438 ALLARD: MOSAIC DISEASE OF TOBACCO 
covered with grayish spots in the tissue of which he found a motile 
bacillus which imparted a yellow color to culture media. He also 
reproduced this disease in healthy plants by experimental inocula- 
tion. Marchal found the disease prevalent in seed beds, especially 
those rich in organic matter. He recommended renewal of the 
seed beds and sterilization as practical methods of control. The 
malady described by Marchal appears not to have been the true 
mosaic disease at all. In all essential points the disease appears 
to be the same trouble that was previously mentioned by Prillieux 
and Delacroix (8). 
In 1898 Beijerinck (x0) published additional facts and observa- 
tions regarding the true mosaic disease. He found that diseased 
sap so filtered as to be entirely free from bacteria still retained its 
power to infect healthy plants, in this respect confirming Iwan- 
owski (7). He showed that a very minute quantity of this 
filtered juice produced the disease in immature, growing tissues. 
He held that dried mosaic material retained its infectious properties 
for some time, and, likewise, that it was not rendered innocuous 
by remaining in the soil throughout the winter. Like Mayer (2) 
and Iwanowski (7), he found that heating mosaic virus to the boiling 
point rendered it harmless. He proved that the virus traveled con- 
siderable distances in plants but produced obvious symptoms only 
in immature tissues. Beijerinck claimed that the soil around dis- 
eased roots may infect healthy roots and that plants in some in- 
stances apparently recovered from the disease temporarily. 
Previous to the work of Beijerinck all investigators of the disease 
were strongly inclined to establish a bacterial origin for it, although 
at that time no direct proof had been obtained. Beijerinck, on 
the other hand, obtaining only negative evidence with regard to 
bacteria, advanced his theories along somewhat different lines. 
He assumed that the virus must be an unorganized material, 
fluidlike in its nature, and capable of symbictic growth in the 
presence of living cells. Just what Beijerinck wished to convey 
by these vague and indefinite terms it is rather difficult to conclude, 
although it would appear as if he were foreshadowing the enzy- 
matic theory of mosaic diseases, a theory which later was developed 
more fully. 
Shortly after Beijerinck (10) published his results, Sturgis (16) 
