From the Vault: Plant Memories, Part 2

My name is Robert Lamb and I'm Joe McCormick, and we're back for part two of our series on the possible evidence for memory and learning in plants. Now, this is one of our series where if you haven't listened to part one yet, you really should go back and do that one first, since we clear a lot of the ground for what we're going to be talking about today. This is one that I think is going to be

kind of hard to jump in in the middle. But in that past episode, for a refresher, we talked about a plant called known as the sensitive plant or the humble plant, the shame plant that touched me not scientific name Mimosa pudica, which is one of the few plants in the world that displays rapid movement or movement on the time scale usually associated with animal life, and we talked about experiments from twenty fourteen that appeared to show

a form of rudimentary learning called habituation in these plants, where for example, if you take a potted Mimosa pudica and you drop it the exact same way over many training sessions, it will adapt so that it no longer closes its leaves defensively in response to a drop, but it will still close its leaves in response to other

types of disturbance. So if this type of finding holds up to scrutiny and replication, it would be evidence that even though this plant has no brain, it has some kind of internal mechanism for learning from experience in order to maximize its fitness. And of course, at some level, learning requires a form of what we would think of

as memory. In order to learn from the past, you have to have some way of being changed by the past, to store the past within you in an organized way that can influence future behavior, which, of course we do with our brains. But if plants in some cases also do this, it's a great question what is the mechanism They obviously don't have brains. And finally, in the last episode, we tried to disentangle different claims about so called plant cognition,

which is a controversial concept. We noted that memory is not the same thing as reasoning, which is not the same as consciousness, which is not the same as emotion or communication or or or plant like psychic plant mind reading, which some people have also claimed evidence oft without much justification, and with the final point being that evidence for one

of these traits is not necessarily evidence for others. But today we're going to look at some more research that has been interpreted as showing plant memory or plant cognition in the past decade, as well as some reaction and criticism to that. Yeah. Now, in the last episode I

mentioned some music. I mentioned both Celtic Frost's metal album to Megatherian Uh and mort Garson's Plantasia, and both were kind of offhand references, and afterwards I was looking into it a little bit more, and I was first of all delighted to see that Plantasia is more widely regarded as a classic than I thought it was. Um, I was familiar with mort Garson's work, and um, you know, I was delighted that his work had recently been reissued

by Sacred Bones Records. I think I had to make do with some some some some bad copies back in the day. Sorry, we refresh on the on the mort Garson album, it was so mort Garson. It was a pioneer of electronic music and synth work. And he had a few different monikers that he used. He did some like some occult sounding sounds and so forth. But he also put out this album Plantasia, which was music to

be played for your plants very much. Jumping in on this The Secret Lives of Plants one, I don't want to say hysteria, We'll say popularity during the nineteen seventies. And as we discussed in that episode, and we'll discuss a little bit here. Yeah, this album is not actually going to help your plants out in any of your plants. Do not care about Mark Garson's discography as much as you do or I do, But it is a very

nice album for human listeners. Sure, And hey, as I said in the last episode, even if it doesn't actually do anything for your plants, which it probably doesn't no reason not to play it for your plants. I mean that sounds fun. Yeah, so I was delighted to see that, even though there was a New York Times article about this album's popularity and increased popularity I think in part due to the reissue, but also they were making the point due to the resurgence and interest in houseplants during

the pandemic, you know, don't. I don't know about about you, but I think I don't know if we actually picked up that. No, we did pick up more house plants. I think some of them were gifted to us. But we have all sorts of little succulents like hanging out all over the house that we accumulated over the past couple of years. I don't know the name for them.

At Rachel has some kind of houseplant that repeatedly produces buds, like I guess, stalks will come off of it, and you can separate them and turn them into their own new potted version of that same plant, kind of like getting a grimlin wet or something. Just you know, they repopulate and go all over the place. So I think we have had at least proliferation of existing plants. Yeah,

and house plants are great, no doubt about it. But on the other hand, I was looking around for stuff on this, and I was kind of taken aback at just how much content there is out there on the

Internet regarding playing music for plants. And while I didn't find anyone actually exalting the benefits of playing Celtic Frost for your philodendrons, there are pages talking about the merits of different musical genres alleged merits, i should say, for plant growth, including the idea that heavy metal can improve plant mass and fruit taste, provided that it's not too noisy or presumably too heavy beautiful. What is the best

thrash metal for your plants? I've got to assume downstream of this, some people who believe in this, really they think their plants have individual tastes, like my plants really love motor Head. Yeah. I mean, I think we said before death metal bands need to get in on beans and realize that in the folklore it canon, bean plants are closely associated with the world of the dead and

this should be embraced. Sure, Now, all this being said, yeah, not every source popping up on the subject is something that I would take to the bank at all. But plants do produce vibrations and can respond to sound vibrations. Now I got interested in this idea thinking about plants responding to sound, and I started wondering about a question. I think this is always something good to wonder about.

When you hear a claim about a life form, you think, what would be the original ecological relevance of this, like in the actual environment, not in a in a house or a lab or something. Why would this kind of stimulus be relevant? So I looked it up in the scientific literature and I did find some interesting examples. One of them was a paper published in Ecologia in twenty fourteen by HIGDM Apple and Reginald B. Cocroft called plants

respond to leaf vibrations caused by insect herbivore chewing. And this study found that if you reproduce the sounds made by a caterpillar feeding on a leaf and then expose those sounds to what's known as a thail cress plant, the plant will respond by producing higher level of glucosinolate and anthocyanin, which are defensive chemicals. So, if this finding is sound, then the plant does actually detect sound, and it is ecologically relevant. Sound is an indicator of nearby predation.

The plant is it is being threatened by what is producing this caterpillar eating sound. Yeah, and there's another study that I believe came out the same year, conducted by Italian botanist Stefano Mancuso, who found that roots could seek out buried pipes of running water seemingly attracted to the sound.

So again, if if these results hold up. Basically, the idea here is you have water running through a pipe that is otherwise, you know, completely set apart from the dirt, from the dirt from the soil, and yet the roots are moving towards the water anyway, how would they know the water? Is there? The ideas that they're picking up on the sound, picking up on the vibrations, right, and so again you could wonder how would that be ecologically relevant?

It seems plausible to me. I mean, they're all kinds of like underground water flows and so and those would of course produce vibrations right now, And you might then wonder, well, okay, if there's a sound of running water and my ambient music, does that mean my plant wants it. I think that's a more Maybe that's a kind of a simple, simplified

argument to make. I think you get into a lot of discussions about like the differences between how the plant is quote unquote hearing and how we are quote unquote hearing something, right, I mean, I would say it's hard to imagine that there's a evolutionarily justified reason a plant would respond to music in particular, But of course there are probably good reasons for plants to respond to certain

types of noise. So to be very generous, I guess it's possible that in some cases, some types of music might accidentally trigger something like a tropism or a stress response in a plant, where it might make the plant, I don't know, look different in some way that the owner would be able to detect. It's possible. I'm sort of skeptical even as far as that goes like the accidental byproduct of certain types of music. But as I said in the last episode, again, if you want to

play music for your plants, go for it. You know, I don't think it makes sense to literally believe it's doing anything for the plant itself, but it sounds like a perfectly wonderful activity. Yeah, especially prints. Everybody loves prints, so it makes sense that plants would love prints as well. Now this is just one of the senses that plants seem to possess. I've read that plants have somewhere between fifteen and twenty distinct senses, and some of these can

be compared to our basic set of human senses. In addition to sound, as Michael Pollen points out in his wonderful article The Intelligent Plant from The New Yorker in twenty thirteen, we have, of course, on the human side, smell and taste, and plants do seem to sense and respond to chemicals in the air or on their bodies. We have sight, and plants react differently to various wavelengths

of light as well as to shadow. So plants like us live in a world of periodic light and darkness, and of course they depend heavily upon the light because of photosenses, So it makes sense that this would be in place. And then we have the sense of touch, and a vine or root seems to know when it

encounters a solid object. So plant roots have been found to be able to sense gravity, moisture, light, pressure, firmness, so you know it's like they're encountering something that seems to be a solid as opposed to something they can continue to grow in into volume, nitrogen, phosphorus, salt, various toxins.

A lot of times, Pollen points out that the roots, the toxins are going to be first encountered by those roots microbes as well as chemical signals from other plants, and in that just a little bit, you get into

the realm of communication. Yeah, And so my read on this domain is that while a lot of the other things in so called plant cognition could be considered pretty controversial, even some of the stuff with better evidence for it, like the memory stuff we're talking about, that's still somewhat controversial. But plant sensation, the plants being able to gather information about all kinds of different things in their environment, that seems to me to be utterly uncontroversial. That's just they

clearly do that right now. A lot of the more controversial and it's just flat out unbelievable stuff you encounter out there about plants listening to music and so forth. This is still st stemming from that nineteen seventy three The Secret Life of Plants book by Tompkins and Bird that we we talked about in the first episode, popular work of mostly pseudoscience. That was also a huge setback

for legitimate research. And we should also point out that make the point here too that there was of course movement in the field of plant research into plants senses and and you know, potentially plant intelligence decades earlier before Baxter, before these these authors wrote this book. For instance, decades before this, scientist jagades Chandra bows demonstrated the plants were

aware of their environment and that they responded to electrical stimulation. Sure, but then comes The Secret Life of Plants, and it was interesting. I was reading what Paullen had to say about it in the in that article, and he points out that this book may have resulted in the self censorship of researchers that were touching on areas of plant cognition or anything that hinted at similarities between plant and

animal senses. Paullen writes, quote, Americans began talking to their plants and playing Mozart for them, and no doubt many still do. This might seem harmless enough, there will probably always be a strain of romanticism running through our thinking about plants. Luther Burr Bank and George Washington Carver both reputedly talk to and listen to the plants they did such brilliant work with. But in the view of many plants scientists, the science the secret life of plants has

done lasting damage to their field. Yeah, and you can understand how this would happen. So there is a there is a very culturally popular work of largely based on pseudoscience or not well founded claims about the about the intelligence or cognition of plants, and then for decades after that you would have some reticence to get into thematically similar research areas, even if you did have a better

evidential grounding for them. Yeah, I have to say it reminds me a little bit of the situation with dolphin communication research coming out in the sixties and seventies, with its reputation somewhat tarnished or at least endangered by some

perspectives by John C. Lilli's work. And also it reminds me a bit of the state of psychedelic research coming out of the same time period, though of course, here with psychedelics there was the added situation of these substances becoming federally outlawed so no one was outlawing speaking to plants or playing music for them after the Secret Life of Plants came out, But we can see how the whole affair became somewhat distracting and off putting to serious researchers.

You know, you're very this is your life's work. You don't want it to be associated with this work of pseudoscience, with this popular conception of what plants are doing, etc. Yeah, I can totally see the parallel to psychedelic research because, yeah, in recent years there's been a thaw on psychedelic research and there's more legitimate experiment being done with them. But I think for a long time, yeah, it wasn't just

the law. There was a I think a scientific stigma about them because there had been a lot of the early work on psychedelics was clearly done by people who were not practicing unbiased objectives science, but had become sort of psychedelic evangelists. And we're we're dedicated proponents of psychedelics, and we're just like, how can I make them look good?

I'll do anything. Yeah, Ti Timothy Learry to be out there being the major figure that fits that classification, and I have to say, in my very brief survey of some of this plant cognition stuff, one thing that does make me a little suspicious, perhaps unfairly, of even the more legitimate seeming plant cognition research, is that plant cognition concepts seem to attract partisans who, at least as far as I can tell, sometimes overextend what can be concluded

based on a piece of research. Like you could look at a single study about you know, habituation or something that looks like learning or memory and plants and conclude from that that this means plants are conscious, they can think, they can read my mind, they have a soul, or so something like that, you know, over extrapolating from actually what is a fairly contained result, or I think also you see examples of some people and I'm not accusing

the researchers themselves of this, but more like people who are excited about this research proponents, people who want to use plant cognition research to prove ideas they've already acquired elsewhere, like ideas about like a universal life spirit permeating all things or something, or who take on a kind of intellectual martyr persona like the closed minded academy wants to destroy the truth, all of which are major red flags.

But of course it's something I've noticed more in the fans of plant cognition research than in the research itself, So I wouldn't hold that against the studies we're about

to talk about. Yeah, anytime science is used to advance a non scientific you know, say a theology or some sort of an ideology, you get into murky territory, even if said theology or ideology isn't, at least on the surface, something that's particularly harmful, even if it's yet something like, oh, all life forms are connected on Earth, you know, Oh, nothing wrong with believing that, is just like this study does not show that, right, right, But the situation is

there is a lot of wonderfully impressive evidence on the different ways that the plant, since their environment, they compete with each other, communicate, and much more. And so this research did continue and and continues to this day. A pollen points to a shifting point around the year two

thousand and six. This is when an article came that came out in Trends and Plant Science by six scientists who were active in this field of research, and they proposed a new field be established plant neurobiology, and Pollen writes that more than a decade after this term was first proposed, the plant science community was still somewhat split on all of this, with some arguing that this was a necessary step in the right direction of reconsidering what

institutes intelligence, and indeed this is something we see similar discussions going on regarding the likes of ants and slime molds, the ideas of you know, emergent intelligence, intelligence without brains, you know, getting outside of the sort of you know, basic human and animal conception of what intelligence is. Right and of course this is also important when we get into discussions of artificial intelligence and contemplations of what alien

intelligence could consist of. Well, this also recalls other types of research along these lines, not in plants, but in say, animals, are parts of animals in which a brain is not present. You know, we did a couple of episodes about the research perhaps indicating that certain types of flatworms could learn without a brain, or that part of their body, when

cut off, could retain memories without the brain present. It's an older series, so I know I'm forgetting some details, but if you want the full story on that, the pair of ses we did. I think we're called devourer of memories. So anyway, plant neurobiology, some people, some researchers in this field, very much behind the idea of this classification, while others considered it kind of a backslide to the seventies, you know, saying, look, we're trying to get past the

stigma of the secret life of plants. This just judges it all back up again. Though though to be clear, none of these plant neurobiology proponents were making these outrageous claims about telepathy or plants having emotions, and the sort of intelligence they're proposing is more in line with the

emergent modes of intelligence that we're discussing here now. One of the key arguments for reconsidering the lives of plants actually comes down to big revelations made through time lapse footage, or if not key to the arguments, key to a way of illustrating and studying the plants in question. By speeding up long shots of growing stems and leaves and vines, were able to sort of translate that timescale of plants

into the time scale of human beings. And it's not just a matter of oh, look, if you speed up the footage, it looks like a vine is crawling. Now the vine is kind of like a snake and a snakes and animal. And now I'm viewing the plant as more of a you know, a rational being sort of thing. I guess that's inherently part of it, at least to

the you know, the casual viewer. You're flipping around on the TV and you happen to come across, you know, one of these Planet Earth documentaries, and you see brilliant footage like that. But in various experiments, it actually allows us, this kind of footage allows us to better consider environmental interactions.

So one example that bald has brought up before, I believe he I think he brings it up in if not in this article, he brings it up in some of his books, but brings it up in some video view footage that was there to the World Science Festival several years back. But you have bean plants that are competing for a single pole on which to grow. And when you when you speed up that footage and you watch the time laps of it, you can see them competing. You can see them both going after the same pole.

You can see one claiming the pole, and then the other retreating, giving up the fight, saying all right, fair enough, you've got it. And so this, you know, this sort of reaction to competition, h you know, rather than inanimate objects is key to many of these studies like this seems to be an area where plants are even more likely to have this sort of rapid response. Yes, though, of course this invites I think highly relevant and interesting

questions about what intelligence actually is. Intelligence is a concept that is notoriously difficult to define, because I mean, just think about it for a second, how would you define intelligence. It's clear like there are some things it seem very clearly suggested by the concept. And one of them, I

think is interesting has to do with speed. Intelligence clearly has something to do with the rate of things, because like a you know, an animal that solves ama is quickly, we look at that behavior and we say, yeah, that's indicative of intelligence. But a slime mold that solves amas slowly, we look at that and say, yeah, that that doesn't so much look like intelligence. So our intuitions have something

to do with speed. But I would also say another part is I think we tend to assume that intelligence involves the selection of behaviors or acquisition of goals in ways that are not strictly instinctually programmed, but are somehow adaptive to individual situations. Though then again, that's often difficult to detect, Like when you see time lapse footage of a beanstock competing for a pole and then reacting to

the pole already being claimed. Don't is that a purely genetically programmed instinctual reaction or should you think of that as in some way individually adaptive or reactive to the specific situation? Yeah? Absolutely, I mean some ut regarding intelligence and certainly cognition. You know, it comes back to the old idea that's just so hard to put aside the human perception of the thing. It's so hard to uh to even think about say intelligence in our household pets

without comparing it to ourselves. Yeah, it's it's it's tricky now, this this you know, coming back to the idea of of neurobiology plant neurobiology. Those opposed to this notion um have frequently stated, well, okay, plants just simply do not have neurons, synapses, or a brain. Those pollen points out. Legitimate scientists in this field are not making that claim they're only suggesting that there might be something analogous to

a brain, to to neurons, etc Um. So Pollen speaks with plant biologists Lincoln Tays who opposes the idea of plant neurobiology as a sort of animism which takes the realities of both short and long term electrical signaling and neurotransmitter like chemicals and plants, and then the argument is over interprets these realities, ultimately leading to quote anthropomorphizing, philosophizing,

and wild speculations. Yeah, and I suppose I can see like the valid point to be made between these two sides, right, I mean, for instance, we often talk about evolution on the show, and it's very easy to fall into the trap of anthropomorphizing evolution, discussing it as if it has a will. You know, this is the sort of thing that can make it easier to comprehend what we're talking about.

It can make it easier to explain some of what's happening, drive home what makes it interesting and making it make it exciting, But you can also do injustice to the appreciation of what it actually is, either subtly or overtly. Yeah, exactly, And likewise seems to me that, Yeah, comparing plants to animals, it can help explain, it can help excite, It can force us to reconsider outdated notions and limitations about what plants are and what they're capable of. But you can

also potentially get into those murky waters. So I'm not saying I think either side is totally in the right here, but I can see why there is an issue. Yeah, but pollen drives something that. Yeah, there are some very strong feelings among plant biologists about all of this, which actually results in at least a little more heat in name calling than usually encounter in the sciences. But perhaps

it's not all bad. Pollen writes quote. The controversy is less about the remarkable discoveries of recent plant science than about how to interpret and name them. Whether behaviors observed in plants which look very much like learning, memory, decision making, and intelligence deserve to be called by those terms, or whether those words should be reserved exclusively for creatures with brains. Yeah, that absolutely tracks with my experience reading about a lot

of this plant cognition stuff. That either way, you have some very interesting experimental results, but a lot of the conflict seems to be in arguing about what those results mean and what is a reasonable way to characterize them. Yeah, now, on the topic of plants and brains, you might wonder, why don't they have a brain. Perhaps you've played a video game before where you have to blast the vital organs out of some sort of monster plant in order to defeat it. Why does that not seem to be

the case. Why is the reality instead that a plant can lose up to around ninety percent of its body without being killed. I mean, this all comes down to the fact that plants are are stationary. They stay in one spot. I mean, with some you know, they are rooted to the ground. We have some situations where yes, plants can travel and to varying degrees, but for the most part, where the plant takes root, the plant stays.

The plant can't run away. It's got to be ready to sacrifice large portions of its body, and so it simply doesn't make sense for it to evolve some sort of a centralized, irreplaceable and insensitive organ like this. The sessile lifestyle requires different approaches to problem solving, and it also ends up being one of the reasons that you

have such a robust biochemical weapons. Why it has such a such a robust biochemical arsenal and the plant the power here, for plants are famous, you know, far more opponent than anything you'll find in animals. And it's why so much of human medicine is based in Okay, I have this ailment, which plant should I eat? And how much of that plant should I eat in order to fight it? Yeah. Another way to put that is just that the plant kingdom is full of internal chemicals that

have potent effects on the physiology of animals. Yeah. And of course Pollen has written about this quite a bit, including the book The Botany of Desire that In this New Yorker article he summarizes the biochemical arsenal quite quite nicely. He says, 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. So, yeah,

I think he puts it quite well there. It's almost like sort of asking yourself, well, okay, I have a computer system. Why doesn't the computer system have a knife. Why does it have a club? It should? It should? Right? Well, no, it has these other things, and it has them to you know, all these other defenses are in place because it's it's fighting a different type of battle on a different scale. So again, yeah, it's so much of the

of what makes the plant different. You know. We can look at the time scale certainly as a huge factor, but also the fact that it is a sessile organism. Yeah, and so if a plant does indeed contains something that

is it could legitimately be considered intelligence. It would need a different kind of substrate to conta that intelligence then the human brain, which is a centralized command center, you know, because again, like you said, the plant might get ninety percent of it might get eaten, and then it needs to be able to grow back. So if you allow for the concept of plant intelligence, it would probably need to somehow be more modular or distributed rather than housed

in a command center like the human brain. And so what would some of these these physical substrates or systems be I think that is largely unknown, though there are some interesting ideas. Like in the previous episode, one of the papers we looked at, the one that looked at habituation in Mimosa pudica, it hypothesized one of the possible substrates of plant memory formation could be what are called calcium ion channels within the plant's tissues, which can form

these kind of sensory chains throughout the plant's body. But it's it's still unknown. But but but I guess we should look at least one more study. Look, it's more lab research. So in the previous study, we looked at the one from twenty fourteen. In the last episode, it found apparent demonstration of a very rudimentary form of learning known as habituation in these sensitive plants that could close their leaves. And habituation could be defined as the diminishment

of a programmed reaction to a repeated stimulus. So maybe you jump with fright when you hear a sudden clattering sound behind you. Most people would, But if that clattering sound is repeated every five minutes, you will eventually stop jumping with fright. You will become accustomed to it. You will just start ignoring it because you've become habituated. And this doesn't require conscious effort. It just happens unconsciously naturally. When you're exposed to the same salient stimulus over and

over again. What seems salient at first has been encountered enough times that your body's just been trained to no longer regard it as salient. It's just noise, it's background. But of course there are other types of learning and memory that could of course be considered more complex. So could plants actually demonstrate any of these other forms of memory as well? The next study I want to talk about looked at whether you could find evidence of classical

conditioning in plants. Classical conditioning is one of the big concepts in behavioral psychology. I'd say it is one of the biggest discoveries of psychology in the last I don't know about the last of the twentieth century. It is a type of unconscious learning, usually observed in animals, in which you repeatedly pair a salient stimulus with a neutral stimulus, and over time the animal will eventually respond to the

previously neutral stimulus the way they respond to the salient one. So, if you concrete examples, the original one is the story of Pavlov's dogs. This goes back to the Russian physiologist von Pavlov, who lived eighteen forty nine to nineteen thirty six. He was studying digestion in dogs, and he started to notice that the dogs in his lab would drool not only when their food was in sight, but when they

saw the specific lab assistant who always fed them. So the production of saliva and the presence of food is a natural, unconditioned response, that's just something that makes sense

for the body to do. The saliva will be useful once you start eating, but the dogs come to associate the assistant with food, so their glands start jacking up the saliva when they see and smell that specific person who feeds them, even though the person themselves is not actually food, And it of course can be any stimulus. The classic example is a sound such as a bell

or a metronome. So if I give you a painful electric shock every time I start playing we Built this City by Starship, you will start to have a reaction to the song without the shock. Even if there's no shock, you hear that first line and you'll probably freeze or WinCE. Anyway, given that there is some preliminary evidence that at least some plant species can exhibit habituation, would it be possible to show this other kind of memory based learning in plants.

Can plants be classically conditioned? To associate a neutral queue with a biologically salient queue. So the study I want to mention was published in Nature Scientific Reports in twenty sixteen by Monica Gagliano, Vladislav Vasovski, Alexander Borbelli, Mavra Grimonprez and Martial Deptchinsky. And it's called learning by association in plants. So the authors justify their investigation by explaining that they think there would in fact be evolutionary pressure on plants

to show associate of learning. So, much like the question we asked earlier about sounds and stuff in plants, it's worth thinking is there actually an ecologically relevant reason for the creature you're studying to have the ability you're looking for? And so they write quote. Incomplex and ever changing environments, resources such as food are often scarce and unevenly distributed

in space and time. Therefore, utilizing external cues to locate and remember high quality sources allows more efficient foraging, thus increasing chances for survival. Associations between environmental cues and food are readily formed because of the tangible benefits they confer, while examples of the key role they play in shaping foraging behaviors are widespread in the animal world. The possibility that plants are also able to acquire learned associations to

guide their foraging behavior has never been demonstrated. Okay, so the same ability to discern and make these associations would potentially be useful for plants, we just haven't documented evidence of it yet. And this study explored the question with the use of a different plant than the other one. We're not talking about Mimosa pudica anymore. In this case, they looked at seedlings of the garden p plant or

Pisum sativum. Now it's worth clarifying that the plant behavior studied in this experiment occurs on a different timescale than the ones we talked about in the previous episode. In the last episode, there were examples of the few plants with the ability to move rapidly, such as the venus flytrap or Mimosa putica, and these rapid movements were examples of what are called nastic reflexes, reflexes that are independent of the direction of the stimulus and they're just guided

by the plant's body form. Nastic movements were contrasted with what are called tropisms, which tend to be slower movements, but are stimulus directed. And the most common plant tropism you will have observed pretty much everybody's seen this is phototropism growing towards a light source, which totally makes sense for a plant because light provides the energy that powers photosynthesis. So you can roughly think of a plant growing toward light much like an animal moving toward a source of food.

And that's what this twenty sixteen experiment was studying, not nastic reflexes, but tropisms growth in the direction of a biologically salient stimulus, in this case light. So the first experimental setup looked like this the author's right quote. In the first experiment, p seedlings, forty five of them were entrained to an eight hour light sixteen hour dark cycle

for five to eight days. In the subsequent three day training period, they were kept in darkness with the exception of one hour light exposures during the three daily training sessions. And during this training period the seedlings, they would place them in what's known as a y maze. So to

picture this, you think of a Y shaped pipe. The seedling is down at the bottom in the single channel part of the tube, and then above it the tube forks off into two arms, and then there are two different training conditions, one in which the seedlings are exposed to a light source from one of the tube with a fan blowing on them from the same arm, and then there's another test condition in which they are exposed to a light source from one arm and a fan

blowing on them from the opposite arm. So we have the light associated with a fan or a light associated with being opposite the fan. So if the plants are capable of classically conditioned associations, one group should learn that the airflow from a fan is positively correlated with food, so it should start to associate a fan with food, and then the other will learn that the airflow is negatively correlated with food, and it should associate going in

the opposite direction of the fan with food. And to make the direction of the incoming light unpredictable, its direction was repeatedly switched around during the training period, though its association or lack of association with the fan was kept

consistent with each plan. And after this training period, the plants were further subdivided to put some in test groups in the other in the control group, and the two test groups would be exposed to a fan from one direction or the other without the light source along with

it the author's right quote. In this group, to control for the influence of innate phototropic response, the fan was placed in the arm opposite to last light exposure in the fan plus light group and on the arm of the last light exposure in the fan versus light group, So that was the second is when they were on opposite sides of the y maze quote. The seedlings of the control group were left undisturbed. On the morning after the testing day, we visually inspected the seedlings and recorded

the arm of the maze they had grown into. So what did they find. Well, in the control group, this is the group that got no fan exposure in the test phase, so no fan, one hundred percent of the plants grew in the direction of the most recent light exposure, wherever the light came from last that's where they went. But in the test groups, the authors report that the

majority of seedlings did indeed show a conditioned response. So in the group that it been trained with the fan and the light on the same side, sixty two percent of them grew toward the fan without the light, And in the group that had been trained with the fan and the light on opposite sides, sixty nine percent grew

away from the fan. So if this holds up, it would appear to show associate of learning in plants, a type of learning that in the majority of cases prevails over the basic reflexive tropism to grow in the direction of wherever the light came from last. But of course it's a good question does this study actually hold up? Will come and come back to that in a minute. Here.

One more thing I wanted to mention, though, is that there were also subsequent experiments in the same study, and the authors found that the associat of learning only succeeded when it took place during the quote daytime from the plant's perspective given its training regimen, which the authors suggest means that there are metabolic demands on the learning process. Quote.

This experiment, in which plants were trained at three different time periods within twenty four hours, revealed that the learning effect disappears when training occurred during the evening hours, when

light would not normally be available. This finding is particularly intriguing and bolsters the argument that associative learning is an adaptive response that is only utilized during daylight hours when it is most useful vin internal circadian clock, which is interesting because that also invokes a sort of second order type of thing that some people would have called a type of plant intelligence, which is its ability to measure

spans of time. Anyway, in the end, the authors of this study, they say, quote, our results show that associative learning is an essential component of plant behavior. We conclude the associative learning represents a universal adaptive mechanism shared by both plants, animals and plants. Now, this was in twenty sixteen, and I did find a study following up on this and attempting a replication and failing. So the attempted replication was by Casey Marcole published in ELFE called lack of

Evidence for associate of Learning in p Plants. The year was twenty twenty. Pretty straightforward. The author tried to repeat the twenty sixteen experiment. They repeated the protocol described in the first experiment, and they write quote, However, a replication of the protocol failed to demonstrate the same result, calling for further verification and study before mainstream acceptance of this

paradigm shifting phenomenon. This replication attempt used a larger sample size and fully blinded analysis, and of course both of those things are always good. Larger samples are good, blinded analysis is always good. I wasn't one hundred percent sure exactly what that meant in this case, but I think it would mean that whoever compiled and analyzed the results of the experiment had no way of knowing which groups the subjects were in, which would help prevent any possible contamination,

intentional or unintentional by experiment or bias. So we're in the middle ground here. One study gets a positive result, a follow up attempt does not, So how do we sort it out? Well? Actually, the authors of the original study replied, publishing a follow up comment in the same journal.

They essentially to summarize their argument. They essentially say that the experiment may not have worked in the replication attempt because of some crucial differences in methodology, mainly that the unconditioned stimulus in this case light was not tightly controlled enough, and that they criticize some things about the plants had been mounted inside their growth case, and the idea that light from one tube may have been penetrating into other tubes,

making a kind of light noisy environment. That there were too many light sources and this would introduce randomness into the results. So to put it in terms of the Pavlov's dog example, this might be a kind of rough comparison, But the unconditioned stimulus in Pavlov's dogs would be food. So if you were to have a poor control of the unconditioned stimulus in that case, it would be kind of like imagining that the dogs had constant ambient access

to food. They were just food bowls constantly full throughout the room they're in. In that case, would they salivate when they saw an assistant coming in to put some more food in one of the bowls, Well, if they've just always got food anyway, probably not right. I don't know. I don't know enough about dogs. Sometimes I feel like sometimes my cat can be kind of like that, where it's like, really that you have food, and here's more food. Now you're excited for this. How about the food you

already have? I trust the research or something. Right, Well, if they've just got food anytime they want it, right, then they wouldn't associate the assistant coming in to fill the food bowls with them getting the food. It would just you know, they would just get the food whenever they want. True. True. So that's what the authors of

the original study argued. But then there was a response to the response in the same journal again where Markel came back and argued, for a number of technical reasons that the differences they highlighted are unlikely to explain the different outcomes. Quote. Despite considerable effort to match the experimental details of the twenty sixteen experiment, the application attempt did not find evidence for associate of learning in PEP plants.

Of course, this does not rule out the existence of such learning, and I sincerely hope that future research demonstrates the phenomenon to be reproducible. So I feel like we're kind of in a middle ground here. Personally, I don't have the expertise or judgment to reach a conclusion on the technical points they're arguing about in the experiment here, So I guess I would just say I'd have to consider the twenty sixteen results very interesting, but heavily caveated

until we see successful replication. Yeah. Now, I will say that the lead author on this paper, Monica Gagliano, I've seen her. She was part of a panel discussion at the World Science Festival back in twenty nineteen, I Believe Intelligence Without Brains. That also featured ants scientist Mark Moffatt, whose work we've discussed in the show before. Oh yeah yeah. Monica Gagliano's research Associate professor in Evolutionary ecology the Biological

Intelligence Lab at Southern Cross University in Australia. Her primary areas of research or marine ecology and plant cognitive ecology. She also has a book out which I was not aware of until I was looking back into her work here, but the book is thus Spoke the Plant. Yeah. She seems to be one of the leading figures in the

plant cognition domain these days. She wrote another article in twenty eighteen summing up some of this recent stuff in ecologia called Plants Learn and Remember, Let's get used to it. Actually sorry, that had three authors. She was the first listed author. Well, I will say she did seem to have a good sense of humor about about herself and about her area of research when I saw her gift that talk. And by the way, if you want to see that talk for yourself, you can find it at

the World Science Festival's website. Just look for Intelligence Without brains. They have the full talk up there now. I guess we've already covered this a good bit earlier on, so

I won't get into too much detail. I did have a few notes about some other articles I was reading, for example, by one author you already cited who came up in Pollen's New Yorker piece, Lincoln Tiez, who has been a critic of so called plant cognition or plant neurobiology, and comments by researchers from this camp, though a lot of this seemed aimed at the kind of thing you were talking about, where they're objecting to certain extrapolations or characterizations,

extrapolations from or characterizations of this research, rather than the research itself, like rejecting the idea of plant consciousness and so forth, And of course that opens its own cannon worms, because of course, you know, there's no actual test for consciousness, even in humans. Consciousness can only be experienced directly in the self and then inferred to exist by analogy and

other humans, and possibly in non human animals. But they've got a number of arguments based on the the just physical anatomical qualities of plants that say, you know, it's very unlikely they would have the whatever kind of computational complexity the I don't know, calcium channels or anything like that, and plants might possess it would be unlikely to possess the level of complexity that we see in animal brains and that we assume to be the necessary basis for consciousness.

But anyway, I mean, so, I think where we're left right now, at least from my point of view, is that we're still in the middle of a research program. There's still like a you know, a lot of basic research in plant cognition going on that maybe in five or ten more years we will have a better idea of what the direct evidence is about what plants can actually do, and then it might we might be more well equipped to argue about whether it actually counts as X, y or z that we you know, words we use

to associate with the mental phenomena of humans. Yeah, yeah, or I don't know, maybe we'll have different terminology at that point that it's yeah, we end up in the same situation where we're trying to divorce the study of intelligence and content and even potentially consciousness, you know, across multiple species and multiple organisms. Despite the fact that we have this this this experience of these things, and this this concept of these things that's you know, closer than

our own breath. One thing that's got me thinking about again this is this is we're in the speculative realm. Now, this is not what's necessarily justified by the existing evidence.

But if you were to discover, for example, that maybe you can't justify the claim that plants can think, but you could justify the claim that plants can learn, it would be an important reminder to not blur all different types of mental phenomenon together into one single substance, Like there may be important differences between, for example, remembering and reasoning that make one but not the other possible given any physical substrates, say like the kinds of I don't know,

computational chemical pathway that would exist in plant stems and roots versus in the neural tissue of a human being or an animal. Maybe human brain tissue can do both, but plant tissue can only do one. And this has

interesting implications for speculating about alien intelligence. If there are other types of intelligence out there in the galaxy, we would tend to assume those intelligences to bundle together all the myriad functions performed by our own primate brains, but it's important to remember those are like specifically primate brains. We've got a very particular type of meat in our heads, and the type of intelligence we're familiar with is what

that meat can do. So what if, like there's another physical substrate that's unfamiliar to us and that constitutes what we would think of as the alien brain, whatever that is, should we be trying to think of it as capable of some of the subdivided parts of intelligence what we think of as intelligence, but not others. Yeah, that's a

great point. And uh, you know, I guess I would hope that we're at least reaching towards a point where we're going to have a more you know, complicated understanding of what memory and learning are because we're already having to contend not just with human and animal memory and learning, but also machine learning and machine memory and you know, potentially plant analogs as well, and so yeah, it just it kind of hopefully forces to push the human experience

and the human model a little further aside and realize that, yeah, this is this is an example of a broader thing, and it is not the thing itself, Like I'm imagining a sci fi concept of story about encountering aliens that maybe, if this makes any sense, what if they could do something that looks like intelligence because they can learn and adapt, but they can't do what we would think of as reasoning. Yeah, like they can learn, but they can't think. I don't know,

I'm not sure that even makes sense. But uh, I don't know. It gets my gears cranking. All right, we just had a brief conversation off Mike. Are we gonna Are we gonna cap this series here? Are we going to go more with the interesting hidden lives of plants, plant cognition, so called plant communication, things like that. Maybe we'll just leave it a mystery. You'll be surprised next Tuesday,

which whether we're onto something else or whether the plants continue. Yeah, and in the meantime, you've you've got some hanging out to do with your various house plants and plants in the yard, maybe plants out in the wild. Um, you know, if if they're within your house, maybe maybe play them a little Starship, play them a little some prints and some of the other musical examples we mentioned these episodes.

We're not saying it's going to do anything, but it might be fun to hang out with your plan and listen to Starship. You know, I think of it like the the semantic contents of talking to your dog, Like if the dog's mostly just going to be responding to the tone of your voice. If I tell my dog he's a he's a bad boy and a good boy voice, he's probably gonna be super happy. But you know, I want to say good boy anyway because that makes me

feel good. All right, Well, we're gonna go and close it out here, but as always, you can find episodes core episodes of Stuff to Blow Your Mind in the Stuff to Blow Your Mind podcast feed every Thursday and Tuesday. You will also find our short form Artifact or Monster Fack episodes on Wednesdays, Listenermail on Mondays, and on Friday, well we do a little Weirdout Cinema. That's when we set aside most serious concerns and just talk about a strange film. And then on the weekend we have a

vault episode that is a rerun from yesteryear. Huge thanks as always to our excellent audio producer Seth Nicholas Johnson, though he is out this week. So big thanks to our excellent guest audio producer Paul deckand huge thanks for stepping in this week, Paul. If you would like to get in touch with us with feedback on this episode or any other, 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.