Which method of propagation includes joining two different parts of a plant for continued growth?

The method of propagation that involves joining two different parts of a plant for continued growth is grafting. This technique is widely used in horticulture to combine the desirable traits of two different plants. For instance, the upper part, or scion, is taken from one plant that has desirable qualities like fruit size or disease resistance, and it is joined to the root system, or rootstock, of another plant that may contribute hardiness or vigor. When done correctly, the cambium layers of both parts grow together, allowing the grafted plant to function as a single, unified plant. This method not only allows for the propagation of certain plants that may not root well from cuttings but also enables the creation of hybrid plants with enhanced characteristics.

In contrast, other methods like division, separation, and layering involve different processes. Division typically separates a plant into multiple parts, each with roots, while separation refers to removing a part of a plant from the main plant, often without any direct joining. Layering involves inducing roots to form on a stem while it is still attached to the parent plant. Thus, grafting is unique in its technique of bringing together distinct parts for a successful continued growth.