The presence of nitrogen-fixing bacteria isoften indicated by the formation of characteristicnodules on the roots of plants involved in the asso-ciations. Free-living nitrogen fixers are also known,and these may play a significant role in the nitrogenbalance of aquatic ecosystems.
Respiration and FermentationChemoheterotrophic microorganisms are found
both in aerobic environments, where oxygen is avail-able, and in anaerobic environments, where oxygenis lacking. The availability of molecular oxygenmay determine the type of energy metabolismemployed by a microorganism. Where oxygen isavailable, many microorganisms obtain energy byrespiration. In respiration, electrons removed fromorganic nutrient sources are transferred through acomplex sequence of reactions to molecular oxy-gen, forming water and carbon dioxide. In the pro-cess, energy is made available to the organisms. Inthe absence of oxygen, some microorganisms areable to carry out a form of anaerobic respiration us-ing nitrate or sulfate in place of oxygen. Deni-trification is an example of anaerobic respiration.
Other anaerobic microorganisms employ fer-mentation. In fermentation, electrons removed fromorganic nutrient sources are transferred to organicmolecules, forming fermentation products, such asalcohols and organic acids, which may be used asnutrient sources by other chemoheterotrophs. Anumber of bacteria, the facultative anaerobes, are ca-pable of performing either aerobic respiration orfermentation, depending on the availability of oxy-gen. These bacteria are able to achieve optimumgrowth in environments, such as soils, where theavailability of oxygen may vary over time.
Effects and UsesThe contributions of microorganisms to the
chemical transformations which characterize anecosystem are many. Along with higher plants,photoautotrophic and chemoautotrophic microor-ganisms capture inorganic carbon dioxide and, us-ing energy from sunlight or chemical reactions,synthesize organic molecules, which are used byanimals and by chemoheterotrophic microorgan-
isms as sources of carbon and energy. Through theprocesses of respiration and fermentation, chemo-heterotrophs return inorganic carbon dioxide to theenvironment.
Much of this recycling of carbon from organicmolecules to carbon dioxide depends on the activi-ties of microbial decomposers, which are able tobreak down organic polymers, such as cellulose.Nitrogen, released from organic molecules bychemoheterotrophs in the form of ammonia, maybe made available to chemohe
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