Dec. ii, 1916 Specific Mosaic Disease in Nicotiana viscosum 
483 
methods of inoculation which have been attempted with these plants 
have been without success. It has been shown that the virus was not 
present in these plants by extracting the sap of all parts of the plants 
and testing its infectivity by making inoculations into young tobacco 
plants. These inoculations have never produced infection. Further¬ 
more, many successful grafts have been made between N. tabacum and 
N. viscosum , using N. tabacum as the stock. As soon as the N. viscosum 
scion had started to grow, the stock (N. tabacum) was inoculated with 
the ordinary form of the mosaic disease. Scions of N. viscosum in many 
instances remained upon the mosaic stocks for many weeks and finally 
blossomed, yet symptoms of the mosaic disease never appeared in the 
blossoms or leaves. In all instances inoculation tests have been made 
to determine if the infective principle of the disease was present in the sap 
of the immune scions. As shown in Table I, these scions in many in¬ 
stances appeared to be entirely free from infection. In other instances 
the sap proved to be more or less infectious to tobacco plants. Why the 
sap of the scion should carry the infective principle at one time and not 
at another can not at present be explained. 
The mosaic disease affecting N. viscosum appears to be identical in 
all its symptoms with the mosaic disease of tobacco (N. tabacum ). The 
virus of the disease, however, has behaved very differently from the virus 
of the mosaic disease of tobacco in all inoculation tests. With the 
exception of Datura fastuosa (Golden Queen variety), and Datura stra¬ 
monium , no other plants of the solanaceous family have been found 
susceptible to the virus of the mosaic disease affecting N. viscosum . 
Although peppers and tomatoes are very susceptible to the virus of the 
mosaic disease of tobacco, these plants appear to be immune from the 
virus of the mosaic disease affecting N. viscosum , or at least highly 
resistant to it, since the most persistent and rigorous needle inoculations 
have failed to produce infection. The most rigorous methods of inocu¬ 
lation have also failed to produce either the mosaic disease of tobacco 
or the mosaic disease of N. viscosum in the Irish potato (Solanum 
tuberosum ). 
Datura stramonium is the only solanaceous plant which has given 
evidence of being susceptible to both mosaic diseases. Inoculations 
made at different times with different lots of virus producing the mosaic 
disease in N. tabacum have given very different results. In some tests 
the plants were highly resistant to infection. In other tests similar 
methods of inoculation gave a high percentage of mosaic-diseased plants. 
It has not been determined whether this variability indicates differences 
in the infective properties of the virus or differences in the relative 
resistance of different lots of plants. In one experiment 18 young 
vigorous plants of Datura stramonium were divided into two lots of 9 
plants each. One lot was inoculated at many points in the stems and 
leaves with the virus of the mosaic disease of N. viscosum . The remain- 
