382 
Journal of Agricultural Research 
voi. n. No. s 
In physiological disturbances, such as the curly-dwarf disease of potatoes 
and the curly-top of sugar beets appear to be, the lehves are the parts 
primarily affected. It is therefore to be expected that any chemical 
differences existing between healthy plants and plants affected with the 
curly-dwarf disease will be most pronounced in the leaves proper. In 
order to be certain of results which represent the activity of the juice of 
Fig. 6.—Curve showing oxidation of leuco base of malachite green in the presence of the juice of potato 
foliage. 
the foliage proper, all experiments with the green parts of the potato 
plant were from this point on carried out on leaves alone. Table IV 
gives the data on the activity of the leaf juice alone. 
Some of these results are also graphically presented in figures 6 to 12. 
(See footnote, p. 379.) For easy comparison the figures obtained with 
healthy leaves; as well as those obtained later with curly-dwarf leaves, 
were plotted on the same systems of coordinates. The continuous lines 
Fig. 7.—Curve showing oxidation of pyrocatecliol in the presence of the juice of potato foliage. 
represent the results obtained with healthy plants, the dotted lines those 
with the diseased ones. 
These curves show great fluctuations cf oxidase content. Barring some 
of the irregularities, probably due to individual peculiarities of the samples 
examined, the curves take a downward direction at first, remain at a low 
level for a prolonged period, and take an upward movement again towards 
the end. The lowest point in the curve is reached generally on the 
fortieth day; the period of low oxidase content extends to a point of time 
between the sixtieth and eightieth day, when the upward movement of 
