Smarty Plants

0:01Hey, happy new year. I'm Latif Nasser. This, of course, is Radiolab. We have got all kinds of surprises in store for you this year. Not even this year, like in the next few months, including the winner of our big year-long Quasimoon naming contest. There is a winner. It's just not official yet. We will announce it the moment we are able to. But for now, as we take our first step into 2025, we wanted to rewind an episode we first released in 2018. It's about plants and their incredible roots. and besides the fact that it's just a super fun to listen to, part of the reason we're replaying it is almost as a reminder of our roots as a show in things like humor and wonder, which we are going to be, you know, working our best to dig up and dish up over the next year.

0:55So to set us off on the right footing, here are Emeritus hosts, Jad and Robert with Smarty Plants. Wait, you're listening. Okay. All right. Okay. All right. You're listening to Radiolab. Radiolab. From WNYC. See. See. Rewind.

1:24Where do we want us to say? Doesn't matter. One or the other. That's it. Good. Thank you. Testing. One, two, this is the headphone. Got that? I'm Jad. I'm Robert. How's that? Better? Oh, much better. This is Radiolab. Can I interrupt? Yes. But could I say something? Me first. Me first. Because I let you go. It's going to be another 20 minutes until I get to talk. A little while back, I had a rather boisterous conversation with these two guys. First of all, like, who are you? I'm Larry Ubell. Yeah. And I'm Alvin Ubell. So you are related and you're both in the plumbing business? Are we related?

1:54Yes, we are related. But we are in the home inspection business. Yeah. They're father and son. It's a family business. We are the principals of Accurate Building Inspectors of Brooklyn, New York. And I've been in the construction industry ever since I'm about 16 years old. I'm 84. Okay. I'm not giving my age. I wanted to talk to them because as building inspectors, there's something they see over and over and over. Yeah. All the time. That is actually a clue in what turns out to be a deep, deep mystery.

2:29Which is what exactly? Well, let us say you have a yard in front of your house. Yours is the back of your house, but let's make it in front. Okay. And right in the middle of the yard is a tree. And the tree happens to be a weeping willow. Just for example. And not too far away from this tree, underground, there is a water pipe. A perfectly good pipe. Connecting your house to the main city water line that's in the middle of the street. The roots of this tree, of course, can go any way they want to go. They can go north, south, east, west, whatever. But the Ubells have noticed that even if a tree is 10 or 20, 30 yards away from the water pipe, for some reason, the tree roots creep with uncanny regularity straight toward the water pipe.

3:11The tree will wrap its roots around that pipe. Around and around and around. In a tangling of spaghetti, like almost, and each one of those lines of spaghetti is squeezing. a little bit, a little bit. Each one an ounce, an ounce, an ounce, an ounce, an ounce. Eventually, over a period of time, it'll crack the pipe like a nutcracker. Yes. You both see this happening all the time. I have done inspections where roots were coming up through the pipe into the house. Into the house? It's amazing. Yes. This actually happened to me. The magnolia tree outside of our house got into the sewer pipes, reached its tentacles into our house, and busted the sewage pipe.

3:52It just happens to a lot of people. It's almost as if these plants, it's almost as if they know where our pipes are. I see what's happening. What? Are you bringing the plant parade again? Is that what this is? Well, of course I am. You're doing the like, okay, first it was the roots under the ground all connected into a whole hive thing. I don't know why you have problems with this. No, because it's like every time I close my eyes, you're coming at it from a different direction. I do, I do. With the plant parade. And I met a plant biologist who's going to lead that parade. She's done three experiments.

4:23And I think if I tell you about what she has done, you, even you, will be provoked into thinking that plants can do stuff you didn't imagine, dream they could do. I know you've, I know you've, but let me give it a try. Okay, I'm game. Let's go to the first. This is the plant and pipe mystery. Hello, finally. Hello, hello, but long last. Now, you might think that the plant sends out roots in every direction. One of the roots just happens to bump into a water pipe and sends a signal to all the others. Come over here. Here's the water. Right. But that scientist I mentioned. My name is Monica Gagliano.

4:59I'm a research associate professor at the University of Sydney. She took that notion out of the garden into her laboratory. Yeah, tested it in my lab. She took some plants, put them in a pot that restricted the roots so they could only go in one of just two directions, toward the water pipe or away from the water pipe. What kind of plot is this? It's shaped like... Like the letter Y, but upside down? So you get the roots can go either to the left or to the right. Oh. Now the plants, if they were truly dumb, they'd go 50-50. It would be all random. Right. But after five days, she found that 80 % of the time, the plants went or maybe chose to head toward the dry pipe that has water in it.

5:38So the question is... A plant that is quite far away from the actual pipe, How does it know which way to turn and grow its roots so that it can find the water? All right. My hypothesis is that what happens is why... Can I have a few minutes? No. You got somewhere to go? No, because I... You got somewhere to go? No. Good. If she's going to do this experiment, most likely she's going to use cold water. She's not going to use hot water because you don't want to cook your plants, you know, and it's more expensive. Why waste hot water? Well, by the way, should we establish? Is it a fact that you're...

6:15Okay, go ahead. You want to contest? He's the right track. You have to understand that the cold water pipe causes even a small amount of water to condense on the pipe itself, on the outside of the pipe. It's kind of like a cold glass sitting on your desk, and there's always a puddle at the bottom. The glass is not broken. It's not leaking. It's not leaking. The water is still in there. So there is some water outside of the pipe. It's condensation. Right. So what they're saying is even if she's totally sealed the pipe so there's no leak at all, the difference in temperature will create some condensation on the outside.

6:49And it's that little, little bit of moisture that the plant will somehow sense. If you look at a root under a microscope, what you see is all these thousands of feelers, like hairs on your head, looking for water, every one of them. And all of a sudden, one of them says, I found a little water. And then all the other one goes in the same direction. These sensitive hairs, he argues, would probably be able to feel that tiny difference. Yes. But Monica says, absolutely not. I purposely removed the chance for a moisture gradient. She made sure that the dirt didn't get wet because she'd actually fastened the water pipe to the outside of the pot.

7:29So it wasn't touching the dirt at all. Wait, so this branching pot thing, the part where the water pipe was, the pipe was on the outside of the pot? That's right, outside. And the plant still went to the place where the pipe was not even in the dirt? Yeah. That is strange. Or is it just the vibration of the pipe that's making it go toward it? They would have to have some. Maybe there's some kind of signal, different kind of signal, traveling through the soil. Monica thought about that and designed a different experiment. Again, if you imagine the pot, my experimental pot. With the forked bottom.

8:05Yeah, but then have. We have two very different options for our plant. On one side, instead of the pipe with water, she attaches an MP3 player with a little speaker playing a recording of... The sound of water. And then on the other side, Monica has another MP3 player with a speaker, but this one plays... Nothing.

8:29So she's got her plants in the pot, and we're going to now wait to see what happens. Remember that the roots of these plants can either go one direction towards the sound of water in a pipe, or the other direction to the sound of silence. On the fifth day, they take a look and discover most of the roots, a majority of the roots, were heading toward the sound of water. Exactly. Exactly. So they just went right for the MP3 fake water, not even the actual water, just the sound of it? Just the sound. That's interesting. It's interesting. That is interesting. But what, how would a plant hear something?

9:12Like they don't have ears or a brain or anything like, they couldn't hear like we hear. Well, maybe. They definitely don't have a brain. No question there. But they do have root hairs. This is Jennifer Frazier. I am the blogger of the artful amoeba at Scientific American. And she was willing to entertain the possibility that plants can do something like hear. So what do we have in our ears that we use to hear sound? Little hairs. Little hairs. Yes. Right? And if you go to too many rock concerts, you can break these hairs, and that leads to permanent hearing loss, which is bad. So maybe the root hairs, which are always found right at the growing tips of plant roots, maybe plant roots are like little ears.

10:01Maybe each root is like a little ear for the plant. I don't know. That is cool. That is definitely cool. The thing I don't get is in animals, the hairs in our ear are sending the signals to a brain, and that is what chooses what to do. That's true. If a plant doesn't have a brain, what is choosing where to go? I don't think Monica knows the answer to that. But she does believe that, you know, that we humans... We are a little obsessed with the brain. And so we are under the impression or I would say the conviction that the brain is the center of the universe. And if you have a brain and a nervous system, you are good and you can do amazing stuff.

10:46And if you don't have one, by default, you can't do much in general. Okay. It's a very biased view that humans have in particular towards others. But still, I mean, to say that a plant is choosing a direction, I don't know. I mean, like when a plant bends towards sunlight, we've all seen houseplants do that, right? Would you say that the plant is seeing the sun? No, I mean, it's just it's reacting to things and there's a series of mechanical behaviors inside the plant that are just bending it in a direction. I mean, couldn't it just be like that? I think that's fair. And I think if I move on to the next experiment for Monica, you're going to find it a little bit harder to object to.

11:30We need to take a break first. But when we come back, the parade that I want you to join will come and swoop you up and carry you along in a flow of enthusiasm.

11:50Latif Radiolab, back with Jad and Robert. Yep. So today we have a triptych of experiments about plants that apparently, jury's still out, are going to make me rethink my stance on plants. Yes. So we're up to experiment two now, are we not? That is correct. So, we are going to meet a beautiful little plant called a mimosa pudica, which is a perfectly symmetrical plant with leaves on either side of a central stem. Yeah, mimosa has been one of the pet plants, I guess, for many scientists for, like, centuries. Because this peculiar plant has a surprising little skill. Yeah, a reflex. An anti-predator reaction?

12:31Like a defensive mechanism. As soon as it senses that a grazing animal is nearby. If a nosy deer happens to bump into it, the mimosa plant. Folds its leaves. Curls all its leaves up against its stem. The whole thing immediately closes up and makes it look like, oh, there's no plant here. Just a boring set of twigs. Nothing delicious at all. So the deer's like, oh, well, never mind. Right. And you can actually see this happen. Okay, so... Anybody can get one of these plants, and we did. And if you just touch it... Can I try it? Yeah, go for it. Even just one leaf, you can actually watch this cascade.

13:17Whoa. Where all the leaves close in, like... Look at that, they all went close. It's sort of startling to see. That's so eerie. So that voice belongs to Atish Batya, who is with Princeton University's Council on Science and Technology. We showed one of these plants to him and a couple of his colleagues, Sharon Dela Cruz and Peter Landegrin. Yeah, there you go. That's neat. Because we wanted them to help us recreate Monica's next experiment. Okay. So maybe could you just describe it just briefly, just what you did? Well, I created this horrible contraption. Apparently, she built some sort of apparatus.

14:02I guess you could call it a mimosa plant drop box. Picture one of those parachute drops that they have at state fairs or amusement parks where you're hoisted up to the top. Except in this case, instead of a chair, they've got a little plant-sized box. Into which she put these sensitive plants. So the plants are now, you know, buckled in, minding their own business, and then Monica would... Drop them. Just about, you know, seven or eight inches. Landing very comfortably onto a padded base made of foam. So no plants would actually hurt in this experiment. But the drop was just shocking and sudden enough for the little plant to...

14:43Close all its leaves. Do its reflex defense thing. Then Monica hoists the plant back up again and drops it again. And again. And again. And after not a whole lot of drops,

15:03the plant, she noticed, stopped closing its leaves. So after the first few, the plants already realized that that was not necessary. The plants stopped, what is it they did? They stopped folding up. She thinks that they somehow remembered all those drops and it never hurt, so they didn't fold up anymore. They'd learned something. Exactly, which is pretty amazing. Couldn't it just be an entirely different interpretation here? Like what? The plants have to keep pulling their leaves up and they just get tired. They run out of energy. Yeah, it might run out of fuel, exactly. It's a costly process for this plant.

15:40She figured out they weren't tired because after dropping them 60 times, she then shook them left to right and they instantly folded up again. It would close up. So it's not that it couldn't fold up. It's just that during the dropping, it learned that it didn't need to. Yeah. That's a learning is something I didn't think plans could do. They do. Oh, this looks so high tech. So we figured, look, if it's this easy and this matter of fact, we should be able to do this ourselves and see it for ourselves. So that's where the scientists from Princeton come in. Peter, Sharon, and Otish. They designed from scratch a towering parachute drop in blue translucent Lego pieces.

16:29So this is our plant dropper, and we can move it up, and we can drop it. So we scrapped in our mimosa plant. A little seatbelt for him for the ride down. And then... And then someone has to count. I'll count. And then we let it drop. Five, four, three, two, one. Drop. Five, four, three, two, one. And we dropped it once and twice again and again. We were waiting for the leaves to, you know, stop folding. We dropped. We dropped. But I don't know. It didn't happen. It was curling up each time? Every time. It just kept curling and curling. Didn't seem to be learning anything. So you couldn't replicate what she saw?

17:13Nothing happened at all. So we went back to Monica. We, as you know, built your elevator. I heard. We told her what we did. What happened to you didn't happen to us. Now, can you imagine what we did wrong? Like, for example, my plants were all in environment control rooms, which is not a minor detail. They're not experiencing extra changes. or for example, I don't know if that was the case for your plants. No, we kept switching rooms because we weren't sure whether you wanted to be in the high light or weak light or some light or no light. I wonder if that was maybe a bit too much. Was it possible that maybe the plants correctly responded by not opening because something really mad was happening around it and it's like, this place is not safe.

18:04Truth is, I think on this point, she's got to, she's right. Oh, no. One time, the plant literally flew out of the pot and upended with roots exposed. It feels like one of those experiments where you just aborted on humanitarian. Yes. So I think what she would argue is that we kind of proved her point. We were so inconsistent, so clumsy, that the plants were smart to keep playing it safe and closing themselves up. Actually, I think you were very successful in your experiment. you found exactly what the plants would do under your circumstances, which were, I don't know, let's say a bit more tumultuous than mine.

18:40And she goes on to argue that had we been a little bit more steady and a little bit more consistent, the plants would have learned and would have remembered the lesson. Because what she does next is three days later, she takes these plants back into the lab. The idea was to drop them again, just to see the difference between the first time you learn something and the next time. Like, would they figure it out faster this time or maybe slower? Yeah. So she takes the plants, she puts them into the parachute drop, she drops them, and she says this time they relaxed almost immediately. Yeah. They remember straight away.

19:13Straight away. All of them know already what to do. They remembered what had happened three days before, that dropping didn't hurt, that they didn't have to fold up. So they didn't. Yeah. And then she waited a few more days and came back. They still remembered. Yeah. A few more days? Yeah. And it was almost like, let's see how much I have to stretch it here before you forget. Eventually, she came back after 28 days. Yes. And they still remember. They still did not close when she dropped them. That's what she says. What was your reaction when you saw this happen? That's producer Annie McKeown. This retention of knowledge.

19:52My reaction was like, oh, s***. That was my reaction. because the only reason why the experiment turned out to be 28 days is because I ran out of time. So they might remember even for much longer time than 28 days. So she's saying they remembered for almost a month? Yeah, I mean, can you remember what you were doing a month ago? No, I actually, like, even this morning, it's already, like, poof, gone. Like, that's a thing. But supposing that she's right. Yeah. Where would a little plant even store a memory? Well, that's what I asked her. I do want to go back, though, for something like learning.

20:31Like, I don't understand. Learning, as far as I understand it, is something that involves memory and storage. And I do that in my brain. That's the place where I remember things. In my brain. Or do you? Yes. Or do you? Is a brain, I think. Is your dog objecting to my analysis? Sorry, we have a dog barking. That's okay. Picasso. Picasso. Pigs. Picasso, enough of that. Pix, it's okay. It's okay, puppy. It's okay. Oh, no.

21:10Picasso, enough of that now. Sorry. Actually, Monica's dog leads perfectly into her third experiment, which, again, will be with a plant, but it was originally done with a dog. So Pavlov started by getting some dogs and some meat and a bell. Science writer Jen Frazier gave us the kind of the standard story. And his idea was to see if he could condition these dogs to associate that food would be coming from the sound of a bell. So he brought them some meat. They would salivate and then eat the meat. Then he would bring them the meat and he would ring a bell. And again, drooling, eating. And he would repeat this.

21:51Ring, meat, eat. Ring, meat, eat. Ring, meat, eat. Finally, one time, he did not bring the meat, but he rang the bell. Sure enough, the dogs began to drool. They had learned to associate the sound of the bell. Which has, you know, for dogs has nothing to do with meat. With when they actually saw and smelled and ate meat. Exactly. Now that's a very, you know, animals do this experiment, but it got Monica thinking. Would the plant do the same? Could a plant learn to associate something totally random, like a bell, with something it wanted, like food? Yeah. Are you, like, aggressively looking around for, like, do you wake up in the morning and say, now what can I get a plant to do that reminds me of my dog or reminds me of a bear or reminds me of a bee?

22:37Not really. And I guess that's, I feel, I feel sort of kind of good to say this. It's like, no, no, I don't, I don't do that. But Monica says what she does do is move around the world with a general feeling of... Huh. What if? So she decided to conduct her experiment. Pretty much like the concept of Pavlov with his dog applied. But instead of dogs, she had pea plants in a dark room. Yeah. And for the meat substitute, she gave each plant a little bit of food. In this case, a little blue LED light. Light is obviously representing dinner. So light is, if you shine light on a plant, you're like feeding it.

23:18Yeah, plants really like light, you know, they need light to grow. So otherwise they can't photosynthesize. So for three days, three times a day, she would shine these little blue lights on the plants. From a particular direction. And she noticed that, unsurprisingly, the plants would always grow towards the light. Anyone who's ever had a plant in a window knows that. And the salivation equivalent was the tilt of the plant? Exactly. And then I needed to, the difficulty, I guess, of the experiment was to find something that will be quite irrelevant and really meant nothing to the plant to start with, like the bell for the dog.

23:54So after much trial and error with clicks and hums and buzzes. All sorts of randomness. She found that the one stimulus that would be perfect was. A fan. A little fan, the same one that I used in computers, like, you know, really tiny. She determined that you can pick a little computer fan and blow it on a pea plant for pretty much ever and the pea plant would be utterly indifferent to the whole thing. The plants didn't care. Then she placed the fan right next to the light so that the light and the fan were always coming from the same direction. And with these two stimuli, she put the plants, the little pea plants, through a kind of training regime.

24:31Little fan goes on, light goes on, both aiming at the pea plant from the same direction and the pea plant leans toward them. Then she takes a little light and a little fan and moves them to the other side of the plant. Turns the fan on, turns the light on, and the plant turns and leans that way. Yeah, fan first, light after. And moved around, but always matched in the same way together. Fan, light, lean. Fan, light, lean. Fan, light, lean. Same as the problem of the bell, the meat, and the salivation. So then at one point, when you only play the bell for the dog, or you, you know, play the fan for the plant, And we know now for the dogs, the dog is expecting, so it's predicting something to arrive.

25:13And Monica wondered, in the plant's case... If there was only the fan, would the plant... Anticipate the light and lean toward it. Or would just be going random. After three days of this training regime, it is now time to test the plants with just the fan, no light. So, Monica moves the fans to a new place one more time. They're switched on, and the pea plants are left alone to sit in this quiet, dark room, feeling the breeze.