The lower part of the plant consists of a root system and a collar, which is called the rootstock. The upper part of the plant consists of the stem (which will bear the fruit), which is called the scion.
The two plants are joined together just above the collar, which is the part of the plant that is located between the roots and the stem.
A rootstock is selected for its disease resistance and vigor, which are then passed on to the scion. The scion is selected for the fruit’s taste qualities.