A thin transverse section of the root reveals the following internal structure under microscope.
Epiblema or piliferous layer: This is the single outermost layer composed of row of loosely-set thin walled cells with a number of unicellular root hairs.
Cortex: It occurs beneath epidermis. This is a many layered zone of parenchymatous cells with conspicuous inter-cellular spaces between them.
Endodermis: The innermost layer of cortex is differentiated as an endodermis. The endodermis is composed of a row of barrel-shaped closely packed cell. Radial walls and often the inner walls develop secondary thickening, known as casparian strips.
Certain cells of endodermis remain thin walled, known as passage cells which facilitate the movement of water from cortex to protoxylem.
Pericycle: This is the ring like layer lying internal to the endodermis. It is made up of both parenchyma and sclerenchyma cells.
Vascular bundles: Polyarch (many in number) and radial i.e. xylems and phloem form an equal number of separate bundles. They are arranged in a ring] Protoxylem occur towards the periphery and Meta xylems lie towards centre, i.e. xylem is exarch. Protoxylems consist of annular and spiral vessels, and Meta xylem of reticulate and pitted vessels.
Conjunctive tissues: The parenchyma in between xylem and phloem bundles! is known as conjunctive tissues.
Pith: Pith is large and central in position. It is composed of loosely arranged’ parenchymatous cells containing abundant starch grain.