Book excerpt: Principles of Plant Infection investigates interactions among pathogens, host plants, the environment, time and space, and their role in plant infection. It describes the principles of infection, particularly of the root, stem, or leaf, as they apply to fungi, bacteria, or viruses. It also highlights the dual nature of resistance and suggests theories of host resistance. Organized into seven chapters, this volume begins with an overview of the relation between the amount of inoculum and the amount of disease it causes. It then turns to a discussion of the disease/inoculum relations of tobacco mosaic virus; how obligate synergism restricts the transmission of pathogens; disease/inoculum relations in root disease; the independent action of spores as inoculum; variable factors other than the amount of inoculum that affect plant disease; and time as a determining factor of the degree of plant infection. The reader is also introduced to endemic disease of plants, the implications of endemicity for plant resistance to disease, the spread of disease via migration of pathogens, and the genetics of host-pathogen interactions. Plant pathologists and plant breeders will gain valuable information from this book.