102 MASS. EXPERIMENT STATION BULLETIN 175. 



of diastase in the mosaic disease are of rather significant import, as can 

 be easily shown. It was pointed out several years ago by Woods {loc. cit.) 

 that the action of oxidizing enzymes when present in solutions containing 

 diastase tended greatly, under ordinary conditions, to inhibit the activities 

 of the diastase. Turning more particularly to the mosaic disease, he made 

 the observation that in the cells of the light green areas, although they 

 formed starch practically in a normal manner, so far as could be observed 

 the starch was not translocated, and that in the morning there was prac- 

 tically as much starch present as at night, which is not the case in a 

 normally functioning leaf. In this case it was found that practically all 

 the starch disappeared in the night and was translocated. 



Recently there has been more or less contention as to the exact method 

 of action of diastase on starch, and within the last two or three years 

 important investigations have resulted in the opinion, substantiated more 

 or less in detail, that the diastase of the older writers is not one enzyme 

 alone, but is made up of at least two components. The first of these 

 breaks down the starches into, or as far as, the erythro-dextrine and 

 achro-dextrine stage, the second component taking up the action from 

 this point and completely hydrohzing the starch to the sugar compoimds 

 which are found to be present, as the next step in the process of metabolism. 



It was in the light of these investigations that the writer took up the 

 question of the diastase activity in the mosaic disease, and it was foimd 

 to be less active in the leaves which showed severe symptoms of the 

 disease than in those which showed only a sHght trace. There was, how- 

 ever, apparently a greater or less breaking down of the starch in all the 

 leaves examined, so far as could be determined by the colorimetric methods, 

 which, although not altogether satisfactory, may be rehed upon as much 

 as any of the present-known methods of determination. At the morning 

 examinations the starch did not in some cases take on the color of the 

 normal starch in the healthy leaves, but was accompanied by a yellow 

 brown to a reddish or violet coloration, dependent somewhat on the 

 strength of the indicator used. The strength of the iodine solution used 

 in this case was a fiftieth normal iodine-potassium iodide solution. This 

 reaction would indicate that the starch to a certain extent had been acted 

 upon at least partially by the diastatic enzymes, and would indicate also 

 that it was possibly the first of the components above mentioned which 

 was more active, and that the second was more or less inhibited in its 

 action. In the normal leaf, of course, there was a certain amount of starch 

 present indicated by the blue coloration of the granules. The amount 

 was slight, however, compared to that in the diseased leaves, and in no 

 case was there any of the brown or violet color, almost complete hydrolysis 

 having apparently taken place very rapidly. This would indicate, as 

 pointed out by Woods, that the oxidizing enzymes, of which we will 

 make mention, and which are present in excessively large amounts in the 

 diseased areas of the leaf, do play an important role in the controlling 

 or inhibiting of the activities of the diastatic enzymes, but not on the 



