The Facts On File DICTIONARY of BOTANY The Facts On File DICTIONARY of BOTANY Edited by Jill Bailey The Facts On File Dictionary of Botany Copyright © 2003 by Market House Books Ltd All rights reserved. No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval systems, without permission in writing from the publisher. For information contact: Checkmark Books An imprint of Facts On File, Inc. 132 West 31st Street New York NY 10001 Library of Congress Cataloging-in-Publication Data The Facts on File dictionary of botany / edited by Jill Bailey. p. cm. Includes bibliographical references (p. ). ISBN 0-8160-4910-6 (hc)—ISBN 0-8160-4911-4 (pbk.) 1. Botany—Dictionaries. I. Title: Dictionary of botany. II. Bailey, Jill. III. Facts on File, Inc. QK9.F33 2002 580'.3—dc2l 2002035202 Checkmark Books are available at special discounts when purchased in bulk quantities for businesses, associations, institutions, or sales promotions. Please call our Special Sales Department in New York at (212) 967-8800 or (800) 322-8755. You can find Facts On File on the World Wide Web at http://www.factsonfile.com Compiled and typeset by Market House Books Ltd, Aylesbury, UK Printed in the United States of America MP 10987654321 This book is printed on acid-free paper PREFACE This dictionary is one of a series covering the terminology and concepts used in important branches of science. The Facts On File Dictionary of Botany is planned as an additional source of information for students taking Ad- vanced Placement (AP) Science courses in high schools, but will also be help- ful to older students taking introductory college courses. This volume covers the whole area of pure and applied plant science includ- ing anatomy and plant morphology, plant physiology, biochemistry, cell bi- ology, genetics, evolution, and ecology. It also covers the taxonomy and classification of plants, with entries for the higher-ranking taxa. The defini- tions are intended to be clear and informative and, where possible, we have provided helpful diagrams and examples. The book also has a selection of short biographical entries for people who have made important contribu- tions to the field. The appendices include lists of webpages and an informa- tive bibliography. The book will be a helpful additional source of information for anyone studying AP Biology, notably the sections on Organisms and Populations, Structure and Function of Plants and Animals, and Molecules and Cells. However, we have not restricted the content to this syllabus. Modern plant science is a subject of considerable importance and we hope that this book will be useful to anyone interested in the subject. ACKNOWLEDGMENTS Consultant Andrew Lack B.Sc., Pd.D. Contributors Eve Daintith B.Sc. Elizabeth Tootill B.Sc. CONTENTS Entries A to Z 1 Appendixes I. SI Units 248 II. Webpages 249 Bibliography 250 A ABA See abscisic acid. abscission The organized loss of part of a plant, usually a leaf, fruit, or unfertilized abaxial In structures such as a leaves flower. An abscission zone occurs at the and petals, the side facing away from the base of the organ. Here a separation layer main axis, i.e. the lower surface. In lateral (abscission layer) is formed by breakdown organs such as leaves, abaxial is synony- or separation of cells and final severance mous with the underside. Compare adax- occurs when the vascular bundles are bro- ial. ken mechanically, e.g. by wind or rain. The abscission layer is activated by increasing abiotic environment The nonliving levels of ethylene and a decreasing concen- factors of the environment that influence tration of auxin ecological systems. Abiotic factors include climate, chemical pollution, geographical absolute humidity See humidity. features, etc. absolute pollen frequency (APF) See pollen analysis. absorption 1. The uptake of liquid by cells and organs. In plants, water and min- eral salts are absorbed mainly by the root hairs, just behind the root tips. 2. The capture of radiant energy by plant pigments. About 80% of the visible light falling on a leaf is absorbed, and about Abscisic acid 10% of the infrared radiation. abscisic acid (ABA)A plant hormone, absorption spectrum A plot of the ab- that functions chiefly as an inhibitor of sorbance by a substance of radiation at dif- growth and cell elongation. Abscisic acid ferent wavelengths, usually of ultraviolet, has a variety of effects related to seed dor- visible, or infrared radiation. It can give in- mancy and stress responses: it regulates formation about the identity or quantity of protein expression in seed development a substance. Chlorophylls, for example, leading to dormancy and is one of the hor- have absorption peaks in the red and blue mones involved in bud dormancy; it regu- (and therefore reflect green light). Com- lates stress responses by, for example, pare action spectrum. closing stomata in times of water shortage and increasing the ability of roots to carry accessory cell See subsidiary cell. water. It can also promote root growth and inhibit shoot growth. Despite its name it accessory chromosome See B chromo- does not directly promote abscission, but some. only indirectly through increasing ethylene production. Formerly it was known as ab- accessory pigment See photosynthetic scisin II or dormin. pigments. 1 acellular acellular Denoting relatively large tis- achene A dry indehiscent fruit formed sues or organisms that are not composed of from an ovary with a single carpel contain- discrete cells and are, in effect, unicellular. ing a single seed, e.g. oak (Quercus). Dif- In flowering plants, for instance, the early ferent types of achenes include the stages of endosperm development are often CARYOPSIS, CYPSELA, NUT, and SAMARA. acellular. Other examples include aseptate fungal hyphae and certain green algae, acicular Needle-shaped. such as Acetabularia. The term is used in preference to unicellular to distinguish acid A substance that gives rise to hy- + such structures (which are often multinu- drogen ions (or H3O ) when dissolved in cleate) from conventional cells and show water. An acid in aqueous solution will their equivalence to multicellular struc- have a pH below 7. Lowry–Brønsted tures. See also coenocyte. theory defines an acid as a substance that exhibits a tendency to release a proton, and Aceraceae A family of temperate and a base as a substance that tends to accept a tropical trees and shrubs that includes the proton. Strong acids (e.g. HNO3) react +. maples and sycamores. completely with water to give H3O Weak acids (e.g. CH3COOH) are only partly dis- + acetaldehyde (ethanal) An aldehyde, sociated because H3O is a stronger acid than the free acids. CH3CHO, that is an intermediate in the conversion of pyruvic acid to ethanol dur- See ing the final stage of glycolysis during acidic stain staining. anaerobic respiration in plants. It is in- acid rain The deposition of acids by nat- volved in the synthesis and breakdown of ural precipitation, mainly by rain but also the amino acid threonine. by snow and fog. Acids are formed by re- action of gaseous waste products, particu- acetic acid (ethanoic acid) A carboxylic larly sulfur dioxide, and also nitrogen acid, CH COOH, obtained by the oxida- 3 oxides, with moisture in the air to form sul- tion of ethyl alcohol. Acetic acid is a com- furic and nitric acids. The subsequent pre- ponent of vinegar (which is obtained by cipitation has led to raised acidity in forests bacterial oxidation of wine waste). It is and lakes, especially in Scandinavia and used as an alternative carbon source by cer- some other parts of northern Europe, dam- tain green algae. When combined with aging the environment. Acid rain is often COENZYME A to form ACETYL COA, it plays a used more loosely for any atmospheric pol- key role in AEROBIC RESPIRATION. lutant that dissolves in precipitation caus- ing environmental damage, such as carbon acetocarmine A stain used to color monoxide or ozone, and these may interact chromosomes deep reddish-black for view- with the acids. ing with a light microscope. Tissues are The most serious pollutant is sulfur fixed in acetic acid before applying aceto- dioxide, which comes mainly from burning carmine. See fixation; staining. coal and is, consequently, less serious now than in the twentieth century. Sulfuric acid acetyl CoA (acetyl coenzyme A) A com- in soils may lead to the formation of am- pound made up of acetyl and coenzyme A monium sulfate, which causes the release linked by a sulfur bridge. Acetyl CoA plays of toxic aluminum and heavy metal ions a key role in metabolism, being a precursor that inhibit metabolic activity. In water- of the KREBS CYCLE and GLYOXYLATE CYCLE, ways these can damage the gills of fish. Un- and the starting point for synthesis of fatty polluted rain is normally slightly acidic acids, terpenes, and some amino acids. The with a pH of 5.0–5.6. synthesis of acetyl CoA is a high-energy process, requiring energy from ATP, which acid soil A soil with a pH less than 6.0. is converted to AMP. Such soils usually form in areas of heavy 2 activation energy rainfall, which causes leaching of lime form bacteria are rodlike structures. The from the surface layers, or over acid sub- Actinobacteria are distinguished by pro- strata such as granite or sand. In the acidic ducing actinospores: entire cells encysted conditions, decomposition of organic ma- in thick walls to form resistant spores. terial in the soil is slow. Acid soils often contain substantial concentrations of iron actinodromous (palmate; digitate) De- and aluminum hydroxides. See brown scribing a form of leaf VENATION in which earth; podsol.