show that the abnormal condition which causes the trouble does not 

 lie in exterior circumstances but rather must be sought in the plant 

 itself. In other words individual cases of the disease are not caused 

 by any improper or unhealthy conditions, but are the result of an 

 inherent, constitutional weakness or misadjustment in the plant 

 which may manifest itself under any or all conditions. The results 

 thus far obtained in this direction appear to indicate that it is in the 

 nutritive functions that the trouble exists. In a plant like the aster 

 nutrition is obtained from two sources: water and mineral salts from 

 the soil, and carbonic acid gas from the air. Both of these go first 

 to the leaves where assimilation takes place, the water and carbonic 

 acid being combined into starch. As this process goes on only 

 under the influence of sunlight the formation of starch in leaves 

 begins each morning at sunrise, goes on through the day, and ceases 

 at nightfall. During the night the starch thus formed is converted 

 into su^ar by the action of diastase, a substance present in the leaves 

 for this purpose as in the saliva and pancreatic juice of animals. A 

 normal, active leaf, therefore, is full of starch each evening, but con- 

 tains next morning scarcely a trace of this sut)stance. Besides dias- 

 tase leaves contain other substances or enzymes of a similar nature, 

 which bring about various changes in the nutrient substances. 



It appears to be in this process of starch conversion or metabolism 

 that the aster trouble is located. If normal leaves are taken late in 

 the day and tested Tjy the customary method of extracting the green 

 color with hot water and alcohol and then soaked in iodine, a deep 

 blue-black color is produced, showing the presence of a large 

 amount of starch. Leaves picked in the morning show none of this 

 substance, all having turned into sugar over night. When leaves 

 affected with the yellow disease are tested in the same way it is 

 invariably found that night or morning, they aite at a/t titnes full of 

 starch. This shows, therefore, a lack of the diastactic action which 

 should turn the starch into sugar and render it available as food for 

 the plant. It is further found that in leaves which have only par- 

 tially lost their green color under the influence of the disease the 

 diseased (light-colored) areas show at all times less starch than the 

 green portions. It is to be expected that less would be produced 

 here, but apparently diastatic action is no more active in the green 

 than in the yellow portion of such leaves. 



