Sap rise in spring

Thomas Bjorkman tnb1 at cornell.edu
Thu Oct 3 07:34:03 EST 1996


In article <52t1bk$3t1 at mserv1.dl.ac.uk>, John Hewitson
<100600.70 at CompuServe.COM> wrote:

> Less than the 10 metres (1 atmosphere), which I believe is the sort of figure
> which root pressure can exert.
> 
> MUST be root pressure.

Since you are thinking about this, you'll be interested in a new model of
the ascent of sap.  See M.J. Canny. 1995.  Annals of Botany 75:343-357. 
In that model, the xylem sap is not under (much) tension and gravitational
pressure is made up for by the tissue squeezing the xylem. This model is
causing some interesting controversy because it rejects the validity of
long-held assumption, yet is rather robust in explaining both the data
that fit the old model as well as some that was through to be artefacts.
-- 
Thomas Björkman    
Dept. of Horticultural Sciences   
Cornell University
-- 
Thomas Björkman    
Dept. of Horticultural Sciences   
Cornell University



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