Dispelling the Myth of the Passive Plant

November 18, 2014 | Posted in: Science

Flore des serres et des jardins de l'Europe, Vol XIV, Louis Van Houtte, 1861.

Flore des Serres et des Jardins de l’Europe, Vol XIV, Louis Van Houtte, 1861.

“That May afternoon, the garden suddenly appeared before me in a whole new light, the manifold delights it offered the eye and nose and tongue no longer quite so innocent or passive. All these plants, which I’d always regarded as the objects of my desire, were also, I realized, subjects, acting on me, getting me to do things for them they couldn’t do themselves.”
Michael Pollan, The Botany of Desire

 

Here, in much of the Northern Hemisphere, the dark and cold days of winter have arrived, and so the landscape is suddenly bereft of the greenery of summer and the fiery display of autumn. The plants that peeked out buds, shoots, and leaves in the spring are now either dust to dust (such is the fate of annuals) or have shed their outer layers to wait out the cold (such is the endurance of perennials). I’d meant sometime this summer to write an ode to the marvelous plant beings that green and clean and sustain life on this planet, but time simply slipped right on by. It’s only now, with the landscape suddenly gone glacial, that I remember my intention. So, here I sit to write my praises to the plants, to offer a eulogy until their rebirth again in the spring.

As we celebrate the end of the harvest season, sitting down together to feast and speak our thanks, the plant kingdom should be first on our lips. For there would be no harvest and no harvester without plants. The oxygen we breathe is available thanks to plant respiration and the sun’s light that falls upon our earth warmed but did not feed before plants, the true alchemists, worked a miracle that is still beyond our full understanding: spinning the sunlight into useable energy within the inner green realms of their being. Nearly all creatures, from top predators to the smallest insects, rely on the sun-nourished plants to sustain them.

Poppies, News of Spring and Other Nature Studies, Maurice Maeterlinck, 1917.

News of Spring and Other Nature Studies, Maurice Maeterlinck, 1917.

“Green plants play a vital role in the flow of energy through all ecological cycles. Their roots take in water and mineral salts from the earth, and the resulting juices rise up to the leaves, where they combine with carbon dioxide (CO2) from the air to form sugars and other organic compounds. (These include cellulose, the main structural element of cell walls.) In this marvelous process, known as photosynthesis, solar energy is converted into chemical energy and bound in the organic substances, while oxygen is released into the air to be taken up again by other plants, and by animals, in the process of respiration.”
Fritjof Capra, The Web of Life: A New Scientific Understanding of Living Systems

What wondrous and essential goodness the plants give to us all, and yet how little we understand them. A seemingly irreconcilable divide separates the plant and animal kingdoms, and it’s obvious to even the most thoughtless human observer that plants are living beings with a very different experience of what it means to be alive on earth. For a human, it’s impossible to grasp the reality of life lived as a plant, and many of us have been guilty of removing all possibilities of awareness and responsiveness from the flora family. We pluck a flower for its beauty and never dream that the plant is aware of our theft and sending out a chemical chorus through its whole being to assess the damage. Mostly we view plants as objects: passive, silent, and unmoving decor on the human stage. Rarely are they seen as protagonists in their own right, striving for what all living beings strive for: continued existence.

Icones Plantarum: Medico, economico, technologicarum, Vol I, Ferdinand Bernhard Vietz, 1800.

Icones Plantarum: Medico, economico, technologicarum, Vol I, Ferdinand Bernhard Vietz, 1800.

This shared struggle to sustain life means that, while the lives of plants are quite different from our own, their existence depends, like ours, on being aware of and correctly responding to dangers and opportunities in their environment. And plants have developed ingenious and manifold ways of perceiving and engaging with the world around them:

“[P]lants have senses and can detect a wide variety of external variables, such as light, water, temperature, chemicals, vibrations, gravity, and sounds. They can also react to these factors by changing the way they grow… They can assimilate information and respond on the whole-plant level. And they use cell-to-cell communication based on molecular and electrical signals, some of which are remarkably similar to those used by our own neurons.”
Jeremy Narby, Intelligence in Nature

Plants are aware when they’re touched, but more than this they can differentiate between types of touching: are they being eaten, clipped, trodden upon, or simply brushed up against? They’re able to detect different forms of light, including red, blue, infrared, and UV, and even know when they’re experiencing a hot stimulus versus a cold. And a plant, though mute and blind by human standards, is incredibly aware of the other organisms that share its locale, aggressing against or avoiding the intrusions of its neighbors according to its own best interest. There’s even a growing number of studies documenting that plants “remember” past events, like infections or weather patterns, and change their physiological structures based on these memories.

Flore des Serres et des Jardins de l'Europe, Vol V, Louis Van Houtte, 1849.

Flore des Serres et des Jardins de l’Europe, Vol V, Louis Van Houtte, 1849.

Silent though they seem to us, plants are elaborate communicators. Using the language of biochemistry they’re exceptional chemical linguists. Their bodies are their laboratories, and over the eons of their evolution plant species have concocted an array of potions meant to seduce, destroy, and convey. Many have evolved to release volatile chemicals when herbivores attack, warning other leaves that danger is imminent. Often these chemicals cause the leaves and flowers to change their flavor or texture to dissuade further munching, and in some cases even release toxins that can kill their assailant. The lima bean, when its nemesis beetles appear to devour its leaves, employs another strategy: its flowers can create a nectar that attracts beetle-devouring arthropods, similar to a besieged kingdom calling in a mercenary force. Many plants have similar symbiotic relationships with various insects (common examples being ants and wasps) to act as guardians in exchange for nectar or other food.

“Unable to run away, plants deploy a complex molecular vocabulary to signal distress, deter or poison enemies, and recruit animals to perform various services for them. A recent study in Science found that the caffeine produced by many plants may function not only as a defense chemical, as had previously been thought, but in some cases as a psychoactive drug in their nectar. The caffeine encourages bees to remember a particular plant and return to it, making them more faithful and effective pollinators.” Michael Pollan, The Intelligent Plant

Perhaps our common underrating of plants is mostly due to the fact that they move on a time scale much slower than our own. To the human eye their growth is only noticeable in blips, when suddenly the bud that was about to bloom is now a wide open pageant, and then, the next time we notice, wilted. For us, it takes the help of time-lapse videos to recognize plants as the incredibly active beings that they truly are:

A plant’s movements, once sped up, are familiarly animate: their roots and tendrils seek like fingertips around them, their leaves and flowers sway about like our own faces seeking the warmth of sun or attention of a familiar. The greatest difficulty for a plant is that though it can move, it cannot locomote. The whole point of roots are to fasten and secure an organism to the earth with the strength to withstand fire, flood, or a herd of herbivores. This has created a very different set of challenges for plants to overcome. They must find a way to survive where they are, no matter how dire the circumstances. There is no relocating to greener pastures.

And no running means that getting eaten is a daily liability. For an organism that can’t escape from predators there’s no advantage to having any indispensable body parts; no reason, in other words, for a brain or other complex organs. Instead, plants evolved a modular design: if a leaf or root gets destroyed, just grow a new one. Most plants could lose up to 90% of their body and still survive and recover. This is a resilience that animals, with our specific and necessary organs, can’t come close to matching.

“All species face the same existential challenges—obtaining food, defending themselves, reproducing—but under wildly varying circumstances, and so they have evolved wildly different tools in order to survive. Brains come in handy for creatures that move around a lot; but they’re a disadvantage for ones that are rooted in place.” Michael Pollan, The Intelligent Plant

For a being that can’t move from place to place, it’s also a trick to get pollinated and spread your seed. Again, plants responded to this challenge with a whole gambit of creative solutions, many of them involving enticing other insects and animals to do the work for them. The allure of flowers is no accident, but a strategic evolutionary method of seduction, the scents and colors all acting as lures, alerting pollinators and seed dispersers that the time has arrived. Most flowers are generous and offer rewards in the form of nectar and fruits in exchange for pollinating services, but others use tricks in the form of smells, shapes, and colors to coax critters into getting dusted in their pollen.

Martin Johnson Heade (1819-1904)

Martin Johnson Heade (1819-1904)

“As one quickly learns in the Amazon rain forest, there is nothing wimpy about a plant. Because trees can’t move to court each other or to defend themselves, they’ve become ingenious and aggressive about survival. Some develop layers of strychnine or other toxic substances just under the bark; some are carnivorous; some devise flowers with intricate feather dusters to touch pollen to any bug, bird, or bat they have managed to lure with siren smells and colors. Some orchids mimic the reproductive parts of a female bee or beetle in order to trick the male into trying to copulate, so it will become dusted with pollen.”
Diane Ackerman, A Natural History of the Senses

Plants feed the whole web of life, and have given us medicines, drinks, spices, intoxicants, fuel, and lumber to make our homes and furniture. We weave their fibers to make cloth, use their pulp to make paper, and collect their oils and butters and suds to care for our bodies. Plants oxygenate and clean the air, create and fertilize the soils, stabilize the climate, and increase rainfall. They beautify our landscapes, and we give them to one another when showing love, or empathy, or gratitude. They fill our world with heavenly scents and wondrous colors, but for their own reasons. And they are aware when we touch them, when we pluck a flower or fruit, trim their leaves or cut them down, move their location or change their soil. At last, let us all agree: plants are not objects but subjects, and our human lives rely on them utterly.

 The following sources informed this post:
What a Plant Knows
, Daniel Chamovitz
Intelligence in Nature, Jeremy Narby
The Botany of Desire, Michael Pollan
The Intelligent Plant, Michael Pollan

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