Question

potatoes and onions are called stems. give reasons

Answer 1

Most people believe that it is a root.  Believe it or not, the potato is actually a stem. The leaves of the potato plant (Solanum tu-berosum) manufacture starch, which is transferred through the plant to its underground stems, known as stolons. Starch collects at the end of the stolons, forming swollen sections called tubers. These are the potatoes.

Answer 2

They are arised from stem..Potato is underground stem modification,where as onion is bulbous stem modification..