As a tree grows older, which of the following increases more rapidly in thickness? A Heart wood B Sap wood C Phloem D Cortex
Heartwood is also called duramen. It is dead, central wood of trees. Its cells usually contain tannins or other substances that make it dark in colour and sometimes aromatic. Heartwood is mechanically strong, resistant to decay, and less easily penetrated by wood-preservative chemicals than other types of wood. One or more layers of living and functional sapwood cells are periodically converted to heartwood. So, when tree grows older, heartwood increases rapidly than sapwood, cortex or phloem. Thus, option A is the correct answer.
