Sap Rise in Spring

David R. Hershey dh321 at PGSTUMAIL.PG.CC.MD.US
Sat Oct 5 01:19:45 EST 1996

I was only referring to sap flow in sugar maple, which is the basis of 
the maple sugar industry. Kramer reviews the literature in his book, 
Plant and Soil Water Relations: A Modern Synthesis, and notes one study 
(Plant Physiology 20:636-648) which found no root pressure during sap flow.
He notes that "considerable confusion" has occurred between sap flow due 
to local stem pressure (e.g. maple, palm) and root pressure (e.g. birch, 

David R. Hershey
Snail mail: 6700 Belcrest Road #112, Hyattsville, MD 20782-1340

Adjunct Professor, Biology/Horticulture Department
Prince George's Community College, Largo, MD 20772-2199

Email: dh321 at

On 4 Oct 1996, Barry Meatyard wrote:

> Dear Plant Edders,
> I've followed the correspondence on this with interest and would like to
> offer a couple of observations.  Like John Hewitson, I've seen exudate from
> a Walnut stump - in this case NOT a distal branch but the main trunk cut
> off as close to the ground as a chain saw allows. The stump was about
> 30-40cm across as I remember and went on seeping for about a week after it
> had been cut. Later when the main part of the stump was removed (but almost
> certainly leaving some roots behind) and the site levelled the earth
> remained damp on the surface even after neighbouring disturbed earth had
> dried out.  This would suggest that in this case at least the stem is NOT
> involved as David Hershey suggests, and whatever is happening is going on
> in the roots.
> I've also experienced at first hand exudate from sycamore (Acer
> pseudoplatanus) which formed a dense hedge down one side of the garden of a
> house I used to live in in Kent UK. I did some serious surgery on the hedge
> to cut it back (it was a few years ago and I can't remember the time of
> year - I suspect it was towards the autumn (fall) as I wouldn't normally do
> that sort of work any earlier - certainly not in the spring because of
> nesting birds - and I can remember leaves being around. The cut stumps
> ended up between 1m - 2m high and 10-15cm in diam.  They dripped copiously
> with the liquid appearing to come from the outer parts of the stems but I
> couldn't establish whether this was coming from the very outer sapwood or
> the phloem. It didn't taste sweet.
> It's all been very interesting......
> Barry
> Dr.Barry Meatyard                       Tel: 01203 524228
> Science and Plants for Schools          Fax: 01203 523237
> Institute of Education                  Email: barry.meatyard at
> University of Warwick
> Coventry
> CV4 7AL
> UK

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