Stems are the part of a plant that grows above the ground. Certain stems show modifications. These stems are unique as they grow differently and have special functions. There are different kinds of modified stems. Some grow horizontally underground near the soil surface such as potatoes. A strawberry grows horizontally above the ground, along the soil surface. They generate new clone plants. Thorns are a protective part of stem that protects the plant from predators, like in cactus. Bulbs are stem that are surrounded by fleshy leaves that store nutrients such as onions.