Rust fungus on a rose leaf. Coloured scanning electron micrograph (SEM) of rust fungus (Phragmidium sp.) spores emerging from a rose (Rosa sp.) leaf (brown). Spores are the reproductive cells of a fungus. Two types of spore are seen, the over-wintering teleutospores (long, khaki) and the summer uredospores (bottom left, bright green). Rust fungi are parasitic on both wild and cultivated plants, often causing severe disease. Magnification: x440 when printed at 10 centimetres tall.