Seeds of Hope

by Jane Goodall

  One of the most important things about roots is that they hold the soil in place. When the early settler farmers moved onto the American prairies, they cut down the trees that grew there and plowed up the land, destroying the native grasses so that they could grow agricultural crops. Over countless thousands of years those native grasses had developed root systems that delved deep, deep into the ground, holding the soil together so that it could withstand the constant stress of the wind. Human interference in this ancient system led to the Dust Bowl of the 1930s, when the soil was blown away in great clouds, much of it ending up in far-off oceans. Something similar happens in China today, where clouds of dust are blown from the deforested center of the country and darken the skies over faraway Beijing for days on end.

  Leaves

  I always love to walk through the trees in the evening, when the sun is low and the leaves are backlit. And each single leaf so beautiful with all its veins etched so clearly, some with an incredibly intricate branching pattern. These veins are the end point of the system that carries water and nutrients up, up from root to leaf. And they are the start of the system that carries the sap, with its dissolved sucrose, back out of the leaf to provide nutrients to the mother tree.

  When I was a child, I used to spend hours searching under the trees, looking for the skeletons of leaves—when all the soft material has rotted away and only the veins remain. It is rare to find a perfect one, without tear or holes, but it is worth searching diligently—for the one that is without blemish is truly a work of art. I still search when I am walking through the Gombe forests.

  The variety of leaves seems almost infinite. They are typically green from the chlorophyll that captures sunlight, and many are large and flat so as to catch the maximum amount. Indeed, some tropical leaves are so huge that people use them for umbrellas—and they are very effective, as I discovered during an aboriginal ceremony in Taiwan, when we were caught in a tropical downpour.

  Orangutans have also learned to use large leaves during heavy rain. My favorite story concerns an infant who was rescued from a poacher and was being looked after in a sanctuary. During one rainstorm she was sitting under the shelter provided but, after staring out, rushed into the rain, picked a huge leaf, and ran back to hold it over herself as she sat back in the dry shelter!

  Some leaves are delicate, some are tough and armed with prickles, yet others are long and stiff, like needles. The often-vicious spines of the cactus are actually modified leaves—in these plants it is the stems that capture the energy from the sun. I used to think that the brilliant red of the poinsettia and the varied colors of bougainvillea were flowers, but of course they are leaves adapted to attract pollinating insects to the very small insignificant-looking flowers in the center. And there are those leaves adapted to capturing insects, some covered with resin-tipped glands that curl over and imprison the prey, others able to snap shut in an instant when an insect touches the hairs, which act as triggers.

  And then there are the most extraordinary leaves of that bizarre plant, Welwitschia mirabilis. Each adult plant has only two leaves. When the seed germinates, it produces two cotyledons—embryonic first leaves. These survive only until the first true leaves have grown big enough. They look ordinary enough, these two long leaves. But they are not. For they continue to grow, those exact same two leaves, for as long as the plant lives—which can be more than a thousand years.

  The Welwitschia was first discovered in Africa’s Namib Desert by Dr. Friedrich Welwitsch in 1859, and it is said that he fell to his knees and stared and stared, in silence. He sent a specimen to Sir Joseph Hooker, at the Royal Botanic Gardens, Kew—and Sir Joseph for several months became obsessed with it, devoting hours at a time to studying, writing about, and lecturing about the botanical oddity. It is, indeed, one of the most amazing plants on Earth, a living fossil, a relict of the cone-bearing plants that dominated the world during the Jurassic period. Imagine—this gangly plant, which Darwin likened to a duckbill platypus of the vegetable kingdom, has survived as a species, unchanged, for 135 to 205 million years. Originally its habitat was lush, moist forest, yet it has now adapted to a very different environment—the harsh Namib Desert.

  The photograph in the color insert shows what looks like many untidy leaves, but they are really only the two. They first appear as the seed germinates—and as the years pass, they become increasingly leathery and tattered, nibbled by animals and buffeted by the wind—but they are never replaced. The tallest plant known is only five feet high; most are no more than twenty inches. Some Welwitschia plants growing in the wild have been carbon-dated and are between five hundred and six hundred years old, but it is thought that some of the largest could be two thousand years old.

  Capturing Sunlight

  At school I had to learn in my biology lessons about photosynthesis—which literally means “synthesis with the help of light.” When I looked at my son’s biology textbook some thirty years later, I was amazed—and shocked actually—by the complex chemical process that he was supposed to learn as a schoolboy. It was the sort of information that was once reserved for university students specializing in botany—the kind of stuff that would have totally disenchanted me from the wonder of plants. And, indeed, it is pure chemistry.

  The point is that plants can capture energy from sunlight. I love how this was described by the German surgeon Julius Robert Mayer in the 1800s. Nature, he said, has solved “the problem of how to catch in flight light streaming to the Earth and to store this most elusive of all powers in rigid form.”

  Plants do this through extremely complex chemical reactions, which can, however, be described quite simply. There are special cells, usually in the leaves, that store chlorophyll molecules. This is the source of their green color. These chlorophyll molecules interact with nearby carbon dioxide (CO2) (which they absorb from the atmosphere) and water (delivered by the plant’s roots) to synthesize glucose and oxygen. The glucose is either used at once, for energy needed by the plant, or it is changed (by another complex chemical process) into starch, which is stored until the plant needs it. Meanwhile oxygen, which is actually considered a “waste product,” is released into the atmosphere, where animals and plants use it for their respiration. It amused me, when I read about this, to think of our so-precious oxygen as a “waste product”—that is chemistry talking. The small amount of CO2 produced by the plants during their respiration (basically their exhalations) is quickly used up by the ongoing photosynthesis process.

  Think about all this for a moment. Our exhalations are nourishing the plants as they capture CO2, and the plants’ exhalations allow us (and them) to breathe. How utterly amazing—awe-inspiring really. One cupful of CO2, a few tablespoons of water, mixed with a beam of sunlight: the ultimate and only recipe for the food that supports all plant life, including algae and other such forms. And since we depend on plants, either directly, by eating them, or indirectly, by eating animals that themselves depend on plants, the process of photosynthesis supports almost all life on Earth.

  Carnivorous Plants

  I am not a devotee of science fiction books, but John Wyndham’s The Day of the Triffids, published in 1951, utterly captivated my imagination. “Triffids” are seven to ten feet tall, have three leg-like appendages that can be rooted into the ground, a sort of trunk, and a funnel-like head containing a sticky substance that attracts and captures insects that are then digested. Within this funnel there is also a stinger that, when fully extended, can measure up to ten feet. Sometimes a triffid will shuffle along the ground on its “legs” and, when it contacts a person, will aim at the face with its stinger. The victim dies quickly, and the triffid roots itself near the body, which it can digest as the flesh decomposes.

  Science fiction, yes, but Mother Nature has designed monsters too—they are smaller, they cannot harm people, but the behavior of some of the carnivorous plants would make terrifying bedside reading for the tiny prey they capture. Take the Darlingtonia pitcher plant, also kno
wn as the cobra pitcher or cobra lily. It has a well-developed forked protrusion on the end of the modified leaf that forms the lip of the pitcher, which is designed to capture insects. This protrusion offers a convenient platform on which a flying insect can land, attracted to the nasty smell from inside the pitcher—well, nasty to us but obviously irresistible to the insect.

  The hapless prey then slips down the walls, helped on its way by both lubricating secretions and downward-pointing hairs, and falls into the water-and-enzyme soup. The small exit is cunningly curled downward and thus hidden from the trapped insect, which exhausts itself by repeatedly crawling up the many translucent false exits. Eventually it will drown, and as it gradually decomposes, it will be absorbed by the plant. Unlike other pitcher plants, this one does not trap rainwater in its pitcher, but pumps up water from its roots, reabsorbing it if the level gets too high.

  This is just one of the plants that have become carnivorous, capturing flies and other insects in a whole variety of ingenious ways and then slowly digesting them in special juices. There are about 630 species in six genera with five different kinds of traps, known as pitfall, flypaper, snap, bladder, and lobster traps. Scientists estimate that they first appeared some two hundred million years ago in marshy, infertile soils that were lacking in essential minerals, especially nitrogen. Only by devising a novel way of getting the necessary nutrients could these plants survive. I get so carried away reading about these cunning plants—it would not be difficult to write a whole chapter about them.

  The best known are the pitcher plants, sundews, Venus flytraps, and bladderworts. I remember our biology teacher bringing a sundew to school for us to see. Somehow my imagination had created a much more impressive being, and I was disappointed to see such a tiny plant, though fascinated by its behavior. Each leaf has a number of resin-tipped glands that serve to attract and capture small insects. Our biology teacher placed an unfortunate fly on this trap and we watched as the leaf curled slowly over it.

  There is one carnivorous genus, Roridula, that has just two species. They are small shrubs with leaves covered by sticky resin glands. The plant cannot absorb or digest the insects that it catches, but it has a partner, an insect similar to and usually referred to as an assassin bug (Pameridea, to give it its proper name). The bug is impervious to the resin because of its thick, greasy covering. It waits among the leaves and quickly pounces on less fortunate insects, then settles down to suck out their innards. Subsequently it produces dung—and it is this that the plant is able to absorb.

  One of these plants, growing in the botanical gardens of Leiden University, once captured a jay! My Dutch botanist friend Rogier van Vugt told me how he had to rescue the bird—with great difficulty! Of course, says Rogier, “Neither the plant nor the insects would eat a bird, but it shows how strong the resin is.”

  Seeds and Fruits

  If plants could be credited with reasoning powers, we would marvel at the imaginative ways they bribe or ensnare other creatures into carrying out their wishes. And no more so than when we consider the strategies devised for the dispersal of their seeds. One such involves coating their seeds in delicious fruit and hoping that they will be carried in the bellies of animals to be deposited, in feces, at a suitable distance from the parent.

  Charles Darwin was fascinated by seed dispersal (well, of course—he was fascinated by everything) and he once recorded, in a letter, “Hurrah! A seed has just germinated after twenty-one and a half hours in owl’s stomach.” Indeed, some seeds will not germinate unless they have first passed through the stomach and gut of some animal, relying on the digestive juices to weaken their hard coating. The antelopes on the Serengeti Plain perform this service for the seeds of the acacia.

  In Gombe the chimpanzees, baboons, and monkeys are marvelous dispersers of seeds. When I first began my study, the chimpanzees were often too far away for me to be sure what they were eating, so in addition to my hours of direct observation I would search for food remains—seeds, leaves, parts of insects or other animals—in their dung. Many field biologists around the world do the same.

  Some seeds are covered in Velcro-like burrs (where do you think the idea of Velcro came from, anyway?) or are armed with ferocious hooks so that a passing animal, willy-nilly, is drafted into servitude. Gombe is thick with seeds like this and I have spent hours plucking them from my hair and clothes. Sometimes my socks have been so snarled with barbs that, by the time they are plucked out, the socks are all but useless. Some seeds are caught up in the mud that waterbirds carry from place to place on their feet and legs.

  I wonder how many dandelion “clocks” are picked and blown by lovesick adolescent girls: “He loves me, he loves me not. He loves me, he loves me not,” and calculating the strength of the last breaths so that they can end, triumphantly, “He loves me!” Those little seeds, each suspended from a perfect parachute, are carried away in the thousands by the summer and autumn winds, colonizing gardens and parks—almost anywhere that plants can grow—and often where they are most definitely not wanted.

  The kapok seed floats through the air attached to the softest white fluff. I watched one chimpanzee infant as he gazed, as though entranced at this spectacle, then reached out to try to catch some. I sometimes do the same! And I have always loved to watch the seeds of the sycamore trees growing in Bournemouth as they set off on their journey in pairs, fastened between two propeller-shaped wings that spin around and around like the blades of a miniature helicopter as they spiral down toward the ground.

  Other seeds, lacking such convenient mechanisms, rely on their pods to shoot them as far away as possible. From my window, at school, I could hear the little pops of the broom pods as they burst open when the seeds were ripe inside and the sun was warm. They were carried several feet—and sometimes ants then carried them farther—which was an advantage only for those that were not eaten. The pods of some plants reach such a state of tension when their seeds are ripe that they seem literally to explode at the slightest touch—like the touch-me-not balsam. And there is a plant in Gombe that splits open, with a loud crack, at the first drop of rain, sending out seeds in all directions. I used to collect these pods and take them to my son, when he was little, and arrange a show for him.

  Seeds come in all shapes and sizes. Most are quite small, but not so the coconut. This giant can be carried for miles across the ocean and, in this way, has enabled coconut palms to colonize almost every tropical island.

  Sex Education

  Plants reproduce both sexually and asexually. Every gardener knows how a cutting, given by a friend, can grow roots and survive. This is how my second husband, Derek Bryceson, and I built up our garden in Dar es Salaam. Some plants, such as the blackberry, form adventitious roots when the tip of a stem arches over and touches the ground. At this place a new plant will grow. Then there are those that send out special stems that are called runners when they grow over the ground, like strawberries, or rhizomes when they grow under the ground, like buttercups. When the runner, or rhizome, is far enough away from the parent plant, the tip puts out roots from which new plants can grow.

  There is no doubt whatsoever that this kind of asexual, or “vegetative,” reproduction can be an immensely efficient strategy. And when plants are introduced to new environments, it can also be very destructive. The water hyacinth is a free-floating aquatic plant with attractive lavender or pink flowers. It originated in South America, but has been introduced widely in tropical and subtropical areas of North America, Asia, Africa, Australia, and New Zealand. It reproduces asexually by runners and is one of the fastest-growing known plants—it can double its population in just two weeks. It clogs waterways and lakes. It starves water of oxygen, killing fish, turtles, and other wildlife. It was actually grown on lakes in World War II to fool Japanese pilots into thinking they could land. Governments have spent a great deal of money in their efforts to control the water hyacinth.

  However, while reproduction without sex may be efficient, it d
oesn’t allow for genetic diversity, and so almost all plants can reproduce sexually as well. We know all about human sex (way too much, in some instances). Most of us are familiar with the couplings of dogs (cats are far more discreet and usually do their thing at night). Country people know about farm animals, and naturalists have found out a great deal about the mating behavior of countless wild mammals, birds, and insects. Much of all the above involves courtship, which may be elaborate. And we have come to realize, with all this private life exposed by patience, binoculars, and DNA analysis, how much cheating goes on.

  What about plants? We can hardly suppose that plants could enjoy sex—but who knows? Maybe, one day, a scientist will detect something akin to the endorphins that are produced in humans during pleasurable experiences (including excitement, love, and orgasm) in some part of a plant when bees are tickling its stamens or brushing against the pistil while it is being pollinated. Nothing in the plant world would really surprise me—but it does seem unlikely. So for now I will stick to the plain and obvious facts.

  The bladder wrack, a common seaweed, was well known by us as children. We loved to walk along the beach at low tide when a storm had cast lots of seaweed onto the beach. We would seek out the strands of bladder wrack and stamp on the partially dried bladders, which made a marvelously satisfying popping sound (the same as when you pop the air bubbles of Bubble Wrap). It is at the tips of these bladders that the sperm and eggs are stored. There are male and female bladder wracks, and reproduction takes place only once a year, when both sperm and eggs are released into the water at the same time. Fertilized eggs sink to the bottom of the sea and soon attach themselves to some hard surface.