They fly, float, hitchhike — and even explode. But the many clever ways seeds get around make sense: after all, a plant’s life depends on finding fertile ground in which to grow. The quest for survival has even led plants to develop delightful and devious ways of fooling us into working for them as they send their seeds out to conquer new lands.

But the plants’ master plan for world conquest is no longer a secret. NATURE’s The Seedy Side of Plants rips the husk off the many remarkable ways plants make sure their offspring are spread far and wide. Apples make themselves as red and tempting as possible to encourage us to pluck them and take a bite so the seeds inside can escape to new ground. An African melon has a mouth-watering method of convincing aardvarks to go to the trouble of tunneling deep into the earth to liberate a few tough pits.

There is no doubt that plants are one of the world’s most successful life forms. Indeed, Earth is a planet of plants, with millions of kinds growing in virtually every environment imaginable, from the driest deserts to the wettest jungles. Even paved parking lots often display a few tufts of tough grass poking up through the cracks. But it didn’t take a gardener’s green thumb to design this global garden. Plants did it themselves, millions of years before humans ever appeared, by evolving countless methods of producing and spreading seeds. These tiny packages of genetic material have proven an almost unstoppable means of ensuring a species’ survival.

At first glance, some seeds’ designs make plants seem downright intelligent. Take apples, for instance. As The Seedy Side of Plants shows, these sweet fruits have evolved to be bright and shiny for good reason: they attract people and other animals. Drawn in by their effective advertising, we do the work of carrying apple seeds to new territory where the species can gain a toehold and expand. Indeed, we like apples so much that we’ve planted orchards especially for our favorite fruit. The practice has prompted some biologists to ask who really is the boss in this relationship: do the apple trees work for us — or do we work for them?

Similar examples can be found throughout nature, from fig-eating bats that become unwitting cargo planes for fig seeds, to squirrels and woodpeckers that unknowingly help oak trees spread their acorns. The Seedy Side of Plants even includes the remarkable tale of an African melon that grows a gourd-shaped bladder of water deep underground. In the dry season, aardvarks sniff out the watery melons, digging deep to quench their thirst. In the process, however, the thirsty aardvarks also sip up a few pit-like seeds, which they later deposit inside fertilizing manure. It’s hard to say who gets the better end of the deal: the melon or the mammal.

Both plant and animal, of course, get something out of these mutually beneficial relationships. Apple trees, for instance, didn’t set out to fool people into picking their fruit. But somewhere along the line, certain apple trees ended up with a combination of genes that made their fruit a bit brighter or sweeter than all the other apples. Since we liked these apples so much, we began selectively planting the trees, and learned how to breed even sweeter varieties. In exchange for the tender, nutritious fruit, the trees get steady care and even protection from potential enemies, such as insects and browsing deer.

Evolutionary accidents may explain how other types of seeds developed, too. On the island of Mauritius, for instance, there once were trees that dropped their tasty fruits full of seeds to the ground. Then, a new bird arrived on the island. It loved the fruits, but the tree’s seeds couldn’t survive the trip through the bird’s stomach. As a result, the tree was in trouble, since fewer of its seeds were surviving. Then, perhaps through a random genetic mutation, one tree, the calvaria, produced fruit with tougher seeds that could survive being eaten by the birds. Given this significant advantage, the tougher calvaria soon began to thrive. Eventually, they crowded out their ancestors completely.

As The Seedy Side of Plants shows, however, evolution can sometimes produce a plant that is too reliant on a particular animal for survival. That’s exactly what happened on Mauritius. There, some biologists believe that lonely 300-year-old calvaria trees await a bird that will never return: the dodo. In 1598, Dutch explorers established a colony on Mauritius. In the search for food to eat and sell, the settlers plundered the island’s natural resources, killing giant turtles, lizards, and the huge, flightless dodo birds with abandon. When the settlers did in the dodo, however, they may have also put the death of the calvaria in motion. Some biologists believe the dodos ate the tree’s fruit, and that the trip through the bird’s stomach helped prepare the seeds for germination. But now that their partner in life is gone, only a few calvaria survive. They are silent reminders of a lost past, with their seed-bearing fruit littering the ground and inviting a feast that will never come.

Plants have spent millions of years learning how to produce seeds that can ensure the birth of a new generation of plants. And people have spent thousands of years struggling to control that powerful force, breeding plants that produce more and better seeds than ever before. Indeed, modern agriculture depends in large part on our ability to control seed production: not only are seeds, from rice to wheat, a major source of our food, but we also depend on being able to store and plant them for the next year’s crop.

Now, however, scientists armed with the tools of modern genetic engineering are engaged in a controversial attempt to turn back the evolutionary clock by creating plants whose seeds do not work. Why would researchers want to prevent a plant from reproducing?

The answer lies in the economics of modern farming, where farmers in industrialized nations are willing to pay a fortune for seeds that can guarantee a bountiful harvest. But such revolutionary seeds are also expensive to develop, and seed companies are spending billions to engineer new varieties of many modern crops — from corn to cotton — that grow or taste better. In the past, a farmer may have been able to buy these relatively expensive seeds, harvest a crop, and then, by saving some of the seeds produced by the superplants, plant a new crop the next year without having to buy a new batch of seeds. Understandably, some companies were unhappy about spending so much to develop seeds that could be so easily “stolen.”

So now, these companies have figured out a way to turn off a plant’s ability to produce viable seed. By inserting a certain gene into the plant, the seed-growing process is short-circuited. While the plants produce lots of seeds, the packets are all sterile.

This “terminator technology,” as it is popularly called, isn’t yet out on the market. It is still being fine-tuned in the laboratory and in test plots. But it has already prompted protests around the world, particularly from poor farmers who depend on saved seeds for the next year’s crop. And some biologists worry the trait could somehow spread to related wild plants, endangering their ability to reproduce. The companies say such fears are unfounded and promise they won’t release the seeds until they’ve been shown to be safe.

The debate is unlikely to be settled soon, but it shows that even seeds no bigger than a speck of dust can spark huge debates.

In their quest to spread their seeds, plants have proved endlessly adaptable. Some, such as dandelions, produce spores that can fly miles on a puff of wind. Others, like coconuts, have engineered seeds that can survive thousand-mile voyages at sea. Some of the most remarkable seeds, however, are those adapted to survive fires so intense they kill virtually everything else in their path.

Many of the world’s pine forests, for instance, grow in arid climates, where a single flash of lightning can spark an inferno. Trees that couldn’t take the heat died out long ago. Those that remain generate seeds that are fire-hardened better than any high-security safe, able to protect their precious genetic cargo from the heat.

Some seeds, however, recall the mythical Phoenix, a bird that would rise from a fire’s ashes to begin life anew. To thrive, these seeds actually need to get burned: intense heat is required to explode their seed cones or crack their hard kernels, so that water can leak in and begin the growth process. Such “fire-germinated” species are common everywhere forest fires occur on a regular basis. In an ironic turn of events, the recent campaign to stamp out forest fires has put some of these species in jeopardy. Indeed, in some parks, rangers now intentionally set forest fires just to make sure certain plants grow.

Many prairie species, for instance, only sprout after fires clear the way. That has made the spring “prairie burn” an annual ritual throughout much of the Midwest, with teams of fire-wielding plant-lovers tromping into the fields in a quest to imitate the grass fires that once swept across the plains. In Michigan, biologists have also become fervent arsonists in an effort to make sure there are enough young jack pines, a kind of tree essential to the survival of an endangered songbird called the Kirtland’s warbler. For some reason, the bird will nest only in the young pines — and the trees will grow only in recently burned forests. That’s because fire is needed to get the pines’ tough cones to crack open and release their cargo of seeds.

Recently, however, biologists have learned that flames aren’t enough to unlock some fire-resistant seeds — they need the smoke as well. In the 1970s, researchers discovered that some seeds germinate when exposed to the merest whiff of wood smoke, even if the seed is buried in the soil. The response makes sense: the seeds can wait years underground until smoke reveals that a fire has taken place overhead, filling the soil with fertilizing ash and clearing away plants that might block the seedling’s light. Having gotten its smoke signal, the young plant can take advantage of the disaster.

But smoke is made of literally thousands of chemicals, and researchers have long puzzled over which ones might be triggering the seeds. Then, in 1997, researchers Jon Keeley and C. J. Fothereringham of Occidental College in California were able to pin down one of the responsible agents: a gas called nitrogen dioxide. They discovered that the seeds of a common wildflower called yellow whispering bells germinated when exposed to even tiny amounts of the gas. The discovery, however, had a troubling side. Nitrogen dioxide is produced by natural fires — but it is also one of the most common pollutants produced by cars and power plants. Tons of the compound fall to Earth every day, carried by rain and dust particles. Some botanists fear the pollution could be tricking sleeping whispering bells seeds into thinking a fire has occurred — causing them to sprout beneath the deadly shade of another plant. That would mean fewer seeds would be around when a fire really occurs.

Like other plants, however, even whispering bells show creative variation in getting their seeds to sprout. While those that live in fire-prone areas need smoke to germinate, whispering bells living in deserts, where fires are scarce, don’t respond to smoke at all. Instead, they have evolved a clever response to the desert’s scouring winds. For these seeds to germinate, they must be blown across rough sand, which scratches the seed’s outer coat. Moisture then leaks in through the scratches, signaling the seed that it is time to grow.

Such strategies don’t surprise botanists. Says one: “If you can think of a way to get a seed to sprout, you can be sure some plant is already doing it.”

They’re cunning and manipulative, and will do anything to get what they want. No, it’s not the cast of your favorite daytime soap. We’re speaking of the ubiquitous plant life that covers our planet, relentlessly evolving elaborate schemes to disperse its seeds and ensure the continuation of its almost limitless species.

How does such a seemingly passive life form accomplish the complex task of reproduction? Many plants take advantage of the primeval forces of Mother Nature herself to help their seeds germinate, sending them far and wide by means of wind, rain, and tides. Others have found ways to hitch rides for their seeds aboard other living things. For example, the burdock plant, which inspired inventor George de Mestral to create Velcro, has pesky burrs that sticks stubbornly to hair and fur.

Fruit, however, is perhaps the most commonly employed medium of seed mobility. Fruit-producing plants rely on the appeal of their fruits for dispersal of the seeds, and have evolved their own unique “marketing strategies” and their own select clientele — animals as well as humans — to help the process along. Even as scientists develop methods to control plant reproduction, each time we yield to the temptation to pluck a ripe juicy apple from its branch, we too become pawns in one of nature’s carefully devised game plans.

Online ontent for The Seedy Side of Plants was originally posted May 1999.