Phloem Xylem Inner Phloem Inner Cambium Figure . : Types of vascular bundles (a) and ( b) - Conjoint, collateral and open; (c) and (d) - Conjoint, collateral and closed (e) and (f) - Conjoint, bicollateral and open; (g) and (h) - Concentric and amphicribral; (i) and ( j) - Concentric and amphivasal; (k) and (l) - Radial separated is called conjunctive tissue . In bean, the conjuctive tissue is composed of parenchyma tissue. Xylem is in exarch condition .
The number of protoxylem points is four and so the xylem is called tetrach . Each phloem patch consists of sieve tubes, companion cells and phloem parenchyma. Metaxylem vessels are generally polygonal in shape. But in monocot roots they are circular.
Primary Structure of Monocot Root-maize Root The transverse section of the monocot root (maize) shows the following plan of arrangement of tissues from the periphery to the centre. Ground plan Root hair Piliferous layer Cortex Endodermis Pith Root hair Piliferous layer Casparian strip Endodermis Pericycle Passage cell Phloem Protoxylem Metaxylem Pith Cortex Passage cell A sector enlarged Figure . : T.S of Monocot root (Maize root) Piliferous Layer or Epiblema The outermost layer of the root is known as piliferous layer . It consists of a single row of thin-walled parenchymatous cells without strips are absent in the endodermis cells which are located opposite the protoxylem elements.
These thin-walled cells without casparian strips are called passage cells through which water and mineral salts are conducted from the cortex to the xylem elements. Water cannot pass through other endodermal cells due to the presence of casparian thickenings. Stele All the tissues present inside endodermis comprise the stele. It includes pericycle and vascular system.
Pericycle Pericycle is generally a single layer of parenchymatous cells found inner to the endodermis. It is the outermost layer of the stele. Lateral roots originate from the pericycle. Thus, the lateral roots are endogenous in origin.
A sector enlarged Ground plan Root hair Piliferous layer Cortex Phloem Metaxylem Conjunctive tissue Root hair Piliferous layer Phloem Pericycle Protoxylem Conjunctive tissue Metaxylem Casparian strip