Question

A highly condensed discoidal stem bearing a large number of fleshy leaves are found in
A. Colocasia
B. Allium
C. Ginger
D. Carrot

Answer 1

Many plants have modified stems and one such modification would be the underground stem, which is a stem modification that grows beneath the ground. The bulb is one example of an underground stem where it possesses a disc-shaped (discoidal) stem with many fleshy leaves.

Complete answer: Plants possess several modified vegetative organs devolved through years of evolutionary stress. Stems have modifications such as underground modifications, subaerial modifications, and aerial modifications. Underground modification of the stem is the most notable form and it has vital importance commercially as several commercially farmed plants have these modifications. Modified underground stems can be distinguished from roots by the presence of nodes and internodes, adventitious root formation, and several internal structures only seen in stems and not in roots. Some of the different types of underground stem modifications are named as rhizome, corm, bulb and tuber. A bulb is a specific form of modification where there is the presence of a disc-shaped structure beneath the stem with fleshy scales or leaves. It is seen in Allium species such as onions and garlic, where several bulbs are tunicated together. Tubers are thick fleshy swollen nodes with small depressions called eyes. The eyes are the nodes of the stem and the most common example would be the potatoes. Carrot is a root and not a modified stem, it is a modification of the taproot.
Therefore the correct answer is option B.

Note: Other stem modifications include the rhizome where there is a thick fleshy stem with nodes and buds. Ginger and banana are common examples of rhizomes. Corm is similar to the rhizome but is more spherical in nature and grows vertically, it has spherical nodes and buds and Colocasia is a good example.