Plant diseases, such as rusts, smuts and mildews, are microscopic fungi responsible for attacking dead organic materials. Unicellular eukaryotes (protozoa and unicellular algae) were considered as a single kingdom, the Protista. The multicellular eukaryotes, were subdivided on the basis of nutrition into three kingdoms, photosynthetic plants (Plantae), absorptive fungi (Fungi), and ingestive animals (Animalia).