Lenticels are small, lens-shaped openings found on the stems and branches of many plants, including trees and shrubs. They allow for gas exchange between the plant and the atmosphere, facilitating the movement of oxygen and carbon dioxide. This process is essential for the plant's respiration and overall health. These structures are typically visible as small dots or lines on the bark and can vary in size and shape depending on the species. Lenticels are particularly important for woody plants, such as apple trees and willow trees, which may have thick bark that limits gas exchange through other means.