138 EXPERIMENT STATION. [Jan. 



peroxidase play an important role in the development of this 

 disease ; but in the work so far carried on in the laboratory at 

 this station it seems more probable that catalase has more to do 

 with the production of a diseased condition. This bears out 

 Loew's^ Iwpothesis to a great extent, as in the preliminary work 

 here it has been found that catalase is present in far greater 

 quantity in health}^ plants than in diseased plants. However, 

 this point cannot be considered proved, as enough work has 

 not yet been done to warrant such a statement. The results 

 so far obtained will be found in this report. 



Description of Mosaic Disease on Tomato. 



The appearance of this disease has been described by many 

 investio'ators, and nearlv all have described it in a similar man- 

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

 tomato. The aeneral characteristics of the disease are the same 

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

 in extreme cases on the tomato, as will be noted from the fol- 

 lowing 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 noticeable, but 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 tomato the light-green areas become yellowish as the 

 disease progresses, and in badly affected plants become finally 

 a purplish-red color. This purplish coloration is found princi- 

 pally 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 disease may reach its maximum with- 

 out showing any reddish coloration whatsoever. The reddish 

 appearance is noticeable only on the upper surface of the leaf, 

 and appears to extend only through the palisade cells. As yet 

 no investigation has been made with reference to its character, 

 but from its appearance under the microscope it is thought that 

 it may be due to the breaking down of the chlorophyll granules, 

 as a result of the diseased condition of the leaf. 



1 Catalase, Oscar Loew, Report No. 68, DeiJartmeut of Vegetable Pathology and Phyai. 

 ology, United States Department of Agriculture. 



