COLLEGE WORK IN PATHOLOGY 



305 



SO closely associated as to be but one in practice, as the recog- 

 nition of the fungus causing the disease is immediately associated 

 with its probable mode of attack. This applies most closely to 

 those groups of disease producing fungi which cause leaf spots on 

 foliage and the common rots on fruits. At intervals diseases 

 are found which are apparently caused by fungi not previously 

 recognized as pathogenic, and in such cases diagnosis and etiology 

 — what the disease is, and how its begins — become distinct steps 

 in the examination. 



The possible treatments for plant diseases include four lines of 

 action. These are (1) killing the spores of the parasite as they 

 germinate on the plant subject to attack, by coating the plant 

 with a protective film of some fungicide. (Apple scab). (2) 

 By kilhng dormant spores while they are inactive on the parts of 

 plants that would become invaded under favorable conditions. 

 (Peach leaf curl) . (3) Killing the fungus itself as it grows over the 

 surface of its host. This is possible only with surface mildews, 

 etc. (4) Removal of wild or cultivated plants upon which the 

 fungus depends for a part of its life cycle. This covers such 

 relations as between barberry and wheat, for wheat rust; cedar 

 trees and apple or pear, for apple rust; goldenrod and grasses, in 

 grass rusts. 



RELATIONS TO OTHER BOTANICAL SUBJECTS 



Plant pathology is contrasted with mycology and bacteriology, 

 which are respectively concerned, not with the disease induced, 

 but with the fungi or bacteria infesting the various host plants 

 which act as nutritive media for the parasites. It is hnked to 

 horticulture, since both are concerned with growing plants, 

 rather than with dead ones ; and to agronomy since many of the 

 diseases concern field crops. 



A knowledge of plant structures (plant morphology), in addition 

 to the general one of growing plants, is an essential detail in the 

 general work on plant diseases. It often happens that two closely 

 related plants are of distinctly different resistance to disease. 

 This difference may be due to various conditions, but is frequently 



