Which of the following is a term for a storage organ that is often underground and capable of growth in plants?

The term that best describes a storage organ that is often underground and capable of growth in plants is indeed a tuber. Tubers are swollen, fleshy underground stems or roots that serve as storage organs for nutrients and energy, allowing the plant to survive adverse conditions and to grow new shoots when conditions are favorable.

Tuberous structures, such as the potato, not only store carbohydrates and nutrients but also have the potential for vegetative reproduction, as they can produce new plants from the eyes or buds on their surface. This ability to both store and grow makes them a significant adaptation for many plants in various environments.

In contrast, while bulbs and rhizomes also serve as storage organs, they have different structural and functional characteristics. For example, bulbs, like those of onions, typically have a concise, layered structure composed of fleshy leaves, while rhizomes are modified stems that grow horizontally under the surface of the soil. The root system, although crucial for anchoring the plant and nutrient uptake, does not specifically refer to a storage organ in the same way tubers do.