Scientists at the University of Bonn carried out extensive research to show that the water-drops rolling off a lotus（莲花）leaf carry away dirt, leaving the surface perfectly clean. This phenomena has been named the "Lotus Effect" and works best on rough surfaces.
Contrary to popular belief, lotus leaves are not smooth at all. When examined under a powerful microscope, the leaf cells show a bumpy surface. That makes the surface rough. As a result, dirt rests only on the tips of the wax crystals（蜡晶体）covering the leaf surface. The roughness reduces the contact area between the dirt and the leaf surface. A rough surface structure with wax crystals makes it impossible for water to stick. Due to the friction（摩擦力）, the water contracts at once. It forms round waterdrops to minimize the contact area with the rough, waxy leaf surface and runs off the leaf very quickly. Since the dirt only rests on the tips of the wax crystals they stick more strongly to the waterdrops than to the leaf surfaces. They are washed away when the water falls on the leaves.
On smooth leaves, the dirt is pushed from one part of the leaf to the other. This is because the dirt has a larger contact area where they can rest comfortably on the flat surface. We must also keep in mind that water usually spreads and only partially runs off the leaves-that too, only if the leaf is tilted! The dirt may get driven, but they are mainly displaced from one side of the leaf to the other.
Scientists say that the "Lotus Effect" is particularly beneficial for it helps to protect the lotus leaves from harmful bacteria. The dirt on the leaves often contains tiny disease causing fungi and bacteria. While most of the bacteria get washed off, the few that remain eventually die since they do not get the water they require for survival and growth.
