Potato tuber is modified /Edible part of potato is

A weak creeping stem, rooting at nodes and bear a series of plants of successive vegetative generations is called

Rhizome of ginger is like the roots of other plants that grows underground. Despite this fact ginger is a stem and not a root. Justify.

Potato and sweet potato

Stem modified into green, flattened branches of unlimited growth for assimilatory function is

Give main functions of stem.