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How do Trees Really lift Water to their Leaves?

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8 years 6 months ago #776 by Andrew
Stefan:
Gravity is not a major enhancing factor in some of those things.

Also, aren't you making the fallacy of false analogy?

Gravity, Learn to live with it, because you can't live without it!

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8 years 6 months ago #777 by Andrew

Andrew wrote: Stefan:
Gravity is not a major enhancing factor in some of those things.

Also, aren't you making the fallacy of false analogy?


Gravity, Learn to live with it, because you can't live without it!

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8 years 6 months ago #778 by Andrew
And all of you know what gravity is?

Please let me know at your earliest convenience as this problem has eluded the greatest minds and to this day still does!

Gravity, Learn to live with it, because you can't live without it!

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8 years 6 months ago #779 by Andrew
Stefan:
Are you saying that you know better than the rest of us what gravity is and how it does and does not work?

Gravity, Learn to live with it, because you can't live without it!

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8 years 6 months ago #780 by Andrew
The plates on the following paper show clearly the size of xylem and number of xylem in comparison to phloem. Tiny amount of return flow in the phloem = solvent dragging on all of the more dilute sap in the xylem, evaporation at the leaves reduces the volume of sap but increases the density of the sap and the denser sap moves down the tiny by comparison phloem vessels.

Experiments with different diameter tubes has shown this to be worth considering.

Using an inverted U tube with 3 tubes one of which contained a small amount of coloured salt solution added at the upper part where the tubes were joined with a T junction, the salt solution moved down as expected and the salt free water in the other two tubes moved up, caused by solvent dragging on all of the water molecules.

In the case of the tree, the narrowing of the xylem vessels in the canopy compared to the xylem vessels in the trunk and branches affords a method of extruding the large volume of water shedding off the majority to evaporation and returning the solutes down the phloem vessels.

The paper also relates to the problem with addressing constant cavitations known to take place and also known to refill and repair the cavitations. The cohesion tension theory relies on root pressure for this, yet the rattan does not exhibit root pressure.

www.amjbot.org/cgi/reprint/89/2/196.pdf
American Journal of Botany 89(2): 196–202. 2002.
XYLEM OF RATTANS: VESSEL DIMENSIONS IN
CLIMBING PALMS1
JACK B. FISHER,2,3,5 HUGH T. W. TAN,4 AND LESLIE P. L. TOH4
environmental factors. During periods of limited rainfall, rattans
and other lianas can experience severe water stress. At
such times, both stomatal closure and stem water storage
would aid survival. In other lianas, water-storing tubers or succulence
of stems and leaves are common (Fisher and Ewers,
1991). Rattans lack tuberous roots and their narrow stems have
a small proportion of parenchyma that could function in water
storage. However, their long stems with a relatively large volume
of water in wide vessels represent a significant water reservoir
that would become available if cavitation of vessels
occurred during periods of extreme water stress (Holbrook,
1995). If cavitation of wide vessels does play a role in water
supply during draught periods, then the question of vessel refilling
must be addressed. Further studies should also focus on
the water capacity of rattan stems compared to nearby nonclimbing
palms, as well as their relative degrees of stomatal
control.
At present, we have no information on production of embolisms
in rattan xylem. Yet the low percentage of nonfunctional
vascular bundles in old stems suggests either a lack of
vessel cavitation or a mechanism for refilling vessels (and tracheids).
Other lianas have root pressure that is sufficient to
refill air-filled xylem, as in Vitis (Sperry et al., 1987), or to
decrease xylem tension and thus assist in removal of embolisms
(Fisher et al., 1997). In a nonclimbing palm, Sperry
(1986) found that embolisms were dissolved when xylem pressure
potential approached that of the atmosphere during periods
of rain. When stem bases of cultivated species of Calamus,
Daemonorops, and Desmoncus (a climbing nonrattan palm)
were cut at dawn during rainy periods, no exudation appeared,
thus indicating no root pressure (Fisher et al., 1997); however,
there was an indication of root pressure in one species of Calamus
cultivated in a mountainous rainforest. We suggest that
future measurements for possible root pressure are needed to
better understand water conduction for rattans growing in natural
environments.


environmental factors. During periods of limited rainfall, rattans
and other lianas can experience severe water stress. At
such times, both stomatal closure and stem water storage
would aid survival. In other lianas, water-storing tubers or succulence
of stems and leaves are common (Fisher and Ewers,
1991). Rattans lack tuberous roots and their narrow stems have
a small proportion of parenchyma that could function in water
storage. However, their long stems with a relatively large volume
of water in wide vessels represent a significant water reservoir
that would become available if cavitation of vessels
occurred during periods of extreme water stress (Holbrook,
1995). If cavitation of wide vessels does play a role in water
supply during draught periods, then the question of vessel refilling
must be addressed. Further studies should also focus on
the water capacity of rattan stems compared to nearby nonclimbing
palms, as well as their relative degrees of stomatal
control.
At present, we have no information on production of embolisms
in rattan xylem. Yet the low percentage of nonfunctional
vascular bundles in old stems suggests either a lack of
vessel cavitation or a mechanism for refilling vessels (and tracheids).
Other lianas have root pressure that is sufficient to
refill air-filled xylem, as in Vitis (Sperry et al., 1987), or to
decrease xylem tension and thus assist in removal of embolisms
(Fisher et al., 1997). In a nonclimbing palm, Sperry
(1986) found that embolisms were dissolved when xylem pressure
potential approached that of the atmosphere during periods
of rain. When stem bases of cultivated species of Calamus,
Daemonorops, and Desmoncus (a climbing nonrattan palm)
were cut at dawn during rainy periods, no exudation appeared,
thus indicating no root pressure (Fisher et al., 1997); however,
there was an indication of root pressure in one species of Calamus
cultivated in a mountainous rainforest. We suggest that
future measurements for possible root pressure are needed to
better understand water conduction for rattans growing in natural
environments.

Gravity, Learn to live with it, because you can't live without it!

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8 years 6 months ago #781 by Andrew
Bored Chemist: aka BC

Quote from: Andrew K Fletcher on 15/11/2009 09:54:11

And all of you know what gravity is?

Please let me know at your earliest convenience as this problem has eluded the greatest minds and to this day still does!


No, but I do know some of it's properties.
For exaple;
It is the force that holds me down on the planet.
It isn't responsible for the heat from the sun
It doesn't push water up trees.
It doesn't drive all life on earth.

The world's great scientists mighht not understand it fully but, unlike you, they know what not to atribute to it.
Why dd you post that rubbish?

Gravity, Learn to live with it, because you can't live without it!

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8 years 6 months ago #782 by Andrew
Gravity is what drives the sun! therefore gravity is responsible for the heat from the sun. No gravity = no sun No gravity = no BC and no earth to stand on! No gravity = nothing

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8 years 6 months ago #783 by Andrew
Madidus_Scientia:
Gravity is a force, not energy.

Gravity, Learn to live with it, because you can't live without it!

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8 years 6 months ago - 8 years 6 months ago #784 by Andrew

Rosy:
Hehe.

Ok, now I'm laughing. We're in real making-stuff-up territory now.

Sure the sun wouldn't be able to exist without gravity, because the matter wouldn't be concentrated in one place... but to say that gravity drives the sun is just ludicrous. What "drives" the sun (in the sense of providing the actual energy) is nuclear fusion. Nuclear fusion is not, repeat not, driven by gravity.


Where does the immense pressure come from that forces the atoms together to create fusion?

Gravity, Learn to live with it, because you can't live without it!
Last edit: 8 years 6 months ago by Andrew.

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