MOSAIC DISEASE OF TOBACCO. 77 



executed experiments,^ proved that the disease was not contagious but 

 was highly infectious. He believed that it could be carried from diseased 

 to healthy leaves simply by touching, especially in the case of the young 

 leaves, a fact that makes it necessary for the workman to use great care 

 when looking for the tobacco bud worms, etc., in the buds. He was of 

 the opinion that a rupture of the leaf was not necessary to induce the 

 mosaic disease in plants. 



Selby 2 a year later showed this to be apparently true for tobacco grown 

 in Ohio, and Hunger's statements were in his opinion in all respects con- 

 firmed. He also reported that "Blossoms of various plants were inocu- 

 lated through the nectar by transmission of nectar from diseased plants, 

 as by insect visitation. A slender brush of horse hair was used for this 

 purpose. No evidences of the disease were observed as a result of this 

 method." 



CUnton' was able to produce the trouble on tomatoes by inoculating 

 with juice from a diseased tobacco plant and from the tomato so infected 

 was able to reproduce the disease on the tobacco again by inoculation 

 from the tomato, again showing the infectious nature of the disease, and 

 that the troubles on the tomato and tobacco were practically identical. 

 This has been repeatedly verified by the writer and many other investi- 

 gators. 



Jensen,* in his work on the disease, came to the conclusion that the 

 right way to get at the methods of control of the disease was by experi- 

 mentation to obtain a resistant strain of tobacco, no matter what the 

 cause of the disease might be, and he carried on some experiments along 

 these lines. As yet no definite results have been reported by the in- 

 vestigators, but the time has probably been too short to obtain results. 



Lodewijks^ stated that by subjecting diseased plants to different col- 

 ored lights he was able to bring about a cure in some cases. He states: — 



The mosaic disease cannot be diminished or prevented by lessened light intensity. 

 Neither diffused nor colored light has any effect on the disease if the healthy leaves 

 are not able to function in normal daylight. Under the latter condition, however, 

 diffused light exerts a retardation, red light diminishes the trouble, and blue light 

 effects a cure. All the results may then be explained by the hypothesis that the 

 virus formation diminishes with the intensity of the light, while in the healthy 

 leaves, through the action of the virus, an anti-virus is formed, the action of which 

 destroys the virus (immunity and antitoxin formation in the case of animals). . . . 



Normally in the metabolism of the tobacco plant a substance is formed, the 

 action of which is opposed to that of the equally normally occurring virus of mosaic 

 disease, perhaps because it binds itself chemically to the latter. 



• Hunger, F. W. T.: Die Verbreitung der Mosaikkrankheit infolge der Behandlung des Tabaks. 

 Centralbl. f. Bakt. Par., etc., II: 11: 405-408 (1908). 



2 Selby. A. D.: Tobacco Disease. Ohio Agr. Exp. Sta. Bui. No. 15, 88-95 (1904). 



• Clinton, G. P.: Notes on Fungous Diseases, etc. Conn. Agr. Exp. Sta. Rept., 1907-08, 857- 

 858. 



• Jensen, H.: Uber die Bekampfung der Mosaikkrankheit der Tabakpflanze. Centralbl. f. 

 Bakt. Par., etc., II: 15: 440^45 (1906). 



5 Lodewijka, T. A., Jr.: Zur Mosaikkrankheit des Tabaks. Rec. Trav. bot. Neerlandais, 

 VII. (1910). 



