Dicot root of Gram consists of:
(1) Epiblema or piliferous layer
This is single outermost layer of thin walled cells; the outer walls of most of these cells extend outwards and form unicellular rot hairs. This layer is used for absorption of water and various numeral salts from the soil and therefore has no cuticle. Root hairs increase the absorbing surface of the root.
(2) Cortex
This consists of many layers of thin walled rounded cells with numerous intercellular spaces between them. Cells of cortex contain leucoplasts and store starch grains.
(3) Endodermis
This is single ring like layer of barrel shaped closely packed without intercellular spaces. Radial walls of thin layer are thickened and thickness extends to the inner walls also. Endodermis is innermost layer of cortex and surrounds the stele as a cylinder.
(4) Pericycle
This lies internal to endodermis and like it, is a single ring like layer; its cells are much smaller and thin walled but with abundant protoplasm.
(5) Conjunctive Tissue
The parenchyma lying in between xylem and phloem bundles constitutes the conjunctive tissue.
(6) Pith
This occupies only a small area in the centre of the root. Sometimes the pith is nearly obliterated owing to the wood vessels meeting in the centre.
(7) Vascular bundles
These are arranged in a ring as in Dicot stem but here xylem and phloem form an equal number of separate bundles and their arrangement is radial. The number of xylem or phloem bundles varies from two to six. The cambium is absent in the young root but soon makes its appearance. Phloem bundle consists of sieve tubes, companion cells and phloem parenchyma. Xylem bundle consists of protoxylem which lies towards the circumference on the pericycle and metaxylem towards the centre. Xylem is exarch in roots and its development is centripetal.
Protoxylem is composed of small vessels (annular and spiral) and metaxylem of bigger vessels (reticulate and pitted). The metaxylem groups often meet in the centre and then the pith gets broken.
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