The Triumph of Seeds by Thor Hanson Read Free Book Online

split thing where the base of the green shoot turned pale. Rather than invest in fat cotyledons, grasses endow their offspring with only a modest lunch and rely instead on fecundity—broadcasting droves of seed in the hope that a few will find purchase. Where a pampered avocado tree might yield 150 single-seeded fruits annually, I recently counted 965 seeds on the wispiest looking bent-grass growing in our driveway. The food stored in a grass seed gives that baby plant enough energy for a quick growth spurt, but would never keep it alive for long in the shade. Instead, young grasses depend on finding open,unoccupied real estate. They prefer soil, but will also germinate on pavement, in gutters, or on the running boards of old pickup trucks. Some species thrive insand or on mud flats, or make a quick living colonizing the shifting gravel of riverbanks. To rock climbers everywhere, grass seeds create the constant need for “gardening,” yanking tufts of new greenery from the tiny cracks and crevices that both climbers and plants hope to cling to.
    Contrary to popular belief, watching grass grow can actually be quite riveting—a story of derring-do combined with sheer tenacity. Though I hated passing up free firewood, I left a stack of the grassy madrona in place to let the drama unfold. Six months later, the meadow lay baked in summer sunshine. I returned to find the logs in their pile, but with hardly a trace of that promising green fringe. Nearly every seedling had withered in the heat, exhausting its tiny lunch long before a root could stretch down to reliable water. But one plant had survived. From the split end of a log near the bottom of the pile, a tuft of velvet grass now sprouted, its tall flower stalk rising upward to sway in the breeze. I carefully lifted the wood and saw where roots had threaded their way through a crevice to find the soil below. In general, scattering seeds on woodpiles spells a death sentence for the baby plants inside. But this one success story, with the hundreds of seeds it would produce, helped justify the tactic.
    While a grass’s profligacy might not have the cozy, nurturing appeal of the well-stocked lunches found in avocados, nuts, legumes, and other plump seeds, it’s certainly asuccessful strategy. Programmed for colonization and survival, the tiny grains of most species can withstand desiccation and long periods of dormancy, traits that help grasses dominate almost every earthly habitat too arid for trees and shrubs. Even Antarctica boasts native grasses, and if you lined up all the flowering plants on earth, nearly one in twenty would be a grass. Ubiquity alone, however, does not a staple make. For all their prolific seed, grasses would hardly be so vital to people without a trick of chemistry. That trick lies in the way they pack their lunch.
    D issecting a grass seed takes steady hands, and if you decide to try it, I suggest skipping the afternoon coffee. My jittery attempts senthalf a dozen wheat grains skittering off the desk before a clean slice finally revealed the pertinent feature: a mass of starch granules that glowed like lumpy marbles in the light of my microscope. Of all the ways that seeds can store energy, from oils and fats to proteins, none makes a better staple food for people than starch. It’s built from long chains of glucose molecules, like sugar beads on a flimsy necklace. Enzymes in the human intestine, and even in our saliva, can break that necklace easily and release the sugars. Tweak the chemistry of starch ever so slightly, however, and you get cellulose, the indigestible plant fiber that makes up stems, twigs, and the trunks of trees. Cellulose and starch differ only in how their glucose chains hold together, a few repositioned atoms that change the flimsy string to an indigestible one,like a steel wire. Without starch’s weak glucose bonds, and our ability to break them, grass seeds would pass through the human gut like a handful of sawdust. As it