Jan. 15, 191S Mosaic Disease of Tobacco 299 



The virus of the mosaic disease is highly infectious to all susceptible, 

 healthy plants. Such plants remain free from this disease so long as all 

 chances of accidental infection are excluded. All evidence at hand in- 

 dicates that something is present in the virus of the mosaic disease which 

 is extraneous to the protoplasmic organization of healthy plants. This 

 substance greatly increases in quantity when introduced into susceptible 

 plants and interferes with normal nutrition and growth. 



Although enzymic activities have been considered responsible for the 

 mosaic disease of tobacco, parasitism, in the writer's opinion, offers by fai 

 the simplest and most reasonable explanation of its origin. It may at 

 least be said that the theory of a parasitic origin for the disease more con- 

 sistently accounts for all the facts at hand than any enzymic conception 

 yet evolved. It seems not only needless but illogical to abandon a simple, 

 direct explanation for one which leads to complexity of thought and yet 

 fails to correlate all the facts at hand. 



