ALLARD: MOSAIC DISEASE OF TOBACCO 441 
When the virus was exposed to the sun in broad, shallow glass 
vessels for one day it was not rendered inert. An exposure for 4 
or § days, however, destroyed its infectious nature. He concludes 
from this that exposure of the uppermost layers of the soil in the 
seed bed to the sun, will afford a practical and efficient means by 
which the planter can rid his soil of mosaic infection. 
Mosaic sap lost its virulence when treated with potassium 
permanganate. Mosaic sap was treated with basic lead acetate 
and filtered, and the filtrate freed of lead with H.S. Air was 
forced into the solution to remove the H.S. The solution was then 
neutralized and sprinkled upon healthy plants. It appeared that 
the virulence was lost. 
Water was then added to the precipitate obtained by adding 
basic lead acetate to the original virus. The lead was removed 
with HS, and this likewise was then driven off as before. The 
filtrate obtained, after filtering, was neutralized, and sprinkled 
upon healthy plants. The virulence was also lost. 
A water extract was obtained from mosaic leaves dried in the 
shade. This solution was virulent when sprinkled upon plants. 
Shade-dried mosaic material was then extracted with cold 
alcohol of 98 per cent. This extract was evaporated at 70° C. 
Water was added to the solid material and sprinkled upon healthy 
plants. The virulence was lost. 
It appears that Raciborski tested the virulence of the mosaic 
sap following the different treatments by sprinkling it upon the 
leaves of healthy plants. As this method of inoculation is some- 
what uncertain, however, conclusions based upon such inoculations 
are open to question. 
In 1899 van Bijlert (20) mentions the occurrence of mosaic in the 
Vicinity of the experimental station at Tandajong, Morawa. In 
one instance a narrow path one meter wide was a sharply dividing 
line between a field of tobacco which became badly mosaic and 
the experimental field which remained free from the disease. 
From the fact that coolies did not work in the experimental 
field, van Bijlert is of the opinion that this largely accounts for the 
freedom of this field from mosaic, although surrounded on all 
sides by mosaic plants. Likewise, he considered that the path 
one meter wide served as an important means of checking the 
spread of the disease. 
