North American Fruit Explorers mailing list at ibiblio

["tanis cuff" <tanistanis@hotmail.com>]

I just ran thru the string on girdling, and had to go review what is phloem 
vs zylem, and wanted to clarify where in the plant the roots deliver up, and 
where the leaves deliver down.

One of the postings I think said the roots deliver via the thin growth layer 
just under the bark.  That's incorrect.  The roots deliver (water & 
minerals) via the tiny tubes in the interior or wood part of a trunk or 
branch.  The leaves deliver carbs & such to the roots via the thin layer 
very close to the bark.  (The inner tubes are the xylem, the outer is the 
phloem.  And if I understand correctly, the famous 'cambial layer' is 
between the 2 and produces new cells for both.)  This is why when a tree is 
girdled, it looks OK for a while: roots can still deliver juice to the 
leaves; but the tree will eventually fail because leaves are not delivering 
food to the roots.  Unless it can throw a water sprout from below the 
girdle, or root suckers, either/both will then connect leaves with the roots 
again.