Do plants remember? Do they communicate? What is the extent of their interaction with their environment? In this classic Stuff to Blow Your Mind series, Robert and Joe dive into the amazing world of plant intelligence research. (originally published 04/12/2022)
Hey, you welcome to Stuff to Blow Your Mind. My name is Robert Lamb and I'm Joe McCormick, and it's Saturday, so we are heading into the vault for an older episode of the show. This one originally aired on April twelfth, twenty twenty two, and it's part one of a series we did on the question of whether plants have memories or anything analogous to memories. I remember thinking the series was really fascinating, so it should be a treat to re explore. Here you go. Welcome to Stuff to Blow Your Mind, a production of iHeartRadio. Hey, welcome to Stuff to Blow your Mind. My name is Robert Lamb and I'm Joe McCormick, and today we're going to be talking about an interesting and perhaps hidden property of plants. And to start us off, I wanted to read a selection from one of the lesser known works by the English Romantic poet Percy Bis Shelley. This is a poem called the Sensitive Plant. Rob Am, I write that you'd never heard of this one before. No, I you know, obviously I've read a little bit of Shelley here and there, but this must I'm assuming this is a deeper cut it is. I think it was one of the final things he wrote before his death, so this would have been I think sometimes in the early eighteen twenties, and it was published I believe as a standalone work at least at some point it was. I was reading through like a book version of it on that had been scanned into Google Books, and every other page on it was like washed out on the scan, so that was beautiful. But yeah, this one's kind of weird. It's it's not one of his best poems, but it has some really great lines in it. So I just wanted to read just a selection from it. It's too long to read in full, but this is an exerpt from the end of Part one of The Sensitive Plant by Percy BIS. Shelley. For the Sensitive Plant has no bright flower. Radiance and odor are not its dour. It loves even like love. Its deep heart is full. It desires what it has not the beautiful, the light winds, which from unsustaining wings shed the music of many murmurings, the beams which dart from many a star of the flowers whose hues they bear afar, the plumid insects, swift and free, like golden boats on a sunny sea, laden with light and odor, which pass over the gleam of the living grass, The unseen clouds of the dew, which lie like fire in the flowers till the sun rides high, then wander like spirits among the spheres, each cloud faint with the fragrance it bears, The quivering vapors of dim noontide, which like a sea over the warm earth, glide in which every sound and odor and beam move as reeds in a single stream, each and all, like ministering angels, were for the sensitive plant, sweet joy to bear, whilst the lagging hours of the day went by like windless clouds over a tender sky, And when evening descended from heaven above, and the earth was all rest, and the air was all love and delight, though less bright was far more deep, and the day's veil fell from the world of sleep, and the beasts and the birds and the insects were drowned in an ocean of dreams without a sound, whose waves never mark, though they ever impressed the light sand which paves it consciousness only overhead. The sweet nightingale ever sang more sweet as the day might fail, and snatches of its elysien chant were mixed with the dreams of the sensitive plant. Ah, very nice. Yeah, so I don't think it's one of Percy's best poems. Like I was saying, the rhythms a little too regular and singsongy. Sometimes. Some of the rhymes are a little obvious, you know, the rhyming love with above and all that. You could imagine like a an eighties rat bait thrown in the background some of those, or this could be a song like every Rose has its Thorn, you know, a monster ballad. But there are also lines. I really love the dew which lies like fire and the flowers, and the nighttime as an ocean paved under with the sands of consciousness. But it's esthetic qualities aside. I think it's really interesting that Percy is suggesting, in his unorthodox and emotionally charged view of the world, that this particular plant, the sensitive plant, which is a species of plant, may somehow have a kind of humanity of its own, like a soul or a mind, or, as I believe he implies later in the poem, an afterlife. So you might wonder why would he say that about this species of plant, which he acknowledges is not a particularly beautiful flower. It's it's a mimosa, so it's got a little pink, puffball kind of thing. Well, I think the answer is actually tied to some of the biological qualities of the sensitive plant as a species. So the sensitive plant is one of the mani names of Mimosa pudica, pudica being Latin for chaste or modest, shamefaced or bashful. And this is a flowering plant in the family Fabasi, which is the pea or lagume family, which means yes, this plant is a cousin of the common being. So we are we are dealing in bean can today, we're getting into into supernatural territory then, oh boy. Mimosa pudica is native to South and Central America and the Caribbean, though since transatlantic contact it has spread to all other parts of the world. I think it's pervasive throughout the tropics, and it's also known by tons of different names. It's called the humble plant, the shame plant, the touch me not, and all of these names connect to the most striking feature of this species, which is that it is a plant that recoils when touched. And this is one of a handful of examples of rapid movement in the plant kingdom, movement on the timescale that we would normally associate only with animals. So, if you want to picture it, the sensitive plant is a spiny little shrub that grows up to about a foot off the ground. It has these pink flower puffs and small forking branches with compound leaves. So to picture the leaves of this plant, they are the ones that kind of like a feather, you know, with a stalk running up the middle, and then lots of tiny, little pinile leaflets shooting out from that middle stalk, parallel to each other and perpendicular to the stalk, like the teeth of a comb, or like the barbs of a feather. And to see the sensitive plant in action, all you need to do is touch a finger on one of these branches, and suddenly what happens is the leaflets all fold inward like a closing suitcase. And then sometimes even the branch or the stalk that they're on will droop away, the stimulus will droop down. From what I can tell, there is not yet a full consensus on the main function of this shrinking behavior in the wild, like, why does it do that? But botanists have long suspected that it's some kind of defensive action by the plant to protect its leaves from grazing herbivores or insects. And this could actually work in multiple ways. So one of them is that maybe it works by physically moving the leaves away from a grazer. You know, something comes, spides, it's munching on the leaves, and this causes the leaves to kind of pull away from the mouth. Or it could work by hiding the leaves so you know, it is disturbed something is around, it might be trying to eat the plant, and by closing up it makes it less obvious where the leaves are. Yeah, and I guess one can imagine this working within the context of a you know, an enormous grazing animal that is eating a lot of plants. And it's maybe not gonna opt to really get particular about this one if this one has made itself smaller, you know, retreated into you know, amidst other plants, et cetera, Like it's just going to keep eating whatever is readily available to eat, right, But I think there's also a focus on insects maybe insects or also the reason it does this, and it could also work maybe by startling a predator like an insect or grazing her before because of course plants don't usually move rapidly like animals do. So you know, if you're an insect or whatever that's grazing and then suddenly there is movement on the timescale of animal movement in your in your vicinity, that might startle you and send you on the run. Yeah, on the timescale of animal movement. That's that's key. Because of course, the other main plant we think of in terms of this is the venus fly plant, which you know, we'll come back to, uh that. You know, that is a plant that is acting aggressively on the timescale of of of animals in an attempt to capture set an. But here we see the reverse. Here we see something that is that is acting, you know, defensively, that is moving away from us, that is not saying I want to touch you and envelop you, but I would rather not touch you at all. Yes, I would rather not. I would prefer not to. Yeah. So usually after a sensitive plant closes up its leaflets and droops away, it will reopen within some short time period, maybe only a few seconds, sometimes a few minutes, but it doesn't take long. It'll it'll open back up, get those leaves out there again, and start all over. And the sensitive plant also has a circadian rhythm to its closure, because it will close its leaves in the darkness and then reopen them in the daylight. Now, I found a wonderful post on j Store Daily by Rebecca Friedel about the history of Mimosa putica and also a similar Old World plant called Biophytum sensitivum, which is actually not a close relative of the sensitive plant, but does almost exactly the same thing with its leaves. So it looks like this would be a case of convergent evolution. But this article points to the work of a sixteenth century Portuguese naturalist living in India named Christo baal Acosta, who authored a book in fifteen seventy eight called Tractado de las Drogas e Medicinas de las Indias Orientales or Treatise on the Drugs and Medicines of the East and East Indies. I really wanted to find an English translation of this so I could quote it directly, because it sounds like it's a hoot, but I could not, So I'm going to have to rely on a couple of secondhand summaries, including a Friedel's article here. But anyway, in this book by Christo Baal Acosta in the sixteenth century, he describes a plant among the medicinal herbs of India called the yerba della more or the herb the herb of love? Do you ever say herb with the H pronounced? Sometimes? I'm afraid I'm going to keep doing that. Yeah, sometimes it slips out. Yeah, I don't know why. I try to fix this in my brain by like saying the name herb without the H pronounce. So like I go, I said, herb Herbert Hoover, Herbert Hoover. That'llfens it. Well, yeah, I mean it's easy to fall into because herbivore, herbivorec Anyway, why the herb of love? Why would it be called the herb of love? Well? Acosta says that, according to an Indian physician he talked to, the herb of love was a potent seduction drug with a one hundred percent success rate never fails. And after this passage, Acosta has an aside to assure readers of this medicinal catalog that he definitely never personally tried to use the sex herb, never, not once. Probably a good thing considering that other more well known sex herbs, if you will, are you know essentially poisons? Right? But aside from the dubious allegations about Cupid's aero type powers, this plant, the Herb of Love is remarkable for its ability to close its leaves rapidly, moving at the speed of an animal recoiling from a needle prick. And I was looking at another source which mentions Acosta. This is by JF. Veldkamp called Notes on Biophytom of the Old World, published in Taxon in nineteen eighty nine. I cite this just because Veldkamp tells a story that Acosta claimed he knew of a philosopher in Malabar, so region along the southwest coast of India. A philosopher who lived in Malabar who was so tortured by the mystery of the Herb of Love's rapid movement that he literally lost his mind trying to study it. He was like, how does it move? And that was it for him. No word on whether that guy ever used it for Cupid zero type purposes. Yeah, because again, and this will going to be something that will will discuss later as well. I mean it's it's acting in a way that other plants do not act. It seems unnatural, right, I mean if I had never seen a rapidly moving plant before and I just stumbled across one of these in the wild saw it folding up like that, I would be freaked out. I don't know what to think of this. I mean, it's hard to imagine because I grew up with venus flytraps, you know, Like I remember when I was a kid and I would have like one of those really boring weekend days where my mom wanted to go to the plant nursery and get some plants around the house. And I think my consolation there was that a couple of times I got a little potted venus flytrap. Yeah. They're pretty fun little plants. They always have a huge container of them out at the at the Bananical Garden in Atlanta for the kids to interact with and inevitably stick little sticks into their into their their their mouths, if you will. Right, so, we know about that one. But if you're previously unfamiliar with a plant like that, or or one of these leaf closing plants like Mimosa pudica or biophytum. I imagine it would be shocking. Yeah, I mean, we are hardwired really to topact that sudden movement in the grass might be something dangerous. It might be a snake, for example, Like, that's the first place my mind goes. If I'm on a walk and there's some sort of rustling in the bushes, it might be a snake, or it's something like a chipmunk or a squirrel. Probably not a squirrel because they're a bit bolder, but certainly the snake is never far from one's mind. Very true. So anyway, for several centuries there was confusion about how to taxonomize this plant that Christal ball Acosta was talking about, the Herb of Love, and Freedell points to an eighteen twenty five volume of the Botanical Register which says, hey, we know about this plant from South America called the Mimosa pudica. It does that leaf shutting thing. So maybe this herb of love that Acosta is talking about in India in the sixteenth century is actually the same plant. After all, it does seem that pretty quickly after transatlantic contact, the mimosa spread all around the globe. But now that doesn't seem to be the case. Botton are pretty clear that the herb of love was actually this other species I mentioned a minute ago, Biophytum sensitivum and Freedel rights. This was funny quote. Perhaps the erotic claims Acosta made so enthralled some that they failed to turn the page to the next entry on Erba mimosa, a likely description of the actual mimosa putica. Do your homework, guys, come on. But anyway, I was thinking about this mechanism, so immediately when I see a plant with rapid movement like this, the leaf closing behavior, I wonder how on earth does it do that? Because, of course we can move rapidly, but we can only do that because we have a nervous system and a muscular skeletal system muscles. Plants don't have either one. There are no muscles and a plant. So what mechanism could a plant use to contract on the order of seconds. Well, scientists have actually figured out the answer to this one. The types of movement on display in the sensitive plant and the rapid moving plants like the venus flytrap are known as seismoonastic movements, and these are an example of a bigger category of nastic movements, which can be defined by their difference from another type of plant movement called tropisms. Now, tropisms, I think we've all seen in action. You know what this is? View ever had house plants? A tropism is growth in a specific direction based on an external stimulus. So plants will grow toward a light source. In fact, right in front of me. Right now, I have a potted plant here on my desk, and over time its leaves all start reaching out for the lamp next to it, until I turn the pot around, and then gradually they all start to hook back in the opposite direction. And it just now struck me for the first time. That might sound kind of cruel, like I'm toying with it, but I really don't think the plant's feelings are hurt. Another example this would be trees seeing to grow around up power lines. Sure, yeah, So plants can grow in different directions responding to objects or stimuli in their environments. Nastic movements, in contrast to tropisms, are not oriented in the direction of a stimulus, but rather are fixed reflexes that are determined by the plant's anatomy. So, for example, a venus fly trap shows a nastic response. It doesn't go off in a particular direction to catch a fly, but rather, when it senses movement in its trap area, the hinge closes. So it has a predetermined, a directionally predetermined movement that is in keeping with the plant's anatomy, not in an adaptable direction. And the sensitive plant is another example of a nastic response. And I think it's interesting to note that the stimulus direction dependent movements of plants tend to be very slow, very very slow, and based on growth. Well, the few plants that are able to move rapidly in all cases that I'm aware of, certainly in most cases their movement is constrained to these directionally fixed reflexes. Now, of course, we animals have the best of both worlds, right, We can move rapidly and we have the flexibility to respond in whatever direction makes sense given the stimulus. But you know that's because we're different types of creatures, different anatomy, different energy requirements and so forth. But okay, that's nastic movements now, seis monastic movements are nastic movements that are triggered by touch or by vibration. Now again without muscles. How it all this work? How does the nastic movement actually happen? Well, here we come to a really excellent new word I learned. The word is terger spelled tur gr. It's a good like a leather diaper, Barbarian name. But it also it is a name for something that happens within plants. It's related to the word turgid or turgidity, and so within plants there is a principle called turger pressure. And one simple way to think about turger pressure is that it is like water pressure inside a plant. So you think about the difference between a wilted flower baking dry in the sun. You know it's parched, and you see it drooping over, and then you think about what that flower does after you water it. If things go well. Usually you give a wilted plant water and its leaves and stems stops sagging and they become rigid again. It stands straight up the you know, the it's it's almost like it's inflated like a balloon. Yeah, And in some plants it's it's it's amazing the difference just a quick watering can have. We have a linen bomb, and I always find that that one among our plants is the first to just immediately seem to give up the ghost and start wilting away. But then you know, you give it enough water and it's just back, just a bushy and full of fly as ever totally. In fact, you might have even observed this, not with a live plants, but giving some veggies in the kitchen a soak or even just to wash. This is a good trick for resurrecting what appeared to be wilted salad greens that are past their prime. You might think they're no good, you know, you got to toss them. You would be surprised how salvageable some greens are after a soak in cold water. Really like like spinach, the surf of spinach. I don't know if I ever tried it on spinach, but I've tried it on other types of greens, like you know, arugula and things like that that are you know, they're starting not not like if they're getting slimy, you know, but if they're just like they're clearly they're getting desiccated and wilted. It looks like, oh, these are going to be no good. Soak them in some cold water. They might come back to life and be crisp again. Okay, I didn't know about this trick, but now I will have to try this sometime. But anyway, So, turger pressure is when a plant's cells are swollen with water so that in the inside of the cells, within the plasma membrane, the water pressure is actually pushing out against the cell wall. And so when turger pressure is high, the plant is said to be turgid, and so to come back to the sensitive plant when the leaves are touched or disturbed and electrochemical chain reaction is set off, It's sensed by cells in the leaves and then it sets off this electrochemical chain reaction that eventually ends in water gushing out from so called motor cells at the base of the leaflets that were previously turgid. So the sudden loss of turger pressure the cells purging their water contents causes the leaflet to move, basically to collapse at it's hinge, and this is known as turger movement. So in a strange way, you can think about it like the plant moving by causing itself to very selectively and rapidly wilt like a parched plant. Then over the course of the following minutes, turger pressure can be restored and the leaves go rigid again, and they go back to their extended state. But to come to the next thing, even more astonishing than the plant's ability to behave physically in ways that seem more at home in animals with muscles, is potential evidence that the Mimosa pudica may also, in a qualified sense, behave mentally in ways that seem more at home in animals with brains. Specifically, there has been research arguing that this plant, an organism entirely without a brain or without a nervous system, actually has its own rudimentary form of memory. And we'll talk about one of the studies allegedly showing this in a minute, But first I thought it might be good to spend a few minutes disentangling concepts about the alleged mental or cognitive properties of plants, because I think once you get into this area, you run a whole gamut of different types of claims of extremely variable evidential backing. Yeah, and you also get into into areas of confusion over like what constitutes animal intelligence and human intelligence and so. Yeah, so I thought it might be helpful to sort through some sort of general ideas regarding the nature of plants in Western thought. Fourth century BC thinker Aristotle, of course, casts along shadow, and he wrote that plants have a vegetative soul or two threpticon, which I believe just means the vegetable soul, not to be confused with two megatherion, which means the great beast in Greek and is of course a Celtic Frost album. But I couldn't help but think of that when I was reading about two threpticon. Yeah, a lot of these well, so there were people in like the nineteenth century and stuff who were very interested in the sensitive plant, and I think a lot of them made references back to Aristotle, like this is what Aristotle was talking about. Plants have a soul, they can feel right, but of course yes and no right, because they are two important things to keep in mind about all of it. First of all, he attributes nourishment and reproduction to the plant soul, and we have to remember that the Greek notion of a soul or suka is rather different than modern or even early Christian notions of a soul. We're not talking about like an inner ghost person that moves on and has an afterlife, that sort of thing. This would be more like the concept of a mind or or would it be like the idea of an animating breath. There are a lot of different ideas of things that get translated into English as soul from the ancient world. Yeah. I was reading about this in an excellent paper that I will probably continue to refer to in this series by Michael Martyr from twenty twelve in Plant Signal Behavior titled Plant Intentionality and the Phenomenological Framework of Plant Intelligence. And in this he writes that the soul in this context, in Aristotle's context, is quote a set of active capacities of an organism, not an invisible entity connected to the divine. Okay, that makes sense. So the soul is sort of like the essence of the organism. It's like what the form of the organism apart from its physical body. Right. And while the vegetative soul here is defined by nourishment and reproduction, animals and humans additionally have capacities of sensation and rational thought added atop these baser soul characteristics. Now, I think an interesting division there is that, So it's attributing animals and humans with sensation and rational thought. I think a lot of people have made what seemed to me to be pretty spurious claims about evidence for rational thought in plants. But I would say it's completely uncontroversial that plants experience a form of sensation. They can gather information about their environment, and they do constantly. Yeah, but in Aristotle's hierarchy, you have basically of animals, and then you have plants, and they of minerals. And there's also this added caveat that aspects of the vegetative soul continue on into forms that follow, which which might not be all that helpful in what we're thinking about here, but perhaps bears mentioning. Now, aristotle shadow again is long, and we see his ideas carried on into medieval Europe. Thirteenth century CE thinker Thomas Aquinas wrote in Puma Theology that quote, the very fact that the acts of the vegetative soul do not obey reason shows that they rank lowest lowest, lower than minerals. Or was he not lower than minerals? But I think it was in reference to animals and of course humans. Yeah. Now, one thing that that Martyr points out is that while the Aristotle view here, you know, it kind of used plants as baser and that they're only carrying out nourishment and reproduction. But he writes that that's that's actually it's actually quite impressive within the modern context of certainly planned intelligence research, because these impulses nourishment and reproduction quote entail complex decisions related to the avaiability of resources. Now that's interesting because that could be on one hand, very true, but also could easily be misinterpreted to lead people to unjustified conclusions. And I want to get into a little more disentangling on concepts in a minute here, but yeah, flag that. Yes, Martyr also adds quote Additionally, plants express almost all known neurotransmitters, confirming the extension of twothrepticon well beyond the activities Aristotle and his followers allotted to them. Hence, the lines of demarcation between the higher and the lower capacities, between consciousness and non consciousness, and by implication, between biological regna are not as rigid as classical thinkers believed. And there are a few other strains of more modern thought that Martyr shares He points out that, according to late eighteenth and early nineteenth century German philosopher Hegel, plants are passive, they have negative selfhood, and they lack quote an organismic whole. Okay, I don't know what that means, but that's Hegel. Yeah, not a not a plant fan. Nineteenth century English naturalist Charles Darwin, on the other hand, this I believe was like a later thing that he wrote about. But he had the root brain hypothesis that held that the root apex of a plant served as a brain like oregon, that was both sensitive and capable of navigating soil in search of resources. Now, I think it might be going a little overboard to call it brain like, but Charles Darwin was clearly enthralled by plants like the venus flytrap, Like he got really excited about what this means. And maybe we can come back to Darwin in part two of this because I think some of his ideas might connect more to to some of the research we're going to talk about later on. Yeah, it's my understanding, and I believe the author mentions this that some of these ideas that Charles Darwin had regarding this root brain hypothesis like they've people have come back to them in modern plant intelligence research and said, well, yeah, there's more to this than the people of Darwin's day thought. Then there's also a nineteenth century German philosopher, Frederick Nietsche, who is very much I believe, inspired by Darwin. In this wrote that a plant's nourishment and growth are expressions of its will to power, or the wills whore mocked, which he identifies as the core driving force behind human beings. Oh my god, So this this potted plant in front of me, when it reaches for the lamp and then I turn it around, I am thwarting its will to power, but I am like the naysaying crowd that it must rebel against and show its might. Yeah, and every day you don't kill it, you make it stronger. Right now. In Eastern thought, there are of course strong traditions of all of this, as discussed in, among other many sources, in Richard Nespit's The Geography of Thought. China's Taoism and Japan's Shintoism both emphasize the spirits of animals, plants, natural objects, and artifacts. And for my part, I've been reading a little bit about this um earlier when I was looking for things to cover for artifact and monster fact episodes. But you know, I don't want to steal any thunder from some possible potential episodes long or short form about these. But you know, we have strong folkloric, legendary, and mythological concepts of plant animal hybrids, which, of course, with all hybrids, they certainly perform various functions in symbolic, metaphoric and supernatural thought, but they also raise the question inevitably of animalness in plants and plantness in animals. You know, like you you can't think of something like say a screaming man Drake, or say the vegetable lamb of Targary. You know this this sheeplike thing that is growing out of the ground that is a plant but also seems like an animal, Like you can't. I don't think you can really have a concept like that without it's sort of by blurring the lines, by invoking the hybrid, making you think about the characteristics of the opposite side that are present in this side. Yeah. Yeah. In fact, I think several years back we did an October episode called something like the Killer Tree that was a Legends of Trees that would eat people. It's a surprisingly common recurring motif, though apparently has no basis in real biology. No, but I mean certainly not at the not not on the the animal time scale of things, but I guess on the plant time scale of things. Yeah, you can get into more nuanced discussions of plants eating people, plants eating human corpses and that sort of thing, right, but not the active predation like in that Oh it's that is like a William freed Can movie about the killer tree that that gobbles people up. Oh my gosh, I don't remember this one. Okay, yeah, we'll have to revisit. But there, Yeah, there are clearly a lot of killer trees and tree I mean you have things like the ants, right, yea trees walking around like humans. And yeah, all these concepts. They they they're performing a number of different functions. But I think one of them is that it inevitably makes you think about about plants and animals, what do they have in common? In what ways do they differ in? Indeed? Yeah, in what ways might they be more alike than we often realize. Another thing is that as we're going forward talking about research potentially indicating something like a plant basis for memory or learning. I think we also have to be very careful because the whole the realm of plant, so called plant cognition research, I think, has a history that is filled with stuff that is not so great. Like there are a number of different concepts regarding the hidden complexity of plants that people seem to get confused with each other. And this is unfortunate because these topics range from what appears to me to be maybe controversial but at least potentially evidence backed biology, and that would be things like, you know, some of the memory research we're going to talk about, all the way over to pure pseudoscience and paranormal stuff. And just to give some quick flavor of the latter end of that spectrum, I'm reminded of something we talked about briefly in an episode that we did a long time ago. Robie, remember when we did the Science of Stranger Things at New York Comic Con. Yes, I do remember this, So it was in the context of that episode we were talking about government research into psychic and paranormal phenomena during the Cold War, which absolutely did happen, and the extent of it is hilarious. But I read a couple of whole books about this. Of course, one if you want to quick read that's very funny is The Men Who Stare at Gohost by John Ronson. But also there was a book by Annie Jacobson that was a big, complete, sort of history of the Stanford Research Institute and all of these normal government research projects that were fueled by Cold War paranoia but looked into They looked into things like remote viewing and telekinesis and stuff like that, and unfortunately, I think a lot of that was just was just tricks and poorly designed experiments. But but but one brief episode from this, one of the people we talked about in that episode was a CIA interrogation expert named Cleave Baxter, who specialized apparently in narcotic and hypnotism based interrogation techniques and then later in the polygraph and according to a twenty thirteen New York Times article I was reading about Baxter by Josh Eels, Baxter developed a method for conducting polygraph sessions called the Baxter zone comparison technique, which according to this article, is still used in polygraph tests today. So cool. Anyway, later in his career, Baxter quite famously became upset with the idea that plants could read our minds, and he claimed to show it with experiments. So the discovery of this The story goes like this. One night in nineteen sixty six, Baxter stayed up all night, he was drinking coffee, and he got an amazing idea. He would hook a potted plant up to a polygraph machine. I guess, I don't know if he was going to see if it was telling lies, or maybe you just I don't know. So allegedly this plant was a quote corn plant or dressina fragrans, which, in a confusing twist, is completely different from the plant za maze, which is the grain plant that produces maize or corn, the food. So this is called a corn plant, but it's not the corn that would be planted in as a crop. The corn plant had been a gift from his secretary, intended to brighten up his office, which I have not seen pictures of. I don't know what was in there, but I'm imagining a kind of dungeon full of chairs with leather straps on them and needles full of quack truth serums. So yeah, you can imagine some plants would be nice, Yeah, you want to get some corn down there. So from here I just want to quote from the article by Eels summarizing this experiment. Quote. In human subjects, a polygraph measures three things pulse, respiration rate, and galvanic skin response otherwise known as perspiration. If you're worried about being caught in a lie, your levels will spike or dip. Baxter wanted to induce a similar anxiety in the plant, so he decided to set one of its leaves on fire, But before he could even get a match, the polygraph registered an intense reaction on the part of the dressina. To Baxter, the implication was as indisputable as it was unbelievable. Not only had the plant demonstrated fear, it had also read his mind. So Baxter became convinced that plants had psychic powers, consisting of a sensibility that he called primary perception, which they could use to read our minds and emotions from Afar and upon this disc every he did what any responsible seeker of the truth would do. He went straight to the popular media, and there was a book based on his claims, and apparently he did a TV spot, multiple TV spots, but I like Johnny Carson and stuff, but one of them I wanted to note was, apparently with Leonard Nimoy, was this in search of. I don't know if the timeframe is right for that. I don't know if the timeframes right either, but yeah, Ansling makes me think of in search of. And unfortunately, skeptical scientists were unable to reproduce his results. They tried to do the same thing and got nothing. But if you poke around about this on the internet, you will find many believers even today, still overflowing with faith in Baxter's claims. It's one of those ideas that lots of people just seemed to like. It feels really true and wholesome and good to believe. Yes, plants can think, they can feel, they can know what we're thinking if we tell them, or maybe even if we don't tell them, if we just think it really hard, they can detect it somehow. But obviously there are there are major problems if you're trying to put together a coherent, scientifically informed worldview. First of all, I would say the theoretical basis is weak. Like you know, we could always discover something new, but it is not clear that there's any kind of physical mechanism that could allow something like that. And then the second part is just the empirical basis, like the controlled experiments by skeptics don't find the same thing. So yeah, this appears to be nonsense. I can't help but wonder if okay, this experiment was sixty six. Frank Herbert's Dune was first published in sixty five, and of course has the very early on in the novel, has the scene where we have the benijesra at test of the box and the com jabbar the box, which of course makes you feel like your hand is burning and on fire. And here in this test behalf part of the plant is actually caught on fire. Wow, that's interesting. Yeah yeah. And the box is supposedly a kind of polygraph of its own yeah yeah, yeah yeah, And of course you have the benegestrate, yeah, truthsayers and so forth. Though, I think in our episode on that did we both come to the conclusion that we think that the real power is the box actually does nothing and it's just all it's all the reverend mother like she's the real test. Yeah. I think it's ultimately unknown, but we did. I think we both liked that idea the most. Yeah, it felt the most herberty of the ideas. It's just a prop But anyway, So to come back to all this, so we're going to be talking about plant memory research. But I think I want to be clear that if you say that a plant could have such a thing as a memory or an ability to learn, that is truly surprising and fascinating. But it is not the same thing as saying or showing that plants can quote think, that plants are conscious, that plants have emotions, or that they get upset when you say or do negative things around them, all of which are claims that people have tried to make over the years, but which seemed to me to be lacking in evidential basis, with the possible exception of quote thinking under some very broad or inclusive definitions of what counts has thought. Yeah. Like Another area related to this is the relationship between plants and sound. So can plants respond to sound, Yes, they can, But can do plants then benefit from listening to music? No, there's there's no evidence for that. But I mean, this was an idea that was very much in the zeitgeist, especially in the nineteen seventies. That's where there was actually a wonderful album that came out, an early electronic music album by Mort Garson, who is a you know, early synth wizard who did a lot of a number of different projects under different names, but he put out this this album titled Mother Earth's Plantasia, and it is supposed to be music that you play for your house plants, and your house plants then benefit from it. I don't think house plants actually get nothing out of listening to this album, but it's a wonderful ambient, experimental electronic album for humans. I love this. I would say I'm all for playing music for your plants. I don't think it does anything for the plants, but playing music for your plants might do something nice for you. Yeah, yeah, just like the plant. The presence of the plants certainly can have a very pleasant effect on the human psyche. So can ambient music. So double up, have them both and benefit. But anyway, before we end part one of the series, I did want to look at at least one of the studies that claims to find evidence for what you might call memory learning or habituation in plants. And in the next episode we'll come back and talk about some reaction, criticism, and follow up of these types of ideas. So this is not without its accompanying controversy, but I thought it would be at least worthwhile to look at like what the evidential claims of the recent research are. Earlier we mentioned that scientists are actually not one hundred percent sure why Mimosa pudica closes its leaves, though it is generally believed to be some kind of defensive reaction to prevent the leaves from being eaten by grazing herbivores or insects. So if that's the case, you might wonder, well, why don't the plants just keep their leaves folded up all the time, then they'd be protected always. Why do they have to do it rapidly suddenly? Well, because if they were to keep their leaves closed all the time, the plant would be drastically reducing its ability to collect sunlight and feed through photosynthesis. And this is the classic risk reward paradigm that we know well with all kinds of animals. You have a small prey animal that might be much safer if it stays in its cozy little burrow all day, but if it never leaves, it foregoes opportunities to get food. It needs to go out to do the things it must do to sustain its life cycle and reproduce. So it's got to find food, it's got to find mates, and you know you're not going to get that just sitting in your hole. You could say the same is true for this plant. So the evolutionary logic that drives the folding behavior of the leaves and the sensitive plant will reward the folding in scenarios where it actually protects the leaf from predation, but it will punish unnecessary folding, which wastes precious opportunities to harvest the sunlight. And we've already seen a couple of demonstrations of this balance. One is that the leaves tend to fold at night time, when there's no point in being exposed because there's no sunlight to absorb. And another is that once the leaves close in response to a seismic stimulus, they reopen again, usually within a few minutes. They're ready to get back to the buffet. But to continue the logic of this risk reward balance, it would also obviously benefit the plant if it had a mechanism for discriminating between a potentially dangerous seismic stimulus and a harmless one. And you can imagine scenarios in the wild where plants are repeatedly shaken in some way or subjected to physical contact with objects in the environment, maybe by wind or something in a way that is not actually a threat to the plant, where closing the leaflets every time that happened would be pointless and harmful to survival. So do these plants have a mechanism that allows them to discriminate like that? And according to this following study, it looks like maybe they do. So. This was a study published in Ecologia in twenty fourteen by Monica Gagliano, Michael Renton, Marshall dip Chinsky, and Stefano Mancuso called experience teaches plants to learn faster and forget slower in environments where it matters. So the authors write in their abstract quote, the nervous system of animals serves the acquisition, memorization, and recollection of information. Like animals, plants also acquire a huge amount of information from their environment, Yet their capacity to memorize and organized learned behavioral responses has not been demonstrated. In mimosa pudica the sensitive plant. The defensive leaf folding behavior in response to repeated physical disturbance exhibits clear habituation, suggesting some elementary form of learning. So how do they actually demonstrate this, Well, they did a series of experiments, but one of their models is they took potted specimens of Mimosa pudica and they mounted them on this contraption that would repeatedly drop the potted plant a distance of fifteen centimeters onto a padded surface. And these drops were organized into repeated sessions of multiple exposures. And sure enough, the plants, after they were repeatedly exposed to the same fifteen centimeter drop, started reopening their leaves more quickly and eventually started ignoring the stimulus more or less entirely, just keeping their leaves open during a drop. And that's really interesting. It might seem to indicate that the plant is becoming habituosed to this particular thing. It's like, okay, being dropped fifteen centimeters is just something that happens. Now, This is just how things are. I know what it feels like. It doesn't hurt me. I'm over it, by the way that I guess I am anthropomorphizing there, So I don't mean to imply that it is actually reasoning out in semantic logic like that, but that's to give you the idea that it's somehow becoming habituated to something that's happening over and over again without hurting it, and it's just learning to ignore that thing. Now, there's an obvious other explanation if this was all they discovered. What if this was just the plant's leaf closing mechanism getting worn out over time, It's just becoming exhausted and running out of the juice that it needs to use to close its leaves. Well, the researchers they thought about this, and they controlled for this by introducing a new novel stimulus after the plant became habituated. This was the shake, so different from the drop, but it would also stimulate the seismonastic closure or of the leaflets to shake the potted plant. And they found that even when a plant had become desensitized to the drop, apparently through habituation, it would still close its leaves just like normal when given a shake. So this would seem to help rule out the idea that it's just the plant's leaf closure mechanisms becoming exhausted by repeated use. Now, there are some more interesting details from this one that we might get into in the next part of this series. For example, they found that apparently this habituation to the fifteen centimeter drop was still present weeks later after the initial sessions, and that it was variable and adaptable depending on the hostility of the conditions, like the light conditions in which it was happening. But maybe if we get into those, we can do that in part two, because I think we need to wrap up part one for now, but I'm so excited all the things we get to talk about when we come back next time. More research on plants in memory. If plants do in fact possess some rudiment reform of memory and learning, how what is the physical basis of that, given of course that they don't have brains, And what would that mean for our understanding of what intelligence and its subdivided parts are. Yeah, yeah, this should continue to be a fun exploration. And this is an exploration that we've we've been talking about doing for years, and I know we've had some listeners right in requesting that we cover this topic. So it's great to finally be able to dive in. All right, So we're gonna go and close it out, but we'll be back next time with more on this topic. In the meantime, if you want to check out other episodes of Stuff to Blow Your Mind, our core episodes come out on Tuesdays and Thursdays, we have a rerun that comes out of vault episode. On the weekend, we do listener mail on Monday, we do a short form artifact or monster fact on Wednesday, and on Friday we set aside most serious matters and just discuss a weird film on Weird House Cinema. Huge things as always to well, actually to our regular producer Seth Nicholas Johnson, and thanks to our guest producer today Paul decand Paul really appreciate you sub an in for us today. If you would like to get in touch with us with feedback on this episode or any other, to suggest a topic for the future, or just to say hello, you can email us at contact at stuff to Blow your Mind dot com. Stuff to Blow Your Mind is production of iHeartRadio. For more podcasts from my Heart Radio, visit the iHeartRadio app, Apple Podcasts, or wherever you're listening to your favorite shows