Sept. 17, 191 7 



Mosaic Disease of Tobacco 



617 



same manner — that is, by cutting the trichomes of healthy plants with 

 sterilized scissors — remained healthy. The preceding test was again 

 repeated with the trichomes of mosaic plants on October 30, 191 5. Of 

 the 10 plants thus treated, 5 were mosaic on November 27, 1915. All 

 controls remained healthy. 



EFFECT OF SPRAYING AND DROPPING THE VIRUS UPON THE LEAVES 



OF TOBACCO PLANTS 



All experiments indicate that the infective principle of the mosaic 

 disease of tobacco does not readily invade uninjured trichomes or leaf 

 tissues. Although infection sometimes follows when the virus is merely 

 sprayed upon the leaves with an atomizer, or dropped carefully upon 

 the surface at one or two points, this appears to be a very uncertain 

 method of producing infection in healthy plants. If, on the other hand, 

 the virus is sprayed upon the leaves and subsequently rubbed in, infection 

 readily follows, probably from the fact that the trichomes are more or 

 less injured (Table II). 



Table II. — Effect of spraying and dropping the virus upon the leaves of 10 Connecticut 



Broadleaf tobacco plants 



EFFECT OF ONE AS COMPARED WITH SEVERAL INOCULATIONS 



Various experiments have shown that infection is more likely to follow 

 if the virus is inoculated into the plants at more than one point. As 

 shown in Table III, the percentage of infection is highest in those tests 

 where many inoculations have been made. 



It is rather interesting to note that, even though the virus be intro- 

 duced into each plant of a series at many points, it is not unusual for 

 some plants to escape infection. 



