Primary Structure of Roots

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Dicot Root (e.g. gram)

Internal structure of a typical dicotyledons root showing following features;

Epiblema: uniseriate outermost layer, unicellular root hairs are formed due to elongation of some cells of epiblema. It protects and absorbs water.

Cortex: large, parenchymatous cells with many intercellular spaces, cortical cells are filled with starch grains and stores food and water.

Endodermis: innermost layer of cortex made up of barrel-shaped cells, casparian strips are present, some cells are opposite to the protoxylem are thin walled and is called as passage cells and help in movement of water and dissolved salts from cortex directly into xylem.

Stele: all tissues inner to endodermis comprise stele.

Pericycle: single-layered, ring-like pericycle is present close to the endodermis on its inner side. Lateral roots are originated from the part of pericycle which is lying opposite to protoxylem.

Vascular bundle: are radial and xylem and phloem are separate and equal in number. Xylem consists of protoxylem (lies towards the periphery, having narrow vessels and tracheids) and metaxylem (lies towards the center, has wider vessels and tracheids). The numbers of xylem bundles are two to six (diarch to hexarch). Phloem is made up of sieve tubes, companion cells and phloem parenchyma.

Pith: very small, parenchymatous and without any intercellular spaces.

Conjunctive parenchyma: Parenchyma which separate xylem and phloem.

Image showing T.S. of dicot root.

Image Showing T.S. Of Dicot Root.

Image showing T.S. of dicot root.

Monocot Root (e.g. maize root)

Internal structure of a typical monocot root showing following features;

Epiblema: single layered, thin walled, colorless, polygonal without intercellular spaces, with presence of unicellular root hairs.

Cortex: large zone, multilayered, loosely arranged parenchyma cells with intercellular spaces and mainly meant for storage of water and food material.

Endodermis: Innermost layer of cortex with characteristic casparian strips and passage cells and consists of barrel shaped parenchyma without intercellular spaces.

Stele: All the tissues present inside endodermis comprise the stele.

Pericycle: Single-layered pericycle, consisting thin walled cells and gives lateral roots only, secondary growth is absent.

Vascular bundle: are radial, xylem and phloem are separated by sclerenchymatous conjunctive tissue. Xylem shows exarch and polyarch condition. Metaxylem elements are oval or circular.

Pith: center portion, large pith consists of thin walled parenchyma cells with intercellular spaces, abundant starch grains and stores food.

Conjunctive parenchyma: lies between the vascular bundles and for storage of water.

Image showing T.S. of monocot root.

Image Showing T.S. Of Monocot Root.

Image showing T.S. of monocot root.

Differences between Dicot and Monocot root

Table showing differences between Dicot and Monocot root.
Table showing differences between Dicot and Monocot root.

Characters

Dicot root

Monocot root

Number of vascular bundles

2 to 6 (di-hexarch) alternate bundles of xylem and phloem

Many (polyarch) alternate bundles of xylem and phloem

Pericycle

Pericycle give rise to lateral roots, cork cambium and part of vascular cambium

Pericycle produces only lateral roots.

Cambium

Present

Absent

Secondary growth

Present

Absent

Pith

Very small or absent

Large

Conjunctive tissue

Parenchymatous

Mostly sclerenchymatous sometimes parenchymatous

Cortex

Comparatively narrow

Very wide

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