Modified stems.

• Rhizomes (iris) are horizontal stems that grow just below the surface, and can produce shoots from axillary buds along the stem.

• Bulbs (onion) are underground shoots that store food in layers of modified leaves.

• Stolons (strawberry) are horizontal stems ("runners") that grow along the surface. New shoots can form at axillary buds along each runner.

• Tubers (potatoes) are enlarged rhizomes specialized for storing food. The "eyes" on a potato are axillary buds that can form new shoots.