The term synergistic action of hormones refers to

Explanation

### Step-by-Step Solution:

1. **Understanding Hormones**: Hormones are chemical messengers in the body that regulate various physiological processes. They can have different effects on growth, metabolism, and development in plants.

2. **Defining Synergistic Action**: The term "synergistic action" refers to the interaction between two or more hormones that work together to produce a greater effect than the sum of their individual effects.

3. **Mechanism of Synergistic Action**: When two hormones act synergistically, they enhance each other's effects. This means that the presence of one hormone can amplify the action of another hormone, leading to a more pronounced physiological response.

4. **Example of Synergistic Action**: For instance, if hormone A promotes cell division and hormone B promotes cell elongation, when these two hormones are present together, they can work in concert to promote overall plant growth more effectively than if either hormone acted alone.

5. **Conclusion**: Therefore, the synergistic action of hormones refers to the cooperative interaction between hormones that leads to an enhanced effect on growth and development processes in plants.