INTERNAL STRUCTURE OF YOUNG ROOT

INTERNAL STRUCTURE OF DICOTYLEDONOUS ROOT

Internal structure of a typical dicotyledon root shows following features.

Epiblema/Epidermis- it is unseriate (single layered) outermost layer. Cuticle and stomata are absent.

Many of the epidermal cells protrude in the form of unicellular root hairs means unicellular root hairs are formed due to elongation of cells of epiblema. Epiblema is also known as Rhizodermis  or Piliferous layer. Root hairs are present in maturation  zone of root. Root hairs ate short lived.

Note : Cells of epiblema which develop root hairs are called trichoblast cells.

Hypodermis is absent in the roots.

Cortex- it is made up of the walled parenchymatous cells with intercellular space.

Chloroplast is absent, so they are non photosynthetic but chloroplast are present in roots of Tinospora, Trapa and Taeniophyllum,so  they are photosynthetic (Assimilatory roots).

Endodermis- the innermost layer of the cortex is called endodermis. It comprises a single layer of barrel shaped cells without any intercellular soace. This layer of barrel shaped cells is situated between the pericycle and cortex. Casparian strips/bands are present on radial and tangential walls of endodermis.

These strips  are made up of ligno suberin means lignin & suberin (mainly suberin).suberin is water impermiable waxy material. Casparian strips were discovered by caspari.

The cells of endodermis which are situated infront of protoxylem cells are devoid of casparian strips. These are called passage cells/path cells.

Passage cells provide path to absorbed water from cortex to pericycle.

Intercellular spaces are absent between the cells of endodermis of root.

Endodermis acts as a water tight jacket (Dam) which prevents leakage of water from stele.

Pericycle:- it is a single or few layers of thick walled parenchymatous cells (it is composed of prodenchyma).

Lateral roots usually originate from the part of pericycle which is lying opposite to protoxylem. Thus lateral roots are endogenous in origin.

Note:

1. The branches of stem (vegetative branches) are exogenous in origin because they originate from extrastelar region.

2. Adventitious roots are endogenous in origin because they originate from stelar region.

Vascular Bundles- vascular Bundles are radial and exarch. Xylem and phloem are separate and equal in number. The number of xylem patches and phloem patches are usually two to four but they may be two to six (diarch to hexarch). Tetrarch condition is found in gram and sunflower.

Parenchyma which is found between the xylem and phloem is called comjuctive tissue.

In dicot root xylem vessels appear angular (polygonal/hexagonal) in T.S.

Pith- in dicot root pith is small (less developed) or inconspicuous or absent.

INTERNAL STRUCTURE OF MONOCOTYLEDONS ROOT

The internal structure of a typical monocotyledons root is similar to Dicotyledons root except some differences which are as follows:- 

1. Number of xylem bundles are usually more than six (polyarch) in monocotyledon root.

2. Pith is large and we'll developed in monocotyledon root.

3. Xylem vessels appear circular or oval in T.S.

4. Monocotyledonous roots do not undergo any secondary growth.

Note- as the epiblema dies off (in old roots), a few outer layers of the cortex become suberized (mainly) or cutinized and form the exodermis. Exodermis is usually found in monocot roots.

Note: velamen:- this spongy tissues is found in areial roots or hanging roots of epiphytes (eg. Orchids- vanda).

1. It is an example of multilayered epidermis.

2. It absorbs atmospheric moisture by imbibition. 

Thank you 😊