(i) Underground parts of a plant are not always roots as some perennial herbs develop their stems underground for the purpose of perennation, and food storage during unfavourable conditions. The stem produces aerial branches every year when conditions become favourable. The underground stems act as storage organs and also help in vegetative propagation by means of their buds. These stems are non-green and leafless like roots but differ from them on the basis of:
(a) presence of nodes and internodes, scale-leaves, and axillary and terminals buds
(b) absence of root hair and root cap.
(ii) Flower is highly modified and condensed shoot meant essentially for the sexual reproduction of the plant. Calyx, corolla, androecium and gynoecium are modifications of leaf for playing various role in reproduction.