The inner dark wood that provides structural support is called?

• A. Sapwood
• B. Heartwood
• C. Xylem
• D. Phloem

Answer: (B)

Heartwood is the inner dark wood that provides structural support. As a tree ages, the central xylem becomes heartwood, which is filled with extractives and resins that darken it and make it more resistant to decay. It no longer conducts water, but it contributes to stiffness and strength of the trunk. The lighter outer wood is sapwood, which is still active in water and mineral transport up the tree. Xylem is the tissue family that includes both sapwood and heartwood, the vessels and cells that move water; phloem is the living tissue outside the xylem that transports sugars.