Pl.ACHD ON A NaTION-WIDF. BaSIS 187 



today points to a virus origin of botli diseases, and that insect 

 vectors transmit eacli disease is now known. The early workers, 

 however, were confident, and rightly, tiiat each disease is caused by 

 a parasitic agency. Root-rot and rust of cotton, as well as a number 

 of diseases of grapes, pear, peach, and apples, had been shown to 

 be due to parasites. That remedies for each and every one had not 

 been discovered was disheartening only to the impatient. Experi- 

 ence showed many times that once the cause was known, the 

 remedy was soon found."' At least, a control measure was soon 

 devised. The important first conquest was to establish the cause 

 of each disease. / 



Smith, by his peach yellows researches, was showing that the 

 disease wms not due to winter injuries. His field experiments were 

 proving that the malady was not due to soil exhaustion, and that 

 the disease was not transmitted through the soil. Budding and 

 grafting experiments were establishing that the disease is trans- 

 missable. Tabular data collected between 1887-1890 indicated the 

 disease occurred more frequently in dry than in wet summers." 

 Some truth seemed to lie in each element and in the older belief 

 that overbearing of the tree was connected. But the disease 

 attacked young and older, unfruitful as well as fruitful, trees. 

 Smith was seeking the real, as distinguished from interrelated, 

 causes. In Kent County, Maryland, and Kent County, Delaware, 

 he saw the disease 



destroy many large orchards in seven to ten years from planting, whereas 

 50 miles away (Caroline County, Maryland) there were peach orchards 

 40 years old still entirely free from the disease but which subsequently 

 became infected. [He] also got, when set into badly diseased orchards, 

 what [he] considered to be a few undoubted cases in peaches worked on 

 plum roots. The tops came from trees that were outside of the diseased 

 area and that remained healthy. ^^ 



He had carried his peach stones to his doctoral examination at 

 the University of Michigan. One of the points proved was that 

 the disease was not carried on seed from diseased trees. Root 

 aphides had been a suspected cause of transmission. His notes 

 of January 7, 1890, show that on this day he received a specimen 



21 



First report etc., op. cit.. 22. 

 ^^ Journal of Mycology 6(3): HO, January 3, 1891. 



" " Synopsis of Researches," prepared by Smith, and published in the Nat'l Acad, 

 of Sci. biog. memoir of Smith prepared by Jones and Rand, op. cit., 18-19. 



