The Triumph of Seeds (15 page)

“To say I was wildly excited would be an understatement,” Elaine Solowey told me, recalling the spring day in 2005 when she noticed a lone shoot poking up through the potting soil. An agricultural expert at a kibbutz in the Negev Desert, Dr. Solowey had planted “hundreds of thousands of trees” in her career before she tried the
Masada dates. “I really didn’t expect anything to come up,” she confessed. “I thought those seeds were as dead as doornails. Deader than doornails!” Solowey credits her collaborator, Sarah Sallon, for dreaming up the whole idea.

“It just seemed meant to be,” Sallon said, when I reached her by phone. “To tell you the truth, I expected it.” It was ten o’clock in Jerusalem and she’d been working late, but Sarah still launched into our conversation with enthusiasm, and somehow also managed to carry on talking with her son in the next room. She even served him a meal. Sarah’s boundless energy made me wonder if the date seed hadn’t sparked to life simply because she’d touched it. Trained as a pediatrician, Sallon has become a world expert on natural medicines, particularly those derived from the native plants of Israel. Her laboratory team works with Solowey’s field crew to raise and test dozens of different medicinal herbs. “But I also became interested in what used to grow here,” she explained, “the things that have disappeared.” Ancient healers used dates from the Judaean palm to treat everything from depression and tuberculosis to common aches and pains. “Bringing it back,” she mused, “might serve a greater purpose.”

The sprouting palm that so surprised Elaine Solowey (but not Sarah Sallon) now stands ten feet tall and bears the name Methuselah, after the oldest character mentioned in the Hebrew Bible. But at 969 years, the biblical Methuselah had scarcely reached middle age compared to this little palm tree. Radiocarbon dating confirms that the dates from Masada had probably been stored there for decades before the fortress fell. Methuselah may look like a young tree, but its nearly 2,000-year lifespan makes it one of the oldest organisms on earth. At that age, who can begrudge it a little pampering? “We built him his own gated garden, with his own watering system, burglar alarm, and security camera,” Elaine said with a laugh. “He is definitely a tree that has everything.”

Elaine used the male pronoun because date palms are unisexual, and when Methuselah flowered for the first time in 2012, he turned out to have blossoms laden with pollen. To fully bring the Judaean
date back from extinction, someone will have to sprout a female seed, too. When I asked Sarah if they were working on it, she seemed almost bursting with the news: “Of course we are!” she exclaimed. “But I can’t tell you about it!” In science, it’s never a good idea to let the cat out of the bag before all the data are analyzed, reviewed, and published. By the time this book is printed, however, Sarah and Elaine may have announced their results to the world. With any luck, those findings will tell us not only how Judaean dates live so long, but their precise flavor and sweetness, and whether or not they can cure a headache.

Methuselah’s story ranks as the oldest known
example of a naturally germinating seed. It’s a tale of incredible endurance that provides a fitting and peaceful complement to the heroic defense of Masada, and makes it possible that Judaean dates may once again
flourish in the Jordan Valley. But it’s hardly the only time that an ancient seed has sprung suddenly and surprisingly to life. In 1940, the study of seed longevity received a jolt when a German bomb hit the botany department at the British Museum. After firefighters extinguished the blaze and cleared away the debris, museum workers returned to find some of their specimens sprouting. Responding to the heat and moisture, the seeds from a silk tree collected in China in 1793 had germinated and sent up perfectly normal-looking shoots. (Three of the seedlings were planted at the nearby Chelsea Physic Garden, where another bomb hit them in 1941.) Ever since then, enterprising botanists have been pushing back the record for longevity—200 years for pincushion proteas and other African exotics discovered in a cache of privateers’ booty; 600 years for a canna lily seed preserved inside a Native American rattle; 1,300 years for Indian lotus seeds recovered from a dry lakebed. The most promising new developments come from the high Arctic, where a team recently transplanted live tissue from a tiny mustard frozen in a squirrel burrow for over 30,000 years. By itself the seed couldn’t germinate, but the fact that any of its parts stayed viable for that long suggests that Methuselah’s record is bound to fall.

“Seeds can have an almost indefinite life-span,” Sarah told me, when I asked her about the limits of dormancy. Elaine’s answer was more prosaic, but probably closer to the truth. All seeds die eventually, she explained, and most die within a few years or decades. But Methuselah had been found in “the perfect place”—entombed deep under a collapsed building in a bone-dry environment where it was protected from insects, rodents, moisture, and the damaging rays of the sun. During the Egyptology craze that swept through Europe and North America in the nineteenth century, people claimed that similar conditions had preserved the grains and peas buried with the pharaohs. Unscrupulous local guides made a brisk business selling “mummy wheat” to tourists, and mainstream magazines, from
Harper’s
to
The Gardener’s Chronicle
, touted its amazing yields and health benefits. Even today, “King Tut Peas” remain a staple offering in seed catalogs. Although there’s no evidence that any of the pharaonic seed claims are true, Methuselah’s story suggests that they may not be impossible.

Bringing back ancient plant varieties makes for headline-grabbing science, but it’s just an extreme example of what seeds do all the time. In the broadest sense, dormancy refers to that quiet pause, however long, between when a seed matures and when it germinates. Garden seeds sold in packets are dormant, and so are the grass seeds you sprinkle in your front yard to plant a lawn: dry, hard, easy to store, and ready to sprout as soon as they hit a patch of damp soil. Without dormancy, farmers and gardeners couldn’t save seed for future plantings; nor would grains or legumes or nuts last so long stored in our cupboards and pantries. We take it for granted, but if seeds couldn’t lie around for months or years on end, our entire food production system would be a folly. But while the endurance of seeds is vital to people and agriculture, it’s even more important to the plants themselves.

Anyone who has blown the fluff from a dandelion is familiar with the idea of seeds dispersing through space. In a very real sense, dormancy allows seeds to disperse through time. It gives plants a
way to position their seeds in a particular moment, that point in the future when conditions will be just right for germination. Plants with long-lived seeds produce babies that will survive whatever winter, drought, or other barrier may stand between them and the next good growing season. They can also hedge their bets against floods, fires, or other chance events that could wipe out every seedling in a given year; dormant seeds will still be there in the soil, waiting for another opportunity. This gives seed plants an obvious evolutionary advantage anywhere that the climate is harsh, unpredictable, or strongly seasonal. It fits neatly into Bill DiMichele’s theory of seeds evolving in the dry, rugged uplands of the Carboniferous, where dormancy gave seeds another clear advantage over their short-lived spore competitors. And it also helps explain why dormancy is the dominant seed strategy in nearly every environment except tropical rainforests, where favorable weather is basically constant and seeds are better off sprouting immediately to avoid greater dangers from rot, pests, and predators.

The plants that first invented dormancy probably did little more than drop their seeds early. These immature cast-offs had no special adaptations—they simply needed more time to develop before they were ready to germinate. Some species still follow a version of this approach, as any gardener who has tried to grow parsley will understand. It takes forever to sprout, because its tiny embryos must grow for days and days
inside
the seeds before they are big enough to put out a root. Over time, most plants developed the habit of holding onto their seeds longer and drying them out, reducing water content by as much as 95 percent. This remains the single most important factor in slowing down a seed’s metabolism, something we’ll discuss in detail in the next chapter. For now, think of desiccation as a starting point from which seed dormancy quickly evolved into an array of strategies so complex they border on the arcane. In general, and in this book, dormancy is defined broadly—any pause, for any length of time, that takes place after a seed matures and before it sprouts. But specialists like Carol Baskin make an important
distinction between seeds that are simply inactive, and those that are technically dormant.

“If a seed is truly dormant and you place it on a moist substrate at favorable temperatures, it will not germinate,” she told me. In other words, dormant seeds don’t simply sit around waiting for rain showers and sunny days. To meet Baskin’s definition of dormancy, a seed must actively resist germination, using a wide array of tricks to stave off that moment of sprouting. This sounds counterintuitive—isn’t the whole point of a seed to germinate?—but it gives seeds a sophisticated way to interact with weather, daylight, soil conditions, and other factors that make up their environment. The most common tactic in temperate regions takes advantage of temperature, requiring the prolonged chilling effects of winter, followed by warming, to make the seeds ready to sprout in the spring. This strategy often works together with light requirements, which can be surprisingly specific. Some wild mustard seeds respond to changes in the angle and length of daylight through six feet of snowpack, while many forest species recognize the difference between full sunlight (a good chance to sprout), and the far-red wavelengths that filter through leaves (too shady). Whatever their needs, dormant seeds cannot and will not germinate until certain conditions are met.

“The evolution of this is driven not so much by the seed as by the seedling,” Carol explained. While germination might be successful in any damp moment, the really important thing is what happens next. A mother plant’s entire investment in nurturing and dispersing her seeds means nothing if they sprout in the wrong season and immediately perish from thirst, cold, heat, or shade. These high evolutionary stakes have led to the highly specific cues needed for dormant seeds to wake up. Some of the most elaborate examples come from fire-prone areas, where young plants grow best after a blaze opens up the habitat and releases a flush of ashy nutrients. Seeds adapted to this system, from particular acacias and sumac to rock rose and gorse, often remain completely waterproof and unable to imbibe until the extreme heat of open flames cracks their
coats or unplugs tiny stoppers to let moisture in. Some species also require exposure to the hot gasses found in smoke, or respond to particular chemicals released from partially charred wood. Germination experts have been known to flash-heat seeds and blast them with smoke in an attempt to simulate wildfires in the lab. For desert plants, the challenge lies in differentiating occasional cloudbursts from the sustained rains that can actually nourish a thirsty seedling. Just how they do it remains controversial, but some experts believe their seed coats contain “rain gauges,” chemicals that inhibit germination until they are leached away by just the right amount of water.

To Carol Baskin and her husband, no aspect of seed biology is more intriguing than how seeds sleep and what it takes to wake them up. “It just fascinates us,” she told me. In all, she and Jerry have identified fifteen different classes and levels of seed dormancy, with many variations on each theme. They vary based on what causes the dormancy (e.g., an impermeable seed coat, an undeveloped embryo, a chemical or environmental constraint), and the “depth” of the dormancy (how difficult it is to overcome). From their backyard in Kentucky to the mountains of Hawaii to the cold deserts of northeastern China, they continue to turn up new wrinkles. What keeps them coming back is how little we actually understand about the process itself. Everyone agrees that desiccation is important, and scientists know many of the chemicals and genes involved, but just how a seemingly lifeless seed recognizes things as diverse as frost, smoke, heat, day length, and the ratios of wavelengths in sunlight remains mysterious. Even the basic distinction between the end of dormancy and the beginning of germination is fuzzy. In science, and life in general, it’s possible to know a lot about what happens without understanding how. I know what happens when I turn on my computer, for example. I can type, search the Internet, or entertain my son’s grandparents with emails and photos of his latest antics. But I don’t have the foggiest notion about how a computer actually works, as my frequent calls to tech support can attest. The science of seed dormancy is more advanced than that, but there’s still a great deal to learn, and that’s what makes it exciting.

At the end of our conversation, I asked Carol if suspended animation was a good analogy for dormancy. (When science can’t provide a complete answer, it’s only natural to turn to science fiction.) “Not exactly,” she responded, “because the seed is still active.” This made me smile—only a seed biologist would call the hard, dry, inert little lump of a dormant seed “active.” But Carol and many others believe that seeds continue metabolizing like any other living thing; they just do it very, very slowly.

When the title character opens his eyes in H. G. Wells’s classic novel
The Sleeper Awakes
, he finds the world transformed. Two hundred years have passed, and everyone he has ever known is dead. On the bright side, his savings account has built up enough compound interest to make him the richest man in history. Dormancy can be a similar experience for a seed—Methuselah, after all, woke up to his own private garden. More typically, seeds sleep through a single season, or perhaps a few years or decades, but the payoff remains significant: favorable growing conditions, and with any luck, a good patch of ground. In the Wells novel, the roused Sleeper immediately meets people in strange robes who try to keep him from claiming his fortune. Seeds also awaken in a state of competition with odd bedfellows, since throughout their slumber and for many years before, other seeds of all varieties have been stacking up in the soil nearby.