"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.