Ri;si:ARCH ON Plant Tumors 511 



By this time it had been shown tliat the causal agents of virus 

 plant diseases " pass filters having pores so minute that they held 

 back the smallest bacteria,"' "- and virus diseases of plants were 

 being dillerentiated from those believed due to bacteria. By 1936 

 more than three thousand papers, exclusive of short reports and 

 casual references, would be published on these subjects, and about 

 two-thirds of them would "' deal with the virus diseases of the 

 following six plants: potato, sugar cane, tobacco, tomato, sugar 

 beet and cucumber." '' By 1926 Smith would say ^'^ of the work 

 on these maladies: 



Known first from tobacco, they have been discovered in the potato and 

 in a great variety of cultivated plants where they had hitherto been over- 

 looked oi- had attracted but little attention, probably because they were 

 not then so prevalent. They are now recognized as amoni:; our worst plant 

 diseases and the obscurity of their origin renders them doubly interesting. 

 . . . Up to this time the cause or causes remain in doubt, but much has 

 been learned respecting signs of these diseases, host plants, and methods 

 of transmission. 



In Connecticut the further work on tobacco mosaic by G. P. 

 Clinton " and at the Bureau of Plant Industry by H. A. Allard 

 of the olBce of tobacco and plant nutrition investigations had 

 added much to the knowledge of this disorder, -° the virus of 

 which in more recent years has been isolated at least in the form 

 of crystal protein by W. M. Stanley and his co-workers at the 

 Rockefeller Institute.*' More recently, too, the very important 

 work of Allard (and W. W. Garner) on the phenomena of 

 "' photoperiodism " has tended to overshadow the former's defi- 

 nitely valuable work on mosaic disease of tobacco. Smith, how- 

 ever, believed that the word of Allard, Schultz, and others on virus 

 plant diseases had made the Bureau of Plant Industry one of the 

 five principal research centers for their study in America. The 

 other four were the work of Doolittle, Johnson, and others at the 

 University of Wisconsin, the work of Eubanks Carsner in the far 



*' L. O. Kunkel, Virus diseases of plants: twenty-five years of progress 1910- 

 1935, Brooklyn Botanic Garden Memoirs 4: 51-55, May 7, 1936. 



^^dern, 51. 



** Fifty years of pathology, op. cil., 35-36. 



^^Conn. Agric. Exp't Sta. Kept. 6: 4l6 flF., 1914; Charles Thorn and E. M. East, 

 George Perkins Clinton, Nat'l Acad, of Sci. Biog. Memo. 20: 183-196, 1939- 



*® See the Journal of Agricultural Research and Phytopathology (1915-1917). 



*^ G. Seiffert, Virus diseases in man, animal and plant, op. cit., 34 flF. 



