When grafting, that has been cut from one plant is attached to the rootstock of another plant.

When grafting, the scion that has been cut from one plant is attached to the rootstock of another plant.

In grafting, a horticulture technique that is practiced, the "upper part of one plant" grows on the "root system of another plant" so they grow as a single plant. The process of grafting can be done only when the weather conditions and the physiological state of the plant are most favorable and advantageous.

There is an array of reasons that this technique is practiced for example to repair damaged plants, make precise plant forms, identify viruses and for many other reasons.

the answer is fifth.