Solution

Stems of various plants have undergone modifications to perform different functions.
1. Underground stems or storage stems:
Examples: Rhizomes, Corms, tubers
In ginger and banana, the underground stem is called as a rhizome. The underground stem in Colocasia (arvi) is known as corm. Rhizomes and corms are underground stems, modified for the storage of food. Also, these stems help in vegetative reproduction of these plants. The tips of the underground stem in potato plants become swollen due to the accumulation of food. The potato is a tuber that helps in the storage of food and bears eyes on it. Subtended by a leaf scar, these eyes bear buds that give rise to new plants.
2. Supportive stems:
Example: tendril
The stem in some weak plants bears thin, slender and spirally-coiled structures called as tendrils that help the plant get attached to nearby structures for support. Tendrils are found in cucumbers, melons and other members of the family Cucurbitaceae.
3. Protective stems:
Example: Thorns
The stem in Bougainvillea and citrus plants (like lemon and orange) bear sharp, pointed structures called as thorns, which provide protection to the plant from herbivores.
4. Photosynthetic stems:
Example: Opuntia
The stem in the Opuntia is green. It carries out the process of photosynthesis in the absence of leaves.
5. Others stem modifications:
In some plants, underground stems such as grasses spread in the soil and help in perenation. These stems are called as runners.
The short lateral stem called as the offset in some aquatic plants (such as Eichhornia) bears leaves and tufts of roots at the node and gives rise to new plants.