water hyacinth float on water surface.why?

 

Water hyacinths are the only large aquatic herb that can float on the water unattached to the bottom. They float on bloated air-filled hollow leaf stalks. The leaves of free-floating water hyacinths are characterised by a bulbous swelling in a section of the petiole. The oxygen bubbles float to the surface of water and get released into the air which provides buoyancy.