MOSAIC DISEASE OF TOBACCO. 97 



amounts of oxidizing enzymes, and showed experimentally that diastatic 

 action is inliibited by the presence of oxidizing enzj-mes. This is the 

 only work that has been accomplished up to the present time, so far as 

 relates to a study of the enzyme activities involved in tliis disease. Only 

 two enzymes have been considered, namely, the oxidase and diastase, 

 and it should be stated that in the light of later developments in the de- 

 termination and estimation of enzyme preparations and activities the 

 results obtained in some cases might well be open to some criticism. 



Loew,^ wliile worldng with tobacco, discovered the presence of an 

 enzyme wliich he called catalase, but he made no observations relative to 

 its activities in the case of mosaic-diseased plants. The results of the 

 writer's studies on enzyme activities of healthy and mosaic plants are 

 detailed below. 



Method. — In the experiments here detailed the enzymes under dis- 

 cussion were studied, in so far as was possible, (1) with regard to their 

 presence or absence in (a) leaves, (b) stems and (c) roots of healthy and 

 diseased plants (tliis was considered necessary, as it has been found that, 

 irrespective of the parts shoTsdng visible symptoms of the disease, the sap 

 from all other parts also is capable of transmitting the trouble) ; (2) with 

 regard to the age of the plant; (3) with regard to the growth of the plant 

 under different conditions. These will be discussed in detail under their 

 respective sections. 



The methods employed for the estimation were for the most part those 

 which by experience have been found satisfactory, and in the main give 

 quantitative results; in some cases the results are more or less qualitative 

 in nature, owing to our present insufficient knowledge of the methods of 

 isolation and action of the enzyme involved. 



It should be stated that plants used in the experiments were both field 

 and greenhouse grown, but no essential differences in results were obtained 

 from the two series. The individual experiments will not be given in 

 detail, but as the determinations of any given series were made in every 

 case in the same manner, only average results with the maximum and 

 minimum readings will be given. The experiments are, however, described 

 in sufficient detail to enable those interested to follow the methods em- 

 ployed closely enough to check up the work of the writer. 



Catalase (leaves). — A comparison was made of the catalase activity 

 of healthy and diseased leaves, as it had been noted as early as 1908 by 

 the writer that there was apparently a great difference between the cat- 

 alase activity of healthy and mosaic-diseased tomato leaves, and later 

 the same was found to be true in the case of tobacco. At that time only 

 rough determinations were made, but since then the ^vriter has made 

 hundreds of determinations, the results of which have borne out the ob- 

 servations made then, and indisputably established the fact that there is 

 a wide difference in the catalase activity of healthy and diseased leaves. 



» Loew, O.: Catalase: A New Enzyme of General Occurrence, with Special Reference to the 

 Tobacco Plant. U. S. D. A., Bur. Plant Ind., Bui. No. 68 (1901). 



