6i6 



Journal of Agricultural Research 



Vol. X, No. 12 



Table I. — Experiments showing infectivity of the virus when inoculated into the trichomes 

 of leaves of tobacco plants — Continued 



It is evident that the infective principle very readily enters a plant 

 through the trichomes, if these are bioken or bruised. The readiness 

 with which plants may be affected in this manner accounts for the high 

 percentage of infection obtained in the touching and handling experi- 

 ments of earlier investigators working with the mosaic disease of tobacco. 



The following experiments indicate that the infective principle of the 

 disease may also be extracted from the trichomes of mosaic plants. On 

 October 23, 1915, the trichomes of the youngest leaves of a mosaic 

 plant were carefully cut with small scissors previously sterilized by 

 boiling. The trichomes of the youngest leaves of a healthy plant were 

 then cut with the same scissors. In this process of cutting the trichomes 

 are more or less bruised and macerated. This operation was repeated, 

 with healthy and mosaic plants alternately, until 10 healthy plants 

 were treated in this manner. Eight of the healthy plants so treated 

 were mosaic on November 3, 191 5. Ten control plants treated in the 



