THE MOSAIC DISEASE OF TOBACCO. 15 



In affected plante of the species Nicotiana paniculata the corolla 

 tube of the small greenish flowers frequently becomes bent or 

 crumpled in the middle. 



VARIETIES AND VARIETAL CROSSES OF NICOTIANA TABACUM. 



In connection with various inoculation experiments with the mosaic 

 disease, practically all the distinct varieties of Nicotiana tabacum 

 and crosses among them have been used. None of them has shown 

 immunity to the disease. The rapidity of development of the disease, 

 the intensity of the mosaic markings of the leaves of affected plants, 

 etc., are more or less dependent upon the variety, its vigor, the size 

 and abundance of the leaves, and their shade of green. The most 

 malignant symptoms of the disease are frequently associated with 

 the more distinctive White Burley variety. In affected plants of this 

 variety badly depauperate and bleached corollas and an intensely 

 chlorotic appearance of all the leaves are of common occurrence. 



THE MOSAIC OF TOBACCO PROBABLY DISTINCT FROM POKEWEED 



MOSAIC. 



It is a fact of considerable interest to note that pokeweed (Phyto- 

 lacca decandra) is attacked by a mosaic disease which produces symp- 

 toms in every way similar to those produced by the mosiac disease in 

 tobacco plants. Although the mosaic disease of pokeweed is highly 

 infectious to healthy pokeweed plants, all experiments to date con- 

 firm the statement that the virus of mosaic pokeweed plants does not 

 produce mosaic symptoms in tobacco plants. Likewise the virus 

 of mosaic tobacco plants has never produced the disease in healthy 

 pokeweed plants. 



Healthy pokeweed plants have been repeatedly cut back and in- 

 oculated for long periods with the virus of mosaic tobacco plants. 

 The same procedure was followed with other pokeweed plants, using 

 the virus of mosaic pokeweed. In the first experiment mosaic 

 symptoms never appeared. The virus of mosaic pokeweed plants, 

 however, produced typical pokeweed mosaic, usually within 15 to 

 20 days following inoculation. 



The following experiments show the results of inoculating different 

 lots of tobacco plants in pots on the same date, some with the virus 

 of mosaic pokeweed plants, others with the mosaic virus from tobacco : 

 On June 13, 15 healthy tobacco plants 6 to 8 inches high were inocu- 

 lated with tobacco mosaic virus. The first symptoms appeared in 

 practically every plant June 22-23, 9 to 10 days later. On June 13, 

 28 similar tobacco plants were inoculated with pokeweed mosaic 

 virus. Symptoms of disease had not appeared in these plants which 

 were left undisturbed until July 11. On that date, 14 of these plants 



