History: Cross-Section of Tree Trunk
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A. CAMBIUM. A very thin layer of living cells lying between the inner bark and sapwood, where the new wood and bark cells develop each year.
B. INNER BARK.
C. OUTER BARK.
D. SAPWOOD.
E. HEARTWOOD.
F. PITH.
G. MEDULLARY RAYS.
H. ANNUAL RING.