Rust fungus spores. Coloured scanning electron micrograph (SEM) of the spores of an unidentified rust fungus (order Uredinales). Rust fungi are parasites which attack plants, causing disease. These spores may either be an infective stage, or may be a dormant, over-wintering stage. Their spiny surface may aid in dispersal. Rust fungi typically form rust-red patches on the leaves and stem of their host plant. They are amongst the most destructive of all plant pathogens, often infecting cereal crops and causing drastic reductions in yields. Such infections have led to famine in certain areas. Magnification: x645 at 6x7cm size.