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ESAU’S PLANT ANATOMYMeristems, Cells, and Tissues of the Plant
Body:Their Structure, Function, and Development
Third Edition
RAY F. EVERTKatherine Esau Professor of Botany and Plant
Pathology, EmeritusUniversity of Wisconsin, Madison
With the assistance ofSusan E. Eichhorn
University of Wisconsin, Madison
A John Wiley & Sons, Inc., Publication
Innodata0470047372.jpg
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Esau’s Plant Anatomy
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ESAU’S PLANT ANATOMYMeristems, Cells, and Tissues of the Plant
Body:Their Structure, Function, and Development
Third Edition
RAY F. EVERTKatherine Esau Professor of Botany and Plant
Pathology, EmeritusUniversity of Wisconsin, Madison
With the assistance ofSusan E. Eichhorn
University of Wisconsin, Madison
A John Wiley & Sons, Inc., Publication
-
Copyright © 2006 by John Wiley & Sons, Inc. All rights
reserved.
Published by John Wiley & Sons, Inc., Hoboken, New
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Library of Congress Cataloging-in-Publication Data:
Evert, Ray Franklin. Esau’s Plant anatomy : meristems, cells,
and tissues of the plant body : their structure, function, and
development / Ray F. Evert.—3rd ed. p. cm. Rev. ed. of: Plant
anatomy / Katherine Esau. 2nd. ed. 1965. ISBN-13: 978-0-471-73843-5
(cloth) ISBN-10: 0-471-73843-3 (cloth) 1. Plant anatomy. 2. Plant
morphology. I. Esau, Katherine, 1898- Plant anatomy. II. Title.
QK671.E94 2007 571.3'2—dc22
2006022118
Printed in the United States of America.
10 9 8 7 6 5 4 3 2 1
http://www.copyright.comhttp://www.wiley.com/go/permissionhttp://www.wiley.com
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Dedicated to the late Katherine Esau, mentor and close friend“In
recognition of her distinguished service to the American community
of plant biologists, and for the excellence of her pioneering
research, both basic and applied, on plant structure and
development, which has spanned more than six decades; for her
superlative performance as an educator, in the classroom and
through her books; for the encouragement and inspiration she has
given a legion of young, aspiring plant biologists; for providing a
special role model for women in science.”
Citation, National Medal of Science, 1989
Katherine Esau
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Contents
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . xv
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . xvii
General References . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . xix
Chapter 1 Structure and Development of the Plant Body—An
Overview . . . . . . . . . . . . . . . . . . . . . . . . 1
Internal Organization of the Plant Body . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 The Body of a Vascular Plant Is Composed of Three Tissue Systems
. . . . . . . . . . . . . . . . . . . . . 3 Structurally Stem,
Leaf, and Root Differ Primarily in the Relative
Distribution of the Vascular and Ground Tissues . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Summary
of Types of Cells and Tissues . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Development of the Plant Body . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7 The Body Plan of the Plant Is Established during Embryogenesis .
. . . . . . . . . . . . . . . . . . . . . . . 7 With Germination of
the Seed, the Embryo Resumes Growth and Gradually Develops into
an Adult Plant . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . 11 REFERENCES . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . 12
Chapter 2 The Protoplast: Plasma Membrane, Nucleus, and
Cytoplasmic Organelles . . . . . . . . . . . . . 15
Prokaryotic and Eukaryotic Cells . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . 16 Cytoplasm . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . 17 Plasma Membrane . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . 19 Nucleus . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Cell Cycle
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . 23 Plastids . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . 25 Chloroplasts Contain Chlorophyll and
Carotenoid Pigments . . . . . . . . . . . . . . . . . . . . . . . .
. . . . 25
vii
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viii | Contents
Chromoplasts Contain Only Carotenoid Pigments . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Leucoplasts Are Nonpigmented Plastids . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 All
Plastids Are Derived Initially from Proplastids . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . 28 Mitochondria
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
31 Peroxisomes . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . 33 Vacuoles . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . 34 Ribosomes . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . 36 REFERENCES .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
37
Chapter 3 The Protoplast: Endomembrane System, Secretory
Pathways, Cytoskeleton,
and Stored Compounds . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. 45
Endomembrane System . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . 45 The Endoplasmic Reticulum Is a Continuous,
Three-dimensional
Membrane System That Permeates the Entire Cytosol . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . 45 The Golgi
Apparatus Is a Highly Polarized Membrane System Involved in
Secretion . . . . . . . . . 48 Cytoskeleton . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . 49 Microtubules Are
Cylindrical Structures Composed of Tubulin Subunits . . . . . . . .
. . . . . . . . . . 49 Actin Filaments Consist of Two Linear Chains
of Actin Molecules in the Form of a Helix . . . . 50 Stored
Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
52 Starch Develops in the Form of Grains in Plastids . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 The
Site of Protein Body Assembly Depends on Protein Composition . . .
. . . . . . . . . . . . . . . . . 53 Oil Bodies Bud from Smooth ER
Membranes by an Oleosin-mediated Process . . . . . . . . . . . . .
. 54 Tannins Typically Occur in Vacuoles but Also Are Found in Cell
Walls . . . . . . . . . . . . . . . . . . . 55 Crystals of Calcium
Oxalate Usually Develop in Vacuoles but
Also Are Found in the Cell Wall and Cuticle . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Silica Most Commonly Is Deposited in Cell Walls . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . 58 REFERENCES
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
58
Chapter 4 Cell Wall . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . 65
Macromolecular Components of the Cell Wall . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Cellulose Is the Principal Component of Plant Cell Walls . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . 66 The Cellulose
Microfi brils Are Embedded in a Matrix of Noncellulosic Molecules .
. . . . . . . . . 67 Principal Hemicelluoses . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . 67 Pectins . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . 68 Proteins . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . 68 Callose Is a
Widely Distributed Cell Wall Polysaccharide . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . 69 Lignins Are Phenolic
Polymers Deposited Mainly in Cell Walls of Supporting and
Conducting
Tissues . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . 69 Cutin and Suberin Are Insoluble Lipid Polymers
Found Most
Commonly in the Protective Surface Tissues of the Plant . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . 71 Cell Wall
Layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . 71 The Middle Lamella Frequently Is Diffi cult to Distinguish
from the Primary Wall . . . . . . . . . . . 72 The Primary Wall Is
Deposited While the Cell Is Increasing in Size . . . . . . . . . .
. . . . . . . . . . . . 72 The Secondary Wall Is Deposited inside
the Primary Wall Largely, If Not Entirely, after the
Primary Wall Has Stopped Increasing in Surface Area . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . 72 Pits and
Primary Pit-Fields . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
74 Origin of Cell Wall during Cell Division . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
76 Cytokinesis Occurs by the Formation of a Phragmoplast and Cell
Plate . . . . . . . . . . . . . . . . . . . 76 Initially Callose Is
the Principal Cell Wall Polysaccharide Present
in the Developing Cell Plate . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . 78 The Preprophase Band Predicts the Plane of the Future Cell
Plate . . . . . . . . . . . . . . . . . . . . . . . 78 Growth of
the Cell Wall . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
The Orientation of Cellulose Microfi brils within the Primary Wall
Infl uences the
Direction of Cell Expansion . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . 82 When Considering the Mechanism of Wall Growth, It Is
Necessary to Distinguish
between Growth in Surface (Wall Expansion) and Growth in
Thickness . . . . . . . . . . . . . . . . . . 83
-
Contents | ix
Expansion of the Primary Cell Wall . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. 83 Cessation of Wall Expansion . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . 84 Intercellular Spaces . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . 84 Plasmodesmata . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . 85 Plasmodesmata May Be
Classifi ed as Primary or Secondary According to Their Origin . . .
. . . . 85 Plasmodesmata Contain Two Types of Membranes: Plasma
Membrane and Desmotubule . . . . . 87 Plasmodesmata Enable Cells to
Communicate . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . 88 The Symplast Undergoes Reorganization
throughout the Course of Plant Growth and
Development . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . 90 REFERENCES . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . 91
Chapter 5 Meristems and Differentiation . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . 103
Meristems . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . 103 Classifi cation of Meristems . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . 104 A Common Classifi cation of Meristems
Is Based on Their Position in the Plant Body . . . . . . 104
Meristems Are Also Classifi ed According to the Nature of
Cells That Give Origin to Their Initial Cells . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Characteristics of Meristematic Cells . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Growth Patterns in Meristems . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
107 Meristematic Activity and Plant Growth . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
Differentiation . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . 110 Terms and Concepts . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . 110 Senescence (Programmed Cell Death) . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . 111 Cellular Changes in Differentiation . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . 113 A Cytologic Phenomenon Commonly Observed in
Differentiating
Cells of Angiosperms Is Endopolyploidy . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 One
of the Early Visible Changes in Differentiating Tissues Is the
Unequal Increase in Cell Size . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
113 Intercellular Adjustment in Differentiating Tissue Involves
Coordinated and Intrusive Growth . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
Causal Factors in Differentiation . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. 115 Tissue Culture Techniques Have Been Useful for the
Determination
of Requirements for Growth and Differentiation . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 The
Analysis of Genetic Mosaics Can Reveal Patterns of Cell
Division
and Cell Fate in Developing Plants . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
117 Gene Technologies Have Dramatically Increased Our Understanding
of Plant Development . . . 117 Polarity Is a Key Component of
Biological Pattern Formation and
Is Related to the Phenomenon of Gradients . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
Plant Cells Differentiate According to Position . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 Plant
Hormones . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . 120 Auxins . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . 121 Cytokinins . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . 122 Ethylene . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
Abscisic Acid . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . 123 Gibberellins . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . 123 REFERENCES . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . 123
Chapter 6 Apical Meristems . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . 133
Evolution of the Concept of Apical Organization . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
Apical Meristems Originally Were Envisioned as Having a Single
Initial Cell . . . . . . . . . . . . . . . 134 The Apical-Cell
Theory Was Superseded by the Histogen Theory . . . . . . . . . . .
. . . . . . . . . . . . . 134 The Tunica-Corpus Concept of Apical
Organization Applies Largely to Angiosperms . . . . . . . . 135
The Shoot Apices of Most Gymnosperms and Angiosperms Show a
Cytohistological Zonation . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . 136
Inquiries into the Identity of Apical Initials . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
136 Vegetative Shoot Apex . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . 138
-
x | Contents
The Presence of an Apical Cell Is Characteristic of Shoot Apices
in Seedless Vascular Plants . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . 139
The Zonation Found in the Ginkgo Apex Has Served as a Basis for
the Interpretation of Shoot Apices in Other Gymnosperms . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . 140
The Presence of a Zonation Superimposed on a Tunica-Corpus Confi
guration Is Characteristic of Angiosperm Shoot Apices . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. 141
The Vegetative Shoot Apex of Arabidopsis thaliana . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
Origin of Leaves . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . 145 Throughout the Vegetative Period the Shoot Apical
Meristem Produces Leaves in a
Regular Order . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . 145 The Initiation of a Leaf Primordium Is Associated
with an Increase
in the Frequency of Periclinal Divisions at the Initiation Site
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 Leaf
Primordia Arise at Sites That Are Correlated with the Phyllotaxis
of the Shoot . . . . . . . . . 149 Origin of Branches . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . 149 In Most Seed Plants
Axillary Meristems Originate from Detached Meristems . . . . . . .
. . . . . . . . 150 Shoots May Develop from Adventitious Buds . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . 152 Root Apex . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . 152 Apical Organization in Roots May Be
either Open or Closed . . . . . . . . . . . . . . . . . . . . . . .
. . . . . 153 The Quiescent Center Is Not Completely Devoid of
Divisions under Normal Conditions . . . . . 157 The Root Apex of
Arabidopsis thaliana . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . 160 Growth of the
Root Tip . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . 165
Chapter 7 Parenchyma and Collenchyma . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . 175
Parenchyma . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . 175 Parenchyma Cells May Occur in Continuous Masses
as Parenchyma Tissue or Be
Associated with Other Cell Types in Morphologically
Heterogeneous Tissues . . . . . . . . . . . . . . 176 The Contents
of Parenchyma Cells Are a Refl ection of the Activities of the
Cells . . . . . . . . . . . 177 The Cell Walls of Parenchyma Cells
May Be Thick or Thin . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . 178 Some Parenchyma Cells—Transfer Cells—Contain Wall
Ingrowths . . . . . . . . . . . . . . . . . . . . . . . 179
Parenchyma Cells Vary Greatly in Shape and Arrangement . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . 181
Some Parenchyma Tissue—Aerenchyma—Contains Particularly Large
Intercellular Spaces . . . . . 182 Collenchyma . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . 183 The Structure
of the Cell Walls of Collenchyma Is the Most Distinctive
Characteristic of
This Tissue . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . 184 Collenchyma Characteristically Occurs in a
Peripheral Position . . . . . . . . . . . . . . . . . . . . . . . .
. 185 Collenchyma Appears to Be Particularly Well Adapted for
Support of
Growing Leaves and Stems . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. 187 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . 187
Chapter 8 Sclerenchyma . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . 191
Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . 192 Fibers Are Widely Distributed in the
Plant Body . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . 192 Fibers May Be Divided into Two Large
Groups, Xylary and Extraxylary . . . . . . . . . . . . . . . . . .
. 194 Both Xylary and Extraxylary Fibers May Be Septate or
Gelatinous . . . . . . . . . . . . . . . . . . . . . . . 196
Commercial Fibers Are Separated into Soft Fibers and Hard Fibers .
. . . . . . . . . . . . . . . . . . . . . . 197 Sclereids . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
198 Based on Shape and Size, Sclereids May Be Classifi ed into a
Number of Types . . . . . . . . . . . . . 198 Sclereids Like Fibers
Are Widely Distributed in the Plant Body . . . . . . . . . . . . .
. . . . . . . . . . . . . 199 Sclereids in Stems . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . 200 Sclereids in Leaves . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . 200 Sclereids in Fruits .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . 201 Sclereids in
Seeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
Origin and Development of Fibers and Sclereids . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202
Factors Controlling Development of Fibers and Sclereids . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . 205 REFERENCES
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
207
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Contents | xi
Chapter 9 Epidermis . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . 211
Ordinary Epidermal Cells . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . 214 Epidermal Cell Walls Vary in Thickness . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . 214 The Most Distinctive Feature of the Outer Epidermal Wall Is
the Presence of a Cuticle . . . . . . 215 Stomata . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
Stomata Occur on All Aerial Parts of the Primary Plant Body . . . .
. . . . . . . . . . . . . . . . . . . . . . . 218 Guard Cells Are
Generally Kidney-shaped . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . 221 Guard Cells Typically
Have Unevenly Thickened Walls with Radially Arranged
Cellulose Microfi brils . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . 222 Blue Light and Abscisic Acid Are Important Signals in
the Control of
Stomatal Movement . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . 224 Development of Stomatal Complexes Involves One or More
Asymmetric Cell Divisions . . . . . . 225 Different Developmental
Sequences Result in Different
Confi gurations of Stomatal Complexes . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
Trichomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . 229 Trichomes Have a Variety of Functions . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . 229 Trichomes May Be Classifi ed into Different
Morphological Categories . . . . . . . . . . . . . . . . . . . .
230 A Trichome Is Initiated as a Protuberance from an Epidermal
Cell . . . . . . . . . . . . . . . . . . . . . . . 230 The Cotton
Fiber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
Root Hairs . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . 234 The Arabidopsis Trichome . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . 235 Cell Patterning in the Epidermis . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . 237 The Spatial Distribution of Stomata and Trichomes
in Leaves Is Nonrandom . . . . . . . . . . . . . . . 237 There Are
Three Main Types of Patterning in the Epidermis of Angiosperm Roots
. . . . . . . . . . 238 Other Specialized Epidermal Cells . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . 239 Silica and Cork Cells Frequently Occur
Together in Pairs . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . 239 Bulliform Cells Are Highly Vacuolated Cells . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . 241 Some Epidermal Hairs Contain Cystoliths . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
242 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . 243
Chapter 10 Xylem: Cell Types and Developmental Aspects . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
255
Cell Types of the Xylem . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . 256 Tracheary Elements—Tracheids and Vessel Elements—Are
the Conducting Cells of the
Xylem . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . 256 The Secondary Walls of Most Tracheary
Elements Contain Pits . . . . . . . . . . . . . . . . . . . . . . .
. . . 260 Vessels Are More Effi cient Conduits of Water Than Are
Tracheids . . . . . . . . . . . . . . . . . . . . . . . . 263
Fibers Are Specialized as Supporting Elements in the Xylem . . . .
. . . . . . . . . . . . . . . . . . . . . . . . 266 Living
Parenchyma Cells Occur in Both the Primary and Secondary Xylem . .
. . . . . . . . . . . . . . 266 In Some Species the Parenchyma
Cells Develop Protrusions—Tyloses—That Enter the
Vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . 267 Phylogenetic Specialization of Tracheary
Elements and Fibers . . . . . . . . . . . . . . . . . . . . . . . .
. . . . 268 The Major Trends in the Evolution of the Vessel Element
Are Correlated with Decrease in
Vessel Element Length . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . 268 Deviations Exist in Trends of Vessel Element Evolution
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
Like Vessel Elements and Tracheids, Fibers Have Undergone a
Phylogenetic Shortening . . . . . 271 Primary Xylem . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . 271 Some
Developmental and Structural Differences Exist between the Earlier
and Later Formed
Parts of the Primary Xylem . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . 271 The Primary Tracheary Elements Have a Variety of Secondary
Wall Thickenings . . . . . . . . . . . 273 Tracheary Element
Differentiation . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . 276 Plant
Hormones Are Involved in the Differentiation of Tracheary Elements
. . . . . . . . . . . . . . . . 280 Isolated Mesophyll Cells in
Culture Can Transdifferentiate Directly into
Tracheary Elements . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . 281 REFERENCES . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . 283
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xii | Contents
Chapter 11 Xylem: Secondary Xylem and Variations in Wood
Structure . . . . . . . . . . . . . . . . . . . . . . . . . 291
Basic Structure of Secondary Xylem . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
293 The Secondary Xylem Consists of Two Distinct Systems of Cells,
Axial and Radial . . . . . . . . . . 293 Some Woods Are Storied and
Others Are Nonstoried . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . 294 Growth Rings Result from the Periodic
Activity of the Vascular Cambium . . . . . . . . . . . . . . . .
294 As Wood Becomes Older, It Gradually Becomes Nonfunctional in
Conduction and Storage . . . 297 Reaction Wood Is a Type of Wood
That Develops in Branches
and Leaning or Crooked Stems . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
299 Woods . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . 302 The Wood of Conifers Is Relatively Simple
in Structure . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . 302 The Axial System of Conifer Woods Consists Mostly or
Entirely of Tracheids . . . . . . . . . . . . . . 302 The Rays of
Conifers May Consist of Both Parenchyma Cells and Tracheids . . . .
. . . . . . . . . . . 303 The Wood of Many Conifers Contains Resin
Ducts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . 304 The Wood of Angiosperms Is More Complex and Varied Than
That of Conifers . . . . . . . . . . . . 306 On the Basis of
Porosity, Two Main Types of Angiosperm Wood Are Recognized:
Diffuse-
porous and Ring-porous . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . 307 The Distribution of Axial Parenchyma Shows Many
Intergrading Patterns . . . . . . . . . . . . . . . . . 309 The
Rays of Angiosperms Typically Contain Only Parenchyma Cells . . . .
. . . . . . . . . . . . . . . . . 310 Intercellular Spaces Similar
to the Resin Ducts of Gymnosperms
Occur in Angiosperm Woods . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
312 Some Aspects of Secondary Xylem Development . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312
Identifi cation of Wood . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . 315 REFERENCES . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . 316
Chapter 12 Vascular Cambium . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . 323
Organization of the Cambium . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . 323 The Vascular Cambium Contains Two Types of Initials:
Fusiform Initials and Ray Initials . . . . 323 The Cambium May Be
Storied or Nonstoried . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . 325 Formation of Secondary Xylem
and Secondary Phloem . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . 326 Initials Versus Their Immediate
Derivatives . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . 327 Developmental Changes . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . 330 Formation of New Ray
Initials from Fusiform Initials or Their Segments Is a Common
Phenomenon . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . 332 Domains Can Be Recognized within the Cambium . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335
Seasonal Changes in Cambial Cell Ultrastructure . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336
Cytokinesis of Fusiform Cells . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . 338 Seasonal Activity . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . 341 The Size of the Xylem Increment Produced
during One Year Generally Exceeds That of the
Phloem . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . 343 A Distinct Seasonality in Cambial Activity Also
Occurs in Many Tropical Regions . . . . . . . . . . . 344 Causal
Relations in Cambial Activity . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 346
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . 348
Chapter 13 Phloem: Cell Types and Developmental Aspects . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
357
Cell Types of the Phloem . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . 359 The Angiospermous Sieve-Tube Element . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . 360 In Some Taxa the Sieve-Tube Element Walls Are Remarkably
Thick . . . . . . . . . . . . . . . . . . . . . . 361 Sieve Plates
Usually Occur on End Walls . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . 364 Callose
Apparently Plays a Role in Sieve-Pore Development . . . . . . . . .
. . . . . . . . . . . . . . . . . . . 364 Changes in the Appearance
of the Plastids and the Appearance of P-protein Are Early
Indicators of Sieve-Tube Element Development . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 365 Nuclear
Degeneration May Be Chromatolytic or Pycnotic . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . 372 Companion Cells . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . 372 The
Mechanism of Phloem Transport in Angiosperms . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . 379 The Source Leaf
and Minor Vein Phloem . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . 382
-
Contents | xiii
Several Types of Minor Veins Occur in Dicotyledonous Leaves . .
. . . . . . . . . . . . . . . . . . . . . . . . 384 Type 1 Species
with Specialized Companion Cells, Termed Intermediary Cells,
Are
Symplastic Loaders . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . 384 Species with Type 2 Minor Veins Are Apoplastic Loaders
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385 The
Collection of Photoassimilate by the Minor Veins in Some Leaves May
Not Involve an
Active Step . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . 385 Some Minor Veins Contain More Than One Kind of
Companion Cell . . . . . . . . . . . . . . . . . . . . . 385 The
Minor Veins in Leaf Blades of the Poaceae Contain Two Types of
Metaphloem Sieve
Tubes . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . 386 The Gymnospermous Sieve Cell . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . 386 The Walls of Sieve Cells Are Characterized
as Primary . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . 387 Callose Does Not Play a Role in Sieve-Pore Development
in Gymnosperms . . . . . . . . . . . . . . . . 387 Little Variation
Exists in Sieve-Cell Differentiation among Gymnosperms . . . . . .
. . . . . . . . . . . 388 Strasburger Cells . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . 390 The Mechanism of Phloem
Transport in Gymnosperms . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . 390 Parenchyma Cells . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . 391 Sclerenchyma Cells . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . 391 Longevity
of Sieve Elements . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391
Trends in Specialization of Sieve-Tube Elements . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392
Sieve Elements of Seedless Vascular Plants . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393
Primary Phloem . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . 393 REFERENCES . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . 398
Chapter 14 Phloem: Secondary Phloem and Variations in Its
Structure . . . . . . . . . . . . . . . . . . . . . . . . . .
407
Conifer Phloem . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . 409 Angiosperm Phloem . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . 412 The Patterns Formed by the Fibers Can
Be of Taxonomic Signifi cance . . . . . . . . . . . . . . . . . . .
. 413 Secondary Sieve-Tube Elements Show Considerable Variation in
Form and Distribution . . . . . . 415 Differentiation in the
Secondary Phloem . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . 417 Sclerenchyma Cells in
the Secondary Phloem Commonly Are Classifi ed as Fibers,
Sclereids,
and Fiber-Sclereids . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . 418 The Conducting Phloem Constitutes Only a Small Part
of the Inner Bark . . . . . . . . . . . . . . . . . 420
Nonconducting Phloem . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . 422 The Nonconducting Phloem Differs Structurally from the
Conducting Phloem . . . . . . . . . . . . . 423 Dilatation Is the
Means by Which the Phloem Is Adjusted to the Increase in
Circumference
of the Axis Resulting from Secondary Growth . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . 424
Chapter 15 Periderm . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . 427
Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . 427 Characteristics of the Components . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . 429 The Phellogen Is Relatively Simple in
Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . 429 Several Kinds of Phellem Cells May Arise from
the Phellogen . . . . . . . . . . . . . . . . . . . . . . . . . . .
429 Considerable Variation Exists in the Width and Composition of
Phelloderm . . . . . . . . . . . . . . . 431 Development of
Periderm . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433 The
Sites of Origin of the Phellogen Are Varied . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . 433 The
Phellogen Is Initiated by Divisions of Various Kinds of Cells . . .
. . . . . . . . . . . . . . . . . . . . . 434 The Time of
Appearance of the First and Subsequent Periderms Varies . . . . . .
. . . . . . . . . . . . . 434 Morphology of Periderm and Rhytidome
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . 437 Polyderm . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . 438 Protective Tissue in
Monocotyledons . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . 438 Wound Periderm . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438
Lenticels . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . 440 Three Structural Types of Lenticels Are
Recognized in Woody Angiosperms . . . . . . . . . . . . . . . 441
The First Lenticels Frequently Appear under Stomata . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . 442 REFERENCES .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
442
-
xiv | Contents
Chapter 16 External Secretory Structures . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . 447
Salt Glands . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . 449 Salt Bladders Secrete Ions into a Large
Central Vacuole . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . 449 Other Glands Secrete Salt Directly to the Outside .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. 449 The Two-celled Glands of the Poaceae . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449
The Multicellular Glands of Eudicotyledons . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . 450
Hydathodes . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . 451 Nectaries . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . 452 The Nectaries of Lonicera
japonica Exude Nectar from Unicellular Trichomes . . . . . . . . .
. . . 455 The Nectaries of Abutilon striatum Exude Nectar from
Multicellular Trichomes . . . . . . . . . . . 456 The Nectaries of
Vicia faba Exude Nectar via Stomata . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . 456 The Most Common Sugars in
Nectar Are Sucrose, Glucose, and Fructose . . . . . . . . . . . . .
. . . . 456 Structures Intermediate between Nectaries and
Hydathodes Also Exist . . . . . . . . . . . . . . . . . . . 459
Colleters . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . 459 Osmophores . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . 461 Glandular Trichomes Secreting
Lipophilic Substances . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . 462 Glandular Trichome Development . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . 463 The Glandular Structures of
Carnivorous Plants . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . 465 Stinging Hairs . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . 466 REFERENCES .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
466
Chapter 17 Internal Secretory Structures . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . 473
Internal Secretory Cells . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . 473 Oil Cells Secrete Their Oils into an Oil Cavity . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . 475 Mucilage Cells Deposit Their Mucilage between the
Protoplast and the Cellulosic Cell
Wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . 476 Tannin Is the Most Conspicuous Inclusion in
Numerous Secretory Cells . . . . . . . . . . . . . . . . . . 477
Secretory Cavities and Ducts . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . 478 The Best-Known Secretory Ducts Are the Resin Ducts of
Conifers . . . . . . . . . . . . . . . . . . . . . . . 478
Development of Secretory Cavities Appears to Be Schizogenous . . .
. . . . . . . . . . . . . . . . . . . . . . 479 Secretory Ducts and
Cavities May Arise under the Stimulus of Injury . . . . . . . . . .
. . . . . . . . . . . 481 Kino Veins Are a Special Type of
Traumatic Duct . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . 482 Laticifers . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . 483 On the Basis of Their
Structure, Laticifers Are Grouped in Two Major Classes:
Articulated
and Nonarticulated . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . 484 Latex Varies in Appearance and in Composition . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
486 Articulated and Nonarticulated Laticifers Apparently Differ
from One Another
Cytologically . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . 487 Laticifers Are Widely Distributed in the Plant
Body, Refl ecting Their Mode of
Development . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . 489 Nonarticulated Laticifers . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . 489 Articulated Laticifers . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . 491
The Principal Source of Commercial Rubber Is the Bark of the
Para Rubber Tree, Hevea brasiliensis . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . 493
The Function of Laticifers Is Not Clear . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. 495 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . 495
Addendum: Other Pertinent References Not Cited in the Text . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. 503
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . 521
Author Index . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . 541
Subject Index . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . 567
-
Preface
It has been over 40 years since the second edition of Esau’s
Plant Anatomy was completed. The enormous expansion of biological
knowledge that has taken place during this period is unprecedented.
In 1965, electron microscopy was just beginning to have an impact
on plant research at the cellular level. Since then, new approaches
and techniques, particularly those used in molecular-genetic
research, have resulted in emphasis and direction toward the
molecular realm of life. Old concepts and principles are being
challenged at virtu-ally every level, often, however, without a
clear under-standing of the bases upon which those concepts and
principles were established.
A biologist, regardless of his or her line of specializa-tion,
cannot afford to lose sight of the whole organism, if his or her
goal is an understanding of the organic world. Knowledge of the
grosser aspects of structure is basic for effective research and
teaching at every level of specialization. The ever-increasing
trend toward a reduction of emphasis on factual information in
contem-porary teaching and the apparent diminution of plant anatomy
and plant morphology courses at many col-leges and universities
make a readily accessible source of basic information on plant
structure more important than ever. One consequence of these
phenomena is a less precise use of terminology and an inappropriate
adoption of animal terms for plant structures.
Research in plant structure has benefi ted greatly from the new
approaches and techniques now available. Many plant anatomists are
participating effectively in the interdisciplinary search for
integrated concepts of growth and morphology. At the same time
comparative plant anatomists continue to create new concepts on the
relationships and evolution of plants and plant tissues with the
aid of molecular data and cladistic analy-ses. The integration of
ecological and systematic plant anatomy—ecophyletic anatomy—is
bringing about a clearer understanding of the driving forces behind
evolutionary diversifi cations of wood and of leaf attributes.
A thorough knowledge of the structure and develop-ment of cells
and tissues is essential for a realistic inter-pretation of plant
function, whether the function concerned is photosynthesis, the
movement of water, the transport of food, or the absorption of
water and minerals by roots. A full understanding of the effects of
pathogenetic organisms on the plant body can only be achieved if
one knows the normal structure of the plant concerned. Such
horticultural practices as grafting, pruning, vegetative
propagation, and the associated phenomena of callus formation,
wound healing, regen-eration, and development of adventitious roots
and buds are more meaningful if the structural features underly-ing
these phenomena are properly understood.
xv
-
xvi | Preface
A common belief among students and many research-ers alike is
that we know virtually all there is to know about the anatomy of
plants. Nothing could be further from the truth. Although the study
of plant anatomy dates back to the last part of the 1600s, most of
our knowledge of plant structure is based on temperate, often
agronomic, plants. The structural features of plants growing in
subtropical and tropical environments are frequently characterized
as exceptions or anomalies rather than as adaptations to different
environments. With the great diversity of plant species in the
tropics, there is a wealth of information to be discovered on the
structure and development of such plants. In addition, as noted by
Dr. Esau in the preface of the fi rst edition of Anatomy of Seed
Plants (John Wiley & Sons, 1960) “ . . . plant anatomy is
interesting for its own sake. It is a gratifying experience to
follow the ontogenetic and evolutionary development of structural
features and gain the realization of the high degree of complexity
and the remarkable orderliness in the organization of the
plant.”
A major goal of this book is to provide a fi rm founda-tion in
the meristems, cells, and tissues of the plant body, while at the
same time nothing some of the many advances being made in our
understanding of their function and development through molecular
research. For example, in the chapter on apical meristems, which
have been the object of considerable molecular-genetic research, a
historical review of the concept of apical organization is
presented to provide the reader with an understanding of how that
concept has evolved with the availability of more sophisticated
methodology. Through-out the book, greater emphasis is made on
structure-function relationships than in the previous two editions.
As in the previous editions, angiosperms are empha-
sized, but some features of the vegetative parts of gymnosperms
and seedless vascular plants are also considered.
These are exciting times for plant biologists. This is refl
ected, in part, in the enormity of literature output. The
references cited in this book represent but a frac-tion of the
total number of articles read in preparation of the third edition.
This is particularly true of the molecular-genetic literature,
which is cited most selec-tively. It was important not to lose
focus on the anatomy. A great many of the references cited in the
second edition were read anew, in part to insure continuity between
the second and third editions. A large number of selected
references are listed to support descriptions and interpretations
and to direct the interested person toward wider reading.
Undoubtedly, some pertinent papers were inadvertently overlooked. A
number of review articles, books, and chapters in books with
helpful reference lists are included. Additional pertinent
references are listed in the addendum.
This book has been planned primarily for advanced students in
various branches of plant science, for researchers (from molecular
to whole plant), and for teachers of plant anatomy. At the same
time, an effort has been made to attract the less-advanced student
by presenting the subject in an inviting style, with numerous
illustrations, and by explaining and analyzing terms and concepts
as they appear in the text. It is my hope that this book will
enlighten many and inspire numerous others to study plant structure
and development.
R. F. E.Madison, Wisconsin
July, 2006
-
Acknowledgments
Illustrations form an important part of a book in plant anatomy.
I am indebted to various persons who kindly provided illustrations
of one kind or another for inclu-sion in the book and to others,
along with publishers and scientifi c journals, for permission to
reproduce in one form or another their published illustrations.
Illus-trations whose source(s) are not indicated in the fi gure
captions are original. Numerous fi gures are from research articles
by me or coauthored with colleagues, including my students. A great
many of the illustrations are the superb work—line art and
micrographs—of Dr. Esau. Some fi gures are expertly rendered
electronic illustrations by Kandis Elliot.
Sincere thanks are extended to Laura Evert and Mary Evert for
their able assistance with the process of obtain-ing
permissions.
I am grateful to the following people, who so gener-ously gave
of their time to review parts of the manu-
script: Drs. Veronica Angyalossy, Pieter Baas, Sebastian Y.
Bednarek, C. E. J. Botha, Anne-Marie Catesson, Judith L. Croxdale,
Nigel Chaffey, Abraham Fahn, Donna Fernandez, Peter K. Helper, Nels
R. Lersten, Edward K. Merrill, Regis B. Miller, Thomas L. Rost,
Alexander Schulz, L. Andrew Staehelin, Jennifer Thorsch, and Joseph
E. Varner. Two of the reviewers, Judith L. Croxdale, who reviewed
Chapter 9 (Epidermis), and Joseph E. Varner, who reviewed an early
draft of Chapter 4 (Cell Wall), are now deceased. The reviewers
offered valuable suggestions for improve-ment. The fi nal
responsibility for the contents of the book, including all errors
and omissions, however, is mine.
Very special acknowledgment is accorded Susan E. Eichhorn.
Without her assistance it would not have been possible for me to
revise the second edition of Esau’s Plant Anatomy.
xvii
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ALEKSANDROV, V. G. 1966. Anatomiia Rastenii (Anatomy of Plants),
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BIEBL, R., and H. GERM. 1967. Praktikum der Pfl anzenanatomie,
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BIERHORST, D. W. 1971. Morphology of Vascular Plants. Macmillan,
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BOLD, H. C. 1973. Morphology of Plants, 3rd ed. Harper and Row,
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EAMES, A. J. 1961. Morphology of Vascular Plants: Lower
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FAHN, A. 1990. Plant Anatomy, 4th ed. Pergamon Press,
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Cyperaceae. Clarendon Press, Oxford.
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Dicotyledons: Leaves, Stems, and Wood in Relation to Taxonomy with
Notes on Economic Uses, 2 vols. Clarendon Press, Oxford.
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Dicotyledons, 2nd ed., vol. I. Systematic Anatomy of Leaf and Stem,
with a Brief History of the Subject. Clarendon Press, Oxford.
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Woody Plants: An Analytical Review of Anatomical, Physiological,
and Morphogenic Aspects. Tech. Bull. No. 1293. USDA, Forest
Service, Washington, DC.
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Struc-ture: Function and Development: A Treatise on Anatomy and
Veg-etative Development, with Special Reference to Woody
Plants.Springer-Verlag, Berlin.
RUDALL, P. 1992. Anatomy of Flowering Plants: An Introduction to
Structure and Development, 2nd ed. Cambridge University Press,
Cambridge.
SACHS, J. 1875. Text-Book of Botany, Morphological and
Physiological. Clarendon Press, Oxford.
SINNOTT, E. W. 1960. Plant Morphogenesis. McGraw-Hill, New
York.
SOLEREDER, H. 1908. Systematic Anatomy of the Dicotyledons: A
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Develop-ment, 2nd ed. Cambridge University Press, Cambridge.
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Gustav Fisher, Jena.
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TOMLINSON, P. B. 1969. Anatomy of the Monocotyledons, vol. III.
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WARDLAW, C. W. 1965. Organization and Evolution in
Plants.Longmans, Green and Co., London.
xx | General References
-
Structure and Development of the Plant Body—An Overview
CHAPTER ONE
The complex multicellular body of a vascular plant is a result
of evolutionary specialization of long duration—specialization that
followed the transition of multicellu-lar organisms from an aquatic
habitat to a terrestrial one (Niklas, 1997). The requirements of
the new and harsher environments led to the establishment of
morphological and physiological differences among the parts of the
plant body so that they became more or less strongly specialized
with reference to certain functions. The rec-ognition of these
specializations by botanists became embodied in the concept of
plant organs (Troll, 1937; Arber, 1950). At fi rst, botanists
visualized the existence of many organs, but later as the
interrelationships among the plant parts came to be better
understood, the number of vegetative organs was reduced to three:
stem, leaf, and root (Eames, 1936). In this scheme, stem and leaf
are commonly treated together as a mor-phological and functional
unit, the shoot.
Researchers in evolution postulate that the organiza-tion of the
oldest vascular plants was extremely simple, perhaps resembling
that of the leafl ess and rootless Devonian plant Rhynia (Gifford
and Foster, 1989; Kenrick and Crane, 1997). If the seed plants have
evolved from rhyniaceous types of plants, which con-
sisted of dichotomously branched axes without append-ages, the
leaf, the stem, and the root would be closely interrelated through
phylogenetic origin (Stewart and Rothwell, 1993; Taylor and Taylor,
1993; Raven, J. A. and Edwards, 2001). The common origin of these
three organs is even more obvious in their ontogeny (develop-ment
of an individual entity), for they are initiated together in the
embryo as the latter develops from the unicellular zygote into a
multicellular organism. At the apex of the shoot the leaf and stem
increments are formed as a unit. At maturity, too, the leaf and
stem imperceptibly merge with one another both externally and
internally. In addition, the root and the stem consti-tute a
continuum—a continuous structure—and have many common features in
form, anatomy, function, and method of growth.
As the embryo grows and becomes a seedling, stem and root
increasingly deviate from one another in their organization (Fig.
1.1). The root grows as a more or less branched cylindrical organ;
the stem is composed of nodes and internodes, with leaves and
branches attached at the nodes. Eventually the plant enters the
reproductive stage when the shoot forms infl orescences and fl
owers (Fig. 1.2). The fl ower is sometimes called
1
Esau’s Plant Anatomy, Third Edition, By Ray F. Evert.Copyright ©
2006 John Wiley & Sons, Inc.
-
2 | Esau’s Plant Anatomy, Third Edition
A
B
C
D
epicotyl
cotyledons
FIGURE 1.1
Some stages in development of the fl ax (Linum usitatis-simum)
seedling. A, germinating seed. The taproot (below interrupted line)
is the fi rst structure to pene-trate the seed coat. B, the
elongating hypocotyl (above interrupted line) has formed a hook,
which subsequently will straighten out, pulling the cotyledons and
shoot apex above ground. C, after emergence above ground, the
cotyledons, which in fl ax persist for about 30 days, enlarge and
thicken. The developing epicotyl—the stem-like axis or shoot above
the cotyledons—is now apparent between the cotyledons. D, the
developing epicotyl has given rise to several foliage leaves, and
the taproot to several branch roots. (From Esau, 1977; drawn by
Alva D. Grant.)
sepals
petals
A
B
C
FIGURE 1.2
Infl orescence and fl owers of fl ax (Linum usitatissimum).A,
infl orescence, a panicle, with intact fl owers showing sepals and
petals. B, fl ower, from which the sepals and petals have been
removed, to show the stamens and gynoecium. Flax fl owers usually
have fi ve fertile stamens. The gynoecium consists of fi ve united
carpels, with fi ve distinct styles and stigmas. C, mature fruit
(capsule) and persistent sepals. (Drawn by Alva D. Grant.)
-
Structure and Development of the Plant Body—An Overview | 3
an organ, but the classical concept treats the fl ower as an
assemblage of organs homologous with the shoot. This concept also
implies that the fl oral parts—some of which are fertile (stamens
and carpels) and others sterile (sepals and petals)—are homologous
with the leaves. Both the leaves and the fl oral parts are thought
to have originated from the kind of branch systems that
charac-terized the early, leafl ess and rootless vascular plants
(Gifford and Foster, 1989).
Despite the overlapping and intergrading of charac-ters between
plant parts, the division of the plant body into morphological
categories of stem, leaf, root, and fl ower (where present) is
commonly resorted to because it brings into focus the structural
and the functional specialization of parts, the stem for support
and conduc-tion, the leaf for photosynthesis, and the root for
anchor-age and absorption. Such division must not be emphasized to
the degree that it might obscure the essential unity of the plant
body. This unity is clearly perceived if the plant is studied
developmentally, an approach that reveals the gradual emergence of
organs and tissues from a relatively undifferentiated body of the
young embryo.
❙ INTERNAL ORGANIZATION OF THE PLANT BODYThe plant body consists
of many different types of cell, each enclosed in its own cell wall
and united with other cells by means of a cementing intercellular
sub-stance. Within this united mass certain groupings of cells are
distinct from others structurally or function-ally or both. These
groupings are referred to as tissues.The structural variations of
tissues are based on differ-ences in the component cells and their
type of attach-ment to each other. Some tissues are structurally
relatively simple in that they consist of one cell type; others,
containing more than one cell type, are complex.
The arrangement of tissues in the plant as a whole and in its
major organs reveals a defi nite structural and functional
organization. Tissues concerned with con-duction of food and
water—the vascular tissues—form a coherent system extending
continuously through each organ and the entire plant. These tissues
connect places of water intake and food synthesis with regions of
growth, development, and storage. The nonvascular tissues are
similarly continuous, and their arrangements are indicative of
specifi c inter-relations (e.g., between storage and vascular
tissues) and of specialized functions (e.g., support or storage).
To emphasize the organization of tissues into large entities
showing topographic continuity, and reveal-ing the basic unity of
the plant body, the expres-sion tissue system has been adopted
(Sachs, 1875; Haberlandt, 1914; Foster, 1949).
Although the classifi cation of cells and tissues is a somewhat
arbitrary matter, for purposes of orderly description of plant
structure the establishment of cat-egories is necessary. Moreover,
if the classifi cations issue from broad comparative studies, in
which the vari-ability and the intergrading of characters are
clearly revealed and properly interpreted, they not only are
descriptively useful but also refl ect the natural relation of the
entities classifi ed.
The Body of a Vascular Plant Is Composed of Three Tissue
Systems
According to Sachs’s (1875) convenient classifi cation based on
topographic continuity of tissues, the body of a vascular plant is
composed of three tissue systems, the dermal, the vascular, and the
fundamental (or ground). The dermal tissue system comprises the
epidermis,that is, the primary outer protective covering of the
plant body, and the periderm, the protective tissue that supplants
the epidermis, mainly in plants that undergo a secondary increase
in thickness. The vascular tissue system contains two kinds of
conducting tissues, the phloem (food conduction) and the xylem
(water con-duction). The epidermis, periderm, phloem, and xylem are
complex tissues.
The fundamental tissue system (or ground tissue system) includes
the simple tissues that, in a sense, form the ground substance of
the plant but at the same time show various degrees of
specialization. Paren-chyma is the most common of ground tissues.
Paren-chyma cells are characteristically living cells, capable of
growth and division. Modifi cations of parenchyma cells are found
in the various secretory structures, which may occur in the ground
tissue as individual cells or as smaller or larger cell complexes.
Collenchyma is a living thick-walled tissue closely related to
parenchyma; in fact, it is commonly regarded as a form of
paren-chyma specialized as supporting tissue of young organs. The
fundamental tissue system often contains highly specialized
mechanical elements—with thick, hard, often lignifi ed
walls—combined into coherent masses as sclerenchyma tissue or
dispersed as individual or as small groups of sclerenchyma
cells.
Structurally Stem, Leaf, and Root Differ Primarily in the
Relative Distribution of the Vascular and Ground Tissues
Within the plant body the various tissues are distributed in
characteristic patterns depending on plant part or plant taxon or
both. Basically the patterns are alike in that the vascular tissue
is embedded in ground tissue and the dermal tissue forms the outer
covering. The principal differences in the structure of stem, leaf,
and root lie in the relative distribution of the vascular and
ground tissues (Fig. 1.3). In the stems of eudicotyledons
-
4 | Esau’s Plant Anatomy, Third Edition
leaf bases
stem inprimary growth
stem insecondary growth
root inroot insecondary growthsecondary growth
root insecondary growth
leaf subtendingthe axillary shoot
primary phloem
primary xylem
axillary shoot
vascular rays
phellem (cork)pericyclevascular cambium
secondary xylem
root apex
rootcap
epidermisvascular cylinder
lateral vein
midvein
vascular bundles
mesophyll
epidermis
cortex
procambiumpith
leaf trace gap
shoot apex young leaves
cortex
primary xylemepidermis
cortex
endodermis
secondary phloem
primary phloem
vascular cylinder
primary phloem
pericycle
epidermis
cortexpith
vascular bundles
primary phloem
primary xylem
vascular cambiumsecondary xylem
primary phloem fiberssecondary phloem
primary xylem
epidermis
cortex
pith
A
B
C
E
H
G
F
root in primary growth
leaf blade
D
FIGURE 1.3
Organization of a vascular plant. A, habit sketch of fl ax
(Linum usitatissimum) in vegetative state. Transverse sec-tions of
stem at B, C, and of root at D, E. F, longitudinal section of
terminal part of shoot with shoot apex and devel-oping leaves. G,
transverse section of leaf blade. H, longitudinal section of
terminal part of root with root apex (covered by rootcap) and
subjacent root regions. (A, ×2/5; B, E, F, H, ×50; C, ×32; D, ×7;
G, ×19. A, drawn by R. H. Miller.)
-
Structure and Development of the Plant Body—An Overview | 5
FIGURE 1.4
Types of stem anatomy in angiosperms. A, transverse section of
stem of Helianthus, a eudicot, with discrete vascular bundles
forming a single ring around a pith. B, transverse section of stem
of Zea, a monocot, with the vascular bundles scattered throughout
the ground tissue. The bundles are more numerous near the
periphery. (From Esau, 1977.)
(eudicots), for example, the vascular tissue forms a “hollow”
cylinder, with some ground tissue enclosed by the cylinder (pith,
or medulla) and some located between the vascular and dermal
tissues (cortex) (Figs. 1.3B, C and 1.4A). The primary vascular
tissues may appear as a more or less continuous cylinder within the
ground tissue or as a cylinder of discrete strands, or bundles,
separated from one another by ground tissue. In the stems of most
monocotyledons (monocots) the vascular bundles occur in more than
one ring or appear scattered throughout the ground tissue (Fig.
1.4B). In the latter instance the ground tissue often cannot be
distinguished as cortex and pith. In the leaf the vascular tissue
forms an anastomosing system of veins, which thoroughly permeate
the mesophyll, the ground tissue of the leaf that is specialized
for photosynthesis (Fig. 1.3G).
The pattern formed by the vascular bundles in the stem refl ects
the close structural and developmental relationship between the
stem and its leaves. The term “shoot” serves not only as a
collective term for these two vegetative organs but also as an
expression of their intimate physical and developmental
association. At each node one or more vascular bundles diverge from
the strands in the stem and enter the leaf or leaves attached at
that node in continuity with the vasculature
of the leaf (Fig. 1.5). The extensions from the vascular system
in the stem toward the leaves are called leaf traces, and the wide
gaps or regions of ground tissue in the vascular cylinder located
above the level where leaf traces diverge toward the leaves are
called leaf trace gaps (Raven et al., 2005) or interfascicular
regions (Beck et al., 1982). A leaf trace extends from its
connection with a bundle in the stem (called a stem bundle, or an
axial bundle), or with another leaf trace, to the level at which it
enters the leaf (Beck et al., 1982).
Compared with the stem, the internal structure of the root is
usually relatively simple and closer to that of the ancestral axis
(Raven and Edwards, 2001). Its rela-tively simple structure is due
in large part to the absence of leaves and the corresponding
absence of nodes and internodes. The three tissue systems in the
primary stage of root growth can be readily distinguished from one
another. In most roots, the vascular tissues form a solid cylinder
(Fig. 1.3E), but in some they form a hollow cylinder around a pith.
The vascular cylinder comprises the vascular tissues and one or
more layers of nonvas-cular cells, the pericycle, which in seed
plants arises from the same part of the root apex as the vascular
tissues. In most seed plants branch, or lateral, roots arise in the
pericycle. A morphologically differentiated
A B
1 m
m
1 m
m
-
6 | Esau’s Plant Anatomy, Third Edition
peridermcollenchyma
leaf tracegap
leaf trace
sympodium
median trace lateral trace
A B
5
75
64
86
4
68
46
57
1 1 1 1
2 2 2
3 3 33
4 8 6 4 6 8 4 6 5 7 56575
FIGURE 1.5
Diagrams illustrating primary vascular system in the stem of elm
(Ulmus), a eudicot. A, transverse section of stem showing the
discrete vascular bundles encircling the pith. B, longitudinal view
showing the vascular cylinder as though cut through median leaf
trace 5 and spread out in one plane. The transverse section (A)
corresponds to the topmost view in B. The numbers in both views
indicate leaf traces. Three leaf traces—a median and two lateral
traces—connect the vascular system of the stem with that of the
leaf. A stem bundle and its associated leaf traces are called a
sympodium. (From Esau, 1977; after Smithson, 1954, with permission
of the Council of the Leeds Philo-sophical and Literary
Society.)
endodermis (the innermost, and compactly arranged, layer of
cells of the cortex in seed plants) typically sur-rounds the
pericycle. In the absorbing region of the root the endodermis is
characterized by the presence of Cas-parian strips in its
anticlinal walls (the radial and trans-verse walls, which are
perpendicular to the surface of the root) (Fig. 1.6). In many roots
the outermost layer of cortical cells is differentiated as an
exodermis,which also exhibits Casparian strips. The Casparian strip
is not merely a wall thickening but an integral band-like portion
of the wall and intercellular substance that is impregnated with
suberin and sometimes lignin. The presence of this hydrophobic
region precludes the passage of water and solutes across the
endodermis and exodermis via the anticlinal walls (Lehmann et al.,
2000).
❙ SUMMARY OF TYPES OF CELLS AND TISSUESAs implied earlier in
this chapter, separation of cells and tissues into categories is,
in a sense, contrary to the fact that structural features vary and
intergrade with each other. Cells and tissues do, however, acquire
differential
properties in relation to their positions in the plant body.
Some cells undergo more profound changes than others. That is,
cells become specialized to varied degrees. Cells that are
relatively little specialized retain living proto-plasts and have
the capacity to change in form and func-tion during their lifetimes
(various kinds of parenchyma cells). More highly specialized cells
may develop thick, rigid cell walls, become devoid of living
protoplasts, and cease to be capable of structural and functional
changes (tracheary elements and various kinds of sclerenchyma
cells). Between these two extremes are cells at varying levels of
metabolic activity and degrees of structural and functional
specialization. Classifi cations of cells and tissues serve to deal
with the phenomena of differentia-tion—and the resultant diversifi
cation of plant parts—in a manner that allows making
generalizations about common and divergent features among related
and unre-lated taxa. They make possible treating the phenomena of
ontogenetic and phylogenetic specialization in a com-parative and
systematic way.
Table 1.1 summarizes information on the generally recognized
cate