50 EXPERDIEXT STATION. [Jan. 



present. It must be understood, however, that there is nothing 

 inherent in the seed itself which wuuhl cause the trouble; it is 

 simply a matter of getting strong, viable seed to produce vigor- 

 ous plants. 



Review. 



A more or less popular account has been given in the preced- 

 ing pages of the cause, appearance and general characteristics 

 of this interesting disease, and a later report v>'ill take up the 

 more technical part of the work, when most of the experiments 

 carried on will be described. At this time a brief review of the 

 l)receding pages will be given, in order to summarize the facts 

 presented. 



1. "Mosaic," "Brindle," "Calico" or "Mottle top" of 

 tobacco is a physiological disease purely and has no fungous or 

 bacterial origin. It is caused by the excessive activity of the 

 oxidase and peroxidase enzymes in the plant and the partial 

 loss of function of catalase, another enzyme, which carries off 

 some of the residual products of the others mentioned. It is 

 not due to one enzyme alone nor to any specialized virus. 



2. It is infectious but not contagions. Care should be exer- 

 cised not to touch the terminal bud of healthy plants with any- 

 thing which has come in contact with diseased plants. 



3. It does not occur in the seed beds when new soil is used 

 nor in properly sterilized seed beds. 



4. Improper sterilization of seed beds or old beds tends to 

 intensify the disease if present. 



5. The tcm])erature of the beds should not be allowed to run 

 too high for any length of time. It is better to run the bed 

 rather cool than too hot. 



G. Where a seed bed is infected it may be grown to grass for 

 a year or two and then used again for tobacco. 



7. An excess of mineral fertilizers in the field does not cause 

 the troulde nor intensify the disease. 



8. Care shoidd be exercised when the stems are used for 

 fertilizer that the stems of mosaic ])lants are not used, as they 

 may prove a source of infection. 



9. Excessively clayey soils should be avoided, especially in 

 growing Havana tobacco. 



10. Once the disease appears on a plant all subsequent growth 



