Light micrograph of a mixture of diatoms, a group of single-celled algae that form an important part of the plankton in fresh and salt waters. A feature of diatoms is there glass-like cell wall, or frustule. The frustule consists of two halves, the valves, which fit together like the two parts of a pill box. One half is slightly bigger & acts as the 'lid' of the box. On division, each valve produces a new half inside itself. The 'lid' generates a cell which is the same size as the original, but the bottom produces a smaller cell. After repeated divisions of the small cell, sexual auxospores are produced to restore the maximum cell size. Magnification: x25 at 35mm size.