Evidence of Plant Intelligence - The Bizarre Polarity of Plants - Rupert Sheldrake

I'm talking about the polarity of plants. I've  been interested in this subject for 50 years or   more. I've always been interested in plants since  I was a child. But when I was an undergraduate at   Cambridge, I got very interested in the ideas  of the German poet and scientist Geothe. And   Geothe was fascinated by polarity in nature.   He thought that as indeed many of the people   at the time thought that there were polarities  all over nature. This was shortly before Faraday   worked on electrical and magnetic polarities.   But there we have obvious polarities north and   south pole of the magnet. We have the positive and  negative polarity in electrical circuits and in   electrostatic phenomena. And he was interested in  the polarity of plants. And the obvious polarity   of plants is between roots and shoots. There's  also a polarity between the top and bottom of   a leaf and the right and left of the leaf. But  the primary polarity is the root shoot polarity.    And this is expressed in all sorts of ways. The  shoots grow up. They're attracted to light. They   grow up straight up against gravity. The le the  trunks of trees. The roots are attracted towards   the darkness. They grow into darkness. they grow  down. So they have opposite behaviors in relation   to light and gravity. And when you cut off a part  of a plant, the top of a plant, it regenerates in   a polar way. Here, for example, is a willow tree  that's been polarded. It's a normal way of pruning   willow trees. And what you see is that at the top  of the trunk, new shoots have come out. A few come   out down a little bit further down, but there are  none towards the base of the trunk. This is clear   polar behavior. And if you take stems of willow,  a branch of willow, and you cut it into bits,   each bit will regenerate and it will form roots  at the bit that was closest to the roots before   and shoots at the other end. They regenerate in a  polar way. And this shows some u a willow branch   that I cut into pieces. On one side you see  the oldest and then on the right hand side   you see the youngest one. And it's each bit has  regenerated uh with roots at the basil end the end   towards the roots in the original tree and shoots  at the other end. So each part when cut away from   the tree has an intrinsic polarity. This is a  little bit like magnets. If you take a magnet,   um here's one long magnet and it will pick up  little bits of metal and attracts metal at both   ends. This magnet will act as an entire  magnet. But if you take break it in half,   this is actually two magnets that have been stuck  together by magnetism. Each of these magnets is   now a complete magnet with a north and a south  pole. They each have their own polarity. And   it's very similar with the willow that I showed  here. Um each part of the willow, it takes on a   polarity of its own. So the polarity of the whole  is expressed in the parts. The polarity runs right   through. And this kind of polarity is established  in plants right from the beginning. In the embryo,   as a plant develops, there's an embryionic root  and an embryionic shoot. And here's a picture   showing a plant growing, a plant embryo. It's of  a shepherd's purse embryo. And at the top, you see   the fossilized egg. And then a line of cells  develop called the suspensor. and that is con   connected to the part of the embryo which becomes  the root tip and the opposite end becomes the   shoot tip. Uh in this particular case you see the  cotalons the seedling leaves folded over in the   fully grown embryo. So this polarity is intrinsic  in the plant. It's established right from the   beginning. It affects the way the plant grows and  the way it behaves. And one of the things that was   discovered very early on by Charles Darwin in fact  is that there's an influence that moves downwards   in plants from the chute tips and from the shoots  towards the roots which maintains this polarity.    And how he discovered this was he found that in  grass seedlings if you cut off the tip and then   you put the tip on one side bit to one side the  seedling will grow more on the side where you've   put the tip something's coming out of the tip  which makes it grow more. If you put take the

tip off altogether it stops growing for a while.   If you put the tip back it starts growing again.    And it was discovered in the early 20th century  that if you put the cut off tip on a little block   of agar, the substance that diffused into it from  the chute tip could diffuse out of the agar and   make things grow again. This was later identified  as the hormone auxin, a u x i n or auxin,   which is one of the principal plant hormones and  one on which I've done a great deal of research.    Um, I spent about 15 years working on Auxin at  Cambridge and elsewhere. And the growth of plants   is stimulated by auxin. It's a growth hormone.   It does a lot of other things as well. Chemically   speaking, auxin is indole acetic acid. It's a  breakdown product of the amino acid tryptophan.    The key thing is that auxins made in the shoots  and it moves down towards the roots in a polar   way. It's transported in a polar way towards  the shoots actively transported. This flow of   auxin towards the roots has a lot of effects. If  you cut off the top of a plant, the apical bud,   the apex is called the apical bud at the top of  the plant. If you cut it off, then side shoots   will grow out uh which normally don't grow out  from the buds at the side of the plants in the   in the axels of the leaves. They're little buds.   When you cut off the top bud, these grow out. The   side shoots grow out. And gardeners do this  all the time. They pinch out the top bud to make   the plant more bushy. Uh if you put oxen on when  you've removed the top bud, that doesn't happen.    What's happening is you're removing a source of  oxen and when you've removed it, you release the   plant from what's called apical dominance. So  auxin by moving down from the top of the plant   suppresses the growth of the side buds and when  you remove the source of the auxin at the top the   sides buds can grow and as it keeps moving down  the plant uh it stimulates the growth of roots   when it gets into the root system. So the more  oxen that comes down from the shoots, the more   lateral roots grow out from the plant. And if you  make a cutting uh then the auxin will move down,   accumulate at the basil end at the morphologically  basal end and stimulate roots to grow. This is   what happened in the willow cutings I showed you.   The auxin moved down in the stems and stimulated   these roots to grow at the base. This is an  intrinsic polarity. It's not to do with gravity.    For example, if you take a weeping willow, the  branches are hanging down. So the basal part   of the branch is not at the bottom as it is in a  normal stem towards the base. It's actually at the   top because the branch is upside down. But  if you take bits of stem from a willow, the auxin   moves in a polar way. It moves upwards because  it's moving upwards towards the root. So it moves   up and then it goes round and down the trunk  towards the roots. It's not moving in accordance   with gravity but in accordance with the intrinsic  polarity of the cells and the tissues. Well,   this is a very important fundamental feature of  plants. It fascinated Geothe. It fascinates me and   uh it's visible whenever you look at a plant. The  very fact the roots are shoes sticking up and the   roots uh the roots are down in the ground  is an expression of this polarity. So I was   interested in the question of how this polarity  is established in the cells. The fact the cells   transport oxin towards the roots towards the root  tips means the cells have an intrinsic polarity   themselves. Why do they have that polarity?   How is it established in the first place?    When I first got interested in this, one  suggestion, the prevailing theory put forward   by a plant researcher called Daphne Osborne in  Cambridge was that this was because the upper ends   of the cells are younger than the lower ends. As  a plant grows, the cells divide, making new cells,   and they grow more and they divide again. And  the result of this is that lower ends of the   cells are always in most plants, at least in many  plants, older than the upper ends. And she thought   the polarity had something to do with the age  of the ends of the cells. So one of the first   things I did to test that theory was to look at  the leaves of monocotyledons. Monocotyledons are   plants like grass, bamboo, daffodil, crocuses,  lillies. They're plants that have flowers in in   threes. Lillies have three petals and then another  three petals. Typically, their flowers are in

three-fold patterns and their leaves are long thin  leaves like grass leaves or bamboo leaves. Now,   the interesting thing about monocotyledons is  that the leaves don't grow from the tip like most   leaves do. They grow the leaves of dicotyledons  like beach trees, cabbages, tomatoes grow from the   tip and from the edges. So the leaves expand. The  growing points are diffused through the leaf but   mainly at the tips and the edges. In the case of  grasses and other molecotens, they grow from the   base. It's as if the leaf is extruded upwards from  the bottom. So the youngest cells are actually at   the base of the leaf and push it up as they grow.   The older cells are at the tip and that's why when   you mow a lawn the grass can go on growing because  you haven't taken away the growing tips by mowing   it. If you mow dicth leadenous plants which are  the ones with these broader leaves and networks   of veins in the leaves then they have to grow a  whole new chute because they grow from the tips   or they have to regenerate side shoots. But the  grass leaves just keep growing because they grow   from the base. And because they grow from the  base, when they form new cells, the new cells   divide to make a new cell. And that's pushed up  the cell and then another new cells made.    And the result is that the oldest cell wall is at  the top, not at the bottom. So it's the reverse of   what's happening in a normal plant stem growing  from the tip. The polarity of the cells in terms   of age is the opposite. Now what about the ability  to transport auxin the polarity as measured by   their physiology? Well, no one had looked at  this. So I did a study of monocot leaves   uh studying how they transported auxin. This  involved a technique which was extremely simple.    It was very a relatively new technique when I  first did this which was in the 1970s involving   radioactive auxin. It's a radioactive tracer.   You could get carbon 14 labeled oxen. How you do   the experiments, you take a bit of stem. Imagine  that's This is the tip end. This   is the root end. Normally it would be growing like  that. And you put a little block of aar agar jelly   on each end. And at one end you put the auxin,  radioactive auxin. Then you wait an hour or two.    It moves at a rate of about 1 cm an hour. And  then you collect the block from the other end   and see how much radioactivity is in it. Now what  happens is that if you put oxen in this block at   the apical end and then after a couple of hours  measure the radioactivity here, there's a lot   because it's transported the auxin this way. If  you do it the other way round, you put the oxen,   the radioactive auxin on the basal end and you  wait a couple of hours and then you see how   much radioactivity is at the apical end moving in  the opposite direction. There's practically none.    Showing that this is a transport system that  only moves things one way. I did these experiments   with a whole variety of monocot leaves,  grass leaves, crocus leaves, daffodil leaves,   rush leaves, lily leaves, orchid leaves and palm  leaves. I published a paper on this in journal,   the journal nature. It's called the polar auxin  transport in the leaves of monocotyledons. And   in this figure here, in this table here, you  can see the actual amounts of auxin that were   transported in each direction. For example, in  daffodil leaves, narcissus species, the amount   moved towards the tip acropetal, in other words,  opposite of the normal direction was zero. whereas   the mount a mount moved in the normal direction  towards the base was 4 4,616 counts per minute.    So clearly there's a extremely strong polarity  and you can see similar figures for these other   leaves some transported more than others but in  all cases the polarity of transport was towards   the roots in other words the same as in all other  plants. So the age of the cell walls, the edge end   of the cells in this case is the opposite of that  in uh stems of growing plants where the older cell   wall is at the top not at the bottom and it makes  no difference to the polarity. So it's nothing to   do with the age of cell walls. There's something  else that's causing the polarity of the plants.    I then looked at the way in which auxin is  transported in stems in the stems of dicotyledon

plants like beach trees, oak trees and tomatoes  and tobacco plants and holly hawks and all these   kinds of plants. As the plants grow, the stems get  thicker, a process called secondary thickening.    And there's a region between the bark and the wood  called the cambium where the cells divide that   way, not that way. They divide that way to produce  new cells grow and that's how the plant gets   thicker. So they're longitudinal cell divisions as  opposed to transverse cell divisions. So I wanted   to see what would happen to oxin transport when  the cells are dividing that way, not that way.    So I looked at the uh transport of oxone in the  stems of tobacco plants in a paper here called the   transport of oxin uh oxin transport in secondary  tissues in the journal of experimental botony.    And what I found was in this first figure which  you see here at the top it shows the top graph   shows the increase in thickness of the stems  as you go down the plant. At the top they're   thinnest and at the bottom they're thickest. And  that simply shows how they're getting thicker.    And the graph below that shows the amount of  oxen transported towards the roots basipetal   towards the base in the whole stems and in ste  segments of the stems where the outer part had   been stripped off. So the upper part of the graph  shows complete stems and the inner part the lower   part with the black uh marks shows the inner part  where you strip off the bark and look at the inner   part of the stem. Both of them are transporting  oxen uh towards the roots at the bottom. You   can barely see it because it goes along almost  along the axis at the bottom is the amount   transported in the opposite direction towards the  tips. So it's extremely polar. There's practically   none moving upwards and practically all moving  downwards towards the roots. The graph here on   the right shows the amount of auxin uh traveling  through the pith. The pith in the center of the   stem which is aging at the axis is different from  the other ones. Actually very little moves through   the pith and as the stem gets older the amount  of auxin goes down. So this is the opposite of   what's happening in the other tissues. The  pith isn't growing and dividing. It's just   getting older. The amount of auxin transported is  getting less. In the other tissues, it's getting   more because the amount of tissue is increasing.   The stem is growing. There's more cells. So it's   the newly formed cells that are transporting it.   I then looked at the different kinds of cells that   transport it in this uh figure here. And you  can see uh the amount transported when you have   the complete stem at the top. Acropetal means  towards the tip. Basipedal means towards the   base. In all cases, the amount moving towards the  tip and the opposite of the normal direction is   practically zero. If you take away the pith and  just look at the outer tissues quite a lot is   transported. What you see by looking at these is  that the transport's happening mostly around the   cambium. the bit between the bark and the wood.   When you pull that off, you damage those cells   and a lot of oxin stops being transported then.   But most of it's actually been transported in   what's called the interior phm bundles of phem the  tubes that conduct sugar in the plant which are on   the edge of the pith inside the wood. Tobacco is  unusual in having an internal phm. Most plants   don't. But most of it's going in these young  cells near the phm. It's not because it's being   transported by the phem itself. It's just  the sensitive oxin transporting cells are near the   phm. So what this shows is that the orxins being  transported by cells that divide longitudinally as   opposed to transversely. So it's still polar going  that way even though the cells are dividing that   way. So again, it's nothing to do with the plane  of cell division. I then looked at the question   of whether you can reverse the polarity of plants  by growing them upside down. If you take a cutting   from a plant and you turn it upside down and you  put rooting hormone, which is synthetic oxen,   on the apical end, you can make roots grow there.   They wouldn't normally. grow   there and then shoots will grow out and grow  up and you can have the whole functioning of   the stem is then inverted. sap is going in the  opposite direction. The sugars are flowing in the

flow from the leaves to the roots in the opposite  direction to the way they'd normally flow. Does   that make oxen move in the opposite direction as  the stem thickens and new cells are formed? Well,   I discussed that in this paper published in the  journal new phytologist called the polarity of   oxen transport in inverted cutings. And I did this  with a number of species uh including tomatoes.    And you can see here a picture of a tomato plant  that was grown from a cutting where the roots are   at the apical end and the shoots are at the basal  end. It's being grown upside down. So the stem   uh was functioning in the exact opposite of the  normal polarity. But then what about the orxin   transport? Well, uh it turned out that the orxing  transport as shown here in this table was uh going   in the normal direction. It still retained its  original polarity despite the fact that everything   else was working in the opposite direction. This  shows that the polarity of the cells is deeply   embedded in their nature. You can't change it  by switching everything else around. They retain   their original polarity. um it's very deeply  embedded in their being. Well, after   these studies, I wanted to find out whether one  can study polarity and find out more about it by   looking at much simpler systems and I did some  research on a tropical fern. I did this research   mainly at the University of Malaya in the bot  department uh where um I worked with a colleague   Dr. V. Ragavan an Indian uh scientist who was the  world expert on the early stages of fern growth   and I worked on a fern called the bird's nest  fern as spleium nidus which grows epithetically on   trees in tropical forests and like other ferns it  forms spores on the backs of the leaves and these   spores when they germinate in a polar  way they first form a little root hair and then   a thread grows out of them called a protonema.   Just a single file of cells which then divides   to form a plate of cells and from that uh the  sexual organs are formed which give rise to   the fern as we know it. The sporopy it's called.   The first stage that germinates from the spore is   called the gito gamito. It has half the number of  chromosomes of the sporopyte. But the point I was   interested in was its polarity. It has a little  root, a risoid, a root cell. And then it grows a   file of cells. One by one, it divides to form this  long thin tube of cells. And the polarity is there   in a single file of cells. It's nothing to do with  oxin transport here. It's just pure polarity. It   must involve nutrients flowing towards the growing  tip from the photosynthesis in the cells that make   them and also things absorbed by the little root  hair, the risoid from the soil. Uh minerals and so   on must all be moving through the cells towards  the growing tip in a polar manner. The cells   are polar. They're polar in their functioning  and the whole thing shows a kind of polarity.    If you cut off the tip then the side uh the  cells in the middle branch. It's a kind of apical   dominance even in this very simple system. So what  I was interested in is do these cells show any   visible signs of polarity that will give a handle  on understanding how polarity is working. And to   do this I used a technique called plasmolysis.   It's been well known for a long time that if you   put plant cells in a strong solution of sugar or  salts by osmosis the cell shrinks because water   moves out of it across the semi-permeable membrane  of the cell and it the cell shrinks inside the   cell wall. Plant cells have a cellulose cell  wall around them and the cell is normally turgid   pressing up against the cell wall swollen with  the water that comes into it. But in these strong   salt solutions, they shrink. They get smaller.   As I say, it's called plasmolysis. When you do   that to the cells in this threadlike structure of  these ferns, the cell shrinks, as you see here,   the shrunken bit where it pulls away from the wall  remains connected to the wall by little threads   called hectian strands after a German botist  called Hec. And the cell you see is pulled away

from the wall. But interestingly when I did this  plasmolysis with a sugar alcohol called manitol   the plasmolysis was polar. In other words the  plasmolysis meant it pulled away from one wall and   remained attached to the other. And it pulled away  from the basal wall the wall towards the risoid or   the base of the plant and remained attached to  the top wall towards the apex the apical wall.    And when one did this with the whole strand,  this is a drawing of one of these threads. It's   called a protoenema. This first strand formed  when the spore germinates. You see the spore,   you see the risoid that's grown out of it. You  see a file of cells moving towards the apical   cell. And when it's plasmalized with manitol,  they all pull away and move towards the   apex detaching from the base of the cell.   And this shows that there's a differential   attachment. There's something different about the  cell membrane at the two ends of the cell. And you   can actually see how it behaves differently.   I looked at the way in which different salts   or and sugars would affect this. And it turns out  that they behave rather differently in all cases.    The majority moved towards the apex, but this  effect was much stronger with some substances   than others. And here you see an effect comparing  the effects of menitol with three other compounds,   all salts. Magnesium sulfate shows a very similar  effect to menitol. Practically all the cells are   polar plasmalized towards the apex shown in red.   That's the percentage shown in red. The percentage   towards the base is shown down here in blue and  the ones that detach from both ends is shown in   yellow. It's practically zero. Magnesium sulfate  shows a very similar effect to manitol. Calcium   nitrate shows a much less pronounced effect. It's  still polar, but more cells remain attached to the   base and some detach from both the apex and the  base of the cell. And potassium nitrate shows even   more than calcium nitrate a tendency to be less  polar than manitol and magnesium sulfate. So this   shows that there's something about the way the  attachment of the cell wall to the cell membrane   works that can be affected by all these salts. Now  this becomes very relevant when we look at the way   in which orin is transported in a polar way in  higher plants. I just want to say one more thing   about polarity. There's an aspect of polarity  which has been very much ignored by researchers   and that's electrical polarity. It's been  known for a long time that when spores or eggs   germinate, there's a polarity between electrical  polarity between the bit that becomes the root   and chute. There's the  whole thing is electrically polarized. It's very   well known in fact that the earth the roots are  in the earth of course the earth is electrically   charged in a negative direction in relation  to the atmosphere. And the further up from   the earth you go, the greater the difference. The  difference near the earth is enormous. It's it's   not microvolts or anything. It's about 100 volts  per meter. So if you go a meter off the ground,   there's a 100 volts difference between the  air there and the ground. 2 m is 200 volts.    And when you look at a diagram diagram  here showing the polarity of the earth and   some coniferous trees, there's an enormous polar  envelope. And the tree because it's connected   to the soil through the sap growing up through the  wood which is electrically conductive. The tree is   negatively charged sticking up into the positive  atmosphere. And so there's a big difference   between the tree and the air around it, which  means that the electric tips of the tree and the   branches and of the shoots attract positive  ions and they affect the electric field all around   them as you see on the left. Now a recent study  with flowers showed that this gradient is present   in the petals. If you shoot out positively charged  paint particles through an electrostatic spray gun   at the petals of flowers, it turns out that the  petals of flowers show this kind of electrical   gradient and the positive particles go to the most  negatively charged bits of the petal which are   the tips. Here you see a series of flowers. On the  left you see the normal flower as it is and on the

right you see the flower after it's been sprayed  with blue um positively charged particles in the   case of the upper flowers and right at the one at  the bottom it's been sprayed with yellow charged   particles and you see that the there's an electric  gradient. You can actually see the electric   gradient in the petals. Oddly enough, and very  surprisingly, no one has yet done this for leaves.    And I think that the electrical polarity of leaves  may well be important in setting up the primary   polarity of the orxin transport system in growing  leaves. It wouldn't be difficult to do this. If   anyone watching this has a electrostatic spray  gun that sprays out positively charged particles,   try it out on some plants in the garden and see  whether you get a pattern like these flowers with   the leaves, whether you get more around the  tips and any sticking out bits. I think it's   very likely you will. This is still an ongoing  investigation. The polarity of plants is an open   topic still not known how this initial polarity  is established. But I think it's very likely   that electric gradients play an important part  not only in germinating spores and eggs but in   developing plants because the whole plant is in an  electrical gradient and somehow once that polarity   has been established in the cells it leads to the  transport of auxin in a rootward direction and   affects all other aspects of plant polarity.   But the auxin is a reflection of a polarity   that's already there. A lot is now known about  the details of how the auxin transport system   works and even at the molecular level where the  polar distribution within the cell of molecules   that are involved in auxin transport is but  it's still not known exactly how that initial   polarity is set up. And that's the bit that  where I think electricity could be playing a   key role. So this is very much an open question.   I've been working on this and thinking about it   for 50 years and I can't give you the final answer  to this because it's not known. Uh no one's done   some of the experiments and some of them could  be quite simple. There is more known about the   details of how that works but about the initial  polarization there's still a lot that isn't known.    Thanks for tuning in to this episode of After  Skool. I hope it will help you to look at plants   in a new way. If you'd like to learn more about my  work, you can go to my website www. sheldrake. org or you can follow my work  through my Substack which   is rupertsheldrake. substack. com. Substack. com