This article provides a diagram of monocot root. Also learn about:- 1. Exodermis 2. Origin of Lateral Roots 3. Root-Stem Transition.
A monocotyledonous root has almost identical structure and plan of arrangement, of tissues, excepting the following points of difference:
(1) Bundles in monocotyledonous roots are numerous and not limited, as in dicotyledonous roots; and the metaxylem cavities are wider.
(2) A large pith is always present.
Exodermis:
The roots have the piliferous layer with root-hairs. When the root-hairs are exhausted a new protective band is formed in the outermost portion of cortex. A few layers of cortex undergo modifications to form the said protective zone called exodermis. Exodermis is almost of universal occurrence in the monocotyledonous roots. In some cases it may be formed before the epidermis is decayed.
Origin of Lateral Roots:
Lateral or branch roots originate from the pericycle, a layer lying inside the stele. So they are endogenous in origin. A few of cells of the pericycle against the protoxylem become meristematic, and then by division produce new cells. These cells by further division give rise to the lateral roots which come out by piercing the endodermis and all the tissues in front of it (Fig. 155).
Root-Stem Transition:
The vascular bundles are continuous in roots and stems. But roots have radial bundles with exarch xylem and stems usually have collateral bundles with endarch xylem. In that case continuity of bundles in the root-stem axis becomes impossible, unless some orientations occur somewhere on the axis. The region where changes really take place is known as transition region.
It is usually the hypocotyl where radial bundles of the roots with exarch xylem are gradually changed into collateral bundles of stems with endarch xylem. There are different ways of transition. The basic point is that the xylem swings or rotates by 180° and joins on the phloem. Thus radial bundles become collateral and exarch xylem becomes endarch.