THE MOSAIC DISEASE OF TOBACCO. 21 



wijks 1 claims to have effected a complete cure by treatment with 

 blue light. The young, mosaic portions of the treated plants were 

 covered, while at the same time the lower apparently healthy leaves 

 were subjected to blue light. He states that the blue light stimu- 

 lated the healthy leaves to produce an antivirus which destroys or 

 renders inert the virus of the disease. Lodewijks also stated that red 

 light decreased the disease and that suffused light checked it. If the 

 malady in question was true infectious mosaic disease, one is inclined 

 to believe that covering the young plants temporarily reduced the 

 color contrasts of the mottled areas. These changes may have led 

 Lodewijks to conclude that a partial or a complete cure had been 

 effected in his experiments. 



In the writer's experimental tests many thousands of affected 

 plants have been kept under observation throughout all phases of 

 the disease. In no instance has there been a case of actual recovery 

 from true mosaic disease. Independent of all external conditions, 

 the disease remains more or less in evidence so long as the plant 

 continues to grow. Likewise the writer has never known a plant 

 of Nicotiana tabacum to die prematurely as a direct result of the 

 disease. Conditions favorable or unfavorable to vigorous growth 

 affect mosaic and healthy tobacco plants in much the same manner. 

 In fact, the most pronounced mosaic symptoms develop only in 

 well-nourished, succulent, rapidly growing plants, which at maturity 

 also are capable of supporting a vigorous secondary (sucker) growth. 



In a seed-bed experiment mosaic plants which had become affected 

 when very small, even though growing in a poor soil, badly crowded, 

 and insufficiently watered, at the end of five months were still main- 

 taining themselves and elongating slowly in spite of the injurious 

 effects of the disease. Several of the more vigorous plants had out- 

 stripped their fellows by a few inches and were preparing to put 

 forth some blossoms. Other tiny plants were completely hidden 

 beneath the thickly crowded leaves of the more vigorous individuals. 

 The leaves of these stunted and overcrowded plants affected with 

 the disease, although distinctly blotched with dark-green areas, were 

 little, if at all, " blistered " or " savoyed." Under conditions form- 

 ing rapid and vigorous growth these dark-green areas usually pro- 

 duce pronounced surface swellings. 



No curative treatment has been found for the mosaic disease of 

 tobacco. Gile, 2 working with pineapple chlorosis in Porto Rico, 

 showed that this condition was completely overcome so long as 



1 Lodewijks, J. A., jr. Zur Mosaikkrankheit des Tabaks. Recueil des Travaux Neer- 

 landais, v. 7, p. 107-129. Abstract in Botanisches Centralblatt, Bd. 114, No. 20, p. 518, 

 1910. 



- Gile, P. L. Relation of calcareous soils to pineapple chlorosis. Porto Rico Agricul- 

 tural Experiment Station, Bulletin 11, p. 33, 2 pi., 1911. 



