Sept. 17, 1917 



Mosaic Disease of Tobacco 



623 



In these experiments the following temperature relations were obtained : 



Table VI. — Temperatures secured at Arlington, Va., in IQ15, in five different parts of 

 a tobacco seed bed sterilized icith steam. Readings taken immediately after lifting the 

 pan, as well as one hour later 



At Mr. Beinhart's suggestion some green mosaic leaves, freshly picked, 

 were buried in the soil at a depth of 4 inches during the process of ster- 

 ilization. Likewise, fresh mosaic virus, mixed in certain proportions 

 with soil, was also buried to a depth of 4 or 5 inches at the same time. 

 Inoculation tests made at once showed that the leaves which were cooked 

 to the point of disintegration, had completely lost their infectious proper- 

 ties, as well as the virus mixed with the soil. In control tests, the same 

 virus mixed with soil in the same proportions, but not subjected to ster- 

 ilization, remained highly infectious, as did unsterilized portions of green 

 mosaic leaves from the same plants. 



Although these experiments with buried mosaic material indicate the 

 thoroughness of steam sterilization, practically every plant obtained 

 from these beds and set in the field at Arlington, Va., sooner or later 

 became mosaic diseased. Late in the season the mosaic disease also 

 made its appearance in the beds themselves at some points. The occur- 

 rence of the disease in a thoroughly sterilized soil can not be reasonably 

 explained on any other basis than that of infection reaching the plants 

 from sources external to the soil. 



RELATION OF THE MOSAIC DISEASE TO INFECTION IN THE SOIL 



Although the mosaic disease is readily communicated to healthy plants 

 by inoculation of the virus into the roots, the disease does not necessarily 

 follow as a result of introducing large quantities of mosaic material into 

 the soil so that the roots must ultimately reach it. Under such condi- 

 tions the disease frequently does not occur at all, although in some 

 experiments the buried, decomposing material still retained its infectious 

 properties, as shown by inoculation tests. Infection from such material 

 in the soil appears to depend upon injury to some portion of the root 



