June, 1913.] 
The Mosaic Disease of the Tomato. 
161 
of this theory are, Mayer (1886); Iwanowski (1892) (a) (1901, 
1903); Prillieux and Delacroix (1894); Marchal (1897); Koning 
(1899 a, 1900 b); Breda de Haan (1899); Behrens (1896). 
Mayer (1886), was perhaps one of the first to suggest bacteria 
as the cause, saying that the disease is of a bacterial nature. 
He says, however, that the organism had not been isolated and 
that nothing is known about its form. Breda de Haan (1899) 
as quoted by Hunger (1905, p. 262), claims it possible to obtain 
a bacterium from the plant tissues and grow it in culture. Pril¬ 
lieux and Delacroix (1894) state that a bacillus 0.7 mic. long 
was associated with grey or yellow spots occurring on tobacco 
leaves, which they took to be mosaic disease. Marchal (1897), 
speaks of finding colonies of bacteria which grew in chains and 
were yellow colored. He claimed that infection occurred in the 
seed-bed. According to Hunger (1905, pp. 259-60), however, 
Iwanowski was the first to find bacteria in connection with mosaic 
disease and certainly his work is the most complete and most 
convincing that has appeared in support of the bacterial theory. 
In (1899, p. 253) he reports, “From a poured plate in which one- 
half drop of mosaic diseased juice was applied, ten transfers 
from different colonies were made to test tubes, and from each 
of these, three plants were inoculated. From numbers 6 and 9, 
two plants showed symptoms of typical mosaic disease within 
2 or 3 weeks.” In a second preliminary paper (1901, p. 148), he 
says, “Therefore a specific bacterium is the cause of mosaic 
disease—-. ” He claims that its discovery is merely a question 
of proper microtechnique. His final paper (1903) discussed 
various bacteria obtained from mosaic disease and gives photo¬ 
graphs showing them as they occur in host cells. According to 
him the reason that Beyerinck was not successful in his attempts 
in isolating bacteria by applying juice to agar tubes, was because 
it was first filtered, which he says prevented growth. He states 
(p. 37), “One of the simplest reasons for not having been able 
to grow this organism from filtered juice is, that the mierob is 
incapable of growing in pure culture and only develops in con¬ 
nection with other bacteria in the soil and in the living plasma 
of the plant.” Such filtered juice, however, will produce the 
disease. This, he explains, by saying, that the mierob forms 
resting spores. Upon this assumption he believed the mierob 
could be grown only from the vegetative form. He used agar 
plates and succeeded in obtaining two colonies which produced 
mosaic disease when reinoculated. He does not mention how 
or where he made his inoculations and his controls do not appear 
to be adequate. The percentage of disease produced by his 
artificial inoculations was small as compared with ordinary juice 
inoculations; this, he explains as due to a reduction in virulence, 
as often is the case when bacteria are grown on artificial media. 
