Question

What are medullary rays and what are their functions?

Answer 1

Hint:Parenchyma is a type of tissue which is soft and is generally found in soft parts of the leaf, bark, pulp of a fruit, pith of stem, etc. They are thin walled and unspecialised. Medullary rays are parenchymatous in nature.

Complete answer:
In a dicot stem, the parenchymal strips which are found between the vascular bundles are known as medullary rays. They are also known as vascular rays or pith rays.
The function of medullary rays is as follows,
>They separate the primary phloem and xylem.
>They have a role in food and tannin storage.
>They help in transport of food.
>They help in radial conduction water, organic substances and minerals from the center to the periphery.
>They also help in gaseous exchange via intercellular spaces.
>They serve as a link between the pith and cortex.

Additional information: Medullary rays are a characteristic feature of dicot stem and old dicot root. In a transverse section of dicot stem from outer to inner layers are,
>Epidermis
>Hypodermis
>Cortex
>Endodermis
>Pericycle
>Vascular bundle - This is where medullary rays are found
>Pith

Note:The presence of medullary rays can be seen in the form of growth rings which are visible to the naked eye. In a transverse section, they are seen as lines which are radiating from the center of the log. They help in estimating the age of the tree.