Strasburger’s Plant Sciences

Strasburgeria robusta Guill.; Strasburgeriaceae named after the founder of this book, Eduard Strasburger

© Pete Lowry, Missouri Botanical Garden

Andreas Bresinsky, Christian Korner, Joachim W. Kadereit,Gunther Neuhaus and Uwe Sonnewald

Strasburger’s Plant Sciences

Including Prokaryotes and Fungi

With 1100 Figures and 63 Tables

Andreas BresinskyBotanical InstituteUniversity of RegensburgRegensburg, Germany

Christian KornerInstitute of BotanyUniversity of BaselBasel, Switzerland

Joachim W. KadereitInstitut fur Spezielle Botanik und Botanischer GartenJohannes Gutenberg-University MainzMainz, Germany

Gunther NeuhausCell BiologyUniversity of FreiburgFreiburg, Germany

Uwe SonnewaldDepartment of BiologyDivision of BiochemistryFriedrich-Alexander-University Erlangen-NurembergErlangen, Germany

Translation and CopyeditingAlison Davies, Stuart Evans (Chapters 1–4, 9, 10)David and Gudrun Lawlor, Stuart Evans (Chapters 5–8)Christian Korner, Stuart Evans (Chapter 11)Christian Korner, Lea Streule (Chapters 12–14)

Alison Davies, Garching, GermanyDavid and Gudrun Lawlor, Harpenden, UKStuart Evans, West Rainton, UKLea Streule, Basel, Switzerland

ISBN 978-3-642-15517-8 ISBN 978-3-642-15518-5 (eBook)ISBN 978-3-642-15519-2 (print and electronic bundle)DOI 10.1007/978-3-642-15518-5Springer Heidelberg New York Dordrecht London

This work is based on the 36th German language edition of Strasburger, Lehrbuch der Botanik, by Andreas Bresinsky, Christian Korner,Joachim Kadereit, Gunther Neuhaus, Uwe Sonnewald, published by Spektrum Akademischer Verlag, Heidelberg 2008.

Library of Congress Control Number: 2013944576

© Springer-Verlag Berlin Heidelberg 2013

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Preface

Eduard Strasburger*February 1, 1844, Warsaw – {May 19, 1912, Bonn

Founder of the Lehrbuch der Botanik fur Hochschulen

(Botany Textbook for Universities)

(Photo by Dr. Wolfram Lobin/Uni Bonn)

The last English translation of Strasburger’s Lehrbuch der Botanik fur Hochschulen (Textbook of Botany for Universities)

was published in 1976 (30th Ed.). Since then, six new German editions have been published and were partially translated

into Italian, Spanish, Serbo-Croatian, Turkish, and Russian. Considering that plant sciences have developed and

expanded considerably since 1976, and that six more German editions have tried to keep pace with these changes,

a new English translation was long overdue. The present edition represents a balanced and comprehensive work on the

plant sciences, the book’s trademark and particular strength. The inclusion of bacteria, archaea, and the various lineages

referred to as fungi may not be justified from a phylogenetic perspective when dealing with plants, but is necessary

considering the important evolutionary and ecological interactions between plants and these organisms.

Strasburger’s Lehrbuch der Botanik fur Hochschulen has been available for almost 120 years now. Starting with its first

edition in 1894, the book has greatly influenced university teaching in Germany and neighboring countries, and its 36

editions also mirror the dynamic history of the plant sciences.The book was first founded by Eduard Strasburger and is

still published under his name. From the beginning, it was a multi-author effort, and Strasburger himself invited his

colleagues at the Botanical Institute of Bonn University as contributors to the first edition. Since that time more than 20

authors from a number of universities in three different countries contributed to the content. Although clearly all authors

of the first and of later editions shaped the book, Strasburger as its founder deserves special recognition. In his honor,

a New Caledonian tree, which is shown on page II, was named Strasburgeria.

Eduard Strasburger studied the natural sciences in Paris, Bonn, and Jena, receiving his doctorate in Jena before

completing his postdoctoral degree (‘‘Habilitation’’) in Warsaw in 1867. He was appointed professor of botany at the

University of Jena in 1869, at the age of 25, andmoved to BonnUniversity in 1881. Under his direction, the Botanical Institute

at Poppelsdorf Palace established itself as an international center of botany. In 1894, together with his colleagues F. Noll, H.

Schenck, andA.F.W. Schimper, he founded the Lehrbuch der Botanik fur Hochschulen, in the past often simply referred to as

the Bonner Lehrbuch. The Kleine Botanische Praktikum fur Anfanger (Short Botanical Practical for Beginners), which also

appeared in multiple editions, and the somewhat more extensive Das Botanische Praktikum (Botanical Practical) have

dominated microscopical laboratory work at universities for a long time. Strasburger’s research interests were primarily

in plant ontogeny and cytology. He discovered that the central processes underlying nuclear division (formation,

division, and movement of chromosomes) are the same in all eukaryotic organisms (1875), and he was the first to

observe that fertilization in flowering plants requires the fusion of the male sperm nucleus with the female egg nucleus.

From this he concluded that the cell nucleus must be the most important carrier of hereditary factors (1884).

The Authors

April 2013

Table of Contents

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

List of Topical Insights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix

List of Boxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi

Volume 1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Part I Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Gunther Neuhaus

1 Molecular Basics: The Building Blocks of Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2 The Structure and Ultrastructure of the Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

3 The Tissues of Vascular Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

4 Morphology and Anatomy of Vascular Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161

Part II Physiology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237Uwe Sonnewald

5 Physiology of Metabolism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239

6 Physiology of Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411

7 Physiology of Movement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531

8 Allelophysiology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569

Volume 2

Part III Evolution and Systematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 607Joachim W. Kadereit . Andreas Bresinsky

9 Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 609

10 Systematics and Phylogeny . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 665

Part IV Ecology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1041Christian Korner

11 Basics of Plant Ecology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1043

12 Plant–Environment Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1065

13 Ecology of Populations and Vegetation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1167

14 Vegetation of the Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1217

Timeline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1263

Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1267

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1273

viii Table of Contents

List of Topical Insights

Topical Insight 5.1: Galactolipids and Membrane Remodeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370

Christoph Benning

Topical Insight 5.2: Genetically Encoded Biosensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407

Wolf B. Frommer

Topical Insight 8.1: Host Targets of Bacterial Effectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 598

Mary Beth Mudgett

Topical Insight 9.1: Homoploid Hybrid Speciation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 656

Loren Rieseberg

Topical Insight 10.1: Origin and Early Evolution of Flowers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1014

Peter K. Endress . James A. Doyle

Topical Insight 12.1: What Plant Ecologists Can and Cannot Learn from a Satellite’s Eye . . . . . . . . . . 1074

Hamlyn G. Jones

Topical Insight 12.2: A World Without Fire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1082

William Bond

Topical Insight 12.3: The Dynamic Pipeline: Coordination of Xylem Safety and Efficiency . . . . . . . . . 1093

Frederick C. Meinzer

Topical Insight 12.4: From Where Do Plants Take Their Water? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1096

Todd E. Dawson

Topical Insight 12.5: Leaf Nitrogen: A Key to Photosynthetic Performance . . . . . . . . . . . . . . . . . . . . 1107

John R. Evans

Topical Insight 12.6: Plant Life in the P-Poor Part of the World . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1114

Hans Lambers

Topical Insight 12.7: Diversity of Traits: A Functional Link to Adaptation, Community Assembly,

and Ecosystem Structure and Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1131

Peter B. Reich

Topical Insight 12.8: Using Stable 13C Isotopes to Study Carbon and Water Relations . . . . . . . . . . . . 1137

Rolf Siegwolf

Topical Insight 13.1: Forest Structure and Gap Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1202

Hank H. Shugart

List of Boxes

Box 2.1: Cell Fractionation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Box 2.2: The Nuclear Spindle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Box 3.1: Residual Meristems and Meristemoids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

Box 4.1: Inflorescence Morphology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

Box 4.2: Types of Stele . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195

Box 4.3: The Leaves of Carnivorous Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218

Box 4.4: Root Metamorphoses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229

Box 5.1: Electrophysiology Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272

Box 5.2: Important Units in Photobiology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342

Box 6.1: Thale Cress: Arabidopsis thaliana (L.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418

Box 6.2: Conventions in Naming Genes, Proteins, and Phenotypes . . . . . . . . . . . . . . . . . . . . . . . . . 422

Box 6.3: Production of Transgenic Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423

Box 6.4: Application of Transgenic Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429

Box 6.5: Evolution of Plant Receptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 528

Box 8.1: Cauliflower Mosaic Virus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 589

Box 8.2: Biology of Crown Gall Tumors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593

Box 9.1: Recording and Analyzing Phenotypic and Genetic Variation . . . . . . . . . . . . . . . . . . . . . . . . 628

Box 9.2: Population Genetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 641

Box 10.1: The Origin of Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 676

Box 10.2: Phylogeny of Plants and Fungi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 678

Box 10.3: From Unicellular Organisms to Multicellular Organisms . . . . . . . . . . . . . . . . . . . . . . . . . . . 695

Box 10.4: Occurence and Habit of Fungi (Including the Cellulose Fungi) . . . . . . . . . . . . . . . . . . . . . . 748

Box 10.5: Uses of Algae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 775

Box 10.6: Occurence and Diversity of Habits in Algae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 779

Box 10.7: Occurence and Ecology of Mosses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 816

Box 10.8: Occurence and Ecology of Ferns and Fern Allies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 874

Box 10.9: Seed Plants (Spermatophytina) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 880

Box 10.10: Poales: The Evolution of Habitat Ecology and Pollination Biology . . . . . . . . . . . . . . . . . . . 949

Box 10.11: Chenopodiaceae: The Evolution of C4 Photosynthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 961

Box 10.12: Asterales: Evolution of Secondary Pollen Presentation . . . . . . . . . . . . . . . . . . . . . . . . . . . 1007

Box 10.13: Mass Extinctions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1018

Box 11.1: Classification of Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1061

Box 12.1: Effects of CO2 on Plant Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1151

Box 13.1: Metapopulations: Consequences of Habitat Fragmentation for Survival of Species . . . . . 1173

Introduction

Botany: A Biological Science

Botany is the science of plants. The term was coined in the

first century by Dioscorides, who used it to mean

a (medicinal) herbal science. In fact, Greek botane means

‘‘grass,’’ as a common forage or economic plant. The

general Greek term for plant is phyton. These days it is

much more common to use the synonymous term ‘‘plant

science’’ than to use ‘‘botany.’’

Plants are primarily defined as those organisms whose

cells contain plastids as well as having true nuclei with

a nuclear membrane and several chromosomes. Plastids

may occur as chloroplasts, or organelles that may become

plastids under the right conditions. Chloroplasts are pho-

tosynthetic organelles that are able to convert light energy

into chemical energy and to fix carbon dioxide. Green

plants are photoautotrophic. Unlike other heterotrophic

(organotrophic) organisms, green plants are able to

survive without organic nutrition.

Fungi are also traditionally included in botany even

though they do not have any plastids. They are heterotro-

phic and behave saprotrophically (feed off dead organic

material), parasitically, or symbiotically (feed off living

organisms). Even though fungi are phylogenetically closer

to animals, they share some features with plants, e.g., they

possess vacuoles in their cell-wall-bound cells, they have a

sessile life style and they take up dissolved nutrients. Fungi

can also form practically obligate symbiotic relationships

with plants (mycorrhiza).

It can be rather problematic to differentiate between

animal and plant among the single-celled protists. Among

the flagellates, even between closely related species in the

same genus, there can be forms with and without plastids:

phytoflagellates and zooflagellates, respectively. The cells

of bacteria and archaea are generally smaller and funda-

mentally more simply organized than the cells of animals,

fungi, and plants (> Fig. 1). Bacteria and archaea do not

have a true cell nucleus and do not undergo cell multipli-

cation by nuclear or cellular division in the way that all

other organisms do, nor do their phototrophic forms

have plastids. The cells in these groups are distinguished

as prokaryotic cells from the eukaryotic cells of all

other organisms. Bacteria and archaea are thus prokary-

otes, whereas all other organisms (plants, fungi, animals;

all protists with a true cell nucleus) are eukaryotes.

There are no intermediate forms between the prokary-

otes and the eukaryotes in modern living organisms.

Even so, the oldest eukaryotes were derived from the

prokaryotes. The investigation of microscopically small

organisms, both prokaryotic as well as eukaryotic, is

a scientific discipline of its own – microbiology. This

includes viruses, viroids, and prions – subcellular systems

that hover at the boundary between the animate and

the inanimate.

Despite all the differences between prokaryotic cells

and eukaryotic cells, and the even more pronounced

differences between the various forms and functions of

the cells of higher animals and plants, there are many basic

commonalities. All organisms share similar molecules and

many fundamental systems essential to life. This also

applies for genes (hereditary factors). This basic unifor-

mity across all life forms indicates a shared phylogenetic

origin: all living organisms (probably) arose from a single

lineage (monophyletic origin).

What Is Life?

Every living system is defined by a particular series of

features. However, only all of these features together

allow the differentiation of an animate from an inanimate

organization. The classic signs of life include:

● Chemical composition. The dry mass of all organisms

is dominated by proteins, nucleic acids, polysaccha-

rides, and lipids. Additionally, there is a wealth of

heterogeneous organic molecules and ions. Organic

molecules, especially macromolecules, are only syn-

thesized by living organisms (biosynthesis with the

help of special catalysts, the enzymes).

● Systematically constructed complex structures. Life

is intrinsically linked to cellular organizational forms.

Even the simplest living organisms are characterized

by complex structures. This means the molecular and

supramolecular components are functionally linked

and dependent on each other. Only by functioning

together properly are they able to bring something to

life. None of the single components alone would be

able to fulfill this. The system is thus more than just

the sum of the parts, and life is always a product of

A. Bresinsky et al., Strasburger’s Plant Sciences, DOI 10.1007/978-3-642-15518-5,# Springer-Verlag Berlin Heidelberg 2013

a system. Below the complexity level of the cell there

is no independent life. The cells always contain

information-bearing structures, an array of various

enzymes, and are separated from their environment

by a selectively permeable membrane. It is not contra-

dictory to say that in most multicellular plants there

are plasmodesma (plasma canals in the cell walls)

between the tissue cells that are united into

a supercellular symplast.

● Nutrition. Organisms are rather ‘‘unlikely’’ construc-

tions in terms of energy and entropy. They are made

up of energy-rich, highly unstable molecules; their

high structural and functional organization represents

low entropy. The support of this labile condition is

only possible with the input of energy. Living systems

are therefore basically open systems; i.e., they take up

energy-rich photons or materials and release energy-

poor material (e.g., CO2, H2O). This metabolism is

intrinsically linked with energy exchange. The metab-

olism results in a constant energy imbalance (dynamic

balance with irreversible subprocesses: so-called flux

equilibrium). Metabolism and energy exchange allow

the energy-demanding construction of (macro)

molecules (anabolism) by linking it to an energy-

producing process such as the capture of solar energy

and/or the breaking up of energy-rich compounds

(catabolism). The low entropy capacity of the organ-

isms is sustained by the donation (dissipation) of

excessive entropy into the surrounding environment.

By using a dissipative structure, the organisms avoid

fatal chaotic events. Thus, life is not really a condition

but is rather a continuous process. Whereas the outer

form of organisms changes rather slowly, there is con-

tinuous turnover at the molecular level.

● Motion. Every actively living organism and every indi-

vidual cell shows signs of motion (motility). However,

many cells/organisms are able to switch to a latent

phase, forming seeds, spores, or cysts. During these

stages of life there are no obvious signs of motility and

almost all criteria for life are arrested.

● Stimulus perception and response.All organisms and

cells must be able to receive and respond to signals

from their environment. The diversity of mechanisms

evolved to do this is incredible.

● Development. Organisms are incapable of retaining

a particular structure indefinitely. No organism looks

the same throughout all its life phases. A newly formed

cell, arising from cell division, grows to the size of its

mother cell (growth). Multicellular organisms usually

start their individual development from just a single

cell (fertilized egg cell, a zygote; spore). Then they

grow by cell division until they reach their final size,

changing their shape in the process. Ontogeny, the

development to a sexually mature multicellular organ-

ism, is associated with morphological processes at the

cellular level that result in the differentiation of the

initially similar embryonic cells.

● Reproduction. The succession of generations is made

up of successive life or reproductive cycles. Life is

perpetuated in this way, in spite of the inability of

individuals to permanently retain a particular devel-

opmental phase and despite the inescapable fact that

all individuals must eventually die. Death is the last

stage in an individual’s development. Unlike ‘‘cata-

strophic death,’’ physiological death is often a result

of inner processes undergoing a program of self-

destruction. Conversely, organisms may only arise as

progeny of conspecific ancestors. Abiogenesis, or

. Fig. 1

Size comparison of prokaryotic cells and eukaryotic cells. (a) Bacterial cells (Escherichia coli). (b) Cells of an Elodea canadensis

leaf. Three plant cell characteristics can be seen: cell walls, chloroplasts, and central vacuoles. Both images are highly

magnified (�380)

2 Introduction

spontaneous generation, of a living system from inan-

imate material is, at least on today’s Earth, inconceiv-

able and has never been proven: omne vivum e vivo

(‘‘every life originates from another life’’). This rather

obvious standpoint is relatively new. Until the ground-

breaking work of L. Pasteur and H. Hoffmann around

1860, it was assumed that microorganisms, even fungi

and nematodes (worms) in fermenting and rotting

liquids, had arisen spontaneously.

● Replication. Reproduction is normally connected

with replication. This ensures the perpetuation of

a species in spite of the loss of individuals as a result

of changing environments. The replication rates are

often astounding in smaller organisms. Under optimal

conditions, bacterial cells can divide every 20 min.

This means that with unrestricted replication of

a single cell, its progeny would form a cell mass the

volume of Earth in less than 2 days. Larger organisms

tend to replicate more slowly, but the individuals are

better protected by a variety of different mechanisms.

● Inheritance. Ontogeny happens in much the same

way from generation to generation. The genetic infor-

mation is amplified and transmitted in the process. It

contains the program for the course of species-specific

ontogeny. The genetic information of all cellular

organisms – prokaryotes and eukaryotes – is saved

(stored) in the bases and nucleotide sequences of

deoxyribonucleic acid (DNA). These are linear or cir-

cular double-stranded macromolecules. Viruses can

store their genetic information in a single-stranded

DNA molecule and in ribonucleic acid (RNA; single

stranded or double stranded).

● Evolution. Copying (replication) and transmission of

the genetic information happens with great precision.

However, over many successive generations, changes

can occur that may be inherited (mutations). These

changes can be induced by environmental factors.

These can be partly a result of inherited switching on

(activation) and off (deactivation) of genes (epige-

netics). In the long term, quite big differences can

develop in a population that can differently affect

the reproductive ability of individuals. This natural

selection results in changes in the characteristics of

the members of a species and in the end can result

in the establishment of new species: evolution

and phylogeny.

A superior criterion for life in all organisms is their

reproductive ability. All remaining characteristics are

either critical to or a result of this central attribute.

The genetic information of all organisms contains the

developmental plan for complex molecular machinery,

whose prime function is its own reproduction. Life is (at

least on today’s Earth) only conceivable and verifiable as

a continuum. This knowledge is supported by the irre-

versibility of individual death and the extinction of

species. There is nothing comparable in inanimate nature.

Origin and Evolution of Life

The living organisms that exist today are the result of

a long evolutionary process. On the basis of radioactivity

and the composition of rock formations, the age of Earth

has been calculated as being about 4.6 billion years. The

study of the remains of organisms (fossils; paleontology)

in various old sediments has shown that other sorts of

plants and animals lived on Earth during earlier geological

epochs. The phylogenetic continuity can be seen in the

floras and faunas of past epochs of the living organisms:

the older they are the more different they are. Larger,

multicellular organisms first appeared toward the end of

the Precambrian (about 570 million years ago). Until then

single-celled organisms had dominated, and these were

mostly prokaryotes. There is evidence that extensive

colonies of cyanobacteria were already present in the

Archean (more than 3 billion years ago): the relevant

sediments in Australia and South Africa contain layered

stromatoliths over 30 cm in size. These are characteristic

biogenic sediments, which are still formed today in warm

waters, and were built by dense layers of phototrophic

cyanobacteria.

How could life have arisen? Answers to this funda-

mental question are sought by trying to recreate or simu-

late the primeval conditions that would have existed on

Earth at that time. A condition for the formation of a

simple self-replicating system was the presence of organic

(macro) molecules. In contrast to today, the conditions on

the still hot planet (Hadean eon) would have enabled

organic molecules to form abiogenically. The first atmo-

sphere contained water vapor as well as carbon dioxide,

nitrogen, and smaller fractions of reducing gasses, but

practically no free oxygen; therefore, there was no ozone

layer that could have filtered the energy-rich UV radiation

from the sun. These conditions would have enabled vari-

ous organic compounds to form. Abiogenic acetic acids

and energy-rich thioesters are even formed in watery mix-

tures of carbon monoxide, sulfuric acid, and metal

sulfides, like those thrown out by deep-sea thermal vents.

Certain places on primitive Earth would have become

enriched in such compounds as long as life did not exist

to digest them and no oxidation destroyed them.

Introduction 3

Even the simplest cells, such as those of the (recently

arisen) saprobiotic mycoplasmas (see below), are very

complex. Their origin from a chaotic mixture of molecular

building blocks via a single chance event is highly improb-

able. However, a likely scenario is that this happened in

a process of hypothetical intermediate steps (multistep

theory): if the necessary individual steps in this prebiotic

evolution were small enough, then the likelihood of them

having really happened over a vast timescale is sufficiently

large. Some molecules which could have arisen

abiogenetically show signs of enzymatic activity; i.e., they

function as biocatalysts. Certain RNA molecules

(ribozymes) can catalyze changes in themselves and,

together with heavy metal ions, can even initiate their

own propagation, albeit rather haphazardly (RNA

world). The decisive step toward independent life was

made when protein catalysts made the effective and pre-

cise replication of nucleic acids possible and the key to the

synthesis of these enzyme proteins was carried by the

nucleic acids. This double-step advance, which was prob-

ably a cumulative result of many small steps, formed a link

between proteins and nucleic acids that is absolutely fun-

damental for life in its current form. Thus, there was

a genetic code that could translate nucleotide sequences

from nucleic acids into protein sequences, and the sepa-

ration of gene (hereditary factor) from phene (a character

based on the hereditary information) was completed.

The first systems capable of self-replication, the hypo-

thetical progenotes and the subsequently evolved pro-

karyotes, were able to live organotrophically as long as

the abiotic formation of organic molecules continued.

However, increasing exploitation of resources to the

point where they became exhausted meant that

phototrophic forms became more prominent. Among

these were some forms that were able to split water to

release oxygen during photosynthesis. This slowly created

an oxidative atmosphere, allowing a much more effective

energy acquisition from organic molecules by cell respira-

tion. At the same time, an ozone layer was formed in the

stratosphere that absorbed the heavily mutagenic UV

radiation from the sun and enabled the colonization of

the ocean surfaces and the land. Fossil evidence from the

long Precambrian evolution is, not surprisingly, rather

rare and incomplete. However, sequence comparisons

from proteins and nucleic acids of related living organisms

can be used to reconstruct phylogeny. The more differen-

tiated the sequences, the earlier the last common ancestor

of the organisms must have lived. Evolutionary changes

have occurred at different rates in different parts of the

(partial) sequences. Therefore, only sequences (or partial

sequences) that change very slowly over time and are fairly

similar even between living, quite distantly related organ-

isms, are used in the reconstruction of early phylogeny.

The comparison of these highly conserved sequences

shows that the split between archaea and bacteria hap-

pened more than 3 billion years ago. Modern eukaryotic

cells have plastids and mitochondria, photosynthetic and

cell-respiration organelles, their own genetic code, and

synthesize some of their proteins themselves. These organ-

elles can only self-replicate and thus have a semiautono-

mous position in eukaryotic cells. They also have

numerous prokaryotic properties, such as the mode of

division, and details of their composition. Plastids seem

to be descendants of once-free-living bacteria, which

became integrated into the cells of primitive eukaryotes

as intracellular symbionts more than one billion years

ago and gradually developed into cell organelles

(Endosymbiont theory).

Remains of multicellular macroorganisms are first

found in sediments that are less than a billion years old.

These organisms are, without exception, eukaryotes.

Even their evolution, which can be increasingly better

reconstructed with molecular systematic techniques, has

been a result of the interaction between chance mutations

and directional selection (Darwinism). This is based on

the assumption that evolution is a result of the sum of

numerous small steps (gradualism). Even so, these have

been interspersed by major evolutionary transitions.

These do not differ from the small steps in terms of how

they arise, but differ rather in the gross effect of many

gradual evolutionary changes. They have been rarer events

than the other gradual evolutionary transitions but have

been more momentous. It seems that, repeatedly, repro-

ductive units that achieved independence at a certain

point in time have merged to form large, more complex

units. Thus, completely novel systems have emerged that

can form the basis of alternative, distinct lineages.

Limits of Life

The question for the limits of life has two components.

First, one can ask for the distributional limits of life, and

second for both lower and upper size limits of individuals.

The first aspect – an ecological component – is that,

despite a phenomenal range of adaptive strategies, general

conditions for life have quite narrow limits. They are

determined by maxima and minima of water content,

temperature, and light. The optimum for most organisms

is median temperatures (10–40�C) and high water

content. For this reason, it is possible to store food at

cool temperatures (fridge, freezer) or by drying

4 Introduction

(legumes, cereals, flour, bread, hay) or by pasteurization

(milk). In nature, the dry and cold regions are particularly

poorly colonized. Many organisms can survive tempera-

tures down to the freezing point of water by having latent

or dormant phases, but still die between 0�C and �10�C.Psychrophilic organisms (e.g., some snow algae) have

optimal growth temperatures between 1 and 2�C. Tem-

peratures over 100�C, which are rarely found on Earth’s

surface (hot springs, volcanoes), can support thermo-

philic organisms. Some archaea have temperature optima

around 100�C, possibly an adaptive relict from primeval

Earth. As phototrophic organisms are mainly responsible

for the production of organic material (biomass), life is

more-or-less restricted to the well-illuminated regions of

Earth’s surface and oceans. Earth is coated with

a comparatively thin biosphere that accounts for less

than 0.01% of its volume.

The largest life forms (both fossil and living) are found

among the vertebrates (dinosaurs, baleen whales) but also

larger and in greater numbers among the conifers and

deciduous trees as well as among clonal organisms such

as poplar (Populus), reed grass (Phragmites), bracken

(Pteridium), and fungi. The giants among the trees

(Sequoia, Cryptomeria, some Eucalyptus) are also the

heaviest life forms.

A more significant question for theoretical biology is

‘‘how small can a life form be?’’ ‘‘What is the lower limit of

complexity for self-replicating biosystems?’’ The smallest

cells are prokaryotic. They are found in mycoplasmas. The

diameter of these cell-wall-less prokaryotic cells is about

0.3 mm and their DNA can only code for about 500

different proteins. This is about the absolute minimum

possible for DNA replication, the realization of the genetic

information stored therein, the support of a heterotrophic

metabolism and energy exchange, and a simple cell struc-

ture (theoretically about 350 genes). In comparison, the

cells of a typical bacterium have a diameter of 2 mm and

contain over 3,000 different proteins; the diameter of most

eukaryotic cells lies between 10 and 100 mm, and the cells

can form over 30,000 different proteins. The complete

sequenced genome of themodel plantArabidopsis thaliana

has about 25,000 genes, 11,000 more than the fruit fly

Drosophila.

Viruses are much more simply organized and most of

them are even smaller. A virion (a viral particle) is not

a cell. Whereas, e.g., the simplest cell has both DNA

(information storage) and RNA (information retrieval),

a virion has neither DNA nor RNA. The nucleic acid is

often only associated with molecules of a single protein

type such as in the tobacco mosaic virus (> Fig. 2), or it

may be surrounded by a protein sheath (capsid) made up

of a single protein or only a few different proteins. This

sort of capsid often has a crystalline symmetry.

Viruses or (bacterio)phages (viruses that attack pro-

karyotic cells) only partially fulfill the conditions neces-

sary for life. They have nometabolism or energy exchange,

no ability to replicate or synthesize proteins, and no ability

to reproduce independently. They can only reproduce by

using the metabolism and energy exchange of a living cell

– they are obligate parasites (‘‘borrowed life’’). The dis-

persal forms – virions – that exist outside living cells

represent lifeless organic systems.

The simplest organizational level is achieved by the

viroids. These are infectious nucleic acids (RNA) with no

associated proteins. The short, ring-shaped RNA mole-

cules do not code for any proteins. Some of the most

dangerous plant parasites known are viroids.

In spite of their particularly simple organization, neither

viruses nor viroids can be considered to be the most prim-

itive forms of life, as their reproduction depends on the

existence of living cells. Rather, they are genetic elements

that became independent of their support cells (vagabond

genes). In fact, there are segments of genetic information in

most (if not all?) eukaryotic cells and prokaryotic cells that

are inherited independently of the gene-carrying structures

(chromosomes, genophores), or at least that are able to

temporarily disassociate themselves from the structures.

This heterogeneous group includes the plasmids of many

bacteria and some eukaryotes, as well as the so-called inser-

tion sequences and transposons (jumping genes).

Biology as a Natural Science

Living nature is impressive because it supports a huge

diversity of life forms. Recording, describing, and system-

atically organizing all living and extinct organism types

(species) is the enormous, as yet unfinished, task of biol-

ogy, in particular, systematics. But biology is not just

restricted to the description of what is there, even more,

it strives to explain this diversity. Besides observation and

comparison, there is the experiment. An experiment is the

observation of a process under artificial predetermined or

controlled varied conditions. Data from experiments and

observations provide the raw material for constructing

hypotheses and theories, contributing toward the expla-

nation of causal relationships. (H. Poincare: ‘‘A heap of

facts is as much a science as a heap of stones make

a house.’’). By forming a repeatedly questioned theoretical

construct (see below), the discovery of correlating laws and

their final formulation into natural laws can incorporate

lots of observations into short, clear units that can then be

Introduction 5

considered. It would be impossible to intellectually pene-

trate the real world with all its basically nonrecordable

structures and experiences without this type of abstrac-

tion. Thus, the natural sciences have become enormously

significant in recent times, especially modern biology

(keywords ‘‘biotechnology,’’ ‘‘gene technology’’).

The sum of recognized natural laws and their inter-

pretation forms the scientific world view, a simplified

reflection of nature presented in perceptions, symbols,

and ideas. This world view is the highest expression of

our understating of nature. It enables mental operations

(thought experiments) that would be too dangerous or

expensive to conduct in the real world. The scientific

world view is thus fundamentally dynamic, as novel infor-

mation is acquired by research, and new interpretations

can be expanded and altered. It is perforce preliminary

and fragmentary and cannot (should not) ever be seen as

being complete. Even so, it is the best that humankind can

offer. The fragmentary character (nature) of the scientific

world view is affected not just by the selection (even if

subconscious) and use of limits of scientific endeavor, but

also by the limits of methodology and primarily by the

limitations imposed by the type of research. These are

indirect in fundamental research as the aims and results

are initially unknown. Indirect aims are researched in that

testable hypotheses are postulated (Greek hypothesis, to

suppose). A hypothesis, a scientific concept, can never

be proven because the data will never be enough. However,

a general theorem can be rejected on the basis of one

contradictory event (asymmetry of verification and falsi-

fication; see K.R. Popper). The assumption ‘‘all roses are

red’’ cannot be proven even with 1,000 red roses, but

can be rejected on the observation of a single yellow or

white rose.

Correlations are based on laws of relationships

derived from observed events (e.g., cigarette smoking/lung

. Fig. 2

Tobaccomosaic virus particles can be seen as rod-shaped particles under an electronmicroscope (EM). Every virion contains

a helical RNA molecule. In the uninjured state, it is made up of a series of 2,130 identical protein molecules each with

158 amino acids. The central axial canal formed in the RNA helix is clearly visible in this negative-contrast slide. Scale bars

(a) 0.1 mm, (b) 0.02 mm (EM images from a F. Amelunxen and b C. Weichan)

6 Introduction

cancer; but also the frequency of storks and human birth

rates in some regions). Correlations can mean there is

a causal relationship, but this does not have to be the

case. If two quantities B and C are correlated, then B can

cause C or the other way round; B and C could be caused

by a third, common, as yet unknown quantity A; they are

correlated but not causally, only coincidentally. Although

the lack of a correlation implies the lack of a causal rela-

tionship, a correlation is not evidence for one; therefore, it

cannot be used for the verification of an assumption.

The asymmetry of verification and falsification means

that forward steps in knowledge are achieved indirectly,

not directly, as inappropriate or inapplicable hypotheses

are rejected (method of trial and error). The aim, the

appropriate knowledge and explanatory reasons, can

only be achieved through disappointment and via detours

(Greek methodos means not only thorough research but

also detour).

With every failed falsification attempt, the probability

of finding the right hypothesis increases. When the hypoth-

esis can be applied to other areas independently of the

original research, it becomes more plausible. Comprehen-

sive hypotheses that, despite many attempts, remain

nonfalsifiable become theories. Theories are elements in

the scientific world view. A theory, e.g., the central biolog-

ical theory of descendancy or evolution, allowsmany events

to be explained and enables the formulation of numerous

testable postulates. From a theoretical scientific viewpoint,

a theory presents a disciplinary matrix or paradigm that

provides the intellectual framework for further experi-

mental work in an area of interest. Surprisingly, even

though specific observations and appropriate experiments

are made on the basis of hypotheses and theories, most

research is not inductive (based on experience and under-

standing) but deductive. It is not primarily targeted at

discovering the unknown or novel, but serves to check

and refine an existing paradigm. Of course, existing

‘‘tested’’ theories can be falsified. Then a new more com-

prehensive theory has to be developed. These scientific

revolutions (see L. Fleck; T.S. Kuhn) are only successful if

they can also explain why the previous theory appeared to

explain so much. Often it becomes apparent that the older

theory does in fact still hold true within certain limits. The

history of scientific biology has many examples of such

scientific revolutions, such as in the developments of cell

biology and genetics.

The teachings of the potential and limits of human

knowledge (as outlined above) form part of epistemology,

which is an important tenet in theoretical science as well as

in philosophy (see, e.g., I. Kant). Even so, the potential to

use knowledge from independent logic or mathematics to

form ideas about real life or nature remained a mystery for

a long time. (A. Einstein: ‘‘The incomprehensibility of the

world lies in its comprehensibility.’’).

Special Position of Biology

The uniqueness of life in nature gives biology a special

position among the sciences. Time and again it has been

questioned whether living systems and systems of abiotic

nature adhere to different laws, and special life forces

(vitalism) have often been postulated. However, to date

there is no known case where physical and chemical laws

have been disobeyed by living organisms. On the other

hand, organisms are incredibly complex systems, which

means that biological systems obey laws that would oth-

erwise not be observed. One speaks of emerging attri-

butes. An important consequence of living systems is that

biological materials cannot be logically or mathematically

penetrated in the same way as objects in physics and

chemistry. Biology is an exact science based on the recog-

nition of natural laws, but observation, description, and

comparison play a much greater role than in physics.

However, a complete derivation of all biological phenom-

ena from chemical and physical laws, in the sense of

a consistent reductionism, would be illusory.

The definition of life as a self-replicating system is

further supported by a fact that emphasizes the unique-

ness of the organism – biological teleonomy. Life forms

behave purposefully, they react expediently, and appear to

be constructed sensibly. Besides the question ‘‘why?’’

(causality), biology (and only biology among the sci-

ences) also justifiably asks ‘‘what for?’’ (finality). This

touches on the cyclical development of life; compare the

terms ‘‘developmental cycle,’’ ‘‘reproductive cycle,’’ and

‘‘generation cycle.’’ From any given starting point, these

cycles proceed along genetically predetermined develop-

mental lines until they return to a comparable starting

point (e.g., egg cells, spores). This results in semicyclical

events and chains of cause and effect. For example,

a particular developmental stage B can arise not only as

a result of the previous stage A but also via the subsequent

stages C, D, etc., also as a cause for the renewed occurrence

of stage A (even if it is chronologically out of sequence).

The final viewpoint bears as much weight as the causal

approach in biology. In inanimate nature, cyclical systems

(e.g., oscillations) do not have mechanisms whereby losses

are compensated for by energy gains, and they finally stop

altogether. Life forms, on the other hand, can replicate by

reproduction. Even in the research of evolution and the

origins of life, biology finds itself in an unusual position.

Introduction 7

While the highest priority is typically the search for natu-

ral laws – reflected in the regular repetition of structures or

processes – in fact here it is the singular, chance event that

is decisive. This is related to the reproduction and selec-

tion of organisms. Natural mutations are chance events

and not predictable. Such mutations can remain neutral

for a very long time until such time as the conditions

suddenly change, making the mutations have negative or

positive effects on the organism. If the mutation has

a favorable effect on the bearer, then according to evolu-

tion by natural selection in successive generations, the

mutation will become fixed. Life forms are, in this respect,

very effective enhancers: all their observable inheritable

traits are derived from improbable and thus rare chance

events (singularities) whose effects are retrospectively

enhanced by reproductive processes.

Animals and Plants

Since the historically based (rather than factually based)

tendency to specialize has been superseded, modern biol-

ogy is dominated by interdisciplinary cooperation.

Knowledge drawn from genetics, biophysics, and bio-

chemistry as well as physiology contributes to a broad

foundation for general biology. Even evolutionary and

developmental biology, as well as molecular and cell biol-

ogy, have grown beyond the boundaries of the classical

disciplines of botany and zoology. However, this connec-

tivity should not be allowed to disguise the fact that the

typical animal and typical plant (both terms used in the

colloquial sense) have numerous differences.

The typical animal is able to migrate. Its body is

compactly constructed, with all organs except those

required to interpret environmental signals being posi-

tioned inside. In order to see them, the animal’s body

has to be opened (‘‘anatomy’’ is derived from the Greek

wordmeaning ‘‘to separate and cut up’’). The large surface

areas necessary for breathing, nutrient resorption, and

excretion are folded inside the body cavity. The outer

surface area is reduced, and so the animal is a ‘‘closed’’

organism. The compact body structure enables the devel-

opment of central organs for circulation and excretion.

Even the nervous system, which enables rapid coordina-

tion, shows a tendency to become centralized over

evolutionary time. Most organs are formed in a limited

number and are at least rudimentarily present in the

embryo, growing proportionately with the growing

organism. Body symmetry is predominantly bilateral and

dorsiventral, as expected when the two perpendicularly

oriented vectors of gravity and motility are present.

Radially symmetrical forms (in the strictest sense) only

occur in sessile or aquatic species. The specialization of

tissues and organs is highly advanced. Even meristems are

specifically determined for the formation of particular

cells (stem cells of blood and immune systems, the skin,

the intestinal epithelium, etc.). The lifetime of even large

animals is limited. Regenerative potential is often quite

low in highly developed animals. Some highly differenti-

ated cells remain active throughout the animals’ lifetime

and are normally not regenerated in the adult phase (large

neurons, striated muscle fibers, cells of the optical lens).

A typical plant is usually ‘‘rooted’’ in one place for the

whole of its lifetime. The pollen, seeds, or spores of the

plant have, theoretically, limitless distribution possibili-

ties. The body area is maximized by unfolding and

branching. The plant is an ‘‘open’’ organism; perennial

plants grow with numerous shoot apices and grow more

in every vegetative period (for trees, annual growth from

all shoot tips, annual rings in the wood, etc.). Metabolic

waste products have to be removed by each cell individu-

ally; instead of centralization there is localized cellular

excretion. The body is mostly radially symmetrical.

There is an enormous regenerative potential; each shoot

apex can, in principle, grow a complete new plant. This

aspect is used extensively in horticulture and agriculture

for the vegetative propagation of plants by grafts, cuttings,

scions, bulbs, bulbils, etc. Furthermore, novel shoot apices

may arise in injury-related callus growths (tissues gener-

ated by chaotic cell proliferation). Thus, cell cultures (even

from single vegetative cells) can be used to successfully

generate whole plants, something that is not possible from

animal cells or tissues. It is not unusual to find plants that

live to 100 or even 1,000 years of age. Clones are immortal.

Thus, e.g., all apples of the same variety are perpetuated,

by grafts, from the same genetic clone as from the apple (of

that sort) that was first discovered, regardless of where it is

now cultivated.

Plants and animals also differ significantly in the struc-

ture and function of their cells. A general comparison

shows that plants cells are not only distinct as a result of

possessing plastids. They are not only phototrophic but

are also osmotrophic (only able to take up substances that

are dissolved), whereas animal cells are phagotrophic (able

to take up nutrients in particulate form). Flagellates

include mixotrophic species that are able to take up nutri-

ents in both ways (> Fig. 3). The plant cell has, in its fully

grown state, a central vacuole that makes up over 90% of

the cell volume, and a cell wall. The cell wall absorbs the

hydrostatic pressure of the vacuole (turgor) that would

otherwise cause the cell to burst. Turgor is a consequence

of osmosis; the molar total concentration of the cell sap in

8 Introduction

the vacuole is far greater than that of the imbibed water in

the cell walls. Animal tissue cells have neither large vacu-

oles nor tough cell walls that have a stabilizing function for

the individual cells. Their turgor is low because they are

surrounded by isotonic body and tissue fluids. Themass of

intercellular substances of the connective and supporting

tissues of animals fixes not cells but supercellular struc-

tures. During plant and fungal cell division, the first wall

primordium arises between the daughter cells via internal

secretion of wall substances. In contrast, typical animal cell

division occurs by pinching off daughter cells from the

mother cell (cleavage), and, whereas the cells of the plant

body are almost without exception anchored to their point

of origin, the cells of animals may migrate and be

translocated during development.

Fungal cells are – apart from not having plastids and

not exhibiting phototropism – more similar to typical

plant cells than animal cells. They are vacuolated,

osmotrophic cells with stable, nonrupturing cell walls

that generally do not cleave but divide by novel cell wall

formation (laid down by internal secretions).

Classification and Significance ofPlant Sciences

The investigation of the plant, fungal, and protist world –

in fact just like for the whole world of organisms – can be

considered from many different viewpoints. For example,

research areas could reflect the hierarchy of structures to

be investigated (> Table 1). Basic research aims to gain

understanding of the origin, diversity, and connectivity

between form and function. This places the research object

to the fore. Applied research is more concerned with

the use of plants, fungi, and microorganisms in human

and animal nutrition; for medicinal, toxic, and drug-

producing plants – the foundations of pharmacology;

plant breeding, genetic manipulation, and biotechnology;

for use in agriculture and forestry; for phytopathology,

pest and weed control; and for landscaping, nature and

animal conservation, and ecology (as defined by the mod-

ern media). Basic research provides the essential back-

ground knowledge for every type of applied research.

In this handbook, the description of the general struc-

tural basics is in Part I. This treats the areas from atomic

up to macroscopic dimensions: the overview ofmolecular

basics is followed by a discussion of the structure and fine

structure of the cell (cytology), followed by discussion of

plant tissues (histology) and then the outer structure as

seen with the naked eye (morphology).

The structures are presented in Part II according to the

general function in metabolic and energy exchange, change

of form (metamorphosis), and motility. The dynamics of

life processes are illustrated by this so-called plant physiol-

ogy. The discussion of the physiology of metabolism is

followed by discussion of developmental physiology and

then physiology of movement. An especially current topic

is allelophysiology – the diversity of physiological rela-

tionships that plants have with other organisms.

The division of this handbook into parts and chapters

should not obscure the fact that modern biology is distin-

guished by its interdisciplinary approach. Areas that were

. Fig. 3

Poterioochromonas malhamensis, a mixotrophic flagellate from the order Chrysomonadales (see also Fig. 10.83) with two

unequal anterior flagella and lobopodium (L) as well as a posterior anchorage appendage (�1,160). The cell on the left has

a nucleus (N) with a nucleolus, plastid (P), and storage vacuole (V). The cell on the right has a large digestive vacuole with

a half-digested algal cell in it (Interference contrast, microflash image from W. Herth)

Introduction 9

once separated have grown together and have given rise to

new, especially productive fields of research. This is what

happened when, e.g., descriptive cell research (cytology),

biochemistry, and molecular biology came together and

formed modern cell biology.

Part III firstly outlines evolution research and deals

with the natural laws and causes governing speciation and

its genetic background. Secondly, it is largely taken up

with botanical systematics. The study of relationships is

based on the results of many other disciplines, and sys-

tematics describes, names, and classifies more than

500,000 known plant species. The classification is based

on the reconstructed phylogeny of the plant kingdom.

Evidence from nucleic acids and proteins (molecular phy-

logeny) and from plant fossils (paleobotany) plays a domi-

nant role. The chapter on systematics contains information

from many different specialized areas that intensively deal

with individual organismal groups (microbiology, bacteri-

ology, mycology, etc.) as well as applied disciplines that

study the practical uses of plants for humans.

Plant ecology deals with the relationships that plants

and plant communities have with their biotic and abiotic

environment. Ecological botany aims to understand facts,

natural laws, and causes for the distribution and gregari-

ousness of plants in space and time.

Plant ecology highlights the significance of plant sci-

ences, especially in the modern world. In terms of energy,

all life on Earth is dependent on phototrophic organisms,

in particular, plants: they are the only relevant (in terms of

sheer numbers) producers and are found at the start of

almost all food chains and at the base of all food pyramids.

This has been true for at least a billion years. Thanks to

their enormous biodiversity, plants support the structure

and functioning of highly diverse ecosystems under a huge

range of conditions, from the Polar Regions to the Tropics.

This diversity and the function of individuals in the

biosphere are severely threatened by the no longer negli-

gible influence of approximately seven billion people.

Unsustainable land use and atmospheric changes mean

the threat to the biosphere has reached global proportions

(global change). Even humans belong to those organisms

whose existence as individuals and species entirely

depends on a stable environment. In these circumstances,

a climate protection scheme based on scientific principles

is more important than ever.

Plant science plays an important role in the develop-

ment of biological sciences. Many fundamental biological

principles have been developed on the basis of plant stud-

ies. These include the discovery of the cell and cell nucleus,

chromosomes, mitosis, meiosis, osmosis, and laws of

genetic inheritance. Even though the solutions to many

problems in modern biology have been found using

microorganisms and certain animals with particularly

appropriate systems, and many medically relevant ques-

tions regarding cancer, immune systems, thought, and

consciousness can only be answered using (higher) ani-

mals, botany nevertheless remains a key area of basic

biological research. This is evidenced by the enormous

advances made in modern plant sciences (see the model

plant Arabidopsis thaliana). As before, the applied plant

sciences are also immensely important. Plants and fungi

play a central role next to bacteria in biotechnology. It is

therefore not surprising that ‘‘green gene technology,’’ the

application of gene technology in agriculture, has rapidly

become increasingly significant. As everywhere in modern

biology, the deciphering of genomes (genomics) is being

continually updated as different protein complements

are discovered (proteonomics) and the metabolites of

different cells in the same organism are analyzed

(metabolonomics).

. Table 1

Biological fields of research and the complexity of the

objects studied

Structure Fields of research

Atoms Biophysics

Molecules Biochemistry

Semantic

macromolecules

Molecular biology

Genes, chromosomes Genetics

Cells Cell biology

Tissues Histology

Organs Anatomy, physiology

Organisms Morphology, developmental

physiology, systematics, phylogeny,

autecology

Populations Reproductive biology, evolutionary

biology

Communities Geobotany, community ecology

Ecosystems Biogeochemistry, ecosystem

biology

10 Introduction