166 PLANT PATHOLOGY 



Mycology is so intimately connected with vegetable pathology 

 that some have thought the terms synonymous. The parasitic fungus 

 is frequently spoken of as the disease. The fundamental concep- 

 tions are distinct, however, even if in practice the work is inter- 

 woven. The mycologist studies fungi for themselves; the patho- 

 logist for the diseases they produce in other words, from the 

 standpoint of the host plant. If we acknowledge indebtedness to 

 the early systematic mycologists, what must we say of the life- 

 history of the fungi? To the studies in the biology of the fungi, as 

 worked out by De Bary and his pupils, we trace the direct start- 

 ing-point of modern investigation work in pathology. By no means 

 are all plant diseases caused by parasitic fungi; yet the fungus 

 diseases are so numerous and important that with their knowledge 

 well under way, we are prepared to understand and distinguish 

 from them the injuries produced by insects and mites, poisons and 

 unfavorable environment, as well as the physiological and other 

 non-parasitic troubles. 



Plant physiology is another of the great aids to pathology. Phys- 

 iology not only enables us to understand the disturbances in growth 

 and nutrition of plants produced by parasitic fungi and other para- 

 sites, but it enables us more fully to understand the non-parasitic 

 diseases. Through the researches of Dr. A. F. Woods an entirely 

 new type of physiological disease is known to be produced by the 

 action of enzyms. The study of enzymic diseases is in its infancy, 

 but promises to enable us to unravel some of the most mysterious 

 plant troubles. In this type of disease we have the curious anomaly 

 of non-parasitic diseases which are contagious or at least commun- 

 icable. 



The closely allied subject of anatomical botany is also of great 

 importance to pathologists. Not only is the knowledge of normal 

 plant anatomy necessary in the study of abnormal structures, but 

 the methods which have been developed in the study of anatomy 

 are in every-day use by the pathologist in his researches. Especially 

 useful are the histological and microscopical methods. Processes of 

 imbedding, sectioning, and staining are absolutely necessary to the 

 study of pathology. 



Cytology is another very useful branch of botany to the patho- 

 logist. The finer studies in parasitism are possible only through a 

 knowledge of normal cytology and through the use of cytological 

 methods of research. Very little in fact has yet been done in cyto- 

 logical pathology, but this is surely one of the most promising lines 

 for the future. 



Plant ecology also lends aid to the pathologist. Disease in plant 

 life may be defined as a condition of the plant by which it is par- 

 tially or wholly incapable of responding to its environment. How- 



