Since definitions of thinking mostly involve mind (generally understood as brain) and/or acts of contemplation, imagination, decision, movement and so on, right there, plants are exempted - and plants are quite obviously rooted in place, so are unable to perform "acts" of any kind, right?
Well, okay, they do grow, and turn toward the light, and sometimes tendrils can wind around things, and some petals can close at night...but those things are all just cellular responses to simple stimuli like light and touch, right?
They're not "acts" like when you decide to go somewhere so you move your muscles and you get there. Leaves move when the wind blows them, but that's just moving because the wind is moving, nothing to do with action or volition or anything like that, right? The other kinds of movement you see in plants is pretty much the same, right?
Well maybe...and then again, maybe not.
Let's think about it <<<>>>> what exactly are we doing? What is "thinking" anyway? We're pretty sure it's occurring in our brains; we know from imaging and scanning that certain parts of our brains "light up" when we think of certain things, or think about them in certain ways; and we know that if brains are injured, some types of thinking can be changed or cease to function.
But consider this...it wasn't so very long ago that people had no idea what all that mushy stuff inside heads was for. If they thought about it at all, they thought that thinking originated in the heart, or maybe the solar plexus - that old "gut feeling," you know?
If you come right down to it, we don't REALLY know what's happening in the brain, how the electronic/chemical stimulation of cells interacts in a perception/memory/integration/abstraction interface to produce thought and action, whether it be the simple thoughts of a worm, or the towering thoughts of a human being. Some theorists are even beginning to wonder if "thinking" might be going on at the molecular level, or even the quantum level, and that the brain is simply a switching station.
Back to the original question - do plants think? (By the way, this is a really huge topic, and I'm going to be batting it around for a long time, so if anyone else has any thoughts/information, feel free to throw them in.) Let's define thinking (at least at this point) as the process of acquiring information from/about the outside world by the stimulation of certain receptors (cells or aspects of cells, probably), that information then translated (somehow) into actions that allow the organism to respond (somehow) to the outside world in ways that are contributory (hopefully) to its survival.
By using this kind of definition, I'm getting away from the idea that "thinking" necessarily involves "words." It does, however, involve ACTIONS based on INFORMATION. Plants definitely acquire/take in information, (something to talk about at a future time,) but do they actually perform any actions, other than simply "growing?" (Which isn't so simple, when you come down to it.)
Other than those few things I mentioned earlier, what kinds of actions could they possibly perform? Well, in order to understand plant movement, you need to adjust your own perceptions.
Ever seen those fast-action films of plants growing and flowers opening? In them you see that plants move to the beat of a drum different than that which animals follow.
As you slow down to their score and measure, you see the twigs and buds on trees and bushes swinging in slow circles, leaves on plants below moving up and down as their growing tips quest 360 degrees around, flowers bending and shaking, stems trembling toward unseen supports and sending out tendrils that dance complicated patterns until they encounter something to grab onto, at which point they quickly pull the rest of the plant to themselves.
Beneath the ground, tiny rootlets burrow through the earth, tasting for moisture and nutrients, responding to the pull of gravity, possibly other imperatives known only to the plants. Seeds burst open, roots hurrying down, stems shooting up in frantic haste to reach the light.
The movement of the stomata on leaves as they transpire air into and out of the plant, when speeded up, looks remarkably like breathing...probably because it is breathing.
Then there are the incredibly fast movements (fast enough for us to see in real time, which means really really fast in plant time) of carnivorous plants closing on their prey, or the Mimosa pudica folding its leaves when they are touched. Some plant tendrils respond to weights as slight as .00025 of a gram. How can they do these things when the have no nerves to transmit stimuli, and no muscles to contract tissues?
In my next post on this subject I'll speculate some more about plant actions, and also how they might acquire and process information about their environments. Leaving you with an interesting little video...
Major source material, The Secret Life of Plants by Peter Tompkins and Christopher Bird. Available from Amazon.
(by Marlie Graves)