Nature's Fabric: Leaves in Science and Culture

By David Lee

Leaves are all around us—in backyards, cascading from window boxes, even emerging from small cracks in city sidewalks given the slightest glint of sunlight. Perhaps because they are everywhere, it’s easy to overlook the humble leaf, but a close look at them provides one of the most enjoyable ways to connect with the natural world.

A lush, incredibly informative tribute to the leaf, Nature’s Fabric offers an introduction to the science of leaves, weaving biology and chemistry with the history of the deep connection we feel with all things growing and green. Leaves come in a staggering variety of textures and shapes: they can be smooth or rough, their edges smooth, lobed, or with tiny teeth. They have adapted to their environments in remarkable, often stunningly beautiful ways—from the leaves of carnivorous plants, which have tiny “trigger hairs” that signal the trap to close, to the impressive defense strategies some leaves have evolved to reduce their consumption. (Recent studies suggest, for example, that some plants can detect chewing vibrations and mobilize potent chemical defenses.) In many cases, we’ve learned from the extraordinary adaptations of leaves, such as the invention of new self-cleaning surfaces inspired by the slippery coating found on leaves. But we owe much more to leaves, and Lee also calls our attention back to the fact that that our very lives—and the lives of all on the planet—depend on them. Not only is foliage is the ultimate source of food for every living thing on land, its capacity to cycle carbon dioxide and oxygen can be considered among evolution’s most important achievements—and one that is critical in mitigating global climate change.

Taking readers through major topics like these while not losing sight of the small wonders of nature we see every day—if you’d like to identify a favorite leaf, Lee’s glossary of leaf characteristics means you won’t be left out on a limb—Nature’s Fabric is eminently readable and full of intriguing research, sure to enhance your appreciation for these extraordinary green machines.
 

• Language: English
• Publisher: University of Chicago Press
• Release date: Sep 28, 2017
• ISBN: 9780226180625

Book preview

NATURE’S FABRIC

NATURE’S FABRIC

Leaves in Science and Culture

David Lee

The University of Chicago Press

Chicago and London

The University of Chicago Press, Chicago 60637

The University of Chicago Press, Ltd., London

© 2017 by The University of Chicago

All rights reserved. No part of this book may be used or reproduced in any manner whatsoever without written permission, except in the case of brief quotations in critical articles and reviews. For more information, contact the University of Chicago Press, 1427 E. 60th St., Chicago, IL 60637.

Published 2017

Printed in China

26 25 24 23 22 21 20 19 18 17    1 2 3 4 5

ISBN-13: 978-0-226-18059-5 (cloth)

ISBN-13: 978-0-226-18062-5 (e-book)

DOI: 10.7208/chicago/9780226180625.001.0001

Library of Congress Cataloging-in-Publication Data

Names: Lee, David Webster, 1942– author.

Title: Nature’s fabric: leaves in science and culture / David W. Lee.

Description: Chicago; London: The University of Chicago Press, 2017. | Includes bibliographical references and index.

Identifiers: LCCN 2016056667 | ISBN 9780226180595 (cloth: alk. paper) | ISBN 9780226180625 (e-book)

Subjects: LCSH: Leaves.

Classification: LCC QK649 .L442 2017 | DDC 581.4/8—dc23 LC record available at https://lccn.loc.gov/2016056667

This paper meets the requirements of ANSI/NISO Z39.48-1992 (Permanence of Paper).

To Gurumayi Chidvilasananda, who has helped me see beyond the science of leaves and forests to realize a greater empathy with nature

CONTENTS

Preface

One  Green Men

Two  Leaf History

Three  Green Machinery

Four  Nature’s Fabric

Five  Leaf Economics

Six  Metamorphosis

Seven  Architecture

Eight  Shapes and Edges

Nine  Surfaces

Ten  Veins

Eleven  Color

Twelve  Food

Thirteen  Homes

Fourteen  Movements

Fifteen  Seeing Leaves

Acknowledgments

Appendix A: Leaf Terminology

Notes for Appendix A

Appendix B: Drying and Preserving Leaves for Craft Projects

Appendix C: Leaves for School Science Labs and Projects

Chapter Notes

Illustration Notes

Index

PREFACE

The world does not need words. It articulates itself

in sunlight, leaves, and shadows. The stones on the path

are no less real for lying uncatalogued and uncounted.

The fluent leaves speak only the dialect of pure being.

The kiss is still fully itself though no words were spoken.

DANA GIOIA, Words

Leaves are present just about everywhere we live. Look at the cracks in a sidewalk, and small leaves peek out. Look at the verdant vegetation in an empty lot. Find exotic tropical foliage on the window ledge of an urban apartment. Leaves may be our most accessible means of encountering some aspect of the natural world. We surely take them for granted, and they mostly fade into the background of our consciousness. Collectively, leaves mark our planet as green. The colors mark the earth as the emerald planet, and leaves are the green fabric that clothes its surface.

My scientific and cultural interests in leaves go back to childhood, and my first data collecting of leaves was the measurement of blueberry leaf size and shape at different elevations on a ridge in the Cascade Range, in 1964. Subsequently, leaves have figured in much of the scientific research and popular writing throughout my scientific career, even to a most recent paper published in 2013, four years after retiring from university teaching. My contributions to the science of leaves, featured in this book, are rather modest, but that interest has given me a perspective to appreciate the significance of the general research on leaves.

My purpose in writing this book is to enhance our appreciation of leaves, and to help us form a stronger connection with nature—wherever we live. I have written stories about leaves to help us appreciate human history, the scientific method, evolution, geometry, biological function, the flux of elements on the planet, the codependence of living creatures, and the subtleties of our responses to the natural world. This book is intended for a nonscientist, teacher, student, landscape designer or architect, gardener, student of natural history, someone looking for ways to strengthen such connections, to add meaning to the elements of nature we mostly take for granted.

Nature’s Fabric has two appendixes that concentrate on our connections to nature through its foliage. The first chapter details our long cultural and spiritual connections with the natural world through its foliage, using the green man and tropical foliage as guides. Chapter 15 speculates on our sensory responses to this green world, building a case for a long evolutionary relationship. This final chapter distinguishes among our two approaches in better understanding our connections to nature: one is the reductionist approach through the application of the scientific method in understanding the brain, and the other is the personal approaches we all take to understanding human consciousness and its connections to nature.

The other thirteen chapters describe different facets of the science of leaves, all in the perspective of centuries of observation and speculation about their function. The appearance of leaves in evolutionary history and the evolutionary logic for their formation and function are described in the second chapter. In chapter 3, Green Machinery, the process of photosynthesis is described in detail, with a historical perspective. It is followed by a chapter on the roles of foliage in the global cycling of carbon dioxide, oxygen, water, and major elements (such as nitrogen), highlighting the importance of vegetation in global climate change. Fittingly, this chapter is titled Nature’s Fabric.

The next six chapters (5–10) outline the science associated with the actual appearance of leaves, discernible from the most casual observations: their toughness and longevity; their symmetry; the architecture of their display on the plant; their edges (whether smooth, lobed, or with teeth); their surfaces (whether smooth or rough), and the new products they have inspired through biomimicry; the appearance and function of veins; and leaf colors. Chapters 11 through 14 concern the interactions of leaves with animals in the natural and human-constructed worlds. In chapter 12, Food, the nutritious value of leaves is highlighted both as important for human welfare and as the principal source of nutrition for most animals. In the latter case, I highlight the kinds of defenses that plants have evolved in their leaves to reduce that consumption. In chapter 13, Homes, I examine leaves as habitats for all sorts of organisms. Some eat portions of the leaves, and others are recruited by plants to defend leaves against consumption by other animals. In chapter 14, Movements, the reader learns how leaves move, in a few cases quite rapidly (and fascinate us with this animal-like activity), focusing on carnivorous plants.

In addition to the chapters, appendixes follow with information particularly useful to educators, particularly for elementary through high school teachers, and parents looking for means to involve their children in nature. The illustrated glossary of leaf terms keeps these esoteric words out of the main text and makes it less intimidating; it also provides a resource for comparing leaf form. In a second appendix, there are clear instructions on how to dry and preserve leaves. Teachers and children can collect and keep their favorite leaves, and collect the types of leaves described in the glossary. Such leaves can then be used in various craft projects. Instructions for clearing and skeletonizing leaves are provided. Along with instructions for staining leaves, these techniques enable us to heighten the beauty of leaf venation, and to compare the different patterns of venation. The third appendix provides resources, including simple techniques and inexpensive instrumentation, for using leaves in science investigations and projects. This includes simple techniques for sectioning leaves for observation in a microscope. All of these techniques involve the use of materials readily available from an art supply or hardware store.

Although the chapters follow a logical progression of topics in the book, I suggest that you pick up the book and look at whatever chapter draws your attention. Links among chapters are provided by page numbers throughout the book.

To further simplify the flow of the text, and yet provide a depth of scientific background that I think is absolutely necessary, the following measures have been adopted. Citations are not given in the text but can be located by the page intervals in the chapter notes, which include phrases indicating how the work was important and information provided by individuals or obtained from websites. Technical terms on leaf architecture are left out of the main text but are included in an appendix. Full lists of the scientific names of common plant names are added to these chapter notes. Thus, you will know when I mention rowan, I actually mean Sorbus aucuparia L. (Rosaceae). I also include a section that describes the figures in detail—that is, where the photograph was taken, the scale of the photo, and full information on the photographer, if not the author. Finally, I use past times as millions of years ago (MYA) and leave out the geological names of past periods.

In 2007 I published Nature’s Palette: The Science of Plant Color. Nature’s Fabric is similar in style, purpose, and intended audience, and is published by the same press. The two books provide a fairly comprehensive description of plants, their diversity, evolution, structure, development, reproduction, interactions with animals, and global importance. Both books were written with the intention of increasing our appreciation of nature. This appreciation adds to our quality of life—and may become more important as trends toward alienation from the environments in which we have evolved increase. The purpose of both books is consistent with the teaching of Baba Dioum, an environmentalist and agronomist from Senegal, who famously wrote:

In the end,

we will conserve only what we love,

we will love only what we understand,

and we will understand only

what we are taught.

I hope this book helps you look behind the appearance of leaves, certainly to their beauty and elegance, and also their importance in our planet’s past, present, and future. Perhaps you will better remember your own emotional responses to leaves in a childhood or other more recent landscape, freshening your appreciation of nature and strengthening your commitments to preserve it.

Chapter One

Green Men

Green Man becomes grown man in flames of the oak

As its crown forms his mask and its leafage his features;

I speak through the oak, says the Green Man,

I speak through the oak, says he.

WILLIAM ANDERSON, The Green Man

These relationships would be no doubt sufficient to show how extended is the science which I am attempting to outline here; but the man who is sensitive to the beauty of nature will also find here the explanation for the influence exerted by nature on the peoples’ taste and imagination. He will delight in examining what is called the character of vegetation, and the various effects it causes in the soul of the observer.

ALEXANDER VON HUMBOLDT, Essay on the Geography of Plants

He looked out beyond me, onto the landscape from a parapet in the Canterbury Quadrangle, at St. John’s College in Oxford, my first green man. I was ready for him. I had been fascinated with leaves, doing research on them for over thirty-five years, and was participating in a workshop at the university, in March 2008, on the subject of autumn leaf color (which I’ll discuss later), and the green man was near our meeting room. I knew a bit about green men, and I immediately recognized the shaggy visage with hair replaced by oak leaves (fig. 1.1). This was not an ancient sculpture. The quadrangle was constructed in 1635 by a wealthy benefactor, alumnus, and former chancellor, William Laud. The green man, among other grotesques, was probably created by a stonemason, Anthony Gore. Later, in looking at my photographs of the quadrangle, I found more stylized green men in the larger friezes aside the openings to the quadrangle.

Figure 1.1 Green men. Left, Canterbury Quadrangle, Oxford University; right, Cernunnos, Celtic god depicted on the Gundestrup cauldron, first century BCE.

Green men are shown with leaves as hair and also sprouted leaves and branches from their eyes, noses, and mouths. I didn’t consider that this green man would begin a book, let alone one about leaves, but I hope to leave you with the appreciation of the deep historical roots that make each of us a green man, whether we are aware of it or not.

I didn’t see the numerous other green men in older colleges of the university and in churches of the city. J. R. R. Tolkien was a student at Oxford (but not at St. John’s) and later returned as a lecturer and professor of Old English. He and C. S. Lewis met weekly at the Eagle and Child Pub, just across the street from the college entrance and actually owned by St. John’s College, and this is where the autumn foliage participants socialized. Green men are found throughout Oxford, on pubs, churches, and college buildings. There is even a Green Man Route promoted by the local tourist board. Perhaps the green men and other figures helped the two authors to visualize characters for The Lord of the Rings and The Chronicles of Narnia, both of which I read to my children.

Green men decorate European cathedrals from the Middle Ages and beyond, and they appear on civic buildings as well. The stonemasons who worked on the Canterbury Quadrangle belonged to a guild of craftsmen in London and likely learned about them during their apprenticeships. This European tradition made its way to the United States in the nineteenth century. There, stonemasons who were trained in Europe put green men on civic buildings and churches, as in Des Moines, Iowa. My cousin Carol Sue’s garden, near the Columbia River in Vancouver, Washington, is overseen by a green man purchased from a local ceramicist.

Where do green men originate from, and what do they mean? Perhaps the earliest graphic representation of a green man decorated a temple at Hatra, in northern Iraq, constructed during the Seleucid Empire (of Greek origin) in the third century BCE, probably destroyed by Islamic militants (ISIS) in 2015. Another decorates the Gundestrup Cauldron, a remarkable silver vessel excavated from a Danish peat bog and dating back to the first century BCE. On the side of this beautifully and richly decorated piece are two images of the Celtic god Cernunnos; in one the beard and hair are leaf-like, and in the other a leafy branch sprouts from his antlers (fig. 1.1). The meanings of the cauldron are controversial, hinting in the yogic pose of Cernunnos of connections with the Vedic culture of early India. At the tenth-century tomb of Harald Bluetooth, the first Christian king of Denmark, a monolith is decorated with a figure entwined with plants. The commonness of green men on medieval cathedrals suggests some relationship to Christian worship, perhaps as a male counterpart to the diving feminine, entwined in the worship of the Virgin Mary.

The green man motif has been around for a long time. Perhaps the first mention of a green man–like being is the monster Huwawa (or Humbaba) from the Sumerian poem The Epic of Gilgamesh, going back at least 5,000 years. Huwawa was the protector of the Cedar Forest that Gilgamesh came to cut down. Perhaps Huwawa reappeared in other forms, including in the Greek myths as Perseus and Medusa.

Associated with this long history are green men in English mythology and history. Robin Hood comes to mind. From the court of King Arthur, the epic Middle English poem of Sir Gawain and the Green Knight was created by an unknown author (one of Tolkien’s first scholarly subjects). The Green Knight arrives during a Christmas feast. He and his horse are a brilliant green in color and decorated with precious jewels.

Yet he wore no helmet and no chain mail either,

Nor any breastplate, nor brassarts on his arms,

He had no spear and no shield for thrusting and striking,

But in his hand he held a branch of holly

That is greenest of all when the groves are bare,

And an ax in the other hand, huge and monstrous,

A fearsome battle-ax to find words to tell of.

The Green Knight offers a challenge to King Arthur: he will allow a knight to cut off his head with his ax, on the condition that he will deliver the same blow a year later. Sir Gawain insists that he undertake the test on behalf of the court. He decapitates the Green Knight, who picks up his head and rides away. A year later Sir Gawain travels to the Green Chapel to meet the Green Knight (with head back in place!) and to undertake the test. It is really a test of chivalry, which Sir Gawain passes. The Green Chapel was apparently located in the small village of King’s Nympton, in North Devon. Its fine old Norman Church is decorated with green men.

In Europe, along with green men, there is a tradition of sacred trees, often identified by their foliage. The immense world tree of Norse mythology was Yggdrasil, an ash. Trees were sacred in Celtic culture, in Ireland, Scandinavia, Gaul, and among the Germanic tribes east of the Rhine River. Predominant in sacredness was the oak. In Celtic culture, the lunar calendar was marked by trees. The Irish developed the Ogham alphabet, used from the fourth to tenth centuries, in which each letter was a tree. The high priests of the Celtic religion, the druids, were knowledgeable about the sacred uses of plants. The name druid may be derived from early Greek roots, as oak knower. Merlin, the wise man of King Arthur’s court, was likely a druid. The best-known story involving their priestly functions is the oak and the mistletoe, described by Pliny in his Natural History and explained by Sir James Frazer’s The Golden Bough. Frazer titled this book after the mistletoe, and he wrote: The first thing to notice about the Golden Bough is that, being a bough, it is poised, as it were, between heaven and earth. According to Pliny, druid priests oversaw the collecting of the rare boughs of mistletoe on the sixth day of the moon in winter, when the oak leaves had already fallen. Mistletoe was collected before it had fallen to the ground, and it was used ceremonially and medically, reputed to enhance the fertility of animals and people. Mistletoe was depicted on human heads in Celtic art. So that opportunity for a romantic kiss at a holiday party may have some hidden baggage—and certainly has an old history. Virgil wrote in the Aeneid:

As in the woods by autumn frost beset

The mistletoe, which springs not from the tree

On which it grows, puts forth a foliage new

And rings the smooth round trunks with saffron tufts

So on the dark tree shone the leafy gold

And tinkled in the breeze. With eager hand

Aeneas grasps and breaks the lingering branch.

The similarity of ceremony and the use of trees by these European cultures suggest a high degree of interaction among them, or perhaps a common origin of their awe of trees in the natural world. Most of them spoke languages related by similar vocabulary and sounds. Over the past two centuries, linguistic analysis has built one of our great intellectual achievements: the Indo-European language tree (fig. 1.2). A search for common (or very similar) characteristics among these languages—French, German, Greek, Latin, Persian, Sanskrit, et cetera—has made possible the construction of an ancestral Proto-Indo-European (or PIE) language, with some speculation about the culture of the PIE-speaking society. Just as biologists use molecular cues from DNA sequences to re-create the evolutionary history of plants (p. 26), linguists have found characteristics among the languages to determine their relationships.

Figure 1.2 The Indo-European language tree, based on work by Thomas V. Gamkrelidze and Vjačeslav V. Ivanov.

Paul Friedrich was the first to analyze these languages for their use of tree names, and he constructed a list of the most important types. This was certainly a conservative list, because names were lost as people settled in places where the trees would not grow, and they adopted names from tribes speaking non-Indo-European languages. His list includes oak, birch, conifers, poplar, willow, apple, maple, alder, filbert, nuts, elms, linden, ash, hornbeam, beech, cherry, and yew. Names were often broad categories, such as nuts, or trees that could be many species (willow). In other cases, the names could be two to three tree species or perhaps even unique. This PIE list of sacred trees (which Friedrich called arboreal units) strongly overlaps with the trees in the Ogham alphabet and the Celtic calendar. Other plants, such as mistletoe and barley, were known to the PIE speakers. The most important tree was the oak (PIE = ayg), which was revered in the high mountain passes and was the abode of the god of thunder. Also of sacred importance were the apple and ash. The ash (PIE = os) was a source of a sweet fluid that was collected and used even in the early twentieth century. There are actually two distinct plants given this name, both with similar leaves. One is the flowering ash, large trees of the genus Fraxinus, and a second is a small mountain-dwelling tree with brilliant red berries during the autumn: rowan. The two PIE words for apple, maHlo- and ăbVl, were transformed to the Latin Malus (the generic name today) and to English as apple.

With the PIE tree flora, attempts have been made to pinpoint the geographical origin of the language and people, varying from southeastern Europe to the Caucasus and adjacent areas of central Asia. Unfortunately, these arboreal units have rather broad distributions and do not allow a resolution to the problem, other than suggesting that forests were important in PIE culture. However, the distribution of these trees expanded into northern Europe after the last ice age. DNA evidence is more consistent with the arrival of the language from the central Asian region of the Altai Mountains into Europe around 4500 BCE, and into England shortly after.

Many trees of cultural importance in Europe and west Asia were probably not known to the PIE speakers. Holly, native to western Europe and culturally important there (the Green Knight carried a bough of holly) is not on Freidrich’s list. Two plants important in early Greek culture are also missing. The true (or bay) laurel is a tree of the Mediterranean region. It was used ceremonially by the Greeks and later by the Romans. As a wreath it was given to victors in athletic and other competitions, although wild olive was also sometimes used. We generally think of the olive branch as a peace offering. In the modern Olympics, a laurel wreath is given to every victor, along with a medal and spray of flowers; winners of the Boston Marathon receive a similar honor. The leaf of the acanthus shrub, with very distinctive shape and toothed edges, was the inspiration for the design of the Corinthian column (fig. 1.3).

Perhaps the Indo-European language that was geographically and ecologically the most distant was the Sanskrit language, along with Vedic culture, established in northern India around 4,000 years ago. It is probably the oldest language of the family still spoken today. Few of the sacred Indo-European trees survive in Sanskrit, mainly because the speakers only encountered a few of the trees in the high valleys of the Himalayan range. Instead, the Indo-Aryans encountered trees of a distinctly tropical flora, which were used and venerated by the indigenous people they encountered. Leaves play a rich role in contemporary Hindu religion, often placed on a tray in worship, including leaves associated with Hindu deities. Leaves with three parts are associated with the trident of Lord Shiva, such as palasa (fig. 1.3). I’m reminded of the three-leaved clover (well, rarely four-leaved), a Christian symbol to the old Irish (fig. 1.3). Also, leaves are used to commemorate the events in the lives of the great saints, such as Lord Buddha. The tree under which the Buddha received enlightenment was the bodhi (or peepul) whose distinctive shape (fig. 10.9) is easily recognized in the early religious artwork. The banyan was also important as a tree in which a seeker might find shelter. In India these trees are sacred in Jain and Hindu traditions and important to Buddhists in nearby countries.

Figure 1.3 Left, distinctive leaf of acanthus, inspiration for the Corinthian column. Center, three-lobed leaf of palasa tree, used by devotees of Lord Shiva, in India. Right, clover, sacred to Christians, especially Irish.

Although green men in European culture most likely came with the Celts in England and adjacent Brittany, it is possible that the figures came from much more ancient Neolithic culture in both places, but we have no record of their languages and little knowledge of their culture.

Similar descriptions of green men and sacred uses of other leaves were present in ancient Semitic cultures, not speaking languages of the Indo-European tree, as in the Sumerian Gilgamesh. There is a green man associated with Islam: Al-Khidr. This mythological figure goes back to the time of Alexander the Great. Alexander was looking for the fountain of eternal life, and he commanded an assistant to throw a dried fish into a spring, thinking that the authentic water would bring the shriveled body back to life. He found the spring with the help of Al-Khidr. This same person was alleged to be the father of the prophet Moses and was recognized by the prophet Muhammad in the Qur’an, where it was revealed that when Al-Khidr sat on barren ground, it soon turned green with vegetation. Hence the color green became sacred in Islam, and the flags of Islamic countries feature green.

A little further afield in Asia and North Africa is the date palm, sacred to the civilizations in Asia and North Africa, but not in the PIE list. The date palm was important in the early civilizations of the Fertile Crescent, in a warmer and more arid climate that would allow date palms to grow, but not temperate forest trees. For the Jewish celebration of Sukkot, the Feast of the Tabernacles held in late September to early October, participants construct a temporary dwelling out of branches and palm fronds in which they eat and pray, and perhaps even sleep. Each day during Sukkot, observing Jews recite special blessings over the lulav and etrog. The latter is citron fruit long cultivated in the area. The lulav is the perfect young and unopened leaf of the date palm, bound with leafy boughs of willow and myrtle. These are collectively known as the four plants, mentioned in the Torah. In the United States, buyers move into the date palm groves of California and select perfect lulav to deliver to the orthodox communities near New York City. The date palm leaf covered the ground for Jesus’s triumphal entry into Jerusalem, long celebrated as Palm Sunday. Since palms were not available in much of the later expansion of Christianity, other plants (some of them sacred to the PIE culture) were substituted, including myrtle.

The earliest Sumerian depictions of leaves are from the royal burial at Ur about 4,500 years ago, probably from rosewood and imported from farther to the east.

Green men and sacred foliage thrive in contemporary culture. In the Lord of the Rings trilogy, written by Tolkien (and popularized by the films of Peter Jackson), the druid was Gandalf the magician, and the green man was Treebeard. Treebeard was the eldest of the Ents, tree-like beings who dwelled in the great woods.

These deep eyes were now surveying them, slow and solemn, but very penetrating. They were brown, shot with green light. Often afterwards Pippin tried to describe his first impression of them. One felt as if there was an enormous well behind them, filled up with ages of memory and long, slow, steady thinking; but their surface was sparkling with the present: like sun shimmering on the outer leaves of a vast tree, or on the ripples of a very deep lake. I don’t know, but if felt as if something that grew in the ground—asleep, you might say, or just feeling itself as something between root-tip and leaf-tip, between deep earth and sky had suddenly waked up, and was considering you, with the same slow care that it had given to its own inside affairs for endless years.

In the Star Wars movies, the druid-like wise figure is Obi-Wan Kenobi, and the green man character is Yoda, who looks like he could’ve been modeled after the grotesque of a medieval cathedral.

Although the examples I have provided here are part of the cultural streams that have contributed to Western culture, such leafy examples can be found in others. While living in Malaysia in the 1970s, my wife, Carol, and I took lessons in Chinese brush painting. We spent many months attempting to depict the foliage of two plants, bamboo and lotus, with a few simple brush strokes, sacred images in Chinese tradition. I was almost always unsuccessful, except in a few moments when I moved beyond frustration and the foliage seemed to appear more or less naturally, as if on its own. In Malaysia I also studied the blue color of leaves of certain rainforest understory plants. One plant, a Selaginella species (fig. 2.8), produced a particularly electric iridescent color. A linguist friend, Gérard Diffloth, studied the language of the Semalai, an aboriginal group living in the mountains. For the Semalai, the tiger was a mythical god-like creature and, according to Diffloth, this plant was given a name that translated roughly as hair on the tiger’s rump. The traditional Malay people, living along the coast and near rivers, called this plant paku merah (peacock fern) and used it in a medicinal tonic, ubat jambu.

Foliage in the Garden of Paradise

I shift from the foliage of natural forests and native trees to groves and gardens, strongly influenced or created by humans. With the rise of civilizations, forests were converted to croplands and were consumed as materials for construction and energy for early industry, such as the smelting of ores. Certain forest trees were particularly important for the construction of ships, for trade and defense. The remaining forests often became the reserves of royalty. Indeed, the name forest has no Latin or Greek roots and comes from the Middle English, to denote royal hunting grounds. In the remaining groves and in gardens, our ancestors placed plants with religious and cultural significance (and some reminders of our forest past) in them. Gardens probably were planted by all cultures practicing agriculture, just by planting useful, sacred, and attractive plants in the open spaces of their villages. From early civilizations of the Near East, the ideal of the garden of paradise arose. In the biblical Genesis, the Garden of Paradise became known as the Garden of Eden, where Adam and Eve first knew guilt and were cast out. These gardens were illuminated through writings and the visual arts during the Christian era. Such gardens were also described in other traditions, particularly in Islam with an account of the Garden in the Qur’an. Rather than the original sin and banishment from the garden, perhaps a better interpretation is that in leaving the garden humans became responsible for their actions and developed the capacity for caring and stewardship, something that tending a garden teaches. David Rosenberg has described the Garden of Eden in poetic terms (based on serious scholarship) highlighting the environmental sensibilities of the people who imagined the garden. He wrote his book The Lost Book of Paradise: Adam and Eve in the Garden of Eden and Adam’s dialogue while living in a garden:

but here my creator set me

to crawl ashore in a great library

the texts of plants, hear the arguments

of animals and the wild wind

from other worlds with this restless mind

moved to learn at a leaf

master the map of hidden roots

follow the road from nostril to flower

to discover desire

dusting me with its future

This powerful metaphor of the garden of paradise inspired the creation of royal and ecclesiastical gardens of form and beauty, and also guided our design of the great and beautiful botanical gardens in Europe (fig. 1.4) as well as those in the colonies of Western nations, such as Calcutta, Bogor, Pamplemousse, Peradeniya, and elsewhere. These gardens were emblematic of an imperial Christian authority in these foreign lands. The gardens became important not only in the gathering of botanical wealth from the subjugated colonies, but also the spreading of environmental knowledge about human harm to the colonial landscapes and, ultimately, about climate change (see p. 76).

Figure 1.4 Botanical Gardens at Padua, established in 1544. Left, view of main gardens, with institute building and conservatory for Goethe’s palm in background. Right, plan of the main garden from the first published description, 1591.

The plants depicted in these European gardens reflected our geographical knowledge of nature; with time and more explorations of the world, garden plants became more exotic and fantastic—part of the paradise vision. Early garden depictions were rather unexciting, with familiar plants chosen as symbols for hope, love, and chastity. I’m not sure if such paintings had much of an impact, as they were completed for the royalty and had few admirers—far more now, 600 years later.

With the introduction of foliage from the tropics, gardens became more fantastic in appearance—and also ultimately had a wider aesthetic impact. The first knowledge of plants of the tropics in the West came from Alexander’s expedition to India. His military officers were instructed to collect information on natural history, plants in particular, and this information was used by Theophrastus, the disciple of Aristotle—who was Alexander’s tutor. The collections included citron, banyan, jackfruit, cotton, banana, ebony, terebinth, rice, date palm, pepper, and cloves. Theophrastus described them in his Enquiry into Plants, later used by Pliny in his Natural History. These manuscripts were copied by Islamic scholars and Christian monks. Cycles of copying ultimately rendered any illustrations useless, and the manuscripts were read by few, principally by medical students and professors in the early universities that appeared in the twelfth century and later.

However, in the late fifteenth century and beyond, the situation changed dramatically. First, the printing press was invented, and books by Theophrastus (with commentaries) and more original contributions were printed and more widely appreciated. Second, advances in ship craft and navigation enabled explorers to move from European countries to different parts of the world—primarily in the tropics—with the aim of discovering the sources of spices. This revolutionized the study of plants, with a more global knowledge and then a generally accepted system of scientific naming by Linnaeus in the eighteenth century.

Fountains of youth were also depicted in writings and paintings. The original story originated with Alexander and Al-Khidr, and was reprised by Ponce de León, who searched for this fountain in Florida. Consequently, gardens of paradise and fountains of youth were imagined destinations of explorers, and artistic depictions of them began to be populated with the fantastic foliage of tropical plants. The frontispiece of John Parkinson’s Paradisi in Sole Paradisus Terrestris is a rendition of a garden of paradise (fig. 1.5). A careful look reveals some of Alexander’s plants, a cotton plant converted into a vegetable sheep and a rather stunted banana. From the New World tropics, Parkinson added a cactus and a pineapple. The garden of paradise enjoyed by Adam and Eve was becoming tropicalized. With continuing tropical exploration, more and more exotic plants were introduced to the private and public gardens of Europe, and more and more people came to appreciate their unique forms and the fantastic diversity of their foliage.

Figure 1.5 Garden of Paradise in the frontispiece for Paradisi in Sole Paradisus Terrestris, by John Parkinson.

Friedrich Wilhelm Heinrich Alexander von Humboldt (for brevity’s sake I’ll refer to him frequently as Humboldt), the greatest scientist and humanist of the nineteenth century, read the accounts of these explorers and became inspired to organize and complete his own voyage, one of the greatest explorations in the history of science. He and botanist colleague Aimé Bonpland left Europe in June 1799, and they traveled through Venezuela, Cuba, Colombia and Ecuador, Peru, Mexico, and the United States before returning to Europe in August 1804 (fig. 1.6). During the expedition they traveled near the source of the Orinoco River and its connection with the Rio Negro (a tributary of the Amazon), and they climbed to 5,300 meters near the summit of Chimborazo, the highest elevation that any European had ascended up to that time. They collected specimens of plants and animals (some 60,000 of the former) and recorded innumerable observations (temperature, altitude, latitude, longitude, barometric pressure, magnetic fields, electric discharges, the blue of the sky, and more). After returning to Europe, Humboldt spent the rest of his life analyzing and summarizing the results of this research. In so doing, he established the sciences of geophysics, physical geography, and plant geography.

Figure 1.6 Alexander von Humboldt and Aimé Bonpland, on the Orinoco River. From the painting by Eduard Ender.

Humboldt was more than a scientist. Before his expedition, he had befriended some of the intellectuals of Germany, especially the great poet and natural philosopher Johann Wolfgang von Goethe. Humboldt’s goals for this expedition were lofty and included a study of the physiological and emotional responses of humans to various environments. He was particularly struck by the effects of tropical vegetation and light on the human psyche. His first experiences of tropical vegetation overwhelmed him and influenced him throughout the rest of his long life. He wrote of his emotional response to tropical vegetation in the first, and most popular, book resulting from this expedition, Aspects of Nature, as well as the final five-volume synthesis of his knowledge of the world and the universe: Cosmos. Humboldt’s ideas about tropical nature in Aspects of Nature influenced European artists long before the more detailed discussions of tropical aesthetics in volume 2 of the Cosmos. In the latter, Humboldt gave detailed descriptions of tropical nature as well as specific recommendations to landscape artists. In the former, he described the plant types (forms of vegetation) that were the most important elements of tropical rainforests: palms (the loftiest and noblest of all vegetable forms); the mimosa form (with delicately pinnate foliage); bananas and the gingers (whose stems are surmounted by long, silky, delicately-veined leaves of thin texture, and bright and beautiful verdure); the pothos or aroids (succulent herbaceous stalks support large leaves . . . always with thick veins); lianas (twining rope plants . . . the utmost vigor of vegetation); arborescent ferns (foliage . . . delicate, of a thinner and more translucent texture); the orchid (distinguished by its bright and succulent leaves and by its flowers of many colors and strange and curious shape); and arborescent grasses or bamboos (an expression of cheerfulness and of airy grace and tremulous lightness, combined with lofty stature). Humboldt wrote in Aspects of Nature:

It is under the burning rays of a tropical sun that vegetation displays its most majestic forms. In the cold north the bark of trees is covered with lichens and mosses, whilst between the tropics the cymbidium and fragrant vanilla enliven the trunks of the anacardias, and of the gigantic fig trees. The fresh verdure of the pothos leaves and of the dracontias contrasts with the many flowers of the Orchideae. . . . A single tree adorned with paullinias, bignonias and dendrobium, forms a group of plants which, if disentangled and separated from each other, would cover a considerable space of ground.

In the tropics vegetation is generally of a fresher verdure, more luxuriant and succulent, and adorned with larger and more shining leaves, than in our northern climates.

Just as the writings and illustrations of his compatriot Georg Forster inspired Humboldt, his publications dramatically affected scientists and artists throughout Europe and in the New World. Humboldt’s influences on artistic expression in the nineteenth century were pervasive and inspired depictions of gardens of paradise that were distinctly tropical. Several European artists followed his steps in the tropics. For some, he wrote prefaces to the folio books of engravings derived from their paintings. He also influenced garden design, including the increased planting of tropical plants for interiors (despite concerns about suffocation at night, p. 49). Several factors increased his popularity. With the continued improvement in printing technology and paper making, books became less expensive and more widely distributed. Thus, Aspects of Nature appeared only three years after his return and was quickly translated into the major European languages. Furthermore, literacy had increased, and ideas were disseminated more quickly and broadly in the nineteenth century. Although paintings of tropical landscapes were generally not widely viewed, their renditions as engravings in books were.

Humboldt also influenced American painting. Trained in the Hudson Valley School with Thomas Cole, Frederic Church traveled to the South American tropics in 1853 and 1857, following Humboldt’s footsteps. The most spectacular of the resulting tropical landscapes is The Heart of the Andes (1859, fig. 1.7), now residing at the Metropolitan Museum of Art in New York City. I was dumbstruck when I first saw it in 1966, as a beginning graduate student at Rutgers University, just outside of the city. The Heart of the Andes was exhibited as a single painting in a special gallery, to a ticket-buying public. Enthusiasts came in droves, first in New York and then in London. Church had hoped to have Humboldt see the painting in Berlin, but the old explorer and humanist died before the painting arrived in Europe. Another important American artist influenced by Humboldt was Martin Johnson Heade, who specialized in more intimate tropical paintings—particularly featuring hummingbirds; Heade and Church were close friends.

Figure 1.7 The Heart of the Andes, painted in 1859 by Frederic Church.

I was not familiar with Humboldt’s writing as a student, but I read other authors who were surely influenced by him: Charles Darwin (The Voyage of the Beagle), Alfred Russel Wallace (The Malay Archipelago), Joseph Conrad (Heart of Darkness, Lord Jim), H. M. Tomlinson (The Sea and the Jungle), Marston Bates (The Forest and the Sea), W. H. Hudson (Green Mansions), Peter Matthiessen (The Cloud Forest), and more. Darwin took Humboldt’s early books on the voyage of the Beagle. His journal included this entry after his first visit to a Brazilian tropical rainforest: Humboldt’s glorious descriptions are and will forever be unparalleled; but even he with his dark blue skies and the rare union of poetry with science which he so strongly displays when writing on tropical scenery, with all this falls short of the Truth. . . . I am at present fit only to read Humboldt; he like another sun illumines everything I behold. Thus, Humboldt indirectly influenced my becoming a botanist and working extensively in the tropics. It was only after living in the tropics that I began to read him, to help me comprehend my own experience of tropical plants and landscapes. And my own research became directed toward the function of the leaves of tropical plants, their aesthetic beauty so elegantly described by Humboldt.

The influences of Humboldt were magnified by international exhibitions, or world fairs, from the early nineteenth century into the twentieth century. Such fairs featured inventions and products, new technology, and culture. European nations were eager to display products from their colonial possessions and to idealize the traditional cultures of their natives, who were the producers of much of that wealth. Notable fairs were the Great Exhibition in London of 1851, with its Crystal Palace (p. 137), and the Exposition Universelle in Paris in 1889. Later in the century, large expositions were held in the United States: the Centennial International Exhibition of 1876 in Philadelphia, the World’s Columbian Exposition in Chicago (1893), the Louisiana Purchase Exposition in St. Louis in 1904, the Panama-California Exposition in San Diego in 1915, and several large world fairs in New York City, the first in 1853. These were huge affairs, the succeeding ones invariably larger than the previous, and they were extremely popular in the United States. The Philadelphia fair attracted 10 million visitors, or 20% of the country’s population at that time, and 27 million attended the Columbian Exposition in Chicago. The expositions generally had horticultural halls, with luxuriant displays of vegetation, both inside and outside during the summer months (fig. 1.8). Visitors even saw indigenous people, such as the Igorot of the Philippines, surrounded by the lush tropical vegetation of their homes. In the twentieth century, the rise of the movie industry added the portrayal of the tropics in Tarzan of the Apes and other films.

Figure 1.8 Horticultural Hall, Philadelphia Centennial International Exhibition, 1876. Left, hall exterior; right, interior planting.

In the United States, such visions of the tropics were employed to stimulate visits and real estate purchases in our warmer subtropical climes: Southern California, Florida, and the offshore possessions of