44 EXPEllLMEXT STATION. [Jan. 



however, we do find a crop which is a failure, or individual vines 

 which are a loss, hut this is due to a lack of proi)cr ]iruning or 

 other coiiditidus which tend to intensify the Imuhle. Small, 

 nul)l)l_v fruit results, of no conunercinl valne, and a generally 

 stunted condition of the vine is always observed. 



The disease as it occurs on tobacco is of more importance 

 from an economic ])oint of view, as, from the fijiures obtained 

 from the United States Department of Agriculture, the annual 

 loss in the United States alone is over $1,000,000 per annum. 

 The trouble may appear in all stages of growth on tobacco, 

 from the seedling to the mature plant. A great many instances 

 are on record of the seedlings being affected in the seed bed, 

 and we have observed it frequently in the past few years on 

 old beds which have been used repeatedly. As has been ob- 

 served by oth(>r writers, it is only occasionally that the first two 

 leaves are afi'ected, but often the succeeding leaves come dis- 

 eased. The cause of the affection in the seed bed will be dis- 

 cussed later in the paper. If diseased plants are transplanted 

 to the field they do not recover, and the wdiole plant becomes 

 affected and worthless commercially. The appearance of the 

 diseased plants in the seed bed is not so characteristic as its 

 appearance on mature plants, but, nevertheless, they can be 

 easily distinguished from the healthy plants. There is at first 

 no distortion, but rather a mottled appearance of light and dark 

 green areas which persist and do not disappear during the day, 

 in opposition to the mottling which is frequently observed 

 when for any reason plants are subjected to abnormal night 

 conditions. The leaves are also somewhat roughened, which 

 is caused by the beginning of the unequal growth of the healthy 

 and diseased areas. When these plants are transplanted to the 

 field we get the characteristic appearance of the disease, al- 

 though sometimes they may not be severely distorted. Leaves 

 of a plant which are not affected will not become diseased, 

 since the disease can only be transmitted through the dividing 

 cells, as has been shown by several investigators and verified 

 at this laboratory. 



As to the cause of this trouble mucli lias l)e(>n written bv 

 various investiaators, but, as some of tlie earlier theories have 



