Aug. 15,1914 
Oxidases in Potatoes 
381 
in size of the stem of a growing plant as compared with the foliage or a 
diminution with age of the activity of the stem juice as compared with the 
activity of the foliage juice would therefore result in a diminution with, 
age of the activity of the juice of the aboveground portion of the plant. 
Consequently oxidase determinations were made on the juice obtained 
from stems of plants 69 days old. The results are given in Table III. 
Table III.— Oxidase activities of the juice of stems of plants 6g days old 
Reagent. 
Activity, a 
Reagent. 
Activity.® 
Benzidin. 
O- ° 3 S 
0 
Phloridzin. 
O. 078 
O 
Pyrogallol. 
Resorcin. 
tf-naphthol. 
0 
Guaiacol. 
. 023 
O 
Teuco base of malachite 
O-cresol . 
green. 
0 
M-cresol. 
. TOT 
Aloin. 
.031 
0 
P-cresol. 
. l68 
Phloroglucin. 
O-toluidin. 
0 
Pyrocatechol. 
. 023 
0 
M-toluidin. 
0 
Tyrosin. 
P-toluidin. 
0 
Hydrochinone. 
0 
a Activity expressed in units as measured in the oxidation of the reagents. 
The stem juice proved to have no activity whatever toward 11 of 
these 18 reagents, and toward the remaining 7 it was slight in com¬ 
parison with the ac- 300 
tivity of the foliage 
juice, as will be 
shown later. That the 
stem during growth 
increased in weight 
more rapidly than the 
remainder of the shoot 
is shown in Table 
IV (column 9V It is 
probable, therefore, 
that the diminish- 
ing activity of the 
juice of the shoots of 
the potato plant was 
due to increasing dilu¬ 
tion with age of the 
very active leaf juice 
with the relatively 
inactive stem juice. 
eo 30 
AGS—OAKS 
40 
so 
eo 
Fig. 5. —Curve showing oxidation of phloridzin in the presence of the 
juice of green potato shoots. 
oxidase activity of the; JUICE of the; leaves 
The leaves proper are the seat of the greatest physiological activity 
in plants. The food of the plant is largely synthesized in the leaves and 
also in part broken down in them, according to the needs of the plant. 
