by Jane Goodall
Flowering plants, of course, have the most complex reproduction. And it is the love of flowers, of the blossoms with their staggering variety of shape, color, and size, that have so bewitched people over the ages. The largest single bloom in the world is that of the “corpse flower” (Rafflesia arnoldii) of Sumatra—it may measure a yard across and weigh as much as fifteen pounds. The flowers actually look and smell like rotting flesh, which is why it’s commonly known as the corpse flower. The smallest, by contrast, is that of the tiny water weed Wolffia, which measures a mere .01 inch across. And, too, there are the perfumes, the sometimes-intoxicating scents produced by flowers, especially those that are put out at night to attract moths and other night pollinators. Even bats.
Flowers are equipped with female and male organs, the pistil and the stamen. The stamen produces the pollen, which must somehow reach the pistil so that the waiting undeveloped seeds can be fertilized. This happens when pollen grains pass through little openings (stigma) at the tip of the pistil and travel down a tube (the style) to the ovum at its base.
The Swedish botanist Carl Linnaeus discussed this in his famous work on the classification of plants. He was dismayed when he learned that one of his articles, translated into English, was banned because it was “lewd and salacious”—“stamen” and “style” had been translated with the words husband and wife. One plant was thus described as having four husbands, two taller than the others; another had twenty husbands or so in the same marriage! At any rate, irrespective of the number of husbands, successful pollination results in the development of a seed.
The countless and cunning ways that plants have devised to get the pollen grains with their live sperm from stamens to pistils are absolutely awesome. Some release their pollen in large quantities, sometimes explosively, into air or water with the hope that it will be transported by the currents of air or water to the waiting pistils. As I write this, the pollen from the pine trees in our garden is being carried by the breeze in yellow clouds. The ground, the cars, our clothes—everything is covered with fine yellow dust. Bad luck for those who suffer from allergies.
Other plants have opted to have their pollen transported by a variety of animals, who are lured into service by enticing fragrances, delicious nectars, and attractive colors. Many kinds of insects serve as pollinators—and so do birds such as hummingbirds, occasionally bats, and even, it has been suggested, small amphibians. Some plants, including many orchids, have very specific needs—only one species of wasp pollinator will do.
Probably the first pollinating insect that springs to mind is the bee. I already described how I loved to watch the bees in the glorious summer days of childhood as they buzzed from flower to flower, probing for nectar and gathering golden pollen on their back legs in what we called their “breadbasket.” This was the bee benefiting from the flower, obtaining the ingredients for making honey and “bee bread” to feed the young back in the hive. But at the same time, as the bees moved from one bloom to the next, pollen was repeatedly brushed off onto the outstretched pistils. So the flowers were achieving their goal as well.
Not all insects are attracted by glorious scent or alluring nectar—certain plants cater to the preference of those that prefer a “fragrance” most horrid to our senses. The titan arum, which stands about six feet tall, and the corpse flower (Rafflesia arnoldii) of Sumatra, which, as mentioned, has the biggest single bloom in the world, both emit a stench that is irresistible to those flies and beetles that eat or lay their eggs on rotting flesh. I well remember when a titan arum was in bloom at the Royal Botanic Gardens, Kew, and lines of people gathered for the dubious thrill of experiencing its vile smell.
Defense Strategies
The other day I watched a cow feeding in a field. She was chewing her way through grass and a whole lot of herbs. There was clearly nothing the plants could do about it. Or was there? There were a few clumps of ragwort in the field, and I noticed how the cow avoided them. She clearly knew, somehow or other (from a bad experience or instinctive reaction to the toxins in its scent), that this plant was poisonous.
Plants are unable to run away or fly, so unless they develop some kind of defense, such as poison, they are liable to become someone’s breakfast, lunch, or dinner. In fact, plants have developed a whole host of ways to protect themselves. Some simply taste nasty, and some of the nasty ones are actually as poisonous as the ragwort is to cows. Deadly nightshade, so often mentioned in the old storybooks, is even more poisonous to us than is the ragwort—children can die from eating as few as three berries—but many birds eat it without any ill effect.
Unfortunately for the ragwort, the caterpillars of the cinnabar moth have become resistant to this poison and live on the leaves. This is, of course, what happens when we spray pesticide on farms or gardens—some insects become resistant, so other forms of poison must be concocted. In nature there is usually a balance so that if an insect predator proliferates unduly, its plant food will diminish to the point where the insect numbers cannot be sustained. And when the predators are then reduced, the plants can make a comeback. Then the whole predator/plant cycle can start again.
Poison is not the only defense—plants have evolved a great variety of other weapons, many of which I learned about as a child as a result of personal experience. Holly trees have leaves with sharp prickles, as we realized each Christmas when collecting some for decorating the rooms, placing sprigs with their bright-red berries behind every picture—and one on the Christmas pudding. When we went picking blackberries in the summer, we returned with arms and legs scratched and bleeding from the thorns on the stems—and it was the same when I picked wild roses, desperate to capture their fragrance and take it home with me.
Nettle leaves are covered with fine stinging hairs. And they are vicious—my mother told me about her time as a schoolgirl when a bullying gang of older girls, which included, I regret to say, her older sister Olly, threw her into a bed of stinging nettles. Fifty years later she still remembered the pain with horror. Even the traditional remedy—pressing dock leaves onto the affected area—did not help such widely tortured skin.
Plants have evolved a variety of impressive defenses. How on earth can this infant vervet monkey move about in this acacia tree with its formidable thorns?! It’s even more incredible to see giraffes eating them. The photo was taken in Lake Manyara National Park in Tanzania. (CREDIT: © THOMAS D. MANGELSEN/WWW.MANGELSEN.COM)
My childhood was free of the two scourges of the American woodlands—poison ivy and poison oak. I have only once had a close encounter with poison ivy—I was fortunate, for it hardly bothered me, although the person I was with was badly affected. I have, however, had many unpleasant experiences with a small and very inconspicuous plant at Gombe that has tiny leaves covered, like those of a nettle, in stinging hairs. And when, intent on watching a chimpanzee, you inadvertently sit on one of these plants in the wet season, the burning itching lasts for well over a day—it is extremely painful. How on earth the minute stinging hairs can attack through two layers of cloth I simply cannot imagine.
I learned a lot about the defenses of the plants that flourished in the Olduvai (or Oldupai) Gorge in Tanzania when I worked there for three weeks in the dry season of 1957. In the daytime I was digging for fossils, along with Mary and Louis Leakey. But every evening, Gillian (the other English girl on the expedition) and I were allowed to wander in the gorge and onto the plains. And there we learned to know and respect the vicious thorns of the acacia trees—and marvel at the sight of a giraffe munching on the spiky foliage with impunity.
We also encountered the wild sisal (Sansevieria ehrenbergii). Indeed, it grows there so prolifically that the Masai, who call it “oldupai,” named the gorge in its honor. A close encounter with those strong spiked leaves, so beloved by the rhino who lived there then, left wounds in our skin that hurt and itched for hours, though we were soothed a little if the wounds were smeared with the sap from a cut leaf. There were euphorbia there too, and one e
vening, as we sat around the campfire, Louis told us how baboons can chew the leaves of the euphorbia for moisture—but that one man, desperately thirsty, almost died when he thought it would be okay for him to do the same. His throat and tongue swelled up so that he could hardly breathe, and he was lucky to survive, for the milky sap, or latex, can be deadly.
Some plants have another extraordinary adaptation to protect not only themselves but also each other from attack by predators—they communicate with each other.
Communication between Plants
The very idea of plants communicating with each other is normally treated with skepticism. Yet new research is substantiating claims, initially made in the 1980s, that some of them actually can. And in two ways: through airborne chemical molecules released by the leaf, and underground, through their roots.
In the early 1980s David Rhoades, a scientist from the University of Washington, announced at a conference his belief that trees were able to communicate with each other. If an herbivorous insect attacked a tree, nearby trees were alerted, most probably through airborne chemicals released by damaged leaves. These airborne chemicals, Rhoades suggested, triggered chemical defense mechanisms in neighboring trees. When I heard about this, I was really excited, and included the information in many of my lectures at the time, although the idea was ridiculed by most scientists.
But gradually the notion of tree-to-tree communication gained credence. In 1983, Dartmouth biologist Jack Schultz and his research assistant Ian Baldwin published a paper in Science that provided evidence of this type of communication between poplar trees and between maples. Rhoades was able to pronounce, triumphantly, “Trees have a few tricks up their leaves—they aren’t static things just waiting to be eaten.”
Meanwhile another research team, from Ben-Gurion University, in Israel, led by biologist Ariel Novoplansky, has shown that distress signals can be communicated plant to plant through their root systems (although the exact mechanism had not yet been worked out). In one study, published in the spring of 2012, five domestic pea plants were subjected to stressful drought conditions. This caused the plants to close their leaves to prevent water loss. At the same time signals were sent out, through their roots, and were picked up by neighboring unstressed plants—which then reacted as though they, too, were suffering drought conditions.
The fact that information of this sort can be sent, received, and stored by plants has profound implications. Novoplansky explained it this way: “The results demonstrate the ability of plants and other ‘simple’ organisms to learn, remember and respond to environmental challenges in ways so far known only in complex creatures with a central nervous system.”
Amazingly, the scientists found that the nonstressed plants that had nevertheless reacted in the same way as their water-deprived neighbors subsequently coped better, when exposed to the stress, than naïve plants.
It reminds me, in a way, of the impact of some of my early discoveries about chimpanzee behavior. In the 1960s science (and religion) believed that humans were the only beings on Planet Earth with personalities, minds capable of thought, and emotions. In other words, we were the only sapient, sentient beings. Research on the chimpanzees at Gombe showed that this was not true and that humans were indeed part of the animal kingdom. Plants have their own magical kingdom, and it certainly does not surprise me that they are capable of communicating in ways once thought unique to complex animals.
Another recent study is revealing a different kind of communication through roots—which also has far-reaching implications. Millions of years ago a fascinating partnership was forged between plants and a unique group of organisms living in the soil, the mycorrhizal fungi. Today, the roots of about 95 percent of all plant species are coated with these threadlike fungi, which act as a kind of secondary root system, creeping way out into the ground, extracting water and minerals. They share these vital resources with their host plant, which, in turn, provides the fungi with sugars.
Suzanne Simard, a forest ecologist from the University of British Columbia, heads a team that is finding ways to “see” under the ground, and this cutting-edge research shows that the mycorrhizal fungi serve to connect the roots of one tree to another, creating an underground network deep down under the forest floor.
Their study site is a Douglas fir forest, and here graduate student Kevin Beiler used a new DNA-reading technology to distinguish between different individual fungi and the roots of different individual trees. It is now clear not only that all the trees in the forest are interconnected below the ground but also that each of the largest and oldest trees serves as a “mother tree,” with younger trees growing within her root-fungi network.
What I find absolutely fascinating is the fact that the “mother tree” sends carbon, nitrogen, and water along her roots, and while these nutrients are absorbed by the fungi, some are passed on, through the fungi’s interconnected threadlike strands, to the roots of seedlings that, living in the gloom of the forest floor, desperately need them. When a mother tree is cut down, this is likely to have an adverse effect on the development of the young, replacement seedling, and thus the regeneration of the entire forest may be compromised.
It seems there is no end to the plant marvels that are taking place around us.
Plants and Humans—A Love Affair
It is hardly surprising, given the endless variety of plants, their beauty, and their fragrance, that they have captured the imaginations of people through the ages. Indeed, our love affair with plants has been interwoven into human history for centuries. Just recently archaeologists discovered that a Bronze Age grave, located south of Perth in Scotland, contained a bunch of meadowsweet blossoms. Dr. Kenneth Brophy of Glasgow University commented that while the dried flowers were nothing much to look at, they represent the first indication that people in the Bronze Age were actually placing flowers with their dead. And of course they would have looked much better when they were freshly picked.
“To find these very human touches is something very rare,” he said, and he suddenly felt that what he was looking at was “not just a series of abstract remains.”
Why were the flowers there? Did those Bronze Age people want to ensure that the dead would have flowers in the afterworld? Were the meadowsweets a favorite flower, something the deceased would enjoy in another world?
How exciting it must have been to find the dried remains of a bouquet of meadowsweet blossoms in a Bronze Age grave, indicating that the people back then were placing flowers with their dead. (CREDIT: UNIVERSITY OF GLASGOW)
In ancient Rome the ground around a grave was sometimes laid out like a garden so that the soul of the departed might enjoy the flowers. Today the custom of leaving flowers on the graves of our loved ones is widespread, so that many graveyards do, indeed, look like gardens. And it is common practice to throw flowers or petals onto the coffin before the earth is shoveled over it. I have not been able to discover how this custom originated—I suppose it means different things to different mourners.
I was enchanted to learn that in Victorian Britain, when some feelings could not be openly spoken of, the “language of flowers” (floriography) was highly developed. By sending particular flowers, or combinations of flowers, it was possible to send almost any message—and many floriography dictionaries were published. This language of flowers apparently originated in Turkey and spread to many different countries. Even today some flowers are still associated with certain feelings—any woman receiving a bouquet of red roses knows exactly what a man is telling her!
When I was running the research center at Gombe, Derek was director of Tanzania’s national parks. He regularly visited each of them, including Gombe, flying the parks’ single-engine plane. One afternoon I saw the plane flying low over the lake. As it drew level with my house on the beach, it waggled its wings, and Derek threw something out of the window, enclosed in a plastic bag. I waded out into the water to retrieve it. A single red rose! This was shortly before he asked me to marry
him.
Plants offer so much to so many. For the scientist there are endless new questions to ponder as modern technologies reveal more facts about plant biology. For the naturalist there is constant opportunity to gain an ever-growing appreciation of the miracles of nature—a simple magnifying glass can open up a whole new world. For the artist—what a richness of material for pen or paintbrush or camera. And for a child there is the magic of a beautiful flower springing from a bulb planted in the soil.
We can all be cheered by the natural beauty that is around us, if only we will look. Even in the busy city streets small plants push bravely up through cracks in the paving. Pause and look at the next one you see, marvel at its determination, its will to live. And give thanks that we live in such a wonderful, magical, and endlessly fascinating kingdom. The kingdom of the plants.
Chapter 3
Trees
I spent hours in Beech, reading books about Africa and doing my homework. Here I am at about thirteen years old. (CREDIT: SALLY PUGH)
I have always loved trees. I remember once, when I was about six years old, bursting into tears and frantically hitting an older cousin (with my little hands only) because he was stamping on a small sapling at the bottom of the garden. He told me he hated trees because they “made wind”! Even at six years of age I knew how wrong he was. I have already mentioned the trees in my childhood garden—the most special was a beech tree. I persuaded Danny to leave “Beech” to me in a “Last Will and Testament” that I drew up, making it look as legal as I could, and she signed it for me on my eleventh birthday.