June, 1913.] The Mosaic Disease of the Tamato. 163 



leaves and shoots to become infected. In regard to the first 

 argument of the virus theory, we see it is not quite in accord with 

 our present knowledge of colloidal diffusion; he eliminates a 

 possibility. The second statement is an assumption, rather than 

 a known fact, for the behavior of the injected juice is problematical. 



Regarding the amounts of juice required for inoculation he 

 says, (1S98, p. 5), "a small drop injected into the plant at the 

 right place will cause numerous leaves and shoots to become in- 

 fected. If these diseased areas are then crushed and the juice 

 injected into healthy plants they may become diseased." From 

 the fact that pouring juice upon the soil causes the disease to ap- 

 pear first upon the youngest leaves, he concludes that the virus 

 has a definite course in the plant. He applied juice and pieces 

 of diseased tissue to agar plates and allowed the virus to diffuse. 

 He carefully separated the upper and lower strata of such agar 

 and used it for inoculation purposes and produced the disease 

 in each case although the disease appeared more slowly when the 

 lower strata was used. It seems strange that this author did 

 not get a bacterial growth from such plates as Iwanowski did. 

 Lodewijks (1910) hypothesizes a virus in these diseased plants 

 which continually disturb merismatic regions. In normal regions 

 an antivirus is produced which helps to neutralize the virus, 

 like a toxin and an anti-toxin. The formation of this virus 

 and anti-virus is influenced by external conditions; when the 

 former is produced in excess, the plant becomes mosaiced and if 

 the anti-virus is more abundant immunity results. Westerdijk 

 (1910) speaks of a virus in tobacco and tomato, but does not 

 express her opinion as to their nature. She believes that the 

 viras of tobacco is distinct from that of the tomato. She says 

 (1910, p. 19), "There are, therefore, two different infectious 

 substances; they affect only their respective hosts." In her 

 histological studies she excludes organisms as a cause, saying, 

 (p. 8), "No organisms were found, neither in the yellow nor 

 blue-green areas." 



(3). The Physiological Theory. — Perhaps the inost varied, 

 but generally accepted theory is the Physiological one. Some 

 investigators explain this disease as an enzymic trouble, while 

 others simply say that it is of a physiological nature, without 

 mentioning any specific factor or group of factors which can be 

 definitely correlated with it. Sturgis (1899), in his first work 

 on tobacco mosaic states, that artificial injuries or abnormal 

 conditions, whereby the functions of the plant are disturbed, 

 are probable factors in producing this disease. Soil and atmos- 

 pheric conditions are important agencies according to his views, 

 and he says that mosaic disease is more prevalent in heavy soils. 

 Hunger (1902), believes this disease to be physiological, occurring 

 when the plants are in a weakened condition, predisposed plants 



