Question

Describe the primary structure of monocot root.

Answer 1

Primary structure of monocot root: The monocot root is circular in outline. The arrangement of tissues is as follows.

1. Rhizodermis of epiblema: The outermost layer is the Rhizodermis. It is made up tubular living cells. Some of the epidermal cells are protruded out in the form of root hairs. These root hairs are useful in the absorption of water. The epiblema gives protection to the roots.

2. Cortex: The cortex is broad and consists of parenchyma cells with large intercellular spaces. The cells are living and possess leucoplasts. Their function is storage. The last layer of the cortex is endodermis. The endodermal cells contain bands like structure made of suberin in their radial and transverse walls. These band-like structures are known as Casparian strips. Those endodermal cells in front of protoxylem are thin walled and known as passage cells. These passage cells conduct water from the cortex to xylem.

Stele: Stele in dicot root is differentiated into pericycle and vascular system.

Pericycle: Pericycle is a single layer of thin-walled parenchyma cells forming the outermost layer of the stele. Lateral roots arise endogenously from pericycle.

Vascular system: The primary xylem and phloem are arranged in alternate radii. Xylem and phloem are separated by the conjunctive tissue. Such a vascular bundle is said to be radial vascular bundles. Xylem occurs in the form of a solid core with a ridge like projections extending towards the pericycle. The number of protoxylem points is four. Hence the xylem is called tetrarch. As the first-formed xylem is pointing towards the periphery the xylem of roots is exarch. Phloem consists of sieve tubes, companion cells and phloem parenchyma. Pith is usually absent.