•UNDEGROUND STEM MODIFICATIONS:
•SUCKER: It arises from the underground part of stem for some distance it grow below the surface of soil then emerges out as a aerial shoot. It grow from axillary bud it has nodes internodes, scale leaves & adventitious roots Ex. Mint
•2.RHIZOME:Perennial underground main stem that grow below the surface of soil If their position below the soil is oblique or upright they are called rootstock rhizomes Ex. Alocasia indica & if the stem is horizontally placed & branched then they are called Straggling rhizomes Ex Ginger . The leaves and shoot are above the surface of soil in both types and both have nodes ,internodes, scale leaves which protect the axillary bud.
3 CORM: Spherical , condensed , fleshy solid vertically growing underground stem with a large apical bud, circular nodes & internodes, basal part have adventitious roots .Axillary buds in the axile of scale leaves .It is unbranched and have reserve food material.Ex Crocus.
4.BULB: Spherical modified underground shoot with reduced disc shaped stem with several fleshy scales enclosing a terminal bud. Reduced stem bear adventitious roots and fleshy sheathing leaf base on its upper side,the leaf base bear axillary bud which may become fleshy to form bulblets. Bulb are of two types:
(a)Tunicated bulb : Concentric layers of fleshy scales surrounding the reduced stem having terminal bud. The outer few scale form a membrane called tunic .In case of simple tunicated the scale leaves ring is surrounded by single tunic Ex Onion And in compound tunicated bulb the fleshy scales represent bulblets and each bulblet surrounded by its own tunic Ex. Garlic
(b) Scaly bulb: These have small separated scale leaves which are not concentric tunic is also absent.Ex Lily
TUBER : Stem tuber arises at underground ends of main stem as a swollen part due to reserve food material . These stem tuber are oval or spherical in shape which do not bear adventitious roots .The skin have lenticels for aeration and depressions called eyes , these represent nodes . The eyes are crowded towards apical end called rose end and less towards the stolon end called heel end . Ex. Potato
Sucker, Rhizome, Corm,Tuber, & Bulb are used in vegetative reproduction . Only bulb and sucker don’t reserve food material the rest have reserve food material . All of these can withstand unfavorable conditions.