THE MOSAIC DISEASE OF TOBACCO. 13 



the mosaic disease can be produced in healthy scions by inoculating 

 the virus into the tissues of N. glauca. Plate V, figure 1, shows a 

 scion of N. glauca growing upon a badly diseased stock of N. rustica. 

 As to the virulent nature of the sap of the Nicotiana glauca stock 

 bearing the mosaic scion of N. tabacum, the following experiments 

 afford conclusive evidence. On February 28 three groups of 25 to 30 

 small plants of the species N. silvestris were inoculated as follows: 

 One group, as a control, was inoculated with the sap of a healthy 

 N. glauca plant. A second group was inoculated with the sap of a 

 stock of N. glauca upon which a mosaic scion of N. tabacum was 

 growing. A third group was inoculated with the juice of the mosaic 

 scion itself. On March 11 the control series was perfectly healthy, 

 but a considerable number of mosaic plants had appeared in the other 

 two groups. On March 21 all the plants in the control lot were 

 healthy, while in the remaining two groups practically every plant 

 had become infected with the mosaic disease. Throughout the ex- 

 periment these plants were carefully screened in a cage so as to ex- 

 clude all insects. 



The above experiment was repeated as follows: Thirteen young 

 Sumatra plants were inoculated with sap from the same stock of Nico- 

 tiana glauca, and 10 other plants were inoculated with the sap of a 

 healthy plant of N. glauca to serve as controls. On April 1, 10 plants 

 of the 13 had developed the disease. Every plant of the control series 

 remained healthy. These experiments were repeated several times 

 at later dates and further confirmed the results of earlier experiments 

 that the sap of the N. glauca scion carried the mosaic virus. 



Hybrids of several distinct species of Nicotiana also have been ob- 

 tained and grown in order to determine their immunity to the mosaic 

 disease during the first generation. It was not possible to carry 

 the work beyond plants of the first generation, since in every instance 

 the plants were absolutely sterile. With a single exception these 

 hybrids have not shown the least degree of immunity. In truth, 

 owing to their exceptionally rapid and vigorous growth, some of 

 these hybrids have proved to be especially good material for the study 

 of the disease in all its phases. The following species hybrids have 

 been made and tested : 



Nicotiana tabacum 2 X N. silvestris $, 



N. longiflora 2 X N. alata $. 



N. tabacum 2 X N. glauca $ . 



JV. tabacum 2 X N. viscosum $ . 



Owing to its extremely rapid and uniform growth, its numerous 

 leaves, and the readiness with which it succumbs to the mosaic disease, 

 the writer has used the hybrid Nicotiana tabacum 2 X N. silvestris $ 

 very extensively in the experimental study of the disease. The hybrid 

 N. tabacum 2 X N. glauca $ also readily succumbs to the disease, 



