Describe modifications of the stem with suitable examples.
Stems of various plants have undergone modifications to perform different functions.
Examples: Rhizomes, Corms, Tubers
In ginger and banana, the underground stem is called a rhizome. The underground stem in Colocasia (arvi) is known as the 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.
Example: tendril
The stem in some weak plants bears thin, slender, and spirally-coiled structures called 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.
Example: Thorns
The stem in bougainvillaea and citrus plants (like lemon and orange) bear sharp, pointed structures called thorns, which provide protection to the plant from herbivores.
Example: Opuntia
The stem in the Opuntia is green. It carries out the process of photosynthesis in the absence of leaves.
In some plants, underground stems such as grasses spread in the soil and help in perennation. These stems are called runners.
The short lateral stem called the offset in some aquatic plants (such as Eichhornia) bears leaves and tufts of roots at the node and gives rise to new plants.