-Priyanti, Subject Matter Expert at Edumarz
Solution: Stems can undergo several modifications, which can be grouped together into three main divisions — underground, sub-aerial and aerial modifications.
Underground:
Rhizome: It is the non-green, fleshy, underground stem with distinct nodes and internodes. The upper portion of rhizome has scaly leaves and the bottom part can bear adventitious roots. Examples include ginger.
Bulb: They look like a highly condensed discoid stem-like structure and maybe scaly or tunicated in nature. The former has fleshy scale leaves and the latter is covered by dry, membranous scale leaves. Base of the bulb comprises a cluster of adventitious roots. Examples include onion and garlic.
Corm: It is a spherical structure with a flattened base that grows vertically. Corms are a condensed form of stem that have adventitious roots at their base or throughout their entire body. Examples include saffron and yam.
Tuber: It is the fleshy part of the plant that stores food. Tubers don’t have adventitious roots, are mostly grown as food and grow very slowly. Examples include potato.
Sub-aerial:
Runner: It’s a horizontal creeper parallel to the soil surface and runs along its length. They can be used to perform vegetative propagation and maybe produced by mother runner going in all directions. Examples include grass and Oxalis.
Sucker: It arises from the basal part of the main stem, and develops adventitious roots and leafy shoots before separating from the main plant. Examples include banana and pineapple.
Stolon: It arises from the base of the main stem, grows aerially for sometime and bend down to touch the ground where the terminal bud gives rise to new stem and adventitious roots. Examples include strawberry.
Offset: It is a short and thick structure that originates from the axis of leaves and grows horizontally. Examples include Pistia.
Aerial:
Stem Tendrils: They are thread-like leafless structures that may be axillary, extra-axillary, apical bud or floral buds. Examples include watermelon and pumpkin.
Thorns: They are hard, pointed structures wherein the terminal bud gets modified into thorns. Examples include Bougainvillea and lemon.
Phylloclades: They consist of leaves modified into scales or spines which are fleshy in nature. Phylloclades are green, carry out photosynthesis and have fleshy internodes. Examples include Opuntia and Euphorbia.
Cladodes: They are non-fleshy phylloclades containing only a single internode. Examples include asparagus.
Bulbils: They are axillary vegetative or floral buds modified for food storage. Examples include Dioscorea.
Thalamus: It is the axis of a flower, bearing floral organs such as calyx, corolla, androecium and gynoecium.