Wednesday, September 2, 2009

Jonathan Silvertown- An Orchard Invisible: A Natural History of Seeds.

Welcome to Texas Gardener’s Seeds, the weekly newsletter for Texas gardeners.
September 2, 2009

The garden reader:
Looking into the seeds of time
By William Scheick
University of Texas at Austin
Jonathan Silvertown. An Orchard Invisible: A Natural History of Seeds. University of Chicago Press, 2009. 216 pp. $25.00.

When observing plants, it's sometimes easy to leap to faulty conclusions. For instance, it's easy to surmise, on the basis of their sheer number, that seed-producing flora must have always dominated the plant kingdom.
Or, on the flipside of this mistaken impression, it's easy to think of the non-seeders, including ferns and mosses, as odd deviations from the norm. In fact, though, seedless plants once ruled our planet's oceans and lands, and the "magic trick" of encapsulating sea-like nutrients inside a seed emerged at some later point in time.
When impression-nurtured beliefs are unchecked by bedrock science, mischief can ensue. Consider the sixteenth-century belief that ferns produce seeds because all plants must grow from seeds.
Never mind that no one could see any fern seed.
There were answers for that, including a legend about what happened to fern flowers. According to this ancient legend, ferns did not contribute any blooms to the Christ child's manger. As a punishment for such "bad-seed" irreverence, ferns were deprived of their flowers and their seed became invisible.
This curse notwithstanding, ferns were still thought long ago to be valuable for various medicinal remedies, and their now-invisible seed was especially prized by the gullible. Some even believed that fern seed could make a person undetectable.
Of course, collecting the invisible fern seed was deucedly difficult.
In An Orchard Invisible Jonathan Silvertown doesn't mention the fern flower legend, but he succinctly explains how invisible fern seed was harvested: "Fern seed could be collected on the stroke of midnight on Midsummer Night's eve, but only by catching it as it fell from the plant onto a stack of twelve pewter plates. It would pass through the first eleven, but be trapped by the twelfth."
A quaint belief, indeed! But I've been around awhile and seen too much, and so I can't help but wonder whether, even today, empty seed packets labeled "Rare Invisible Fern Seed" might sell pretty well.
As the Jack-and-the-beanstalk story highlights, seeds do seem to be magical. Seeds, though, are actually down-to-earth devices far more complex and ingenious than represented in any fairytale.
In An Orchard Invisible Silvertown explores the history and science of this complexity. He ponders various seed-mysteries, such as nature's always unsuccessful repeated "attempts to break the habit of sex in plants." Cross-fertilization, it turns out, is inextricably interwoven with genetic variation, random adaptability, inherited mutation and chance survival.
Why, Silvertown also wonders, is the nutrient-thick coco de mer so large — the biggest known seed, in fact? It's easy but mistaken to believe that, as its popular name suggests, this "bizarre and wonderful monstrosity" floats to and germinates on distant beaches.
A Maldive coconut is not the only strange fruit feature. Silvertown finds even fruit coloration to be more mysterious than meets the eye. And he examines, as well, why seeds that fly awkwardly on single, unilateral wings vastly outnumber those that glide.
Silvertown suggests, too, that caffeine in a coffee bean possibly functions like a poison deterring the encroachment of nearby plants. But, he adds, if it's obvious why some seeds are poisonous, why are so many not?
The notorious suicide tree (Cerbera odollam) bears fibrous-shelled fruits, each with two lethal seeds. (Photo by William Scheick)

Silvertown doesn't mention it, but the world's most infamous, if understudied, poisonous seeds are found in the four-inch, fibrous-shelled fruits of the suicide tree (Cerbera odollam). The alkaloid toxin in the seeds of this tropical oleander relative has been implicated in numerous deaths — most of them decidedly not suicides.
Silvertown examines the place of unseen cheaters in our gardens. For example, while hardworking female yucca moths diligently collect pollen to fertilize the plant that will host their eggs, cheater moths skip pollen-collection and simply deposit eggs in fruit previously pollinated by the diligent moths. By colonizing already developed fruit unlikely to be aborted by a plant, these cheaters potentially jeopardize the entire symbiotic moth-yucca relationship — yet they somehow don't.
There aren't only selfish moths and wasps. Silvertown also puzzles over "selfish DNA" — free-agent "genes that jump around the chromosomes, sometimes playing havoc with the genome." Corn, for instance, is botanically notorious for its thousands of selfish DNA.
In An Orchard Invisible Silvertown "look[s] into the seeds of time," but unlike Banquo in Shakespeare's Macbeth, he is willing to speculate on the patterns behind "which grain will grow and which will not." The result is ample food for thought.

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