A thin cross-section of the root of a monocot shows two regions.
1. Extrastellar and intrastellar zones.
(i) Epiblema : Epiblema is single layered. It consists of unicellular rhizomes. It is composed of parenchyma cells. It absorbs water and mineral salts and protects the interior.
(ii) Cortex: Cortex is multilayered and composed of parenchyma cells. Cells are spherical and have intercellular spaces (may sometimes contain arenchyma or vacuoles). It stores food.
(iii) Endodermis: It is composed of single layered and tubular cells. The cells are densely packed and without gaps. The lateral and outer walls of the cells are thick. There are thin-walled passage cells or passage cells. It controls water penetration.
2. Intrastellar region
The region from the pericycle to the pith in the center of the root is called the stilt or intrastilt zone. Its various parts are-
(i) Pericycle: Under the endodermis there is a single layered pericycle. It is composed of parenchyma cells. The cells are very densely packed.
(ii) Vascular bundle: The number of xylem or phloem bundles is more than six. It is arranged radially and cyclically. Protoxylem towards the periphery and metaxylem towards the center i.e. exarch. It transports water, minerals and food.
(iii) Pith : The part surrounded by vascular bundles located in the center of the root is called pith. It is composed of parenchyma cells. The cells are round, thin-walled, and saccate. The raw root has a large pith. It stores food.
(iv) Medullary ray: The part from medulla to pericycle through the vascular bundle is called medullary ray. It is composed of narrow, long and thin-walled parenchyma cells. It separates the xylem and phloem and maintains the connection between the pith and the pericycle.