Sept. 17, 1917 Mosaic Disease of Tobacco 625 



than do varieties of N. tabacum. The symptoms are confined to a sparse 

 and indistinct mottling along the veins of some of the leaves. This 

 mottling in some instances is too faint to be detected readily, except in 

 transmitted light, and may be entirely wanting. This behavior of A^. 

 glauca is rather exceptional and has been the subject of considerable 

 investigation. In February, 191 4, a number of young, vigorous plants 

 of that species growing in the greenhouse were inoculated repeatedly 

 with the virus of the mosaic disease until most of them showed more or 

 less evidence of developing disease. Bight of these, which showed more 

 clearly defined symptoms, were finally tested by injecting the expressed 

 sap of each into a series of plants of A^. tabacum. The sap of all proved 

 exceptionally virulent, producing in most instances 100 per cent of infec- 

 tion in each lot of 10 plants. After the initial expression of the disease 

 the symptoms gradually became more attenuated, until they were barely 

 distinguishable. In July three of these plants were cut back severely 

 and were immediately transplanted to the field. Growth was resumed, 

 but no symptoms of the mosaic disease whatever could be detected. 

 However, inoculation tests have shown that the sap of these plants con- 

 tained the infective principle of the disease. In October these plants 

 were again taken from the field and transplanted in the greenhouse for 

 the winter. Although growth appeared normal and symptoms of the 

 mosaic disease could not be detected with certainty, experiments have 

 shown repeatedly that the infective principle of the disease was still 

 present in the expressed sap. This behavior of N. glauca is not entirely 

 without its analogy, since Baur,^ working with infectious chlorosis of the 

 Malvaceae, has found by grafting immune with susceptible sorts that 

 the virus of the disease may pass into immune sorts of abutilon without 

 producing any indications of disease. Baur is of the opinion, however, 

 that the virus does not continue to live and to multiply in the infected 

 immune plants after they have been severed from the diseased plants. 



Experiments have shown that when scions of the immune species, N. 

 glutinosa, have been grafted upon mosaic-diseased plants of N. tabacum 

 the infective principle of the disease may pass into A^^. glutinosa without 

 the subsequent development of symptoms of the mosaic disease. 



It has not been determined whether the infective principle continues 

 to live and to multiply in such A^. glutinosa plants after they have been 

 separated from the mosaic diseased plants of N. tabacum. 



In the case of N. glauca it is e\'ident that the infective principle, after 

 being inoculated into the tissues of the leaves, propagates itself readily 

 and becomes disseminated to all parts of the infected plant, producing 

 systemic infection. 



Although it has not yet been shown that a permanent systemic infec- 

 tion may occur in young growing plants of N. tabacum without the 



1 Baur, Erwin. tJBER die inPBKTIosb chlorosb der mai,VACKEN. In Sitzber. K. Preuss. Akad" 

 Wiss., 1906, Heft I, 11-29. 1906. 



