1917] 
FREIBERG—MOSAIC DISEASES 187 
the chlorotic spots. It was also observed that when unboiled 
juice from tobacco leaves, possessing strong oxidase activity, 
was added to a digestion mixture of starch and taka-diastase, 
no diastatic action took place. When the juice was boiled 
and the oxidizing enzyme was killed before addition to the 
digestion mixture, diastatie action occurred. Combining these 
observations, Woods concluded that the inability of the chlo- 
rotie spots to rid themselves of their starch, as seemed to be 
demonstrated by his tests, was attributable to the action of 
oxidases on diastase. 
In order to test this idea of Woods more conclusively, the 
writer examined diseased leaves early in the morning by the 
method described above, but always found an excess of starch 
in that portion of the section representing the darker area. 
Plants were then placed in the dark room and kept there for 
54 hours. At the end of this time sections were cut and ex- 
aminations made for starch. Observations on a number of 
leaves and a large number of sections showed that at the end 
of this period no starch whatever was present in the lighter 
or chlorotic areas, while the mesophyll of the darker areas 
still contained varying amounts. This, then, is in accord 
with the general observation that the dark tissue con- 
tains more starch regardless of the time of day when tests 
are made. It is quite probable that oxidizing enzymes may 
influence the activity of diastase, but when adding a strong 
extract from diseased tobacco leaves to a starch digestion 
mixture, we are adding innumerable unknown factors, the ef- 
fects of which might easily be confused with those exhibited 
to a more or less pronounced degree by one of the known 
constituents when added alone in a pure state. 
Sugar.—A microchemical test for sugar which has been 
long employed is the production of a fine red precipitate when 
treated with dilute Fehling’s solution. Sections of tissue 
were placed on the slide, a drop of Fehling’s solution added, 
and the mount warmed gently over a flame. No satisfactory 
results were obtained, which, in part at least, might be at- 
tributed to the great diffusibility of the sugar out of the cells 
as soon as they were killed and the difficulty with which the 
