GardenBanter.co.uk - View Single Post - Water transport to the top of tall trees.

Peter Jason · 01-09-2012, 12:48 AM posted to sci.bio.botany

On 31 Aug 2012 11:37:21 GMT,
wrote:

In article ,
Peter Jason wrote:
A vacuum will hold up a column of water about 10
meters, so how does water get to the top of very
tall trees?
Peter

The water isn't held up by vacuum (actually the external air pressure, not
the vacuum per se) but by capillary action in series of very fine tubes.
The cohesion of the water molecules to each other is what keeps the
water up and rising as water evaporates from the periphery of the tree.

N.B. This is why you cut off the bottom of flower stems before you put
the bouquet in water.

Thank you. I was also wondering why water
evaporates more quickly from cotton (cellulosic)
materials faster than from polyester, nylon, glass
wool, and rubber foam etc. Indeed the difference
is quite marked.

As an experiment I put a petri dish on to a
balance and in its center weighed a 1 gram piece
of various substrates such as filter paper, cotton
wool, cotton pajamas, nylon rope, glass wick,
canvas, orlon and the like. In the center of
these materials I placed 1gm of distilled water.
In all cases the cellulose materials dried much
faster than any other. Almost twice as fast.

Strange, because this is the opposite I expected
given the OH groups on the cellulose and their
likely hood of their forming H-bonds with the
water and so retaining it. EG a nylon shirt will
dry faster than a cotton one, or so it seems
though evidently the nylon article will contain
less water when wet.