Plant Memories, Part 1

Do plants remember? Do they communicate? What is the extent of their interaction with their environment? In this Stuff to Blow Your Mind series, Robert and Joe dive into the amazing world of plant intelligence research. 

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Episode Transcript

Speaker 1 (00:03):
Welcome to Stuff to Blow Your Mind production of My
Heart Radio. Hey, welcome to Stuff to Blow your Mind.
My name is Robert Lamb and I'm Joe McCormick. And
today we're gonna be talking about an interesting and perhaps
hidden property of plants. And to start us off, I

(00:26):
wanted to read a selection from one of the lesser
known works by the English romantic poet Percy Biss Shelley. Uh,
this is a poem called the Sensitive Plant. Rob Am,
I write that you've never heard of this one before. No,
you know, obviously I've I've read a little bit of
Shelley here and there, but this this must I'm assuming
this is a deeper cut. It is. I think it

(00:47):
was one of the final things he wrote before his death,
So this would have been I think sometimes in the
early eighteen twenties. Um, 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 have been scanned into Google books, and every
other page on it was like washed out on the scan.
So so that was beautiful. But um, yeah, this one's

(01:11):
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, uh, 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 Miss Shelley. For the Sensitive Plant
has no bright flower, radiance and odor or not its dour.

(01:32):
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,

(01:53):
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,
and 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

(02:16):
like a sea over the warm earth, glide in which
every sound and odor and beam move as reads 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,

(02:39):
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,

(03:04):
sang more sweet as the day might fail, and snatches
of its elazy enchant were mixed with the dreams of
the sensitive plant. Very nice. Yeah, so I don't think
it's one of Percy's best poems. Like I was saying,
the rhythm is a little too regular and sing songy.
Sometimes some of the rhymes are a little obvious, you know,
the rhyming love with above and all that. You could

(03:25):
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,
monster ballad. But but there are also lines that really
love the dew which lies like fire, and the flowers
and the nighttime as a as an ocean paved under
with the sands of consciousness. But it's aesthetic qualities aside.

(03:48):
I think it's really interesting that Percy is suggesting in
his unorthodox and emotionally charged for you 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, and afterlife.

(04:10):
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 many names of Mimosa pudica,

(04:33):
pudica being Latin for chaste or modest, shamefaced or bashful.
And this is a flowering plant in the family Fabasi,
which is the pa or legume family, which means, yes,
this plant is a cousin of the common being. So
we are we are dealing in being can today, we're
getting into into supernatural territory then, oh boy. Mimosa pudica

(04:56):
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 by tons of different names.
It's called the humble plant, the shame plant, that touch
me not, and all of these names connect to the

(05:17):
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 time scale that we
would normally associate only with animals. So, if you want
to picture it, the sensitive plant is a spiny little

(05:39):
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 opinionle leaflets shooting out from

(06:00):
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.

(06:21):
And then sometimes even the branch or the stalk that
they're on will droop away from the stimulus, will droop down.
From what I can tell, there is not yet a
full consensus on the main function of the shrinking behavior
in the wild, like why does it do that? But
botanists have long suspected that it's some kind of defensive

(06:43):
action by the plant to protect its leaves from grazing
herbivores or insects. And this can 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 bides it's munching the leaves, and this causes
the leaves to kind of pull away from the mouth

(07:04):
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,
you know, of an enormous grazing animal that is eating
a lot of plants and it's maybe not gonna stop

(07:26):
to really get particular about this one, if this one
has made itself uh smaller, you know, retreated into you know,
amidst other plants, etcetera. Like, it's just gonna keep eating
whatever is readily available to eat, Right, But I think
there's also a focus on insects. Maybe insects are also
the reason it does this, And it could also work

(07:47):
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 time scale of animal movement in your in
your vicinity that might startle you and send you on
the run. Yeah, on the time scale of animal movement.

(08:09):
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, well we'll come back to
uh that you know, that is a plant that is
acting aggressively on the timescale of of of animals um
in an attempt to capture a set animal. But but
here we see the reverse. Here we see something that

(08:29):
is uh 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. Uh. So usually after
a sensitive plant closes up its leaflets and droops away,
it will reopen within some short time period, maybe only

(08:50):
a few seconds, uh sometimes a few minutes, but it
doesn't take long. It'll it'll open back up, get those
leaves out there again, and and 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

(09:14):
Friedel about the history of mimosa putica, and also a
similar Old World plant called Biophytem 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

(09:36):
century Portuguese naturalist living in India named Cristo baal Acosta,
who authored a book in fifteen seventy eight called Tractado
de las Drogas e Metaicinas de las Indias Orientales or
treat Us 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

(09:57):
it sounds like it's a hoot, But I could not,
so I'm gonna have to rely on a couple of
secondhand summaries, including a Friedel's article here. But anyway, in
this book by Christo ball 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 do you ever say herb with

(10:19):
the H pronounced sometimes I'm afraid I'm gonna keep doing that. Yeah,
sometimes it slips out. I don't know why. I try
to fix this in my brain by like saying the
name herb without the H pronounced so like I I go,
I I said herb Herbert Hoover, Herbert Hoover. That that'll
fix it. Well, yeah, I mean it's easy to fall

(10:40):
into because herbivore, herbivoret. 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 percent success rate never fails. And after this passage,
Acosta has an aside to assure readers of this medicinal

(11:03):
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 aerbs, if you will,
are you know, essentially poisons right, But aside from the
dubious allegations about cupids ero type powers, this plant, the
herb of Love is remarkable for its ability to close

(11:25):
its leaves rapidly, moving at the speed of an animal
recoiling from a needle prick, and uh, I was looking
at another source which mentions Acosta. This is by JF.
Veld Camp called Notes on biophytem of the Old World,
polished in tax On in ninety nine. I cite this
just because veld Camp tells the story that Acosta claimed

(11:47):
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
of Love's rapid movement that he literally lost his mind
trying to study it. He was like, how does it move?
And and that was that was it for him. No

(12:08):
word on whether that guy ever used it for cupid
zero type purposes. Yeah. Because again, and this will be
something that we'll just we'll 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 like stumbled across one of these in the wild,

(12:28):
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
fly traps, you know, Like I remember when I was
a kid, and uh, 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

(12:48):
the house. And I think my consolation there was that
a couple of times I got a little pott of
venus fly trap. Yeah, they're they're pretty fun little plants.
They always have a huge container off them out at
the UH at the Botanical Garden in Atlanta for the
kids to interact with an inevitably stick a little sticks
into their into their their their mouths, if you will. Right, So,

(13:10):
we we know about that one. But if you're previously
unfamiliar with the plant like that, or or one of
these leaf closing plants like Mimosa putica or biophytum uh,
I imagine it would be shocking. Yeah. I mean we're
hardwired really to to expect that sudden movement in the
grass might be something dangerous. It might be a snake,

(13:32):
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 it might be a snake,
or or it's something like you know, chipmunk or squirrel.
Probably not a squirrel because they're a bit bolder. But
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 Christo Baul Acosta

(13:56):
was talking about, the herb of love and free Dell
points to an i've volume of the Botanical Register which says, hey,
we know about this plant from South America called the
Mimosa putica. It does that leaf shutting things. So maybe
this herb of love that Acosta is talking about in
India and the sixteenth century is actually the same plant.

(14:16):
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. Botanists are pretty
clear that the herb of love was actually this other
species I mentioned a minute ago, Biophytum sins ativum and
freedl rights. This was funny quote. Perhaps the erotic claims

(14:37):
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

(14:58):
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 used to
contract on the order of seconds. Well, scientists have actually

(15:20):
figured out the answer to this one. The types of
movement on display in the sensitive plant and other rapid
moving plants like the venus fly trap are known as
seismo nastic 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,

(15:42):
tropisms I think we've all seen in action. You know
what this is if you've 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 out. I
have a potted plant here on my desk, and over time,

(16:04):
it's leaves all start reaching out for the lamp next
to it, until I turned the pot around, and then
gradually they all start to hook back in the opposite direction.
And uh, 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

(16:26):
power lines. Sure. Yeah, So plants can grow in different directions,
responding to objects or 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

(16:49):
fly trap shows a nastic response. It doesn't go off
in a particular direction to catch a fly, but rather
when it since his movement in its trap area, the
hinge clothses, 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

(17:13):
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, while 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

(17:36):
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.

(17:59):
But okay, that's now stick movements now seised monastic movements
are nastic movements that are triggered by touch or by vibration.
Now again, um, 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 turger spelled t u r g o r uh.

(18:22):
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. Uh.
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

(18:43):
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

(19:04):
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 can have. Uh. We have a linen bomb, uh.
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

(19:25):
you know, bushy and full of life as ever totally.
In fact, you might have even observed this not with
a live plants, but uh, giving some veggies in the
kitchen a soak or even just a 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 gotta toss them. You
would be surprised how salvageable some greens are after a

(19:47):
soak in cold water. Really like like spinach, this verst
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 uh, you know, they're starting not like if they're
gonna 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, So come in
some cold water. They might come back to life and

(20:09):
be crisp again. I didn't know about this trick, but
now I 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. Uh, the water pressure is actually pushing
out against the cell wall, and so when turger pressure

(20:30):
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, you know, that'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

(20:51):
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.
That it's hinge, and this is known as turger movement.
So in in in a strange way, you can think
about it like the plant moving by causing itself to

(21:14):
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 ridgid again and they
go back to their extended state. But to come to
the next thing, UH, even more astonishing than the plant's
ability to behave physically in ways that seem more at

(21:35):
home in animals with muscles. Is potential evidence that the
Mimosa putica 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

(21:57):
has its own rudimentary form of memory. And uh, 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

(22:18):
of different types of claims of extremely variable evidential backing. Yeah,
and you also get into into areas of confusion over
like what constitutes uh, you know, animal intelligence and human
intelligence and so 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 b c. E.

(22:43):
Thinker Aristotle, of course, casts along shadow, and he wrote
that plants have a vegetative soul or to threapticon, which
I believe just means the vegetable soul, not to be
confused with two megathereon, which means the great beast in
Greek and is of course a uh a Celtic frost
album um. But I couldn't help but think of that

(23:04):
when I was reading about twopon. 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 and like, is this is what Aristotle was talking about?
Plants have a soul, they can feel right. But but
of course yes and no right, because they are two
important things to keep in mind about all of it.

(23:25):
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

(23:48):
like 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 in Plant Signal
Behavior titled Plant Intentionality and the Phenomenological Framework of Plant Intelligence,

(24:14):
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

(24:37):
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, uh so it's attributing
animals and humans with sensation and rational thought. I think

(24:57):
a lot of people have made some what seemed to
me to be pretty um 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 have animals and

(25:20):
then you have plants in the minerals. Uh. And there's
also this added caveat that aspects of the vegetative soul
continue on into forms that follow um, 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

(25:44):
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?
That I think it would say in reference to animals
and of course humans. Now, one thing that that martyr
points out is that while the aristotle view here, uh,

(26:06):
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 availability of resources. Now that's interesting because that could be,

(26:30):
on one on one hand, very true, but also could
easily be misinterpreted to 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 two threpticon well beyond the activities

(26:52):
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

(27:15):
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 um thing that he wrote about. But

(27:37):
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

(27:57):
fly trapp Like he got really excited about what this means.
And uh, maybe we can come back to Darwin in
in 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 uh, and I believe the author
mentions this that some of these ideas that Charles Charles
Darwin had regarding this root brain hypothesis, like they've people

(28:19):
have come back to them, uh in modern plant intelligence
research and and said, well, yeah, and then there's more
to this than than people of of Darwin's day thought.
Then there's also a nineteenth century German philosopher, Frederick Niici,
who is very much I believe inspired by Darwin. In
this wrote that a plant's nourishment and growth are expressions

(28:39):
of its will to power, or the wills who mocked,
which he identifies as the core driving force behind human beings.
Oh my god, So this this plot, 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 I am like the naysaying
crowd that it must rebel against and and show its might. Yeah.

(29:02):
And every day you don't kill it, you make it stronger,
right now. Um. In Eastern thought, there of course strong
traditions of all of this, as discussed in, among other
many sources, uh In Richard Nesbits The Geography of Thought.
China's Taoism and japan Japan's Shinto is Um both emphasize
the spirits of animals, plants, natural objects, and artifacts. Uh

(29:26):
And 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 um,
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

(29:46):
um concepts of plant animal hybrids, which, of course, with
all hybrids, they certainly perform various functions and symbolic um
uh you know, metaphoric and per natural thought. But they
also raised the question inevitably of animal nous and plants
and plant nous in animals. You know, like you you

(30:09):
can't think of something like say a screaming man dreak,
or say the vegetable lamb of Targari. 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 its sort of by blurring
the lines, by invoking the hybrid, making you think about

(30:31):
the characteristics of the opposite side that are present in
this side. Yeah, yeah uh. In fact, I think several
years back we did a an October episode called something
like the Killer Tree that was legends of of trees
that would eat people. It's a surprisingly common recurring motif,
though apparently has no basis in in real biology. No,

(30:54):
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 not the active predation like in that Oh that
is like a William Friedkin movie about the killer tree
that gobbles people up. Oh my gosh, I don't remember

(31:18):
this one. Okay, yeah, well we'll have to revisit. But there, Yeah,
there are clearly a lot of killer trees. And I
mean you have things like the ants, right, uh, trees
walking around like humans. And yeah, all these concepts they
they they're they're performing a number of different functions. But
I think one of them is that it inevitably makes

(31:38):
you think about about plants and animals, what do they
have in common when and 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

(32:02):
for memory or learning, I think we also have to
be very careful because the whole the realm of plant
uh 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

(32:24):
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 gonna talk about, all the way over to pure
pseudoscience and paranormal stuff. And uh, just to give some
quick flavor of the latter end of that spectrum, I'm

(32:45):
reminded of something we talked about briefly in an episode
that we did a long time ago. Rob, You remember
when we did the Science of Stranger Things that 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

(33:07):
it is hilarious. But I read a couple of whole
books about this. One, uh, of course, one if you
want a quick read that's very funny is The Men
Who Stare It Goes 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 paranormal government research projects that were fueled by

(33:30):
Cold War paranoia, but looked into that. They looked into
things like remote viewing and UH and and UH 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

(33:52):
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 New York Times article
I was reading about Baxter by Josh Eels, Baxter developed
a method for conducting polygraph sessions called the Baxter zone

(34:15):
comparison technique, which, according to this article, is still used
in polygraph test today. So cool. Anyway, later in his career,
Baxter quite famously became obsessed 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

(34:38):
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. Uh. So, allegedly
this plant was a quote corn plant or dressina fragrance, which,
in a confusing twist, is completely different for the plant

(35:00):
z 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
a 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

(35:21):
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? Uh, so from here, I
just want to quote from the article by Eels summarizing this, uh,
this this experiment quote. In human subjects, a polygraph measures
three things pulse, respiration rate, and galvanic skin response otherwise

(35:42):
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
and intense reaction on the part of the Dressina. To Baxter,

(36:03):
the implication was as indisputable as it was unbelievable. Not
only had the plant demonstrated fear, it had also read
his mind. Uh. 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

(36:24):
from afar. And upon this discovery, he did what any
responsible seeker of the truth would do. He went straight
to the popular media. Uh. And there was a book
based on his claims, and apparently uh 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

(36:45):
don't know if the time frames right for that. I
don't know if the time frames right either, but anseling
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 round about this on the internet, you will find
many believers even today still overflowing with faith in Baxter's claims.

(37:09):
It's one of those ideas that lots of people just
seem 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

(37:31):
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,

(37:55):
this appears to be nonsense. I can't help but wonder
if okay, this experiment was sixty six. Uh, Frank Herbert's
Dune was first published in sixty five, and of course
has the you know, very early on in the novel
has the scene where we have the Benegesta test of
the box and the com jabbar the box, which of
course makes you feel like your hand is burning and

(38:17):
on fire. And here in this test behalf that part
of the plant is actually caught on fire. Wow, that's interesting.
Yeah uh yeah. And the box is supposedly a kind
of polygraph of its own. Yeah yeah, yeah yeah. And
of course you have the Benegestate yeah, you know, truthsayers
and so forth. Though, I think in our episode on
that did we both come to the conclusion that we

(38:38):
think that the real power is the box actually does
nothing and it's just all in. 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 we both
liked that idea the most. Yeah, it felt the most
herbert E of the ideas. It's just a prop But anyway,
So to come back to all this, so we're gonna
be talking about plant memory research. But I think I

(39:00):
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

(39:22):
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
an evidential basis, with with the possible exception of quote
thinking under some very broad or inclusive definitions of what
counts as thought. Yeah. Like another area related to this
is the relationship doing plants and sound. So can plants

(39:45):
respond to sound, Yes they can, But can do plants
then benefit from listening to music? There's no evidence for that.
But I mean, this was an idea that was very
much in tho zeitgeist, especially in the UH That's where
we there was actually a wonderful album that came out,
an early electronic music album by Mort Garson, who is

(40:08):
a you know, early synth wizard who did a lot
of a number of different projects under different names, but
he put out this uh. This album titled UH Mother
Earth's plant Asia, and it is supposed to be music
that you play for your house plants, and your house
plants then benefit from it. Um. I don't think, you know,
house plants actually get nothing out of listening to this album.

(40:31):
But it's a wonderful ambient, experimental electronic album for 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 UH ambient music.

(40:53):
So double up, have them both and benefit. But anyway,
before we end part one of this 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

(41:14):
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 what
the evidential claims of the recent research are. So earlier
we mentioned that scientists are actually not sure why Mimosa
putica closes its leaves, though it is generally believed to

(41:35):
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?
Would then they'd be protected always? Why do they have
to do it rapidly suddenly? Uh? Well, because if they
were to keep their leaves closed all the time, the

(41:56):
plant would be drastically reducing its ability to collect unlight
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 and it's 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 that

(42:18):
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. And 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,

(42:43):
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,

(43:04):
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

(43:26):
in some way or subjected to physical contact with objects
in the environment, maybe by wind or something uh in
a way that is not actually a threat to the plant.
Were 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

(43:48):
according to this following study, it looks like maybe they do. So.
This was a study published in Ecologia in by Monica Gagliano,
Michael Renton, Martial dip Chinsky, and stuff Fauno Mancuso called
experience teaches plants to learn faster and forget slower in
environments where it matters. So the authors write in their

(44:08):
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 putica, the sensitive plant. The defensive leaf

(44:30):
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 putica and they mounted them on this contraption

(44:52):
that would repeatedly drop the potted plant a distance of
fifteen centimeters onto a padded surface, and the 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

(45:13):
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
habituated 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.

(45:35):
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
in uh 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

(45:57):
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,

(46:21):
so different from the drop, but it would also stimulate
the seismonastic closure 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

(46:45):
by repeated use. Now, there are some more interesting details
from this and this one that we might get into
in the in the next part of this series. For example,
they found that apparently this uh, this habituation to the
fifteen centimeter drop was still present weeks later after the
initial sessions, and that it was variable and adaptable depending

(47:05):
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 come back next time. More
research on plants and memory. Uh. If plants do in
fact possess some rudimentary form of memory and learning, how

(47:29):
what is the physical basis of that, given of course
that they don't have brains, uh? 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 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

(47:49):
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 on this topic. Uh. 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
fault episode. On the weekend, we do listener mail on Monday,

(48:12):
we do a short form artifactor Monster Fact on Wednesday,
and on Friday we set aside most serious matters and
just discuss a weird film on Weird House Cinema. Huge
thanks as always to UH well, actually to our regular
producer Seth Nicholas Johnson, and thanks to our guest producer
today Paul decand uh Paul really appreciate you seven in

(48:33):
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

(48:54):
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