Question

Plants showing anomalous secondary growth include
A. Agave
B. Dracaena
C.Yucca
D. All of the above

Answer 1

Hint: Anomalous secondary growth is observed in some monocots in which growth of the secondary cambium is observed in the hypodermis region.

Complete answer:
Anomalous or abnormal secondary growth doesn’t follow normal secondary growth in which vascular cambium produces xylem on inside and phloem on outside. It is mainly observed in some monocots such as Dracaena, Agave, Yucca and Bougainvillea. In this type of growth, a series of cambia is formed outside the oldest phloem. Another type is observed in the arborescent stem, where the growth of secondary cambium occurs in the hypodermis, which later forms patches of meristematic cells and conjunctive tissue. Secondary vascular bundles are then formed from these patches of meristematic cells. Main tissue responsible for secondary growth is vascular cambium and is present in roots and stems The vascular cambium produces a ring of meristematic cells that produces secondary phloem towards bark and secondary xylem is produced towards pith. Two types of vascular cambium are Fascicular cambium/intrafascicular cambium and interfascicular cambium. Vascular cambium also forms inner bark and wood. It also increases the thickness of the tree. Cork cambium which is lateral meristem which produces phelloderm layer and cork cells. Cork cells cork cambium and phelloderm are collectively called periderm. It produces bark of the tree.

Hence, the correct answer is option (D).

Additional information:
Importance of secondary growth:
a. Old and non-functional tissues of plants are replaced with new tissues through secondary growth
b. It increases the age of plant as plants having secondary growth live longer than those who do not show secondary growth
c. Tissues produced after secondary growth protect older tissues from insects and outer environment

Note: Dracaena, Yucca and Agave belong to family Liliaceae and show abnormal secondary growth. In Dracaena, secondary growth is brought about by a special cambium called secondary thickening meristem. This meristem produces conjunctive tissue and secondary vascular bundles and an indefinite amount of secondary tissues were formed.