28.
A. If the tree was cut in circumference completely through
layer A, the tree below that point would eventually
die.This occurs because the phloem, found outside layer A,
carries organic molecules to the lower plant. If the lower stem can't quickly
grow leaves, the cells in the root and trunk run out of food.
B. The cutting process across the stem's circumference is known
as girdling.
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Long & Slichter