A classic work and the first to comprehensively study this interesting life form, which has an important role in decomposing plant material. Myxomycetes (slime moulds) were once considered a special group of fungi. However they are now grouped within Amoebozoa as unicellular protists that adopt a multicellular aggregate form in certain conditions. Introductory chapters cover life-history, structure, ecology, distribution, how to find and collect material, bark culture techniques, microscopic examination, and herbarium storage of 'slime-moulds'. The detailed accounts cover identification, keys, descriptions and illustrations. They also include notes on differences from other similar species. This is a reprint of the enlarged 2020 edition with a 20-page supplement including new species, together with 54 colour photos. It is a guide to the British and Irish species, including keys, descriptions, and illustrations showing the diagnostic features along with introductory chapters on life history, structure, ecology and distribution, collecting, techniques, and preservation.