North American Fruit Explorers mailing list at ibiblio

[Heron Breen <breen@fedcoseeds.com>]

Sorry, a correction folks. Down near the bottom of this explanation it say 
that 
sugar released into the vessels during late winter freezing and thawing would 
have 
gone to the buds to help the prepare for WINTER if we didn't tap the tree. 
This 
should say SPRING. Sorry, I was losing my concentration toward the end.
Heron

On Mon Dec 12 18:01 , Heron Breen <breen@fedcoseeds.com> sent:

>
>Hi sportsfans,
>Offlist, Jerry Lehman asked me about how my previous posts about plant 
>physiology 
>relate to Maple Sugaring. I think explaining the conditions around the human 
>production of maple syrup will continue the cycle of physiology we started. 
>So 
here 
>goes:
>
>All summer long, the tree is transporting sugar solution down the phloem, 
>and 
>parenchyma cells are sucking as much as they can hold as the fluid descends. 
>The 
>solution is sugar and some water. The cambium layer is using a lot of this 
>sugar 
to 
>divide and create new Phloem parts and new xylem parts, as well as new 
>"hungry" 
>parenchyma cells within the xylem. Meanwhile water is "pumping" up from the 
>roots 
>to the leaves for transpiration/photosynethesis. 
>When I previously posted, I seperated the dead water transport vessels in 
>the 
xylem 
>(wood) and the parenchyma sugar storage/transport cells. These cells do 
>interact, 
>actually, but it is good to keep them clear in your mind before melding 
>them. As 
>the sugar solution is transported into the wood, parenchyma and other 
cells, "fill" 
>up and/or use some of the sugar and water for cell functions. Sometimes, if 
>the 
>tree is really going great and has lots of leaves and sun, the parenchyma 
>can't 
>store all the sugar and water at their disposal. This would be similar to 
>our 
>bodies only being able to absorb so much vitamin C and hour, regardless of 
>intake. 
>Many parenchyma cells abut the water transport vessels and "leftover" water 
>regularly returns to the vessels for another journey to the top. Sometimes a 
>small 
>amount of leftover sugar gets released into the vessels as well. But this is 
>a 
very 
>very little amount of sugar and it gets put back into use by cambium up top. 
>This 
>description might encourage one to think of these vessels and parenchyma as 
>able 
>and readily willing to share their goods regularly. This is not the case. 
>For more 
>than 75% of the year, they are mostly seperate.
>This changes in the Fall. Almost all the stored sugar is meant for the 
>spring push 
>of buds, flowers, leaves. Throughout the Fall, parenchyma are turning the 
>sugars 
>into starch (long-term storage form of sugar). A lot of this starch is 
>"dumped" 
>(see below paragraphs for "dumped" explanation) into the vessels and pumped 
>by the 
>water upward and outward. Buds formed that summer are given a massive amount 
>of 
>starch build-up in the wood behind the bud to draw from in the spring. 
>Remember 
>photosynthesis is barely happening during spring (a little from the cortex) 
>and 
>trees come out of dormancy and begin cambial activity from the top down, so 
>the 
>starch needs to be already in place for a bud to grow either leaf or flower. 
>Most 
>buds are on wood that have a limited number (sometimes only 1 or 2) of 
>growth 
rings 
>worth of xylem backing it up for fuel, so parenchyma from more thick xylem 
>send 
>theirs. This sugar release into the vessels from the parenchyma takes place 
>after 
>the leaves have fallen usually. This is why collecting scionwood and dormant 
>cuttings in the fall can have variable results and must generally be done in 
>late 
>November into December at the earliest here in Maine. 
>This brings us to maple syrup. Along with parenchyma and vessels, there are 
>lots 
of 
>fiber cells in the wood. They store water as well as adding the structural 
>integrity of the tree. Fiber cells need to be dead to function structurally, 
>and 
>their walls are made up of criss=crossing layers of bundled cellulose (which 
>is in 
>turn bundled starch chains) and lignin which is the equivalent of tree 
>lanolin. 
The 
>cambium makes all these cells. The interior of the cell is called the lumen. 
>The 
>interior and exterior can store huge amounts of water, and this determines 
>the 
>weight of a piece of wood "dry" or "green". They fill and empty depending on 
>many 
>factors. After feeding the living cells around them, their excess water 
>would also 
>end up in the transport vessels.
>These fiber cells go through the winter with water in their lumens 
>(interiors). As 
>it gets cold, this water freezes into pure crystals. In maple sugaring time, 
>the 
>cold nights followed by warm days freezes then thaws this water. As the 
>water 
>thaws, vapor/gas is produced. We've all seen this from ice cubes in the 
>freezer 
and 
>snowbanks. I do not honestly know why ice does this, so someone else will 
>have to 
>fill in here. Nor do I know what makes up the vapor. This vapor goes through 
>the 
>walls of the fiber cell into the rest of the xylem. There it exerts pressure 
>on 
the 
>rest of the cells present, the parenchyma and xylem. The parenchyma are 
>squeezed 
>and some more of their starch goes the only place in can: into the water 
>transport 
>vessels. The water transport vessels themselves are under pressure and, if 
>we 
>didn't tap the tree, this starch would go up to help buds prepare for 
>winter. This 
>process is going on all late fall and winter, as freezing and thawing take 
>place 
>within the tree. It is a fairly passive process, compared to phloem 
>transport and 
>photosynthesis. The starch stops travelling when it gets to the buds and 
>collects 
>there ready for Spring usage.
>When we tap the tree, we are releasing that pressure. The tree, if 
>punctured, is 
>literally willing to squirt its "sap" out whatever whole. Tapping in the 
>trunk 
>yields more "sap" because more parenchyma cells and transport vessels are 
>present 
>due to thicker xylem compared to farther up the tree. This freezing and 
>thawing 
>period of time is the only time that enough starch is being dumped into the 
vessels 
>for that solution to be called "sap". If a tree is tapped in the summer, it 
>will 
>not yield much if any syrup, just plain water with a drop of sugar per 
>gallon 
>probably.
>So, my fingers are worn out and probably your eyes, so I'll stop there for 
>now. 
>Elaborate, question, and correct at your leisure. Pardon my sentence 
>structure and 
>spelling.
>sincerely,
>Heron Breen
>zone 4, Maine
>PS Next time: the short course on a tree going "dormant" from September 
>onward, 
>including the theories of why rootstocks influence early or late dormancy 
>and 
>winter hardiness. Maybe by next week after my fingers rest.
>
>
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