Produced by Chris Curnow, Lisa Reigel, and the Online Distributed Proofreading Team at https://www.pgdp.net (This file was produced from images generously made available by The Internet Archive) Transcriber's Notes: Variations in spelling and hyphenation have been left as in the original. Words in italics in the original are surrounded by _underscores_. Words in bold in the original are surrounded by =equal signs=. Ellipses match the original. A few typographical errors have been corrected. A complete list as well as other notes follows the text. DISEASE IN PLANTS DISEASE IN PLANTS BY H. MARSHALL WARD, Sc.D., F.R.S. FELLOW OF SIDNEY SUSSEX COLLEGE, HONORARY FELLOW OF CHRIST'S COLLEGE AND PROFESSOR OF BOTANY IN THE UNIVERSITY OF CAMBRIDGE PRESIDENT OF THE BRITISH MYCOLOGICAL SOCIETY, AND FELLOW OF THE LINNEAN AND ROYAL HORTICULTURAL SOCIETIES; HONORARY FELLOW OF THE MANCHESTER LITERARY AND PHILOSOPHICAL SOCIETY AND OF THE BOTANICAL SOCIETY OF EDINBURGH London MACMILLAN AND CO., LIMITED NEW YORK: THE MACMILLAN COMPANY 1901 _All rights Reserved_ GLASGOW: PRINTED AT THE UNIVERSITY PRESS BY ROBERT MACLEHOSE AND CO. PREFACE. It has often been represented to me that the cultivators of plants, among whom are to be included planters and foresters, as well as agriculturists and gardeners of every kind, are more particularly concerned with, and interested in, the maladies themselves of the plants they grow, than in the life-history of the fungi, insects or other organisms to which they are due, or in the physiological processes which are involved; and although it is impossible to really understand any disease unless we also understand the processes by which it is brought about, there is room for sympathy with the point of view of the cultivator. He says, in effect, "I do not want to know all about the biology of the fungus of wheat-rust, or of the _phylloxera_, nor do I want to learn what experts can tell me about the action of bacteria in soil, or the process of starch-formation in the leaves: I have neither the time nor the means to master these details. What I want is guidance as to what is wrong with my tomatoes, apple trees, chrysanthemums, fir trees, turnips, etc., and what I am to do to set things right." Just so. With the latter part of this cry one must sympathize, much as a doctor does with the wail of the parent who calls him in to cure his sick child--we need not stop to classify or compare the motives of the parent and the cultivator, and perhaps I had done better to select a breeder of sheep with his flock and a veterinary doctor in the