Hard· Secondary Growth (Stem) (Cork Cambium)· +4 / −1
In old trees the greater part of secondary xylem becomes dark brown and resistant to insect attack due to:
(a) secretion of secondary metabolites in the lumen of vessels
(b) deposition of organic compounds like tannins and resins in the central layers of stem
(c) deposition of suberin and aromatic substances in the outer layer of stem
(d) deposition of tannins, gum, resin and aromatic substances in the peripheral layers of stem
(e) presence of parenchyma cells, functionally active xylem elements and essential oils
Choose the correct answer from the options given below: