The difference between stock and scion are:

Stock

  • A rooted stem into which a scion or a bud is grafted is called a stock.
  • Gene transfer for alfalfa improvement

    Image Source: naaic.org/TAG/TAGpapers/arcioni/fig8.jpg

    Stock is selected for its adaptability, resistance to diseases etc.

Scion

  • A piece of young stem or bud which is inserted into a root stock is called scion.
  • Scion is selected for good quality of fruits, flowers, resistance to diseases etc.