Merged differential interference contrast and epifluorescence microscope image of two cells of the centric diatom Thalassiosira pseudonana. Red, chlorophyll autofluorescence; blue, DAPI staining showing the nucleus; green, overexpressed green fluorescent protein (GFP) derived from transforming the cell with a GFP gene. The cell is shaped like a long can. The circular cell is a valve (end-on) view; the diameter is about 5 μm. The adjacent cell is lying on its side.