Just curious. As I understand it the evaporation of moisture is what
draws the sap from the toots up the tree. Does this mean that the sap
does not rise until the leaves unfurl? If so where do the leaves obtain
the energy to be "kick started"?

In article ,
Broadback writes:
|
| Just curious. As I understand it the evaporation of moisture is what
| draws the sap from the toots up the tree. Does this mean that the sap
| does not rise until the leaves unfurl? If so where do the leaves obtain
| the energy to be "kick started"?

'Tain't so. Sounds plausible, until you think about it. If that
were so, how would the sap reach the top of a 50' tree? Even a
vacuum will raise water only 30'.

That explanation was proposed and debunked by early in the 19th
century - but, like all myths, cannot be killed by mere disproof.


Regards,
Nick Maclaren.

"Nick Maclaren" wrote in message
...

In article ,
Broadback writes:
|
| Just curious. As I understand it the evaporation of moisture is what
| draws the sap from the toots up the tree. Does this mean that the sap
| does not rise until the leaves unfurl? If so where do the leaves obtain
| the energy to be "kick started"?

'Tain't so. Sounds plausible, until you think about it. If that
were so, how would the sap reach the top of a 50' tree? Even a
vacuum will raise water only 30'.

That explanation was proposed and debunked by early in the 19th
century - but, like all myths, cannot be killed by mere disproof.


Regards,
Nick Maclaren.



Interesting post on this at another forum:
http://www.city-data.com/forum/garde...ap-rising.html

pk

PK wrote:
"Nick Maclaren" wrote in message
...

In article ,
Broadback writes:
|
| Just curious. As I understand it the evaporation of moisture is what
| draws the sap from the toots up the tree. Does this mean that the sap
| does not rise until the leaves unfurl? If so where do the leaves
obtain
| the energy to be "kick started"?

'Tain't so. Sounds plausible, until you think about it. If that
were so, how would the sap reach the top of a 50' tree? Even a
vacuum will raise water only 30'.

That explanation was proposed and debunked by early in the 19th
century - but, like all myths, cannot be killed by mere disproof.


Regards,
Nick Maclaren.



Interesting post on this at another forum:
http://www.city-data.com/forum/garde...ap-rising.html

pk

Very interesting PK, does not answer my question though. OK Nick if that
theory is wrong what is the actual answer as to how sap gets up the tree?

In article ,
Broadback writes:
|
| | Just curious. As I understand it the evaporation of moisture is what
| | draws the sap from the toots up the tree. Does this mean that the sap
| | does not rise until the leaves unfurl? If so where do the leaves
| obtain
| | the energy to be "kick started"?
|
| 'Tain't so. Sounds plausible, until you think about it. If that
| were so, how would the sap reach the top of a 50' tree? Even a
| vacuum will raise water only 30'.
|
| That explanation was proposed and debunked by early in the 19th
| century - but, like all myths, cannot be killed by mere disproof.
|
| Very interesting PK, does not answer my question though. OK Nick if that
| theory is wrong what is the actual answer as to how sap gets up the tree?

Well, it appears that I was wrong! Mostly.

It seems that the plant physiologists do regard evaporation of moisture
as being the driving force, but the books I looked at gloss over the
physics so badly as to make the explanation physical nonsense. And they
were undergraduate plant physiology references, too! My daughter
confirms that corresponds with what they were taught.

Reading between the lines, it seems that the mechanism is driven as
you might expect, but with surface tension of the hydrophilic cell walls
being a critical aspect. However, the way that solar energy is translated
into potential energy is still baffling the plant physiologists - after
over a century of studying the problem!

And neither book had even a hint of an answer to your question.


Regards,
Nick Maclaren.

In article ,
says...

In article ,
Broadback writes:
|
| | Just curious. As I understand it the evaporation of moisture is what
| | draws the sap from the toots up the tree. Does this mean that the sap
| | does not rise until the leaves unfurl? If so where do the leaves
| obtain
| | the energy to be "kick started"?
|
| 'Tain't so. Sounds plausible, until you think about it. If that
| were so, how would the sap reach the top of a 50' tree? Even a
| vacuum will raise water only 30'.
|
| That explanation was proposed and debunked by early in the 19th
| century - but, like all myths, cannot be killed by mere disproof.
|
| Very interesting PK, does not answer my question though. OK Nick if that
| theory is wrong what is the actual answer as to how sap gets up the tree?

Well, it appears that I was wrong! Mostly.

It seems that the plant physiologists do regard evaporation of moisture
as being the driving force, but the books I looked at gloss over the
physics so badly as to make the explanation physical nonsense. And they
were undergraduate plant physiology references, too! My daughter
confirms that corresponds with what they were taught.

Reading between the lines, it seems that the mechanism is driven as
you might expect, but with surface tension of the hydrophilic cell walls
being a critical aspect. However, the way that solar energy is translated
into potential energy is still baffling the plant physiologists - after
over a century of studying the problem!

And neither book had even a hint of an answer to your question.


Regards,
Nick Maclaren.

Trees do all sorts of clever stuff, I remember reading something about
Oak trees pumping water with their deep tap roots and pushing this out
into the soil near the surface where their feeder root system is in
prolonged dry weather. So they obviously have quite a degree of control
in the process are are not just at the mercy of the elements. I will try
and find the artical as it may shed some light on the way the system
works (which I always thought was mainly capillary, but then they must
be able to turn that off in winter?)
--
Charlie Pridham, Gardening in Cornwall
www.roselandhouse.co.uk
Holders of national collections of Clematis viticella cultivars and
Lapageria rosea

On 26 Feb 2008 10:05:36 GMT, (Nick Maclaren) wrote
and included this (or some of this):

In article ,
Broadback writes:
|
| Just curious. As I understand it the evaporation of moisture is what
| draws the sap from the toots up the tree. Does this mean that the sap
| does not rise until the leaves unfurl? If so where do the leaves obtain
| the energy to be "kick started"?

'Tain't so. Sounds plausible, until you think about it. If that
were so, how would the sap reach the top of a 50' tree? Even a
vacuum will raise water only 30'.

Then try Osmosis. It's very powerful, and not limited to 30'

http://en.wikipedia.org/wiki/Osmosis


--
®óñ© © ²°¹°-°²

In article ,
®óñ© © ²°¹°-°² writes:
|
| 'Tain't so. Sounds plausible, until you think about it. If that
| were so, how would the sap reach the top of a 50' tree? Even a
| vacuum will raise water only 30'.
|
| Then try Osmosis. It's very powerful, and not limited to 30'
|
| http://en.wikipedia.org/wiki/Osmosis

An old and good physical rule is that, if your explanation allows
you to construct a perpetual motion machine, your explanation is
wrong.

Osmosis still requires energy to drive it.


Regards,
Nick Maclaren.

On 27 Feb 2008 17:06:46 GMT, (Nick Maclaren) wrote
and included this (or some of this):


In article ,
®óñ© © ²°¹°-°² writes:
|
| 'Tain't so. Sounds plausible, until you think about it. If that
| were so, how would the sap reach the top of a 50' tree? Even a
| vacuum will raise water only 30'.
|
| Then try Osmosis. It's very powerful, and not limited to 30'
|
| http://en.wikipedia.org/wiki/Osmosis

An old and good physical rule is that, if your explanation allows
you to construct a perpetual motion machine, your explanation is
wrong.

Osmosis still requires energy to drive it.

Osmosis is not perpetual motion. The attractant is fuelled by our
beneficent sun.


--
®óñ© © ²°¹°-°²

In article ,
says...
On 27 Feb 2008 17:06:46 GMT, (Nick Maclaren) wrote
and included this (or some of this):


In article ,
®óñ© © ²°¹°-°² writes:
|
| 'Tain't so. Sounds plausible, until you think about it. If that
| were so, how would the sap reach the top of a 50' tree? Even a
| vacuum will raise water only 30'.
|
| Then try Osmosis. It's very powerful, and not limited to 30'
|
| http://en.wikipedia.org/wiki/Osmosis

An old and good physical rule is that, if your explanation allows
you to construct a perpetual motion machine, your explanation is
wrong.

Osmosis still requires energy to drive it.

Osmosis is not perpetual motion. The attractant is fuelled by our
beneficent sun.



Can't be that alone, as if you prune something off it bleeds all night
long.
--
Charlie Pridham, Gardening in Cornwall
www.roselandhouse.co.uk
Holders of national collections of Clematis viticella cultivars and
Lapageria rosea

In article ,
®óñ© © ²°¹°-°² writes:
|
| | Then try Osmosis. It's very powerful, and not limited to 30'
| |
| | http://en.wikipedia.org/wiki/Osmosis
|
| An old and good physical rule is that, if your explanation allows
| you to construct a perpetual motion machine, your explanation is
| wrong.
|
| Osmosis still requires energy to drive it.
|
| Osmosis is not perpetual motion. The attractant is fuelled by our
| beneficent sun.

That is an evasion. Osmosis requires a concentration gradient or
similar, and causes a pressure differential. A reduction cannot
raise water by more than 30' and all of the books indicate that the
maximum actual excess pressure is nothing like the 1 MPa per 30m
needed. Good try, but no banana.

It would be easy if plants had anything like venous return valves,
to act as a pump, but they don't.

The question remains is HOW does the sun's radiation get transferred
into the movement of the water? And I believe that is unknown.


Regards,
Nick Maclaren.

Broadback says...
Just curious. As I understand it the evaporation of moisture is what
draws the sap from the toots up the tree. Does this mean that the sap
does not rise until the leaves unfurl? If so where do the leaves obtain
the energy to be "kick started"?


I think that at least part of the mechanism involves the
roots pumping the water upwards. I seem to remember from my
student days that this was sometimes with considerable
force which can actually made the leaves "bleed" - a
process called "gutation" if I remember correctly.

There are also other mechanisms such as capillary action to
draw water along very fine tubules.
--
David in Normandy.
To e-mail you must include the password FROG on the
subject line, or it will be automatically deleted.

In article ,
says...
Broadback says...
Just curious. As I understand it the evaporation of moisture is what
draws the sap from the toots up the tree. Does this mean that the sap
does not rise until the leaves unfurl? If so where do the leaves obtain
the energy to be "kick started"?


I think that at least part of the mechanism involves the
roots pumping the water upwards. I seem to remember from my
student days that this was sometimes with considerable
force which can actually made the leaves "bleed" - a
process called "gutation" if I remember correctly.

There are also other mechanisms such as capillary action to
draw water along very fine tubules.

Found the artical I was looking for The words belong to John Tulett of
Edinburgh, the spelling mistakes are mine!

Plant roots take up inorganic ions from the soil and transfer them to the
xylem from which they can not leak back. Water is drawn in by Osmosis
which creates a positive pressure in the xylem . Because of this pressure
xylem sap leaks from pores. Guttation happens at night where the normal
stomata (pores) close and the water is then forced out through the
hydathodes, we see this as dew drops. (some plants do this more than
others ie grass)
Some useful ions are probebly recovered by the hydathodes and some of the
ions in the xylem may have been recirculated.
It is a similar process that brings calcium to developing fruits and when
this is interupted as when the atmosphere in a greenhouse at night is too
dry tomato fruits can suffer blossom end rot and drop off.

It would appear that although the above was written as an answer to a
question on why does dew form it at least starts to explain what
pressures the system
--
Charlie Pridham, Gardening in Cornwall
www.roselandhouse.co.uk
Holders of national collections of Clematis viticella cultivars and
Lapageria rosea

On Feb 27, 7:50*pm, Charlie Pridham
wrote:
In article ,
says...



Broadback says...
Just curious. As I understand it the evaporation of moisture is what
draws the sap from the toots up the tree. Does this mean that the sap
does not rise until the leaves unfurl? If so where do the leaves obtain
the energy to be "kick started"?

I think that at least part of the mechanism involves the
roots pumping the water upwards. I seem to remember from my
student days that this was sometimes with considerable
force which can actually made the leaves "bleed" - a
process called "gutation" if I remember correctly.

There are also other mechanisms such as capillary action to
draw water along very fine tubules.

Found the artical I was looking for The words belong to John Tulett of
Edinburgh, the spelling mistakes are mine!

Plant roots take up inorganic ions from the soil and transfer them to the
xylem from which they can not leak back. Water is drawn in by Osmosis
which creates a positive pressure in the xylem . Because of this pressure
xylem sap leaks from pores. Guttation happens at night where the normal
stomata (pores) close and the water is then forced out through the
hydathodes, we see this as dew drops. (some plants do this more than
others ie grass)
Some useful ions are probebly recovered by the hydathodes and some of the
ions in the xylem may have been recirculated.
It is a similar process that brings calcium to developing fruits and when
this is interupted as when the atmosphere in a greenhouse at night is too
dry tomato fruits can suffer blossom end rot and drop off.

It would appear that although the above was written as an answer to a
question on why does dew form it at least starts to explain what
pressures the system
--
Charlie Pridham, Gardening in Cornwallwww.roselandhouse.co.uk
Holders of national collections of Clematis viticella cultivars and
Lapageria rosea- Hide quoted text -

- Show quoted text -

Thank you all for a fascinating thread! It's when I read something
like this that I think there's life in the usenet beast yet :-)

Cat(h) (and that I am reminded just how brilliant Nature is)

Cat(h) wrote:
Snip
Cat(h) (and that I am reminded just how brilliant Nature is)

As I wrote in the starter for five it was just a curious question,
especially as to what "kick starts" the leaves. If the answer confounds
the intelligentsia here, never mind the plant physiologists, just
imagine how my head is spinning. Thanks for all the contributions.