Is cohesion theory correct?

kai liu KRL121 at psuvm.psu.edu
Sun Dec 3 13:02:51 EST 1995


Dear netters,
Some people are challenging the cohesion theory. Canny (1995) gave a new
theory for ascent of sap. Zimmermann's pressure proble can't get negative press
ure lower than -0.7 MPa in a high tension plant. However, the pressure
chamber yielded "xylem tension", the negative pressure, is -1 to -16 MPa.
Smith (1994) found that the negative pressure in biological system only
can maintain about -1 MPa.
Is the pressure chamber measure the real negative pressure in plant xylem?
Canny (1995) analysised that there was some tissure pressure involved.
The pressure chamber can not directly measure the negative pressure.
I am confident that pressure chamber measured pressure is larger than

the real pressure. If you have interest, I can give you the reason.
The pressure proble also have some problems. When puncture the proble to
vessels, it will release the pressure by caviation or disrupting water flow.

Recently, I developed a methods to measure the negative presure in the
xylem. It can be used to test the cohesion theory and the pressure chamber
technique.

I need some professor's support to do this project because I am just a
student came from China. If you have some interest in this topic and can
support a Ph.D student, we can work together. You can gain a lot from
this project because it can make you famous.



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