Sept. 17. I9I7 Mosaic Disease of Tobacco 621 



On February 25, 191 4, five plants, three of which were White Burley 

 and two Maryland Mammoth, were inoculated at the middle of one-half 

 of a leaf near the margin and cut along the same side of the midrib as 

 in leaf C, Plate 63. Five similar plants were inoculated in the same 

 manner without cutting the leaf blade along the midrib. The disease 

 made its appearance in these two lots of plants as follows : 



Series inociilated and cut along the midrib: 



Two White Buriey plants became mosaic 11 days after inoculation. 



One White Buriey plant became mosaic 14 days after inoculation. 



Two Maryland Mammoth plants became mosaic 18 days after inoculation. 

 Series inoculated but not cut along the midrib : 



One plant remained healthy. 



One White Buriey plant became mosaic 10 days after inoculation. 



Two Maryland Mammoth plants became mosaic 10 days after inoculation. 



One Maryland Mammoth plant became mosaic 18 days after inoculation. 



' These tests are sufficient to show that cutting across the midrib or 

 severing all the larger lateral veins on one or both sides of the midrib 

 does not prevent the final dissemination of the virus from distant points 

 of inoculation in the leaf to other leaves of the plant. Although it is 

 possible that the virus dose not travel as rapidly following this treat- 

 ment, the differences do not appear to be consistently and strikingly 

 conspicuous. Even though cutting across the midrib near the petiole 

 permanently interrupts the main vascular system of the leaf, yet multi- 

 plication and diffusion of the virus from cell to cell, aided perhaps by the 

 finely anastomosing lateral veins would sooner or later allow the virus 

 to reach the petiole and pass into the rest of the plant. To what extent 

 the virus of mosaic is carried directly through the vascular system, along 

 with the transpiration stream is not known. 



REMOVAL OF THE VIRUS FROM THE HANDS BY THOROUGH WASHING 



In the following experiments the hands were covered with fresh virus 

 before handling the plants. Bach leaf of a series of 10 plants was then 

 rubbed vigorously between the fingers. Following this treatment the 

 hands were washed thoroughly several times with soap and water and 

 wiped dry. The leaves of young, healthy plants were then rubbed 

 between the fingers as before. The results in Table V show that this 

 is a practical and efficient means of removing infection from the hands. 

 4600°— 17 3 



