`"____________"` is applied to cuttings to induce root initiation in horticulture.

Answer

To answer the question, "____________" is applied to cuttings to induce root initiation in horticulture, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Context**: The question pertains to horticulture, specifically regarding the process of inducing root formation in plant cuttings.

2. **Identifying the Key Term**: In horticulture, certain substances are used to promote root growth in cuttings. The key term we are looking for is a type of plant hormone.

3. **Recognizing the Relevant Hormone**: The hormone that is primarily responsible for promoting root initiation in plant cuttings is called "auxin." Auxins are a class of plant hormones that play a crucial role in the growth and development of plants.

4. **Function of Auxin**: Auxin not only promotes the initiation of roots but also aids in the growth of existing roots. It is known to stimulate root branching and helps in the overall development of the root system.

5. **Mechanism of Action**: Auxin is transported from the stem down to the roots, which facilitates the root development process. This downward transport is essential for the effective functioning of auxin in promoting root growth.

6. **Final Answer**: Therefore, the complete answer to the question is: "Auxin" is applied to cuttings to induce root initiation in horticulture.

### Final Answer:
"Auxin" is applied to cuttings to induce root initiation in horticulture.