Question

Multiseriate vascular rays are present opposite to the protoxylem in old
A. Dicot stems
B. Dicot roots
C. Monocot stems
D. Monocot roots

Answer 1

Vascular rays are also called Pith rays or Medullary rays. They are cellular structures made up of parenchyma tissue that runs from inside to outside and are majorly responsible for the conduction of various substances like- water, minerals, or organic substances.

Complete answer:
Medullary rays develop from the inside to outside or from the center to the periphery, dividing the vascular bundles. They are living primary tissue running vertically or at right angles with the xylem and phloem and are perpendicular to the growth rings. They are generally found in the stems of the wooden plants running from pith to the bark, supplying minerals and nutrients to the surface of the tree.
These rays are a combination of xylem and phloem rays and maintain a living link in the stems.
These rays are of two types- Primary medullary rays and Secondary medullary rays. The former appears in the young plants, and the latter appears in the plants with a secondary thickening. The former runs from cortex to pith, whereas the latter runs from pith to bark. The latter is also called vascular rays and is present in the stems of dicots and gymnosperms. They originate from the vascular cambium. These rays can be uniseriate (one cell wide) or multiseriate (two or more than two cells wide). They terminate at the xylem and phloem tissues and are produced during secondary growth in dicot stems.

In dicot stems, the protoxylem lies inside, and the metaxylem lies outside. The multiseriate vascular or secondary rays are present in the woody dicot stems and run from the pith to the bark. The protoxylem lies inside towards the pith in the stem. Therefore, the vascular rays will lie opposite them.

Option A: Dicot stems is the correct option.
All the other options are irrelevant.

Hence, the correct answer is option (A)

Note: The growth that results due to the cell division in the lateral meristem is called secondary growth. It leads to an increase in the diameter of the roots and stems of the plant. In dicot stem or woody plants, the secondary xylem lies towards the center while the secondary phloem lies towards the outer region. Vascular cambium initiates this process in the Steele region.