Plant Minds

Plants have minds because their activities disclose a world of things that have significance for them. Following Evan Thompson, we can call this an enactive approach to plant minds.

What is it to disclose a world of things that have significance? Focus on the most familiar case of a thing with a mind, a human being. Here at my desk in Carlisle, PA, I sit, typing these words on this keyboard, for this post, for The Brains Blog. My white coffee mug rests to my right, ready to be sipped. Thompson‘s Mind in Life is next to it. On my left lies a stack of just-completed logic tests, to be graded. A bowl of almonds sits there too. My to-do lists lays in front of the keyboard. Steve Reich’s Music for 18 Musicians tingles around the room.

This is a world of things that have significance for me. These things are not merely aggregates of matter, made of the elements of the Periodic Table, obeying laws of physics. Rather, I’m surrounded by an array of things that are for something, writing this post, and being a teacher. Desk, keyboard, coffee, book, tests, and food have a purpose within those projects; there are ways they should and should not be used. These things are “disclosed” because they have significance in virtue of their place in my projects of writing and teaching, an activity which in turn has its significance in virtue of its place in several wider contexts: my personal life, my job, and contemporary philosophy.

Magnolia, by James Sias

Focus now on a magnolia. It is deceptively easy to think it just sits there, as if it were always there, looking lovely. By actively creating and maintaining itself, it too induces an array of things that matter to it. It does not exist in mere space surrounded by mere matter. Some things it actively seeks, or is drawn toward; others it actively avoids. Mattering needs to be understood in terms of the magnolia’s ongoing self-production, and cannot be smoothly assimilated to the “behavior” of mere puddles or water wheels, since those things don’t engage in any sort of self-creation, and nothing “shows up” to them as to-be-acted-upon in some way or other, as possibilities or opportunities for action.

Think of the magnolia’s origin. Decades ago, a seed settled, pressed unwittingly into the soil by squirrels, raccoons, chipmunks, and deer. It arrived along a network of impromptu streamlets, the result of spring rains, from another teacup magnolia. That seed was a marvelous thing:  the tiny germ of what would become an enormous tree, shrouded in a case of nutrients, shrouded again in a hard protective coat, able to withstand substantial temperature changes and mechanical perturbations.

A lot had to happen for the magnolia’s initial shoot to make its way to the surface. Absorbing water from the soil, its cells expanded and divided, over and again. Surrounding the membranes were rigid walls made of cellulose, a type of carbohydrate, the main substance in wood. They also contained various lipids, which are waterproof. Cells eventually differentiated and specialized, forming distinct types of tissue, such as the epidermis. Walls of the cells of the epidermis created cutin and other waxes that are indigestible and unappealing to many bacteria, fungi and animals

Once it broke ground, to get energy through photosynthesis, our magnolia seedling needed light and carbon dioxide for photosynthesis. First building buds along its stem, it created branches and leaves, which increased its access to light and carbon dioxide. These leaves were also a burden, for they increased the mechanical stress on the whole plant, by catching wind, acting like sails. The tree must have created cells that were not so rigid that branches or the stem would crack under temporary but sustained and substantial increases of pressure. Exposure to wind, like exposure to sunlight, depends on atmospheric conditions, topography, and the size and distribution of neighboring plants. These fluctuate over time. Our tree had to adjust accordingly.

Below the surface, in the soil, the roots continued to grow, increasing the surface area that was exposed to water, increasing how much water and nutrients the plant absorbed. The larger root system also helped anchor the plant, counterbalancing the increase in size above the surface.

Photosynthesis is the main means by which our magnolia created energy. It involves a careful tradeoff. Gas exchange is the process by which a plant absorbs carbon dioxide and releases oxygen. It occurs through hundreds of stomata, pores found mainly on the underside of leaves. They are spaces bordered by two “guard cells.” When those cells swell with water, the stoma opens. When they are not swollen, the stoma is closed. Typically, stomata open during the day, when sunlight is available for photosynthesis. They close at night, when sunlight isn’t available for photosynthesis. Gas exchange inevitably results in water loss, or transpiration, because water vapor escapes through the stomata. So, our magnolia must have carefully regulated the opening and closing of its stomata.

Day after day, month after month, year after year, our magnolia did these things. Representative of the majority of plants (the vascular, seed-bearing, flowering plants), throughout its life, our magnolia has actively maintained itself in the face of changing and sometimes dangerous conditions, thereby disclosing a world of things with significance for it. Many of its responses to its environment register the significance of items in ways that guide its behavior, enabling its ongoing existence. For this reason it is plausible to say that it perceives, and in that respect, has a mind.

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7 Comments

  1. Hi Chauncey, thanks so much for your posts this week. I have two big-picture questions, each building off of a question I asked you before.

    – Regarding the question whether plants represent: suppose you are right that there’s no explanatory payoff in postulating internal representations as causes of the plant’s behavior. Yet in this last post you say:

    “Representative of the majority of plants (the vascular, seed-bearing, flowering plants), throughout its life, our magnolia has actively maintained itself in the face of changing and sometimes dangerous conditions, thereby disclosing a world of things with significance for it. Many of its responses to its environment register the significance of items in ways that guide its behavior, enabling its ongoing existence. For this reason it is plausible to say that it perceives, and in that respect, has a mind.”

    I am open to the idea that this sort of organism-level description could be apt even if there aren’t any representational states at the sub-organism level. But isn’t there *a* sense of representation in which perceiving, or registering the significance of, items in the world around one is itself a form of representation? After all, that’s what paradigmatically representational achievements like perception, thought, etc. amount to. (Obviously I am not using ‘representation’ in a weighty sense here: perception will be representational in this sense even on a direct realist view.) On this way of thinking, your view would seem to be that (some) *plants* represent their environments even though there (perhaps) aren’t any internal states of those plants that do so. Would you be comfortable with this way of putting it?

    – I also asked what was the value in saying that plants “have minds” rather than that they perceive, act, remember, etc. But now I am wondering whether your conclusion couldn’t be put by saying that plants have *souls* in the Aristotelian sense, where this isn’t a way of postulating any immaterial entity over and above the suitably arranged parts with their teleological organization. Of course Aristotelians traditionally deny that plants are sentient — though it would be an interesting exercise to figure out whether the perceptual capacities you ascribe to (some) plants would count as sentience on an Aristotelian view. Anyway, while I understand that this language sounds outmoded, I wonder if it could introduce a richer array of possible distinctions than if we talk only of “minds”.

    I hope these questions aren’t too weird! Thanks again for taking the time to discuss your really interesting work.

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    • Chauncey Maher

      Thanks, John, for the thoughtful questions, but also for the chance to participate here. Let me address your first question in this reply and your second one in my next reply. Yes, I agree there is a sense in which plants represent something when they (allegedly) perceive it. At least this much: various of its states covary with the thing it perceives. This sort of representation or information does not involve accuracy conditions or truth conditions, though it might involve a sort of correctness condition. Plants have at least that sort of (thin or weak) representation. A richer sort of representation involves accuracy conditions or truth conditions. The paradigm here is a sentence of a natural language or a picture. Following Robert Cummins, I believe these sorts of representations have targets and contents. The target is the thing to which the representation is supposed to apply; the content is what the representation “says” of the target, how it portrays the target as being. I don’t believe there is yet good reason to think that plants have this sort of (thick or strong) representation.

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      • Thanks, Chauncey. I was thinking of something a little bit different than this. Consider how on a ‘direct realist’ view perception might be seen not as a representational state of the organism but as a relation between the organism and the environment in virtue of which the organism is able to cognize things, respond intelligently to stimuli, etc. (I take it that Gibson’s view is along these lines.) This is compatible with holding that there are states of the organism that represent its environment, but arguably doesn’t require that, at least if organism-level properties are sufficiently distinct from sub-organism-level ones. (I am using ‘organism-level’ instead of ‘person-level’ for obvious reasons.) And it’s an open question whether perception so construed has targets, contents, accuracy conditions, etc. Maybe that’s implausible in this case, or too unclear to be helpful, but it’s the sort of thing I was driving at.

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    • Chauncey Maher

      In your second question, I like the thrust of your suggestion. Specifically this: “introduce a richer array of possible distinctions than if we talk only of “minds”.” And I agree that Aristotle is relevant, even if he doesn’t have a pat answer. As I suspect you know, the term in Aristotle that is now commonly translated as ‘soul’ is ‘psyche’. His idea seemed to be that plants, animals, and humans share a distinctive sort of goal-directed order. And nous or mind or intellect, which Aristotle thought was displayed uniquely by humans, is a specific (and especially advanced?) form of that sort of order. I like the idea that the capacities that are or appear to be uniquely human be understood as substantively comparable to the order displayed by other living things. The harder work is to get more specific about the similarities and differences. A crude version of this aspiration: in thinking about minds, we need to get past this typology: rocks, human artifacts, nonanimal organisms, higher animals (birds, dogs, chimps), humans. We especially need to populate the middle with better categories.

      (Having defended plant minds, I might not be in a good position to say what is too weird!)

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  2. David Duffy

    Couldn’t this same line of argument be used to infer mind in single cells? For example, bacteria quorum sensing, “clever” anticipation in timing of encystment and shifting of metabolism, and chemotaxis are behaviours at about the same level of complexity.

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  3. Richard Soundy

    Unfortunately I am unable communicate my thoughts on the same level the previous posters to this article. Basically, in my opinion all living things must have a mind and a key part of that mind is the various sensory devices that exist to fulfill the our mere existence on this planet. Some can fly, some can swim, some can run and some are anchored …. but, we quickly adabt by using or self tuning our sensory powers to meet something we all require, that being our need to create a symbiotic relationship with one another.
    A tree cannot talk, run or dance as a form of communication, but it quickly understands that it’s best bet is to bring things to it instead – scent (as in smell), colour, canopy-of-protection and edable fruit/leaves all bring their requirements to them instead of trying to chase after others. It is capable of touch (feeling) via its root system. Not bad and possibly even a mind of a genious at work here!

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