Q.Explain, how stem is modified variously to perform different functions?

Underground stem modifications each have a classic textbook example: Bulb = onion, Corm = Colocasia, Rhizome = Canna, Tuber = potato — matching to (1)-(iii), (2)-(i), (3)-(ii), (4)-(iv).

Underground stems are modified for perennation (surviving unfavourable seasons) and food storage, and each type has a distinctive structure:

• Bulb (1) — a highly reduced, disc-like stem bearing fleshy scale leaves that store food, as in onion, Allium cepa → matches (iii).
• Corm (2) — a short, vertical, swollen underground stem (condensed rhizome) covered by scaly leaves, as in Colocasia (and Amorphophallus) → matches (i).
• Rhizome (3) — a horizontal underground stem that grows parallel to the soil surface, storing food and bearing nodes/internodes and buds, as in Canna (and ginger, turmeric) → matches (ii). …

A corm is an underground, condensed, vertical stem modified for food storage → (c) Stem.

Underground plant parts must be classified by their internal features, not merely by where they grow. A root lacks nodes, internodes, buds and scale leaves; a stem always shows them.

• A corm bears distinct nodes and internodes, scale leaves, and axillary/terminal buds. …

A potato tuber is a swollen underground stem (a stem modification for food storage), identifiable by the presence of nodes and internodes.

The potato plant's underground stem produces slender lateral branches (stolons) whose tips swell with stored starch to form tubers. Being a stem, the tuber retains nodes bearing axillary buds ('eyes') th …

A corm is a stem modification: a short, vertically-growing, food-storing underground stem, condensed into a rounded/disc-like shape, and — because it is a STEM, not a root — it still shows nodes, internodes, scale leaves and buds. (Examples: Colocasia, Gladiolus, Amorphophallus, Crocus.)

Since this answer is text-only, the diagram is given here as a clearly labelled structural description rather than a hand-drawn image; a student should reproduce it as an actual labelled sketch on the exam paper.

Structure of a corm (labelled parts):

1. Main axis / corm body — a short, swollen, disc-shaped or rounded stem, oriented vertically, that stores food (mainly starch).
2. Nodes and internodes — present but very close together (internodes highly condensed), which is what gives away that this is a stem and not a root or a bulb-like leaf-storage organ.
3. Scale leaves — thin, dry, membranous leaves borne at each node, covering and protecting the corm.
4. Axillary buds — found in the axil of each scale leaf; several of these grow out to form new corms (vegetative propagation), as seen in Colocasia and Gladiolus "cormels".
5. Apical/terminal bud — at the top of the corm, it grows upward each season to produce the aerial shoot (leaves and, eventually, the inflorescence). …