Onion stores food in

Give scientific reasons: Although ginger grows under the soil,it is a stem,not a root.

Potato is multiplied vegetatively with the help of

The rhizome of ginger resembles the roots of other plants as it grows underground. Despite this fact,ginger is a stem and not a root. Justify.

The stem is generally $P$ when young and later becomes $Q$ in color.
$P \quad Q$

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