Pericycle [100% from NCERT]

  100% from NCERT 

• The Ground Tissue System

All tissues except epidermis and vascular bundles constitute the ground
tissue. It consists of simple tissues such as parenchyma, collenchyma
and sclerenchyma. Parenchymatous cells are usually present in cortex,
pericycle, pith and medullary rays, in the primary stems and roots. In
leaves, the ground tissue consists of thin-walled chloroplast containing
cells and is called mesophyll.

The ground tissue system forms the main bulk of the

plant. It is divided into three zones – cortex, pericycle and pith.

• Dicotyledonous Root

The outermost layer is epiblema. Many of
the cells of epiblema protrude in the form of
unicellular root hairs. The cortex consists of
several layers of thin-walled parenchyma cells

with intercellular spaces. The innermost

layer of the cortex is called endodermis.

It comprises a single layer of barrel-shaped

cells without any intercellular spaces. The

tangential as well as radial walls of the

endodermal cells have a deposition of

water-impermeable, waxy material suberin

in the form of casparian strips. Next to

endodermis lies a few layers of thick-walled

parenchyomatous cells referred to as

pericycle. Initiation of lateral roots and

vascular cambium during the secondary

growth takes place in these cells. The pith

is small or inconspicuous. The

parenchymatous cells which lie between

the xylem and the phloem are called

conjuctive tissue. There are usually two

to four xylem and phloem patches. Later,

a cambium ring develops between the

xylem and phloem. All tissues on the

innerside of the endodermis such as

pericycle, vascular bundles and pith

constitute the stele.

• Monocotyledonous Root

The anatomy of the monocot root is similar

to the dicot root in many respects .

 It has epidermis, cortex, endodermis,

pericycle, vascular bundles and pith. As

compared to the dicot root which have fewer

xylem bundles, there are usually more than

six (polyarch) xylem bundles in the monocot

root. Pith is large and well developed.

Monocotyledonous roots do not undergo

any secondary growth.

• Dicotyledonous Stem

The transverse section of a typical young

dicotyledonous stem shows that the epidermis

is the outermost protective layer of the stem.

Covered with a thin layer of cuticle, it may bear trichomes and

a few stomata. The cells arranged in multiple layers between epidermis and

pericycle constitute the cortex. It consists of three sub-zones. The outer

hypodermis, consists of a few layers of collenchymatous cells just below the

epidermis, which provide mechanical strength to the young stem. Cortical

layers below hypodermis consist of rounded thin walled parenchymatous

cells with conspicuous intercellular spaces. The innermost layer of the cortex

is called the endodermis. The cells of the endodermis are rich in starch

grains and the layer is also referred to as the starch sheath. Pericycle is

present on the inner side of the endodermis and above the phloem in the

form of semi-lunar patches of sclerenchyma. In between the vascular bundles

there are a few layers of radially placed parenchymatous cells, which constitute

medullary rays. A large number of vascular bundles are arranged in a ring ;

the ‘ring’ arrangement of vascular bundles is a characteristic of dicot stem.

Each vascular bundle is conjoint, open, and with endarch protoxylem. A

large number of rounded, parenchymatous cells with large intercellular

spaces which occupy the central portion of the stem constitute the pith.

• Secondary Growth in Roots

In the dicot root, the vascular

cambium is completely secondary in

origin. It originates from the tissue

located just below the phloem

bundles, a portion of pericycle tissue,

above the protoxylem forming a

complete and continuous wavy ring,

which later becomes circular . Further events are similar to

those already described above for a

dicotyledon stem.

• Development of root nodules in soyabean

Infected thread carries the bacteria

to the inner cortex. The bacteria get modified into rod-shaped

bacteroids and cause inner cortical and pericycle cells to divide.

Division and growth of cortical and pericycle cells lead to nodule

formation,

 Question:  From NCERT  | NEET   || [Difficult level:Easy] Explanations are 100% from NCERT 

.In dicot roots, the initiation of the lateral roots and the vascular cambium during the secondary growth takes place in:

(1) Pericycle

(2) Endodermis

(3) Conjuctive tissue

(4) Epidermis

.

.

 ✅ 

 Answer ▽ ✅Verified 

(1) Pericycle