Describe various stem modifications associated with food storage, climbing and protection.
Stem modification for food storage: - a) Rhizome: - The stem is thickened, prostate, and grows horizontally beneath the soil. The stem is branched & each branch ends in the terminal bud. Adventitious roots arise in profusion. Example: - Fern, water lily, turmeric etc. b) Bulb: - Highly condensed & discoidal stem. Terminal bud in the centre produces an aerial root that produces flowers. From the base of the stem adventitious roots develop. Leaves store food material. Terminal buds and scale leaves are present. Example: - Onion and garlic. c) Corm: - A condensed form of rhizome with auxiliary buds & scale leaves. It is the swollen base of the underground stem axis. Nodes and internodes are present. Example: - Jimikand, Saffron, Colocasia. d) Tuber: - It grows horizontally and swells at the apex. Adventitious roots arise during sprouting. It has numerous buds that develop into new plants. Example: - Potato, Helianthus. Stem Modification for Climbing: - Tendril: The axillary bud of some plants becomes elongated and coiled to form tendrils. Tendril coils around support, assisting the plant in climbing. Example: - Grapevine and pumpkin. Stem Modification for Protection: Thorn: A modified thorn is present in the leaf axil or on the apex of the stem. Thorns protect the plant from grazing animals. Example: - Bougainvillea and citrus.
