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Author Topic: How do Trees Really lift Water to their Leaves?  (Read 244837 times)

Offline Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #225 on: 02/11/2008 22:20:56 »
The void vanishes each time when the tube is lowered back to ground level due to the compression of the atmosphere. Sorry for not including this as did not realise this was what you were asking. A direct question always helps.
 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #226 on: 03/11/2008 10:27:00 »
I'm sorry; were the following extracts not direct enough?

Quote from my post of  29 Oct:
Your original post did not discuss how the space at the top had formed. Are you suggesting that the gap at the top of the tube was a vacuum? In which case , when you removed your 'extra force', the water would have gone back up to the top (as Galileo et al have found). If the gap remained, then it was full of air. This air can only have got there as bubbles from the bottom, out of solution or via a leak in your 'sealed end.  It must have come from somewhere.
Quote from my post of 29 Oct (later):
How about my question regarding the space that you saw above the column of water? Did it stay there? Was it air? How did it get there?  There is an interesting practical question here.


My comments referred to the single tube - to avoid confusion. It was clearly in that context.  Your last answer seems to refer to the high level U tube experiment. You see, I think that you really don't want the single tube to work because it would go against your theory. However, if you can clear up this problem then I would take that back, of course.

Did you also not read my direct statement that you were wrong when you wrote the tension is the same throughout the column? That needs an explanation from you, I think.

I also made a direct comment, earlier, using chewing gum as a metaphor for water at the top of a tube. No comment about that, either; was it irrelevant?

I just saw this statement from you whilst I was revisiting past posts:
"Stop thinking of water as water, start thinking of it as a solid."
Were you joking?  Can that be taken seriously? At what point do we have to treat a bowl of water as a bowl of solid? You could freeze it - but I don't think that's what you meant. When does a water molecule, at room temperature, know how to treat its neighbours differently? When is it part of a solid and when is it part of a liquid?
 

Can I recap on your recent single tube experiment? As I understand it you used a single tube, less than 10m long and whirled it around to simulate a longer tube. You noticed cavitation at the top whilst it was revolving and this cavitation disappeared when you stopped.  IS this correct?
What was the actual length and at what speed did you rotate the tube? How did you see the effects?

I'm not sure but I got the impression that you repeated this with a U tube and the water ran out. This is what you'd expect because of asymmetry.

Last comment, for now: Could you please define what Density Flow means? I can't find it anywhere apart from in your writings.

« Last Edit: 03/11/2008 12:32:32 by sophiecentaur »
 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #227 on: 03/11/2008 13:56:20 »
Sorry but I just spotted this in your last post.
Quote
You say water would move away from the inside of the tube. As water is already compressed by gravity, where is it going to move to? It can't move down the tube because it is linked to other molecules balancing the downward pull equally on the opposite side of the U tube. It canít flow out because this would require cavitations to form, again to break the cohesive bond.

I was 'indoctrinated' into mechanics when at School, along with Newton's Laws. Forces add vectorially (would you not agree?).
At the top of the tube (when it is >10m, to keep the diagram simple), we have cohesive forces, acting towards all the nearby water molecules and the weight of the molecule, acting downwards. Nothing is being 'compressed by gravity', the molecule is just being pulled downwards by its own weight. The other molecules are all pulling away from it. These all produce a resultant force which acts away from the wall. Unless this force is canceled by an equal and opposite adhesion force, the molecule will move away from the wall. It can only stay where it is when the forces are balanced. Can you possibly disagree with that?
When this molecule moves away, it, of course, would let all the other molecules move - they are under tension- and they can flow out of the bottom of the tube as long as there is an unbalance in the forces.
Unless you have adhesion - not just a bit, but of equal value to balance the other forces involved - the bead will part company with the wall. If you don't agree with that then you need to go away and learn the basics of how forces work.
Needless to say, this applies to any shape of container, be it U tube, or an upside down Poseidon in the well known film.
You don't have to pick me up on this example because, in that case, the adhesive forces are not enough AND cavitation will occur. But that isn't the point of the argument.  The point is that, if the column stays up, it must involve both 'strong' adhesion and a delay in cavitation.
 

Offline Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #228 on: 03/11/2008 14:22:12 »
A density flow is what it says it is. Density flow is the movement of a denser solution acted upon by gravity from an elevated point towards the ground, which in turn induces a return flow. So it is a flow and a return flow system. This simple density flow is what drives a non-pumped domestic hot water system. The heat source alters the density of the water causing it to rise. The copper coil inside the hot water tank causes the water to become denser as it transfers the heat from the tube to the water inside the tank, causing it to flow back down to the source of heat, where the circulation process continues. A self circulation heating system operates by the force created by the density difference between the hot and cold fluid.



 A video on Youtube shows the flow through a clear glass vase. Watching it you could easily miss the point that for a downward flow of denser solutes, there must be a return flow to the surface, water molecules will always move to where molecules have moved from, just the same as they would when molecules move away from the inside of the pipe.

Your post asking about the void related to the single capped tube. I said that water flowed out of the tube when the experiment was performed, so could not have returned to fill up the void.

Damn, just realised a mistake with that capped experiment.  Maybe if we have a single capped end of tube and the open end in a vessel rather than being exposed to the air will assist the water to resist the centrifugal force longer. This would require affixing the bottle in some way to the end of the tube to prevent it from flying off.

There was no point swinging round a U tube in the same way because water would not remain in it. Again however if the both ends of the tubes were in a container and it was swung round it may prove interesting.

The chewing gum analogy necking, I did mention that as one molecule moves away from the wall of the tube another will replace it providing of course that the cavitation is not sufficient to cause the bead of water to fail.

Popping out so will get back to this on return
 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #229 on: 03/11/2008 15:51:28 »
OK on the term 'density flow'. In a hot water (convection) system, the energy comes in the form of thermal energy. To keep it going you need to keep the energy flow by maintaining a temperature difference.

Quote
The heat source alters the density of the water causing it to rise.
That's schoolboy howler number one. Water will not rise unless it is pushed. There are no strings pulling it up. What pushes it? It is the more dense cold water which displaces it.
Andrew, if you are not thorough with well known matters like that then how can you hope to make any worthwhile advances in Science?

Quote
Your post asking about the void related to the single capped tube. I said that water flowed out of the tube when the experiment was performed, so could not have returned to fill up the void.
So what was in the space over the water? If there was a permanent 'void' at the top then it must have been AIR! That means either a leak into the top or bubbles floating up from the bottom. I wish you could explain exactly what happened. It certainly casts doubt on the experiment.

Quote
water molecules will always move to where molecules have moved from,
Here's another cause and effect problem. The more dense solution displaces the less dense. Why? Because the more dense is pulled down harder than the less dense and pushes it out of the way. When you add the solution, you increase the overall pressure at the bottom of the container.
How does that apply to molecules as they move from the surface when water evaporates? You imply that you would get 'strings of water' leaping up into the air.

Quote
I did mention that as one molecule moves away from the wall of the tube another will replace it
And where does this molecule come from?  Does there have to be a flow? Do you inject them into the top? Get your model sorted out; it really is dodgy. Or are you only considering the situation when you have enough gum flow to allow the molecules to come from the other side? You are implying that there is a minimum speed at which this would work. Any slower and the gum will 'neck'. My diagram applies to the gum just the same as the water. Are you arguing with the basics of force vectors?
« Last Edit: 03/11/2008 19:03:32 by sophiecentaur »
 

Offline Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #230 on: 03/11/2008 19:04:15 »
Sophie. Why do you mock?  In my density flow tube, we clearly see one side of a soft walled tube pulled in and one side bulging out. We clearly see water leaving one vessel into another and the same goes for a closed loop of tubing.

Your statement that water will not rise unless it is pushed may need a little edit, else you will have the entire cohesion tension fringe of science after you. They state as one molecule leaves a leaf (scuse the pun)  another is pulled behind it to replace it and this believe it or not is largely accepted science and all science has to offer with regards to the ascent of sap in tall trees, perhaps you should take a leaf out of their books?

And yes there are strings pulling on the fluid, strings of particles linked together just like RD suggested in his chain analogy. Using food colouring we can see how the flow occurs, we do not see a uniform full bore flow but a considerable amount of turbulence as some of the coloured salt solution is flowing down the return flow side of the inverted U tube which rolls in a circular motion as salt free water is drawn past it. Fascinating to watch by the way and well worth studying. It shows how molecules pull on each other too. What do you suggest might be pushing water out of the top of a giant sequoia towering well over a hundred metres? Root pressure? Magic?

The central heating system shown was merely to illustrate that a downward flow will result in a return flow. But more to the point to coin one of your phrases; ĎHow do molecules of water know they are in a U tube, a central heating system, a single upright capped tube, a tree or indeed a human í? Why should we expect that an upward flow or downward flow inside a tree will not produce a return flow? Schoolboy stuff this, but before the education system gets in their way!

And let us not forget your meniscus example where adhesion is pulling the water up at the edges, or have you forgotten this argument already?

I have not said there is a minimum flow at which this will work. I have said that we have an excellent opportunity to study cavitation in this model due to itís stability and this is the first time the speed at which cavitation takes place in water suspended in a meta-stable state. There is another thing I would like to add. It would appear that cohesion is taking place in the upward flowing leg of the suspended tube. I may certainly have missed some cavitations forming in the 24 meterís of water filled tubing on the down flow side, but suspect that the saline flows, which represents the phloem in trees is repairing the voids? Or is the positive pressure evident by the outflow from the bottle at ground level sufficient to prevent them from occurring in the down flow side? Even the bench top model produces cavitations over time.

The rotating tube failed because the open end allowed all the water to come out of the tube emptying it completely so unable verify if there was void in it or not.

To conduct a 24 meter single tube experiment would be a pain in the back side. Have you ever tried filling a six mil bore tube with water and making sure there are no bubbles in it, that is capped at one end? I have, and will not be attempting to fill a 24 meter one.


OK on the term 'density flow'. In a hot water (convection) system, the energy comes in the form of thermal energy. To keep it going you need to keep the energy flow by maintaining a temperature difference.

Quote
The heat source alters the density of the water causing it to rise.
That's schoolboy howler number one. Water will not rise unless it is pushed. There are no strings pulling it up. What pushes it? It is the more dense cold water which displaces it.
Andrew, if you are not thorough with well known matters like that then how can you hope to make any worthwhile advances in Science?

Quote
Your post asking about the void related to the single capped tube. I said that water flowed out of the tube when the experiment was performed, so could not have returned to fill up the void.
So what was in the space over the water? If there was a permanent 'void' at the top then it must have been AIR! That means either a leak into the top or bubbles floating up from the bottom. I wish you could explain exactly what happened. It certainly casts doubt on the experiment.

Quote
water molecules will always move to where molecules have moved from,
Here's another cause and effect problem. The more dense solution displaces the less dense. Why? Because the more dense is pulled down harder than the less dense and pushes it out of the way. When you add the solution, you increase the overall pressure at the bottom of the container.
How does that apply to molecules as they move from the surface when water evaporates? You imply that you would get 'strings of water' leaping up into the air.

The moecule I mentioned was a water molecule, so presumably it would have come from the water inside the tube.

Quote
I did mention that as one molecule moves away from the wall of the tube another will replace it
And where does this molecule come from?  Does ther have to be a flow? Do you inject them into the top? Get your model sorted out; it really is dodgy. Or are you only considering the situation when you have enough gum flow to allow the molecules to come from the other side? You are implying that there is a minimum speed at which this would work. Any slower and the gum will 'neck'. My diagram applies to the gum just the same as the water. Are you arguing with the basics of force vectors?
« Last Edit: 03/11/2008 19:08:01 by Andrew K Fletcher »
 

Offline Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #231 on: 03/11/2008 19:48:35 »
We have a U tube filled with degassed water to add stability. Adhesion must apply to the entire length of wetted inside of the strong nylon tubing. I agree so far at least. The molecules are all happily stuck fast to the tube. Still with you here so far. It can be as strong as you like and I am entirely happy with this and indeed it is perfectly logical and obvious. In fact I would go so far as to say the water stuck to the inside of the tube forms itís own water tube. This provides an environment for water to flow either way in this suspended tube providing it is below 10 meters. If we pull both ends out of the water below 10 meters water flows out one side and the other side is emptied out of same side as it is pulled around by the out-flowing water, just like a syringe draws water from a vessel. So the water molecules involved in adhesion do not prevent free movement through the tube, but do prevent the water inside from necking, as in your chewing gum analogy. Above the 10 meter mark we do not have gravity pushing down and the atmosphere, which in turn pushes down on the water in the open vessel that in turn forces water up the tube or in this case assists it to stay there below the vacuum / void point.

So there is an attraction to the wall of the tube and molecules should align to the tube to form adhesion by using the opposite polarity to the nylon tube molecules-whether this is relevant at the moment Iím not sure. Nevertheless water can flow out either side of the tube, so adhesion does not prevent the outflow in the U tube. So cohesion must be the main stabilising force. What I hope I have said here is that although the water is stuck to the inside of the tube, water can move freely it does not arrest the water column so cannot be responsible for holding the open ended water filled tubes that we have exposed to the atmosphere by removing them from the water. So why does the water not flow out? What explanation other than the elasticity of water which is related directly to the cohesion of water will account for the water rapidly rising up the exposed tubes forming a level a considerable distance from the ends of the tubes?   
 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #232 on: 03/11/2008 21:03:32 »
Andrew. You are in your own little Science Cloud Cuckoo Land, I'm afraid. Three is just no point in continuing with this. You are not even aware of how much Science you are rejecting.
Over and out.
 

Offline Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #233 on: 03/11/2008 23:08:44 »
You can't have it both ways either the water is stuck to the tube or it is not. But only the molecules closest to the tube count. The rest of the water does not come into contact with the tube so relies on cohesion and is therefore free to flow either way but not without having an affect on the molecules next to those that are flowing. The question is really why don't you repeat the damned experiments and draw your own informed conclusions, rather than summising what you think must be happening?

By the way cloud Cuckoo land is way above 24 meteres vertically. And unlike the cohesion tension theory you et al adhere to, it does not suck.
 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #234 on: 05/11/2008 11:02:03 »
I'm sorry but your last post, as they all tend to, consists of a non-logical, circular argument. I just can't cope with it any more.
Thoroughly examine what you have said.
 

Offline Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #235 on: 05/11/2008 15:42:32 »
Sophie I don't know how to put it into words that you can understand. Trying to say that even if the molecules are stuck to the tube it does not prevent freeflow from the tube as observed below 10 meters, if that makes sense. So adhesion while important is simply not as important as the cohesion in water molecules which is why the Brixham experiment works. My work is logical and has convinced a lot of professional people at professor level. 
 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #236 on: 05/11/2008 19:22:47 »
Of course the water can flow - it's a liquid. But what you ignore constantly is that, if there is no adhesion then it will leave the wall (it will flow away from the wall). You talk about water 'flowing in' to to make up the space but where will it come from? From which side? It will merely form a neck because each of your down tubes pull it in different directions. You are surely not suggesting that there is enough velocity in the flow to keep it moving, are you. It doesn't have to flow to work, in any case - you say.
Don't you see the very basic inconsistency in your version of what goes on at the top?
Give it some serious thought.
A rope can be as strong as you like but if you don't tie it on, it comes adrift. The molecules at the interface are the only thing which can keep the water in place up there - if you detach them, the column will pull apart due to necking.
Are you saying that a smooth bore metal tube >10m would work also? It is known to have lower adhesion to water than  water cohesion, remember.
Let's face it, you have assumed that the single tube will not work on the grounds that you believe you have an explanation how the U tube works. That is a totally circular argument and can't prove anything. You are totally locked into this misconception and have given no justification for it.
You have yet to answer a lot of my objections to your basic Science statements - like the tension in the column being the same. Any comments?
There - you've started me off again - blast.
« Last Edit: 05/11/2008 19:27:47 by sophiecentaur »
 

Offline Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #237 on: 06/11/2008 08:58:58 »
I did reply to your question about tension being the same throughout the columns of water on both sides. Tension is applied to every single water molecule. This dragging effect was realised by Professor H.T.Hammel, ever wrote a paper on it relating to how current understanding of osmosis is totally wrong. Dissolved solutes apply the tension as they move from one point to another due to the effects of gravity and in doing so cause the whole of the liquid to move in the direction of flow. One would think that the bead of water breaks because the tension is greater in the area that breaks. But this is not entirely accurate. Cavitations take place along the column of water rather than just at the top. It is the tiny cavitations that join together that eventually cause the columns to separate and the levels to return back to the 10-meter mark.

When I conducted these experiments, I did so because everyone else had assumed there was no point because of historic experiments with water in tubes. Clearly they were wrong. The experiment you keep trying to justify is the very same experiment that has failed for 300 years. Modifying it slightly may as you say improve the possibility of prolonging it before it collapses, and as it is your idea then it is you that should test it. As I have said it is a pain filling a closed loop tube with a liquid. But having thought about this it could prove easy to do with a smaller tube inserted inside the 6 mil tube to push water in under pressure right to the end, withdrawing the inner tube as the water is injected. The tube would need to be relatively stiff to be able to push it right to the closed end of the 6 mil bore 24 meter tube.

The justification I have given to the U tube experiment is that it clearly does work, even when scaled down.

Remember. The U tube experiment was relating to the shape of vessels in nature. Trees do not have tall tubes that flow up to the top and end, they have circular vessels that entertain a circulation, something worth remembering.

A lot of people are reading this thread, would anyone else like to add their thoughts on whether a single capped tube would cause water to remain inside at 24 meters or even above 10 meters? The end of the tube should be globe shaped or rounded and smooth. Are there any schools or colleges interested in performing this experiment in the name of science?
 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #238 on: 06/11/2008 14:38:56 »
So you are saying that the force on the bottom link of a hanging chain is the same as that on the top link?
What about the weight of the chain? This is the most elementary mechanics and doesn't need to refer to Prof Hammel or osmosis. That is just a smokescreen.

What you say about tension is merely an unsubstantiated statement - not a reasoned argument. Solutes will tend to fall because they are more dense. A stone will do the same thing in water.

You have no proof that the U tube is any different from the single tube because you have not done a control experiment. Yes, it would be a pain but, without it, you have not proved a difference. You are the one who needs to prove it - not me; those are the rules, I'm afraid. Old ideas are "Innocent until proved guilty."

You can't seem to deal with my 'necking' / adhesion argument and what would happen at the top if it weren't for adhesion so I presume you have no answer.

I would have to decline your kind offer to demonstrate your ideas to a bunch of innocent Schoolkids because your whole methodology is flawed. They could really do without that sort of influence until they are equipped with some logical thinking skills.
"In the name of Science"?? What Science? Science is consistent - or aims to be so. You have introduced an inconsistent idea which is not proven. You just get upset when it is not accepted.
Give me a good, logical, argument which refutes the logic of how the column of water would not stay up there unless stuck to the tube. And would it work in a metal U tube?

We have already accepted that your experiment worked. That is an interesting and surprising result. It's your explanation which is not acceptable because it does not stand the logic test. The one doesn't follow from the other.

And 'scaling down' is not valid because you have not scaled the ambient pressure. Can you argue with that?

Quote
Remember. The U tube experiment was relating to the shape of vessels in nature. Trees do not have tall tubes that flow up to the top and end, they have circular vessels that entertain a circulation, something worth remembering.
Can you repeat that in a way that makes sense, please? Tubes don't flow. Which are the circles? What does "entertain circulation" mean?
 

Offline Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #239 on: 06/11/2008 21:27:34 »
Put another way: The sap that flows in the tree is not on a one way trip to atmospheric liberation, it circulates around the tree evaporating water from it to the atmosphere, just the same as we do not excrete blood unless wounded, a tree does not excrete sap but evaporates solute free water from the sap.
Can see I missed some words from the last post now sorry.

I know this conversation has become heated at time. I just want to say that I am grateful for your thoughts even if at times I appear to be unhappy with some of your less than civil comments. The original explanation for the tubular experiment was written for students at Junior and secondary level in order to introduce the concept of a flow and return mechanism, without clouding it and making it too complicated for them to understand it. I still feel I did a good job regarding this and had no problem convincing both students and teachers with the experimental model and indeed the flow and return argument in trees.

I am beginning to take on board that a more detailed explanation is required for eventual publication, and as you say the need to test a single tube, a metallic tube, a plastic tube filled with mercury etc etc. I am also beginning to understand, thanks to you and others why a simple explanation may prove too problematic for people to grasp the behaviour of stretched fluids without seeing it for themselves, again thank you for enlightening me on how this is interpreted by others.


 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #240 on: 06/11/2008 22:52:37 »
That's OK as far as it goes Andrew.
I see that you are totally convinced that your Science is correct.
It is not 'too problematic' for me to understand what you are saying. It is 'too problematic' for me to accept it. There's a big difference.
As I have said several times. Your experiment show evidence of a phenomenon which is novel but your explanation is just too naive. I don't need to see it for myself. I believe you saw what you saw.
I also believe in well founded Science. Results, in general, agree very well with the established theories.  You, apparently don't understand these theories or you would be looking for an explanation for your phenomenon amongst them, rather than making up your own incomplete one.
Science tries not to be a matter of opinion; we try to base it on rigorous logic. When someone brings up an objection, for instance, based on vectorial addition of forces the objection has to be answered with rigour. You have chosen not to consider how this shows flaws in your explanation. If you explanation were correct, you could explain such an apparent anomaly.
You seem to be leaving this dialogue, assuming that you are, in fact right and ignoring objections.
Please don't have the temerity to object to conventional Science teaching on the grounds that we tell kids to believe things "because we say so". That is just what you have been trying to do -and with far less justification and track record. If a student objects to any of the standard Science I present them with, I am in a position to justify it right up to the wire. I would not dream of belittling them merely on the grounds that they have 'interpreted it' wrong. I will give them a full and rigorous explanation after having worked, if necessary, for a long time to reconcile their ideas.
I see you regard yourself as a heroic figure, battling against the massed ignorance of the Science establishment.In fact you are a Don Quixote, tilting at Scientific Windmills and failing to see what is actually going on around you.
Please try to read some established texts. They cannot all be wrong in every respect so they may just be more right than you are about this topic - if only you could understand what they are really saying.
It's never to late for some independent learning and self education. I do it every day.
 

Offline Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #241 on: 07/11/2008 14:04:00 »
Transpiration-Pull http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/X/Xylem.html

In 1895, the Irish plant physiologists H. H. Dixon and J. Joly proposed that water is pulled up the plant by tension (negative pressure) from above.

As we have seen, water is continually being lost from leaves by transpiration. Dixon and Joly believed that the loss of water in the leaves exerts a pull on the water in the xylem ducts and draws more water into the leaf.

But even the best vacuum pump can pull water up to a height of only 34 ft or so. This is because a column of water that high exerts a pressure (~15 lb/in2) just counterbalanced by the pressure of the atmosphere. How can water be drawn to the top of a sequoia (the tallest is 370 feet high)? Taking all factors into account, a pull of at least 270 lb/in2 is probably needed.

The answer to the dilemma lies the cohesion of water molecules; that is the property of water molecules to cling to each through the hydrogen bonds they form.


When water is confined to tubes of very small bore, the force of cohesion between water molecules imparts great strength to the column of water. Tensions as great as 3000 lb/in2 are needed to break the column, about the value needed to break steel wires of the same diameter. In a sense, the cohesion of water molecules gives them the physical properties of solid wires.

Because of the critical role of cohesion, the transpiration-pull theory is also called the cohesion theory.
Some support for the theory

    * If sap in the xylem is under tension, we would expect the column to snap apart if air is introduced into the xylem vessel by puncturing it. This is the case.
    * If the water in all the xylem ducts is under tension, there should be a resulting inward pull (because of adhesion) on the walls of the ducts. This inward pull in the band of sapwood in an actively transpiring tree should, in turn, cause a decrease in the diameter of the trunk.

         * The rattan vine may climb as high as 150 ft on the trees of the tropical rain forest in northeastern Australia to get its foliage into the sun. When the base of a vine is severed while immersed in a basin of water, water continues to be taken up. A vine less than 1 inch in diameter will "drink" water indefinitely at a rate of up to 12 ml/minute.

      If forced to take water from a sealed container, the vine does so without any decrease in rate, even though the resulting vacuum becomes so great that the remaining water begins to boil spontaneously. (The boiling temperature of water decreases as the air pressure over the water decreases, which is why it takes longer to boil an egg in Denver than in New Orleans.)
    * Transpiration-pull enables some trees and shrubs to live in seawater. Seawater is markedly hypertonic to the cytoplasm in the roots of the coastal mangrove, and we might expect water to leave the cells resulting in a loss in turgor and wilting. In fact, the remarkably high tensions (on the order of 500Ė800 lb/in2) in the xylem can pull water into the plant against this osmotic gradient. So mangroves literally desalt seawater to meet their needs.

Problems with the theory

When water is placed under a high vacuum, any dissolved gases come out of solution as bubbles (as we saw above with the rattan vine). This is called cavitation. Any impurities in the water enhance the process. So measurements showing the high tensile strength of water in capillaries require water of high purity ó not the case for sap in the xylem.

So might cavitation break the column of water in the xylem and thus interrupt its flow? Probably not so long as the tension does not greatly exceed 270 lb/in2.

By spinning branches in a centrifuge, it has been shown that water in the xylem avoids cavitation at negative pressures exceeding 225 lb/in2.

Sequoias can successfully lift water 358 ft (109 m) ó which would require a tension of 270 lb/in2.
However, such heights may be approaching the limit for xylem transport. (The tallest tree ever measured, a Douglas fir, was 413 ft. high.) Measurements close to the top of the tallest living sequoia (370 ft high) show that the high tensions needed to get water up there have resulted in:

    * smaller stomatal openings, causing
    * lower concentrations of CO2 in the needles, causing
    * reduced photosynthesis, causing
    * reduced growth (smaller cells and much smaller needles).
« Last Edit: 07/11/2008 15:23:31 by Andrew K Fletcher »
 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #242 on: 07/11/2008 15:43:30 »
Facts quoted above, from others, could well be true.
It is your interpretation of them that is flawed.
Merely posting yards of interesting botanical information does not detract from the fact that your Science is wrong.
As usual, you have no answers to the more searching questions.
Give my regards to Sancho Panza.
 

Offline Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #243 on: 07/11/2008 17:08:50 »
Whatever
 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #244 on: 07/11/2008 23:20:51 »
Interestingly, nowhere in your recent long post do you quote anyone denying the effects of adhesion. Nor do you quote anyone even hinting at your U tube theory.
It's just a re run of the previous stuff about the cohesion in water being very high, on occasions. A bit pointless as I have already agreed that the evidence for cohesion is compelling.
It's your personal interpretation that needs explaining and justifying.
 

Offline Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #245 on: 08/11/2008 09:13:11 »
1.  No tree to my knowledge has a cap on the top.
2.   Circulation in a tree flows predominantly down in the phloem from source to sink. Source being leaves, sink being lower than the leaves.
3.   Evaporation from the leaf cannot take place without a change in density in the sap that flows through the leaves. It is bad science to ignore this fact!
4.   The model we are debating while interesting is merely an experiment that was designed to show the power of a flow and return system that benefits from gravity, not to reflect the perfect anatomy of a tree.
5.   I have never denied adhesion is important. The fact that I never mentioned it by name, but did mention it by including that a soft walled tube necks as the tension is applied, based on observations with other experiments using soft walled tubes, and further mentioning it in the varicose veins study again a soft walled tube behaving in exactly the same way as my experiments is not the bad science you purport it to be. I have said that adhesion relies on cohesion but cohesion does not rely on adhesion, including that even when water is stuck to the side of a water filled conduit, it does not arrest the flow of water through the conduit. Yet in a single upright tube capped at the top this is what will happen and water inside the tube will be pulling down against the top of the rounded capped tube. Adhesion inside the vertical single tube will enable cohesion to be pulling inwards and downwards. Adhesion is not therefore a force, the force is the body of water on the molecular bonding between the water / tubular interface.
6.   And what if? What if I jump through your hoop, conduct your experiment and prove it one way or another? What have I accomplished? Who is going to listen? Does this mean it will become accepted?
7.   Or does it mean that you et al will find yet another reason to continue to believe in the leaf sucking cohesion tension impossibility of the first degree?  Come on here, play devils advocate for an hour or so and see through their smoke and mirrors theory. Leaves cannot suck water up a tree, no matter what spin is put on the theory it is still completely and utterly flawed.

The longer last post did provide you with evidence towards answering your many questions. It relates to the strength of cohesion, includes adhesion in exactly the same way I included my mention in the necking of tubes, It includes the vine experiment showing water boiling at ground level due to the tension applied in the stem, proving that tension occurs throughout the column of water as I had said it would do. And observed it doing as tiny vapour cavitations formed along the length of suspended tube, and go back into the water when the tube is lowered.

It mentions also the spinning / centrifuging of branches to test the cohesion which reflects the tubular experiment I swung round carefully. Although this needs to be done again with a water filled bottle on the end of it to produce a compared tension. Remember the tube used will easily withstand the crushing force.

I do not see many people rushing forward to defend the existing theory. Many thousands of people have read this thread now. Why do you think this is so? And finally the required tension of a giant sequoia at 270 pounds per square inch. Impressive tension that. If it is in place someone should have measured it by now?


Ulrich Zimmerman.
The Cohesion Theory considers plant xylem as a 'vulnerable pipeline' isolated from the osmotically connected tissue cells, phloem and mycorrhizas living in symbiosis with plant roots. It is believed that water is pulled exclusively by transpiration-induced negative pressure gradients of several megapascals through continuous water columns from the roots to the foliage. Water under such negative pressures is extremely unstable, particularly given the hydrophobicity of the inner xylem walls and sap composition (lipids, proteins, mucopolysaccharides, etc.) that prevents the development of stable negative pressures larger than about −1 MPa. However, many plant physiologists still view the Cohesion Theory as the absolute and universal truth because clever wording from the proponents of this theory has concealed the recent breakdown of the Scholander pressure bomb (and other indirect methods) as qualified tools for measuring negative pressures in transpiring plants. Here we show that the arguments of the proponents of the Cohesion Theory are completely misleading. We further present an enormous bulk of evidence supporting the view that Ė depending on the species and ecophysiological context Ė many other forces, additional to low tensions, can be involved in water ascent and that water can be lifted by a series of watergates (like ships in staircase locks). http://www3.interscience.wiley.com/journal/118760238/abstract?CRETRY=1&SRETRY=0
I have asked Ulrich if he would like to take a look at this thread and add a comment.
 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #246 on: 08/11/2008 09:46:41 »
In case you hadn't noticed, the reason I keep asking the same question is because you have not answered it yet.
You have just replied with more acres of stuff from other people and with second hand arguments which don't deal with the issue.
My question is, and has always been, to you personally.
Like a cabinet minister under tight interviewing, you have still not answered it. I have no strong opinions about the stuff you have just written about. I just want to know, in terms of the actual science, how you can still insist on the difference between your U tube, which you have tried and my single tube, which you haven't tried.
Not one of your references deal with that.
Your replies would only need to be a couple of paragraphs long if you were to stick to the issue.

Yes, there have been thousands of visits to this and the 'siphon' thread. The only recent contributions, however, have asked you to answer my question. You still haven't.

Perhaps an honest reply would be that you don't understand enough of it to explain the phenomenon thoroughly. There would be no shame in that.
 

Offline Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #247 on: 08/11/2008 11:23:31 »
Your experiment idea is a test of adhesion, and yes I do understand why you feel this may be strong enough to support the water. But this experiment has been conducted my many people over many years using many different materials, all of who have failed just like the great philosophers of science did over 300 years ago. If it were to succeed what then? Would this change my own experiment one bit? Not a chance, because as I have said and will say again the experiment performed as it was expected to perform and water was observed to flow around it from one vessel to another. The fact that you have a problem with what goes on at the molecular level inside a U tube compared to the inside of a capped end tube is fascinating but hardly going to destroy my own observations whichever way it goes is it?

You keep trying to throw a protective shield around students steering them from what you see as heretical science. But then fail to address the flaws in the accepted science.

Adhesion inside the tube is an obvious stabilising force preventing the water from pealing away from the walls of the tube. The downward force of the column of water pulls on the water molecules in the opposite side of the loop of tubing, which in turn balances out the opposing force enabling the water to become stretched by the weight of the two columns of water. The water inside your capped tube can only be stretched to the point that the water is able to stick to the capped end of the tube.  We are talking about 6 mil bore tubing here, not some micro-bore capillary tubing.

I have not tested the experiment with metal tubing, and do not have access to a 48 meter length of unblemished metal tubing do you know where one could be found? Remember soldered joints will provide nucleation sites so canít be used.

You have failed to answer my questions on paragraphs six and seven. I would like you to answer them if you feel you can. Is there going to be an opened door at the end of it and if so can I have it in writing please.
 

lyner

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Re: How do Trees Really lift Water to their Leaves?
« Reply #248 on: 08/11/2008 19:02:47 »
Quote
Your experiment idea is a test of adhesion, and yes I do understand why you feel this may be strong enough to support the water.

"MAY BE"??? I am saying, with better logic than any single one of your own 'original' ideas, that the adhesion has to be equal or greater than cohesion for your U tube or a single tube to work. If you can't understand my reasoned argument for that then that is your problem.

Quote
You keep trying to throw a protective shield around students steering them from what you see as heretical science. But then fail to address the flaws in the accepted science.
The problem is that your 'Science' is not even complete enough to be heretical.
I would protect them from what you have said so far in the same way that I would urge them to take care when reading adverts for snake oil and lunatic political parties.

Yes, I would say that any theory which ignores the simplest bit of vectorial force addition was nonsense. You do not even realise that what you are saying fails in this respect. You are implying that
"Forces Add Vectorially Except at the Top of a U Tube. In this situation we can ignore that particular bit of Science". 
Is that  supposed to be serious Science?
Describing the adhesion as a 'stabilising force' is to show that you don't understand the whole basis of vector addition. Why not use the proper terminology - which keeps bridges and planes up in the air and allows people to do Physics, Engineering and Chemistry with great success. This is not new Science and it is really not open to debate - certainly not by someone who seems not even to understand it. (Do you understand the 'triangle of forces' and what it implies in this context?)


Paras 6 and 7: I would fully expect the single tube to behave the same as the U tube but, as you say, it is more difficult to implement. It is you who claim that it wouldn't work on grounds which just demonstrate that you don't understand the basics.

You can buy long rolls of annealed copper tubing (10 mm microbore) in very long lengths. You would find it difficult to do the same experiment, though. I guess you would have to detect the amount of water suspended in it by weighing it. Adhesion between water and metals being what it is, I should expect the 10m limit would apply, so you could prove it one way or another with 21m of tube.
Smoke and mirrors? Can you show in a rigorous way how any aspect of modern Science is just Smoke and Mirrors? This is another of your Windmills.
Where do you get your ideas about the Science establishment. You put me in mind of Jude the Obscure, who was rejected by the Establishment in the Distant University City because he had tried to educate himself and had actually GOT IT WRONG. He was the only one who was surprised at what happened.
Give a Scientist, who is worthy of the name, a good reason to think that an existing theory is wrong and  he will bust a gut trying to PROVE it is wrong. He won't rant and rave that the system is flawed and that everyone is being horrible to him. He will scrutinise the new idea and try, in an informed way, to get the right answer.
 Clearly, you think your education in Science gave you a bad deal; that's sad but, unlike after a war, it is the losers who try to write the history. Mine certainly gave me a very good deal and I learned a lot throughout my life; it continues. What I did learn at a very early age is that if you can't answer a question you admit it and ask for help.

Quote
The fact that you have a problem with what goes on at the molecular level inside a U tube compared to the inside of a capped end tube is fascinating but hardly going to destroy my own observations whichever way it goes is it?
Do you actually read what I have written?
My idea does not attempt to destroy your observations - it successfully destroys your INTERPRETATION of them. Can you find, anywhere in this or the Siphon thread, a comment of mine which casts doubt on your observations?
Do you really want to ignore what happens at the molecular level and how the most basic bit of mechanics applies? It's a bit too rigorous and hard-fact for you, perhaps.

What you are basically saying is that you are right because you say so and the whole of Science is out to get you and your teachers were rubbish.
That's an opinion but proving the Science is a bit more involved than that.
« Last Edit: 09/11/2008 10:56:14 by sophiecentaur »
 

Offline Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #249 on: 10/11/2008 09:14:42 »
Ive found a supplier of 50 meter micro-bore copper tubing, cost £88.62 including VAT.
http://www.mytub.co.uk/product_information.php?product=309455

Maybe your school might be interested in testing both models? I can supply the school with the plastic pipe for free.

RE Smoke and Mirrors and Snake Oil Salesmen. First of all Proper snake oil from the water snake has some very interesting properties. The problem arose when Westerners jumped on the bandwagon selling inferior products that used the success of the original oils to market their own oils. Either way someone gets paid. I get paid nothing for this research. So the innuendo you implied is unwarranted.

On BBC Radio 2 this morning a Professor was talking about new Statins, based on speculative trials, he was deliberately trying to increase the market share for what he implied was a new wonder drug. It allegedly reduces the risk of stroke and heart attacks in people who do not have a problem with stroke or heart attacks. His company has identified that the entire human race should be medicated with this new wonder drug and the National Health should but canít afford to pay the many hundreds of millions of pounds required to get the whole of the UK popping pills.

He referred to NICE in an obscured way saying that they advise the use of statins in certain cases. This was very deceptive of such a high ranking academically qualified professional. Not a single mention of any contraindications ether, one would have thought there may be some if a large scale study over say 10 years or more had been conducted. After all Statins are known to have contra indication.

Will you be advising your students against listening to the real snake oil sales-people?
Quote
"Doctors unhappy : http://news.bbc.co.uk/1/hi/health/7326870.stm
Dr Peter Trewby, a consultant physician at Darlington Hospital who has studied how willing patients are to take preventative medicines like statins, believes we are already prescribing too many statins.
He said: "We are turning healthy people into patients, we are medicalising people and making them worry about their health unnecessarily.
"I would take a statin if I had a heart attack but I certainly wouldn't take on otherwise."
Many GPs have told The Investigation they feel that they are being pressurised to prescribe statins to patients some of whom have almost no chance of benefiting.
Dr Stephen Fox, a GP from Leigh in Lancashire became so worried by the level of side effects he was seeing in his elderly patients that he is asked the NHS if there was any research evidence on statins and the over-75s.
He was told there was none.
He said "At some point you have to ask where is the line going to be drawn - does absolutely everybody have to be on these?"
Lunatic political parties attack countries that are unable to defend themselves, blow them to bits with high tech weapons massacre men women and children that have no interest in war or politics in the name of Oil, Sorry "weapons of mass distraction"!
 
« Last Edit: 10/11/2008 09:39:52 by Andrew K Fletcher »
 

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Re: How do Trees Really lift Water to their Leaves?
« Reply #249 on: 10/11/2008 09:14:42 »

 

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