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Synopsis This book is designed particularly for the use of students and instructors whose practical interest in the subject is a desire to know how to recognize, understand, and prevent plant diseases, and to whom the elementary course in plant pathology is a necessary part of the background for useful work in agriculture. Some knowledge of the principles underlying the science of plant pathology is indispensable for an understanding of the behaviour of plant pathogens and the results of their activities, and to enable the student to adapt his basic training to new plant disease situations with which he many be faced. The principles of the science are brought out in fairly detailed accounts of one or more disease of each type. The treatment of numerous diseases of the same type is more limited, with discussion unusual features, recognition, and control. In the closing chapters, the principles of plant pathology encountered one by one in the study of the various disease types are organized in form to serve as a unifield treatment and review of the leading features of the science and as a compact source of information on disease control procedures. These factors have made it seen desirable to limit to a minimum the treatment of such academic aspects of plant pathology as history, mycology, and parasitism per se. Understanding and appreciation of these aspects of the science are essential for the professional plant pathologist, but in a terminal course primarily for agricultural students the practical aspects of the science must receive first consideration. The arrangement of diseases within chapters is a compromise in which the systematic relationship of pathogens are given first consideration, but with such modification as is necessary to avoid too abrupt and illogical transitions between disease types. All diseases caused by species of Fusarium, for example, could hardly by treated together without violation of pathologic unity. The chapter on virus diseases Has been completely rearranged in groupings of the mosaic, yellows, phloem necrosis, and scaly bark types followed by the potato and stone fruit virus complexes. Plant diseases like, Apple bitter rot, sugar cane red rot, cabbage yellows, black root rot to tobacco, early blight of potato and tomato, tomato leaf mold and leaf spot, potato ring rot and scab, aster yellows. Sugar beet curly top, phloem necrosis of elm, citrus psorosis, golden nematode of potato, and witchweed have been given in detail. Seed treatment and spraying and dusting of fruits and vegetables is also given. Attention is given to the latest development in control practices, including the slurry, pelleting, and vapor-heat methods of seed treatment, the new nonmetallic organic fungicides, and innovations in methods of spraying and dusting.