Introduction:
Potatoes and sweet potatoes are both popular tuberous vegetables that are commonly consumed worldwide. While they may look similar in shape and texture, their external features clearly differentiate them. The potato is considered a stem and the sweet potato is classified as a root. This can be justified by examining their external features in detail.

Potato: A Stem Vegetable
The potato belongs to the Solanaceae family and is scientifically known as Solanum tuberosum. It is an underground stem or a modified stem known as a tuber. Several external features support the classification of potato as a stem vegetable:

1. Eyes and Buds: Potatoes have small depressions called "eyes" on their surface, which are actually dormant buds. These buds are capable of sprouting new shoots when conditions are favorable, indicating their stem-like nature.

2. Stolon: Potatoes develop stolons, which are horizontal stems that grow above the ground. These stolons produce the tubers underground, further supporting the stem classification.

3. Leaves: While not visible externally, potatoes do have leaves. These leaves grow above the ground from the main stem of the plant.

Sweet Potato: A Root Vegetable
The sweet potato belongs to the Convolvulaceae family and is scientifically known as Ipomoea batatas. It is a true root vegetable, and several external features highlight its root-like characteristics:

1. Fibrous Roots: Sweet potatoes have numerous fibrous roots that grow from the base of the plant and penetrate the soil. These roots are responsible for absorbing nutrients and water from the ground, characteristic of a root system.

2. No Eyes or Buds: Unlike potatoes, sweet potatoes lack the distinct eyes or buds on their surface. Instead, they have a smooth skin without any visible protrusions.

3. Storage Function: Sweet potatoes store excess nutrients in their enlarged storage roots, which are thick and fleshy. This is a key characteristic of a root vegetable, as roots typically serve as nutrient storage organs.

Conclusion:
Based on the external features discussed above, it is clear that potatoes are stem vegetables and sweet potatoes are root vegetables. The presence of eyes and buds, the development of stolons, and the absence of fibrous roots and visible eyes distinguish potatoes as stem vegetables. On the other hand, the fibrous roots, lack of eyes or buds, and the storage function of the enlarged roots classify sweet potatoes as root vegetables.