Growth of SIN on agar as seen at the light microscope. Starting from 3 cells (1) the filament grows by division of the cells at both edges (2,3,4,5). The ramification and angle, pointed by arrows in (2), remain at the same distance in the following stages confirming growth at the periphery. In (6) the curvature specific for the strain is apparent at both ends. New filaments start from rupture points, running along the first filament (7) and projecting outside. Insets show enlargements of the region pointed by arrows in panel 2. In (8), advanced stage of colony formation: the structure is enriched by many filaments, becoming as in Fig. 1 after 24 hours. Scale bar: 1–4 = 100μm; 5–8 = 500 μm.