Light micrograph of a microbial mat on a roof. Various algae have united to form an interwoven mat. The base is formed by a thick layer with many Oscillatoria cyanobacteria filaments. Embedded in this are algae of the genus Actinotaenium, with the symmetrical cells typical of the algae genus. The Actinotaenium cells each have 2 chloroplasts with marginal lamellae and one pyrenoid each. Furthermore, 2 diatom cells are visible, recognisable by the brown colouring of the chloroplasts. Microscopic contrast method : Differential interference contrast. Magnification 600x at a print width of 10 cm.