Xylem and such

P.Clifford at Queens-Belfast.AC.UK P.Clifford at Queens-Belfast.AC.UK
Thu Nov 14 05:11:11 EST 1996

Re: Xylem and such.  The question as to whether a dead plant will still conduct
water can be answered based on the known facts about water movement in the xylemof living plants.  This is due mainly to the tension induced in the xylem by
transpiration at the leaves (i.e. the cohesion-tension theory of water flow).
It is very much dependent on the cell walls of living cells of the stomatal
cavities of leaves presenting a large apoplastic surface for water loss from
stomata.  It would also be dependent on the dead cells of the xylem being 
surrounded by living cells of the plant body.  Water flow through a dead plant
with say its roots in water would be quite limited because the xylem conduits
no longer have water in them and the driving force for water movement being
provided by evapoation has now been lost.  A dead plant would behave much like 
a length of wood with its base in water - there would be some movment of the water in the longitudinal direction but nothing like what goes on in the living
plant.  This could easily be checked by using dyes and sectioning at various
levels at various times after immersing the roots of a dead plant in water
containing the dye.  It was a good question for your teacher to ask - answering
it makes sure you really understand the basics of water movement in the xylem.

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