Tài liệu Plant Resins Chemistry, Evolution, Ecology, and Ethnobotany ppt

Plant Resins
Plant Resins
Chemistry, Evolution,
Ecology, and
Ethnobotany
JEAN H. LANGENHEIM
Timber Press
Portland
• Cambridge
Page 1, Agathis australis, kauri; page 2, Boswellia, frankincense.
All drawings by Jesse Markman, maps by Gulla Thordarsen and Jesse Markman.
Copyright © 2003 by Jean H. Langenheim
All rights reserved
Published in 2003 by
Timber Press, Inc. Timber Press
The Haseltine Building 2 Station Road
133 S.W. Second Avenue, Suite 450 Swavesey
Portland, Oregon 97204, U.S.A. Cambridge CB4 5QJ, U.K.
Printed in Hong Kong
Library of Congress Cataloging-in-Publication Data
Langenheim, Jean H.
Plant resins : chemistry, evolution, ecology, and ethnobotany / Jean H. Langenheim.
p. cm.
Includes bibliographical references (p. ).
ISBN 0-88192-574-8
1. Gums and resins. 2. Gums and resins—Utilization. I. Title
SB289 .L36 2003
620.l'924—dc21
2002028941

. . . gum, the gum of the mountain spruce.
He showed me lumps of the scented stuff
Like uncut jewels, dull and rough.
—Robert Frost, “The Gum-Gatherer,”
from Mountain Interval, 1920
Contents
Preface 13
Acknowledgments 18
PART I
The Production of Resin by Plants 21
Chapter 1 What Plant Resins Are and Are Not 23
Definitions of Resin 23
Terpenoid Resins 26
Terpenoid Synthesis 26
Terpenoid Loss 33
Characteristic Components 34
Phenolic Resins 40
Synthesis and Characteristic Components 41
Substances Confused or Intermixed with Resin 45
Gums 45
Mucilages 47
Oils and Fats 48
Waxes 49
Resin Compounds in Latex 49
Miscellaneous Intermixed Compounds 50
Chapter 2 Resin-Producing Plants 51
Resin-Producing Conifers 52
Classification 52
Pinaceae 54
Araucariaceae 59

Podocarpaceae 62
Cupressaceae 63
5
6 | CONTENTS
Resin-Producing Angiosperms 67
Classification 67
Basal Group 69
Monocots 70
Eudicots 73
Evolutionary Trends in Resin-Producing Plants 98
Taxonomic Distribution of Resin Producers 98
Convergence in Aspects of Resin Production 101
Status of Evolutionary Interpretation 103
Chapter 3 How Plants Secrete and Store Resin 106
Ultrastructural Features of Resin Secretory Structures 107
Sites of Synthesis 107
Export of Resin Components 110
Internal Resin Secretory Structures 112
Canals Versus Pockets or Cysts 112
Conifers 114
Angiosperms 122
Resin in Laticifers 127
Evolution of Internal Secretory Structures 128
External Resin Secretory Structures 130
Glandular Trichomes 130
Epidermal Cells and Bud Trichomes 135
PART II
The Geologic History and Ecology of Resins 141
Chapter 4 Amber: Resins Through Geologic Time 143
How Is Resin Fossilized and When Is It Amber? 144

Distribution of Amber Deposits 147
Sources of Amber 150
Botanical Evidence 150
Chemical Evidence 153
Geologic History of Amber-Producing Plants 156
Amber from Conifers 157
Amber from Angiosperms 172
Amber of Unknown Botanical Source 187
CONTENTS | 7
The Floras of Amber Forests 189
Baltic Amber Forests 189
Dominican and Mexican Amber Forests 192
Renewed Interest in Amber Research 194
Chapter 5 Ecological Roles of Resins 196
Ecologically Important Properties of Resin 196
Variation in Resin Composition 199
Variation in Resin Quantity 202
Resin Defense of Conifers 203
Ponderosa Pine as a Model System 204
Other Conifer Resin Interactions 210
Ecological Roles in Tropical Angiosperms 219
Copious Resin Production in Tropical Trees 219
Hymenaea and Copaifera as Model Systems 220
Other Angiosperm Resin Interactions 229
Roles of Surface-Coating Resins 237
Shrubs and Herbs in Xeric Communities 237
Subarctic and Boreal Trees 244
Ecosystem Interactions of Resins 247
Resin Use by Bees in the Temperate Zones 248
Pharmaceutical Use of Resin by Coatis 249

Resins as Beetle Pheromones 250
Role of Resin in Ecosystem Nutrient Cycling 251
Herbivore-Induced Terpene Emissions and Tropospheric
Chemistry 252
Future Ecological Research on Resins 253
PART III
The Ethnobotany of Resins 255
Chapter 6 Historical and Cultural Importance of Amber and Resins 257
Amber Trade from the Stone Age to the Classical Age 260
Old Stone Age to the Iron Age 260
Greeks and Romans 267
Baltic Amber from the Middle Ages to the Present 269
Medieval and Renaissance Periods 270
8 | CONTENTS
Seventeenth Through Nineteenth Centuries 273
Twentieth and Twenty-first Centuries 275
Amber in Other Areas 278
Burmese Amber into China 278
Pre-Columbian Amber Trade in Mesoamerica 280
Resin Figurines from Costa Rican Burial Sites 280
Dominican Amber 282
Incense Trade Routes 283
Cannabis and Trade in Its Resin 290
Old World Hashish Cultures 290
Prohibition 295
Resins in Indigenous Cultures 296
Mesoamerica and the Maya 296
Southeast Asia and the Semelai 297
Resins in the Economies of the United States, New Zealand,
and Africa 298

Naval Stores in the United States 298
Kauri Resin in New Zealand 302
Copal in Africa 304
Chapter 7 Oleoresins 306
Naval Stores from Conifers 307
United States 307
Europe 319
Asia 323
Latin America 326
Africa 328
Cedarwood Oil 329
Oily Resins from Tropical Angiosperms 331
Dipterocarps 331
Legumes 334
Chapter 8 Fragrant and Medicinal Balsams 341
The Balsams 342
Conifer Balsams 342
Leguminous Balsams 343
CONTENTS | 9
Storax and Styrax 347
Elemis 356
Old World Elemis 356
New World Elemis 357
Other Important Balsams 362
Boswellia 363
Commiphora 368
Bursera 373
Chapter 9 Varnish and Lacquer Resins 375
Dammars 375
Confusion in Terminology and Plant Sources 375

Local Use and Export 376
Dammar as a Source of Petroleum 379
Gamboge 381
Sandarac 382
Mastic 385
Varnish 385
Other Uses 388
Acaroid Resin 390
Hard Copals 392
Leguminous Copals 393
Araucarian Copals 399
Lacquers and Specialty Varnishes 406
Anacard Lacquers 406
Barniz de Pasto and Other Rubiaceous Resins 408
Araliaceous Varnishes 410
Amber Varnish 410
Shellac 410
Chapter 10 Miscellaneous Resins 412
Umbelliferous Resins 412
Ammoniacum 412
Asafoetida and Galbanum 413
Silphium 416
10 | CONTENTS
Convolvulaceous Resins 418
Jalap 418
Other Ipomoea Resins 420
Scammony 420
Hashish and Hops Resin 421
Hashish 421
Hops 425

Propolis 427
Allergenic Anacard Resins 429
Poison Ivy, Poison Oak, and Poison Sumac 430
Other Poisonous Anacards 433
Chemistry of the Poisonous Resins 434
Labdanum 435
Desert Shrub Surface Resins 437
Myoporaceae 438
Asteraceae 439
Dragon’s Blood 441
Other Resins 444
Podophylloresin 444
Poplar Bud Resins 445
Guaiac 447
Creosote Bush Resin 447
Gharu Wood 448
Guayule Resin 450
Resins from Latex 452
Conifer Resins 453
Amber in Medicine 455
Chapter 11 Future Use of Resins 457
Traditional Uses 458
Amber Jewelry and Artwork 458
Incense 458
Other Special Uses 459
Medicinal Uses 459
New Therapeutic Uses for Resins 459
Propolis 460
Marijuana 461
CONTENTS | 11

Industrial Uses 463
Chemical Feedstocks 463
Fuel Sources 465
Tropical Forest Management for Resin Use 466
Extractive and Indigenous Reserves 468
Agroforestry 469
Plantations 471
Enrichment Planting 472
Enhanced Pest Protection of Resin-Producing Trees 473
Archeology and Anthropology of Resins 475
Appendix 1 Resin-Producing Conifers 477
Appendix 2 Resin-Producing Angiosperms 480
Appendix 3 Skeletons of Characteristic Components of Fossil Resins 486
Appendix 4 Age, Location, and Plant Source of Amber Deposits 488
Appendix 5 Common Names, Plant Sources, and Uses of Resins 490
Glossary 494
References 501
Plant Index 569
Subject Index 581
Color plates follow page 432
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13
Preface
When I was asked by Timber Press to write a new book on resins, including
amber—Howes’s 1949 Vegetable Gums and Resins was the most recent such
effort—the breadth of interdisciplinary coverage seemed too ambitious for an
individual person. There have been so many advances in resin research in the
past half century, including the development of new fields of research such as
chemical ecology, and the exploration of other interesting facets about resins
made possible by new chemical, molecular, and microscopic techniques. With

a little thought, however, I realized that my years of resin research had pre-
pared me to accept the challenge enthusiastically, a challenge that has been
stimulating and rewarding.
My interest in resins began with ambers formed over geologic time and
proceeded rapidly to the evolutionary significance of the ecological roles
resins play in plants. These were natural interests, arising from my training as
an ecologist and paleobotanist. Later, my queries turned to how humans have
used resins throughout history, and my interest in that intensified when I
taught an undergraduate course, Plants and Human Affairs, and coauthored
a textbook on the subject. I became convinced that resins are remarkable
materials indeed, especially in their diversity and the length of time they have
been such versatile substances in the lives of plants and humans. A university
colleague, a philosopher, suggested that resin had created a “cosmos” for me
because of the variety of topics I had been led to investigate: paleobotany,
chemistry, systematics, ecology, anthropology, ethnobotany, art history, etc.
There is no doubt, however, that I could only have delved into such wide-
ranging topics with the collaboration and expertise of many individuals,
which increased the value and enjoyment of the experience. Although most of
the people associated with the development of my research were not directly
involved in my writing Plant Resins, I want to acknowledge their contribu-
14 | PREFACE
tions to the learning experiences that enabled me to accept the challenge. It
also is interesting how serendipity played a role in the people I met or the
events that took place, helping me as my research interests ramified.
My research into plant resins began as a member of a paleoecological
expedition to study amber in Chiapas, Mexico, led by entomologists from the
University of California, Berkeley. My role in this expedition was to deter-
mine which trees produced the resin in which a diversity of insects had been
beautifully preserved and the kind of forest in which the trees and insects had
lived. Previously, amber had not been analyzed chemically as a resin but

rather had been described inorganically as a gemstone. My first hint of the
botanical source of the Mexican amber was a chemical one—its use by the
Maya as incense. The burning incense did not smell like burning pine resin,
which had long been thought to be the source of the well-known Baltic amber
and was assumed to be the source of Mexican amber. Thus I collected resins
from all the kinds of resin-producing trees in Chiapas for chemical compari-
son with the amber, ushering me into the world of tropical resins and the for-
ests in which the trees grew.
Fortunately, at this time I became a research fellow at Harvard University
in the laboratory of the geochemist and paleobotanist Elso Barghoorn, who
enthusiastically encouraged my exploration of the chemical criteria for deter-
mining the botanical sources of amber through geologic time. It was neces-
sary to use solid-state analytic techniques, such as infrared spectroscopy,
because the polymerization of amber precluded dissolving it for standard
organic chemical analysis. I subsequently collaborated with spectral chemist
Curt Beck of Vassar College, who I had serendipitously discovered was using
infrared spectroscopy to determine the archeological provenance of Euro-
pean amber. My approach at that time established a new direction in the
study of plant origins of ambers, by including chemosystematic data. Addi-
tionally, my approach had an even larger perspective, of integrating paleo-
ecological data into the understanding of amber-producing plants. These
chemical and paleoecological studies, together with my background as a plant
ecologist, prepared me to be intrigued by the correlation that the greatest
diversity of trees producing copious amounts of resins are tropical angio-
sperms (plants with true flowers). This interest coincided with the rapid
advance of the field of biochemical ecology, and I was swept along with the
tide of its development.
PREFACE | 15
To understand tropical resin production, I decided to use the leguminous
tree Hymenaea as a model, partly because I had determined it as the source of

the amber in a number of large New World deposits. The genus has an amphi-
Atlantic distribution, and the history of utilization of leguminous resins
increased my growing interest in ethnobotany. Field investigation of Hymen-
aea led me from Mexico through Central America to South America and
Africa. The formation of the Organization for Tropical Studies (OTS) coin-
cided with my early studies of Hymenaea in Central America, and assistance
from numerous OTS colleagues from various colleges and universities (too
many to name) helped promote the ramifications of my overall investigation
of Hymenaea and my interest in other resin-producing plants.
The center of distribution of Hymenaea is Amazonia and I had the good
fortune to be introduced to the region by the late Richard E. Schultes, long-
time Amazonian ethnobotanical researcher at the Harvard University Botan-
ical Museum. He helped initiate my Amazonian research, which continued
for many years, and importantly, further enhanced my interest in ethnob-
otany. Successful work on Brazilian Amazonian resin-producing plants also
would not have been possible without the strong support and interest of
Paulo Machado and Warwick Kerr, former directors of the Instituto Nacional
de Pesquisas da Amazônia in Manaus; Paulo Cavalcante, Museu Goeldi in
Belém; and others again too numerous to mention. Additionally, I had the
unflagging interest and cooperation of Ghillean Prance, then director of
research at the New York Botanical Garden, and later, director of the Royal
Botanic Gardens, Kew, who was leading the research for Flora Amazônica.
Before I could investigate resin production throughout the geographic
range of Hymenaea, revising the systematics of the genus was necessary since
species had often been described from poor specimens collected during floris-
tic surveys. This is a common situation for many of the plants belonging to
tropical resin-producing families, a problem whose consequences are noted
throughout Plant Resins. The Hymenaea revision, done in collaboration with
a graduate student, Y. T. Lee, was approached as an interface between sys-
tematics and ecology, with amber providing the evolutionary context. During

this revisionary work I interacted closely with tropical legume systematists
such as the late Pat Brenan, Royal Botanic Gardens, Kew, and J. Léonard,
Université de Bruxelles, a specialist on African copal producers. This opened
my thinking on the important relationships of African and New World trees.
16 | PREFACE
My interest in tropical resin-producing plants also expanded to discussion
of taxonomic problems with specialists, including Douglas Daly, New York
Botanical Garden (Burseraceae); T. C. Whitmore, Oxford University (Aga-
this); and Peter Fritsch, California Academy of Sciences (Styracaceae), among
others.
As my resin studies progressed, I had to learn more about the constituents
of present-day rather than fossil resins. Thus I embarked on a determination
of the components of Hymenaea resins with doctoral graduate students Susan
Martin and Allan Cunningham, with assistance from chemists E. Zavarin,
Forest Products Laboratory, University of California, Berkeley; George Ham-
mond, University of California, Santa Cruz; A. C. Oehschlager, Simon Fraser
University; and Duane Zinkel, Forest Products Laboratory, University of Wis-
consin, Madison.
How resin is secreted into storage structures is significant to both plant
defense and human use of resins. So another door to learning opened. In
exploring the anatomy of secretory structures in Hymenaea, I was aided by
the late Ralph Wetmore and I. W. Bailey as well as Margaret McCully, at
Harvard University at the time, all of whom enthusiastically supplied the
needed expertise. Lynn Hoefert, U.S. Department of Agriculture, Salinas,
California, also assisted a graduate student, Gail Fail, with ultrastructural
studies of resin secretion in Hymenaea. I increased my knowledge of resin
secretory structures through contact with other researchers, too, including A.
Fahn, Hebrew University of Jerusalem, and B. Dell and A. J. McComb, Uni-
versity of Western Australia, who studied secretory systems in a variety of
resin-producing plants.

A major interest in the chemical ecology of Hymenaea was followed by
comparison with the related legume, Copaifera. These investigations involved
collaboration with another group of graduate students (Will Stubblebine,
David Lincoln, José Carlos Nascimento, Matthew Ross, Craig Foster, Robert
McGinley, Cynthia Macedo, Eric Feibert, and Susanne Arrhenius) on plant
interactions with insects and fungi. Other avenues to understanding resin
production were opened by graduate students (George Hall, Francisco
Espinosa-García, and Wendy Peer) who worked on the chemical ecology of
redwoods (Sequoia). I also enjoyed numerous stimulating discussions on
defensive mechanisms of other resin-producing plants with colleagues,
including Karen Sturgeon, then at the University of Colorado; Kenneth Raffa,
PREFACE | 17
University of Wisconsin, Madison; Marc Snyder, Colorado College; John
Bryant, University of Alaska; and numerous others.
Archeological and anthropological studies of resin and amber were car-
ried out in Angola in collaboration with Desmond Clarke, University of Cal-
ifornia, Berkeley. By serving on doctoral dissertation committees at Yale Uni-
versity and the University of Texas, Austin, I learned about the use of resin by
the Semelai in peninsular Malaysia (with Rosemary Gianno) and by the Maya
in Mexico and Central America (with Kirsten Tripplett). Moreover, these
kinds of studies provided opportunities to observe art objects made from
amber, and contacts with museums around the world. And who would not
avail themselves of the opportunities to collect and enjoy amber jewelry!
Thus, from my varied experiences in research on resin and amber, I saw
the need for an up-to-date book because so much disparate information is
scattered throughout the literature. I decided that the book should tell the
whole story of these fascinating plant substances. Despite the importance of
a multidisciplinary approach, and my hope of raising awareness of that, I
divided the book into three parts to make it easier to use by readers with
diverse backgrounds, interests, and goals, who I knew might turn to such a

volume for information. These parts may be read in any order, depending on
the reader’s interest. A glossary is also provided. The three chapters in Part I,
The Production of Resin by Plants, provide biochemical, developmental, and
systematic information. However, this information is repeatedly projected
toward discussionof thevalue ofresins toplants andhumans inParts IIand III.
Central to understanding the remainder of the book is my operational defini-
tion of resin, presented in Chapter 1. This definition comes from my struggle
with the confused and vague usage of the term resin that has persisted
through the years. I hope that my definition provides rigor and clarity by dis-
tinguishing resins from other materials with which they are commonly con-
fused (e.g., gums and mucilage) based on three criteria: chemistry, secretory
structures, and ecological roles in the plant.Part I also includes a discussion of
more recent major breakthroughs in the understanding of terpenoid biosyn-
thesis and the ultrastructural evidence for its compartmentation, and how this
new information solves mysteries encountered in ecological studies of resins.
The secretory structures are characterized, and the importance of under-
standing their functions in ecological interactions and human use is discussed.
Furthermore, I introduce the reader to the distribution of resin-producing
18 | PREFACE
plants throughout the plant kingdom and for the first time present evolu-
tionary convergences in different aspects of resin production.
Part II, The Geologic History and Ecology of Resins, includes topics that
have been at the heart of much of my own research. The two chapters have a
phytocentric approach whereas other publications covering these subjects
are more insect-oriented. Questions on when resins first evolved and on
which groups of resin producers have a geologic record are addressed in
Chapter 4. Chapter 5 addresses the question of whether resin production is
primarily a defense against herbivores and pathogens, and presents ecologi-
cal and evolutionary data that support this view.
Part III, The Ethnobotany of Resins, presents in six chapters the substan-

tial roles that different kinds of resins have played in most cultures of the
world throughout human history. In Chapter 11, I consider whether the
importance of resin to humans will become a historical remnant as they are
replaced by petrochemicals and other alternatives, or whether new technol-
ogies as well as policies that preserve plant resources, particularly in the trop-
ics, will enable change in uses of resins and an important future for them.
Plant Resins only provides a progress report on our current knowledge—I
hope this synthesis of the many facets of resins will stimulate future research
on these remarkable plant products.
Acknowledgments
For Plant Resins specifically, I am grateful to friends, colleagues, and organi-
zations who have contributed photographs as well as to those who provided
comments that greatly improved the clarity of the chapters.
Numerous colleagues who shared photographs from their own resin
research include Scott Armbruster, Norwegian University of Science and
Technology; John Lokvam, and John Bryant, University of Alaska, Fairbanks;
Ben LePage, University of Pennsylvania; A. Fahn, Hebrew University of
Jerusalem; Duncan Porter, Virginia Polytechnic University; T. C. Whitmore,
Oxford University; Robert Clarke, International Hemp Association; J. J.
Hoffmann, S. P. McLaughlin, and D. L. Venable, University of Arizona;
Robert Adams, Baylor University; Manuel Lerdau, State University of New
York, Stonybrook; Jason Greenlee, Fire Research Institute, Fairfield, Wash-
ington; Hanna Czeczott, Museum Ziemi, Warsaw, Poland; Adam Messer,
ACKNOWLEDGMENTS | 19
University of Georgia; David Rhoades, Seattle, Washington; William Gittlin,
Berkeley, California; Douglas Daly, New York Botanical Garden; John
Dransfield, Royal Botanic Gardens, Kew; Rosemary Gianno, Keene State
College, New Hampshire; M. Pennacchio, University of Technology, Western
Australia; Bill Thomson, University of California, Riverside; J. G. Martínez-
Avalas, Universidad Autónoma de Tamaulipas; Rudolf Becking, Humboldt

State University, California; S. P. Lapinjoki, Kuppio University, Finland;
William Crepet, Cornell University; Margaret McCully, Carleton University,
Canada; Kennedy Warne, New Zealand Geographic magazine; Robert
Wheeler, U.S. Forest Service, Fairbanks, Alaska; and Vito Polito, University of
California, Davis. I owe special thanks to David Grimaldi, American Museum
of Natural History, who so generously provided numerous amber photo-
graphs from his research and from his book, Amber, Window to the Past. Ialso
gratefully acknowledge the following organizations for providing photo-
graphs: Royal Botanic Gardens, Kew; Danish National Museum, Copen-
hagen; and the National Library of New Zealand, Wellington.
I also express my gratitude to those who critically reviewed various drafts
of different chapters: Ken Anderson, Argonne National Laboratory; Eliza-
beth Bell, Santa Clara University; Laurel Fox, University of California, Santa
Cruz; Peter Fritsch, California Academy of Sciences; Jonathan Gershenzon,
Max Planck Institute for Chemical Ecology; Cheryl Gomez, UCSC; David
Grimaldi, American Museum of Natural History; Karen Holl and Ingrid
Parker, UCSC; Campbell Plowden, Penn State University; Kirsten Tripplett,
University of California, Berkeley; and Duane Zinkel, Forest Products Labo-
ratory, Madison, Wisconsin. Again, I extend special thanks to Susan Martin,
U.S. Department of Agriculture Research Laboratory, Ft. Collins, Colorado,
and Marc Los Huertos and Thomas Hofstra , UCSC, for their particular care
and thoughtfulness in reviewing numerous chapters. I also appreciate the
generosity of the time given by classical historian Gary Miles, UCSC, and
anthropologist Rosemary Joyce, UC Berkeley, to discuss details of the Chap-
ter 6 time line.
I greatly appreciate the efforts of Gulla Thordarsen in drafting maps.
Jesse Markman’s contributions are special in that he did all drawings of plants,
most maps, and generally shared in most aspects of the book’s development.
Jesse and I are grateful to Ann Caudle, Science Communications Program,
University of California, Santa Cruz, for her assistance and critical comments

20 | PREFACE
on the plant drawings. The diligent help of the UCSC reference librarians
was invaluable, and the cheerful persistence of the interlibrary loan librarians
was essential in obtaining literature unavailable in our library. I am also grate-
ful for the conscientious efforts of my editor at Timber Press to see that Plant
Resins is as error-free and as understandable to a broad audience as possible.
Finally, the book would not have been possible without Dorothy Hollinger’s
tireless word processing of the numerous drafts.
PART I
The Production of Resin
by Plants
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CHAPTER 1
What Plant Resins Are and Are Not
The literature on resins, although relatively abundant, is not very pre-
cise as far as exact use of terms is concerned. . . . confusion which, in a
way, reflects the complexity of the world of resins.
—Jost et al. 1989
To understand the many topics covered in Plant Resins, it is necessary to have
a clear idea of what plant resin is and how it differs from other substances
that have been called resins. Different readers doubtless have different con-
cepts of what resin is. Some may be surprised at the number of plants that
produce resin (Chapter 2) and consequently at the breadth and depth of the
influence that resins have had throughouthistory (Chapter 6). The characteriz-
ation of resins has changed greatly with the development of chemical, molec-
ular, and microscopic technologies to analyze them. Associated with these
technological breakthroughs have been advances in evolutionary and eco-
logical concepts regarding the functions of resins in plants.
Definitions of Resin
Resin is sometimes referred to in a general manner, such as sap or exudate,

both of which include numerous substances from plants. Throughout written
history there has been a tendency to characterize resin vaguely as any sticky
plant exudate. In some dictionaries, this definition has been extended to
include substances that are mainly insoluble in water and that ultimately
harden when exposed to air. Nevertheless, the vagueness of even this
amended definition has led to continued confusion with other plant exudates,
including gums, mucilages, oils, waxes, and latex. Some terms such as gum
23
24 | CHAPTER 1 What Plant Resins Are
have often been used synonymously with resin; in fact, one prominent forest
products researcher has referred to the use of these terms as “haphazard”
(Hillis 1987). A better definition of resin, however, has awaited more knowl-
edge about their chemistry, secretory structures, and functions in the plant.
Interest in the chemistry of resins and the secretory structures in which
they are synthesized and stored began in the later 19th century in Germany.
A pioneering book, Die Harze und die Harzebehälter, resins and resin-con-
taining structures, was published by Tschirch and his students in 1906. Recog-
nition that detailed chemical knowledge of plant exudates would be valuable,
perhaps essential, for their commercial utilization led to the voluminous pub-
lications in the 1930s by Tschirch and Stock (1933–36) and others (e.g., Barry
1932). Nonetheless, only with the advent of various kinds of chromatography
and spectroscopy in the 1940s and 1950s was real progress made in identify-
ing the chemical constituents of resins and quantifying their composition. All
the exudates that have been confused with resin in the past can now be distin-
guished from resin in their pure form by chemical composition and by the bio-
synthetic pathways through which they are formed. Information about resin
secretory structures has become available through advances in plant anatomy,
including electron microscopy (Chapter 3), and from ecological studies regard-
ing the survival roles played by resins (Chapter 5). Together, these data provide
criteria for a definition to minimize the confusion surrounding the term resin.

Thus in Plant Resins, plant resin is defined operationally as primarily a
lipid-soluble mixture of volatile and nonvolatile terpenoid and/or phenolic
secondary compounds that are (1) usually secreted in specialized structures
located either internally or on the surface of the plant and (2) of potential
significance in ecological interactions. Note that resins consist primarily of
secondary metabolites or compounds, those that apparently play no role in
the primary or fundamental physiology of the plant. In addition to being pre-
formed and stored in secretory structures, resins sometimes may be induced
at the site of an injury without forming in a specialized secretory structure.
Moreover, resin occurs predominantly in woody seed plants. Amber is fos-
silized resin (Chapter 4).
Although terpenoid resins constitute the majority of copious internally
produced resins that have been used commercially, some important resins are
phenolic. Phenolic resin components occurring on the surfaces of plant
organs have been used, particularly in medicines, and may be useful as a bio-