English: SEM Foto.Diatom samples were treated with cold acid method (Krammer & Lange-Bertalot, 1986).Diverse of diatom algae. The cells are surrounded by a rigid two-part box-like cell wall composed of silica, called the frustule.The outer of the two half-walls is the epitheca and the inner the hypotheca. In the picture you can find representatives of both genera Navicula Bory,Nitzschia Hassall,Cymbella C.Agardh.