June, 1913.] Tfie Mosaic Disease of the Tomato. 157 



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 (1S9S), 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, 190-1, 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, confinned 

 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; furthennore 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- 

 chjk (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 



