Tag: internal structure of root, stem and leaf

In a young dicot stem, the cambium is single layered. It is made by the intrafascicular cambium present within the vascular bundles and the dedifferentiation of the parenchyma cells of the medullary rays between the vascular bundles, called interfascicular cambium. Their combination gives a circular cambium that produces xylem elements on the inner side and the phloem elements on the outer side.

Cork cambium is secondary or lateral meristematic tissue that grows beneath the epidermis and replaces it in dicot roots and stems and is responsible for the secondary growth of the tree.

The pericycle is a thin layer located between the endodermis and phloem in plant roots. In dicot stems, it is located around the ring of vascular bundles in the stele. The nature of pericycle is sclrenchymatous. 

Bast fibers are made up of sclerenchymatous cells and are absent in primary phloem but present in secondary phloem of dicots and are elongated , unbranched and have pointed needle like apices and are devoid pf protoplasm at maturity and dead.

• Pericycle is a cylinder of parenchymal and sclerenchyma cells which lie just below the endodermis of the plants. 
• In dicot stem, the pericycle is heterogenous made of parenchyma and sclerenchyma alternatively in irregular patches but they are not multilayered.
• So, the correct answer is 'In a dicot stem, the pericycle is usually multilayered'.

Casparian strips occur in radial walls of endodermis. The Casparian strip is a band of cell wall material deposited on the radial and transverse walls of the endodermis, and is chemically different from the rest of the cell wall - the cell wall being made of lignin and without suberin - whereas, the Casparian strip is made of suberin and sometimes lignin. It blocks the passive flow of materials such as water and solutes into the stele of a plant.
Thus, the correct answer is option A.

Open vascular bundle contains an interfascicular cambium in between phloem and xylem. Phloem and xylem are not in direct contact with each other. 

Starch sheath is endodermis of dicot stem. The endodermis is the central, innermost layer of cortex in some land plants. The endodermis is the boundary between the cortex and the stele. The endodermis helps regulate the movement of water, ions and hormones into and out of the vascular system. It may also store starch, be involved in perception of gravity and protect the plant against toxins moving into the vascular system.