FIELD WORK IN PLAXT PATHOLOGY. 105 



4. Su})[)lement;il woi'k on the etiology of diseases. 



In the colleeti<)u of material, essentially the same methods 

 must he eniployed as the mycologist uses, l)ut the pathologist 

 must go even farther, and collect what the mycologist Avould pass 

 as worthless. For exam})le, while the sporoplioreis alone of a 

 wood-destroying fungiis would suffice for the systematic mycolo- 

 gist, the pathologist must have in addition a sufficient amount 

 of the host to enable him to study the pathological anatomy and 

 to determine the extent of the injury. Or again, while the 

 superficial hark containing the fruit of a "canker"-producing 

 fungus might serve the purpose of the mycologist, the patho- 

 logical collector must delve deeper and determine the extent to 

 which the host is invaded by the disease-producing organism. 



If the host is of importance in mycological collecting, it is 

 doubly so in the collection of pathological material, for the path- 

 ologist is even more concerned with the host than he is with the 

 fungus causing the disease. At this point I may take the oppor- 

 tunity to emphasize the importance of a wide knowledge of the 

 species and varieties of cultivated plants, and of the wild forms 

 also ; not knoAvledge culled from books, but actual knowledge of 

 plants in their field garments. While it would be of little value 

 to the mycologist to know whether a given "cedar rust" specimen 

 was from a Wealthy or Ben Davis tree, or some other apple, such 

 facts as this and similar ones are of importance to the patholo- 

 gist, as it is from the accumulation of such data that resistance 

 and susceptibility of varieties become known. 



In pathological collecting, specimens of the host plant 

 should be taken to show as many stages in the progress of the 

 disease as possible, as the pathologist must learn to recognize or 

 diagnose diseases not alone from the fruiting stage of the causal 

 organism, but from specimens taken at various times during the 

 progress of the disease. 



One \)nvf of pathology has been seriously neglected in much 

 of our field work and in many of our text-books. T refer to 

 accurate observations and statements in regard to the symptoms 

 attending or accompanying a given disease. What a misnomer 



