Always with feet in the water, this is the life of many aquatic plants. And always with their head in the air, where is a lot of oxygen and carbon dioxide, which plants need. But how can they transport these gases to the rhizosphere, where the roots are, where they also need these gases?
The photo shows the internal structure of the stems of different species of plants on the banks. Note hollow shapes and others with bleached fabric somewhat bumpy. This is called aerenchyma. It consists of inflated cells or large intercellular spaces, forming large cavities within the plant. There the air passes with the vital gases of the plant. The structure of the aerenchyma is typical for plants that live in swampy and aquatic places, that is, it is the anatomical adaptation to oxygen-deprived environments.
For the maintenance of plants, the existence of aerenchyma has to be respected. If you do any pruning of dry plants always do it 20 cm above the water surface, to avoid that water can enter into these “transport channels” of the cut plant and cause them to rot.