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.
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.