The union of a small piece of bark with a bud and a root stock is called?

The term for the union of a small piece of bark with a bud and a root stock is indeed known as bud grafting. This method is commonly used in horticulture to propagate plants and create new varieties.

In bud grafting, a bud from the desired plant is taken and inserted into a rootstock, which is the part of the plant that provides the root system. The cambium layers of both the bud and the rootstock must be aligned to ensure a successful graft union, allowing the bud to grow and develop into a new plant. This technique is particularly valued because it enables the propagation of specific plant traits, such as disease resistance or improved fruit quality, by combining the strengths of different plant varieties.

Other options such as cutting, layering, and seedling refer to different propagation methods. Cutting involves taking a part of a plant, often a stem or leaf, and encouraging it to root. Layering involves inducing roots to form on a stem while it is still attached to the parent plant. Seedling refers to a young plant that has developed from a seed, which does not involve grafting techniques. Each of these methods has its own applications and benefits in plant propagation, but bud grafting specifically addresses the combination of a bud with a