INTRODUCTION So widely spread and, it may be added, often so intelligent is the interest now taken in the incidence and the dissemina- tion of the diseases which affect cultivated plants, and at the same time so important is a proper conception of the causa- tions and the treatment of these diseases, that a work which deals with them cannot fail to be welcomed. Much has been and much is daily being done to advance our knowledge of plant-diseases and to increase our ability to cope with the practical difficulties that their presence creates. But the literature of the subject is so widely scattered, and the results of individual investigations so often tend, when settling some immediate difficulty, to create new difficulties, to open up new lines of research, and to indicate new principles of treat- ment, that in the absence of a compact, general review of the actual state of affairs, the practical man is apt to feel at a loss as to how matters really stand, and at times is disposed to doubt the soundness of the advice he is urged to follow. The conditions necessary for the preparation of such a work as is called for are in the first place an intimate knowledge of the labours of a host of investigators widely scattered throughout the world, with at the same time ready access to the literature in which these results are embodied. But, in addition to this, the work must be something very much more than a mere compilation of the statements of others it must be the outcome of long-continued, personal investigation of the morphological and biological peculiarities of many that cause or are associated with cases types of the organisms of disease in plants, by a writer who is not only capable ofrepresenting accurately the views of others, but is competent to give reasons for the faith which he himself professes. Mr. Massee has already shown, and nowhere more notably than in A Text-book of Plant Diseases, published by him in 1899, second edition 1903, how fully he is endowed with the qualifications required in the author of a work like the pre- sent. Various passages in that Text-book, useful and trust- worthy as it has proved as a guide to the results obtained up to the date of its publication, already, however, serve rather as records of what was then believed than of what is now actually known. A further issue of what has so soon become, in some respects, a historical landmark rather than a conspectus of existing information, being undesirable, Mr. Massee has found it preferable to prepare a new work on somewhat different lines and covering a rather wider field. This work, it is hoped, may take the place of the Text-book, the issue of which has become exhausted, and should prove as helpful to those who stand in so much need of assistance as its predecessor has done. ROYAL BOTANIC GARDENS, KEW, zthJanuary 1910. D. PRAIN. PREFACE DISEASES of plants are numerous and undoubtedly do much injury. This, however, is not so much due to a lack of known, reliable, preventive or curative methods, as to a lack of application on the part of those who should be most interested in the matter. If the various well proved remedial measures now known, which are neither exorbitantly expensive nor diffi- cult of application, were honestly carried out, the loss from fungus and animal pests would be very materially reduced. The most important of remediable and preventive measures combined iscleanliness…