# Hosepipe into Space **URL:** \ **Category:** Factual Questions\ **Created:** [September 27, 2007, 10:00am UTC](https://boards.straightdope.com/t/hosepipe-into-space/420662 "2007-09-27T10:00:04Z")\ **Posts on this page:** 18\ **Page:** 4
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [September 29, 2007, 2:15pm UTC](https://boards.straightdope.com/t/hosepipe-into-space/420662/61 "2007-09-29T14:15:30Z")
[QUOTE=The Them] You guys are nuts. I agree that constructing a 75-mile high column and pumping seawater to the top are simple enough,… [/QUOTE] Compared to say, moving the Earth into a diffenent orbit perhaps. But in the state I like to call “reality” it would be well beyond current engineering capabilities and material strength. [QUOTE=scr4] It depends on how fast it’s moving. If the water is ejected at less than 7 km/s or so, it will simply fall back down to earth. If it’s moving faster, but below 11 km/s or so, it will go into orbit around the earth. If it’s faster than 11 km/s, it will break free of earth’s gravity, but it will still orbit the sun. I can’t remember off hand how fast it needs to be to escape the solar system entirely. [/QUOTE] Solar escape velocity is about 42 km/s at Earth’s orbit. Since the Earth has an average orbital speed of about 29.8km/s you’d have a hell of a lot of extra speed to make up. Assuming our hosepipe is fixed in rotation and you’re not adding any extra energy to the water, you’d have to be at least geostationary orbit (~35.8\*10[sup]3[/sup] km) before it wouldn’t automatically fall back down on the Earth. If you are going to give it extra speed at the end, you’re going to need to add about 6.5km/s. Either way, the pressure required to sustain a free-standing column of water is going to cause cavitation–that is, the force holding up the water and the attraction of gravity pulling down on the water is going to make an internal pressure so low that the water will become vapor and the column will collapse. [QUOTE=Peter Morris] Just tell me something about transpiration in trees. The loss of water at the leaves pulls up the water through the xylem, is that correct? There’s no other mechanism needed to push the water up, is that right? And this alone allows the water to go higher than 30’. Is that right, or have I misunderstood? Is there any limit to how high water can go through transpiration? [/QUOTE] The actual mechanic of transpirational pull alone doesn’t draw up water to the branches and leaves in a tall tree; as previously mentioned, there is also the capillary action in the xylum and the fact that, in trees, the water is in a thicker, more viscious colloid which helps suspend it. Fundamentally you can’t consider the xylem to be just a tube with a continuous stream of water suspended and motivated strictly by a pressure differential; it’s more like a sponge, such that when the upper part “dries out” from water being transported to leaves it draws the fluid below it, and so forth, moving more like a series of rocket climbers ascending a chimney than a stream flowing upward. On that basis there is no limit to the height water can be drawn up by such a mechanism because any given section is already self-supporting. A tree just isn’t a good analogue to a hosepipe. I’m no expert on trees but I would guess that the maximum height of a tree depends on the structural strength of the tree in resisting wind or ice loads and the size of the root ball in terms of both anchoring it too the ground and absorbing enough water to support growth. I doubt that the ability to transport water has any limitation on height. Regarding the debate over osmosis (and without entering into any of the vituperation), while osmosis–the movement of water across a permeable membrane via a difference in concentrations of ions in solution–is critical to allowing the roots to absorb water, it plays no role in transporting water up the trunk and to the leaves and other living parts of the trees, and indeed, osmotic pressure differences are dramatically smaller than what would be necessary to lift water more than a few inches. Osmosis just isn’t a mechanism by which the overall process of transpiration moves water from the roots to the leaves in trees. Stranger ---
**Author:** ![Peter\_Morris](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/peter_morris/32/359_2.png) [@Peter\_Morris](https://boards.straightdope.com/u/Peter_Morris)\ **Post date:** [September 29, 2007, 2:38pm UTC](https://boards.straightdope.com/t/hosepipe-into-space/420662/62 "2007-09-29T14:38:02Z")
[QUOTE=Stranger On A Train] The actual mechanic of transpirational pull alone doesn’t draw up water to the branches and leaves in a tall tree; as previously mentioned, there is also the capillary action in the xylum … Fundamentally you can’t consider the xylem to be just a tube … it’s more like a sponge … On that basis there is no limit to the height water can be drawn [/QUOTE] So, instead of a hosepipe, what if we have a network of tiny little tubes. Filled, if you like, with a viscious colloid. In other words, artificial xylem, that works on the same mechanism as a plant’s natural xylem. Would that be able to send a continuous stream of water into space? ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [September 29, 2007, 5:39pm UTC](https://boards.straightdope.com/t/hosepipe-into-space/420662/63 "2007-09-29T17:39:13Z")
[QUOTE=Peter Morris] So, instead of a hosepipe, what if we have a network of tiny little tubes. Filled, if you like, with a viscious colloid. In other words, artificial xylem, that works on the same mechanism as a plant’s natural xylem. Would that be able to send a continuous stream of water into space? [/QUOTE] Here’s and article on [maximum tree height.](http://www.ubcbotanicalgarden.org/weblog/000444.php) ---
**Author:** ![Omphaloskeptic](https://avatars.discourse-cdn.com/v4/letter/o/bcef8e/32.png) [@Omphaloskeptic](https://boards.straightdope.com/u/Omphaloskeptic)\ **Post date:** [September 29, 2007, 7:22pm UTC](https://boards.straightdope.com/t/hosepipe-into-space/420662/64 "2007-09-29T19:22:40Z")
[QUOTE=Stranger On A Train] Fundamentally you can’t consider the xylem to be just a tube with a continuous stream of water suspended and motivated strictly by a pressure differential; it’s more like a sponge, such that when the upper part “dries out” from water being transported to leaves it draws the fluid below it, and so forth, moving more like a series of **rocket climbers** ascending a chimney than a stream flowing upward. [/QUOTE] (bolding mine) Is this a new X-treme! sport, or is this just what mountain climbers are forced to do in Florida? Actually, rockets seems like a good technique for offwidths… > [@](#): > > _Compared to say, moving the Earth into a diffenent orbit perhaps. But in the state I like to call “reality” it would be well beyond current engineering capabilities and material strength._ Oh sure. “Engineering capabilities”, “material strength”, “NP-hard”–these are just fancy words you lazy engineers use so you can spend more time rocket climbing. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [September 29, 2007, 8:02pm UTC](https://boards.straightdope.com/t/hosepipe-into-space/420662/65 "2007-09-29T20:02:11Z")
[QUOTE=Stranger On A Train] The actual mechanic of transpirational pull alone doesn’t draw up water to the branches and leaves in a tall tree; as previously mentioned, there is also the capillary action in the xylum and the fact that, in trees, the water is in a thicker, more viscious colloid which helps suspend it. Fundamentally you can’t consider the xylem to be just a tube with a continuous stream of water suspended and motivated strictly by a pressure differential; it’s more like a sponge, such that when the upper part “dries out” from water being transported to leaves it draws the fluid below it, and so forth, moving more like a series of rocket climbers ascending a chimney than a stream flowing upward. On that basis there is no limit to the height water can be drawn up by such a mechanism because any given section is already self-supporting. A tree just isn’t a good analogue to a hosepipe. I’m no expert on trees but I would guess that the maximum height of a tree depends on the structural strength of the tree in resisting wind or ice loads and the size of the root ball in terms of both anchoring it too the ground and absorbing enough water to support growth. I doubt that the ability to transport water has any limitation on height. Regarding the debate over osmosis (and without entering into any of the vituperation), while osmosis–the movement of water across a permeable membrane via a difference in concentrations of ions in solution–is critical to allowing the roots to absorb water, it plays no role in transporting water up the trunk and to the leaves and other living parts of the trees, and indeed, osmotic pressure differences are dramatically smaller than what would be necessary to lift water more than a few inches. Osmosis just isn’t a mechanism by which the overall process of transpiration moves water from the roots to the leaves in trees. Stranger [/QUOTE] Good post, nice explanation. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [September 30, 2007, 1:09am UTC](https://boards.straightdope.com/t/hosepipe-into-space/420662/66 "2007-09-30T01:09:19Z")
OK, just to put this nonsense by Dr. Deth to rest: “Water transport **in nonvascular plants** without tracheids and vessels is accomplished primarily by osmosis and imbibition, where water simply soaks up into the plant tissue like a sponge. This explains the ascent of water in mosses and liverworts (phylum Bryophyta), but **does not account for the rise of water in tall trees and shrubs.** ” [http://waynesword.palomar.edu/trjuly99.htm](http://waynesword.palomar.edu/trjuly99.htm) “Although root pressure [ie osmotic pressure] plays a role in the transport of water in the xylem in some plants and in some seasons, it **does not account for most water transport** … although root pressure may play a significant role in water transport in certain species (e.g., the coconut palm) or at certain times, most plants meet their needs by transpiration-pull.” [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/X/Xylem.html](http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/X/Xylem.html) “Root pressure… Water, therefore, moves in by osmosis… Root pressures of this kind can push water several **centimetres** up a plant.” [http://www.cix.co.uk/~argus/Dreambio/plant%20water%20relations/water%20transport%20theory.htm](http://www.cix.co.uk/~argus/Dreambio/plant%20water%20relations/water%20transport%20theory.htm) “Water enters the plant through osmosis… **Root pressure does not account for xylem transport** … root pressure is at most 0.1–0.2 MPa, however, inadequate to get fluids to tree heights. The transpiration–cohesion–tension mechanism accounts for xylem transport” [http://www2.gsu.edu/~bioslp/Biol2108/PPhys.htm](http://www2.gsu.edu/~bioslp/Biol2108/PPhys.htm) I’m sure anyone who bothers to read you contributions have noticed you moving from “osmosis is important because it getswater into roots” to “it’s all about pressure compensation in the stem” Clearly you have no idea of the subject you are disccusing and are just latching onto any reference that Google throws up. [QUOTE=DrDeth] there are two competing theories for the mechanism: \*\*the Compensating Pressure Theory \*\*and **the Cohesion Theory**. [/quote] Yes, and neither of them proposes that osmosis has any role to play whatsoever in moving water to the tops of trees. The Tension Cophesion hypothesis has been well discussed. The Pressure Compensation hypothesis is essentially the same but with pressure maintained and embolisms sealed via pressure and fluid flow from the phloem. FFS [here](http://www.publish.csiro.au/view/journals/dsp_journal_fulltext.cfm?nid=102&f=FP06108) is a fairly simple article of the Pressure Compensation hypothesis. [here is another](http://aob.oxfordjournals.org/cgi/content/abstract/75/4/343). Even these state unequivocally that “Water transport in the xylem of vascular plants is **driven by pulling forces created at leaf capillary surfaces** ” and "the driving force and the transmission of the force are the same as in the Cohesion Theory, but the operating pressure of the xylem is raised into a stable range by compensating tissue pressures pressing upon the tracheary elements. The tissue pressure **does not propel the transpiration stream, which is still driven by evaporation** , but protects the stream from cavitation Understand now? Water transport is driven by evaporation and coheison, not osmosis. The fact that you have been unable to provide any references which suggest that osmosis plays any role is all we really need to know. > [@](#): > > Osmosis (or reverse osmosis, which uses the identical mechanism) Yes, I think I can leave this here. Anyone who wants to look up osmosis and reverse osmosis on Wikipedia or any other source will see for themselves just how much credibility to somone who makes a statement like this. They not only use identical mechanims, they are polar opposites. Osmosis operates as a source of pressure, it increases the pressure differential of a system. Reverse osmosis requires pressure to operate, it decreases the prssure differential of a system. Identical mechanisms indeed. > [@](#): > > I debate by cites and facts.. Yes, myself, Jshore, DUckDuckGoose, Colibri and many others have noticed that… NOT. :rolleyes: > [@](#): > > …you use ad hominen and presonal attacks. Dude you have a history of this sort of behaviour. People can best judge your input if they are made aware of it. > [@](#): > > I will no longer debate with you until you change your tactics As I and many others have said, we don’t want to debate you at all in GQ. We just ask that you not post ignorance rubbish. That is made worse when you try to defend it with misundertsood Google results. We’d also appreciate you stopping this this nonsense of blatantly moving the goalposts. Anyone who would claim that pressure dispersal pattern in reverse osmois and osmosis have identical mechanisms isn’t worth debating. However we can’t just let this nonsense slip through unchallenged, particlulary as you post this sort of rubbish in a regular basis. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [September 30, 2007, 2:34am UTC](https://boards.straightdope.com/t/hosepipe-into-space/420662/67 "2007-09-30T02:34:30Z")
[QUOTE=David Simmons] Here’s and article on [maximum tree height.](http://www.ubcbotanicalgarden.org/weblog/000444.php) [/QUOTE] Hmmm…well, as I said, I’m no expert on trees. I’m surprised that they consider the transpirational pull by itself as a limitation. I’d expect it to be more the amount of total energy required to elevate it to the higher branches, or the amount of water within range of the root system. [QUOTE=Omphaloskeptic] > [@Stranger On A Train](#): > > Fundamentally you can’t consider the xylem to be just a tube with a continuous stream of water suspended and motivated strictly by a pressure differential; it’s more like a sponge, such that when the upper part “dries out” from water being transported to leaves it draws the fluid below it, and so forth, moving more like a series of **rocket climbers** ascending a chimney than a stream flowing upward. (bolding mine) Is this a new X-treme! sport, or is this just what mountain climbers are forced to do in Florida? [/QUOTE] You don’t know excitement until you’ve hung off the edge of a gantry on trying to check interstage connections on a Minotaur I on Wallops Island in December. Stranger ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [September 30, 2007, 2:56am UTC](https://boards.straightdope.com/t/hosepipe-into-space/420662/68 "2007-09-30T02:56:25Z")
[QUOTE=Stranger On A Train] I’m surprised that they consider the transpirational pull by itself as a limitation. [/quote] It’s not the transpirational pull _per se_ that is the limitation. It’s the fact that you need to maintain a high enough pressure to allow the water to flow into the leaf tissues after it has got there. IOW you can get the water to the top of the tree, but if the pressure is so strongly negative that it is sucking water _out_ of the leaf cells rather than allowing it to flow in then it’s a wasted effort. Since we are dealing with a negative presure pump (contrary to DrDeth’s claim of an osmotic pump) the higher you want to pull the water the more negative the line gets and at some point you have an operating pressure more strongly negative than the positive osmotic pressure of the leaf cells. At that point you can still lift the water higher, but you can’t use it to keep cells alive. > [@](#): > > I’d expect it to be more the amount of total energy required to elevate it to the higher branches The amount of energy is effectively limitless since it comes directly from heat energy and not from ATP. > [@](#): > > …or the amount of water within range of the root system. The amount of available water does become a factor in areas with seasonal rainfall, hence the reason why desert plants are reduced to shrubs. But in areas with high rainfall the water is effectively limitless, which is why the largest trees only exist in wet forests. As rainfall declines so does tree height. ---
**Author:** ![samclem](https://avatars.discourse-cdn.com/v4/letter/s/a9a28c/32.png) [@samclem](https://boards.straightdope.com/u/samclem)\ **Post date:** [September 30, 2007, 5:43am UTC](https://boards.straightdope.com/t/hosepipe-into-space/420662/69 "2007-09-30T05:43:05Z")
[QUOTE=DrDeth] **Blake** , you are a smart guy, but I am done with you. I debate by cites and facts, you use ad hominen and presonal attacks. I will no longer debate with you until you change your tactics. [/QUOTE] Free at last! Free at last! Thank Og almighty, I’m free at last! From your lips to the ears of the GQ moderators. ---
**Author:** ![WoodenTaco](https://avatars.discourse-cdn.com/v4/letter/w/45deac/32.png) [@WoodenTaco](https://boards.straightdope.com/u/WoodenTaco)\ **Post date:** [September 30, 2007, 6:03am UTC](https://boards.straightdope.com/t/hosepipe-into-space/420662/70 "2007-09-30T06:03:56Z")
[QUOTE=Peter Morris] So, instead of a hosepipe, what if we have a network of tiny little tubes. [/QUOTE] Just like the Internet, but extending into space. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [September 30, 2007, 6:28am UTC](https://boards.straightdope.com/t/hosepipe-into-space/420662/71 "2007-09-30T06:28:21Z")
[QUOTE=Blake] … “Although root pressure [ie osmotic pressure] plays a role in the transport of water in the xylem in some plants and in some seasons, it **does not account for most water transport** … although root pressure may play a significant role in water transport in certain species (e.g., the coconut palm) or at certain times, most plants meet their needs by transpiration-pull.” [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/X/Xylem.html](http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/X/Xylem.html) “Root pressure… Water, therefore, moves in by osmosis… Root pressures of this kind can push water several **centimetres** up a plant.” [http://www.cix.co.uk/~argus/Dreambio/plant%20water%20relations/water%20transport%20theory.htm](http://www.cix.co.uk/~argus/Dreambio/plant%20water%20relations/water%20transport%20theory.htm) “Water enters the plant through osmosis… **Root pressure does not account for xylem transport** … root pressure is at most 0.1–0.2 MPa, however, inadequate to get fluids to tree heights. The transpiration–cohesion–tension mechanism accounts for xylem transport” [http://www2.gsu.edu/~bioslp/Biol2108/PPhys.htm](http://www2.gsu.edu/~bioslp/Biol2108/PPhys.htm) … Yes, and neither of them proposes that osmosis has any role to play whatsoever in moving water to the tops of trees. The Tension Cophesion hypothesis has been well discussed. The fact that you have been unable to provide any references which suggest that osmosis plays any role is all we really need to know. … . [/QUOTE] Blake, I never claimed that “osmosis has any role to play whatsoever in moving water to the tops of trees” except insofar as it get water into the roots, which starts the entire Transport system. You cites show that clearly. Do you deny that Osmosis gets water into the roots, and that water starts the whole water transport system? Here’s what I said "Right, exactly as I said: (from the wiki link provided right there) “Also, osmosis is responsible for the ability of plant roots to suck up water from the soil. Since there are many fine roots, they have a large surface area, water enters the roots by osmosis.” No osmosis, no water to take further up. Thus “Osmosis is a big part of it.” **Is** “osmosis responsible for the ability of plant roots to suck up water from the soil”? Here’s what _someone_ said right here in this thread\* “Osmosis plays a role in getting wtaer into the roots form the soil.\*”(sic). That was _you,_ Blake. 😃 I also said “Osmosis … _begins_ … the water transport system- as again can be seen clearly in the links and cites I provided. _Yes, it is NOT the major mechanism of Transport between the two_. But exactly what that mechanism is hotly debated.” So I even specifically stated that Osmosis does not play a role in getting water to the tops of tree- other that getting it into the roots, which starts it. Far from "that osmosis has any role to play whatsoever in moving water to the tops of trees ". Is “osmosis responsible for the ability of plant roots to suck up water from the soil.”? Or not? Is that a fact or isn’t it? Is _that water_ not then tranported \*through other mechanisms \*up through the plant? Look at your own cites "Although root pressure [ie osmotic pressure] plays a role in the transport of water in the xylem in some plants and in some seasons, it does not account for most water transport… although root pressure may play a significant role in water transport in certain species (e.g., the coconut palm) or at certain times, most plants meet their needs by transpiration-pull…Root pressure… Water, therefore, moves in by osmosis… Root pressures of this kind can push water several centimetres up a plant…Water enters the plant through osmosis… " Then you go on to say “The fact that you have been unable to provide any references which suggest that osmosis plays any role is all we really need to know.” :rolleyes: You _own cites_ show that Osmosis has a role. You said so yourself “Osmosis _plays a role_ …”. It’s role is primarily at the roots. That’s _a role._ After that- _not so much_, as I said repeatedly. After those cites are you going to deny that “osmosis is responsible for the ability of plant roots to suck up water from the soil.”? 😃 Now yes, I worded my first post poorly. **I apologize for that, everyone.** :smack: I posted a quick line, without a lot of thought as to exactly how to word it. But I did include a link to my cite, and if anyone had thought to click, follow and read, they would have seen that all I was stating is that “Also, osmosis is responsible for the ability of plant roots to suck up water from the soil. Since there are many fine roots, they have a large surface area, water enters the roots by osmosis.” That was right there in my link. - Mea culpa. \* Yes, I fucked up. I posted an ambiguous short post, and my fuck up was my assumption that dudes would click, follow and _read_ my cite and see what I was talking about After all, we didn’t really need a long explanation about “water transport in plants”. Sorry, my bad. One could slam me by the use of the word “big” in my original statement. Yes, it was _opinion,_ _hyperbole_. Sue me. 😛 Getting the water into the roots is IMHO a rather critical start of the whole Transport process. But that’s just IMHO. I could be wrong. So, to restate again: “Osmosis is responsible for the ability of plant roots to suck up water from the soil” and “Osmosis is NOT the major mechanism of Transport.” But you insist on debating, even though we completely agree 😛 . Yeah, you don’t like “Osmosis is a big part of it.” I get that, and like I said- I am sorry for the wording there.\* Mea Culpa\*. But if you had just followed the link and read my cite, or if you had tried "\* A good rebuttal could have explained that the water transport system does start with Osmosis, gone on to explain the two competing theories and transpiration, and concluded that “big” was likely too strong a word. Of course, a good rebuttal would have included some interesting cites and links, too. \*we wouldn’t be having this 8 post hijack. **Blake** , sure I sometimes post without thinking through all the possible ways my posts can be mis-interpreted by others. That does lead to confusion :smack: sometimes. I am sorry for that-\* everyone.\* But your anger and hatred here is rather disturbing to me, I worry about you, dude. Please don’t be so angry, it’s just a Message board. \*Relax, chill out. \* 🆒 Don’t worry: if you are right, then you can destroy me by facts, anger isn’t nessesary. In fact- \*Please \*destroy me with facts, that fights ignorance. Cool cites by the way, thanks! 🆒 I am truely sorry I made you so angry. ☹ ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [September 30, 2007, 7:28am UTC](https://boards.straightdope.com/t/hosepipe-into-space/420662/72 "2007-09-30T07:28:38Z")
[QUOTE=samclem] Free at last! Free at last! Thank Og almighty, I’m free at last! From your lips to the ears of the GQ moderators. [/QUOTE] Sorry, dude. :smack: **Blake** and I _both_ made the same promise and we \*both \*didn’t keep it. ☹ _“Ah, the irony! It burns!”_ 😃 I PMed him with a deal: “Tell ya what Blake- if you agree never to insult another poster (outside the PIT) I’ll agree to stop posting in any Biology related GQ threads you have posted in. OK?” So if he agrees, you Mods will get a lot less reports and no more **DrDeth** / **Blake** “debates”. How’s that for a win-win? 🙂 Sorry for all the extra work, dude. Keep it up, we love you anyway. 🆒 ---
**Author:** ![samclem](https://avatars.discourse-cdn.com/v4/letter/s/a9a28c/32.png) [@samclem](https://boards.straightdope.com/u/samclem)\ **Post date:** [September 30, 2007, 3:01pm UTC](https://boards.straightdope.com/t/hosepipe-into-space/420662/73 "2007-09-30T15:01:04Z")
[QUOTE=DrDeth] Sorry, dude. :smack: **Blake** and I _both_ made the same promise and we \*both \*didn’t keep it. ☹ _“Ah, the irony! It burns!”_ 😃 I PMed him with a deal: “Tell ya what Blake- if you agree never to insult another poster (outside the PIT) I’ll agree to stop posting in any Biology related GQ threads you have posted in. OK?” So if he agrees, you Mods will get a lot less reports and no more **DrDeth** / **Blake** “debates”. How’s that for a win-win? 🙂 Sorry for all the extra work, dude. Keep it up, we love you anyway. 🆒 [/QUOTE] …and my job would be more boring without the two of youse. XOXOXO --your pal, Sam ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [September 30, 2007, 5:54pm UTC](https://boards.straightdope.com/t/hosepipe-into-space/420662/74 "2007-09-30T17:54:10Z")
[QUOTE=DrDeth] > [@Stranger On A Train](#): > > The actual mechanic of transpirational pull alone doesn’t draw up water to the branches and leaves in a tall tree; as previously mentioned, there is also the capillary action in the xylum and the fact that, in trees, the water is in a thicker, more viscious colloid which helps suspend it. Fundamentally you can’t consider the xylem to be just a tube with a continuous stream of water suspended and motivated strictly by a pressure differential; it’s more like a sponge, such that when the upper part “dries out” from water being transported to leaves it draws the fluid below it, and so forth, moving more like a series of rocket climbers ascending a chimney than a stream flowing upward. On that basis there is no limit to the height water can be drawn up by such a mechanism because any given section is already self-supporting. A tree just isn’t a good analogue to a hosepipe. > > I’m no expert on trees but I would guess that the maximum height of a tree depends on the structural strength of the tree in resisting wind or ice loads and the size of the root ball in terms of both anchoring it too the ground and absorbing enough water to support growth. I doubt that the ability to transport water has any limitation on height. > > Regarding the debate over osmosis (and without entering into any of the vituperation), while osmosis–the movement of water across a permeable membrane via a difference in concentrations of ions in solution–is critical to allowing the roots to absorb water, it plays no role in transporting water up the trunk and to the leaves and other living parts of the trees, and indeed, osmotic pressure differences are dramatically smaller than what would be necessary to lift water more than a few inches. Osmosis just isn’t a mechanism by which the overall process of transpiration moves water from the roots to the leaves in trees. > > Stranger Good post, nice explanation. [/QUOTE] True enough but if you accept[this cite](http://www.sciam.com/askexpert_question.cfm?articleID=000EE0FE-66F1-1C72-9EB7809EC588F2D7), and [and this one](http://www.cix.co.uk/~argus/Dreambio/plant%20water%20relations/water%20transport%20theory.htm) (from a **Blake** post), it’s not 100% accurate. From first cite. > [@](#): > > The xylem is also composed of elongated cells. Once the cells are formed, they die. But the cell walls still remain intact, and\*\* serve as an excellent pipeline\*\* to transport water from the roots to the leaves. A single tree will have many xylem tissues, or elements, extending up through the tree. Each typical xylem vessel may only be several microns in diameter. > "The physiology of water uptake and transport is not so complex either. The main driving force of water uptake and transport into a plant is transpiration of water from leaves. Transpiration is the process of water evaporation through specialized openings in the leaves, called stomates. The evaporation creates a negative water vapor pressure develops in the surrounding cells of the leaf. Once this happens, water is pulled into the leaf from the vascular tissue, the xylem, to replace the water that has transpired from the leaf. This pulling of water, or tension, that occurs in the xylem of the leaf, will extend all the way down through the rest of the xylem column of the tree and into the xylem of the roots due to the cohesive forces holding together the water molecules along the sides of the xylem tubing. **(Remember, the xylem is a continuous water column that extends from the leaf to the roots.)** Finally, the negative water pressure that occurs in the roots will result in an increase of water uptake from the soil.. And from the second cite > [@](#): > > The most important of these is the cohesion tension hypothesis. > Water evaporates from\*\* spongy mesophyll cells into the air spaces of the leaf.\*\* Water then diffuses out of the leaf via the stomata. The loss of water means that the water potential of these cells decreases. Since water always moves from a region of high water potential to a region of low water potential, water now moves from into them from the adajacent cells. This causes the water potential of these to decrease, and so on, all the way back to the xylem. The loss of water from the xylem causes a negative pressure or tension which lifts water up the xylem. **Within the xylem the columns of water are held together by cohesion (the molecules are hydrogen bonded to each other) and by adhesion (the attraction between a water molecule and the side of the xylem).** Movement of this column of water (often hundreds of columns because there are hundreds of xylem vessels in the xylem of a tree) is known as the transpiration stream. Both agree that the water transport system through the xylem in the stem, or trunk, is through tubes composed of the xylem cells and that both the cohesion of the water molecules to each other and and the second cite mentions the adhesion to the cell walls play a part in maintaing a continuous column of water from roots to leaves. However, the adhesion, capillarity, can’t lift water very far. The leaves are the spongy material, not the xylem. In addition, not all tree sap is syrupy. Maple sap is watery and must be cooked down to evaporate the water and produce maple syrup. All of the sites I checked concerning maximum tree height stressed that the tree height is limited by lack of water. The water cohesion is only so strong and can only lift the water to some fixed height. As a speculation, it might be that trees grow throughout their lives and the reason that sequoias and redwoods get so tall is that they live so long. Douglas fir’s can live to be over a thousand years old and they also get tall. Working against this idea is the fact that olive trees can also live a long time and don’t get all that tall. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [October 1, 2007, 1:47am UTC](https://boards.straightdope.com/t/hosepipe-into-space/420662/75 "2007-10-01T01:47:02Z")
[QUOTE=David Simmons] All of the sites I checked concerning maximum tree height stressed that the tree height is limited by lack of water. The water cohesion is only so strong and can only lift the water to some fixed height. [/quote] That’s an oversimplification. It’s not the height that cohesion can lift to, since if that was the limitation plants could be quite a bit taller. The problem is that cohesion lifts by negative pressure, it pulls water up the trunk. Once the pressure becomes too strongly negative the leaf cells can no longer draw water out of the pipes. So thatis the limitation, not the height that the plants can lift to. > [@](#): > > As a speculation, it might be that trees grow throughout their lives and the reason that sequoias and redwoods get so tall is that they live so long. Nope, because many desert trees, such as the olives you mentioned, live just as long and don’t get to even 50 feet in height. Tree size isn’t correlated with lifespan at all. It is well correlated with rainfall however because soil moisture determines xylem pressure. ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [October 1, 2007, 2:38am UTC](https://boards.straightdope.com/t/hosepipe-into-space/420662/76 "2007-10-01T02:38:54Z")
[QUOTE=Blake] Nope, because many desert trees, such as the olives you mentioned, live just as long and don’t get to even 50 feet in height. Tree size isn’t correlated with lifespan at all. It is well correlated with rainfall however because soil moisture determines xylem pressure. [/QUOTE] Blake is 100% correct here. The oldest trees are widely thought to be the bristlecone pines. > **[Bristlecone pine](https://en.wikipedia.org/wiki/Bristlecone_pine)** > > The term bristlecone pine covers three species of pine tree (family Pinaceae, genus Pinus, subsection Balfourianae). All three species are long-lived and highly resilient to harsh weather and bad soils. One of the three species, Pinus longaeva, is among the longest-lived life forms on Earth. The oldest of this species is more than 4,800 years old, making it the oldest known individual of any species. Many scientists are curious as to why this tree is able to live so long. In one study, they di _“The oldest single living organisms known are bristlecone pines, though some plants such as creosote bush or aspen form clonal colonies that may be many times older. … The oldest bristlecone pines are single plants that have been alive for a little less than 5,000 years. These very old trees are of great importance in dendrochronology or tree-ring dating.”_ They are generally rather small and scrubby for pine trees, and exactly like Blake sez, get very little rainfall. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [October 1, 2007, 2:53am UTC](https://boards.straightdope.com/t/hosepipe-into-space/420662/77 "2007-10-01T02:53:33Z")
[QUOTE=DrDeth] Blake is 100% correct here. The oldest trees are widely thought to be the bristlecone pines. > **[Bristlecone pine](https://en.wikipedia.org/wiki/Bristlecone_pine)** > > The term bristlecone pine covers three species of pine tree (family Pinaceae, genus Pinus, subsection Balfourianae). All three species are long-lived and highly resilient to harsh weather and bad soils. One of the three species, Pinus longaeva, is among the longest-lived life forms on Earth. The oldest of this species is more than 4,800 years old, making it the oldest known individual of any species. Many scientists are curious as to why this tree is able to live so long. In one study, they di _“The oldest single living organisms known are bristlecone pines, though some plants such as creosote bush or aspen form clonal colonies that may be many times older. … The oldest bristlecone pines are single plants that have been alive for a little less than 5,000 years. These very old trees are of great importance in dendrochronology or tree-ring dating.”_ They are generally rather small and scrubby for pine trees, and exactly like Blake sez, get very little rainfall. [/QUOTE] it was just an idle speculation. I question whether the bristlecones are a good example though. They live in a really harsh environment. Their territory is in the White Mountains which are just east of the Sierra Nevada range which takes most of the moisture out of the air. Ergo, bristlecones are in a high altitude and arid desert. Who knows how big they would get if they had a chance? 😉 On the desert the effect of water can be quite spectacullar. Below a conyon not far from here you walk through greasewood (creosote)bushes (which, as you said, might possibly be even older than the bristlecomes) that are 4’ to 5’ tall. In one step you go into bushes 10’ to 12’ tall. You can easily trace the path of an underground stream down the alluvial fan. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [October 1, 2007, 5:38am UTC](https://boards.straightdope.com/t/hosepipe-into-space/420662/78 "2007-10-01T05:38:46Z")
[QUOTE=David Simmons] I question whether the bristlecones are a good example though. They live in a really harsh environment…Who knows how big they would get if they had a chance? [/QUOTE] That’s the point. Bristelcones, olives and mallees all live for millenia but none exceed 50’ in height. Therefore height does not correlate with age. In contrast many rainforest trees live for les than 50 years and routinely exeed 120 feet in height. Therfare height does not correlate with age. What height does correlate to very well is rainfall, or more particularly minimum soil moisture. That tells us that whatever is limiting tree height has somehting to do with how high water can be lifted. How big would they get given the chance? Well some of this is genetic of course. Plants in arid environments that try to exceed their maximal environrmental height will cavitate and die. As such they have evolved to become short statured species. But the fact that 100% of desert species have evolved to become short statured is itself strong evidence that water determines height. Interetsingly there are a number of Australian desert species that exit in range of forms. The desert forms exist as shrubs 2 - 5 metres in height. The same species from more humid envrionments routinely exist as trees 15-30 metres in height. Once again this suports the hypothesis that height is determnied by water, not by age. [Previous page](https://boards.straightdope.com/t/hosepipe-into-space/420662.md?page=3)