Friday, December 27, 2013

The Intelligent Plants - Michael Pollan

“If you are a plant, having a brain is not an advantage,” Stefano Mancuso points out. Mancuso is perhaps the field’s most impassioned spokesman for the plant point of view. A slight, bearded Calabrian in his late forties, he comes across more like a humanities professor than like a scientist. When I visited him earlier this year at the International Laboratory of Plant Neurobiology, at the University of Florence, he told me that his conviction that humans grossly underestimate plants has its origins in a science-fiction story he remembers reading as a teen-ager. A race of aliens living in a radically sped-up dimension of time arrive on Earth and, unable to detect any movement in humans, come to the logical conclusion that we are “inert material” with which they may do as they please. The aliens proceed ruthlessly to exploit us. (Mancuso subsequently wrote to say that the story he recounted was actually a mangled recollection of an early “Star Trek” episode called “Wink of an Eye.”)

In Mancuso’s view, our “fetishization” of neurons, as well as our tendency to equate behavior with mobility, keeps us from appreciating what plants can do. For instance, since plants can’t run away and frequently get eaten, it serves them well not to have any irreplaceable organs. “A plant has a modular design, so it can lose up to ninety per cent of its body without being killed,” he said. “There’s nothing like that in the animal world. It creates a resilience.”

Indeed, many of the most impressive capabilities of plants can be traced to their unique existential predicament as beings rooted to the ground and therefore unable to pick up and move when they need something or when conditions turn unfavorable. The “sessile life style,” as plant biologists term it, calls for an extensive and nuanced understanding of one’s immediate environment, since the plant has to find everything it needs, and has to defend itself, while remaining fixed in place. A highly developed sensory apparatus is required to locate food and identify threats. Plants have evolved between fifteen and twenty distinct senses, including analogues of our five: smell and taste (they sense and respond to chemicals in the air or on their bodies); sight (they react differently to various wavelengths of light as well as to shadow); touch (a vine or a root “knows” when it encounters a solid object); and, it has been discovered, sound. In a recent experiment, Heidi Appel, a chemical ecologist at the University of Missouri, found that, when she played a recording of a caterpillar chomping a leaf for a plant that hadn’t been touched, the sound primed the plant’s genetic machinery to produce defense chemicals. Another experiment, done in Mancuso’s lab and not yet published, found that plant roots would seek out a buried pipe through which water was flowing even if the exterior of the pipe was dry, which suggested that plants somehow “hear” the sound of flowing water.

The sensory capabilities of plant roots fascinated Charles Darwin, who in his later years became increasingly passionate about plants; he and his son Francis performed scores of ingenious experiments on plants. Many involved the root, or radicle, of young plants, which the Darwins demonstrated could sense light, moisture, gravity, pressure, and several other environmental qualities, and then determine the optimal trajectory for the root’s growth. The last sentence of Darwin’s 1880 book, “The Power of Movement in Plants,” has assumed scriptural authority for some plant neurobiologists: “It is hardly an exaggeration to say that the tip of the radicle . . . having the power of directing the movements of the adjoining parts, acts like the brain of one of the lower animals; the brain being seated within the anterior end of the body, receiving impressions from the sense organs and directing the several movements.” Darwin was asking us to think of the plant as a kind of upside-down animal, with its main sensory organs and “brain” on the bottom, underground, and its sexual organs on top.

- Michael Pollan on The Intelligent Plants: Scientists debate a new way of understanding flora (hope he writes a book on this soon)

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