158 



EXrElilMEXT STATION. 



[Jan. 



ered iu connection with tobacco by Loew/ was present in both 

 healthy and diseased leaves in comparatively small amounts, 

 but that there was practically no ditlerence in the amounts pres- 

 ent. Twenty samples of licallhy and diseased leaves were 

 tested, and below will be found a table containing the averages 

 of these tests. The comparative amounts present were repre- 

 sented by the oxygen developed from a standard solution of 

 liydrcigen 2)eroxide, which contained o })cr cent. H2O::. 



Table II. — Amount of Oxygen developed from Healthy and Abnormal 



Leaves. 



The sain pie.? were shaken during the test, as this has been found to increase the amount of 

 oxygen developed. 



Fifteen grams of leaves were used in each case. 



Individual variations were found in most cases between leaves of different kinds, but not sufTi- 

 cient to warrant distinctive mention. 



Thus, in respect to the amount of catalase present we liiid 

 that there is a difference between this disease and mosaic, for 

 in the case of mosaic disease there is less catalase present in 

 the diseased leaves than in the healthy ones.- 



Colorimetric tests of healthy and diseased leaves were made 

 to determine the relative amounts of nitrates present, and it 

 was found that in the case of diseased leaves a deeper color Avas 

 obtained than in the case of healthy specimens. The test for 

 nitrates used was the well-known diphenyl amine reaction. 

 Only approximate results were obtained, but sufficient to show 

 that nitrates were more abundant in diseased leaves than in 

 normal specimens. This tends to confirm the idea that this dis- 

 ease is more a form of malnutrition or overfeeding than a spe- 

 cific trouble, such as " mo.snic." 



Aside from Ihc direct work on the disease it was observed in 

 some few cases that diseased leaves were more liable to the 



1 U. S. Dept. Agr., Report No. 68. 



2 Mass. Agr. Exp. Sta. report, 1908. 



