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Nicolaier (1884), Kitasato (1889) giving the proof of its causal connection. 

 One of the most striking developments was in connection with malaria, known 

 in various forms since ancient times. Laveran (1880) had come to the conclu- 

 sion that its spread was associated in some manner with mosquitoes and Ross 

 (1898) demonstrated conclusively that a species of Anopheles was the carrier 

 and, further, that the causal organism underwent cyclic changes in both mos- 

 quitoes and man. Soon after, the method of distribution of yellow fever was 

 discovered. Finlay (1881) believed that mosquitoes might be the carrier and 

 Reed and his associates (1900) demonstrated that the mosquito Aedes calopus 

 was the responsible agent. The application of these discoveries led to the eli- 

 mination of yellow fever as a serious disease in most parts of the world. 



The story of plant pathology contains many chapters which are concerned 

 with disastrous diseases of economic plants. Frequently the outbreaks are due 

 to the introduction of susceptible hosts to new regions where an indigenous 

 parasite attacks them. In some cases a pathogen is carried to other parts of the 

 world, where it finds susceptible hosts. 



The potato blight, which appeared in England and Ireland in 1845, focused 

 attention on this particular disease and led to great advances in plant pathology, 

 although the immediate results were disastrous for the people who depended 

 on potatoes for their food. Frequently since then potato blight has occurred in 

 destructive forms, and continues to be under constant investigation for methods 

 of control. The coffee disease, caused by Hemileia vastatrix, appeared in Cey- 

 lon about 1869 and during the following years proved to be very destructive. 

 The final result was that the growing of coffee was given up in Ceylon, being 

 replaced by tea plantations, and coffee culture developed in Brazil. 



The American chestnut blight was first observed in Greater New York in 

 1904 and the evidence is that the causal organism, Endothia parasitica, came 

 from the Orient on nursery stock. Since the first appearance of the disease our 

 native chestnut tree has been practically wiped out. The white pine blister rust 

 caused by Cronartium ribicola was first noted in America in 1906 on three 

 year old white pine seedlings imported from Germany. Previous to that, the 

 disease had spread widely through Europe on the American white pine, which 

 had been introduced. Shortly after the pathogen appeared in America it spread 

 far and wide on the five-needle pines and necessitated radical methods of con- 

 trol, which involved the attempted eradication of wild and cultivated species of 

 Rihes adjacent to the white pine forests. , 



The rust of wheat caused by Puccinia graminis doubtless accompanied the 

 introduction of wheat into new regions and, wherever wheat is grown, dam- 

 age has been done. In the United States, 1904, 1916 and 1935 are especially 

 noted for the destructive outbreaks. 



Since 1867 progress in plant pathology has proceeded along several lines. 



