June, 1913.] The Mosaic Disease of the Tomato. 
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positive results by inoculating with healthy as well as diseased 
tissue. The same results were obtained by Woods (1899, 1902). 
When an excess of virus is used, this disease on tobacco according 
to Beyerinck (1898), developes hypertrophies. Heintzel (1902) 
finds that the injection of small quantities of fluid from a diseased 
plant produced the mottled effect, while a large amount pro¬ 
duced hypertrophies. 
Disease Spread by Contact. —Some experimenters have trans¬ 
mitted this disease under field conditions by touching alternately 
diseased and healthy tobacco plants. Koning (1899) believes that 
mosaic disease is spread in the field by handling plants. Hunger 
(1903, 1904, 1905, p. 286), in his ‘touching experiments’ was 
successful in spreading this disease and “he believes that much 
of the disease as it appears is due to negligence on the part of the 
laborers in the field.” Selby (1904), as stated above, confirmed 
Hunger’s experiments, producing the disease in the same manner 
by touching. Hinson and Jenkins (1910) also believe that the 
disease may be spread in this manner. 
Spontaneous Occurrence. —Sturgis (1900) comments on the 
sporadic nature of this disease and states that it is not uncommon 
to find healthy and diseased plants growing in the same spot. 
Woods (1902, p. 18) says, “of the remaining twenty-five con¬ 
trols, four were affected with the disease without apparent cause. ” 
Iwanowski (1903), could not account for the appearance of disease 
in plants which had in no way been treated, ‘they simply ap¬ 
peared spontaneously.’ Hunger (1904), likewise could not ac¬ 
count for these sudden appearances where plants had not been 
touched; furthermore the disease did not always appear where 
diseased and healthy tobacco plants were alternately touched. 
Westerdijk (1910), speaks of it as reoccurring periodically after 
it has once appeared in a greenhouse where tomatoes have been 
grown, although a new strain of seed was used each season. 
Producing the Disease at Will. —Woods’ (1902) experiments 
show this disease may be produced at will, by pruning, mechani¬ 
cally injuring the plant in various ways or even by injecting 
distilled water! Hunger (1905), confirmed Woods’ pruning ex¬ 
periments with tomatoes of various sorts, including red and yel¬ 
low, rough and smooth fruiting varieties. He failed, however, to 
duplicate Woods’ results in tobacco. Allard (1912), says that a 
true infectious mosaic disease cannot be produced by pruning 
plants. 
Cross Inoculation. —It is not possible to transfer this disease 
from the tobacco to the tomato or vice versa, according to Wester¬ 
dijk (1910, p. 18-19). “It is not inconceivable that the virus 
of the tobacco ought to be transmissible to the tomato and in¬ 
versely, because the plants are closely related. This, however, 
s not the case. Numbers of tomato plants were inoculated 
