"Rust, Smut, Mildew, & Mould: An Introduction to the Study of Microscopic Fungi" by M. C. Cooke is a scientific publication written in the late 19th century. This work serves as an introductory guide to the study of microscopic fungi, exploring the structure, function, and classification of various species, particularly those known for causing plant diseases. The book is directed towards both amateur mycologists and established botanists, aiming to fill a gap in literature on this lesser-known area of botany. The opening of the book establishes the need for a comprehensive resource on microscopic fungi, particularly in light of the significant developments in microscopy and fungal taxonomy. Cooke discusses the common obstacles faced by enthusiasts and researchers due to the lack of accessible guides and detailed descriptions of fungi. The introduction includes appealing examples of fungi affecting plants, such as "Æcidium tragopogonis", and outlines the importance of understanding the intricate relationships between these organisms and their plant hosts. By framing the study of microscopic fungi as a fascinating and unexplored domain, the author invites readers to embark on their own discoveries in this vital field of botany. (This is an automatically generated summary.)