Question

Phellem, phellogen and phelloderm together form
a)Perisperm
b)Perianth
c)Pericycle
d)Pericarp
e)Periderm

Answer 1

Hint:In the older stem and roots of dicotyledons and gymnosperms, due to continuous formation of secondary tissues, the epidermis gets stretched and ultimately tends to rupture. This is followed by the death of epidermal cells and development of a new protective layer.

Complete answer:
When the epidermis becomes damaged by wounding or extensive secondary growth, it is replaced by a new protective layer. Structurally, this layer consists of three parts –
(1) a meristem known as phellogen or cork cambium, (2) the layer of cells cut off by phellogen on the outer side known as the phellem or cork, and (3) the cells cut off by phellogen towards inner side known as the phelloderm. These three tissues are collectively referred to as the periderm.
Phellogen: It consists of meristematic cells. In contrast to vascular cambium, phellogen is relatively simple in structure and composed of one type of cells. Origin of phellogen (cork cambium) generally takes place in sub-epidermal layers. The cells of the phellogen are rectangular in shape, having vacuolated protoplasts.
Phellem (cork): The cells that constitute phellem are called cork cells. They are like the phellogen cells from which they are derived. There are no intercellular spaces among cork cells.
Phelloderm: The phelloderm cells resemble those of cortical cells in wall structure and contents. The shape of cells is however similar to that of phellogen cells.

                  

Enlarged portion of Transverse section of an older dicotyledonous stem showing Periderm.

The definitions of other options are :-
a)Perisperm is the layer of nutritive tissue that surrounds the embryo of a seed in some angiosperm plants.
b)Perianth is the outer layer of a flower that consists of calyx (whorl of sepals) and corolla (whorl of petals).
c)Pericycle is the thin layer of plant tissue that lies just below the endodermis.
d)Pericarp is the outer layer of a fruit and this tissue develops from the ovary wall of the flower. It is composed of three layers – epicarp, mesocarp and endocarp.

Thus, the option E, i.e., Periderm is the correct answer.

Note:Periderm acts as the first line of defence for plants. It protects the plants from biotic and abiotic agents and provides mechanical support to the plants. Due to its defensive function, the periderm is enriched in various useful plant products like alkaloids, terpenes and phenolic compounds.