Sap rise in spring

John Hewitson 100600.70 at CompuServe.COM
Wed Oct 2 01:16:20 EST 1996


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,                                                                  |
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