Question

How can an underground stem be differentiated from a root?

Answer 1

In a flowering plant, the underground portion constitutes the root system while the part above the ground constitutes the shoot system. The prolongation of the radicle leads to the formation of the primary root which grows inside the soil. Whereas it is developed from the germinating seed's embryo.

Complete answer:

Underground stem	Roots
The underground stem is the modification of the stem.	The underground root is not the modification.
It arises from the plumule	It arises from the radicle.
The stem is differentiated among the nodes and internodes.	The root does not differentiate into nodes and internodes.
Scale leaves are pretty the nodes of the stem.	Scale leaves are absent in the roots.
Branches arise exogenously	Branches arise endogenously
The stem bears fruits and flowers	Fruits and flowers are absent in roots.
The stem bears axillary buds	Roots do not have axillary buds.
No root hairs.	Roots hairs are present.
Absence of root cap.	Root cap is present.
They usually function for the storage of food.	They always function for the storage of food.
Stems perform the function of transportation of nutrients, water, and minerals.	These functions are not shown by roots. They just take in water from the soil.

Note: Underground stems of potato, ginger, turmeric, etc are modified to store food in them. They also act as the perennation organ to tide over conditions unfavorable for growth. The function that roots perform is the absorption of minerals and water from the soil, storing of reserve food material, and synthesis of plant growth regulators.