440 ALLARD: MOSAIC DISEASE OF TOBACCO 
He did not, however, attempt to determine the exact nature of this 
response in affected plants. 
In the Verslag omtrent den staat van ’Slands Plantentuin te 
Buitenzorg over het jaar 1899 (19, pp. 73-78) the supposed bacterial 
nature of mosaic is discussed. Cultures of various organisms 
supposed to be responsible for mosaic were isolated from the 
tissues of such plants. These were inoculated into healthy plants, 
but with somewhat uncertain results. In many cases it was stated 
that only a slight indication of the disease followed, which, with 
the further development of the plants, often disappeared entirely. 
This was explained on the grounds that obscure conditions of one 
sort or another had weakened the virulence of the cultures. 
It was shown that the so-called ‘‘ wit kop”’ was simply a manifes- 
tation of mosaic. It was stated that sprinkling the virus upon 
healthy plants produced disease, as did placing finely cut mosaic 
material beneath the roots at transplanting. Sprinkling mosaic 
sap upon the soil ten days before transplanting, and working it 
into the soil did not produce mosaic. 
Mosaic material was dried in the sun ten days and worked 
lightly into the soil. Other plots were similarly treated with 
mosaic material dried in the shade. It was stated that some 
mosaic followed each operation. In such tests, however, it may 
be said that there is no very certain means of determining to what 
extent this treatment of the soil was actually responsible for the 
disease until controls are taken into consideration. It is a well- 
known fact that mosaic may be prevalent in a field quite inde- 
pendently of any test. 
Raciborski (19) in 1898-99 reported the results of his work 
with mosaic. He examined microtome sections of the leaves and 
stems of mosaic plants for bacteria, but found no evidence of 
organisms either in the cells or intercellular spaces. He deter- 
mined the effects of different temperatures, exposure to the sun, 
etc., upon the virulence of the sap of mosaic plants. Some of his 
conclusions were as follows: 
Mosaic sap did not lose its virulence when heated 5 minutes 
at 62°C. When heated one minute at too® C, the sap still pro- 
duced mosaic after 10-14 days. The virulence was lost entirely, 
however, when the sap was heated 15 minutes at 100° C.- 
