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 investiga- 

 tion of the morphological and biological peculiarities of many 

 types of the organisms that cause or are associated with cases 

 of disease in plants, by a writer who is not only capable of 



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