In old trees the greater part of secondary xylem is dark brown and resistant to insect attack due to:(a) Secretion of secondary metabolites and their deposition in the lumen of vessels.(b) Deposition of organic compounds like tannins and resins in the central layers of the stem.(c) Deposition of suberin and aromatic substances in the outer layer of the stem.(d) Deposition of tannins, gum, resin and aromatic substances in the peripheral layers of the stem.(e) Presence of parenchyma cells, functionally active xylem elements and essential oils.Choose the correct answer from the options given below:
- A(a) and (b) only
- B(c) and (d) only
- C(d) and (e) only
- D(b) and (d) only
Solution & Step-by-step Explanation
This describes Heartwood.(a) is correct: Deposition of metabolites in vessels makes them non-functional but durable.(b) is correct: Tannins and resins accumulate in the innermost (central) layers.(c) refers to cork/bark.(d) is incorrect: Deposition occurs in the central layers, not peripheral (that is Sapwood).(e) refers to Sapwood.Statements (a) and (b) are correct for Heartwood.