Plants which grow partially or completely in water are called hydrophytes or aquatic plants. Mechanical tissues are completely absent or poorly developed in hydrophytes. It is one of the adaptation seen in hydrophytes. If these plants are removed from the water, they hang limply. They are normally supported by water all around them and so have no need of mechanical strengthening. Indeed, this would be a distinct disadvantage as it would limit flexibility in the event of changes in water level or water movement