Answer:
The plant with the root system is called the <em>rootstock or rooted part.</em>
The portion of the plant with the buds is called the <em>scion</em>.
Explanation:
The rootstock or rooted part of the graft is the plant that contains an adequate radicular system that can be used to hold or insert the cut stem of another plant or a bud plant. This last superior portion that is going to be graft is known as scion.
The rootstock is used to avoid dryness, salinity, water excess, nematodes problems, among others. The original plant of the rooted part is already used to the soil, and this is why it is chosen. Otherwise, all these conditions would affect the plant that the producer wants to grow and it would be more difficult to make it survive.
The scion has the genes or varieties that the producer wants to grow. They are chosen because of certain desired characteristics, such as fruit, flowers, leaves, among others. In general, the fruit trees are chosen for grafting.