Treesgrow in girth throughout their lives, through the action of two "lateral meristems," the vascular cambium (which forms xylem and phloem) and the cork cambium (which forms the bark). Helpful references: this Wikipedia article and images from my slides.
Some FAQs:
- Annual rings appear because the wood that is created in the spring has larger cells that those created later in the season. Wood of most tropical trees do not have annual growth rings.
- When the bark of a tree is peeled all the way to the wood, the tree will die because
- the phloem has been removed so sugars cannot be transported between leaves and roots.
- the phloem will not be replaced since the entire cambium has been removed.
- The center of most trees is dead at maturity. Tannins are deposited there in the heart wood, to prevent fungal infections.
- In the spring, sap flows only in the outer, living band of wood, called the "sap wood."
- The wood of many trees have bands of living tissue, called rays, running from the center of the tree out to the bark. The rays store food (starch) to fuel the spring flush of growth and are valued for their figurative patterns in the stripes of tiger oak and other decorative woods.
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