Question

Secondary cortex is also known as
A. Phellem
B. Phelloderm
C. Phellogen
D. Bark

Answer 1

Hint: Secondary cortex is a thin- walled parenchyma cell which has a cellulosic cell wall. It is composed of cork and cambium.

Complete answer:
-Vascular cambium is situated between the primary xylem and the primary phloem within the vascular bundle. The cells of vascular cambium divide and form the secondary xylem which are composed of tracheids and vessel elements to the inside and secondary phloem which are composed of sieve element and companion cells to the outside. As a result of continued activity of vascular cambium, the girth of the stem goes on increasing. The continuous increase in the girth results in the rupture of the outermost layer called epidermis and outer cortical layers. Due to the ruptures, they need to be replaced to shelter the stem. New protective cell layers are provided by another lateral meristem called cork cambium.
As the secondary tissues develop, the pressure starts killing epidermal cells which are then substituted with periderm. Periderm consists of phellogen, phellem and phelloderm. Cork cambium is the meristematic part of the periderm. Its cells have tannins and chloroplasts. The cells divide and form new cells on both the sides.
-Phellogen is also called cork cambium. It is a ring of meristematic tissue formed in the dicotyledonous stem during the ongoing process of secondary growth. The cork is generated towards the periphery and secondary cortex towards the inner side.
-Phellem or cork are compactly arranged and have a thin cellulosic cell in the beginning. As they mature there is a gradual loss of living matter and their cell becomes thick. It shelters the inner part of the stem.
-Phelloderm is the parenchymatous tissue which originates from the phellogen towards its inner side known as the secondary cortex. It is a living tissue having a cellulosic cell wall. Phelloderm is also known as the secondary cortex.
-Bark contains living and non -living tissue. Outside the vascular cambium all the tissues which are present together are known as bark.

Hence, the correct answer is option (B).

Note: Secondary growth means the replacement of old non-functional plant tissues with new active tissues. It is the outward growth of the plant body. Mainly seen in woody plants as they grow much taller than the other plants and need more support in stem and roots. Cork cambium and vascular cambium are important for secondary growth.