Rust fungus. Coloured scanning electron micrograph (SEM) of the fungus Uromyces fabae, which causes rust disease, growing on the leaf of a mallow plant. This view shows the surface of the leaf (at lower frame). Bursting through the surface is a pustule of string- like hyphae, or branching filaments, of the fungus with rounded tips producing spores. Rust is named for the brown pustules it produces on the surface of infected leaves. These rust spots contain millions of spores ready to spread the infection. Magnification: x73cm at 5x7cm size. Magnification; x250 at 8x10 size."