MOSAIC DISEASE OF TOBACCO. 117 



Summary. 



1. The mosaic disease is not caused by fungi or bacteria. It has never 

 been possible to demonstrate the presence of these organisms in the tis- 

 sue of any part of the plant. 



2. The disease is highly infectious, particularly when inoculated into 

 young plants, all subsequent growth exhibiting marked symptoms. 



3. The disease is not contagious. 



4. Until more is known about the action of the so-called "ultramicro- 

 scopic" organisms, the disease cannot be ascribed to an organism of that 

 class, as the character and reactions of the causal agent do not in many 

 respects coincide with reactions of that class of organisms. 



5. Many of the reactions of the causal agent are of such a nature as to 

 indicate that it is either an enzyme, an aggregate of enzymes, or the prod- 

 uct of enzyme activities. 



6. The enzyme activities of diseased plants are greatly altered, far more 

 than is usually the case in plants which are attacked by pathogenic fungi 

 or bacteria. 



7. As a result of the writer's experiments, it is believed that the disease 

 is primarily induced by a disturbance in the enzjone activities and their 

 relation to each other, due to abnormal metabolism, and not by any 

 parasite. 



8. The pathogenicity of a disease is not necessarily a proof that it is of 

 parasitic origin, as it is conceivable that similar conditions may exist 

 relative to enzjnue activities, although the extent of such action is not 

 known at present. 



9. On fields where the mosaic disease is prevalent, the primary infec- 

 tion can usually be traced to the seed bed, and many healthy seedlings 

 are infected by the workmen when setting the plants. It is estimated 

 that about 80 per cent, of the infection occurs in this manner. 



10. Owing to the nature of the disease the matter of absolute preven- 

 tion and control is difficult, but with careful attention to details of ster- 

 ilization of the seed bed, and handling of the plants at time of trans- 

 planting, a large percentage of infection may be avoided. 



