Apple
If one wants to grow a certain type of apple, it is not possible to do this by planting a seed from the wanted type. The seed will have DNA from the apple that the seeds came from, but it will also  have DNA from the apple flower that pollinated the seeds, which might be a different variant of apple. This means that the tree which would grow from planting would be a mixture of two, or a hybrid. In order to grow a certain type of apple, a small twig, or 'scion', is cut from the tree that grows the type of apple desired, and then added on to a specially grown stump called a rootstock. The tree that grows will create apples of the type needed.