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Internal Structure of Roots

This illustration shows a longitudinal section through a carrot root tip.

This illustration shows a transverse section through a dichotyledonous root. Details of the cells in each tissue are shown.

In a dicotyledonous root the vascular tissue has the xylem at the centre with phloem occurring between the extensions of the xylem.

In a dicotyledonous root the vascular tissue has the xylem at the centre with phloem occurring between the extensions of the xylem.

Notice the following parts:

Piliferous layer: Cells of this layer are thin walled for efficient passage of water and mineral salts. On maturity it is replaced by a less permeable epidermis.

Cortex: is made of loosely parked thin walled parenchyma cells. Acts as a storage tissue. Water molecules pass through it to the xylem.

Endodermis: Is made of a single layer of cells surrounding the vascular bundle that is made of xylem and phloem. The endodermis controls the amount of water entering the xylem.

Pericycle: Is made of a single layer of cells giving rise to lateral roots.

Vascular bundles: Occupy the central position. Each bundle consists of xylem and phloem.

Root hairs: microscopic outgrowths on the piliferous layer. These are thin walled. They are numerous in number, hence provide a large surface area for absorption of water and mineral salts.

Note that the monocotyledonous root has pith at the centre and that the phloem and xylem alternate around the pith.

The piliferous layer cells are thin walled for efficient passage of water and mineral salts. On maturity the piliferous layer is replaced by a less permeable epidermis.

Endodermis: This is a single layer of cells surrounding the vascular bundles. It controls the amount of water entering the xylem.

Pericycle: This is a single layer of cells giving rise to lateral roots.Vascular bundles: These occupy the central position.Each bundle consists of xylem and phloem tissues.