Brief notes on the Internal structure of root

Root is the part of the plant axis that mostly remains underground. It is a simple organ and lacks any lateral appendages and nodes. The internal structure is very simple and shows lit­tle difference at different level. The primary structure of the root in a trans­verse section shows three distinct re­gions (a) Epidermis (b) Cortex (c) Stele.

Epidermis: It is the outer most layer of the root and is also known as epiblema or piliferous layer. Gener­ally, it is one layered and bears tubu­lar extension of the epidermal cells called, epidermal hairs (or root hairs). Root hairs are unicellular and continuation of the epidermal cell. They are short, thin so that they can enter into the soil capillaries and increase the surface area of absorption.

Cortex: It is a broad zone of pa­renchyma cells and there is no hypodermis. The cells are regularly ar­ranged and with intercellular spaces. Endodermis is its inner layer and con­tains one layer of barrel shaped cells. Sometimes starch grains are found and in that case it is called the starch sheath. Passage cells are found in the endodermal layer

Stele: It is a very narrow zone bounded by pericycle. Generallypericycle is one or two layered and parenchymatous. Sometimes, patches of sclerenchyma may be seen. Stele con­tains vascular bundles. Vascular bun­dles are radial, closed and exarch in nature with centripetal development of xylem. The number of vascular bundles vary from dicotyledons to monocotyledons. Pith is very narrow or absent. When present it is parenchymatous in nature.