[IAWA Forum] More questions on Circulation within a tree.

From: "Andrew K Fletcher" <Gravity@blueyonder.co.uk>
Subject: [IAWA Forum] More questions on Circulation within a tree.
Date: Fri, 2 Jun 2006 13:15:37 +0100
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A while ago, the question of density changes in residual leaf and branch =
fluids as a direct result of the efficient transpiration from the leaves =
of a tree was put to the group. Judging from the responses which were =
also posted at the request of one of the groups members, it would be =
fair to deduce that there is a general acceptance that density changes =
would be an inevitable consequence of the evaporation of 98% of the =
water from the leaves.

several members also began to question what would happen to the sap once =
the density had increased and indeed it was suggested that it would be =
acted upon by gravity and that the sap would be moved as a result of =
this interaction with gravity.

This brings me to the next part of this important question for the =
group.

Explaining the results of Eduard Strasburger's experiment
Andrew K Fletcher
Evaporation from the leaves alters the density of the sap at the leaf, =
and gravity pulls the denser sap down. This generates a positive =
pressure in front of the falling sap, and a tension / negative pressure =
behind the falling sap, which initiates a simple flow and return, much =
the same as found in a simple flow and return domestic central heating =
system, where the heat from the boiler alters the density of the water =
causing the heated water to rise, where it is cooled inside the hot =
water tank via a coiled copper tube, returning the cooled water back to =
the boiler.=20
The German botanist Eduard Strasburger's famous experiment - where he =
killed all of the cells in a tree by cutting off the roots, while =
submerged in a bath of picric acid - demonstrated that transpiration and =
circulation was maintained for three weeks, after the death of the tree.

I put it to the group that either the picric acid or the copper sulphate =
solution used by Strasburger, caused the minerals and sugars held within =
the dying leaves and branches to be released over the 2 weeks and that =
this was all that would be required for a simple flow and return system =
to maintain the circulation and transpiration. Furthermore, the =
experiment does suggest that no living process need be involved in the =
bulk flow of a tree.

This would result in a downward flow caused by the liberated solutes and =
this would in turn generated suction at the base of the tree sufficient =
to draw in more dilute solution from the bath, and that this flow would =
continue until the liberated salts and sugars had either all reached the =
picric acid / copper sulphate bath, or that the liberated salts and =
sugars had changed the density of the fluid within the tub to =
counterbalance any falling solutes.

Andrew K Fletcher, UK=20

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<DIV><FONT face=3DArial size=3D2><FONT size=3D3><FONT face=3D"Times New =
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size=3D3><FONT face=3DArial size=3D2><SPAN=20
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<DIV><FONT face=3DArial size=3D2><FONT size=3D3><FONT face=3D"Times New =
Roman"><SPAN=20
class=3DsurveyDebateDate><FONT face=3DArial><FONT size=3D2>A while ago, =
the question=20
of density changes in residual leaf and branch fluids as a direct result =
of the=20
efficient transpiration from the leaves of a tree was put to the group. =
Judging=20
from the responses which were also posted at the request of one of the =
groups=20
members, it would be fair to deduce that there is a general acceptance =
that=20
density changes would be an inevitable consequence of the evaporation of =
98% of=20
the water from the =
leaves.</FONT></FONT></SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><FONT size=3D3><FONT face=3DArial =
size=3D2><SPAN=20
class=3DsurveyDebateDate></SPAN></FONT></FONT></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2><FONT size=3D3><FONT face=3DArial =
size=3D2><SPAN=20
class=3DsurveyDebateDate>several members also began to question what =
would happen=20
to the sap once the density had increased and indeed it was suggested =
that it=20
would be acted upon by gravity and that the sap would be moved as a =
result of=20
this interaction with gravity.</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><FONT size=3D3><FONT face=3DArial =
size=3D2><SPAN=20
class=3DsurveyDebateDate></SPAN></FONT></FONT></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2><FONT size=3D3><FONT face=3DArial =
size=3D2><SPAN=20
class=3DsurveyDebateDate>This brings me to the next part of this =
important=20
question for the group.</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><FONT size=3D3><FONT face=3D"Times New =
Roman"><SPAN=20
class=3DsurveyDebateDate><FONT face=3DArial><FONT=20
size=3D2></FONT></FONT></SPAN></FONT></FONT></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2><FONT size=3D3><FONT face=3D"Times New =
Roman"><SPAN=20
class=3DIndexAlphabeticalTitle><B>Explaining the results of Eduard =
Strasburger's=20
experiment</B></SPAN><BR class=3DNetscapeDummy><SPAN=20
class=3DIndexAlphabeticalAuthor>Andrew K Fletcher</SPAN><BR=20
class=3DNetscapeDummy></FONT></FONT><SPAN class=3Dbodyp>Evaporation from =
the leaves=20
alters the density of the sap at the leaf, and gravity pulls the denser =
sap=20
down. This generates a positive pressure in front of the falling sap, =
and a=20
tension / negative pressure behind the falling sap, which&nbsp;initiates =
a=20
simple flow and return, much the same as found in a simple flow and =
return=20
domestic&nbsp;central heating system, where the heat from the boiler =
alters the=20
density of the water causing the heated water to rise, where it is =
cooled inside=20
the hot water tank via a coiled copper tube, returning the cooled water =
back to=20
the boiler. </SPAN></DIV>
<P><SPAN class=3Dbodyp>The&nbsp;</SPAN><SPAN class=3Dbodyp>German =
botanist Eduard=20
Strasburger's famous experiment - where he killed all of the cells in a =
tree by=20
cutting off the roots, while submerged in a bath of picric acid - =
demonstrated=20
that transpiration and circulation was maintained for three weeks, after =
the=20
death of the tree.</SPAN></P>
<P><SPAN class=3Dbodyp>I put it to the group that either the picric acid =
or the=20
copper sulphate solution used by Strasburger, caused the minerals and =
sugars=20
held within the dying leaves and branches to be released over the 2 =
weeks and=20
that this was all that would be required for&nbsp;a simple flow and =
return=20
system to maintain the circulation and transpiration. Furthermore, the=20
experiment does suggest that no living process need be involved in the =
bulk flow=20
of a tree.</SPAN></P>
<P><SPAN class=3Dbodyp>This would result in a downward flow caused by =
the=20
liberated solutes and this would in turn generated suction at the base =
of the=20
tree sufficient to draw in more dilute solution from the bath, and that =
this=20
flow would continue until the liberated salts and sugars had either all =
reached=20
the picric acid / copper sulphate bath, or that the liberated salts and =
sugars=20
had changed the density of the fluid within the tub to counterbalance =
any=20
falling solutes.</SPAN></P>
<P><SPAN class=3Dbodyp><B xmlns:script=3D"urn:my-script-blocks">Andrew K =

Fletcher</B>, UK </SPAN></P></FONT></BODY></HTML>

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