Pneumatophores are essential for breathing in certain species of trees such as mangroves. These structures are specialized roots that grow upwards from the waterlogged soil or water surface, allowing oxygen to reach the submerged roots. The pneumatophores contain pores called lenticels which facilitate the exchange of gases between the roots and the atmosphere. This adaptation is necessary for survival in waterlogged soils where oxygen is limited, and it helps the trees to grow and thrive in these environments. Therefore, the correct answer is "breathing."