Just an observation:
In spring, a wallnut tree near my house can be seen to drip sap from the BROKEN
end of a branch, about 4 metres above ground level (knocked by passing lorries
each year).
Can't be adhesion/cohesion or any force which involves a "suck", can it?
Can't be running out from branches higher up the tree, can it?
Less than the 10 metres (1 atmosphere), which I believe is the sort of figure
which root pressure can exert.
MUST be root pressure.
That's what my students and I usually decide as we watch it drip.
Perhaps next spring we should strap a manometer onto the end of the branch?
We could prune a branch as a demo. if the lorries don't oblige.
__________________________________________________________________________
| Dr. John Hewitson |
| Berrystead Barn +44 (0)1832 272 209 phone/fax |
| Oundle, |
| Peterborough, PE8 4DY, UK e-mail 100600.70 at compuserve.com |
|__________________________________________________________________________|
