Assertion : In woody stems, the amount of heart wood continues to increase year after year. Reason : The cambial activity continues uninterrupted.

Step-by-step solution

Heartwood formation occurs spontaneously because it is a genetically programmed process. As a result of continued secondary growth for several years, the older parts of the stem and its old branches have a part of its secondary xylem rendered non - functional. Such a modified and non - functional secondary xylem is called the heart wood or duramen, the functional outer younger rings of secondary xylem constitute the sap wood or alburnum. With the passage of time and addition of new outer rings of secondary xylem du