150 EXPERIMENT STATION. [Jan. 



der contlitioiis whifb tend to produce the disease thau is the 

 tomato. 



In tlie ease of tobacco, A. F. Woods ^ found that when a 

 ])lant was grown in soil containing small roots of diseased plants 

 the disease occurred in a short or long period of time, as the 

 case might be. In our observations on the tomato we have been 

 nnable to verify this statement, as in no case has the disease 

 appeared when normal ])lants were grown in soil which con- 

 tained roots of plants which had been badlv diseased, and in 

 the gi'owing of tomatoes year after year in the station gretin- 

 houses there has never been the slightest evidence of infection 

 arising from the soil. 



In the case of the tomatoes grown under glass, the disease 

 did not make its appearance when the plants were left normal, 

 but occurred wdien the plants were pruned. These conditions 

 held time for soils in which there were diseased roots as well as 

 for those in which tomatoes had not previously been grown. 



The appearance of mosaic disease has been described by many 

 investigators, and nearly all have described it in a similar man- 

 ner, but more particidarly with reference to tobacco than to the 

 tomato. The general characteristics of the disease are the same 

 for both plants, but some difference is found in its appearance in 

 extreme cases on the tomato, as will be noted from the following 

 description. 



In the first stages of the disease the leaf presents a mottled 

 appearance, being divided into larger or smaller areas of light 

 and dark green patches. At this point, however, no swelling 

 of the areas is nftticciiblc, l>ut as the disease progresses the 

 darker portions grow more rapidly, while the light-green areas 

 do not grow so rapidly, and leaf distortion is brought about. 

 In the case of tomato, the light-green areas become yellowish 

 as lh(» disease ])r()gresses, and in badly afFoctcnl jdants become 

 finally a pur])lish red color. This ])urplish coloration is found 

 principally on plants which are exposed to strong light, but 

 does not always occur, as it has been found that sometimes, even 

 in badly infested plants, the dis(»ase may reach its maximum 

 without showing any reddish coloration whatever. The reddish 



» U. S. Dept. Agr., Bur. of Plant Itul., Bui. No. 18. 



