Final answer:
Mound layering (option c) is the correct term for piling soil around the base of a shrub's limb to induce root formation. It's a common technique used in horticulture for plant propagation and does not harm the plant when performed properly.
Step-by-step explanation:
Piling soil around the base of a shrub to induce roots to form at the base of the limb is called mound layering (option c). This horticultural technique encourages the formation of new roots at a point on the stem that is still attached to the parent plant. It's commonly used for plants like jasmine and bougainvillea that can be propagated through layering. The stem is partially buried in the soil, and this region will eventually develop its roots. It is essential to choose young stems that can bend easily without injury for this method to be effective. In contrast to mound layering, other types such as simple layering or air layering involve manipulating the stem in different ways to induce rooting. For instance, with air layering, part of the stem's surface is removed, and it's covered with moist material—such as moss—and wrapped to encourage root development. As for misconceptions about layering, it is not true that layering would kill the stem (as suggested in option e). In fact, this practice is a well-established and effective method of vegetative propagation that does not harm the plant when done correctly.