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ALLARD: MOSAIC DISEASE OF TOBACCO 437 
pheric changes, unfavorable conditions of whatever sort affecting 
the roots, i. e., mechanical injury, nematodes, parasitic fungi, etc., 
were not in any way responsible for the origin of the disease, im- 
portant conclusions which several workers in the United States 
seem not to have known. He recognized the sporadic occurrence 
of the disease in the field, and finally concluded that its spread 
must be through the soil, both in the field and in the seed bed, 
He recognized the fact, however, that a transfer of the disease by 
means of the soil had never been proved. It is plainly indicated 
that Mayer held the soil in some way responsible for the origin of 
the disease, since he advised renewal of soil in hotbeds, crop 
rotation, removal of the stubs of mosaic plants, the use of chemica] 
rather than animal manures, etc. Although Mayer did not isolate 
any organisms responsible for the disease, he finally concluded 
that it was of bacterial origin. 
In 1892 Iwanowski (7) brought out additional important facts 
relative to the mosaic disease and confirmed many of the conclusions 
of Mayer. He, like Mayer, found that the sap of mosaic plants 
produced the disease in healthy plants and also that it lost its 
virulence when heated nearly to the boiling point. His results 
with filtered sap did not agree with the conclusions of Mayer, who 
stated that twice filtering through common filter paper rendered 
the diseased juice innocuous. On the contrary, Iwanowski found 
that the sap retained its virulence even after it had been filtered. 
In agreement with Mayer, Iwanowski also held the view that the 
disease was bacterial or parasitic in its nature. He did not, how- 
ever, isolate any organism specifically connected with the disease, 
although he claims to have seen such organisms in the tissues 
of affected plants. 
In 1894 two French investigators, Prillieux and Delacroix (8) 
described a tobacco trouble occurring in France, which they 
believed to be the true mosaic disease. Its presence was indicated 
on the leaves by the occurrence of spots in which they found a 
motile bacillus united in chains. It appears, however, that the 
disease described by these investigators was entirely distinct from 
the true mosaic of Mayer. 
In 1897 Marchal (9g) published a paper, ‘‘La mosaique du 
tabac.” He stated that the leaves of affected plants became 
