1908.] PUBLIC DOCUMENT— No. 33. 137 



observations on the tomato we have been unable to verify this 

 statement, as in no case has the disease appeared when normal 

 plants were grown in soil which contained roots of plants which 

 had been badly diseased, and in the growing of tomatoes year 

 after year in the station greenhouses there has never been the 

 slightest evidence of infection arising from the soil. 



In the case of tomatoes grown under glass the disease did 

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

 occurred when the plants were pruned. These conditions held 

 true for soils in which there were diseased roots, as well as for 

 those in which tomatoes had not previously been grown. 



In the coming year the work will be renewed, and the disease 

 studied under field conditions in the case of tobacco, and ex- 

 periments carried on to determine the possibility of its occur- 

 rence in the seed bed and also after being transplanted from 

 the seed bed to the field. It is thought that the conditions 

 under which the transplanting takes place may account for the 

 presence of this disease in some cases. One case, at least, has 

 come to our notice which seems to indicate that the disease may 

 result from improper handling. In the particular case referred 

 to, two lots of plants were taken from the same seed bed. One 

 lot was well moistened before being removed, and the second 

 lot was removed in a dry condition. The same machine planted 

 both lots, and it was reported that at least 70 per cent, of the 

 plants removed from the seed bed in the drier state became 

 more or less diseased, while of those properly removed and 

 carefully handled only two or three plants became affected. It 

 has also been frequently observed, in connection with the trans- 

 planting of aster seedlings from the same bed under identical 

 conditions, that one lot will show the "yellows" badly, and 

 another lot scarcely at all when transplanted into different 

 localities. 



In connection with the field work, experiments of a more 

 technical character will be carried on in the laboratory, with a 

 view to ascertaining the effects which different enzymes (oxidase, 

 peroxidase, catalase, etc.) found in growing plants have upon 

 the production of the disease. Woods 1 infers that oxidase and 



i Mosaic Disease of Tobacco. A. F. Woods, Bulletin Xo. IS, Bureau of Plant Industry, 

 United States Department of Agriculture. 



