"Martin" wrote in message
...
On Thu, 12 Aug 2004 21:18:05 +0000 (UTC), "Franz Heymann"
wrote:


"Kay" wrote in message
...
snip
OK. That figures. So what is the mechanism for plants that fold
their
leaves at night, I wonder?

Can't help with that one.

simple ...
http://www-saps.plantsci.cam.ac.uk/records/rec117.htm
:-)

It sounds somewhat adcanced for school level, but maybe I'm behind the
times.
Nevertheless, it was a very interesting link.

Franz

"Tim Challenger" wrote in message
...

I doubt if any metabolites are involved in the transport of water
to
the leaves. Surely osmotic pressure is enough to do the job?

Osmotic pressure does the job of course to a certain extent and for
short
plants this is normally enough, but *water tension* is another major
factor*.

I have my doubts. I have never heard a convincing explanation of that
concept.
On the other hand, I know that sea water is rather more concentrated
than the sap in a plant, and I do remember that the osmotic pressure
of seawater is enough to raise a column of sea-water to a height of
more than 700 feet.

"Martin" wrote in message
...
On Fri, 13 Aug 2004 16:58:48 +0000 (UTC), "Franz Heymann"
wrote:


"Tim Challenger" wrote in message
...

I doubt if any metabolites are involved in the transport of
water
to
the leaves. Surely osmotic pressure is enough to do the job?

Osmotic pressure does the job of course to a certain extent and
for
short
plants this is normally enough, but *water tension* is another
major
factor*.

I have my doubts. I have never heard a convincing explanation of
that
concept.
On the other hand, I know that sea water is rather more
concentrated
than the sap in a plant, and I do remember that the osmotic
pressure
of seawater

21.5 atmospheres
http://dbhs.wvusd.k12.ca.us/webdocs/...-Equation.html

is enough to raise a column of sea-water to a height of
more than 700 feet.

688 feet?

I had the dead sea in mind. {:-))

Franz

"Martin" wrote in message
...
On Sat, 14 Aug 2004 14:42:13 +0000 (UTC), "Franz Heymann"
wrote:


"Martin" wrote in message
.. .
On Fri, 13 Aug 2004 16:58:48 +0000 (UTC), "Franz Heymann"
wrote:


"Tim Challenger" wrote in message
...

I doubt if any metabolites are involved in the transport of
water
to
the leaves. Surely osmotic pressure is enough to do the
job?

Osmotic pressure does the job of course to a certain extent
and
for
short
plants this is normally enough, but *water tension* is another
major
factor*.

I have my doubts. I have never heard a convincing explanation
of
that
concept.
On the other hand, I know that sea water is rather more
concentrated
than the sap in a plant, and I do remember that the osmotic
pressure
of seawater

21.5 atmospheres

http://dbhs.wvusd.k12.ca.us/webdocs/...-Equation.html

is enough to raise a column of sea-water to a height of
more than 700 feet.

688 feet?

I had the dead sea in mind. {:-))

or even the IJsselmeer? My GPS gives interesting altitude values
when
I sail on the IJsselmeer.

I did the calculation using 32 feet of pure water = one atmosphere.

Wrong of course, I don't know how many feet of sea water = one
atmosphere.

What I am trying to say is that, as usual, you were right :-)

Thanks for the compliment, but we all know that that is wrong.
{:-((

Franz