INTRODUCTION 



BOTH plants and animals are subject to diseases which 

 reduce their vitality, check development, or cause 

 abnormal growths, and frequently result in the death 

 of the affected individuals. When these diseases attack 

 the cultivated plants on which mankind depends for 

 food, clothing, building materials, fuel, etc., they always 

 cause loss. Such losses may be comparatively in- 

 significant or they may be sufficiently great to cause 

 financial disturbances and suffering in the community 

 or nation. In many cases these losses have been so 

 I reat as to cause local famine, and sometimes they have 

 i en .so great as to increase the cost of the agricultural 

 p oducts throughout the world. As a result of certain 

 '-'nown diseases, the export trade in many agri- 

 al oroducts has been greatly reduced or completely 

 .oy 1 in parts of the world. 



Tht Diseases of plants are so common that it is 

 : C8 y impossible to find a field, orchard, or garden 

 ,d there are not more or less diseased plants, 

 disease is not prevalent it does not attract the 

 i n of the casual observer, but when it becomes 



e ic it becomes an economic factor in the lives of 



t ywer, the tradesman, the carrier, the consumer, 



equently the manufacturer. If the loss is very 

 It becomes of national and sometimes of inter- 

 tic, il importance, and frequently involves extensive 

 tudies y experts to determine the cause and devise 

 methods of control or eradication. 



It is well known that many plant diseases, although 

 recognised by the grower, receive very little attention 



B 



